Measurement of the interfacial strength of thin metal film by laser spallation method for advanced wafer level package

As the semiconductor industry advances, the thermomechanical failures such as thin-film cracking or interfacial delamination in multilayered structures have emerged as a critical reliability issue during both manufacturing and operation. To predict such reliability problems, a quantitative measurement method for thin film/substrate interfacial properties that reflected manufacturing process is required. In this study, the laser spallation method is performed to investigate the influence of Argon plasma pre-treatment on the interfacial strength of aluminum film/silicone substrate quantitatively. A Michelson interferometer was used to calculate the free-surface displacement caused by laser ablation. Compressive stress was derived using elastic wave propagation theory and the tensile stress acting on Al-Si interface was calculated by wave propagation simulation model. In addition, optical imaging analysis was conducted to investigate wafer backside fractures and thin film delamination induced by loading laser. The study finding revealed that the interfacial strength of plasma treated specimen was improved by more than 200% compared to non-treated specimen.