JP3193366B2 - Semiconductor fabrication method - Google Patents

Description

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

[Conventional technology]

Conventionally, polycrystalline semiconductor devices have been developed using low pressure CVD or plasma C
Non-single-crystal semiconductor film formed by VD method at 550 ~ 650 ℃
At a temperature of several hours to several tens of hours and thermally recrystallized to obtain a polycrystalline semiconductor film, which has been manufactured using this polycrystalline semiconductor film.

[Problems of the prior art]

When a non-single-crystal semiconductor film is obtained by a low-pressure CVD method, there is a problem that it is difficult to form a film uniformly on a large-area substrate.

In addition, when a non-single-crystal semiconductor film is obtained by a plasma CVD method, there is a problem that it takes time to form the film.

As a means for solving such a problem, there is a method using a sputtering method.

Particularly in the magnetron type sputtering method, a) electrons are confined near the target by a magnetic field, and damage to the substrate surface by high energy electrons is suppressed.

B) High-speed film formation over a large area at low temperatures.

C) Since no dangerous gas is used, safety and industrial efficiency are high.

There are advantages such as. However, it is known that a non-single-crystal semiconductor film obtained by a sputtering method has a microstructure and is difficult to thermally recrystallize.

In addition, when a polycrystalline semiconductor is obtained by thermally recrystallizing a non-single-crystal semiconductor obtained by a gas phase chemical reaction method or a sputtering method, there is a problem that a substrate must be heated at a temperature of about 600 ° C. for a long time. is there.

As the substrate, it is preferable to use an industrially inexpensive glass substrate, but the temperature around 600 ° C is the strain point of the glass substrate, and thin-film transistors obtained by thermal recrystallization are used for large-area liquid crystal display devices. In this case, the following problem occurs due to the influence of the shrinkage of the glass substrate.

B) Shrinkage of the glass substrate in the thermal recrystallization step changes the photolithography pattern after this step, making it difficult to align the mask in the subsequent step.

B) Shrinkage of the glass substrate in the thermal crystallization step generates stress inside the recrystallized polycrystalline semiconductor. It has been experimentally confirmed that this stress adversely affects the electrical characteristics of the polycrystalline semiconductor.

[Object of the invention]

SUMMARY OF THE INVENTION The present invention is directed to a process of obtaining a polycrystalline semiconductor by thermally recrystallizing a non-single-crystal semiconductor obtained by an industrially useful sputtering method. By solving the problem of shrinkage of the glass substrate at the time of crystallization, and further solving this problem of shrinkage, the generation of stress in the polycrystalline semiconductor during the thermal recrystallization process caused by the shrinkage of the glass substrate is minimized. ,
It is an object of the present invention to improve the electrical characteristics of a semiconductor device formed of a semiconductor provided over the substrate and to clean the surface of a glass substrate without complicating a manufacturing process.

[Configuration of the invention]

The present invention includes a step of heat-treating a glass substrate at a temperature equal to or lower than the strain point of the glass substrate in a nitrogen atmosphere containing hydrogen, and a sputtering method on the glass substrate in an inert gas atmosphere containing hydrogen. A semiconductor manufacturing method including a step of forming a non-single-crystal semiconductor film and a step of crystallizing the non-single-crystal semiconductor film obtained by the sputtering method at a temperature of 600 ° C. or lower.

The heat treatment of the glass substrate at a temperature lower than its strain point in a hydrogen-added nitrogen atmosphere is performed because the glass substrate is subjected to the heat applied in the step of polycrystallizing a non-single-crystal semiconductor provided on the glass substrate. Is to minimize the shrinkage of the semiconductor substrate, and thereby improve the electrical characteristics of the semiconductor provided on the glass substrate.

This is because, due to the shrinkage of the glass substrate due to the heat applied at the time of thermal recrystallization, stress is generated in the polycrystalline semiconductor thermally recrystallized on the glass substrate, and this stress causes This is based on the experimental fact that an interface state in a manufactured polycrystalline semiconductor is increased and electrical characteristics of the polycrystalline semiconductor are reduced.

The reason why hydrogen is added to the inert gas at the time of this heat treatment is to remove hydrogen by a cleaning effect, particularly, adsorbed oxygen adsorbed on the glass substrate.

The heating at the time of this heat treatment is performed in an electric furnace. However, hydrogen in the atmosphere may be activated by using an optical CVD device provided with a heating device to further enhance the effect of cleaning the surface of the glass substrate.

