CH 31 vapor etching of GaAs in a vertical rotating-disk reactor

A detailed computer model which predicts etch rates and spatial uniformity for chemical vapor etching of GaAs with CH3I in a vertical rotating-disk organometallic vapor phase epitaxy (OMVPE) reactor has been developed. Etch rate predictions compare favorably with experiments performed in the vertical reactor at several temperatures ranging from 525 to 590°C and CH3I mole fractions from 0.005 to 0.050 in an H 2 carrier gas. Agreement between the data and the model verifies our earlier assertion that gas phase decomposition of CH3I is the rate-limiting step, and that the etchant species are I and to a lesser extent CH 3 radicals. Predictions further show that radial etch rate uniformity improves from a 5% variation over 50% of the substrate at low rotation (20-100 rpm) to a 5% variation over 80% of the substrate at 500 rpm. Increasing rotation rate also reduces the etch rate, a result that is in contrast to earlier results for OMVPE growth from TMGa and AsHy These contrasting results arise because growth is rate limited by gas phase diffusion of TMGa, whereas CH3I vapor etching is rate limited by gas phase decomposition of CH3I.