JPH1055963A - Method for forming non-single crystal semiconductor thin film and forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a semiconductor layer with high resistance at such a temperature that a glass substrate is used by dissolving a non-film formation gas by plasma and introducing into a reaction chamber a film formation gas containing atoms constituting mainly a non-single crystal semiconductor thin film a specified time after the non-film formation gas is introduced. SOLUTION: A non-film formation gas is introduced into a reaction chamber 10, and it is applied with high frequency while synchronizing it with the introduction of the non-film formation gas. As a result, a plasma is formed and a non- film formation gas is dissolved by the plasma. Next, a film formation gas is introduced into the reaction chamber 10 a specified time after the introduction of non-film formation gas. The film formation gas reacts with a dissolved substance of the non-film formation gas and a non-single crystal semiconductor thin film is formed on a substrate 13 to be treated which is housed in the reaction chamber 10. The film formation gas contains atoms constituting mainly a non-single crystal semiconductor thin film, and an SiH4 , etc., are used for forming film of polycrystal silicon. The non-film formation gas is an inactive gas or hydrogen, or halogen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for forming a non-single-crystal semiconductor thin film on a substrate to be processed by utilizing a chemical vapor reaction, and more particularly, to a method and an apparatus formed by such a method and apparatus. The present invention relates to a thin film transistor using a non-single-crystal semiconductor thin film and an active matrix liquid crystal display device using the thin film transistor.

[0002]

2. Description of the Related Art Since display devices such as electroluminescence, light emitting diodes, plasma displays, fluorescent display tubes, and liquid crystal display devices can be made thinner, display devices such as office equipment and computers or special display devices. There is a growing demand for applications to various display devices.

[0003] Among these display devices, a thin film transistor (Thin Film Transistor:
An active matrix type liquid crystal display (Active Ma) using a TFT as a pixel switching element.
trix-Liquid Crystal Displ
ay: AM-LCD) is expected as a display with high image quality, high quality, and low power consumption, and is being researched and developed by each company.

A pol using polycrystalline silicon (poly-Si) as a channel active layer of a TFT for AM-LCD.
The y-SiTFT has a high mobility of a channel active layer and can have high definition when applied to a pixel TFT. Further, the y-SiTFT can be used not only as a pixel switching element but also as a peripheral driving circuit for controlling the pixel TFT. There is a transfer that can be used. Therefore, the poly-Si TFT is
The peripheral driving circuit portion can be formed simultaneously with the pixel portion (a driving circuit integrated LCD), so that the mounting cost of the driving circuit chip can be reduced and the frame can be narrowed.

At present, commercially available drive circuit integrated type LC
D is a small and medium-sized display used for a projection type display and a viewfinder. In the manufacturing process, a high-temperature process is used because a solid-phase growth method (a process of about 600 ° C.) or a thermal oxide film (a process of 900 ° C. or more) is used for forming a poly-Si film. Therefore, it is required to use an expensive quartz substrate or a high heat-resistant substrate.

Therefore, a poly-Si film and a gate oxide film equivalent to those obtained by a high-temperature process are formed by a-Si film.
(Amorphous silicon) If low-cost large-area glass substrates used in TFTLCDs can be formed in a low-temperature process of 450 ° C or less (temperature that glass substrates can withstand), cost reduction and throughput improvement such as multi-panel LCD panels The effect is great.

[0007] Excimer laser annealing (Excimer Laser Anneal) is used as a poly-Si film forming technique and an impurity activating technique by a low temperature process.
1: The crystallization technology and activation technology of an a-Si film by ELA) have been studied. According to this technique, the a-Si film is instantaneously melted and crystallized, so that heat damage to the substrate is small,
Use of a low-cost glass substrate becomes possible.

A part of a cross-sectional structure of a general liquid crystal display device using a poly-Si TFT will be described with reference to FIG. This liquid crystal display device is manufactured as follows.
First, after a transparent insulating film 101 is coated on a transparent insulating substrate 100, an a-Si: H film is formed on the transparent insulating film 101 to a thickness of 50 nm by, for example, a conventional plasma CVD method. : Dehydrogenation is performed by performing thermal annealing on the H film, and then the a-Si film is instantaneously heated and melted by ELA to be changed to a poly-Si film, whereby the high-resistance semiconductor layer 102 serving as a channel is formed. You.

[0010] In contact with the high-resistance semiconductor layer 102, there are low-resistance semiconductor layers 103 and 104, which are made of poly-S
It is formed by injecting impurities such as P into the i-film and then activating it by heat or the like. High resistance semiconductor layer 102
On top are normal pressure CVD (APCVD) and plasma CVD
(PECVD), electron cyclotron resonance (ECR)-
The gate insulating film 106 has a thickness of 70 n
It is formed to a thickness of m to 100 nm.

The gate electrode 1 is formed on the gate insulating film 106.
08 is provided. Further, the low-resistance semiconductor layer 103,
A source electrode 109 and a drain electrode 110 are connected to 104, respectively. An interlayer insulating film 111 is formed to insulate the gate electrode 108 from the source electrode 109 and the drain electrode 110. The pixel electrode 113 made of a transparent conductive film such as ITO is connected to the drain electrode 110.

The liquid crystal display device configured as described above has the following problems. That is, in the crystallization step of the a-Si film by excimer laser annealing, it is difficult to increase the diameter of the excimer laser, and it is necessary to irradiate the laser repeatedly. At that time, irradiation unevenness occurs due to fluctuation of the laser between shots. As a result, the liquid crystal display device has a problem in that the screen is blurred (uneven) and it is difficult to obtain a good display. As a measure for solving such a problem, a method of forming a high-resistance semiconductor layer without using an ELA process has been studied, but a satisfactory method has not yet been obtained.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it has been possible to form a high-resistance semiconductor layer at a temperature at which a glass substrate can be used, and to reduce display deterioration. It is an object of the present invention to provide a method and an apparatus for forming a thin film, which make it possible to obtain a liquid crystal display device having excellent display characteristics.

