COMPOSITION CHANGES IN AR--BOMBARDED SIC - AN ATTEMPT TO DISTINGUISH BALLISTIC AND CHEMICALLY GUIDED EFFECTS( AND E)

We study with Auger electron spectroscopy (AES) the composition change s in amorphous SiC films with excess (i.e. free) C induced by bombardm ents either with 30 keV Ar+ or with 3 KeV e-. In Ar+-bombarded films t he C accumulates at the surface without apparent depletion in the bomb arded region, while the Si accumulates at the surface accompanied by m ajor depletion near the Ar+ range. Significantly, movement of C to the surface occurs also due to e- bombardment. The C profile modification s are explained by assuming that a long range force (especially that p rovided by unbalanced surface charges) operates on the free C present in the SiC films, whereas the Si transport towards the surface is prom oted by the bombardment-induced defects. Whether the direction of the Si motion is determined by the C enrichment at the surface (which trap s the Si chemically), or by an interstitial flux (as has been establis hed with such systems as Ni-Si) cannot be determined, but it is still possible to assert that the composition changes are more nearly due to defects (whence showing chemical guidance) than ballistic (whence ran dom). We finally note that the C at the surface will tend to be sputte red away.