JP2008004815A - Plasma processing method and photoelectric conversion element fabricated using the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a matter that the electric energy being fed to plasma increases because a high voltage must be applied between the electrodes in order to generate and sustain uniform plasma between the electrodes at a second plasma processing step when a first plasma processing step and the second plasma processing step of higher discharge start voltage are performed in the same plasma reaction chamber. <P>SOLUTION: When pulse modulated AC power is employed in the second plasma processing step of high discharge start voltage, uniform plasma is generated and sustained between the electrodes and the electric energy being fed between the electrodes can be reduced. Consequently, plasma processing speed is lowered and control of processing amount is facilitated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a plasma processing method and a photoelectric conversion element manufactured using the method, and more specifically, a plasma processing method and a method for performing at least two plasma processing steps in the same plasma reaction chamber. It is related with the photoelectric conversion element manufactured in this way.

  Conventionally, as a plasma CVD apparatus for forming a semiconductor thin film layer, an in-line method in which a plurality of plasma reaction chambers (also referred to as chambers, hereinafter the same) are connected in a straight line, or an intermediate chamber in the center, and a plurality of plasmas around the plasma chamber are provided. A multi-chamber system in which reaction chambers are arranged is employed. However, in the in-line method, since the flow line for substrate conveyance is linear, the entire apparatus must be stopped even when maintenance is partially required.

  On the other hand, the multi-chamber method is a method in which a substrate to be deposited is moved to each plasma reaction chamber via an intermediate chamber, and is movable so that airtightness can be maintained between each plasma reaction chamber and the intermediate chamber. Since the partition is provided, even if a problem occurs in one plasma reaction chamber, the other plasma reaction chamber can be used, and the production is not completely stopped. However, in this multi-chamber type production apparatus, there are a plurality of flow lines of the substrate through the intermediate chamber, and it is inevitable that the mechanical structure of the intermediate chamber becomes complicated. For example, a mechanism for moving the substrate while maintaining airtightness between the intermediate chamber and each plasma reaction chamber is complicated and expensive. There is also a problem that the number of plasma reaction chambers arranged around the intermediate chamber is spatially limited.

  In view of such problems, Patent Document 1 discloses that a p-type semiconductor layer, an i-type crystalline silicon-based photoelectric conversion layer, and an n-type semiconductor layer are successively formed in the same plasma CVD plasma reaction chamber. In addition, a method for manufacturing a silicon-based thin film photoelectric conversion device is proposed in which the p-type semiconductor layer is formed under the condition that the pressure in the plasma reaction chamber is 5 Torr (667 Pa) or more. According to this method, it is said that a photoelectric conversion device having good performance and quality can be manufactured with a simple device at low cost and high efficiency.

As described above, in order to reduce the apparatus cost by efficiently using the plasma CVD apparatus, attempts have been made to perform different film forming steps in the same plasma reaction chamber.
JP 2000-252495 A

  However, when two or more plasma CVD processes with different processing conditions are performed in the same plasma reaction chamber, or when two or more plasma processing processes with different processing conditions are performed, such as when performing a plasma CVD process and a plasma etching process. Causes the following problems.

In thin film formation and etching, a plasma CVD apparatus using parallel plate electrodes or an etching apparatus is generally used. In this apparatus, the voltage at which glow discharge occurs between parallel plates (discharge start voltage) is expressed as a function of the product of the distance d (m) between parallel plate electrodes and the gas pressure p (Torr) according to Paschen's law. Although the relationship between the discharge start voltage and the pd product varies depending on the type of gas, the discharge start voltage becomes the lowest value when the pd product is 10 ⁻² to 10 ⁻¹ . Spark discharge occurs when electrons accelerated by an electric field collide with gas molecules and ionize the gas, so collisions are unlikely to occur when the amount of gas decreases, and conversely when electrons increase, the electrons are sufficiently accelerated before the collision. Since it becomes difficult, it has the lowest value for the gas pressure.

  Here, in the same plasma reaction chamber where the interelectrode distance d is substantially constant, when performing processes with different gas pressures and gas types, the interelectrode distance d is set so that the discharge start voltage is minimized under one condition. Then, the discharge start voltage increases under the other processing condition, and a larger voltage needs to be applied to generate plasma. When the magnitude of the applied voltage is insufficient, plasma is not generated or even if it is generated, uniform plasma cannot be maintained.

  In addition, the structure in which the inter-electrode distance d can be adjusted is limited in its movable range, and it is possible to minimize the discharge start voltage for each plasma processing step or make the discharge start voltage substantially the same for each plasma processing step. However, the discharge start voltage may be different for each plasma processing step.

  That is, when plasma processing steps with different processing conditions are performed in the same plasma reaction chamber, the gas used in each step or the gas pressure is different, so that the discharge starting voltage increases in one step and is uniform in that step. It is necessary to apply a large voltage to generate and maintain the plasma.

  Therefore, when a large voltage is applied between the electrodes, a uniform plasma can be generated and maintained between the electrodes, but an excessive amount of power is input between the electrodes, and the amount of power used for gas decomposition increases. For this reason, there arises a problem that the plasma processing speed is increased and it becomes difficult to control the processing amount.