[0013]

In order to solve the above problems, the present invention (claim 1) provides a non-single-crystal semiconductor thin film in a reaction chamber for accommodating a substrate on which a non-single-crystal semiconductor thin film is formed. Introducing a non-film-forming gas that does not contain atoms mainly comprising forming a plasma by applying a high frequency to the non-film-forming gas in synchronization with the introduction of the non-film-forming gas; A predetermined time after the introduction of the non-film-forming gas and the introduction of the non-film-forming gas, a film-forming gas containing atoms mainly constituting the non-single-crystal semiconductor thin film is introduced into the reaction chamber, and the non-single-crystal There is provided a method for forming a non-single-crystal semiconductor thin film, comprising a step of forming a semiconductor thin film.

Further, according to the present invention (claim 2), a film forming gas containing atoms mainly constituting a non-single-crystal semiconductor thin film is supplied into a reaction chamber for accommodating a substrate on which a non-single-crystal semiconductor thin film is formed. Introducing, in synchronization with the introduction of the film forming gas, applying a high frequency to the film forming gas to form a plasma,
A step of decomposing the film forming gas by this plasma, and after a predetermined time from the introduction of the film forming gas, into the reaction chamber,
There is provided a method for forming a non-single-crystal semiconductor thin film, comprising a step of introducing a non-film-forming gas not containing atoms mainly constituting the non-single-crystal semiconductor thin film.

Further, the present invention (Claim 3) is characterized in that in the above-described method for forming a non-single-crystal semiconductor thin film (Claim 1 or 2), a series of steps is repeated a plurality of times.
Further, the present invention (claim 4) provides a reaction chamber in which a substrate to be processed is accommodated, and a deposition gas supply flow for supplying a deposition gas containing atoms mainly constituting a non-single-crystal semiconductor thin film to the reaction chamber. A passage, a film-forming gas exhaust passage connected to the film-forming gas supply passage for exhausting the film-forming gas, and a non-film-forming film containing no atoms mainly constituting a non-single-crystal semiconductor thin film in the reaction chamber. A non-deposition gas supply flow path for supplying gas; a non-deposition gas exhaust flow path connected to the non-deposition gas supply flow path for discharging the non-deposition gas; Means for forming a plasma by introducing high frequency or microwave into the film forming gas, and alternately supplying the film forming gas and the non-film forming gas to the reaction chamber, and reducing the pressure fluctuation in the reaction chamber. Then, the supply of the film forming gas and the non-film forming gas to the reaction chamber is cut off. For example, to provide a forming apparatus of a non-single-crystal semiconductor thin film characterized by comprising a means for switching the supply and exhaust of the reaction chamber of the film forming gas and / or non-film gas.

The present invention (claim 5) provides a high-resistance semiconductor layer formed on a substrate, a gate electrode formed on the high-resistance semiconductor layer via a gate insulating film, and the high-resistance semiconductor layer. A low-resistance semiconductor layer formed on both sides of the layer, and a source electrode and a drain electrode electrically connected to the low-resistance semiconductor layer, wherein the high-resistance semiconductor layer is formed of the non-single-crystal semiconductor thin film described above. There is provided a thin film transistor formed by a forming method (claim 1, 2 or 3).

Further, according to the present invention (claim 6), a pair of substrates arranged to face each other, a pixel display portion electrode arranged in a matrix on one of the opposing surfaces of the pair of substrates, A switching transistor formed on a pixel display portion of the one substrate and connected to the pixel display portion electrode; and a liquid crystal layer sealed between the pair of substrates. A liquid crystal display element characterized by the above-mentioned thin film transistor (claim 4).

Hereinafter, the present invention will be described in more detail. The deposition gas refers to a gas containing atoms mainly constituting a non-single-crystal semiconductor thin film. When amorphous silicon or polycrystalline silicon is deposited, a hydrogen derivative of silicon such as SiH ₄ or SiF _And halogen derivatives of silicon such as ₄ .

The non-film-forming gas means a gas which does not contain atoms mainly constituting the non-single-crystal semiconductor thin film, and includes an inert gas such as nitrogen, helium, and argon, and a halogen such as hydrogen and fluorine.

The high frequency introduced into the non-film-forming gas is 13.
It can be 56 MHz, 27.12 MHz, or 400 MHz. In case of 13.56 MHz high frequency, power
Is 20 W to 1500, and the power density is 50 mW / cm
^It is preferably ^{2 to} 100 mW / cm ² . The duty ratio is about 5 to 95%, and the frequency is 5 kHz to 20%.
It is also possible to use a pulse-modulated high frequency whose power changes like a 0 kHz pulse.

The first invention provides a method for forming a non-single-crystal semiconductor thin film. In this method, a non-deposition gas is first introduced into a reaction chamber, and then a high frequency is applied to the non-deposition gas in synchronization with the introduction of the non-deposition gas. As a result, plasma is formed, and the non-film-forming gas is decomposed by the plasma. Next, a predetermined time after the introduction of the non-film-forming gas, the film-forming gas is introduced into the reaction chamber. Then, a decomposition product of the non-film-forming gas reacts with the film-forming gas to form a non-single-crystal semiconductor thin film on the substrate to be processed accommodated in the reaction chamber.

Preferred embodiments of the first invention include the following. (1) By the reaction between the decomposed non-film-forming gas and the film-forming gas,
A non-single-crystal semiconductor thin film is formed on a substrate to be processed.

(2) The introduction of the non-deposition gas is stopped simultaneously with the introduction of the deposition gas. (3) The high frequency is applied in a pulse form. (4) The non-deposition gas is introduced in synchronization with ON of the pulsed high frequency, the introduction of the non-deposition gas is stopped in synchronization with OFF, and the deposition gas is introduced, and in synchronization with the next ON. The introduction of the deposition gas is stopped.

