JPH0982700A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent micro trenches from being produced in a transistor forming region by a method wherein pinholes are restrained from being formed in a buffer layer when a field oxide film is formed. SOLUTION: A silicon nitride film 5 is selectively formed on the surface of a SIMOX wafer 4, and a silicon single crystal layer 3 as the outermost layer of the SIMOX wafer 4 is selectively and thermally oxidized using the silicon nitride film 5 as a mask, whereby a field oxide film 7 is selectively formed on the SIMOX wafer 4. The silicon nitride film 5, the silicon single crystal layer 3, and a buried oxide film 2 located in a region where no field oxide film 7 is formed are removed, and an MOS-type transistor is formed in an element forming region on the silicon substrate 1 where no field oxide film 7 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to LOCOS (Local Oxidation of S
The present invention relates to a method of manufacturing a semiconductor device in which element isolation is performed by the (ilicon) method.

[0002]

2. Description of the Related Art As a conventional method for forming an element isolation region, a selective oxidation method (LOCOS method) is generally used. However, according to the conventional LOCOS method, the field oxide film slightly invades directly under the silicon nitride film and grows, so that a so-called bird's beak is formed, which is a great obstacle to high integration of the LSI.

[0003] In order to improve this, several selective oxidation methods, which are improvements over the conventional selective oxidation method, have been proposed. Part 1
One is, for example, JP-A-56-70644 and JP-A-6-70644.
JP-A-3-302536 or JP-A-4-357838.
As described in Japanese Patent Laid-Open Publication No. 2004-242242, a polysilicon film is formed between a silicon oxide film and a silicon nitride film, the silicon nitride film is patterned, and then selective oxidation is performed (polybuffer LOCOS method).

[0004]

The conventional polybuffer LOCOS method will be described with reference to FIG. First, as shown in FIG. 3A, the silicon substrate 11
After the pad oxide film 12, the polysilicon film 13 and the silicon nitride film 14 are sequentially formed on the silicon oxide film 14, the silicon nitride film 14 is formed into a pattern having openings in the region where the field oxide film is formed, as shown in FIG. 3B. Pattern.

Next, as shown in FIG. 3C, a heat treatment is performed using the silicon nitride film 14 as a mask to form a field oxide film 15. At this time, since the polysilicon film 13 is used as the buffer layer, the pinhole 16 is generated in the polysilicon film 13 on the transistor formation region due to the stress caused by the field oxidation process. Next, FIG.
As shown in (d), the silicon nitride film 14 is removed.
In this removal step, a chemical solution for removing the silicon nitride film 14 is passed through the pinhole 16 and the pad oxide film 12 is removed.
And the pad oxide film 12 is removed at the same time.

As a result, as shown in FIG. 3E, when the polysilicon film 13 is removed, the silicon substrate 11 immediately below the pinhole 16 is also etched at the same time. Therefore, as shown in FIG. As shown, when the pad oxide film 12 is removed, there is a problem that the micro-trench 17 is generated in the silicon substrate 11 in the element formation region.

Therefore, an object of the present invention is to prevent pinholes from being generated in the buffer layer when the field oxide film is formed by the LOCOS method, so that microtrench finally occurs in the transistor formation region. It is an object of the present invention to provide a method for manufacturing a semiconductor device capable of suppressing the occurrence of the above.

[0008]

In order to achieve the above object, a method of manufacturing a semiconductor device according to the present invention is an SOI (Silicon) having a laminated structure of a thick silicon single crystal substrate, a silicon oxide film, and a thin silicon single crystal. on Insulator) substrate, and a silicon nitride film (Si ₃
N ₄ film, etc.) is deposited on the entire surface, and the silicon nitride film is patterned to expose the thin silicon single crystal in the element isolation region, and the thin silicon single crystal in the exposed element isolation region and the silicon single crystal substrate Is thermally oxidized using the silicon nitride film as a mask to form a thick field oxide film in the element isolation region. Then, a transistor is formed in the element formation region surrounded by the field oxide film.

That is, according to the method of manufacturing a semiconductor device of the present invention, a semiconductor substrate having a laminated structure in which a buried oxide film is formed between the first single crystal semiconductor layer and the second single crystal semiconductor layer is formed. A step, a step of selectively forming a nitride film on the second single crystal semiconductor layer, and a heat treatment using the nitride film as a mask to selectively form a field oxide film on the semiconductor substrate. A step of removing the nitride film, the second single crystal semiconductor layer and the buried oxide film in a region where the field oxide film is not formed, and the semiconductor in a region where the field oxide film is not formed Forming a transistor on the substrate.

[0010]

According to the present invention, S having a laminated structure of the first silicon single crystal layer / buried oxide film / second silicon single crystal layer
A nitride film is selectively formed on the surface of an IMOX (separation by implanted oxygen) wafer, and this nitride film is used as a mask to selectively thermally oxidize the second silicon single crystal layer, which is the uppermost layer of the SIMOX wafer, A field oxide film is selectively formed on the SIMOX wafer, and is formed under the nitride film, the second silicon single crystal layer, and the second silicon single crystal layer on the SIMOX wafer in the element formation region where the field oxide film is not formed. The buried oxide film thus formed is removed, and a transistor is formed on the first silicon single crystal layer in the element formation region where the field oxide film is not formed.
It is possible to prevent pinholes from being generated in the second silicon single crystal layer in the element formation region, and it is possible to suppress generation of micro-trench generated in the element formation region.

