The Annealing Effect of the High-Pressure Phases of Silicon During Micro-Laser Assisted Machining

Micro-laser assisted machining (μ-LAM) is a novel micro/nano machining technique developed for ductile mode machining of ceramics and semiconductors. Ductile mode material removal is possible in a nominally brittle material due to the high-pressure phase transformation (HPPT) phenomenon during the machining process. The μ-LAM system utilizes an IR laser beam to preferentially heat and soften the workpiece material during the material removal process. The μ-LAM process has several direct benefits observed during the machining process: allows for deeper cuts in the ductile regime due to the enhanced ductility of the workpiece material, higher material removal rates as a result of deeper cuts, lower cutting forces due to the reduced workpiece hardness from the heating process, and less tool wear from the reduced hardness and lower cutting forces. The μ-LAM process also has an added benefit that eliminates any subsurface damage in the form of high-pressure phases (HPPs) that usually remain after the ductile mode material removal process. This paper discusses this added benefit that occurs due to an annealing effect that re-crystallizes the HPPs back to its original crystalline phase. Single point scratch tests are used to form the HPPs by performing ductile mode μ-LAM on single crystal silicon (Si). Micro-Raman (μ-Raman) spectroscopy is used to characterize the machined surface/subsurface and identify the HPPs and annealed phase.