JPH06151834A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce damage to a substrate when forming the gate electrode of a MIS type transistor. CONSTITUTION:After a polycrystalline silicon thin film 3 is formed on a gate dielectric film 2, the surface of the first polycrystalline silicon thin film 3 is naturally oxidized and then a second polycrystalline silicon thin film 4 is formed on it. Then, after the second polycrystalline silicon thin film 4 is etched to the pattern of gate electrode, the first polycrystalline silicon thin film 3 at a part which is not covered with the second polycrystalline silicon thin film 4 is completely oxidized thermally. Therefore, even if the gate dielectric film 2 is extremely thin, the first polycrystalline silicon thin film 3 and a natural oxide film 9 on it contribute to etching control, thus reducing the etching damage to the substrate when forming the gate electrode.

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 MIS type semiconductor device, for example, and more particularly to a method of manufacturing a semiconductor device in which damage to a semiconductor substrate is prevented during etching of a gate electrode.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of MIS transistors, the gate oxide film thereof tends to be further thinned according to the scaling rule. To give an example, 0.1-0.1 which is currently being considered at the research and development level
In a MIS transistor having a gate length of about 0.4 μm, it is necessary to reduce the gate oxide film thickness to about 40 to 150 Å.

[0003]

Problems of the prior art will be described with reference to FIG.

According to a usual method for manufacturing a MIS type transistor, first, as shown in FIG. 2A, for example, a gate oxide film 12 is formed on a p-type silicon substrate 11 in a water vapor atmosphere by burning hydrogen and oxygen, for example. By heat treatment, for example, a film thickness of 80 Å is formed.

Next, as shown in FIG. 2B, the polycrystalline silicon thin film 14 is formed, for example, by a low pressure CVD method, for example, 300.
It is formed to a film thickness of 0Å. After that, the photoresist 1 is formed on the portion where the gate electrode is to be formed by the photolithography technique.
8 is selectively formed.

Next, as shown in FIG. 2C, reactive ion etching is performed to selectively remove a portion of the polycrystalline silicon thin film 14 which is not covered with the photoresist 18 to remove the gate electrode 14. Form.

At this time, in the above-mentioned miniaturization level MIS transistor, when the gate electrode is processed by dry etching, for example, a semiconductor thin film used for the gate electrode made of polycrystalline silicon and a base of the semiconductor thin film are formed. For example, unless a sufficient etching selection ratio (ratio of etching rates) with the gate dielectric film made of a silicon oxide film is secured, the gate dielectric film does not function as an etching stopper, and the damage layer 10 due to plasma on the silicon substrate is not formed. I can do it.

Further, as shown in FIG. 2D, the gate oxide film 12, which is the gate dielectric film, is completely removed except for the portion directly below the gate electrode, and the silicon substrate 11 is removed.
Is unnecessarily etched.

In the state of being damaged as described above, M
When the IS type transistor is formed, it is impossible to realize a normal transistor operation due to an excessive leakage current in the drain diffusion layer.

[0010]

In order to solve the above-mentioned problems, a method of manufacturing a semiconductor device according to the present invention comprises a step of forming an insulating film on one main surface of a first conductivity type semiconductor substrate, and a step of forming the insulating film. A step of forming a first semiconductor film on the film, a step of forming a second semiconductor film on the first semiconductor film, and a step of partially etching away the second semiconductor film to form a gate electrode. The method includes a step of forming and a step of partially heat-treating the first semiconductor film.

In a preferred aspect of the present invention, the film thickness of the first semiconductor film is smaller than the film thickness of the second semiconductor film.

[0012]

In the method of manufacturing a semiconductor device according to the present invention, the first semiconductor film is formed on the insulating film which is, for example, the gate dielectric film, and then the second semiconductor film is formed on the insulating film. After selectively etching the second semiconductor film, leaving only the portion to be the gate electrode, heat treatment is performed in, for example, an oxidizing atmosphere to remove all the portion of the first semiconductor film other than the portion of the gate electrode. Transform into an oxide film.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a method for manufacturing a MIS type transistor will be described below with reference to FIG.

First, as shown in FIG. 1A, for example, p
The gate oxide film 2 is heat-treated in a water vapor atmosphere by burning hydrogen and oxygen, for example, to have a film thickness of, for example, 80 Å, and then the first polycrystalline silicon thin film 3 is subjected to low pressure CVD. Depending on the law, for example, 200Å
The film is formed to a film thickness of, and then left in the atmosphere for a certain period of time.
Then, after this, the second polycrystalline silicon thin film 4 is formed to a film thickness of, for example, 3000 Å by the low pressure CVD method.

According to the above-mentioned process, between the first polycrystalline silicon thin film 3 and the second polycrystalline silicon thin film 4, the natural deposits that are adhered when the first polycrystalline silicon thin film 3 is left in the atmosphere. The oxide film 9 exists, for example, about 10 Å, and the first polycrystalline silicon thin film 3 and the second polycrystalline silicon thin film 4 are electrically connected to each other, but the natural oxide film 9 is sandwiched therebetween. Has become.

Next, as shown in FIG. 1B, a photoresist 8 is selectively formed by photolithography on the portion where the gate electrode is to be formed, and reactive ion etching is performed in this state. , A portion of the second polycrystalline silicon thin film 4 not covered with the photoresist 8 is selectively removed.

At this time, in this embodiment, the natural oxide film 9 is etched after the second polycrystalline silicon thin film 4 is removed, and as a result, the etching end point in the reactive ion etching apparatus is finished. Is detected and the first polycrystalline silicon thin film 3 is exposed, or
A part of the native oxide film 9 remains on the surface.

Thereafter, as shown in FIG. 1C, a heat treatment is performed in, for example, a dry oxygen atmosphere to completely form the oxide film 5 in the portion other than immediately below the gate electrode of the first polycrystalline silicon thin film 3. Transform. And, for example, 5 × 10 ¹⁵ c
Arsenic ions 6 are ion-implanted at m ⁻² to form the ion-implanted layer 7, and then heat treatment is performed in a nitrogen atmosphere.
As shown in FIG. 1D, an n-type source / drain diffusion layer 7'is formed.

[0019]

According to the method of manufacturing a semiconductor device of the present invention, for example, when a gate electrode is formed, the gate dielectric film does not function as an etching stopper, and the silicon substrate is damaged by, for example, plasma and spreads. In addition, it is possible to prevent the problem that the gate dielectric film is completely removed and the silicon substrate is unnecessarily etched.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method of manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a conventional method of manufacturing a semiconductor device.

[Explanation of symbols]

 1 p-type silicon substrate 2 gate oxide film 3 first polycrystalline silicon thin film 4 second polycrystalline silicon thin film 5 oxide film 7'source / drain diffusion layer 8 photoresist 9 natural oxide film

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 21/336

Claims (2)

[Claims] 1. A step of forming an insulating film on one main surface of a first conductivity type semiconductor substrate, a step of forming a first semiconductor film on the insulating film, and a step of forming a first semiconductor film on the first semiconductor film. A step of forming a second semiconductor film, a step of partially etching away the second semiconductor film to form a gate electrode, and a step of partially heat-treating the first semiconductor film. A method for manufacturing a semiconductor device, comprising: 2. The film thickness of the first semiconductor film is smaller than the film thickness of the second semiconductor film.
A method for manufacturing a semiconductor device as described above.