Anisotropic etching of InP with low sidewall and surface induced damage in inductively coupled plasma etching using SiCl4

We report on the sidewall and surface characterization of InP etched patterns obtained by inductively coupled plasma (ICP). The fabrication of InP based optoelectronic integrated circuits requires dry etching processes, normally using CH4/H2 gas mixtures, with low induced damage, high and reproducible etch rate, and controlled etch direction. These requirements imply the use of a high-density plasma source, which reduces the energy of ions impinging on the wafer surface while keeping a sufficient etch rate. We introduce here the use of an ICP to etch InP. We show that one can obtain anisotropic processes in SiCl4 chemistry avoiding the carrier compensation due to the H+ bombardment. The surface morphology and the pattern profiles are observed by scanning electron microscopy and by atomic force microscopy. Auger electron spectroscopy and secondary ion mass spectroscopy are used to obtain the elemental composition in the top 30 nm of the etched surface and to evaluate contamination. Transmission electron microscopy is used to observe the sidewall damage on patterns delineated by e-beam lithography. The effects of ion density, ion energy, pressure, reactor environment, and surface temperature are observed. Finally, surface damage induced on InP etched substrates are characterized through photoluminescence intensity. We observed the destructive effects of high ion energy etching processes, already reported in CH4/H2 chemistry. Some very low bias voltage processes (as low as 5 V) have been studied in the ICP equipment. It is found that extremely low surface damage and very low sidewall amorphization can be obtained in such processes while keeping high etch rate and anisotropy.