[0011]

DETAILED DESCRIPTION OF THE INVENTION One embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a manufacturing process diagram showing a first embodiment of the present invention.

First, as shown in FIG. 1A, a single crystal silicon substrate 1 is ion-implanted with oxygen and then annealed to form a silicon substrate (first single crystal semiconductor layer) 1, a buried oxide film. 2. SIMOX wafer 4 having a laminated structure of a silicon single crystal layer (second single crystal semiconductor layer) 3.
To form In the present embodiment, the film thickness of the buried oxide film 2 is about 20 nm and the film thickness of the thin silicon single crystal layer 3 is 5 nm.
It was set to about 0 nm.

Next, as shown in FIG. 1B, a silicon nitride film 5 having a thickness of about 250 nm is formed on the entire surface of the silicon single crystal layer 3 by the CVD technique.

Next, as shown in FIG. 1C, the silicon nitride film 5 in the element isolation region 6 is selectively removed by the photolithography technique and the well-known anisotropic dry etching technique.

Next, as shown in FIG. 1D, a thin silicon single crystal layer 3 of the element isolation region 6 is formed by an oxidation diffusion technique in an atmosphere of 1000 ° C. and H ₂ O / O ₂ = 10: 1. The silicon substrate 1 is selectively oxidized to form a field oxide film 7 having a film thickness of about 400 nm. At this time, since the buffer layer is the thin silicon single crystal layer 3, pinholes unlike the conventional case where a polysilicon film is used as the buffer layer do not occur in the silicon single crystal layer 3.

Next, as shown in FIG. 1E, the silicon nitride film 5 is removed in hot phosphoric acid.

Next, as shown in FIG. 1F, the thin silicon single crystal layer 3 is removed by anisotropic dry etching. At this time, since the buried oxide film 2 is not removed by phosphoric acid at all, no micro-trench occurs in the silicon substrate 1 in the element formation region 8 when the thin silicon single crystal layer 3 is removed.

Thereafter, as shown in FIG. 1G, the buried oxide film 2 on the silicon substrate 1 in the element forming region is removed.

Next, as shown in FIG. 2, the silicon substrate 1
A gate oxide film 9 formed by thermal oxidation on the entire upper surface, a polycrystalline silicon film 10 containing impurities on the gate oxide film 9,
A silicon oxide film 21 is sequentially formed by the CVD method. After that, the gate insulating film 9, the polycrystalline silicon film 10, and the silicon oxide film 21 are selectively patterned by photolithography, and the polycrystalline silicon film 10 is processed into a gate electrode shape. After forming the impurity diffusion layer 18 having a shallow junction depth in the silicon substrate 1 on both sides of the gate electrode 10, a silicon oxide film is deposited on the entire surface of the silicon substrate 1 by the CVD method. The silicon oxide film is etched back to form a sidewall oxide film 19 made of a silicon oxide film on the sidewall of the gate electrode. Then, using the silicon oxide film 21 and the sidewall oxide film 19 as a mask,
Impurities are ion-implanted into the silicon substrate 1 to form an impurity diffusion layer 20 having a deep junction depth in the silicon substrate 1.

Through the above steps, the field oxide film 7 and the MOS transistor 22 are formed on the silicon substrate 1.

In the method of manufacturing a semiconductor device according to the embodiment of the present invention, the silicon nitride film 5 is selectively formed on the surface of the SIMOX wafer 4, and the silicon nitride film 5 is used as a mask to remove the maximum amount of the SIMOX wafer 4. The upper layer silicon single crystal 3 is selectively thermally oxidized to selectively form the field oxide film 7 on the SIMOX wafer 4, and the silicon nitride film 5 and the silicon single film in the region where the field oxide film 7 is not formed are formed. The crystal 3 and the buried oxide film 2 formed under the silicon single crystal 3 are removed, and a MOS transistor is formed on the silicon substrate 1 having a single crystal structure in the element formation region where the field oxide film 7 is not formed. As a result, when forming the field oxide film 7, generation of pinholes in the buffer layer is suppressed, and generation of micro-trench in the element formation region 8 is prevented. It is obtain things.

[0022]

According to the present invention, since the micro-trench does not occur on the surface of the silicon substrate in the transistor formation region when forming the element isolation region, the present invention is extremely useful for manufacturing a semiconductor device.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention in the order of manufacturing steps.

FIG. 2 is a cross-sectional view showing an embodiment of the present invention in the order of manufacturing steps.

FIG. 3 is a cross-sectional view showing a conventional method for manufacturing a semiconductor device in the order of steps.

[Explanation of symbols]

 1 Silicon Substrate 2 Buried Oxide Film 3 Single Crystal Silicon Layer 4 Wafer 5 Silicon Nitride Film 6 Element Isolation Area 7 Field Oxide Film 8 Element Formation Area 9 Gate Oxide Film

Claims (1)

[Claims] 1. A step of forming a semiconductor substrate having a laminated structure in which a buried oxide film is formed between a first single crystal semiconductor layer and a second single crystal semiconductor layer, and the second single crystal semiconductor. A step of selectively forming a nitride film on the layer; a step of selectively forming a field oxide film on the semiconductor substrate by performing heat treatment using the nitride film as a mask; and a step of forming the field oxide film. A step of removing the nitride film, the second single crystal semiconductor layer and the buried oxide film in a region where no field oxide film is formed, and a step of forming a transistor in the semiconductor substrate in a region where the field oxide film is not formed. A method of manufacturing a semiconductor device, comprising: