JP4162727B2 - Method for manufacturing semiconductor device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a semiconductor device using a crystalline semiconductor and a manufacturing method thereof.
[0002]
[Prior art]
A thin film transistor (hereinafter referred to as TFT) using a thin film semiconductor is known. This TFT is formed by forming a thin film semiconductor on a substrate and using this thin film semiconductor. This TFT is used in various integrated circuits, and is particularly attracting attention as a switching element provided with each pixel of an electro-optical device, particularly an active matrix liquid crystal display device, and a driver element formed in a peripheral circuit portion. .
[0003]
As a thin film semiconductor used for a TFT, it is easy to use an amorphous silicon film, but there is a problem that its electrical characteristics are low. In order to obtain improved TFT characteristics, a silicon thin film having crystallinity may be used. The crystalline silicon film is called polycrystalline silicon, polysilicon, microcrystalline silicon, or the like. In order to obtain this silicon film having crystallinity, an amorphous silicon film is first formed and then crystallized by heating.
[0004]
However, crystallization by heating requires a heating temperature of 600 ° C. or more and takes 20 hours or more, and there is a problem that it is difficult to use a glass substrate as a substrate. For example, Corning 7059 glass used for an active type liquid crystal display device has a glass strain point of 593 ° C., and there is a problem with heating at 600 ° C. or higher in consideration of an increase in area of the substrate. That is, when a commonly used Corning 7059 glass substrate is subjected to a heat treatment at a temperature of 600 ° C. or higher for 20 hours or longer, the substrate shrinks or bends significantly.
[0005]
In order to solve such a problem, it is necessary to perform heat treatment at as low a temperature as possible. On the other hand, it is required to shorten the time of the heat treatment process as much as possible for the purpose of increasing productivity.
[0006]
Further, when the amorphous silicon film is crystallized by heating, the entire silicon film is crystallized, and it is impossible to partially crystallize or control the crystallinity of a specific region. There's a problem.
[0007]
As a method for solving this problem, there is a technique of selectively performing crystallization by artificially forming a portion or region that becomes a crystal nucleus in an amorphous silicon film and then performing a heat treatment. JP-A-2-140915 and JP-A-2-260524. This technique is intended to generate crystal nuclei at predetermined positions in an amorphous silicon film.
[0008]
For example, in Japanese Patent Laid-Open No. 2-140915, an aluminum layer is formed on an amorphous silicon film, crystal nuclei are generated at the portion where the amorphous silicon and aluminum are in contact, and a heat treatment is performed. A configuration is described in which crystal growth is performed from this crystal nucleus by applying. Japanese Patent Laid-Open No. 2-260524 describes a configuration in which tin (Sn) is added to an amorphous silicon film by an ion implantation method, and crystal nuclei are generated in a region where the tin ions are added.
[0009]
However, Al and Sn are substitutional metal elements that form an alloy with silicon and diffuse into the silicon film.IntrusionNot done. Crystallization proceeds in such a manner that a portion where silicon and an alloy are formed becomes a crystal nucleus, and crystal growth is performed from that portion. As described above, when Al or Sn is used, crystal growth is performed from a portion into which Al or Sn is introduced (that is, an alloy layer of these elements and silicon). In general, crystallization proceeds through a two-step process of generating an initial nucleus and growing a crystal from the nucleus. Substitution-type metal elements such as Al and Sn are effective for generating initial nuclei, but have little effect on subsequent crystal growth. Therefore, when Al or Sn is used, it is not possible to lower the temperature and shorten the time particularly when compared with the case where the amorphous silicon film is simply crystallized by heating. That is, it does not have a significant advantage over the conventional crystallization process of an amorphous silicon film simply performed by heating.
[0010]
BACKGROUND OF THE INVENTION
According to the study by the present inventors, a trace amount of an interstitial element with respect to silicon, such as nickel and palladium, is deposited on the surface of the amorphous silicon film, and then heated to about 550 ° C. for about 4 hours. It has been found that crystallization can be carried out in a treatment time of In this case, not only the process of initial nucleation but also subsequent crystal growth can be facilitated, and the heating temperature can be greatly lowered and the heating time can be shortened as compared with the conventional method using only heating. can do.
[0011]
In order to introduce such a small amount of element (a metal element that promotes crystallization), plasma treatment, vapor deposition, or ion implantation may be used. Plasma treatment is a parallel plate type or positive column type plasma CVD apparatus using a material containing a metal element as an electrode and generating a plasma in an atmosphere of nitrogen or hydrogen to form a metal element on the amorphous silicon film. It is a method of adding.
[0012]
As a metal element for promoting the above crystallization,IntrusionTypes of elements such as Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, and Au can be used. theseIntrusionThe element of the type diffuses into the silicon film in the heat treatment process. And aboveIntrusionAs the type elements diffuse, the crystallization of silicon proceeds. That is, the aboveIntrusionThe metal of the type promotes the crystallization of the amorphous silicon film by the catalytic action that has been diffused.
[0013]
Therefore, crystallization can be advanced by a method different from the case where crystallization gradually proceeds from the crystal nucleus. For example, when heat treatment is performed after the metal element is introduced into a specific place of the amorphous silicon film, crystallization proceeds in a direction parallel to the film plane from the region where the metal element is introduced. This length is several tens of μm or more. Further, when the metal element is introduced into the entire surface of the amorphous silicon film, the entire film can be uniformly crystallized. Of course, in this case, the entire film has a polycrystalline or microcrystalline structure, but it does not have a structure having a clear grain boundary at a specific location. Therefore, it is possible to form a device with uniform characteristics by utilizing an arbitrary location of the film.
[0014]
Also aboveIntrusionSince the element of the type diffuses quickly into the silicon film, the introduction amount (addition amount) is important. That is, if the amount introduced is small, the effect of promoting crystallization is small and good crystallinity cannot be obtained. Moreover, when there are too many the introduction amounts, the semiconductor characteristic of silicon will be impaired.
[0015]
Therefore, there exists an optimum amount of the metal element introduced into the amorphous silicon film. For example, when Ni is used as the metal element for promoting the crystallization, the concentration in the crystallized silicon film is 1 × 10¹⁵cm^-3If it is above, the effect which promotes crystallization can be acquired, and the density | concentration in the crystallized silicon film is 1x10.¹⁹cm^-3It has been found that the semiconductor properties are not hindered if: The concentration here is defined by the minimum value obtained by SIMS (secondary ion analysis).
Moreover, the effect can be acquired also about metal elements other than Ni enumerated above in the same concentration range as Ni.
[0016]
In order to make the concentration of the element that promotes crystallization, such as nickel, in the crystalline silicon film after crystallization (in this specification, the element that promotes crystallization is referred to as a metal element) optimal range, When these elements are introduced into the amorphous silicon film, the amount thereof needs to be controlled.
[0017]
When nickel was used as the metal element, an amorphous silicon film was formed, and nickel was added by plasma treatment to produce a crystalline silicon film. The crystallization process was examined in detail. found.
(1) The nickel concentration in the region where nickel is directly introduced is high.
(2) The nickel concentration is high at the tip of the region where the crystal is grown in the direction parallel to the substrate from the region where nickel is directly introduced.
(3) By the hydrofluoric acid treatment, countless holes are opened in a region where the nickel concentration is high.
[0018]
The optical microscope photograph regarding the matter of said matter (3) is shown in FIG. FIG. 11 schematically shows FIG. FIG. 11 corresponds to FIG. The left portion shown in the photograph of FIG. 10 is a portion where nickel is directly introduced (corresponding to the region indicated by 801 in FIG. 11). The central portion (region indicated by 803 in FIG. 11) is a region in which crystal growth (as indicated by an arrow 802 in FIG. 11) is performed in a direction parallel to the substrate from a region where nickel has been directly introduced. . Further, the region on the right side of FIG. 10 (corresponding to the region 805 in FIG. 11) is a region that remains amorphous.
[0019]
As is apparent from FIG. 10, innumerable holes are formed between a region where crystal growth is performed parallel to the substrate (corresponding to 803 in FIG. 11) and an amorphous region (corresponding to 805 in FIG. 11). There is a linear area that opens. This region is completely removed and the hole is opened. This region (indicated by 804 in FIG. 11) has been found to be the tip of crystal growth where nickel is present at a high concentration. Further, by further observing the state shown in FIG. 10, it has been confirmed that innumerable small holes are opened even in a region where the crystal is grown in a direction parallel to the substrate indicated by reference numeral 803 in FIG. 11.
[0020]
The invention disclosed in this specification has been made in view of the above experimental facts. In other words, hydrofluoric acid (of course, buffer hydrofluoric acid) may be applied to the crystalline silicon film that has been crystallized by heating due to the action of the metal element, and the high concentration of the metal element present in the film is removed. Thus, a crystalline silicon film having a low concentration of metal element in the film is obtained.
[0021]
[Problems to be solved by the invention]
The present invention provides a thin film silicon semiconductor having crystallinity by heat treatment at 600 ° C. or lower using a metal element.
(1) The amount of metal element is controlled and introduced, and the amount is minimized.
(2) Use a highly productive method.
(3) Crystallinity higher than that obtained by heat treatment is obtained.
(4) The concentration of the metal element in the crystalline silicon film is reduced as much as possible.
The problem is to satisfy at least one of the above requirements.
[0022]
[Means for Solving the Problems]
In order to satisfy the above object, the present invention obtains a silicon film having crystallinity using the following means.
A single metal element or a compound containing the metal element that promotes crystallization of the amorphous silicon film is held in contact with the amorphous silicon film, and the amorphous silicon film contains the single metal element or the metal element. In the state where the compound is in contact, heat treatment is performed to crystallize part or all of the amorphous silicon film. Then, by performing hydrofluoric acid treatment (etching treatment) using an etching solution containing hydrofluoric acid or buffer hydrofluoric acid or hydrofluoric acid diluted to an appropriate concentration, localization (nickel segregates and concentration locally) Is removed) (this metal element is considered to form a silicide with the metal locally), and as a result, the concentration of the metal element in the film is reduced. Then, by irradiating with laser light or strong light, the holes generated in the above-described etching process (the localized metal and silicon silicide is removed to form innumerable holes) are eliminated, and the crystallinity is excellent. A silicon film is obtained. Moreover, the defect density in a film | membrane is reduced by adding heat processing after irradiation of a laser beam. The solution for performing the hydrofluoric acid treatment can be used as long as it can etch silicide. Of course, what etches silicon itself cannot be used.
