JP2535654B2 - Method of manufacturing thin film transistor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for manufacturing a thin film transistor using a polycrystalline semiconductor.

[Prior Art] A technique for obtaining a polycrystalline semiconductor by thermally recrystallizing an amorphous silicon semiconductor obtained by a vapor phase chemical reaction method or a sputtering method is known.

[Problems of conventional technology]

When a polycrystalline semiconductor is obtained by thermally recrystallizing an amorphous silicon semiconductor obtained by a vapor phase chemical reaction method or a sputtering method, the substrate must be heated at a temperature of about 600 ° C. for a long time.

As the substrate, it is preferable to use an industrially inexpensive glass substrate, but the strain point temperature of the glass substrate is about 600 ° C., and the thin film transistor obtained by thermal recrystallization is used for a large area liquid crystal display device or the like. When applied, the following problems arise due to the shrinkage of the glass substrate.

B) Due to the shrinkage of the glass substrate in the thermal recrystallization step, the photolithography pattern after this step is deformed, and mask alignment in the subsequent step becomes difficult.

B) Due to the shrinkage of the glass substrate in the thermal recrystallization process,
Stress is generated inside the recrystallized polycrystalline semiconductor. It has been experimentally confirmed that this stress adversely affects the electrical characteristics of the polycrystalline semiconductor.

In addition, there is a problem that oxygen is mixed in the non-single-crystal semiconductor layer again in the thermal recrystallization step.

For example, an a-Si semiconductor is likely to combine with oxygen, and when an a-Si semiconductor layer mixed with oxygen is thermally recrystallized to obtain a p-Si (polycrystalline silicon) film, the p-Si (polycrystalline silicon) The electrical characteristics will be extremely low.

Conventionally, a method of performing a thermal recrystallization step in an ultra-high vacuum state has been known, but it is not industrially suitable because a large effect cannot be obtained and the step becomes complicated.

[Object of the Invention]

The present invention solves the problem of shrinkage of a glass substrate, which is a problem in the step of obtaining a polycrystalline semiconductor by thermally recrystallizing a non-single crystal semiconductor obtained by a vapor phase chemical reaction method or a sputtering method, And minimizing the occurrence of stress in the polycrystalline semiconductor in the thermal recrystallization step due to the shrinkage of the glass substrate, and improving the electrical characteristics of the thin film transistor, which is a semiconductor device made of a semiconductor provided on this substrate. It is an object of the present invention to eliminate the influence of oxygen upon thermal recrystallization of a non-single crystal semiconductor by an effective and inexpensive method.

[Structure of Invention]

The present invention includes a step of heat-treating a glass substrate at a temperature equal to or lower than a strain point of the glass substrate in a step of manufacturing a thin film transistor, and a non-single-crystal semiconductor layer which is an active layer directly or indirectly on the heat-treated glass substrate. And heating at least a part of the non-single-crystal semiconductor layer in hydrogen or carbon monoxide or in an atmosphere of an inert gas to which hydrogen or carbon monoxide is added to crystallize the channel formation region. A method of manufacturing a thin film transistor, comprising the steps of obtaining.

The heat treatment of the glass substrate at a temperature below its strain point is
The shrinkage of the glass substrate with respect to the heat applied in the step of polycrystallizing the non-single crystal semiconductor provided on the glass substrate is minimized, and further, the electrical characteristics of the semiconductor provided on the glass substrate are thereby reduced. Is to improve.

This is because the shrinkage of the glass substrate due to the heat applied during the thermal recrystallization causes stress in the thermally recrystallized polycrystalline semiconductor on the glass substrate, which causes the stress on the substrate. This is based on the experimental fact that the interface state in the produced polycrystalline semiconductor becomes high and the electrical characteristics of the polycrystalline semiconductor deteriorate.

The heat treatment is performed in order to change the property of the glass substrate with respect to heat by preheating the glass substrate.

The heating during this heat treatment is performed in an electric furnace in an inert gas at atmospheric pressure.

The step of thermally recrystallizing a non-single crystal semiconductor by heating is performed in an electric furnace.

Polycrystallization by heating in the recrystallization step by heating in an atmosphere of hydrogen or carbon monoxide or an inert gas to which hydrogen or carbon monoxide is added causes polycrystallization or polycrystallization. This is to prevent the semiconductor from reacting with oxygen in the process of thermal recrystallization.

The non-single-crystal semiconductor here means an amorphous state,
It refers to a semiconductor in a semi-amorphous state, a microcrystalline state, and an incomplete polycrystalline state with room for further recrystallization.

In addition, the microcrystalline state means a state in which crystalline states are scattered in an amorphous state.

The step of providing a non-single-crystal semiconductor refers to a step of providing a non-single-crystal semiconductor by a vapor phase chemical reaction method, a sputtering method, a vacuum deposition method, an ion cluster beam method, a molecular beam epitaxy method, a laser ablation method, or the like.

