JPH0456449B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to an improvement in a film-forming method for forming an amorphous silicon film or the like on a film-forming object by gas glow discharge decomposition or the like. [Technical background of the invention and its problems] In recent years, so-called plasma, which forms a film on a film-forming object such as a substrate, by glow discharge decomposition of gas, etc.
CVD deposition method is used for solar cells, thin film transistors,
It is often used to form films of amorphous silicon, amorphous silicon carbide, amorphous silicon nitride, etc. for applications in photoelectric conversion devices such as contact image sensors and electrophotographic photoreceptors, and electronic devices. It is being The requirements for forming these films include uniform large-area films, good optical and electrical properties, and high-speed film formation. Figure 1 shows the plasma produced using the conventional film-forming method.
The outline of the CVD film forming apparatus is shown, and this apparatus basically consists of a reaction vessel 1, a source gas supply device 2, an exhaust device 3, and a discharge power source 4. Further, a support stand 7 containing a built-in heating means 6 is installed at the lower part of the reaction chamber 5 of the reaction vessel 1, and at an upper position facing the support stand 7, the reaction vessel 1
An electrode 9 is installed which is electrically insulated through the wall and an insulator 8. A conductive substrate (hereinafter simply referred to as a substrate) 10, which is a film-forming object, is placed on the support table 7, and this substrate 10 is heated by the heating means 6 built into the support table 7. It's becoming like that. Further, the electrode 9 is connected to the output part of the discharge power source 4, and the support base 7 is electrically connected to the reaction vessel 1 and has a ground potential. On the other hand, the raw material gas 11 supplied with a controlled flow rate from the raw material gas supply device 2 is supplied to the gas inlet 1
2 into the reaction chamber 5, and the gas is introduced into the reaction chamber 5 through the gas outlet 1.
3, the reaction chamber is evacuated by an exhaust device 3 while the pressure inside the reaction chamber is kept constant. In this state, by applying a voltage to the electrode 9 by the discharge power source 4, plasma is generated in the reaction chamber 5, and a film is formed on the heated substrate 10. Here, the frequency of the discharge power source 4 can range from direct current to high frequency radio waves. However, in film formation using this apparatus, the plasma positive column does not exist near the substrate 10 and the reaction chamber 5
There was a problem in that the plasma density in the vicinity of the substrate 10 did not increase even if the discharge power was increased because the plasma was diffused throughout the interior of the substrate, so a dramatic increase in the film forming rate could not be expected. Therefore, the inventors of the present invention have recently developed an apparatus as shown in Fig. 2, which makes it possible to significantly increase the film formation rate by partially improving the apparatus shown in Fig. 1 above. . The added improvement is that the space containing the support base 7 and the electrodes 9 is surrounded by a material 14 through which source gas flows and which can serve as a plasma barrier. For example, a metal mesh such as stainless steel or an insulating porous material is used as the material 14. In the case of a metal mesh, it is preferable to use a ground potential, and the electrode 9
and face each other at a distance that allows for Dark Space Shield. This improvement makes it possible to concentrate the plasma between the support base 7 and the electrode 9, and to supply the necessary amount of raw material gas to the plasma space without too much or too little, resulting in fewer defects and at the same time significantly increasing the film formation speed compared to the conventional method. It became possible to form a film in an increased state. However, by concentrating the plasma between the support base 7 and the electrode 9, a potential gradient due to the plasma potential is generated near the plasma anode, that is, the substrate 10, which is the object to be film-formed, and the plasma is positively charged. The ion species are accelerated toward the substrate 10. For this reason, the structure is such that the substrate 10 is subjected to ion bombardment during film formation, and defects are likely to occur in the film. On the other hand, as mentioned above, the requirements for film formation include a uniform large area film, good optical and electrical properties, and high speed film formation. Among these films, when amorphous silicon is used in devices such as solar cells, electrical properties, sometimes the mobility of photogenerated carriers,
