Polymer free reactive ion beam etching of InP using N2/(CH3)3N

We have studied trimethylamine ((CH₃)₃N or TMA) based reactive ion beam etching (RIBE) of InP. It is found that by optimising TMA flow and rf power it is possible to minimise, but not completely avoid, polymer formation in TMA-RIBE. An important finding in this work is that by addition of N₂ the etch process can be made polymer free, while remarkably, all the other advantages such as reasonable etch rates and smooth surface morphologies obtained with pure TMA-RIBE are retained. We have also evaluated etch damage for TMA-RIBE, Ar/TMA-RIBE and N₂ milling by using Au/InP metal semiconductor (MS) contacts. The contacts made on the etched surfaces show near ohmic behaviour, and from the SIMS measurements we find that the etch processes produce a nitrogen containing layer close to the surface. Interestingly, if the dry etched samples are annealed in a PH ₃ ambient at 650°C before contact evaporation Schottky diode behaviour similar to the control sample is recovered. Further, the SIMS measurement show that the annealing step is accompanied by a reduction in the nitrogen content