JPH07249772A - Polysilicon thin film transistor and its fabrication - Google Patents

Abstract

PURPOSE:To provide a polysilicon thin film transistor in which the hydrogenation can be performed effectively. CONSTITUTION:An active layer polysilicon film 2 is deposited on a silicon substrate 1, a gate oxide 3 is then deposited on the film 2 followed by formation of a gate electrode 5. A layer insulating film 4 is then formed on the entire surface. A source-drain region 6 is formed on the polysilicon film 2 while being connected with a source-drain electrode 7 through a contact hole made through the layer insulating film 4. A silicon nitride 8 and an amorphous silicon 9 are deposited on the entire surface. Since the amorphous silicon 9 is covered with the silicon nitride 8, external diffusion from the silicon nitride 8 is prevented at the time of hydrogenation and hydrogen is fed from the amorphous silicon 9 to the silicon nitride 8. The silicon nitride 8 and the amorphous silicon 9 can be deposited continuously by altering the conditions of one plasma CVD system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polycrystalline silicon thin film transistor (TFT) and a manufacturing method thereof.

[0002]

2. Description of the Related Art TFT using polycrystalline silicon as an active layer
Since (polycrystalline silicon TFT) requires a high temperature process for manufacturing, it has a drawback that quartz, which is expensive and difficult to increase in area, must be used as a substrate material. On the other hand, the driving capability of the transistor is high, the miniaturization is easy due to the self-aligned structure, and the function similar to that of the LSI can be provided. By utilizing this feature, LCD (Liquid Crystal Display) using polycrystalline silicon TFT
Not only the display section but also the peripheral drive circuit (driver) can be integrated, and the screen size can be reduced without reducing the resolution, and the field of application is expanding.

However, polycrystalline silicon has a drawback in that the bonds of silicon atoms in the crystal planes and crystal grain boundaries are not sufficient and there are many crystal defects. If there are crystal defects, fixed charges and interface states are likely to be formed.
It becomes difficult to improve the electrical characteristics of T. Therefore, a process of reducing defects and stabilizing the crystal structure by bonding hydrogen atoms to crystal defect portions of polycrystalline silicon (called hydrogenation treatment) is performed. By carrying out this hydrogenation treatment, the electrical characteristics of the polycrystalline silicon TFT can be improved.

Conventionally, there are the following methods for hydrogenating a polycrystalline silicon TFT. (1) A method in which the active layer (polycrystalline silicon) is directly exposed to hydrogen plasma and hydrogen in the hydrogen plasma is diffused into the active layer.

(2) A method of forming an amorphous silicon film containing hydrogen by a plasma CVD method and diffusing hydrogen in the amorphous silicon film into an active layer by a subsequent heat treatment. In this case, the position where the amorphous silicon film is formed is located under the active layer, the surface of the active layer, or the like.

(3) A method of forming a silicon nitride film containing hydrogen by a plasma CVD method and diffusing hydrogen in the silicon nitride film into an active layer by a subsequent heat treatment (on a polycrystalline silicon TFT manufactured by a usual method) A silicon nitride film is formed as a passivation film and heat treatment is performed).

However, the method (1) has a drawback that the surface of the active layer is damaged by hydrogen plasma and the characteristics are deteriorated. Further, the above method (2) -has a drawback that the characteristics of the active layer are adversely affected. The method (2) -has the drawback that the characteristics of the active layer are adversely affected when the silicon nitride film is not removed, and the process is complicated when the silicon nitride film is removed. By the way, since the heat treatment is performed at a high temperature (about 900 ° C.) when implanting and activating the impurities in the active layer, the hydrogen diffused in the active layer by the hydrogenation treatment may escape from the active layer. . That is, it is desirable that the hydrogenation process be performed after implanting impurities into the active layer to activate it.

