JPH05166784A - Cleaning method for substrate - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a novel substrate cleaning method capable of efficiently cleaning and removing foreign matter having a minute particle size that cannot be sufficiently removed by a conventional cleaning method. [Constitution] As for the state of adhesion of foreign matter to a semiconductor substrate, as shown in FIG. 4, when the particle size is 0.1 μm or less, the particle size of the foreign matter and the adhesion energy are in a linear relationship. It was found that the smaller the value, the smaller the adhesion energy. Therefore, in the cleaning method of the present invention, whether the fine foreign matter on the semiconductor substrate is removed from the substrate by reducing its adhesion energy,
Alternatively, it is removed by applying energy larger than the adhesion energy from the outside. As a method of reducing the adhesion energy, for example, there is a method of irradiating an energy beam such as a laser beam onto a foreign substance to destroy the particles, and a method of applying energy is a method of heating in a cleaning liquid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate cleaning method represented by a semiconductor element manufacturing process, and is particularly suitable for removing extremely minute foreign substances as the elements become highly integrated and highly densified. A method for cleaning a substrate.

[0002]

2. Description of the Related Art In a recent fine processing process for electronic devices such as semiconductor devices and liquid crystal devices, which are highly integrated and have a high density, removal of minute foreign substances is an important task of substrate cleaning technology. Taking semiconductor devices as an example, the next generation
In a 6 Mbit DRAM, the minimum processing size is 0.5 μm, and it is said that the particle size of the foreign matter to be removed is 1/10 of that, so the foreign matter with the particle size of 0.05 μm must be removed. In the next 64M, the minimum processing size will be 0.3 μm, so 0.03 μm foreign matter must be removed. At 256M, the minimum processing size will be 0.2 μm, so even 0.02 μm foreign matter will be removed. The peach will be removed.

In the conventional semiconductor element manufacturing process, a technique generally known as ultrasonic cleaning is used to apply a force to a foreign substance adhering to a substrate by a cleaning liquid or the like to separate the foreign substance from the substrate for cleaning. ing. Note that, as a technique related to this type of technology, for example, Journal of Electric Material, Volume 8,
Pp. 885-864 (1979) [J. Electr
o. Materi. , Vol. 8, pp885-86
4 (1979)].

[0004]

However, with respect to the above-mentioned next-generation and next-generation foreign particles having extremely small particle sizes,
At present, no complete removal technology has been established, and
The state of attachment and the mechanism of attachment are also under study and have not been clarified yet. Therefore, the purpose of the present invention is to clarify the adhesion state and adhesion mechanism of foreign matter to the substrate by cleaning the foreign matter with a very small particle size in the above-described next-generation and next-generation semiconductor device manufacturing processes. It is to establish a cleaning technique and provide an effective cleaning method.

[0005]

In order to achieve the above object, the inventors of the present invention first clarified the attachment state of foreign matter on a substrate by quantum chemical calculation, and based on the knowledge obtained from it. I was able to find a completely new cleaning method. That is, the cleaning method of the present invention reduces the adhesion energy of minute foreign matter on the substrate,
Alternatively, it is removed from the substrate by applying energy.

In order to explain the principle of the present invention, the process of obtaining the present invention and reaching the present invention will be described in detail below with reference to the drawings. Considering a state in which a foreign substance is attached to the substrate, the relationship between the distance between the foreign substance surface and the substrate surface (distance between the foreign substance and the substrate) and the potential energy between the two surfaces is as shown in FIG. Becomes Here, considering what kind of state foreign matter is attached to the substrate, it is nothing but the so-called foreign matter having the lowest potential energy, which is present in a stable state on the substrate. Then, such an attached state corresponds to the valley bottom of the potential curve in FIG. On the contrary, this means that the adhesion distance and the adhesion energy of the foreign matter can be obtained by obtaining the potential curve between the foreign matter and the substrate.

This leads to the result that in order to remove the foreign matter from the adhered state, it is sufficient to apply an energy higher than this adhesion energy. However, it is extremely difficult to obtain this experimentally, and there is no example that it was measured in the past. Also, theoretically
There is no example in which the potential curve as shown in FIG. 1 is obtained for the substrate system.

