JPH05198567A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To provide a semiconductor device having a precisely formed isolation region having smaller bird's beaks by using local oxidation. CONSTITUTION:A semiconductor device includes a LOCOS structure formed by selective oxidation of the surface of a substrate 1 using a nitride mask 4a formed on an oxide film 2 covering the substrate. Specifically, the nitride mask 4a is formed on a polysilicon layer deposited over the oxide film 2. The nitride mask is used to selectively oxidize the polysilicon layer and the surface of the substrate to an isolation region 5. FETs are formed in the areas separated by the isolation region 5. The oxide film 2 serves as the gate oxide of the FETs 2a. After the isolation region, the polysilicon layer is selectively etched to form the gate electrodes 3a of the FETs.

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, and more particularly to a method for selectively oxidizing a silicon surface having a small bird's peak.

As a method for isolating active regions on a silicon substrate, S is formed by selective oxidation using a nitride film mask.
LOCOS forming an insulating separation band composed of iO ₂ is generally widely used.

However, with the recent miniaturization and speeding up of elements, it is becoming increasingly necessary to form fine element regions precisely. Therefore, there is a demand for an element isolation method that can reduce the bird's peak generated by the insulative isolation band penetrating inside the nitride film mask when the insulative isolation band is formed.

[0004]

2. Description of the Related Art FIG. 3 is an explanatory view of a conventional embodiment, showing a LOCOS process by a cross section of a silicon substrate.

In the conventional LOCOS, first, as shown in FIG.
Referring to, a thermal oxide film 2 is formed on the surface of the silicon substrate 1, and a silicon nitride film is deposited and etched on the thermal oxide film 2.
A nitride film mask 4a is formed so as to cover the region where elements are to be isolated.

Next, referring to FIG. 3B, the surface of the silicon substrate 1 is thermally oxidized by using the nitride film mask 4a, and an insulating separation band 5 made of SiO _{2 is} formed outside the region covered with the nitride film mask 4a. To form the element isolation.

In such a method, oxygen diffuses inside the nitride film mask 4a through the oxide film 2 interposed between the nitride film mask 4a and the substrate 1, so that an insulating separation band is formed inside the periphery of the nitride film mask 4a. And a bird's peak 8 is generated.

For this reason, the region where the element is isolated is smaller than the nitride film mask, so that the size and shape cannot be precisely formed in a fine region. In order to avoid such inconvenience, a method of reducing the bird's peak by thinning the oxide film 2 to prevent oxygen from diffusing from the periphery of the nitride film mask 4a is used.

However, since the oxide film 2 has a function as a stopper in etching for forming the nitride film mask 4a, when the oxide film 4a is thinned, the nitride film mask 4a is formed without damaging the surface of the substrate 1. Difficult to do.

Further, since the oxide film 2 serves as a stress relieving layer of the nitride film, if it is made too thin, damage due to stress occurs. For this reason, the oxide film 2 cannot be thinned unnecessarily, and thus the conventional method of thinning the oxide film has a limit in suppressing the bird's peak.

[0011]

As described above, in the conventional method for forming the insulating separation band, the oxide film interposed between the substrate and the nitride film mask cannot be thinned, so that the bird's peak should be reduced. Therefore, there is a drawback that the element isolation region cannot be formed precisely.

According to the present invention, by forming an insulating separation band by oxidizing a polysilicon layer in close contact with a nitride film mask,
An object of the present invention is to provide a method of manufacturing a semiconductor device having an insulating separation band with a small bird's peak and being precisely formed.

[0013]

FIG. 1 is a diagram for explaining the principle of the present invention. FIGS. 1 (a) and 1 (b) show a process of insulation separation, and FIGS. 1 (c) and 1 (d) show a gate structure. Each manufacturing process is represented by a cross section.

In order to solve the above problems, the first structure of the present invention is provided on the oxide film 2 formed on the surface of the silicon substrate 1 with reference to FIGS. 1 (a) and 1 (b). In a method of manufacturing a semiconductor device including LOCOS (localized oxidation of silicon) for selectively oxidizing the surface of the silicon substrate 1 using the nitride film mask 4a, the nitride film mask 4
a is provided in close contact with the polysilicon layer 3 deposited on the oxide film 2, and the surface of the polysilicon layer 3 and the surface of the silicon substrate 1 are selectively oxidized by using the nitride film mask 4a to form an element. It is characterized by having a step of forming an insulating separation band 5 for separation, and the second configuration is
With reference to FIGS. 1C and 1D, there is shown a method of manufacturing a semiconductor device having a field effect transistor which is element-isolated by the insulating isolation band 5 formed using the first configuration,
The oxide film 2 is replaced with the gate oxide film 2 of the field effect transistor.
after the step of forming a and the step of forming the insulating separation band 5, a step of forming part of the polysilicon layer 3 as the gate electrode 3a of the field effect transistor by selective etching of the polysilicon layer 3. It is characterized by having and.

