JPS61196549A - Manufacture of semiconductor integrated circuit device - Google Patents

Abstract

PURPOSE:To enable a nitride film to work as an etching mask for a oxide film and to enable to obtain a flat surface for a semiconductor integrated circuit by a method wherein the nitride film is formed on the isolated oxide film alone on the periphery of the element region even after the isolating process ends. CONSTITUTION:A first pad oxide film 22 and a first nitride film 23 are selectively provided on the surface of a silicon substrate 21. An etching is performed on a part of the silicon substrate 21, which is exposing within the part of an opening part 24, and a groove 25 is formed. A second pad oxide film 26 is formed on the inner wall of the groove 25, and a second nitride film 27 and a third oxide film 28 are coated on the whole surface thereof. Parts of the oxide film 28 and the nitride film 27, which are located right under the opening part 24, are selectively removed. An isolated oxide film 31 is formed in the groove part. A part of the nitride film 23 and a part of the rest part of the nitride film 27 are selectively removed and the nitride films 23 and 27 are left on parts only of the isolated oxide film 31, which are located on the peripheral part of the element region. After the oxide film 27 is removed, an oxide film 32 is formed and a resist pattern 34 is formed. An edge 35 is formed in such a way as to locate on the region of the nitride film 27. An etching is performed on the oxide film 32, the element region 36 is made to expose and a diffusion layer 37 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a semiconductor integrated circuit device, and particularly to element isolation technology.

(Prior art) The degree of integration of semiconductor integrated circuit devices continues to increase, and in the development of next-generation high-density integrated circuit devices, along with miniaturization of elements, the selective oxidation isolation method (LOG), which has been widely used in the past, is required.
This is a new element isolation that replaces O3). Therefore, many new separation technologies have been proposed so far (for example, Goto et al. I EDM82-58; Tamaki et al. I EDM
82-62. Takemoto et al. I EDM83-51).

The improved selective oxidation separation method can be cited as one of the powerful methods that has a relatively simple process and good compatibility with the conventional LOCO3 method (Japanese Patent Application No. 76,200/1982).
.

FIGS. 2A to 2E are cross-sectional views for explaining the manufacturing process of the improved selective oxidation separation method disclosed in Japanese Patent Application No. 58-76200. In the figures shown below, only the portion related to the formation of the isolation oxide film is shown, and the diffusion layer and the like are omitted.

First, as shown in FIG. 2(A), a thin pad oxide film (silicon oxide film) 2 and a nitride film (silicon nitride film) 3 are coated on the surface of the element formation region of the silicon substrate 1, as in the normal LOCO3 method. be provided selectively.

Next, as shown in FIG. 2(B), the silicon substrate 1 is etched using the two-layer films 3, 2 as a mask to compensate for the increase in volume due to oxidation, and the V2 of the planned isolation oxide film is etched.
A groove 4 of a certain depth is formed.

In the normal LOCO3 method, selective oxidation is performed in this state, but then the oxidation progresses in a wedge shape on the surface of the element region along the pad oxide film 2, forming a so-called bird's beak, expanding the width of the isolation region, and increasing the width of the isolation region. A bulge of the isolation oxide film around the region, that is, a bird's head occurs, and the flatness is impaired.

Therefore, in the improved selective oxidation separation method disclosed in Japanese Patent Application No. 58-76200, a second layer is formed on the inner wall of the trench 4, as shown in FIG.
A pad oxide film 5 is formed, and a second nitride film 6 is further deposited on the entire surface. Next, using reactive ion etching (RIE), using the undercut-shaped "eaves" 7 made of the first and second nitride I#, 3.6 as a mask, as shown in FIG. 2(D), Next, the second nitride film 6 on the bottom of the trench 4 is selectively removed.

After that, when selective oxidation is performed, a bird's beak is formed on the side wall of the trench 4 along the second pad oxide film 5, so that an isolation structure with a thick isolation oxide film 8 as shown in FIG. 2(E) is obtained. .

The bird's beak forming portion 9 on the side wall of the groove extending along the second pad oxide film 5 has the thickness of the second pad oxide film.

It depends on the second nitride film thickness 1 selective oxidation source degree, etc. Therefore, if the processing conditions are appropriate, the bird's beak stops at the end portion 10 of the device region and does not invade inside the device region.

As described above, in the improved selective oxidation separation method I, a surface with good flatness free of bird's beaks and bird's heads can be obtained at the end of the separation process.

On the other hand, an advantage of the conventional LOCO3 method is that a self-alignment process using an isolation oxide film can be adopted in the element formation process.

FIGS. 3A to 3D show cross-sectional explanatory views of the self-alignment process in the LOGO8 structure. Figure 3 (A) is L
FIG. 3 is a cross-sectional view at the time when the separation process by the OGOS process is completed. In the normal LOCO5 method, the bird's beak 11 invades the element region, and the bird's head 12 is further formed.

