HIGH-RATE, ANISOTROPIC DRY ETCHING OF INP IN HI-BASED DISCHARGES

Electron cyclotron resonance HI/H2Ar discharges with additional rf-induced dc biasing of the sample have been used to obtain extremely anisotropic dry etching of InP. At a fixed ratio of 10 HI/10 H-2/5 Ar (total flow rate 25 sccm) and 1 mTorr pressure, both n+ and p+ InP have etch rates of approximately 875 angstrom x min-1 at - 100 V bias and approximately 3000 angstrom min-1 at - 400 V bias. The etch rates increase rapidly with total discharge pressure, reaching 4000 angstrom min-1 at 20 mTorr and - 100 V dc bias. Rates in excess of 1-mu-m min-1 are obtained with higher HI flow rates or higher biases. Features 0.5-mu-m wide and 13-mu-m high have been etched, demonstrating the promise of this gas chemistry for production of laser mesas on InP and related materials with substantially faster etch rates (typically a factor of 8-10) relative to the more conventional CH4/H-2 mixtures. The etched surfaces are smooth, with no evidence for iodine-containing residues or preferential loss of either In or P. Both photoresist and SiO2 masks show minimal erosion in this mixture because of the ability to obtain practical etch rates at low pressure and low self-bias.