RIE OF A T-SHAPE REFRACTORY OHMIC CONTACT FOR SELF-ALIGNED HETEROJUNCTION BIPOLAR-TRANSISTOR

Reactive ion etching (RIE) of Ge/Mo/W layers has been investigated to fabricate a T-shape emitter ohmic contact for self-aligned AlGaAs/GaAs heterojunction bipolar transistors. SF6 + O2 mixtures have been used as etching gases. The etch rates of Ge, Mo, and W have been measured as a function of RF power, pressure, and gas flow. In order to investigate the contamination from the RF cathode, studies have been carried out with silicon or quartz cathode. This study has led to the result that no detectable contamination occurred with a quartz cathode. A highly anisotropic etching of W and Mo layers has been achieved, while the isotropic etching of Ge has permitted the T-shape profile to be obtained. Moreover, laser reflectometry used for end-point detection proved to be very efficient and has allowed the achievement of a good reproducibility of the process. © 1990, The Electrochemical Society, Inc. All rights reserved.