JPS637374A - Method and apparatus for forming functional deposited film by microwave plasma cvd method - Google Patents

Abstract

PURPOSE:To form a functional deposited film having a uniform film thickness over the entire surface of a large-area substrate by apparently closing an aperture of a discharge means to a film forming chamber by a space constructing member which discharges gases smoothly and shuts off the leakage of microwaves. CONSTITUTION:A microwave reflecting member 10 having the space construction is provided to the aperture part of the discharge pipe 5 to a vacuum chamber 7 and the aperture is apparently closed. The reflecting member 10 is constituted of a metal which does not give ill effect to the deposited film to be formed during the film formation and has preferably open cell structure or open network structure having about 1mm-3.58cm diameter of the spaces. Gaseous raw materials are released in this state from an annular gas releasing pipe 8 into a plasma inducing chamber 7 and microwaves 4 are projected from an introducing window 2. The microwaves 4 are effectively reflected by the member 10 and only the gases are smoothly discharged. The film forming chamber 7 acts as a microwave resonator and the desired deposited film is stationarily and stably formed on the substrate 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a film deposited on a substrate, particularly a functional film, particularly a semiconductor device, a photoreceptor device for electrophotography, a line sensor for image input, and an imaging device. The present invention relates to a method and apparatus for forming functional deposited films such as amorphous semiconductor films used in chairs, photovoltaic devices, etc.

[Description of prior art]

Conventionally, element members used in semiconductor devices, photoreceptor devices for electrophotography, line sensors for image input, imaging devices, photovoltaic devices, and other various electronic devices, optical devices, etc., have been made of amorphous silicon, such as hydrogen atoms or A deposited film of an amorphous semiconductor such as amorphous silicon (hereinafter referred to as "a-3i (H, Some of them are put into practical use.

Then, such a deposited film is deposited using a plasma CVD method, that is,
It is known that it is formed by a method in which a raw material gas is decomposed by direct current, high frequency, or microwave glow discharge, and a thin film is formed on a substrate such as glass, quartz, heat-resistant synthetic resin film, stainless steel, or aluminum. Various devices have been proposed for this purpose.

By the way, the plasma CVD method (hereinafter referred to as rMW-PCVD method) using microwave glow discharge decomposition has recently been introduced.
has been attracting attention at the industrial level, and the M W −
The apparatus for forming a deposited film by the PCVD method is as follows:
A typical device configuration is shown in the schematic cross-sectional view of FIG.

In FIG. 3, 1 is a vacuum container, 2 is a microwave introduction window (made of quartz, alumina, ceramics, etc.), 3 is a microwave waveguide, 4 is a microwave from a microwave power source (not shown), and 5 is an exhaust device (not shown) 6 is a substrate, 7 is a vacuum chamber, 8 is a raw material gas supply pipe that communicates with a raw material gas supply source (not shown), and 9 is a built-in heater 9' for heating the base. The respective substrate holders are shown.

The deposited film is formed using this apparatus in the following manner. That is, the inside of the vacuum container 1 is
The substrate 6 is evacuated to a degree of vacuum of 10-5 torr, and the substrate 6 is heated and maintained at 250° C. with a heater 9. Next, in the case of forming, for example, an amorphous silicon deposited film, a silane gas (for example, 5IF4 gas) is supplied at a flow rate of 5 through a raw material gas supply means (not shown).
00sec, hydrogen gas (H2 gas) flow rate 200sec
cm of mixed raw material gas is discharged into the vicinity of the base 6 in the vacuum container 1 through the ring-shaped raw material gas discharge ring 8 having a plurality of gas discharge holes inside while maintaining a vacuum degree of I x 10-2 torr. do.

Next, from a microwave power source (not shown), for example, a frequency 2
．． A microwave 4 of 45GH2 is introduced into the vacuum chamber 7 via the microwave waveguide 3 and the microwave introduction window 2 having a microwave resonant structure.

Plasma is thus generated in the vacuum chamber 7, causing chemical interaction and forming a deposited film on the surface of the substrate 6.

