JPH08316189A - Substrate cleaning method - Google Patents

Abstract

(57) [Summary] [Method] In a method of supplying cleaning gas and solvent vapor to a substrate 30 to clean the surface of the substrate 30, a condensation layer of the cleaning gas and solvent vapor on the surface of the substrate 30. The substrate 3 is formed by using a monolayer condensed layer obtained by controlling the number.
A cleaning process of 0 is performed. [Effect] The generation of particles is small, the etching characteristics inside the fine pores are good, and the controllability of the etching is also good.

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.

[0002]

2. Description of the Related Art Conventionally, as a cleaning technique in a semiconductor process, a wet cleaning technique has been mainly used. However, particles in a cleaning liquid adhere to a substrate, a product called a watermark is formed on the substrate, and a fine particle is formed. There was a problem that it was not suitable for cleaning the part. Therefore, in recent years, vapor cleaning technology has been studied under atmospheric pressure or reduced pressure.

Vapor cleaning under atmospheric pressure is disclosed in, for example, Japanese Patent Laid-Open No.
According to the technique disclosed in Japanese Laid-Open Patent Publication No. 62-173720, vapor of hydrogen fluoride (HF) aqueous solution is supplied into a container accommodating a silicon substrate to remove the silicon natural oxide film on the substrate surface, and thereafter, There is a method in which hydrogen fluoride is washed off from the substrate surface with water vapor (H ₂ O) and then dried. Further, according to the technique disclosed in Japanese Patent Publication No. 62-502930, there is a method of supplying anhydrous hydrogen fluoride gas to the surface of the substrate together with water vapor to remove the oxide film from the substrate. For example, according to the technique disclosed in Japanese Patent Publication No. 4-502981, the vapor cleaning by depressurization is performed by supplying hydrogen fluoride gas together with water vapor to the surface of the substrate and relatively high pressure (for example, 4.7 × 10 ⁴ Pa). ) Has been reported. With these methods,
In both cases, a multilayer condensed layer of two or more HF / H ₂ O molecular adsorption layers is formed on the substrate surface, and etching proceeds due to the chemical reaction between the condensed layers and the oxide film.

[0004]

According to the techniques disclosed in Japanese Patent Laid-Open No. 62-173720, Japanese Patent Laid-Open No. 62-502930, and Japanese Patent Laid-Open No. 4-502981, the surface of the substrate is cleaned during the cleaning process. Above, a condensed layer of the HF / H ₂ O multimolecular adsorption layer is formed. Therefore, when the silicon oxide film is removed by etching from the substrate, there is a problem that by-products of the etching reaction tend to remain as particles without being separated from the substrate surface. Further, since the cleaning treatment liquid for the condensed layer is not supplied inside the fine holes, there is a problem that the etching characteristics inside the fine holes are insufficient. Furthermore, it is difficult to control etching because the etching rate strongly depends on the partial pressure of the solvent vapor.

An object of the present invention is to provide a method for cleaning a substrate, in which generation of particles is small, etching characteristics inside fine pores are good, and etching controllability is also good.

[0006]

In order to achieve the above object, the substrate cleaning method of the present invention is obtained by controlling the number of condensed layers of cleaning gas and solvent vapor on the substrate surface.
It is characterized in that etching is performed using a monolayer condensed layer. In order to form this monolayer condensed layer, the cleaning gas partial pressure is fixed so that the etching rate of the silicon oxide film on the substrate surface is constant and does not depend on the solvent vapor partial pressure. Gas and solvent vapors are supplied to the substrate.

[0007]

When the cleaning gas and solvent vapor are adsorbed on the surface of the substrate by the condensed layer of the monomolecular layer, the etching proceeds by the surface reaction. Therefore, as shown in FIG. 2, the by-products of the etching reaction are easily separated from the substrate surface, and the residue is reduced. Further, since the vapor is supplied to the surface in the fine pores without being condensed to perform the etching, the etching characteristics inside the fine pores are improved. Furthermore, since the etching is performed in the pressure range where the etching rate does not depend on the partial pressure of the solvent vapor, the controllability of the etching becomes good.

