JPS5828733B2 - Manufacturing method of semiconductor device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a semiconductor device.

In order to obtain a high-density semiconductor device, an important factor in the manufacturing process is whether or not the opening width of the impurity diffusion mask can be made fine.

Conventionally, this impurity diffusion mask is generally obtained by selectively etching an oxide film formed on the main surface of a semiconductor substrate using photolithography.

However, this method has limitations on the opening width due to light diffraction phenomena and variations in the etching rate of the oxide film.

Another method is to form an impurity diffusion mask by selectively oxidizing a semiconductor substrate.

That is, as shown in FIGS. 1A to 1D, first, the main surface of the silicon substrate 1 is heat-treated in a steam atmosphere to form a silicon thermal oxide film 2 with a film thickness of 50 OA, and a film thickness of 50 OA is formed on this upper surface. For example, CVD (Chem 1cal Vapor D)
(eposition) method (FIG. 1a).

Next, the silicon nitride film 3 is etched by a selective etching method using photolithography to remove the silicon nitride film in areas other than the opening forming area (FIG. 1b).

Then, by heat treatment again in a steam atmosphere,
A silicon thermal oxide film 2 is formed to a thickness of about 1.5 μm in the region not covered with the silicon nitride film 3 (FIG. 1C).

After the silicon nitride film 3 is completely removed, the silicon thermal oxide film 2 is etched until a part of the silicon substrate 1 is exposed.

However, even in this method, there is a limit on the opening width for the same reason as in the above-mentioned method, and the minimum value is about 5 μm.

Accordingly, an object of the present invention is to provide a method for manufacturing a semiconductor device that is highly integrated by forming an impurity diffusion mask with finer dimensions.

In order to achieve such an object, the present invention includes a step of forming a mask made of a silicon nitride film on a silicon oxide film formed on the surface of a silicon substrate, and selective oxidation by heat treatment in a steam atmosphere. At the same time, a step of forming a silicon nitride film on the surface of the silicon substrate under the edge of the silicon nitride film, a step of heat-treating in an oxidizing atmosphere after removing the mask, and a step of forming a silicon oxide film on the upper surface of the silicon substrate on the surface of the silicon substrate. This step consists of etching until the silicon nitride film formed on the surface is exposed, and then removing the silicon nitride film.

Hereinafter, the present invention will be explained in detail using Examples.

FIGS. 2a to 2d are cross-sectional process diagrams showing essential parts of an embodiment of the method for manufacturing a semiconductor device according to the present invention.

The steps will be explained below in order. FIG. 2C: A silicon substrate 1 which has been subjected to the step C in FIG. 1 is prepared.

In this case, the silicon nitride film 3 that served as a mask for selective oxidation
It is conventionally known that a silicon nitride film 4 having a width of approximately 1 μm is formed on the silicon thermal oxide film 2' under the end of the silicon oxide film 2'.

When high-temperature treatment is performed in a steam atmosphere using the silicon nitride film 3 as a mask (see Figure 1C), the moisture in the steam and the silicon nitride film 3 acting as a mask combine to form Si3N4+H2O.
-') A reaction of Si02 + NH3 occurs, and the NH3 generated thereby diffuses in the silicon oxide film 2 produced by selective oxidation, and connects to the silicon substrate 1 and Si + NH3 → Si3N4 + H
A reaction as shown in 2 occurs and a silicon nitride film 4 is formed.

FIG. 2C: The silicon nitride film 3, which served as a mask during selective oxidation, is completely removed using a suitable etching solution.

FIG. 2C: The silicon thermal oxide films 2 and 7 are further formed by performing heat treatment again in an oxidizing atmosphere.

In this case, the silicon thermal oxide film 2'' on the silicon nitride film 4 becomes thicker because the silicon nitride film 4 acts as a mask and blocks the reaction between oxygen in the oxidizing atmosphere and silicon in the semiconductor. Instead, a recess 5 is formed in this region with respect to the silicon thermal oxide film in other regions.

FIG. 2d: The silicon thermal oxide film formed on the main surface of the silicon substrate 1 is etched until the surface of the silicon nitride film 40 is exposed.

Then, only the exposed silicon nitride film 4 is etched to expose a partial region of the silicon substrate 1.

In this way, the opening is formed in the region where the silicon nitride film 4 is formed, and since the width of the silicon nitride film is about 1 μ, an opening with a width of about 1 μ can be obtained. Become.