The strain point of glass is that the viscosity of glass is 4 × 10 ¹⁴ poise (log
It is defined as the temperature when η = 14.5).

〔Example〕

Hereinafter, a coplanar thermal recrystallization p-Si according to the present invention will be described.
An example of manufacturing a TFT (polycrystalline silicon thin film transistor) will be described with reference to FIG.

In this example, a thermally recrystallized p-Si TFT was produced on a glass substrate (AN-2 non-alkali glass) (1) which was heat-treated at a temperature of 610 ° C. for 12 hours.

First, a glass substrate (AN-2 non-alkali glass) is heat-treated at a temperature of 610 ° C. for 12 hours.

The heat treatment method is performed in an electric furnace in an inert gas (N ₂ ) at atmospheric pressure.

Further, this heat treatment was also carried out in hydrogen or carbon monoxide or in an inert gas to which hydrogen or carbon monoxide was added to wash adsorbed oxygen on the glass substrate.

Next, the SiO ₂ film (2) is formed to a thickness of 200 nm by the RF sputtering method.

Film forming conditions are pressure 0.5pa, temperature 100 ℃, RF frequency 13.56MH.
z, RF output is 400W.

An a-Si active layer (3) is deposited on top of it by RF sputtering.
Deposit to a thickness of 0 nm.

Film forming conditions are pressure 0.5pa, temperature 150 ℃, RF frequency 13.56MH.
z, RF output is 400W.

Then, the a-Si film (3) was thermally recrystallized at a temperature of 600 ° C. for 96 hours in a nitrogen atmosphere containing 50% of carbon monoxide.

 Thermal recrystallization was carried out at atmospheric pressure in an electric furnace.

Device separation patterning was performed on the thermally recrystallized thermally recrystallized p-Si to obtain the shape of (a). Note that (3) in FIG. 1 is a crystallized channel formation region.

Next, the n ⁺ a-Si film (4) was formed into a film with a thickness of 50 nm by the PCVD method under the following conditions.

Film forming conditions are pressure 6.65pa, temperature 350 ℃, RF frequency 13.56M.
Hz, RF output 400W, PH ₃ (5%): SiH ₄ : H ₂ = 0.2: 0.3: 50sccm
Is.

Then, gate region patterning was performed to form the shape of (b).

Next, a gate oxide film (SiO ₂ ) (5) having a thickness of 100 nm was formed by the sputtering method under the following conditions to obtain the shape of (c).

Film formation conditions are pressure 0.5pa, temperature 100 ℃, RF frequency 13.56M.
Hz, RF output is 400W.

Next, contact hole opening patterning was performed to obtain the shape of (d).

Finally, an aluminum electrode (6) was formed to a thickness of 300 nm by vacuum vapor deposition and patterned to obtain the shape of (e) to complete the p-Si TFT.

In the p-Si TFT shown in FIG. 1 (e), S is Sou
rce electrode, G is a Gate electrode, and D is a Drain electrode.

In order to show the effect of heat treatment of the glass substrate, which is a component of the present invention, p-SiTFT (7) of this example and a glass substrate (Asahi Glass AN-2 non-alkali glass) that has not been heat treated are shown below. P-Si manufactured by the same method as in the example
The results of three types of comparative evaluation of the TFT (8) and the p-Si TFT (9) manufactured on the quartz substrate by the same method as in this example are shown.

As a result of the comparative evaluation, the I _D -V _G characteristics as shown in FIG. 2, the relationship between the gate voltage V _G and the field effect mobility μ for each substrate shown in FIG. 3, and the field effect transfer as shown in FIG. A board-dependent surname of degree μ was obtained.

As is clear from FIG. 2, the p-Si TFT of the present embodiment.
(7) is a glass substrate that has not been heat-treated (AN of Asahi Glass
-2 compared with non-alkali glass) was produced in this example a similar way to the top p-SiTFT (8), the drain current (I _D) - gate voltage characteristics (V _G) has been improved greatly, the The electrical characteristics are p-Si provided on the quartz substrate.
It can be seen that it is approaching the TFT (9).

In addition, referring to FIGS. 3 and 4, p− prepared by the same method as that of this example on a glass substrate (AN-2 non-alkali glass of Asahi Glass) whose field effect mobility μ was not heat-treated.
It can be seen that it is larger than the SiTFT (8) and shows the same value as the field effect mobility of the p-SiTFT (9) provided on the quartz substrate.

Hereinafter, a step of polycrystallizing the non-single-crystal semiconductor film, which is one of the constituent elements of the present invention, by heating in an atmosphere of hydrogen or carbon monoxide or an inert gas to which hydrogen or carbon monoxide is added Shows the effect of.

