PLASMA-ETCHING OF GAAS AND ALGAAS USING 300 KHZ AND 13.56 MHZ EXCITATION-FREQUENCY

A pulse-plasma etch process for GaAs and Al0.3Ga0.7As at 300 kHz and/o r 13.56 MHz excitation frequency using a gas mixture of ClCH3/H-2 is r eported. The plasma etching is performed using a reactive ion etch (RI E) reactor combined with an external helical RF coil. The GaAs over Al 0.3Ga0.7As etch selectivity is investigated as a function of driven el ectrode frequency and duty cycle. The addition of a capacitive coupled plasma driven by an external RF Coil is also investigated. In the nor mal RIE configuration but at the 300 kHz excitation frequency, the GaA s etch rate is found to be greater than at 13.56 MHz, although the GaA s over Al0.3Ga0.7As etch selectivity (3:1) is not altered. These resul ts illustrate the effect of plasma excitation frequency either side of the ion transition frequency (approximately 2 MHz). The use of the ex ternal RF coil is found to increase the GaAs over Al0.3Ga0.7As etch se lectivity to 10:1. The etch process is interpreted as a competitive et ch-deposition process which is controlled by the ion/radical flux at t he semiconductor surface.