By the way, since the plasma generated in the vacuum chamber 7 is an ionized body consisting of electrons and ion particles, it acts as an electrical conductor of -species. In particular, the frequency 2.45GHz
When the plasma is excited by microwave power of
Ion particles that can move to follow these high-frequency vibrations are limited to those with low mass, such as electrons. Therefore, when considering the density of the generated plasma, it is sufficient to focus on the electron density. However, the plasma generated under the conditions of vacuum degree of 2 x 10-2 torr and microwave power of 200 W has an electron temperature of Te = 4 electron volts (hereinafter referred to as eV).
), and the electron density is ne = l Q”m
-3 low pressure discharge plasma, 2.45GHz
The microwaves are reflected at the plasma interface at a distance of several tens of micrometers from the introduction window and cannot enter the plasma, and the plasma density rapidly attenuates as the distance from the introduction window increases.

Therefore, if a desired amorphous silicon deposited film is to be formed on a large-area substrate using microwave plasma using the conventional apparatus described above, it is necessary to use a large-diameter microwave introduction window. When installing such a large-diameter microwave introduction window in the equipment,
The scale of the device is unavoidably small, and since the microwave introduction window also serves as one wall of the vacuum vessel 1, there is a separate problem regarding the strength of the device, and special consideration must be taken in the device design. In addition, when the volume of the vacuum chamber 7 becomes too large, the utilization efficiency of the raw material gas decreases. Make it into something.

The above is about the case where the base is flat, but from the viewpoint of making the base cylindrical and increasing its area, the device was designed as shown in Figure 2 using the device principle shown in Figure 3. When a desired deposited film is formed on the surface of a large-area cylindrical substrate, there are various problems as described below.

In Fig. 2, 1 is a cylindrical vacuum container, 2 is a circular microwave introduction window (made of quartz, alumina, ceramics, etc.),
3 is a microwave waveguide, 4 is a microwave from a microwave power source (not shown), 5 is an exhaust pipe that communicates with an exhaust device (not shown) via an exhaust pulp (not shown), and 6 is installed on the substrate holding cylinder 9 7 is a vacuum chamber; 8 is a raw material gas release ring communicating with a raw material gas supply source (not shown);
Reference numeral 9 indicates a substrate holding cylinder containing a substrate heating heater 9'.

The formation of a deposited film on the cylindrical substrate 6 using the apparatus shown in FIG. 2 is performed in the same manner as in the case of the apparatus shown in FIG. 3 described above.

By the way, when forming a deposited film using the apparatus shown in FIG.
When setting it to 2 Torr, 8 X 10-3 Torr K
The state of deposited film formation in the case of 5 X 10-3 Torr K is
Observation from the viewpoint of the sl:H:X film deposition rate distribution is as follows.

That is, the graph shown in FIG. 4 represents the film deposition rate distribution when microwave power is input from the top of a cylindrical substrate having a length of 400++ on.

In the graph of Fig. 4, the solid line a is 2X10-”To
This is the film deposition rate distribution for a-8i:H:X film deposition at a vacuum degree of rr, and the dashed line 6 is 8X10-3'I'
It is a film deposition rate distribution in the case of film deposition of a-8i:H:X at a vacuum degree of orr.

From the graph of FIG. 4, it can be seen that the film forming area is larger in curve A than in curve a. From this, one would think that as the degree of vacuum increases, the mean free path of the active species that contribute to film formation will lengthen, thereby expanding the film formation area, but this is not actually the case.

That is, the vacuum degree (internal pressure) of the vacuum chamber 7 is set to 5X10-3 Torr.
If the film formation operation is performed in the same manner as described above with the temperature r, an intermittent discharge trap will occur and stable film formation will not be possible.

Further, when observing the dark conductivity σd (Ω-'cm-') and the bright/dark conductivity ratio (S/N ratio), it is as follows.

