JP2006156878A - Deposition film formation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress in a plasma CVD apparatus local deposition of by-products on the wall surface of the exhaust port of a shield member, thereby forming a deposition film having stable properties for a long time. <P>SOLUTION: Deposition film formation apparatus generates plasma in a discharge space between a power application electrode 206 and a substrate 201 within a vacuum chamber to decompose a source gas introduced into the vacuum chamber, so that a deposition film is formed on the substrate. In the apparatus, a shield member 215 is provided in at least part of circumference of the electrode 206, and the shape of the member 215 is changed in the direction of an exhaust downstream side, and a region is provided in which an exhaust channel formed by the shield member and an opposing wall surface has an area that is continuously reduced in its section from an exhaust upstream side to the exhaust downstream side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a deposited film forming apparatus for forming, for example, a silicon-based thin film solar cell on a substrate.

  As a typical electronic device using photovoltaic power, for example, a solar cell is known. Solar cells convert solar energy or other light energy into electrical energy, and are attracting attention as part of future energy measures as a clean energy source.

  In solar cells, which are regarded as important as a part of measures for new energy in the future, low cost and high performance are the major research and development issues for the time being. Until now, a microcrystalline silicon thin film solar cell has been studied as one of the solar cells that realize low cost and high performance. Microcrystalline thin-film solar cells can be formed with a CVD system, which makes it possible to easily increase the area, which is difficult for crystalline solar cells using single-crystal or polycrystalline silicon wafers by bulk growth. Therefore, it is known that it is possible to save the raw material gas. In addition, in order to absorb sunlight efficiently, a microcrystalline silicon thin film or an amorphous silicon film with a different wavelength band that absorbs light is used as a light absorption layer so as to match the energy distribution of sunlight, and each of the stacked solar High efficiency solar cells such as batteries have been studied.

  As a method for improving the mass productivity of solar cells, there is a roll-to-roll system as disclosed in Patent Document 1. This method consists of a discharge chamber for forming a plurality of silicon films and a band-shaped substrate that penetrates the gas gate provided to separate the atmosphere in the discharge chamber while connecting these discharge chambers. This is a method in which a thin film is continuously deposited on a belt-like substrate and wound up sequentially, and is excellent in mass productivity.

  Up to now, it has become possible to obtain a conversion efficiency that is quite high, but there is still room for improvement in order to achieve further price reduction. One of them is that the film forming speed is low. Various countermeasures for increasing the film forming speed have been studied so far. For example, Patent Document 2 discloses that the film formation rate can be increased by reducing the distance between the power application electrode and the substrate that can be an electrode. Also, by making the distance between the power application electrode and the aperture adjustment plate wider than the distance between the power application electrode and the substrate, turbulence such as stagnation and accumulation in the flow of the source gas does not occur, and the by-product It is disclosed in Patent Document 3 that generation can be suppressed and a high-quality thin film can be deposited.

JP-A-6-23243 Japanese Patent Publication No. 5-56850 JP 2001-214277 A

  In recent years, the use of such a high-speed film formation method has gradually reduced the price of solar cells, but various methods are being sought for the creation of further inexpensive solar cells.

  As one method for reducing the cost, it is conceivable to further increase the film forming speed as described above. As the method, a larger power is applied to the electrode, or the pressure in the discharge space is increased to increase the applied power density and the decomposition rate of the raw material gas is improved, or the raw material gas is increased to increase the raw material gas. A method of increasing the amount of gas decomposition or a method of expanding the discharge space by reducing the distance between the power application electrode and the substrate can be considered. This will be described below with reference to FIG.

FIG. 5 schematically shows a cross-sectional view of a general parallel plate capacitively-coupled deposited film forming apparatus. A rectangular parallelepiped vacuum vessel 502 (not shown in its entirety) and the vacuum vessel 502 are shown in FIG. A discharge chamber 505 provided in the interior and a belt-like substrate 501 introduced into the discharge chamber 505 are configured. Further, a raw material gas such as SiH ₄ or H ₂ is introduced from the raw material gas introduction tube 507, and power is applied to the electrode 506 from the power source 504 to generate plasma in the discharge chamber 505, and a semiconductor film is formed on the strip substrate 501. Form a film. Residual gas remaining in the discharge chamber 505 is exhausted between a plate-like member (hereinafter referred to as an opening adjusting plate) 509 and the shield wall 515, and is exhausted to the outside through an exhaust pipe 508. (A) shows the position of the shield wall forming the exhaust port.

  However, when a film is formed for a long time using this method, by-products are locally deposited in the vicinity of (A) of the shield wall 515 that forms the exhaust port, and the film formation conditions are greatly increased due to a decrease in exhaust capability. As a result, a new problem has occurred that the performance of the deposited film is greatly reduced.

  An object of the present invention is to provide a film forming apparatus having an exhaust port formed by an opening adjusting plate and a shield wall in view of the problems of the prior art, and in particular, by-products are locally generated near (A) of the shield wall. An object of the present invention is to provide a deposited film forming apparatus capable of suppressing deposition and forming a deposited film having stable performance over a long period of time.

In order to achieve the above-mentioned object, the present invention generates a plasma in a discharge space between a power application electrode and a substrate that can be disposed opposite to the power application electrode in a vacuum chamber, thereby generating a vacuum. In a deposited film forming apparatus for decomposing a source gas introduced into a chamber and forming a deposited film on a substrate, a shield member is provided on at least a part of the periphery of the power application electrode, and the shield member is disposed in the exhaust downstream direction. The cross-sectional area of the exhaust path composed of the shield member and the wall surface facing the shield member has a region that continuously decreases from the exhaust upstream side to the exhaust downstream side.
Further, the thickness of the shield member is changed.
Furthermore, the shield member has a bent shape.

  According to the present invention, since the cross-sectional area of the exhaust path formed by the wall surface facing the shield member has a region that continuously decreases from the exhaust upstream side to the exhaust downstream side, even when film formation is performed for a long time. By-products can be prevented from being locally deposited in the region facing the exhaust path of the shield member, and a deposited film with stable performance can be formed. Thereby, the mass productivity of thin film devices, such as a solar cell, can be improved and cost reduction is attained.

An example of the deposited film forming apparatus of the present invention is a parallel plate capacitively coupled deposited film forming apparatus as shown in FIG. FIG. 1 is a schematic sectional view of a deposited film forming apparatus according to an embodiment of the present invention. The apparatus shown in this figure includes a rectangular vacuum vessel 102 coupled to another vacuum vessel adjacent by a gas gate 103, a discharge chamber 105 provided inside the vacuum vessel 102, and a gas gate 103. It is composed of a strip-like substrate 101 introduced into the discharge chamber 105. By introducing a gas such as H ₂ or He into the gas gate 103 via the gate gas introduction pipe 117, it is possible to separate the atmospheric gas and pressure in the adjacent vacuum vessel.

  The discharge chamber 105 provided inside the vacuum vessel 102 has a hollow rectangular parallelepiped shape in which one surface of the discharge chamber is an opening, and the opening is provided close to the belt-like substrate 101. After the strip substrate 101 is introduced into the discharge chamber 105, it is heated by the lamp heater 113 and the temperature is adjusted using the thermocouple 114. The temperature of the strip-shaped substrate 101 during discharge is adjusted in the range of 100 ° C. to 500 ° C. A parallel plate type power application electrode 106 is provided in the discharge chamber 105, and power can be supplied from a high-frequency power source (not shown) to generate plasma in the discharge chamber.

  In the present specification, an electrode to which power is applied or an electrode facing the substrate is referred to as a power application electrode. The power application electrode has a DC power, a low frequency from 5 kHz to 500 kHz, and a frequency from 500 kHz to 30 MHz. DC power, low frequency plasma, high frequency plasma, VHF plasma can be generated by applying high frequency up to 30MHz or power of VHF from 30MHz to 500MHz, respectively, and gas etc. can be decomposed and thin films such as semiconductors Is deposited on the substrate.

  The source gas is introduced from the gas supply source (not shown) into the discharge chamber 105 by the source gas introduction tube 107 penetrating the wall of the vacuum vessel 102 and heated by the block heater 109. The discharge chamber 105 is provided with an exhaust pipe 108 for exhausting the source gas. The source gas flows in parallel with the transport direction of the belt-like substrate 101 (from right to left in the figure), and power is applied to the discharge chamber 105. After flowing over the electrode 106, the exhaust pipe 108 exhausts the discharge chamber and the vacuum vessel. Part of the gas gate gas and source gas in the vacuum vessel is exhausted from the discharge chamber external exhaust port 110 provided in a part of the exhaust pipe 108.

