JPH0268930A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent removal of a semiconductor layer during etching of a semiconductor nitride film through an improved selective oxidation method by carrying out selective oxidization by use of a mask which is made by laminating a first semiconductor oxide film, a semiconductor layer, a second semiconductor oxide film and a semiconductor nitride film successively. CONSTITUTION:When a semiconductor device is manufactured by oxidizing a semiconductor region 1 selectively, selective oxidization is carried out by using a mask of an oxidization-resistant mask which is made by laminating a first semiconductor oxide film 2, a semiconductor layer 3, a second semiconductor oxide film 4, and a semiconductor nitride film 5 successively. Then the semiconductor nitride film 5 is selectively removed against the second semiconductor oxide film 4 and an oxide film 7 which is selectively formed. For example, a silicon oxide film 2, a polysilicon layer 3, and a silicon oxide film 4 are formed on a silicon substrate 1. Then after a silicon nitride film 5 is formed, a specified region is removed through etching. A field oxide film 7 is formed through selective oxidization, the silicon nitride film 5 of a mask layer is removed by hot phosphoric acid, and the silicon oxide film 4 and the polysilicon layer 3 are removed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the so-called LOCOS (local oxj
dati.

The present invention relates to a method of manufacturing a semiconductor device in which selective oxidation is performed using a pattern of a semiconductor oxide film and an oxidation-resistant film, such as a method such as a method of manufacturing semiconductor devices.

[Summary of the invention]

A first invention of the present application is a method for manufacturing a semiconductor device in which a semiconductor oxide film, a semiconductor layer, and a semiconductor nitride film are stacked as a mask layer for performing selective oxidation, in which a second semiconductor oxide film is formed on the semiconductor layer. This method prevents the removal of the semiconductor layer during etching of the semiconductor nitride film by forming a . Further, a second invention of the present application provides a method for manufacturing a semiconductor device in which a semiconductor oxide film, a semiconductor layer, and a semiconductor nitride film are stacked as a mask layer for performing selective oxidation. The semiconductor layer is formed into a tapered shape, and ions are implanted into the tapered semiconductor layer to form a low concentration impurity region, thereby improving the breakdown voltage of the channel stopper region.

[Conventional technology]

A selective oxidation method (so-called LOCO3 method) is generally widely known as a method for forming element isolation regions such as field oxide films used for element isolation in semiconductor integrated circuits.

This selective oxidation method is a method in which an oxide film and a nitride film functioning as an oxidation-resistant film are formed in a desired pattern on a semiconductor region, and regions without a pattern are oxidized. However, in the conventional selective oxidation method, the bird's beak becomes longer depending on the thickness of the field oxide film, which is disadvantageous for high integration.

Therefore, several selective oxidation methods have been proposed that are improvements on the conventional selective oxidation methods. One method is to provide a silicon nitride film on a silicon oxide film with a polysilicon layer interposed therebetween.
This is a method of performing selective oxidation using these as a mask layer, for example, JP-A-61-74350, JP-A-56-70
There are techniques described in Japanese Patent Publication No. 644 or Japanese Patent Publication No. 63-23656.

Here, we will briefly explain the selective oxidation technology using a mask layer with a polysilicon layer interposed.
As shown, a silicon oxide film 52. is formed as a mask layer on a silicon substrate 51. Polysilicon layer 53. A silicon nitride film 54 is laminated.

The silicon nitride film 54 is buttered, and the removed portion 5
5 is a region where a field oxide film is to be formed. Ion implantation is performed into this removed portion 55 to form a channel stopper region. The dopant is of the same conductivity type as the substrate.

Next, as shown in FIG. 3, selective oxidation is performed using the mask layer. Since the polysilicon layer 53 functions as a buffer layer and the silicon oxide film 52 is extremely thin, a field oxide film 56 with a short bird's beak is formed in the removed portion 55.

Then, as shown in FIG. 3C, the silicon nitride IPJ54. The polysilicon layer 53 is removed, a channel stopper region 57 is formed under the field oxide film 56, and an n-type impurity region 58 and the like are formed by introducing impurities for an active region.

[Problem to be solved by the invention]

However, even with the improved ii oxygen oxidation technology, problems arise when removing the mask layer and withstand voltage problems.

That is, after forming the field oxide film 56, it is necessary to remove the silicon nitride film 54 and the polysilicon layer 53.
4), the underlying polysilicon layer 5
3 is locally etched by hot phosphoric acid. Therefore, the thickness of the film 61 shown by the dotted line in FIG. In this case, even the silicon substrate 5I is locally etched. Further, stress during oxidation may also create holes in the polysilicon layer 53, and similarly, the silicon substrate 51 may be locally etched when the polysilicon layer is removed.

