Fracture of Low-k Dielectric Films and Interfaces

Abstract

The mechanical properties of organosilicate glass films, also known as carbon‐doped oxide (CDO) films, were investigated and compared to dielectric constant, chemistry, interfacial properties and reliability performance. The techniques of four‐point bending and channel cracking were employed to measure the interfacial adhesion and cohesive strength of CDO films. The effect of compositional variations of the films on dielectric constant and elastic modulus was studied. It was found that changes in CDO film composition which decrease k also decrease the mechanical strength of the film. By contrast, a similar study of the effect of CDO film composition on interfacial adhesion showed that changes in film composition which decrease k have little effect on the adhesion energy of dielectric cap films to the low‐k film. The most significant factor controlling adhesion was found to be surface treatment conditions of the low‐k film. Studies of crack propagation in CDO films and interfaces as a function of humidity were carried out. It was shown that the phenomenon of stress‐corrosion cracking, whereby cracking is facilitated by the presence of moisture, is more pronounced for interfacial fracture than for CDO cohesive fracture. The effect of copper line orientation on fracture at the cap to Cu/low‐k interface was investigated using specially fabricated patterned test structures. It was found that the adhesion energy of the dielectric cap to patterned Cu/low‐k interface is lower for crack propagation parallel to the metal line direction than for propagation orthogonal to the metal line direction, consistent with stress relaxation results for identical test structures. Correlations between dielectric cap to Cu adhesion, stress relaxation and electromigration lifetime are shown.