[0015]

The operation of the present invention will be described with reference to FIG. In the first configuration of the present invention, referring to FIG. 1A, an oxide film 2 is formed on the surface of a silicon substrate 1, and a polysilicon layer 3 is deposited on the oxide film 2.

The nitride film mask 4a is formed by depositing a nitride film on the polysilicon layer 3 and etching the nitride film. In such a structure, since the etching rate ratio between the nitride film and the polysilicon is large, the polysilicon layer 3 becomes a good stopper in the etching for forming the nitride film mask 4a, and a precise mask can be manufactured. Further, since the polysilicon layer is not over-etched, it is possible to prevent a large bird's peak from being generated due to the progress of oxidation from the side wall surface exposed by the over-etching. Therefore, element isolation can be made precise.

Next, in this structure, referring to FIG. 1B, the polysilicon layer 3 is selectively oxidized using the nitride film mask 3 and further oxidized to the surface layer of the substrate 1 to a desired thickness. To form the insulating separation zone 5.

In this structure, since the nitride film mask 4a is provided in close contact with the polysilicon layer 3 to be oxidized,
Since oxygen does not diffuse through the oxide film under the nitride film mask 4a unlike the conventional LOCOS, the bird's peak is small in the oxidation of the polysilicon layer 3.

Even if the nitride film mask 4a is provided in close contact with the polysilicon layer 3, the stress is relieved due to the presence of the polysilicon layer 3 and no defect occurs in the silicon substrate 1.

Further, in this structure, the insulating separation band 5 is formed mainly by oxidizing both the polysilicon layer 3 and the surface of the substrate 1. Therefore, the thickness of the surface of the substrate 1 that is oxidized is sufficient because of the difference between the thickness of the insulating separation zone 5 and the thickness of the layer obtained by oxidizing the polysilicon layer 3. For this reason, the oxide layer on the surface of the substrate 1 that is oxidized by oxygen diffused and transmitted through the oxide film 2 may be thin, and the diffusion of oxygen in the oxide film 2 that causes the bird's peak can be limited to a short time. However, even if the oxide film 2 exists, the bird's peak is small.

Further, since the polysilicon layer 3 suppresses the bending of the nitride film mask 4a caused by the generation of the bird's peak, a stress that inhibits the progress of the bird's peak is generated, and as a result, the growth of the bird's peak is suppressed. is there.

Furthermore, since the polysilicon layer 3 has a smaller internal stress than the nitride film, the oxide film for stress relaxation can be thinned, and this also contributes to the suppression of the bird's peak.

A second structure of the present invention relates to a method for easily manufacturing a fine field effect transistor using the first structure. In the second configuration, as a premise, referring to FIG. 1B, oxide film 2 is formed as a gate oxide film material, and polysilicon layer 3 is deposited as a gate electrode material.

Next, after forming the insulating separation band 5 through the steps of the first constitution, the gate electrode of the field effect transistor is formed in the insulating separated area by the following steps. First, referring to FIG. 1C, a mask having a pattern shape of the gate electrode 3a, for example, a resist mask is formed on the polysilicon layer 3, and the gate oxide film 2a formed of a part of the oxide film 2 is used as a stopper. The silicon layer 3 is etched, and as shown in FIG. 1D, a part of the polysilicon layer 3 is formed on the gate electrode 3a.

The impurity doping step and the wiring step can be performed by a usual method. With this configuration, there is no need to provide special steps for forming the gate oxide film and depositing the gate electrode material, and therefore the manufacturing process of the field effect transistor is simplified.

Further, the etching of the polysilicon layer 3 can be performed in the same manner as the conventional method, and the present invention can be easily applied in the conventional process. Therefore, a fine field effect transistor can be manufactured precisely and easily.

[0027]

EXAMPLES The present invention will be described in detail with reference to examples.
FIG. 2 is a process chart of an embodiment of the present invention, which is a cross-sectional view showing the manufacturing process of a field effect transistor.

