JPH07321106A - Modifying method for silicon oxide thin film and manufacture of thin film transistor - Google Patents

Abstract

PURPOSE:To obtain a silicon oxide thin film of excellent quality by a low temperature process by a method wherein gas plasma below a specific temperature, mainly composed of oxygen, irradiates the silicon oxide thin film formed at the temperature lower than a specific value. CONSTITUTION:The plasma of gas below 600 deg.C, mainly composed of oxygen, is applied to the silicon thin film 5 which is formed at 600 deg.C or lower. For example, a polycrystalline silicon thin film is formed on a light-transmitting glass substrate 1 as an active semiconductor layer 2, and it is processed into an insularly form. A silicon oxide thin film is formed thereon as a gate insulating layer 5 at the substrate temperature of 420 deg.C by an atmospheric pressure CVD method. Then, substrate temperature is set at 400 deg.C, and the plasma, formed by decomposing oxygen gas by high frequency discharge of discharge power of the density of 1W/cm<2>, is projected. Then, tantalum film is formed as a gate electrode 6 using a sputtering method, and after processing. impurities are introduced using the gate electrode 6 as a mask, and a source region 3 and a drain region 4 are 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 modifying a silicon oxide thin film applied to a semiconductor device or the like, and a method for manufacturing a thin film transistor applied to a liquid crystal display device, an image sensor or the like using this modification method. It is about.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been installed in viewfinders of home video cameras and notebook personal computers. Among these liquid crystal display devices, active matrix type liquid crystal displays capable of displaying particularly high image quality. Devices are receiving attention. In this active matrix type liquid crystal display device, as a switching element of the pixel electrode,
Thin film transistor (Thin Film Transi)
Stor) is often used.

An example of such a thin film transistor is disclosed in IEICE Technical Report Vol. 92, No. 119, pp. 35-40. A method of manufacturing this thin film transistor will be described. First, a polycrystalline silicon thin film is formed as a semiconductor layer on a quartz substrate, and then a silicon oxide thin film is formed as a gate insulating layer by a thermal oxidation method. A gate electrode is formed on the silicon oxide thin film, and a source / drain region is formed in the polycrystalline silicon thin film by an ion implantation method using the gate electrode as a mask. After that, an interlayer insulating film, a source electrode and a drain electrode are formed to complete the thin film transistor.

[0004]

In the above-mentioned conventional manufacturing method, a quartz substrate having a high heat resistant temperature is used, and the technology cultivated in the field of LSI is applied. Therefore, a high-quality gate insulating layer and an interface between the gate insulating layer and the semiconductor layer can be obtained by using a thermal oxidation method which is a high temperature process of about 1000 ° C. for forming the gate insulating layer. However, since the quartz substrate is expensive, the heat-resistant temperature is about 600 ° C, but on a cheap glass substrate,
There has been a demand for a method of forming a gate insulating layer made of a good quality silicon oxide thin film and a good quality interface between the gate insulating layer and the semiconductor layer.

An object of the present invention is to provide a method for modifying a silicon oxide thin film, which can obtain a good quality silicon oxide thin film in a low temperature process, and a high quality gate insulating layer and a gate insulating layer and a semiconductor layer in a low temperature process. Another object of the present invention is to provide a method of manufacturing a thin film transistor that can obtain a high-quality interface with.

[0006]

A method for modifying a silicon oxide thin film according to a first aspect of the invention is characterized in that a silicon oxide thin film formed at a temperature of 600 ° C. or lower is treated with plasma of a gas containing oxygen as a main component at 600 ° C. or lower. It is characterized by irradiation at a temperature.
The method for modifying a silicon oxide thin film according to claim 2 is the method for modifying a silicon oxide thin film according to claim 1, wherein the silicon oxide thin film is formed by an atmospheric pressure CVD method, a low pressure CVD method, a plasma CVD method, a sputtering method, or ECR. -It is formed by the CVD method or the liquid phase deposition method.

