JPH08172086A - Manufacture of semiconductor device using selective oxidizing method - Google Patents

Abstract

PURPOSE: To reduce the generation of bird's beaks and to prevent an oxide region, which rises steeply on the periphery of an element region, from being left by a method wherein a thin Si film is formed on the side-walls of a mask pattern, this thin Si film is oxidized by a selective oxidizing process and an Si oxide film formed by the oxidation of the thin Si film is removed by etching. CONSTITUTION: A mask pattern 4 for selective oxidation is formed on an Si substrate 1 and films of two layers of a first film 5 capable of forming an oxide film and a dummy film 6 thicker than the film 5 are deposited on the substrate 1 in such a way as to cover the pattern 4. These films of the two layers are etched by anisotropic etching and films 5a and 6a of two layers are left only on the sidewalls of the pattern 4. The dummy film 6a of the left films of the two layers is removed by isotropic etching and the surface, which is not covered with the pattern 4, of the substrate 1 is selectively subjected to thermal oxidation. An oxide film 8 formed by oxidizing the pattern 4 and the film 5 is removed by isotropic etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device using a selective oxidation method, and more particularly to a method of manufacturing a semiconductor device in which bird's beaks generated during selective oxidation are suppressed.

The selective oxidation method (LOCOS) is widely used as an element isolation method for Si integrated circuit devices. In order to improve the degree of integration of the integrated circuit device and the utilization factor of the substrate area, there is a demand for a technique for reducing bird's beaks generated during selective oxidation.

[0003]

2. Description of the Related Art A silicon nitride film has a high oxygen shielding ability. When a pattern of a silicon nitride film is formed on a Si substrate and the Si substrate is exposed to a high temperature atmosphere containing oxygen or water vapor,
A thick thermal oxide film can be formed on the surface of the Si substrate that is not covered with the Si nitride film. The thermal oxide film has good quality, and the selective thermal oxide film is widely used as a field oxide film for element isolation.

Si nitride has a coefficient of thermal expansion different from that of Si. If a Si nitride film is directly formed on the surface of a Si substrate, Si
It gives a strong stress to the substrate surface. Therefore, a thin Si oxide film is usually inserted as a stress relaxation pad film between the Si substrate and the Si nitride film.

When a pattern for selective oxidation of a Si oxide film and a Si nitride film is formed on a Si substrate and the exposed Si substrate is thermally oxidized, oxygen penetrates laterally from the position of the Si oxide film,
The Si surface under the Si nitride film is also oxidized. When Si changes to oxidized Si, the volume expands and lifts the Si nitride film. Then, oxygen is more likely to enter from the lateral direction, and the oxidized Si region called bird's beak is nitrided with Si.
It forms under the film.

The bird's beak is formed under the Si nitride film and reduces the dimensional accuracy of the element region (moat) surrounded by the field oxide film, and reduces the area utilization rate of the Si substrate surface. Therefore, some methods for reducing the occurrence of bird's beaks have been proposed.

FIG. 3 shows an example of a selective oxidation method capable of reducing the occurrence of bird's beak. As shown in FIG. 3 (A), S
A region (element region or moat) where a pad film 52 of SiO _{2 and} a Si nitride film 53 functioning as an oxygen shielding film are deposited on the surface of the i substrate 51 and a field oxide film is not formed.
Are patterned by photolithography so that A polycrystalline Si film 55 is deposited on the Si substrate 51 so as to cover the patterned Si nitride film 53.

As shown in FIG. 3B, the polycrystalline Si film 55 is anisotropically etched by reactive ion etching using plasma, and the polycrystalline Si sidewall 55a is formed only on the sidewalls of the mask patterns 52 and 53. Leave.

