Numerical and experimental study on the thermal damage of thin Cr films induced by excimer laser irradiation

Single-shot laser damage of thin Cr films on glass substrates has been studied to understand the cracking and peeling-off mechanism. A mathematical model is developed for the calculation of transient heat transfer and thermal stresses in Cr films during excimer laser irradiation and cooling, the transient temperature, and the stress-strain fields are analyzed by using a three-dimensional finite-element model of heat flow. The finite-element program ABAQUS, with user subroutines, is adopted to perform the numerical analysis. A KrF excimer laser is used in experiments as a source of UV radiation. Morphological inspection of damaged Cr films is carried out by using scanning electron microscopy and the threshold fluences for visible damages are investigated for various film thicknesses. According to the numerical analysis for the experimentally determined cracking and peeling-off conditions, cracking is found to be the result of the tensile brittle fracture due to the excessive thermal stresses formed during the cooling process, while peeling off is found to be the combined result of films bulging from the softened glass surface at higher temperature and the tensile brittle fracture during the cooling process. (C) 1999 American Institute of Physics. [S0021-8979(99)09720-0].