(5) The non-film-forming gas is introduced in synchronization with the ON of the pulsed high frequency, the introduction of the non-film-forming gas is stopped within 5 seconds after the OFF, and the film-forming gas is introduced. (6) The introduction and stop of the non-film-forming gas and the introduction and stop of the film-forming gas are repeatedly performed a plurality of times.

(7) The non-film forming gas is H ₂ , and the film forming gas is SiH ₄ or a mixed gas of SiH ₄ and SiF ₄ . (8) non-film gas is H _2, the film forming gas is SiH _4, the flow rate ratio of the H ₂ and SiH ₄ is 2: 1 to 200: 1
That.

A second invention provides a method for forming a non-single-crystal semiconductor thin film. In this method, a deposition gas is first introduced into a reaction chamber, and a high frequency is applied to the deposition gas in synchronization with the introduction of the deposition gas. As a result, plasma is formed, and the film-forming gas is decomposed by the plasma. Thereafter, a predetermined time after the introduction of the deposition gas,
A non-deposition gas is introduced to form a polycrystalline semiconductor thin film on the substrate.

Preferred embodiments of the second invention include the following. (1) An amorphous semiconductor and a polycrystalline semiconductor are deposited on a substrate to be processed by decomposition of a deposition gas by plasma,
Amorphous semiconductor is removed by supplying a non-deposition gas, and a polycrystalline semiconductor thin film is formed on a substrate to be processed.

(2) The introduction of the film forming gas is stopped simultaneously with the introduction of the non-film forming gas. (3) The high frequency is applied in a pulse form. (4) The film forming gas is introduced in synchronization with the ON of the pulsed high frequency, the introduction of the film forming gas is stopped in synchronization with the OFF, and the non-film forming gas is introduced.

(5) The film forming gas is introduced in synchronization with the ON of the pulsed high frequency, the introduction of the film forming gas is stopped within 5 seconds from the OFF, and the non-film forming gas is introduced. (6) The introduction and stop of the non-film-forming gas and the introduction and stop of the film-forming gas are repeatedly performed a plurality of times.

(7) The non-film-forming gas is SiF ₄ , the film-forming gas is SiH ₄ , and the flow rate ratio between H ₂ and SiH ₄ is:
2: 1 to 200: 1. A third invention provides an apparatus for forming a non-single-crystal semiconductor thin film. The apparatus includes a reaction chamber in which a substrate to be processed is stored,
A gas supply system for supplying a film-forming gas and a non-film-forming gas to the reaction chamber, and means for introducing a high frequency or microwave to the film-forming gas and / or the non-film-forming gas to form plasma are provided. .

In particular, the gas supply system is provided with two paths, a path for supplying a deposition gas to the reaction chamber and a path for supplying a non-deposition gas to the reaction chamber, and a valve is provided so that each can be switched. Installed. An exhaust path is connected to each path, and a valve is attached so that supply and exhaust to the reaction chamber can be switched.

That is, by operating such a valve, a path for supplying the film-forming gas and a path for supplying the non-film-forming gas to the reaction chamber are switched. The supply and exhaust of the film-forming gas and the non-film-forming gas to and from the reaction chamber are switched so as to suppress the fluctuation, and the total flow rate of the gas flowing through each flow path is always kept constant.

In order to keep the total flow rate of the gas flowing through each flow path constant, it is preferable that the conductance of the flow path to the reaction chamber and the conductance of the exhaust flow path be the same.

An apparatus for forming a non-single-crystal semiconductor thin film according to the present invention comprises:
The present invention is not limited to a normal plasma CVD apparatus using a high frequency, that is, RF, but is applied to a plasma CVD using a microwave electron cyclotron (ECR) plasma in which a plasma formed by a microwave and an electron impact action by a magnetic coil are combined. It is also possible.

According to a fourth aspect, there is provided a thin film transistor including a high-resistance semiconductor layer formed by the method according to the first or second aspect. In a fifth aspect,
A liquid crystal display element using such a thin film transistor as a switching transistor is provided.

As described above, according to the present invention, E
Without using the poly-Si forming process by LA,
Plasma CVD at a temperature at which glass substrates can be used
It is possible to form a high resistance semiconductor layer by the method,
This makes it possible to efficiently obtain a liquid crystal display element having good display characteristics without display deterioration of the display device due to uneven shot of ELA.

[0037]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is a view schematically showing a non-single-crystal semiconductor thin film manufacturing apparatus according to this embodiment. In FIG. 1, an upper electrode 11 and a lower electrode 12 are disposed in a reaction chamber 10 in which a thin film is formed. On the lower electrode 12, a transparent insulating substrate such as a glass or quartz substrate is provided. The processing substrate 13 is placed. Further, a gas supply unit 14 for supplying a source gas used for forming a thin film and an exhaust unit 15 for evacuating the reaction chamber 10 to a vacuum are connected to the reaction chamber 10.

The gas supply unit 14 includes a plurality of pipes, three mass flow controllers (MFC-1 to MFC-3) attached to these pipes for controlling the gas flow rate, and five valves (valve-1). ~ Valve-5) and these MFCs
And a gas controller 16 for controlling the operation of the valve
It is composed of

The upper electrode 11 is connected to a high-frequency power supply for supplying energy for decomposing the raw material gas introduced into the reaction chamber 10 and a control for temporally controlling ON / OFF of the high-frequency power supply. A heater 18 for heating the substrate 13 to be processed is built in the lower electrode 12.

The gas controller 16 of the gas supply unit 14
The control unit 17 is connected to a high-frequency power supply / control device 19 for controlling these. Next, the operation of the non-single-crystal semiconductor thin film manufacturing apparatus configured as described above will be described with reference to the flow chart of the source gas (opening / closing procedure of the valve) and the on / off time chart of the high frequency power supply shown in FIG. explain.

First, after setting the substrate 13 on the lower electrode 12 in the reaction chamber 10, the exhaust system 15 is
To a desired degree of vacuum in the reaction chamber 10, for example, 5 × 10 ^−6.
Exhaust to Torr or less. Next, the valve-1, the valve 2a, and the valve 3b are opened. In this state, gas 1 and gas 2 are introduced into the reaction chamber 10. At the same time, the gas 3 is exhausted by the exhaust system 22 without passing through the reaction chamber 10.

