JP2012124395A - Method and apparatus of manufacturing thin film solar cell, and thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To switch the conditions of deposition processing of a solar cell quickly.SOLUTION: When the amorphous Si layer 142A and a microcrystalline Si layer 142B of the semiconductor layer 14 in a solar cell element 100 of a thin film solar cell are formed by plasma CVD, processing conditions are switched while sustaining excitation of plasma. In order to sustain excitation of plasma P, pressure in a vacuum chamber 22 is controlled in the processing of changing the gas flow rate when a transition is made from formation of the amorphous Si layer to formation of the microcrystalline Si layer.

Description

  The present invention relates to a method for manufacturing a thin film solar cell, a manufacturing apparatus, and a thin film solar cell. More specifically, the present invention relates to a manufacturing method, a manufacturing apparatus, and a thin film solar cell for a thin film solar cell including a semiconductor layer having a laminated structure using a plasma CVD method.

  Conventionally, a thin film solar cell is used as a solar cell that generates power using sunlight. Microcrystalline silicon (Si) can be given as a material that has attracted particular attention as a material for a photoelectric conversion layer for a thin film solar cell. When a microcrystalline Si layer is formed on one surface of a support substrate, the metal element constituting the electrode layer disposed on the support substrate penetrates into the microcrystalline Si semiconductor layer by diffusion, and the photoelectric conversion of the photoelectric conversion layer Reduce efficiency. The causative metal element is a metal element of an electrode layer typically made of metal. In addition, for example, if a transparent electrode layer is used for the electrode layer, the metal element produced by reducing the metal oxide of the transparent electrode layer by hydrogen plasma during the formation of microcrystalline Si has the same adverse effect. Effect. Therefore, in order to reduce the influence of metal elements on the microcrystalline Si layer, an amorphous Si layer is arranged at a position in contact with the electrode layer on the substrate, and a microcrystalline Si layer is further laminated on the substrate type solar. A battery structure has been proposed (Patent Document 1: Japanese Patent Laid-Open No. 11-274540).

  In order to form the laminated structure disclosed in Patent Document 1, in order to form the microcrystalline Si layer after the formation of the amorphous Si layer, the gas serving as the atmosphere of the substrate is changed inside the vacuum chamber of the film forming apparatus. With work. The procedure for this change is as follows. First, the plasma that has been excited is stopped. Next, the gas in the atmosphere at that time is exhausted. Further, a new film forming gas is introduced into the same vacuum chamber to adjust (regulate) the pressure. Finally, the plasma is excited again (for example, Patent Document 1, paragraphs [0085] to [0086]). Such a method for forming a semiconductor layer by plasma CVD with plasma stoppage is also disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 2008-181960).

JP 11-274540 A JP 2008-181960 A

  However, when processing with plasma stoppage is actually performed using the same film forming chamber disclosed in Patent Document 1, it takes time to switch the film forming condition from one to another, and consequently Reduce the manufacturing efficiency of solar cells. That is, as disclosed in Patent Document 1, after the film formation of the amorphous Si layer is completed, in order to change the atmosphere gas, the plasma is stopped and the gas is exhausted, and the pressure is adjusted by newly introducing the gas. The series of operations of starting the film formation of the microcrystalline Si layer after exciting the plasma is a process that takes time to such an extent that a decrease in manufacturing efficiency becomes a problem.

  Further, Patent Document 2 discloses a plasma CVD film forming method with plasma stop in connection with a super straight type solar cell that receives light through a light-transmitting substrate. Also in this disclosure, a process of stacking a plurality of semiconductor films using the same film formation chamber is performed (for example, Patent Document 2, paragraphs [0041], [0043] to [0041], etc.). According to the disclosure of Patent Document 2, between two steps in which layers having different conductivity types are stacked, hydrogen gas is introduced as a replacement gas, and then a new source gas is introduced to stabilize the pressure. A process of exciting the plasma again after waiting is performed (paragraphs [0043] to [0051]). Further, according to the disclosure of Patent Document 2, the process of exciting the plasma after the introduction of the replacement gas and the subsequent stabilization of the pressure is performed between the two processes in which the layers having the same conductivity type are stacked. (Paragraphs [0043] and [0058]). That is, in the method disclosed in Patent Document 2, the procedure of introducing replacement gas, exhausting, and re-excitation of plasma is performed, and the film forming method is switched as in the film forming method disclosed in Patent Document 1. Therefore, it takes time to reduce the production efficiency.

  Here, one of the major factors that increase the time when the film forming conditions are switched by the conventional method is that time is required for the operation of stopping and re-exciting the plasma. Conventionally, when switching film forming conditions, as disclosed in Patent Documents 1 and 2, the plasma is stopped and the film forming process is temporarily interrupted. This is because an abnormal film may be formed when the plasma is not stopped. Even if the film formation conditions are switched without stopping the plasma, the plasma is stopped unintentionally during the switching operation or during the switching process in the film forming apparatus, and the re-excitation operation is performed. It may be necessary.

  The present invention improves the mass productivity of a high-performance thin-film solar cell by shortening the switching time of the film-forming condition of the plasma CVD method in a solar cell including a semiconductor layer in which films having different film-forming conditions are stacked. It contributes to.

  The inventors of the present application, when switching the film formation conditions of the plasma CVD method without intentionally interrupting the plasma, may form an abnormal film as described above, or may stop the plasma unintentionally. Investigate the cause. And it was found that the direct cause was the pressure fluctuation inside the vacuum chamber.

  According to this knowledge, it should be possible to suppress abnormal film formation and sudden stop of plasma by suppressing pressure fluctuations inside the vacuum chamber. However, when switching the film forming conditions, even if it is attempted to suppress the fluctuation of the pressure in the vacuum chamber, the fluctuation is actually unavoidable in many cases. Then, when the cause of the pressure fluctuation was further investigated, it was found that the change in the flow rate of the gas supplied to the vacuum chamber was related to the pressure fluctuation.

  That is, the flow rate of the gas supplied to the vacuum chamber is normally defined as the volume of gas supplied per unit time (for example, the gas volume in the standard state). If the gas flow rate is changed abruptly, the pressure inside the vacuum chamber will fluctuate greatly even if it is controlled by some means so as to suppress the pressure fluctuation. The pressure fluctuation caused the abnormal film formation and the unintended plasma stop as described above.

  Therefore, when switching the film formation conditions, an attempt was made to change the gas flow rate under conditions that do not cause pressure fluctuations. As a result, abnormal film formation was suppressed and unintended plasma discharge did not stop. Became clear.

  That is, in one aspect of the present invention, there is provided a method for manufacturing a thin-film solar cell including a semiconductor layer including either a nip junction structure or a pin junction structure, wherein the surface of the electrode on the substrate on which the electrode is formed is provided. A first film forming step of forming an n-type or p-type amorphous Si layer in the vacuum chamber by a plasma CVD method under a first condition, and the same as the amorphous Si layer in contact with the surface of the amorphous Si layer A second film forming step of forming a conductive type microcrystalline Si layer inside the vacuum chamber by a plasma CVD method under a second condition, and a transition from the first film forming step to the second film forming step. A gas supplied to the vacuum chamber in a transition step while maintaining the pressure inside the vacuum chamber so as to continue the excitation of the plasma Total flow, the method of manufacturing the thin film solar cell comprising a transition step to be changed from the total flow rate of the gas contained in the first condition to the total flow rate of the gas contained in the second condition is provided.

