Three dimensional material removal model of laser-induced backside wet etching of sapphire substrate with CuSO4 solutions

The mechanism of laser-induced backside wet etching (LIBWE) of sapphire substrate with CuSO4 solution is considered as a two-step process. First, it deposits the layer from copper sulfate solution on the backside of sapphire substrate by 1064 nm laser irradiation. Then it is followed by the absorption of deposited layer to laser irradiation, resulting in the etching of the sapphire. Therefore, the material removal of LIBWE is based on laser interaction with multilayer materials (sapphire substrate--deposition layer--liquid solution). A three-dimensional thermal model is established to simulate the material removal during the LIBWE process by considering the material data variations of temperature, enthalpy change and latent heat fusion. The model can predict the groove shape influenced by the laser processing parameters (laser fluence, scanning velocity and scanning pass). The simulation results indicate that the groove depth increases with the decreasing of scanning velocity, the increasing of laser fluence and the scanning pass. The groove width is comparable with the focal beam diameter. Some peaks and valleys occur at the bottom of the groove. A comparison between the modeling and experiment indicates that the groove shape in simulation agrees well with the experiment data at laser pulse energy of 4.3 mJ/pulse, scanning velocity of 15 mm/s and the scanning pass of 4. i.e, the present physical model is effective and feasible.