X-RAY PHOTOELECTRON-SPECTROSCOPY DAMAGE CHARACTERIZATION OF REACTIVELY ION ETCHED INP IN CH4-H-2 PLASMAS

The plasma-surface interaction during CH4-H-2 reactive ion etching pro cessing of InP is described in detail by means of plasma diagnostics ( optical emission spectroscopy and mass spectrometry) and x-ray photoel ectron spectroscopy (XPS) surface analysis. The influence of the input power is carried out for different CH4-H2 mixtures in terms of InP et ch rate, etch product and CH3 radical detection and surface damage cha racterization. In particular detailed XPS results allow the study of t he changes in the stoichiometry and amorphization of the surface with the input power. In addition, for a given power, the quality of the et ched surface improves by increasing the fraction of methane in the gas mixture. As an example, the best surface stoichiometry (InP0.86) is o btained for a pure methane plasma running at a high power (300 W). In general, it is shown that the lower the P depletion, the lower the amo rphization, which is indicative of a general improvement of the etched surface quality. Based on the XPS results, a three-layer model is pro posed for the representation of the surface in the course of etching. The damaged layer situated over the bulk InP is composed of a superfic ial P-depleted layer and of a stoichiometric amorphized InP layer. Usi ng the curve-fitting of the P 2p spectra, the thickness of the differe nt layers is estimated. As an example, a damaged layer as low as 37 An gstrom thick is obtained for pure methane plasma at 15 mTorr and a pow er of 300 W, whereas our standard conditions (10% CH4-H-2, 50 mTorr, a nd 80 W) give a damaged layer of 90 Angstrom. The experimental observa tions give evidence of the need for both ion bombardment and active ne utral species to obtain etching. The improvement of the etch process i s then explained by an improved In removal rate which is actually the limiting step in the etching mechanism of InP. (C) 1998 American Vacuu m Society.