JP2000183053A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device with which the loss of thickness in an LOCOS film can be reduced and the isolation characteristic of element can be improved. SOLUTION: A pad oxide film 120, a pad polysilicon film 130, a silicon oxide film 140, and a mask nitride film 150 are formed sequentially on a silicon substrate 110. Then the mask nitride film 150 and silicon oxide film 140 in the region of element isolation film to be formed are removed selectively through etching. An edge part 300 in the removed region is cut by side etching to form a groove 310 in the edge part 300. Furthermore an acid resistant film 170 is formed over the entire upper surface thereof, and it is etchbacked entirely thereon, while a sidewall 172 is left as it is. Thus, the sidewall 172 is formed in a state in which it partly penetrates the groove 310, and the growth of a top bird's beak part 182 can be suppressed in the subsequent growth step of a LOCOS film 180.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming an element isolation region on a semiconductor substrate by a LOCOS method.

[0002]

2. Description of the Related Art Hitherto, as a method of manufacturing a semiconductor device, a method of forming an element isolation region by a PPL (Poly Pad LOCOS) method has been proposed (for example, Japanese Patent Application Laid-Open Nos. 9-82699 and 10-82). 928
No. 05). FIG. 4 is an explanatory view showing a conventional example of such a working process by the PPL method. First, FIG.
As shown in (a) to (d), a pad oxide (SiO ₂ ) film 20 and a pad polysilicon (P) are formed on a silicon substrate 10.
(polysilicon) film 30, silicon oxide (SiO ₂ ) film 4
0, a mask nitride (SiN) film 50 is formed. Specifically, the pad oxide film 2 is oxidized by oxidizing the upper surface of the silicon substrate 10.
0, and a pad polysilicon film 30 is formed thereon by CVD. Then, the pad polysilicon film 3
The silicon oxide film 40 is formed by oxidizing the upper surface of the mask 0, and a mask nitride film 50 is formed thereon by CVD.

As shown in FIGS. 4E and 4F, a photoresist film 60 is formed except for a region of an element isolation film to be formed, and a mask nitride film 50 and a silicon oxide film 40 are selectively formed by etching. Remove. After this, FIG.
As shown in (a) to (c), after a LOCOS film 70 is grown by thermal oxidation in a region of an element isolation film to be formed, a mask nitride film 50, a silicon oxide film 40, and a pad are formed by three-stage Light (Wet) etching. The polysilicon film 30 is removed, and the process proceeds to the next step.

[0004]

In the PPL method as described above, even if the pad oxide film 20 is thinned, the silicon substrate 10 is not etched in the etching step of the mask nitride film 50, so that damage and defects are not generated. There is an advantage that can be suppressed.

However, in this PPL method,
After the LOCOS film 70 is grown as described above, the mask nitride film 50, the silicon oxide film 40, and the pad polysilicon film 30 are removed by three-stage etching. Therefore, the removal amount of the LOCOS film 70 (LO
(COS film thickness loss) is increased, which causes problems such as adversely affecting element isolation characteristics. In addition, since the removal amount in the subsequent process is large, the initial LOCOS film 7
0 needs to be increased, for example, LOCOS
The top bird's beak 70A of the film 70 is greatly extended, and this also causes a problem such as adversely affecting element isolation characteristics.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a semiconductor device capable of reducing LOCOS film thickness loss and improving, for example, element isolation characteristics.

[0007]

According to the present invention, there is provided a method for forming a pad oxide film, a pad polysilicon film, a silicon oxide film, and a mask nitride film on a silicon substrate. A step B of selectively etching and removing the mask nitride film, the silicon oxide film, and the pad polysilicon film in the region of the element isolation film to be formed;
A step C of shaving the edge portion of the region removed by the step B by side etching, and a step D of forming an oxidation-resistant film on the region removed by the steps B and C and the upper surface of the mask nitride film; A step E of removing the oxidation-resistant film by etch-back over the entire surface while leaving a sidewall of the oxidation-resistant film at an edge of the region removed in the step B; Step F of subjecting the film to thermal oxidation to form an element isolation film
And characterized in that:

