JPH08250463A - Method for manufacturing semiconductor device - Google Patents

Abstract

(57) [Summary] [Object] To reduce a step on the surface of a silicon substrate formed by removing a sacrificial oxide film when removing a damaged layer formed on the surface of a silicon substrate by CF ₄ plasma etching by sacrificial oxidation. [Structure] The surface of the silicon substrate 1 damaged by CF ₄ plasma etching is heated to 50 Å by a thermal oxidation method.
The sacrificial oxide film 6 having a thickness of less than 100 Å is formed, and the sacrificial oxide film 6 is removed by wet etching. [Effect] The damaged layer formed on the silicon substrate 1 can be sufficiently removed, and the step difference on the surface of the silicon substrate 1 due to the removal of the sacrificial oxide film 6 can be reduced to reduce the deterioration of the dielectric strength voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a technique for removing a damaged layer on the surface of a silicon substrate.

[0002]

2. Description of the Related Art A conventional method of manufacturing a semiconductor device will be described with reference to FIGS.

First, as shown in FIG. 4A, a silicon oxide film 32, C is formed on a silicon substrate 31 by a thermal oxidation method.
A polycrystalline silicon film 33 by the VD method and a silicon oxide film 34 by the CVD method are sequentially formed. After that, a photoresist (not shown) is formed on the silicon oxide film 34,
The photoresist is patterned. Then, using the photoresist pattern as a mask, the silicon oxide film 34, the polycrystalline silicon film 33, and the silicon oxide film 3 are formed.
2 is sequentially anisotropically etched, and on the silicon substrate 31,
A gate oxide film 32 made of a silicon oxide film 32, a gate electrode 33 made of a polycrystalline silicon film 33, and a cap oxide film 34 made of a silicon oxide film 34 are formed respectively.
Then, the silicon oxide film 35 is formed on the entire surface by the CVD method.
Is deposited.

Next, as shown in FIG. 4B, the silicon oxide film 35 is left only on the side wall of the gate electrode 33 by plasma etching using CF ₄ gas.

At this time, the exposed surface of the silicon substrate 31 is also etched. For example, as shown in the enlarged view of FIG. 5, when the silicon substrate 31 is plasma-etched,
C _x F _y (x and y are real numbers) on the surface of the silicon substrate 31.
Adsorption layer 311 containing Si, and Si under the adsorption layer 311
The C layer 312 and the damage layer 313 are formed respectively. These adsorption layer 311, SiC layer 312, and damage layer 31
3 causes abnormal oxidation and deterioration of electrical characteristics such as withstand voltage.

Then, next, as shown in FIG.
A sacrificial oxide film 36 having a film thickness t of 100 Å or more is formed on the entire surface of the silicon substrate 31.

Then, as shown in FIG. 4D, the sacrificial oxide film 36 is removed by wet etching.

[0008]

However, as described above, the adsorption layer 311 formed on the silicon substrate 31,
When the sacrificial oxide film 36 having a thickness of 100 Å or more is formed in order to remove the SiC layer 312 and the damaged layer 313, the gate oxide film 32 is removed after the sacrificial oxide film 36 is removed as shown in FIG. And the region Y below the sidewall oxide film 35
Since the silicon substrate 31 has a large step Z in the area X and the other area X, there is a problem that the withstand voltage is deteriorated and the product yield is reduced.

Therefore, an object of the present invention is to provide an adsorption layer, SiC, formed on the surface of a silicon substrate by plasma treatment.
It is an object of the present invention to provide a method for manufacturing a semiconductor device, which can sufficiently remove a layer and a damaged layer, and which does not cause a decrease in yield due to a deterioration in withstand voltage due to a step of a silicon substrate.

[0010]

In order to solve the above-mentioned problems, in the method of manufacturing a semiconductor device of the present invention, a thickness of 50 Å or more and less than 100 Å is provided on the surface of a silicon substrate plasma-treated with a gas containing CF _4. After the sacrificial oxide film is formed, the sacrificial oxide film is removed by a wet etching method.

