JP2013045799A - Film formation device and film formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film formation device and a film formation method, in which it is difficult for a product material to adhere around an exhaust port.SOLUTION: A film formation device comprises: a reaction chamber to which reaction gas is supplied for film formation processing; a base plate 101 constituting the reaction chamber; and a base plate cover 103 provided on the base plate 101 and covering an entire face of the base plate 101. An exhaust port 6 for exhausting the excessive reaction gas from the reaction chamber is provided on the base plate 101, and a through hole 107 having a shape and a size fitted with the exhaust port 6 is provided on the base plate cover 103. An end face 109 of the through hole 107 on a downstream side of the reaction gas projects more than an end face 110 of the exhaust port 6. It is preferable that the base plate cover 103 has a protrusion part 108 on a face opposed to the base plate 101.

Description

  The present invention relates to a film forming apparatus and a film forming method.

  Conventionally, an epitaxial growth technique has been used for manufacturing a semiconductor element that requires a relatively large crystal film, such as a power device such as an IGBT (Insulated Gate Bipolar Transistor).

  In the vapor phase growth method used for the epitaxial growth technique, the pressure in the reaction chamber is set to normal pressure or reduced pressure while the substrate is placed in the reaction chamber. Then, a reactive gas is supplied into the reaction chamber while heating the substrate. Then, a gas undergoes a thermal decomposition reaction or a hydrogen reduction reaction on the surface of the substrate to form a vapor phase growth film. A gas generated by the reaction or a gas not used in the reaction is discharged to the outside through an exhaust port provided in the reaction chamber.

  The reaction chamber has a structure in which a bell jar is disposed on a base plate. In addition, a rotating body unit is disposed in the reaction chamber, and the substrate is placed on an annular holding portion provided on the upper surface of the rotating body unit. A heater for heating the substrate is provided below the holding portion. A terminal for introducing a current into the heater, an electric wire, an electrode for supporting the heater, and the like are part of the rotating body unit, and are arranged inside the rotating shaft that penetrates the central portion of the base plate.

  The exhaust port is provided in the base plate. As described above, the reaction gas that has not contributed to the vapor phase growth reaction is discharged to the outside of the reaction chamber through the exhaust port. Here, since the reaction chamber becomes very hot during the vapor phase growth reaction, a flow path of cooling water is provided inside the base plate. Furthermore, since heat is released to the outside from the exhaust port, the temperature around the exhaust port is lowered, and products resulting from the reaction gas are likely to adhere.

  Therefore, in Patent Document 1, the base plate is covered with a plate member made of quartz glass except for the exhaust port portion, and a gap is provided between the plate member and the base plate, so that the plate member is heated to a high temperature. A film forming apparatus that maintains and suppresses product deposition is disclosed.

  However, the film forming apparatus of Patent Document 1 cannot prevent the product from adhering to the exhaust port portion. Since the exhaust port cannot be removed, there is a problem that it takes a long time to remove the attached product.

  On the other hand, Patent Document 2 discloses a film forming apparatus in which an exhaust port cover is detachably inserted into an exhaust port. The exhaust port cover includes a flat plate-like flange portion and a cylindrical portion, the flange portion is supported on the surface of the base plate, and the cylindrical portion is inserted into the exhaust port. According to this structure, the exhaust port cover can be removed and cleaned during maintenance, so that the product attached to the exhaust port and its surroundings can be removed.

JP-A-9-283450 Japanese Patent Laid-Open No. 10-209049

  However, in the structure of Patent Document 2, since the reaction gas goes around to the back side of the exhaust port cover, the product adheres between the exhaust port cover and the base plate, and it is difficult to remove the exhaust port cover during maintenance. there were.

  The present invention has been made in view of these problems. That is, an object of the present invention is to provide a film forming apparatus and a film forming method in which a product hardly adheres to the periphery of an exhaust port.

  Other objects and advantages of the present invention will become apparent from the following description.

A first aspect of the present invention is a film forming apparatus including a reaction chamber in which a reaction gas is supplied and a film forming process is performed.
A base plate constituting the reaction chamber;
A base plate cover installed on the base plate and covering the entire surface of the base plate;
The base plate is provided with an exhaust port for discharging excess reaction gas from the reaction chamber,
The base plate cover has a through hole with a shape and size that fits into the exhaust port.
The end face of the through hole on the downstream side of the reaction gas is characterized by protruding from the end face of the exhaust port.

