JP2846534B2 - Plasma CVD apparatus and method for forming functional deposited film using the same - Google Patents

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 functional deposited film, and more particularly to a discharge ignition method and a laminated thin film element such as a photovoltaic element in a semiconductor deposited film forming apparatus using low-temperature plasma. The present invention relates to a method and an apparatus for forming a thin film to be used on a substrate.

[0002]

2. Description of the Related Art A low-temperature plasma process for a semiconductor functional element, an integrated circuit, and a magnetic element has been developed as a part of dry, low-temperature process, and fine pattern processing techniques. As a typical plasma process,
Plasma CVD and chemical dry etching by sputter deposition using a physical action and chemical reaction are known.

[0003] The low-temperature plasma is obtained by low-pressure gas glow discharge. One of the methods of generating the discharge is to apply a direct current or a high-frequency electric field to two plane electrodes separated from each other, and to obtain a plasma by causing a dielectric breakdown by impact of electrons and molecules accelerated in the electric field. This is a polarized glow discharge method. As another generation method, a non-polar discharge method using a high-frequency electric field is also known.

FIG. 13 shows a typical plasma CVD type film forming apparatus using a polarized high frequency glow discharge method. Two opposing plane parallel electrodes 1312 and 1313 are provided in an airtight container 1316 that can be evacuated and evacuated.
A high frequency voltage can be applied to the planar electrodes 1312 and 1313 from outside. Base 13 on which film is formed
Reference numeral 18 is fixed on the flat electrode. A film forming raw material gas is introduced into the container 1316 by the gas supply means 1319, and a high frequency voltage is applied between the planar electrodes to generate a discharge to form a film on the substrate. Gas type, gas supply amount,
The pressure, high frequency and high frequency power are selected to obtain the desired film quality (film formation conditions).

[0005] As a means for initiating discharge, there is a method in which an electric field between the electrodes is increased by supplying high-frequency power to lead to dielectric breakdown. Generally, the discharge starting power is the distance between the electrodes,
It depends on the electrode area, gas type and pressure. The high-frequency power required for starting discharge is often higher than the high-frequency power at the time of film formation, and a high-output high-frequency power supply is required, which raises the problem of increasing the apparatus cost.

In order to solve this problem, there is a method of starting discharge in a gas atmosphere having a low discharge starting power and gradually replacing the gas with a film forming material gas.

However, the two methods have different matching conditions of the high-frequency supply circuit at the start of discharge and at the time of film formation, so that two matching adjustments are required before film formation, which complicates the operation. There is also.

[0008] Further, the inside of the film forming container is contaminated with the deposited film during the two alignment adjustment times. Also, the source gas is wasted.

In a production line, this is undesirable as a factor that causes an increase in tact time and an increase in cost.

As a solution to the above-mentioned problem, a discharge ignition device is known. Reference numeral 1308 in FIG. 13 indicates a discharge ignition circuit. By superimposing and applying a DC high voltage together with a high-frequency power between the parallel plane electrodes 1312, 1313, the electric field emission of electrons is promoted, and the electrons are used as a seed for discharge. Further, in order to increase the electric field strength between the electrodes, a metal electrode having a small area which is close to and opposed to the high frequency application electrode is provided separately to apply a DC high voltage.

However, in the above-described discharge igniter, when a high DC voltage is applied, an arc discharge often occurs, and the metal forming the electrode evaporates and mixes as an impurity in a film formed on the substrate, thereby deteriorating the film quality. Is awake.

In order to prevent the electrode forming metal from reaching the substrate during the arc discharge, the substrate is isolated from the discharge by the shutter from the start of the operation of the discharge ignition device to the start of the discharge and the matching. The method has been taken. However, there remains a problem that the metal forming the discharge ignition electrode scattered on the film forming furnace wall and the high-frequency electrode is sputtered during the film formation and is taken into the formed film on the substrate, thereby deteriorating the film quality.

In the non-polar discharge method, a similar discharge starting means is employed. FIG. 14 shows a film forming apparatus using a microwave plasma CVD method as a non-polar discharge method. A microwave waveguide 142 generated by a high-frequency power supply 1415
The microwave propagating through 0 is introduced by microwave applicator means 1421. The film-forming source gas led into the container by the gas supply means 1419 is dissociated and discharged by the microwave to form a film on the base 1418 provided in the discharge space in the container. This device is also provided with a discharge igniter 1408 to facilitate the start of discharge.

The characteristic of the microwave discharge is 13.56 MH
High-density plasma is obtained compared to radio-frequency discharge in the radio frequency band represented by z, gas dissociation and decomposition are promoted, high-speed film formation is possible, and gas utilization efficiency is high. It is. On the other hand, since the frequency is high, in other words, the wavelength is short, it is difficult to obtain a uniform discharge over a large area. In order to obtain a uniform discharge, the microwave discharge is performed in a pressure range (10 ^-4 to 10 ^-1 Torr) lower than the pressure (10 ^-2 to several Torr) of the high-frequency discharge in the radio frequency band. As the discharge starting means, an ignition device similar to that used for radio frequency band radio frequency discharge is used, and the problems involved are the same as described above.

In recent years, research and development for mass production of functional deposited films has been actively conducted. For example, in manufacturing a large-area solar cell using amorphous silicon, a source gas containing an element serving as a dopant such as phosphine (PH ₃ ) or diborane (B ₂ H ₆ ) is mixed with silane or the like as a main source gas. Glow discharge decomposition to obtain a semiconductor film having a desired conductivity type. Therefore, since a semiconductor junction can be easily formed by sequentially forming these semiconductor films on a desired substrate, a solar cell can be manufactured at a considerably lower cost than a crystalline silicon solar cell.

Then, regarding the above-mentioned glow discharge decomposition,
RF (radio frequency) glow discharge decomposition techniques have been established in the art and are being widely used. However, as described above, a high-quality deposited film can be obtained only when the deposited film is formed at a low speed with low power as described above.
It has been extremely difficult to form a high-quality deposited film at high speed over a large area using high power and to manufacture a solar cell on an industrial scale so as to meet the power demand. Therefore, as a method of avoiding this difficulty, a plasma process using a microwave has been attracting attention. The reason why this process attracts attention is that, since the microwave frequency band is short, it is possible to increase the power density in the film formation chamber as compared with the case where RF is used, and it is possible to efficiently generate and sustain plasma. What you can do.