[0011]

In the present invention, the thickness of the sacrificial oxide film is 50Å
Since it is less than 100Å, the adsorption layer, the SiC layer and the damage layer formed on the surface of the silicon substrate can be sufficiently removed, and the step formed on the silicon substrate after removing the sacrificial oxide film can be reduced. Therefore, it is possible to reduce the deterioration of the withstand voltage, and it is possible to prevent the product yield from decreasing.

If the thickness of the sacrificial oxide film is less than 50Å, the adsorption layer, the SiC layer and the damaged layer cannot be removed sufficiently.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments with reference to FIGS.

First, as shown in FIG. 1A, a silicon oxide film 2 formed by a thermal oxidation method and a CVD film are formed on a silicon substrate 1.
Then, a polycrystalline silicon film 3 by the CVD method and a silicon oxide film 4 by the CVD method are sequentially formed. After this, the silicon oxide film 4
A photoresist (not shown) is formed on the above, and the photoresist is patterned. Then, using the photoresist pattern as a mask, the silicon oxide film 4, the polycrystalline silicon film 3 and the silicon oxide film 2 are anisotropically etched sequentially to form a gate oxide film 2 made of the silicon oxide film 2 on the silicon substrate 1. The gate electrode 3 made of the polycrystalline silicon film 3 and the cap oxide film 4 made of the silicon oxide film 4 are formed respectively. Then, using the LPCVD method,
The silicon oxide film 5 is deposited on the entire surface under the temperature condition of 675 ° C.

Next, as shown in FIG. 1B, the silicon oxide film 5 is left only on the side wall of the gate electrode 3 by plasma etching using CF ₄ gas. This time,
The exposed surface of the silicon substrate 1 is also etched, and an adsorption layer containing C _x F _y (x and y are real numbers) is formed on the surface of the silicon substrate 1, and a SiC layer and a damage layer are formed under the adsorption layer. (See FIG. 5).

Therefore, as shown in FIG. 1 (c), oxygen:
The silicon substrate 1 is thermally oxidized in an atmosphere of hydrogen = 2: 1 at a temperature of 800 ° C., and a film thickness of 80 is formed on the surface of the silicon substrate 1.
A sacrificial oxide film 6 of Å is formed.

Next, as shown in FIG. 1 (d), 0.5%
The sacrificial oxide film 6 is removed by wet etching with hydrofluoric acid.

Through the above steps, the adsorption layer, the SiC layer and the damage layer on the surface of the silicon substrate 1 generated during plasma etching are substantially completely removed, and the silicon substrate 1 generated during the wet etching step of the sacrificial oxide film 6 is performed. It is possible to reduce the level difference. Therefore, the deterioration of the withstand voltage is reduced, the yield can be prevented from lowering, and the abnormal oxidation or the withstand voltage deterioration due to the remaining damaged layer does not occur.

Although the sacrificial oxide film 6 has a film thickness of 80 Å in the above-mentioned embodiment, if the sacrificial oxide film 6 has a film thickness of 50 Å or more and less than 100 Å, substantially the same effect as that of the above-mentioned embodiment is obtained. Can be obtained. The thickness of the sacrificial oxide film 6 is 5
If it is less than 0 Å, the damaged layer generated in the silicon substrate 1 cannot be completely removed, so that abnormal oxidation, breakdown voltage deterioration and the like occur.

Next, the effect of the present invention will be described with reference to FIGS.

Graph A in FIG. 2 shows the film thickness of the thermal oxide film when a silicon substrate having no damaged layer is thermally oxidized to form a thermal oxide film on the surface of the silicon substrate. The film thickness of the thermal oxide film was 100Å.

On the other hand, the graph B in FIG. 2 is obtained by subjecting the surface of the silicon substrate to plasma treatment using CF ₄ gas to form a damaged layer on the surface of the silicon substrate, and then performing the graph A.
The film thickness of the thermal oxide film when the thermal oxide film is formed under the same conditions as in FIG. The film thickness of the thermal oxide film in this case was about 80Å. From this result, it is understood that when the silicon substrate on which the damaged layer is formed is thermally oxidized, the film thickness of the thermal oxide film formed is different as compared with the case of the normal silicon substrate shown in Graph A. This is because the CF ₄ gas reacts with Si of the silicon substrate during plasma etching to deposit a layer of SiC on the surface of the silicon substrate. When thermal oxidation is performed in this state, the SiC layer is more likely to be formed than the silicon substrate. This is because the oxidation rate is low.

