JP5315228B2 - Film forming apparatus and method for manufacturing solar cell - Google Patents

Description

  The present invention relates to a flexible substrate transfer apparatus and a film forming apparatus.

  In recent years, a process that can be produced at low cost is expected in mass production of thin film solar cells. As one of the means to reduce manufacturing costs, each unit operation such as film formation, printing, laser processing, etc. is performed in-line while winding a flexible substrate wound in a roll shape on the other roll. Thus, a continuous processing method is known. This method is called a roll-to-roll (hereinafter referred to as roll-to-roll) method.

  In particular, as a method for increasing the productivity of the thin film forming process, a film forming apparatus provided with a roll-to-roll type conveying apparatus as shown in, for example, Japanese Patent Laid-Open Nos. 58-216475 and 59-34668 is used. However, it is effective to perform continuous conveyance and continuous film formation.

  In a film forming apparatus provided with a roll-to-roll type transport device, continuous film formation is performed while continuously transporting a flexible film substrate, but in order to obtain a desired film thickness efficiently. One method is to increase the length of the discharge electrode for film formation and increase the transport speed.

  However, when a flexible substrate is deposited while being transported by a transport device, if a generally small and inexpensive parallel plate type film deposition device is used, wrinkles that occur on the substrate cause uneven film deposition. It was a problem. FIG. 1 shows a parallel plate type film forming apparatus. 1A is a side view of the entire film formation apparatus, and FIG. 1B is a view of the vicinity of the electrode 108 together with the flexible substrate 101 from below. The electrode 108 is grounded, and a heater is incorporated so that the flexible substrate 101 can be heated as necessary. The substrate is installed by first unwinding the flexible substrate 101 from the unwinding roll 105 and passing through the substrates provided on the substrate transfer portion side surfaces of the unwinding vacuum chamber 110 and the film forming vacuum chamber 102, respectively. , And between the electrode 108 and the counter electrode 109, and further wound around the take-up roll 104 through the gap 112 on the right side of the film forming vacuum chamber. In order to keep the substrate parallel to the electrodes, a constant rotational torque is generated in the winding roll 104 and the unwinding roll 105 to apply tension to the substrate. At this time, the flexible substrate is floating in the space between the guide rollers 106 and 107. In addition, since the flexible substrate expands and contracts, there is a force that extends in the transport direction and a force that contracts in the width direction at each part of the flexible substrate that is floating in space when tension is applied to the substrate. However, it becomes a factor which generates the wrinkle 111. When the flexible substrate is heated by a heater, the expansion and contraction becomes large, and the generation of wrinkles appears remarkably. In addition, the wrinkled portion at the time of film formation is exposed to the discharge space for film formation, which causes uneven film formation. The longer the electrode length, that is, the longer the part where the substrate floats in the space, the higher the frequency of wrinkle generation.

In order to prevent the generation of wrinkles on the flexible substrate, there is a cylindrical can method as one method. A film forming apparatus provided with a transfer apparatus using a cylindrical can system is disclosed in, for example, Japanese Patent Laid-Open No. 58-216475. By applying tension to the flexible substrate and bringing it into close contact with the curved surface of the cylindrical can, which is a part that supports conveyance, wrinkles generated on the substrate can be suppressed. In the conventional cylindrical can system, the region used as the film-forming ground electrode is a part of the cylindrical can, and the apparatus is enlarged in proportion to the electrode area.
In particular, an increase in size is remarkable in a multi-chamber type film forming apparatus in which a large number of vacuum chambers are connected in a row in order to continuously form PIN layers for solar cells.

  In a film forming apparatus provided with a transfer apparatus using a cylindrical can system, an increase in size is inevitable, but a method using an improved parallel plate system is also conceivable in consideration of the downsizing of the apparatus. The portion that contacts the flexible substrate and supports the conveyance may be curved. FIG. 2 shows a transport apparatus using a curved electrode as a transport support portion, and a film forming apparatus provided with the transport apparatus. The curved electrode 201 serves both as a transport support portion and a discharge ground electrode. By applying tension to the flexible substrate 204, the substrate is brought into close contact with the curved electrode, and wrinkles generated on the substrate can be suppressed. In terms of downsizing the apparatus, it is significantly better than the cylindrical can method, and may be as large as the parallel plate method. However, the problem is that if the substrate is transported in a tensioned state, the substrate is transported while contacting the curved electrode, so that the back surface of the flexible substrate and the curved electrode are rubbed and the back surface of the substrate is damaged. It is. In addition, since the frictional force increases as the electrode length increases, the force to wind up the substrate when transporting the substrate also increases, and the force applied to the substrate also becomes significant.