[0023]
In the above structure, the treatment by heating may be performed without irradiating laser light or strong light. Alternatively, only laser light or strong light irradiation may be performed. However, the combined use of laser light or intense light irradiation and an annealing step by heating is extremely useful because of their synergistic effect. That is, in particular, by irradiating a laser beam or strong light, the aperture portion formed in the previous etching step (particularly the minute aperture portion formed in the lateral growth region (region indicated by 803 in FIG. 11)). The crystallinity is excellent by obtaining the effect that a silicon film having good crystallinity can be obtained and the effect that the defects in the film can be reduced by performing heat treatment. A crystalline silicon film with few defects can be obtained.
[0024]
As a method for introducing a metal element that promotes crystallization, a method by applying a solution containing the metal element to the surface of the amorphous silicon film is useful. Use of this method makes it easy to control the amount of the metal element.
[0025]
The metal element may be introduced on the upper surface or the lower surface of the amorphous silicon film. If a metal element is introduced into the upper surface of the amorphous silicon film, a solution containing the metal element may be applied on the amorphous silicon film after the amorphous silicon film is formed. If a metal element is introduced into the lower surface of the silicon film, a solution containing the metal element is applied to the base surface before forming the amorphous silicon film, and the metal element is held in contact with the base surface. That's fine.
[0026]
It is also useful to form an active region having at least one PN, PI, NI, or other electrical junction of a semiconductor device using a crystalline silicon film formed by using the invention disclosed in the specification of the invention. Examples of the semiconductor device include a thin film transistor (TFT), a diode, and an optical sensor. Moreover, resistance tolerance and a capacitor can also be formed using this invention.
[0027]
As a method of applying a solution containing an element that promotes crystallization on the amorphous silicon film, an aqueous solution, an organic solvent solution, or the like can be used as the solution. Here, the inclusion includes both the meaning of inclusion as a compound and the meaning of inclusion by simply dispersing.
[0028]
As the solvent containing a metal element, a polar solvent selected from water, alcohol, acid, and ammonia can be used.
[0029]
When nickel is used as a catalyst and this nickel is included in a polar solvent, nickel is introduced as a nickel compound. The nickel compounds typically include nickel bromide, nickel acetate, nickel oxalate, nickel carbonate, nickel chloride, nickel iodide, nickel nitrate, nickel sulfate, nickel formate, nickel acetylacetonate, 4-cyclohexylbutyric acid. A material selected from nickel, nickel oxide and nickel hydroxide is used.
[0030]
As the solvent containing a metal element, a nonpolar solvent selected from benzene, toluene, xylene, carbon tetrachloride, chloroform, and ether can be used.
[0031]
In this case, nickel is introduced as a nickel compound. As this nickel compound, typically, one selected from nickel acetylacetonate and nickel 2-ethylhexanoate can be used.
[0032]
It is also useful to add a surfactant to a solution containing a metal element. This is for increasing the adhesion to the surface to be coated and controlling the adsorptivity. This surfactant may be applied on the surface to be coated in advance.
[0033]
When nickel alone is used as the metal element, it needs to be dissolved in an acid to form a solution.
[0034]
The above is an example using a solution in which nickel, which is a metal element, is completely dissolved, but even if nickel is not completely dissolved, powder of nickel alone or a compound of nickel is uniformly distributed in the dispersion medium. Materials such as dispersed emulsions may be used. Alternatively, a solution for forming an oxide film may be used. As such a solution, Oka (Ohka Diffusion Source) manufactured by Tokyo Ohka Kogyo Co., Ltd. can be used. If this OCD solution is used, a silicon oxide film can be easily formed by coating on the surface to be formed and baking at about 200 ° C. Moreover, since it is also free to add an impurity, it can utilize for this invention. In this case, a metal element is contained in the oxide film, the oxide film is provided in contact with the amorphous silicon film, and heating (350 ° C. to 400 ° C.) is performed to diffuse the metal element into the amorphous silicon film. Further, after the oxide film is further removed, heat treatment may be performed for crystallization. The heat treatment for crystallization may be performed at a temperature of 450 ° C. to 600 ° C., for example, 550 ° C. for about 4 hours.
[0035]
In order to obtain high crystallinity, it is useful to perform the crystallization at a high temperature of 600 ° C. (crystallization temperature of the amorphous silicon film) to 1100 ° C. It is important that the heating temperature at this high temperature is equal to or higher than the crystallization temperature of the amorphous silicon film that is the starting film. The crystallization temperature of this amorphous silicon film varies depending on the film forming method and film forming conditions of the amorphous silicon film. Generally, it is about 580 to 620 ° C. Note that in the case of performing the heat treatment at this high temperature, it is necessary to use a glass substrate or a quartz substrate with high heat resistance.
[0036]
These are the same even when a material other than nickel is used as the metal element.
[0037]
When nickel is used as a metal element for promoting crystallization and a polar solvent such as water is used as a solution solvent containing the nickel, the solution is repelled when directly applied to the amorphous silicon film. Sometimes. In this case, a thin oxide film having a thickness of 100 mm or less is first formed, and a solution containing a metal element is applied thereon, whereby the solution can be applied uniformly. Also effective is a method of improving wetting by adding a material such as a surfactant to the solution.
[0038]
Further, by using a nonpolar solvent such as a toluene solution of nickel 2-ethylhexanoate as the solution, it can be directly applied to the surface of the amorphous silicon film. In this case, it is effective to apply in advance a material such as an adhesive used in resist application. However, when the coating amount is too large, attention should be paid because it interferes with the addition of the metal element into the amorphous silicon.
[0039]
The amount of the metal element contained in the solution depends on the type of the solution, but as a general tendency, it is desirable that the nickel amount is 200 ppm to 1 ppm, preferably 50 ppm to 1 ppm (weight conversion) with respect to the solution. . This is a value determined in view of the nickel concentration in the film and the hydrofluoric acid resistance after crystallization is completed.
[0040]
By performing laser light irradiation performed after the heat treatment, the crystallinity of the silicon film crystallized by the heat treatment can be further increased. Further, in the case where crystallization is caused partially by heat treatment, further crystal growth can be performed from the portion by irradiation with laser light, and a higher crystallinity state can be realized.
[0041]
As the laser beam, a pulsed excimer laser beam can be used. For example, KrF excimer laser (wavelength 248 nm), XeCl excimer laser (wavelength 308 nm), XeF excimer laser (wavelength 351, 353 nm), ArF excimer laser (wavelength 193 nm), XeF excimer laser (wavelength 483 nm), or the like can be used. As the excitation method, a discharge excitation method, an X-ray excitation method, a light excitation method, a microwave discharge excitation method, an electron beam excitation method, or the like can be used.
[0042]
Further, instead of laser light irradiation, a method of irradiating strong light, particularly infrared light may be employed. Infrared light is not easily absorbed by glass and is easily absorbed by a silicon thin film, which makes it possible to selectively heat a silicon thin film formed on a glass substrate. This method using infrared light is called rapid therma annealing (RTA) or rapid thermal process (RTP).
[0043]
In the invention disclosed in this specification, in addition to the promotion of crystallization by the laser light irradiation, further heat treatment may be performed. This heat treatment may be the same as the heat treatment conditions for crystallizing the amorphous silicon film. Of course, it does not need to be exactly the same, and may be performed at a temperature of 400 ° C. or higher.
[0044]
Defects in the crystalline silicon film can be reduced by heat treatment performed after irradiation with the laser light or strong light. FIG. 8 shows the result of measuring the spin density of the crystalline silicon film manufactured under the conditions described in the item of sample conditions by an electron spin resonance method (ESR). What is described in the item of sample conditions in FIG. 8 is heating temperature and heating time in a nitrogen atmosphere, and further LC is laser beam irradiation. In addition, samples other than the samples indicated as having no Ni are those obtained by crystallization using nickel as a metal element. The g value is an index indicating the position of the spectrum, and g = 2.0055 is a spectrum caused by an unpaired bond. Therefore, it can be understood that the spin density shown in FIG. 8 corresponds to the dangling bonds in the film.
[0045]
As can be seen from FIG. 8, the sample 4 has the smallest spin density, and there are few unpaired bonds in the film. This can be said to indicate that there are few defects and levels in the film. For example, when Sample 3 and Sample 4 are compared, it can be seen that the spin density can be reduced by about one digit. That is, it can be seen that defects or levels in the crystalline silicon film can be reduced by one digit or more by applying heat treatment after laser light irradiation.
[0046]
Further, as can be seen from a comparison between the sample 2 and the sample 3 in FIG. 8, even if the laser beam is irradiated, the spin density hardly changes. That is, it can be seen that laser light irradiation has no effect on reducing defects in the film. However, according to the analysis by transmission electron micrographs, it has been found that there is an extremely high crystallinity promoting effect by laser light irradiation. Therefore, in order to promote the crystallinity of the crystalline silicon film once crystallized by heating, laser light irradiation is extremely effective, and the film whose crystallinity is promoted is again subjected to heat treatment. Is extremely effective in reducing defects in the film. Thus, a silicon film having excellent crystallinity and a low defect density in the film can be obtained.
[0047]
In the present invention, crystal growth can be selectively performed by selectively applying a solution containing a metal element. Particularly in this case, crystal growth can be performed in a direction substantially parallel to the surface of the silicon film from the region where the solution is applied toward the region where the solution is not applied. In this specification, a region where crystal growth is performed in a direction substantially parallel to the surface of the silicon film is referred to as a laterally crystallized region.
[0048]
In addition, it has been confirmed that the concentration of the metal element is low in the region where the crystal is grown in the lateral direction. Although it is useful to use a crystalline silicon film as the active layer region of the semiconductor device, it is generally preferable that the impurity concentration in the active layer region is low. Therefore, it is useful for device fabrication to form the active layer region of the semiconductor device using the region where the crystal is grown in the lateral direction.
[0049]
In the present invention, the most prominent effect can be obtained when nickel is used as the metal element, but the other usable metal elements are preferably Fe, Co, Ni, Ru, Rh, Pd, Os. Ir, Pt, Cu, Ag, and Au can be used.