Therefore, in the present invention, in order to obtain the potential curve between the foreign matter and the substrate, first, the potential curves of minute portions are obtained, and these are calculated in all regions where the interaction between the foreign matter and the substrate is considered. The addition was performed and the potential curve between the foreign substance and the substrate was obtained.

It is generally said that most of foreign matter-substrate interactions are van der Waals interactions.
Therefore, the ab-initio molecular orbital method including the electron correlation correction was used for the calculation of the interaction of the minute portion. In the experimental example of the present invention, the surface of the foreign matter and the substrate was the Si wafer substrate surface after the hydrofluoric acid treatment whose surface state was clear. It has been reported that about 0.12% of hydroxyl groups (OH) are present on the surface of Si and some fluorine (F) remains, and the rest is terminated with hydrogen (H) [Applied Physics No. 59. Vol. 11, No. 1441-1450 (November 10, 1990)]. Therefore, in this experimental example, 0.13% of OH and 99.87% of H as shown in FIG.
The potential curve on the Si (111) plane of was obtained.

First, the potential energy at each distance between H and OH at the end on both surfaces of the foreign substance and the substrate and Si at the second layer is ab-initio.
It was obtained by the molecular orbital method. Then, their potential energies were fitted as a function of distance. The function obtained here is applied to all the parts that are considered to be interacting between the surface of the foreign substance and the substrate, and the results are added together, so that the foreign substance-substrate potential curve with the particle size shown in FIG. 3 as a parameter. Got That is, this potential curve is calculated by measuring the particle diameter of the foreign matter, 0.03 μm, 0.0
It was determined at 4 μm, 0.05 μm, and 0.1 μm, respectively. In this figure, the bottom of the curve is a state in which foreign matter is attached to the substrate, and the depth of the energy is the attachment energy.

Next, the adhesion energy obtained in FIG.
The adhesion energy for each particle size of the foreign matter is shown in FIG. According to this, it can be seen that the particle size and the adhesion energy have a linear relationship at 0.1 μm or less. That is,
The adhesion energy decreases as the particle size decreases. Furthermore, if this straight line is approximated by a linear function by the method of least squares,
Adhesion energy E (eV) = 151.7r-0.442
It becomes 9. Here, r is a particle size (μm).

Next, in order to confirm the validity of the values obtained above, comparison was made with the actually measured values. Up to now, there has been no report of experimentally obtaining the adhesion energy, but there have been some reports of obtaining the adhesion force of fine foreign matter to the substrate. For example, Chikao Kanaoka et al .: Powder Engineering Bulletin 24, 4
No., pp. 233-239 (1987), and Toru Niida: Seminar Program for Adhesion Control of Fine Particles in Water, pp. 14-25 (1991).

To obtain the adhesive force from the adhesive energy,
Since the differential of energy is a force, in the present invention, the maximum value of the slope of the potential curve of FIG. 3 can be obtained in order to obtain the adhesive force in the above-mentioned example. FIG. 5 collectively shows the measured values of the relationship between the particle size and the adhesive force (data with particle sizes of 1.0 μm or more in the figure) and the calculated values of the present invention. Figure 5
Well-known measured values in the vapor phase are shown in white. The value obtained in the experimental example of the present invention is shown by a black circle in the figure, and since both are on the same straight line, the value obtained in the experimental example of the present invention is also recognized to be connected to a known actual measurement value. The reliability is considered to be high. In addition, the well-known actual measurement values indicated by black squares in the figure are experimental values in the liquid phase, and it was found that the adhesive force was 1/10 of the adhesive force in the gas phase, and the adhesion energy was 1/10. It is considered to be.
It is considered that the adhesion energy becomes small because the distance between the foreign substance and the substrate becomes long because the solvent molecules such as water enter between the foreign substance and the substrate, and the distance becomes to the right of the valley bottom of the potential curve in FIG.

