Development Of Soft Abrasive Wheel Used In Ultra-precision Grinding Silicon Wafer

Monocrystalline silicon wafers are the most widely used substrates in IC manufacturing fields. The surface quality and subsurface damage situation directly affects the property, the rate of finished products and the lifetime of IC device. With the increasing of the wafer diameter, some new processes for wafer machining are being researched. Among them, the ultra-precision grinding with fixed abrasive wheel is taking the place of lapping and becomes mainstream processing technology for manufacturing of bare wafers and back thinning of patterned wafers. But now the wheels used in the ultra-precision grinding of silicon wafer are fine grain diamond wheel, and inevitably generate deep damage layer. The ground wafer surface also needs to be machined by CMP in order to super smooth, free damage wafer surface. Therefore, it is necessary to study the processing method with the new type grinding wheel, which can get super smooth, low damage ground surface.An innovative low damage grinding method for silicon wafers using a soft abrasive grinding wheel is put forward in this paper. Based on the material properties of monocrystalline silicon and the 1 test of nine soft abrasive lapping plate, the formulation of soft abrasive wheel is designed and optimized. The soft abrasive wheel with #3000 CeO₂ abrasive for wafer ultra-precision grinding is developed and a detachable and interchangeable structable of wheel used on the VG401 MK II ultra-precision grinding machine is designed. The dressing method of soft abrasive wheel is studied, and the dressing tool for the soft abrasive wheel is developed. The grinding performances of soft abrasive wheel are studied in terms of surface roughness, surface topography, surface defect and subsurface damage of the ground wafers by use of 3D Optical Profiler, AFM, SEM, TEM. The experiment results show that the wafer surface roughness ground by soft abrasive wheel is sub-nanometer, the ground surface also doesn't have grinding marks which must appear on the surface ground by diamond grinding wheel. Besides, the subsurface damage ground by soft abrasive wheel has no microcracks and dislocation which also appear on the subsurface ground by diamond grinding wheel and is composed of 0.01μm amorphous layer, that is only 1/17 of diamond grinding wheel. The surface/subsurface quality ground by soft abrasive wheel is closed to it by CMP. The chemical reaction among abrasives, additives and silicon is analyzed by XPS inspection of product component on the ground wafer surface. The mechanism of material removal on the wafer surface can be explained as chemical and mechanical recombination action. Based on the of material removal mechanism of soft abrasive wheel, the formulation of soft abrasive wheel is further improved and solves the grinding burn which often occurs on the wafer surface ground by initial soft abrasive wheel.