  In one embodiment of the present invention, a manufacturing apparatus for manufacturing a thin film solar cell including a semiconductor layer including either a nip junction structure or a pin junction structure, wherein an electrode is formed on at least one surface. A vacuum chamber for forming at least one of the semiconductor layers on the surface of the electrode of the substrate by a plasma CVD method, and connected to the vacuum chamber. A gas supply system for supplying gas to the inside of the vacuum chamber; a pressure sensor provided in the vacuum chamber for detecting the pressure inside the vacuum chamber; and connected to the vacuum chamber; An exhaust system for exhausting gas, and a power supply system for supplying power for exciting plasma to the film-forming electrode inside the vacuum chamber Connected to the gas supply system, connected to the gas flow control unit for controlling the flow rate of the gas supplied from the gas supply system to the inside of the vacuum chamber, the pressure sensor, and the exhaust system, the pressure sensor A pressure control unit for controlling the pressure inside the vacuum chamber by changing the exhaust amount of the exhaust system based on a signal from the control unit, and a command value or a control signal for the gas flow rate control unit and the pressure control unit. A sequence control unit that outputs and controls a processing operation, and the sequence control unit forms an n-type or p-type amorphous Si layer on the surface of the electrode by a plasma CVD method under a first condition. From the film forming process, a second crystalline silicon layer having the same conductivity type as the amorphous Si layer is formed by a plasma CVD method under a second condition in contact with the surface of the amorphous Si layer. When making a transition to processing, the gas flow rate control unit controls the pressure inside the vacuum chamber so that the excitation of the plasma is continued by the pressure control unit. There is provided a thin-film solar cell manufacturing apparatus for performing a processing operation for changing the total flow rate from the total gas flow rate included in the first condition to the total gas flow rate included in the second condition.

  In one embodiment of the present invention, the semiconductor layer including either the nip junction structure or the pin junction structure is a thin film solar cell formed on a surface of the electrode on which the electrode is formed. The n-type or p-type semiconductor layer forming the nip junction structure or the pin junction structure includes an n-type or p-type amorphous Si layer formed by a plasma CVD method under a first condition in a vacuum chamber, A microcrystalline Si layer having the same conductivity type as that of the amorphous Si layer, formed by plasma CVD under two conditions, is a laminate formed in this order from the surface side of the electrode, and the microcrystalline Si layer While the pressure inside the vacuum chamber is maintained so that plasma excitation is continued, the total flow rate of the gas supplied to the vacuum chamber is included in the gas included in the first condition. The thin film is a layer formed by changing the processing condition of the plasma CVD method from the first condition to the second condition by changing from the total flow rate of the gas to the total gas flow rate included in the second condition. A solar cell is provided.

  In each aspect of the present invention described above, the nip junction structure is an n-type conduction type arbitrary semiconductor layer from the substrate side, an i-type conduction type arbitrary semiconductor layer (intrinsic semiconductor layer), and , P-type conduction type arbitrary semiconductor layers are stacked in this order. On the contrary, the pin junction structure is a structure in which each layer is laminated from the substrate side. Each of the semiconductor layers herein may be a single film or layer, or may be a stacked body. Any one of the nip junction structure and the pin junction structure constitutes, for example, a photoelectric conversion layer of a solar cell alone, or a plurality of stacked layers constitute a photoelectric conversion layer of a solar cell.

  In addition, the material of the semiconductor layer other than that in which the material is specified is arbitrary. Typical examples of the material of the semiconductor layer include silicon (Si) and silicon-germanium (SiGe). Furthermore, any gas can be employed for the source gas and dilution gas used for forming the semiconductor layer, the kind of the element doped for determining the conductivity type, the doping gas, and the like.

  The plasma CVD method is a film forming technique in which a raw material gas is introduced into a vacuum chamber or a vacuum chamber whose pressure is reduced, and a decomposition product of the raw material gas is deposited using plasma excited by high frequency or DC power. .

The amorphous Si layer is, for example, an amorphous layer of hydrogenated thin film Si in which dangling bonds are terminated by hydrogen atoms. In order to change the conductivity type of amorphous Si to n-type, for example, P (phosphorus) is introduced in addition to silicon. Therefore, in order to form an amorphous Si film, for example, a silane gas such as monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ) is used as a source gas for silicon. In addition, as a doping source gas (doping gas) introduced in addition to the silane gas for forming the amorphous Si film, phosphine (PH ₃ ) and diborane (B ₂ ) are used to make the conductivity type n-type and p-type. A gas such as H ₆ ) is used.

  In any aspect of the present invention, when a semiconductor layer having a stacked structure in which semiconductor films having different film formation conditions are stacked is formed by plasma CVD, the film formation conditions are switched while plasma excitation is continued. This makes it possible to shorten the time for switching conditions in the plasma CVD method.

It is a schematic sectional drawing which shows the structure of the solar cell in one embodiment of this invention. It is a block diagram which shows schematic structure of the film-forming apparatus in one embodiment of this invention. It is a flowchart which shows the manufacturing process of the solar cell element in embodiment with this invention. It is a flowchart which shows in detail the process which forms especially a semiconductor layer among the manufacturing processes of the solar cell element in one embodiment of this invention. It is a timing chart for demonstrating the process performed in the process which forms the semiconductor layer of one embodiment of this invention. It is a schematic sectional drawing which shows the structure of the solar cell in one embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described. In the following description, unless otherwise specified, common parts or elements are denoted by common reference numerals throughout the drawings. In the drawings, each element of each embodiment is not necessarily shown in a scale ratio.

<First Embodiment>
[Construction]
FIG. 1 is a schematic cross-sectional view showing the structure of a solar cell element 100 in an embodiment of the present invention. The solar cell element 100 of the present embodiment is a substrate type solar cell element that includes a back electrode layer 12, a semiconductor layer 14, and a transparent electrode layer 16 on one surface of a substrate 10.

  The substrate 10 is made of, for example, a glass substrate or a flexible resin substrate, and is a substrate having heat resistance that can withstand the heat of film formation. A back electrode layer 12 is formed on one surface thereof, that is, the surface located above the paper surface in FIG. The back electrode layer 12 is formed of a metal layer such as a silver alloy. On the surface of the back electrode layer 12, a hydrogenated thin film Si layer formed by plasma CVD is formed as a semiconductor layer 14. The semiconductor layer 14 is formed so as to form a stacked structure of a nip junction structure of an n-type semiconductor layer 142, an i-type semiconductor layer 144, and a p-type semiconductor layer 146 from the substrate 10 side. The n-type semiconductor layer 142 is a stacked body in which an n-type amorphous Si layer 142A and an n-type microcrystalline Si layer 142B are stacked. A transparent electrode layer 16 is formed on the upper surface of the semiconductor layer 14. In the solar cell element 100, light (hν) serving as an energy source of the solar cell is incident on the semiconductor layer 14 from above in FIG. 1 through the transparent electrode layer 16. On the upper surface of the transparent electrode layer 16, a collecting electrode layer 16 </ b> A for reducing the substantial electric resistance of the transparent electrode layer 16 is formed in a comb shape by a metal film or the like, for example. FIG. 1 is drawn as a schematic cross-sectional view in the direction of cutting a portion corresponding to the comb-like teeth.

  Therefore, the solar cell element 100 is a thin film solar cell including the semiconductor layer 14 having only a single nip junction structure. The semiconductor layer 14 is formed on the surface of the back electrode layer 12 of the substrate 10 on which the electrode which is the back electrode layer 12 is formed. The n-type semiconductor layer 142 having a nip junction structure is a stacked body in which an n-type amorphous Si layer 142A and an n-type microcrystalline Si layer 142B are stacked in this order on the surface of the back electrode layer 12. In order to form the n-type semiconductor layer 142, a plasma CVD method is employed in which film formation is performed using plasma inside the vacuum chamber. In addition, the n-type microcrystalline Si layer 142B is formed from the first condition for forming the n-type amorphous Si layer 142A by the deposition condition by the plasma CVD method, and the second condition for forming the n-type microcrystalline Si layer 142B. It is a layer formed by transitioning to conditions while plasma excitation continues. Details of the transition will be described below by explaining the manufacturing process.

