Constraint Effects on Thin Film Channel Cracking Behavior

Abstract

-One of the most common forms of cohesive failure observed in brittle thin film subjected to a tensile residual stress is channel cracking, a fracture mode in which through-film cracks propagate in the film. The crack growth rate depends on intrinsic film properties, residual stress, the presence of reactive species in the environments, and the precise film stack. In this paper, we investigate the effect of various buffer layers sandwiched between a brittle carbon-doped-silicate (CDS) film and a silicon substrate on channel cracking of the CDS film. The results show that channel cracking is enhanced if the buffer layer is more compliant than the silicon substrate. Crack velocity increases with increasing buffer layer thickness and decreasing buffer layer stiffness. This is caused by a reduction of the constraint imposed by the substrate on the film and a commensurate increase in energy release rate. The degree of constraint is characterized experimentally as a function of buffer layer thickness and stiffness, and compared to the results of a simple shear lag model that was proposed previously. The results show that the shear lag model does not accurately predict the effect of the buffer layer.3

Fracture, delamination, and buckling of elastic thin films on compliant substrates

“…While some experimental observations clearly showed channel cracks with no delamination [16,19], others observed delamination of the interface [16,20] (Fig. 1b).…”

“…The effect of constraint can be partly lost as the substrate deforms plastically [13] or viscoelastically [14,15]. More recent studies have investigated the effects of stacked buffer layers [16,17] and patterned film structures [6]. In most of these studies, the interfaces between [11,12].…”

“…In an experimental study by Tsui et al [16], no interfacial delamination was observed for channel cracking of a low k film directly deposited on a Si substrate, while a finite delamination was observed when a polymer buffer layer was sandwiched between the film and the substrate. These observations are consistent with the delamination map.…”

“…Therefore, fracture of the low-k dielectrics by channel cracking is typically not accompanied by interfacial delamination. However, when a more complaint buffer layer is added adjacent to the low-k film, interfacial delamination can occur concomitantly with channel cracking of the low-k film [16]. Moreover, a relatively stiff cap layer (e.g., SiN) is often deposited on top of the low-k film [7].…”

Influence of Interfacial Delamination on Channel Cracking of Brittle Thin Films

“…1). Previous studies have shown that the driving force for the steady state growth of a channel crack (i.e., energy release rate) depends on the constraint effect of surrounding layers [1,4]. For a brittle thin film on an elastic substrate, the driving force increases for increasingly compliant substrates [5,6].…”