That is, the distribution of the dark conductivity σd(Ω-'crn'') in the substrate axis direction for the a-8i:H:X deposited film shown in the graph of FIG. 4 is as shown in the graph of FIG. In addition, the distribution of the bright/dark conductivity ratio of these deposited films in the direction of the substrate axis is 6th.
As shown in the graph in the figure. In addition, in the graphs of FIGS. 5 and 6, the solid line a is 2 X 10-2 Torr
This is for a deposited film of a-Si:H:X at a vacuum level of 8 x 1O-3.
This is for a deposited film of a-Si:H:X at a vacuum degree of Torr.

Judging from the graph in Figure 6, it can be said that a film with a good S/N ratio can be obtained in the region where the film deposition rate is slow, but in short, the characteristic distribution is about one digit in terms of dark conductivity in the direction of the substrate axis. It makes a difference.

Therefore, it is understood that it is extremely difficult to regularly and stably form a desired deposited film on a large-area cylindrical substrate using an apparatus of the type shown in FIG.

[Purpose of the invention]

It is an object of the present invention to overcome the above-mentioned problems in devices of the above-mentioned type, and to improve the production of amorphous silicon (a-3i) semiconductor films, especially large-area semiconductor devices, photovoltaic devices, electrophotographic photoreceptor devices, etc. It is an object of the present invention to provide a method and apparatus for stably forming functional deposited films as element members used in various electronic elements, optical elements, etc., by MW-PCVD.

[Structure of the invention]

The present invention was developed by the inventor of the present invention, who has conducted extensive research in order to solve various problems in the above-mentioned type of apparatus and achieve the above-mentioned object of the present invention. As a result of my efforts, I was able to complete it.

The inventor first developed a low-pressure discharge plasma (electron density ne=1015 to 1017rr?) excited by microwaves.
), we determined that the shape of the plasma generation chamber (vacuum chamber) must have a structure that acts as a microwave resonator.

In other words, in the case of a device having a structure having a central conductor (cylindrical base) as shown in FIG. It is necessary to have the structure of

Based on this knowledge, we investigated the type of equipment shown in Figure 2 above and found that the reason why the microwave plasma becomes unstable in the high vacuum atmosphere in this equipment is that the plasma generation chamber (vacuum chamber) However, it has been found that because the plasma does not have a coaxial or semi-coaxial resonator structure, the plasma generation region changes depending on the degree of vacuum and deviates from the desired resonance conditions.

That is, if a space other than the space forming the coaxial resonator structure, such as an exhaust port, has an opening through which microwaves can enter, the space also acts as a part of the microwave resonator,
In particular, if there is an exhaust port or the like in the microwave propagation path in a high vacuum atmosphere, the resonance conditions will deviate.

Incidentally, the design of the above-mentioned apparatus is as follows: - Generally speaking, the microwave introduction window of the coaxial plasma generation chamber (vacuum chamber) is set to the TE11 mode, and the vacuum chamber is constructed in accordance with the well-known coaxial resonator theory. It has a shape with a frequency of 2.
When a microwave of 45GH2 is injected and the opening diameter of the exhaust pipe is set to be 3.58cn1 or more, the microwave also enters the exhaust port and acts as part of the resonator, causing the above-mentioned problem. However, in order to avoid this problem, the equipment must be designed separately.

However, it is practically difficult to set resonance conditions in consideration of such a plurality of structures.

Under these circumstances, the present inventor focused on the case where the base body is made into a cylindrical shape, and developed the apparatus shown in FIG. A large number of through holes (1ran~3.
58 cm) metal plate (punching metal)
In addition, one metal mesh screen plate to a mesh size of 3.58 crn was installed so as to apparently cover the opening, and the apparatus was operated to try to form a film on the surface of the cylindrical substrate. It has been found that the problem has been solved and a desired deposited film can be formed uniformly over the entire surface of the substrate even if the substrate has a large area.