The method for modifying a silicon oxide thin film according to claim 3 is the method for modifying a silicon oxide thin film according to claim 1 or 2, wherein the discharge power density of plasma of a gas containing oxygen as a main component is 0. It is set to 5 W / cm ² or more and 2 W / cm ² or less. A method of manufacturing a thin film transistor according to claim 4, wherein a step of forming a semiconductor layer on the insulating substrate, a step of forming a gate insulating layer on the semiconductor layer, and a step of forming a gate electrode on the gate insulating layer, A step of forming a source region and a drain region by adding an impurity which serves as a donor or an acceptor to a partial region of the semiconductor layer; and a step of forming a source electrode and a drain electrode electrically connected to the source region and the drain region. A method of manufacturing a thin film transistor, comprising:
It is characterized in that a silicon oxide thin film formed at a temperature of ° C or lower is irradiated with plasma of a gas containing oxygen as a main component at a temperature of 600 ° C or lower.

According to a fifth aspect of the present invention, in a method of manufacturing a thin film transistor, a step of forming a gate electrode on an insulating substrate, a step of forming a gate insulating layer on the gate electrode, and forming a semiconductor layer on the gate insulating layer. A step of forming a source region and a drain region by adding an impurity serving as a donor or an acceptor to a partial region of the semiconductor layer, and forming a source electrode and a drain electrode electrically connected to the source region and the drain region A method of manufacturing a thin film transistor, the method including:
It is characterized in that a silicon oxide thin film formed at a temperature of ° C or lower is irradiated with plasma of a gas containing oxygen as a main component at a temperature of 600 ° C or lower.

The method of manufacturing a thin film transistor according to claim 6 is the method of manufacturing a thin film transistor according to claim 4 or 5, wherein the discharge power density of plasma of a gas containing oxygen as a main component is 0.5 W / cm ² or more, It is set to 2 W / cm ² or less. A method of manufacturing a thin film transistor according to claim 7, wherein in the method of manufacturing a thin film transistor according to claim 4, 5 or 6, the semiconductor layer is a polycrystalline silicon thin film, a microcrystalline silicon thin film, an amorphous silicon thin film, or a single crystal silicon. It is made of a thin film.

The method of manufacturing a thin film transistor according to claim 8 is the method of manufacturing a thin film transistor according to claim 4, 5, 6 or 7, wherein a glass substrate is used as the insulating substrate.

[0011]

According to the method for modifying a silicon oxide thin film of the present invention, the quality of the silicon oxide thin film is improved by irradiating the silicon oxide thin film with plasma of a gas containing oxygen as a main component. Further, since the formation of the silicon oxide thin film and the plasma irradiation are performed in a low temperature process of 600 ° C. or lower, a good quality silicon oxide thin film can be formed on the substrate having a low heat resistant temperature.

According to the method of manufacturing a thin film transistor of the present invention, a silicon oxide thin film having a gate insulating layer formed at a temperature of 600 ° C. or lower is irradiated with plasma of a gas containing oxygen as a main component at a temperature of 600 ° C. or lower. By this formation, a gate insulating layer made of a good quality silicon oxide thin film can be formed by a low temperature process of 600 ° C. or lower, and
It is possible to improve the quality of the interface between the gate insulating layer and the semiconductor layer,
A high-performance thin film transistor can be manufactured.

[0013]

Embodiments of the present invention will be described below. [First Embodiment] FIGS. 1A to 1F are process sectional views showing a method of manufacturing a thin film transistor according to a first embodiment of the present invention. In this embodiment, a method for manufacturing a top gate type thin film transistor will be described.

First, a transparent glass substrate (insulating substrate) 1
A polycrystalline silicon thin film having a film thickness of 100 nm is formed as the active semiconductor layer 2 by, for example, a low pressure CVD method, and is processed into an island shape by using photolithography and etching. On top of that, as the gate insulating layer 5, for example, atmospheric pressure CVD
By the method, a silicon oxide thin film having a film thickness of 200 nm is formed at a substrate temperature of 420 ° C. After that, the substrate temperature is set to 400 ° C., and the oxygen gas is irradiated with plasma decomposed by high frequency discharge at a discharge power density of 1 W / cm ² (FIG. 1A).
Here, when the discharge power density was 0.5 W / cm ² or less, a sufficient effect of modifying the gate insulating layer 5 (silicon oxide thin film) could not be obtained. It was also found that at 2 W / cm ² or more, plasma damage adversely affects the threshold voltage and mobility of the thin film transistor. Therefore, the discharge power density must be 0.5 W / cm ² or more and 2 W / cm ² or less.