Here, the flow rates of the gas 2 and the gas 3 are set to be the same so that the pressure in the reaction chamber 10 does not fluctuate when switching. In addition, a line to the reaction chamber 10 and an exhaust system 22 are provided so that the gas flow is not disturbed when switching.
It is better to keep the conductance of the line to the same.

Next, the exhaust system 15 is adjusted to
Is set to 0.5 Torr, for example. At the same time, the substrate 13 is heated to a desired temperature, for example, about 350 ° C. by the heater 18 built in the electrode 12. Substrate 13
Reaches a desired temperature, and when the temperature is stabilized, the high-frequency power supply is turned on for a time A. When the time A elapses, at the same time, the valve 2A is closed, the valve 2B is opened, and the valve 3A is opened and the valve 3B is closed. In this state, only the time B is maintained.

After the lapse of time B, the high frequency power supply is turned on, and at the same time, the valve 2A is opened and the valve 2B is closed. Further, the valve 3A is closed and the valve 3B is opened. In this state, it is held for the time A.

The above operation is repeated a desired number of times to form a film on the substrate. By appropriately selecting the times A and B, the gas flow rate, and the like, thin films having various film qualities can be formed. For example, a case where hydrogen is supplied from MFC-1 and MFC-2 and silane is supplied from MFC-3 will be described below.

First, in a period A during which the high-frequency power supply is turned on, as shown in the following equation, hydrogen molecules are decomposed by high frequency to form hydrogen radicals H. H ₂ → H ・ + H ・ In this period A, there are no atoms constituting the film,
No film formation occurs.

Next, when the gas is switched and the high frequency is turned off, that is, in the period B, the reaction between H. generated in the period A and SiH ₄ occurs as shown in the following equation. SiH ₄ + H.fwdarw.SiH _3. + H ₂ By increasing the ratio of generated H. and introduced SiH ₄ to H., the generated Si-containing fragments are mostly SiH _3. Will occupy. From previous studies, to obtain a high quality a-Si film,
It is said that more SiH ₃ is better. Therefore, by selecting such a method, a high-quality device having a high-quality a-Si film can be formed.

In this case, for example, hydrogen is 80 sccm by MFC-1 and hydrogen is 20 scc by MFC-2.
m, 20 sccm of SiH ₄ is introduced by MFC-3. The high frequency is 13.56 MHz and 20 W
Power of about 1500W is supplied. The power density is preferably about 50 mW / cm ² to 100 mW / cm ² . If the power is too high, the trap level density in the film increases, and a device with good performance cannot be obtained.

The period A and the period B are preferably about 10 seconds to 10 minutes, and need not be the same time. As shown in FIG. 2, the timing of applying the high frequency is the same as when gas 2 and gas 3 are switched, or as shown in FIG.
After F is turned off, it is desirable to switch within, for example, 5 seconds, that is, within a time period in which radicals do not disappear. The time is preferably within the residence time (time during which the gas stays in the reaction chamber on average) determined by the lifetime of the radical, the volume of the reverse chamber, the gas flow rate, the pressure, and the like.

The input RF may be a CW high frequency, but in order to control the reactive species to be generated, a modulated high frequency modulated pulse whose power changes in a pulse shape having a duty ratio of about 5 to 95% and a frequency of 5 kHz to 200 kHz. May be.

As an example of conditions for forming a microcrystalline semiconductor film, for example, hydrogen is converted to 1 by MFC-1.
98 sccm, 2 sccm hydrogen by MFC-2, M
2 sccm of SiH ₄ is introduced by FC-3. Also,
The high frequency is 13.56 MHz and a power of about 20 W to 1500 W is applied. Power density, 50mW / cm
^It is preferably about ^{2 to} 100 mW / cm ² .

As an example for forming a polycrystalline semiconductor film, for example, hydrogen is applied for 190 seconds by MFC-1.
cF, 10 sccm of SiF ₄ by MFC-2, M
10 sccm of SiH ₄ is introduced by FC-3. The high frequency is 13.56 MHz and a power of about 20 W to 1500 W is applied. In terms of power density, 50mW /
It is preferably about cm ^{2 to} 100 mW / cm ² .

Example 2 Using a device similar to the non-single-crystal semiconductor thin film manufacturing apparatus shown in FIG. 1 used in Example 1, a non-single-crystal semiconductor thin film is formed as follows.

From MFC-1, 50 sccm of hydrogen was supplied.
From 500 sccm, MFC-2, SiH ₄ is, for example, 50 sccm, and from MFC-3, SiF ₄ is 50 s, for example.
Flow ccm. The flow rates of the MFC-2 and the MFC-3 are set to be the same.

Each operation procedure will be described with reference to the flow chart of the flow of the source gas (opening / closing procedure of the valve) and the ON / OFF timing of the high frequency power supply shown in FIG. First, after the substrate 13 is set on the lower electrode 12 in the reaction chamber 10, the reaction system 1 is
The inside of 0 is evacuated to a desired degree of vacuum, for example, 5 × 10 ⁻⁶ Torr or less. Next, the valve-1, the valve 2A and the valve 3B are opened. In this state, gas 1 (hydrogen) and gas 2 (SiH ₄ ) are introduced into the reaction chamber 10. At the same time, gas 3 (SiF ₄ ) is supplied to the reaction chamber 1 by the exhaust system 22.
It is exhausted without passing through zero.

Next, the exhaust system 15 is adjusted to
Is set to 1 Torr, for example. At the same time, the substrate 13 is heated to a desired temperature, for example, about 400 ° C. by the heater 18 built in the electrode 12. When the substrate 13 reaches a desired temperature and the temperature is stabilized, the high frequency power
Just turn on. After the time A has elapsed, the valve 2
A is closed, 2B is opened, and valve 3A is opened, and valve 3B is closed. In this state, only the time B is maintained.