Next, based on the above-described novel analysis of the adhered state of the foreign matter, the basic concept of the foreign matter removal by the conventional cleaning method will be described in order to consider the foreign matter removal method. Conventional ultrasonic cleaning and cleaning by flow try to achieve removal of foreign matter by mechanical or physical force. Then, for example, how much force is required to remove minute foreign matter of 0.1 μm or less was calculated. First, when ultrasonic cleaning is considered, foreign matter is removed by vibrating water molecules by ultrasonic waves to move foreign matter and thereby exerting a force acting on the mass of foreign matter.

In such a conventional method, the smaller the foreign matter, the smaller the force applied thereto becomes in inverse proportion to the cube of the particle size. That is, it indicates that the smaller the foreign matter, the more difficult it is to remove. Therefore, when dealing with removal of foreign matter by physical force, it is necessary to consider the removal effect of foreign matter due to adhesion force per unit mass. Based on this idea, FIG. 6 shows the particle size of the foreign matter and the adhesive force per unit mass. It is clear from this figure that the adhesive force per unit mass rapidly increases as the particle size of the foreign matter becomes smaller, and the smaller the foreign matter becomes, the more difficult it becomes to remove by force. This means that in the actual process, ultrasonic waves can be removed up to 0.3 μm, for example, Journal of Electric Materials, Volume 8, pp. 885-864 (1979) [J. Electro. Mater
i. , Vol. 8, pp885-864 (1979)]
Qualitatively agrees with.

Further, when removing foreign matter by the flow of fluid, it is necessary to consider the force applied to the cross-sectional area of the foreign matter.
The adhesive force per unit cross-sectional area was determined. FIG. 7 shows the particle size of foreign matter and the adhesive force per unit cross-sectional area. Also in this case, it can be seen that the removal becomes more difficult as the particle size of the foreign matter becomes smaller, similar to the ultrasonic wave.

That is, conventional removal by physical “force” becomes more and more difficult as the particle size of the foreign matter becomes smaller. However, in the cleaning method of the present invention, as shown in FIG.
As can be seen from the above, since the adhesion energy decreases as the particle size decreases, it is based on a completely new finding that was not previously considered that foreign particles with smaller particle size are more advantageous to remove by applying energy from the outside. It was made. That is, the energy is removed by externally applying an energy larger than the adhesion energy of the foreign matter. However, by further reducing the adhesion energy of the foreign matter, the applied energy can also be reduced, and heat or minute heat is applied to the minute foreign matter. A method of adding energy such as light to remove it is effective.

Specific examples of the foreign matter removing method of the present invention include the following specific examples. (1) As shown in FIG. 4, the adhesion energy of the foreign matter of 0.05 μm in the gas phase is 7 eV, but in the liquid phase it is about 1/10 of that, 0.7 eV. Can be removed by applying heat energy. For example, it can be removed by heating with a heater or an infrared lamp as shown in FIG. (2) In the liquid phase, by adding solvent molecules larger than water (for example, organic molecules having a large molecular weight such as alcohol) that easily enter between the foreign matter and the substrate, the adhesion energy of the foreign matter is further reduced, and then heat energy is applied. To remove. (3) Since foreign matter having a smaller particle size has a smaller adhesion energy even in the gas phase, the foreign matter is first broken down by a laser or the like to form small pieces, and then heat energy is applied to remove the foreign matter.

By the above method, it has become possible to easily remove the foreign matter of fine particles which has been difficult to remove by the conventional cleaning technique. This cleaning method is not limited to the semiconductor substrate, and is similarly effective for other liquid crystal substrates as image display elements.

[0020]

As shown in FIG. 4, for example, in the state of adhesion between the semiconductor substrate and the foreign matter, the particle size and the adhesion energy have a linear relationship when the particle size is 0.1 μm or less, that is, when the particle size becomes large, the adhesion energy becomes large. It can be said that the larger the value is and the smaller the value, the smaller the attachment energy. Therefore, in the present invention, the fine foreign matter on the substrate is removed from the substrate by reducing its adhesion energy. The same purpose can also be achieved by applying energy larger than the adhesion energy.