As shown in FIG. 3C, the structure shown in FIG. 3B is thermally oxidized in an oxidizing atmosphere. Si nitride film 53
Since the area covered with is shielded from oxygen, thermal oxidation does not proceed. Since the side wall 55a is made of Si, it is thermally oxidized and changes into the side wall oxide film 55b. In addition, the exposed surface of the Si substrate 51 and the sidewall oxide film 5
The lower part of 5b is thermally oxidized to form a thick field oxide film 58. At this time, the side surface of the oxidized Si pad film 52 is
Since it is covered with the sidewalls 55a, it is hardly oxidized, and the field oxide film 58 does not enter below the Si nitride film 53, so that the bird's beak can be prevented from occurring.

As shown in FIG. 3D, the silicon nitride film 53 is formed.
Is removed with hot phosphoric acid, and the oxidized Si pad film 52 therebelow is removed with dilute hydrofluoric acid. Although the surface of the field oxide film 58 is slightly etched when the oxidized Si pad film 52 is removed, since the oxidized Si pad film 52 is thin,
Most of the field oxide film 58 remains as it is.

[0011]

According to the prior art shown in FIG. 3, bird's beaks can be prevented from occurring and the element region 56 can be formed with high precision, but the periphery of the element region 56 is nearly vertical. An oxide film region 55b having a side surface 57 that rises at an angle is formed. Such a side wall 57
If, for example, an electrode layer is deposited on the oxide films 56b and 58 having the, the coverage on the side wall portion 57 is deteriorated.
Further, even if such an electrode layer is patterned by photolithography, a residue may remain under the side wall 57.

An object of the present invention is to provide a method of manufacturing a semiconductor device capable of performing highly accurate selective oxidation. Another object of the present invention is to provide a method for manufacturing a semiconductor region using a selective oxidation method which can reduce the occurrence of bird's beaks and which does not leave an oxidation region which rises sharply around the element region.

[0013]

A method of manufacturing a semiconductor device according to the present invention comprises a step of forming a mask pattern for selective oxidation on a Si substrate, and an oxide film formed on the Si substrate so as to cover the mask pattern. And a dummy film thicker than the first film are deposited, and the two-layer film is etched by anisotropic etching to leave the two-layer film only on the side wall of the mask pattern. A step of removing the remaining two-layer dummy film by isotropic etching, a step of selectively thermally oxidizing the surface of the Si substrate not covered with the mask pattern, the mask pattern and the first step. And removing the oxide film obtained by oxidizing the first film by isotropic etching.

[0014]

[Function] Thin Si is formed on the side wall of the mask pattern for selective oxidation.
By forming a film and protecting the sidewalls, bird's beaks are reduced.

Even if this thin Si film is oxidized in the selective oxidation step, it can be easily removed by etching the Si oxide film because it is thin. Thin Si
Even if the oxidized Si oxide film is removed, the selectively oxidized thick Si oxide film can be left.

By making the thickness of the thin Si film on the side wall of the mask pattern thicker than that of the oxidized Si pad film of the mask pattern, the reduction of bird's beak in the selective oxidation becomes more reliable.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a semiconductor device according to an embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 1A, for example, p-type S
On the surface of the i substrate 1, for example, SiO _{2 having a} thickness of 10 nm
Pad film 2 formed of a film, S nitride having a thickness of about 120 nm
The i film 3 is deposited. A photoresist layer is applied on the Si nitride film 3 and exposed and developed to form a resist pattern.
Using the resist pattern as a mask, the underlying Si nitride film 3 and the pad film 2 are etched to form a mask pattern 4 formed of the pad film 2 and the Si nitride film 3.

A polycrystalline Si film 5 having a thickness of 15 nm, for example, is deposited on the Si substrate 1 so as to cover the mask pattern 4, and subsequently an oxidized Si film 6 having a thickness of about 85 nm is polycrystalline Si.
Deposit on the membrane 5. The polycrystalline Si film 5 is a protective film that protects the sidewalls of the mask pattern 4 during selective oxidation, and the oxidized Si film is a dummy film used when patterning the protective film 5.