  In the first aspect of the present invention, the base plate cover preferably has a protrusion on a surface facing the base plate.

A second aspect of the present invention is a film forming method for supplying a reaction gas into a reaction chamber to form a predetermined film on a substrate and discharging excess reaction gas from an exhaust port provided in a base plate constituting the reaction chamber. In
A base plate cover having a shape and size that fits into the exhaust port and with the end surface of the through hole on the downstream side of the reaction gas protruding from the end surface of the exhaust port is placed on the base plate to form a predetermined film. It is characterized by this.

  In the second aspect of the present invention, after the predetermined film is formed, the base plate cover is preferably removed from the base plate and washed.

  In the second aspect of the present invention, it is preferable to provide a protrusion on the surface of the base plate cover facing the base plate so that a predetermined gap is formed therebetween.

  According to the first aspect of the present invention, since the end surface of the through hole of the base plate cover on the downstream side of the reaction gas protrudes from the end surface of the exhaust port, the reaction gas hardly enters the gap between the base plate and the base plate cover. Therefore, it becomes difficult for the product to adhere to the periphery of the exhaust port.

  According to the second aspect of the present invention, since the base plate cover in which the end surface of the through hole on the downstream side of the reaction gas protrudes from the end surface of the exhaust port is installed on the base plate to form the predetermined film, the base plate and the base plate It is possible to prevent the reaction gas from flowing into the gap of the cover and make it difficult for the product to adhere to the periphery of the exhaust port.

It is typical sectional drawing of the film-forming apparatus of this Embodiment. It is a top view of the base plate in this Embodiment. It is a perspective view of the base plate cover in this Embodiment. It is an expanded sectional view around an exhaust port in the present embodiment.

  FIG. 1 is a schematic cross-sectional view of the film forming apparatus of the present embodiment. In this figure, components other than those necessary for explanation are omitted. Also, the scale is changed from the original scale so that each component can be clearly seen.

  As shown in FIG. 1, the film forming apparatus 100 has a chamber 1 as a reaction chamber. The chamber 1 has a structure in which a bell jar 102 is disposed on a base plate 101. The base plate 101 and the bell jar 102 are connected by a flange 10, and the flange 10 is sealed with a packing 11. The base plate 101 can be made of, for example, SUS (Steel Use Stainless).

  During the vapor phase growth reaction, the temperature in the chamber 1 becomes extremely high. Therefore, for the purpose of cooling the chamber 1, a cooling water flow path 3 is provided inside the base plate 101 and the bell jar 102.

  The bell jar 102 is provided with a supply port 5 for introducing the reaction gas 4. On the other hand, the base plate 101 is provided with an exhaust port 6, and after the reaction or unreacted reaction gas 4 is exhausted to the outside of the chamber 1 through the exhaust port 6.

  The exhaust port 6 is connected to the pipe 12 by a flange 13. The flange 13 is sealed with a packing 14. The packing 11 and the packing 14 are made of fluorine rubber having a heat resistant temperature of about 300 ° C.

  Inside the chamber 1, a hollow cylindrical liner 2 is arranged. The liner 2 is provided for the purpose of partitioning the inner wall 1a of the chamber 1 and the space A in which the vapor phase growth reaction on the substrate 7 is performed. Thereby, it is possible to prevent the inner wall 1a of the chamber 1 from being corroded by the reaction gas 4. Since the vapor phase growth reaction is performed at a high temperature, the liner 2 is made of a material having high heat resistance. For example, a SiC member or a member formed by coating SiC on carbon can be used.

  In the present embodiment, for convenience, the liner 2 is divided into two parts, a body part 2a and a head part 2b. The body part 2a is a part in which the susceptor 8 is disposed, and the head part 2b is a part having an inner diameter smaller than that of the body part 2a. The trunk portion 2a and the head portion 2b integrally constitute the liner 2, and the head portion 2b is located above the trunk portion 2a.