These high characteristics are required because the lifespan greatly affects the performance of devices. However, in general, when high-speed film formation is pursued, the defect density in the film increases, so it has been extremely difficult to achieve high-speed film formation while maintaining high running properties of the optical carrier. [Object of the Invention] The present invention was made based on the above circumstances, and its purpose is to provide a film forming method that can form a film having good optical and electrical properties at high speed. This is what I am trying to do. [Summary of the Invention] In order to achieve the above object, the present invention introduces a source gas into a reaction chamber that accommodates an electrode and an object to be film-formed, and creates an electric field between the electrode and a portion that supports the object to be film-formed. In a film forming method in which plasma is generated by applying a plasma to form a film on the object to be film-formed, a source gas flows through at least a region including the object to be film-formed and an electrode, and can act as a barrier to the plasma. The film is formed by surrounding the film with a substance and further providing a grid near the film-forming object in the above region to suppress ion bombardment to the film-forming object.The grid reduces the potential gradient near the film-forming object. Set it to zero or negative to suppress the acceleration of ion species, that is, ion bombardment, to the object to be coated,
It is designed to prevent defects in the film and improve optical and electrical characteristics while maintaining high-speed film formation. [Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 3 and 4. FIG. 3 schematically shows a plasma CVD film forming apparatus capable of carrying out the film forming method of the present invention, in which raw material gas flows through a space including a support 7 and an electrode 9, and a metal mesh or the like that can act as a barrier to plasma is provided. Surrounded by substance 14, and further this substance 14
A grid 15 located substantially parallel to the film-forming surface of the substrate 10 is installed near the upper side of the substrate 10 as a film-forming object in the area surrounded by . As shown in FIG. 4, this grid 15 is at the same ground potential as the substrate 10, and the potential gradient between the substrate 10 and the grid 15 is zero as shown in FIG. Therefore, due to the arrangement of the grid 15, the substrate 10
Since the potential gradient in the vicinity becomes zero, acceleration of the ion species, that is, ion bombardment towards the substrate 10 can be suppressed. Therefore, it is possible to suppress ion bombardment on the film-forming surface of the substrate 10, reduce defects in the film, and improve the running performance of the optical carrier. At this time, the plasma density near the substrate 10 is increased due to the flow of the raw material gas 11 and the presence of the substance 14 that can act as a plasma barrier, so that a sufficiently satisfactory film formation rate can be maintained. Become. In addition, in the above-mentioned embodiment, the grid 15
In the above description, the ground potential is the same as that of the substrate 10, and the potential gradient between the substrate 10 and the grid 15 is zero. However, the present invention is not limited to this, and as shown in FIGS. A negative electrical bias may be applied to the substrate 10 to reverse the potential gradient between the substrate 10 and the grid 15 compared to the case without the grid 15, thereby further suppressing ion bombardment. Further, as shown in FIGS. 8 and 9, two grids 15 are arranged perpendicularly to the film-forming surface of the substrate 10, and the grids 15 on the electrode side
A negative bias is applied to the grid 15 on the substrate side.
may be set to zero potential to further suppress ion bombardment. As explained above, according to the present invention, a film can be formed at high speed and with excellent optical and electrical properties, especially optical carrier running properties. Next, a detailed example will be explained. A-Si films were formed using each of the film forming apparatuses described above. The substrate 10 used was Corning 7059 glass with surface-type Ni-Cr electrodes deposited on it.
First, as shown in FIG. 1, sample No. 1 was prepared in the case where the source gas flows and no metal mesh is used as the material 14 that can act as a plasma barrier.
shall be. Next, the cathode and anode shown in FIG. 2 are covered with a metal mesh 14, and this is used as a sample.
Set it as No.2. Furthermore, there is a case where the cathode and anode shown in FIG. 3 are covered with a metal mesh and at the same time a grid 15 is placed near the substrate 10, that is, the anode, and this is the case where the grid 15 is at ground potential as shown in FIG. Grid 15 as shown in
The tests were conducted on three types: one in which a negative bias is applied to the grid, and the other in which there are two grids 15, one of which is at ground potential and the other is a negative bias, as shown in Figure 8. Sample No. 3, Sample No. 4, and Sample No. It was set as .5. The following film forming conditions for each sample were common. Raw material gas used: SiH ₄ 100c.c./min High frequency power supply: 13.56MHz 60W Reaction pressure: 0.75 Torr Substrate temperature: 220°C Also, in samples No. 4 and No. 5, the bias voltage of grid 15 that applies negative bias teeth,
30V, 100V, and 200V were used. After film formation, the specific resistance of each sample was measured at a steady current in the dark and when irradiated with light equivalent to AM1. This specific resistance during light irradiation is a value that serves as an index for determining the mobility and lifetime of the photogenerated carrier. Table 1 shows the film formation speed of each sample, specific resistance in the dark (ρd), specific resistance in the light irradiation (ρp)
shows.

