High rate sapphire (Al₂O₃) etching in inductively coupled plasmas using axial external magnetic field

BCl₃/HBr inductively coupled plasmas magnetized by external magnetic fields was used to achieve high etch rate of sapphires and high etch selectivities over photoresist. The etch characteristics such as etch rates of sapphire and photoresist, etch selectivity over photoresist, plasma density, and etch profiles etc. were investigated as functions of applied external magnetic field strength, working pressure, and dc bias voltage. The obtained highest etch rate of sapphire was approximately 7700 Å/min at -800 V of dc bias voltage and 20 Gauss (G) of external magnetic field, when 1400 W of inductive power, 10 mTorr of 90% BCl₃/10% HBr were used. The etch selectivities over photoresist were varied from approximately 0.6 to 0.8, where, it increased up to 0.8 with an increasing external magnetic field, however, it decreased with an increasing dc bias voltage.