Research On Laser Thermal Stress Cleaving Method For Silicon Wafers With Pre-microcrack On Surface

Currently,silicon wafers are widely used in the manufacture of semiconductor devices.Silicon wafer dicing is a key process in the packaging process.The traditional ultra-thin diamond wheel cutting method has low processing efficiency,and the finished product kerf is prone to chipping.The laser thermal stress cleaving method for cutting silicon wafers is a highly efficient and environmentally friendly new processing method that has the potential to replace the traditional processing forms.It realizes the separation of materials through the expansion of cracks,and the finished product kerf is smooth and flat.At present,laser thermal stress cleavage methods also have some problems such as the edge effect and the asymmetric cutting track deviation caused by the prefabricated cracks on the initial terminal.Therefore,in order to solve these problems,it is of great engineering significance to study the technology of laser thermal stress cutting silicon wafer with prefabricated microcrack on the surface.Firstly,the interaction of 1064 nm semiconductor laser and single crystal silicon,the mechanism of surface micro crack propagation and the extended conditions were analyzed based on the theories of heat transfer,thermoelasticity,and fracture mechanics.A finite element model of pre-cracked laser thermal stress cutting of silicon wafers was established.The crack propagation process was analyzed by temperature field and stress field,and the model was verified by temperature measurement experiments.Secondly,build a test platform and design laser alignment with the prefabricated micro-crack on the surface.Focus on the upper laser and cut the laser below the glass platform gap.By comparing the kerf quality of laser thermal stress cleavage with pre-groove respectively by ultra-thin diamond grinding wheel,UV nanosecond laser and femtosecond laser.After comprehensive consideration,the ultra-thin diamond grinding wheel is determined as the most suitable crack prefabrication method.Aiming at the edge effect of current laser thermal cracking and the problem of asymmetrical cutting trajectory deviation,through the experiments of laser thermal stress separation of silicon wafers with prefabricated micro-crack on surface,it is proved that the edge effect would be improved by prefabricating micro-crack on the surface,and In the case of asymmetrical cutting,the cutting trajectory is corrected,but due to the large transverse pulling force during the cutting process of the singlegrain width strip chip,the strip chip tears.Finally,the micro-crack were prefabricated on the surface of silicon wafers by ultra-thin diamond grinding wheels,and the pre-groove depth and laser process parameters were changed to investigate the criteria for crack propagation.Further,the single factor experiment was used to discuss the influence of the process parameters and the thickness of the silicon wafer on the quality of the laser thermal stress cutting process.Through comparison experiments of ultra-thin diamond grinding wheels,laser ablation cutting and laser thermal stress cleavage,it can be seen that the last one is better than other two processing methods for cutting silicon wafers.