In addition, in this case, in the formation of the openings, there is no mask shift or the like because selective etching by photolithography is not performed as in the conventional method (reproducibility is excellent, and pattern defects due to mask defects do not occur).

Note that since the thickness of the silicon nitride film 4 is generally small, in order to reduce the thickness of the silicon nitride film 4, heat treatment is performed at as high a temperature as possible in the step shown in FIG.
NH3 generated by the reaction between silicon nitride film 3 and moisture
In the process shown in Figure 2C, the oxidation temperature was set at 900°C so that it could withstand the oxidation as a mask.
It has been experimentally proven that good results can be obtained when the temperature is below 0.degree. C. and the water vapor during oxidation is above 1 atm.

This example describes a method for forming a mask when forming an impurity diffusion layer with a uniform diffusion depth.
In particular, when the depth of the impurity diffusion layer is small, strong stress is applied to the peripheral portion of the impurity diffusion layer when forming the electrode, and as a result, abnormal diffusion of the electrode material is induced in this portion, resulting in a PN junction failure.

For this reason, in the past, the diffusion depth at the periphery of the impurity diffusion layer was determined to be deep.

Hereinafter, a mask forming method for forming a fine impurity diffusion layer in such a structure will be explained in order of steps using the main part process diagrams shown in FIGS. 3A to 3C.

FIG. 3C: Prepare a silicon substrate 1 having the configuration shown in exposure diagram d, and place the silicon substrate 1 on the exposed part of the silicon substrate 1.
An impurity diffusion layer 6 is formed by diffusing impurities of a conductivity type different from that of the first and second conductivity types.

FIG. 3b: Using an etching solution that etches only the silicon oxide film, the silicon oxide films 2 and 2' are etched only beyond the thickness of the silicon oxide film 2', so that a part of the surface of the silicon substrate 1 is exposed.

FIG. 3C: An impurity of a conductivity type different from that of the silicon substrate 1 is diffused into the exposed surface of the silicon substrate 1 to form a relatively thin impurity diffusion layer 6'.

In this way, the depth of the impurity diffusion layer can be reduced in the area where stress is applied during electrode formation, and the width of the impurity diffusion layer in the area where the depth is reduced is as small as approximately 1μ, compared to conventional methods. As a result, an impurity diffusion layer with extremely high density can be obtained.

In this embodiment, the diffusion layer region is generally described, but it can be applied to the formation of the emitter layer of a bipolar transistor or the source region and drain region of an MIS type transistor.

As described above, according to the method for manufacturing a semiconductor device according to the present invention, an impurity diffusion mask with finer dimensions can be formed,
This makes it possible to achieve high integration.

[Brief explanation of the drawing]

1A to 1D are cross-sectional process diagrams showing essential parts of an example of a conventional semiconductor device manufacturing method, and FIGS. 2A to 2D are sectional process diagrams showing essential parts of an embodiment of a semiconductor device manufacturing method according to the present invention. 3A to 3C are cross-sectional process diagrams showing essential parts of another embodiment of the method for manufacturing a semiconductor device according to the present invention. 1... Silicon substrate, 2, 2'... Silicon thermal oxide film, 3, 4... Silicon nitride film,
5... Concave portion, 6, σ... Impurity diffusion layer.

Claims (1)

[Claims] 1. A step of forming a mask made of a silicon nitride film on a silicon oxide film formed on the surface of a silicon substrate, and selectively oxidizing the silicon under the edge of the mask by heat treatment in a steam atmosphere. a step of forming a silicon nitride film on the surface of the substrate; a step of heat-treating in an oxidizing atmosphere after removing the mask; A method of manufacturing a semiconductor device, comprising the steps of: etching the silicon nitride film until it is exposed; and then removing the silicon nitride film. 2. Forming a mask made of a silicon nitride film on the silicon oxide film formed on the surface of the silicon substrate, selectively oxidizing the silicon nitride film by heat treatment in a water vapor atmosphere, and at the same time forming a silicon nitride film on the silicon substrate surface under the edge of the mask. a step of forming a film; a step of heat-treating in an oxidizing atmosphere after removing the mask; and etching the silicon oxide film on the top surface of the silicon substrate until the silicon nitride film formed on the surface of the silicon substrate is exposed. After that, a step of removing the silicon nitride film, a step of diffusing impurities into the silicon substrate surface exposed by removing the silicon nitride film, and a step of removing the silicon oxide film in the region where the mask is formed are performed. 1. A method for manufacturing a semiconductor device, comprising the steps of: diffusing impurities into an exposed silicon substrate surface.