Limitations of Cl2/O2-based ICP-RIE of deep holes for planar photonic crystals in InP

A detailed study of dry‐etching of high‐aspect‐ratio holes into an indium phosphide substrate is presented for a Cl2/O2‐based plasma chemistry. The etching is performed in an inductively coupled plasma reactive ion etching reactor. The separate influence of the various etching parameters on the quality of the etched holes is identified. Quality measures such as high aspect ratio, hole cylindricity and verticality as well as sidewall smoothness can be controlled by varying the ICP power, the relative O2 flow rate and the self‐bias of the plasma. We were able to clearly identify trade‐offs that have to be made and limitations of the etching chemistry/technology used: If the aspect ratio improves, then the cylindricity also improves, whereas the verticality and the sidewall smoothness degrade. In previous reports, a certain ambiguity is generally observed in the sense that different process parameters exhibit partially contradicting trade‐offs. We show that this behaviour can be remedied by a careful selection of the variable parameters. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)