For example, in US Pat. Nos. 4,517,223 and 4,504,518, a glow discharge is generated by each microwave power, and a deposited film is formed on a substrate at a low pressure. A method of forming is disclosed. According to these publications, these deposited film forming methods form a film under a low pressure, so that when a large power is applied, recombination of radicals causing deterioration of the deposited film characteristics is prevented. Less, less generation of fine powder composed of polysilane etc. in plasma, improvement of film formation speed,
It is understood that there are such advantages.

However, in a plasma process using a microwave, the wavelength of the microwave is extremely short, about 1/180 of that of the conventional RF, and unlike the RF, there is no electrode. There is a problem that it is easy to occur. For example, there are still many unsolved problems in forming a desired deposited film uniformly on a large-area substrate such as a band-shaped substrate.

As an example of avoiding such a problem, JP-A-63-55112 discloses a microwave plasma CVD.
A method for producing a functional deposition film by a method is disclosed. In this method, for a device provided with microwave introduction windows facing each other, conventionally, opposed rectangular microwave introduction windows as shown in FIG. 15 (a) are installed such that their longitudinal directions are parallel. On the other hand, as shown in FIG. 15B, they are installed so that their longitudinal directions are orthogonal to each other. In this way, by introducing microwaves from the arranged microwave introduction window, microwave power can be supplied over a wide range, so that a functional deposited film can be formed over a large area. Further, when the microwave introduction windows are orthogonal to each other, the directions of the electric field (or magnetic field) are orthogonal to each other. There is an advantage that it becomes easy to be confined.

[0020]

Among the above-mentioned prior arts, the manufacturing by the polarized high-frequency glow discharge method requires a high-output high-frequency power source at the time of starting discharge, so that the apparatus cost is increased. There is a problem. In order to prevent this, the method of starting discharge using a gas having a low discharge start power and gradually replacing the gas requires two adjustments before film formation, which complicates the operation. There is. This complicated operation also occurs when the matching conditions of the high-frequency circuit at the time of forming the film at the start of discharge are different.

The method of accelerating the discharge by adding a discharge igniter has a problem that the quality of the formed film is deteriorated by the metal forming the discharge ignition electrode.

On the other hand, in the case where the opposed rectangular microwave introduction windows shown in FIG. 15B are arranged so that their longitudinal directions are orthogonal to each other to supply microwave power over a wide range, each microwave introduction window is provided. Are arranged so as to be orthogonal to each other, the height of the discharge furnace must be equal to or longer than the long side of the rectangular cross section of the microwave introduction window, and the microwave shown in FIG. The volume of the discharge furnace is inevitably larger than when the introduction windows are arranged in parallel. When the volume of the discharge furnace is increased, there has been a problem that the supply power of the microwave must be increased in order to make the power density of the microwave equal to that of the discharge furnace having a small volume.

Further, considering that the utilization efficiency of the raw material gas is equal to the area of the substrate surface exposed to plasma with respect to the total surface area in the discharge furnace, when the area of the substrate surface exposed to plasma is the same, the volume of the discharge furnace is reduced. As the surface area increases and the total surface area increases accordingly, the utilization efficiency of the raw material gas decreases.

In addition, in the production of a functional deposited film such as a photovoltaic element, there is known a method in which a high-quality deposited film can be produced by applying a DC or high frequency bias voltage together with microwave power. However, it is not easy to apply a bias voltage uniformly on the surface of the substrate, and as the volume of the discharge furnace increases, it becomes more difficult to apply a bias evenly, and it is necessary to uniformly produce a high-quality functional deposition film. Was difficult.

The present invention overcomes the above-mentioned problems in the conventional low-temperature plasma process, in particular, the silicon-based film forming process, and makes it easy to form a high-quality silicon-based functional element with a small amount of impurities in the formed film. It is an object of the present invention to provide a discharge ignition method.

Another object of the present invention is to facilitate the start of discharge in a silicon-based film forming process using low-temperature plasma, and to further reduce the manufacturing cost of a film forming apparatus.

[0027]

Means for Solving the Problems Plasma CVD of the present invention
The device is a plasma CVD device provided with a discharge ignition device for promoting electric field emission of electrons, wherein a discharge promotion electrode constituting the discharge ignition device is formed of silicon.

In this case, a distance adjusting mechanism for adjusting the distance between the electrodes for promoting discharge may be provided.

According to another aspect of the present invention, there is provided a plasma CVD apparatus for generating plasma in a discharge furnace by introducing microwaves from a microwave introduction window. In addition, a microwave reflector that can be opened and closed is provided in the discharge furnace to adjust the amount of microwave introduced from each microwave introduction window according to its reflection angle.

In this case, a microwave reflecting plate may be provided for each of the plurality of microwave introducing windows.

Further, the plurality of microwave introduction windows may be formed in a rectangular shape and arranged so that the directions of the electric fields of the microwaves supplied to the discharge furnace are parallel to each other.

Further, an electrode for applying a bias voltage may be provided at the bottom of the discharge furnace.

Microwave plasma CVD provided with a plurality of microwave introduction windows and microwave reflectors as described above
As a method of forming a functional deposited film using the apparatus, when starting a discharge, only a microwave reflection plate provided on a predetermined one of a plurality of microwave introduction windows is opened to introduce one microwave. The microwave is introduced only from the window to locally start the discharge, and then, while maintaining the discharge state, the microwave reflection plate provided on the adjacent microwave introduction window is opened and the microwave is introduced from the microwave introduction window. The microwave may be introduced to expand the local discharge region, and thereafter, the discharge region may be sequentially expanded by the same procedure to form a large-capacity microwave plasma to form a functional deposition film. .