[0050]
Further, the method for introducing a metal element is not limited to using a solution such as an aqueous solution or alcohol, and a substance containing a metal element can be widely used. For example, a metal compound or oxide containing a metal element can be used.
[0051]
  In the present invention, in order to improve the crystallization rate, the laser beam or intense light irradiation step and the heat treatment step for reducing defects in the film may be alternately repeated twice or more. It is also effective to irradiate the laser beam multiple times. In this case, it is preferable to gradually increase the irradiation energy density every time the laser beam is irradiated.That is, a first step of introducing a metal element that promotes crystallization into the amorphous silicon film, a second step of performing heat treatment, a third step of removing the metal element, and laser light or strong light In the fourth step, laser light or strong light may be irradiated a plurality of times, and the irradiation energy density may be increased stepwise.For example, when laser light irradiation is performed twice, weak laser light may be irradiated for the first time and then strong laser light may be irradiated. By doing so, the influence of the remaining metal component can be reduced.In the above configuration, the laser beam or the strong light may be irradiated in an oxygen atmosphere or air.
[0052]
It is also effective to remove the metal elements and organic substances present on the surface by washing the surface of the crystalline silicon film obtained by the action of the metal element. In particular, it is effective to perform this cleaning after forming an island-shaped semiconductor region constituting the active layer.
[0053]
As such a cleaning method, a treatment process using a solvent having a strong oxidizing power such as ozone water, and an etchant (an etchant containing hydrofluoric acid such as FPM) having a large oxide removal effect after the process is used. The process consisting of the etching process used is very effective.
[0054]
In this process, organic substances and metal elements present on the surface of the active layer are converted into oxides by a solvent having a strong oxidizing power, and the oxide is further etched away to clean the exposed surface of the active layer. It has a great effect on suppressing the generation of trap levels due to organic substances and metal elements. This effect can be seen as remarkable in the characteristics of the actually manufactured thin film transistor.
[0055]
[Action]
The amorphous silicon film can be crystallized at a low temperature in a short time by the action of an interstitial element which is an element for promoting crystallization. Specifically, a crystalline silicon film can be obtained by performing a heat treatment at 550 ° C. for about 4 hours, which has been impossible in the past. Also, interstitial elements with respect to silicon promote crystallization while diffusing into the silicon film, so that a crystalline silicon film without a clear grain boundary is obtained unlike crystal growth from a crystal nucleus. Can do.
[0056]
Further, the localized nickel silicide portion can be removed by performing a treatment using hydrofluoric acid on the crystalline silicon film crystallized by heating by the action of the metal element. That is, a region where the nickel concentration is locally increased (nickel silicide is formed in this region) can be removed. And the density | concentration of the metal element in a film | membrane can be made low. Then, by irradiating laser light or strong light after the treatment using hydrofluoric acid, minute holes formed in the film can be eliminated. Further, by applying heat treatment, a silicon film with few defects in the film and high crystallinity can be obtained.
[0057]
By performing the hydrofluoric acid treatment, the concentration of the metal element in the film can be reduced by about 1 to 2 digits. For example, the introduction amount of the metal element is 1 × 10¹⁵~ 1x10¹⁹cm^-3Even so, by performing the hydrofluoric acid treatment, the concentration of the metal element in the film is 1 × 10¹⁸cm^-3It can be as follows. In addition, defects in the film can be reduced by further heat treatment after the laser light irradiation. As an etchant for performing hydrofluoric acid treatment, generally used buffer hydrofluoric acid may be used, but it is more effective to use FPM made of a mixture of hydrofluoric acid, superwater and water. Note that the concentration of the metal element in this specification is defined as the minimum value of the concentration distribution obtained by SIMS (secondary ion analysis method).
[0058]
Further, the crystalline silicon film is obtained by oxidizing impurities such as metal elements and organic substances on the surface of the crystalline silicon film using a solvent having a strong oxidizing power, and etching and removing this with an etchant containing hydrofluoric acid. The trap level density at the surface of the substrate can be lowered. And thereby, the characteristic of a thin film device can be improved.
[0059]
【Example】
[Example 1]
In this embodiment, a metal element that promotes crystallization is contained in an aqueous solution, applied onto an amorphous silicon film, then crystallized by heating, and treated with buffered hydrofluoric acid to crystallize the silicon film. The metal component localized inside is removed. Furthermore, by irradiating with laser light, the pores (defects) of the previously removed metal component part are eliminated, and a silicon film having a low content of metal element and excellent crystallinity is obtained. It is.
[0060]
The steps up to the introduction of a metal element (here, nickel is used) will be described with reference to FIG. In this embodiment, Corning 7059 glass is used as the substrate. Moreover, the magnitude | size shall be 100 mm x 100 mm.
[0061]
First, an amorphous silicon film is formed in a thickness of 100 to 1500 nm by plasma CVD or LPCVD. Here, the amorphous silicon film 12 is formed to a thickness of 1000 mm by plasma CVD. (Fig. 1 (A))
[0062]
Then, hydrofluoric acid treatment is performed to remove the dirt and the natural oxide film, and then the oxide film 13 is formed to a thickness of 10 to 50 mm. If the contamination can be ignored, the natural oxide film may be used as it is instead of the oxide film 13.
[0063]
Since the oxide film 13 is extremely thin, the exact film thickness is unknown, but is considered to be about 20 mm. Here, the oxide film 13 is formed by irradiation with UV light in an oxygen atmosphere. The film formation was performed by irradiating with UV in an oxygen atmosphere for 5 minutes. As a method for forming the oxide film 13, a thermal oxidation method may be used. Further, treatment with hydrogen peroxide may be used.
[0064]
This oxide film 13 is for spreading the acetate solution over the entire surface of the amorphous silicon film, that is, for improving the wettability in the subsequent step of applying an acetate solution containing nickel. For example, when an acetate solution is directly applied to the surface of the amorphous silicon film, the amorphous silicon repels the acetate solution, so that nickel cannot be introduced to the entire surface of the amorphous silicon film. That is, uniform crystallization cannot be performed.
[0065]
Next, an acetate solution is prepared by adding nickel to the acetate solution. The nickel concentration is 25 ppm. Then, 2 ml of this acetate solution is dropped on the surface of the oxide film 13 on the amorphous silicon film 12, and this state is maintained for 5 minutes. Then, spin drying (2000 rpm, 60 seconds) is performed using a spinner. (Fig. 1 (C), (D))
[0066]
When the concentration of nickel in the acetic acid solution is 1 ppm or more, preferably 10 ppm or more, it becomes practical. When a nonpolar solvent such as a toluene solution of nickel 2-ethylhexanoate is used as the solution, the oxide film 13 is not necessary, and a metal element can be directly introduced onto the amorphous silicon film.
[0067]
By performing this nickel solution coating process once to a plurality of times, a layer containing nickel having an average film thickness of several to several hundreds of mm is formed on the surface of the amorphous silicon film 12 after spin drying. be able to. In this case, nickel in this layer diffuses into the amorphous silicon film in the subsequent heating step, and acts as a catalyst for promoting crystallization. Note that this layer is not necessarily a complete film.
[0068]
After application of the solution, the state is maintained for 1 minute. The concentration of nickel contained in the silicon film 12 can be finally controlled by this holding time, but the greatest control factor is the concentration of the solution.
[0069]
In a heating furnace, heat treatment is performed at 550 ° C. for 4 hours in a nitrogen atmosphere. As a result, the crystalline silicon thin film 12 formed on the substrate 11 can be obtained.
[0070]
The above heat treatment can be performed at a temperature of 450 ° C. or higher. However, if the temperature is low, the heating time must be lengthened and the production efficiency is lowered. On the other hand, if it is 550 ° or more, the problem of heat resistance of the glass substrate used as the substrate will surface.
[0071]
In this embodiment, the method of introducing the metal element onto the amorphous silicon film is shown, but the method of introducing the metal element under the amorphous silicon film may be adopted. In this case, the metal element may be introduced onto the base film using a solution containing the metal element before forming the amorphous silicon film.
[0072]
Here, since nickel element is introduced over the entire surface, the entire film grows in a direction perpendicular to the substrate. When the silicon film 12 having crystallinity is obtained by heat treatment, the heat treatment is performed using 1/100 buffer hydrofluoric acid. In this step, the nickel component localized in the film (existing as nickel silicide) is removed. Here, by removing the nickel component, the nickel concentration in the film can be reduced. Then, a KrF excimer laser (wavelength 248 nm, pulse width 30 nsec) is 200 to 350 mJ / cm in a nitrogen atmosphere.² Irradiate several shots at a power density of. By irradiating this laser light, the nickel component portion (which is a fine hole) removed in the previous step can be eliminated.
[0073]
This step may be performed by the infrared light irradiation described above. In this step, it is effective to increase the pulse width of the excimer laser light. This is because the melting time on the surface of the silicon film generated by the laser light irradiation can be lengthened and the crystal growth in a minute portion can be promoted.
[0074]
By performing this laser light irradiation, the crystallinity of the silicon film can be further improved, and at the same time, minute openings generated in the treatment process using buffer hydrofluoric acid can be eliminated. After the laser light irradiation is completed, heat treatment is performed at 550 ° C. for 4 hours in a nitrogen atmosphere. This heat treatment can be performed at a temperature of 400 ° C. or higher. By performing the heat treatment after the laser light irradiation, defects in the silicon film can be reduced. Thus, a crystalline silicon film having a low nickel concentration in the film, excellent crystallinity, and at the same time having few defects can be obtained.
[0075]
[Example 2]
This embodiment is an example in which a 1200 珪 素 silicon oxide film is selectively provided in the manufacturing method shown in Embodiment 1, and nickel is selectively introduced using the silicon oxide film as a mask.
[0076]
FIG. 2 shows an outline of a manufacturing process in this example. First, a silicon oxide film 21 serving as a mask is formed on a glass substrate (Corning 7059, 10 cm square) to a thickness of 1000 mm or more, here 1200 mm. Regarding the film thickness of the silicon oxide film 21, it has been confirmed by the inventors' experiments that there is no problem even at 500 mm, and it may be thinner if the film quality is dense.