  It is a film forming device with a transfer device of the same scale as a conventional parallel plate method, and can be downsized compared to a film forming device with a conventional cylindrical can type transfer device. An object of the present invention is to provide a transport apparatus capable of continuous transport while preventing damage to the back surface of the flexible substrate and a film forming apparatus provided with the transport apparatus.

  The present invention relates to a transport apparatus having a means for continuously transporting a flexible substrate from one end to the other end, and a film forming apparatus provided with the transport apparatus, wherein the one end and the other end Are provided with a plurality of cylindrical rollers arranged so that central axes thereof are parallel to each other along an arc having a radius R, and the flexible substrate is conveyed in contact with each of the plurality of cylindrical rollers. It is a film forming apparatus provided with a transfer device and a transfer device characterized by using a mechanism. Tension is applied to the flexible substrate to bring it into close contact with each of the plurality of cylindrical rollers, preventing wrinkling of the flexible substrate and enabling continuous conveyance while preventing damage to the back surface of the substrate. Details are shown in FIG. First, consider a curved surface 301 having an arc with a radius R (302) from the central axis 303. The curved surface 301 is shown for explanation, and there is no actual object. Next, a plurality of cylindrical rollers 304 having an arbitrary length are continuously arranged on the curved surface 301 so as to be as small as possible. At this time, each central axis 305 of the plurality of cylindrical rollers 304 is on the curved surface 301 and is parallel to the central axis 303 of the curved surface 301. Further, the flexible substrate 306 is brought into close contact with each of the plurality of cylindrical rollers by applying tension. Here, it should be noted that the plurality of cylindrical rollers 304 are arranged so that the holding angle at which the flexible substrate 306 contacts each cylindrical roller 304 is always positive. The transport apparatus provided with means for continuously transporting the flexible substrate of the present invention and the film forming apparatus provided with the transport apparatus will be referred to as a curved roller system.

  A method for arranging the cylindrical rollers is described and shown in FIG. As shown in FIG. 4 (A), the curved surface 401 on which the central axis of the cylindrical roller is arranged as one kind, and the cylindrical rollers 402 may be arranged on the curved surface at equal intervals, and the interval may be changed as necessary. As shown in FIG. 4B, they may be arranged side by side on a plurality of curved surfaces 401 and 403 having different curvatures, or the diameter of the cylindrical roller 402 may be changed. According to another concept, when the flexible substrate 407 is brought into contact with each of the plurality of cylindrical rollers, the arc angle of the portion 404 where the flexible substrate contacts each cylindrical roller, that is, the holding angle 405 is a positive value. If necessary, the holding angle may be arbitrary. To stabilize the film formation state in the transfer direction, it is convenient to set the holding angle to a fixed angle, but if there are mechanical restrictions such as the entire transfer device must be housed in a vacuum chamber, set it freely. You can also. This is nothing but changing the curvature 406 of the curved surface.

  FIG. 5 (A) shows a conventional parallel plate type film forming discharge electrode, and FIG. 5 (B) shows a film forming discharge electrode that also serves as a conveyance supporting part of a curved roller type conveying device. A state in which tension is applied and the flexible substrate is brought into close contact with the curved surfaces of a plurality of cylindrical rollers is shown. In the conventional parallel plate type electrode 504, even if the tension 501 to the flexible substrate 512 is increased, the substrate surface 507 that opposes the electrode only has a component force 503 parallel to the electrode in the vertical direction. Cannot be obtained. There are only component forces 509 and 510 at both ends of the parallel plate type electrode. Even in the case of the curved roller system, if the cylindrical rollers 511 are aligned in a straight line, the component force 505 in the vertical direction cannot be obtained, but the holding angle 508 at which the flexible substrate 512 contacts each cylindrical roller 511 is If the value is positive, a component force 506 is generated in a direction in which the substrate is pressed against the electrode. However, in FIG. 5B, the tension and the component force are shown on the assumption that the flexible substrate and the cylindrical roller are in point contact. In the curved roller type electrode, the holding angle of each cylindrical roller is set to a positive value, so that the flexible substrate can be pressed against all the cylindrical rollers. That is, the flexible substrate can be brought into close contact with the film-forming discharge electrode that also serves as the transport support portion of the transport apparatus.

  FIG. 6 shows a film forming apparatus provided with a curved roller type conveying apparatus. In the curved roller system, the distance between the cylindrical rollers is as close as possible, and the flexible substrate is placed on the continuous curved surface in the cylindrical can system by shortening the portion where the flexible substrate is floating in the space. It is possible to obtain the same adhesion effect as that obtained when the substrates are adhered, and it is possible to prevent film formation unevenness during film formation due to wrinkles and wrinkles of the flexible substrate. Further, by rotating each cylindrical roller 602 during conveyance of the flexible substrate, scratches on the back surface of the substrate due to rubbing between the substrate and the film-forming discharge electrode can be suppressed.