  The present invention has been made in view of the above points, and in the case where at least two plasma processing steps having different plasma generation voltages (discharge start voltages) are performed in the same plasma reaction chamber, uniform plasma is obtained in both steps. Is generated and maintained between the electrodes, and the amount of electric power supplied between the electrodes is reduced, the plasma processing speed is reduced, and the processing amount is easily controlled, and the photoelectric conversion manufactured using the method An object is to provide an element.

The present invention is a plasma processing method for performing at least two plasma processing steps in the same plasma reaction chamber,
A first plasma processing step using CW AC power as a power source for plasma processing;
Using a pulse-modulated AC power as a power source for plasma processing, a second plasma processing step having a higher discharge start voltage than the first plasma processing step;
A switching step of appropriately switching between the first plasma processing step and the second plasma processing step;
Is a plasma processing method.

  According to this method, when performing at least two plasma processing steps in the same plasma reaction chamber, the CW AC power is used as the plasma processing power in the plasma processing step where the discharge starting voltage is low, and the discharge starting voltage is high. In the plasma processing step, pulse-modulated AC power is used as power for plasma processing, so that even in a plasma processing step with a high discharge starting voltage, uniform plasma is generated and maintained between the electrodes, and between the electrodes. The amount of power input can be reduced, the plasma processing speed can be reduced, and the processing amount can be easily controlled.

  Furthermore, the present invention provides the plasma processing method in which the first plasma processing step and the second plasma processing step are performed with the same electrode-to-electrode distance between the cathode / anode electrode pair installed in the plasma reaction chamber. It is.

  Further, the present invention is the plasma processing method, wherein the gas pressure in the plasma reaction chamber is different between the first plasma processing step and the second plasma processing step.

  Further, according to the present invention, the gas introduced into the plasma reaction chamber and decomposed in the first plasma processing step is more dependent on the applied voltage than the gas introduced into the plasma reaction chamber and decomposed in the second plasma processing step. This is a plasma treatment method that is easily ionized.

  Furthermore, the present invention is the plasma processing method, wherein the first plasma processing step is a film forming step by a plasma CVD method, and the second plasma processing step is a step of performing a plasma etching process.

  Further, the present invention is the plasma processing method, wherein the plasma etching processing is performed by plasma etching the film attached in the plasma reaction chamber in the first plasma processing step.

  Furthermore, the present invention is the plasma processing method, wherein the first plasma processing step is a step of forming a film of at least one semiconductor layer of the photoelectric conversion element by a plasma CVD method.

  Furthermore, the present invention is the plasma processing method, wherein the first plasma processing step and the second plasma processing step are steps of forming a semiconductor film by a plasma CVD method.

  Further, according to the present invention, a crystalline silicon based semiconductor layer is formed by the plasma CVD method in the first plasma processing step, and an amorphous silicon based semiconductor layer is formed by the plasma CVD method in the second plasma processing step. And a plasma processing method of performing plasma etching on the film deposited in the plasma reaction chamber by the second plasma processing step after forming the crystalline silicon semiconductor layer and the amorphous silicon semiconductor layer. .

  Furthermore, the present invention is a photoelectric conversion element manufactured using the plasma processing method.

  The present invention is a plasma processing method in which at least two plasma processing steps are performed in the same plasma reaction chamber, and includes a first plasma processing step using CW AC power as a power source for plasma processing, and a power source for plasma processing. Using a pulse-modulated AC power, a second plasma processing step having a higher discharge starting voltage than the first plasma processing step, and a switching step for switching between the first plasma processing step and the second plasma processing step as appropriate; The plasma processing method which has these.

  According to this method, when at least two plasma processing steps having different discharge start voltages are performed in the same plasma reaction chamber, the CW AC power is used as power for plasma processing in the first plasma processing step having a low discharge start voltage. In the second plasma processing step where the discharge starting voltage is high, pulse-modulated AC power is used as the power for plasma processing, so that the cathode and anode are also used in the second plasma processing step where the discharge starting voltage is high. A large voltage can be applied between the electrodes, and at the same time the time average of the input power can be reduced, so that a uniform plasma is generated and maintained between the electrodes, the plasma processing speed is reduced, and the processing amount can be controlled. Can be easy.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view of a plasma processing apparatus in which the plasma processing method of the present invention is implemented.

  The plasma processing apparatus of FIG. 1 is a semiconductor layer deposition apparatus by a plasma CVD method having a parallel plate type electrode structure in which a cathode electrode 102 and an anode electrode 103 pair are installed in a sealable plasma reaction chamber 101. The distance between the cathode electrode 102 and the anode electrode 103 is determined according to desired processing conditions, and is generally several mm to several tens mm. Outside the plasma reaction chamber 101, a power supply means 108 for supplying power to the cathode electrode 102 and an impedance matching circuit 105 for impedance matching between the power supply means 108 and the cathode electrode 102 / anode electrode 103 pair are installed. Yes.

  The power supply means 108 is connected to one end of the power introduction line 106 a and the other end is connected to the impedance matching circuit 105. One end of the power introduction line 106 b is connected to the impedance matching circuit 105, and the other end is connected to the cathode electrode 102.

  The power supply means 108 only needs to be capable of CW (continuous waveform) AC output and pulse-modulated (on / off control) AC output, and is usually composed of an AC power source and a modulation circuit. The frequency of the output AC power is generally 13 or 56 MHz, but is not limited to this, and frequencies in the range of several kHz to VHF band or microwave band may be used. Further, the ON time / OFF time at the time of pulse modulation can be arbitrarily set, and is set in the range of several μs to several milliseconds.