Furthermore, when the energy and dose of ion implantation for forming the channel stopper region 57 are increased in an attempt to increase the field inversion voltage, the withstand voltage of the junction 62 between the channel stopper region 57 and the impurity region 58 deteriorates. I will do it.

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the improved selective oxidation method, an object of the present invention is to provide a method for manufacturing a semiconductor device that solves the problems during etching, breakdown voltage, and the like.

(Means for Solving the Problems) A method for manufacturing a semiconductor device according to the first invention of the present application for achieving the above-mentioned object is a method for manufacturing a semiconductor device in which a semiconductor region is selectively oxidized. , 1st
semiconductor oxide film, semiconductor layer.

Selective oxidation is performed using a mask in which a second semiconductor oxide film and a semiconductor nitride film are sequentially laminated. Here, a silicon oxide film may be used as the semiconductor oxide film, a polysilicon layer may be used as the semiconductor layer, and a silicon nitride film may be used as the semiconductor nitride film. The second semiconductor oxide film may be formed by oxidizing the surface of a polysilicon layer. Next, the semiconductor nitride film is selectively applied to the second semiconductor oxide film and the selectively formed oxide film. remove. This removal can be carried out using, for example, hot phosphoric acid (H, PO, ).

Further, a method of manufacturing a semiconductor device according to a second invention of the present application is a method of selectively oxidizing a semiconductor region to form an element isolation region, and first, a semiconductor oxide film and a semiconductor layer are formed on the semiconductor region. It is formed by sequentially stacking semiconductor nitride films. Here, a silicon oxide film may be used as the semiconductor oxide film, a polysilicon layer may be used as the semiconductor layer, and a silicon nitride film may be used as the semiconductor nitride film. Next, the semiconductor nitride film is selectively etched away. This etching removal forms a removed portion. Next, the semiconductor layer is formed into a tapered shape at the end of the removed portion. The tapered shape can be formed by isotropic etching, by oxidizing a part of the polysilicon layer, by making the resist layer sag at its edges, or by S1C1a.
Various methods can be used, such as etching using +N2 gas under required conditions. Next, impurity ions that will become a channel stopper region are selectively implanted into the removed portion, and the semiconductor region corresponding to the tapered portion is
Introduce impurities at a lower concentration than other parts. Then, selective oxidation is performed using a semiconductor nitride film or the like as a mask to form element isolation regions. After this selective oxidation, impurities are introduced into the region adjacent to the channel stopper region.

[Effect]

In the first invention of the present application, since the semiconductor oxide film is formed between the semiconductor layer and the semiconductor nitride film, the semiconductor oxide film functions as an etching stopper, and when the semiconductor nitride film is removed, the semiconductor oxide film functions as an etching stopper. There is no problem that even the underlying semiconductor layer is removed.

In addition, in the second invention of the present application, since the semiconductor layer is formed in a tapered shape at the end of the removed portion, when ion implantation is subsequently performed for forming the channel stone bar region, the tapered shape is Due to the ion stopping power depending on the thickness of the semiconductor layer, the channel stomper region has a distribution in which the concentration decreases on the end side.

Therefore, the high concentration impurity regions do not collide with each other near the junction, and the breakdown voltage of the junction is improved.

〔Example〕

Preferred embodiments of the present invention will be described with reference to the drawings.

First Embodiment This embodiment is an embodiment according to the first invention of the present application, in which a silicon oxide film is formed between a silicon nitride film and a polysilicon layer to solve the problem when etching the silicon nitride film. This is the way to solve it. Hereinafter, this embodiment will be explained with reference to FIGS. 1a to 1".

First, as shown in FIG. 1a, a silicon oxide film 2 as a pad oxide film is formed on a silicon substrate 1 by a method such as thermal oxidation. The thickness of this silicon oxide film 2 is assumed to be thin, for example, about 50 people. Next, a polysilicon layer 3 is formed on this silicon oxide film 2 by a CVD method or the like. Polysilicon layer 3 functions as a buffer layer during selective oxidation. That is, this polysilicon layer 3 is used to relieve stress and reduce bird's beak.

