SURFACE-ROUGHNESS DEVELOPMENT DURING SPUTTERING OF GAAS AND INP - EVIDENCE FOR THE ROLE OF SURFACE-DIFFUSION IN RIPPLE FORMATION AND SPUTTER CONE DEVELOPMENT

Surface diffusion is shown to be the important factor in sputter-induced ripple and cone development on GaAs and InP surfaces for conditions typical of depth profiling when using surface analysis techniques. Ripple formation has been observed on both GaAs and InP when sputtered using Cs+ and O2+ ion beams. For GaAs, the ripple "wavelength" increases with sample temperature in the range from 45 to 100-degrees-C, in qualitative agreement with the surface diffusion model of Bradley and Harper. No ripple formation is observed when the GaAs sample is cooled to -30-degrees-C where surface diffusion is limited, or heated above 100-degrees-C, where a proposed surface phase change may alter the diffusion rate. Ripple development also occurs on InP, but it is impossible to observe at 100-degrees-C due to extensive cone formation. At this elevated temperature, Ar+ sputtering of InP leads to a surface enrichment of indium that is accompanied by a change in the In M4,5N4,5N4,5 Auger line shape toward that for indium metal. This result, together with the observation that cone formation is eliminated for sputtering at -20-degrees-C, supports the intrinsic model where sputtering causes indium enrichment and surface diffusion that results in the agglomeration of indium metal into clusters. These clusters produce cone formation, possibly through the difference in sputter rates of indium and InP.