  On the other hand, the anode electrode 103 is electrically grounded, and the workpiece 107 is placed on the anode electrode 103.

  The work 107 may be placed on the cathode electrode 102, but is generally placed on the anode electrode 103 in order to reduce film quality deterioration due to ion damage in the plasma.

  A gas inlet 110 is provided in the plasma reaction chamber 101. A gas 118 such as a dilution gas, a material gas, or a doping gas is introduced from the gas inlet 110.

  In addition, a vacuum pump 116 and a pressure adjusting valve 117 are connected in series to the plasma reaction chamber 101 so that the gas pressure in the plasma reaction chamber 101 is kept substantially constant.

(Embodiment 1)
The plasma processing method according to the present embodiment includes a plasma CVD process (including a first plasma processing process) for forming a thin film on the work 107 by plasma CVD, and a plasma etching process for etching another work 107. The (second plasma treatment step) is performed in the same plasma reaction chamber 101.

  The plasma CVD process only needs to include at least one first plasma processing process using CW AC power, and may include a plasma CVD process using pulse-modulated AC power. The plasma CVD process may be a process for forming a single-layer film or a process for forming a multi-layer film. In this embodiment, a plurality of layers of films are formed by a plasma CVD process.

  On the other hand, the plasma etching step is a step of performing plasma etching using pulse-modulated AC power having a higher discharge starting voltage than the first plasma processing step.

This embodiment will be described in detail below.
Examples of the plasma CVD process include a process for forming a semiconductor layer of a silicon-based thin film photoelectric conversion element having a pin structure using SiH4 gas diluted with H2 gas as a material gas and B2H6 and PH3 as doping gases. In the first plasma processing step included in this plasma CVD step, the pressure in the plasma reaction chamber 101 is adjusted to a constant value (for example, about 500 Pa) by the pressure adjusting valve 117, and the cathode 102 is supplied with power supply means 108. The CW AC power output from is input. Here, the distance between the cathode electrode 102 and the anode electrode 103 is about several mm to several tens mm. This inter-electrode distance is determined by desired film forming conditions. Through this process, a silicon-based thin film is formed on the workpiece 107.

  On the other hand, in the plasma etching process, a partially masked silicon substrate is set as the work 107, and NF3 gas diluted with, for example, several times as much Ar gas is used as an etching gas. In this step, the pressure in the plasma reaction chamber 101 is adjusted to a constant value (for example, about 500 Pa), and pulse-modulated AC power output from the power supply means 108 is input to the cathode electrode 102. As the etching gas, a gas obtained by diluting a fluorine-based etching gas such as CF4 gas with an inert gas such as Ar gas in addition to the NF3 gas can be used. By this step, a desired etching process can be performed on the surface of the silicon substrate that is not masked.

  The plasma CVD process and the plasma etching process were performed in the same plasma reaction chamber 101. In both processes, the distance between the cathode electrode 102 and the anode electrode 103 was constant, and the set gas pressure was also substantially the same. In this case, although the pd product described above is substantially constant in each process, the mixed gas of NF3 gas and Ar gas used in the plasma etching process is compared with the mixed gas of SiH4 gas and H2 gas used in the plasma CVD process. Therefore, the discharge start voltage in the plasma etching process is higher than that in the plasma CVD process. Therefore, in order to generate and maintain a uniform plasma between the electrodes in the plasma etching process, it is necessary to apply a larger voltage. When CW AC power is used in this process, the amount of power input when generating and maintaining the plasma becomes excessive, and plasma is generated in the insulating portion other than between the cathode electrode 102 and the anode electrode 103. The part may be damaged.

  In this embodiment, since the pulse-modulated AC power is input to the cathode electrode 102 in the plasma etching process, a large voltage is applied between the cathode electrode 102 and the anode electrode 103 to easily generate uniform plasma. In addition, by adjusting the pulse duty ratio, the input power amount can be kept small. Thereby, the etching rate can be reduced, the control of the etching rate can be facilitated, and damage to the apparatus can be prevented.

  The embodiment of the present invention is not limited to this, and may include a plasma CVD process including a plasma etching process and a first plasma processing process having a discharge start voltage smaller than that of this process. Usually, the gas used in the plasma CVD process is different from the gas used in the plasma etching process, and a difference occurs in the discharge start voltage in both processes, so the plasma processing method of the present invention can be applied. In addition, even when the set pressure conditions in the plasma reaction chamber 101 in each process are different, the difference in the discharge start voltage may be increased, and the plasma processing method of the present invention is effective.

(Embodiment 2)
In the present embodiment, at least two plasma CVD processes having different discharge start voltages are performed in the same plasma reaction chamber 101. As an example, a process of forming a semiconductor layer of a silicon-based thin film photoelectric conversion element is performed. Described below.

  The plasma processing apparatus in which this embodiment is performed is the same as that in FIG. In the plasma processing apparatus of FIG. 1, a transparent substrate 201 on which a transparent conductive film 202 is formed as a work 107 is placed on the anode electrode 103. The transparent substrate 201 may be provided on the cathode electrode 102, but is generally provided on the anode electrode 103 in order to reduce film quality deterioration due to ion damage in plasma.