  The manufacturing process of the solar cell element 100 is demonstrated based on FIGS. FIG. 2 is a configuration diagram showing a schematic configuration of a film forming apparatus 200 for forming the n-type semiconductor layer 14. FIG. 3 is a flowchart showing the overall manufacturing process of the solar cell element 100 of the present embodiment. FIG. 4 is a flowchart showing in detail the process S14 for forming the n-type semiconductor layer 14 in the entire manufacturing process. FIG. 5 is a timing chart for explaining the processing performed in FIG.

[Configuration of deposition system]
First, the configuration of the film forming apparatus 200 will be described with reference to FIG. The film forming apparatus 200 is a film forming apparatus having a parallel plate type discharge structure. That is, the ground electrode 24 and the shower head electrode 26 are stored in the vacuum chamber 22 of the film forming apparatus 200. The ground electrode 24 and the shower head electrode 26 are arranged at a certain distance from each other, and the substrate to be subjected to the film formation process, that is, the back electrode layer 12 is formed during the film formation process. A substrate 10 is placed in the gap between them. At this time, the surface of the substrate 10 on which the back electrode layer 12 is formed is disposed in a direction toward the shower head electrode 26, and the entire substrate 10 is disposed at a position substantially in contact with the ground electrode 24. The ground electrode 24 incorporates a heater 24H for controlling the temperature at the time of film formation of the substrate 10, and is electrically connected to the ground. In FIG. 2, the ground electrode 24, the showerhead electrode 26, and the substrate 10 are illustrated in a direction extending in the vertical direction of the drawing. As a configuration of the film forming apparatus that can be adopted as the present embodiment, the orientations of the ground electrode 24, the showerhead electrode 26, and the substrate 10 are arbitrary, and are not particularly limited such as horizontal and vertical.

  The vacuum chamber 22 is provided with a gas supply system 220 that supplies gases such as source gas, dilution gas, and doping gas to the inside thereof. These gases are mixed and supplied from a large number of holes. In FIG. 2, the gas supply system 220 includes gas supply systems 220 </ b> A and 220 </ b> B that are two gas supply systems. However, the number of gas supply systems of the film forming apparatus 200 of the present embodiment is not particularly limited to only two systems. As part of the gas supply system 220, a gas cylinder 222 and a control valve 224 for adjusting the flow rate are included. These elements are included in each of the gas supply system 220A and the gas supply system 220B, and are distinguished by reference numerals with similar alphabets as necessary. The control valves 224A and 224B are controlled to perform different operations from the gas flow rate control unit 226 connected thereto. The gas flow rate control unit 226 adjusts the opening degree of each of the control valves 224A and 224B, for example, and adjusts the flow rate of each gas supplied from the gas supply systems 220A and 220B to the inside of the vacuum chamber 22 through the shower head electrode 26. The target value (set value or command value) is controlled.

  The vacuum chamber 22 is provided with a pressure sensor 244 for detecting the internal pressure. The vacuum chamber 22 is connected to an exhaust system 240 that exhausts the gas inside. In the exhaust system 240, a pressure control valve 246 is inserted between the vacuum chamber 22 and the vacuum pump 242 used for exhaust. A pressure control unit 248 is connected to the pressure control valve 246, and a pressure measurement signal from the pressure sensor 244 is input to the pressure control unit 248. The pressure control unit 248 changes the exhaust speed of the exhaust system 240 based on the signal from the pressure sensor 244, that is, the exhaust amount, and performs closed-loop feedback control so that the pressure inside the vacuum chamber 22 matches the pressure command value. Running. This control is performed, for example, by adjusting the opening of the pressure control valve 246 when the vacuum pump 242 is continuously operating at a constant speed. That is, when the pressure value indicated by the signal from the pressure sensor 244 is higher than the pressure command value, the conductance of the path from the vacuum chamber 22 to the vacuum pump 242 is increased by opening the pressure control valve 246 more than before. The exhaust speed is increased. When the pressure value indicated by the signal from the pressure sensor 244 is lower than the pressure command value, the reverse operation is performed. Thus, the pressure control unit 248 automatically controls the pressure in the vacuum chamber 22 by control such as PD control (proportional derivative control) or PID control (proportional integral derivative control).

  The film forming apparatus 200 includes a power supply system 260 for exciting plasma. The power supply system 260 supplies power for exciting plasma in a space toward the surface of the back electrode layer 12 of the substrate 10 inside the vacuum chamber 22. Specifically, the power supply system 260 is connected to the shower head electrode 26 and either the ground electrode 24 or the ground, and includes a power supply 262 and a matching circuit 264. A power control unit 266 is connected to the power supply system 260. The power control unit 266 is connected to the power supply 262 or the matching circuit 264 included in the power supply system 260. With this configuration, the power control unit 266 can change the operating conditions of the power supply 262 or the matching circuit 264, and can control the output power from the power supply system 260, that is, the plasma power.

  In addition to the above-described elements, the film forming apparatus 200 includes arbitrary elements for appropriately executing the film forming processing operation. For example, the film forming apparatus 200 includes a heating power supply system for controlling the substrate 10 to an appropriate temperature by the heater 24H, a substrate driving system for appropriately transporting the substrate 10, and the like. The gas from the showerhead electrode 26 is turned into plasma by the discharge of electric power supplied between the ground electrode 24 and the showerhead electrode 26 and is deposited on the back electrode layer 12 of the substrate 10 as a decomposition product. Go. In FIG. 2, the state is schematically drawn by the plasma P. A range in which a target film is formed by the plasma P is a film forming region in the film forming apparatus 200.

  A sequence control unit 28 is also connected to the film forming apparatus 200. The sequence control unit 28 is connected to the above-described gas flow rate control unit 226, pressure control unit 248, and power control unit 266, and controls to control the overall processing operation of the film forming apparatus 200 for each control unit. It is carried out. In order to control this control operation, a control signal and a command value are transmitted from the sequence control unit 28 to each control unit. The sequence control unit 28 has a built-in sequence program that determines what control signal and command value are transmitted to which control unit at what timing, or accepts an operation input by an operator from the outside.

[Manufacturing process]
Next, the process of manufacturing the solar cell element 100 shown in FIG. 1 using the film forming apparatus 200 described above will be described mainly with reference to FIGS.

  First, the back electrode layer 12 is formed on the substrate 10 (FIG. 3, S12). The material used for the back electrode layer 12 is a single-layer metal layer such as a silver (Ag) alloy or aluminum (Al), or a transparent electrode layer made of a metal oxide or the like above the metal layer. A laminated body of a metal layer / transparent electrode layer. The process for forming the back electrode layer 12 is performed by any process that can form the back electrode layer 12 to have desired properties. For this purpose, for example, a forming method such as a sputtering method, a vacuum deposition method, a spray film forming method, a printing method, a coating method, or a plating method is appropriately used.

  Next, as an initial process for forming the semiconductor layer 14 having the nip junction structure, the n-type semiconductor layer 142 is formed (S14). As shown in FIG. 4, the formation process S14 of the n-type semiconductor layer 142 further includes a process of forming the n-type amorphous Si layer 142A (S142) and a process of forming the n-type microcrystalline Si layer 142B (S146). Contains. The entire process S14 of forming the n-type semiconductor layer 142 is performed by a plasma CVD method using the vacuum chamber 22 (FIG. 2). That is, the processes S142 and S146 are performed while the substrate 10 is stationary by the film forming apparatus 200 that is a plasma CVD apparatus, together with the processes performed between them. It should be noted that, as shown in FIG. 4, the plasma is continuously excited through the processes S142 and S146.