[0034]

The present inventor describes the findings obtained through intensive studies in order to solve the above-mentioned problems in the conventional silicon-based film forming apparatus using low-temperature plasma and to achieve the object of the present invention. In the discharge igniter described in the section of the prior art, even if the electrode to which a DC voltage is applied is changed from metal to silicon, if a spark (dielectric breakdown) occurs due to the application of a high DC voltage, the silicon melts and scatters. May be. However, even if the scattered silicon is taken into the silicon formation film on the base, damage to the silicon formation film is insignificant.

Further, the silicon electrode is formed in a needle shape,
It was found that the electric field strength between the electrodes was increased by making the electrodes close to each other by about 3 mm, and dielectric breakdown easily occurred.

However, since the silicon electrode has a larger work function than the conventional metal electrode, the field emission of electrons from the electrode and the secondary emission due to ion collision are necessary for performing pilot discharge between the electrodes. In order to promote electron emission, it is necessary to apply a higher voltage than a conventional metal electrode.

In order to improve the above drawbacks, a method of emitting electrons from a silicon electrode, which can be used as a starting point for the main discharge, was studied. When the silicon electrodes to which a voltage is applied are brought into contact with each other, a short circuit occurs, and a large current flows at the tips of the two needle-shaped electrodes, which promotes the electric field emission of electrons by sparks and thermionic emission by heat generation. As a result, it was found that a pilot flame which induces the start of the main discharge could be sufficient.

When a plurality of microwave introduction windows for introducing microwaves are provided and a microwave reflection plate for adjusting the amount of introduced microwaves is provided, microwaves can be used efficiently. The plasma generation region in the discharge furnace can be different at the start of discharge and at the time of film deposition, respectively, and plasma suitable for the condition of the discharge furnace can be generated.

[0039]

(Embodiment 1-1) FIG. 1 is a view showing a high-frequency plasma CVD type film forming apparatus employing a discharge ignition method of the present invention.

The opposed flat electrode 1 is provided inside a container 116 which is configured to be airtight and can be evacuated from the exhaust port 117.
12, 113 (radius 5 cm, distance between electrodes 3 cm) are installed. A high frequency power supply 115 is provided between these electrodes.
Applies a high frequency power of 13.56 MHz. A substrate 118 on which a thin film is formed is fixedly provided on the flat electrode 113, and a raw material gas for forming the thin film is introduced into the container 116 by a gas introducing means 119.

The discharge ignition device employing the discharge ignition method of the present invention comprises electrodes 101 and 102, a DC power supply 105, and a distance adjusting mechanism 106.

Adjacent to the plane electrodes 112 and 113, φ2m
The electrodes 101 and 102 made of silicon, which are formed in a needle shape and opposed to each other, are provided with a DC power source 1 outside the container.
A voltage from 05 to several tens (kV) can be applied. The distance between the electrodes 101 and 102 can be adjusted from 0 to 5 mm by the distance adjusting mechanism 106.

Using the film forming apparatus shown in FIG. 1, the performance of the discharge ignition system was examined using high-frequency power required for starting discharge. Silane (SiH ₄ ) as a source gas for film formation is introduced into the container 116 evacuated to a reduced pressure state by gas introduction means 11.
9 and high-frequency power was applied between the opposed flat electrodes 112 and 113. Next, 10 kV from the DC power supply 105 was applied by the DC voltage application switch 107 of the discharge ignition device.
Was applied between the electrodes 101 and 102.

For comparison, the electric power at the time of starting the discharge by increasing the high-frequency power without using the discharge ignition device was also monitored.

FIG. 2 shows test conditions and results. It can be seen that the high frequency power required for starting the discharge was reduced by the discharge ignition device using the discharge ignition system of the present invention.

Embodiment 1-2 FIG. 3 is a view showing a microwave plasma CVD type film forming apparatus employing the discharge ignition method of the present invention.

The microwave applicator 321 receives microwaves of 2.45 GHz transmitted through the microwave waveguide 320 in a 15 cm + 15 cm + 20 cm container 316 that is configured to be airtight and can be evacuated from the exhaust port 317. be introduced. At the tip of the microwave applicator means, a microwave permeable window 322 is provided to isolate the microwave waveguide 320 at atmospheric pressure from the inside of the container 316 in a reduced pressure state. The source gas for film formation is introduced by gas supply means 319.

The discharge ignition device employing the discharge ignition method of the present invention comprises electrodes 301 and 302, a DC power supply 305, and a distance adjusting mechanism 306.

Adjacent to the plane electrodes 31 and 2313, φ2m
The electrodes 301 and 302 made of silicon and provided to face each other with a needle-shaped tip are provided with a DC power source 3 outside the container.
A voltage from 05 to several tens kV can be applied. Electrode 3
The distance between 01 and 302 can be adjusted from 0 to 5 mm by a distance adjusting mechanism 306.

In the apparatus of the present embodiment, the substrate 318 on which the film is formed is a base 331 parallel to the microwave introduction direction.
Fixed on top.

Using the film forming apparatus shown in FIG. 3, the performance of the discharge ignition system was examined based on the microwave power required for starting discharge.

At reduced pressure, silane (SiH ₄ ) and hydrogen (H ₂ ) were introduced into the container 316 being evacuated by gas introduction means 319 as source gases for film formation. In addition, microwave power is stored in the container 316 by the microwave applicator means 3.
Charged via 21.

Next, a DC voltage of 10 kV was applied between the electrodes 301 and 302 from the DC power supply 305 by the DC voltage application switch 307 of the discharge ignition device. The microwave power supply used was a 1.5 KW continuous oscillation specification with a maximum output. The pressure inside the container is controlled by the conductance variable valve 330.
Was adjusted.

FIG. 4 shows the results of the above test. Electrode 30
With the firing device the distance between 1,302 as 1 mm, the pressure is reduced the discharge start microwave power at 10 ^-2 Torr or more, effective was the but as the ignition device, a pressure is 10 ^-2 Torr or less No effect was observed.

When a high voltage was applied by bringing the silicon electrodes into contact with each other, it was effective as an ignition device up to the order of 10 ^-3 Torr.

If the film forming conditions are a pressure of 5 mTorr and a microwave power of 300 W, an output of 1.5 KW is not required as a microwave power supply, and a small power supply of about 600 W is sufficient. There is a large amount of reduction in apparatus cost caused by downsizing of a microwave power supply in response to an increase in apparatus cost due to installation of an ignition device.