  Dilution gas, material gas, and doping gas are introduced from the gas introduction port 110. A gas containing hydrogen gas is used as the dilution gas, a silane-based gas, methane gas, germane gas, or the like is used as the material gas, diborane gas is used as the p-type impurity doping gas, and phosphine gas is used as the n-type impurity doping gas.

  FIG. 2 is a schematic cross-sectional view of the silicon-based thin film photoelectric conversion element according to this embodiment. A first electrode 202 is formed on a substrate 201, and a first p-type semiconductor layer 211, an i-type amorphous silicon-based photoelectric conversion layer 212, and a first n-type semiconductor layer 213 are sequentially stacked on the first electrode 202. Then, the first pin structure laminate 214 is formed. Subsequently, the second p-type semiconductor layer 221, the i-type crystalline silicon-based photoelectric conversion layer 222, and the second n-type semiconductor layer 223 are sequentially stacked, and the second pin structure stacked body 224 is formed. The first pin structure laminate 214 and the second pin structure laminate 224 constitute a double pin structure laminate 230, and the second electrode 203 is formed on the double pin structure laminate 230, and the silicon-based thin film photoelectric The conversion element 206 is completed.

  As the substrate 201, a glass substrate having heat resistance and translucency in a plasma CVD film forming process, or a resin substrate such as polyimide is generally used. In this embodiment, a glass substrate is used as the substrate 201.

As the first electrode 202, a transparent conductive film such as SnO ₂ , ITO, ZnO or the like is used. These are generally formed by a method such as CVD, sputtering, or vapor deposition. In the present embodiment, SnO ₂ was used as the first electrode 202.

  The double pin structure laminate 230 is formed by plasma CVD in the same plasma reaction chamber 101. In the present embodiment, a double pin structure in which p-type, i-type, and n-type semiconductors are sequentially stacked from the substrate 201 is employed.

  In the present embodiment, the first p-type semiconductor layer 211 is a boron-doped p-type amorphous silicon carbide semiconductor layer, the i-type amorphous silicon-based photoelectric conversion layer 212 is an i-type amorphous silicon semiconductor layer, The first n-type semiconductor layer 213 was an n-type crystalline silicon semiconductor layer doped with phosphorus. As the silicon-based semiconductor layer, silicon, silicon carbide, silicon germanium, or the like is generally used. As a doping material for the conductive semiconductor layer, boron, aluminum, or the like is used for p-type, and phosphorus or the like is used for n-type. It is common.

As the second electrode 203, a metal such as silver or aluminum, a transparent conductive film such as SnO ₂ , ITO, or ZnO or a laminate of these is used. These are generally formed by a method such as CVD, sputtering, or vapor deposition. In this embodiment, ZnO and silver were laminated in this order as the second electrode 203.

Hereinafter, a film forming method of the double pin structure laminate 230 will be described in detail.
The double pin structure laminate 230 is formed by plasma CVD in the same plasma reaction chamber 101.

The p-type amorphous silicon carbide semiconductor layer that is the first p-type semiconductor layer 211 can be formed under the following film formation conditions. The pressure in the plasma reaction chamber 101 during film formation is desirably 200 Pa or more and 3000 Pa, and is set to 400 Pa in this embodiment. Further, it is desirable that the base temperature of the substrate 201 be 250 ° C. or less, and in this embodiment, the substrate temperature is 180 ° C. Further, as power for plasma processing to be input to the cathode electrode 102, pulse-modulated AC power with a frequency of 13.56 MHz was used. The power density per unit area of cathode 102 is preferably set to be 0.01 W / cm ² or more 0.3 W / cm ² or less, in the present embodiment was 0.1 W / cm ^2. The on-time and off-time at the time of pulse modulation can be set according to a desired film forming speed, and are usually set in the range of about several microseconds to several milliseconds. In this embodiment, the on time is 50 μs and the off time is 100 μs.

  As the mixed gas introduced into the plasma reaction chamber 101, a gas containing silane gas, hydrogen gas, methane gas, and diborane gas is used. The raw material gas introduced into the plasma reaction chamber 101 preferably contains a silane-based gas and a diluent gas containing hydrogen gas, and may be any material that contains methane or trimethyldiborane. The flow rate of the hydrogen gas with respect to the silane gas is preferably several times to several tens of times, and in this embodiment, it is 10 times.

  The film thickness of the first p-type semiconductor layer 211 is preferably 2 nm or more in order to give a sufficient internal electric field to the i-type amorphous silicon-based photoelectric conversion layer 212, and the light of the first p-type semiconductor layer 211 that is an inactive layer. In order to suppress the amount of absorption and increase the light reaching the i-type amorphous silicon-based photoelectric conversion layer 212, it is desirable to be as thin as possible, and is usually set to 50 nm or less. In the present embodiment, the thickness of the first p-type semiconductor layer 211 is 20 nm.

