JPH065589A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain an element isolation insulating film which provides high dimensional uniformity by installing a polysilicon film as a reflection preventative film on an Si3N4 film which is used as an oxidation resistant film. CONSTITUTION:A pad SiO2 film 12 is formed on a silicon substrate 11 and an Si3N4 film 13 is formed thereon. Furthermore, there is formed a polysilicon film 14 having a specified film thickness as a reflection preventative film. The polysilicon film has a greater reflective index compared with the pad SiO2 film and the Si3N4 film, which makes it possible to reduce the reflectivity from a base film dramatically. It is, therefore, possible to obtain a resist pattern which eliminates variabilities in pattern dimensions attributable to a multiple reflection effect and hence form an element isolation insulating film which provides high dimensional uniformity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming an element isolation insulating film having high dimensional uniformity.

[0002]

2. Description of the Related Art In general, a method of forming an element isolation insulating film by a selective oxidation method selectively heats a silicon substrate by selectively performing thermal oxidation using a Si ₃ N ₄ film having oxidation resistance as a mask. The element isolation insulating film is formed. Here, the process of forming the Si ₃ N ₄ film in a predetermined region on the silicon substrate is as described below.

That is, as shown in FIG. 4, a Si ₃ N ₄ film (3) is formed on a silicon substrate (1) via a pad SiO ₂ film (2), and this Si ₃ N ₄ film (3) is formed. A resist film (4) is applied to the entire surface of the. And photolithography
By applying the technique, the resist film (4) is processed into a predetermined resist pattern. After that, the Si ₃ N ₄ film is selectively etched using the processed resist pattern as a mask.

[0004]

In the above photolithography process, the dimension of the processed resist pattern varies due to multiple reflection of light from the underlying film. This variation is reflected in the pattern dimension variation of the etched Si ₃ N ₄ film and further in the element isolation insulating film dimension.

Conventionally, this point has not been so seriously considered because the reflectance of the Si ₃ N ₄ film or the like is lower than that of the aluminum film and the size of the element isolation insulating film is relatively large. However, in recent years, as the degree of integration and miniaturization of semiconductor integrated circuits has advanced, the size of the element isolation insulating film has been miniaturized to about 1 micron or less, and the dimensional variation of the resist pattern described above becomes an element isolation characteristic. It came to have a bad influence.

In the above photolithography process,
The cause of the variation in the resist pattern is that the reflectance of the base film is as high as 50% to 60% (it depends on the film thickness of the Si ₃ N ₄ film (3) and the pad SiO ₂ film (2)), and the resist film is large. This is because the so-called multiple reflection effect is caused in (4). The present invention has been made in view of the above-described problems, and an object thereof is to realize a method for forming an element isolation insulating film having high dimensional uniformity by removing variations in resist patterns.

[0007]

According to the present invention, in patterning a Si ₃ N ₄ film (13) used as an oxidation resistant film, a polysilicon film (as a reflection preventing film) is formed on the Si ₃ N ₄ film (13). 14) is provided and the main feature is to perform a photolithography process.

[0008]

According to the above means, the polysilicon film (14)
Has a larger refractive index than the Si ₃ N ₄ film (13), the reflectance can be greatly reduced by appropriately selecting the film thickness. As a result, it is possible to eliminate the variation in the resist pattern size due to the conventional multiple reflection effect, and as a result, it is possible to form the element isolation insulating film having a highly uniform size.

[0009]

1 to 7 are sectional views showing a method of manufacturing a semiconductor device according to an embodiment of the present invention. The following is a description in the order of the drawings. Figure 1: on a silicon substrate (11), by a thermal oxidation method to form a pad SiO ₂ film (12), on the pad SiO ₂ film (12), Si ₃ N ₄ film by the low pressure CVD method (1
3) is formed. Further, on the Si ₃ N ₄ film (13), a polysilicon film (14) as a reflection preventing film having a predetermined film thickness described later is formed by a low pressure CVD method.

FIG. 2: This step is the most characteristic step of the present invention. That is, the resist film (15) is applied on the entire surface of the polysilicon film (14), and the silicon substrate (1
A photomask (16) is arranged above 1) and the resist film (15) is exposed. Here, the polysilicon film (1
Since 4) has a larger refractive index than the pad SiO ₂ film (12) and the Si ₃ N ₄ film (13), the reflectance from the underlying film can be adjusted by selecting an appropriate film thickness. Can be significantly reduced. As a result, it is possible to obtain a resist pattern in which variations in pattern dimensions due to the multiple reflection effect are removed. FIG. 3 shows a first example of the computer simulation result of the polysilicon film thickness dependency of the reflectance. Here, the pad SiO ₂ film (12) had a film thickness of 500Å, the Si ₃ N ₄ film (13) had a film thickness of 1500Å, and the wavelength of incident light was 435 nanometers.