In addition, the step of thermally recrystallizing a non-single-crystal semiconductor by heating it is performed in an electric furnace in an inert gas at atmospheric pressure or in as high a vacuum as possible. For example, when an a-Si film is used as a non-single-crystal semiconductor film,
This is because the characteristics of the p-Si (polycrystalline silicon) film obtained by the recrystallization are not deteriorated due to the bonding of the oxygen atoms to the Si atoms during the thermal recrystallization of the Si film.

Therefore, it is important to perform the heating in the step of thermal recrystallization in an inert gas. This is because it is necessary to prevent the semiconductor from reacting with a gas (eg, oxygen) in the process of thermal recrystallization.

Here, the non-single-crystal semiconductor means an amorphous state,
A non-single-crystal semiconductor in a semi-amorphous state, an incomplete polycrystalline state, and a microcrystalline state.

The incomplete polycrystalline state refers to a state in which crystal growth is insufficient and there is room for crystal growth, and the microcrystalline state refers to a state in which a crystalline state exists in an amorphous state. It points.

The strain point of the glass is 4 × 10 ¹⁴ poise (log
η = 14.5).

The step of forming a non-single-crystal semiconductor film by a sputtering method on the glass substrate in an atmosphere of an inert gas containing hydrogen includes the steps of:
-Si film has few microstructures in the film.
This is based on the result of an experiment conducted by the present inventors that thermal recrystallization can be performed at a temperature of 600 ° C. or less.

Conventionally, a obtained by a sputtering method to which hydrogen is added
Although an example in which a thin film transistor is manufactured using an -Si film is known, its electrical characteristics are known to be low.

Therefore, an a-Si film is generally obtained by a sputtering method without adding hydrogen.

However, the present inventor can prevent the formation of a microstructure in the formed a-Si film by adding hydrogen in the sputtering method.
It has been discovered that it can be thermally recrystallized at temperatures below ℃.

 The present invention is based on this experimental fact.

[Example 1] In this example, in a nitrogen atmosphere containing hydrogen,
Heat-treat the glass substrate at a temperature below its strain point,
Form an a-Si film on a glass substrate by RF sputtering,
It was thermally recrystallized in a nitrogen atmosphere at 600 ° C.

The glass substrate used in this example was Asahi Glass's AN-
A non-alkali glass with a strain point of 616 ° C.

First, a heat treatment was performed on the glass substrate at a temperature of 610 ° C. for 12 hours.

The heat treatment is performed by adding 50% of hydrogen to an inert gas (N ₂ ) at atmospheric pressure in an electric furnace.

Next, an SiO ₂ film was formed to a thickness of 200 nm on the heat-treated glass substrate by a magnetron-type RF sputtering device, and an a-Si film was formed thereon to a thickness of 100 nm by a magnetron-type RF sputtering device. did.

The deposition conditions were as follows: hydrogen partial pressure 0.75 mTorr, argon partial pressure
The target was 3.00 mTorr, RF power 400 W, and a Si target was used.

First, an experimental result on prevention of shrinkage of a glass substrate during heating, which is one of the objects of the present invention, will be described.

FIG. 1 shows the case where the heat treatment was not performed on the glass substrate (AN-2 non-alkali glass) subjected to the heat treatment used in the present embodiment (A) and the glass substrate of the same material (B).
3 shows the temperature dependence of the shrinkage ratio of the glass.

As is clear from FIG. 1, the shrinkage of the glass substrate (A) subjected to the heat treatment is 1/5 or less of the shrinkage of the glass substrate (B) not subjected to the heat treatment.

Also, it can be seen that shrinkage has a temperature dependence of the active form, and tends to increase exponentially with increasing temperature.

FIG. 2 shows a glass substrate (AN-2 non-alkali glass) (A) heat-treated at a temperature of 610 ° C. for 12 hours and an untreated glass substrate (AN-2 non-alkali glass) as in the present embodiment. 3) shows the dependence of the shrinkage ratio of the glass on the heating time when (B) is heated at a constant heating temperature of 600 ° C.

As is clear from FIG. 2, the glass shrinkage is largest for the first few hours, and tends to saturate as the heating time becomes longer.

When heated for 96 hours, the shrinkage of the heat-treated AN-2 non-alkali glass (B) is about 2000 ppm, and the heat-treated A
The shrinkage of the N-2 non-alkali glass (A) was about 500 ppm.

From the above, it can be seen that the heat treatment of the glass substrate in advance can minimize the shrinkage of the glass substrate due to the heat applied in the step of polycrystallizing the non-single-crystal semiconductor provided over the glass substrate.

