JPH02135754A - Manufacture of semiconductor substrate - Google Patents

Abstract

PURPOSE:To prevent a silicon nitride film from peeling at the time of supply of molten silicon and to effectively fill a groove by forming a silicon oxynitride thin film on a silicon dioxide film on the surface of a semiconductor substrate. CONSTITUTION:A silicon oxynitride thin film 25 is so formed from a silicon dioxide film 24 toward the forming surface on the film 24 as to increase the composition ratio of oxygen to nitrogen in the film. The silicon oxynitride exhibits properties of intermediate of those of the silicon dioxide and the silicon nitride according to the composition ratio of the oxygen to the nitrogen. Thus, when molten silicon is dripped on the film 25 in a later step, both are not peeled, since both has similar thermal expansion coefficient, the molten silicon fills the V-shaped groove 23 on the surface by wettability of the molten silicon similar to that of the silicon nitride.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application) The present invention relates to a method for manufacturing a semiconductor substrate used in a semiconductor integrated circuit. The present invention relates to a method for forming a polycrystalline silicon layer thereon by depositing and solidifying molten silicon.

(Prior art) A method of forming a silicon dioxide film on the surface of a semiconductor substrate including the inside of a groove, and forming a polycrystalline silicon layer thereon by adhering and solidifying molten silicon is as follows. It should be applied to the manufacturing ft method. Therefore, as the above-mentioned conventional method, a conventional method for manufacturing a g-electrical isolation substrate will be described with reference to FIG.

The manufacturing method of this dielectric isolation substrate is disclosed in Japanese Patent Application Laid-Open No. 60-1827.
It is disclosed in Publication No. 38.

First, as shown in FIG. 2(al), a single crystal silicon substrate 1 is anisotropically etched to form a V-shaped groove 2.

Next, as shown in FIG. A silicon nitride film 4 having a thickness of about 0.1 μm is formed thereon by a known CVD method.

After that, melted silicon at a temperature of about 1440°C was heated to 13
Polycrystalline silicon layer 5 with a thickness of about 500 μm is formed on silicon nitride film 4 by supplying the molten silicon onto silicon substrate 1 kept at about 00° C., spreading the molten silicon over the entire surface of the substrate, and cooling it.

Here, the silicon nitride film 4 is necessary because the molten silicon penetrates into the V-shaped groove 2 and fills the inside of the V-shaped groove 2, and the molten silicon is directly deposited on the silicon dioxide film 3 for insulation isolation. This is because if the polycrystalline silicon is dropped, unfilled areas 11 of polycrystalline silicon as shown in FIG. 3 will occur in the V-shaped F's2 due to poor wettability between the silicon dioxide film and molten silicon.

After that, the surface of the polycrystalline silicon layer 5 is ground to a flat processing reference surface 6, and then the back side of the single crystal silicon substrate 1 is
By removing by grinding and polishing until the tip of the letter Fli2 is exposed, a dielectric isolation substrate shown in FIG. 2 tc+ can be obtained.

(Problem to be Solved by the Invention) However, in the above-mentioned conventional manufacturing method, when high-temperature molten silicon is supplied onto the silicon nitride film 4 in the form of droplets having a certain mass or more, insulation separation occurs. Due to the difference in thermal expansion coefficient between the silicon dioxide film 3 and the silicon nitride film 4, a sudden thermal stress is generated at the interface between the two films, causing the silicon nitride film 4 to peel off and the V-groove 2 to be filled with molten silicon. There was a problem that it was not done. In such unfilled areas, depressions (unfilled areas 11) are formed on the surface of the dielectric isolation substrate shown in FIG. As a result, the manufacturing yield of semiconductor integrated circuits has been reduced.

An object of the present invention is to provide a method for manufacturing a semiconductor substrate that can eliminate the above-mentioned problem of unfilled trenches due to peeling of the silicon nitride film when supplying molten silicon and ensure filling of the trenches. shall be.

(Means for Solving the Problems) In the present invention, a silicon dioxide film is formed on the surface of a semiconductor substrate having a groove, a silicon oxynitride-based ri4 film is formed on the silicon dioxide film, and a polycrystalline silicon film is formed on the silicon dioxide film. A silicon layer is formed by depositing molten silicon. Furthermore, the silicon oxynitride-based r41# is silicon oxynitride, which has a higher oxygen composition ratio than silicon dioxide or the center part of the film in the part in contact with the silicon dioxide film, and silicon nitride or silicon oxynitride in the surface part, which has a higher oxygen composition ratio than the silicon dioxide or the center part of the film. A silicon oxynitride-based R film consisting of silicon oxynitride with a higher nitrogen composition ratio than the other parts.

(Function) In the present invention, a silicon oxynitride thin film having the above-mentioned film structure is formed on a silicon dioxide film on the surface of a semiconductor substrate.
O, N, ) exhibits intermediate properties between silicon dioxide and silicon nitride depending on the composition ratio of MZ and nitrogen, and by having the above-mentioned film structure, molten silicon can be converted into silicon oxynitride in a later process. When dropped onto a Ride-based thin film, the film does not peel off at the interface with the silicon dioxide film for insulation isolation due to the same coefficient of thermal expansion as silicon dioxide, and on the surface, molten silicon similar to silicon nitride does not peel off. The wettability of the molten silicon ensures that the molten silicon fills the groove.