As shown in FIG. 1 (B), CF ₄ + CHF
A stack of the Si oxide film 6 and the polycrystalline Si film 5 is anisotropically etched by reactive ion etching by plasma etching using ₃ as an etching gas, and the oxidized Si pattern 6a and the polycrystalline Si pattern are formed only on the sidewalls of the mask pattern 4. Leave 5a. That is, the oxidized Si pattern 6a and the polycrystalline Si pattern 5a form sidewalls.

As shown in FIG. 1C, the oxidized Si pattern 6a is removed by selective wet etching using dilute hydrofluoric acid or the like. The polycrystalline Si pattern 5a is not etched and remains on the side wall of the mask pattern 4. At this time, the polycrystalline Si pattern 5a covers the side wall of the mask pattern 4 and slightly extends on the surface of the substrate 1. When the Si oxide film 6 and the polycrystalline Si film 5 having the above thickness are used,
The width of the polycrystalline Si pattern 5a remaining on the surface of the Si substrate 1 is, for example, about 100 nm.

As shown in FIG. 1D, the structure shown in FIG. 1C is loaded into an oxidizing atmosphere containing water vapor and oxygen,
For example, a selective thermal oxide film 8 having a thickness of about 250 nm at 900 ° C.
To form. During the selective oxidation, the polycrystalline Si pattern 5a left on the side wall of the mask pattern 4 is also oxidized and becomes an oxidized Si pattern 5b. When the thickness of the polycrystalline Si film 5 is about 15 nm, the thickness of the formed oxidized Si pattern 5b is about 30 nm at most.

Next, as shown in FIG. 2E, the Si substrate 1 is immersed in hot phosphoric acid, and the Si nitride film 3 is removed by etching. A thick selective oxide film 8 and oxidized S are formed on the surface of the Si substrate 1.
The i pattern 5b and the oxidized Si pad film 2 remain.

As shown in FIG. 2 (F), the Si substrate 1 is immersed in dilute hydrofluoric acid to etch the surface Si oxide film to a thickness of about 40 nm. By this etching, the oxidized Si pad film 2 is removed and the oxidized Si pattern 5b is also etched. Although the surface of the selective oxide film 8 is also etched, of the total thickness of 250 nm, only the surface layer of 40 nm is etched, and most of it remains as the field oxide film 8a. The Si surface of the element region 9 is exposed in the region surrounded by the field oxide film 8a.

Although the thickness of the pad film 2 is about 10 nm and the thickness of the polycrystalline Si film 5 is about 15 nm, the thickness of the polycrystalline Si film 5 is smaller than that of the pad film 2 as described above. By making the thickness thicker, the side surface of the pad film 2 is surely covered with the polycrystalline Si film 5, and the invasion of oxygen during the selective oxidation is effectively reduced.

As shown in FIG. 2F, a semiconductor element is formed in the element region 9 of the Si substrate 1 on which the field oxide film 8a is formed to complete the semiconductor device. For example, FIG. 3 (G)
As shown in, the surface of the Si substrate 1 is thinly thermally oxidized to form the gate oxide film 10. Polycrystalline S on the gate oxide film 10
An i gate electrode layer 11 and a silicide gate electrode layer 12 such as WSi are deposited to form a polycide gate electrode layer.
The polycide gate electrode layer is patterned using photolithography to form a gate electrode pattern.

After forming the gate electrode pattern, n-type impurities are lightly ion-implanted to form the LDD regions of the source / drain regions 16. After forming the LDD region, a Si oxide film is deposited on the surface and anisotropic etching is performed to leave the sidewall oxide film 14 on the sidewall of the gate electrode. After forming the sidewall oxide film 14, n
The source / drain regions 16 are formed by ion implantation of type impurities.

After that, an interlayer insulating film 17 such as BPSG is formed on the surface of the Si substrate and patterned by photolithography to form contact holes. A source / drain electrode 18 is formed by depositing an electrode layer on the interlayer insulating film 17 in which the contact hole is formed and patterning it by using photolithography. In this way,
A MOS transistor is formed in the element region surrounded by the field oxide film 8a.