In the method for manufacturing a semiconductor device according to the present invention,
First, in a step A, a pad oxide film, a pad polysilicon film, a silicon oxide film, and a mask nitride film are sequentially formed on a silicon substrate, and then, in a step B, the mask in a region of an element isolation film to be formed is formed. The nitride film, the silicon oxide film, and the pad polysilicon film are selectively etched and removed. Next, in step C, the edge portion of the region removed in step B is cut by side etching. By the side etching in the step C, the edge of the silicon oxide film at the edge is shaved to form a groove at the edge.

Next, in step D, an oxidation resistant film is formed on the region removed in steps B and C and on the upper surface of the mask nitride film. The oxidation resistant film formed in the step D is formed so as to fit into the groove formed in the edge in the step C. Next, in step E, the oxidation-resistant film is removed by etch back over the entire surface, with the sidewall of the oxidation-resistant film left at the edge of the region removed in step B. Thermal oxidation is performed on the pad oxide film in the region of the isolation film to form an element isolation film.

In this step F, at the time of growth of the element isolation film, the side wall of the oxidation resistant film and the groove formed in the edge of the side wall are formed on the outer peripheral portion of the element isolation film. This suppresses the growth of the top bird's beak. Therefore, since an element isolation film having a short top bird's beak portion can be formed, the etching amount of the element isolation film in post-processing can be significantly reduced, and, for example, the element isolation characteristics can be improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing a semiconductor device according to the present invention will be described below. 1 to 3
FIG. 2 is an explanatory view showing a method for manufacturing a semiconductor device according to the present invention, showing working steps by the PPL method.

First, as shown in FIGS.
Pad oxidation (Si) is applied on a silicon substrate (Si) 110.
O ₂ ) film 120, pad polysilicon (PolySi)
A film 130, a silicon oxide (SiO ₂ ) film 140, and a mask nitride (silicon nitride film; SiN) film 150 are sequentially formed (Step A). More specifically, the upper surface of the silicon substrate 10 is oxidized to form a pad oxide film 120, on which a CVD
Thus, a pad polysilicon film 130 is formed. Then, the upper surface of the pad polysilicon film 130 is oxidized to form a silicon oxide film 140, on which a mask nitride film 150 is formed by CVD.

Next, as shown in FIGS. 1E and 1F, the photoresist film 16 is removed except for the region of the element isolation film to be formed.
Then, the mask nitride film 150 and the silicon oxide film 140 are selectively removed by etching (step B). Next, the edge portion 300 in the region removed by the etching (step B) shown in FIG. By the side etching in this step C, as shown in FIG.
The edge of the silicon oxide film 140 of 0
A groove 310 is formed at 00.

Next, as shown in FIG. 1 (g), an oxidation resistant film (silicon nitride film; SiN) 170 is formed on the entire upper surface of the substrate formed in the above steps (step D). FIG.
(S) and (T) are enlarged cross-sectional views showing the state of the edge portion 300 after the step D and the next step E. As illustrated, the oxidation resistant film 17 formed in this step D
0 is the groove 3 formed in the edge 300 in the step C.
It is formed in a state where it can be inserted into the recess. Next, as shown in FIG. 1G, the oxidation-resistant film 170 is left in a state where the sidewall 172 of the oxidation-resistant film 170 is left at the edge portion 300.
Is removed by etch back over the entire surface (step E).

Thereafter, as shown in FIG. 2C, a LOCOS film (element isolation film) 180 is grown by thermal oxidation in a region of the element isolation film to be formed (step F). In this step F, the top bird's beak portion 182 connected to the silicon oxide film 140 is formed on the outer peripheral portion of the LOCOS film 180.
Then, a bottom bird's beak (finally remaining beak) portion 184 connected to the pad oxide film 120 is formed. When the LOCOS film 180 is grown, the oxidation resistant film 1
The growth of the top bird's beak portion 182 formed on the outer peripheral portion of the LOCOS film 180 is suppressed by the side wall 172 formed by Become.