  A shower plate 15 is provided in the upper opening of the head 2b. The shower plate 15 functions as a gas rectifying plate that uniformly supplies the reaction gas 4 to the surface of the substrate 7. The shower plate 15 is provided with a plurality of through holes 15a, and the reaction gas 4 introduced into the chamber 1 from the supply port 5 flows down toward the substrate 7 through the through holes 15a. Here, it is preferable that the reaction gas 4 efficiently reaches the surface of the substrate 7 without vainly diffusing. For this reason, the inner diameter of the head 2b is designed to be smaller than that of the body 2a. Specifically, the inner diameter of the head 2 b is determined in consideration of the position of the through hole 15 a and the size of the substrate 7.

  Further, a susceptor 8 that supports the substrate 7 is disposed inside the chamber 1, specifically, in the body 2 a of the liner 2. The susceptor 8 is made of a high heat resistant material. For example, when SiC is epitaxially grown on the substrate 7, the substrate 7 needs to have a high temperature of 1500 ° C. or higher. For this reason, for example, a surface of isotropic graphite coated with SiC by a CVD (Chemical Vapor Deposition) method is used for the susceptor 8. The shape of the susceptor 8 is not particularly limited as long as the substrate 7 can be placed thereon, and is appropriately selected from a ring shape or a disk shape.

  The substrate 7 is heated by a heater 9 disposed inside the rotary cylinder 17. The heater 9 can be a resistance heating type heater, and includes a disc-shaped in-heater 9a and an annular out-heater 9b. The in-heater 9 a is disposed at a position corresponding to the substrate 7. The outheater 9 b is disposed above the inheater 9 a and at a position corresponding to the outer peripheral portion of the substrate 7. Since the temperature of the outer peripheral portion of the substrate 7 is likely to be lower than that of the central portion, the temperature decrease of the outer peripheral portion can be prevented by providing the outheater 9b.

  The in-heater 9a and the out-heater 9b are supported by a conductive booth bar 20 having an arm shape. The booth bar 20 is configured by a member formed by coating carbon with SiC, for example. The booth bar 20 is supported by a quartz heater base 21 on the side opposite to the side supporting the in-heater 9a and the out-heater 9b. Then, the booth bar 20 and the electrode bar 23 are connected by the conductive connecting part 22 made of a metal such as molybdenum, so that power is supplied from the electrode bar 23 to the in-heater 9a and the out-heater 9b. Specifically, electricity is supplied from the electrode rod 23 to the heating elements of these heaters (9a, 9b), and the heating elements are heated.

  The surface temperature of the substrate 7 can be measured by the radiation thermometers 24a and 24b. In FIG. 1, a radiation thermometer 24 a is used to measure the temperature near the center of the substrate 7. On the other hand, the radiation thermometer 24 b is used to measure the temperature of the outer peripheral portion of the substrate 7. These radiation thermometers can be provided in the upper part of the chamber 1 as shown in FIG. In this case, by making the upper part of the bell jar 102 and the shower plate 15 made of transparent quartz, temperature measurement by the radiation thermometers 24a and 24b can be prevented from being hindered by these.

The measured temperature data is sent to a control mechanism (not shown) and can be fed back to each output control of the in-heater 9a and the out-heater 9b. As an example, when SiC epitaxial growth is performed, the set temperature of each heater can be set as follows. Thereby, it is possible to heat the board | substrate 7 to about 1650 degreeC.
Temperature of inheater 9a: 1680 ° C
Temperature of outheater 9b: 1750 ° C

  A rotating shaft 16 and a rotating cylinder 17 provided at the upper end of the rotating shaft 16 are disposed on the body 2 a of the liner 2. The susceptor 8 is attached to the rotary cylinder 17, and the susceptor 8 rotates via the rotary cylinder 17 when the rotary shaft 16 rotates. During the vapor phase growth reaction, the substrate 7 is rotated together with the rotation of the susceptor 8 by placing the substrate 7 on the susceptor 8.

  The reaction gas 4 that has passed through the shower plate 15 flows down toward the substrate 7 through the head 2b. Due to the rotation of the substrate 7, the reactive gas 4 is attracted to the substrate 7 and becomes a vertical flow in the region from the shower plate 15 to the substrate 7. The reaction gas 4 that has reached the substrate 7 flows in a substantially laminar flow in the horizontal direction without forming a turbulent flow on the surface of the substrate 7. In this way, new reaction gases 4 come into contact with the surface of the substrate 7 one after another. Then, a thermal decomposition reaction or a hydrogen reduction reaction is caused on the surface of the substrate 7 to form an epitaxial film. In the film forming apparatus 100, the distance from the outer periphery of the substrate 7 to the liner 2 is narrowed so that the flow of the reaction gas 4 on the surface of the substrate 7 becomes more uniform.

