JPH033948B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of manufacturing an insulation isolation structure thereof.

In order to integrate a large number of elements on a semiconductor substrate to form an electronic circuit, it is necessary to electrically insulate and separate the elements from each other. As an insulation separation method,
Separation methods using Pn separation and selective oxidation of S are widely used. In particular, highly integrated silicon
In LSI, a selective oxidation method using a nitride layer as a mask is used. However, in this selective oxidation method, since the oxide film grows in the lateral direction, the insulation isolation region becomes wider than the mask dimension, resulting in a reduction in the element area. Furthermore, the selective oxidation method has a problem in that deep insulation isolation is difficult.

Recently, the groove separation method has been attracting attention as a method to overcome these drawbacks of the selective oxidation method. This trenching separation method involves digging trenches by anisotropic etching in the areas of the silicon substrate that are to be insulated and separated.
This is a method of filling this groove with an insulator. In the groove separation method, by using anisotropic etching, it is possible to prevent the spread in the lateral direction. In addition, the depth of the groove can be controlled freely.
Deep insulation separation can also be easily achieved.

In order to fill the trench, an insulating film that has good coverage over the underlying stepped portion and can be grown thickly is essential. Such a film includes polycrystalline silicon grown in a high temperature and reduced pressure vapor phase. However, since polycrystalline silicon is not an insulating film, it is necessary to form an oxide film of approximately 0.1 to 0.2 μm on the surface of the groove formed in the silicon substrate, or to oxidize the surface of the embedded polycrystalline silicon. . At this time, the film becomes thinner at the corners of the groove, and the dielectric strength may not be sufficient. Another drawback is that the surface of the insulating region is difficult to flatten due to the growth of the oxide film.

If an oxide film is used to fill the trench, this problem will disappear. However, it is difficult to obtain an oxide film with good coverage and good film quality over the stepped portions of the base.

The present invention has made it possible to fill the grooves using a PSG film that has poor coverage but can be grown thickly and has relatively good film quality.

According to the present invention, the steps include: forming a groove substantially perpendicularly to the main surface of a semiconductor substrate; forming a thin silicon oxide layer on the surface of the groove; and forming a first silicon oxide glass layer on the silicon oxide layer. The first silicon oxide glass layer is fluidized by a step of depositing a silicon oxide glass and a heat treatment in a steam atmosphere at about 950° C., and the first silicon oxide glass layer above the opening of the groove is rounded. and thereafter depositing a second silicon oxide glass layer on the first silicon oxide glass layer, and fluidizing the second silicon oxide glass layer by heat treatment. A method for manufacturing the device is obtained.

The details of the present invention will be explained below. FIG. 1 shows a state in which a groove is formed in a silicon substrate. A thermal oxide film 3 having a thickness of several tens of nanometers to about 0.1 μm is formed in order to reduce interface states and interface fixed charges on the groove surface.

FIG. 2 shows a state in which a PSG film 4 having a thickness less than half of that in the groove is grown in a vapor phase. At corner 5, PSG
The membrane grows abnormally and a lump 5 is formed. Because of these nodules, if a thick PSG film is grown all at once, the nodules will block the entrance, creating a cavity in the groove that cannot be completely filled.

FIG. 3 shows the state after the PSG film 4 is grown and then heat-treated in a steam atmosphere at about 950°C.
The PSG film becomes fluid at high temperatures, the bumps 5 disappear due to surface tension, and the corners 6 or 7 become rounded.

If the corners are rounded, no bumps will occur even when the second PSG film 8 is grown. Therefore, as shown in FIG. 4, the trench can be completely filled with the PSG film.
Next, by heat-treating again in a steam atmosphere at about 950°C, the surface of the groove can be made flat.
Finally, by etching the PSG films 4 and 5 on the silicon surface, the PSG films are left only in the grooves, completing an insulating isolation structure, as shown in FIG.

After growing the second PSG film, in order to flatten the surface, in addition to steam treatment at about 950°C,
A method may also be used in which a resist film or a liquid film such as a silica film is applied, solidified, and then etched (wet or plasma etched) so that the etching rate is approximately equal to that of the PSG film.

Filling the inside of the groove with a PSG film brings about various advantages as described below.

(1) Due to the gator effect of the PSG film, Si/
Stabilizes the SiO ₂ interface and suppresses channel leakage current.

(2) Since the viscosity of the PSG film decreases at high temperatures, high-temperature heat treatment alleviates stress on the silicon substrate due to thermal stress caused by differences in thermal expansion coefficients. Therefore, crystal defects are less likely to occur in the silicon substrate.

(3) The residual stress of the PSG film at room temperature is due to SiO ₂ and
Since it is smaller than Si ₃ N ₄ etc., cracks will not occur even if the film thickness is increased.

(4) Since the PSG film is an insulator, complete insulation isolation is possible. There is no breakdown voltage problem or instability due to charge accumulation, which is a problem when polycrystalline silicon is heated.

As is clear from the above explanation, according to the present invention,
The surface is flat, crystal defects are less likely to occur, and it is electrically stable, making it possible to perform insulation separation suitable for miniaturization.

[Brief explanation of the drawing]

FIGS. 1 to 5 are sectional views of elements in order of process for explaining embodiments of the present invention. In the figure, 1... silicon substrate, 2...
Groove, 3... thermal oxide film, 4... first PSG film, 5
... bump, 6, 7 ... corner part, 8 ... second
It is a PSG film.

Claims (1)

[Claims] 1. Forming a groove substantially perpendicular to the main surface of the semiconductor substrate, forming a thin silicon oxide layer on the surface of the groove, and depositing a first silicon oxide glass layer on the silicon oxide layer. and 950℃
a step of fluidizing the first silicon oxide glass layer by heat treatment in a steam atmosphere to form a roundness in the first silicon oxide glass layer above the opening of the groove; A semiconductor device comprising: depositing a second silicon oxide glass layer on the first silicon oxide glass layer; and fluidizing the second silicon oxide glass layer by heat treatment. Production method.