Example 1-3 The discharge of the present invention was applied to a film forming apparatus (electrodeless microwave CVD method) for laminating an nip three-layer separation film by a substrate load lock transfer method shown in FIG. A single cell of an amorphous silicon solar cell was fabricated with an ignition device. Furthermore, in order to investigate the performance degradation of the cell due to the contamination of impurities from the discharge ignition device, a single cell was similarly prepared by mounting the conventional metal electrode discharge ignition device on the film forming device, and the quantum efficiency of the cell was compared. did.

In the film forming apparatus of this embodiment, the apparatus shown in FIG. 1 is connected between the carry-in chamber 551 and the carry-out chamber 505 by the gate valve 5.
06.

The single cell was formed by the following method. The substrate 561 made of stainless steel is set in the loading chamber 501 from the outlet 551, and the chamber is evacuated to a reduced pressure. Then, the gate valve 506 is opened, and the substrate is transferred to the n-layer deposition chamber 502 which has been evacuated to a reduced pressure in advance. Then, after the microwave was supplied to the film formation chamber, microwave discharge was started by the discharge ignition device 572 to form the n-layer.

After the formation of the n-layer, the substrate is similarly transported to the i-layer formation chamber 503 to form the i-layer, and then the p-layer formation chamber 50 is formed.
In step 4, a p-layer was formed.

Table 1 shows the conditions for forming the n, i, and p layers.

[0062]

[Table 1] The quantum efficiency of the cell was measured by irradiating AM1 light. FIG. 6 shows a quantum efficiency spectrum of the manufactured cell. Compared with a cell made using a conventional metal electrode discharge igniter, a cell made using the silicon electrode discharge igniter of the present invention has improved quantum efficiency in both the short wavelength region and the long wavelength region. ing.

When the elemental analysis in the thickness direction of the cell was separately performed by SIMS, it was found that the cell formed using the conventional discharge igniter made of a metal electrode had the vicinity of the interface between the ni layer and the i-layer.
The constituent elements of the metal electrode were detected near the p-layer interface.

When the discharge igniter made of a metal electrode is used, the decrease in the quantum efficiency of the cell is caused by the interface between the ni layer and the ip layer.
It was determined that it was caused by mixing of the metal electrode material at the layer interface.

From the above, it was found that a high-quality formed film and a functional element can be obtained by performing a low-temperature plasma film forming process using the discharge ignition method of the present invention.

Next, an embodiment according to the second configuration of the present invention will be described.

While each of the above embodiments is directed to a discharge igniter for performing microwave discharge, this embodiment is an improvement in a microwave introduction window.

First, the relationship between the relative angle of the opposed rectangular microwave introduction window and the leakage power of the microwave when no discharge occurs is examined.

FIG. 7 is a diagram schematically showing the apparatus used in the experiment.

In FIG. 7, reference numeral 701 denotes a discharge furnace;
703 is a rectangular waveguide, 704 and 705 are rectangular microwave introduction windows, 706 is a raw material gas introduction tube, 707 is a mesh-shaped exhaust port, 708 is a microwave power supply, 709 is an isolator, 710 and 711 are power monitors, 712 denotes a non-reflection terminal, and 713 denotes a film forming chamber.

The rectangular waveguides 702 and 703 are made of Toshiba Corporation having a waveguide cross section of 27 mm × 96 mm, and the rectangular microwave introduction windows 704 and 705 have the same size. Therefore,
The discharge furnace so that the microwave single mode H ₀₁ are introduced.

Microwave power supply 708, isolator 7
09 and a power monitor 710 are connected in this order by a waveguide 702, and are further connected to a discharge furnace 701 installed in a film forming chamber 713 through the microwave introduction window 704. The microwave power generated from the microwave power supply 708 is supplied to the inside of the discharge furnace 701 from the microwave introduction window 704 through the rectangular waveguide 702. Here, the power monitor 710 uses an incident power (hereinafter referred to as P
_f referred to as) and the reflected power from the discharge furnace (hereinafter this is referred to as P _r) monitoring. In addition, the isolator 709, and to avoid P _r from entering the power supply 708.
The microwave introduction window 705 installed opposite to the microwave introduction window 704 is connected to the power monitor 711 and the isolator 709 in this order, and the microwave leaks out of the discharge furnace 701 through the microwave introduction window 705. power (hereinafter referred to as P _t) the power monitor 711
Monitor by Microwave introduction windows 704, 705
Has a structure in which the relative angle between them can be continuously changed. When the relative angle is θ, θ = 0 ° when the microwave introduction windows 704 and 705 are parallel to each other.
And Further, a non-reflection terminal 712 is connected to the other end of the power monitor 711 so that the reflected wave does not return.

(Experiment 1) The experiment was performed as follows using the experimental apparatus shown in FIG. First, after the inside of the discharge furnace 701 was evacuated from the exhaust port 707 by a vacuum pump (not shown), He 300 sccm was introduced from the raw material gas introduction pipe 706. Next, microwave power (supposed to be 300 W in this case) was supplied from a microwave power supply 708 to the microwave introduction window 704 via the waveguide 702 to such an extent that no discharge occurred. At this time, P _f
And _Pr were monitored. It was also measured by a power meter 711 connected to P _t leaking to the other microwave introducing window 705 side to the waveguide 703. This measurement was performed by changing the relative angle (θ) of the facing waveguide from 0 ° to 180 °.
To 10 ° at 10 ° intervals.

FIG. 8 shows the result at that time. The horizontal axis represents the relative angle between the waveguides 702 and 703, and the vertical axis represents the microwave power introduced from the microwave introduction window 704 into the discharge furnace 701 and the waveguide from the discharge furnace 701 through the microwave introduction window 704. The reflected power returning to 702 and the microwave power leaking to the facing microwave introduction window 705 side are shown.

