JPS59202649A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form an insulating film functioning as an isolating section in a recessed section, to remove a steep groove and to form a surface approximately flat to the surface of a semiconductor substrate by leaving a second anti-oxidation film only to the side surface section of the recessed section and selectively oxidizing the substrate while using first and second anti-oxidation films as masks. CONSTITUTION:A thin SiO2 film 16 is formed on the surface of a recessed section 15 while using a Si3N4 film 13 as a mask. A Si3N4 film 17 is formed, and the Si3N4 film 17 remains only on the side surface section of the recessed section 15 through anisotropic dry etching. An isolation SiO2 film 18 is shaped through selective oxidation while employing the Si3N4 films 13 and 17 as masks. Sections among the Si3N4 film 17, a Si substrate 10 and a poly Si film 12 are also oxidized to some extent to form a SiO2 film 18' at that time, and the Si3N4 film 17 is pushed up in the upper direction. When the Si3N4 films 13, 17, the poly Si film 12 and SiO2 films 11, 18' are etched through isotropic dry etching, the isolation SiO2 film 18 with a surface approximately flat to the Si substrate 10 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of forming an isolation region of a semiconductor device.

Conventional Structure and Problems Conventionally, as a method for forming element isolation regions in the manufacture of semiconductor devices, there is a method of forming an isolation insulating film by selective oxidation using a silicon nitride film (S13N4 film) as an oxidation prevention mask. However, S on the surface of the semiconductor substrate (Si substrate)
When an i3N4 film pattern is formed and selectively oxidized, Si3N
The bottom of the edge portion of the four-layer pattern is also oxidized, resulting in so-called bird's beaks and bird's heads. However, in order to eliminate the occurrence of bird's beaks and bird's heads, the method of selective oxidation is to form a Si3N4 film on the side surface of the recess in the area to be selectively oxidized. An example of the conventional example will be explained with reference to FIG.

After forming a silicon oxide film (S z O2 film) 2 and a 513N4 film 3 on a Si substrate 1, the Si3N4 film 3, SiO2 film 2 and Si substrate 1 in a predetermined isolation region are etched to a desired depth 1 using photoetching technology. A recess 4 is formed by etching. Next, a thin Sio2 film 5 is formed on the surface of the recess 4 using the Si3N4 pattern 3 as an oxidation prevention mask. Thereafter, a Si3N4 film 6 is formed on the Si substrate 1, and the 813N'4 film 6 on the bottom of the recess 4 is etched by anisotropic etching.
When etched, 513N4 and groove 6 remain only on the side surface of the recess 4 (Fig. 1a).

After that, selective oxidation is performed using 813N4 B[3 and 6 as a mask to prevent dredging, as shown in No. 11g1b, S which becomes separated.
1021i Ya7 is formed.

, -h Medication Distribution 1 According to the method shown in Figure 1, the occurrence of bird's beak and bird's head can be suppressed. However, as shown in Figure 1,
When the surface of the 5iO2j1 rod 70 is oxidized until it becomes almost flat with the surface of the S1 substrate 1, a groove 8 is formed around the S102 film 7 whose oxidation is suppressed by the Si3N4 film 6. If there is such a full 8, when a wiring pattern is formed, At may remain in the groove 8, causing a short circuit. In order to prevent short-circuits, it is better to make the At overetch longer, but this will cause side etching of other Al wiring parts, resulting in extremely poor design accuracy. In particular, since microfabrication of Al wiring is important in realizing ultra-LSI, the steep groove 8 becomes a major obstacle in increasing the density of ultra-LSI.

Further, as oxidation is promoted, stress due to the volumetric expansion of the SiO2 film 7 is applied to the Si substrate 1, particularly the edges 9 of the recesses 4, resulting in the occurrence of many crystal defects, which becomes a factor that reduces the yield of transistors.

By the way, according to the study of the present inventor, as shown in FIG. 2, if the selective oxidation is stopped midway, grooves will not be generated in the Si○2 film 7', and the Si substrate 1 will also be free from crystal defects due to stress. I found that it did not occur. That is, Si3N4
The gap between the film 6 and the S1 substrate 1 is also oxidized to some extent, and the formed S
The 813N4 film 6 is pushed upward by the i○2 film 7''.

Therefore, no grooves were observed at this stage.

Moreover, since the stress was low, no crystal defects were observed. However, in order to flatten the surface of the Si02 film 7' and the surface of the St substrate 1, oxidation is further promoted, and when the structure is oxidized as shown in Figure 1, grooves 8 are generated and crystal defects due to stress occur. were occurring in large numbers. Because the second
In the figure, if oxidation is further promoted after the groove edge, Si3N4
The SiC film 7'' between the film 6 and the Si substrate 1 does not become thicker because oxidation is suppressed by the 513N4 film 3 and the 513N4 film 6. Therefore, the Si3N4 film 6 cannot be pushed upward any further. Oxidation progresses only at the bottom of the 513N4 film 6, as shown in Figure 1, and grooves 8 are formed where oxidation has been suppressed by the 513N4 film 6.Furthermore, due to the promotion of oxidation at this time, Stress is applied to the edge portion 9 of the crystal, causing crystal defects.

