Research On High-efficiency And Low-damage Grinding Process Of Silicon Wafer

Monocrystalline silicon wafer is the most important substrate material in integrated circuit industry. In order to meet the requirements of large diameter of silicon wafer and super thin chip, it needs to remove the machining allowance rapidly in machining of silicon wafer. Along with the decrease of integrated circuit feature size, it puts forward higher request for surface/subsurface quality of silicon wafer. However, conventional machining process of silicon wafer has disadvantages of low-efficiency, high-cost, low-accuracy, difficulty of automation and pollution. Therefore, it is necessary to research the novel high-efficiency and low-damage machining process of silicon wafer. Aiming at improving silicon wafer surface quality and machining efficiency, this paper proposed the grinding process of silicon wafer which combined the precision grinding with diamond grinding wheel and the ultraprecision mechanical chemical grinding with soft abrasive grinding wheel. The influence mechanism of grinding conditions on surface/subsurface quality in the grinding with diamond grinding wheel and the mechanical chemical grinding with soft abrasive grinding wheel were discussed. The new process which used mechanical chemical grinding with soft abrasive grinding wheel was also researched. The main research contents and results of this paper are as following:First, this paper presented an analysis of the model of grain depth-of-cut in grinding of silicon wafer with diamond grinding wheel. The effects of grinding parameters on surface/subsurface quality of silicon wafer were studied through the model and grinding experiments. The process strategy of controlling silicon wafer surface/subsurface quality was proposed based on the study. The results indicated that with the decrease of wheel grain size, wheel feedrate, wafer speed and the increase of wheel speed, the surface roughness and subsurface damage decreased in the grinding with diamond grinding wheel.Second, the compositions of soft abrasive grinding wheel used in mechanical chemical grinding were optimized and the grinding wheel was manufactured accordingly. The grinding experiments of silicon wafer were conducted to study the grinding performance of the newly developed soft abrasive grinding wheel. Scanning electron microscope, three dimensional surface profiler and transmission electron microscope were used to inspect the surface profile, surface roughness and subsurface damage of silicon wafer ground by soft abrasive grinding wheel. The experiment results showed that the surface of mechanical chemical ground silicon wafer was ultra-smooth with surface roughness of Ra0.4nm and no damage was found in the subsurface but an amorphous layer of13nm. The experiments were conducted to study the effects of grinding parameters on material removal rate and the grinding parameters of soft abrasive grinding wheel were optimized accordingly. The maximum material removal rate of3.93mm3/min was obtained.Finally, aiming at the targets of increasing machining efficiency and decreasing surface/subsurface damage of silicon wafer, the new process which combined the precision grinding with#600and#3000diamond grinding wheel and the ultraprecision mechanical chemical grinding with soft abrasive grinding wheel was proposed. The grinding experiments of silicon wafer using new process were conducted, which realized high-efficiency and low-damage grinding process of silicon wafer, compared to conventional machining process. The machining efficiency nearly doubled and the surface roughness of silicon wafer less than Ra lnm was acquired.