Therefore, the above method (3) is generally used. However, since the silicon nitride film has many pinholes, voids are generated in the silicon nitride film at the stage of heat treatment after depositing the silicon nitride film, and hydrogen atoms escape to the outside (called outward diffusion). Therefore, the amount of hydrogen diffused from the silicon nitride film to the active layer is reduced by the amount of the outward diffusion, and there is a drawback that an efficient hydrogenation treatment cannot be performed.

[0009]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
As disclosed in Japanese Patent No. 65066, there is proposed a method in which a heat treatment is performed after forming a dense silicon oxide film having fewer pinholes on the silicon nitride film.
However, according to the research by the present inventor, although the silicon oxide film has a slower hydrogen diffusion rate than the silicon nitride film,
After all, it was found that outward diffusion occurs. Therefore, it is difficult to diffuse sufficient hydrogen into the active layer even by the method disclosed in the publication, and there is a problem that effective hydrogenation treatment cannot be performed. In addition, it is necessary to use the ozone CVD method to form a dense silicon oxide film. On the other hand, since the silicon nitride film is formed by the plasma CVD method, it is necessary to use both the plasma CVD method and the ozone CVD method in the method disclosed in the publication, which means that the manufacturing apparatus becomes large and the process becomes complicated. There are also problems.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a polycrystalline silicon thin film transistor which can be effectively hydrogenated. Another object of the present invention is to provide a method for manufacturing a polycrystalline silicon thin film transistor that can be effectively hydrogenated.

[0011]

The gist of the invention according to claim 1 is that in a polycrystalline silicon thin film transistor covered with a silicon nitride film, the silicon nitride film is covered with a non-single crystal silicon film. .

A second aspect of the present invention is summarized in the polycrystalline silicon thin film transistor according to the first aspect, wherein the non-single-crystal silicon film is an amorphous silicon film.

A third aspect of the present invention relates to the method for manufacturing a polycrystalline silicon thin film transistor according to claim 1 or 2, wherein a step of forming and covering a silicon nitride film on the polycrystalline silicon thin film transistor, The gist of the present invention is to include a step of forming and covering a non-single-crystal silicon film on the silicon nitride film and a step of subjecting the polycrystalline silicon thin film transistor to hydrogenation treatment by performing heat treatment.

A fourth aspect of the present invention is characterized in that, in the method for manufacturing a polycrystalline silicon thin film transistor according to the third aspect, both the silicon nitride film and the non-single crystal silicon film are formed by a CVD method. .

According to a fifth aspect of the present invention, the step of forming a silicon nitride film on a polycrystalline silicon thin film transistor to cover it and performing a heat treatment while exposing the surface of the silicon nitride film to hydrogen plasma are performed. The gist of the invention is that the thin film transistor is provided with a hydrogenation process.

[0016]

According to the first aspect of the present invention, the surface of the polycrystalline silicon thin-film transistor covered with the silicon nitride film is covered with the non-single-crystal silicon film having a slow hydrogen diffusion rate, so that the hydrogenation treatment is performed. Outward diffusion can be prevented. In addition, since hydrogen is contained in the non-single-crystal silicon film, hydrogen is supplied from the non-single-crystal silicon film to the silicon nitride film during the hydrogenation treatment, so that the hydrogen in the silicon nitride film is not depleted. Absent. Therefore, effective hydrogenation treatment can be performed.

According to the second aspect of the invention, since the amorphous silicon film has a very slow hydrogen diffusion rate, the effect of preventing outward diffusion during the hydrogenation treatment is enhanced. Claim 3
According to the invention described in (1), the polycrystalline silicon thin film transistor according to (1) or (2) can be easily manufactured by a general and simple method.

According to the invention described in claim 4, the same CV
Both the silicon nitride film and the non-single-crystal silicon film can be easily and easily formed simply by changing the forming conditions in the D apparatus.

According to the fifth aspect of the invention, hydrogen is supplied from the hydrogen plasma to the silicon nitride film during the hydrogenation process, and the hydrogen in the silicon nitride film is not depleted. It can be treated.