Examples of the source gas include gasifiable compounds containing silicon atoms such as SiH ₄ , Si ₂ H ₆ , and SiF ₄ . In the case of using an alloy system, it is desirable to add a gasifiable compound containing Ge or C such as GeH ₄ or CH ₄ to the raw material gas. Examples of the dilution gas include H ₂ and He. Further, a gasifiable compound containing nitrogen, oxygen or the like may be added as a dilution gas for the source gas.

A discharge space formed between the power application electrode 106 and the strip substrate 101 in the discharge chamber 105, for example, when the area facing between the belt-like substrate and the power application electrode is 0.005m ³ ~0.3m ^3, The pressure in the discharge space is used in the range of 100 Pa to 5000 Pa.

  The substrate 101 may be a translucent insulator such as a glass substrate mounted on a substrate support and a non-translucent conductor such as a stainless steel substrate. Further, it may be a strip-like long substrate wound around a coil, a flexible insulating material such as a polymer film formed with a conductive thin film, or a flexible conductive substrate such as stainless steel.

  In the present invention, in the deposited film forming apparatus having the configuration as in the above example, the shield member (shield wall 515) as shown in FIG. 5 is provided on at least part of the periphery of the power application electrode. By using a member whose shape is changed in the exhaust downstream direction, the cross-sectional area of the exhaust path formed by the wall surface (surface of the opening adjustment plate) facing the shield member is changed from the exhaust upstream side to the exhaust downstream side. An area that is continuously reduced is provided.

  The form example which represented typically the positional relationship of the shield member and opening adjustment board in this invention, etc. is shown in FIG. 2 thru | or FIG.

  In FIG. 2, a shield member (shield wall 215) is used in which the thickness is changed by inclining the middle part of the surface facing the opening adjustment plate 209. This is an example of continuously decreasing from the exhaust side to the exhaust downstream side.

  FIG. 3 shows a shield member (shield wall 315) having a thickness changed from the upper end portion of the surface facing the opening adjustment plate 309, and the cross-sectional area of the exhaust path in the inclined portion is the upstream side of the exhaust. This is an example of continuously decreasing from the exhaust side to the exhaust downstream side.

  FIG. 4 shows an example in which a shield member (shield wall 415) bent in a U-shape is used so that the cross-sectional area of the exhaust path continuously decreases from the exhaust upstream side to the exhaust downstream side.

  The shield member according to the present invention is not limited to the linear inclination as described above, and may be a member whose shape is changed by adding a curved inclination, for example. In short, there is no particular limitation as long as it is possible to provide a region where the cross-sectional area of the exhaust path continuously decreases from the exhaust upstream side to the exhaust downstream side.

  According to the present invention, by using the shield member as described above, by providing a region where the cross-sectional area of the exhaust path continuously decreases from the exhaust upstream side to the exhaust downstream side, the region facing the exhaust path of the shield member can be obtained. It is possible to suppress local accumulation of by-products. This is thought to be due to the fact that the rapid decrease in the exhaust speed of the residual gas in the region facing the exhaust path of the shield member can be suppressed, and the exhaust speed has increased by continuously decreasing. For this reason, by always ensuring a sufficient space for the exhaust port, the residual gas on the cathode surface can be exhausted all the time, the film formation state on the cathode surface can be made uniform, and the discharge is stabilized. As a result, the film quality of the substrate is improved. Further, it is considered that the impedance of the discharge space in the vicinity of the aperture adjusting plate has changed due to the change in the shape of the shield wall, and the discharge at the cathode end is thereby stabilized, so that the film quality of the substrate is improved.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1
FIG. 2 shows a schematic cross-sectional view of a shield wall, a substrate, an aperture adjustment plate, and the like used as Example 1 of the present invention. A rectangular parallelepiped vacuum vessel 202 (not shown in its entirety), a discharge chamber 205 provided inside the vacuum vessel 202, and a belt-like substrate 201 introduced into the discharge chamber 205 are configured. Further, a source gas such as SiH ₄ or H ₂ is introduced from the source gas introduction pipe 207, and power is applied to the power application electrode 206 from the power source 204, thereby generating plasma in the discharge chamber 205, and generating a semiconductor on the strip substrate 201 A film is formed. The residual gas remaining in the discharge chamber 205 is exhausted from between the opening adjusting plate 209 and the shield wall 215 and exhausted to the outside through the exhaust pipe 208.

