JPH0817738A - Formation method for crystalline semiconductor thin film - Google Patents

Abstract

PURPOSE:To form a high-quality crystalline silicon semiconductor thin film at a high-speed depositing speed by heating a gaseous mixture containing a compound gas including silicon atoms in advance to sufficiently increase the temperature of the gaseous mixture and after that, decomposing it by plasma. CONSTITUTION:A substrate 110 is placed in a substrate preparing and taking-out chamber 10 and evacuation for high vacuum is performed by a vacuum pump 9. After that, the substrate 110 is transferred into a film forming chamber 101 through a vacuum separation valve 2. After it is transferred, the evacuation for high vacuum is performed. The heat setting of a gas heating device 224 is performed in advance, and a mono-silane gas is made to flow through a gas flow rate regulating device 226 and at the same time an automatic pressure regulating valve 108 is operated. After that, a high-frequency voltage from a high-frequency power supply 103 is applied to high-frequency electrodes 102 to generate plasma. Plasma generating electrodes are formed in parallel flat plates and a high-frequency power supply is used for a power supply for generating plasma.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for forming a high-quality crystalline semiconductor film having high carrier mobility in improving the performance of semiconductor devices.

[0002]

2. Description of the Related Art Silicon thin films can change their crystallinity and structure from amorphous depending on the manufacturing method and the like, and various forms are used in consideration of device application. Therefore, an amorphous solar cell using a silicon thin film has been widely researched and developed as a thin film solar cell because the amorphous silcon thin film has a large visible light absorption coefficient. In order to improve the open-circuit voltage in this amorphous solar cell, the photoelectric characteristics of the p-type semiconductor thin film must be improved, and in particular, the optical bandgap and the electrical conductivity must be increased at the same time. I won't. In addition, regarding the improvement of the characteristics of the amorphous solar cell, similarly for the n-type semiconductor thin film, there has been a demand for a technique in which the optical bandgap and the electric conductivity must be simultaneously improved. A crystalline thin film has been proposed as a material satisfying these requirements, but in the prior art, if the film thickness is thin, the crystallinity is poor, and
There are many defects. Also, in the conventional process, high density plasma diluted with hydrogen is used to obtain a crystalline thin film, so there is a large amount of base damage due to ion bombardment, or 400 ° C.
However, there is a problem that a relatively high substrate temperature is required, and it has been difficult to obtain a crystalline thin film that improves the characteristics of an amorphous solar cell.

On the other hand, since the polycrystalline silicon thin film solar cell has a lower mobility than that of single crystal silicon, research has been conducted on improving the performance of a thin film having a thin material. Considering the practical application of solar cells, it is necessary to obtain a high-quality crystalline thin film at high speed and low temperature, and a thin film deposition method that fully satisfies these conditions has not been put into practical use. Methods such as solid phase melting to improve crystallinity and quality are used. At present, a substrate temperature of 8000 ° C. or higher is used to obtain a crystalline thin film, and a high temperature of 1000 ° C. or higher is used to obtain a higher quality crystalline thin film. However, there is a high demand for low temperature growth from the viewpoint of expanding the utilization of the substrate and device applicability.
Currently, there are many problems in high temperature processes.

A thin film transistor is a device using a silicon thin film. A thin film transistor is a device used for driving a liquid crystal and used for a liquid crystal display device. At present, a thin film transistor using an amorphous silicon thin film is widely used, but since the mobility of amorphous silicon is low, use of a polycrystalline silicon thin film is also considered. Since it is necessary to form a polycrystalline silicon thin film for thin film transistors on a glass substrate,
If possible, it is required to grow at 600 ° C or lower. However, at present, a film forming technique capable of forming a crystalline thin film at a low temperature while maintaining quality has not been obtained.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to develop a technique for forming a high quality crystalline silicon semiconductor thin film at a low substrate temperature and a high deposition rate with less process damage to an underlayer or the like.

[0006]

Means for Solving the Problems The inventors of the present invention have made extensive studies to solve the above problems, and as a result, formed a semiconductor thin film on a substrate by plasma decomposition of a mixed gas containing a compound gas containing silicon atoms. In this case, the mixed gas containing the compound gas containing the silicon atoms is preheated, the mixed gas is heated to a sufficiently high temperature, and then plasma decomposed to obtain a high-quality crystalline silicon semiconductor thin film at a high deposition rate. It was found that it can be formed and completed the present invention.

That is, according to the present invention, when a semiconductor thin film is formed on a substrate by plasma decomposition of a mixed gas containing a compound gas containing silicon atoms, the mixed gas containing a compound gas containing silicon atoms is heated in advance. The method for forming a crystalline semiconductor thin film is characterized in that plasma decomposition is performed after the temperature of the mixed gas is sufficiently raised, and the temperature of the mixed gas heated to a high temperature is preferably 200 ° C or higher.
It is a method for forming a crystalline semiconductor thin film having a temperature of less than 800 ° C., and a compound gas containing silicon atoms has a general formula Si _n H
_{2n + 2} (n = 1 to 4 is an integer of 4) is a crystalline semiconductor thin film forming method which is a silane, also, the substrate temperature is a crystalline semiconductor thin film forming method of 50 ℃ or more and less than 800 ℃,
Further, it is a method for forming a crystalline semiconductor thin film, wherein a mixed gas containing a compound gas containing silicon atoms further contains a compound gas containing halogen atoms.

The present invention will be described in detail below. First, referring to the attached drawings, FIG. 1 is a schematic view showing an example of a semiconductor thin film manufacturing apparatus for carrying out the present invention, in which 1 is a substrate loading / unloading chamber, 2 is a partition valve,
9 is a vacuum exhaust system, 101 is a film forming chamber, 102 is a high frequency electrode, 103 is a high frequency power supply, 104 is a substrate heating plate, and 105
Is a substrate temperature adjuster, 106 is a gas flow rate adjusting system, 107 is a pressure sensor, 108 is a pressure adjuster, 109 is a vacuum exhaust system, 110 is a substrate, 111 is a gas temperature sensor, 201
Is a gas heating chamber, 207 is a pressure sensor, 208 is a pressure regulator, 209 is a vacuum exhaust system, 211 is a gas temperature sensor, 224 is a gas heater, 225 is a gas heating regulator, 2
Reference numerals 26 respectively denote gas flow rate regulators.

In the present invention, the compound gas containing a silicon atom is a hydrogenated silane represented by the general formula Si _n H _{2n + 2} (n = 1 to 4, n; natural number), Si _m H _{2m + 2- x} C l _x (m = 1
~ 4, x = 0 ~ 2m + 2 m; natural number) and Sim _m H _{2m + 2-X} F _X (m = 1
Is a halogen (chlorine or fluorine) -containing silane compound represented by ˜4, x = 0 to 2 m + 2 m; a natural number, and is monosilane, disilane, trisilane, tetrasilane, dichlorosilane, difluorosilane, or the like. Moreover, mixing these gases does not hinder the present invention. Further, the hydrogen atom of these compounds is substituted with a methyl group or an ethyl group, monomethylsilane, methylsilane such as dimethylsilane, organosilicon compounds such as ethylsilane such as monoethylsilane are also included, and the mixed use with the gas is In particular, it does not matter from the effect of the present invention.

The mixed gas is a compound gas containing a halogen atom in the above silane compound, specifically, a compound gas further containing a fluorine atom, a chlorine atom, etc., and generally used is hydrogen fluoride gas. , Fluorine gas, chlorine gas, nitrogen trifluoride, carbon tetrafluoride, difluorosilane, silicon tetrafluoride, dichlorosilane and the like. In addition, mixed gas of these gases or helium, argon,
You may introduce inert gas, such as neon, and support gas, such as nitrogen. Hydrogen gas can also be used as a mixed gas, and further,
An inert gas such as helium, argon, or neon, or a supporting gas such as nitrogen may be introduced at the same time as the hydrogen gas.

The dilution addition rate is in the range of 0.1 to 100% (volume ratio) when expressed as the ratio of the silane compound to the added gas, and is appropriately selected in consideration of the film forming rate and film characteristics. is there.

In addition to the gases shown above, mixing a hydrocarbon compound gas and an organic silicon compound gas does not hinder the present invention. The hydrocarbon compound and the organosilicon compound gas are saturated hydrocarbon compounds such as methane and ethane, unsaturated hydrocarbon compounds such as ethylene and acetylene, methylsilane, dimethylsilane, disilylmethane,
Examples include organic silane compounds such as dimethyldisilane.
These gases are used as a film forming raw material, a reactive gas, an inert gas,
The introduction as a mixed gas with a supporting gas does not hinder the present invention.

Depending on the desired crystalline thin film, p-type or n-type
A doping gas may be added in order to form a type semiconductor. As the doping gas, in order to obtain a p-type semiconductor, a gas containing a Group III element, a boron hydride such as diborane, a boron halide compound such as boron trifluoride, or an organic boron compound such as trimethylboron is used. To obtain an n-type semiconductor, a gas containing a group V element,
Gases such as phosphorus compounds such as phosphine, arsenic hydrogen compounds such as arsine, organic phosphorus compounds such as trimethyl phosphorus and trimethyl arsenic, and organic arsenic compounds are used. These gases can be added separately from the compound gas containing silicon atoms, and can be used to obtain a crystalline thin film whose conductivity is changed. Further, even if these gases are introduced as a mixed gas with a reactive gas, an inert gas, a supporting gas, a hydrocarbon compound, and an organic silicon compound, the present invention is not hindered.

The flow rate of the compound gas containing silicon atoms is 1
~ 1000 cc / min, the film forming pressure is in the pressure range in which plasma is generated, and is 1 mtorr ~ 760 torr. Generally, since high frequency discharge of 13.56 MHz and direct current discharge using direct current voltage are used, it is preferable and practical to use 10 mtorr to 5 torr for simplicity. The plasma input power is 1 mW / cm ² to 10 W / cm ² , and more preferably 0.01 to 1.00 W / cm ² . Further, the input power, the flow rate, and the pressure can be arbitrarily selected according to the film forming rate. These conditions do not hinder the practice of the present invention.

The means for generating the plasma used for decomposing the compound gas containing silicon atoms has been described above, but the means for applying the AC voltage or the DC voltage or the electric field of microwave (2.45 GHz) is introduced into the vacuum chamber. Use the method. 13.56 MH due to handling and availability of power supply
It is preferable to use a radio wave of z and a high frequency of VHF of 50 MHz or more. Also, commercial AC waves of 1 kHz to 10 MHz and commercial 50 and 60 Hz can be used.

The specific thickness of the semiconductor thin film to be formed is not critically limited and is, for example, about 1 nm to 50 μm. In addition, the present invention is not limited in any way. It is selected depending on the material and device to which the crystalline thin film produced by the present invention is applied. In the case of a doped layer such as p layer or n layer of an amorphous solar cell, it is 5 nm to 5 nm.
0 nm is used, 100 nm is sufficient for thin film transistors.

The gas heating for preheating the mixed gas containing the compound gas containing silicon atoms to raise the temperature in the present invention will be described. As shown in FIG. 1, the gas heating mechanism introduces a mixed gas containing a compound gas containing silicon atoms into a gas heating device from a gas flow controller, and a desired temperature is set in the gas heating zone. To a sufficiently high temperature. The temperature of the gas is raised by passing it through a heater heated to a desired temperature with a heating controller. The temperature of the gas thus heated is measured by a temperature measuring device at the gas outlet, and the temperature of the gas in the present invention is 200 ° C or higher and lower than 800 ° C. Preferably 250 ° C
Or more and less than 700 ℃, more preferably 300 ℃ or more 65
The temperature is lower than 0 ° C, more preferably 350 ° C or higher and lower than 600 ° C. The temperature of the gas is an important condition for carrying out the present invention. If the temperature is lower than 200 ° C. and is too low, the effect of the invention is extremely weak due to the influence of heating by the plasma or the substrate temperature. At a significantly high temperature of 800 ° C. or higher, the gas mixture containing the compound gas containing silicon atoms causes thermal decomposition, which significantly reduces the effect of the invention. Therefore, it can be seen that the temperature of the gas is an important condition for carrying out the present invention.

Next, regarding the substrate temperature in the present invention,
explain. The substrate temperature in the present invention is the temperature of the substrate on which the crystalline thin film is formed, and is 50 ° C or higher and lower than 800 ° C. It is a well-known fact that a substrate temperature exceeding 800 ° C., specifically, an extremely high temperature such as 900 ° C. or more, is a temperature at which a crystalline thin film is conventionally formed, and is a known fact. In order to carry out the present invention more effectively, the temperature is 50 ° C. or higher and lower than 800 ° C., preferably 100 ° C. or higher and lower than 700 ° C., more preferably 150 ° C. or higher and 600 ° C., further preferably 150 ° C. or higher and 50 ° C. or higher.
The temperature is below 0 ° C., and the effect of the present invention becomes more remarkable at these substrate temperatures. In the practice of the present invention, it is clear that the range of the substrate temperature does not interfere and is appropriately selected.

The substrate used here is not particularly limited as long as heat resistance is taken into consideration. As the translucent substrate, conventionally used glass substrate materials such as soda lime glass, borosilicate glass, and quartz glass are useful, and further, a metal or a material obtained by forming a metal on the above glass can be used as a substrate material. . Further, a substrate in which a transparent electrode is formed on the above glass substrate or a metal substrate can also be used as a substrate for a solar cell, and as the transparent electrode, a metal oxide such as tin oxide, indium oxide, or zinc oxide or a light-transmitting substrate is used. A metal or the like can be effectively used. Further, a crystalline silicon substrate can also be used. The p-type and n-type crystalline silicon semiconductor thin films doped with boron or phosphorus can be applied to a doped layer of a crystalline silicon solar cell or an amorphous solar cell or a thin film transistor.
Obviously, it is not worth mentioning that the object of the present invention is the application to said device. Hereinafter, an example of an embodiment of the present invention will be described with reference to examples.

[0020]

EXAMPLE 1 A concrete apparatus for carrying out the present invention is shown in FIG.
The substrate (110) is installed in the substrate loading / unloading chamber (1), and high vacuum exhaust is performed for 30 minutes by the vacuum exhaust pump (9). Then, the film is transferred to the film forming chamber (101) through the vacuum isolation valve (2). Transfer. After the transfer, high vacuum evacuation for 10 minutes was performed. In advance
The gas heater (224) is set to 600 ℃, the temperature of the gas is set to 600 ℃, and the monosilane gas flow rate controller (2
At the same time as flowing 5 cc / min through 26), activate the automatic pressure regulating valve (108) so that the pressure becomes 50 mtorr,
Shed for 10 minutes. After that, application of high frequency voltage from the high frequency power source (103) to the high frequency electrode (102) was started to generate plasma. The electrodes for plasma generation were in the form of parallel plates, and the power supply for generating plasma was a high frequency power supply of 13.56 MHz. For substrate heating, a substrate heating plate (104) is used, and a substrate temperature adjuster (1
05), substrate temperature 200 ℃, reaction pressure 50 mtor
At r, a high frequency power of 50 mW / cm ² was applied to generate plasma. Here, a quartz glass substrate was used as the substrate. The film formation rate was found by dividing the thickness of the formed film by the time taken for the deposition. As a result, the film formation rate was 83Å / sec. When the presence or absence of crystallization of these samples was evaluated by Raman scattering spectrum, the Raman scattering spectrum of 520 cm ^-1 due to silicon crystals was observed in this sample, and a crystalline semiconductor thin film was obtained. confirmed. The crystal grain size determined by X-ray diffraction was about 1000Å. The specific resistance of this sample was 2 × 10 ^-1 Ω · cm, and the specific resistance decreased with crystallization. The hole mobility measured by the van der Paw method was 24 cm ² / V / sec.

Example 2 Example 2 was repeated except that the temperature of the gas was 500 ° C.
A semiconductor thin film was produced under the same conditions. When Raman scattering spectrum was measured, it was attributed to crystalline silicon.
A Raman scattering spectrum of 20 cm ^-1 was observed. The crystal grain size was about 800Å. The specific resistance was 6 × 10 ^-2 Ω · cm and the hole mobility was 10 cm ² / V / sec.

Example 3 Example 3 was repeated except that the temperature of the gas was changed to 200 ° C.
A semiconductor thin film was produced under the same conditions.

Example 4 Example 4 was repeated except that the temperature of the gas was 700 ° C.
A semiconductor thin film was produced under the same conditions.

Example 5 In Example 1, the substrate temperature was 300 ° C. and the gas temperature was
A semiconductor thin film was prepared under the same conditions except that the temperature was set to 600 ° C.

Example 6 A semiconductor thin film was prepared under the same conditions as in Example 5, except that the substrate temperature was 400 ° C.

Example 7 A semiconductor thin film was prepared under the same conditions as in Example 5, except that the substrate temperature was 500 ° C.

Example 8 Disilane (Si ₂ H ₆ ) was added to a compound gas containing silicon atoms.
Using, the semiconductor thin film was prepared as shown in Example 1. The temperature of the gas was 400 ° C., 10 cc / min was flown, and the pressure was 100 mtorr. Substrate temperature is 300 ℃, high frequency power is 10
A plasma was generated by applying 0 mW / cm ² . The substrate used is a quartz glass substrate.

Example 9 A semiconductor thin film was prepared under the same conditions as in Example 8 except that the substrate temperature was 500 ° C.

Example 10 A semiconductor thin film was produced as shown in Example 1 by using difluorosilane (SiH ₂ F ₂ ) containing a fluorine atom as a compound gas containing a silicon atom. The temperature of the gas was set to 600 ° C., 20 cc / min was passed, and the pressure was set to 200 mtorr. The substrate temperature was 350 ° C, and high frequency power of 150 mW / cm ² was applied to generate plasma. The substrate used is a quartz glass substrate.

Example 11 Using the film-forming layer shown in Example 1, monosilane 10 cc / mi
n, at a gas temperature of 600 ° C, introduced into the film formation chamber through a gas heater, and at the same time fluorine gas (diluted with helium
20% concentration) 20 cc / min was introduced into the film forming chamber through the gas flow rate regulator (125). Plasma was generated at a high frequency power of 200 mW / cm ² and a reaction pressure of 200 mtorr. A semiconductor thin film was prepared at a substrate temperature of 200 ° C. using a quartz glass substrate.

Example 12 Using the film-forming layer shown in Example 1, monosilane 10 cc / mi
n, at a gas temperature of 600 ° C, introduced into the film formation chamber through a gas heater, and at the same time, 5 cc / min of phosphine (PH ₃ ) (1% concentration by dilution with hydrogen) was passed through a gas flow rate controller. Introduced. High frequency power 100mW / cm ² , reaction pressure 10
Plasma was generated at 0 mtorr. A semiconductor thin film was prepared at a substrate temperature of 200 ° C. using a quartz glass substrate.

Example 13 In Example 11, instead of phosphine gas, dibonran (B ₂ H ₆ ) (concentration of 2000 ppm diluted with hydrogen) 3 cc / m
In was introduced into the film forming chamber through a gas flow rate controller. Plasma was generated at a high-frequency power of 100 mW / cm ² and a reaction pressure of 100 mtorr. A semiconductor thin film was prepared at a substrate temperature of 200 ° C. using a quartz glass substrate.

Comparative Example 1 In Example 1, the gas was not particularly heated (room temperature, 25
A thin film was formed.

Comparative Example 2 In Example 1, the temperature of the gas cannot be said to be sufficiently high.
A thin film was formed by heating to 100 ° C.

Comparative Example 3 In Example 1, the formation state of the semiconductor thin film was observed without generating plasma by high frequency.

Comparative Example 4 In Example 1, heating was performed so that the temperature of the gas became 900 ° C. to form a thin film. Although a crystalline thin film could be obtained, the film formation rate was significantly reduced.

Comparative Example 5 In Example 1, the gas was not particularly heated and the substrate temperature was 80%.
A thin film was formed at 0 ° C. As described above, the results of Examples are shown in Table 1 and the results of Comparative Examples are shown in Table 2.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

As is apparent from the above Examples and Comparative Examples, the crystalline semiconductor thin film produced by this method has extremely good crystallinity and electrical characteristics and can be produced at low temperature and at high speed. I understand. That is, compared to the conventional technology, a high-quality crystalline semiconductor thin film can be formed at low temperature and high speed,
It has been found that the crystalline semiconductor thin film forming technique of the present invention is effective. That is, the crystalline semiconductor thin film developed by the present invention can be applied to a thin film transistor such as a solar cell, and improves the performance of these devices.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a semiconductor thin film manufacturing apparatus for carrying out the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate loading / unloading chamber 2 Partition isolation valve (vacuum isolation valve) 9 Vacuum pump or other vacuum exhaust system 101 Film deposition chamber 102 High frequency electrode 103 High frequency power supply 104 Substrate heating plate 105 Substrate temperature regulator 106 Gas flow rate regulation system 107 Pressure sensor 108 Automatic pressure regulator (automatic pressure regulating valve) 109 Vacuum exhaust system 110 Substrate 111 Gas temperature sensor 201 Gas heating chamber 207 Pressure sensor 208 Pressure regulator 209 Vacuum exhaust system 211 Gas temperature sensor 224 Gas heater 225 Gas heating regulator 226 Gas Flow regulator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location H01L 31/04 (72) Inventor Mitsuru Sadamoto 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd. In the company

Claims (5)

[Claims] 1. When forming a semiconductor thin film on a substrate by plasma decomposition of a mixed gas containing a compound gas containing silicon atoms, the mixed gas containing the compound gas containing silicon atoms is heated in advance to form a mixed gas. A method for forming a crystalline semiconductor thin film, which comprises subjecting a substrate to a sufficiently high temperature and then plasma decomposing it. 2. The temperature of the mixed gas heated to a high temperature is
The method for forming a crystalline semiconductor thin film according to claim 1, wherein the temperature is 200 ° C or higher and lower than 800 ° C. 3. The method for forming a crystalline semiconductor thin film according to claim 1, wherein the compound gas containing silicon atoms is a silane represented by the general formula Si _n H _{2n + 2} (n = 1 to 4). 4. The method for forming a crystalline semiconductor thin film according to claim 1, wherein the temperature of the substrate is 50 ° C. or higher and lower than 800 ° C. 5. The method for forming a crystalline semiconductor thin film according to claim 1, wherein the mixed gas containing the compound gas containing silicon atoms further contains a compound gas containing halogen atoms.