Beading instabilities in thin film lines with bamboo microstructures

Abstract

Thin film interconnect lines with bamboo grain structures are theoretically analyzed to determine the microstructural conditions under which the line is stable against beading (island formation) induced by surface energy. The equilibrium grain shape is one which meets the substrate at the equilibrium wetting angle, meets other grains at the equilibrium grain boundary groove angle and has a surface of constant curvature. For any initial cross-sectional area, only one grain size satisfied these three conditions. The grain shape, grain size and resistance of the equilibrium thin film interconnect line are derived. Lines with grain sizes less than the equilibrium grain size may adjust by buckling or undergoing grain growth. However, lines with grain sizes in excess of the equilibrium grain size develop breaks or opens. While these changes in line microstructures cannot be prevented, they may be drastically retarded by slowing the rate of surface diffusion. © 1986.