Optical Emission End-Point Detection for Via Hole Etching in InP and GaAs Power Device Structures

Abstract

AbstractNarrow (∼30 μm ϕ) via holes have been etched in both InP and GaAs substrates using either C12/CH4/H2 /Ar or BC13/C12 discharges, respectively. High density (∼5×1011 cm−3), low pressure (1 mTorr for C12/CH4/H2/Ar or 15 mTorr for BC13/C12) conditions, combined with sidewall passivation obtained using AZ 4620 photoresist masks, produce the correct profiles for subsequent metallization to complete the via connection. Optical emission monitoring of the 417.2 nm Ga line during GaAs etching or of the 325.6 nm In line during InP etching provided a sensitive, non invasive and reliable indicator of endpoint for both types of substrates. The intensity of these lines was proportional to the microwave input power at fixed dc bias and pressure. The via holes are suitable for a range of InP and GaAs microwave power devices, including Heterojunction Bipolar Transistors and High Electron Mobility Transistors.