Ultra-fast annealing to reduce the residual stress in ultra-thin chips using flash light

Abstract

The continuing trend of miniaturization in electronic equipment includes demands for thinner and smaller semiconductor devices with higher performance. To ensure the reliability of electronic devices and to enable high-throughput packaging processes, the mechanical properties of ultra-thin chips need to be accurately understood. One important consideration is the residual stress generated during wafer thinning due to the shear force between the grinding wheel and polish pad; this stress can degrade the fracture strength of ultra-thin devices. To reduce this residual stress, we developed a flash light irradiation annealing technique, including optimization of the irradiation conditions of flash light energy, pulse number and pulse duration. The distributions of residual stresses within ultra-thin flash memory chips before and after the annealing were measured using Raman spectroscopy, and their fracture strength was measured using a ball-on-ring test. Also, transmission electron microscopy (TEM) analysis and beam transfer function tests were performed to investigate the changes in mechanical properties and changes to the silicon lattice effected by the annealing. The ultra-fast flash light annealing was found to reduce the residual stress of ultra-thin chips by 50%, thereby improving their fracture strength by 20% compared to unannealed chips.