After the separation process is completed, as shown in FIG. 3(B),
Furthermore, a resist pattern 15 having an opening 14 is formed on the element region where a diffusion layer is to be formed. At this time 11. The resist pattern 15 has a wide opening 14 that covers not only the element region but also the bird's head 12 on the isolation oxide film.

Subsequently, as shown in FIG. 3(C), the oxide film 13 is etched using the resist pattern 15 as a mask.
The element region 16 where the diffusion layer is to be formed is exposed. Thereafter, the resist pattern 15 is removed and a diffusion layer is formed in the element region 16. By repeating the oxidation, etching, and diffusion steps on the device region as many times as necessary, a device having the final isolation structure shown in FIG. 3(D) is formed.

The advantage of the self-alignment process shown in FIG. 3 is that accurate alignment is not required when forming the resist pattern 15, and openings can be reliably formed in desired device regions 16. That is, the diffusion layer can be formed in a self-aligned manner, which is advantageous for downsizing the device. Furthermore, LOGO
It is also advantageous that it can be formed in 8 steps and can be downsized and reduced in size in the 8-step process.

These advantages are generally pointed out as advantages of the oxide film separation method.

Incidentally, cross-sectional views when this self-aligned process is applied to the improved selective oxidation separation method are shown in FIGS. 4(A) to 4(D). FIG. 4(A) is a cross-sectional view at the time when the separation process is completed by the improved selective oxidation separation method, and there is no bird's beak invading the element region, and no bird's head is formed.

After the separation step, as shown in FIG. 4(B), an oxide film 13 to serve as a diffusion mask is formed on the element region, and a resist film 13 having an opening 14 is formed over the element region where a diffusion layer is to be formed. A pattern 15 is formed. Next, Figure 4 (C)
As shown in FIG.
The n-oxide FF 113 is etched to expose the element region 16 where a diffusion layer is to be formed.

(Problem to be Solved by the Invention) At this time, since no bird's head is formed in the isolation oxide film formed by the improved selective oxidation separation method, the device is etched by etching the isolation oxide film by the self-alignment process. A deep recess 17 is formed in the isolation oxide film around the region. Furthermore, since the shoulder portion 18 of the element region is exposed due to the deep depression, as shown in FIG. 4(D), when forming the diffusion layer,
A deep diffusion layer 19 is likely to be formed along the sidewall of the isolation oxide film, causing deterioration of the reverse breakdown voltage of the junction, which is also unfavorable in terms of characteristics.

In other words, when using the improved selective oxidation separation method, applying the conventional self-alignment process not only impairs flatness but also adversely affects the formation of the diffusion layer, causing variations in device characteristics and defects. It had the following drawbacks.

(1! Techniques for solving the IJ problem) In order to solve the above problems, the present invention uses an improved selective oxidation isolation method that allows only the ( In other words, the nitride film is formed only on the periphery of the isolation oxide film.

(Function) In this way, the nitride film acts as an etching mask for the oxide film in the later self-alignment process.

(Example) Examples of the present invention will be described below with reference to the drawings. 1st
Figures (A) to (1) are process cross-sectional views showing one embodiment of the present invention.

First, as in the conventional method, as shown in FIG. The membrane is selectively provided. In other words, after the first pad oxide film 22 and the first nitride film 23 are sequentially formed on the silicon substrate 21, the openings 24 are formed in these films 23.22 over the isolation oxide film formation region. . Here, the thicknesses of the first pad oxide film 22 and the first nitride film 23 are assumed to be 500 and 2000, respectively, as an example.

Next, as shown in FIG. 1(B), in order to compensate for the increase in volume due to oxidation, the two-layer film 23° substrate 21 is etched to form a groove 25 with a zero depth of about 7,000, for example. . At this time, an undercut occurs under the first nitride film 23 and the first pad oxide film 22, and the groove 25 becomes a groove larger than the opening 24. Note that the first pad oxide film 22 exposed by this undercut will be removed next, but may be left as is.

Subsequently, as shown in FIG. 1C, a second pad oxide film 26 is formed on the inner wall of the groove 25 to a thickness of 500 to 1500 mm by thermal oxidation.
A second nitride film 27 and a third oxide film 28 are formed on the entire surface with a film thickness of about 500 to 100% by CVD.
0 thickness, 500 to 2000 thicknesses, and are deposited one after another.

Next, as shown in 1rIl(D), the third oxide film 28 and the second nitride film 27 directly under the opening 24 are selectively removed using reactive ion etching (RIE).

Thereafter, the extension of the bird's beak 29 on the sidewall formed along the second pad oxide film 26 extends to the device region ib! tM start
BirdRri n -n #k +L -a-x
By selectively oxidizing the silicon substrate 21 by approximately 1.6 mm using the second nitride film 23 and 27 as a mask, as shown in FIG. 1(E), An isolation oxide film 31 is then formed in the trench. At this time, the second nitride film 27. Parts of the third oxide film 28 and the first nitride film 23 are pushed up onto the isolation oxide film 31.

