JPH0410419A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce unevenness and stress on a semiconductor surface by a method in which the surface of a silicon substrate is selectively anodized to form porous silicon, and the porous silicon is oxidized to form silicon oxide for device isolation. CONSTITUTION:A silicon oxide film 2 and a silicon nitride film 3 are formed on a p-type silicon substrate 1, and these films are etched away in selective regions where silicon oxide is to be formed. The surface of the substrate in these regions is anodized to form a porous silicon 4. The anodization is carried out, for example, by supplying current to the p-type silicon substrate 1 in a mixture of ethanol and hydrofluoric acid (HF:H2O:C2H5OH=1:1:2) so that an electrochemical reaction may take place to make the silicon surface porous. The substrate is heat-treated in an oxygen atmosphere to form silicon oxide 5 for device isolation on the porous silicon 4.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and particularly to a technique for forming a silicon oxide film for element isolation.

BACKGROUND OF THE INVENTION In recent semiconductor processes, the photolithography process has become more and more precise, so a high level of flatness of the surface of the semiconductor substrate is required in order to bring the mask into close contact with the semiconductor substrate.

Conventionally, an example of a method for manufacturing this type of semiconductor device has a structure as shown in FIGS. 2(a) and 2(b).

First, as shown in FIG. 2(a), a silicon oxide film 12 and a silicon nitride film 13 are placed on a P-type silicon substrate 11.
After forming the silicon oxide film 12 and the silicon nitride film 13 in the region where the element isolation silicon oxide film 15 is to be formed.
is removed by etching (.

Next, as shown in FIG. 2(b), thermal oxidation is performed in a gas containing oxygen to form a silicon oxide film 15 for element isolation.

Problems to be Solved by the Invention In such a conventional process, when forming the silicon oxide film 15 for element isolation on the P-type silicon substrate 11, the silicon oxide film 15 for element isolation is first formed on the P-type silicon substrate 11. Board 1
Open end 1 of silicon oxide film 12 formed on 1
Since it is formed by sinking into the P-type silicon substrate 11 below 2', the open end 12' of the silicon oxide film 12 and the open end 13' of the silicon nitride film 13 formed thereon are pushed in. It is said that it is not suitable for the subsequent miniaturization process due to the occurrence of unevenness on the element surface, and that stress is generated around the silicon oxide film 15 for element isolation, causing crystal defects in the P-type silicon substrate 11. There was a problem.

The present invention has been made in view of these points, and can solve the above problems, reduce the occurrence of unevenness due to the formation of the silicon oxide film 15 for element isolation, and reduce stress from the silicon oxide film 15 for element isolation. It is an object of the present invention to provide a method for manufacturing a semiconductor device in which a silicon oxide film 15 for element isolation is formed.

Means for Solving the Problem In order to solve this problem, a method for manufacturing a semiconductor device according to the present invention includes a method for manufacturing a semiconductor device of the present invention. The surface layer of the silicon substrate is transformed into a porous silicon layer by anodization, and the porous silicon layer is oxidized to form a silicon oxide film for element isolation.

Effect With this configuration, the porous silicon layer modified by the anodization method contains many micropores and has a very large surface area, so a silicon oxide film for element isolation is applied to the porous silicon layer by thermal oxidation in a later step. Even if it is formed, not only the surface layer but also the surface of the internal micropores are oxidized, so the volume increase of the surface layer is small.

EXAMPLE An example of the semiconductor device of the present invention will be described below with reference to the drawings.

As shown in FIG. 1(a), after forming a silicon oxide film 2 and a silicon nitride film 3 on a P-type silicon substrate 1, the silicon oxide film 2 and the silicon The nitride film 3 is removed by etching.

Next, as shown in FIG. 1(b), the surface layer of the P-type silicon substrate 1 in a region where a silicon oxide film for element isolation is to be formed is transformed into a porous silicon layer 4 using an anodization method. The porous silicon layer 4 is obtained by anodizing a silicon single crystal in a hydrofluoric acid solution, and has a thickness of several to several tens of nm.
It contains many micropores and has a very large surface area (20
0 to 800+J/cd), oxidation can be performed in a short time and at a low temperature. An example of a method for converting the surface layer of a P-type silicon substrate into a porous silicon layer 4 using an anodization method will be described. A P-type silicon substrate 1 was heated in a hydrofluoric acid solution (HF:H2O:C2H50H=
1:1:2), several mA/c! By increasing the current for several tens of seconds, the surface of the P-type silicon substrate 1 is transformed into a porous silicon layer 4 with a thickness of several hundred nm by an electrochemical reaction.

Furthermore, as shown in FIG. 1C, thermal oxidation is performed in a gas containing oxygen to form a silicon oxide film 5 for element isolation on the porous silicon layer 4.

The steps shown in FIGS. 1(b) and 1(C) correspond to the steps shown in FIG. 2(b) of the conventional example, and the subsequent semiconductor device forming steps are connected to normal steps.

Effects of the Invention As is clear from the description of the embodiments above, the method for manufacturing a semiconductor device of the present invention reduces the occurrence of unevenness accompanying the formation of a silicon oxide film for element isolation, and also reduces the unevenness caused by the formation of a silicon oxide film for element isolation. By reducing stress, crystal defects in the silicon substrate can be reduced.

Furthermore, since thermal oxidation can be performed in a shorter time and at a lower temperature than before, bird's beak can be reduced and thermal stress can also be reduced.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a semiconductor element substrate showing a method for manufacturing a semiconductor device according to an embodiment of the present invention in order of steps, and FIG. 2 is a cross-sectional view of a semiconductor element substrate showing an embodiment of a conventional method for manufacturing a semiconductor device in order of steps FIG. 1...Silicon substrate, 2...Silicon oxide film, 3...Silicon nitride film, 4...
・Porous silicon layer, 5...Silicon oxide film for element isolation.

Claims (1)

[Claims] After forming a silicon oxide film on a silicon substrate and further forming a silicon nitride film on the silicon oxide film, forming the silicon oxide film for element isolation in order to form a silicon oxide film for element isolation on the silicon substrate. After removing the silicon oxide film and the silicon nitride film formed on the silicon substrate in the area where the silicon oxide film is to be formed, and masking the area where the silicon oxide film for element isolation is not to be formed, the silicon oxide film and the silicon nitride film formed on the silicon substrate are removed. A method for manufacturing a semiconductor device, comprising the steps of transforming a substrate surface layer into a porous silicon layer by anodization, and oxidizing the porous silicon layer.