Improvement of uniformity in conventional RIE process for via hole fabrication in GaAs based MMICs [HEMTs]

One of the main steps not only in minimizing size and complexity but also improving performance of MMICs, is the fabrication of well controlled via holes through the GaAs substrate by dry etching techniques (RIE, ICP, ECR etc.). RIE usually suffers front non-uniformity created by the large etch depths encountered, thus increasing the dimension of via holes used. In this work, a simple technique is demonstrated, utilizing conventional RIE equipment, together with an AlGaAs etch stop layer grown below the active device layers, allowing better process control. A tree step RIE process enables full wafer processing without sacrificing good dimension control of the fabricated patterns. The process suggested is compatible with commonly used techniques and requires no complicated etching systems thus making it an appealing option for via holes fabrication.