JPH04367221A - Method and apparatus for formation of nonsingle-crystal silicon film - Google Patents

Abstract

PURPOSE:To form a stable and high-quality film wherein its deterioration is small by a method wherein a nonsingle-crystal silicon film is deposited while repeating alternately the steps of depositing nonsingle-crystal silicon layers on a substrate and irradiating the deposited nonsingle-crystal silicon layer with a hydrogen plasma. CONSTITUTION:A nonsingle-crystal silicon film is formed by repeating alternately the steps of depositing single-crystal silicon films on a substrate and irradiating the deposited nonsingle-crystal silicon film with a hydrogen plasma. When the nonsingle-crystal silicon film is deposited, high-frequency electric power and microwave electric power are applied. When it is irradiated with the hydrogen plasma, microwave electric power is applied and high-frequency electric power is not applied. For example, while a raw-material gas (CH4 or the like) is being decomposed by RF electric power during the deposition time tD, a hydrogen plasma is applied by means of microwave electric power and nonsingle-crystal silicon is deposited; after that, the raw-material gas is stopped during the tA, and only the hydrogen plasma is applied by means of microwave electric power.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for forming a non-single crystal silicon film, and more particularly to a method and apparatus for forming a non-single crystal silicon film suitable for large-area non-single crystal silicon devices. .

0002

[Prior Art] Conventionally, a deposited film for a non-single crystal silicon device (non-single crystal includes amorphous, microcrystal, and polycrystal), such as an amorphous silicon film (hereinafter abbreviated as a-Si film), has been manufactured. The method is RF using SiH4 or Si2H6 as a film forming gas.
A plasma CVD method (so-called GD method), a microwave plasma CVD method, or a reactive sputtering method performed in Ar plasma using a Si target in the presence of hydrogen gas has been used.

Furthermore, in addition to this, optical CV
D method, ECRCVD method, Si vapor deposition method in the presence of hydrogen gas, etc. have been reported.
There are also examples of film formation using the VD method.

Most of the a-Si films obtained by these methods are so-called hydrogenated a-Si containing 10% or more hydrogen, and only those that exhibit properties as electronic materials that can be used in a-Si devices All contain 10% or more hydrogen.

The most widespread method for producing such a-Si films is the plasma CVD method, in which S
Using iH4 or Si2 H6 gas, dilute with hydrogen gas as necessary to achieve 13.56MHz or 2.45G.
Plasma is generated with a high frequency of Hz, and the plasma decomposes the film forming gas to create a reactive precursor, and the a-Si film is deposited on the substrate.

[0006] In the film forming gas, PH3, B2 H6
, BF3, etc., an n-type or p-type a-Si film is formed, and various a-Si devices have been made using these.

In the case of an a-Si film, unlike single-crystal Si, it can be formed on a low-temperature substrate or a glass substrate, it can easily be made into a large area, and it has stronger light absorption than crystals and isotropic properties. Because it has no direction and has no direction, it has opened up a field of use different from that of crystals. Main non-monocrystalline silicon devices include solar cells, image sensors such as line sensors and area sensors, TFTs or TFT arrays or matrices used for driving liquid crystal displays and switching optical sensors, and electrophotographic photoreceptors. Although there are examples such as single optical sensors, the core of non-single crystal silicon devices is the above-mentioned large-area device that takes advantage of its characteristics.

[0008]

[Problems to be Solved by the Invention] However, non-conforming materials such as a-Si films produced by conventional film-forming processes such as plasma CVD, which are applied to devices using photoelectric conversion such as image sensors and solar cells, are difficult to solve. Single crystal silicon suffers from photodegradation (so-called Stabler-Wron).
There is a problem in that the characteristics deteriorate due to the phenomenon (ski effect).

The cause of this photodeterioration is thought to be that the photoelectric conversion efficiency decreases due to dangling bonds existing in the a-Si film or weak bonds between Si being broken.

The degree of photodegradation varies depending on the process conditions of the a-Si film (substrate temperature, film forming pressure, source gas concentration, decomposition power, etc.).

[0011] Also, among the commonly produced ones,
The film contains 10 at% or more of hydrogen,
For this reason, a dense structure cannot be obtained.

