Numerical Simulation And Experimental Investigation In Laser-Induced Backside Wet Etching Of Sapphire

Sapphire with high wear resistance, high hardness and stable chemical performance characteristics, is widely used in the field of industry and national defense field. For example, sapphire is the main industrialization substrate for blue LED (Light Emitting Diode), smart phone screen, wear resistant bearing material and windows material. Because the physical properties of sapphire, the conventional diamond processing method is difficult to machining with some shortcomings such as chipping, tool wear and crack. By contrast, laser-induced wet backside etching(LIWBE) is a kind of machining method has great development prospects, especially the processing of sapphire, quartz, glass and other transparent hard brittle materials. LIBWE is a sophisticated machining process. During this process, many problems and phenomena are involved, like material properties, phase transformation and heat convection. In order to improve the technology of LIBWE, numerical simulation and experimental investigations about LIBWE of sapphire process were carried out in this paper.In this paper, the solution of CUSO4 is applied in the experimental research of laser-induced backside wet etching sapphire substrate with 1064nm laser. First of all, the meaning and importance of laser-induced wet backside ecthing sapphire, the research significance and research status at home and abroad. Secondly, the mechanism of laser induced liquid phase deposition was analyzed during the LIWBE process and appropriate working liquid was selected. Simultaneously, theoretical thermal reaserch was studied and the mechanism of deposition was explained by the experimental results. The material removed mechanism and the forming process of the groove were concerned, too. Thirdly, according to the experimental data, considering the material data variations of temperature, the enthalpy change and latent heat fusion, a 3D multimedium physical model is developed to simulate thermal history during LIBWE process with numerical method. The model concerned not only the transient temperature field induced by laser pulses but also the characteristics of the groove section. Finally, series process experiments were executed and verified the model. The main research methods and conclusions were listed as follows:1. Experiments of laser-induced wet backside etching were conducted, the depth of deposition was 2μm at the backside of sapphire substrate along the scanning direction. Based on the previous theoretical researches and coupled laser thermal effect, the chemical equations were speculated. Simultaneously, the chemical components contained cuprous oxide and copper oxide by XPS and Auger spectra. The chemical equations were deduced by experimental and theoretical results.2. During the LIBWE experiments, some interesting phenomena were found:sapphire cannot be etched at the first time or previous times; once the sapphire was etched, sapphire can be etched subsequent every time. After several scanning times, the roughness of grooves varied from smooth to roughness by high temperature. This feature is beneficial for the accumulation of deposition and processing of LIBWE more easily or stably.3. According to the experimental data, a 3D multimedium physical model was developed to simulate thermal history during LIBWE process with numerical method. The model concerned not only the transient temperature field induced by laser pulses but also the characteristics of the groove section. The results show that the temperature of laser spot’s center rose dramatically and reached the maximum at the end of pulse duration. Both the temperature plots and the cross section are similar to a flat Gaussian distribution. The depth of groove decreases when the scanning speed increases and effective pulse numbers decreases, too. In the section of groove, some peaks and valleys occurred at the bottom of the groove. When the scanning velocity is 4mm/s, this phenomenon is more obvious.4. Comparison between the modeling and experiment indicated that the groove-profile in simulation agreed well with the experiment data, i.e., the present physical model is effective and feasible. When the laser energy density reached to 26.5J/cm2, the sapphire material can be etched. The width/depth of groove decreased with the increase of scanning velocity. A linear relationship between the depth of groove and scanning passes. Those experimental results were according with the FE model. This means that the basically ass μ me and equivalent number of pulses are right. The section of groove were similar with the groove-profile in simulation, the experimental data (depth/width) agreed well with results of simulation and the feature at the bottom of groove was similar with simulation results, too. That is to say, the numerical model is effective and feasible.