In other words, it has been found that if the 513N4 film 6 is pushed up in the two-part direction as oxidation is promoted, no grooves are formed.

Purpose of the Invention In view of these conventional problems, the present invention is capable of forming a silicon oxide film as an insulating separation film that has no steep grooves and has a surface that is almost flat with the surface of a semiconductor substrate, and that also reduces the stress applied to the semiconductor substrate. It is an object of the present invention to provide a method for manufacturing a semiconductor device with small crystal defects.

Structure of the Invention The present invention provides a first insulating film, a semiconductor film, and a first anti-oxidation film in a predetermined region after sequentially forming a first insulating film, a semiconductor film, and a first anti-oxidation film on a semiconductor substrate.
The anti-oxidation film, the semiconductor film, the first insulating film, and the semiconductor substrate are etched to a desired depth to form four parts. Next, using the first anti-oxidation film as a mask, a thin second film is applied to the surface of the four parts.
After forming the insulating film, a second anti-oxidation film is formed on the semiconductor substrate. After that, by anisotropic etching, the second oxidation-preventing film remains only on the four side surfaces, and selective oxidation is performed using the first and second oxidation-preventing films as masks, thereby forming the insulation that is divided into the recesses. It is characterized by the use of a unique method of forming a film.

In other words, when forming an element isolation region, a semiconductor film is formed on the semiconductor substrate other than the recess that will become the element isolation region.In this way, the isolation insulating film in the recess can be oxidized until it becomes almost flat with the semiconductor substrate surface. Even if the second oxidation prevention film is formed, the second oxidation prevention film is pushed upward as the semiconductor film is oxidized, so that a groove is not formed in the isolation insulating film. Moreover, since stress is applied to the semiconductor film when pushing up the second oxidation-preventing film, stress is not applied to the semiconductor substrate and no crystal defects occur. This will be explained in detail below using the drawings.

Example theory! FIG. 3 shows a first embodiment of the method for manufacturing a semiconductor device forming element isolation according to the present invention.

On the Si substrate 10, an insulating film such as a Si◯2 film 11°, a semiconductor film such as a polycrystalline silicon film (PolySi film) 12, and an oxidation prevention film such as a Si3N4 film 13 are successively formed.

Thereafter, a photoresist pattern 14 is formed on the area other than the isolation area by photolithography. Then, using the photoresist pattern 14 as a mask, the 513N4 film 13, the PolySi film 12, the S102 film 11, and the S1 substrate 1o are etched to a desired depth by anisotropic dry etching to form a recess 15 (see FIG. 3a). )
. The etching depth of the recess 15 is preferably approximately half the thickness of the isolation insulating film. Next, after removing the photoresist pattern 14, a thin Si*2 film 16 is completely etched on the surface of the recess 15 using the 513N4 film 13 as a mask. 16 (Figure 3b).

Next, after forming the 513N4 film 17 on the Si substrate 10 (FIG. 3C), the 513N4 film 17 is etched by anisotropic dry etching.
When the N4 film 17 is etched, the 813N4 film 17 remains only on the side surfaces of the recess 15 (FIG. 3d).

Next, the isolation S z 02 film 18 is formed by selectively oxidizing the 513N4 films 13 and 17 as a mask. At this time, the 513N4 film 17, the Si substrate 10 and the Po
1y The space between the Si film 12 is also slightly oxidized and the Si○2 film 18'
is formed, and the Si3N4 film 17 is pushed upward. (Figure 3e).

Next, 513N4 films 13, 17, PolySi
If the film 12 and the SiO2 film 11.18' are etched by isotropic dry etching, S as shown in FIG.
Isolated SiO2 film 1 having a substantially flat surface with the i-substrate 10
8 is formed.

As described above, according to the first embodiment, the 513N4 films 13 and 1
7 as a mask, selectively oxidize the SiO2 film 18 until it becomes almost flat with the surface of the substrate 10.

No groove is formed in the SiO2 film 18 even if

In this case, since the Poly Si film 12 is formed on the Si substrate 10, the S z 02 film 1 is formed between the 513N4 film 17, the S1 substrate 1o, and the Poly Si film 12.
8' is formed. In the conventional method, a SiO2 film is formed by heating the 513N4 film and S on the side surfaces of the recess, but the oxidation is suppressed by the 813N4 film formed on the top surface of the 81 substrate. tl(
Oxidation between the 813N4 film on the 11th surface and the 81st substrate is suppressed.

However, in the present invention, since the Po1ySi film 12 is formed on the 81 substrate 1o, the 513N4 film 17 and the Po1ySi film 12 are formed on the 81 substrate 1o.
Oxidation also progresses between the ySi films 12 to form S z 02 films 18'. This 5102 film 18' becomes thicker as the oxidation progresses, thereby pushing the Si3N4 film 17 upward. Therefore, as the S 102 film 18 is oxidized, the 813N4 film 17 is pushed upward, so that no groove is formed in the S i O 2 film 18 .

Moreover, the stress when pushing the 513N4 film 17 upward is not applied to the PolySi l]%12.
No stress is applied to the Si substrate 10, and no crystal defects occur.

