JPS63244627A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce the thermal distortion of a semiconductor substrate by a method wherein the surface of the semiconductor substrate is oxidized via two or more masks whose thickness differs from one another according to film thicknesses of oxide films. CONSTITUTION:When a semiconductor device containing field oxide films having different film thicknesses is to be manufactured on a semiconductor substrate, thicknesses of masks to be used for field oxidation are decided according to the different thicknesses of desired oxide films; a field oxidation process including the masks is executed. That is to say, because the field oxidation process is executed via the masks of the different thicknesses, desired oxide films 6, 7 according to the thicknesses are formed on a semiconductor substrate 1 during one operation. By this setup, the semiconductor substrate is not influenced thermally; a photolithographic process is executed onto the flat surface; it is possible to obtain the semiconductor substrate with high accuracy and reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device having a field oxide film of increasing thickness on a semiconductor substrate.

[Prior Art] FIGS. 2A to 2F are schematic process cross-sectional views according to a conventional manufacturing method.

The manufacturing method will be described below with reference to the drawings.

For example, an underlying oxide film 2 of about 500 layers is formed by thermal oxidation on a semiconductor substrate 1 made of silicon, and a nitride film 3 is further formed thereon by a CVD method or the like. Nitriding 1
A first resist 4 is formed on the resist 13 and patterned by photolithography to form a desired mask pattern (see FIG. 2A).

Next, using the first resist 4 as a mask, the exposed nitride 113 is removed by etching, and then the remaining first resist 4 is removed and the patterned nitride film 3 is covered with an oxide 1
! 2 (see Figure 2B).

The semiconductor substrate 1 is field oxidized using the patterned nitride film 3 as a mask to form a first field oxide film 6 of about 16000 Å at a desired position, and then the nitride 1113 is removed (see FIG. 2C).

Subsequently, the underlying oxidation II of the semiconductor substrate 1 including the top of the first field oxide film 6 is performed! After forming the nitride film 9 again on the entire surface of the nitride film 2, a second resist 5 patterned in the same manner as described above is formed thereon (see FIG. 2D).

Furthermore, after etching and removing the exposed nitride film 9 using the second resist 5 as a mask, the remaining second resist 5 is removed, leaving the desired patterned nitride film 9 (see Figure 2E). .

Finally, using the patterned nitride film 9 as a mask,
Field oxidation is performed again to form a second field oxide film 7 of about 8000 Å thinner than the first field oxide film, and the nitrided [I9] is removed to complete the formation of field oxide films with different thicknesses. (See Figure 2F)
.

[Problems to be Solved by the Invention] In the conventional manufacturing method as described above, since the field oxidation process is performed twice, the thermal strain experienced by the semiconductor substrate becomes large due to this thermal influence, resulting in the formation of crystal defects. was causing the occurrence of

Further, after the flatness of the semiconductor substrate surface is impaired by the completion of the first oxidation, a photolithography process is performed again, which has the problem that the precision of mask alignment cannot be improved.

This invention was made to solve this problem, and it is possible to form oxide films with different thicknesses with less thermal influence.
Moreover, it is an object of the present invention to provide a manufacturing method that improves mask alignment accuracy in a photolithography process.

Means for Solving Problem E] In the method for manufacturing a semiconductor device according to the present invention, the film thickness of the mask used during field oxidation is formed to correspond to the different film thicknesses of the desired oxide film, and the mask There are some things that undergo field oxidation, including

[Operation] In the present invention, field oxidation is performed through masks having different thicknesses of m, so that a desired field oxide film depending on the film thickness is formed on the semiconductor substrate 1 at one time. Furthermore, since only one field oxidation is required, photolithography for mask formation can be performed on a flat surface.

[Embodiment] FIGS. 1A to 1H are schematic cross-sectional views of steps in an embodiment of the present invention.

Hereinafter, the manufacturing method of the present invention will be explained with reference to the drawings.

For example, an underlying oxide film 2 of about 50 OA is formed by thermal oxidation on a semiconductor substrate 1 made of silicon, and a nitride film 113 of about 80 OA is further formed thereon by CVD or the like (see FIG. 1A).

A first resist 4 is formed on the nitride film 3 and patterned by photolithography to form a desired mask pattern corresponding to the area where the field oxide film will not be formed, that is, the active region. (see figure).

