JPH0722618A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form a gate electrode of low resistance by a method wherein a first amorphous Si film and a polycrystalline Si film are formed on a gate oxide film, a second amorphous Si film is formed by implanting impurity ions, and the first and the second amorphous Si films are turned into polycrystalline Si films. CONSTITUTION:A gate oxide film 12 is formed on the surface of an Si substrate 10, and a first amorphous Si film 22 is formed on the film 12. A polycrystalline Si film 24 is formed, and a second amorphous Si film 26 is formed by doping the polycrystalline Si film 24 with P. The first and the second amorphous Si films 22, 26 are turned into a polycrystalline Si film 28 having large crystal grains. In the polycrystalline Si film 28, crystal grain boundary where P is segregated becomes little, and uniform diffusion into Si crystal grains is obtained. Thereby the resistance of a gate electrode is reduced, and throughput can be improved.

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 in which a gate electrode is formed on a gate oxide film.

[0002]

2. Description of the Related Art In the basic structure of a MOSFET (MOS transistor), a gate electrode is formed on the surface of a Si substrate through a gate oxide film (SiO ₂ ) having a thickness of several hundred liters, and a source and a drain are formed on the left and right of these. The gate electrode is generally made of polycrystalline Si.
A conventional method of forming a gate electrode will be described with reference to FIG.

FIG. 2 shows a conventional method of forming a gate electrode.
FIG. First, on the surface of the Si substrate 10, the thickness number
Polycrystalline Si film 1 through 100Å gate oxide film 12
4 is formed (FIG. 2A). Lower resistance of polycrystalline Si
In order to do so, the polycrystalline Si film 14 is doped with P (phosphorus).
Then, the polycrystalline Si film 16 containing P at a high concentration is formed.
(FIG.2 (b)). Method of P-doping the polycrystalline Si film 14
The mainstream method is the so-called lindepo process. Linde
In the po process, the Si substrate having the structure shown in FIG.
Charge it into the furnace and add POCl₃ Steam, O₂ Gas, N ₂ 
Gas is flowed and heat treated at a temperature of about 900 ° C
P is diffused into the Si film 14. This Lindepo
In addition to the process, ion implantation of P ions into the polycrystalline Si film 14
By adding P into the polycrystalline Si film 14,
There is also a way to Polycrystalline Si film containing P in high concentration
After forming 16, the resist 18 is used to form a predetermined shape.
Then, the polycrystalline Si film 16 is etched (FIG. 2 (c)).
After that, the resist 18 is removed to form the gate electrode 20.
(FIG. 2 (d)).

By the way, as devices are miniaturized,
There is a demand for a gate electrode having a lower resistance. In order to further reduce the resistance of the gate electrode, it is necessary to uniformly diffuse a large amount of P in the crystal grains of polycrystalline Si forming the gate electrode. However, if the crystal grains of polycrystalline Si are small, there are many grain boundaries, and P segregates at these grain boundaries, making it difficult to uniformly diffuse a large amount of P into the crystal grains.

Therefore, in the process shown in FIG. 2A, a method of forming an amorphous Si film in place of the polycrystalline Si film 14 and implanting P ions into this amorphous Si film has been studied and implemented. . According to this method, the amorphous Si film is changed into a polycrystalline Si film having large crystal grains by the heat treatment after the formation of the amorphous Si film, so that a large amount of P can be uniformly diffused in the crystal grains. .

[0006]

However, polycrystalline Si
The film has a film formation rate of 100 Å / min at a temperature in the range of about 620 ° C to 630 ° C. On the other hand, the amorphous Si film is formed at a film formation rate of 20 Å / min. Is formed by. Therefore, FIG.
When the amorphous Si film is formed to have the same film thickness in place of the polycrystalline Si film 14 in the step shown in (a), the processing time becomes about 5 times, the processing capacity is greatly reduced, and the throughput is reduced. In addition, the amorphous S
The i film is formed by using a silane gas, but it is known that the film forming rate becomes faster if a disilane gas is used instead of the silane gas. However, in the method using disilane gas, for example, when 100 wafers are loaded into one furnace and collectively processed, the uniformity of the film thickness within one wafer or between wafers deteriorates, and the processing in one batch A new problem arises in that the number of sheets must be reduced.

Further, as in the prior art, only a polycrystalline Si film is formed on the gate oxide film, and impurities are ion-implanted into the polycrystalline Si film to change the polycrystalline Si film into an amorphous Si film. A method is also possible. But,
In order to change the entire polycrystalline Si film into an amorphous Si film by this method, it is necessary to implant the impurity ions with such energy that the impurity ions penetrate through the gate oxide film. When the impurity ions penetrate the gate oxide film and reach the Si substrate, a problem such as a threshold voltage shift occurs. Therefore, a method of forming only a polycrystalline Si film on the gate oxide film and implanting impurity ions cannot be adopted.

In view of the above circumstances, it is an object of the present invention to provide a method of manufacturing a semiconductor device in which a gate electrode having a resistance lower than that of a conventional one is formed.

[0009]

A method of manufacturing a semiconductor device according to the present invention for achieving the above object comprises a method of manufacturing a semiconductor device in which a gate electrode is formed on a gate oxide film. A first amorphous Si film is formed on the first amorphous Si film, and a polycrystalline S film is formed on the first amorphous Si film.
An i film is formed, and impurity ions are implanted into the polycrystalline Si film to form a second amorphous Si film.
It is characterized in that the first and second amorphous Si films are changed into polycrystalline Si films by changing the film into a film and heat-treating the substrate on which the second amorphous Si film is formed.