In order to lower the hydrogen concentration in this film, if hydrogen is simply reduced under high temperature conditions, the crystallization of Si will be promoted, the light absorption coefficient will decrease, and the uniformity will be reduced due to the influence of crystal grain boundaries. However, there are disadvantages such as a decrease in the optical density, which is often inconvenient especially when used in a light-receiving device.

Further, even when used in thin film transistors, the above-mentioned deterioration and non-uniformity cause serious problems in characteristics.

[0014] Such deterioration and instability of a-Si devices are particularly serious in the case of large-area devices, and pose a problem in that they impede manufacturing yield and cost. (Objective of the Invention) Therefore, the present invention provides a method for forming a stable, high-quality non-single-crystal silicon film with little deterioration, and by using this method, an a-Si device with similar excellent characteristics can be produced. The purpose is to provide.

[0015]

[Means and Effects for Solving the Problems] The above-mentioned object of the present invention is to provide a method for manufacturing non-single crystal silicon, for example, an a-Si device, by using the following method in the step of forming an a-Si layer. achieved.

That is, a method for depositing a non-single-crystal silicon film in which the steps of depositing a non-single-crystal silicon layer on a substrate and irradiating the deposited non-single-crystal silicon layer with hydrogen plasma are alternately repeated. In this example, radio frequency (RF) power and microwave power are used when depositing a non-single crystal silicon layer, and microwave power is used when irradiating hydrogen plasma. Further, in the above method, the RF power is turned ON/OFF in accordance with the switching between the time of depositing the non-single crystal silicon layer and the time of irradiation with hydrogen plasma.

Another object of the present invention is to solve the above-mentioned problems by using a film-forming apparatus capable of carrying out the film-forming method described above.

The means of the present invention and its effects will be explained in more detail below.

The procedure for depositing an a-Si film in the present invention is as shown in FIG. The process consists of repeating a set of steps of irradiating hydrogen plasma for a certain period of time tA. During the deposition time tD,
While the raw material gas (SiH4 or Si2 H6) is decomposed using RF power, hydrogen plasma is irradiated using microwave power to deposit non-single crystal silicon, and the subsequent tA
During this period, the source gas is stopped and only hydrogen plasma is irradiated using microwave power. During this time, RF power is stopped.

As an example, let the deposition rate during tD be VD
Then, the deposited film thickness L after each step is repeated n times and the time tT required for this are simply calculated as follows.

[0021]

[Equation 1] L=vD tP n

[0022]

[Equation 2] tT = (tD + tA)n Therefore, the average deposition rate VD is

[0023]

[Math. 3] VD = L/tT = tD / (tD+tA
)*VD. When a film is actually formed, L almost matches the value of the above formula. An appropriate film thickness can be obtained even if tD, vD, and tA are constant or varied in each step.

During tA, the surface of the deposited film is irradiated with atomic hydrogen from a hydrogen microwave plasma. The mechanism behind this is not necessarily clear, but it is thought that hydrogen atoms penetrate into the deposited film to some extent, extracting excess hydrogen atoms existing in the film, and recombining the Si network (structural relaxation). A dense a-Si film with fewer ring bonds can be obtained.

Furthermore, if the thickness of the deposited film in each step is too thin, it will not be possible to maintain a stable amorphous structure, and hydrogen in the film will be extracted by the supply of hydrogen atoms, promoting microcrystalization and polycrystalization. Ru. On the other hand, if it is too thick, hydrogen atoms will not penetrate well into the deposited film, making it difficult for structural relaxation to proceed in the film. Therefore, non-single crystal silicon containing a-Si or μc-Si is formed depending on the thickness of the film deposited during tD, the amount of atomic hydrogen supplied to the film surface, and the irradiation time TA.

Since radio frequency (RF) power is stopped during hydrogen plasma irradiation, the hydrogen concentration in the film can be reduced to 5 at% or less without increasing plasma damage due to RF plasma and without increasing dangling bonds. can be reduced to.

[0027]

【Example】

(Example 1) Examples of the present invention will be described in detail below. FIG. 2 is a schematic structural diagram of a film forming apparatus used in this example. By using the apparatus shown in FIG. 2 to form an a-Si film, a pin-type photovoltaic device having the pin configuration shown in FIG. 3 was manufactured. FIG. 3 schematically shows the pin-type photovoltaic device produced in this example.