The i-type amorphous silicon semiconductor layer that is the i-type amorphous silicon-based photoelectric conversion layer 212 can be formed under the following film formation conditions. The pressure in the plasma reaction chamber 101 during film formation is desirably 200 Pa or more and 3000 Pa, and is set to 400 Pa in this embodiment. Further, it is desirable that the base temperature of the substrate 201 be 250 ° C. or less, and in this embodiment, the substrate temperature is 180 ° C. Further, CW AC power having a frequency of 13.56 MHz was used as power for plasma processing input to the cathode electrode 102. The power density per unit area of cathode 102 is preferably set to be 0.01 W / cm ² or more 0.3 W / cm ² or less, in the present embodiment was 0.1 W / cm ^2.

  As the mixed gas introduced into the plasma reaction chamber 101, a gas containing silane gas and hydrogen gas is used. The flow rate of hydrogen gas with respect to silane gas is preferably 5 to 20 times, and an amorphous i-type photoelectric conversion layer having good film quality can be formed. In this embodiment, it is 10 times.

  The film thickness of the i-type amorphous silicon-based photoelectric conversion layer 212 is set to a value of 0.1 μm to 0.5 μm in consideration of light absorption and characteristic deterioration due to light degradation. In the present embodiment, the i-type amorphous silicon-based photoelectric conversion layer 212 has a thickness of 0.3 μm.

  Here, it is generally known that if the film formation speed of the i-type amorphous silicon-based photoelectric conversion layer 212 is too high, film quality deterioration such as an increase in defect density in the film occurs. Control is important. In this embodiment, when the film quality needs to be improved due to the film thickness setting, AC power pulse-modulated for plasma processing may be used to reduce the film forming speed.

The n-type crystalline silicon semiconductor layer that is the first n-type semiconductor layer 213 can be formed under the following film formation conditions. The pressure in the plasma reaction chamber 101 during film formation is desirably 240 Pa or more and 3600 Pa or less, and is 2000 Pa in this embodiment. Further, it is desirable that the base temperature of the substrate 201 be 250 ° C. or less, and in this embodiment, the substrate temperature is 180 ° C. Further, CW AC power having a frequency of 13.56 MHz was used as power for plasma processing input to the cathode electrode 102. The power density per unit area of cathode 102 is preferably set to be 0.02 W / cm ² or more 0.5 W / cm ² or less, in the present embodiment was 0.3 W / cm ^2.

  As the mixed gas introduced into the plasma reaction chamber 101, a gas containing silane gas, hydrogen gas, and phosphine gas is used. The flow rate of the hydrogen gas with respect to the silane gas is desirably about 30 to several hundred times, and is set to 100 times in this embodiment.

  The film thickness of the first n-type semiconductor layer 213 is preferably 2 nm or more in order to give a sufficient internal electric field to the i-type amorphous silicon-based photoelectric conversion layer 212. The light of the first n-type semiconductor layer 213 that is an inactive layer is used. In order to suppress the amount of absorption, it is preferably as thin as possible, and is usually 50 nm or less. In the present embodiment, the thickness of the first n-type semiconductor layer 213 is 40 nm.

Thus, the first pin structure laminate 214 is formed.
Next, a method for forming the second pin structure laminate 224 will be described.

The p-type crystalline silicon semiconductor layer that is the second p-type semiconductor layer 221 can be formed under the following film formation conditions. The pressure in the plasma reaction chamber 101 during film formation is desirably 240 Pa or more and 3600 Pa or less, and is 2000 Pa in this embodiment. Further, it is desirable that the base temperature of the substrate 201 be 250 ° C. or less, and in this embodiment, the substrate temperature is 180 ° C. Further, CW AC power having a frequency of 13.56 MHz was used as power for plasma processing input to the cathode electrode 102. The power density per unit area of cathode 102 is preferably set to be 0.02 W / cm ² or more 0.5 W / cm ² or less, in the present embodiment was 0.3W / cm ^2.

  As the mixed gas introduced into the plasma reaction chamber 101, a gas containing silane gas, hydrogen gas, and diborane gas is used. The flow rate of the hydrogen gas with respect to the silane gas is desirably about 30 to several hundred times, and is set to 100 times in this embodiment.

  The film thickness of the second p-type semiconductor layer 221 is preferably 2 nm or more in order to give a sufficient internal electric field to the i-type crystalline silicon-based photoelectric conversion layer 222, and the light absorption of the second p-type semiconductor layer 221 that is an inactive layer. In order to suppress the amount and increase the light reaching the i-type crystalline silicon-based photoelectric conversion layer 222, it is desirable that it is as thin as possible, and is usually set to 50 nm or less. In the present embodiment, the thickness of the second p-type semiconductor layer 221 is 40 nm.

  The second p-type semiconductor layer 221 may be formed of a layer made of an alloy material such as amorphous and crystalline silicon carbide or amorphous silicon germanium. The second p-type semiconductor layer 221 may be a stack of a plurality of different thin films.

The i-type crystalline silicon-based photoelectric conversion layer 222 can be formed under the following film formation conditions. The pressure in the plasma reaction chamber 101 during film formation is desirably 240 Pa or more and 3600 Pa or less, and is 2000 Pa in this embodiment. Further, it is desirable that the base temperature of the substrate 201 be 250 ° C. or less, and in this embodiment, the substrate temperature is 180 ° C. Further, CW AC power having a frequency of 13.56 MHz was used as power for plasma processing input to the cathode electrode 102. The power density per unit area of cathode 102 is preferably set to be 0.02 W / cm ² or more 0.5 W / cm ² or less, in the present embodiment was 0.3 W / cm ^2.