  More specifically, the n-type amorphous Si layer formation process (first film formation step, first film formation process) S142 and the n-type microcrystalline Si layer formation process (second film formation step, second film formation process). In S146, film forming conditions, that is, various setting conditions and operating conditions in the plasma CVD method are different. In the present embodiment, the film formation condition of the plasma CVD method in the n-type amorphous Si layer formation process S142 is referred to as a first condition, and the film formation condition of the plasma CVD method in the n-type microcrystalline Si layer formation process S146 is referred to as a second condition. . The first condition and the second condition, which are film forming conditions, are a set of several setting conditions or operating conditions. The values included in the first condition and the second condition are, for example, values for the flow rates of various gases into the vacuum chamber 22, values for the pressure in the vacuum chamber 22, and plasma excitation. It is the value of the output power from the power supply 262 (FIG. 2). These values are controlled by the gas flow rate control unit 226, the pressure control unit 248, and the power control unit 266, respectively. The sequence control unit 28 transmits a control signal or a command value to the control units 226, 248, and 266, thereby controlling a processing procedure using the film forming apparatus 200 in the present embodiment. Therefore, typically, the numerical values included in the first condition and the second condition correspond to each command value transmitted for control.

  Further, this process will be described more specifically with reference to FIG. In the n-type semiconductor layer forming process S14 of the present embodiment, several processes are executed after the n-type amorphous Si layer forming process S142 is completed and before the n-type microcrystalline Si layer forming process S146 is started. . A series of processes during this period are collectively referred to as a transition process S144. In general, the transition process S144 is performed from a plasma CVD film forming condition (first condition) for the n-type amorphous Si layer forming process S142 to a plasma CVD film forming condition for the n-type microcrystalline Si layer forming process S146. This is a process of changing the film formation condition to (second condition). In FIG. 5, the Roman numerals “I” and “II” shown on the axes indicate the values of the setting conditions included in the first condition and the second condition, respectively.

  As shown in FIGS. 4 and 5, in the transition process S144, first, a process (S1442) of changing the total flow rate of the gas supplied into the vacuum chamber 22 is executed, and then the pressure in the vacuum chamber 22 is changed. Then, a process of changing the plasma excitation power is executed (S1446). In the process S1442 for changing the total gas flow rate, a process for increasing the flow rate of the gas to be increased first (S1442A) is performed, and then a process for decreasing the flow rate of the gas to be decreased (S1442B) is performed. . The reason is that if the gas flow rate is small, pressure fluctuation is likely to occur and the plasma may become unstable. Thus, the transition process S144 is executed through the process S1442 for changing the total gas flow rate while keeping the gas flow rate higher than the smaller flow rate value in the first condition or the second condition.

The transition process S144 will be described in order. First, as the first half of the process S1442 in which the total gas flow rate is changed, a process (S1442A) for increasing the flow rate of the increased gas is performed. The gas to be increased is an arbitrary gas such as a source gas, a dilution gas, and a doping gas, focusing only on the flow rates of the first condition and the second condition, and the flow rate is increased in the second condition in view of the first condition. Any gas. For example, the flow rate of hydrogen gas (H ₂ ), which is a diluent gas described later, is increased when transitioning from the first condition to the second condition (see, for example, Table 1). FIG. 5 schematically shows how the setting value command value changed in each process of FIG. 4 and the actual numerical value change. In particular, the curve 42A schematically shows the change of the flow rate of the gas species whose flow rate is adjusted (increased) in the process S1442A over the respective steps. Since there is no particular difference in the gas flow rate between the command value and the actual numerical value, the curve 42A represents both of them.

Next, as the second half of the process S1442 for changing the total gas flow rate, a process for reducing the flow rate of the gas to be reduced (S1442B) is performed. The gas to be reduced is an arbitrary gas whose flow rate is reduced under the second condition in view of the first condition. For example, the flow rate of monosilane gas (SiH ₄ ), which is a raw material gas to be described later, is reduced when transitioning from the first condition to the second condition. This is schematically illustrated by a curve 42B in FIG. Curve 42B also represents both the command value and the actual numerical value.

  A change in the total gas flow rate (total flow rate) of these processes S1442A and S1442B is shown in FIG. In FIG. 5, the process S1442B for decreasing the gas flow is started after the process S1442A for increasing the gas flow rate is completed. However, this description is merely for ease of explanation. The process S1442A for increasing the gas flow rate included in the process S1442 for changing the total gas flow rate of the present embodiment and the process S1442B for decreasing the gas flow rate are not limited to those sequentially processed in this way. For example, the process S1442 for changing the total gas flow rate can typically be changed within a range in which the total gas flow rate (curve 42) does not fall below the value of the first condition. For example, even if the process S1442B is started immediately after the process S1442A is started, if the gas flow rate decrease is changed more gently than the gas flow rate increase, the total gas flow rate is set to the first condition. It is also possible to perform a process of changing the flow rate to the total flow rate of the second condition so as not to fall below the total flow rate. Further, as shown in the curve 42 in FIG. 5, in the process S1442 for changing the total gas flow rate, the period during which the total gas flow rate in the middle exceeds the final second condition, It does not matter if there is a period that decreases toward the total flow rate.

  Here, as clearly shown in FIG. 2, the pressure inside the vacuum chamber 22 is detected by the pressure sensor 244, and is feedback controlled by adjusting the opening of the pressure control valve 246 through the pressure controller 248. . For this reason, the pressure control unit 248 automatically controls the pressure inside the vacuum chamber 22 so as to conform to the pressure command value at each time point, and this is especially seen through the period of the process S1442 in which the total gas flow rate is changed. Automatic control continues. For this reason, in the process S1442 for changing the total gas flow rate, the gas flow rate is changed while the pressure is maintained within the predetermined fluctuation range from the pressure command value. In FIG. 5, the pressure variation is shown as a curve 44. Here, the curve 44C shows the pressure command value, and the predetermined fluctuation range Δ is clearly shown as the upper limit allowed for the pressure and the width from the curve 44C until the adjustment. It should be noted that the range of pressure fluctuation that is desirably controlled in the control by the pressure control unit 248, or the actual range of fluctuation that needs to be suppressed, is mainly used for film formation. Is determined based on the stability of the plasma to be produced. In general, when the stability of plasma is lowered, an abnormal film is formed or the discharge is stopped. For these reasons, the solar cell element may be defective, and an operation for re-excitation of plasma is required, which may stop the film formation process and increase the time. For this reason, it is preferable to measure in advance a pressure range in which plasma stability can be ensured, and to set the pressure command value and the fluctuation range so as to be included in the pressure range. Whether the pressure is actually well controlled depends on various conditions. The conditions include the internal volume of the vacuum chamber 22, the conductance of the exhaust path including the pressure control valve 246, the exhaust capacity of the vacuum pump 242, the total gas flow rate, and the like.

  In addition, the aspect of the change of the gas total flow rate in the process S1442 for changing the total gas flow rate in the present embodiment can be defined by another expression. That is, the rate of change in the change in the total gas flow rate is determined so that the pressure in the vacuum chamber 22 controlled by the pressure control unit 248 does not change beyond a predetermined fluctuation range from the pressure command value. I can say that. Actually, when the change rate of the gas flow rate in process S1442A or S1442B is increased to make the change in flow rate too steep, the pressure control unit 248 automatically attempts to adapt the pressure inside the vacuum chamber 22 to the pressure command value. The control operation cannot be followed and the pressure deviates from the predetermined fluctuation range Δ. Such a change in the gas flow rate at such a steep change speed is inappropriate as an aspect of the change in the total gas flow rate in the process S1442 for changing the total gas flow rate in the present embodiment. For this reason, determining the change rate of the total gas flow rate so that the pressure controlled by the pressure control unit 248 is within the range of fluctuation from the pressure command value changes the total gas flow rate of the present embodiment. It can be said that it is processing S1442 to do. In FIG. 5, although the pressure fluctuation range Δ from the pressure command value is selected to be equal to the upper limit side and the lower limit side, it is also possible to select the upper limit side and the lower limit side unevenly. included. Thereby, the pressure can be controlled more precisely.

