SURFACE MODIFICATION OF SI, GAAS AND INP BY 1-10 KEV AR AND N ION BOMBARDMENT

Abstract

Auger electron spectroscopy (AES), angle-resolved x-ray photoelectron spectroscopy (AR.XPS) and atomic force microscopy (AFM) have been employed in this investigation of surface modification of Si (100), GaAs (100) and InP (JOO) induced by 1-10 keV Ar•, N' and N/ bombardment. During Ar+ bombardment of Si samples the incorporation of Ar in the samples was observed. The surface Ar concentration decreases with increasing bombardment energy. No Ar bubbles were found on the surfaces of Ar+ - bombarded samples under the present experimental conditions suggesting that Ar is trapped as an interstitial impurity rather than in the vacancy sites. The SiC formed by ion beam mixing of C contamination atoms at the surface with substrate Si atoms was found in Ar+ -bombarded samples. No strong dependence of carbide depth distribution with bombardment energy was observed. Ar' ion beam also has been used to bombard GaAs and InP. Ar+ bombardment causes averagely As-depleted and P-depleted altered layers in GaAs and InP respectively. However, the elemental depth distributions are inhomogeneous in these altered layers. For GaAs, it was found that the As concentration at the surface is higher than that in the subsurface region at 5 keV Ar+ bombardment, but it was not found at I and 3 keV Ar+ bombardment. For InP, the P concentration at the surface is lower than that in the subsurface region at all energies Ar+ bombardment. The results can be discussed in the context of preferential sputtering, radiation-enhanced diffusion/segregation and altered layer thickness dependence on Ar+ ion energy. The investigation of silicon nitride formation as a function of N' or N/ ion energy, dose and incident angle shows that there is not pronounced difference between N' and N/ bombardment. The nitride layers formed by 4-I O ke V ion bombardment are relatively uniform and have a composition of stoichiometric silicon nitride (SbN4), but that formed by 2 keV ion bombardment is N-rich on the surface. The thicknesses of nitride layers appear to increase with ion energy in the range of 2-10 keV. The ratio of N to Si surface atoms increases rapidly at initial ion doses, slow down, and finally reaches a constant value as the ion dose is increased to the limit of saturation. Complete nitridation could be achieved at incident angles between 0' and 30' to the surface normal. At incident angles exceeding 30', the degree of nitridation decreases. The observed ion dose, energy and angular dependence of ion beam nitridation of Si can be explained in terms of sputtering yields, indicating that the growth kinetics can be described by a dynamic process which includes only the accumulation of N and sputter removal of the surface layer. A simple altered layer model has been proposed to describe the dynamic process.