As shown in FIG. 8, when no discharge occurs, when the facing waveguides are parallel (θ = 0 °), about 80% of the microwave power introduced from the waveguide 702 is facing. When the opposing waveguide is vertical (θ = 90 °) while the leakage is occurring from the guiding waveguide 703, it is understood that the microwave is not leaking to the opposing waveguide 703. . Further, in the case of θ = 0 ° and θ = 90 °, when the supplied microwave power is further increased, θ =
In the case of 90 °, discharge easily occurred, but θ = 90 °
In the case of 2, no discharge occurred even if 2 kW of microwave power was introduced.

(Experiment 2) Next, the relationship between the relative angle θ of the opposing waveguides and the leakage power of the microwave when a discharge is occurring was examined.

In the experiment, after the inside of the discharge furnace 701 was evacuated by a vacuum pump (not shown) using the experimental apparatus shown in FIG. 7, He 300 sccm was introduced from the source gas introduction pipe 706, and the microwave was passed through the waveguide 702. Electric power was introduced from a microwave power supply 708 to cause discharge. Thereafter, the microwave power (P _f ) supplied while maintaining the discharge state is increased by 3
It was adjusted to 00W. In this case the P _f and P _r is measured by the power monitor 710, it was further measured by a power monitor 711 connected to the waveguide 703 side that faces the P _t leaking to the microwave introducing window 705 side. This measurement was performed by changing the relative angle of the facing waveguides from 0 ° to 180 ° every 10 °.

FIG. 9 shows the result at that time. The horizontal axis is the relative angle between the waveguides 702 and 703 facing each other, and the vertical axis is the microwave power introduced from the microwave introduction window 704 into the discharge furnace 701 and the waveguide from the discharge furnace 701 through the microwave introduction window 704. The reflected power returning to 702 and the microwave power leaking to the facing microwave introduction window 705 side are shown. As shown in FIG. 5, when a discharge occurs, θ is changed from 0 ° to 90 °.
It was found that almost no microwave power leaked to the opposing waveguide 703 even if it was changed up to °. In other words, most of the supplied microwave power is either consumed for discharge, or returns as reflected power to the waveguide on the side that supplies microwaves. It is considered that the microwave can hardly reach the introduction window 705.

From the above results, when the opposed rectangular microwave introduction windows are arranged in parallel in the discharge furnace, if microwave power is introduced from one of the microwave introduction windows before discharge occurs, the other will be used. A large amount of microwaves leak from the microwave introduction window, but once a discharge occurs, the supplied microwave power efficiently maintains the discharge regardless of the relative positional relationship between the facing waveguides Was found to be able to consume.

Next, an experiment was carried out using an apparatus as shown in FIG. 10 which best represented the features of the present invention. FIG.
, 1001 is a discharge furnace, 1002 and 1003 are waveguides, 1004 and 1005 are microwave introduction windows, 1006
Is a source gas introduction pipe, and 1007 is an exhaust port also serving as a mesh electrode. The exhaust port 1007 is connected to a bias voltage applying means (not shown) so that a bias voltage can be applied. 1008 is a microwave reflecting plate,
1009 is a substrate, 1010 is a substrate heater, 1011
Denotes a film forming chamber, 1012 and 1013 denote microwave power sources, 10
14 is a shutter.

The microwave power sources 1012 and 1013 are connected to the microwave introduction windows 1004 and 1005 respectively.
02, 1003, and to the discharge furnace 1001 installed in the film forming chamber 1011 through the microwave introduction windows 1004, 1005.

Here, it is preferable that the microwave introduction window is made of a material that transmits microwaves and at the same time keeps secret between the inside of the film forming chamber and the outside. In the microwave band to be used, it is sufficient that the dielectric loss tan δ is small, but at the same time, a material having a high thermal conductivity and a high resistance to thermal shock is desirable. Materials suitable for such conditions include beryllia, alumina ceramics, boron nitride, quartz, and the like, and alumina ceramics is particularly optimal.

The microwave introduction windows 1004 and 1005 are installed facing each other and in parallel (θ = 0 °).

The reflector 1008 installed on the microwave introduction window 1005 can be freely opened and closed. When the reflector is closed, the microwave is introduced between the discharge furnace 1001 and the microwave introduction window 1005. It is a structure that can not go back and forth.

(Experiment 3) The experiment was performed as follows using the apparatus shown in FIG. First, the inside of the discharge furnace 1001 was evacuated by a vacuum pump (not shown), and then He 300 sccm was introduced from the raw material gas introduction pipe 1006. Next, with the microwave reflecting plate 1008 closed, microwave power is supplied from the microwave power supply 1012 to the microwave introduction window 1.
When introduced into the discharge furnace 1001 via 004,
Discharge occurred easily. After confirming that the discharge occurred, the microwave reflecting plate 1008 was opened, and microwave power was introduced from the microwave power supply 1013 from the microwave introduction window 1005 side. At this time, there was no disturbance in the discharge state,
A stable discharge state was always maintained.

From the above results, in the apparatus of the present invention,
It has been found that by providing the above-mentioned reflector, even when θ of the opposing waveguides is 0 °, discharge easily occurs and a stable discharge state can be obtained.

However, the stability of these discharges depends on the distance between the microwave introduction windows, the magnitude of the microwave power to be introduced, and the type and flow rate of the raw material gas. It goes without saying that you need to decide.

The microwave reflecting plate of the present invention is configured to completely cover the microwave introducing window. When the reflecting plate is closed, there is no microwave leakage between the microwave introducing window and the discharge furnace, and the microwave reflecting window is opened. On the contrary, it is desirable that the structure be such that it does not become a large reflector. Further, it is preferable that the microwave reflecting plate of the present invention be closely attached to the microwave introducing window.

It is desirable that the discharge furnace and the microwave reflecting plate of the present invention be made of a metal member having a small ohmic loss. More specifically, it may be made of silver, copper, or aluminum, or may be formed by plating these metals on another material. In this apparatus, a member plated with silver on stainless steel is used.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

Example 2-1 An amorphous silicon film was formed on a substrate by the method of the present invention using the apparatus shown in FIG.