First, referring to FIG. 2A, a thermal oxide film having a thickness of, for example, 15 nm is formed as a gate oxide film 2a on one surface of the silicon substrate 1. Then, the polysilicon layer 3 is deposited to a thickness of 100 nm, for example, by the CVD method.

Next, a nitride film (Si ₃ N ₄ ) is deposited to a thickness of 150 nm by the CVD method. Next, the nitride film is photo-etched to cover the region where the field effect transistor is to be formed as an element isolation region.
a is formed.

For etching the nitride film, for example, C
RIE (reactive ion etching) using a mixed gas of HF and CF can be used. The selection ratio at this time can be set to about 20 or more, which is a significant improvement over the selection ratio of about 2 when the conventional underlying layer is an oxide film.

Next, referring to FIG. 2B, the polysilicon layer is oxidized by selective thermal oxidation using a nitride film mask, and a part of the substrate is oxidized to remove a 600 nm thick oxide film. Insulating separation band 5 is formed.

At this time, the size of the bird's peak is 0.2.
μm, which was suppressed to about 60% of the size of the bird's peak of 0.35 μm in the case of forming an insulating separation band of the same thickness using a nitride film mask of the same thickness. ..

Then, referring to FIG. 2C, the nitride film mask 4a is removed by immersing in hot phosphoric acid. Then, although not shown, if necessary, impurity ions are implanted to form a channel. The polysilicon layer may be doped with impurities during deposition, or may be doped after forming the channel.

Next, referring to FIG. 2D, a WSi layer 7 having a thickness of 100 nm, for example, is deposited by, for example, the CVD method, and P is ion-implanted after the deposition. Then, FIG.
Referring to (e), a gate-shaped resist mask 6 is formed on the WSi layer 7 by photolithography, and the WSi layer 7 is etched using this resist mask 6 to perform WS.
The i pattern 7a is formed. The WSi layer 7 is etched by ECR etching using a mixed gas of chlorine and oxygen, for example.

Next, referring to FIG. 2 (f), the polysilicon layer 3 is patterned by ECR etching using a gas containing HBr, for example, using the resist mask 6 and the WSi pattern 7a as masks, and the gate of polysilicon is formed. The electrode 3a is formed.

In the etching of polysilicon, the gate oxide film 2a sufficiently functions as a stopper.
Next, although not shown, after ion-implanting into the source and the drain, referring to FIG. 2G, the resist mask 6 is removed to complete the field effect transistor.

According to this embodiment, a field effect transistor can be formed in a region precisely defined as an element isolation region with a small number of steps.

[0038]

According to the present invention, oxygen is diffused from the periphery of the nitride film mask to below the mask by forming a part of the insulating separation zone by oxidizing the polysilicon layer that adheres to the nitride film mask. Therefore, it is possible to form an insulation separation band having a small bird's peak, and it is possible to provide a method for manufacturing a semiconductor device having a precisely formed insulation separation band.

Further, by using the oxide film and the polysilicon layer used for forming the insulating separation band as the gate oxide film and the gate electrode, the manufacturing process of the field effect transistor can be shortened.

Therefore, it greatly contributes to the performance improvement of the semiconductor device.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention.

FIG. 2 is a process chart of an embodiment of the present invention

FIG. 3 is an explanatory diagram of a conventional example

[Explanation of symbols]

 1 substrate 2 oxide film 2a gate oxide film 3 polysilicon layer 3a gate electrode 4a nitride film mask 5 insulating separation band 6 resist mask 7 WSi layer 7a WSi pattern 8 bird's peak

Claims (2)

[Claims] 1. A LOC for selectively oxidizing the surface of a silicon substrate (1) by using a nitride film mask (4a) provided on an oxide film (2) formed on the surface (1) of the silicon substrate.
In a method of manufacturing a semiconductor device including OS (localized oxidation of silicon), the nitride film mask (4a) is closely provided on a polysilicon layer (3) deposited on the oxide film (2), A step of forming an insulating isolation band (5) for element isolation by selectively oxidizing the surfaces of the polysilicon layer (3) and the silicon substrate (1) using a nitride film mask (4a). A method for manufacturing a semiconductor device, comprising: 2. A method for manufacturing a semiconductor device having a field effect transistor, which is formed by using the method according to claim 1 and is element-isolated by the insulating isolation band (5), wherein the oxide film (2) is formed. After the step of forming the gate oxide film (2a) of the field effect transistor and the step of forming the insulating separation band (5), the polysilicon layer (3) is selectively etched by the polysilicon layer (3). A step of forming a part of the above as a gate electrode (3a) of the field effect transistor.