[0021]

Example A cleaning effect of the present invention was investigated by using a Si wafer having polystyrene particles attached as foreign matter as a sample substrate. First, a Si substrate for evaluation was prepared by the following manufacturing method. Disperse polystyrene particles in ultrapure water and add HCl.
Was added to prepare a solution having a pH of about 2. Next, the Si substrate was immersed in this solution for 10 minutes and dried with a spinner. Adhesion density of polystyrene particles is from 1 μm to 0.2
.mu.m was determined by an optical microscope, and 0.1 .mu.m to 0.
Laser scattering method for 08 μm, 0.04 μm
Fine particles of m or less were obtained by SEM.

First, in order to examine the cleaning and removing effect by the conventional method, the evaluation Si substrate was immersed in ultrapure water, and the removal rate of polystyrene particles when ultrasonic waves were applied was obtained and used as a comparative example. Next, as a first method for investigating the cleaning effect of the present invention, the removal rate of polystyrene particles when the Si substrate for evaluation was immersed in ultrapure water and heated was determined. The heating conditions were heating with a heater and the temperature of the solution in which the substrate was immersed was set to about 70 ° C. Further, as a second method, the removal rate of polystyrene particles when the Si substrate for evaluation was immersed in ultrapure water to which 0.5 vol% of ethanol was added and heated as in the first method was obtained. These removal rates are summarized in Table 1 for each particle size.

[0023]

[Table 1]

As shown in Table 1 above, for foreign matter having a smaller particle size,
It can be seen that the cleaning effect of the present invention is great. Further, it can be seen that the effect is further improved by adding the solvent. It was found that the present invention becomes more effective as the particle size of the foreign matter becomes smaller (0.1 μm or less). However, since the experimental conditions are not always optimal, a larger removal effect may be seen depending on the conditions. Therefore, effective cleaning can be performed by removing foreign matters having a large particle size by the conventional cleaning method and removing fine particles by the present invention.

Further, since the method of destroying a foreign substance by laser irradiation is a method of reducing the particle size of the foreign substance and reducing the adhesion energy, it can be understood by analogy from the results in Table 1 that a sufficient removal effect can be expected. ..

Hereinafter, a specific example of the cleaning method of the present invention will be described as a representative example in the case of being applied to an actual semiconductor element manufacturing process, in comparison with a conventional cleaning method. In Fig. 9, implantation (abbreviation of ion implantation), diffusion, oxidation,
The cleaning process in a CVD process is shown. The details of the cleaning in the figure are shown below.

In the conventional cleaning process after implantation, as shown in FIGS. 10 (a) to 10 (h), ashing was first performed, and then ammonia, hydrogen peroxide and water were mixed at an appropriate ratio. Washing with a solution, followed by washing with water, then with a mixed solution of hydrochloric acid, hydrogen peroxide and water in an appropriate ratio, washing with water, then washing with an aqueous HF solution (1:99), washing with water, It dries.

On the other hand, the cleaning process of the present invention has the above-mentioned "means for solving the problem" after the conventional cleaning process.
By the removal method of (3) of the present invention described in the section 1), the fine foreign matters remaining without being removed are further reduced, and then the fine foreign materials of the above (1) and (2) of the present invention are used. Is to be removed.

In the conventional cleaning process before oxidative diffusion, as shown in FIGS. 11A to 11E, first, cleaning is performed with a solution in which ammonia, hydrogen peroxide and water are mixed at an appropriate ratio. Then, it is washed with water, then with an HF aqueous solution (1:99), then with water, and dried.

On the other hand, in the cleaning process of the present invention, after the conventional cleaning process, the fine foreign matters remaining without being removed are further reduced by the removing method (3) of the present invention,
Then, the minute foreign matter is removed by using the removal methods (1) and (2) of the present invention. In the cleaning, the conventional cleaning process before CVD is as shown in (a) to (c) of FIG.
First, as shown in, washed with an HF aqueous solution (1:99),
Then, it is washed with water and dried. On the other hand, in the cleaning process of the present invention, after the conventional cleaning process, the fine foreign matter remaining without being removed is further reduced by the removing method (3) of the present invention, and then (1) and () of the present invention. The minute foreign matter is removed by using the removal method of 2). By the cleaning process described above, it becomes possible to remove foreign matters having a fine particle diameter, which were difficult to remove by the conventional method, by the present invention. In this example, the substrate to be cleaned is the semiconductor substrate, but it is needless to say that the same is also applicable to a liquid crystal display device substrate for forming a circuit element including a thin film transistor, a display pixel and the like on a glass substrate. Nor.