Next, the gate electrode 6 has a film thickness of 200 n.
A film of tantalum of m is formed by a sputtering method and processed by photolithography and etching. Next,
Using the gate electrode 6 as a mask, for example, ions containing phosphorus generated by decomposing phosphine gas diluted with hydrogen by high frequency discharge are accelerated without mass separation and introduced as impurities to serve as a donor, and the source region 3 and the drain are drained. Area 4
Are formed (FIG. 1B).

Next, as the interlayer insulating layer 7, for example, normal pressure C
After forming a silicon oxide thin film by the VD method, a contact hole is formed by photolithography and etching. Further, as the source electrode 8 and the drain electrode 9, for example, titanium and aluminum are formed in the order of 10 and 10 respectively.
A thin film transistor is completed by forming and processing a film having a thickness of 0 nm and 500 nm (FIG. 1C).

As described above, according to the first embodiment,
By irradiating the silicon oxide thin film formed as the gate insulating layer 5 with plasma generated by high-frequency discharge decomposition of oxygen gas, the quality of the silicon oxide thin film is improved, and at the same time, the active semiconductor layer 2 and the gate insulating layer 5 (silicon oxide thin film) ) And the interface is improved. Therefore, a high performance thin film transistor can be manufactured.

The effect of plasma irradiation of oxygen gas will be described below with reference to one example. The sample comparatively evaluated here is a P-type crystalline silicon wafer having a resistivity of 10 Ωcm and a film thickness of 200 n at a substrate temperature of 420 ° C. by an atmospheric pressure CVD method.
After forming a silicon oxide thin film of m
A MOS capacitor which was heated to 400 ° C. for post metallization annealing after irradiating plasma decomposed by high frequency discharge with oxygen gas at a power density of 1 W / cm ² for 30 minutes to form 300 nm of aluminum as an upper electrode; MOS without plasma irradiation
It is a capacitor. The results of evaluating this are shown in Table 1. Table 1 is a comparison of characteristics of silicon oxide thin films with and without oxygen gas plasma irradiation.

[0019]

[Table 1]

From Table 1, it is understood that the dielectric strength, the fixed charge density in the oxide film, and the interface state density are improved by the plasma irradiation. [Second Embodiment] FIGS. 2A to 2D are process sectional views showing a method of manufacturing a thin film transistor according to a second embodiment of the present invention. In this embodiment, a method of manufacturing a bottom gate type thin film transistor will be described.

First, a transparent glass substrate (insulating substrate) 1
A 100 nm-thick tantalum film is formed as a gate electrode 16 on the substrate 1 by a sputtering method, and is processed by using photolithography and etching. On top of that, a substrate temperature of 420 is formed as the gate insulating layer 15 by, for example, an atmospheric pressure CVD method.
A silicon oxide thin film having a film thickness of 200 nm is formed at a temperature of ℃.
After that, the substrate temperature is set to 400 ° C. and oxygen gas is set to 1.5 W
The plasma decomposed by the high frequency discharge is irradiated at a discharge power density of / cm ² (FIG. 2A). At this time, in order to obtain sufficient effect without damaging the plasma irradiation, as described in the first embodiment, the discharge power density is set to 0.5 W / cm ² or more and 2 W / cm ² or less. There must be.

Next, a 100-nm-thick polycrystalline silicon thin film is formed as the active semiconductor layer 12 by, for example, a low pressure CVD method, and is processed into an island shape by using photolithography and etching. Next, a mask for introducing impurities is formed with a photoresist 21 on the active semiconductor layer 12.
For example, ions containing phosphorus generated by decomposing phosphine gas diluted with hydrogen by high-frequency discharge are accelerated without mass separation and introduced as impurities serving as donors to form source region 13 and drain region 14 (FIG. Two
(B)).