After the time B has elapsed, the valve 2A is opened,
Close the valve 2B. Further, the valve 3A is closed and the valve 3B is opened, and at the same time, the high frequency power supply is turned on, and this state is maintained for the time A.

The above operation is repeated a desired number of times to form a film on the substrate. By appropriately selecting the times A and B, the gas flow rate, and the like, thin films having various film qualities can be formed.

The period A and the period B are preferably about 1: 1 to 1: 100, more preferably about 1:25 to 1:75.
In the first period A, amorphous and polycrystalline are formed, and in the next period B, the amorphous film is removed from the formed film. In the next period A, the remaining crystalline film is removed. Furthermore, many polycrystalline thin films are formed using the nuclei as a nucleus, and amorphous is formed in a certain portion. In the next period B, the amorphous portion is removed, and in the next period A, a crystalline film is formed again.

The period A is about 5 seconds to 1000 seconds, and the period B is preferably a time corresponding to the above ratio.
When a film is formed by flowing SiH ₄ and SiF ₄ at the same time as in the conventional method, the flow rate of SiH ₄ relative to SiF ₄ must be very small, for example, 1: 5.
It must be set to 0, and there is a problem in the controllability of the flow rate.
On the other hand, according to the method according to the present embodiment in which SiH ₄ and SiF ₄ are alternately flowed, the flow rates of SiF ₄ and SiH ₄ can be set to the same value, and the controllability of the flow rate is improved.

As shown in FIG. 4, the high-frequency is applied at the same time as switching between the gas 2 and the gas 3 or, as shown in FIG. 3, after the RF is turned off, for example, within 5 seconds. That is, it is desirable to switch within a time period in which radicals do not disappear. This time is preferably within the residence time (time during which the gas remains in the reaction chamber on average) determined by the life of the radical, the volume of the reverse chamber, the gas flow rate, the pressure, and the like.

The input RF may be a high frequency of CW. However, in order to control the generated reactive species, the power is changed into a pulse having a duty ratio of about 5 to 95% and a frequency of 5 kHz to 200 kHz. High frequency may be used.

As an example for forming a polycrystalline semiconductor film, a high frequency is 13.56 MHz and is 20 W to 15 W.
Input power of about 00W. Power density is 5
0mW / cm ² ~100mW / cm ² about is good.

In order to speed up the removal of the amorphous region, a high-frequency power optimum for etching may be supplied in the period B as shown in FIG. Third Embodiment FIG. 6 is a view schematically showing an apparatus for manufacturing a non-single-crystal semiconductor thin film according to the present embodiment. This non-single-crystal semiconductor thin film manufacturing apparatus has the same structure as that of FIG. 1 except that the exhaust system 22 is not provided.
Is similar to the non-single-crystal semiconductor thin film manufacturing apparatus shown in FIG.

Each operation procedure will be described with reference to the flow chart of the source gas flow (gas flow rate) and the ON / OFF timing of the high frequency power supply shown in FIG. First, after setting the substrate 13 on the lower electrode 12 in the reaction chamber 10,
The inside of the reaction chamber 10 is evacuated to a desired degree of vacuum, for example, 5 × 10 ⁻⁶ Torr or less by the exhaust system 15 via the valve 21. Next, the valve-1 and the valve 2A are opened. In this state, gas 1 and gas 2 are introduced into the reaction chamber.

Next, the exhaust system 15 is adjusted to
Is set to 0.5 Torr, for example. At the same time, the electrode 12
The substrate 13 is heated to a desired temperature, for example, about 350 ° C. by a heater 18 built therein. When the substrate 13 reaches a desired temperature and is stabilized, the high frequency power supply is turned on for a time A.

When the time A has elapsed, the flow rate of the MFC-2 is decreased, and at the same time, the flow rate of the MFC-3 is increased, and the gas 2 and the gas 3 are switched. Here, the flow rates of the gas 2 and the gas 3 are set such that there is no pressure fluctuation in the reaction chamber 10 when switching.
Keep the total flow rate constant. When the switching is completed, the state is maintained for the time B in that state.

After the time B has elapsed, the MF
The flow rate of C-2 is increased while the flow rate of MFC-3 is decreased. When the gas switching is completed, the high frequency power supply is turned on for a time A.

Next, when the time A elapses, the flow rate of the MFC-2 is decreased, and at the same time, the flow rate of the MFC-3 is increased.
And gas 3. Here, the total flow rate of the gas 2 and the gas 3 is kept constant so that there is no pressure fluctuation in the reaction chamber 10 when switching. When the switching is completed, the state is maintained for the time B in that state.

When the time B has elapsed, the MF
Increase the flow rate of C2 and at the same time decrease the flow rate of MFC-3.
When the gas switching is completed, the high frequency power supply is turned on for a time A.

The above operation is repeated a desired number of times to form a thin film on the substrate 13. By appropriately selecting the times A and B, the gas flow rate, and the like, thin films having various film qualities can be formed. For example, MFC-1, MFC-
The case where hydrogen is supplied from 2 and silane is supplied from MFC-3 will be described.

In this case, for example, hydrogen is 80 sccm by MFC-1 and hydrogen is 20 scc by MFC-2.
m, 20 sccm of SiH ₄ is introduced by MFC-3. The high frequency is 13.56 MHz and 20 W
A power of about 1500 W is supplied. In the power ^{density, 50mW / cm 2 ~100mW / cm} 2 about good. If the power is too high, the trap level density in the film increases, and a device with good performance cannot be obtained. Period A and period B are preferably about 10 seconds to 10 minutes, and need not be the same time.

As shown in FIG. 7, the period during which the high frequency is applied is preferably a period in which the switching between the gas 2 and the gas 3 is completed, and the period during which the high frequency is turned off is as shown in FIG. It may be after the flow rate of 3 becomes constant. For example, if the gas switches within 5 seconds, RF may be applied for a longer period of time. In any case, ON / OFF at timing when active species are generated effectively.
It is important to. The time is preferably within the residence time (time during which gas remains in the reaction chamber on average) determined by the life of the radical, the volume of the reverse chamber, the gas flow rate, the pressure, and the like.