[0031]

EFFECTS OF THE INVENTION In the present invention, in the conventional foreign matter removal using "force", it becomes more difficult to remove fine foreign matter as the particle size becomes smaller, while as the foreign particle size becomes smaller, the adhesion energy becomes smaller. Since the particle size becomes smaller, more foreign energy is applied to the foreign material and the foreign material is removed by breaking the bond between the foreign material and the substrate, so that even a minute foreign material can be removed.

[Brief description of drawings]

FIG. 1 Foreign material surface with foreign matter attached on the substrate
A potential curve showing the relationship between the distance between the substrate surfaces and the potential energy between both surfaces.

FIG. 2 is a diagram showing a foreign substance and a surface state of the substrate when the foreign substance is attached to the substrate.

FIG. 3 is a particle-substrate potential curve for explaining the principle of the present invention.

FIG. 4 is a diagram showing the adhesion energy at each particle size of a foreign substance for explaining the principle of the present invention.

FIG. 5 is a diagram showing a relationship between a foreign matter adhesion force and a particle size.

FIG. 6 is a diagram showing the relationship between the adhesive force per unit mass and the particle size.

FIG. 7 is a diagram showing the relationship between the adhesive force per unit cross-sectional area and the particle size.

FIG. 8 is a diagram illustrating a method of heating a wafer.

FIG. 9 is a semiconductor manufacturing process flow chart (from implantation to C
Up to VD).

FIG. 10 is a cleaning process flow chart after implantation in a semiconductor manufacturing process.

FIG. 11 is a cleaning process flow chart before oxidation and diffusion in a semiconductor manufacturing process.

FIG. 12 is a cleaning process flow chart before CVD in a semiconductor manufacturing process.

[Explanation of symbols]

1 ... Wafer, 2 ... Heater, 3 ...
Infrared lamp.

Front page continuation (72) Inventor, Osamu Oka, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefectural Institute of Industrial Technology, Hitachi, Ltd.

Claims (8)

[Claims] 1. A method for cleaning a substrate, comprising a cleaning step for reducing the adhesion energy of minute foreign matter adhered on the substrate. 2. The method for cleaning a substrate according to claim 1, wherein the cleaning step for reducing the adhesion energy of the minute foreign matter comprises the step of irradiating the foreign matter on the substrate with a laser to break the foreign matter into fine particles. .. 3. A cleaning step for reducing the adhesion energy of the minute foreign matter comprises a step of spreading a cleaning solution thinly on the substrate surface, irradiating a laser under the condition of total reflection, and removing the foreign matter from the substrate together with the cleaning solution. The method for cleaning a substrate according to claim 1 or 2, further comprising: 4. A cleaning step for reducing the adhesion energy of the minute foreign matter is constituted by a step of removing the foreign matter from the substrate by applying energy larger than the adhesion energy to the minute foreign matter on the substrate. A method of cleaning a substrate. 5. An energy (e) of 151.7r-0.4429 or more for a minute foreign matter having a particle size r of 0.05 μm or less.
The method for cleaning a substrate according to claim 4, further comprising the step of applying V). 6. A substrate is irradiated with a laser to reduce the particle diameter of foreign matter to 0.
5. The method for cleaning a substrate according to claim 4, further comprising the step of applying a larger energy than the adhesion energy to remove the foreign matter from the substrate after the particles are disintegrated into small particles of 05 μm or less. 7. The method for cleaning a substrate according to claim 4, wherein the cleaning liquid is thinly applied to the surface of the substrate, and a laser is irradiated under the condition of total reflection to remove foreign substances from the substrate together with the cleaning liquid. 8. The method for cleaning a substrate according to claim 1, wherein the substrate is a semiconductor substrate.