[0008]

【Example】

Example 1 An example of the present invention will be described below.
FIG. 3 is a conceptual diagram showing an example of an apparatus for carrying out the present invention. Cleaning chamber 10 is made of silicon carbide for chemical resistance and prevention of contamination. A gas inlet 11 is provided at the upper part of the cleaning chamber 10, and an exhaust port 12 is provided at the lower part. The gas inlet 11 is connected to a hydrogen fluoride aqueous solution (azeotropic aqueous solution) or pure water vaporizer 21 and a mass flow controller 22 by a Teflon tube 20, and an inert gas such as nitrogen is introduced into the mass flow controller 22. Has become. A silicon substrate 30 is arranged in the cleaning chamber 10 so as to be perpendicular to the gas inflow direction, and the temperature of the silicon substrate 30 is controlled by passing circulating water through a substrate support (not shown). .

Using the apparatus thus constructed, the substrate cleaning process was performed under a reduced pressure in the cleaning chamber. The pressures of hydrogen fluoride (HF) and water vapor (H ₂ O) can be arbitrarily set by adjusting the pressure in the cleaning chamber and the vaporizer temperature. In this example, a silicon thermal oxide film was used for the substrate, and the substrate temperature was room temperature (23 ° C.).

FIG. 4 shows a typical example of H ₂ O partial pressure dependence of etching rate. Here, the oxide film thickness was measured by ellipsometry. As shown in the figure, as the partial pressure of H ₂ O increased, the etching rate increased, then became constant, and then decreased. As described above, it was found that there are three regions (hereinafter, referred to as region 1, region 2, and region 3 as shown in the drawing) due to the difference in the H ₂ O partial pressure dependency of the etching rate. In addition, the boundary between regions 1 and 2 matches the saturated vapor pressure of about 33 ° C, and the boundary between regions 2 and 3 is room temperature (about 23 ° C).
It was in agreement with the saturated vapor pressure of.

FIG. 5 shows a possible etching mechanism. Region 1 is a condensed region of the polymolecular layer, and the decrease in the etching rate when the H ₂ O partial pressure is increased is due to the decrease in the HF concentration in the condensed layer (water film). Further, the region 2 is a saturated region of the monomolecular adsorption layer, and the region 3 is an unsaturated region of the monomolecular adsorption layer (a region in which the layered condensed layer is not yet formed), both of which cause etching due to surface reaction. When the substrate temperature is room temperature, the boundary between the region 2 and the region 3, that is, the boundary between the saturated region and the unsaturated region of monolayer adsorption coincides with the saturated vapor pressure at room temperature (about 23 ° C.), which is condensed. (Including saturated monolayer adsorption)
This is because the substrate needs to be supplied with vapor having a saturated vapor pressure or higher in order to cause the phenomenon. The monomolecular adsorption layer referred to here corresponds to a state in which the value obtained by dividing the amount of condensation by the surface area corresponds to approximately one molecular layer.

FIG. 1 summarizes the experimental results of examining three regions of etching when the substrate temperature is room temperature. The representative experimental values that serve as the boundaries of the three regions are indicated by circles (○) in the figure.
The boundaries of the figure are isotherms of pressures corresponding to saturated vapor pressures of room temperature (about 23 ° C.) and about 33 ° C., respectively.

In the condensed layer region (region 1) of the multi-molecular layer and the saturated monomolecular adsorption layer region (region 2) of the present invention, particles (0 The number of particles of 0.3 μm or more) was examined. As a result, the number of particles generated in the area 1 was at the level of several hundreds to several thousands, but the number of particles generated in the area 2 of the present invention was 10 or less.

The diameter is 0.2 to 0.5 μm and the depth is 2 μm.
Contact holes were formed in the silicon thermal oxide film by using a dry etching technique. Under the condition of the region 2 of the present invention, even the bottom of the hole is uniformly etched and the etching shape in the fine portion is uniform, whereas under the conventional condensation condition (region 1), the closer to the bottom of the hole, the harder it is to etch. The etching shape was uneven.