[0020]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a coplanar type polycrystalline silicon TFT of this embodiment. An active layer polycrystalline silicon film 2 is formed on a quartz substrate 1. A gate oxide film 3 is formed on the polycrystalline silicon film 2. A gate electrode 5 is formed on the gate oxide film 3. An interlayer insulating film 4 is formed on the entire surface of these (quartz substrate 1, polycrystalline silicon film 2, gate electrode 5). N ⁺ type source / drain regions 6 are formed in the polycrystalline silicon film 2. Each of the source / drain regions 6 is connected to the source / drain electrode 7 through a contact hole formed in the interlayer insulating film 4. A silicon nitride film 8 is formed so as to cover the coplanar type polycrystalline silicon TFT thus formed. An amorphous silicon film 9 is formed on the silicon nitride film 8. The silicon nitride film 8 and the amorphous silicon film 9 function as a passivation film.

Next, the manufacturing method of this embodiment will be described in sequence. Step 1 (see FIG. 2); quartz substrate 1 by low pressure CVD method
A polycrystalline silicon film 2 is formed on top. Next, the polycrystalline silicon film 2 is etched so as to have a desired shape. Then, the gate oxide film 3 is formed on the polycrystalline silicon film 2 by the thermal oxidation method. Then, a polycrystalline silicon film is formed on the gate oxide film 3 by the low pressure CVD method. The polycrystalline silicon film is etched to form the gate electrode 5. Next, phosphorus ions are implanted into the polycrystalline silicon film 2 by the self-alignment method using the gate electrode 5 as a mask to form the source / drain regions 6. Further, heat treatment is performed in a nitrogen atmosphere at about 900 ° C. to activate the implanted phosphorus ions. Then, the interlayer insulating film 4 made of a silicon oxide film is formed on the entire surface of the device by the CVD method. Next, after forming a contact hole in the interlayer insulating film 4, an aluminum layer is formed on the entire surface of the device by a sputtering method, and the aluminum layer is etched to form the source / drain electrodes 7.

Step 2 (see FIG. 3); by plasma CVD, monosilane (SiH ₄ ) gas flow rate; 4 sccm, ammonia (NH ₃ ) gas flow rate; 10 sccm, pressure; 0.5 To
rr, RF power; 150 W, substrate temperature; 350 ° C., silicon nitride film 8 (film thickness;
3000 Å) is formed.

Step 3 (see FIG. 1): SiH ₄ gas flow rate; 4 sccm, pressure; 0.5 Torr, by plasma CVD method
Under the conditions of RF power: 150 W, substrate temperature: 350 ° C., the amorphous silicon film 9 (film thickness;
1000 Å) is formed. Here, the only difference between step 2 and step 3 is that in step 3, the introduction of NH ₃ gas is stopped. Therefore, the silicon nitride film 8 and the amorphous silicon film 9 can be continuously formed by simply changing the forming conditions in the same plasma CVD apparatus.

Step 4: About 4 for the device (polycrystalline silicon TFT passivated by the silicon nitride film 8 and the amorphous silicon film 9) manufactured in the above steps.
Heat treatment is performed at 00 ° C. to perform hydrogenation treatment. That is,
Since the silicon nitride film 8 contains a large amount of hydrogen, heat treatment diffuses the hydrogen into the polycrystalline silicon film 2 of the active layer. At this time, since the diffusion rate of hydrogen in the amorphous silicon film 9 is extremely slow, the hydrogen in the silicon nitride film 8 is confined by the amorphous silicon film 9 so that outward diffusion hardly occurs and the polycrystalline silicon is efficiently polycrystallized. It is diffused in the silicon film 2. Further, since the amorphous silicon film 9 also contains hydrogen, the hydrogen is diffused into the silicon nitride film 8 by heat treatment. That is, since the silicon nitride film 8 is replenished with hydrogen from the amorphous silicon film 9, the hydrogen in the silicon nitride film 8 is not exhausted. Therefore, the polycrystalline silicon film 2 of the active layer 2
Enough hydrogen can be diffused.