[0077]
Then, the silicon oxide film 21 is panned into a required pattern by a normal photolithography patterning process. Then, a thin silicon oxide film 20 is formed by irradiation with ultraviolet rays in an oxygen atmosphere. The silicon oxide film 20 is produced by irradiating UV light for 5 minutes in an oxygen atmosphere. The thickness of the silicon oxide film 20 is considered to be about 20 to 50 mm (FIG. 2A). Note that the silicon oxide film for improving the wettability may be added just well depending on the hydrophilicity of the silicon oxide film of the mask when the size of the solution and the pattern match. However, such an example is special, and it is generally safer to use the silicon oxide film 20.
[0078]
In this state, 5 ml of an acetate solution containing 100 ppm of nickel was dropped as in Example 1 (in the case of a 10 cm square substrate). At this time, spin coating is performed with a spinner at 50 rpm for 10 seconds to form a uniform water film on the entire substrate surface. Furthermore, after maintaining for 5 minutes in this state, spin drying is performed at 2000 rpm for 60 seconds using a spinner. In addition, you may perform this holding | maintenance, rotating 0-150 rpm on a spinner. (Fig. 2 (B))
[0079]
Then, the amorphous silicon film 12 is crystallized by performing heat treatment at 550 degrees (nitrogen atmosphere) for 4 hours. At this time, crystal growth is performed in the lateral direction from the region of the portion 22 where nickel is introduced to the region where nickel is not introduced, as indicated by 23. In FIG. 2C, 24 is a region where nickel is directly introduced and crystallization is performed, and 25 is a region where crystallization is performed in the lateral direction. In these 25 regions, it has been confirmed that crystal growth is performed substantially in the <111> axis direction. In addition, it is confirmed by a TEM photograph (transmission electron micrograph) that the region indicated by 25 is progressing in the form of a column or a branch in a direction parallel to the substrate.
[0080]
After the crystallization step by the heat treatment, the localized crystal component is removed using 1/100 buffer hydrofluoric acid. Here, 1/100 buffer hydrofluoric acid was used, but the concentration may be determined as appropriate. As an etching solution used here, hydrofluoric acid or a solution containing hydrofluoric acid can be used. As this solution, a solution for etching silicon silicide or silicon oxide can be used.
[0081]
Next, the crystallinity of the silicon film 12 is further improved using a XeCl laser (wavelength 308 nm). By the laser irradiation performed in this step, the hole portion (formed as a result of removing localized nickel silicide) formed in the previous etching step can be eliminated. That is, the surface of the silicon film is brought into a molten state by irradiation with laser light, and this opening can be eliminated. In this step, in the previous heat treatment, crystallization progresses between columns or columns or between branches and branches in a portion where the crystal has grown in a columnar shape or a branch shape in a direction parallel to the substrate. That is, the crystallization rate can be increased. Thus, by this step, the crystallinity of the region 25 grown in the lateral direction can be greatly increased.
[0082]
In the laser light irradiation step, it is effective to heat the substrate or the surface to be irradiated with the laser light. The heating temperature is preferably about 200 ° C to 450 ° C.
[0083]
When the laser light irradiation is completed, a heat treatment is performed at 550 ° C. (nitrogen atmosphere) for 4 hours to further reduce defects in the film.
[0084]
In this example, the concentration of nickel in the region where nickel was directly introduced was changed to 1 × 10 6 by changing the solution concentration and the holding time.¹⁵atoms cm^-3~ 1x10¹⁹atoms cm^-3In the same manner, the concentration of the lateral growth region can be controlled to be lower than that.
[0085]
The crystalline silicon film formed by the method as shown in this embodiment is characterized by good hydrofluoric acid resistance. This is a matter of course considering that the hydrofluoric acid treatment is performed once.
[0086]
For example, it is necessary to form a silicon oxide film functioning as a gate insulating film or an interlayer insulating film on a crystalline silicon film, and then form an electrode through a drilling process for forming the electrode. There is a case. In such a case, a process of removing the silicon oxide film with buffer hydrofluoric acid is usually employed. However, when the hydrofluoric acid resistance of the crystalline silicon film is low, it is difficult to remove only the silicon oxide film, and there is a problem that the crystalline silicon film is also etched.
[0087]
However, when the crystalline silicon film is resistant to hydrofluoric acid, the difference (selection ratio) between the etching rates of the silicon oxide film and the crystalline silicon film can be increased, so only the silicon oxide film is selected. This is extremely significant in the manufacturing process.
[0088]
As described above, the region in which the crystal grows in the lateral direction has a low concentration of metal element and good crystallinity, so that it is useful to use this region as the active region of the semiconductor device. For example, it is extremely useful to use as a channel formation region of a thin film transistor.
[0089]
Example 3
In this embodiment, a TFT is obtained using a crystalline silicon film manufactured by using the method of the present invention. The TFT of this embodiment can be used for a driver circuit or a pixel portion of an active matrix type liquid crystal display device. Needless to say, the application range of the TFT is not limited to the liquid crystal display device but can be used for a generally-known thin film integrated circuit.
[0090]
FIG. 3 shows an outline of the manufacturing process of this example. First, a base silicon oxide film (not shown) is formed to a thickness of 2000 mm on a glass substrate. This silicon oxide film is provided to prevent diffusion of impurities from the glass substrate.
[0091]
Then, an amorphous silicon film is formed to a thickness of 500 mm by the same method as in the first embodiment. Then, after hydrofluoric acid treatment for removing the natural oxide film, a thin oxide film is formed to a thickness of about 20 mm by irradiation with UV light in an oxygen atmosphere. The thin oxide film may be produced by a method using overwater treatment or thermal oxidation.
[0092]
Then, an acetate solution containing 10 ppm of nickel is applied, held for 5 minutes, and spin dried using a spinner. Thereafter, the silicon oxide films 20 and 21 are removed with buffer hydrofluoric acid, and the silicon film is crystallized by heating at 550 ° C. for 4 hours. (The process up to this point is the same as the manufacturing method shown in Example 1)
[0093]
By performing the heat treatment, a silicon film in which an amorphous component and a crystal component are mixed can be obtained. This crystal component is a region where crystal nuclei exist. Thereafter, hydrofluoric acid treatment is performed using 1/100 buffer hydrofluoric acid. Further, irradiation of KrF excimer laser light at 200 to 300 mJ promotes the disappearance of the holes generated by the hydrofluoric acid treatment and the crystallinity of the silicon film. In this laser light irradiation step, the substrate is heated to about 400 ° C. By this step, crystal growth is performed using a crystal nucleus present in the crystal component as a nucleus.
[0094]
Next, the crystallized silicon film is patterned to form island-like regions 104. This island-shaped region 104 constitutes the active layer of the TFT. Then, silicon oxide 105 having a thickness of 200 to 1500 mm, here 1000 mm is formed. This silicon oxide film also functions as a gate insulating film. (Fig. 3 (A))
[0095]
Care must be taken in the production of the silicon oxide film 105. Here, TEOS was used as a raw material, and decomposed and deposited by RF plasma CVD with oxygen at a substrate temperature of 150 to 600 ° C., preferably 300 to 450 ° C. The pressure ratio between TEOS and oxygen was 1: 1 to 1: 3, the pressure was 0.05 to 0.5 torr, and the RF power was 100 to 250 W. Alternatively, the substrate temperature was set to 350 to 600 ° C., preferably 400 to 550 ° C. using TEOS as a raw material together with ozone gas by low pressure CVD or normal pressure CVD. After film formation, annealing was performed at 400 to 600 ° C. for 30 to 60 minutes in an oxygen or ozone atmosphere.
[0096]
In this state, crystallization of the silicon region 104 may be promoted by irradiation with KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) or strong light equivalent thereto. In particular, RTA (rapid thermal annealing) using infrared light can selectively heat only silicon without heating the glass substrate, and also has an interface state at the interface between the silicon and the silicon oxide film. Since it can be reduced, it is useful in the manufacture of an insulated gate field effect semiconductor device.
[0097]
After completion of the laser light irradiation, heat treatment is performed at 550 ° C. for 4 hours in a nitrogen atmosphere.
[0098]
Thereafter, an aluminum film having a thickness of 2000 μm to 1 μm is formed by electron beam evaporation, and this is patterned to form the gate electrode 106. Aluminum may be doped with scandium (Sc) in an amount of 0.15 to 0.2% by weight. Next, the substrate is immersed in an ethylene glycol solution of tartaric acid having a pH of approximately 7 to 1 to 3%, and anodization is performed using platinum as a cathode and the aluminum gate electrode as an anode. The anodization is terminated by first increasing the voltage to 220 V at a constant current and holding it in that state for 1 hour. In this embodiment, 2 to 5 V / min is appropriate for the voltage increase rate in the constant current state. In this manner, the anodic oxide 109 having a thickness of 1500 to 3500 mm, for example, 2000 mm is formed. (Fig. 3 (B))
[0099]
Thereafter, an impurity (phosphorus) was implanted into the island-like silicon film of each TFT by the ion doping method (also called plasma doping method) using the gate electrode portion as a mask. As a doping gas, phosphine (PH_Three ) Was used. Dose amount is 1-4 × 10¹⁵cm^-2And
[0100]
Further, as shown in FIG. 3C, irradiation with a KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) is performed to improve the crystallinity of the portion where the crystallinity has deteriorated due to the introduction of the impurity region. Laser energy density is 150-400mJ / cm² , Preferably 200 to 250 mJ / cm² It is. Thus, N-type impurity (phosphorus) regions 108 and 109 are formed. The sheet resistance in these regions was 200 to 800 Ω / □.
[0101]
In this process, instead of using laser light, a flash lamp is used to raise the temperature to 1000 to 1200 ° C. (silicon monitor temperature) in a short time and heat the sample, so-called RTA (rapid thermal annealing) (RTP) Or a strong light equivalent to a so-called laser beam such as a rapid thermal process).
[0102]
Thereafter, a silicon oxide film having a thickness of 3000 mm is formed on the entire surface as an interlayer insulator 110 by using TEOS as a raw material and a plasma CVD method using this and oxygen, a low pressure CVD method using ozone, or an atmospheric pressure CVD method. The substrate temperature is 250 to 450 ° C., for example, 350 ° C. After film formation, this silicon oxide film is mechanically polished to obtain surface flatness. (Fig. 3 (D))
[0103]
Then, the interlayer insulator 110 is etched to form contact holes in the source / drain of the TFT as shown in FIG. 1E, and wirings 112 and 113 of chromium or titanium nitride are formed.
