ETCHING BEHAVIOR OF SI(001)-2X1 STUDIED WITH OPTICAL ANISOTROPY

Etching of single-domain Si(001)-2 x 1 by 800-eV Ar+ ions has been stu died using surface-induced optical-anisotropy measurements in the temp erature range from 293 to 870 K. At 293 K, the surface area which is d istorted by one impinging ion is determined to be 3.9 x 10(-14) cm(2), and at this temperature no annealing was observed. With increasing te mperatures the etch behavior gradually changes from mere roughening to a situation where ion-induced surface damage is restored. At 670 K an d 10(11) ions cm(-2) s(-1), no ion-induced changes in the optical anis otropy could be observed, and hence D-B, step etching occurs. During i on bombardment at higher temperatures we observed the development of p rotrusions on the surface with facets in the (11l) directions. Protrus ions were also found during etching by O-2 at 1020 K, and their develo pment is attributed to pinning at residual contaminations. Formation o f protrusions during sample cleaning may be responsible for the large scatter in reported optical-anisotropy data of clean single-domain Si( 001)-2 x 1. This illustrates the importance of a well-controlled sampl e preparation procedure.