A film forming apparatus provided with a curved roller type conveying apparatus and a film forming apparatus provided with a cylindrical can type conveying apparatus are shown in FIG. . 7A is a film forming apparatus using an electrode that also serves as a curved roller type conveying device and also serves as a conveyance supporting unit. FIG. 7B is a cylindrical can type conveying device that also serves as a conveying support unit. A film forming apparatus using a cylindrical can electrode 710.
7A is a curved roller system with a curvature radius of R1000 mm, and the conveyance apparatus of FIG. 7B is a cylindrical can system with a radius of R500 mm. The total electrode area of each device is comparable. In the cylindrical can system, the diameter is half of the radius of curvature in the curved roller system, but the entire cylindrical can must be installed in the apparatus, and the enlargement of the apparatus cannot be avoided. Actually, not only the difference in size in the side view but also the difference in volume of the vacuum chamber is important in the vacuum apparatus. The wall of the vacuum chamber must be thick and strong as the vacuum chamber becomes larger. For this reason, the weight of the apparatus becomes considerably large, and the floor strength of the building becomes a problem. In a vacuum apparatus using a cylindrical can diameter R500 mm, the weight may be 2 t. As the vacuum chamber becomes larger, the vacuum pump used for the exhaust system becomes larger and expensive. In a film forming apparatus that can obtain the same electrode area, particularly a vacuum apparatus, downsizing the apparatus has many advantages.

FIG. 8 shows a state of heat conduction to the substrate when a plurality of cylindrical rollers in the curved roller system also serve as a heater for heating the flexible substrate. In heat conduction from the heater block 803 including the heater main body to the flexible substrate 807, the region 801 is heat conduction by contact with the cylindrical roller 804, and the region 802 is heat by radiation from the heater block 803 and the cylindrical roller 804. It is conduction.
When the substrate is transported, the substrate alternately passes through the regions 801 and 802, but the heater block / roller gap 805 and the heater block / substrate gap 806 may be adjusted so that fluctuations in the substrate temperature can be suppressed. In addition, the substrate temperature may differ between the high temperature and the gas introduction even if the heater set temperature is the same. Since it may vary depending on the transfer speed, care should be taken when measuring the substrate temperature or designing.

  A conventional cylindrical can type transfer system using a curved roller type transfer apparatus and a film forming apparatus provided with a transfer apparatus according to the present invention. The film forming apparatus provided with the apparatus can be reduced in size, and the conveyance apparatus and the conveyance apparatus capable of continuous conveyance are provided while preventing wrinkles of the flexible substrate and preventing scratches on the back surface of the flexible substrate. A film forming apparatus could be provided.

Flexible substrate in parallel plate type film forming apparatus Flexible substrate in curved electrode type film forming apparatus Curved roller type cylindrical roller concept Curved roller type cylindrical roller arrangement Mechanical description of tension acting on flexible substrates. Curved roller film deposition system Comparison of size between cylindrical can system and curved roller system Curved roller heat transfer Substrate temperature measurement in curved roller film deposition system Substrate width direction film thickness measurement in curved roller type film deposition system

  Examples of the present invention will be described below. First, the conveyance support part of the conveyance apparatus by a curved surface roller system was manufactured. The conveyance support part was comprised from the some cylindrical roller which is a curved surface block and a movable part for conveying the heat from a heater equally. The material used was an aluminum alloy with good thermal conductivity. The size of the curved surface block was 428 mm × 300 mm, the maximum thickness was 30 mm, and the curvature radius R of the curved surface was 1000 mm. Next, 42 cylindrical rollers having a diameter of 9 mm were attached along the curved surface via bearings. The angle between the cylindrical rollers was 0 ° 35 '. The interval 805 between the cylindrical roller 804 and the heater block 803 shown in FIG. 8 was 1 mm. The distance 806 between the flexible substrate 807 and the heater block was 7 mm.