【table】

〔Effect of the invention〕

As explained above, the present invention introduces a raw material gas into a reaction chamber that accommodates an electrode and an object to be film-formed, and applies an electric field between the electrode and the part that supports the object to be film-formed to generate a plasma. In the film forming method for forming a film on the object to be film-formed, the region including at least the object to be film-formed and the electrode is surrounded by a material through which a source gas flows and can act as a barrier to plasma, and further The film forming method is characterized in that a grid is provided near the object to be film-formed in the above region to suppress ion bombardment to the object to be film-formed. Therefore, it is possible to provide a film forming method that can form a film having good optical and electrical characteristics at high speed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional film forming apparatus, FIG. 2 is a schematic diagram of a film forming apparatus which is an example of a prior art improved version of the conventional apparatus, and FIG. 3 is a diagram of a film forming apparatus capable of implementing the present invention. A schematic configuration diagram showing one embodiment of the device, FIG. 4 is a diagram schematically showing the electrical connection state of the grid in the same embodiment, and FIG. 5 is a diagram showing the potential distribution between the electrode and the substrate in the plasma. FIG. 6 and FIG. 7 are explanatory diagrams showing a first other embodiment to which the present invention can be applied. FIG. 6 is a diagram schematically showing the electrical connection state of the grid, and FIG. 8 is an explanatory diagram showing the potential distribution between the electrode and the substrate in plasma, and FIGS. 8 and 9 show a second other embodiment to which the present invention can be applied. FIG. A diagram schematically showing an electrical connection state,
FIG. 9 is an explanatory diagram showing the potential distribution between the electrode and the substrate in plasma. 5...Reaction chamber, 7...Support stand, 9...Electrode, 1
1... Raw material gas, 14... Substance such as metal mesh, 15... Grid.

Claims (1)

[Scope of Claims] 1. A space including the electrode, the object to be deposited, and the grid is surrounded by an electrically grounded cylindrical metal mesh that allows the flow of source gas through the mesh and can act as a plasma barrier. In a reaction chamber under reduced pressure containing a metal mesh, a necessary amount of raw material gas is passed through the mesh into the metal mesh by flowing the raw material gas through the space region within the metal mesh and the region around the metal mesh. a step of introducing a gas into the inner side; and a step of generating a plasma in a region between the electrode and the object to be film-formed together with this gas introduction step, and causing atoms contained in the source gas to be formed on the object to be film-formed. a film forming step of forming a film; and a step of forming a film so that a potential gradient becomes negative or zero on the grid provided between the electrode in the metal mesh and the object to be filmed during execution of this film forming step. A method for forming a film, comprising: applying a bias voltage to suppress ion bombardment on an object to be film-formed. 2. The film forming method according to claim 1, wherein the grid is a metal mesh located substantially parallel to the film forming surface of the film forming object. 3. The film forming method according to claim 1, wherein a plurality of grids are arranged in a direction perpendicular to the film forming surface of the film forming object.