JP2000100812A - Method for forming silicon nitride film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride film whose controllability of film thickness is satisfactory, even if the film is thin through the means of a CVD method by providing trichlorosilane (SiCl4) and ammonia (NH3) on the surface of a processed object as raw gases. SOLUTION: N2 gas is supplied into a heat treatment container 8, where a temperature is maintained to that at which a natural oxide film is difficult to adhere. A water board 10 where the multiple stages of wafers W are kept is stored, the inner part of the container 8 is set to a sealed state, N2 gas is discharged, and ammonia (NH3) gas is continuously supplied instead. At processing a success film, tetrachlorosilane (SiCl4) is supplied, in addition to NH3 gas. At this time, it turns into 3SiCl4+4NH3=Si3N4+12HCl by thermal CVD method film forming reaction. Then, a silicon nitride (Si3N4) film is formed. The film is superior in insulating property. In particular leak current is less, the film can be thinned and the characteristic can be improved, when it is used as the insulating film of the capacitor of a semiconductor integrated circuit such as DRAMs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a silicon nitride film having good electrical characteristics as an insulating film or the like.

[0002]

2. Description of the Related Art In general, when a semiconductor integrated circuit is manufactured, various films such as a silicon film and a silicon oxide film are formed on the surface of a semiconductor wafer or a glass substrate, or oxidized or various heat treatments are performed. Is applied. In order to improve the characteristics of such a semiconductor integrated circuit, it is particularly important to improve the characteristics of individual transistors and capacitors incorporated therein. By the way, recent demands for higher density, higher integration, and multi-layering of semiconductor integrated circuits require further thinning. For this reason, various types of insulating films are required to have the same or better electrical characteristics such as insulating properties while achieving thinning.

[0003] Under such circumstances, there is a demand for a material having good electrical characteristics that can maintain a predetermined capacity in a small area while suppressing a leak current even if an insulating film such as a capacitor is made thin. I have. As a material for such an insulating film, a silicon nitride film (silicon nitride film) represented by Si ₃ N ₄ has been attracting attention because of its high dielectric constant and excellent insulating properties. Conventionally, this silicon nitride film has been conventionally subjected to thermal CVD in a temperature range of 650 to 750 ° C. using dichlorosilane (SiH ₂ Cl ₂ ) and ammonia (NH ₃ ) as source gases.
(Chemical Vapor Deposition
The film is formed by the n) method.

[0004]

As described above, a silicon nitride film formed by using dichlorosilane and ammonia has a certain degree of excellent electrical properties such as insulating properties. Contains a hydrogen group, so that several nm (3 to 5 n
When the film thickness is as extremely small as about m), the hydrogen groups may cause a leak current, and may not always exhibit high insulating properties. In addition, when a film is formed using dichlorosilane and ammonia as source gases as described above, the film formation rate is considerably high. Therefore, when a silicon nitride film having a very small thickness of about several nm is formed as described above, In addition, there was a problem that the film thickness could not be controlled with high accuracy and the desired film thickness could not be set with high accuracy.

[0005] The present invention focuses on the above problems,
It was created to solve this effectively. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a silicon nitride film which is excellent in insulating properties and has good controllability of the film thickness even when forming a very thin film.

[0006]

The present inventors have conducted intensive studies on silicon nitride films. As a result, they are liquid at room temperature, highly corrosive, and do not react unless they are at a higher temperature than dichlorosilane. The use of trichlorosilane (SiCl ₄ ), which has been used only in the field of Si epitaxial growth, which requires a process at a high temperature of about 1100 ° C. due to the difficulty in obtaining a silicon nitride film having good characteristics. The present invention has been made by finding out that the above-mentioned facts can be obtained.

According to a first aspect of the present invention, a silicon nitride film is formed on a surface of an object by thermal CVD using SiCl ₄ and NH ₃ as source gases.

As a result, even if the film thickness is extremely small, electrical characteristics such as insulation can be greatly improved, and the controllability of the film thickness during film formation can be improved. In this case, prior to the film forming process, if the surface of the object to be processed is subjected to nitridation with NH _{3 at} a high temperature, the natural oxide film adhering to the interface is nitrided, Is improved, so that the insulation can be further improved. This nitriding treatment is performed, for example, at 700 to 1000
It is good to carry out within a temperature range of ° C.