As described above, in the state where the polysilicon film (14) is not present (film thickness = 0), the reflectance is as large as about 55%, but by setting the film thickness of the polysilicon film (14) to 380Å, The reflectance can be reduced to about 3%. This is because the reflected light from the base film and the reflected light from the polysilicon film thickness (14) have an opposite phase relationship to cancel each other. FIG. 4 shows a second example of the computer simulation result of the polysilicon film thickness dependency of the reflectance. Here, the pad SiO ₂ film (12) has a thickness of 600
Å, the film thickness of the Si ₃ N ₄ film (13) was 1750 Å, and the wavelength of incident light was 435 nanometers. With no polysilicon film thickness (14) (film thickness = 0), the reflectance is 62%.
The thickness of the polysilicon film (14) is 13
By setting 0 Å, the reflectance can be reduced to about 10% as in the first example.

According to the first and second simulation results, the pad SiO ₂ film (12) and Si _{3 serving as the} base film are formed.
By providing a polysilicon film (14) having an appropriate film thickness according to the film thickness of the N ₄ film (13) and performing exposure,
It is shown that the reflectance can be reduced significantly. The simulation method described above will be briefly described. Pad SiO ₂ film (12), Si ₃ N ₄ film (1
3) and the refractive index, absorption coefficient and film thickness of the polysilicon film (14) are taken into consideration and are based on the simulation model described in detail in the following documents. P. H. Berning: "Theory and
calculation of Optical Thi
n Films ”, Physics of Thin
Films, Vol-1, George Hasse
d. , New York; Academic Pres
s (1963) pp69-121. FIG. 5: The exposed resist film (15) is developed. In the case of a positive type resist, as shown in the figure, the resist film (15) in the exposed portion is removed.

FIG. 6: Developed resist film (15)
Using the as a mask, the polysilicon film (14), the Si ₃ N ₄ film (13) and the pad SiO ₂ film (12) are sequentially etched. As a result, the Si ₃ N ₄ film (13) is formed in the predetermined region. FIG. 7: The resist film (15) is removed.

FIG. 8: A device isolation insulating film (17) is selectively formed on a silicon substrate (11) by a thermal oxidation method as in a conventional method.
To form. Here, the polysilicon film (14) is oxidized and converted into a SiO ₂ film (18). FIG. 9: The SiO ₂ film (18), the Si ₃ N ₄ film (13) and the pad SiO ₂ film (12) are removed, and the formation process of the element isolation insulating film (17) is completed.

[0015] The film thickness in this manner, in the photolithographic process for patterning the the Si ₃ N ₄ film (13) according to the present invention, on the the Si ₃ N ₄ film (13), to reduce the reflectivity Since the anti-reflection polysilicon film (14) selected in (1) is provided, a resist pattern with high dimensional accuracy can be formed. Therefore, if the Si ₃ N ₄ film (13) is etched using this resist pattern and further the element isolation insulating film (17) is formed by thermal oxidation as in the usual method, as a result, element isolation with high dimensional uniformity is obtained. The insulating film (17) can be formed.
In the above description, the pad S is used as the base film for simplicity.
Although the laminated film of the iO ₂ film (12) and the Si ₃ N ₄ film (13) has been described, the present invention is not limited to this, and any base film including at least a Si ₃ N ₄ film as an oxidation resistant film may be used. The invention is likewise applicable. Further, the antireflection film is not limited to the polysilicon film, and another material having a larger refractive index than the Si ₃ N ₄ film, for example, an amorphous silicon film is also effective.

[0016]

According to the present invention, a polysilicon film (14) is provided as an antireflection film on the Si ₃ N ₄ film (13) and exposure is performed, whereby a resist pattern caused by the multiple reflection effect is produced. It is possible to eliminate the dimensional variation. As a result, the element isolation insulating film (17) having high dimensional uniformity
Can be formed. In particular, it is suitable for manufacturing a semiconductor integrated circuit miniaturized to about 1 micron or less.

[Brief description of drawings]

FIG. 1 is a first cross-sectional view showing a method of manufacturing a semiconductor device according to an embodiment of the invention.

FIG. 2 is a second cross-sectional view showing the method of manufacturing the semiconductor device according to the embodiment of the invention.

FIG. 3 is a drawing showing a first example of polysilicon film thickness dependence of reflectance.

FIG. 4 is a drawing showing a second example of the polysilicon film thickness dependency of reflectance.

FIG. 5 is a third cross-sectional view showing the method of manufacturing the semiconductor device according to the embodiment of the invention.

FIG. 6 is a fourth cross-sectional view showing the method for manufacturing the semiconductor device according to the embodiment of the invention.

FIG. 7 is a fifth cross-sectional view showing the method of manufacturing the semiconductor device according to the embodiment of the invention.

FIG. 8 is a sixth cross-sectional view showing the method for manufacturing the semiconductor device according to the embodiment of the invention.

FIG. 9 is a seventh cross-sectional view showing the method for manufacturing the semiconductor device according to the embodiment of the invention.

FIG. 10 is a cross-sectional view showing a method of manufacturing a semiconductor device according to a conventional example.

Claims (2)

[Claims] 1. A step of laminating and forming a Si ₃ N ₄ film and an antireflection film on a silicon substrate; a step of forming a predetermined resist pattern on the antireflection film by a photolithography method; A step of selectively etching the Si ₃ N ₄ film and the antireflection film using the resist pattern as a mask; and a device isolation by selectively performing thermal oxidation using the Si ₃ N ₄ film as an oxidation resistant mask. And a step of forming an insulating film. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the antireflection film is a polysilicon film.