Experimental Research On Ultra-precision Grinding Technology For Silicon Wafer Thinning

With the fast development of portable electronic products, semiconductor silicon wafers need to be backside thinning to meet the requirement of thinner and thinner chips as wafers trend to become larger in diameter. Based on summarizing the research on silicon wafer thinning technology at home and abroad, aim at the key factors such as silicon wafer surface and sub-surface damage form ground by diamond grinding wheel, damage layer depth and its distribution pattern, The flexural deformation of ultra-thin silicon wafer, Edge chipping of the silicon wafer during the grinding process and so on which affect the processing of wafer thinning. Carried out detailed theoretical analysis and experimental research, proposed an optimal program called single-process of grinding process for wafer thinning.First of all, the surface damage type, the damage layer depth and its distribution pattern of the silicon wafer by using diamond grinding wheel were analyzed. Through the angle polishing tests, the effect of abrasive size of wheel on damage depth was also studied, the result showed that the damage depth of silicon wafer's grinding surface increased with the growth of the abrasive size. Additionally, the depth of the damage layer had no obvious relationship with the crystal orientations or the radial locations of the wafer surface, and it was uniform on the wafer surface.Second, the law of the deflection form of the ultra-thin silicon wafer grinded by diamond wheel was studied by using the Stoney formular. It showed that the silicon wafer curvature is inversely proportional to the square of the wafer thickness when the curvature of the wafer was small. Also, the optimum thickness of silicon wafer ground by #600, #2000 and #3000 diamond wheel was predicted. Then we conducted grinding experiments and curvature measurements to verify this prediction.Furthermore, the edge chipping of the silicon wafers grounded by diamond wheel had been investigated. The effects of the wheel size, the feed rate, the rotation direction, the thickness of the wafers on edge chipping were analyzed. The results showed that the larger the wheel size was, the smaller the thickness of the wafer as well as the grinding wheel feed rate was greater then the more serious of the edge chipping was of the silicon wafer. And the edge chipping of silicon wafer by homodromy grinding was worse then contrarotation grinding, Additionally, the edge chipping shap in the <100> crystal orientation was "triangle", and in the <110> crystal orientation was "rectangular" or "ladder-like rectangular". Finally, this paper put forward the new process plan based on the diamond wheel grinding and soft abrasive grinding, designed the wafer vacuum suction and the dressing disc for soft abrasive grinding wheel, the process parameters of the diamond wheel grinding experiments was optimized. By using the diamond wheel and the soft abrasive we eventually obtained 40μm thickness of ultra-thin silicon wafer.