(Embodiment) Referring to Figures ta) to [d] below, an embodiment of the present invention will be described by taking a dielectric isolation substrate as an example.

As shown in FIG. 1(a), a single-crystal silicon substrate 21 is oxidized to form a silicon dioxide film 22 with a thickness of about 1 μm on its surface.

Next, as shown in FIG. 1(b), the silicon dioxide film 22 is partially opened by photolithography and etching, and the single crystal silicon substrate 21 is anisotropically formed using the remaining silicon dioxide film 22 as a protective mask. By etching, a V-shaped groove 23 having a depth of about 50 μm is formed.

Next, as shown in FIG.
2, the single crystal silicon substrate 21 is oxidized again and V
A silicon dioxide film 24 having a film thickness of about 2 μm and having an insulating isolation width of T is formed on the surface of the substrate including the groove 23 .

Next, a silicon oxynitride (SiO,N,) thin film 25 with a thickness of about 0.2 μm is formed on the silicon dioxide film 24 by a known CVD method.
The film is formed so that the composition ratio y/x of nitrogen to oxygen in the film increases from the side toward the formation surface. Here, the portion of the thin film 25 in contact with the silicon dioxide film 24 may be made entirely of silicon oxide, and the surface thereof may be made entirely of silicon nitride.

Note that the silicon oxynitride-based thin film is S i I
(obtained by thermal decomposition of 4・NH,・N20 gas,
By increasing the mixture ratio of Nil and /N20 as the film is formed, a silicon oxynitride-based four-film Z5 having the above film structure can be formed. In addition, silicon oxynitride exhibits five properties between those of silicon dioxide and silicon nitride depending on its oxygen and nitrogen composition ratio, and by having the above-mentioned film structure, molten silicon can be converted into silicon in a later process. When dropped onto the nitride-based thin film 25, the film does not peel off at the interface with the silicon dioxide film 24 for insulation isolation due to its coefficient of thermal expansion similar to that of silicon dioxide, and the surface of the nitrided Due to the wettability of molten silicon similar to that of silicon, the V of the molten silicon
Filling of the groove 23 is ensured.

Hereinafter, according to the conventional manufacturing method, molten silicon at a temperature of about 1440°C is supplied onto the silicon substrate 21 maintained at 1300 to 1400°C by dropping or spraying from a nozzle, the molten silicon is spread over the substrate surface, and then cooled. As a result, a polycrystalline silicon layer 26 with a thickness of about 550 μm is deposited on the silicon oxynitride thin film 25. At this time, as mentioned above, the silicon oxynitride-based R4 film 25 does not peel off, and the molten silicon remains in the V-shaped groove 25.
Make sure it is filled inside. After that, the polycrystalline silicon layer 26
After grinding the surface to a flat processing reference surface 27, the back side of the single crystal silicon substrate 21 is removed by grinding and polishing until the tip of the V-shaped groove 23 is exposed.
Complete a dielectric isolation substrate in which single crystal silicon islands 28 are electrically isolated from each other as shown in d).

Although the above embodiment deals with a dielectric S substrate, the present invention can also be applied to other similar methods of manufacturing semiconductor substrates.

(Effects of the Invention) As described above in detail, according to the present invention, silicon oxynitride-based r11II! 11 Particularly, in the area in contact with the silicon dioxide film on the surface of the semiconductor substrate, silicon oxynitride has a higher oxygen composition ratio than that of silicon dioxide or the central part of the film, and in the surface part, silicon oxynitride has a higher oxygen composition ratio than that of silicon nitride or the central part of the film. In order to form a silicon oxynitride-based thin film composed of silicon oxynitride with a high ratio, a silicon oxynitride film is used to ensure filling when supplying high-temperature molten silicon based on the difference in thermal expansion coefficient with the silicon dioxide film. It is possible to prevent the film from peeling off and to ensure that the grooves are filled with molten silicon. Therefore, for example, it is possible to prevent the occurrence of depressions on the surface of a dielectric isolation substrate, and when an integrated circuit is formed, it is possible to prevent wiring from breaking due to the depressions, thereby improving the manufacturing yield of semiconductor integrated circuits. You can do it.

[Brief explanation of the drawing]

FIG. 1 is a process sectional view showing an embodiment of the method for manufacturing a semiconductor substrate of the present invention, FIG. 2 is a process sectional view showing a conventional method for manufacturing a dielectric isolation substrate, and FIG. 3 is a nitriding process in the conventional method. FIG. 3 is a cross-sectional view illustrating unfilled grooves of molten silicon that would occur in the absence of a silicon film. 21. Single crystal silicon substrate, 23. V-shaped groove, 24.
- Silicon dioxide film, 25...Silicon oxynitride type #FJ, 2s...Polycrystalline silicon layer. A sectional view of a manufacturing process according to an embodiment of the present invention A sectional view of a conventional manufacturing process

Claims (1)

[Claims] (a) forming a silicon dioxide film on the surface of the semiconductor substrate including the inside of the groove of a semiconductor substrate having a groove; A silicon oxynitride-based thin film consisting of silicon oxynitride, which has a higher oxygen composition ratio than the central part, and silicon nitride in the surface part, or silicon oxynitride, which has a higher nitrogen composition ratio than the central part of the film. The process of forming (
c) forming a polycrystalline silicon layer on the thin film by depositing and solidifying molten silicon.