  As the mixed gas introduced into the plasma reaction chamber 101, a gas containing silane gas and hydrogen gas is used. The flow rate of the hydrogen gas relative to the silane gas is preferably about 30 to 100 times, and in this embodiment, it is 100 times.

  The thickness of the i-type crystalline silicon-based photoelectric conversion layer 222 is preferably 0.5 μm or more and more preferably 1 μm or more in order to ensure a sufficient amount of light absorption as the photoelectric conversion layer. Further, the thickness of the i-type crystalline silicon-based photoelectric conversion layer 222 is preferably 20 μm or less and more preferably 15 μm or less because it is necessary to ensure the productivity of the device. In the present embodiment, the i-type crystalline silicon-based photoelectric conversion layer 222 has a thickness of 2 μm.

  In this embodiment, since a high-quality film needs to be formed at a higher film formation rate as the i-type crystalline silicon-based photoelectric conversion layer 222, the configuration of the plasma processing apparatus is set as the film formation condition in this step. The setting was most suitable. Specifically, the distance between the cathode electrode 102 and the anode electrode 103 was 15 mm, and the same configuration was used in all other steps.

In this way, i-type crystalline with sufficient crystallization rates peak intensity ratio I ₅₂₀ / I ₄₈₀ of the peak is 5 to 10 at 520 nm ^-1 to a peak at 480 nm ^-1 as measured by Raman spectroscopy A silicon-based photoelectric conversion layer 222 is obtained. In addition, as the i-type crystalline silicon-based photoelectric conversion layer 222, an i-type crystalline silicon thin film or a crystalline silicon thin film having a weak p-type or weak n-type containing a small amount of impurities and having a sufficient photoelectric conversion function is used. May be. Furthermore, the i-type crystalline silicon-based photoelectric conversion layer 222 is not limited to the crystalline silicon thin film, and a thin film such as silicon carbide or silicon germanium that is an alloy material may be used.

The n-type crystalline silicon semiconductor layer that is the second n-type semiconductor layer 223 can be formed under the following film formation conditions. The pressure in the plasma reaction chamber 101 during film formation is desirably 240 Pa or more and 3600 Pa or less, and is 2000 Pa in this embodiment. Further, it is desirable that the base temperature of the substrate 201 be 250 ° C. or less, and in this embodiment, the substrate temperature is 180 ° C. In addition, CW AC power having a frequency of 13.56 MHz was used as power for plasma processing input to the cathode electrode 102. The power density per unit area of cathode 102 is preferably set to be 0.02 W / cm ² or more 0.5 W / cm ² or less, in the present embodiment was 0.3 W / cm ^2.

  As the mixed gas introduced into the plasma reaction chamber 101, a gas containing silane gas, hydrogen gas, and phosphine gas is used. The flow rate of the hydrogen gas with respect to the silane gas is desirably about 30 to several hundred times, and is set to 100 times in this embodiment.

  The film thickness of the second n-type semiconductor layer 223 is preferably 2 nm or more in order to give a sufficient internal electric field to the i-type crystalline silicon-based photoelectric conversion layer 222, and the light absorption of the second n-type semiconductor layer 223, which is an inactive layer. In order to suppress the amount, it is preferably as thin as possible, and is usually 50 nm or less. In the present embodiment, the thickness of the second n-type semiconductor layer 223 is 40 nm.

  The second n-type semiconductor layer 223 may be formed of an alloy material such as crystalline silicon carbide or silicon germanium.

  As described above, the first pin structure stacked body 214 and the second pin structure stacked body 224 are continuously formed in the same plasma reaction chamber 101.

  Thereafter, a silicon-based thin film photoelectric conversion element 206 can be manufactured by forming a conductive film such as ZnO and a metal film such as aluminum or silver by sputtering or vapor deposition and forming the second electrode 203. it can.

  In the present embodiment, in the film forming process of the p-type amorphous silicon carbide semiconductor layer which is the first p-type semiconductor layer 211, pulse-modulated AC power is used as a power source for plasma processing (second plasma processing process). In the film formation process (first plasma treatment process) of the i-type crystalline silicon-based photoelectric conversion layer 222, pulse-modulated AC power was used.

  In the film forming step of the i-type crystalline silicon-based photoelectric conversion layer 222, in order to maintain the desired film quality such as the crystallization rate and the crystal grain size of the film to be formed, the cathode electrode 102 and the anode electrode It is necessary to set the apparatus configuration such as the distance between 103 to be suitable for this process. For example, in the step of forming the i-type crystalline silicon-based photoelectric conversion layer 222, the cathode electrode 102 and the anode are formed more than when an amorphous silicon-based half layer layer (for example, an amorphous silicon carbide semiconductor layer) is formed. In general, the distance between the electrodes 103 is narrowed and the pressure in the plasma reaction chamber 101 is set high.

  Thus, in the same plasma reaction chamber 101 of the apparatus set so as to be suitable for the film forming process of the i-type crystalline silicon-based photoelectric conversion layer 222, the p-type amorphous layer that is the first p-type semiconductor layer 211 is formed. When the silicon carbide semiconductor layer is formed, the discharge start voltage is higher than in the case of the film formation process of the i-type crystalline silicon-based photoelectric conversion layer 222 because the film formation conditions (particularly, the set pressure in the plasma reaction chamber 101) are different. .

