COMPARISON OF BROMINE ETCHING OF POLYCRYSTALLINE AND SINGLE-CRYSTAL CU SURFACES

The etching of polycrystalline Cu surfaces by Br-2 was studied using t emperature programmed desorption and scanning tunneling microscopy, an d the results were compared with a recent study of the interaction of Br-2 with Cu(100). For both Cu surfaces, the etching mechanism could b e described as a two step process: adsorption rate limited CuBr format ion followed by CuBr desorption. The adsorption rate was found to be s tructure sensitive. At 325 K, the sticking coefficient for CuBr format ion was higher on Cu(100) than on polycrystalline Cu. For both surface s, increasing the temperature during dosing decreased the CuBr formati on rate. The decrease was larger for polycrystalline Cu and so the str ucture sensitivity increased with increasing temperature. The removal of CuBr by sublimation was found to depend more strongly on surface st ructure. For low CuBr coverages on Cu(100), a CuBr desorption peak was observed at 450 K, a temperature lower than anticipated from CuBr vap or pressure data. When the CuBr coverage was increased, the peak at 45 0 K shifted to higher temperatures and eventually disappeared; the rem aining CuBr desorption peaks were consistent with sublimation of bulk CuBr. A CuBr desorption peak at 450 K was also observed on polycrystal line Cu. On the polycrystalline surface, however, this peak saturated at high coverages but did not shift to higher temperatures. The intens ity of the 450 K desorption peak depended on the treatment of the poly crystalline surface. Annealing was found to increase the peak intensit y while sputtering and Br-2 etching were found to decrease the intensi ty. Scanning tunneling microscopy images following each of these treat ments suggested that the 450 K desorption peak is associated with narr ow terraces on the surface. The images also revealed that etching grea tly increases terrace widths suggesting that steps act as Cu atom sour ces for CuBr formation, and thus that Br-2 etching of Cu can be consid ered the reverse of step flow growth. (C) 1997 American Vacuum Society .