JPS6115978A - Plasma cvd device - Google Patents

Abstract

PURPOSE:To provide a plasma CVD device constituted in such a manner that a gaseous raw material can be smoothly supplied without generating abnormality in discharge by specifying the inside diameter of many gas supply holes formed to an electrode. CONSTITUTION:The electrode forming a gas chamber and a substrate to be formed with a film thereon are disposed apart from each other at a prescribed space. The gaseous raw material is released from the many gas supply holes formed to the electrode toward the substrate so that the film is formed on the substrate by plasma discharge. The inside diameter of the gas supply holes 16 provided to the electrode 13 is restricted to <=2mm.. The holes 16 are preferably made into the shape formed by rounding the edge on the substrate side (c), and increasing the depth of the hole (d) or chamfering the edge on the substrate side (e). The abnormal discharge at the holes 16 is eliminated by such device, by which the uniformily of the film is improved.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a plasma CV method for forming a film on a cylindrical substrate.
Regarding D device.

(Prior Art) Plasma CVD technology is a film forming technology characterized by being able to grow thin films at relatively low temperatures. In plasma CVD technology, for example, by placing a reactive gas in a discharge plasma state using high-frequency discharge, the chemical bonds of the reactive gas are decomposed at low temperatures to create activated particles, and the interaction between these activated particles is The reaction results in the formation of a CVD film.

The properties of plasma CVDIE are influenced by a number of factors. These factors include production temperature, production gas ratio, production pressure,
Electrode structure, reaction vessel structure, pumping speed, generated RF power,
There are RF frequencies, plasma generation methods, etc. therefore,
In order to form a plasma CVD film, many factors must be controlled.

Plasma CVD technology is used to form films of various substances, and can also form films of amorphous silicon (aSi), for example. a-3i is also suitable as an electrophotographic photoreceptor. When used as a photoreceptor for electrophotography,
The a-8i film is a relatively thick (
20 to 50 μm) and must be formed uniformly.

FIG. 4 schematically shows an example of a conventional plasma CVD apparatus for A-8I. Substrate 1 consisting of an aluminum cylinder
is provided inside 14 of the cylindrical electrode 2 so as to be rotatable around its axis. The electrode 2 consists of two cylindrical plates 2a and 2b that share the same axis as the base 1, and is connected to the gas chamber 3.
is divided by these two cylindrical plates 2a and 2b. The outer cylindrical plate 2a is provided with an inlet 4 for introducing raw material gas from a gas supply device (not shown), while the inner cylindrical plate 2b is provided with an internal space (discharge area) of the cylindrical plate 2b. A large number of small gas supply holes (not shown) are provided for introducing raw material gas into the chamber. The base 1 and the electrode 2 are placed in a chamber 5. The gas introduced into the chamber 5 through the gas supply hole is exhausted by the vacuum pump 7 through the lower part of the chamber 5 or the exhaust port 6. R
The F power source 8 is connected to the electrode 2 via the inlet 4, while the base 1 is grounded. Although not shown, the heaters are attached to the base 1 and the electrode 2, respectively, and connected to a heater power source.

FIG. 5 schematically shows another example of the conventional plasma CVD apparatus for A-8I. The first difference from the device shown in FIG. 4 is that the electrode 2 is now part of the chamber 5. The chamber 5 consists of an upper part 5a and a lower part 5b of the electrode 2, and the lower part 5b is insulated from the electrode 2. The second difference is that the upper side wall of the electrode 2 is disk-shaped, and a large number of small gas supply holes are uniformly provided in the portion facing the discharge area. The third difference is that the upper part 5a of the chamber and the side wall 2c define one chamber 3a, and the introduction port 4 is attached to the upper part 5a. The raw material gas is first supplied to the gas chamber 3a as shown by the arrow in FIG.
and then flows, partly directly and partly indirectly via the gas chamber 3, into the discharge region.

