Low Pressure Phase Transformations During High-Speed, High-Temperature Scratching of Silicon

Higher temperature assisted processing of silicon, such as heat-assisted diamond turning, is often being considered to improve surface integrity. At higher temperatures and under mechanical loading and unloading, caused by a moving tool, silicon deforms plastically often in association with occurrence of phase transformations. This paper investigates such phase transformations in rotational scratching of single crystal (100) p-type silicon with a conical diamond tool under various furnace-controlled temperatures ranging from room temperature (RT) to 500 °C and at scratching speeds comparable to that used in the diamond turning process (1 m/s). Phase transformation study, using Raman spectroscopy, at various crystal orientations, shows differences in phases formed at various temperatures when compared to that reported in indentation. The tendency to form phases is compared between scratched and diamond turned surfaces at RT, and also with that reported at low scratching speeds in the literature. Analytical indenting-based pressure calculations show that at higher temperatures, phase transformations can happen in silicon at significantly lower pressures. Analysis of depths of the scratched groove indicates that at temperatures beyond a certain threshold, plastic deformation and significant elastic recovery may be causing shallow grooves. Abrasive wear coefficients are thus seen to decrease with the increase in temperatures. This study is expected to help tune heat-assisted diamond turning conditions to improve surface formation.