## 3 Results and Discussion  
### Material Removal Rate and Surface Roughness of the SiC Wafers Achieved by Grinding  
The material removal rate of SiC wafers is very important in grinding processes. Therefore, in this study, the material removal rates of different diamond grinding plates under the same experimental conditions were investigated. Figure 9a shows the material removal rate of the SiC wafer achieved by the different diamond grinding plates at the same rotation speed and pressure. The material removal rate is defined as the thickness removed in units of time. The figure shows that the material removal rate for Grinding-2 was 2.2 \(\upmu\)m/min. This was higher than the rates for Grinding-1 and Grinding-3 (1.5 \(\upmu\)m/min and 1.8 \(\upmu\)m/min, respectively). The material removal rates of Grinding-1 and Grinding-3 could be enhanced by 31.8% and 18.2%, respectively. Figure 9b also shows the variation in the grinding ratio using different diamond grinding plates. As can be seen in the figure, the grinding ratio of Grinding-1 was about 2.4, which was 14.3% and 50% higher than the ratios of 2.1 and 1.6 for Grinding-2 and Grinding-3, respectively. In practice, a lower grinding ratio is not always desirable unless consumption of the grinding surface is the chief concern, in which case Grinding-1 would be recommended. The reason for the high grinding ratio was the strength of the grit binder. This also meant that worn-out diamond grit would remain held in place by the binder and that new sharp edges would not be exposed. The retention of the blunt diamond grit would result in rubbing, rather than a cutting action, and the material removal rate would go down. This was an interesting observation and may have been the result of the porous nature of Grinding-2 and Grinding-3, which allowed more self-sharpening and increased the fresh diamond grit cutting efficiency. On the other hand, Grinding-1 could hold the diamond grit more strongly and there was less self-sharpening (see Figure 10). This reduced the cutting ability and could even cause deterioration of the wafer surface. Grinding wheel wear is generally correlated with the amount of workpiece material ground by the grinding ratio parameter, which is defined as the volume of material removed divided by the volume of wheel wear. In practice, the grinding ratio varies widely and can be between 1 and 200 or even more. The grinding ratio depends on the type of wheel and the workpiece and process parameters, but the grinding ratio is usually less than 1 for materials that are difficult to cut. Images of the surface roughness measured by the Zygo interferometer are shown in Figures 11 and 12. The surface of the wafer lapped by Grinding-1 was much rougher than that produced by Grinding-3. For Grinding-1, the _Sa_ value was about 41 nm and the _Sz_ value was about 1129 nm. For Grinding-2, _Sa_ was about 37 nm and _Sz_ was about 832 nm. These were markedly higher than the _Sa_ of about 25 nm and the _Sz_ of about 651 nm achieved with Grinding-3. Clearly, the reason for these differences was that Grinding-3 had better self-sharpening action. However, this higher lapping plate consumption led to a shorter working life, which is a problem that needs to be solved.  
Figure 8: Wear rate of diamond grinding plates.  
Figure 11: Surface roughness of ground SiC wafers: (**a**) Sa and (**b**) Sz.  
Figure 12: Zygo images of SiC surface: (**a**) Grinding-1; (**b**) Grinding-2; (**c**) Grinding-3.  
Figure 9: Silicon carbide material removal rate: (**a**) material removal rate; (**b**) grinding ratio.