As described above, according to the present embodiment, by covering the silicon nitride film 8 with the amorphous silicon film 9, the outward diffusion from the silicon nitride film 8 is prevented and the amorphous silicon film 9 is removed from the silicon. Hydrogen can be supplied to the nitride film 8. As a result, efficient and effective hydrogenation treatment can be performed.

By the way, the amorphous silicon film formed by the plasma CVD method has a slower hydrogen diffusion rate than the silicon oxide film formed by the ozone CVD method.
Therefore, the outward diffusion can be suppressed more in the present embodiment than in the method disclosed in the above-mentioned Japanese Patent Laid-Open No. 3-165066.

Further, the amorphous silicon film 9 can be easily formed by changing the conditions for forming the silicon nitride film 8 in the same plasma CVD apparatus. Therefore, according to the present embodiment, the manufacturing apparatus does not become large and the process does not become complicated unlike the above-mentioned publication (where the silicon oxide film is formed by the ozone CVD method).

Therefore, in this embodiment, more efficient and effective hydrotreating can be performed easily than the method according to the above publication. (Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

Coplanar polycrystalline silicon T of this embodiment
The structure of FT is obtained by removing the amorphous silicon film 9 from the first embodiment. Next, the manufacturing method of this embodiment will be sequentially described.

Step I (see FIG. 2) and step II (see FIG. 3): Since they are the same as step 1 and step 2 of the first embodiment, the description thereof will be omitted. Step III (see FIG. 4); In the same plasma CVD apparatus as in Step II, the introduction of SiH ₄ gas is stopped (the introduction of NH ₃ gas is continued) and the substrate temperature is set to about 400 ° C. Then, the NH ₃ gas is decomposed to generate hydrogen plasma, and the device (polycrystalline silicon TFT passivated by the silicon nitride film 8) manufactured in the above process is subjected to heat treatment and hydrogenation treatment. To be done. At this time, the silicon nitride film 8 is replenished with hydrogen from hydrogen plasma, so that the hydrogen in the silicon nitride film 8 is not depleted. Therefore, sufficient hydrogen can be diffused into the polycrystalline silicon film 2 of the active layer. In addition, polycrystalline silicon T
Since the FT is passivated by the silicon nitride film 8, each part of the polycrystalline silicon TFT (source / drain electrode 7, gate electrode 5, polycrystalline silicon film 2) is not damaged by hydrogen plasma.

As described above, according to the present embodiment, hydrogen can be replenished to the silicon nitride film 8 from hydrogen plasma, so that an effective hydrogenation treatment can be performed as in the first embodiment. Further, in order to generate hydrogen plasma after forming the silicon nitride film 8, it is sufficient to simply stop the introduction of SiH ₄ gas in the same plasma CVD apparatus.
The manufacturing equipment does not become large and the process does not become complicated.

The above-described embodiments may be modified as follows, and in that case, the same effects as those of the above-mentioned embodiments can be obtained. 1) In the first embodiment, the amorphous silicon film 9 is replaced with a polycrystalline silicon film. In this case, since the polycrystalline silicon film can be formed on the silicon nitride film 8 only by changing the substrate temperature to about 500 ° C. in the process 3, the process becomes complicated as compared with the first embodiment. Absent.
The diffusion rate of hydrogen in the polycrystalline silicon film formed by the plasma CVD method is slower than that of the silicon oxide film formed by the ozone CVD method, though not so much as that of the amorphous silicon film formed by the plasma CVD method. Therefore, if the amorphous silicon film 9 is replaced with a polycrystalline silicon film, the hydrogenation treatment is performed more effectively than the method disclosed in Japanese Patent Laid-Open No. 165066/1993, although not as much as the first embodiment. be able to.

2) In the first embodiment, the amorphous silicon film 9 is removed after the step 4 (after the hydrogenation treatment). In this case, since the light transmittance of the device is improved due to the absence of the amorphous silicon film 9, the brightness can be increased when the device is used for an LCD.

