Laser treatment of silicon at nitrogen ambient: thermal stress analysis

Laser control melting of silicon surface is carried out at nitrogen gas environment and temperature rise as well as thermal stress developed in the irradiated region is simulated using the finite element method. The residual stress developed in the surface region after the laser treatment is measured using the XRD technique and the measurement results are compared with the predictions. The fracture toughness of the laser treated surface is also measured using the indentation tests. The structural and morphological changes in the laser irradiated region are examined using the scanning electron microscope. It is found that beta phase silicon nitride was formed in the surface region of the laser treated workpiece. The temperature gradient close to the laser beam spot attains significantly high values due to the high heating and cooling rates. This, in turn, results in high stress levels in this region during the laser treatment process. The laser treated surface was free from the defects including microcracks, voids and cavitations.