INFLUENCE OF O-2(-INDUCED RIPPLE TOPOGRAPHY ON SILICON() ENERGY, FLUX, AND FLUENCE ON THE FORMATION AND GROWTH OF SPUTTERING)

The formation of ripples on Si(100) by O-2(+) sputtering at an angle o f incidence of 40 degrees and energies from 1 to 9 keV has been studie d using secondary ion mass spectrometry and scanning electron microsco py. At 1 keV no ripples are observed. Between 1.5 and 9 keV ripples ar e observed oriented perpendicular to the ion direction with average wa velengths that increase, from similar to 100 to 400 nm, approximately linearly with O-2(+) energy. Two-dimensional fast Fourier transforms o f secondary electron images are used to investigate the frequency dist ribution of the ripples. For the conditions studied, the distributions of frequencies appear approximately Gaussian. At 1.5 keV, the wavelen gth and growth rate with sputtered depth are independent of flux for f luxes from 15 to 150 mu A/cm(2). Accompanying ripple formation are cha nges in secondary ion yields. The changes occur abruptly at depths tha t increase, from similar to 0.2 to 5.6 mu m, with O-2(+) energy. In co ntrast, sputtering with Ar+ at 1.5 and 7 keV to depths 5-10 times thos e that produce ripples with O-2(+) produce no observable topography. T hese results are discussed using several existing theories for ripple formation and growth. Ripple growth and the variations in secondary io n yield are modeled by accounting for the change in local angles of in cidence as the ripples grow. This model describes well the variation i n secondary ion yield assuming an exponential growth rate. Ripple form ation is discussed in terms of a balance between roughening (by sputte ring-induced surface stress and by the dependence of the sputtering yi eld on surface curvature) and smoothing (by both diffusion and ion mix ing). Variation in ripple wavelength with energy is not simply explain ed by these theories. Surface smoothing by cascade ion mixing can, how ever, make the wavelength, as observed, independent of ion flux. Final ly, the possibility of formation of ripples by phase separation within the SiOx surface layer is discussed. (C) 1996 American Vacuum Society .