  In the present embodiment, a shield wall 215 having a thickness of 50 mm and a change in thickness at an angle of 30 degrees with respect to a surface perpendicular to the surface perpendicular to the belt-like substrate 201 by 5 mm on the exhaust downstream side is used. As a result, the width of the exhaust path constituted by the opposing wall surfaces of the shield member and the opening adjustment plate was reduced from 50 mm to 25 mm.

The discharge space formed between the power application electrode 206 in the discharge chamber 205 and the strip substrate 201 is set to 0.03 m ³ . The mixed gas ratio of SiH ₄ gas, SiF ₄ gas and H ₂ gas is SiH ₄ gas and H ₂ gas is H ₂ / SiH ₄ = 25, and the mixed gas ratio of SiH ₄ gas and SiF ₄ gas is SiF ₄ / SiH ₄ = 1.25 flows in the discharge chamber 205. As the power, high frequency power having a frequency of 60 MHz is applied to the power application electrode 206. The temperature of the strip-shaped substrate during discharge is adjusted at 200 ° C. Under this condition, plasma was generated, and a silicon thin film was formed while the strip substrate 201 was stationary.

  FIG. 6 is a copy diagram of the film state on the belt-like substrate 201 formed by the present embodiment. As shown in FIG. 6, in this example, no by-product was deposited on the strip substrate 201, and the film was formed with a uniform film thickness distribution 601 in the width direction (vertical direction in the figure) of the strip substrate 201.

(Example 2)
FIG. 3 shows a schematic cross-sectional view of a shield wall, a substrate, an opening adjusting plate, and the like used as Example 2 of the present invention. A rectangular parallelepiped vacuum vessel 302 (not shown in its entirety), a discharge chamber 305 provided inside the vacuum vessel 302, and a belt-like substrate 301 introduced into the discharge chamber 305 are configured. In addition, a source gas such as SiH ₄ or H ₂ is introduced from the source gas introduction tube 307, and plasma is generated in the discharge chamber 305 by applying power from the power source 304 to the power application electrode 306. A film is formed. The residual gas remaining in the discharge chamber 305 is exhausted from between the opening adjusting plate 309 and the shield wall 315 and exhausted to the outside through the exhaust pipe 308.

  In this embodiment, a shield wall 315 having a 30-degree angle with respect to a plane perpendicular to the belt-like substrate 301, an inclination length of 50 mm, and a thickness change is used. As a result, the width of the exhaust path constituted by the opposing wall surfaces of the shield member and the opening adjustment plate was reduced from 50 mm to 25 mm.

  Then, plasma was generated under the same conditions as in Example 1, and a silicon thin film was formed while the strip substrate 301 was stationary. As a result, as in Example 1, there was no deposition of by-products on the strip substrate 301, and the film was formed with a uniform film thickness distribution.

(Example 3)
FIG. 4 shows a schematic cross-sectional view of a shield wall, a substrate, an aperture adjustment plate, and the like used as Example 3 of the present invention. It is composed of a rectangular parallelepiped vacuum vessel 402 (not shown in its entirety), a discharge chamber 405 provided inside the vacuum vessel 402, and a strip-like substrate 401 introduced into the discharge chamber 405. In addition, a source gas such as SiH ₄ or H ₂ is introduced from the source gas introduction tube 407, and plasma is generated in the discharge chamber 405 by applying power to the power application electrode 406 from the power source 404, and the semiconductor substrate is formed on the strip substrate 401. A film is formed. The residual gas remaining in the discharge chamber 405 is exhausted from between the opening adjustment plate 409 and the shield wall 415 and exhausted to the outside through the exhaust pipe 408.

  In this embodiment, a 3 mm thick SUS304 plate bent at an angle of 30 degrees with respect to a plane perpendicular to the belt-like substrate 401 and having an inclination length of 50 mm was used as the shield wall 415. As a result, the width of the exhaust path constituted by the opposing wall surfaces of the shield member and the opening adjustment plate was reduced from 50 mm to 25 mm.

  Then, plasma was generated under the same conditions as in Example 1, and a silicon thin film was formed while the strip substrate 401 was stationary. As a result, the film was formed with a uniform film thickness distribution on the belt-like substrate 401 without depositing by-products as in Example 1.

(Comparative example)
As a comparative example, as shown in FIG. 5, a conventional shield wall 515 having a constant cross-sectional area of an exhaust path composed of a shield member and an opening adjustment plate facing the shield member 515 is used. A silicon thin film was formed.