In FIG. 3, this example is a photovoltaic element having a structure in which light enters from the upper part of the figure.
00 is a photovoltaic element main body, 301 is a substrate, 302 is a lower electrode, 303 is an n-type semiconductor layer, 304 is an i-type semiconductor layer,
305 is a p-type semiconductor layer, 306 is an upper electrode (transparent electrode)
, 307 represent current collecting electrodes.

In the a-Si film forming apparatus shown in FIG.
is a reaction chamber, 201 is a substrate, 202 is a cathode electrode, 203 is an anode electrode, 204 is a heater for heating the substrate, 205 is a grounding terminal, 206 is a matching box, 207 is a 13.56MHZ RF power supply, 208 and 214 are exhaust pipes, 209 and 215 are exhaust pumps, 2
10, 211 is a film forming gas introduction pipe, 216, 217 is an air operated valve, 220, 230, 240, 250, 260, 2
22, 232, 242, 252, 262 are valves, 22
1,231,241,251,261 are mass flow controllers, 270 are microwave plasma generators, 27
2 is a microwave waveguide, 271 is a plasma generation chamber, 27
3 indicates a 2.45GHz microwave power source.

An air-operated valve 21 is provided in the film-forming gas introduction pipe 211.
6,217 are installed, and air operated valves 216,
217 so that one side is open and the other side is closed, the deposition gas introduction pipe 211 or the exhaust pipe 2 can be opened.
14. When the air-operated valve 217 is open, the deposition gas is introduced into the reaction chamber 200 and is exhausted out of the system by the exhaust pump 209 through the exhaust pipe 208.

Furthermore, when the air-operated valve 216 is open, the film-forming gas does not pass through the reaction chamber 200 and is discharged out of the system by the vacuum pump 215. The other gas introduction pipe 210 is supplied with H2 and Ar from a cylinder (not shown), communicated with the plasma generation chamber, and supplied to the reaction chamber 200. Microwaves supplied from the microwave power source 273 pass through the waveguide 272 and reach the plasma generator 2.
Enter 70.

In this apparatus, the film forming gas is introduced into the inlet pipe 211.
Alternatively, the mass flow will operate normally no matter which direction the exhaust pipe 214 is connected. Furthermore, by switching the air-operated valve, the film-forming gas flows at a constant flow rate without stagnation.

Next, a procedure for manufacturing a photovoltaic device having a pin configuration shown in FIG. 3 using the a-Si film of the present invention in the i-layer will be explained.

First, the surface was polished to 0.05 μmRm.
5cm square size stainless steel (SUS)
304) Put the substrate 301 into a sputtering device (not shown),
After evacuating the inside of the device to 10 −7 torr or less,
Introducing Ar gas and setting the internal pressure to 5mtorr at 200W.
A DC plasma discharge was generated with a power of 200 Å, and sputtering was performed using an Ag target to deposit approximately 5000 Å of Ag.

Thereafter, the target was changed to ZnO, DC plasma discharge was generated under the same internal pressure and power conditions, and sputtering was performed to deposit ZnO with a thickness of about 5000 Å.

After producing the lower electrode 302 through the above steps, the substrate 301 is taken out and attached to the anode 203 in the reaction chamber 200, sufficiently evacuated by the vacuum pump 209, and the reaction chamber 200 is evacuated using an ion gauge (not shown). After confirming that the degree of vacuum is 10-6 torr or less and the substrate temperature stabilized at 250°C, close the valve 26.
0 and 262, and control the flow rate of the mass flow controller 261 to supply Si from a SiH4 gas cylinder (not shown).
30 sccm of H4 gas was introduced into chamber 200 through air operated valve 217.

Similarly, valves 220 and 222 are opened,
The mass flow controller 221 controls the flow rate and H2
Supply gas at 30 sccm, open the valves 240 and 242, and control the flow rate with the mass flow controller 241 to supply 10 sccm of PH3 gas diluted to 5% with H2 gas.
cm was introduced.

[0038] The internal pressure of the reaction chamber 200 is set to 0.5 to
After adjusting to rr, 10 W power was applied from the RF power source 207 via the matching box 206, plasma discharge was performed for 3 minutes, and an n-type a-Si layer 303 was deposited to a thickness of 400 Å.