As described above, according to the first embodiment of the present invention,
When the silicon oxide film was etched under the experimental conditions shown by the shaded area in FIG. 1, the oxide film could be etched with almost no particles generated. Further, the etching characteristics in the fine portion were also good.

The effect of Example 1 was also effective in the substrate cleaning method characterized in that the cleaning gas was hydrogen fluoride vapor and the solvent vapor was a mixed vapor of isopropyl alcohol.

Further, the effect of Example 1 was also effective in the method of cleaning a substrate, characterized in that the cleaning gas was a halide such as hydrogen chloride or boron trichloride.

(Embodiment 2) Using the apparatus configured as shown in FIG. 3, the cleaning treatment of the substrate was carried out under the pressure of the cleaning chamber under the atmospheric pressure. The pressures of HF and H ₂ O were arbitrarily set by adjusting the amount of nitrogen as a diluent gas to be introduced. The substrate temperature was set to room temperature (23 ° C).

When the HF partial pressure of the cleaning gas is constant,
When the region of the present invention is determined so that the etching rate of the silicon oxide film on the substrate surface is constant without depending on the increase or decrease of the H ₂ O partial pressure of the solvent vapor, the region shown by the hatched portion in FIG. 1 is obtained.

In the condensation layer region (region 1) of the multi-molecular layer and the saturated monomolecular adsorption layer region (region 2) of the present invention, particles (0 The number of particles of 0.3 μm or more) was examined. As a result, the number of particles generated in the area 1 was at the level of several hundreds to several thousands, but the number of particles generated in the area 2 of the present invention was 10 or less.

The effect of the second embodiment is to raise the substrate temperature,
For example, even when the temperature was controlled to 30 ° C., the same effect as when the substrate temperature was room temperature was obtained. The boundary line between the region 2 and the region 3 was about 30 ° C., and the boundary line between the region 1 and the region 2 was an isotherm of a pressure corresponding to a saturated vapor pressure of about 40 ° C.

As described above, according to the second embodiment, the oxide film could be etched under the pressure of the cleaning chamber at atmospheric pressure with almost no particles generated.

(Embodiment 3) In the present embodiment, H ₂ O in the cleaning chamber when the apparatus configured as shown in FIG. 3 is used.
An example of setting the partial pressure and the HF partial pressure is shown. These partial pressures can be set by adjusting the pressure in the cleaning chamber and the vaporizer temperature. That is, 1) in H ₂ O vaporization formula for the flow velocity of H ₂ O vapor generated from the device Figure 6 (a), showing a conceptual diagram of a H ₂ O vapor generated in H ₂ O carburetor. Carrier gas N2 with flow velocity x (slm) is H ₂
O 2 vaporizer (vaporizer temperature; T (° C), vaporizer internal pressure; y
(Pa)), and H ₂ O vapor having a flow rate a (slm) is generated. Assuming that saturated vapor is generated from the vaporizer, the following relational expression holds for the flow velocity and pressure.

[0024]

A / x = P′H ₂ O / (y−P′H ₂ O) (Equation 1) P′H ₂ O: Water vapor pressure at T (° C.) Therefore, it is generated from the H ₂ O vaporizer. The flow rate of H ₂ O vapor is shown by the following equation.

[0025]

[Number 2] _{a = (x × P'H 2 O} ) / (y-P'H 2 O) ... ( Equation 2) 2) calculated representation of the flow rate of HF / H ₂ O vapor generated from HF vaporizer 6 (b) shows a conceptual diagram of HF / H ₂ O vapor generation in the HF vaporizer. Carrier gas N with flow velocity x '(slm)
2 was introduced into the HF vaporizer (vaporizer temperature; T '(° C), vaporizer internal pressure; y' (Pa)), and HF of flow rate a '(slm)
/ H ₂ O vapor shall be generated. Assuming that saturated vapor is generated from the vaporizer, the following relational expression holds for the flow velocity and pressure.