  With the above configuration, the vapor phase growth reaction can be performed while heating and rotating the substrate 7. By rotating the substrate 7, the reaction gas 4 is efficiently supplied to the entire surface of the substrate 7, and an epitaxial film with high film thickness uniformity can be formed. In addition, since new reaction gases 4 are supplied one after another, the film forming speed can be improved.

  Of the reaction gas 4, a gas that is not used for the vapor phase growth reaction and a gas generated by the vapor phase growth reaction are discharged from the exhaust port 6 provided in the base plate 101.

  FIG. 2 is a plan view of the base plate 101. The base plate 101 is provided with exhaust ports 6 at two locations. In addition, the number of the exhaust ports 6 is not limited to this. Further, the base plate 101 is also provided with a through hole 104 through which the rotating shaft 16 of FIG.

  On the base plate 101, a base plate cover 103 having a shape and a size covering the entire surface of the base plate 101 is detachably installed. The base plate cover 103 can be made of, for example, quartz.

  FIG. 3 is a perspective view of the base plate cover 103. The through hole 106 is provided at a position corresponding to the through hole 104 of the base plate 101, and the rotating shaft 16, the electrode bar 23, and the connecting portion 22 that connects the booth bar 20 and the electrode bar 23 in FIG. The through-hole 107 is provided at a position corresponding to the exhaust port 6 of the base plate 101 and has a shape and a size that fit into the exhaust port 6.

  FIG. 4 is an enlarged cross-sectional view of the periphery of the exhaust port 6. This figure shows a state in which the base plate cover 103 is installed on the base plate 101. As illustrated, the through hole 107 of the base plate cover 103 is fitted into the exhaust port 6 of the base plate 101.

  Since the heat in the chamber 1 is released through the exhaust port 6, the temperature in the vicinity of the exhaust port 6 tends to be lower than the temperature of other portions. As described with reference to FIG. 1, the cooling water flow path 3 is provided inside the base plate 101. For this reason, the temperature of the base plate 101 is lower than that of surrounding members. For this reason, the temperature around the base plate 101 is particularly low in the vicinity of the exhaust port 6 (for example, 100 ° C. or lower). Therefore, when the reaction gas 4 touches this part, the product resulting from the reaction gas 4 tends to adhere. For example, when the reaction gas is a silicon-based gas, a product such as oily silane adheres.

  In the conventional exhaust port portion, for example, as disclosed in Patent Document 2, the end surface of the exhaust port cover and the end surface of the base plate are formed so as to substantially coincide with each other on the downstream side of the exhaust port. For this reason, a part of the reaction gas passing through the exhaust port may wrap around the back side of the exhaust port cover and touch the cooled base plate to form a product. Since this product adheres between the exhaust port cover and the base plate, when the amount of the product increases, the exhaust port cover adheres to the base plate through the product, and it becomes difficult to remove the exhaust port cover.

  Therefore, the present inventor has considered a structure in which the end surface of the base plate cover protrudes from the end surface of the base plate on the downstream side of the flow in order to prevent the reaction gas from flowing around. Specifically, as shown in FIG. 4, the downstream end surface 109 of the reaction gas 4 is protruded from the downstream end surface 110 of the exhaust port 6 of the base plate 101 in the through hole 107 of the base plate cover 103. The length of the protrusion part L can be about 30 mm, for example. According to this structure, when the reaction gas 4 is exhausted from the exhaust port 6, it can be prevented that the reaction gas 4 enters the gap between the base plate 101 and the base plate cover 103. Accordingly, it is possible to prevent the product from adhering between the base plate 101 and the base plate cover 103.

  As shown in FIG. 4, the base plate cover 103 preferably has a protrusion 108 on the surface facing the base plate 101. By providing the protrusions 108, the gap between the base plate 101 and the base plate cover 103 can be made a predetermined distance or more. Thereby, even if a product adheres to this gap, a phenomenon in which the base plate cover 103 and the base plate 101 are bonded via the product can be made difficult to occur. In addition, the product is expected to easily adhere to the vicinity of the protrusion 108, but since the contact area between the protrusion 108 and the base plate 101 is small, the base plate cover 103 can be easily removed from the base plate 101.