  A film forming apparatus provided with a transfer apparatus as shown in FIG. 6 is prepared. This apparatus includes a flexible substrate transfer device, a vacuum chamber, a film forming gas introduction system, an exhaust system, and a high frequency power supply introduction system, and film formation is performed by plasma CVD. First, the conveyance support part 610 of the conveyance apparatus by a curved surface roller system was attached to the heater 609, and the conveyance apparatus of the curved surface roller system was comprised. The conveyance support part of the curved roller type conveyance device was used as a ground electrode. The high frequency power supply introduction system was constituted by the ground electrode by the curved roller method and the high frequency power supply side electrode 608. Next, the flexible substrate 601 was unwound from the unwinding roll 607 and installed so as to be wound on the winding roll 608 through the guide roll 606 and the ground electrode 610 using a curved roller system. At this time, since a constant rotational torque is applied to the unwinding roll 607 in the reverse direction with respect to the winding roll 608, the flexible substrate 601 is under tension, and the curved surface of the ground electrode by the curved roller system is used. Close contact with.

  In order to measure the change in surface temperature of the flexible substrate 601, the thermocouple 611 was fixed at a position on the surface of the flexible substrate, and the flexible substrate 601 was taken up by the take-up roll 608 and conveyed. At this time, the temperature change before and after the portion where the thermocouple portion fixed to the flexible substrate contacts the ground electrode 610 by the curved roller method was recorded every second. The measured values are shown in FIG. The measured value was shown by the difference from the substrate temperature average value when the flexible substrate was in contact with the ground electrode by the curved roller method. As a result, the substrate temperature was almost constant when the substrate was in contact with the electrode by the curved roller system, and it was not a problem of temperature unevenness. Strictly speaking, there is a temperature difference between the contact heat conducting portion 801 of the flexible substrate and the cylindrical roller shown in FIG. 8 and the radiant heat conducting portion 802 from the cylindrical roller and the roller block, and this temperature difference is 1 ° C. It became less than. For comparison, FIG. 9B shows data when the flexible substrate passes through a flat plate ground electrode portion having a built-in heater in a parallel plate type film forming apparatus provided with a transfer device. Since the flat plate ground electrode incorporating the flexible substrate and the heater is spaced apart by 2 mm and is not in contact, heat conduction to the substrate when passing through the flexible substrate is always heat conduction by radiation. Even if compared with this data, it can be said that the temperature unevenness due to the curved roller type electrode is suppressed without any problem.

  The wrinkles of the flexible substrate and the film formation unevenness caused by the wrinkles were observed. First, a PEN (polyethylene naphthalate) film was used for the flexible substrate, and the flexible substrate was placed in the transport system of the film forming apparatus provided with the transport device shown in FIG. The flexible substrate 601 was observed from the lower part of the ground electrode by the curved roller system, but no wrinkles were found on the substrate. Next, silane gas and hydrogen gas were introduced into the film formation chamber 604 and discharged between the high-frequency power supply side electrode 608 and the ground electrode 610 using a curved roller system, and a non-single-crystal silicon film was formed on the flexible substrate. . Non-single crystal silicon refers to amorphous silicon, microcrystalline silicon, and thin film polycrystalline silicon. This film was scanned in the width direction of the substrate using a spectrophotometer, and the film thickness was measured. The results are shown in FIG. FIG. 10A shows the film thickness distribution in the substrate width direction of film formation by the parallel plate type film forming apparatus, and FIG. 10B shows the film thickness distribution of film formation by the curved roller type film forming apparatus. In the parallel plate type film forming apparatus, since there is a wrinkle of the substrate during film formation, the film thickness distribution is about ± 10%, and color unevenness was observed visually. In the film formation by the curved roller type film forming apparatus, there was no wrinkle of the substrate at the time of film formation, the film thickness distribution was suppressed to about ± 5%, and the color unevenness could hardly be visually confirmed. As a result, it can be said that the film thickness unevenness was suppressed.

DESCRIPTION OF SYMBOLS 101 Flexible substrate 102 Film-forming vacuum chamber 103 Gap 104 for letting a substrate pass Winding roll 105 Unwinding roll 106, 107 Guide roller 108 Electrode 109 Counter electrode 110 Unwinding vacuum chamber 111 Wrinkle on flexible substrate 112 Gap on the right side of vacuum chamber for film formation 113 Vacuum chamber for winding 201 Curved electrode 202 Counter electrode 203 Guide roller 204 Flexible substrate 205 Wrinkle 301 on flexible substrate Curved surface 302 having an arc of radius R Curved radius of curvature 303 Curved Central Axis 304 Cylindrical Roller 305 Cylindrical Roller Central Axis 306 Flexible Substrate 401 Curved Surface 402 Cylindrical Roller 403 Other Kind of Curved Surface 404 Part 405 Where the Flexible Substrate Contact Each Cylindrical Roller Holding Angle 406 Curvature curvature 407 Flexible substrate 501 Tension 502 to flexible substrate Vertical direction The component force 503 in the direction parallel to the electrode 504 The conventional parallel plate type electrode 505 The component force 506 in the vertical direction The component force 507 in the direction of pressing the substrate against the electrode 507 The substrate surface 508 that opposes the electrode Angle 509, 510 Component force 511 Cylindrical roller 512 Flexible substrate 601 Flexible substrate 602 Cylindrical roller 603 Unwinding vacuum chamber 604 Deposition vacuum chamber 605 Unwinding vacuum chamber 606 Guide roller 607 Unwinding roller 608 Winding roller 609 Substrate heating heater 610 Conveying support section and ground electrode 611 of a conveying device using a curved roller method Thermocouple 701 Flexible substrate 702 Curved roller method ground electrode 703 Counter electrode 704 Unwinding vacuum chamber 705 For winding Vacuum chamber 706 Deposition chamber 707 Unwinding roller 708 Winding roller 709 Guide rollers 710 cylindrical can type electrodes 801 and 802 heat transfer area 803 heater block 804 cylindrical roller 805 heater block and the roller clearance 806 heater block and substrate gap 807 flexible substrate with a built-in heater body