  Therefore, in order to generate and maintain a uniform plasma in the film forming process of the p-type amorphous silicon carbide semiconductor layer which is the first p-type semiconductor layer 211 having a relatively high discharge start voltage, a larger input power is required. If the input power is increased, the plasma processing speed increases and the film formation speed increases. The p-type amorphous silicon carbide semiconductor layer which is the first p-type semiconductor layer 211 has a very thin thickness of 50 nm or less, and it is necessary to reduce the deposition rate in order to control the thickness.

  Therefore, in the present embodiment, in the step of forming the p-type amorphous silicon carbide semiconductor layer that is the first p-type semiconductor layer 211, pulse-modulated AC power is used as a power source for plasma processing. Thereby, it is possible to achieve both a decrease in the film formation rate and generation and maintenance of uniform plasma. That is, by using pulse-modulated AC power, it is possible to suppress the input power amount, reduce the deposition rate, increase the instantaneous input power and voltage, and generate and maintain uniform plasma between the electrodes. It becomes possible.

(Embodiment 3)
In the plasma processing method of the present embodiment, the substrate 201 is set on the anode electrode 103 in the plasma reaction chamber 101, and after performing the plasma CVD process of forming the double pin structure laminate 230 on the substrate 201, A plasma etching process in which the substrate 201 on which the heavy pin structure laminate 230 is formed is taken out of the plasma reaction chamber 101 and the remaining films on the cathode electrode 102 and the anode electrode 103 and the inner wall of the plasma reaction chamber 101 in the plasma reaction chamber 101 are etched. Are performed in this order.

  The plasma CVD process includes a first plasma processing process for forming a crystalline silicon-based photoelectric conversion layer using CW AC power. The plasma etching step is a step of performing plasma etching using a pulse-modulated AC power having a higher discharge start voltage than the first plasma processing step, and the cathode electrode 102 in the plasma reaction chamber 101 in the plasma CVD step. The silicon-based semiconductor film attached to the anode electrode 103 and the inner wall of the plasma reaction chamber 101 is etched.

  As in the present embodiment, the plasma CVD process only needs to include at least the first plasma processing process using CW AC power, and may include a film forming process using pulse-modulated AC power. The plasma etching process may be any process in which the discharge starting voltage is higher than that of the first plasma processing process and the plasma etching is performed using pulse-modulated AC power.

The plasma processing apparatus in which this embodiment is performed is the same as that in FIG.
On the substrate 201, a double pin structure laminate 230 is formed under the same conditions as in the second embodiment.

  After performing the plasma CVD process for forming the double pin laminated body 230 a plurality of times, the plasma etching process for etching the cathode electrode 102 and the anode electrode 103 in the plasma reaction chamber 101 and the residual film on the inner wall of the plasma reaction chamber 101 By performing the above, the apparatus can be cleaned. The conditions for the plasma etching process can be the same as those for the plasma etching process of the first embodiment.

  Generally, the film forming conditions and apparatus configuration of a high-quality crystalline silicon-based thin film layer are limited in the setting range, and therefore the apparatus configuration is designed to suit the conditions.

  When the first plasma processing step for forming the crystalline silicon-based thin film layer using CW AC power is included in the plasma CVD step as in this embodiment, the apparatus configuration such as the interelectrode distance is It is set to be suitable for the process. In this apparatus, when the plasma etching process, which is the second plasma treatment process, is performed, the discharge start voltage increases because the gas used is difficult to ionize. In the present embodiment, in the plasma etching step, pulse-modulated AC power is applied to the cathode electrode 102, so that a large voltage is applied between the electrodes to generate and maintain a uniform plasma between the electrodes, and The amount of input power can be kept small. Further, this method can reduce the possibility of damaging the insulating portion of the device even when plasma is generated in a portion other than between the electrodes.

(Embodiment 4)
The plasma processing method of this embodiment will be described below.

  The plasma processing apparatus in which the plasma processing method of the present embodiment is implemented has the same configuration as that shown in FIG.

  In the present embodiment, after performing the plasma etching process of the first embodiment, the substrate 201 is set, the plasma CVD process of the third embodiment in which the double pin structure laminate 230 is formed, and the substrate 201 is taken out. Is repeatedly performed.

  The plasma etching step is performed before the first pin structure laminate 214 is formed, and the semiconductor film attached to the cathode electrode 102, the anode electrode 103, and the inner wall of the plasma reaction chamber 101 is etched from the outermost surface layer. In order to form the double pin structure laminate 230 with good reproducibility, it is preferable that the environment in the plasma reaction chamber 101 is substantially the same at the start of the film formation, and that the plasma is stable and impurities are mixed. In order to prevent this, it is desirable that a film having a certain film surface is formed on the inner wall of the cathode electrode 102, the anode electrode 103 and the plasma reaction chamber 101, and an i-type semiconductor layer is formed on the remaining film outermost surface. It is further desirable that it is exposed.

  By this step, the double pin structure laminate 230 having good quality can be repeatedly formed in the same plasma reaction chamber 101.

  In the plasma etching process, in order to etch the residual film previously formed on the inner wall of the cathode electrode 102, the anode electrode 103, and the plasma reaction chamber 101 to expose the i-type semiconductor layer on the surface, the etching film thickness is Control is important and the etch rate needs to be reduced.

