Apparatus and method for production of electronic devices

Abstract: An apparatus for production of electronic devices includes a vacuum vessel having first and second pairs of opposed electrodes provided therein; a gas inlet for introducing a material gas into the vacuum vessel; and first and second power sources for applying first and second high frequency voltages between the first pair of electrodes and between the second pair of electrodes, respectively, to cause plasma discharge, the first and second high frequency voltages being modulated in accordance with first and second pulse waves, respectively; wherein ON periods of the first and second pulse waves are controlled so as not to coincide with each other.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for production of electronic devices and, more particularly, to an apparatus and a method for production of electronic devices, which are suitable, in the electronic industry, for a plasma excited chemical vapor deposition apparatus (hereinafter referred to as "plasma CVD apparatus") for forming a semiconductor film or an insulating film such as of hydrogenated amorphous silicon (hereinafter referred to as "a-Si:H"), or for a plasma etching device for processing a semiconductor device or a liquid crystal device. 2. Description of the Related Art Plasma CVD apparatuses for deposition of a thin film in a gaseous atmosphere produced by plasma excitation and decomposition of a material gas and plasma etching apparatuses for processing a semiconductor device or a liquid crystal display device are widely used for production of electronic devices which involves processing of a metal film, a semiconductor film and/or a dielectric film, or a crystalline wafer. In order to achieve a higher through-put (productivity) in these production apparatuses, it is particularly important to process a multiplicity of substrates at a time. To this end, the size of a reaction chamber, the sizes of cathode and anode electrodes and the numbers of the cathode and anode electrodes are increased. It is also important to increase the processing speeds of the apparatuses for a higher through-put. One known approach to the increase of the processing speed for film deposition is to employ a high-speed and high-quality a-Si:H film deposition technique by a short-pulse VHF plasma CVD method (see, for example, Japanese Unexamined Patent Publication No. Hei 7(1995)-166358). The processing speed of a plasma CVD apparatus may be increased by increasing an electric power, a frequency or the like for the plasma discharge. If the processing speed exceeds a certain level, however, abnormal discharge phenomena such as production of particles (powder) and occurrence of discharge in an unintended space (other than a space where a substrate to be processed is placed) are liable to take place, making it impossible to carry out a desired process. It has been known that pulse-modulated discharge is effective for suppression of the production of the particles (Y.Watanabe, et al., Appl. Phys. Lett., 57. 1616 (1990)). The level of the electric power at which the abnormal discharge starts occurring depends upon the discharge frequency, the size of electrodes and the like which are employed for the discharge. For a higher through-put, it is necessary to process a multiplicity of substrates at a time, i.e., to increase the number of electrodes. Where a high frequency power is applied to a plurality of electrodes placed in a single space (in a vacuum vessel), however, plasma interference occurs, so that the abnormal discharge phenomena are liable to occur. This results in a reduction in processing speed per electrode as compared with a case where a single electrode is employed. SUMMARY OF THE INVENTION In view of the foregoing, the present invention is directed to providing a production apparatus and a production method, which prevent the reduction in processing speed per-electrode when a plurality of electrodes are employed for processing a plurality of substrates, thereby drastically improving the mass-productivity of electronic devices such as solar batteries and liquid crystal display devices which utilize a-Si:H thin films in the electronic industry. In accordance with one aspect of the present invention, there is provided an apparatus for production of electronic devices, which comprises: a vacuum vessel having first and second pairs of opposed electrodes provided therein; a gas inlet for introducing a material gas into the vacuum vessel; and first and second power sources for applying first and second high frequency voltages between the first pair of electrodes and between the second pair of electrodes, respectively, to cause plasma discharge, the first and second high frequency voltages being modulated in accordance with first and second pulse waves, respectively; wherein ON periods of the first and second pulse waves are controlled so as not to coincide with each other. In accordance with another aspect of the present invention, there is provided a method for production of electronic devices, which comprises the steps of: placing components to be processed between a first pair of opposed electrodes and between a second pair of opposed electrodes in a vacuum vessel; introducing a material gas into the vacuum vessel; and applying first and second high frequency voltages between the first pair of electrodes and between the second pair of electrodes, respectively, to cause plasma discharge, the first and second high frequency voltages being modulated in accordance with first and second pulse waves, respectively; wherein ON periods of the first and second pulse waves are controlled so as not to coincide with each other. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram illustrating the construction of an electronic device production apparatus which is applied to a plasma CVD apparatus in accordance with an embodiment of the present invention; and Fig. 2 is a timing chart showing modulating pulse waveforms in accordance with the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION In the present invention, the expression "first and second pairs of opposed electrodes" means at least two pairs of opposed electrodes, so that three or more pairs of opposed electrodes may be employed. The opposed electrodes are, for example, electrode plates opposed to each other in a parallel relation. A component, such as a wafer, to be processed is placed on one of the opposed electrodes in each pair. The one electrode on which the component is to be placed is generally referred to as a cathode electrode, which is grounded. The other electrode is referred to as an anode electrode. In the present invention, the vacuum vessel is designed so that the material gas introduced therein can be maintained at a pressure level of about 10 -1 torr to about 1 torr. Where the inventive apparatus is employed as a plasma CVD apparatus for formation of a-Si:H films, SiH 4 , Si 2 H 6 , a gas mixture containing SiH 4 or Si 2 H 6 and any of CH 4 , C 2 H 6 , PH 3 , B 2 H 6 and GeH 4 , or a gas mixture containing any of H 2 , He, Ar, Xe and Kr diluted with SiH 4 or Si 2 H 6 , for example, is used as the material gas. For formation of an Si oxide film, an SiH 4 -N 2 O gas, for example, is used as the material gas. Where the inventive apparatus is employed as a plasma etching apparatus, CF 4 , CF 3 , Cl, CF 2 , Cl 2 , CFCl 3 , CF 3 BR or CCl 4 is used as a reaction gas for processing of an Si-based component, and CF 4 , C 2 F 6 , C 3 F 8 or CHF 3 is used as a reaction gas for processing of an SiO 2 -based component. In the present invention, the gas inlet is adapted to supply the gas into the vacuum vessel, for example, from a gas cylinder. The first and second power sources are adapted to output pulse-modulated high frequency voltages to cause plasma discharge between the first pair of electrodes and between the second pair of electrodes, respectively. The high frequency outputs of the first and second power sources preferably have the same frequency, but may have different frequencies. The frequency of the high frequency voltage may be in a frequency band between a radio frequency and a ultra high frequency, for example, including a radio frequency of 13.56MHz, a very high frequency (VHF on the order of several tens MHz) and a ultra high frequency (UHF on the order of several hundreds MHz). The first and second power sources are adapted to pulse-modulate the high frequency voltages in accordance with first and second pulse waves, respectively, and apply the pulse-modulated voltages between the respective pairs of electrodes. At this time, the ON periods of the modulating pulse waves are controlled by the first and second power-sources so as not to coincide with each other. This prevents the plasma discharge interference between the first pair of electrodes and the second pair of electrodes even if the power for the plasma discharge is increased. Accordingly, the abnormal discharge can be prevented. The ON periods of the modulating pulse waves may be from 1µs to 100µs, and the OFF periods of the pulse waves may be from 5µs to 500µs. A duty ratio of not greater than 20% for the modulating pulse waves further effectively prevents the abnormal discharge. The present invention will hereinafter be described in detail by way of an illustrated embodiment. Fig. 1 is a diagram illustrating the construction of an electronic device production apparatus, and Fig. 2 is a timing chart of modulating pulse waves for modulating the high frequency voltages applied between respective pairs of electrodes in the apparatus. The electronic device production apparatus is herein used as a plasma CVD apparatus. As shown in Fig. 1, two anode electrodes 2A and 2B and two cathode electrodes 3A and 3B are disposed in a parallel relation within a vacuum vessel 1. Substrates to be processed (components to be processed) 6A and 6B are placed on the cathode electrodes 3A and 3B, respectively. The cathode electrodes 3A, 3B are electrically grounded to the vacuum vessel 1, and therefore their potentials are at a ground level. A gas inlet 7 is provided at the top of the vacuum vessel 1, and a material gas is introduced into the vacuum vessel 1 from a gas cylinder 10 through a valve 11 and the gas inlet 7. The gas introduced into the vacuum vessel 1 is drawn out via a main valve 8 by a vacuum pump 9. Pulse-modulated high frequency power generators 4A and 4B are connected to the anode electrodes 2A and 2B, respectively, via lines extending through central portions of right and left walls of the vacuum