  When such an operation is executed by the film forming apparatus 200, the operation of each control unit is as follows. The sequence control unit 28 controls the entire processing operation by transmitting control signals and command values to the pressure control unit 248 and the gas flow rate control unit 226. The pressure control unit 248 controls the pressure inside the vacuum chamber 22 to such a pressure that the plasma excitation can be continued during the transition process S144. On the other hand, the gas flow rate control unit 226 controls to change the total flow rate of the gas supplied to the vacuum chamber 22 from the total flow rate of the gas included in the first condition to the total flow rate of the gas included in the second condition. To do. This control operation is related to each other, and while the gas flow rate control unit 226 changes the total gas flow rate, the pressure control unit 248 automatically controls the pressure inside the vacuum chamber to be adapted to a certain pressure command value. ing. When this related operation is viewed as the operation of the gas flow rate control unit 226, the gas flow rate control unit 226 determines the pressure in the vacuum chamber 22 continuously controlled by the pressure control unit 248 from the pressure command value. An operation is performed in which the gas flow rate is changed at a change speed that does not deviate from the range of the fluctuation range Δ. In order to execute such processing operation, the sequence control unit 28 transmits a control signal and a necessary command value to the pressure control unit 248 and the gas flow rate control unit 226.

  When the process S1442 for changing the total gas flow rate is completed, the process for changing the pressure inside the vacuum chamber 22 is performed (S1444, FIG. 4). Here, in the state where the total gas flow rate is set to the second condition by the process S1442 for changing the total gas flow rate, the pressure changing process S1444 inside the vacuum chamber 22 is stably performed, that is, formed. It is possible to carry out the process without causing any abnormality in the formed film and without the risk of stopping the plasma. A curve 44 in FIG. 5 also shows how the pressure is changed. It should be noted that the process S1444 for changing the pressure inside the vacuum chamber 22 is shown in the curve 44C of the change in the pressure command value in FIG. Other modes adopted as changes in the pressure command value for changing the pressure include a mode in which the pressure command value is changed stepwise or in a polygonal line shape.

  When the pressure changing process S1444 inside the vacuum chamber 22 is finished, the plasma power is changed to the second condition (S1446). In this plasma power changing process S1446, for example, the output of the power source 262 that supplies power to the ground electrode 24 and the shower head electrode 26, which are film forming electrodes, is changed, or the circuit constants of the matching circuit 264 are changed. Is done. In FIG. 5, the state of the plasma power increasing in the plasma power changing process S <b> 1446 is shown by a curve 46. Since there is no particular difference between the command value and the actual numerical value of the plasma power, the curve 46 represents both of them.

  When the transition process S144 is completed as described above, the n-type microcrystalline Si layer formation process S146 is subsequently performed. As shown in FIG. 3, an i-type microcrystalline Si layer is formed (S16), and then a p-type microcrystalline Si layer is formed (S18). When the semiconductor layer 14 (FIG. 1) is completed, the transparent electrode layer 16 is formed (S20), and the collector electrode layer 16A is formed (S22). The collecting electrode layer 16A may be made of a metal such as silver (Ag), aluminum (Al), nickel (Ni), or an alloy made of any one of these metals. The collector electrode layer 16A can be a multilayer film or a single layer film. The collecting electrode layer 16A may be formed by sputtering, vacuum deposition, spray film formation, ink jet printing, screen printing, or the like. In the present embodiment, a Ti / Ag collector electrode layer is formed by electron beam evaporation using a mask as the collector electrode layer 16A.

  Then, the board | substrate cutting | disconnection / mounting process S24 is performed as needed, and the solar cell element 100 is produced. Note that the cutting / mounting process S24 includes known mounting processes such as a patterning process using laser scribing and a sealing process for improving weather resistance.

[Example (first embodiment)]
Next, the details of the manufacturing process and the performance of the sample will be described for the sample of Example 1 of the solar cell element having the same structure as the solar cell element 100 of FIG. 1 manufactured according to the present embodiment. The details and performance of the production of the comparative example 1 sample and the comparative example 2 sample for comparison will also be described. For the sake of explanation, reference numerals to the respective drawings are clearly indicated as appropriate.

[Example 1 sample]
Example 1 Samples were prepared according to the steps described in relation to FIGS. A back electrode layer 12 was formed on one surface of the substrate 10 (S12). As the back electrode layer 12, a silver alloy is formed on one surface of the substrate 10 so as to have a thickness of about 300 nm, and a transparent electrode layer 12 made of zinc oxide (ZnO) is formed on the surface of the back electrode layer 12. It was formed to have a thickness of about 100 nm. Both of these layers were formed by sputtering.

  Next, a hydrogenated thin film Si layer was formed as the semiconductor layer 14 by plasma CVD (S14 to S18). At this time, as a film forming apparatus for performing the plasma CVD method, a film forming apparatus 200 (FIG. 2) having a parallel plate type discharge structure by the ground electrode 24 and the shower head electrode 26 was used. In order to form the semiconductor layer 14, first, formation processing S <b> 14 (FIG. 3) of the n-type semiconductor layer 142 was performed by the film formation apparatus 200. The details of this processing were performed by the processing shown in FIG. In the formation process S14 of the n-type semiconductor layer 142, a transition process S144 was performed between the formation process S142 of the n-type amorphous Si layer 142A and the formation process S146 of the n-type microcrystalline Si layer 142B. Plasma excitation was continued during the formation process S14 of the n-type semiconductor layer 142. Table 1 clearly shows the setting conditions of the film forming conditions employed in the n-type amorphous Si layer forming process S142 and the n-type microcrystalline Si layer forming process S146 as the first condition and the second condition, respectively.

  The setting conditions other than those shown in Table 1 were such that the frequency of plasma discharge was 13.56 MHz, and the set temperature of the substrate 10 was set to 180 ° C. The film thickness of the n-type amorphous Si layer 142A formed in the n-type amorphous Si layer forming process S142 was about 10 nm.

In the transition process S144, first, a process S1442 for changing the total gas flow rate was performed. Specifically, the process S1442A for increasing the flow rate of the increased gas was first performed, and then the process S1442B for decreasing the flow rate of the decreased gas was performed. As shown in Table 1, the flow rate of the diluent gas H ₂ was increased in the process S1442A because the flow rate increased in the second condition as viewed from the first condition. On the other hand, since the flow rates of the source gas SiH ₄ and the doping gas H ₂ diluted PH ₃ gas (concentration 1000 ppm) were reduced in the second condition as seen from the first condition, the flow rates were reduced in the process S1442B. . The total gas flow rate was 72 sccm under the first condition, whereas it was 460 sccm under the second condition. For this reason, when viewed from the first condition, the total gas flow rate is increased under the second condition. The process S1442 for changing the total gas flow rate is set so that the processes S1442A and S1442B are both processed in 3 seconds. In this embodiment, as shown in FIG. 5, the processing S1442A and the processing S1442B are performed by sequential processing. Through this process S1442 for changing the total gas flow rate, the internal pressure of the vacuum chamber 22 is adapted to 0.6 Torr (89.3 Pa), which is the set pressure (pressure command value) of the first condition. It was automatically controlled by the pressure control unit 248, and the pressure fluctuation range (Δ in FIG. 5) was set to 0.1 Torr (13.3 Pa). Although the signal from the pressure sensor 244 was separately monitored, the pressure fluctuation exceeding the fluctuation range Δ from the pressure command value was not particularly observed through the process S1442 for changing the total gas flow rate.

  When the process S1442 for changing the total gas flow rate is completed, the process of changing the pressure in the vacuum chamber 22 is performed S1444, and the set pressure (pressure command value) of the second condition is 0.9 Torr (120.0 Pa). The pressure inside the vacuum chamber 22 was controlled to fit. This process was also completed in 3 seconds. The pressure changing process S1444 inside the vacuum chamber 22 was executed stably.