  The distance between the cathode electrode 102 and the anode electrode 103 of the plasma processing apparatus of this embodiment is designed to be suitable for a plasma CVD process for forming an i-type crystalline silicon-based photoelectric conversion layer. For this reason, in the plasma etching process using a mixed gas of an inert gas and a fluorine-based etching gas, the etching gas is difficult to be ionized by voltage application, and thus a high applied voltage is required for the generation of plasma.

  In the plasma etching process, AC power pulse-modulated for plasma generation is used as in the first embodiment. Thereby, even when a high voltage is applied for the purpose of generating and maintaining uniform plasma between the electrodes, the amount of electric power applied can be reduced, and the etching rate can be reduced. Further, by adjusting the duty ratio of the pulse, the input power amount can be adjusted, and the etching film thickness can be easily controlled.

(Embodiment 5)
The present embodiment will be described with reference to the drawings. FIG. 3 is a schematic diagram of the plasma processing apparatus according to the present embodiment, and has a structure in which a plurality of pairs of anode electrodes 103 and cathode electrodes 102 are connected from the power supply means 108 to one impedance matching circuit 105.

  In the case of this structure, it is difficult to simultaneously generate glow discharge plasma in a plurality of anode electrode 103 / cathode electrode 102 pairs. That is, when glow discharge plasma is generated in a part of a plurality of electrode pairs, the impedance between the electrodes is reduced, the power supplied between the other electrodes is reduced, and the plasma between these electrodes is reduced. The problem that does not occur occurs.

  This problem is particularly problematic in processes where the power and voltage applied to the cathode electrode 102 are small, and it is necessary to apply a larger voltage between the electrodes. The greater the voltage applied between the electrodes, the higher the probability that glow discharge plasma will be generated simultaneously between the electrodes, and uniform plasma can be generated and maintained between the electrodes.

  In the plasma processing apparatus having the configuration of the present embodiment, when performing a plasma etching step with a large discharge start voltage, it is more difficult to simultaneously generate and maintain glow discharge plasma between all electrodes, and a higher applied voltage I need it. Even in such a case, it is effective to use pulse-modulated AC power as in the first to fourth embodiments.

It is a schematic sectional drawing of the plasma processing apparatus which concerns on Embodiment 1-4 of this invention. It is a schematic sectional drawing of the silicon-type thin film photoelectric conversion element which concerns on this Embodiment 3 of this invention. It is a schematic sectional drawing of the plasma processing apparatus which performs the plasma processing method concerning Embodiment 5 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Plasma reaction chamber 102 Cathode electrode 103 Anode electrode 105 Impedance matching circuit 107 Work 108 Power supply means 201 Substrate 206 Silicon-type thin film photoelectric conversion element 211 1st p-type semiconductor layer 212 i-type amorphous silicon-type photoelectric conversion layer 213 1st n-type semiconductor layer 214 first pin structure laminate 221 second p-type semiconductor layer 222 i-type crystalline silicon-based photoelectric conversion layer 223 second n-type semiconductor layer 224 second pin structure laminate

Claims (10)

A plasma processing method for performing at least two plasma processing steps in the same plasma reaction chamber,
A first plasma processing step using CW AC power as a power source for plasma processing;
Using a pulse-modulated AC power as a power source for plasma processing, a second plasma processing step having a higher discharge start voltage than the first plasma processing step;
A switching step of appropriately switching between the first plasma processing step and the second plasma processing step;
A plasma processing method comprising: 2. The first plasma processing step and the second plasma processing step are performed in a configuration in which a distance between electrodes of a cathode / anode electrode set in the plasma reaction chamber is the same. The plasma processing method as described. 3. The plasma processing method according to claim 1, wherein a gas pressure in the plasma reaction chamber is different between the first plasma processing step and the second plasma processing step. 4. The gas introduced and decomposed in the plasma reaction chamber in the first plasma treatment step is more easily ionized by an applied voltage than the gas introduced and decomposed in the plasma reaction chamber in the second plasma treatment step. The plasma processing method according to any one of claims 1 to 3. 5. The method according to claim 1, wherein the first plasma processing step is a film forming step by a plasma CVD method, and the second plasma processing step is a step of performing a plasma etching process. The plasma processing method according to item. 6. The plasma processing method according to claim 5, wherein in the plasma etching process, the film deposited in the plasma reaction chamber in the first plasma processing step is plasma etched. The plasma processing method according to claim 6, wherein the first plasma processing step is a step of forming a film of at least one semiconductor layer of the photoelectric conversion element by a plasma CVD method. The plasma according to any one of claims 1 to 4, wherein the first plasma treatment step and the second plasma treatment step are steps of forming a semiconductor film by a plasma CVD method. Processing method. A crystalline silicon-based semiconductor layer is formed by plasma CVD in the first plasma treatment step, an amorphous silicon-based semiconductor layer is formed by plasma CVD in the second plasma treatment step, and the crystal The film attached to the plasma reaction chamber is plasma-etched by the second plasma treatment step after forming the conductive silicon semiconductor layer and the amorphous silicon semiconductor layer. 5. The plasma processing method according to any one of 4 above. The photoelectric conversion element manufactured using the plasma processing method of any one of Claims 7-9.

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