FIG. 6 shows another example of the conventional plasma CVD apparatus for A-8I. Substrate 1, 1 consisting of four aluminum cylinders
．． ... are arranged in a row with their axes parallel so that they can rotate around the axis.

This -row of substrates, 1,1. . . . Flat electrodes 2.2 are arranged on both sides. This electrode 2 has an outer wall 2a and an inner wall 2.
b, and a gas chamber 3 is defined between the outer wall 2a and the inner wall 2b. The outer wall 2a is provided with an inlet 4 for introducing gas from the outside, while the inner wall 2b is provided with an inlet 4 for supplying source gas to the space (discharge area) between the inner wall 2b and the base 1. A number of small gas supply holes (not shown) are provided. In the figure, arrows indicate the supply of gas through this source gas. Substrate 1, 1. ...and electric fii2.
2 is installed inside the chamber 5. The gas introduced into the discharge region through the gas supply hole is exhausted from an exhaust port 6 provided in the chamber 5 by a vacuum pump 7 (not shown) and maintained at a predetermined pressure. The RF power source 8 is connected to the electrode 2 via the inlets 4, 4, while the base 1,
1. ... is grounded. Although not shown, the heaters are connected to the bases 1, 1 . ... and the electrodes 2, 2.

Film formation of a-3i by plasma CVD is performed as follows. According to Paschen's law, the self-sustaining discharge starting voltage changes depending on the product pd of the distance d between the electrode 2 and the substrate 1 and the gas pressure p. Conventionally, this gap d was determined when the gas pressure was I.
In the vicinity of Torr, the voltage is selected within the range of 30 to 50III111, where the self-sustaining discharge starting voltage is almost minimum.
Usually, about 40 mm is selected. In this area,
It has the advantage that it is easy to obtain stability of discharge and uniform supply of gas to the substrate. A raw material gas such as silane is introduced from the gas chamber 3 into the open space between the electrode 2 and the base 1, as shown by the fourth arrow, through a number of gas supply holes provided in the cylindrical plate 2b. . The pressure within the chamber is maintained at 0.1 to several Torr. The substrate 1 is rotated at 10 to 30 rpm to maintain uniformity of film formation.

The temperature of the base body 1 is heated to 150 to 300°C.

When an RF lightning voltage is applied across the gap between the electrode 2 and the electrode (substrate) 1, a glow discharge occurs, the source gas is decomposed, and an a-8i film is formed on the substrate 1.

(Problems to be Solved by the Invention) As a means for obtaining a plasma CVD film with a uniform film thickness, as in the plasma CVD apparatus shown in FIGS. 4 to 6, a large number of small diameter gas The best method is to blow the raw material gas from the supply hole onto the substrate.

When it is necessary to increase the film formation rate, the amount of raw material gas supplied must be increased. Therefore, it is necessary to increase the diameter or number of gas supply holes.

When the diameter of the gas supply hole is increased, the discharge becomes disordered around the hole. For this reason, peeling of the film and fine powder ((SiH2
). ) is generated and incorporated during film formation on the substrate, deteriorating the film quality. As a result, this becomes one of the causes of drum noise (abnormal points such as pinholes that appear as white spots) in electrophotography. Furthermore, if the flow rate of the source gas from the gas supply hole is high, turbulence will occur, which will have undesirable effects such as kicking up dust within the chamber. Therefore, it is preferable to set the diameter of the gas supply hole to a size that does not disturb the discharge, set the number of gas supply holes to such an extent that the pressure inside the gas chamber is slightly higher than the pressure inside the chamber, and make the flow rate of the source gas gentle. it is conceivable that.

In the plasma CVD apparatus disclosed in Japanese Unexamined Patent Publication No. 59-38377, the diameter distribution of the gas supply hole can be adjusted by threading the gas supply hole for the purpose of adjusting the film thickness. That is, the gas supply hole can be closed with a screw, and the gas supply hole can be closed mainly with a screw opening in the axial direction, thereby making it possible to reduce the hole diameter. By the way, in this conventional example, the supply of raw material gas is adjusted for the purpose of adjusting the film thickness.

