JP2009289782A - Plasma cvd device and method for manufacturing thin amorphous silicon film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma CVD device for forming a thin film such as amorphous silicon of high quality with little formation of defects and mixture of high-order silane, and a method for manufacturing a thin amorphous silicon film. <P>SOLUTION: The plasma CVD device includes a vacuum vessel 1, an evacuation device 2 for keeping the vacuum vessel at a reduced pressure, a first electrode 3 having a plurality of gas supply holes, a high frequency power source 6 connected with the first electrode, and a second electrode 4 provided oppositely to the first electrode for keeping a substrate approximately parallel to the first electrode. An obstacle for shutting a straight gas flow path directing from the gas supply holes of the first electrode to the second electrode is provided between the first and second electrodes. In addition, the obstacle is a flat plate having a plurality of apertures which are provided on a part not covering the straight gas flow path. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a plasma CVD apparatus and an amorphous silicon thin film manufacturing method.

  As one method for forming a thin film of amorphous silicon or the like, a plasma-enhanced chemical vapor deposition (CVD) method (hereinafter referred to as plasma CVD method) is a well-known technique. FIG. 8 is a schematic sectional view for explaining a conventional general parallel plate type plasma CVD apparatus. The inside of the vacuum vessel 1 is depressurized by a vacuum exhaust device 2, source gas is supplied from a plurality of gas supply holes 5 provided in the first electrode 3, and power is supplied by a high-frequency power source 6 connected to the first electrode 3. Then, plasma is generated, and a thin film is formed on the surface of the substrate 7 held on the second electrode 4. The source gas is supplied into the first electrode 3 through the gas supply pipe 8 and is uniformly introduced from the plurality of gas supply holes 5 to the surface of the substrate 7 through the inside of the first electrode 3.

  For example, in order to obtain a high-quality film as an amorphous silicon thin film used for a solar cell, formation of dangling bonds (dangling bonds) that cause film defects and higher-order silane ((SiH2) n: n = 2 to 2). Incorporation of 5) into the membrane must be suppressed. In order to suppress the defect, the substrate surface temperature is preferably 220 ° C. to 250 ° C. (Non-patent Document 1). If the temperature is lower than this range, surface reaction on the surface of the amorphous silicon thin film during film formation is suppressed, resulting in a film with many defects. If the temperature is higher than this range, hydrogen is desorbed from the surface. This is because defects occur and the number of defects increases, or damage to the underlayer when a solar cell is manufactured becomes a problem. The gas temperature in the plasma is also an important factor. This is because when the gas temperature in the plasma is lowered, the three-body reaction that occurs when generating higher-order silane is promoted, and there is a concern that higher-order silane is taken into the film (Non-Patent Document 2). Since this higher order silane causes photodegradation of the amorphous silicon solar cell, it is necessary to suppress the incorporation into the film as much as possible.

Several means have been proposed to solve such problems. For example, a method of suppressing a decrease in the substrate temperature by heating a gas introduced into a plasma atmosphere and further heating the substrate is disclosed (Patent Document 1). Furthermore, a means for controlling the surface temperature of the substrate by changing the temperature of the gas introduced into the electrode is disclosed (Patent Document 2).
JP-A-8-91987 JP2000-273737 A. Matsuda et al. Solar Energy Materials & Solar Cells 78 (2003) 3-26 Madoka Takai et al. APPLIED PHYSICS LETTERS 77 (2000) 2828

  However, even if the gas to be introduced is heated as described above, if the gas is introduced into the vacuum vessel from the gas supply hole, the flow rate becomes several m / s or more. There is a problem that the capability of the mechanism is not realistic. Glass generally used as a substrate is a material having low thermal conductivity. Therefore, even if the electrode holding the substrate is heated and heated from the rear surface of the glass, it is considered that the temperature of the glass surface layer is lowered when the surface is cooled by the gas flow. Even if the gas can be heated, the gas temperature decreases due to adiabatic expansion due to the pressure difference when it is introduced from the gas supply hole into the vacuum vessel. As a result, the temperature of the glass surface layer is lowered. It is expected that.

  Therefore, an object of the present invention is to prevent a decrease in the substrate temperature and the gas temperature by controlling the flow of the gas introduced into the vacuum vessel, such as high-quality amorphous silicon with less formation of defects and high-order silane contamination. It is an object of the present invention to provide a plasma CVD apparatus capable of forming a thin film and an amorphous silicon thin film manufacturing method using the same.

In order to achieve the above object, the present invention provides:
A vacuum vessel;
An evacuation device for holding the vacuum vessel at a reduced pressure;
A first electrode having a plurality of gas supply holes;
A high frequency power source connected to the first electrode;
A plasma CVD apparatus comprising: a second electrode disposed opposite to the first electrode for holding the substrate substantially parallel to the first electrode;
Plasma CVD, characterized in that an obstacle for blocking a straight gas flow path from the gas supply hole of the first electrode to the second electrode is disposed between the first electrode and the second electrode. Providing equipment.

The present invention also provides:
Hold the vacuum container in a vacuum,
Supplying a source gas composed of a gas containing at least silane and hydrogen from a plurality of gas supply holes provided in the first electrode;
Applying high frequency power to the first electrode to generate plasma in the source gas;
A method for producing an amorphous silicon thin film, wherein an amorphous silicon thin film is formed by depositing the raw material gas on a substrate held by a second electrode placed opposite to the first electrode,
An obstacle is provided so as to block a straight gas flow path from the gas supply hole of the first electrode to the second electrode, and the source gas supplied from the gas supply hole of the first electrode Provided is a method for producing an amorphous silicon thin film, which is caused to collide with the obstacle before reaching a second electrode.

  According to the present invention, as described below, by controlling the flow of the gas introduced into the vacuum vessel, the gas temperature and the substrate temperature are prevented from being lowered, and the amount of defects formed and the amount of higher-order silane mixed are small. A plasma CVD apparatus capable of forming a high-quality amorphous silicon thin film and a method for producing a high-quality amorphous silicon thin film can be provided.

  Hereinafter, examples of the best mode of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic sectional view showing an example of the plasma CVD apparatus of the present invention. A vacuum evacuation device 2 for holding the vacuum container at a reduced pressure is connected to the vacuum container 1, and a first electrode 3 and a second electrode 4 are disposed substantially in parallel inside the vacuum container 1. ing.

  A plurality of gas supply holes 5 are arranged in the first electrode 3. In order to supply gas uniformly from the surface of the first electrode 3, it is preferable to provide a large number of gas supply holes 5 having a small diameter. The diameter of the gas supply hole 5 is 0.1 mm or more and 2 mm or less, more preferably 0. 3 mm or more and 1 mm or less are good. The in-plane arrangement of the gas supply holes 5 in the first electrode 3 is preferably a regular lattice arrangement from the viewpoint of uniformity, but is arranged at an arbitrary position in the plane in consideration of the internal structure of the first electrode 3 and the like. It doesn't matter.

  A high frequency power source 6 is connected to the first electrode 3, and plasma is generated in the vacuum container by applying a high frequency high voltage to the first electrode 3. The frequency of the high frequency can be arbitrarily selected, but from the viewpoint of productivity and uniformity, it is preferably 100 kHz to 100 MHz, more preferably 10 MHz to 60 MHz.

  The second electrode 4 holds the substrate 7 substantially parallel to the first electrode 3. The second electrode 4 preferably includes a heating mechanism 9 for heating the substrate 7. The second electrode 4 may be electrically grounded, but a bias voltage may be applied by a DC power source or an AC power source (not shown).

  In the present invention, an obstacle 10 that blocks a straight gas flow path from the gas supply hole 5 of the first electrode 3 toward the second electrode 4 is disposed between the first electrode 3 and the second electrode 4. To do. Here, the straight gas flow path is a three-dimensional figure formed by a trajectory formed when the plane formed by the outlet of the gas supply hole 5 of the first electrode is moved in the direction of the second electrode 4 perpendicular to the plane. Is the space area occupied by. Due to the obstacle 10, the gas ejected from the gas supply hole 5 does not directly collide with the substrate, but always collides with the obstacle 10 and then moves toward the substrate surface. As a result, it is possible to avoid a decrease in the substrate temperature due to the low temperature gas hitting the substrate directly. Examples of the shape of the obstacle 10 include a configuration in which a plurality of cylindrical objects as shown in FIG. 1 are arranged in parallel, and a configuration in which a plurality of triangular prisms and square columns are arranged in parallel instead of a cylindrical object. However, in the present invention, as shown in FIG. 2, the obstacle 10 is a flat plate 11 (hereinafter referred to as a plate-like obstacle 11) in which a plurality of openings 12 are formed, so that the openings 12 do not cover the straight gas flow path. It is preferable to install a plate-like obstacle 11 on the surface. By providing the plate-like obstacle 11, the gas supplied from the gas supply hole 5 once stays in a space between the first electrode 3 and the plate-like obstacle 11 and then a plurality of openings of the plate-like obstacle. 12 will leak into the space on the second electrode 4 side. By not allowing the gas flow coming out of the gas supply hole 5 to reach the substrate 7 in this way, a temperature drop of the substrate 7 can be avoided and the substrate temperature can be stabilized during film formation. preferable.

