ICP-RIE etching of self-aligned InP based HBTs with Cl-2/N-2 chemistry
We report on a simple Inductively Coupled Plasma-Reactive Ion Etching (ICP-RIE) process with Cl-2/N-2 chemistry to process InP based, self-aligned HBTs with sub-micron emitters. Since the layer to be etched is in the range of 150 nm (the thickness of emitter cap and emitter layers), a low etch rate is beneficial. On the other hand, it is also necessary to use chemistries without hydrogen to prevent any possible hydrogen passivation. Therefore, in this work, Cl-2/N-2 chemistry is selected and a plasma process providing an etch rate of 120 nm/min is optimized. Not only the etch rate but also the electrical and the surface quality of the wafers are examined. It has been illustrated that the etch rate of the optimized process is uniform over the wafer and it is reproducible. In addition to that, it has been shown with electrical measurements that there is no degradation in the material quality. To test the optimized process. sub-micron HBTs are fabricated and the RF measurements have shown an f(max) of 340 GHz which make them to be used in high speed communication systems. In addition to that, lower and controlled under etch gives better current gain distribution over the wafer leading better device models and resulting in better yield in MMICs. (C) 2011 Elsevier B.V. All rights reserved.