Ripple structure of crystalline layers in ion-beam-induced Si wafers

Abstract

Ion-beam-induced ripple formation in Si wafers was studied by two complementary surface sensitive techniques, namely atomic force microscopy (AFM) and depth-resolved x-ray grazing incidence diffraction (GID). The formation of ripple structure at high doses $(\ensuremath{\sim}7\mathbf{\ifmmode\times\else\texttimes\fi{}}{10}^{17}\phantom{\rule{0.3em}{0ex}}\mathrm{ions}∕{\mathrm{cm}}^{2})$, starting from initiation at low doses $(\ensuremath{\sim}1\mathbf{\ifmmode\times\else\texttimes\fi{}}{10}^{17}\phantom{\rule{0.3em}{0ex}}\mathrm{ions}∕{\mathrm{cm}}^{2})$ of ion beam, is evident from AFM, while that in the buried crystalline region below a partially crystalline top layer is evident from GID study. Such ripple structure of crystalline layers in a large area formed in the subsurface region of Si wafers is probed through a nondestructive technique. The GID technique reveals that these periodically modulated wavelike buried crystalline features become highly regular and strongly correlated as one increases the Ar ion-beam energy from 60 to 100 keV. The vertical density profile obtained from the analysis of a Vineyard profile shows that the density in the upper top part of ripples is decreased to about 15% of the crystalline density. The partially crystalline top layer at low dose transforms to a completely amorphous layer for high doses, and the top morphology was found to be conformal with the underlying crystalline ripple.