Next, a second embodiment of the present invention will be described using FIG. 4.

A 5102 film 21 + Si3N4 film 22° PolySi film 23 and a 513N4 film 24 are sequentially formed on the 81 substrate 20. Thereafter, a photoresist pattern 25 is formed using photolithography technology, and a 513N4 film 24 and a PolySil film 23,5i are formed by anisotropic dry etching.
3N422, the Si○2 film 21, and the Si substrate 2o are etched to a desired depth to form a recess 26 (see Fig. 4a).
).

Next, after removing the photoresist pattern 25, 513
Using the N4 film 24 as a mask, a thin S10 film is applied to the surface of the recess 26.
Two films 27 are formed (FIG. 4b).

Next, on the 81 substrate 20, 5i3N4 was formed on the 81 substrate 20.
The difference in etching the removal 28 is 5i3N4ttJ (28 remains (No. 413: i
c).

Next, an isolated S 102 film 29 is formed by oxidizing with JXX acid using the 5131\1411 layers 24 and 28 as a mask. At this time, the space between the 513N4!1 shear 28, the Si substrate 2Q, and the PolySi film 23 is also slightly oxidized.
The 02 membrane 29' is formed and the 513N4 membrane 28 is pushed in the two-part direction (FIG. 4d).

Next, S 13N 4 films 24 , 28 , Po1y
When etching the S1 film 23 and the Si○2 film 29',
An S 102 film 29 is formed as shown in FIG.

Furthermore, 513N4 film 22 and 5102 film 21 in the desired area
By etching and selectively oxidizing the Si substrate 20, another isolation 5IO2 film 30 such as the 41st Zif can be formed.

As described above, according to the second embodiment, the isolation SiO2 film 29 having a flat surface without grooves can be formed as in the first embodiment. In this embodiment, 81 substrate 20 and Po1
There is no particular problem whether there is a 5131N4 film 22 between the ySill film 23, and the oxygen necessary to oxidize the Po1ySi film 23 is supplied by the Si○2 film 27, and the Si○
Two films 29' are formed.

The stress when pushing the 513N4 part 28 in one direction is the same as in the first embodiment.
3, no crystal defects occur in the 81 substrate 2Q.

Furthermore, in this example, the 813N4 film 22 is coated with other molecules 4f.
It can be used as a selective oxidation mask when forming tU 5IO2g 30.

Second, in the first and second embodiments, the thickness of the Po1ySi film may be as long as the depth of the recess.

Moreover, the film thickness of the S102 films 18' and 29' is
Since it is extremely thin compared to the thickness of the O2 films 18 and 29, the separation S h O2 films 18 and 29 do not spread much in the lateral direction.

Effects of the Invention As described above, according to the present invention, a semiconductor film is formed on a semi-rod substrate, and the semiconductor film is formed only on the side surfaces of the second and fourth parts. By selectively oxidizing using the anti-oxidation film as a mask, bird's beaks and bird's heads can be eliminated, and in addition, the thinning 11-edge II!
There are almost no sharp @ grooves. bird head, sudden
Since there are no gaps, the surface of the semiconductor substrate is flat, and no short circuits occur due to stepped lines or unetched wiring during wiring, and the process is stabilized, leading to improved yields. In addition, bird's beaks do not occur even after a try, so there is no collapse of the active region of the transistor, which greatly contributes to high density and high integration.

Furthermore, since the semiconductor film is formed on the semiconductor substrate, the stress during selective oxidation that pushes up the anti-oxidation film formed on the curved side of the recess due to the isolation insulating film is applied to the semiconductor film and Since almost no stress is applied to the substrate, no crystal defects occur, which greatly helps improve transistor yields.

As described above, the present invention is a method for manufacturing a semiconductor device that achieves higher density, higher integration, and improved yield.

[Brief explanation of the drawing]

1(a), (bz is a process cross-sectional view showing a conventional semiconductor device manufacturing method. FIG. 2 is a sectional view halfway through the conventional semiconductor device manufacturing process shown in FIG. 1. a) - (0
4(a) to (f7) are cross-sectional views of the manufacturing process of a semiconductor device according to another embodiment of the present invention. 20---...Si substrate, 12, 23-=-
Po1ySi! fig, 13, 17, 22, 24; 28
...S 13N 4IpJ, 1 8,
2 9 , 3 0 ... S 102
ill. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 7 Figure 2 Figure 3 Figure 3 Figure 4

Claims (2)

[Claims] (1) A step of sequentially forming a first insulating film, a semiconductor film, and a first antioxidant film on the whole surface of a semiconductor substrate, and forming a recess by etching the insulating film and the semiconductor substrate to a desired depth; forming a thin second insulating film on the surface of the recess; and forming a second anti-oxidation film on the semiconductor substrate. a step of etching the second oxidation prevention film to leave the second oxidation prevention film only on the side surfaces of the recess; and selective oxidation using the first and second oxidation prevention films as masks. A method of manufacturing a semiconductor device, comprising the step of: forming an isolation insulating film in the recess. (2) The method for manufacturing a semiconductor device according to claim 1, wherein the first insulating film is made of a silicon oxide film and a silicon nitride film.