  After finishing the pressure changing process S1444, the plasma power changing process S1446 was performed. The time required for this treatment was about 1 second.

  Next, an n-type microcrystalline Si layer forming process S146 was performed by the film forming apparatus 200 under the second condition shown in Table 1. The setting conditions other than those shown in Table 1 were such that the frequency of plasma discharge was 13.56 MHz and the set temperature of the substrate 10 was set to 180 ° C. Also in the above-described n-type amorphous Si layer forming process S142, since the same plasma discharge frequency and substrate set temperature were used, these were not changed including the transition process S144. The film thickness of the n-type microcrystalline Si layer 142B formed in the n-type microcrystalline Si layer forming process S146 was about 10 nm.

Next, as an i-type semiconductor layer formation process S16 (FIG. 3), an i-type semiconductor layer (i-type microcrystalline Si layer) 144 was formed by a plasma CVD method. The film formation conditions at this time were a discharge frequency of 40.68 MHz, a discharge power of 200 W, a film formation temperature of 180 ° C., a film formation pressure of 12 torr (1600 Pa), an SiH ₄ gas flow rate of 25 sccm, and an H ₂ gas flow rate of 1750 sccm. The film formation time in this process was 1700 seconds. The film thickness of the formed i-type semiconductor layer (i-type microcrystalline Si layer) 144 was 2 μm. Note that the i-type semiconductor layer forming process S <b> 16 was performed using another film forming apparatus having the same structure as the film forming apparatus 200 without using the film forming apparatus 200.

Further, as a p-type semiconductor layer formation process S18, a p-type semiconductor layer (p-type microcrystalline Si layer) 146 was formed by a plasma CVD method. The film formation conditions at this time are: discharge frequency 13.56 MHz, discharge power 40 W, film formation temperature 140 ° C., film formation pressure 0.9 torr (120.0 Pa), SiH ₄ gas flow rate 4 sccm, H ₂ gas flow rate Was formed at a flow rate of 40 sccm using H ₂ diluted B ₂ H ₆ gas (1000 ppm). The film formation time in this process was 600 seconds. The film thickness of the formed p-type semiconductor layer (p-type microcrystalline Si layer) 146 was 30 nm. The p-type semiconductor layer forming process S18 was also performed using another film forming apparatus having a structure similar to that of the film forming apparatus 200.

  And the transparent electrode layer 16 was formed on the semiconductor layer 14 (FIG. 1) which is a photoelectric converting layer. As the transparent electrode layer 16, in the sample of Example 1, an ITO transparent electrode was formed by sputtering. Further, a Ti / Ag collector electrode layer was formed as the collector electrode layer 16A. At this time, a mask was used for patterning, and an electron beam evaporation method was used.

[Comparative Example 1 Sample]
Next, a sample of Comparative Example 1 was produced. The sample of Comparative Example 1 was manufactured by forming only the n-type microcrystalline Si layer 142B as the n-type semiconductor layer 142 and not forming the n-type amorphous Si layer 142A (see Table 1). That is, a solar cell element having substantially the same structure as that shown in FIG. 1 was produced except that the n-type amorphous Si layer 142A was not formed, and the steps thereof were also shown in FIG. In the manufacturing process, first, the back electrode layer 12 was formed on the substrate 10 by sputtering (S12). Next, a hydrogenated thin film Si was formed by a plasma CVD method. This process corresponds to the n-type semiconductor layer formation process S14 in FIG. However, in this n-type semiconductor layer forming process, as shown in Table 1, the n-type microcrystalline Si layer, i.e., the n-type semiconductor layer, is processed only by the process under the same film forming conditions as the second condition adopted in the sample of Example 1. A semiconductor layer 142 was formed. This n-type semiconductor layer forming process is equivalent to performing only the process S146 without performing the processes S142 to S1446, as described with reference to FIG. The film forming conditions for the n-type semiconductor layer forming process were partly different from the second conditions for the sample of Example 1, and the processing time was increased to 460 seconds. As the formation process of the n-type semiconductor layer, film formation was performed using a film formation apparatus having a structure similar to that of the film formation apparatus 200 in FIG. Subsequent processes, i.e., i-type semiconductor layer forming process, p-type semiconductor layer forming process, transparent electrode layer forming process, and collector electrode layer forming process are performed under the same conditions as the processes of S16 to S24 in the sample of Example 1. did.

[Comparative Example 2 Sample]
Furthermore, a comparative example 2 sample employing a process closer to that of the example 1 sample was produced. As a sample of Comparative Example 2, a solar cell element having the same structure as that shown in FIG. 1 was produced, and the production process was performed by the steps shown in FIG. The structure of the film forming apparatus employed for film formation is not particularly different from the structure of the film forming apparatus 200. However, the operation of the control unit of the film forming apparatus was different from the operation of the film forming apparatus 200 for the sample of Example 1. Table 1 shows the film forming conditions, that is, the first condition and the second condition of the plasma CVD method employed as the n-type amorphous Si layer forming process S142 and the n-type microcrystalline Si layer forming process S146 in the sample of Comparative Example 2. These were the same as the first condition and the second condition of the sample of Example 1. Subsequent processes, i.e., i-type semiconductor layer forming process, p-type semiconductor layer forming process, transparent electrode layer forming process, and collector electrode layer forming process are the same under the same conditions as S16 to S24 in the sample of Example 1. The process was carried out.

The difference between the sample of Comparative Example 2 and the sample of Example 1 is that the sample 122 of Comparative Example 2 is not subjected to the process 122 for changing the total gas flow rate shown in FIG. ) Was performed to change the gas atmosphere inside. In this replacement process, the plasma was completely stopped, the gas was once exhausted, the gas was introduced for the second condition, the pressure was adjusted, and the plasma was re-excited. That is, by first stopping the plasma, the n-type amorphous Si layer forming process corresponding to the n-type amorphous Si layer forming process S142 of FIG. 2 is completed. At this time, the gas type, flow rate, and pressure of the first condition remain unchanged. Therefore, the supply of these gases is stopped, the exhaust speed is increased in order to switch the gas atmosphere, the gas in the vacuum chamber is exhausted, and a dilution gas (H ₂ gas) for the second condition, a source gas ( SiH ₄ gas) and doping gas (H ₃ diluted PH ₃ gas) are introduced. At this time, the flow rate is set to the value of each setting condition, and the pressure control valve 246 is adjusted to regulate the inside of the vacuum chamber. After these preparations were completed, the power source and the matching circuit were adjusted so that the plasma was excited again to obtain the desired power. In this manner, the n-type microcrystalline Si formation process similar to S146 in FIG. 2 was started. This replacement process took about 420 seconds (about 7 minutes) from the completion of the formation process of the n-type amorphous Si layer to the start of the formation process of the n-type microcrystalline Si.

[Performance of each sample of Example 1, Comparative Example 1 and Comparative Example 2]
The photoelectric conversion efficiency of the solar cell element of each sample of Example 1, Comparative Example 1, and Comparative Example 2, that is, the solar cell efficiency, was measured and averaged by 5 samples. The results are shown in Table 2. In Table 2, the solar cell efficiency is represented by a relative value where the maximum value of the conversion efficiency of Comparative Example 1 is 1.

  As shown in Table 2, the solar cell efficiencies of the sample of Example 1 and the sample of Comparative Example 2 were almost equal to each other, and these values were higher than the solar cell efficiency of Comparative Example 1. This is because both the sample of Example 1 and the sample of Comparative Example 2 include an n-type semiconductor layer 142 in which an n-type amorphous Si layer 142A and an n-type microcrystalline Si layer 142B are stacked, whereas the sample of Comparative Example 1 is an n-type semiconductor. The inventor of the present application considers that the layer 14 includes only the n-type microcrystalline layer 142B.