An object of the present invention is to provide a plasma CVD apparatus equipped with a gas supply hole that does not cause abnormal discharge and can smoothly supply raw material gas.

(Means for Solving the Problems) Present Invention 1 This plasma CVD apparatus has a vacuum chamber in which source gas is supplied, but electrodes forming a gas chamber and a substrate on which a film is to be formed are arranged in a predetermined position. In a plasma CVD apparatus that forms a film on a substrate by plasma discharge while emitting raw material gas toward the substrate from a large number of gas supply holes formed in the electrode, the above gas supply method is used. It is characterized in that the inner diameter of the hole is 2 mm or less.

(Function) By setting the inner diameter of the gas supply hole to 2111 [11 or less], abnormalities in plasma discharge near the gas supply hole are eliminated. Therefore, the uniformity of film formation is improved. Further, peeling of the film and generation of fine powder near the gas supply hole are eliminated, and deterioration of film quality caused by these being taken into the film formation is prevented.

(Example) Using the apparatus shown in FIG. 2, the relationship between discharge conditions and the hole diameter of the gas supply hole was investigated. In this device, an electrode 13 provided with a gas chamber 12 and a base 14 are placed facing each other in a chamber 11 . The electrode 13 has an inlet 1 for introducing raw material gas.
5 is provided, and a large number of gas supply holes 16, 16, etc. are opened on the side facing the base 14. An exhaust port 17 is provided in the chamber 11. Now, connect the base 14 to the heater 1.
heating indirectly via the substrate holder 20 containing 9;
Source gas is supplied to gas supply hole 3.6-. 16. When a high-frequency electric field is applied, a plasma discharge is generated in the discharge region shown by stippled lines between the electrode 13 and the base 14, and the base 1
An a-8i film is deposited on 4.

The occurrence of a discharge abnormality in plasma CVD can be detected by abnormal lighting of the gas supply hole. The present inventors investigated various relationships between discharge conditions and the dimensions of the gas supply hole, and found that the degree of abnormality that occurs varies depending on the discharge conditions even with the same gas supply hole.Also, even under the same discharge conditions, the shape of the gas supply hole It was found that there were differences depending on the size and dimensions.

First, the relationship between discharge conditions and the hole diameter of the gas supply hole will be explained. In plasma discharge, in the discharge region, ion sheaths 21 and 21 are provided near the electrode 13 and the base 14, respectively, and bright portions 22 and 22 are provided in contact therewith.
occurs. (The ion sheath is darker than the bright area, so it is also called a dark space.) When the width of the ion sheath 21 is di and the inner diameter of the gas supply hole 16 is φ, the abnormal light emission is φ, as described next. It was found that this phenomenon occurs after >2di.

Figures 1 (a), (b), and (c) show the changes in the discharge state near the gas supply hole 16 when the inner diameter φ is changed, respectively, for φ~cli and φ~2di. If φ>2
The discharge state in the case of di is schematically shown. Inner diameter φ is electrode 2
When the width di of the side ion sheath 21 is exceeded, the shape of the ion sheath 21 begins to change. Furthermore, the inner diameter φ is 2di
If it becomes larger, the bright part 22 will enter into the gas supply hole 16, and the vicinity of the gas supply hole 16 will become abnormally bright.

The width di of the ion sheath 21 on the electrode 2 side is 0.5 m when the RF frequency is 13.56 MHz and the RF power is 0.1 W/am2. Approximately '1 mm, 2, O at ITorr
Torr is approximately 1.5 mm. Film formation is usually 0.5
．． -1.5'rprr, so if the inner diameter φ of the gas supply hole 16 is set to 2.0cm or less, abnormal light emission will not occur.

