Ratcheting induced crack growth in semiconductor devices

Semiconductor devices integrate dissimilar materials, including semiconductors, ceramics, metals, and polymers. These materials have different coefficients of thermal expansion, so that the devices develop stresses when temperature changes. Here we study a failure mode caused by cyclic changes in temperature. Under certain conditions, thermal cycling causes a metal to accumulate plastic deformation cycle by cycle, a phenomenon called ratcheting. The ratcheting in the metal can drive a crack to grow in a nearby brittle material. We simulate a representative structure using the finite element method. As the temperature cycles, the plastic deformation in the metal ratchets, and the energy release rate of the crack in the brittle material increases. After a large number of temperature cycles, the metal no longer ratchets, and the energy release rate plateaus. We find that this plateau is well approximated by the energy release rate in a structure where the metal is replaced by a void, calculated by a monotonic change in temperature. This simplification reduces computational cost for modeling ratcheting induced cracking. We also examine the effects of material and geometric parameters. It is hoped that this study will aid the design of semiconductor devices.