The first oxide formed on the gate oxide film
Instead of the amorphous Si film, a single crystal Si film may be formed on the gate oxide film.

[0011]

According to the method of manufacturing a semiconductor device of the present invention, the first amorphous Si film is formed on the gate oxide film,
A polycrystalline Si film is formed on the first amorphous Si film. Impurities are ion-implanted into this polycrystalline Si film, but due to the damage effect at the time of this ion implantation, that is, the impurity ions collide with Si atoms to destroy the crystallinity of the polycrystalline Si film, The Si film changes to a second amorphous Si film. The second amorphous Si film formed by this ion implantation and the first amorphous Si film formed on the gate oxide film are changed by heat treatment to a polycrystalline Si film having a large crystal grain size.
Therefore, the crystal grain boundaries in which the impurities are segregated are reduced, and the impurities are uniformly diffused in the Si crystal grains. As a result, a gate electrode having a resistance lower than that of the conventional one can be formed. In addition, since the Si film formed on the gate oxide film before the implantation of the impurity ions is partly an amorphous Si film and the rest is a polycrystalline Si film, all of the Si film is amorphous Si film.
The throughput is higher than when using a film.
Since the amorphous Si film is once formed on the gate oxide film and the polycrystalline Si film is formed on this amorphous Si film, it is not necessary to implant the impurity ions with energy enough to penetrate the gate oxide film. Also, the polycrystalline Si film can be changed to an amorphous Si film.

Here, the first formed on the gate oxide film
When a single crystal Si film is formed on the gate oxide film instead of the amorphous Si film of
The film also becomes a film which is considerably close to a single crystal film. The closer the film is to a single crystal film, the better the in-plane uniformity of the wafer and the easier it is to suppress the resistance value.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for manufacturing a semiconductor device of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing formation of a gate electrode. First, through the gate oxide film 12 having a thickness of 100 Å formed on the surface of the Si substrate 10,
An amorphous Si film 22 having a thickness of 1000Å is formed at a temperature of about 500 ° C. by low pressure CVD using SiH ₂ gas (FIG. 1A). Subsequently, the temperature was changed to 610 ° C., and the other conditions remained the same, while the thickness of the polycrystalline Si was 2500 Å.
The film 24 is formed (FIG. 1B). This gives a thickness of 3
A 500 Å Si film is formed. Next, the polycrystalline Si film 2
In order to dope P with 4 and change the polycrystalline Si film 24 into an amorphous Si film, the polycrystalline Si film 24
Then, P ions are implanted at 100 KeV and 1 × 10 ¹⁶ cm ⁻² . As a result, the polycrystalline Si film 24 changes to the amorphous Si film 26 containing P at a high concentration (FIG. 1).
(C)). After that, a heat treatment such as an oxidation process is performed. By these heat treatments, the amorphous Si films 22 and 2 are
6 changes into a polycrystalline Si film 28 having a large crystal grain size (FIG. 1 (d)). According to the conventional method shown in FIG.
The grain size of polycrystalline Si deposited at about ℃ is 0.1-0.2μ
m, but the crystal grain size of the polycrystalline Si film 28 is 1.0
It becomes more than μm. Therefore, the crystal grain boundaries in which P segregates are reduced, and P diffuses uniformly in the Si crystal grains. As a result, the resistance of polycrystalline Si becomes 100 Ω / □ by the ion implantation of about 1 × 10 ¹⁶ cm ^-2 . The Si film formed on the gate oxide film before the implantation of the impurity ions is an amorphous Si film 22 having a thickness of 1000 Å and is made of polycrystalline Si.
The membrane 24 has a thickness of 2500Å. As described above, the deposition rate of the polycrystalline Si film is 100 Å / min. , The deposition rate of the amorphous Si film was 20Å / min. Then, the total time for forming the amorphous Si film 22 and the polycrystalline Si film is about 75 minutes. On the other hand, the time required to form an amorphous Si film having a thickness of 3500Å is about 175 minutes. Therefore, according to the method for manufacturing the semiconductor device of the present embodiment, the resistance of the gate electrode can be made low, and the throughput is increased as compared with the case where the entire Si film is an amorphous Si film.

[0014]

As described above, according to the method of manufacturing a semiconductor device of the present invention, the polycrystalline Si film is changed into the amorphous Si film by utilizing the ion implantation of impurities, and the amorphous Si film is formed by the subsequent heat treatment. Since the polycrystalline Si film having a large crystal grain size is used, the resistance of the gate electrode can be reduced, and the throughput can be increased as compared with the case where the entire Si film is an amorphous Si film.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a step of forming a gate electrode by a method of manufacturing a semiconductor device according to the present invention.

FIG. 2 is a cross-sectional view showing a conventional method of forming a gate electrode.

[Explanation of symbols]

 10 Si Substrate 12 Gate Oxide Film 22 Amorphous Si Film 24 Polycrystalline Si Film 26 Amorphous Si Film Containing P in High Concentration 28 Polycrystalline Si Film with Large Grain Size

Claims (2)

[Claims] 1. A method of manufacturing a semiconductor device, wherein a gate electrode is formed on a gate oxide film, wherein a first amorphous Si film is formed on the gate oxide film, and the first amorphous Si film is formed on the first amorphous Si film. A polycrystalline Si film is formed, and impurity ions are implanted into the polycrystalline Si film to change the polycrystalline Si film into a second amorphous Si film, and a substrate on which the second amorphous Si film is formed is formed. A method of manufacturing a semiconductor device, characterized in that the first and second amorphous Si films are changed into a polycrystalline Si film by heat treatment. 2. A single crystal Si film is formed in place of the first amorphous Si film.
A method for manufacturing a semiconductor device as described above.