Dry Etching Techniques for MMIC Fabrication on GaAs

During the fabrication of a GaAs monolithic microwave integrated circuit, there are a number of steps which necessitate the etching of GaAs, namely; mesa etching (for device isolation), gate recessing (to control the saturation current levels), substrate thinning for (transmission line impedance control), through substrate via holes (to reduce interconnection inductances) and scribe-line etching (for yield enhancement). Reproducible dry etch processes have been developed for these steps. However, the diversity of the process constraints imposed by these fabrication steps has led to a number of process operation regimes: for example, resulting in average etch rates ranging from less than 1000Å/min up to 10u/min for 2″ GaAs substrates. The process details are discussed with particular emphasis on the rate limiting steps and the factors governing the reactive gas/surface reaction rates.