Using the patterned first resist 4 as a mask,
For example, the exposed nitride film 3 is OF.

Dry etching is performed using a gas system until the film thickness reaches 20 OA. In this case, since the etching rate of the nitride film is known, the film thickness can be easily controlled by setting the etching time (see FIG. 1C).

Furthermore, the first resist 4 and the exposed nitride 11
A second resist 5 is formed on the entire surface of the resist 3 and patterned by photolithography to form a desired mask pattern corresponding to the area where a thin field oxide film is to be formed (see FIG. 1D).

Next, using the first resist 4 and the second resist 5 as masks, the exposed areas are nitrided! 13 for example CFa
After removal by gas-based dry etching (see Figure 1E), when the first resist 4 and second resist 5 that were used as masks are removed, the patterned nitride 113, which has a partially increased film thickness, becomes the underlying layer. (See Figure 1F).

The patterned nitride lI3 is used as a mask (the patterned nitride film 3
If field oxidation is performed to form an oxide film of about 16,000 Å in a region without oxidation, the entire portion of the nitride film 3 with a thickness of 200 Δ will be oxidized, and the semiconductor substrate 1 will be oxidized.
Second field oxidation F of about 6000-8000A on top
J7 is formed consecutively to field oxide II 6 of ff11. Note that the thick a portion of the nitrided FJ 3 is not completely oxidized and remains as residual nitrided 118, and the active f! Prevents oxidation in the range that should be in the 4th region (1st G
(see figure).

Finally, by removing the remaining nitride II8, a semiconductor device is completed in which a field oxide film, in which the desired film py is formed, is formed on the semiconductor substrate 1 (see FIG. 1H).

In the above embodiment, IS# is limited, but this is just an example, and any field oxide film can be formed by arbitrarily changing the thickness of the nitride film and the degree of field oxidation. .

Further, in the above embodiment, a nitride film is used as a mask, but the same effect can be obtained even if other masks having the same n-ability are used.

Second, although the above embodiments are based on two different film thicknesses, it goes without saying that three or more different film thicknesses can also be applied.

Further, in the above embodiment, only the oxidation step is described, but it goes without saying that processing steps such as etching the underlying oxide film or the semiconductor substrate can be included before field oxidation.

[Effects of the Invention] As described above, the present invention allows desired field oxide films with different thicknesses to be formed in one field oxidation through masks with different thicknesses, thereby preventing thermal effects on the semiconductor substrate. Moreover, since photolithography can be performed on a flat surface, there is an effect that a highly accurate and reliable semiconductor device can be obtained.

[Brief explanation of the drawing]

1A to 1H are schematic process cross-sectional views showing one embodiment of the present invention, and FIGS. 2A to 2F are schematic process cross-sectional views according to a conventional manufacturing method. In the figure, 1 is a semiconductor substrate, 3 is a nitride film, 4 is a first resist, 5 is a second resist, 6 is a first field oxide film, and 7 is a second field oxide film. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (5)

[Claims] (1) A method for manufacturing a semiconductor device, which comprises forming on a semiconductor substrate at least two oxide films having different thicknesses, the method comprising: forming on the semiconductor substrate at least two oxide films having a thickness corresponding to the thickness of the oxide film; A step of forming masks having different film thicknesses as described above, and a step of forming the oxide film by oxidizing the semiconductor substrate through the mask, and depending on the film thickness of the mask, A method for manufacturing a semiconductor device, in which the thickness of the oxide film to be formed changes. (2) The step of forming the mask includes: forming a layer to serve as the mask on the semiconductor substrate; forming a patterned first resist on the layer; and forming the first resist on the semiconductor substrate. removing the exposed layer to a desired thickness as a mask; forming a further patterned second resist on the layer from which the desired thickness has been removed; and using the second resist as a mask. 2. The method of manufacturing a semiconductor device according to claim 1, further comprising the step of removing the exposed layer as a mask. (3) The method for manufacturing a semiconductor device according to claim 1 or 2, wherein the mask is formed by a photolithography method and an etching method. (4) The method for manufacturing a semiconductor device according to claim 1, 2, or 3, wherein the mask is a nitride film. (5) The method for manufacturing a semiconductor device according to any one of claims 1 to 4, wherein the semiconductor substrate is a silicon substrate.