[Time required for each sample of Example 1, Comparative Example 1 and Comparative Example 2]
Although the sample of Example 1 and the sample of Comparative Example 2 showed the same solar cell efficiency, there was a great difference in the processing time of the production process. Table 3 is a table showing the time required for each step for Example 1, Comparative Example 1 and Comparative Example 2. In Table 3, also in Comparative Example 1 and Comparative Example 2, in order to show each process corresponding to the n-type amorphous Si layer forming process S142 and the n-type microcrystalline Si layer forming process S146, Similar symbols (S142, S146) indicate. The time required for the processes S142 and S146 is the same as that described in Table 1.

  The replacement process of the sample of Comparative Example 2 took about 420 seconds (about 7 minutes). In contrast, the time required for the transition process of the sample of Example 1 is S1442A (about 3 seconds), S1442B (about 3 seconds), pressure change processing S1444 (about 3 seconds), and plasma power change processing S1446 (about 1 second) was about 10 seconds in total. Reflecting these differences in the required time, the required time for forming the n-type semiconductor layer when producing the sample of Example 1 is about 410 seconds (about 6 minutes) compared to the case of the sample of Comparative Example 2. 50 seconds). Further, when the total time required for forming the n-type semiconductor layer is compared, in comparison with the time required for the sample of Comparative Example 1 (460 seconds) in which only the n-type microcrystalline Si layer is formed, Comparative Example 2 The time required for the sample (about 810 seconds) increased by about 350 seconds, whereas the time required for the sample of Example 1 (about 400 seconds) was reduced by about 60 seconds. .

  Therefore, for example, in the conventional production line constructed for producing the sample of Comparative Example 1, the n-type amorphous Si layer 142A and the n-type microcrystalline Si layer 142B are formed in order to improve the solar cell efficiency. It is assumed that the structure of the solar cell element is changed. If the manufacturing process of the comparative example 2 sample is employed for this purpose, the tact time of the manufacturing line increases by about 350 seconds only in the process of forming the n-type semiconductor layer. This reduces the throughput of the entire manufacturing process of the solar cell element, that is, the production amount per unit time. On the other hand, even if the same n-type amorphous Si layer 142A is formed and the n-type microcrystalline Si layer 142B is formed, the n-type semiconductor layer adopting the film forming apparatus 200 or including the transition process S144, for example. When the manufacturing process of the sample of Example 1 is carried out by adopting the forming process S14, a tact time of the manufacturing line rather has a margin of about 60 seconds. That is, by performing the n-type semiconductor layer forming process S14 in the conventional manufacturing line constructed for manufacturing the sample of Comparative Example 1, or by adopting the film forming apparatus 200 if necessary, At least the throughput of the entire manufacturing process of the solar cell element does not decrease. If the throughput of the entire manufacturing process of the solar cell element is determined by the time required for the process of manufacturing the n-type semiconductor layer 14 in the conventional manufacturing line for manufacturing the sample of Comparative Example 2, the sample for Example 1 By implementing the formation process S14 and adopting the film forming apparatus 200 if necessary, the throughput of the entire manufacturing process of the solar cell element can be increased.

<First Embodiment: Modification 1>
In the above-described embodiment, the case where the single junction structure of the nip junction structure is employed as the cell structure of the thin-film solar battery has been described. However, in the present embodiment, a thin film solar cell having another structure can be adopted. For example, by executing the transition process of the present embodiment, the same effect as described above can be exhibited also in the process of manufacturing a thin film solar cell employing another structure as the semiconductor layer.

  FIG. 6 is a schematic cross-sectional view showing the structure of a solar cell element 300 of Modification 1 in which this embodiment is modified. Unlike the above-described solar cell element 100 (FIG. 1), the solar cell element 300 is a super-straight type solar cell element having a pin junction structure, and includes a transparent electrode layer 32, a semiconductor layer on a translucent substrate 30. 34 and the back electrode layer 36 are provided in this order. The substrate 30 is made of a translucent substrate such as glass. A transparent electrode layer 32 is formed on one surface of the substrate 30, that is, the surface positioned upward in FIG. 6. A hydrogenated thin film Si layer is formed as a semiconductor layer 34 on the surface of the transparent electrode layer 32. This semiconductor layer 34 is formed by plasma CVD into a pin junction structure of a p-type semiconductor layer 342, an i-type semiconductor layer (i-type microcrystalline Si layer) 344, and an n-type semiconductor layer (n-type microcrystalline Si layer) 346 from the substrate side. It is formed by the law. Among these, the p-type semiconductor layer 342 is a stacked body of a p-type amorphous Si layer 342A and a p-type microcrystalline Si layer 342B. A back electrode layer 36 is formed on the upper surface of the semiconductor layer 34. In the solar cell element 300, since the transparent electrode layer 32 is formed on the translucent substrate 30, the light (hν) serving as the energy source of the solar cell is incident on the semiconductor layer 34 from below in FIG. It is a solar cell.

  The solar cell element 300 is a thin film solar cell including a semiconductor layer 34 having only a single pin junction structure. The p-type semiconductor layer 342 is a stacked body in which a p-type amorphous Si layer 342A and a p-type microcrystalline Si layer 342B are stacked in this order on the surface of the back electrode layer 32. In the formation of the p-type semiconductor layer 342, for example, a plasma CVD method in the vacuum chamber 22 similar to the film forming apparatus 200 shown in FIG. For this reason, the p-type microcrystalline Si layer 342B has a first film formation condition for forming the p-type microcrystalline Si layer 342B from the first condition for forming the p-type amorphous Si layer 342A. It is a layer formed by transitioning to two conditions while continuing plasma excitation. Since the transition process for changing the film formation condition of the plasma CVD method from the first condition to the second condition reflects the plasma property with respect to the gas flow rate and pressure, the conductivity type of the semiconductor layer is changed from n-type to p-type. Even if it is changed, it can be executed in the same manner. Therefore, also in the manufacturing process of the solar cell element 300, the transition process can be performed in a manner according to the manufacturing process of the solar cell element 100 described above.

  As described above, by adopting the transition process of the present embodiment, even in the manufacturing process of the solar cell element 300 having the pin junction structure, the plasma is not stopped, and a state in which the plasma may be stopped unexpectedly is generated. Thus, it is possible to change the film forming conditions in a short time.

  Furthermore, the transition process of the present embodiment can also be applied to the case where a material other than those specified so far, such as amorphous SiGe, is employed, and in this case, the film forming condition switching process of the plasma CVD method is shortened. It can be done in time. In addition, when the transition process of this embodiment is executed, a thin film solar cell having a multi-junction structure such as a tandem structure or a triple structure obtained by stacking a plurality of nip junction structures or pin junction structures is employed. However, it is possible to perform the switching process of the film forming process conditions of the plasma CVD method in a short time.

<First Embodiment: Modification 2>
In addition, some of the processing operations described based on the operation of the film forming apparatus 200 in the present embodiment described above can be executed by an operator operating the film forming apparatus, for example. . Therefore, the aspect which implements this Embodiment mentioned above can be implemented as a combination of a time-dependent process procedure as a manufacturing method of a thin film solar cell. Even in this case, it can be implemented as a combination process such as partially automatic or partially manual. For example, the pressure control unit 248 (FIG. 2) continuously performs feedback control using the pressure sensor 244 and the pressure control valve 246, and the operator manually selects the gas flow rate as described above. When the process of changing the total gas flow rate is performed according to the above, the process of this embodiment can be performed by combining automatic feedback control and manual gas flow rate control.

  The embodiment of the present invention has been specifically described above. The above-described embodiments and examples are described for explaining the invention, and the scope of the invention of the present application should be determined based on the description of the claims. Moreover, the modification which exists in the scope of the present invention including other combinations of each embodiment is also included in a claim.

  In any aspect of the present invention, it contributes to the popularization of solar power generation equipment using a solar cell in which a semiconductor layer having a stacked structure in which semiconductor films having different film forming conditions are stacked is formed by a plasma CVD film forming method.