Therefore, since the LOCOS film 180 of the short and thin top bird's beak portion 182 can be formed, the etching amount of the LOCOS film 180 in the post-processing can be greatly reduced. The part indicated by the circle a in FIG.
Although the shape becomes complicated depending on the shape such as 2, it is simplified in the figure. Thereafter, as shown in FIGS. 2A to 2C, the mask nitride film 150, the silicon oxide film 140, and the pad polysilicon film 130 are removed by three-stage Light (Wet) etching, and the process proceeds to the next step. (Steps GI).

[0017]

As described above, in the method of manufacturing a semiconductor device according to the present invention, a pad oxide film, a pad polysilicon film, a silicon oxide film, and a mask nitride film are sequentially formed on a silicon substrate and then formed. The region of the element isolation film to be removed is selectively etched and removed, and the edge of the removed region is cut by side etching, and an oxidation-resistant film is formed from the upper surface. The entire surface was etched back with the sidewalls left, and thereafter, thermal oxidation was performed on the pad oxide film in the region of the element isolation film to form an element isolation film.

Therefore, a part of the sidewall made of the oxidation-resistant film is formed in a structure in which the groove formed in the silicon oxide film at the edge by the side etching is formed. The growth of the top bird's beak formed in the portion is suppressed. Therefore, since a short and thin device isolation film of the top bird's beak portion can be formed, the etching amount of the device isolation film in post-processing can be significantly reduced,
Film loss is reduced.

The reduction in the film thickness loss can improve the element isolation characteristics and reduce the inter-substrate capacitance. Further, since the oxide film thickness for growing the element isolation film can be reduced, cost can be reduced due to reduction in processing time. Further, since the oxide film thickness of the element isolation film can be reduced, the element isolation characteristics can be improved by reducing bottom bird's beak (final residual beak).

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing work steps according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing work steps according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a working process according to the embodiment of the present invention.

FIG. 4 is an explanatory view showing a conventional example of a working process by the PPL method.

[Explanation of symbols]

110: silicon substrate, 120: pad oxide film, 1
30 pad polysilicon film, 140 silicon oxide film, 150 mask nitride film, 160 photoresist film, 170 oxidation resistant film, 172 side wall, 180 LOCOS film, 182 ... top bird's beak part, 300 ... edge part, 310 ... groove part.

Claims (4)

[Claims] A step of sequentially forming a pad oxide film, a pad polysilicon film, a silicon oxide film, and a mask nitride film on a silicon substrate; and forming the mask nitride film and silicon in a region of an element isolation film to be formed. A step B of selectively etching and removing the oxide film and the pad polysilicon film; a step C of removing an edge portion of the region removed in the step B by side etching; and a removal in the steps B and C. Forming an oxidation-resistant film on the removed region and the upper surface of the mask nitride film; and forming the oxidation-resistant film on the edge of the region removed in the step B while leaving the sidewall formed of the oxidation-resistant film. A step E of removing the passivation film by etch back over the entire surface; and performing thermal oxidation on the pad oxide film in the region of the element isolation film;
A method for manufacturing a semiconductor device, comprising: a step F of forming an element isolation film. 2. The semiconductor device according to claim 1, wherein both the mask nitride film and the oxidation resistant film are made of a silicon nitride film.
The manufacturing method of the semiconductor device described in the above. 3. The side etching in the step C,
The edge portion of the silicon oxide film at the edge portion is shaved to form a groove portion at the edge portion, and the oxidation-resistant film formed in the step D is formed so as to fit into the groove portion formed at the edge portion. 2. The method for manufacturing a semiconductor device according to claim 1, wherein 4. A step G of removing the remaining portions of the mask nitride film and the oxidation-resistant film by etching after the step F, and a step H of removing the silicon oxide film by etching.
2. The method of manufacturing a semiconductor device according to claim 1, further comprising: a step I of removing the pad polysilicon film by etching.