JPS60236245A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain an oxidation resistant film having excellent oxidation resistance and buffer effect in the step of forming a field oxide film by forming a silicon nitride oxide film in a specific triple structure as an oxidation film. CONSTITUTION:A silicon nitride oxide film of 3-layers having a relation of n1<n3<n2 of n1, n2, n3 of refractive indexes is coated in the order of n1, n2, n3 on a semiconductor substrate 1. For example, a silicon oxide-rich silicon nitride oxide film 7 of n1=1.6, a silicon nitrode-rich silicon nitride oxide film 8 of n2=1.9 and a silicon nitride oxide film 9 of n3=1.85 are, for example, coated under reduced CVD. The films 7, 8, 9 are patterned except an element forming region, thermally oxidized to obtain a field oxide film 4. The film 7 contributes to the buffer effect, the film 8 contributes to the oxidation resistance, and the warpage of the periphery can be suppressed by the thick film 9.

Description

Detailed Description of the Invention (a) 1 Technical Field of the Invention The present invention involves selectively providing a silicon dioxide film on a silicon substrate using a silicon oxynitride (S1ON) film as an oxidation-resistant mask, and applying this silicon dioxide film to a field. The present invention relates to a method of manufacturing a semiconductor device using an oxide film for element isolation.

(h) Background of the Technology In order to isolate constituent elements in a semiconductor device such as an integrated circuit, the field oxide film is often deposited on a portion other than the element region.

FIG. 1 is a cross-sectional view of a silicon substrate after a field oxide film is formed.

In the figure, 1 is a silicon substrate, 2 is a buffer film, 3 is an oxidation-resistant film, and 4 is a field oxide film.

In order to increase the isolation effect between elements, it is necessary to increase the thickness of field oxide film 4 to 8000 Å or more. Conventionally, as the oxidation-resistant film 3 when forming such a thick oxide film, a silicon nitride film deposited by a vapor phase growth (CVD) method has been deposited to a thickness of 1,000 to 2,000 layers over the device region. In this case 1, silicon nitride is extremely hard and the silicon substrate 1 is in close contact with it.
Crystal dislocations are likely to occur due to strain caused by the difference in thermal expansion coefficients.

ii. Furthermore, if the CVD silicon nitride film 3 comes into direct contact with the silicon substrate 1, there is a risk that an interface level may be formed in the silicon substrate, or that impurities may enter the silicon substrate 1 during heat treatment in a subsequent step.

In order to prevent the above two drawbacks, the buffer (pad) film 2
An extremely thin silicon dioxide film having a thickness of about 500 mm is placed under the silicon nitride film 3 to alleviate these effects.

However, by placing the silicon dioxide film 2 under the silicon nitride film 3, the following drawbacks arise.

That is, in the oxidation step of forming the field oxide film 4,
Oxygen crowds from the side of silicon dioxide film 2, and silicon nitride film 3
As shown in the figure, an I-silicon oxide film with a beak-like cross-sectional shape called a so-called bird's beak is formed, and the opening size of the field oxide B1i, 4 becomes smaller than the expected value, making it difficult for microfabrication. is disadvantageous.

(C), Prior Art and Problems In order to eliminate the above drawbacks when using a silicon nitride film as an oxidation-resistant film, the applicant has disclosed the use of silicon oxynitride instead of a silicon nitride film. There is (Unexamined Japanese Patent Application Publication No. 5)
6-93344). The outline will be explained below using the figures.

FIG. 2 is a cross-sectional view of a silicon substrate showing a conventional field oxide film forming process when a silicon oxynitride film is used as the oxidation-resistant film. In the figures below, the same numbers indicate the same objects.

In FIG. 2 tal, silicon oxynitride 89.5 having a certain composition is deposited on -L of the silicon substrate l.

The deposition method is silane (Sitln) by plasma CVD.
, ammonia (NH3) and nitrogen oxide (N20) are sent to a normal pressure container at a constant ratio, and the IOW RF is applied at 13.56 MIIz.
By applying electric power, CV is applied to the silicon substrate 1 placed in the container.
A silicon oxynitride film 5 is deposited.

In FIG. 2 (bl), the silicon oxynitride film 5 is patterned using a normal glue and polish process, leaving the silicon oxynitride film 5 in the element formation region.

In FIG. 2C, a silicon dioxide film 6 is obtained in which the field oxide film 4 and the silicon oxynitride film 5 are converted by thermal oxidation at 1000'C or more.

In FIG. 2 [dl], the silicon dioxide film 6 converted into silicon oxynitride 1195 is removed using hydrofluoric acid.

However, when using the silicon oxynitride film 5 as an oxidation-resistant film, if the silicon oxide-rich silicon oxide nitride film is made with emphasis on the buffering effect, the oxidation resistance will be sacrificed; However, if a silicon oxynitride film such as silicon nitride or silicon is used, the buffering effect is sacrificed.