The active energy of the glass substrate (AN-2 non-alkali glass) determined from the experimental data is about 0.08 eV,
This corresponds to the transition temperature (668 ° C.) of the 2 non-alkali glass, which is considered to be related to the properties of the glass.

To find the active energy from this experimental data,
R = Aexp, which is an equation representing the straight line of the graph shown in FIG.
The relational expression of (−E _a / kT) was used.

A is a proportional constant, the E _a is activation energy, k is Boltzmann's constant.

FIG. 3 shows a heat-treated glass substrate (AN
-2 non-alkaline glass), a 200 nm thick SiO ₂ film is formed by magnetron RF sputtering, and then an a-Si film is formed on the SiO ₂ film by magnetron RF sputtering to form a 100 nm film.
A semiconductor (a) deposited to a thickness of 600 m and thermally recrystallizing the a-Si film at a temperature of 600 ° C. for 96 hours and a glass substrate without heat treatment, Magnetron type
After forming the SiO ₂ film in a thickness of 200nm by an RF sputtering method, an a-Si film by plasma CVD thereon is deposited to a thickness of 100 nm, over 96 hours time at a temperature of 600 ° C. a-S
A semiconductor (b) in which the i-film was thermally recrystallized, and a 200 nm thick SiO ₂ film formed on a quartz substrate by magnetron RF sputtering, and then a was formed thereon by plasma CVD.
Raman spectra of three types of semiconductors (c) in which a-Si films were deposited to a thickness of 100 nm and thermally recrystallized from a-Si films at a temperature of 600 ° C. for 96 hours. Of FIG.

The Raman spectrum indicates the degree of crystallinity by the intensity of the vertical axis and the sharpness of the peak.

As is clear from FIG. 3, the polycrystalline silicon semiconductor (b) provided on the glass substrate which was not heat-treated at a temperature lower than the strain point and the polycrystalline silicon semiconductor (c) provided on the quartz substrate were used. As compared with the film, the crystallinity of the film of the polycrystalline silicon semiconductor (a) provided on the glass substrate which is heat-treated at a temperature lower than its strain point in this embodiment is remarkably strong, and its peak is also higher on the quartz substrate. It can be seen that it sharply emerges at the same position as the provided polycrystalline silicon semiconductor.

Moreover, the comparative examples (b) and (c) are obtained by recrystallizing the a-Si film obtained by the plasma CVD method.

From this, it can be seen that a high-quality polycrystalline silicon film can be obtained by recrystallizing the a-Si film obtained by the magnetron RF sputtering method at a temperature of 600 ° C.

Conventionally, a method provided on a quartz substrate has been regarded as the best method for thermally recrystallizing an a-Si film obtained by a plasma CVD method to obtain a polycrystalline silicon film. Therefore, an a-Si film obtained by magnetron-type RF sputtering was deposited on a glass substrate heat-treated at a temperature below its strain point.
The peak of the Raman spectrum of the polycrystalline silicon semiconductor (a) film obtained by recrystallization at a temperature of 600 ° C. is obtained by thermally recrystallizing an a-Si film obtained by a plasma CVD method on a quartz substrate. It is considered that the sharp appearance at the same position as that of the semiconductor (c) means that the film of the polycrystalline silicon semiconductor (a) obtained in the present example has characteristics as a pure polycrystalline silicon semiconductor.

However, in the structure of the present invention, instead of the above-mentioned sputtering method, a vapor phase chemical reaction method, a vacuum deposition method, an ion cluster beam method, a molecular beam epitaxy method, and a laser ablation method are used to provide a non-single-crystal semiconductor on a heat-treated glass substrate. A non-single-crystal semiconductor may be provided over a glass substrate by using a deposition method or the like.

Hereinafter, in order to show the effect of the magnetron-type RF sputtering method to which hydrogen was added, the present embodiment (A) and the argon partial pressure of 3.75 without adding hydrogen during magnetron-type RF sputtering under the manufacturing conditions of this embodiment (A) were used. The film (D) manufactured at mTorr, the hydrogen partial pressure was 0.15 mTorr and the argon partial pressure was 3.50 mTorr at the time of RF sputtering under the manufacturing conditions of this embodiment (A).
14 shows the results of comparative evaluation of the film (E) produced as (1).

FIG. 4 shows the embodiment (a) and the comparative example (D) described above.
It shows the laser Raman spectrum of (E).
As shown in FIG. 4, the film (D) produced by adding hydrogen during RF sputtering without adding hydrogen and the partial pressure of argon was 3.75 mTorr, and the hydrogen partial pressure was 0.15 mTo
In the film (E) produced at rr and an argon partial pressure of 3.50 mTorr, a peak at 520 cm ⁻¹ indicating the crystallinity of polycrystalline silicon was not observed.

