Large size plasma generation using multicathode direct current geometry for diamond deposition
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Large size plasma generation using multicathode direct current geometry for diamond deposition Young-Joon Baik, Jae-Kap Lee, Wook-Seong Lee, and Kwang Yong Eun Thin Film Technology Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul, 130-650, Korea (Received 10 June 1997; accepted 5 September 1997)
The deposition area of diamond film is increased by applying a geometry of multiple cathodes and a single anode in direct current (dc) plasma assisted chemical vapor deposition (PACVD). Each cathode is made of Ta and connected independently to its own dc power supply. The operating pressure is 1.3 3 104 Pa (100 Torr), and methane-hydrogen mixed gas is used as reaction gas. The voltage and the current applied to each cathode are 650 V and 4 A, respectively. The transition from a diffuse glow to an arc is prevented by maintaining cathode temperatures above 2000 ±C, which inhibits carbon deposition on the cathodes. Translucent diamond film of 3 in. diameter, thicker than 200 mm, is grown using seven cathodes with 3% CH4 –H2 mixed gas for 110 h. The deposition area can be increased further by increasing the number of cathodes.
Since the first report of diamond synthesis from gas phase,1 the development of a large area and high growth rate synthesis method has been a target for the commercialization of diamond products. Deposition using direct current (dc PACVD)2 is one of the methods, by which diamond can be deposited with high growth rate comparable to that of the dc arc jet chemical vapor deposition (CVD) method.3 Its simple structure and low gas consumption make it more viable for economic deposition than the arc jet CVD. Stability and deposition area, however, are the main issues in this system. Since the operating pressure is above 1.3 3 104 Pa (100 Torr), a diffuse discharge tends to transit to an arc easily. The deposition area is limited by a small size of the plasma due to the high operating pressure. In order to enlarge the plasma, the electric power to the plasma should be increased, but the transition to the arc limits the power input. Recently, efforts for the suppression of the unwanted arc transition was reported, by applying a magnetic field4 or by using a pulse power supply.5 Diamond films on a 3 cm diameter substrate were deposited by using the above methods. Mainly filament-shaped or fiber-like carbon deposited on the cathode results in the arc transition. Thermodynamic conditions inhibiting carbon deposition were calculated and verified experimentally.6,7 At cathode temperatures above 2000 ±C, no carbon was deposited on the cathode during diamond deposition (hereafter, we will call this a hot cathode and that 944
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J. Mater. Res., Vol. 13, No. 4, Apr 1998
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of others4,5 a cold cathode). Using the hot cathode, the plasma was maintained for a time long enough to grow 1 mm thick diamond film without any additional modification of the plasma. There was, however, a power
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