[0009] The process temperature of the film forming process is 6
When the temperature is in the range of 50 to 800 ° C., the film formation rate can be made smaller than in the case of the conventional film formation using dichlorosilane, so that the controllability of the film thickness can be improved.

Further, by using the silicon nitride film as an insulating film of a capacitor of a semiconductor integrated circuit, it is possible to contribute to a reduction in the thickness of the capacitor while maintaining the capacitance characteristics, the insulating characteristics and the like of the capacitor. .

Further, the film forming process is performed by a vertical batch type heat treatment apparatus capable of raising and lowering the temperature at a high speed.
The whole process can be performed quickly. Further, by loading the object to be processed into the heat treatment apparatus at a low temperature of 400 ° C. or less, the growth of a natural oxide film can be further suppressed, which can further contribute to the improvement of insulation properties. .

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for forming a silicon nitride film according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a view showing a vertical batch type heat treatment apparatus for carrying out the method of the present invention, and FIG. 2 is a schematic configuration diagram showing a heat treatment apparatus and a gas supply system. First, the heat treatment apparatus will be described. Here, for example, in order to enable a high-speed temperature rise and a high-speed temperature decrease of a semiconductor wafer to be processed,
As the heat treatment apparatus, for example, a vertical heat treatment apparatus capable of rapidly raising and lowering the temperature is used. As shown in the figure, this batch type vertical heat treatment apparatus 2 has a cylindrical outer cylinder 4 having a ceiling with a transparent heat-resistant material, for example, quartz and having an open bottom, and a predetermined interval inside the outer cylinder 4. It has a heat treatment vessel 8 consisting of a cylindrical inner cylinder 6 arranged concentrically, and has a double pipe structure. Inside the heat treatment container 8, a large number of semiconductor wafers W as objects to be processed, for example, about 100 8-inch wafers can be accommodated in a quartz wafer boat 10 which is also arranged in multiple stages at a predetermined pitch in the vertical direction. Has been made.

At the lower end opening of the heat treatment container 8, there is provided a flange cap portion 12 for opening and closing the same in an airtight manner. The wafer boat 10 is mounted on the cap portion 12 via a heat insulating tube 14 made of quartz. Is placed. The cap unit 12 is connected to a boat elevator 15 via an arm 16, and by moving the cap unit 12 up and down, the wafer W mounted on the wafer boat 10 can be inserted into and removed from the heat treatment container 8. The heat retaining cylinder 14 is connected to a motor or the like via a rotating shaft 18 and a rotating belt (not shown), and is rotatable. Therefore, during the heat treatment, the wafer W is rotated together with the wafer boat 10 to ensure uniformity of the heat treatment. Also,
A manifold 20 made of, for example, stainless steel is provided below the outer cylinder 4 of the heat treatment container 8, and a lower end of the inner cylinder 6 is supported by a protrusion 21 provided inside the manifold 20. A gas nozzle 22 for introducing a tetrachlorosilane (SiCl ₄ ) gas as a raw material gas and a gas nozzle 24 for introducing an NH ₃ gas are introduced into the lower portion of the inner cylinder 6 of the manifold 20. Further, N ₂ gas can be introduced from the gas nozzle 24. Further, the manifold 20 is provided with an exhaust port 26 connected to a vacuum pump (not shown), so that the inside of the container 8 can be evacuated to a desired degree of vacuum from the gap between the outer cylinder 4 and the inner cylinder 6. It has become.

On the other hand, a cylindrical heat insulating layer 28 made of, for example, a ceramic fiber heat insulating material is provided on the outer periphery of the heat treatment container 8 so as to cover the side and the ceiling. For example, a heater 30 as a heating source arranged in a cylindrical shape coaxially or coaxially is arranged at a high density. The heater 30 is made of, for example, a heating resistor (a Kanthal super heating source manufactured by Kanthal Co.) having molybdenum disilicide (MoSi ₂ ) as a main component. Has the property of increasing. This heater 30 is
While the surface load of the conventional FeCrAl heating source is 2 W / cm ² at 1200 ° C., it is 10 to 30 W / cm ^2.
The heat generation amount is as large as about ² and several times to several tens times, and the wafer W can be heated at a high speed of, for example, 50 to 200 ° C./min.