After that, the gas supply is stopped, and the reaction chamber is evacuated again until the degree of vacuum becomes 10-6 torr or less. Then, the valves 220 and 222 are opened and the H2
Gas was introduced into the reaction chamber 200 at 30 sccm.

Next, with the air-operated valve 217 open, the valves 260 and 262 are opened to control the flow rate of the mass flow controller 261, and the flow rate of SiH4 gas is 30 sccm.
was flowed into the film-forming gas introduction pipe.

In this state, the reaction chamber pressure is set to 0.1 t.
Adjusted to orr. In this state, 10W of radio frequency (RF) power is applied from the RF power source 207 to generate SiH4 plasma discharge, and on the other hand, H2 plasma is generated in the microwave plasma generation chamber 271, and atomic hydrogen is transferred to the reaction chamber. Deposition of the a-Si film was started while supplying 200 ml of the a-Si film.

After depositing the a-Si film for 30 seconds, the radio frequency (RF) power is stopped and the air operated valves 216, 217
The SiH4 gas was exhausted from the exhaust pipe 214 by reversing the opening and closing of the chamber, the supply of SiH4 gas to the chamber was stopped, and hydrogen (H2) plasma irradiation was performed for 40 seconds.

Thereafter, radio frequency (RF) power is turned on again and SiH4 gas is introduced into the chamber at the same time to deposit an a-Si film for 30 seconds.

That is, in this way, the introduction of SiH4 gas and the input of radio frequency (RF) power are turned on and off, and then turned off.
As a result of repeating the hydrogen plasma irradiation process 200 times during F, a 6000 Å thick i-type a-
A Si layer 304 was deposited.

After depositing the i-type a-Si:H layer 304, after stopping the plasma discharge and cutting off the gas supply, the degree of vacuum in the reaction chamber was lowered to below 10-6 torr, and the substrate temperature was changed to 200°C. After stabilizing, valves 220, 22
2,230,232,260,262 and the air operated valve 217 were opened, and 1 sccm of SiH4 gas and 10 sccm of B2 H6 gas diluted to 5% with H2 gas were added.
H2 gas was introduced into the reaction chamber 200 at 300 sccm.

After adjusting the chamber pressure to 0.1 torr, 50 W of power was applied from the RF power source 207 to generate plasma discharge and film formation was performed for 15 minutes to completely remove the p layer 305.
00 Å deposited.

Next, the substrate 301 is placed in the reaction chamber 200.
, and put it in a resistance heating vapor deposition device (not shown).
After evacuating the inside of the device to 10-7 torr or less and maintaining the substrate temperature at 160°C, oxygen gas was introduced and the internal pressure was reduced to 0.
．． After setting the torque to 5 mtorr, an alloy of In and Sn was vapor-deposited by resistance heating to form a transparent conductive film (ITO) which also had an anti-reflection effect.
A film) of 700 Å was deposited to form the upper electrode 306.

After completion of the vapor deposition, the sample was taken out and separated into 1 cm×1 cm cells using a dry etching device (not shown), and then an aluminum current collecting electrode 307 was formed using another vapor deposition device.

As a comparative example of this example, a conventional method was used to form the i-layer, in which SiH4 gas was not intermittently introduced, but plasma discharge was used in which high frequency power was continuously applied. Similarly, a photovoltaic device having a pin structure was fabricated. The gas flow rate, pressure, high frequency power, and i-layer film thickness were the same as in Example 1.

These samples were exposed to 100 AM-1.5 sunlight spectrum using a solar simulator.
By irradiating with an intensity of mW/cm2 and determining the voltage-current curve, the initial photoelectric conversion efficiency η(0) of the photovoltaic element was determined.
was measured.

Next, the optimum load was calculated from the open circuit voltage VOC and short circuit current VSC obtained by determining the voltage-current curve, and a load resistance was connected to each sample. Next, apply the same AM1.5 light (1
00 mW/cm2) for 500 hours, the photoelectric conversion efficiency η(500) when the sample was irradiated with AM1.5 light was determined in the same manner as described above.

[0052] The thus obtained η(500) and η
(0), the deterioration rate {1-η(500)/η(0)} was calculated. Further, the hydrogen concentration in the i-layer was determined by infrared absorption spectroscopy using a sample deposited on a Si wafer.