Next, a graph C in FIG. 2 shows that a silicon substrate surface is subjected to plasma treatment using CF ₄ gas to form a damage layer on the silicon substrate surface, and then the damage is caused by plasma treatment using oxygen. Remove the layers,
After that, the film thickness is obtained when a thermal oxide film is formed under the same conditions as in graph A. The thickness of the thermal oxide film in this case is about 13
It was 0Å. That is, the damaged layer was removed from the silicon substrate by oxygen plasma, but the film thickness was abnormally larger than that in graph A. The damaged layer is removed by this oxygen plasma as follows. That is, the adsorption layer is decomposed by oxygen plasma, and SiC + 2O ₂ → S
A reaction of iO ₂ + CO ₂ occurs to form an oxide film.
Therefore, the oxide film is removed by wet processing, and at the same time, the damaged layer is removed. However, according to this treatment, oxygen remains on the surface of the silicon substrate. Therefore, if thermal oxidation is performed in that state, the oxidation rate of Si becomes higher than that in the case of graph A, and as a result, the film thickness increases. Of.

Next, graph D in FIG. 2 shows that after a silicon substrate surface is subjected to plasma treatment using CF ₄ gas to form a damaged layer on the silicon substrate surface, an atmosphere of oxygen: hydrogen = 2: 1. Then, the silicon substrate is thermally oxidized under the condition of a temperature of 800 ° C., a sacrificial oxide film having a film thickness of 80 Å is formed on the surface thereof, and the sacrificial oxide film is removed by wet etching. This is the film thickness of the thermal oxide film when the film was formed. In this case, an oxide film having the same film thickness of 100 Å as in the case of graph A was obtained. That is,
An oxide film thickness equivalent to that of the reference was obtained. From this result, it can be seen that the sacrificial oxide film having the film thickness according to the present invention completely removed the adsorption layer, the SiC layer, and the damaged layer formed during the plasma etching containing the CF ₄ gas. Therefore, the oxidation rate was the same as in the case of graph A in which there was no plasma damage, and an oxide film having the same film thickness was obtained.

FIG. 3 is a graph showing the relation between the film thickness of the sacrificial oxide film and the yield of the product. When the film thickness of the sacrificial oxide film is 100 Å or more as in the conventional case, it is formed on the silicon substrate. It can be seen that the insulation breakdown voltage deteriorates due to the step, and the yield rapidly deteriorates. On the other hand, when the thickness of the sacrificial oxide film is less than 50 Å, a damaged layer remains in the silicon substrate, so that the dielectric strength also deteriorates and the yield deteriorates. On the other hand, in the range of 50 Å or more and less than 100 Å of the present invention, a good yield can be obtained.

[0026]

According to the present invention, it is possible to reduce the deterioration of the dielectric strength of the semiconductor device and prevent the yield from decreasing.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a method of manufacturing a semiconductor device according to an embodiment of the present invention in the order of steps.

FIG. 2 is a graph showing the film thickness of a thermal oxide film formed when the surface of a silicon substrate is thermally oxidized.

FIG. 3 is a graph showing the relationship between the film thickness of a sacrificial oxide film and the product yield.

FIG. 4 is a schematic cross-sectional view showing a conventional method of manufacturing a semiconductor device in the order of steps.

FIG. 5 is an enlarged schematic cross-sectional view showing a damaged layer formed on the surface of a silicon substrate by CF ₄ plasma etching.

[Explanation of symbols]

 1 Silicon Substrate 2 Gate Oxide Film 3 Gate Electrode 4 Cap Oxide Film 5 Sidewall Oxide Film 6 Sacrificial Oxide Film 311 Adsorption Layer 312 SiC Layer 313 Damage Layer

Claims (1)

[Claims] 1. A sacrificial oxide film having a thickness of 50 Å or more and less than 100 Å is formed on the surface of a silicon substrate plasma-treated with a gas containing CF _4, and then the sacrificial oxide film is removed by a wet etching method. A method for manufacturing a characteristic semiconductor device.