Next, as the source electrode 18 and the drain electrode 19, for example, titanium is formed to a film thickness of 300 nm,
After processing, a silicon oxide thin film is formed as the protective film 20 by, for example, an atmospheric pressure CVD method, and then a hole 22 for taking out an electrode is formed by photolithography and etching to complete a thin film transistor (FIG. 2).
(C)).

As described above, according to the second embodiment,
Similar to the first embodiment, the quality of the silicon oxide thin film is improved by irradiating the silicon oxide thin film formed as the gate insulating layer 15 with plasma obtained by high-frequency discharge decomposition of oxygen gas. Further, since the surface of the silicon oxide thin film is also improved in quality, the interface between the active semiconductor layer 12 and the gate insulating layer 15 (silicon oxide thin film) is also improved in quality. for that reason,
A high-performance thin film transistor can be manufactured.

In the first and second embodiments, the silicon oxide thin film formed at 420 ° C. by the atmospheric pressure CVD method is used as the gate insulating layers 5 and 15, but this is 600 ° C.
Any silicon oxide thin film formed below may be used, for example, low pressure CVD method, plasma CVD method, sputtering method, EC
It may be formed by the R-CVD method or the liquid phase deposition method. Further, the substrate temperature was 400 ° C. and the plasma decomposed by the high frequency discharge of oxygen gas was irradiated, but the plasma irradiation may be performed at a substrate temperature of 600 ° C. or lower. Therefore, a high-quality silicon oxide thin film (gate insulating layers 5, 1
5) can be formed by a low temperature process of 600 ° C. or lower, and the cost of the thin film transistor can be reduced by using an inexpensive glass substrate having a heat resistant temperature of about 600 ° C.

In the first and second embodiments, a polycrystalline silicon thin film formed by the low pressure CVD method is used as the active semiconductor layers 2 and 12, but any thin film that works as an active semiconductor may be used. It may be an amorphous silicon thin film, a microcrystalline silicon thin film, a single crystal silicon thin film, a compound semiconductor, or a polycrystalline silicon thin film formed by irradiating an amorphous silicon thin film with laser light.

In the first and second embodiments, polycrystalline silicon thin films are used as the active semiconductor layers 2 and 12. However, in order to lower the energy barrier of grain boundaries of the polycrystalline silicon thin films, hydrogen plasma is used. Irradiation and implantation of hydrogen ions are even better. Although tantalum is used as the gate electrodes 6 and 16 in the first and second embodiments, any material that works as an electrode may be used. For example, a metal such as titanium, chromium, molybdenum, or aluminum, or a large amount of impurities may be used. It may be a polycrystalline silicon thin film doped with a transparent conductive layer such as ITO (indium tin oxide).

Although phosphorus is used as an impurity for forming the source regions 3 and 13 and the drain regions 4 and 14 in the first and second embodiments, this is used when an n-channel thin film transistor is manufactured. Any material such as arsenic that acts as a donor may be used, and in the case of manufacturing a p-channel thin film transistor, any material such as aluminum or boron that acts as an acceptor may be used.

In the first and second embodiments, as a method of adding impurities, ions containing phosphorus generated by decomposition by high frequency discharge are accelerated without mass separation and introduced as impurities. Can be any method that can add impurities, such as an ion implantation method and a plasma doping method. Although the silicon oxide thin film formed by the atmospheric pressure CVD method was used as the interlayer insulating layer 7 in the first embodiment, this is, for example, a low pressure CVD method or a plasma CVD method.
Any method that works as an insulating layer, such as a silicon oxide thin film formed by a sputtering method, a sputtering method, an ECR-CVD method, a liquid phase deposition method, or a silicon nitride thin film formed by a plasma CVD method, may be used.