As a result, the a-Si:H film of the present invention was
The photovoltaic element with a pin configuration used for the layer had an initial conversion efficiency of 1.2 and a deterioration rate of 0.1. Since the optical device manufactured according to the conventional comparative example had an initial conversion efficiency of 0.85 and a deterioration rate of 0.8, it can be seen that the device of this example had a high initial conversion efficiency and a low deterioration rate. In particular, the decrease in deterioration rate is remarkable.

Further, the hydrogen concentration in the i-layer was 3 at % in the present example and 9 at % in the comparative example.

(Example 2) In order to investigate the basic characteristics of an a-Si film, a-Si was deposited on a 50 mm x 50 mm Corning 7059 substrate under the same conditions as in Example 1 by the method of the present invention without making it into a device. Only the film was formed.

The steps of s-Si film deposition and H2 plasma irradiation were repeated 300 times to form an a-S film of about 9000 Å.
i film was deposited.

A comb-shaped aluminum electrode with a gap width of 250 μm was deposited on this film, and the photoelectric conductivity was measured.
It was determined that the film was 0-4 to 10-5 s/cm, which was larger than the conventional film and of good quality.

[0058] Furthermore, photodeterioration was also significantly reduced. Further, the Raman spectrum does not have a peak near 520 cm-1, but only a peak near 480 cm-1. This means that the film produced according to the present invention maintains an amorphous structure.

[0059]

[Effects of the Invention] As explained above, according to the present invention,
This method involves repeating the deposition of a non-monocrystalline silicon film and irradiation of the deposited film with hydrogen plasma. Plasma damage is reduced by stopping radio frequency (RF) power during hydrogen plasma irradiation, and photovoltaic damage to the non-monocrystalline silicon film is reduced. Improving conversion efficiency,
It is possible to reduce the photodegradation rate and the hydrogen concentration in the film, thereby improving the characteristics of non-single-crystal silicon devices, and further improving yields and reducing manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the film forming method of the present invention,

[Figure 2
]A schematic diagram showing a film forming apparatus for producing the non-single crystal silicon film of the present invention,

FIG. 3 is a diagram schematically showing a photovoltaic device with a pin configuration using the non-single crystal silicon (a-Si:H) film of the present invention in the i-layer.

[Explanation of symbols]

200 Reaction chamber 201 Substrate 202 Cathode electrode 203 Anode electrode 204 Substrate heater 205 Grounding terminal 206 Matching box 207 Radio frequency (RF) power source 208, 214 Exhaust pipe 209, 215 Exhaust pump 210, 211 Gas introduction pipe 220, 230, 240, 250, 260, 222, 2
32,242,252,262 valve 221,
231, 241, 251, 261 Mass float controller 270 Microwave plasma generator 271
Plasma generation chamber 272 Microwave waveguide 301 Substrate 302 Lower electrode 303 N-type semiconductor layer 304 I-type semiconductor layer 305 P-type semiconductor layer 306 Transparent electrode 307 Current collector electrode

Claims (3)

[Claims] 1. A method for forming a non-single-crystal silicon film, comprising alternately repeating steps of depositing a non-single-crystal silicon film on a substrate and irradiating the deposited non-single-crystal silicon film with hydrogen plasma. , depositing a non-single crystal silicon film, applying high frequency power and microwave power during deposition of the non-single crystal silicon film, applying the microwave power during the hydrogen plasma irradiation, but not applying the high frequency power; A method for forming a non-single crystal silicon film characterized by: 2. The non-single crystal silicon film according to claim 1, wherein the source gas is decomposed by the high-frequency power to deposit the non-single crystal silicon film, and the hydrogen plasma irradiation is performed by the microwave power. Method for forming silicon film. 3. A reaction vessel into which a raw material gas is introduced, a means for inputting high frequency power and microwave power to the raw material gas to decompose it and depositing a non-single crystal silicon film, and a means for inputting only the microwave power. a non-single-crystal silicon film characterized by comprising: means for irradiating the deposited non-single-crystal silicon film with hydrogen plasma; and means for alternately performing the depositing means and the means for irradiating hydrogen plasma. Film deposition equipment.