The input RF may be a high frequency of CW, but in order to control the generated reactive species, a pulse-modulated pulse whose power changes in the form of a pulse having a duty ratio of about 5 to 95% and a frequency of 5 kHz to 200 kHz is used. High frequency may be used.

As an example of conditions for forming a microcrystalline semiconductor film, for example, hydrogen is converted to 1 by MFC-1.
98 sccm, 2 sccm hydrogen by MFC-2, M
2 sccm of SiH ₄ is introduced by FC-3. Also,
The high frequency is 13.56 MHz and a power of about 20 W to 1500 W is applied. 50mW / c in power density
The range is preferably from m ² to 100 mW / cm ² .

As an example for forming a polycrystalline semiconductor film, for example, hydrogen is applied for 190 seconds by MFC-1.
cF, 10 sccm of SiF ₄ by MFC-2, M
10 sccm of SiH ₄ is introduced by FC-3. The high frequency is 13.56 MHz and is 20 W to 1500 W.
Input about power. 50mW in power density
/ Cm ² to 100 mW / cm ² .

Example 4 A non-single-crystal semiconductor thin film is formed as follows using an apparatus similar to the non-single-crystal semiconductor thin film manufacturing apparatus shown in FIG. 6 used in Example 3.

From MFC-1, hydrogen was added at 50 sccm
500 sccm, for example, 50 sccm of SiH ₄ from MFC-2, and 50 sccc of SiF ₄ from MFC-3.
m. The flow rates of MFC-2 and MFC-3 are set to be the same.

Each operation procedure will be described with reference to the flow chart of the source gas flow (opening / closing procedure of the valve) and the ON / OFF time chart of the high frequency power supply shown in FIG. First,
After the substrate 13 is set on the lower electrode 12 in the reaction chamber 10, the inside of the reaction chamber 10 is evacuated to a desired degree of vacuum, for example, 5 × 10 ⁻⁶ Torr or less by the exhaust system 15 via the valve 21. Next, the valve-1 and the valve 2A are opened. In this state, gas 1 (hydrogen) and gas 2
(SiH ₄ ) is introduced.

Next, the inside of the reaction chamber 10 is adjusted to, for example, 1 Torr by adjusting the exhaust system 15. At the same time, the substrate 13 is heated to a desired temperature by a heater 18 built in the electrode 12.
For example, it is heated to about 400 ° C. When the substrate reaches a desired temperature and stabilizes, the high frequency power supply is turned on for a time A.

After the lapse of time A, the flow rate of MFC-2 is decreased, and at the same time, the flow rate of MFC-3 is increased to switch between gas 2 and gas 3 (SiF ₄ ). Here, the total flow rate of the gas 2 and the gas 3 is kept constant so that there is no pressure fluctuation in the reaction chamber 10 when switching. When the switching is completed, the state is maintained for the time B.

After the time B has elapsed, the MF
Increase the flow rate of C-2 and simultaneously decrease the flow rate of MFC-3. When the gas switching is completed, the high frequency power
Just turn on.

Next, after the time A has elapsed, the flow rate of the MFC-2 is reduced, and at the same time, the flow rate of the MFC-3 is increased.
And gas 3. Here, the total flow rate of the gas 2 and the gas 3 is kept constant so that there is no pressure fluctuation in the reaction chamber 10 when switching. When the switching is completed, the state is maintained for the time B in that state.

After the time B has elapsed, the MF
Increase the flow rate of C-2 and simultaneously decrease the flow rate of MFC-3. When the gas switching is completed, the high frequency power
Just turn on.

The above operation is repeated a desired number of times to form a film on the substrate 13. By appropriately selecting the times A and B, the gas flow rate, and the like, thin films having various film qualities can be formed.

The high frequency is applied during the period when the switching between the gas 2 and the gas 3 is completed, as shown in FIG. 7, or as shown in FIG. 8, when the RF is OFF, the flow rate of the gas 3 is constant. It may be after it becomes. For example, if the gas switches within 5 seconds, the RF may take longer. It is important to turn ON / OFF at a timing at which active species are effectively generated. The time is preferably within the residence time (time during which the gas stays in the reaction chamber on average) determined by the lifetime of the radical, the volume of the reaction chamber, the gas flow rate, the pressure, and the like.

The input RF may be a high frequency of CW. However, in order to control the generated reactive species, the power is changed into a pulse having a duty ratio of about 5 to 95% and a frequency of 5 kHz to 200 kHz. High frequency may be used.

The period A and the period B are preferably about 1: 1 to 100, more preferably about 1:25 to 75. In the first period A, amorphous and polycrystalline are formed, and in the next period B, the amorphous film is removed from the formed film. In the next period A, the remaining crystalline film is formed. On top of that, many polycrystalline thin films are formed using the nuclei as a nucleus, and amorphous is formed in a certain portion. In the next period B, the non-crystalline portion is removed, and in the next period A, a crystalline film is formed.

The period A is about 5 to 1000 seconds, and the period B has a good time with respect to the above ratio.
As in the conventional method, when forming a film by flowing SiH ₄ and SiF ₄ at the same time, SiH ₄ relative SiF ₄
Has to be made very small, for example, 1:50, and there is a problem in the controllability of the flow rate. On the other hand, according to the method according to the present embodiment, the flow rates of SiF ₄ and SiH ₄ can be made the same, and the controllability of the flow rate is improved.

The input RF may be a CW high frequency, but in order to control the generated reactive species, a pulse-modulated pulse whose power changes in the form of a pulse having a duty ratio of about 5 to 95% and a frequency of 5 kHz to 200 kHz is used. High frequency may be used.