On the other hand, in this example (A), it can be seen that the peak at 520 cm ^-1 indicating the crystallinity of this polycrystalline silicon is remarkably sharp.

This is because the microstructure was removed by adding hydrogen during RF sputtering, and the activation energy required for recrystallization was reduced.

The above experimental results show that there is a minimum hydrogen partial pressure (threshold pressure partial pressure) for thermally recrystallizing a non-single-crystal semiconductor.

Example 2 Hereinafter, an example in which a thermally recrystallized p-SiTFT is manufactured using the present invention will be described with reference to FIG.

In this example, a thermally recrystallized p-Si TFT was formed on a glass substrate (AN-2 non-alkali glass) (1) that had been subjected to a heat treatment at a temperature of 610 ° C. for 12 hours.

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

The heat treatment is performed in an electric furnace in an atmosphere in which 50% of hydrogen is added to an inert gas (N ₂ ) at atmospheric pressure.

Next, an SiO ₂ film (2) is formed to a thickness of 200 nm by magnetron type RF sputtering.

The film formation conditions are a pressure of 0.5 pa, a temperature of 100 ° C., an RF frequency of 13.56 MHz, and an RF output of 400 W in an argon atmosphere.

An a-Si active layer (3) is deposited thereon with a thickness of 100 nm by a magnetron type RF sputtering method.

The deposition conditions were 0.75 Torr of hydrogen partial pressure and 3.00 Torr of argon partial pressure.
In the atmosphere of r, the temperature is 150 ° C, the RF frequency is 13.56 MHz, and the RF output is 400 W.

Thereafter, the a-Si film (3) was thermally recrystallized in a nitrogen atmosphere at a temperature of 600 ° C. for 96 hours.

Thermal recrystallization is performed in an inert gas (N ₂ ) at atmospheric pressure in an electric furnace.

Device separation patterning was performed on the heat-recrystallized heat-recrystallized p-Si to obtain the shape shown in FIG.

Next, an n ⁺ a-Si film (4) was formed to a thickness of 50 nm by a magnetron type RF sputtering method under the following conditions.

The deposition conditions were 0.75 Torr of hydrogen partial pressure and 3.00 Torr of argon partial pressure.
r, PH The temperature is 150 ° C, the RF frequency is 13.56 MHz, and the RF output power is 400 W in an atmosphere having a partial pressure of ₃ Torr and 0.05 Torr.

Thereafter, gate region patterning was performed to obtain the shape shown in FIG.

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

The deposition conditions are pressure 0.5pa, temperature 100 ° C, RF frequency 13.56MH
z, RF output is 400W.

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

Finally, an aluminum electrode (6) was formed to a thickness of 300 nm by vacuum evaporation, and was patterned to obtain the shape of (e), thus completing a p-SiTFT.

Incidentally, in the p-Si TFT shown in FIG.
An rce electrode, G is a Gate electrode, and D is a Drain electrode.

Hereinafter, the p-
SiTFT (a ') and a of FIG. 5 (3) in this embodiment.
FIG. 6 shows the results of comparative evaluation of p-Si TFTs (b ′) obtained by plasma CVD instead of magnetron type RF sputtering for the −Si active layer.

Comparison of the results, I _D -V _G characteristics shown in FIG. 6, the relation between the gate voltage VG and the field effect mobility μ of the specific substrate shown in FIG. 7 was obtained.

As is clear from FIG. 6, the p-SiTFT of this embodiment is
(A ') is, p-SiTFT (b Comparative Example' compared to), the drain current (I _D) - no significant difference in the gate voltage (V _G) characteristics, its electrical properties are substantially the same.

7, it can be seen that the field effect mobility μ shows the same value in the example and the comparative example.

From the above, the characteristics of p-Si TFT using p-Si (polycrystalline silicon) film obtained by thermal recrystallization of a-Si film obtained by magnetron type RF sputtering method and obtained by PCVD method -Si using p-Si thermally recrystallized a-Si film
It turned out that the characteristics of the TFT were almost the same.

Next, the effect of heat treatment of the glass substrate in a nitrogen atmosphere to which hydrogen has been added will be described.

FIG. 8 shows a p-SiTFT (a ') according to an embodiment of the present invention and a glass substrate (Asahi Glass AN
Drain current (I _p ) with p-SiTFT (d ′) fabricated on the same method as in this example on (−2 non-alkali glass).
It shows the gate voltage (V _G ) characteristics.

