Impact of laser spike annealing dwell time on wafer stress and photolithography overlay errors

The use of strained SiGe is essential to improvement in device performance. However, the structure is susceptible to strain relaxation and wafer deformation during thermal annealing. The accumulation of stress in the wafer needs to be controlled to minimize photolithographic overlay errors. Laser spike annealing offers negligible pattern effects, closed-loop temperature control, and localized heating, which help control stress intensity and variation. This paper describes the effect of dwell time on deformation and its contribution to overlay error. By the use of a stress measurement technology, the coherent gradient sensing (CGS) interferometer, a detailed characterization of deformation induced during micro-second laser annealing can be correlated to the overlay error.