The present invention has been completed based on the knowledge obtained and the confirmed facts, and the functional deposited film forming apparatus of the present invention has a substrate holding means inside, a source gas supply means and an exhaust means An apparatus for forming a functional deposited film by the MW-PCVD method, in which a wall of the film forming chamber is constituted by a microwave transmitting window that allows microwaves from a microwave power source to pass through from one direction. The opening of the exhaust means to the front membrane chamber is formed of a material that can effectively reflect microwaves, and is apparently closed with a gap structure member that allows smooth gas discharge and blocks leakage of the microwaves. It is characterized by the fact that

The apparatus for forming a functional deposited film by the MW-PCVD method of the present invention having the above-mentioned configuration is typically of the type shown in FIG.

However, this is merely an example, and the present invention is not limited to this device example in any way.

The content of the present invention will be explained in more detail below using the example of the apparatus shown in FIG. 1 above. In FIG. 1, parts common to the previous figures are indicated by the same symbols.

The deposited film forming apparatus using the MW-plasma CVD method of the present invention is fundamentally different from the apparatus shown in FIG. 2 in that the film forming chamber 7 is made to act as a microwave resonator.

That is, the apparatus of the present invention, represented by the example of the apparatus shown in FIG. is set up. The microwave reflecting member having the gap structure must function to effectively reflect microwaves, allow smooth discharge of gas, and block microwave leakage. It is also necessary that the microwave reflecting member having the gap structure be made of a metal that does not generate ions, particles, etc. that would adversely affect the deposited film formed by the action of microwaves during film formation. For this reason, the gap structure of the microwave reflecting member with the gap structure can be a continuous perforation structure, a continuous network structure, or in some cases a continuous lattice structure. desirable.

In the case of a perforated structure, their size can be arbitrarily selected within the range of diameter 1++aw to 3.58α, but a diameter of approximately ICrn is preferable.

The same is true for mesh structures, and the mesh size is
It can be arbitrarily selected within the range of 1st period to 3.58 crn, but is preferably about 1 crn. Preferred examples of the constituent metal materials include aluminum, stainless steel (SUS), pure copper, and nickel-plated iron.

The above description is for the case where the base is cylindrical, but the present invention is of course effective also when the device structure shown in FIG. 3 is used to make a large flat base. Even in such cases, a desired functional deposited film can be formed by attaching the above-mentioned gap structure member to the exhaust port.

〔Example〕

Hereinafter, the formation of a desired functional deposited film by operating the apparatus for forming a functional deposited film by the MW-plasma CVD method of the present invention will be explained with reference to Examples. There are no restrictions whatsoever.

Example 1 (Formation of functional deposited film) In the apparatus shown in FIG. 1, the silane gas (SiF4) flow rate was 5.
00sccm, hydrogen gas (H2) flow rate 200secm
The mixed raw material gas was discharged into the plasma generation chamber 7 from a ring-shaped gas discharge pipe 8 provided near the MW introduction window. The structure of the plasma generation chamber (vacuum chamber 7) is 20cm in diameter! n,
An aluminum cylinder of 8α (diameter) x 42.5 crn (length) was placed in the center of a cylindrical metal chamber/bar with a length of 43 crn (as a base).

The exhaust pipe 5 is located at the reflecting end face facing the microwave introduction window 2, and the metal microwave reflecting plate 10 is provided at the opening of the exhaust pipe 5.
was installed.

In this device, the substrate surface temperature is 250°C and the degree of vacuum is 5X.
At 10-3 torr and 2 x 10-” torr,
800 W of microwave power with a frequency of 2.45 GH2 was input. The plasma was self-excited by the smell, and the discharge was carried out for one hour to examine the discharge stability, but the discharge was extremely stable compared to the case of the apparatus shown in FIG.

A film composed of a-3i:H:F was deposited under the above conditions, and the resulting film was deposited on the surface of the cylindrical substrate.
The film thickness distribution in the axial direction of the substrate, dark conductivity, and bright/dark conductivity ratio (SIN ratio) were measured. Each measurement value is shown in Figures 7 and 8.
9 and 9.