  FIG. 7 shows a copy diagram of the film state on the belt-like substrate 501 formed by this comparative example. As shown in FIG. 7, in this comparative example, a by-product 702 adhered without depositing a thin film in the vicinity of the exhaust port, and a non-uniform film thickness distribution 701 was laminated. This is because by-products are locally deposited in the vicinity of (A) of the shield wall, the exhaust port formed by the opening adjusting plate and the shield wall is narrowed, and the exhaust capability of residual gas on the cathode is reduced. This is probably because the discharge on the cathode became unstable.

  FIG. 8 is a graph showing a comparison between Example 1 (solid line) and a comparative example (broken line) with respect to the rate of non-defective solar cells against the film formation time. Here, the non-defective product rate at the initial stage of film formation created in Example 1 is defined as 1 for comparison. In the comparative example, the yield rate decreased as the film formation time elapses. However, in Example 1, it was possible to suppress the non-defective product rate which decreases as the film formation time elapses. This is presumably because by-products deposited locally in the vicinity of (A) of the shield wall float in the discharge space and adhere to the deposition substrate.

  FIG. 9 is a graph showing a comparison between Example 1 (solid line) and a comparative example (dashed line) with respect to the fill factor of the solar cell with respect to the film formation time. Here, the curve factor of the solar cell at the initial stage of film formation created in Example 1 is defined as 1 for comparison. Since there is a difference in the fill factor at the initial stage of film formation, it is considered that the slope of the earth shield wall changed the impedance of the discharge space in the vicinity of the aperture adjustment plate. The film quality is considered to have improved. In the comparative example, the fill factor decreased as the film formation time passed. However, in Example 1, it was possible to suppress the curve factor that decreases as the film formation time elapses. This is probably because by-products are no longer deposited locally in the vicinity of (A) of the shield wall, so that the exhaust capability of the residual gas is improved and the discharge is stabilized.

It is typical sectional drawing which shows the basic composition of the deposited film formation apparatus which concerns on embodiment of this invention. It is typical sectional drawing, such as a shield wall used as Example 1 of this invention, a board | substrate, and an opening adjustment board. It is typical sectional drawing, such as a shield wall used as Example 2 of this invention, a board | substrate, and an opening adjustment board. It is typical sectional drawing, such as a shield wall used as Example 3 of this invention, a board | substrate, and an opening adjustment board. It is typical sectional drawing, such as a shield wall in a conventional deposited film formation apparatus, a board | substrate, and an opening adjustment board. It is a copy figure of the film | membrane state on the strip | belt-shaped board | substrate formed into a film in Example 1 of this invention. It is a copy figure of the film | membrane state on the strip | belt-shaped board | substrate formed into a film in the comparative example. It is the graph which showed the comparison of Example 1 and a comparative example about the non-defective item rate of the solar cell with respect to film-forming time. It is the graph which showed the comparison of Example 1 and a comparative example about the curve factor of the solar cell with respect to film-forming time.

Explanation of symbols

101, 201, 301, 401, 501: Strip substrate 102, 202, 302, 402, 502: Vacuum vessel 103: Gas gate 105, 205, 305, 405, 505: Discharge chamber 106, 206, 306, 406, 506: Electric power Application electrodes 107, 207, 307, 407, 507: source gas introduction pipes 108, 208, 308, 408, 508: exhaust pipe 109: block heater 110: discharge chamber external exhaust port 113: lamp heater 114: thermocouple 117: gate gas Introducing tubes 204, 304, 404, 504: power sources 209, 309, 409, 509: opening adjustment plates 215, 315, 415, 515: shield walls (shield members)

Claims (3)

In the vacuum chamber, plasma is generated in a discharge space between the power application electrode and a substrate that can be arranged opposite to the power application electrode, to decompose the source gas introduced into the vacuum chamber, In a deposited film forming apparatus for forming a deposited film on the top,
A cross-sectional area of an exhaust path having a shield member at least part of the periphery of the power application electrode, the shield member having a shape that changes in the exhaust downstream direction, and a wall surface facing the shield member Has a region that continuously decreases from the exhaust upstream side to the exhaust downstream side.   The deposited film forming apparatus according to claim 1, wherein a thickness of the shield member is changed.   The deposited film forming apparatus according to claim 1, wherein the shield member has a bent shape.

Images