[0026]

[Number 3] a '/ x' = P " HF · H 2 O / (y'-P" HF · H 2 O) ... ( number _{3) P "HF · H 2} O: T 'HF in (℃) / H ₂ O vapor pressure (Ind. Eng. Chem., Vol. 41, pp. 1504-1508, (1949).) Therefore, the flow rate of HF / H ₂ O vapor generated from the HF vaporizer is shown by the following equation. Be done.

[0027]

A ′ = (x ′ × P ″ HF · H ₂ O) / (y′−P ″ HF · H ₂ O) (Equation 4) The HF aqueous solution contains an azeotropic aqueous solution (38.4 wt% HF). 36.
Since 0 mol% HF) is used, the flow rates of HF vapor and H ₂ O vapor generated from the HF vaporizer are

[0028]

## EQU00005 ## HF flow velocity = 0.36.times.a '... (Equation 5)

[0029]

[6] of H ₂ O flow rate = 0.64 × a '... a (6).

3) Calculation formulas for H ₂ O partial pressure and HF partial pressure in the cleaning chamber As shown in FIGS. 6 (a) and 6 (b), H
If F vapor and H ₂ O vapor are generated and introduced into the cleaning chamber, the flow velocity ratio of each gas is

[0031]

(N ₂ flow rate): (H ₂ O flow rate): (HF flow rate) = (x + x ′): (a + 0.64a ′): (0.36a ′) (Equation 7) The mole fraction X is

[0032]

XH ₂ O = (a + 0.64a ′) / (x + x ′ + a + a ′) (Equation 8)

[0033]

XHF = (0.36a ') / (x + x' + a + a ') (Equation 9) Therefore, assuming that the pressure in the cleaning chamber is PT, H ₂ O
The partial pressure (PH ₂ O) and the HF partial pressure (PHF) are shown by the following equations.

[0034]

PH ₂ O = PT × XH ₂ O = {PT × (a + 0.64a ′)} / (x + x ′ + a + a ′) = [PT × {(xxP′H ₂ O) / (y−P ′ H ₂ O) +0.64 (x ′ × P ″ HF · H ₂ O) / (y′−P ″ HF · H ₂ O)}] / {x + x ′ + (xx × P′H ₂ O) / (Y−P′H ₂ O) + (x ′ × P ″ HF · H ₂ O) / (y′−P ″ HF · H ₂ O)} (Equation 10)

[0035]

PHF = PT × XHF = (PT × 0.36a ′) / (x + x ′ + a + a ′) = {PT × 0.36 (x ′ × P ″ HF · H ₂ O) / (y′−P ″ HF · H ₂ O)} / {x + x ′ + (x × P′H ₂ O) / (y−P′H ₂ O) + (x ′ × P ″ HF · H ₂ O) / (y′− P ″ HF · H ₂ O)} (Equation 11) 4) Setting example of partial pressure in cleaning chamber by adjusting vaporizer temperature Based on Equations 10 and 11, the HF vaporizer temperature is fixed and the H ₂ O vaporizer temperature is set. H _{2 in} the cleaning chamber obtained by changing
The O partial pressure is shown in FIG. Further, the HF partial pressure in the cleaning chamber, which was obtained by fixing the H ₂ O vaporizer temperature and changing the HF vaporizer temperature, is shown in FIG. 7 (b). A Baratron (trade name) manufactured by MKS Co., Ltd. was used for measuring the pressure in the cleaning chamber (PT) and the pressure in the vaporizer (y and y ').

As described above, according to the third embodiment, the H ₂ O partial pressure and the HF partial pressure in the cleaning chamber can be set by adjusting the pressure in the cleaning chamber and the vaporizer temperature.

(Embodiment 4) In Embodiment 4, an example in which the time dependency of the etching film thickness is evaluated by using the apparatus configured as shown in FIG. A silicon thermal oxide film was used for the substrate, and ellipsometry was used for film thickness measurement. The substrate temperature was room temperature.