As is clear from FIG. 7, compared with the deposition rate distribution (curve b in FIG. 4) when a-8i film was deposited at a vacuum of 8 x 10-3 torr using the apparatus shown in FIG. As a result, the film formation area has expanded significantly.

Also, compared to the 5 X 10-3 torr curve a, the 2
When the A-8i film was deposited at a vacuum level of 1O-3 torr curve, the film formation area was further expanded and a nearly uniform deposition rate distribution could be obtained up to a distance of 25 crn from the microwave transmission window. . In addition, the dark conductivity (Fig. 8, curves a, b) and the bright/dark conductivity ratio (Fig. 9, curves a, b)
), the uniform area has also expanded.

Example 2 (Preparation of photoreceptor drum) The apparatus shown in FIG. 1 was constructed in the same manner as in Example 1, and an aluminum cylinder similar to that used in Example IK was used as the cylindrical base 6. The film forming conditions were as shown in Table A below, and the apparatus was operated in the same manner as in Example 1. It was created.

When the photoreceptor drum created as described above was attached to a modified Canon copier NP7550 and an image was produced, no image unevenness was observed even when the process speed was increased to output 100 sheets of A4 size paper per minute. Good images were obtained without image memory.

In addition, when we tested the durability by adding abrasive to the toner as an accelerated test under these conditions, we found that even after printing 1 million sheets of A4 size paper, changes in the thickness of the surface layer due to wear were observed, but image unevenness and No memory problems were observed.

[Summary of effects of the invention]

According to the present invention, in order to make the film-forming chamber act as a microwave resonator, the microwaves input into the space such as the exhaust port related to the film-forming chamber are blocked so as not to obstruct the passage of gas. , the resonance conditions of the film forming chamber do not fluctuate due to internal pressure, making it possible to stably generate low ionization plasma in the film forming chamber maintained at high vacuum, thereby making it possible to generate stable low ionization plasma on the entire surface of a large substrate. A functional deposited film that is homogeneous, has a uniform thickness, and exhibits excellent desired properties can be efficiently formed without reducing the film deposition rate.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view of an apparatus using the MW-plasma CvD method of the present invention. FIG. 7 shows the film deposition rate distribution in the apparatus of the present invention, FIG. 8 shows the dark conductivity distribution of the deposited film formed by the apparatus of the present invention, and FIG. 9 shows the bright conductivity distribution of the deposited film. /Dark conductivity ratio distribution. FIG. 3 is a schematic cross-sectional view of a conventional MW-PCVD apparatus for flat substrates.
The figure is a schematic cross-sectional view of a deposition apparatus adapted for use on cylindrical substrates. FIG. 4 shows the deposition rate distribution in the apparatus, and FIGS. 5 and 6 respectively show the dark conductivity distribution and bright/dark conductivity ratio distribution of the deposited film formed by the apparatus. In the figure, 1...vacuum container, 2...microwave introduction window, 3...
・Waveguide, 4...Microwave, 5...Exhaust port, 6.
...Substrate, 7... Film formation chamber (plasma generation chamber), 8...
- Raw material gas release ring, 9... heater for heating the substrate,
10... Gap structure member (microwave shielding member).

Claims (2)

[Claims] (1) When forming a functional deposited film on a substrate surface by the microwave plasma CVD method, the film forming chamber into which microwaves are injected from one direction acts as a microwave resonator. Microwave plasma C characterized in that the space such as the exhaust port is designed so as not to obstruct the passage of gas and to block microwaves input therein.
A method for forming a functional deposited film using the VD method. (2) The wall of the film forming chamber is composed of a microwave transmission window which has a substrate holding means inside, is equipped with a raw material gas supply means and an exhaust means, and allows transmission of microwaves from a microwave power source from one direction. In the apparatus for forming a functional deposited film by a microwave plasma CVD method, at least an opening of the exhaust means to the film forming chamber is formed of a material that can effectively reflect microwaves, and the gas can flow smoothly. A microwave plasma CV characterized in that it is apparently closed by a gap structure member that allows discharge and blocks leakage of the microwave.
A device for forming a functional deposited film using the D method.