On instability-induced debond initiation in thin film systems

Thin films bonded to substrates are common in semiconductor dielectric stacks and in other applications. Often, in these systems, the mismatch in the Coefficient of Thermal Expansion between the films and the substrate result in significant compressive stresses during processing. These compressive stresses may lead to instabilities and possibly debonding. In the present study, we develop analytical descriptions of buckling and wrinkling-induced debonding by incorporating a cohesive zone model. The temperature excursion leading to buckling or wrinkling, the peak deflection values of the films, the wavelength of the wrinkling pattern, as well as the temperature excursion to the onset of damage are estimated analytically by minimizing the total energy of the combined film-cohesive zone system. Analytical estimates of cohesive stiffness and strength are provided based on (possibly experimentally) observed temperature excursions to the onset of instability and debonding. A non-dimensional grouping of parameters combining characteristics of film, cohesive zone and geometry is identified to be of importance in separating regimes with different debonding characteristics. Special conditions for the non-dimensional grouping emerge for film wrinkling to occur. Full-field simulations based on an incremental Spectral Method are presented to study wrinkling. This approach extends the applicability of the Spectral Method to phenomena involving non-linear foundations, non-monotonic and non-proportional loading. Results from numerical simulations using the incremental Spectral Method are compared with analytical estimates. The analytical derivation is found to provide reasonable estimates of wrinkling wavelength and amplitude but overestimates the cohesive strength.