By the way, if there is a protrusion on the edge of the gas supply hole 16, even if the above relationship φ<2di is satisfied, the electric field will become stronger at the protrusion and abnormal light emission will occur. Therefore, we studied the relationship between discharge and the shape of the gas supply hole 16. Figure 3 (,)~
Five types of gas supply holes 16 shown in (e) were machined.

In these figures, the base 14 is placed on the right side of the electrode 13. 3(a) shows a case where there is a protrusion on the edge on the base 14 side, FIG. 3(b) shows a case where a circular opening is provided, and FIG. 3(c) shows a case where the edge on the base 14 side has a radius. If you add
In FIG. 3(d), R is also added to the green on the base 14 side.
In addition, when the depth of the hole is increased, FIG. 3(e) shows a case where the edge on the base body 14 side is chamfered.

The evaluation of the properties during plasma discharge for each shape is shown by the symbols at the bottom of each figure in FIGS. 3(,) to (e).

◎ means good, ○ means good, and X means bad.

The gas supply holes 16 having the shapes shown in FIGS. 3(c) to 3(e), that is, the gas supply holes 16 whose edges facing the base body 14 are rounded or chamfered, are effective in suppressing discharge abnormalities. It turned out to be true. This is thought to be because there are no sharp edges on the edge of the hole opening on the base 14 side, so the distortion of the lines of electric force is reduced.

In addition, the gas supply holes 16 having the shapes shown in (c) to (, e) blow out the raw material gas more slowly than those shown in (,) and (b), and the peeling of the film around the holes due to stress is reduced. Therefore, better film formation can be obtained.

In the plasma CVD apparatus shown in FIGS. 4 to 6, the hole diameter of the gas supply hole 16 is 2 mm, and FIGS.
It was processed into the shape shown in (e). The properties of the resulting film were good.

(Effect of the invention) The homogeneity of the film was improved by eliminating abnormal discharge at the gas supply hole. That is, (1) film formation properties around the gas supply holes were improved, and deterioration in film quality caused by peeling of the film on the electrodes was eliminated. (2) The generation of fine powder in the abnormal discharge area was eliminated, and the deterioration of film quality caused by this was eliminated. (3) The discharge was stable and uniform, and the reproducibility of the film formation properties was improved.

As a result of improved film formation properties, noise in electrophotography was reduced.

[Brief explanation of drawings]

Figures 1 (a), (b), and (c) show φ to d, respectively.
i. FIG. 2 is a cross-sectional explanatory diagram schematically showing the state of discharge in the vicinity of the gas supply type when φ~2di and φ>2di. FIG. 2 is a schematic cross-sectional view of the plasma CVD apparatus. FIGS. 3(a) to 3(e) are cross-sectional explanatory views showing the shapes of the gas supply holes, respectively. 4 to 6 are schematic cross-sectional explanatory views of conventional plasma CVD apparatuses, respectively. 1... Base body, 2... Electrode, 3, 3a...
Gas chamber, 4...Inlet, 5...Chamber, 6.
··exhaust port,? ...Vacuum pump, ...RF main power supply 11...Chamber, 1
2... Gas chamber, 13... Electrode, 14... Substrate, 15... Inlet, 16... Gas supply hole,
17...Exhaust port, 18...RF main power supply
19...Heater, 21.21...Ion sheath, 22.22...Bright area. Patent applicant Minolta Camera Co., Ltd. Representative
People Patent Attorneys Aobai Ao and 2 others 1st rlA 2nd rIA Figure 3 (q) (b) (c) (d)
(・)Fourth cause

Claims (1)

[Claims] (1) In a vacuum chamber, an electrode forming a gas chamber to which raw material gas is supplied and a substrate on which a film is to be formed are arranged at a predetermined interval, and a large number of gas supply holes are formed in the electrode. A plasma CVD apparatus for forming a film on a substrate by plasma discharge while discharging source gas toward the substrate, characterized in that the inner diameter of the gas supply hole is 2 mm or less.