Sidewall roughness during dry etching of InP

A common feature of mesa structures formed by dry etching of III-V materials is the presence of corrugations or ribbing on the mesa sidewalls. The authors show that this sidewall roughness results from a replication of the roughness present at the edges of the masking material on the semiconductor. Using a photoresist mask free of sidewall roughness they demonstrate that it is possible to achieve a completely smooth mesa in InP with CH₄/H₂/Ar plasma etching. This is particularly important in minimizing light scattering in certain types of long wavelength lasers. It is also shown that the mask sidewall roughness does not worsen during the plasma exposure, even for long (2 h) etching runs.