The p-SiTFT (7) of the present example and the p-SiTFT (7) of the comparative example in which the thermal recrystallization step was performed in an atmosphere of 100% nitrogen.
-SiTFT drain current (I _D) of (10) - shows the gate voltage characteristics (V _G) in FIG. 5.

It can be seen from FIG. 5 that the characteristics of the p-SiTFT (7) of this example are significantly higher than those of the p-SiTFT (10) of the comparative example.

In addition, the p-Si TFT obtained by the process shown in this example
A field effect mobility of (7) of 120 cm ^-2 / V _s or more was obtained at a rate of 10% or more in the finished product excluding defective products. The field effect mobility of p-SiTFT (10) obtained by the process of obtaining SiTFT is 1
Nothing over 00 cm ^-2 / V _s was obtained.

This is considered to be because oxygen was completely removed by the oxidative action of carbon monoxide when recrystallized in an atmosphere of 50% carbon monoxide at 600 ° C. for 96 hours.

Furthermore, the shrinkage of the glass substrate in the thermal recrystallization process is 1/5 or less compared to the conventional glass substrate without heat treatment, so the mask alignment error in the photolithography process is 1/5 or less compared to the conventional method. One of the characteristics of p-Si TFTs by recrystallization is that the advantage of being able to collectively fabricate p-Si TFTs in the same process over a large area could be further enhanced.

In this example, the starting material for thermally recrystallizing the a-Si semiconductor provided on the glass substrate was used, but the present invention provides a non-single crystal semiconductor other than the a-Si semiconductor on the glass substrate. It is also effective in some cases.

In addition, although a coplanar type thin film transistor was manufactured in this example, heat treatment of a glass substrate which is a feature of the present invention and heating in an atmosphere of hydrogen or carbon monoxide or an inert gas to which hydrogen or carbon monoxide is added are performed. In order to obtain a thin film transistor by crystallizing a non-single crystal semiconductor, a method of producing a thin film transistor using a polycrystalline semiconductor layer of another type, that is, a staggered type, an inverted staggered type, an inverted coplanar type, etc. Is also useful.

〔The invention's effect〕

With the structure of the present invention, a non-single crystal semiconductor obtained by a vapor phase chemical reaction method, a sputtering method, or the like is thermally recrystallized, which causes a problem in a step of obtaining a polycrystalline semiconductor. The problem of shrinkage can be solved, and the difficulty of mask alignment due to the shrinkage of the glass substrate in the photolithography process, which was a problem in the prior art, can be significantly improved.

Further, by performing heat treatment on the glass substrate to reduce shrinkage of the glass substrate at the time of heating, generation of internal stress generated in a polycrystalline semiconductor which is provided on this substrate and obtained by thermal recrystallization can be suppressed. It was possible to improve the electrical characteristics of the semiconductor device made of this polycrystalline semiconductor.

Furthermore, by carrying out the thermal recrystallization step in an atmosphere of hydrogen or carbon monoxide or an inert gas to which hydrogen or carbon monoxide is added, the influence of oxygen on the semiconductor layer, which is a big problem in the prior art, is reduced. It can be effectively eliminated without increasing, and a thin film transistor having high electric characteristics can be obtained.

[Brief description of drawings]

FIG. 1 shows a manufacturing process of the p-Si TFT manufactured in this example. And p-SiTFT manufactured in FIG. 2 embodiment shows a I _D (drain current) -V _G (gate voltage) characteristics of the p-SiTFT are comparative examples. FIG. 3 shows the gate voltage V _G and the field effect mobility μ of the p-Si TFT manufactured in this example and the p-Si TFT of the comparative example.
It shows the relationship with. FIG. 4 shows the field effect mobility μ of the p-SiTFT manufactured in the example and the p-SiTFT of the comparative example. Figure 5 is shows the effect of thermal recrystallization in inert gas from which carbon monoxide has been added, the I _D (drain current) -V _G (gate voltage) characteristics of a comparative example with the present embodiment It is shown. (1) …… Glass substrate (2) …… SiO ₂ film (3) …… a-Si active layer (4) …… n ⁺ a-Si film (5) …… Gate oxide film (SiO ₂ ) (6) ) …… Aluminum electrode (S) …… Source electrode (G) …… Gate electrode (D) …… Drain electrode

Claims (1)

(57) [Claims] 1. A step of manufacturing a thin film transistor, a step of heat-treating a glass substrate at a temperature not higher than a strain point of the glass substrate, and a non-single-crystal semiconductor which is an active layer directly or indirectly on the heat-treated glass substrate. A step of providing a layer, and at least a part of the non-single-crystal semiconductor layer is crystallized by heating it in an atmosphere of hydrogen or carbon monoxide or an inert gas to which hydrogen or carbon monoxide is added to crystallize the channel formation region. A method for manufacturing a thin film transistor, comprising the step of: