JPH0330319A - Amorphous semiconductor thin film - Google Patents

Abstract

PURPOSE:To obtain a highly stable thin film efficiently by performing repeatedly manufacturing processes through which a semiconductor thin film consisting of 10at.% or less bound hydrogen is formed and its thin film is exposed to a discharge atmosphere containing a reaction gas. CONSTITUTION:A semiconductor thin film is formed by performing repeatedly a film formation process 1 through which the semiconductor thin film consisting of 10at.% or less bound hydrogen is formed and a film-reforming process 2 through which the thin film is exposed to a discharge atmosphere containing a reaction gas. Then, film formation conditions when a great quantity of hydrogen not exist in an atmosphere are selected so that the quantity of bound hydrogen in the semiconductor thin film is 10at.% or less, especially it is preferable to be 3at.% or less. Further, the thickness of the semiconductor thin film which is formed at a time among repeating processes is defined to 3-1000Angstrom and, for example, such an operation is repeated 40 times to form thin films. lt is preferable for a film formation temperature to be determined by making its temperature conform to the reforming process 2. Then, repeating time of both processes 1 and 2 is exceedingly shortened by adopting film-formation means so that basically the temperature of respective processes is determined without relying upon materials. A highly stable thin film is thus obtained efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to improving the performance of an amorphous solar cell, and particularly relates to the amorphous Fl! Concerning technology to improve the quality of II.

(Background Art) Amorphous solar cells have already been put into practical use as a low-output energy supply source for driving calculators and watches. However, as in photovoltaic applications, 0.1 W
As for energy supply sources with large output as mentioned above,
Performance and stability are not satisfactory, and various studies are being conducted to improve performance. However, this improvement in performance is essential for hydrogenated amorphous silicon, which is formed by film formation methods such as plasma CVD, photoCVD, and thermal CVD, and is difficult to improve. There was also a pessimistic view.

In order to solve this problem, Japanese Patent Laid-Open No. 14420/1983 proposes repeating the formation of a thin film and the plasma treatment using hydrogen or a halogenated substance, but the improvement in characteristics was not satisfactory. We believed that this problem was due to the fact that a large amount of hydrogen was entrained during film formation, forming hydrogenated amorphous silicon.
It was disclosed in No. 8909. In other words, the film formation process involves forming amorphous silicon with a low hydrogen content, and then improving the properties of this film. However, in this method, the film formation process and modification process are In the process, temperature conditions had to be changed significantly and long processing time was required.The present invention further improves this point dramatically.

[Basic coloring of the invention]

By adopting a film-forming method in which the temperature for forming a semiconductor thin film with a small amount of bound hydrogen (hereinafter referred to as film-forming) is basically determined regardless of the original F+, the film-forming process and modification process can be This significantly shortens the repetition time.

(Disclosure of the Invention) The present invention comprises a process for forming a semiconductor thin film having a bound hydrogen content of IO atomic % or less (hereinafter referred to as a film formation process) and a process for exposing it to a discharge atmosphere containing a reactive gas (hereinafter referred to as a modification process). It is a semiconductor thin film formed by repeating the above steps, and more preferably, in repeating the film forming step and the modification step, the thickness of the semiconductor thin film formed in one repeat is 3 to 1000. It is a semiconductor thin film.

In the film forming process of the present invention, a film forming method that reduces the amount of bound hydrogen 1 is adopted. Specifically, physical film deposition methods such as vacuum evaporation, sputtering, and ion blating, and chemical vapor deposition (CVD) such as optical CVD and plasma CVD are used.
This is a process of forming a film using a method. The modification step is a step of improving the properties of a semiconductor thin film by generating a discharge containing a non-depositing reactive gas and exposing the thin film to the atmosphere of this discharge.

In the present invention, the film formation process and the modification process to form a thin film with a small amount of bound hydrogen are repeated, and the thickness of the semiconductor thin film formed by one repetition is 3 to 10%.
Although it is sometimes preferable to specify 00 people, other film forming conditions do not particularly impede the effects of the present invention.

First, an effective physical film forming method will be explained below.

Silicon, silicon carbide,
Substantially hydrogen-free substances such as elements, compounds, and alloys such as silicon nitride, silicon-germanium alloy (or composite powder), and silicon-tin alloy (or composite powder) can be effectively used as targets. Other than these, elements, compounds, and alloys such as carbon, germanium, and tin can also be used.

The film forming conditions in the present invention are not particularly limited, except that the amount of bound hydrogen is less than the value specified in the present invention, that is, the amount of bound hydrogen in the semiconductor thin film is 10
atomic % (hereinafter a(χ) or less, preferably 5 a
tx or less, particularly preferably 3atX or less,
Film forming conditions are selected such that a large amount of hydrogen does not exist in the atmosphere. In addition, if it exceeds 10 atomic %, the effect will be very small (and the purpose of the present invention cannot be achieved.Of course, as long as these conditions are satisfied, inert gas, hydrogen, carbonization Films can be formed in an atmosphere of hydrogen, fluorine, oxygen gas, etc.Specifically, the gas flow rate is
1 to 100 sec, reaction pressure is 0.001 mto
The range is rr = 10 mtorr. Also, depending on the film formation speed, fi! - Film forming conditions such as pressure and power can be selected as desired. Regarding the film formation temperature, film formation is performed by controlling the substrate temperature. Although the temperature range is basically not subject to any restrictions, it is preferable to set the temperature in accordance with the reforming process. Specifically, it is selected within a temperature range of 500°C or less.

Next, a specific example of an effective CVD method will be shown below.

One ship type 5iJIz++”z as raw material gas for film formation
Silane compounds such as monosilane, disilane, trisilane, and tetrasilane expressed by the formula (wherein is a natural number), fluorinated silane, silicon carbide, hydrocarbons, and the like are used. In addition, hydrogen,
It is also possible to introduce gases such as fluorine, chlorine, helium, argon, neon, nitrogen, etc. together with the raw material gas. When using these gases, o, oi ~ 1
It is effective when used in a range of 0.00% (volume ratio), and is appropriately selected in consideration of the film formation rate and film characteristics (hydrogen content, etc.).

As with the physical film-forming method, there are no particular limitations on the film-forming conditions other than reducing the amount of bonded hydrogen. The amount of bonded hydrogen in the semiconductor'3 antinode is 10 aLX or less, preferably 5atX or less, particularly preferably 3a
Film forming conditions are selected so that the amount is t% or less. If it exceeds 10 atomic %, the effect becomes very small and the object of the present invention cannot be achieved.

The specific conditions will be disclosed below. In photo-CVD, film formation is performed by decomposing a source gas using an ultraviolet light source with a wavelength of 350 na or less, such as a low-pressure mercury lamp, deuterium lamp, or rare gas lamp. As conditions during film formation, gas flow 11=
100 sccm, reaction pressure of 15 mtorr to atmospheric pressure, substrate temperature of 200 to 600'C, and considering the heat resistance of the M plate, the film formation time considered from the film formation rate, the plasma treatment temperature of post-processing, etc., more preferably 300 sccm. ~500°
It is appropriately selected within the range of C.

In addition, regarding plasma CVD, the discharge method is as follows:
Methods such as high frequency discharge, direct current discharge, microwave discharge, and ECR discharge can be effectively used. Raw material gas flow 11
~900 sec, reaction pressure 0.001IltOrr
A range of ~atmospheric pressure and power of 1 mW/cJ to 10 W/cJ is sufficient. These film forming conditions are changed as appropriate depending on the film forming rate and the discharge method. Substrate temperature is 200-60
The temperature is 0°C, more preferably 300 to 500°C. Note that within this range, higher temperatures are more preferable.

In the present invention, the reforming step involves introducing a non-depositing reactive gas into the reforming chamber, generating a discharge, and adding to this discharge atmosphere,
This is a process of exposing the thin film formed in the film forming process.

As a method for generating discharge, high frequency discharge, direct current discharge, microwave discharge, ECR discharge, etc. can be effectively used. Non-depositing reactive gases include hydrogen, fluorine, fluorine compounds, etc., and hydrogen gas, hydrogen fluoride gas, fluorine gas, nitrogen trifluoride, carbon tetrafluoride, etc. can be effectively used. Further, a mixed gas of these gases may be used.

Specific conditions for the modification step will be disclosed next. The discharge is performed at a discharge power of 1 to 500-1, a flow rate of non-depositing reactive gas, and a flow rate of 5 to 500-1.
500sccm, pressure, 0. It is generated and maintained in the range of OO 1 mL to atmospheric pressure. The temperature conditions in the modification process are controlled by the temperature of the substrate. This substrate temperature is
The temperature is the same as or lower than the substrate temperature in the film forming process, and is preferably 200 to 600°C from room temperature.
It is oc.

In one film forming process, 3 to 1000 people are preferred. Further, a film thickness of less than 3 layers is not preferable because, although the modification effect is achieved, the number of repetitions of film formation and modification increases from the viewpoint of practicality. Note that the overall thickness of the semiconductor thin film is not particularly limited, but is usually about 8 to 10 m.
Preferably at the level of a monk.

The time required for one cycle is not particularly limited, but is within 1000 seconds. It is preferable that the time from the film forming process to the modifying process and the time from the modifying process to the film forming process be as short as possible; this time depends on the shape and dimensions of the apparatus and the vacuum IJl-gas system. Specifically, the time can be shortened to less than 30 seconds.

There are no limitations on the substrate on which the semiconductor thin film of the present invention is to be formed, other than that it can withstand the process temperature of the present invention. Translucent materials such as blue plate glass, borosilicate glass, and quartz glass, metals, ceramics, heat-resistant polymer materials, and the like can be used as the substrate. Further, it goes without saying that substrates on which electrodes are formed, which are used for solar cells, sensors, etc., can also be effectively used in the present invention.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

[Example 1] An example of an apparatus for implementing the present invention is shown in 1rA. The apparatus is composed of a film forming chamber 1 and a reforming chamber 2, each of which has a sputtering device for depositing silicon and an electrode for generating electric discharge. These two chambers are connected by a transport device, and the substrate can be continuously moved between the two chambers to repeat film formation and modification. For sputtering, high-frequency magnetron sputtering was used in consideration of film formation speed and other factors.

As a starting material, high purity silicon was set as a cathode, and argon gas was introduced at 10105e. The substrate temperature was set at 300'C, which is the temperature for the next modification step, and the pressure in the reaction chamber was set at 0.6 mtorrs.The substrate on which a Sil film was deposited by applying 1000 kHz of high-frequency power was 6
It was transferred to the reforming chamber within 0 seconds. It was confirmed that the amount of bound hydrogen in this sin film was 1aL% or less, as shown in Comparative Example 1 below. In the reforming chamber, hydrogen gas 1
00sec+*, pressure 0.2 Lorr, high frequency power 50W was applied to generate high frequency discharge, and 5iF for 30 seconds.
1 membrane was exposed during a discharge. The substrate that had undergone the modification process was transferred to the film formation chamber again, and the film formation process and the modification process were repeated under the same conditions. By repeating the test 40 times, one membrane for about 4000 people was obtained. Here, the substrate is a Si1 film formed on a quartz substrate using a quartz glass substrate and a single crystal Si3 plate.
The optical properties of the film were measured, and a metal bridge was formed on a part of the film to measure the electrical properties. In addition, the sample formed on the single crystal Si substrate was measured by infrared absorption spectrum.
This was used as a sample to estimate the amount of bound hydrogen. The amount of bonded hydrogen can be determined using the secondary ion '11 analysis method (SIM
Confirmed by S).

As a result, the properties of the obtained S1 thin film are as follows: optical bandgap 1.65 eV, pseudo sunlight (A?l-1
,5) Electrical conductivity under 100IIW/c irradiation (photoconductivity)
is 2 x 10-'S/c+*, dark conductivity is 7 x
10-”S/cm, activation energy 0.82e
V, and the amount of bound hydrogen was 5atχ.

Furthermore, in order to examine the photostability of this Si thin film, it was continuously irradiated with simulated sunlight AM-1 at 5100 mW/cm for 20 hours, and changes in photoconductivity were observed. The change in photoconductivity after 20 hours with respect to the initial photoconductivity was 5% or less, and it was found that the thin film was extremely stable.

[Example 2] In Example 1, only the film forming thickness and the modification time were changed to about 3 people and 6 seconds, respectively.

The film formation thickness was changed by changing the film formation time. In Example 1, the film formation rate by sputtering was found to be about 1 input/second, so in this example, the time for one film formation was set to 3 seconds. Film formation process - Modification process 135
After 0 repetitions, approximately 4000 thin films were obtained. The same measurements as in Example 1 were carried out and the following results were obtained. Optical bandgap 1.59e, simulated sunlight CAM-1
,5) roomW/c - conductivity under irradiation (photoconductivity) is 3X 10-'S/cm, dark conductivity is 5X10"S/c
m, activation energy 0. "80eν, amount of bonded hydrogen 3
It was ad.

Furthermore, in order to investigate the photostability of this 5iFll film,
Simulated sunlight AM-1, 5100 mW/cd was continuously irradiated for 20 hours, and changes in photoconductivity were observed. The change in photoconductivity after 20 hours with respect to the initial photoconductivity was 5% or less, and it was found that the thin film was extremely stable.

Although this example is very effective, the number of times of film formation and modification was more than 30 times that of Example 1.

[Example 3] In Example 1, only the film forming thickness and the modification time were changed to about 1000 people and 300 seconds, respectively. The film formation thickness was changed by changing the film formation time.

In Example 1, the film formation rate by sputtering was found to be about 1 input/second, so in this example, the time for one film formation was set to 1000 seconds. Approximately 4000 thin films were obtained by repeating the film forming process and the modification process four times. Example 1
A similar measurement was carried out and the following results were obtained. Optical bandgap 1.73eV, TM-like solar light (AM-1
, 5) The conductivity (photoconductivity) under 100 mW/c+a irradiation is 5 X 10-'S/cm, and the dark conductivity is 5 X
10-” S/c+*, activation energy 0.87
eV.

The bonded hydrogen was 118atχ.

Furthermore, in order to investigate the photostability of this Sll film, we conducted a pseudo(
After that, the sunlight was continuously irradiated with M-1,5100s+W/c- for 20 hours, and changes in photoconductivity were observed. The change in photoconductivity after 20 hours with respect to the initial photoconductivity is about 8χ,
It turned out to be an extremely stable thin film.

[Comparative Example 1] In Example 1, after the formation of the Sil film, the Fit film was formed to a thickness of 4000 mm without going through the modification process. −
'S/cm, dark conductivity 6xlO-'S/cm,
The amount of bound hydrogen was less than 1 at%. This film property is significantly lower than the film property shown in Example 1 (it does not exhibit photoelectric properties and cannot be used as a material for a photoelectric conversion IA element. In this comparative example, the amount of bound hydrogen is 10 at
This shows that even if it is less than X, the effects of the present invention cannot be exhibited unless the modification step is performed.

[Comparative Example 2] In Example 1, after forming the Si thin film to a thickness of 4000 mm (bonded hydrogen content was 111 aL% or less), a modification process was performed. The properties of the three films obtained by this method, in which the modification was carried out for a discharge time of 1200 seconds, were as follows: photoconductivity 2X 10-
'S/c++, dark conductivity lXl0-' S/cm, and the amount of bonded hydrogen was 11 atχ. This film property was lower than the film property shown in Example 1, and exhibited properties similar to those of a Si thin film obtained by the conventional glow discharge method or photo-CVI method. When this photostability was measured,
The rate of change in photoconductivity shows a change of approximately one order of magnitude, compared to the conventional s
The comparative example, which was about the same as the i thin film, clarifies the importance of the amount of bound hydrogen in the present invention, and the loa
It is clear that when the amount of bound hydrogen exceeds tχ, there is no effect even in repeating the film formation-modification process.

(Comparative Example 3) In Example 1, the film formation process was carried out by reactive sputtering in which hydrogen was added to Ar. When the amount was measured, it was confirmed that it was 13ai,%.) The properties of the thin film obtained by the 0-piece method were as follows: photoconductivity: 5 x 10-'S/cm; dark conductivity: 6 x 10-'S/cm.
- ”S/c@, and the amount of bonded hydrogen is 12 atχ
Met. This film property was lower than the film property shown in Example 1, and exhibited properties similar to those of a Si thin film obtained by a conventional glow discharge method or photo-CVO method. When this photostability was measured, the rate of change in photoconductivity decreased after about 50 m, and although it was more effective than the conventional Si thin film, the effect was extremely small compared to the present invention. It was something.

Similar to Comparative Example 2, this comparative example is an example that clarifies the importance of the amount of bound hydrogen. Even if the I thickness is selected under favorable conditions and the film formation-modification process is repeated,
This clearly shows that the effect is small.

〔Effect of the invention〕

As is clear from the above Examples and Comparative Examples, the amorphous semiconductor thin film produced using this method has extremely good photoelectric properties and is stable against light irradiation, which is an essential problem. is also significantly improved. This leads to improvement in the photoelectric conversion efficiency and reliability of the amorphous solar cell. Therefore, the present invention can provide a technology that enables high conversion efficiency and high reliability required for power solar cells, and is an extremely useful invention for the energy industry.

[Brief explanation of drawings]

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

Claims (2)

[Claims] (1) A semiconductor thin film formed by repeatedly performing the step of forming a semiconductor thin film having a bound hydrogen content of 10 at % or less and the step of exposing it to a discharge atmosphere containing a reactive gas. (2) In repeating the process of forming a semiconductor thin film with a bound hydrogen content of 10 atomic % or less and the process of exposing it to a discharge atmosphere, the thickness of the semiconductor thin film formed in one repetition is 3.
2. The semiconductor thin film according to claim 1, which has a thickness of from 1000 Å to 1000 Å.