Research has been undertaken in several major research laboratories to achieve a commercially successful GaAs via hole etching process. This work presents the achievement of results with the desired characteristics for through-wafer GaAs interconnects or vias, for production of MMICs.

We report vias acceptable for use in the production of microwave GaAs field effect transistors fabricated by a reactive ion etching process. Using conventional resist masks and non toxic gases, aspect ratios of up to 10:1 have been achieved with via sizes as small as 40μm × 40μm. Typical wafer thicknesses were greater than 100μm and the process showed high selectivity to the frontside metallization. The etching conditions had to be varied as a function of overall substrate area and exposed GaAs. To determine optimum process parameters, the RF power and resultant DC bias; gas flow rates and ratios; and system pressure were systematically varied. The effects of changes in area of wafer to be etched and of the composition of the electrode material were also studied. Details are presented of the optimum etching parameters for use in 2″ and 3″ GaAs MMIC production.