vessel 1. By a pulse signal delay circuit 5, the ON periods of modulating pulse waves for modulating the high frequency voltages applied to the respective anode electrodes 2A, 2B are controlled so as not to coincide with each other. The vacuum vessel 1 has a sectional area of 1.6m x 1.6m as measured parallel to the surfaces of the electrodes. The anode electrodes 2A, 2B and the cathode electrodes 3A, 3B each have a size of 700mm x 700mm. A gas mixture of silane and hydrogen is used as the material gas. Discharge parameters to be employed include a frequency of 27.12MHz, an ON period of the modulating pulse waves of 10µsec, and a duty ratio of 20%. Under such conditions, plasma discharge is allowed to occur between the electrodes 2A and 3A and between the electrodes 2B and 3B with the material gas being introduced into the vacuum vessel 1 to form a-Si:H films on the respective substrates 6A and 6B. In an experiment, when the ON periods of the modulating pulse waves for modulating the high frequency voltages applied to the anode electrodes 2A and 2B are allowed to coincide with each other, abnormal discharge occurred at a discharge power of 500W. When the ON periods of the pulse waves are offset from each other by 25µsec, normal discharge (between the anode electrodes and the cathode electrodes) is ensured at a discharge power up to 950W. Therefore, the apparatus allows for high speed film formation even when two substrates are simultaneously processed, thereby improving the mass-productivity. Although an explanation has been given to a case where the electronic device production apparatus is applied to the plasma CVD apparatus in this embodiment, the electronic device production apparatus is applicable to a plasma dry etching apparatus for etching a film with species activated by plasma particles and plasma excitation, and provides for the same effects. Where the electronic device production apparatus according to the present invention is applied to a plasma CVD apparatus for processing a plurality of substrates with the use of plural pairs of electrodes, the reduction in the processing speed per electrode pair can be prevented, thereby improving the mass-productivity of electronic devices such as solar batteries and liquid crystal display devices which utilize a-Si:H thin films in the electronic industry. Where the electronic device production apparatus according to the present invention is applied to a plasma etching apparatus for etching a film with species activated by plasma particles and plasma excitation, the mass-productivity of electronic devices such as liquid crystal display devices can be improved.

Claims: An apparatus for production of electronic devices, which comprises: a vacuum vessel (1) having first (2A, 3A) and second pairs (2B, 3B) of opposed electrodes provided therein, wherein components to be processed (6A, 6B) can be placed between the electrodes of each pair; a gas inlet (7) for introducing a material gas into the vacuum vessel; and first and second power sources (4A, 4B) for applying first and second high frequency voltages between the first pair of electrodes and between the second pair of electrodes, respectively, to cause plasma discharge, the first and second high frequency voltages being modulated in accordance with first and second pulse waves, respectively; wherein ON periods of first and second pulse waves are controlled so as not to coincide with each other. An apparatus as set forth in claim 1, wherein each of the first and second high frequency voltages has a frequency in a frequency band between a radio frequency and a ultra high frequency. An apparatus as set forth in claim 1, wherein the ON periods of the first and second pulse waves are from 1µs to 100µs, and OFF periods of the first and second pulse waves are from 5µs to 500µs. An apparatus as set forth in claim 1, wherein the first and second pulse waves have a duty ratio of not greater than 20%. A method for production of electronic devices, which comprises the steps of: placing components to be processed between a first pair of opposed electrodes and between a second pair of opposed electrodes in a vacuum vessel; introducing a material gas into the vacuum vessel; and applying first and second high frequency voltages between the first pair of electrodes and between the second pair of electrodes, respectively, to cause plasma discharge, the first and second high frequency voltages being modulated in accordance with first and second pulse waves, respectively; wherein ON periods of the first and second pulse waves are controlled so as not to coincide with each other. An apparatus as set forth in claim 5, wherein each of the high frequency voltages has a frequency in a frequency band between a radio frequency and a ultra high frequency. An apparatus as set forth in claim 5, wherein the ON periods of the first and second pulse waves are from 1µs to 100µs, and OFF periods of the pulse waves are from 5µs to 500µs. An apparatus as set forth in claim 5, wherein the first and second pulse waves have a duty ratio of not greater than 20%.

Inventors: MASHIMA SATOSHI, MONOTO KATSUHIKO, MASHIMA, SATOSHI, MONOTO, KATSUHIKO
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 2000
Main classification: H01J37
IPC codes: H01L21, C23C16, H01J37