The lower portion of the heat insulating layer 28 is joined to the lower portion of the heat treatment container 8 via a heat insulating seal member 32, and a ring-shaped cooling header 34 is provided below this lower portion along the circumferential direction. The cooling header 34 is connected to a cooling gas introduction passage 38 provided with a blower fan 36 on the way, and from the cooling header 34 to the inside of the gap between the outer peripheral wall of the heat treatment container 8 and the inner wall of the heat insulating layer 28. A suitable number of cooling nozzles 40 are provided to cool the wafer W at a high speed by blowing a cooling gas onto the outer peripheral wall of the heat treatment container 8 at the time of temperature reduction after the heat treatment. . The cooling rate at this time is, for example, 30 to 100.
° C / min. Then, on the ceiling of the heat insulating layer 28,
An exhaust port 42 for discharging the cooling gas is formed,
The exhaust port 42 is provided with a shutter 44 which can be opened and closed to close the wafer W during heat treatment.

The heat treatment apparatus 2 configured as described above includes:
As shown in FIG. 2, SiCl ₄ and NH ₃
And a system for supplying an inert gas such as N ₂ gas. Specifically, SiCl _{4, which} is liquid at normal temperature, is stored in a SiCl ₄ tank 46, and this tank 46 is heated and maintained at a temperature equal to or higher than the vaporization temperature, for example, about 55 ° C. by a heating source 48 having a temperature control function. The SiCl ₄ tank 46 is connected to the film forming gas nozzle 22 of the heat treatment apparatus 2 via a SiCl ₄ gas passage 50. An on-off valve 52, a regulator 54, a flow controller 56 such as a mass flow controller for controlling the flow rate, and the like are sequentially provided in the middle of the SiCl ₄ gas passage 50. Further, for example, a tape heater 58 is wound around the SiCl ₄ gas passage 50 from the outlet of the tank 46 to the film forming gas nozzle 22 to prevent re-liquefaction, and the passage 50 is vaporized by the SiCl ₄ gas. Above temperature,
For example, it can be heated and maintained at about 75 to 85 ° C.

Further, N ₂ gas cylinder 62 for storing a NH ₃ gas cylinder 60 and the N ₂ gas storing NH ₃ gas
Are connected to branch gas passages 64 and 66, respectively, and the branch gas passages 64 and 66 join to form a gas passage 68 which is connected to the other gas nozzle 24. And
Opening / closing valves 70 and 72 and flow controllers 74 and 76 such as mass flow controllers are interposed in the branch gas passages 64 and 66, respectively. The number of the gas nozzles 24 may be increased, and the NH ₃ gas and the N ₂ gas may be independently introduced into the heat treatment vessel 8 from different nozzles.

Next, the method of the present invention performed using the apparatus configured as described above will be described. FIG. 3 is a diagram showing a timing chart for explaining the method of the present invention. In FIG. 3, the vertical axis indicates temperature. First,
Prior to loading the wafer W into the heat treatment container 8, a temperature within a range of 300 to 600 ° C., which is a temperature at which a natural oxide film is unlikely to adhere to the wafer W, within the heat treatment container 8, for example, 4
The wafer boat 10 holding a large number of wafers W in multiple stages in this state is supplied with a predetermined flow rate of N ₂ gas into the heat treatment vessel 8 in order to maintain the temperature at 00 ° C. and further suppress the generation of a natural oxide film. The container 8 is loaded from below and raised to be accommodated in the container, and the lower end opening is closed with the cap portion 12 to make the inside of the container 8 airtight (period A). If the temperature of the container 8 is lower than 300 ° C., it takes more time than necessary for the subsequent temperature increase.

