Dry etching of photonic crystals in InP based materials

Photonic crystal (PC) etching in InP/GaInAsP using two different processes, namely Ar/CH4/H-2 based Reactive Ion Etching (RIE) and Ar/Cl-2 based Chemically Assisted Ion Beam Etching (CAIBE), is investigated in detail and the results are compared. Our goal was to identify the limits of the processes and to optimize process parameters for PC etching. With Ar/CH4/H-2 RIE, we obtained PC holes with smooth profiles. However, the etch depth depends strongly on the hole diameter; the smaller the hole diameter, the smaller is the obtained hole depth. This together with the obtained hole profiles indicates the presence of an etch-limiting mechanism and is attributed to inefficient removal of etch-products. In the case of Ar/Cl-2 CAME, we find that both shape and depth of the holes, depend on sample temperature, Cl-2 flow and etching duration. By optimizing the process parameters, we show that it is possible to balance the physical and chemical components in the etch process. We demonstrate that Ar/Cl-2 CAME is a promising process for PC etching in InP. With this process, we can obtain sufficiently deep holes (2.3-2.5 mum) even for hole diameters as small as 220nm.