Next, the surface of polysilicon layer 3 is oxidized to form silicon oxide film 4, which is a second semiconductor oxide film. This film thickness is, for example, about 50 people. It is also possible to form a silicon oxide film without surface oxidation. Next, as shown in FIG. 1, a silicon nitride film 5 is formed on the entire surface of the silicon oxide film 4 by the CVD method. This silicon nitride film 5 functions as an oxidation-resistant film for selective oxidation.

After forming the silicon nitride film 5, as shown in FIG. 1C, the area where the field oxide film is to be formed is removed by etching using photolithography. A removed portion 6 is formed by this etching, and the polysilicon N3 is exposed at the bottom of this removed portion 6.

Next, as shown in FIG. 1d, selective oxidation is performed. By this selective oxidation, field oxide film 7 is formed reflecting the pattern of removed portion 6.

At this time, oxidation progresses laterally at the interface between the silicon oxide film 2 and the silicon substrate 1, but the polysilicon layer 3
By this action, a field oxide film 7 with a sufficiently small bird's beak can be obtained. Furthermore, the stress of selective oxidation is also alleviated by the silicon oxide film 4, which is the second semiconductor oxide film, and it is possible to prevent holes from being formed in the polysilicon N3.

Next, as shown in FIG. 1e, the silicon nitride film 5 of the mask layer is removed with phosphoric acid.

At this time, since the silicon oxide film 4 is formed under the silicon nitride film 5, the polysilicon layer 3 thereunder is not removed. Therefore, adverse effects on the substrate are prevented.

Next, as shown in FIG. 1r, the thin silicon oxide film 4 that served as a protective film for the polysilicon layer 3 is removed, and the polysilicon N3 is further removed.

Thereafter, a gate oxide film and an impurity region are formed to complete the device.

In the semiconductor device manufacturing method of this embodiment, since the silicon oxide film 4 functions as a protective film during etching of the silicon nitride film 5, there is a problem that the polysilicon layer 3 is locally removed. can be prevented. Furthermore, the stress during selective oxidation is also alleviated by the silicon oxide film 4, and the formation of holes in the polysilicon layer 3 can be prevented.

Second Embodiment This embodiment is a method for manufacturing a semiconductor device using an improved selective oxidation method aimed at improving breakdown voltage. Hereinafter, this embodiment will be explained with reference to FIGS. 2a to 2".

First, as shown in FIG. 2a, a silicon oxide film 22 as a pad oxide film is formed on a silicon substrate 21 by a method such as thermal oxidation. The thickness of this silicon oxide film 2 is assumed to be thin, for example, about 50 people. next,
Polysilicon N23 is deposited on this silicon oxide film 2 by CVD.
Formed by law, etc. Polysilicon layer 23 functions as a buffer layer during selective oxidation. That is, this polysilicon layer 23 is used to relieve stress and reduce bird's beak. A silicon nitride film 24 is formed on this polysilicon layer 23 by the CVD method.

Here, a silicon oxide film may be used as in the first embodiment. Then, a resist layer 25 is formed on the silicon nitride film 24, and this resist layer 25 is a window formed in the area where the field oxide film is to be formed.
is formed.

Next, as shown in FIG. 2, the silicon nitride film 24 is etched away using the patterned resist layer 25 as a mask. Due to this buttering, polysilicon N23 is formed at the bottom of the removed portion 27 of the silicon nitride film 24.
is exposed.

Next, as shown in FIG. 2C, the polysilicon layer 23 is etched into a tapered shape at the end of the removed portion 27 to provide a tapered portion 28 in the polysilicon layer 23. Then, as shown in FIG. This taper part can be formed in two days by isotropic etching, by oxidizing a part of the polysilicon layer, by making a resist layer sag at its edges, or by using SiC/! n+
Various methods may be used, such as etching using Nz gas under required conditions. The tapered portion 28 has a shape in which the film thickness gradually decreases from the end of the removed portion 27 of the silicon nitride film 24 toward the center, and does not necessarily have a linear slope. The function of this tapered portion 28 is to vary the ion implantation stopping power at each location due to the difference in film thickness of the polysilicon layer 23 along its slope, thereby obtaining a distribution that reflects the slope of the impurity concentration. be. At the center of the removed portion 27 without the tapered portion 28, the silicon oxide film 22 is exposed.

Next, as shown in FIG. 2d, ion implantation is performed to form a channel stopper region. This ion implantation is selectively performed using the patterned silicon nitride film 24 and the tapered portion 28 of the polysilicon layer 23 as a mask. The implanted impurities are p-type boron, etc. if the substrate is p-type, and n-type phosphorus, etc. if the substrate is n-type.
Arsenic, etc. In this embodiment, boron ions are implanted.