[0030]

According to the method for modifying a silicon oxide thin film of the present invention, the quality of the silicon oxide thin film is improved by irradiating the silicon oxide thin film with plasma of a gas containing oxygen as a main component. Further, since the formation of the silicon oxide thin film and the plasma irradiation are performed in a low temperature process of 600 ° C. or lower, a good quality silicon oxide thin film can be formed on a glass substrate or the like having a low heat resistant temperature.

In the method of manufacturing a thin film transistor according to the present invention, a gate insulating layer is formed by irradiating a silicon oxide thin film formed at a temperature of 600 ° C. or lower with plasma of a gas containing oxygen as a main component at a temperature of 600 ° C. or lower. By doing
By the low temperature process of 600 ° C. or lower, the gate insulating layer made of a good quality silicon oxide thin film can be formed and the interface between the gate insulating layer and the semiconductor layer can be made good quality. Therefore, a high-performance thin film transistor can be manufactured at low cost by using a glass substrate or the like having a low heat resistant temperature.

[Brief description of drawings]

FIG. 1 is a process sectional view showing a method of manufacturing a thin film transistor according to a first embodiment of the present invention.

FIG. 2 is a process sectional view showing a method of manufacturing a thin film transistor according to a second embodiment of the present invention.

[Explanation of symbols]

 1,11 Translucent glass substrate 2,12 Active semiconductor layer 3,13 Source region 4,14 Drain region 5,15 Gate insulating layer (silicon oxide thin film) 6,16 Gate electrode 8,18 Source electrode 9,19 Drain electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Kawamura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Yutaka Miyata, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (8)

[Claims] 1. A plasma of a gas containing oxygen as a main component is applied to a silicon oxide thin film formed at a temperature of 600 ° C. or lower.
Irradiating at a temperature of 0 ° C. or lower, a method for modifying a silicon oxide thin film. 2. A silicon oxide thin film is formed using a normal pressure CVD method, a low pressure CVD method, a plasma CVD method, a sputtering method, an ECR-
The method for modifying a silicon oxide thin film according to claim 1, wherein the method is a CVD method or a liquid phase deposition method. 3. The method for modifying a silicon oxide thin film according to claim 1, wherein the discharge power density of plasma of a gas containing oxygen as a main component is 0.5 W / cm ² or more and 2 W / cm ² or less. 4. A step of forming a semiconductor layer on an insulating substrate, a step of forming a gate insulating layer on the semiconductor layer,
Forming a gate electrode on the gate insulating layer; forming a source region and a drain region by adding an impurity serving as a donor or an acceptor to a partial region of the semiconductor layer; the source region and the drain; A method of manufacturing a thin film transistor, comprising: forming a source electrode and a drain electrode electrically connected to a region, wherein the gate insulating layer contains oxygen as a main component in a silicon oxide thin film formed at a temperature of 600 ° C. or lower. A method of manufacturing a thin film transistor, which comprises irradiating a plasma of a gas having a temperature of 600 ° C. or lower to form the thin film transistor. 5. A step of forming a gate electrode on an insulating substrate, a step of forming a gate insulating layer on the gate electrode, and a step of forming a semiconductor layer on the gate insulating layer,
Forming a source region and a drain region by adding an impurity serving as a donor or an acceptor to a partial region of the semiconductor layer; and forming a source electrode and a drain electrode electrically connected to the source region and the drain region The method of manufacturing a thin film transistor, comprising: irradiating a silicon oxide thin film formed at a temperature of 600 ° C. or lower with plasma of a gas containing oxygen as a main component at a temperature of 600 ° C. or lower. A method of manufacturing a thin film transistor, which comprises: 6. The method of manufacturing a thin film transistor according to claim 4, wherein the discharge power density of plasma of a gas containing oxygen as a main component is 0.5 W / cm ² or more and 2 W / cm ² or less. 7. The method of manufacturing a thin film transistor according to claim 4, wherein the semiconductor layer is formed of a polycrystalline silicon thin film, a microcrystalline silicon thin film, an amorphous silicon thin film, or a single crystal silicon thin film. 8. The method for manufacturing a thin film transistor according to claim 4, 5, 6 or 7, wherein a glass substrate is used as the insulating substrate.