If necessary, an interlayer insulating film is further formed,
The formation of the via hole and the formation of the upper layer electrode are repeated, and the surface is covered with the cover film. According to this embodiment, since the side wall of the mask pattern for selective oxidation is covered with the polycrystalline Si pattern 5a, the degree of oxidation of the Si substrate 1 via the pad film 2 under the Si nitride film 3 is reduced. The occurrence of bird's beaks is reduced.

Further, the polycrystalline Si film 5a is oxidized to form an oxidized Si pattern 5b, but since it is thin, it can be easily removed by subsequent Si oxide etching. In this way, the field oxide film 8a that defines the element region can be formed with high accuracy, and the side wall portion that sharply rises can be prevented from occurring.

The case where the sidewall of the mask pattern for selective oxidation is covered with a protective film of a polycrystalline Si film and the oxidized Si film is formed as a dummy film for patterning this protective film has been described. Material is polycrystalline Si, oxidized Si
Not limited to For example, it will be apparent to those skilled in the art that amorphous Si may be used instead of polycrystalline Si.

Further, instead of the polycrystalline Si film 5, Si nitride is used.
Membranes can also be used. When using a silicon nitride film,
Since thickening also lowers the selective oxidation of the Si substrate 1, it is preferable to reduce the thickness to, for example, 3 to 5 nm. In this case, the dummy film is made of polycrystalline Si or oxidized Si.
And the like. A thin Si nitride film having a thickness of about 3 to 5 nm can be easily oxidized at the time of selective oxidation, and a field oxide film is formed below it.

When the protective film is formed of such thin Si nitride, the protective film is simultaneously etched in the step of removing the selective oxidation mask pattern 4. Other materials may be used as the protective film as long as they can reduce the rate of oxygen or water vapor in the atmosphere reaching the pad film. As the dummy film, any material may be used as long as it can be used for forming the sidewall.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0035]

As described above, according to the present invention, the field oxide film can be formed with high accuracy.

When a field oxide film with reduced generation of bird's beaks is formed, even if a protrusion is formed around the element region, it can be easily removed by etching because it is thin. Therefore, even when an electrode or the like extending on the field oxide film is formed, it is possible to reduce the occurrence of disconnection and residue.

[Brief description of drawings]

FIG. 1 is a schematic sectional view for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a schematic cross sectional view for illustrating the method for manufacturing the semiconductor device according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view for explaining a prior art selective oxidation method that reduces the occurrence of bird's beaks.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Si substrate 2 Pad film 3 Si oxide film 4 Mask pattern 5 Polycrystalline Si film 6 Si oxide film 8 Selective oxide film 9 Element area 10 Gate oxide film 11 Polycrystalline Si gate electrode 12 Silicide gate electrode 14 Sidewall oxide film 16 Source / Drain region 17 Interlayer insulation film 18 Source / drain electrode

Claims (3)

[Claims] 1. A step of forming a mask pattern for selective oxidation on a Si substrate; a first film capable of forming an oxide film on the Si substrate and covering the mask pattern; and a dummy thicker than the first film. A step of depositing a two-layer film of the film, a step of etching the two-layer film by anisotropic etching to leave the two-layer film only on the sidewall of the mask pattern, a dummy film of the remaining two-layer film, etc. A step of removing by means of isotropic etching, a step of selectively thermally oxidizing the Si substrate surface not covered by the mask pattern, and a step of isotropic etching of the oxide film in which the mask pattern and the first film are oxidized. A method of manufacturing a semiconductor device, the method including: a step of removing. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the first film is made of Si. 3. The mask pattern includes a pad film of silicon oxide having a first thickness and an oxygen shielding film of silicon nitride formed on the pad film, and the mask pattern includes a first film formed of Si.
3. The method of manufacturing a semiconductor device according to claim 2, wherein said film has a second thickness larger than said first thickness, and said dummy film is a silicon oxide film.