[0104]
Conventionally, a crystalline silicon film into which nickel has been introduced using plasma treatment has a low selectivity to buffer hydrofluoric acid compared to a silicon oxide film, and thus is often etched in the contact hole forming step. .
[0105]
However, when nickel is introduced using an aqueous solution at a low concentration of 10 ppm as in this embodiment, the resistance to hydrofluoric acid is high, so that the formation of the contact hole can be performed stably and with good reproducibility.
[0106]
Finally, annealing in hydrogen at 300-400 ° C. for 0.1-2 hours completes the hydrogenation of silicon. In this way, the TFT is completed. A large number of TFTs manufactured at the same time are arranged in a matrix to complete an active matrix liquid crystal display device. This TFT has source / drain regions 108/109 and a channel formation region 114. Reference numeral 115 denotes an NI electrical junction.
[0107]
When the configuration of this example is adopted, the concentration of nickel present in the active layer is 3 × 10¹⁸cm^-31x10 to a degree or less¹⁵atoms cm^-3~ 3x10¹⁸atoms cm^-3It is thought that.
[0108]
The TFT manufactured in this example has a mobility of 150 cm with an N channel.² / Vs or more is obtained. V_thHave been confirmed to have small and good characteristics. Furthermore, it has been confirmed that the variation in mobility is within ± 10%. This small variation is considered to be due to a process of incomplete crystallization by heat treatment and promotion of crystallinity by irradiation with laser light. If only laser light is used, the N channel type is 150 cm.² / Vs or more can be easily obtained, but the variation is large and the uniformity as in this embodiment cannot be obtained.
[0109]
Example 4
In this embodiment, as shown in Embodiment 2, nickel is selectively introduced, and an example is shown in which an electronic device is formed using a region in which crystal growth has occurred in the lateral direction (direction parallel to the substrate). When such a configuration is adopted, the nickel concentration in the active layer region of the device can be further reduced, and a very preferable configuration can be obtained from the viewpoint of electrical stability and reliability of the device.
[0110]
FIG. 4 shows a manufacturing process of this example. First, the substrate 201 is cleaned, and a silicon oxide base film 202 having a thickness of 2000 mm is formed by plasma CVD using TEOS (tetraethoxysilane) and oxygen as source gases. Then, an intrinsic (I-type) amorphous silicon film 203 having a thickness of 500 to 1500 mm, for example, 1000 mm is formed by plasma CVD. Next, a silicon oxide film 205 having a thickness of 500 to 2000 mm, for example, 1000 mm is continuously formed by plasma CVD. Then, the silicon oxide film 205 is selectively etched to form an exposed region 206 of amorphous silicon.
[0111]
Then, a solution (here, an acetate solution) containing nickel element, which is a metal element that promotes crystallization, is applied by the method shown in Example 2. The concentration of nickel in the acetic acid solution is 100 ppm. In addition, the detailed process sequence and conditions are the same as those shown in the second embodiment. This step may be performed by the method shown in Example 3 or Example 4.
[0112]
Thereafter, heat annealing is performed in a nitrogen atmosphere at 500 to 620 ° C., for example, 550 ° C. for 4 hours to crystallize the silicon film 203. In crystallization, crystal growth proceeds in a direction parallel to the substrate as indicated by an arrow starting from a region 206 where nickel and a silicon film are in contact with each other. In the figure, a region 204 indicates a portion crystallized by direct introduction of nickel, and a region 203 indicates a portion crystallized in the lateral direction. The crystal in the horizontal direction indicated by 203 is about 25 μm. Further, it has been confirmed that the crystal growth direction is approximately the <111> axis direction. (Fig. 4 (A))
[0113]
After the crystallization step by the heat treatment, hydrofluoric acid treatment is performed using 1/100 buffer hydrofluoric acid. Further, by irradiation with infrared light, the crystallinity of the anil and the silicon film 203 in the openings (portions where the localized nickel component (nickel silicide) has been removed) generated in the previous hydrofluoric acid treatment is promoted. This step is performed by irradiating infrared light having a wavelength of 1.2 μm. By this step, an effect equivalent to that obtained by high-temperature heat treatment for several minutes can be obtained.
[0114]
A halogen lamp is used as the infrared light source. The intensity of the infrared light is adjusted so that the temperature on the single crystal silicon wafer of the monitor is between 900-1200 ° C. Specifically, the temperature of the thermocouple embedded in the silicon wafer is monitored, and this is fed back to the infrared light source. In this embodiment, the temperature rise is constant, the speed is 50 to 200 ° C./second, and the temperature drop is natural cooling to 20 to 100 ° C. Since this infrared light irradiation selectively heats the silicon film, heating of the glass substrate can be minimized.
[0115]
Further, a heat treatment is performed at 550 ° C. for 4 hours in a nitrogen atmosphere to reduce defects in the film. Next, the silicon oxide film 205 is removed. At this time, the oxide film formed on the surface of the region 206 is also removed at the same time. Then, after patterning the silicon film 204, the island-shaped active layer region 208 is formed by dry etching. At this time, the region indicated by 206 in FIG. 4A is a region where nickel is directly introduced even though the nickel component is removed, and is a region where nickel is present at a relatively high concentration. It has also been confirmed that nickel is also present at a relatively high concentration at the tip of crystal growth. In these regions, it has been found that the nickel concentration is higher than in the middle region. Therefore, in this example, in the active layer 208, these high nickel concentration regions were not overlapped with the channel formation region. By doing so, a region having a low nickel concentration and high crystallinity can be used as the active layer of the device.
[0116]
Then, the surface of the active layer (silicon film) 208 is oxidized by leaving it in an atmosphere of 10 atm and 500 to 600 ° C., typically 550 ° C. containing 100% by volume of water vapor, to oxidize the surface of the active layer (silicon film) 208. A silicon film 209 is formed. The thickness of the silicon oxide film is 1000 mm. After the silicon oxide film 209 is formed by thermal oxidation, the substrate is held at 400 ° C. in an ammonia atmosphere (1 atm, 100%). In this state, the substrate is irradiated with infrared light having a peak at a wavelength of 0.6 to 4 μm, for example, 0.8 to 1.4 μm for 30 to 180 seconds, and the silicon oxide film 209 is nitrided. Apply. At this time, 0.1 to 10% HCl may be mixed in the atmosphere.
(Fig. 4 (B))
[0117]
Subsequently, an aluminum film (including 0.01 to 0.2% scandium) having a thickness of 3000 to 8000 mm, for example, 6000 mm is formed by a sputtering method. Then, the gate electrode 210 is formed by patterning the aluminum film. (Fig. 2 (C))
[0118]
Further, the surface of the aluminum electrode is anodized to form an oxide layer 211 on the surface. This anodization is performed in an ethylene glycol solution containing 1 to 5% tartaric acid. The thickness of the resulting oxide layer 211 is 2000 mm. Note that the oxide 211 has a thickness for forming an offset gate region in a subsequent ion doping step, and thus the length of the offset gate region can be determined by the anodic oxidation step. (Fig. 4 (D))
[0119]
Next, by an ion doping method (also called plasma doping method), self-alignment is performed in the active layer region (which constitutes the source / drain and channel) using the gate electrode portion, that is, the gate electrode 210 and the surrounding oxide layer 211 as a mask. In particular, an impurity imparting N conductivity type (here, phosphorus) is added. As doping gas, phosphine (PH_Three ) And the acceleration voltage is set to 60 to 90 kV, for example, 80 kV. The dose is 1 × 10¹⁵~ 8x10¹⁵cm^-2For example, 4 × 10¹⁵cm^-2And As a result, N-type impurity regions 212 and 213 can be formed. As is apparent from the figure, the impurity region and the gate electrode are in an offset state separated by a distance x. Such an offset state is particularly effective in reducing leakage current (also referred to as off-current) when a reverse voltage (minus in the case of an N-channel TFT) is applied to the gate electrode. In particular, in the TFT for controlling the pixels of the active matrix as in this embodiment, it is desired that the leakage current is low so that the charge accumulated in the pixel electrode does not escape in order to obtain a good image. It is effective.
[0120]
Thereafter, annealing is performed by laser light irradiation. As the laser light, a KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) is used, but other lasers may be used. The laser light irradiation condition is an energy density of 200 to 400 mJ / cm.² For example, 250 mJ / cm² And 2 to 10 shots, for example, 2 shots, were irradiated at one place. The effect may be increased by heating the substrate to about 200 to 450 ° C. during the laser light irradiation. (Fig. 4 (E))
[0121]
Subsequently, a silicon oxide film 214 having a thickness of 6000 mm is formed as an interlayer insulator by a plasma CVD method. Further, a transparent polyimide film 215 is formed by spin coating to flatten the surface.
[0122]
Then, contact holes are formed in the interlayer insulators 214 and 215, and TFT electrodes and wirings 217 and 218 are formed of a multilayer film of a metal material, for example, titanium nitride and aluminum. Finally, annealing is performed at 350 ° C. for 30 minutes in a hydrogen atmosphere of 1 atm to complete an active matrix pixel circuit having TFTs. (Fig. 4 (F))
[0123]
Since the TFT manufactured in this embodiment can obtain high mobility, it can be used for a driver circuit of an active matrix liquid crystal display device.
[0124]
Example 5
FIG. 5 shows a cross-sectional view of the manufacturing process of this example. First, a silicon oxide base film 502 having a thickness of 2000 mm is formed on a substrate (Corning 7059) 501 by sputtering. The substrate is annealed at a temperature higher than the strain temperature before or after the formation of the base film, and then slowly cooled to below the strain temperature at 0.1 to 1.0 ° C./min. There is little shrinkage of the substrate in the accompanying processes (including the thermal oxidation process of the present invention and the subsequent thermal annealing process), and mask alignment is prepared. In the Corning 7059 substrate, after annealing at 620 to 660 ° C. for 1 to 4 hours, 0.03 to 1.0 ° C./min, preferably 0.1 to 0.3 ° C./min, and then slowly cooled to 400 to 500 It is good to take it out when the temperature drops to ℃.
