Optical emission end point detection for via hole etching in InP and GaAs power device structures

Abstract

Narrow (about 30 μm diameter) via holes have been etched in both InP and GaAs substrates using Cl 2 CH 4 H 2 Ar and BCl 3 Cl 2 discharges respectively. High density (about 5 × 10 11 cm −3 ), low pressure (1 mTorr for Cl 2 CH 4 H 2 Ar or 15 m Torr for BCl 3 Cl 2 ) conditions, combined with side wall 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 end point for both types of substrates. The intensity of these lines was proportional to the microwave input power at fixed d.c. 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