By this ion implantation, impurities are implanted at a high concentration in the center of the removed portion 27 where there is no tapered portion 28, and impurities are implanted in the lower part of the tapered portion 28 so as to have an impurity concentration distribution along the slope. become. That is, on the end side of the removed portion, the impurity concentration becomes gradually lower.

Next, as shown in FIG. 2e, selective oxidation is performed. By this selective oxidation, a field oxide film 29 is formed reflecting the pattern of the removed portion 27. At this time, oxidation progresses laterally at the interface between the silicon oxide film 22 and the silicon substrate 21, but due to the action of the polysilicon layer 23, the field oxide film 2 has a sufficiently small bird's beak.
9 is obtained. Further, the tapered portion 28 of the polysilicon layer 23 also contributes to stress relief.

Next, the silicon nitride film 24 and the polysilicon layer 23 are removed, and after annealing, forming a gate oxide film, a gate electrode, an impurity diffusion region, etc., an n-type high concentration impurity is added adjacent to the field oxide film 29. Region 30 is silicon substrate 2
Formed on the surface of 1. Furthermore, a channel stopper region 31 made of a p-type impurity region is formed under the field oxide film 29. Here, the impurity concentration of this channel stopper region 31 is equal to that of the field oxide film 2.
9, the concentration is low on the end side 31b, and the concentration is high on the center side 31a. Therefore, the n-type high concentration impurity region 30 is in contact with the low concentration impurity region on the end side 31b, and the high concentration impurity regions do not collide with each other.
This means that deterioration of the junction breakdown voltage can be prevented.

In this way, in the semiconductor device manufacturing method of this embodiment, since the tapered part 28 is formed at the end of the removed part by selective oxidation, the impurity concentration distribution due to ion implantation for forming the channel stopper region is on the center side. The concentration is high at the edges, and the concentration is low at the edges.

Therefore, the field inversion voltage can be made high in the high concentration part on the center side, and at the same time, the junction breakdown voltage can also be made high because the end part is low concentration.

〔Effect of the invention〕

In the method for manufacturing a semiconductor device according to the first invention of the present application,
Since the second semiconductor oxide film is formed on the semiconductor layer, the semiconductor nitride film after selective oxidation can be reliably and selectively removed, so that the semiconductor layer is not locally removed. It is possible to prevent problems that may adversely affect the board.

Further, in the method for manufacturing a semiconductor device according to the second invention of the present application,
Since the semiconductor layer is tapered at the edges of the portion removed by selective oxidation, when ion implantation is performed to form a channel stopper region, the channel stopper region has a low concentration at the edges and a high concentration at the center. will be obtained. Therefore, the junction breakdown voltage can be improved, and at the same time, the field inversion voltage can also be increased.

[Brief explanation of the drawing]

1a to 1f are process cross-sectional views for explaining an example of a method for manufacturing a semiconductor device according to the first invention of the present application, and FIGS. 2a to 2f are process sectional views of the second invention of the present application. 3A to 3C are process cross-sectional views for explaining an example of the method for manufacturing a semiconductor device according to the invention, and FIGS. Each is a process sectional view. ■, 21...Silicon substrate 2.22...Silicon oxide film 3.23...Polysilicon layer 4...Silicon oxide film 5.24...Silicon nitride film 6.27...Removed portion 7.29...Field oxide film 28...Tapered portion 31...Channel stopper region 30...High concentration impurity region

Claims (2)

[Claims] (1) In a method for manufacturing a semiconductor device in which a semiconductor region is selectively oxidized, the oxidation-resistant mask includes a first semiconductor oxide film, a semiconductor layer,
selectively oxidizing the second semiconductor oxide film and the selectively formed oxide film using a mask in which a second semiconductor oxide film and a semiconductor nitride film are sequentially stacked; A method for manufacturing a semiconductor device, comprising the step of removing a nitride film. (2) A method for manufacturing a semiconductor or device in which a semiconductor region is selectively oxidized to form an element isolation region, including a step of sequentially stacking a semiconductor oxide film, a semiconductor layer, and a semiconductor nitride film on the semiconductor region. , a step of selectively etching away the semiconductor nitride film, a step of forming the semiconductor layer in a tapered shape at the end of the removed portion, and selectively implanting impurities into the removed portion to become a channel stopper region. A method for manufacturing a semiconductor device comprising the steps of: introducing an impurity at a lower concentration into the semiconductor region corresponding to the tapered portion than in other portions; and performing selective oxidation to form an element isolation region.