  Next, an example of a film forming method in the present embodiment will be described with reference to FIGS.

  The film forming apparatus 100 of the present embodiment is suitable for forming a SiC epitaxial growth film, for example. Therefore, in the following, the formation of a SiC epitaxial film is taken as an example.

As the substrate 7, for example, a SiC wafer can be used. However, the present invention is not limited to this, and a wafer made of another material may be used depending on the case. For example, another insulating substrate such as a Si wafer, SiO ₂ (quartz), a semi-insulating substrate such as high-resistance GaAs, or the like can be used.

As the reaction gas 4, for example, propane (C ₃ H ₈ ), silane (SiH ₄ ), and hydrogen gas as a carrier gas can be used. In this case, disilane (SiH ₆ ), monochlorosilane (SiH ₃ Cl), dichlorosilane (SiH ₂ Cl ₂ ), trichlorosilane (SiHCl ₃ ), tetrachlorosilane (SiCl ₄ ), or the like may be used instead of silane. Is possible.

  First, the substrate 7 is placed on the susceptor 8.

  Next, the substrate 7 is rotated while the inside of the chamber 1 is at a normal pressure or an appropriate reduced pressure. The susceptor 8 on which the substrate 7 is placed is disposed at the upper end of the rotating cylinder 17. Therefore, when the rotating cylinder 17 is rotated through the rotating shaft 16, the susceptor 8 is rotated and the substrate 7 is also rotated at the same time. The number of rotations can be about 50 rpm, for example.

  Next, the substrate 7 is heated by the heater 9. In SiC epitaxial growth, the substrate 7 is heated to a predetermined temperature between 1500 ° C. and 1700 ° C., for example. Further, since the inside of the chamber 1 becomes high temperature due to the heating of the substrate 7, cooling water is supplied to the flow path 3 provided inside the base plate 101 and the bell jar 102. Thereby, it can prevent that the chamber 1 heats up excessively.

  After confirming that the temperature of the substrate 7 has reached, for example, 1650 ° C. by the radiation thermometers 24a and 24b, the rotational speed of the substrate 7 is gradually increased. For example, the rotational speed can be increased to about 900 rpm. Further, the reaction gas 4 is introduced from the supply port 5.

  The reactive gas 4 flows through the through hole 15a of the shower plate 15 and into the space A where the vapor phase growth reaction to the substrate 7 is performed. By passing through the shower plate 15, the reaction gas 4 is rectified and flows substantially vertically toward the substrate 7 that rotates below, forming a so-called vertical flow.

  The reaction gas 4 that has reached the surface of the substrate 7 causes a thermal decomposition reaction or a hydrogen reduction reaction on this surface to form a SiC epitaxial film. Excess reaction gas 4 that has not been used in the vapor phase growth reaction and gas generated by the vapor phase growth reaction are exhausted to the outside through an exhaust port 6 provided below the chamber 1.

  A base plate 101 is disposed below the chamber 1. A base plate cover 103 is installed on the base plate 101. The base plate 101 is provided with an exhaust port 6. In addition, the through hole 107 of the base plate cover 103 has a size and a shape that fits into the exhaust port 6.

  According to the present embodiment, as shown in FIG. 4, the end surface 109 of the through hole 107 of the base plate cover 103 on the downstream side of the reaction gas 4 protrudes from the end surface 110 of the exhaust port 6 of the base plate 101. It is possible to suppress the reaction gas 4 from flowing into the gap between the 101 and the base plate cover 103. Therefore, it is possible to make it difficult for the product to adhere between the base plate 101 and the base plate cover 103.

  In addition, since the base plate cover 103 has the protruding portion 108 on the surface facing the base plate 101, even if a product adheres to the gap between the base plate 101 and the base plate cover 103, it is difficult to cause such adhesion through the product. be able to.

  After the SiC film having a predetermined thickness is formed on the substrate 7, the supply of the reaction gas 4 is terminated. Subsequently, heating by the heater 9 is stopped, and the substrate 7 waits for the temperature to drop to a predetermined temperature.

  After confirming that the temperature of the substrate 7 has been cooled to a predetermined temperature by the radiation thermometers 24 a and 24 b, the substrate 7 is carried out of the chamber 1.

