Stress-corrosion cracking of low-dielectric-constant spin-on-glass thin films

Variations in the electrical and mechanical properties of silsesquioxane sp in-on-glass thin films are examined as a function of curing time and temper ature. Particular attention is paid to the tradeoff between producing low-d ielectric-constant films, suitable for advanced microelectronic interconnec tion structures, and mechanically stable films, able to withstand semicondu ctor wafer fabrication processes. Two critical aspects of the mechanical st ability of spin-on glasses are shown to be the positive thermal expansion m ismatch with silicon, leading to tensile film stresses, and reactivity with water, leading to susceptibility to stress-corrosion cracking. An absolute reaction-rate model is used to predict crack velocity using a deleted-bond model and fused silica as a basis and is compared with observed steady-sta te crack velocities as a function of film thickness and variations in the c uring process. An implication is that on curing, the driving force for film fracture, determined by thermal expansion mismatch, increases less rapidly than the fracture resistance, determined by polymerization. (C) 1999 The E lectrochemical Society. S0013-4651(98)10-060-5. All rights reserved.