[0125]
Next, an intrinsic (I-type) amorphous silicon film having a thickness of 500 to 1500 mm, for example, 1000 mm is formed by plasma CVD. Then, nickel is introduced as a metal element for promoting crystallization into the surface of the amorphous silicon film by the method shown in the first embodiment. Then, it is crystallized by annealing in a nitrogen atmosphere (atmospheric pressure), 550 ° C. for 4 hours. Then, hydrofluoric acid treatment is performed using 1/50 buffer hydrofluoric acid to remove nickel components (nickel silicide) localized in the film. Furthermore, KrF excimer laser is irradiated to further promote crystallization. Further, heat treatment is performed at 550 ° C. for 4 hours in a nitrogen atmosphere. Then, the silicon film is patterned to a size of 10 to 1000 μm square to form an island-like silicon film (TFT active layer) 503. (Fig. 5 (A))
[0126]
Thereafter, an atmosphere of oxygen containing 70 to 90% of water vapor, 1 atmosphere, 500 to 750 ° C., typically 600 ° C. is formed using a pyrogenic reaction method at a ratio of hydrogen / oxygen = 1.5 to 1.9. To do. By leaving it in this atmosphere for 3 to 5 hours, the surface of the silicon film is oxidized to form a silicon oxide film 504 having a thickness of 500 to 1500 mm, for example, 1000 mm. It should be noted that due to such oxidation, the surface of the initial silicon film is reduced by 50 mm or more, and as a result, the contamination of the outermost surface portion of the silicon film does not reach the silicon-silicon oxide interface. is there. That is, a clean silicon-silicon oxide interface is obtained. Since the thickness of the silicon oxide film is twice that of the silicon film to be oxidized, a silicon oxide film having a thickness of 1000 mm is oxidized to obtain a silicon oxide film having a thickness of 1000 mm. The thickness will be 500 mm.
[0127]
In general, the thinner the silicon oxide film (gate insulating film) and the active layer, the better the characteristics of improving mobility and reducing off-current. On the other hand, the initial amorphous silicon film is easily crystallized as the film thickness increases. Therefore, conventionally, there has been a contradiction in terms of characteristics and process regarding the thickness of the active layer. The present invention solves this contradiction for the first time, that is, a thick amorphous silicon film is formed before crystallization to obtain a good crystalline silicon film. Next, by oxidizing the silicon film, the silicon film is thinned to improve the characteristics as a TFT. Further, this thermal oxidation has a feature that the amorphous component and the crystal grain boundary in which recombination centers are likely to exist are easily oxidized, and as a result, the number of recombination centers in the active layer is reduced. This increases the product yield.
[0128]
After the silicon oxide film 504 is formed by thermal oxidation, the substrate is annealed at 600 ° C. for 2 hours in a dinitrogen monoxide atmosphere (1 atm, 100%). (Fig. 5 (B))
Subsequently, polycrystalline silicon (containing 0.01 to 0.2% phosphorus) having a thickness of 3000 to 8000 mm, for example, 6000 mm is formed by low pressure CVD. Then, the gate electrode 505 is formed by patterning the silicon film. Further, an impurity (in this case, phosphorus) is given to the active layer region (which constitutes a source / drain and a channel) by an ion doping method (also called a plasma doping method) in a self-aligning manner using this silicon film as a mask. ) Is added. As doping gas, phosphine (PH_Three ) And the acceleration voltage is set to 60 to 90 kV, for example, 80 kV. The dose is 1 × 10¹⁵~ 8x10¹⁵cm^-2For example, 5 × 10¹⁵cm^-2And As a result, N-type impurity regions 506 and 507 are formed.
[0129]
Thereafter, annealing is performed by laser light irradiation. As the laser light, a KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) was used, but other lasers may be used. The laser light irradiation condition is an energy density of 200 to 400 mJ / cm.² For example, 250 mJ / cm² Then, 2 to 10 shots, for example, 2 shots are irradiated at one place. The effect may be increased by heating the substrate to about 200 to 450 ° C. during the laser light irradiation. (Fig. 6 (C))
[0130]
Further, this step may be a method by lamp annealing using near infrared light. Near-infrared rays are more easily absorbed by crystallized silicon than amorphous silicon, and effective annealing comparable to thermal annealing at 1000 ° C. or higher can be performed. On the other hand, the glass substrate (far infrared light is absorbed by the glass substrate, but visible / near infrared light (wavelength 0.5 to 4 μm) is hardly absorbed) is hardly absorbed. Since it is not heated and only a short time is required, it can be said that it is an optimal method in a process where shrinkage of the glass substrate is a problem.
[0131]
Subsequently, a silicon oxide film 508 having a thickness of 6000 mm is formed by plasma CVD as an interlayer insulator. Polyimide may be used as the interlayer insulator. Further, contact holes are formed, and TFT electrodes and wirings 509 and 510 are formed of a metal material, for example, a multilayer film of titanium nitride and aluminum. Finally, annealing is performed at 350 ° C. for 30 minutes in a hydrogen atmosphere of 1 atm to complete the TFT. (Fig. 6 (D))
[0132]
The mobility of the TFT obtained by the method shown above is 110 to 150 cm.² / Vs and S value were 0.2 to 0.5 V / digit. Further, when a P-channel TFT in which boron is doped in the source / drain by a similar method was also produced, the mobility was 90 to 120 cm.² / Vs and S value are 0.4 to 0.6 V / digit, and the mobility is 20% or more higher than when a gate insulating film is formed by a known PVD method or CVD method, and the S value is 20 More than%.
Also, from the viewpoint of reliability, the TFT manufactured in this example showed a good result that is not inferior to a TFT manufactured by high-temperature thermal oxidation at 1000 ° C.
[0133]
Example 6
FIG. 6 shows a cross-sectional view of the manufacturing process of this example. The TFT shown in this embodiment relates to a TFT arranged in a pixel portion of an active matrix type liquid crystal display device.
[0134]
First, a silicon oxide base film 52 having a thickness of 2000 mm is formed on a substrate (Corning 7059) 51. Further, an intrinsic silicon film having an amorphous silicon film thickness of 200 to 1500 mm, here 800 mm, is formed by plasma CVD. Then, nickel, which is a metal element, is introduced by the method shown in Example 1 and further subjected to heat treatment at 550 ° C. for 4 hours in a nitrogen atmosphere, thereby transforming into a crystalline silicon film. Then, hydrofluoric acid treatment is performed using 1/70 buffer hydrofluoric acid to remove nickel components localized in the film. The crystallinity of this crystalline silicon film is further promoted by irradiation with KrF excimer laser light. Further, heat treatment is performed at 550 ° C. for 4 hours in a nitrogen atmosphere.
[0135]
The crystalline silicon film thus obtained can be a crystalline silicon film having no specific crystal grain boundary in a specific region, and an active layer of a TFT is formed at an arbitrary location on the surface thereof. Can do. That is, since the entire film is crystallized uniformly, even if thin film transistors are formed in a matrix, the physical properties of the crystalline silicon film constituting the active layer of the TFT can be made uniform throughout. As a result, a large number of TFTs with small variations in characteristics can be formed. Moreover, since the nickel component in the film can be extremely reduced, the stability of the device can be enhanced.
[0136]
Then, patterning is performed to form island regions 53 made of crystalline silicon. Further, a silicon oxide film 54 having a thickness of 1000 mm is formed so as to cover the island region. In the following, an example in which one TFT is formed will be described with reference to FIG. 6, but in practice, the required number of TFTs are formed simultaneously in a matrix.
[0137]
Subsequently, an aluminum film (containing 0.1 to 0.3% by weight of scandium) having a thickness of 3000 to 8000 mm, for example, 6000 mm is deposited by sputtering. Then, a thin anodic oxide having a thickness of 100 to 400 mm is formed on the surface of the aluminum film. Then, a photoresist having a thickness of about 1 μm is formed on the aluminum film thus treated by spin coating. Then, the gate electrode 55 is formed by a known photolithography method. Here, a photoresist mask 56 remains on the gate electrode. (Fig. 6 (A))
[0138]
Next, the substrate is immersed in a 10% oxalic acid aqueous solution and anodized at a constant voltage of 5 to 50 V, for example, 8 V, for 10 to 500 minutes, for example, 200 minutes, so that a porous anodic oxide having a thickness of about 5000 mm is obtained. 57 is formed on the side surface of the gate electrode. Since the mask material 56 exists on the upper surface of the gate electrode, the anodic oxidation hardly proceeds. (Fig. 6 (B))
[0139]
Next, the mask material is removed, the top surface of the gate electrode is exposed, the substrate is immersed in an ethylene glycol solution of 3% tartaric acid (pH adjusted to neutral with ammonia), and an electric current is passed through the substrate. Anodization is performed by increasing the voltage to 100 V at ˜5 V / min, for example, 4 V / min. At this time, not only the top surface of the gate electrode but also the side surface of the gate electrode is anodized to form a dense nonporous anodic oxide 58 having a thickness of 1000 mm. The withstand voltage of this anodic oxide is 50V or more. (Fig. 6 (C))
[0140]
Next, the silicon oxide film 54 is etched by dry etching. In this etching, the anodic oxides 37 and 38 are not etched, and only the silicon oxide film is etched. Further, the silicon oxide film under the anodic oxide remains as the gate insulating film 59 without being etched. (Fig. 6 (D))
[0141]
Next, the porous anodic oxide 57 is etched using a mixed acid of phosphoric acid, phosphoric acid, acetic acid, and nitric acid to expose the nonporous anodic oxide 58. Then, an impurity (phosphorus) is implanted into the silicon region 33 by the plasma doping method using the gate electrode 35 and the porous anodic oxide 37 on the side surface as a mask. As doping gas, phosphine (PH_Three ) And the acceleration voltage is 5 to 30 kV, for example, 10 kV. The dose is 1 × 10¹⁴~ 8x10¹⁵cm^-2For example, 2 × 10¹⁵cm^-2And
[0142]
In this doping step, high-concentration phosphorus is implanted into the region 60 not covered with the gate insulating film 59. However, in the region 61 whose surface is covered with the gate insulating film 59, the gate insulating film is an obstacle. Thus, the doping amount is small, and in this embodiment, only 0.1 to 5% of impurities in the region 60 are implanted. As a result, an N-type high concentration impurity region 60 and a low concentration impurity region 61 are formed. (Fig. 6 (E))
[0143]
Thereafter, laser light is irradiated from the upper surface, laser annealing is performed, and the doped impurities are activated. Subsequently, a silicon oxide film 62 having a thickness of 6000 mm is formed as an interlayer insulator by plasma CVD. And the ITO electrode 64 used as a pixel electrode is formed. Further, contact holes are formed, and electrodes / wirings 63 for the source and drain regions of the TFT are formed of a metal material, for example, a multilayer film of titanium nitride and aluminum. Finally, annealing was performed at 350 ° C. for 30 minutes in a hydrogen atmosphere of 1 atm. Through the above steps, a thin film transistor is completed. (Fig. 6 (F))
[0144]
In this embodiment, the same structure as a so-called low concentration drain (LDD) structure can be obtained. Although the LDD structure has been shown to be effective in suppressing deterioration due to hot carriers, the same effect can be obtained with the TFT fabricated in this example. However, compared to a process for obtaining a known LDD, this embodiment is characterized in that LDD can be obtained by a single doping step. Further, the present embodiment is characterized in that the high concentration impurity region 60 is defined by using the gate insulating film 59 defined by the porous anodic oxide 57. That is, finally, the impurity region is indirectly defined by the porous anodic oxide 57. As is apparent from this example, the width x of the LDD region is substantially determined by the width of the porous anodic oxide.
