Magnetron plasma etching has been found to be a promising technique for micromachining of single-crystal silicon carbide to fabricate microscopic structures comprising integrated mechanical, electronic, and optical devices. Silicon carbide offers several advantages over silicon for the development of future devices. In comparison with silicon, silicon carbide is harder and stiffer, is less chemically reactive, and has greater thermal conductivity; moreover, silicon carbide-based electronic devices can operate at temperatures higher than silicon-based electronic devices can withstand. Etching techniques for micromachining of silicon are well known, but the lesser chemical reactivity of silicon carbide makes it necessary to devise alternative etching techniques.
In the present magnetron-plasma-etching technique as in the ECR etching technique, a magnetic field is used to increase the density of the plasma. Unlike in ECR etching, the main body of the plasma is confined in proximity to the sample. Such confinement results in a high concentration of reactive chemical species together with a high flux of bombarding ions at the sample, making it possible to achieve rapid etching.
Magnetron plasma etching of SiC was demonstrated in preliminary experiments in a vacuum chamber, using a magnetron sputter gun as a cathode. The duration of each etch was 7 min. At a radio-frequency power of 250 W, a maximum etch depth of 4.5 | m was achieved with a gas mixture of 0.6 CHF3 + 0.4 O2 at a total pressure of about 2.7 Pa. This depth corresponds to an etch rate of about 640 nm/min, which is a relatively high rate, significantly higher than that which has been achieved using an ECR plasma. The etched surface was found to have a root-mean-square surface roughness of only 20 A. The reaction of aluminum and fluorine yields a nonvolatile product, which makes aluminum suitable for use as a mask material to provide selective etching in fluorine-based plasmas. At the radio-frequency power of 250 W, aluminum films were etched at a high rate. At a radio-frequency power of 50 W, silicon carbide was etched at a rate of 170 nm/min, while aluminum was etched at 1/12 that rate.