Subsequently, as shown in FIG. 1(F), a third oxide film 28 is formed.
The first nitride film 23 and the second nitride film 2 are
7 is selectively removed, and the second nitride film 27 is left only on the isolation oxide film 31 at the periphery of the element region, in other words, only on the periphery of the isolation oxide film 31.

Next, after removing the third oxide film 28, in order to perform a self-alignment process, as shown in FIG.
A resist pattern 34 having an opening 33 is formed on the element region where the diffusion layer is to be formed. Here, the edge 35 of the resist pattern 34 is
The nitride film 27 is formed over the region of the nitride film 27. That is, when forming the resist pattern 34, the region of the second nitride film 27 is provided as a mask alignment margin for the self-alignment process.

Subsequently, as shown in FIG. 1()T), the oxide film 3 is formed using the resist pattern 34 and the second nitride film 27 as a mask.
Etching step 2 is performed to expose the element region 36 where the diffusion layer is to be formed. Thereafter, the resist pattern 34 is removed and a diffusion layer 37 is formed in the element region 36.

Then, the oxidation/etching/diffusion process on the element region, that is, the self-alignment process, is repeated as many times as necessary, and then an oxide film 38 is formed on the element region as shown in FIG. 1(I).
is formed, the second nitride film 2 is formed as necessary.
By removing 7, a surface with good flatness can be obtained even in the final separated shape after element formation.

In the above embodiment, the third oxide film 28 in FIG. 1(C) may be replaced with a polycrystalline silicon film. That is, since polycrystalline silicon is oxidized and converted into an oxide film in the isolation oxide film forming process, it has the same effect as the third oxide film 28 shown in one embodiment.

(Effects of the Invention) As described in detail above, according to the present invention, in the improved selective oxidation separation method, even after the separation process is completed, the isolation oxide film remains only on the isolation oxide film around the element region. Since the nitride film is formed only on the periphery of the device, this nitride film acts as an etching mask for the oxide film in the later self-alignment process, preventing deep depressions from forming in the isolation oxide film around the device area. , a flat surface is obtained. Therefore, a flat bonding surface can be obtained also in the diffusion layer, and stable device characteristics can be obtained.

Furthermore, according to the present invention, since the third film is formed on the second nitride film on the trench sidewall, the oxidation rate of the second nitride film in the selective oxidation step is reduced, and the oxidation resistance is reduced. The thickness of the nitride film required as a mask can be reduced. Reducing the thickness of the nitride film can be expected to have a great effect on the selective oxidation process.

As described above, this invention is a technology that combines the improved selective oxidation separation method, which is excellent in miniaturization and planarization, and the self-alignment technology, which is an advantage of the oxide film separation method, without losing the advantages of both. This prevents the occurrence of depressions and defects, which are drawbacks of the conventional method, and makes it possible to simultaneously form an element isolation region and an element region having fine and flat surfaces.

Therefore, the present invention can be widely used in manufacturing highly integrated and high-performance semiconductor integrated circuit devices, regardless of bipolar type or MOS type.

[Brief explanation of drawings]

FIG. 1 is a process cross-sectional view showing an embodiment of the method for manufacturing a semiconductor integrated circuit device of the present invention, and FIG. 2 is a cross-sectional view showing, in order of process, a method for forming an isolation oxide film region by a conventional improved selective oxidation separation method. , Figure 3 is a cross-sectional view of the process when self-alignment technology is applied to the isolation oxide film region formed by the conventional LOCO5 method, and Figure 4 is a cross-sectional view of the process formed by the conventional improved selective oxidation separation method. Aro-2]・-Silicon base, 22・・First pad oxide film,
23 - First nitride film, 24... Opening, 25... Groove, 26... Second pad oxide film, 27... Second nitride film, 28... Third oxide film, 31... Isolation oxide film. Figure 1 Figure 3 Figure 4

Claims (3)

[Claims] (1) A first pad oxide film and a first pad oxide film on a silicon substrate.
nitride films are sequentially formed, openings are formed in the nitride films and oxide films, and a portion of the silicon substrate corresponding to the openings is formed under the first nitride film and the first pad oxide film. forming a groove with an undercut, forming a second pad oxide film on the inner surface of the groove, and sequentially forming a second nitride film and a third film on the entire surface; After that, a step of selectively removing the third film and the second nitride film directly under the opening, and then oxidizing the silicon substrate using the first nitride film and the second nitride film as a mask, A step of forming an isolation oxide film in the groove portion and pushing up a second nitride film, a third film, and a part of the first nitride film thereon, and then using the third film as a mask. manufacturing a semiconductor integrated circuit device comprising the step of: removing a portion of the first nitride film and the second nitride film to leave the second nitride film only on the peripheral portion of the isolation oxide film; Method. (2) The method for manufacturing a semiconductor integrated circuit device according to claim 1, wherein the third film is an oxide film. (3) The semiconductor according to claim 1, wherein the third film is a polycrystalline silicon film, and the polycrystalline silicon film becomes an oxide film through an oxidation process during formation of the isolation oxide film. A method of manufacturing an integrated circuit device.