Claims (14)

One of the two opposing electrodes has a plurality (excluding 2) of cylindrical rollers,
The plurality of cylindrical rollers are arranged along an arc;
The other of the two electrodes has a curved surface along the arc;
A flexible substrate is conveyed by the plurality of cylindrical rollers ,
The film forming apparatus characterized in that the holding angle at which the flexible substrate contacts the cylindrical roller is positive . One of the two opposing electrodes has a plurality (excluding 2) of cylindrical rollers,
The plurality of cylindrical rollers are arranged along an arc;
The other of the two electrodes has a curved surface along the arc;
A plurality of vacuum chambers for film formation in which a flexible substrate is conveyed by the plurality of cylindrical rollers ;
The film forming apparatus characterized in that the holding angle at which the flexible substrate contacts the cylindrical roller is positive . In claim 2,
A film forming apparatus comprising: means for introducing a gas into the film forming vacuum chamber; and means for exhausting the gas. In any one of Claims 1 thru | or 3,
A transporting part for the flexible substrate;
The conveyance part of the flexible substrate has the conveyance support part and first and second rollers,
An unwinding vacuum chamber and a winding vacuum chamber;
The first roller is disposed in the unwinding vacuum chamber,
The second roller is disposed in the take-up vacuum chamber,
The transport support portion is disposed between the first roller and the second roller,
The film forming apparatus is characterized in that the flexible substrate is conveyed by being unwound from the first roller and wound up by the second roller. In any one of Claims 1 thru | or 4,
One of the two electrodes is grounded;
The other of the two electrodes is connected to a power source. In any one of Claims 1 thru | or 5,
One of the two electrodes is also used as a heater.   7. The film forming apparatus according to claim 1, wherein the film forming apparatus is a plasma CVD apparatus. A method for producing a solar cell, wherein a film is formed on the flexible substrate while conveying the flexible substrate,
The film formation is performed while bringing the flexible substrate into contact with the curved surfaces of a plurality (excluding 2) of cylindrical rollers provided on one of the two electrodes,
The plurality of cylindrical rollers are arranged along an arc;
The holding angle at which the flexible substrate contacts the cylindrical roller is positive,
The other of said two electrodes has the curved surface along the said arc, The manufacturing method of the solar cell characterized by the above-mentioned. A method for producing a solar cell, wherein a flexible substrate is transported in a plurality of film-forming vacuum chambers while forming a film on the flexible substrate,
The film formation is performed while bringing the flexible substrate into contact with the curved surfaces of a plurality (excluding 2) of cylindrical rollers provided on one of the two electrodes,
The plurality of cylindrical rollers are arranged along an arc;
The holding angle at which the flexible substrate contacts the cylindrical roller is positive,
The other of said two electrodes has the curved surface along the said arc, The manufacturing method of the solar cell characterized by the above-mentioned. In claim 8 or claim 9 ,
A method for manufacturing a solar cell, wherein film formation is performed on the flexible substrate between one of the two electrodes and the other of the two electrodes. In any one of Claims 8 to 10 ,
The conveyance of the flexible substrate is performed by the plurality of cylindrical rollers and the first and second rollers,
The first roller unwinds the flexible substrate, the second roller winds the flexible substrate,
During the conveyance of the flexible substrate, a torque reverse to that of the second roller is applied to the first roller. In any one of Claims 8 thru | or 11 ,
The method of manufacturing a solar cell, wherein the film formation is performed by plasma CVD. In any one of Claims 8 to 12 ,
One of the two electrodes is grounded;
The other of the two electrodes is connected to a power source. In any one of Claims 8 to 13 ,
One of the two electrodes is also used as a heater.

Images