As an example of conditions for forming a polycrystalline semiconductor film, a high frequency is 13.56 MHz and 20 W to 20 W.
Power of about 1500W is applied. In the power ^{density, 50mW / cm 2 ~100mW / cm} 2 about good.

In order to speed up the removal of the amorphous region, a high frequency power optimal for etching may be supplied in the period B as shown in FIG. Example 5 In Examples 1 to 4, 13.56 MHz, 27.12 MH
The case where the gas is decomposed by the high frequency of 400 MHz is shown. On the other hand, in Example 5, the microwave CV shown in FIG.
D, ECR (microwave electron cyclotron resonance) -C
This is an example in which a film forming apparatus using a VD method is used. That is, the first to fourth embodiments are parallel plate type plasma CVD apparatuses, but in the present embodiment, the gas is decomposed by microwave or ECR. The power input method and the timing chart are the same as in the first to fourth embodiments.

The film forming apparatus shown in FIG. 10 has the same gas supply system and exhaust system as the apparatus shown in FIG. 1, but differs in the following points. That is, in the device shown in FIG. 1, while the high-frequency power supply / control unit 17 applies a high frequency,
Is a device for applying microwaves.
The reaction chamber is configured as follows.

The reaction chamber 30 includes a plasma generation chamber 31 and a film formation chamber 32, both of which are connected via a plasma extraction window 33. The microwave is applied to the waveguide 3
The magnetic coil 35 is introduced into the plasma generation chamber 31 through the space 4, and is arranged around the plasma generation chamber 31.

An important point in this embodiment is that the energy for gas flow and decomposition can be changed in a pulsed manner with time. Embodiment 6 This embodiment is an example in which the present invention is applied to the manufacture of a thin film transistor.

Using the same apparatus as the non-single-crystal semiconductor thin film manufacturing apparatus shown in FIG. 1 used in Example 1, the flow of the source gas (opening / closing procedure of the valve) and the turning on / off of the high frequency power supply shown in FIG. Along the off-time chart, a non-single-crystal semiconductor thin film is formed as follows. First, after setting a transparent insulating substrate 13 coated with a transparent insulating film on the lower electrode 12 in the reaction chamber 10, the interior of the reaction chamber 10 is evacuated to a desired degree of vacuum by an exhaust system 15 through a valve 21. For example, 5x
Exhaust to 10 ^-6 Torr or less. Then, valve 1,
The valve 2A and the valve 3B are opened. In this state, gas 1 and gas 2 are introduced into the reaction chamber 10. At the same time, the gas 3 is exhausted to the other side by the exhaust system 22 without passing through the reaction chamber 10.

Here, the flow rates of the gas 2 and the gas 3 are set to be the same so that the pressure in the reaction chamber 10 does not fluctuate when switching. Then, the exhaust system 15 is adjusted to adjust the reaction chamber 10.
Is set to 1 Torr, for example. At the same time, the substrate 13 is heated to a desired temperature, for example, about 350 ° C. by the heater 18 built in the electrode 12. When the substrate 13 reaches a desired temperature and is stabilized, the high frequency power supply is turned on for a time A.

When the time A has elapsed, at the same time, the valve 2A
Is closed, 2B is opened, and valve 3A is opened, and valve 3B is closed. In that state, it is held for the time B. Time B
Is turned on, the high frequency power is turned on, and at the same time, the valve 2A
Is opened, and the valve 2B is closed. Further, the valve 3A is closed and the valve 3B is opened. In this state, the time A is held.

The above operation is repeated a desired number of times, for example, 10 times.
This is repeated 00 times to form a film on the substrate. here,
The gas flowing through each line is, for example, MFC-1
When hydrogen is supplied from the MFC-2, SiF ₄ is supplied from the MFC-2, and silane is supplied from the MFC-3, in the period A, the amorphous component of the formed film is etched by the decomposition product of the SiF ₄ and hydrogen. In the period B, a silicon film is formed with SiH ₄ and hydrogen. Thereafter, the amorphous component is removed from the silicon film deposited in the next period A. By repeating such operations, high-quality polycrystalline silicon with high crystallinity can be formed.

Thus, a polycrystalline silicon film is formed on substrate 13 to a thickness of, for example, 50 nm. Then
This polycrystalline silicon film is patterned to form a high resistance semiconductor layer of a thin film transistor. Next, on this high resistance semiconductor layer, APCVD, PECVD, ECR-PEC
A gate insulating film is formed by VD or the like. On the gate insulating film, a gate electrode is formed of, for example, a MoTa alloy, a MoW alloy, aluminum, or the like.

After that, using the gate electrode as a mask, an impurity is implanted into a part of the high-resistance semiconductor layer by ion implantation or the like, and the impurity is activated to form a low-resistance semiconductor layer. Next, an interlayer insulating film is formed, a contact hole is opened, a source / drain electrode is formed,
The thin film transistor is completed.

The thin film transistor formed by such a method had a film thickness more uniform than that of the thin film transistor using the high resistance semiconductor layer formed by ELA, and was uniform in both mobility and Vth. This device is used as a pixel TFT for liquid crystal display
In addition, when the TFT was used as a TFT for a driving circuit, a uniform image without unevenness was obtained.

In the above description, the coplanar type TFT is used.
Has been described, but various modifications can be made without departing from the spirit of the present invention. For example, a CMOS formed by an n-channel TFT and a p-channel TFT may be used. In particular, CMO
When a driving circuit is formed by S, a liquid crystal display device with low power consumption can be obtained.

For the pixel TFT, the leakage current (TF
An LDD structure may be used to reduce the current flowing when T is OFF, or a multi-gate (double-gate) TFT having a plurality of gate electrodes may be used.

The type of gas flowing through each line, the flow rate, time A and time B, the pressure in the reaction chamber, the substrate temperature, etc.
It can be appropriately changed according to the desired film and film quality. Instead of SiH ₄ , a higher silane such as Si ₂ H ₆ may be used. Also, instead of SiH ₄ , Si ₂ H
A halogen derivative of a higher silane such as ₆ may be used.

