Explore of warpage origination in WLP and processing influence factors by experiment and theoretical modeling
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Thick Cu films are widely used in wafer level packaging, and the stress evolution during subsequent thermal cycling as well as the induced wafer warpage may make a significant impact on product yielding and needs to be investigated. The stress evolution behavior of 5 μm thick as-electroplated Cu films during thermal cycling are in situ investigated by wafer warpage measurement. It is revealed by microstructure analyses that the grain growth during thermal cycling is ignorable in current work, but dramatic atomic diffusion has occurred, suggesting the deformation mechanism is dominated by diffusional creep. As the dominant diffusion mechanism differs at different temperatures, an equivalent diffusional energy that has a linearly correlation to temperature is proposed, and consequently a stress evolution model based on the equivalent diffusional energy is deduced. Compared with conventional work, the current model has fewer fitted parameters, and shows better agreement with the experiment results.
KeywordsStress Evolution Diffusional Creep Diffusional Energy Film Stress Normal Stress Distribution
This work is supported by National Natural Science Foundation of China (Grant No. NSFC61574154) and Natural Science Foundation of Shanghai (No. 13ZR1447300).
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