In FIG. 8A, the pressure in the cleaning chamber is 4.7 × 1.
The time dependence of the etching film thickness at 0 ⁴ Pa is shown. The etching rate was constant when the H ₂ O vaporizer temperature was 30 ° C to 40 ° C, and decreased when the temperature was raised from 45 ° C to 60 ° C. On the other hand, FIG. 8 (b) shows the time dependence of the etching film thickness at 1.6 × 10 ⁴ Pa. The etching rate is 40% at H ₂ O vaporizer temperature.
It increased with the increase from ℃ to 55 ℃.

As described above, according to the fourth embodiment, by adjusting the pressure in the cleaning chamber and the vaporizer temperature, it is possible to set three regions depending on the difference in the H ₂ O partial pressure dependency of the etching rate. The constant etching rate region of the present invention can be realized. In addition, the etching rate is H ₂ O
Since etching is performed in the pressure range that does not depend on the partial pressure,
The controllability of etching is also improved.

[0040]

EFFECT OF THE INVENTION When supplying the cleaning processing gas and the solvent vapor to the substrate, the cleaning processing of the substrate is characterized in that the cleaning processing gas and the solvent vapor are adsorbed by the monomolecular layer on the substrate. According to the invention, generation of particles is small, etching characteristics inside fine pores are good, and etching controllability is also good.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a pressure region of a cleaning treatment condition of the present invention.

FIG. 2 is an explanatory view showing the operation of the present invention.

FIG. 3 is a block diagram of the vapor cleaning apparatus according to the first embodiment of the present invention.

FIG. 4 is a characteristic diagram showing the H ₂ O partial pressure dependence of the etching rate in Example 1 of the present invention.

FIG. 5 is an explanatory diagram showing an etching mechanism according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram of a vaporizer according to a third embodiment of the present invention.

FIG. 7 is a characteristic diagram showing the relationship between the vaporizer temperature and the partial pressure in the cleaning chamber according to the fourth embodiment of the present invention.

FIG. 8 is a characteristic diagram showing the relationship between the etching time and the etching amount in Example 4 of the present invention.

[Explanation of symbols]

10 ... Washing room, 11 ... Gas inlet, 12 ... Exhaust, 20
... Teflon tube, 21 ... Vaporizer, 22 ... Mass flow controller, 30 ... Silicon substrate.

Claims (12)

[Claims] 1. When cleaning gas and solvent vapor are supplied to a substrate, the cleaning gas and solvent vapor are adsorbed on the substrate substantially as a monomolecular layer. Processing method. 2. The substrate cleaning method according to claim 1, wherein, when the partial pressure of the cleaning gas is constant, the etching rate of the silicon oxide film on the surface of the substrate is constant independent of the solvent vapor partial pressure. Processing method. 3. The method of cleaning a substrate according to claim 1, wherein the cleaning gas is hydrogen fluoride vapor and the solvent vapor is water vapor. 4. The method for cleaning a substrate according to claim 1, wherein the cleaning gas is hydrogen fluoride vapor and the solvent vapor is a volatile organic solvent such as alcohol. 5. The method for cleaning a substrate according to claim 1, wherein the cleaning gas is a halide such as hydrogen chloride or boron trichloride. 6. The method for cleaning a substrate according to claim 1, wherein the inert gas used as a carrier gas or a diluent gas for the cleaning gas and the solvent vapor is nitrogen or argon. 7. The method of cleaning a substrate according to claim 1, wherein the temperature of the substrate is controlled to a constant temperature. 8. The method of cleaning a substrate according to claim 7, wherein the temperature of the substrate is controlled to a temperature near room temperature by water cooling or the like. 9. The method of cleaning a substrate according to claim 1, wherein the cleaning process of the substrate surface is performed under reduced pressure (atmospheric pressure or less). 10. The method for cleaning a substrate according to claim 9, wherein the hydrogen fluoride vapor pressure and the water vapor pressure are within the pressure range shown in FIG. 11. The method for cleaning a substrate according to claim 1, wherein the surface of the substrate is cleaned under atmospheric pressure. 12. The method for cleaning a substrate according to claim 11, wherein the hydrogen fluoride vapor pressure and the water vapor pressure are within the pressure range shown in FIG.