Characterization of deformation induced by micro-second laser anneal using CGS interferometry

The understanding and control of mechanical stresses accumulated during device fabrication is becoming more critical at advanced technology nodes. For example, e-SiGe is being used more and more extensively to strain the channel and improve PMOS performance. However, increases in Ge concentration result in increased susceptibility to strain relaxation and severe wafer deformation during advanced thermal processing. As a result, the precise control of the stress induced during annealing is becoming increasing important. This paper describes the use of a stress measurement technology, the Coherent Gradient Sensing (CGS) interferometer, for the characterization of deformation induced during micro-second laser annealing. The unique features of the CGS technique enable not only the characterization of the magnitude of wafer bow and warp, but the local uniformity of strain relaxation. Results are presented showing the relationship between wafer deformation and the fundamental parameters of micro-second laser annealing. In addition, the effects of processing history on laser anneal-induced deformation will also be evaluated, and techniques for managing stress accumulation across an entire process flow will be discussed.