[0145]
Higher degree of integration can be performed by using the manufacturing method of this embodiment. In this case, it is more convenient to change the width x of the offset region or the LDD region in accordance with the required characteristics of the TFT. In particular, when the configuration of this embodiment is employed, a reduction in the OFF current can be realized, which is optimal for a TFT intended for charge retention in the pixel electrode.
[0146]
Example 7
FIG. 7 shows a block diagram of an electro-optical system using an integrated circuit in which a display, a CPU, and a memory are mounted on a single glass substrate. Here, the input port reads an externally input signal and converts it into an image signal, and the correction memory is a memory specific to the panel for correcting the input signal etc. in accordance with the characteristics of the active matrix panel. is there. In particular, this correction memory is used for financing and individually correcting information unique to each pixel as a nonvolatile memory. That is, if a pixel of the electro-optical device has a point defect, a signal corrected accordingly is sent to the pixels around the point to cover the point defect and make the defect inconspicuous. Alternatively, when a pixel is darker than surrounding pixels, a larger signal is sent to the pixel so that the surrounding pixels have the same brightness.
[0147]
The CPU and the memory are the same as those of an ordinary computer. In particular, the memory has an image memory corresponding to each pixel as a RAM. Moreover, the backlight which irradiates a board | substrate from a back surface can also be changed according to image information.
[0148]
Then, in order to obtain the width of the offset region or the LDD region suitable for each of these circuits, 3 to 10 lines of wiring may be formed so that the anodization conditions can be individually changed. Typically, in an active matrix circuit, the channel length is 10 μm, and the width of the LDD region is 0.4 to 1 μm, for example, 0.6 μm. In the driver, the channel length is 8 μm, the channel width is 200 μm, and the width of the LDD region is 0.2 to 0.3 μm, for example, 0.25 μm. Similarly, in the P-channel TFT, the channel length is 5 μm, the channel width is 500 μm, and the width of the LDD region is 0 to 0.2 μm, for example, 0.1 μm. In the decoder, an N-channel TFT having a channel length of 8 μm and a channel width of 10 μm and a width of the LDD region of 0.3 to 0.4 μm, for example, 0.35 μm. Similarly, in a P-channel TFT, the channel length is 5 μm, the channel width is 10 μm, and the width of the LDD region is 0 to 0.2 μm, for example, 0.1 μm. Furthermore, the width of the LDD region may be optimized for the CPU, input port, correction memory, memory NTFT and PTFT in FIG. 6 as with the high frequency operation and low power consumption decoder. Thus, the electro-optical device 74 can be formed on the same substrate having an insulating surface.
[0149]
The present invention is characterized in that the width of the high resistance region can be varied to 2 to 4 types or more depending on the application. Further, this region does not have to be the same material and the same conductivity type as the channel formation region. That is, it is also possible to form a high resistance region by adding a small amount of N-type impurity in NTFT, a small amount of P-type impurity in PTFT, and selectively adding carbon, oxygen, nitrogen, or the like. This is effective in eliminating the trade-off between deterioration and reliability, frequency characteristics, and off current.
[0150]
In addition, as the TFT of the driver circuit that drives the TFT provided on the pixel electrode, it is desirable to use the TFT shown in FIGS.
[0151]
Example 8
This embodiment is characterized by being formed by the following manufacturing steps.
(1) The amorphous silicon film is crystallized by heat treatment using nickel element.
(2) The silicon film crystallized in the above step is subjected to hydrofluoric acid treatment using 1/100 buffer hydrofluoric acid to remove nickel components (nickel silicide) localized in the silicon film.
(3) The crystallinity of the silicon film crystallized in the step (1) is promoted by performing laser light irradiation.
(4) A gate electrode is formed, and impurity ions are implanted using the gate electrode as a mask to form source / drain regions.
(5) Heat treatment is performed to recrystallize the source / drain regions and activate the implanted impurities.
As described above, this embodiment is characterized in that heat treatment-nickel removal-laser light irradiation-heat treatment is performed. Here, the first heat treatment is for crystallization of the amorphous silicon film, the laser light irradiation is for promoting crystallization of the amorphous silicon film, and the second heat treatment is for the source. / For recrystallization of the drain region, activation of impurities implanted in the region, and removal of defects in the channel formation region.
[0152]
A manufacturing process of the thin film transistor illustrated in FIG. 9 is described below. First, a base silicon oxide film 902 is formed to a thickness of 2000 mm on a glass substrate 901 by sputtering. Next, an amorphous silicon film is formed to a thickness of 1000 mm by plasma CVD or low pressure thermal CVD. Then, nickel element is introduced into the surface of the amorphous silicon film using nickel acetate. Then, heat treatment is performed to crystallize the amorphous silicon film, so that a crystalline silicon film 903 is obtained. Here, a crystalline silicon film is obtained by performing heat treatment at 550 ° C. for 4 hours.
[0153]
After completion of the heat treatment, the nickel component localized (segregated) in the film is removed by hydrofluoric acid treatment using 1/100 buffer hydrofluoric acid. Next, XeCl excimer laser (wavelength 308 nm), XeF excimer laser 300 mJ / cm² The crystallinity of the crystalline silicon film 903 is promoted. (Fig. 9 (A))
[0154]
Next, the crystalline silicon film 903 is patterned to form an active layer of the thin film transistor. Then, a silicon oxide film serving as a gate insulating film is formed to a thickness of 1000 mm by plasma CVD. After the gate insulating film is formed, a film containing aluminum as a main component is formed to a thickness of 5000 mm and patterned to form the gate electrode 905. Then, an oxide layer 906 is formed around the gate electrode 905 by performing anodic oxidation in the electrolytic solution using the gate electrode 905 as an anode. Here, the thickness of the oxide layer 905 is 2000 mm.
[0155]
Next, impurity ions are implanted using the gate electrode 905 and the oxide layer 906 around the gate electrode 905 as a mask to form a source region 907, a drain region 911, a channel formation region 909, and offset gate regions 908, 910 in a self-aligning manner. To do. Here, phosphorus ions are used as impurity ions in order to obtain an N-channel thin film transistor. At this time, the source / drain regions are made amorphous by ion bombardment. (Fig. 9 (B))
[0156]
Next, in the step shown in FIG. 5C, the source region 907 and the drain region 911 are recrystallized and the implanted phosphorus ions are activated by performing a heat treatment at 500 degrees for 2 hours. In this step, crystal growth as indicated by an arrow 912 proceeds from the interface between the offset gate region 908 having crystallinity and the source region 907 that is amorphized. This crystal growth proceeds using the offset gate region 908 as a nucleus. Similarly, crystal growth as indicated by an arrow 912 proceeds from the interface between the offset gate region 910 having crystallinity and the drain region 911 that is amorphized. This crystal growth easily proceeds at a temperature of 500 degrees or less due to the action of phosphorus ions implanted in the source / drain regions. In addition, since a continuous crystal structure can be obtained from the offset gate region, concentration of defects due to lattice mismatch can be prevented.
[0157]
What is necessary is just to perform the heat processing process performed at the process of this (C) at the temperature of 300 degreeC or more. In the case of this embodiment, aluminum is used for the gate electrode, and there is a problem of heat resistance of the glass substrate. Therefore, it may be performed at a temperature of 300 to 600 degrees.
[0158]
In the heat treatment step shown in (C), it is effective to combine annealing by irradiation with laser light or strong light before or after the heat treatment step.
[0159]
Next, an interlayer insulating film is formed to a thickness of 6000 mm by plasma CVD, and a source electrode 914 and a drain electrode 915 are further formed. Then, heat treatment is performed in a hydrogen atmosphere at 350 degrees to perform hydrogenation, thereby completing the thin film transistor shown in FIG.
[0160]
In the present embodiment, the structure in which the offset gate regions 908 and 910 are formed is shown. However, when the offset gate region is not formed, in the heating step (C), the channel forming region having crystallinity Crystallization proceeds to the source / drain regions.
[0161]
Example 9
In this embodiment, an active layer of a thin film transistor is formed using a crystalline silicon film crystallized using nickel, and various cleaning or etching (for removing metal elements and various impurities) is performed on the active layer. The effect of cleaning or etching is mainly described.
[0162]
The comparison in this example is based on various characteristics of the thin film transistor from which the difference in the conditions of the cleaning or etching process for the active layer was obtained. FIG. 12 shows the difference in conditions of the cleaning or etching process. The difference in the manufacturing process of the thin film transistor is only the conditions of the cleaning or etching process for the active layer shown in FIG.
[0163]
In the conditions shown in FIG. 12, the condition No. 1 is a condition for cleaning (etching) the surface of the active layer using 1/50 BHF (buffer hydrofluoric acid). No. 2 is a condition for cleaning the surface of the active layer with FPM (a mixture of hydrogen peroxide and hydrofluoric acid diluted with water). No. 3 is a condition for performing cleaning with ozone water after cleaning the active layer with FPM. No. 4 is a condition for cleaning the active layer with ozone water after cleaning with ozone water.
[0164]
No. 5 is a condition for cleaning the surface of the active layer with a mixed solution of sulfuric acid / hydrogen peroxide / hydrochloric acid / hydrochloric acid and 1/100 hydrofluoric acid. No. 6 is a condition in which the active layer is further washed with FPM after being washed with sulfuric acid / hydrogen peroxide. No. 7 is a condition for cleaning the active layer with ozone water and further cleaning with BHF containing a surfactant.