  The plurality of openings 12 formed in the plate-like obstacle 11 is a supply in which the total opening area of all the openings is the sum of the areas of the outlets of the gas supply holes 5 of the first electrode 3. It is preferable that it is larger than the total hole area from the viewpoint of lowering the flow rate of the gas flow, preferably the total opening area is 10 times or more, more preferably 50 times or more, more preferably 100 times or more the total supply hole area. Is good. Although any material can be selected as the material for the plate-like obstacle 11, it is preferable to use a metal or ceramic from the viewpoint of heat resistance and mechanical strength. For example, aluminum is used as the metal, and alumina is used as the ceramic. Can be used. The plate-like obstacle 11 may be of any thickness, but if it is too thin, the mechanical strength is weak and there is concern about deformation due to heat. If it is too thick, the plasma may become unstable or will not light up. To do. Therefore, the thickness of the plate-like obstacle 11 is 1 mm or more and 10 mm or less, preferably 2 mm or more and 8 mm or less, more preferably 3 mm or more and 6 mm or less.

  FIG. 3 is a schematic plan view showing an example of the first electrode 3. Here, a circular electrode is shown as an example, but the shape of the electrode may be rectangular or arbitrary. A plurality of gas supply holes 5 are provided on the surface of the first electrode 3, and in the case of the example of FIG. 3, the gas supply holes 5 are arranged in a lattice shape. In the present invention, the plate-like obstacle 11 blocks the straight gas flow path from the gas supply hole 5 of the first electrode 3 toward the second electrode 4. As described above, the gas straight flow path is a space area occupied by a solid figure formed by a locus formed by moving a plane formed by the outlet of the gas supply hole 5 in the direction of the second electrode 4 perpendicular to the plane. It is. For example, if the outlet shape of the gas supply hole 5 is circular, the straight gas flow path is a cylindrical space area, and if the outlet shape is square, the straight gas flow path is a prismatic space area. The plate-like obstacle 11 has a shape in which the straight gas flow path is blocked, that is, the space region is completely divided into two by the plate-like obstacle. Examples of the plate-like obstacle 11 applicable to the first electrode 3 shown in FIG. 3 are shown in FIGS. The plate-like obstacle 11 shown in FIG. 4 is provided with a plurality of circular openings 12 in a portion that does not reach the straight gas flow path from the gas supply hole 5 in FIG. 3 when installed on the first electrode 3 shown in FIG. It is a thing. Similarly, when the plate-like obstacle 11 shown in FIG. 5 is installed with respect to the first electrode 3 shown in FIG. 3, a plurality of rectangular openings are formed in a portion that does not reach the straight gas flow path from the gas supply hole 5 in FIG. 3. 12 is provided. Further, the plate-like obstacle 11 shown in FIG. 6 has a plurality of circles and strips connecting these circles including a portion that blocks the straight gas flow path from the gas supply hole 5 in FIG. The other part is made into the opening 12 while leaving. By applying the plate-like obstacle 11 like these, it is possible to reliably prevent the gas flow coming out of the gas supply hole 5 from reaching the substrate 7 directly, so that the substrate temperature is lowered or unstable. This is preferable because it is possible to prevent such a phenomenon.

  Furthermore, the plate-like obstacle 11 in the present invention preferably has a heating mechanism. This is because the temperature decrease of the substrate 7 can be prevented as a result of the heated plate-like obstacle 11 heating the gas. Furthermore, in the case of the present invention, due to the effect of positively colliding the gas exiting the gas supply hole 5 with the plate-like obstacle 11 and the effect of retaining the gas between the plate-like obstacle 11 and the first electrode 3. It is preferable because the heat exchange between the plate-like obstacle 11 and the gas can be promoted and the gas can be efficiently heated. As an example of the heating mechanism of the plate-like obstacle 11, the plate-like obstacle 11 is formed of a conductor and then resistance heating by passing an alternating current is used, or a heat medium flows inside the plate-like obstacle 11. For example, it is possible to use a heat medium whose temperature is controlled by forming a path, but any other method may be used.

  FIG. 7 is a schematic sectional view showing another example of the plasma CVD apparatus of the present invention. The plate-like obstacle 11 according to the present invention preferably includes a recess 13 at a position where the gas linear flow path is blocked on the surface facing the first electrode 3. In the case of FIG. 7, the concavity 13 has a conical recess as the recess 13. When such a concave portion is provided in the plate-like obstacle 11, the gas flow coming out of the gas supply hole 5 collides with the concave portion 13 of the plate-like obstacle 11, thereby disturbing the flow, and the plate-like obstacle 11 and the first obstacle 11. It is preferable because the time during which the gas stays between the electrodes 3 is increased and as a result, the heating of the gas is promoted. The shape of the recess 13 may be an arbitrary shape such as a pyramid shape, a hemispherical shape, a cylindrical shape in addition to a conical shape. Although there is no restriction | limiting in particular about the depth of the recessed part 13, If there is too deep, there exists a concern which produces | generates powder from the gas which remained in the recessed part 13, and accumulate | stores in the recessed part 13, and when too shallow, the heating effect of gas cannot fully be exhibited. Therefore, it is preferably 1 mm or more and 6 mm or less, more preferably 2 mm or more and 4 mm or less.