First, a 40 cm × 20 cm square 7059 glass substrate 1009 previously formed by vapor deposition of Cr1000 ° as a comb-shaped electrode was placed on a substrate holder (not shown).
Was installed. Next, the substrate 1009 is heated to a predetermined temperature by the substrate
Is closed, and the raw material gas introduction pipe 1 is inserted into the discharge furnace 1001.
From 006, 280 sccm of SiH ₄ was introduced, and simultaneously, microwave power was introduced from a microwave power supply (not shown) into the discharge furnace 1001 via the waveguide 1002 and the microwave introduction window 1004. At this time, the microwave reflecting plate 1008 was closed so that microwaves did not leak to the microwave introduction window 1005 side. After the discharge has occurred, the microwave reflecting plate 1008 is opened, microwave power is introduced from the microwave power supply 1013 also from the facing waveguide 1003, and discharge is caused from both sides of the microwave introduction window to generate the microwave. The power introduced from the introduction windows 1004 and 1005 was adjusted to 400 W each. Further, an appropriate DC bias voltage was applied to the substrate from the bias voltage applying means 1005. Thereafter, after confirming that the discharge was stabilized, the shutter 1009 was opened, and an amorphous silicon film was formed on the substrate for 100 seconds. Table 2 summarizes the film forming conditions at that time.

Here, the rectangular waveguide used was made by Toshiba Corporation, and the lengths of the long side and the short side were 96, 2 respectively.
7 mm, the height of the discharge furnace was 40 mm, and was shorter than the length of the long side.

[0094]

[Table 2] The amorphous silicon film obtained by the above method is 5 cm ×
When the film was cut into 5 cm squares and each film thickness was measured using a stylus-type film thickness meter, the average value was 1.23 μm, and the film thickness distribution of the entire substrate was 5%. From this, it can be seen that the average film forming speed is 123 ° / s (± 5% distribution). In addition, an electrode was attached on the amorphous silicon film by using an ultrasonic solder, and dark conductivity (σd) was measured. As a result, the dark conductivity is 3.0 × ⁻¹⁰ ± 2 × ⁻¹⁰ S
/ Cm, and it was confirmed that a uniform and good quality amorphous silicon film was formed over the entire substrate.

(Comparative Example 2-1) The same apparatus configuration and film formation as in Example 1 except that the microwave reflecting window was removed using opposed microwave introduction windows as in the conventional apparatus. An amorphous silicon film was formed under the conditions. However, as shown in FIG. 15 (b), the size of the discharge furnace is higher when the microwave introduction windows are orthogonal than when the microwave introduction windows are parallel, as shown in FIG. Also increases. Also, the bottom of the discharge furnace was a mesh-shaped exhaust port / electrode as in Example 2-1 so that a bias voltage could be applied by bias voltage applying means (not shown).

The production was performed in the same manner as in Example 2-1.
After introducing 280 sccm of SiH _{4 into the} sample 01 to generate plasma, the microwave power introduced from the opposed microwave introduction windows was adjusted to 400 W, and 100
An amorphous silicon film was deposited on the substrate for seconds.

The thickness of the amorphous silicon film obtained by the above method was measured using a stylus-type film thickness meter and found to be 1.10 μm, and the average film formation rate was 110 °.
/ S. The thickness distribution of the entire substrate was ± 5%. An electrode was attached to the amorphous silicon film with an ultrasonic solder, and the dark conductivity was measured. As a result, the dark conductivity was 3 × ^-10 S / cm except for the outer peripheral portion of the substrate.
However, the outer peripheral portion of the substrate was found to have a high dark conductivity of about 8 × ^-10 S / cm.

As described above, from Example 2-1 and Comparative Example 2-1, the film forming rate of Example 2-1 incorporating the method of the present invention is higher, and therefore the gas use efficiency is improved. There was found. Furthermore, it has been found that the method of the present invention can achieve uniformity (particularly remarkable at the outer peripheral portion of the substrate) in the electrical conductivity, which is dark conductivity. this is,
It is considered that the present invention makes it possible to bring the bottom of the discharge furnace closer to the substrate, and thus to apply a bias voltage to the substrate uniformly.

(Example 2-2) Using the roll-to-roll apparatus shown in FIG. 11, the n, i and p-type amorphous silicon films were successively successively formed on the strip-shaped substrate by the following operation according to the method of the present invention. Formed. In FIG. 11, reference numerals 1101 and 1103 denote a film formation chamber formed by a 13.56 MHz high frequency (hereinafter abbreviated as RF) plasma CVD method, 1102 denotes a film formation chamber formed by a microwave plasma CVD method, and 1104 and 1105 denote supply of a belt-like substrate. Room, take-up room. The respective film forming chambers are connected by a gas gate 1106. Reference numeral 1107 denotes a band-shaped substrate which passes through three film forming chambers before being transported from the supply chamber to the winding chamber, and has a three-layer functional deposition film, for example, pi on its surface.
A semiconductor for an n-structure photovoltaic device is formed. Note that 11
Reference numeral 08 denotes a belt-like sheet made of a heat-resistant nonwoven fabric, which is wound at the same time as the belt-like substrate is wound, thereby preventing the surface of the belt-like substrate from being damaged.

In each of the film forming chambers 1101 to 1103, a heater 1109 for heating the substrate, a source gas introducing pipe 1110 for introducing a source gas supplied from a gas supply unit (not shown) into the film forming chamber, and an exhaust unit (not shown) are provided. An exhaust pipe 1111 for exhausting the film formation chamber, a discharge electrode 1112 for supplying RF power for generating discharge by applying energy to the film formation gas in the film formation chamber;
A microwave introduction window 1113 for introducing microwaves into the discharge furnace 1117 and a microwave reflector 1118 provided on the microwave introduction window are provided.
In 01 and 1103, a deposited film is formed by the RF plasma CVD method, and in the film forming chamber 1102, a film is deposited by the microwave plasma CVD method. A scavenging gas is introduced into the gas gate 1106 from a scavenging gas introduction pipe 1114 to prevent mixing of a film formation gas in a neighboring film formation chamber. Also, 1
Reference numeral 115 denotes supply chambers 1104 and 11 of the belt-like base 1107.
Reference numeral 1116 denotes an exhaust pipe for exhausting the film in each of the film forming chambers 1.
101, 1102, and 1103, a pressure gauge for measuring pressures in the supply chamber 1104 and the winding chamber 1105 of the belt-shaped base 1107.