[0165]
After the cleaning step under each condition as shown in FIG. 12, a gate insulating film is formed. Further, gate electrodes are formed, source / drain regions are formed, interlayer insulating films are formed, and source / drain electrodes are formed to complete the thin film transistor.
[0166]
V of the thin film transistor obtained in FIG._th(Threshold) data is shown. The substrate number on the horizontal axis in the figure corresponds to the experiment number in FIG. As is apparent from FIG. 13, the thin film transistor under the experimental conditions 2 to 7 is an N-channel type V_thHas a normally-off characteristic of 2 to 3 V plus (the transistor is turned off when the voltage applied to the gate electrode is 0 V or higher).
[0167]
P channel type V_thHas a normally-off characteristic of -1 to -2V. Such characteristics are preferable when a thin film transistor is actually used. However, in the case of condition 1, P channel type and N channel type V_thThere is a difference in characteristics, which is not preferable.
[0168]
In FIG._thThe standard deviation indicating the degree of variation in the value of is shown. From this figure, in the case of condition 1 and condition 4 and condition 7, V has the least variation._thIt can be seen that the characteristics are obtained. This is most significant when these conditions are adopted._thThis means that thin film transistors with uniform characteristics can be obtained.
[0169]
However, as shown in FIG. 13, the characteristics of Condition 1 are not preferable. Therefore, V_thFrom the comprehensive viewpoint of the characteristics and the variation of the values, the conditions 4 and 7 are preferable.
[0170]
FIG. 15 shows OFF current characteristics corresponding to each condition. FIG. 15 shows the case of N channel type and V_D= 14V, V_GIt shows the value of OFF current when = 4.5V. For the P channel, V_D= 14V, V_GThe value of OFF current in the case of = 4.5V is shown.
[0171]
As can be seen from FIG. 15, in the case of condition 4 and condition 7, the lowest OFF current value is obtained in both the N channel type and the P channel type.
[0172]
FIG. 16 shows the standard deviation of the OFF current value shown in FIG. As is apparent from FIG. 15, the OFF current characteristic with the least variation can be obtained in the case of condition 4.
[0173]
The following conclusions can be obtained from the data shown above.
“Overall, by performing cleaning with ozone water and then cleaning (etching) with an etchant containing hydrofluoric acid, a thin film transistor having good characteristics and no variation in characteristics can be obtained.”
[0174]
It is considered that a significant effect can be obtained by performing such processing for the following reason.
[0175]
In an ideal state, a silicon atom bond on the surface of the active layer needs to be terminated by a hydrogen atom. However, most of them are actually terminated by impurities such as organic substances.
[0176]
Such a state leads to generation of trap levels at a high density.
Further, when the metal element contributing to crystallization is exposed on the surface of the active layer, a trap level is formed there.
[0177]
Furthermore, when the active layer of the thin film transistor is formed by patterning, a dangling bond is formed on the surface of the active layer. In particular, when dry etching using plasma is used, this tendency becomes obvious due to plasma damage.
[0178]
In any case, this state leads to the formation of trap levels at a high density.
[0179]
Such trap levels are V_thShift and variations thereof, and further causes an increase in OFF current value and variations thereof. That is, V due to carrier movement through the trap level._thShift and OFF current value increase. Further, since the movement of carriers via this trap level is unstable, the above V_thThe shift and the OFF current value vary.
[0180]
In such a state, when the treatment as shown in Condition 4 or Condition 7 in FIG. 12 is performed on the surface of the active layer, impurities such as organic substances and metal elements existing on the surface of the active layer are removed. be able to.
[0181]
That is, first, an organic substance or a metal element is converted into an oxide by treatment with ozone water having a strong oxidizing power, and further, this oxide is removed by etching using an etchant solution containing hydrofluoric acid, thereby existing on the surface of the active layer. The trap level can be reduced.
[0182]
What is important here is that treatment with ozone water having strong oxidizing power is performed in order to convert the organic substance or metal element to be removed first into an oxide. Then, this oxide is removed.
[0183]
【effect】
The amorphous silicon film is crystallized in a short time at a low temperature by introducing a metal element, and further, a localized metal component is removed by performing a hydrofluoric acid treatment, and further irradiated with laser light or strong light, By manufacturing a semiconductor device using a crystalline silicon film to which heat treatment is performed thereafter, a device with high productivity and good characteristics can be obtained.
In particular, a crystalline silicon film having a low metal element concentration in the film can be obtained at a lower temperature than in the past, and by using this crystalline silicon film, a highly stable thin film transistor with little variation in characteristics can be obtained. it can.
In addition, it is useful to manufacture various semiconductor devices using a crystalline silicon film obtained by utilizing the invention disclosed in this specification.
[0184]
In addition, the crystalline silicon film is first washed with a solvent having a strong oxidizing power, and further washed with a solvent having a function of removing oxides, so that a metal element or an organic substance existing on the surface of the crystalline silicon film is obtained. And the characteristics of the obtained semiconductor device can be improved. Further, stability of characteristics of the obtained semiconductor device can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a process of an example.
FIG. 2 is a diagram showing a process of an example.
FIG. 3 is a diagram showing a manufacturing process of the example.
FIG. 4 is a diagram showing a manufacturing process of an example.
FIG. 5 is a diagram showing a manufacturing process of an example.
FIG. 6 is a diagram showing a manufacturing process of an example.
FIG. 7 is a diagram showing a configuration of an example.
FIG. 8 is a diagram showing the results of ESR measurement.
FIG. 9 shows a manufacturing process of the example.
FIG. 10 is a photograph showing a state of a thin film of a crystalline silicon film treated with hydrofluoric acid.
11 is a diagram schematically showing the photograph of FIG.
FIG. 12 is a diagram showing cleaning conditions for an active layer.
FIG. 13 shows V due to the difference in experimental conditions._thThe figure which shows the average value.
FIG. 14 shows V depending on experimental conditions._thThe figure which shows standard deviation of.
FIG. 15 is a diagram showing an average value of OFF current values depending on experimental conditions.
FIG. 16 is a diagram showing a standard deviation of an OFF current value due to a difference in experimental conditions.
[Explanation of symbols]
11 .... Glass substrate
12. Amorphous silicon film
13... Silicon oxide film
14... Acetic acid solution film containing nickel
15 ... Spinner
21... Silicon oxide film for mask
20... Silicon oxide film
11 .... Glass substrate
104 ... Active layer
105 ... Silicon oxide film
106 ... Gate electrode
109 ... Oxide layer
108 ... Source / drain region
109 ... Drain / source region
110... Interlayer insulating film (silicon oxide film)
112 ... Electrodes
113 ... Electrode

Claims (11)

Introducing into the amorphous silicon film a metal element that promotes crystallization of the amorphous silicon film,
The amorphous silicon film introduced with the metal element is heated to form a crystalline silicon film,
By etching the crystalline silicon film by using an etching solution containing hydrofluoric acid, after removal of the silicide of the metal element and silicon of the crystalline silicon film, with respect to the crystalline silicon film A method for manufacturing a semiconductor device, characterized by irradiating laser light or strong light. Introducing into the amorphous silicon film a metal element that promotes crystallization of the amorphous silicon film,
The amorphous silicon film introduced with the metal element is heated to form a crystalline silicon film,
By etching the crystalline silicon film using an etching solution containing hydrofluoric acid, the silicide of the metal element and silicon in the crystalline silicon film is removed, and then the crystalline silicon film is applied to the crystalline silicon film. Irradiate with laser light or strong light,
A method for manufacturing a semiconductor device, comprising: heating a crystalline silicon film irradiated with the laser light or the strong light. Introducing into the amorphous silicon film a metal element that promotes crystallization of the amorphous silicon film,
The amorphous silicon film introduced with the metal element is heated to form a crystalline silicon film,
By etching the crystalline silicon film by using an etching solution containing hydrofluoric acid, after removal of the silicide of the metal element and silicon of the crystalline silicon film, a laser beam to the crystalline silicon film A method for manufacturing a semiconductor device, wherein the semiconductor device is irradiated a plurality of times. Introducing into the amorphous silicon film a metal element that promotes crystallization of the amorphous silicon film,
The amorphous silicon film introduced with the metal element is heated to form a crystalline silicon film,
By etching the crystalline silicon film by using an etching solution containing hydrofluoric acid, after removal of the silicide of the metal element and silicon of the crystalline silicon film, a laser beam to the crystalline silicon film Alternatively, a method for manufacturing a semiconductor device is characterized in that intense light is irradiated a plurality of times and the irradiation energy density is increased stepwise. Introducing into the amorphous silicon film a metal element that promotes crystallization of the amorphous silicon film,
The amorphous silicon film introduced with the metal element is heated to form a crystalline silicon film,
By etching the crystalline silicon film by using an etching solution containing hydrofluoric acid, after removal of the silicide of the metal element and silicon of the crystalline silicon film, a laser beam to the crystalline silicon film Alternatively, a method for manufacturing a semiconductor device is characterized in that the step of irradiating intense light and the heat treatment step for reducing defects in the crystalline silicon film are alternately repeated twice or more. 5. The method for manufacturing a semiconductor device according to claim 4 , wherein the laser light or the intense light is irradiated in an oxygen atmosphere or air. In any one of claims 1 to 5, a method for manufacturing a semiconductor device, characterized in that the laser beam is irradiated in a nitrogen atmosphere. In any one of claims 1 to 7, by irradiation of the laser light or the strong light, the method for manufacturing a semiconductor device, characterized in that extinguishing the holes formed in the crystalline silicon film by the etching. In any one of claims 1 to 8, as the metal element, Fe, Co, Ni, Ru , Rh, Pd, Os, Ir, Pt, Cu, Ag, is one selected from Au or more kinds of elements A method for manufacturing a semiconductor device, which is used. 10. The method according to claim 1, wherein the metal element is introduced into the amorphous silicon film by applying a solution containing the metal element to the surface of the amorphous silicon film. A method for manufacturing a semiconductor device. 10. The metal element according to claim 1, wherein the metal element is introduced into the amorphous silicon film by applying a solution containing the metal element and a surfactant to the surface of the amorphous silicon film. A method for manufacturing a semiconductor device.

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