Next, the supply of N ₂ gas is stopped, the inside of the heat treatment vessel 8 is evacuated to discharge N ₂ gas (period B), and NH ₃ gas is supplied at a predetermined flow rate instead ( In the period C), after a while, the amount of power input to the heater 30 is rapidly increased to rapidly raise the temperature of the wafer W at a rate of about 50 to 100 ° C./min (period D).
The pretreatment is performed for a predetermined period of time, for example, about 30 minutes while maintaining the temperature within the above range, for example, 900 ° C. (period E). The wafer W is subjected to a surface treatment by this pre-processing.
Nitrogen treatment of organic contaminants and natural oxide film of SiO ₂ that may be slightly attached to the surface of the surface, and then improve the characteristics of the interface with the silicon nitride layer to be laminated on this It is supposed to. At this time, the flow rate of the NH ₃ gas is, for example, about 2000 sccm, and the process pressure is about 6 Torr.

After the pre-processing (surface processing) is completed, the wafer W is heated to a predetermined processing temperature, for example, 700.
The temperature is rapidly decreased to, for example, 30 to 100 ° C./min (period F) to stabilize the temperature (period G), and a silicon nitride film is formed at this temperature (period H). . During the past, it continues to supply NH ₃ gas, also continue to supply NH ₃ gas during the deposition process. During this film forming process, tetrachlorosilane (SiCl ₄ ) is supplied at a predetermined flow rate in addition to the NH ₃ gas. As shown in FIG. 2, this tetrachlorosilane is gasified from the liquid SiCl ₄ by heating and maintaining the inside of the SiCl ₄ cylinder 46 at, for example, 55 ° C., and heat-treated through the SiCl ₄ gas supply passage 50 while controlling the flow rate. It is supplied to the container 8. In this case, since the SiCl ₄ gas supply passage 50 is heated to about 85 ° C. by the tape heater 58, the SiCl ₄ gas is stably supplied without being reliquefied. At this time, heat C
The silicon nitride film (S
i ₃ N ₄ ) are formed. 3SiCl ₄ + 4NH ₃ → Si ₃ N ₄ + 12HCl

The process conditions for this film formation are as follows: NH ₃ gas is in a range of 100 to 1000 sccm, for example, 200 sc
cm, the SiCl ₄ gas is in the range of 10-100 sccm, for example, about 20 sccm, and the pressure is 0.1-1.0.
Torr, for example, about 0.2 Torr,
The processing time depends on the film thickness to be formed.
In the case of nm, it is about 30 minutes. Thus, Si
When the silicon nitride film formation process is completed by a thermal CVD method using a source gas composed of Cl ₄ and NH ₃ , the supply of the NH ₃ gas and the SiCl ₄ gas is stopped, and the inside of the heat treatment container 8 is evacuated. To remove residual gas (period I), and perform cycle purge, for example, for 30 minutes.
The temperature is rapidly lowered at a rate of about 100 ° C./min to cool the wafer W to a temperature at which a natural oxide film is hardly generated, for example, 400 ° C. (period J). Thereafter, the wafer W processed therefrom is unloaded while the N ₂ gas is supplied into the heat treatment container 8, and the process is terminated (period K).

The silicon nitride film thus formed is subjected to thermal C by using dichlorosilane and NH ₃ gas.
Compared with the conventional silicon nitride film formed by the VD method, it has excellent insulation properties, and particularly when used as an insulating film of a capacitor of a semiconductor integrated circuit such as a DRAM, the leakage current is reduced and the thickness is reduced. Is possible, and the characteristics can be improved. The reason why the leak current can be reduced in this way is that the conventional silicon nitride film using dichlorosilane (SiH ₂ Cl ₂ ) containing hydrogen in the source gas causes hydrogen to be contained in the film and causes leakage current. However, when tetrachlorosilane (SiCl ₄ ) containing no hydrogen is used in the source gas as in the present invention, hydrogen is not contained in the silicon nitride film. Conceivable. In addition, by performing a pretreatment of nitriding the wafer surface before forming the silicon nitride film, the natural oxide film and organic substances adhered to the surface are nitrided and removed, so that the characteristics at the interface are reduced. The improved insulating properties can be further improved.