FIG. 8 shows a p-SiTFT according to an embodiment of the present invention.
It can be seen that the characteristic of (a ′) is better than the p-SiTFT (d ′) of the comparative example. This is because oxygen atoms on the glass substrate, which deteriorate the electrical characteristics of p-SiTFT, were etched by hydrogen.

Conventionally, the glass substrate was cleaned in a separate process after the heat treatment process.In view of the fact that simplification of the process is a major industrial problem when manufacturing TFTs, this inert Heat treatment of a glass substrate in a gas is very effective.

Note that a glass substrate that had been subjected to ultrasonic cleaning before heat treatment was used.

It was also effective to perform the thermal recrystallization in an inert atmosphere at atmospheric pressure or reduced pressure to which hydrogen or carbon monoxide was added. For reference, FIG. 9 shows the drain current (I _D ) -gate of p-SiTFT obtained by performing the thermal recrystallization in the process of this embodiment in a nitrogen atmosphere at atmospheric pressure containing 50% of carbon monoxide. It shows the characteristics of voltage (VG). Note that the concentration of hydrogen or carbon monoxide may be 50% or more.

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

〔The invention's effect〕

By adopting the structure of the present invention, a high-quality polycrystalline semiconductor can be obtained by thermally recrystallizing a non-single-crystal semiconductor obtained by a sputtering method having excellent safety and industrial properties. P-Si with high characteristics using semiconductor
I got TFT.

In addition, by solving the problem of shrinkage of the glass substrate, which is a problem in the thermal recrystallization step, it is possible to suppress the generation of internal stress generated in the polycrystalline semiconductor provided on the glass substrate and obtained by thermal recrystallization. did it. As a result, the electrical characteristics of a semiconductor device made of a polycrystalline semiconductor provided on a glass substrate could be improved.

Furthermore, the surface of the glass substrate can be cleaned at the same time as the heat treatment of the glass substrate, and an industrially useful effect can be obtained without complicating the steps in manufacturing a semiconductor device.

[Brief description of the drawings]

FIG. 1 shows the temperature dependence of the glass shrinkage rate of the glass substrate manufactured in the first embodiment. FIG. 2 shows the time dependence of the glass shrinkage rate of the glass substrate manufactured in the first embodiment. FIG. 3 shows the effect of the heat treatment of the glass substrate, Example 1
3 shows Raman spectra of a semiconductor on a glass substrate manufactured in the above Example and a comparative example. FIG. 4 shows Raman spectra of this example and a comparative example showing the effect of the sputtering method to which hydrogen was added. FIG. 5 shows a manufacturing process of the p-Si TFT manufactured in the second embodiment. Figure 6 shows the I _D (drain current) -V _G (gate voltage) characteristics of the p-SiTFT a comparative example with p-SiTFT prepared in Example 2. Figure 7 shows the relationship between V _G of p-SiTFT a comparative example with p-SiTFT prepared in Example 2 (gate voltage) field effect mobility mu. Figure 8 is shows the effect of cleaning by the hydrogen of the glass substrate surface, I _D (drain current) of the p-SiTFT a comparative example with p-SiTFT prepared in Example 2 -V _G (gate voltage) characteristics It is shown. FIG. 9 shows a reference example obtained by thermal recrystallization of a non-single-crystal semiconductor film in a hydrogen-added nitrogen atmosphere.
Shows the I _D (drain current) -V _G (gate voltage) characteristics of the Si TFTs. (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 (3)

(57) [Claims] 1. A non-single-crystal semiconductor film is formed on a glass substrate by heat-treating the glass substrate at a temperature not higher than its strain point in an inert gas atmosphere containing hydrogen. A semiconductor manufacturing method, characterized by crystallizing a film. 2. In a hydrogen-containing inert atmosphere, a glass substrate is heat-treated at a temperature equal to or lower than its strain point, an insulating film is formed on the glass substrate, and a non-single-crystal semiconductor film is formed on the insulating film. A semiconductor manufacturing method, comprising: forming a film; and crystallizing the non-single-crystal semiconductor film. 3. A heat treatment of a glass substrate at a temperature below its strain point in an inert atmosphere containing hydrogen, forming an insulating film on the glass substrate, and forming a non-single-crystal semiconductor film on the insulating film. Is formed by sputtering, and the non-single-crystal semiconductor film is crystallized at a temperature of 600 ° C. or lower.