Smooth and anisotropic reactive ion etching of GaAs slot via holes for monolithic microwave integrated circuits using Cl-2/BCl3/Ar plasmas

A process to produce very smooth and highly anisotropic through-the-wafer s lot via holes using reactive ion etching in Cl-2/BCl3/Ar mixtures has been developed. In this study, we have extensively investigated the GaAs etch ra te and resultant etch profiles as functions of bias voltage, gas ratio, flo w rate, chamber pressure, aspect ratio, and etch time. An optimum via hole etching process using a Plasma Therm 790 reactive ion etching system was de termined to be 300 V bias voltage, gas flow ratio of Cl-2:BCl3 :Ar=4:3:10, and chamber pressure of 15 mTorr. The average etch time for 20 mu m wide X 60 mu m long vias on a 50 mu m thick 3 in. diam wafer is 180 min using a to tal how rate of 50 seem, which corresponds to an average etch rate of 0.3 m u m/min. This process has been successfully implemented on two-stage Ka-ban d monolithic microwave integrated circuit driver amplifiers fabricated by T RW. Under a pulsed bias with V-ds=5.0 V and an input power of 15 dBm, the a verage power added efficiency was greater than 40% with a 13-14 dB gain bet ween 32 and 36 GHz. A peak power added efficiency of 44% was achieved at 35 GHz. (C) 1999 American Vacuum Society. [S0734-211X(99)01501-2].