Study On Reaction Mechanism Of Si And Pure Ceo2 For Chemical-Mechanical-Grinding Process

The thinning process of silicon wafer for power device in automotive applications requires stress relief and relatively high Si removal rate. The innovative process of chemical mechanical grinding (CMG) has been developed for the surface finishing of Si wafer by means of solid state chemical reaction with CeO2 abrasives under dry condition. However, the reaction mechanisms of Si and pure CeO2 in the dry CMG process are yet fully understood. The chips of Si wafer produced during CMG process were analyzed using x-ray diffraction (XRD), transmission electron microscopy (TEM), and TEM/energy dispersive x-ray fluorescence spectrometer. Those analyses clearly indicated that the chips were thin, elongated, and acicular, as well as partially curved. The large amount of Si in amorphous phase and CeO2 were detected in the CMG chips by XRD, except Si crystalline. The reaction experiments between Si and CeO2 were also performed where the pellets composed of mixed Si/CeO2 powders were heat treated at 400-1200 degrees C in both air and vacuum (10(-4) torr), then quenched. The specimens heated in air and vacuum above 900 degrees C contained Si, CeO2, a trace of amorphous phase, CeSi1.9 (cerium-silicon alloy), and Ce4.667(Si4)3O (cerium silicate), respectively. This means that the reaction mechanism in heat treatment of the Si/CeO2 powders is not exactly the same as CMG process. The findings from analyses of CMG chip products proved that the reaction of 2CeO(2)+Si -> Ce2O3+SiO (amorphous) took place during CMG process of Si wafer using CeO2 fixed abrasive. The produced Ce2O3 can be easily transformed to CeO2 by the reaction Ce2O3+1/2O(2)-> 2CeO(2).