First, a belt-shaped stainless steel substrate 1107 having a width of 40 cm, a length of 50 cm, and a thickness of 0.2 mm was placed in the supply chamber 1.
It was set so that it was unwound from 104, passed through three film forming chambers 1101 to 1103, and wound up in a winding chamber 1105.

Next, the vacuum chambers of the respective chambers are sufficiently evacuated by the respective exhaust pipes 1111 and 1114, and then the source gas introduction pipes 1110 into the respective film forming chambers are continuously exhausted.
Each film forming gas was introduced, and while checking the pressure gauge 1115, the amount of exhaust was adjusted to adjust each film forming chamber to a predetermined pressure. Ar was introduced into the gas gate 1106 as a scavenging gas at 200 sccm each.

[0103] Heating is performed at a predetermined temperature from the back surface of the band-shaped base 1107 by a heater 1109, and RF power is applied from the discharge electrode 1112.
Electric power and microwave power are introduced from the microwave introduction window 1113 to generate plasma discharge in each film forming chamber by the method of the present invention using the microwave reflecting plate 1118, and the belt-shaped substrate is transported at a constant speed. Then, n,
i-type and p-type amorphous silicon films were sequentially and continuously formed. Table 3 shows the manufacturing conditions in each film forming chamber.

[0104]

[Table 3] At this time, the deposition rates of the deposition chambers 1101 to 1103 were 20 ° / s, 120 ° / s, and 15 ° / s, respectively.

The strip-shaped substrate on which the amorphous silicon film obtained by the above method was deposited was taken out of the roll-to-roll apparatus, cut into a size of 10 cm × 40 cm, placed in a single-chamber vacuum evaporation apparatus, and subjected to a vacuum evaporation method as shown in Table 4. The ITO transparent conductive film was laminated under the conditions shown in FIG.
The photovoltaic element shown in FIG. In FIG. 12, reference numeral 1201 denotes a base; 1202, an n-type layer;
Reference numeral 3 denotes an i-type layer, 1204 denotes a p-type layer, and 1205 denotes an ITO transparent conductive film.

[0106]

[Table 4] After the obtained photovoltaic elements were cut into 5 cm squares, each was measured with a solar simulator to show good photoelectric conversion efficiency. The distribution of the photoelectric conversion efficiency in a 10 cm × 40 cm substrate was within 5%. (Comparative Example 2-2) In the apparatus shown in FIG. 11, the height of the discharge furnace 1117 was set to be three times the height of the discharge furnace used in Example 2-2, and the opposed rectangular microwave introduction windows were orthogonal. An amorphous silicon film was formed under the film forming conditions shown in Table 3 using exactly the same apparatus as in Example 2-2 except that it was disposed.

At this time, the film forming speed is controlled in the film forming chambers 1101 to 110-1.
20 ° / s, 110 ° / s, 15 ° / s for each of 103
Since the film forming rate was lower only in the film forming chamber 1102 than in the case of Example 1, the transport speed was reduced accordingly, and in the film forming chambers 1101 and 1103, the film thickness was reduced by a partition plate (not shown). Was adjusted to form a functional deposition film having the same layer configuration and thickness as in Example 2-1.

The strip-shaped substrate on which the amorphous silicon film obtained by the above method was deposited was taken out of the roll-to-roll apparatus, cut into a size of 10 cm × 40 cm, placed in a single-chamber vacuum evaporation apparatus, and subjected to a vacuum evaporation method as shown in Table 4. The ITO transparent conductive film was laminated under the conditions shown in FIG.
The photovoltaic element shown in FIG.

After the obtained photovoltaic elements were cut into 5 cm squares, each was measured with a solar simulator. The center showed good photoelectric conversion efficiency in the width direction of the substrate. In some cases, sufficient photoelectric conversion efficiency cannot be obtained, so that the distribution of photoelectric conversion efficiency is 1
More than 0% was present.

Example 2-3 n, i, p were formed on a strip-shaped substrate in the same manner as in Example 2-2 except that the conditions for forming a deposited film in each film forming chamber were changed as shown in Table 5. An amorphous silicon germanium semiconductor film was continuously formed to form a photovoltaic device.

[0111]

[Table 5] At this time, the deposition rates of the deposition chambers 1101 to 1103 were 15 ° / s, 125 ° / s, and 20 ° / s, respectively.

The strip-shaped substrate on which the amorphous silicon film obtained by the above method was deposited was taken out of the roll-to-roll apparatus, cut into a size of 10 cm × 40 cm, placed in a single-chamber vacuum evaporation apparatus, and subjected to a vacuum evaporation method as shown in Table 4. The ITO transparent conductive film was laminated under the conditions shown in FIG.
The photovoltaic element shown in FIG.

After the obtained photovoltaic elements were cut into 5 cm squares, each was measured with a solar simulator to show good photoelectric conversion efficiency. Also, 10cm × 4
The distribution of the photoelectric conversion efficiency in the 0 cm substrate was within 6%.

Further, similarly to Comparative Example 2-2, the height of the discharge furnace was set to be three times as high as that of the discharge furnace used in this example, and the rectangular microwave introduction windows were arranged perpendicular to each other. Except for this point, a photovoltaic element was formed using the same apparatus as in Example 2-3 under the film forming conditions shown in Table 5. However,
The transport speed was reduced as in Comparative Example 2-2, and the film thickness was adjusted using a partition plate (not shown). The obtained photovoltaic element was 5c
After cutting into m-square, each was measured by a solar simulator. As a result, a good photoelectric conversion efficiency was shown at the center with respect to the width direction of the substrate, but a sufficient photoelectric conversion efficiency was not obtained at the end. There were things. The distribution of the photoelectric conversion efficiency was 12% or more as a whole.

[0115]

Since the present invention is configured as described above, it has the following effects.

According to the first aspect of the present invention, by performing a discharge ignition method in which a DC voltage is applied using silicon as an electrode, the amount of impurities mixed into the film in the silicon-based film forming plasma process is reduced, and the method is improved. There is an effect that a quality film can be formed and a functional element can be easily formed. In addition, since it is easy to start discharging with low power, there is an effect that the manufacturing cost of the film forming apparatus can be reduced.