100 Solar cell elements
10, 30 Substrate 12 Back electrode layer 14, 34 Semiconductor layer 142 n-type semiconductor layer 142A n-type amorphous Si layer 142B n-type microcrystalline Si layer 144 i-type semiconductor layer (i-type microcrystalline Si layer)
146 p-type semiconductor layer (p-type microcrystalline Si layer)
DESCRIPTION OF SYMBOLS 16 Transparent electrode layer 16A Current collection layer 200 Film-forming apparatus 22 Vacuum chamber 24 Ground electrode 24H Heater 26 Shower head electrode 28 Sequence control part 220, 220A, 220B Gas supply system 222, 222A, 222B Gas cylinder 224,224A, 224B Control valve 226 Gas flow control unit 240 Exhaust system 242 Vacuum pump 244 Pressure sensor 246 Pressure control valve 248 Pressure control unit 260 Power supply system 262 Power supply 264 Matching circuit 266 Power control unit 32 Transparent electrode layer 342 p-type semiconductor layer 342A p-type amorphous Si layer 342B p-type microcrystalline Si layer 344 i-type semiconductor layer (i-type microcrystalline Si layer)
346 n-type semiconductor layer (n-type microcrystalline Si layer)
36 Transparent electrode layer 42 Curve (total gas flow rate)
42A curve (flow rate of gas to be increased)
42B curve (reduced gas flow)
44 Curve (Internal pressure of chamber)
44C curve (pressure command value)
46 Curve (Plasma power)

Claims (11)

A method of manufacturing a thin-film solar cell including a semiconductor layer including either a nip junction structure or a pin junction structure,
A first film forming step of forming an n-type or p-type amorphous Si layer on the surface of the electrode on which the electrode is formed, in a vacuum chamber by a plasma CVD method under a first condition;
A second film forming step of forming a microcrystalline Si layer having the same conductivity type as the amorphous Si layer in contact with the surface of the amorphous Si layer inside the vacuum chamber by a plasma CVD method under a second condition;
It is a transition step for making a transition from the first film forming step to the second film forming step, and is supplied to the vacuum chamber while maintaining the pressure inside the vacuum chamber so as to continue the excitation of plasma. A transition step in which the total gas flow rate is changed from the total gas flow rate included in the first condition to the total gas flow rate included in the second condition. The transition step includes:
A gas total flow rate changing step for changing a total flow rate of the gas supplied to the inside of the vacuum chamber;
The method of manufacturing a thin-film solar cell according to claim 1, further comprising: a pressure changing step of changing the pressure inside the vacuum chamber from the pressure of the first condition to the pressure of the second condition in this order. The gas total flow rate changing step includes:
Starting to increase the gas flow rate of the gas species having a high flow rate in the second condition as viewed from the first condition from that in the first condition to that in the second condition;
3. The step of starting to decrease the gas flow rate of the gas type having a small flow rate in the second condition in view of the first condition from that in the first condition to that in the second condition is included in this order. Manufacturing method of a thin film solar cell. The transition step includes:
A plasma power changing step of changing the power for plasma excitation supplied to the film-forming electrode inside the vacuum chamber from the power of the first condition to the power of the second condition is further included after the pressure changing step. The manufacturing method of the thin film solar cell of Claim 2. Through the gas total flow rate changing step, the pressure inside the vacuum chamber is controlled to match a pressure command value,
The method for manufacturing a thin-film solar cell according to claim 2, wherein in the gas total flow rate changing step, the total gas flow rate is changed while maintaining the pressure within a range of a predetermined fluctuation range from the pressure command value. A manufacturing apparatus for manufacturing a thin film solar cell including a semiconductor layer including either a nip junction structure or a pin junction structure,
A substrate on which an electrode is formed on at least one surface is stored, and at least one layer forming the semiconductor layer is formed on the surface of the electrode on the substrate by a plasma CVD method. A vacuum chamber,
A gas supply system connected to the vacuum chamber and supplying gas to the inside of the vacuum chamber;
A pressure sensor provided in the vacuum chamber for detecting the pressure inside the vacuum chamber;
An exhaust system connected to the vacuum chamber and exhausting gas inside the vacuum chamber;
A power supply system for supplying power for exciting plasma to the film-forming electrode inside the vacuum chamber;
A gas flow rate control unit that is connected to the gas supply system and controls the flow rate of the gas supplied from the gas supply system to the inside of the vacuum chamber;
A pressure control unit connected to the pressure sensor and the exhaust system, and controlling a pressure inside the vacuum chamber by changing an exhaust amount of the exhaust system based on a signal from the pressure sensor;
A sequence control unit that controls the processing operation by outputting a command value or a control signal to the gas flow rate control unit and the pressure control unit, and
The sequence control unit is in contact with the surface of the amorphous Si layer from the first film forming process of forming an n-type or p-type amorphous Si layer on the surface of the electrode by a plasma CVD method under a first condition. When the process proceeds to the second film forming process in which a microcrystalline Si layer having the same conductivity type as the amorphous Si layer is formed by the plasma CVD method of the second condition, the pressure controller is made to continue plasma excitation. While controlling the pressure inside the vacuum chamber, the gas flow rate control unit includes the total flow rate of the gas supplied to the vacuum chamber from the total flow rate of the gas included in the first condition to the second condition. An apparatus for manufacturing a thin-film solar cell that executes a processing operation to change the total flow rate of the gas to be generated. The sequence controller is
When transitioning from the first film forming process to the second film forming process,
Causing the gas flow rate control unit to change the total flow rate of the gas to the vacuum chamber from the total flow rate of the first condition to the total flow rate of the second condition;
The manufacturing method according to claim 6, wherein the pressure control unit controls processing operations in this order so as to change the pressure inside the vacuum chamber from the first condition to the second condition. apparatus. In the process of changing the total flow rate of the gas,
The sequence controller is connected to the gas flow rate controller.
Starting the increase in the gas flow rate of the gas type having a high gas flow rate in the second condition from the first condition to that in the second condition from the first condition,
The processing operation is controlled in this order so that the gas flow rate of the gas type having a small gas flow rate in the second condition in view of the first condition is started to decrease from that in the first condition to that in the second condition. The manufacturing apparatus according to claim 6. A power control unit that is connected to the power supply system and controls output power from the power supply system;
The sequence control unit outputs a command value or a control signal to the power control unit to control a processing operation,
The sequence control unit, after the pressure control unit changes the pressure inside the vacuum chamber, supplies power for plasma excitation to the power control unit to the film-forming electrode inside the vacuum chamber. The manufacturing apparatus according to claim 7, wherein the processing operation is controlled so that the first condition is changed to the second condition. While the gas flow control unit changes the total flow rate of the gas, the sequence control unit allows the pressure control unit to adjust the pressure inside the vacuum chamber to a certain pressure command value, while the gas flow control unit The process operation is controlled so as to change the gas flow rate while maintaining the pressure inside the vacuum chamber within a predetermined fluctuation range from the pressure command value. apparatus. A thin film solar cell in which a semiconductor layer including either a nip junction structure or a pin junction structure is formed on the surface of the electrode on which the electrode is formed,
The n-type or p-type semiconductor layer forming the nip junction structure or the pin junction structure includes an n-type or p-type amorphous Si layer formed by a plasma CVD method under a first condition in a vacuum chamber, and a second layer. A microcrystalline Si layer having the same conductivity type as that of the amorphous Si layer formed by a plasma CVD method under conditions is a laminate formed in this order from the surface side of the electrode,
While the microcrystalline Si layer maintains the internal pressure of the vacuum chamber so as to continue plasma excitation, the total flow rate of gas supplied to the vacuum chamber is set to the total flow rate of gas included in the first condition. The thin film solar cell is a layer formed by changing the processing conditions of the plasma CVD method from the first condition to the second condition by changing to the total gas flow rate included in the second condition.

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