3) In step III of the second embodiment, NH
_{The 3} gas is replaced with a mixed gas of NH ₃ gas and hydrogen gas or a single hydrogen gas. In this case, when a mixed gas of NH ₃ gas and hydrogen gas is used, hydrogen plasma can be more effectively generated, and the efficiency of hydrogenation treatment can be improved. On the other hand, when hydrogen gas alone is used, it is not necessary to recover toxic NH ₃ gas, and therefore the manufacturing apparatus can be simplified.

4) The first embodiment and the second embodiment are combined and implemented. That is, hydrogen plasma is generated after the amorphous silicon film 9 is formed, and hydrogen is supplied to the silicon nitride film 8 through the amorphous silicon film 9.

5) A CVD method (ECR plasma CV) capable of forming the silicon nitride film 8 and the amorphous silicon film 9 (or the polycrystalline silicon film) at a low temperature, not the plasma CVD method.
D method, photo-excited CVD method, etc.).

By the way, the non-single-crystal silicon film in this specification is not only an amorphous silicon film but also a polycrystalline silicon film, or a laminated state or a mixed state of an amorphous silicon film and a polycrystalline silicon film. Including membranes.

[0039]

As described in detail above, according to the present invention, it is possible to provide a polycrystalline silicon thin film transistor which can be effectively hydrogenated. In addition, the polycrystalline silicon thin film transistor can be effectively hydrogenated by a simple method.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a first embodiment embodying the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing process of a first embodiment and a second embodiment of the present invention.

FIG. 3 is a cross-sectional view showing the manufacturing process of the first and second embodiments.

FIG. 4 is a cross-sectional view showing the manufacturing process of the second embodiment.

[Explanation of symbols]

 2 Polycrystalline silicon film of active layer 3 Gate oxide film 4 Interlayer insulating film 5 Gate electrode 6 Source / drain region 7 Source / drain electrode 8 Silicon nitride film 9 Amorphous silicon film as non-single crystal silicon film

[Procedure amendment]

[Submission date] May 20, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

However, the method (1) has a drawback that the surface of the active layer is damaged by hydrogen plasma and the characteristics are deteriorated. Further, the above method (2) -has a drawback that the film quality of the active layer is adversely affected. The method (2) -has a drawback that the quality of the active layer is adversely affected when the silicon nitride film is not removed, and the process is complicated when the silicon nitride film is removed. By the way, since the heat treatment is performed at a high temperature (about 900 ° C.) when implanting and activating the impurities in the active layer, the hydrogen diffused in the active layer by the hydrogenation treatment may escape from the active layer. . That is, it is desirable that the hydrogenation process be performed after implanting impurities into the active layer to activate it.

Claims (5)

[Claims] 1. A polycrystalline silicon thin film transistor covered with a silicon nitride film (8), wherein the silicon nitride film is covered with a non-single crystalline silicon film (9). 2. The polycrystalline silicon thin film transistor according to claim 1, wherein the non-single crystal silicon film (9) is an amorphous silicon film. 3. A step of forming and covering a silicon nitride film (8) on a polycrystalline silicon thin film transistor, a step of forming and covering a non-single-crystal silicon film (9) on the silicon nitride film, and a heat treatment. The method for producing a polycrystalline silicon thin film transistor according to claim 1 or 2, further comprising the step of subjecting the polycrystalline silicon thin film transistor to hydrogenation treatment. 4. The method for manufacturing a polycrystalline silicon thin film transistor according to claim 3, wherein both the silicon nitride film and the non-single crystal silicon film are formed by a CVD method. 5. A polycrystalline silicon thin film transistor is formed by forming a silicon nitride film (8) on the polycrystalline silicon thin film transistor and covering it, and performing heat treatment while exposing the surface of the silicon nitride film to hydrogen plasma. A method of manufacturing a polycrystalline silicon thin film transistor, which comprises a step of performing a hydrogenation process.