Mechanism of bump formation on glass substrates during laser texturing

A quantitative model is proposed to elucidate and predict the dome-shaped surface topography resulting from CO2 laser heating of glass substrates. In the analysis, a permanent structural change in glass is induced by a higher glass transition temperature due to the faster cooling process, with a final topography being determined by the temperature history resulting from the absorbed laser energy. The analysis is validated by experiment, which focuses on the energies which trigger the permanent deformation and induce a dome-shaped topography. The dimensions (maximum height and base area) of the bump show a logarithmic dependence on energy as expected from the theory. Using the constants determined from the experimental data and our analysis, bump profiles over a range of laser fluences are predicted. These two constants provide the information for determining the new glass transition temperature and the threshold energy needed to form a permanent bump. The result also suggests that the topography is mostly determined from the conditions at the end of the laser pulse. The effects of thermally induced stress on the model, and the physics of bump formation in chemically strengthened glass are addressed. (C) 1999 American Institute of Physics. [S0021-8979(99)04315-7].