Next, the silicon nitride according to the method of the present invention will be described.
Of nitride film and silicon nitride film by conventional method
Was evaluated, and the results will be described. Figure
4 is a silicon nitride film according to the method of the present invention and a conventional method.
Showing leakage current of silicon nitride film
It is rough. At this time, the film thicknesses are both 3.3 nm. This
As is clear from the graph of FIG.
The nitride film is different from the conventional silicon nitride film.
Low leakage current and excellent insulation.
Revealed. FIG. 5 shows a silicon nitride according to the method of the present invention.
Of nitride film and silicon nitride film by conventional method
Thickness and leak current 1.0 × 10^-8A / cm^Two Application at
4 is a graph showing a relationship with a voltage. It is clear from this graph
As described above, when the film thickness is constant, 1.0 × 10
^-8A / cm^Two The applied voltage when the leakage current of
Of the present invention more than the silicon nitride film by the conventional method
The silicon nitride film by the method is higher,
Insulation is good. In other words, for example, when the applied voltage is
1.0 × 10 at 1V ^-8A / cm^Two Allows for leakage current
If it is possible, conventional silicon nitride film
A film thickness of about 4.3 nm is required,
For a nitride film, a film thickness of about 3.8 nm is sufficient.
It is determined that it is suitable for semiconductor integrated circuits in response to thinning.
You.

FIG. 6 is a graph showing the relationship between the film forming rate and the film forming temperature of the silicon nitride film according to the method of the present invention and the silicon nitride film according to the conventional method. As is clear from this graph, at 650 ° C. or higher, the film formation rate of the silicon nitride film of the present invention is smaller than that of the conventional silicon nitride film. It is clear that the method of the present invention having a smaller film forming rate is more excellent in controlling the film thickness for forming the film. However, the film formation temperature is 800 ° C
If the thickness is larger than 1 nm, the film formation rate exceeds 1 nm / min. Therefore, it is difficult to precisely control the film thickness in forming a thin film having a thickness of about several nm. , Thus the aforementioned period H
Should be set in the range of 650 to 800 ° C. In addition, the uniformity of the thickness of the silicon nitride film in the plane and between the planes of the method of the present invention was evaluated, and the results are shown in Table 1.

[0025]

[Table 1]

In the evaluation, the wafers formed at the top (TOP), the center (CTR), and the bottom (BTM) of the wafer boat were taken out, and the film thickness at nine positions uniformly distributed for each wafer was measured. It was measured. As a result of calculating the numerical values in Table 1, the in-plane uniformity of the film thickness was ± 1.07 to 1.45%, and the inter-surface uniformity of the film thickness was ± 4.07%. It turned out to be almost the same as in the method. In the above embodiment, the case where the silicon nitride film is used as the insulating film of the capacitor has been described as an example. However, the present invention is not limited to this, and the silicon nitride film may be used as the gate insulating film or the interlayer insulating film of the transistor. Of course. Further, in the above embodiment, the case where the method of the present invention is performed by a batch type vertical heat treatment apparatus is described as an example. However, the present invention is not limited to this, and a horizontal heat treatment apparatus or a single wafer heat treatment apparatus may be used. Of course. Further, the object to be processed is not limited to a semiconductor wafer, but may be applied to an LCD substrate, a glass substrate, and the like.

[0027]

As described above, according to the present invention,
The following excellent functions and effects can be exhibited. As described in claim 1, by forming a silicon nitride film by a thermal CVD method using SiCl ₄ and NH ₃ as source gases, the insulating property is higher than that of a conventional film and the electric characteristics are better. A film can be formed. As described in Claims 2 and 3, if the surface of the object to be processed is subjected to nitriding treatment before film formation, an organic substance or a natural oxide film attached to the surface is nitrided, so that the interface can be improved. An insulating film having more excellent characteristics can be formed.
As defined in claim 4, the process temperature at the time of film formation is 6
By setting the temperature within the range of 50 to 800 ° C., the film forming rate can be reduced and the controllability of the film thickness can be improved. By using the silicon nitride film according to the method of the present invention as an insulating film of a capacitor, a capacitor having a small thickness and good characteristics can be formed. As defined in claim 6, if the film forming process of the method of the present invention is performed by a heat treatment apparatus capable of raising and lowering the temperature at a high speed, it is possible to improve the throughput without requiring much time when raising and lowering the temperature. As set forth in claim 7, the heat treatment apparatus has a temperature of 400 ° C.
If the object is loaded in the following low temperature state, a natural oxide film generated on the object is further suppressed,
Further, a silicon nitride film having excellent characteristics can be formed.