According to the second aspect, in addition to the above effects, there is an effect that the discharge can be easily performed by changing the distance between the electrodes according to the pressure state in the discharge furnace.

According to the third aspect, a bias voltage can be uniformly applied to the entire substrate.
Gas utilization efficiency has been improved, and high quality functional
In addition, there is an effect that it can be manufactured at low cost.

According to the fourth aspect, there is an effect that each of the above effects can be further improved.

According to the fifth aspect, particularly,
There is an effect that the gas use efficiency at the start of discharge can be improved.

In the sixth aspect, particularly,
There is an effect that a bias voltage can be uniformly applied to the entire substrate.

According to the method of the seventh aspect, there is an effect that a high quality functional deposited film can be formed uniformly.

[Brief description of the drawings]

FIG. 1 is a diagram showing a high-frequency plasma CVD type film forming apparatus employing a discharge ignition method of the present invention.

FIG. 2 is a diagram showing test conditions and results when a performance of a discharge ignition system is tested using the film forming apparatus shown in FIG.

FIG. 3 is a view showing a microwave plasma CVD type film forming apparatus employing the discharge ignition method of the present invention.

FIG. 4 is a diagram showing the results obtained when the performance of the discharge ignition method was examined using the microwave power necessary for starting discharge, using the film forming apparatus shown in FIG.

FIG. 5 is a diagram showing a configuration of a film forming apparatus for stacking a nip three-layer separation film of a substrate load lock transport system by the discharge ignition device of the present invention.

FIG. 6 is a diagram showing a quantum efficiency spectrum of a cell manufactured by the apparatus shown in FIG.

FIG. 7 is a diagram showing a configuration of a comparative example for testing the performance of the example according to the second configuration of the present invention.

FIG. 8 is a view showing an experimental result obtained by the experimental apparatus shown in FIG. 7;

FIG. 9 is a view showing an experimental result obtained by the experimental apparatus shown in FIG. 7;

FIG. 10 is a diagram best representing the features of the second configuration of the present invention.

FIG. 11 is a view showing a roll-to-roll apparatus using the second configuration of the present invention.

FIG. 12 is a schematic sectional view of a photovoltaic element manufactured by the apparatus shown in FIG.

FIG. 13 is a diagram showing a configuration of a conventional example.

FIG. 14 is a diagram showing a configuration of a conventional example.

FIG. 15 is a diagram showing a configuration of a conventional example.

[Explanation of symbols]

101, 102, 301, 302 Electrode 105, 305 DC power supply 106, 306 Distance adjustment mechanism 107, 307 Discharge ignition switch 112, 113 Opposite plane electrode 115 High frequency power supply 116, 316 Container 117, 317, 707, 1007 Exhaust port 118, 318 , 1201 Substrate 119 Gas introduction means 319 Gas supply means 320 Microwave waveguide 321 Microwave applicator means 322 Window 330 Variable conductance valve 331 Unit 501 Loading chamber 502 n-layer deposition chamber 503 i-layer deposition chamber 504 p-layer deposition Room 505 Unloading room 506 Gate valve 551 Outlet 561,1009 Substrate 572 Discharge igniter 701,1001 Discharge furnace 702,703 Square waveguide 704,705,1004,1005 Microwave introduction window 706 Source gas introduction 708, 1012, 1013 Microwave power supply 709 Isolator 710, 711 Power monitor 712 Non-reflection termination 713, 1011 Deposition chamber 1002, 1003 Waveguide 1006 Source gas introduction window 1008 Microwave reflection plate 1010 Substrate heater 1202 N-type layer 1203 i-type layer 1204 p-type layer 1205 ITO conductive film layer

──────────────────────────────────────────────────続 き Continuing on the front page (72) Naoto Yoshiri, Inventor 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Akira Sakai 3- 30-2 Shimomaruko, Ota-ku, Tokyo Ki Inside Canon Inc. (72) Inventor Masahiro Kanai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Shuichiro Sugiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroshi Echizen 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-62-204530 (JP, A) JP-A-2-151102 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 21/205 C23C 16/50 C30B 25/02

Claims (7)

(57) [Claims] 1. A plasma CVD apparatus comprising a discharge ignition device for promoting electric field emission of electrons, wherein a discharge promotion electrode constituting the discharge ignition device is formed of silicon. CVD equipment. 2. The plasma CVD apparatus according to claim 1, further comprising a distance adjusting mechanism for adjusting a distance between electrodes for promoting discharge. 3. A microwave plasma CVD apparatus for generating plasma in a discharge furnace by introducing microwaves from a microwave introduction window, wherein a plurality of the microwave introduction windows are provided.
A microwave plasma CVD apparatus, comprising: a microwave reflector that is openable and closable for adjusting the amount of microwave introduced from each microwave introduction window according to its reflection angle. 4. The microwave plasma C according to claim 3,
In a VD apparatus, a microwave plasma CVD apparatus is provided with a microwave reflecting plate in each of a plurality of microwave introduction windows. 5. The microwave plasma CVD apparatus according to claim 3, wherein the plurality of microwave introduction windows are rectangular, and directions of microwave electric fields supplied to the discharge furnace are parallel to each other. A microwave plasma CVD apparatus, wherein: 6. The microwave plasma CVD apparatus according to claim 3, wherein an electrode for applying a bias voltage is provided at a bottom of the discharge furnace. Wave plasma C
VD device. 7. A method for forming a functional deposition film using the microwave plasma CVD apparatus according to claim 4, wherein when starting discharge, a plurality of microwave introduction windows are provided. Opening only the microwave reflection plate provided in a predetermined one of them, introducing microwaves from only one microwave introduction window to locally start discharge, and then while maintaining the discharge state Opening the microwave reflection plate provided in the adjacent microwave introduction window, introducing microwaves from the microwave introduction window to expand the local discharge region, and thereafter sequentially expanding the discharge region by the same procedure Forming a large-capacity microwave plasma to form a functional deposited film.