TOPOGRAPHY DEVELOPMENT ON THE SURFACE OF A SEMICONDUCTOR HETEROSTRUCTURE UNDER AR-BEAM MILLING( ION)

The topography development on the cross-section surface of a single he terostructure bombarded by 5 keV Ar+ ions was studied. From calculatio ns based on the angular dependence of the sputtering rate, it was esta blished that by inclination of its surface from the original flat posi tion the epitaxial layer is able to compensate for a sputtering rate d ifference with the substrate. This inclination for a non-rotating spec imen depends on bombardment angle in such a way that the topographical relief abruptly becomes rather smooth when the bombardment angle reac hes a certain value THETA(cr). A further increase beyond THETA(cr), i. e. more grazing incidence, invokes a further, but much slower, suppres sion of the topography build-up. The data of experiments on ion millin g of AlGaAs/GaAs heterostructures with various Al concentrations in th e epitaxial layer are in good agreement with the calculations. The exp eriments have shown the THETA(cr), for AlxGa1-xAs with x = 0.12, 0.27 and 0.60 to be 57-degrees, 60-degrees and 63-degrees, respectively. Th e results obtained enable one to improve the conditions for ion millin g in specimen preparation for TEM as well as in some other analytical and technological applications.