[Brief description of the drawings]

FIG. 1 is a view showing a vertical batch type heat treatment apparatus for carrying out a method of the present invention.

FIG. 2 is a schematic configuration diagram showing a heat treatment apparatus and a gas supply system.

FIG. 3 is a diagram showing a timing chart for explaining the method of the present invention.

FIG. 4 is a graph showing leakage currents of a silicon nitride film according to a method of the present invention and a silicon nitride film according to a conventional method.

FIG. 5 is a graph showing the relationship between the thickness of a silicon nitride film according to the method of the present invention and a silicon nitride film according to a conventional method, and the applied voltage at a leak current of 1.0 × 10 ⁻⁸ A / cm ² .

FIG. 6 is a graph showing a relationship between a film forming rate and a film forming temperature of a silicon nitride film according to a method of the present invention and a silicon nitride film according to a conventional method.

[Explanation of symbols]

2 Heat treatment apparatus 4 Outer cylinder 6 Inner cylinder 8 Heat treatment vessel 10 Wafer boat 22 Film deposition gas nozzle 30 Heater 46 SiCl ₄ tank 48 Heat source 50 SiCl ₄ gas passage 58 Tape heater 60 NH ₃ gas cylinder 62 N ₂ gas cylinder W Semiconductor wafer (coated) Processing body)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigehiko Saida 8 Shinsugita-machi, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Masayuki Imai 650 Mitsuzawa, Hosaka-cho, Nirasaki, Yamanashi Prefecture Tokyo Electron Stock In-company (72) Inventor Hiroaki Ikegawa 650 Mitsuzawa, Hosaka-cho, Nirasaki, Yamanashi Prefecture Inside Tokyo Electron Limited (72) Inventor Tsukasa Yonekawa 650 Mitsuzawa, Hosaka-cho, Nirasaki, Yamanashi Prefecture Tokyo Electron Limited (72) Inventor Yamamoto Hiroyuki 1-241 Machiya, Shiroyama-cho, Tsukui-gun, Kanagawa Prefecture F-term (reference) 4K030 AA03 AA06 AA13 AA18 BA40 CA04 CA12 DA02 FA10 GA12 JA10 KA04 KA23 LA02 LA15 5F045 AA06 AB33 AC03 AC15 AD11 AD12 AD13 AD14 AE19 AF03 BB02 BB16 DC63 DP19 EC02 EK06 HA 06 5F058 BA06 BA11 BC08 BE10 BF04 BF24 BF30 BJ01

Claims (7)

[Claims] 1. The method according to claim 1, wherein the surface of the object to be processed is SiCl ₄ and NH _3.
Characterized in that a silicon nitride film is formed by a thermal CVD method using as a source gas. 2. The film formation of a silicon nitride film according to claim 1, wherein the surface of the object to be processed is subjected to a nitriding treatment with NH _{3 at} a high temperature prior to the film forming process. Method. 3. The method according to claim 2, wherein the nitriding is performed within a temperature range of 700 to 1000 ° C. 4. The process temperature of the film forming process is 650.
The method for forming a silicon nitride film according to any one of claims 1 to 3, wherein the temperature is in the range of -800C. 5. The method for forming a silicon nitride film according to claim 1, wherein the silicon nitride film is used as an insulating film of a capacitor of a semiconductor integrated circuit. 6. The film formation of a silicon nitride film according to claim 1, wherein the film formation process is performed by a vertical batch type heat treatment apparatus capable of rapidly raising and lowering the temperature. Method. 7. The method for forming a silicon nitride film according to claim 6, wherein the object to be processed is loaded into the heat treatment apparatus at a low temperature of 400 ° C. or lower.