Thermal stress fracture mode of CO2 laser cutting of aluminum nitride

Abstract

A thermal stress fracture mode of material removal by laser cutting was conducted in 1-mm thick wafers of aluminum nitride (AlN) using a continuous wave CO2 laser with a defocused beam. In this mode, a thin layer (10–20 μm) of AlN surface was melted in an oxygen environment to form aluminum oxide. Solidification of the melt layer coupled with thermal expansion mismatch generated thermal stresses that in turn created a crack along the middle path of the laser beam, resulting in material separation. Thermochemical modeling of laser heating, oxide forming, and subsequent cooling of AlN was performed to validate the formation of cracks as well as material separation through unstable crack propagation. A comparison with the conventional “evaporation/melt and blow” laser cutting method showed that the thermal stress method offers significant benefits such as improved precision, better cut quality, higher cutting speed, and lower energy losses.