DAMAGE TO INP AND INGAASP SURFACES RESULTING FROM CH4/H2 REACTIVE ION ETCHING

Structural and electrical damage imparted to InP and In 0.72Ga0.28As0.6P0.4 (λg≅1.3 μm) surfaces during CH4/H 2 reactive ion etching (RIE) have been examined. X-ray photoelectron spectroscopy was used to monitor changes in the surface chemistry, Rutherford backscattering spectrometry was used to measure crystallographic damage, and current-voltage and capacitance-voltage measurements were made to examine electrically active damage and its depth. Two classes of damage are observed: crystallographic damage originating from preferential loss of P (As) and/or ion bombardment-induced collision cascade mixing and, for p-type material, hydrogen passivation of Zn acceptors. Etching at 13.6 MHz, 60-90 mTorr, 10% CH 4/H2, and bias voltages of ∼300 V contains gross (≳1%) damage as measured by RBS to within 40 Å and electrically active damage to within 200 Å of the surface. This is a factor of 3-6 shallower than other RIE processes operated below 10 mT with comparable or higher bias voltages. Acceptor passivation of both InP and InGaAsP, arising from the association of hydrogen with Zn sites, occurs to a depth of 2000 Å after RIE and causes a decrease in carrier concentration in this layer. The effect is reversed, however, by rapid thermal processing at temperatures between 350 and 500 °C.