Apparatus for low-temperature growth of diamond-containing films
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. INTRODUCTION There are a multitude of diamond growth processes. Depending on the carbon sources, when they are a solid source, typically graphite, either evaporation1 or sputtering2 is made. When they are gases, such as methanes or other hydrocarbons, alcohols, etc., a discharge process is generally applied.3'4 The discharge is achieved by applying a DC, AC, or microwave field. In addition, auxiliary excitation sources can be provided to control the deposition process and to manipulate the deposition conditions, thus enhancing the growth rate as well as the quality of the produced material. The present work is concerned with the introduction and the modification of a DC glow discharge process. This paper will present, first, the glow discharge and deposition system; second, a graphite hot cathode is proposed; and third, the operational procedure is outlined. II. DEPOSITION SYSTEM The central subject of the deposition system is a carbon ion source. This source consists of a hot filament cathode K and an anode A, as shown in Fig. 1. Some aspects of the cathode will be discussed in Sec. III. The anode A is made of graphite or refractory metals in a cylindrical configuration with an opening either on the top or on the side of the cylinder as the ion beam exits. The beam direction is along the magnetic field direction. In the lower portion of A, a gas inlet, I, is provided to introduce hydrocarbon gas with a controlled amount of pressure of about 100 microns. The gas injection is directed toward the hot filament to produce a dissociation of the carbon compounds and to facilitate ionization between the electrodes K and A. a)This
author is deceased. J. Mater. Res., Vol. 4, No. 5, Sep/Oct 1989
-0 M (S)
I
J_
C+
FIG. 1. A schematic of diamond film deposition systems: K: filament cathode, A: anode, C + : carbon ion plasma, I: CH4 gas inlet, S: substrate, H: substrate heater, G: grid, and M: magnet.
The beam which exits from the gap of the anode is a plasma consisting of positively charged ions of carbon or hydrocarbon and negatively charged electrons. The positive and negative species tend to recombine and to emit light and thus the ionic character is lost. A grid G is provided with a negative bias in order to repel electrons; thus only the ions will continuously move toward the substrate target S. The target is negatively biased to attract positive ions, thus enhancing the deposition. It should be noted that the size of the applied biased voltage is dependent on the geometrical separation among A, G, and S. A set of typical values are the following: the distance between A and G is 5 mm; the applied voltage is 50 volts; the distance between G and S is 5 cm; the voltage is 100 volts. The substrate S is attached to a holder on which a thermocouple T is attached to monitor the temperature. A heater H is provided to raise the temperature of the sub1989 Materials Research Society
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P. H. Fang and J.H. Kinnier: Diamond-containing films
strate. In the operation, the required temperature is regulated by a balance betwee
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