  After the above steps are completed, it is preferable to remove the base plate cover 103 from the base plate 101 and perform cleaning to remove the product attached to the base plate cover 103. Further, the product adhering to the base plate 101 can also be removed at this time. The product is expected to easily adhere to the vicinity of the protrusion 108 of the base plate cover 103, but since the contact area between the protrusion 108 and the base plate 101 is small, the base plate cover 103 can be easily removed from the base plate 101. is there.

  Subsequently, when performing the film forming process, the base plate cover 103 is again placed on the base plate 101. The cleaning with the base plate cover 103 removed is not required every time one film forming process is completed, and every time the predetermined number of times is finished or the amount of the attached product exceeds a predetermined amount. You may go to

  According to the film forming method of the present embodiment, since the base plate cover in which the end face of the through hole on the downstream side of the reactive gas protrudes from the end face of the exhaust port is installed on the base plate, the film forming process is performed. When exhausted from the exhaust port, it is possible to suppress wrapping around the gap between the base plate and the base plate cover. Therefore, it is possible to reduce the adhesion of the product around the exhaust port.

  Further, in the film forming method of the present embodiment, the protrusions are provided on the surface of the base plate cover that faces the base plate, and a predetermined gap is formed between them, so that the base plate is interposed via the product. Bonding of the cover and the base plate can be suppressed. In addition, since the contact between the base plate and the base plate cover is through an extremely narrow area through the protrusions, the base plate cover can be easily removed from the base plate even if the product adheres.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the example in which the film is formed on the substrate while rotating the substrate has been described. However, in the present invention, the film may be formed without rotating the substrate.

  Moreover, although the epitaxial growth apparatus was mentioned as an example of the film-forming apparatus in the said embodiment and the formation of the SiC crystal film was demonstrated, it is not restricted to this. As long as the reaction gas is supplied into the reaction chamber and the substrate placed in the reaction chamber is heated to form a film on the surface of the substrate, other film forming apparatuses may be used. It can also be used to form a film.

  In addition, although descriptions of parts that are not directly required for the present invention, such as apparatus configuration and control method, are omitted, the required apparatus configuration, control method, and the like can be appropriately selected and used. .

  In addition, all film forming apparatuses and elements having various elements that can be appropriately modified by those skilled in the art are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Chamber 1a Inner wall 2 Liner 2a Body part 2b Head 3 Flow path 4 Reaction gas 5, 25 Supply port 6 Exhaust port 7 Substrate 8 Susceptor 9 Heater 9a In-heater 9b Out-heater 10, 13 Flange 11, 14 Packing 12 Piping 15 Shower plate 15a, 104, 106, 107 Through-hole 16 Rotating shaft 17 Rotating cylinder 20 Booth bar 21 Heater base 22 Connecting portion 23 Electrode rod 24a, 24b Radiation thermometer 100 Film forming apparatus 101 Base plate 102 Berja 103 Base plate cover 108 Protruding portion 109, 110 End face

Claims (5)

In a film forming apparatus including a reaction chamber in which a reaction gas is supplied and a film forming process is performed,
A base plate constituting the reaction chamber;
A base plate cover that is installed on the base plate and covers the entire surface of the base plate;
The base plate is provided with an exhaust port for discharging excess reaction gas from the reaction chamber,
The base plate cover is provided with a through hole having a shape and size to be fitted to the exhaust port,
An end face of the through hole on the downstream side of the reaction gas protrudes from an end face of the exhaust port.   The film forming apparatus according to claim 1, wherein the base plate cover has a protrusion on a surface facing the base plate. In a film forming method for supplying a reaction gas into a reaction chamber to form a predetermined film on a substrate and discharging excess reaction gas from an exhaust port provided in a base plate constituting the reaction chamber,
A base plate cover having a shape and size that fits into the exhaust port, and an end surface of the through hole on the downstream side of the reaction gas projecting from the end surface of the exhaust port is installed on the base plate, and A film forming method comprising forming a predetermined film.   4. The film forming method according to claim 3, wherein after the predetermined film is formed, the base plate cover is removed from the base plate and washed. 5. The film forming method according to claim 3, wherein a protrusion is provided on a surface of the base plate cover facing the base plate so that a predetermined gap is formed therebetween.

Images