In addition, as in this example, the silicon oxynitride film 5 formed by plasma CVL contains a large amount of hydrogen (contains many pinballs) and has poor film quality, resulting in defects in the gate oxide film formed after the silicon oxynitride film 5 is removed. Easy to occur.

(d)1 Objective of the invention The objective of the present invention is to eliminate the above-mentioned drawbacks of the prior art,
It is an object of the present invention to provide a manufacturing method that provides an oxidation-resistant film with excellent oxidation resistance and buffering effect.

(C) 1 Structure of the Invention The above object is to provide a semiconductor substrate with a refractive index of nl+, respectively.
A three-layer silicon oxynitride film with nt+13 and the relationship n<13<nz is formed by il 1 + n 2. n
This is achieved by the method of manufacturing a semiconductor device according to the present invention, in which the silicon oxynitride film is used as a mask to form an oxide film on the substrate region not covered with the silicon oxynitride film.

According to the present invention, by changing the mixing ratio of the supplied gas when forming a silicon oxynitride film by CVD, it is possible to easily create various compositions and obtain an oxidation-resistant film with excellent oxidation resistance and buffering effect.

(r) 1 Embodiment of the Invention FIG. 3 is a cross-sectional view of a silicon substrate, not showing the culm, of field oxide film formation according to the present invention when a silicon oxynitride film is used as the oxidation-resistant film.

In FIG. 3 ta+, the thickness of the silicon substrate 1 is 100~
Silicon oxide-rich silicon oxide nitride with a refractive index of 300 people n+-1,6! 7, refractive index n2 = 1 with a thickness of about 200 people
．． 9, silicon nitride-rich silicon oxynitride film 8, thickness 200
Oxynitride 1 with refractive index n of 0-3000, □-1,85
1 elemental film 9 is deposited.

Incidentally, the refractive index is 1.46 for silicon dioxide and 2 for nitride.
．． It is 0.

The deposition method is to send a mixed gas of silane (Silla), ammonia (Nlh), and nitrogen oxide (NO) to a vacuum container by low-pressure CVD and deposit silicon at 700°C in the container. - Applying 71 a CVD silicon oxynitride film 7.8.9 on top of the plate 1.

In FIG. 3 fbl, the silicon oxynitride film 7.8.9 is patterned using reactive ion etching using normal lithography step 1, leaving only the element formation region.

In FIG. 3 fc), a field oxide film 4 is obtained by thermal oxidation at 900° C. or higher.

In FIG. 3 fd), the silicon oxynitride films 7 and 8 are removed using hot phosphoric acid, and the silicon oxynitride films 9 are removed using hydrofluoric acid.

By adopting such a triple structure, the silicon oxide-rich silicon oxynitride film 7 contributes to the buffering effect, and the silicon nitride-rich silicon oxynitride film 8 contributes to the oxidation resistance. In order to prevent the periphery of the silicon oxide film from warping, it can be suppressed with a thick silicon oxynitride film 9. Every time the thickness of the silicon oxynitride film 9 is increased by 1000, the bird's beak length B shown in FIG. 1 can be reduced by about 1000.

In addition, as in the embodiment, the silicon oxynitride film 7 is formed by low pressure CVD.
, 8.9 have good film quality and do not adversely affect the gate oxide film formed after removing the silicon oxynitride film 7.8.9.

(g) Effects of the Invention As described above in detail, the present invention can provide a manufacturing method that provides an oxidation-resistant film with excellent -4 oxidation properties and buffering effects.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a silicon substrate after field oxide film formation;
FIG. 2 is a cross-sectional view of a silicon substrate showing a conventional field oxide film forming process when a silicon oxynitride film is used as the oxidation-resistant film, and FIG. 3 is a cross-sectional view of a silicon substrate when a silicon oxynitride film is used as the oxidation-resistant film. FIG. 2 is a cross-sectional view of a silicon substrate showing a field oxide film forming process according to the present invention. In the figure, 1 is a silicon substrate, 2 is a buffer film, 3 is an oxidation-resistant film, 4 is a field oxide film, 5 is a silicon oxynitride film, 6 is a silicon dioxide film, 7 is a refractive index n, and 1°6 oxidation film. A silicon-rich silicon oxynitride film, 8 is a silicon nitride film with a refractive index n2 = 1.9, and a silicon oxynitride film with a refractive index n3 = 1.8.
The silicon oxynitride lI9 of No. 5 is shown.

Claims (1)

[Claims] On the semiconductor substrate, the refractive index is nl + 02 + 13, respectively,
Three layers of silicon oxynitride films satisfying the relationships n, <n, and <n are deposited in the order of nl+02+13, and the silicon oxynitride film is used as a mask to cover the substrate area not covered with the silicon oxynitride film. A method for manufacturing a semiconductor device, comprising forming an oxide film.