  Using the plasma CVD apparatus of the present invention described above, a glass substrate is placed on the second electrode 4 and evacuated, and then a source gas containing at least silane and hydrogen is introduced from the gas supply pipe 8 to generate high frequency. When a plasma is generated by the power source 6 and an amorphous silicon thin film is formed on the surface of the substrate, a high-quality film in which high-order silane is less mixed and defects are reduced as compared with a film formed by a conventional parallel plate plasma CVD apparatus. Is obtained. Further, by applying this high-quality amorphous silicon thin film to a solar cell, it is possible to create a solar cell with high conversion efficiency with little light deterioration.

  The present invention can be applied not only to a plasma CVD apparatus and amorphous silicon thin film formation but also to an etching apparatus, various other thin film formations, a plasma surface treatment apparatus, etc., but the application range is not limited thereto. .

It is a schematic sectional drawing which shows an example of the plasma CVD apparatus of this invention. It is a schematic sectional drawing which shows another example of the plasma CVD apparatus of this invention. It is a schematic plan view which shows an example of the 1st electrode 3 in this invention. In this invention, it is a schematic plan view which shows the example of the plate-shaped obstruction 11 applicable to the 1st electrode 3 shown in FIG. FIG. 4 is a schematic plan view showing another example of the plate-like obstacle 11 that can be applied to the first electrode 3 shown in FIG. 2 in the present invention. FIG. 4 is a schematic plan view showing another example of the plate-like obstacle 11 that can be applied to the first electrode 3 shown in FIG. 2 in the present invention. It is a schematic sectional drawing which shows another example of the plasma CVD apparatus of this invention. It is a schematic sectional drawing explaining the conventional parallel plate type plasma CVD apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Evacuation apparatus 3 1st electrode 4 2nd electrode 5 Gas supply hole 6 High frequency power supply 7 Board | substrate 8 Gas supply pipe 9 Heating mechanism 10 Obstacle 11 Flat plate (plate-like obstruction formed) )
12 Opening 13 Recess

Claims (8)

A vacuum vessel;
An evacuation device for holding the vacuum vessel at a reduced pressure;
A first electrode having a plurality of gas supply holes;
A high frequency power source connected to the first electrode;
A plasma CVD apparatus comprising: a second electrode disposed opposite to the first electrode for holding the substrate substantially parallel to the first electrode;
A plasma CVD apparatus in which an obstacle that blocks a straight gas flow path from the gas supply hole of the first electrode toward the second electrode is disposed between the first electrode and the second electrode.   The plasma CVD apparatus according to claim 1, wherein the obstacle is a flat plate in which a plurality of openings are formed, and the openings are formed in a portion that does not cover the straight gas flow path.   The plasma CVD apparatus according to claim 2, wherein the flat plate in which the plurality of openings are formed includes a heating mechanism.   4. The plate according to claim 2, wherein the flat plate in which the plurality of openings are formed is provided with a recess in a position facing the gas supply hole of the first electrode on the surface on the first electrode side. Plasma CVD equipment. Hold the vacuum container in a vacuum,
Supplying a source gas composed of a gas containing at least silane and hydrogen from a plurality of gas supply holes provided in the first electrode;
Applying high frequency power to the first electrode to generate plasma in the source gas;
A method for producing an amorphous silicon thin film, wherein an amorphous silicon thin film is formed by depositing the raw material gas on a substrate held by a second electrode placed opposite to the first electrode,
An obstacle is provided so as to block a straight gas flow path from the gas supply hole of the first electrode to the second electrode, and the source gas supplied from the gas supply hole of the first electrode A method of manufacturing an amorphous silicon thin film that collides with the obstacle before reaching the second electrode.   6. The method for producing an amorphous silicon thin film according to claim 5, wherein the obstacle is a flat plate in which a plurality of openings are formed, and the openings are formed in a portion that does not reach the gas straight flow path.   The method for producing an amorphous silicon thin film according to claim 6, wherein the flat plate in which the plurality of openings are formed is heated.   8. The plate according to claim 6, wherein the flat plate in which the plurality of openings are formed is provided with a recess at a position facing the gas supply hole of the first electrode on the surface on the first electrode side. A method for producing an amorphous silicon thin film.

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