[0106]

As described in detail above, according to the present invention,
Without using a poly-Si forming process by ELA, the plasma C is used at a temperature at which a glass substrate can be used.
A high-resistance semiconductor layer can be formed by a VD method, whereby a liquid crystal display element having good display characteristics without display deterioration of a display device due to uneven shot of ELA can be efficiently obtained.

[Brief description of the drawings]

FIG. 1 is a view showing an apparatus for manufacturing a non-single-crystal semiconductor thin film used in a first embodiment of the present invention.

FIG. 2 is a diagram showing a timing chart of opening / closing a valve and turning on / off a high-frequency power supply according to the first embodiment of the present invention.

FIG. 3 is a diagram showing another example of a timing chart of opening / closing a valve and turning on / off a high-frequency power supply according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a timing chart for opening and closing a valve and turning on / off a high-frequency power supply according to a second embodiment of the present invention.

FIG. 5 is a diagram showing another example of a timing chart for opening / closing a valve and turning on / off a high-frequency power supply according to a second embodiment of the present invention.

FIG. 6 is a diagram showing an apparatus for manufacturing a non-single-crystal semiconductor thin film used in a third embodiment of the present invention.

FIG. 7 is a diagram showing a timing chart of opening / closing a valve and turning on / off a high-frequency power supply according to a third embodiment of the present invention.

FIG. 8 is a diagram showing another example of a timing chart for opening / closing a valve and turning on / off a high-frequency power supply according to a fourth embodiment of the present invention.

FIG. 9 is a diagram showing still another example of a timing chart for opening / closing a valve and turning on / off a high-frequency power supply according to a fourth embodiment of the present invention.

FIG. 10 is a diagram showing an apparatus for manufacturing a non-single-crystal semiconductor thin film used in a fifth embodiment of the present invention.

FIG. 11 is a cross-sectional view illustrating a part of a structure of a general liquid crystal display device using a poly-Si TFT.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Reaction chamber 11 ... Upper electrode 12 ... Lower electrode 13 ... Substrate 14 ... Gas supply part 15, 22 ... Exhaust system 16 ... Control device which controls a gas supply part and a high frequency power supply control part 17 ... High frequency power supply and its ON / OFF Control unit 18 ... heater 19 ... 21 ... valve 30 ... reaction chamber 31 ... plasma generation chamber 32 ... film formation chamber 33 ... plasma extraction window 34 ... waveguide 35 ... magnetic coil 101 ... substrate protection film 102 ... High resistance semiconductor layer 103 Source region 104 Drain region 106 Gate insulating film 108 Gate electrode 109 Source electrode 110 Drain electrode 111 Interlayer insulating film 113 Pixel electrode.

Claims (6)

[Claims] A step of introducing a non-film-forming gas not containing atoms mainly constituting the non-single-crystal semiconductor thin film into a reaction chamber containing a substrate to be processed on which the non-single-crystal semiconductor thin film is formed; Applying a high frequency or microwave to the non-deposition gas in synchronization with the introduction of the film gas to form a plasma, decomposing the non-deposition gas by the plasma, and after a predetermined time from the introduction of the non-deposition gas Introducing a film-forming gas containing atoms mainly constituting the non-single-crystal semiconductor thin film into the reaction chamber to form a non-single-crystal semiconductor thin film on the substrate to be processed. A method for forming a semiconductor thin film. 2. A step of introducing a deposition gas containing atoms mainly constituting the non-single-crystal semiconductor thin film into a reaction chamber containing a substrate to be processed on which the non-single-crystal semiconductor thin film is deposited; Synchronously with the introduction, a high frequency or microwave is applied to the film forming gas to form a plasma, a step of decomposing the film forming gas by the plasma, and a predetermined time after the introduction of the film forming gas, into the reaction chamber. And a step of introducing a non-film-forming gas not containing atoms that mainly constitute the non-single-crystal semiconductor thin film. 3. The method for forming a non-single-crystal semiconductor thin film according to claim 1, wherein each of the series of steps is repeated a plurality of times. 4. A reaction chamber accommodating a substrate to be processed, a film formation gas supply flow path for supplying a film formation gas containing atoms mainly constituting a non-single-crystal semiconductor thin film to the reaction chamber, A film formation gas exhaust passage connected to a gas supply passage for exhausting the film formation gas, and a non-film formation gas supplying an atom-free non-film formation gas mainly constituting the non-single-crystal semiconductor thin film to the reaction chamber. A film-forming gas supply channel, a film-forming gas exhaust channel connected to the film-forming gas supply channel and exhausting the film-forming gas, and a non-film-forming gas connected to the non-film-forming gas supply channel. A non-film-forming gas exhaust passage for exhausting gas; a means for introducing high frequency or microwave into the film-forming gas and / or the non-film-forming gas to form plasma; and a reaction between the film-forming gas and the non-film-forming gas Supply to the chamber alternately and minimize pressure fluctuations in the reaction chamber Means for switching between supplying the film-forming gas and the non-film-forming gas to the reaction chamber and switching between supplying and exhausting the film-forming gas and / or the non-film-forming gas to the reaction chamber. An apparatus for forming a non-single-crystal semiconductor thin film. 5. A high-resistance semiconductor layer formed on a substrate, a gate electrode formed on the high-resistance semiconductor layer via a gate insulating film, and a low-resistance semiconductor formed on both sides of the high-resistance semiconductor layer. A semiconductor layer, comprising: a source electrode and a drain electrode electrically connected to the low-resistance semiconductor layer;
A thin film transistor formed by the method for forming a non-single-crystal semiconductor thin film according to claim 1. 6. A pair of substrates arranged to face each other, a pixel display portion electrode arranged in a matrix on one of the opposite surfaces of the pair of substrates, and a pixel display portion of the one substrate. 6. A switching transistor formed and connected to the pixel display section electrode, and a liquid crystal layer sealed between the pair of substrates, wherein the switching transistor is
A liquid crystal display device, which is the thin film transistor according to claim 1.