## 3 Results and Discussions  
Figure 3 shows variations in the average removal rates of SiC when using the conventional polishing pad (IC1000) and pads impregnated with Fe and Al\({}_{2}\)O\({}_{3}\) under identical experimental parameters. Each experiment was repeated thrice to ensure reproducibility of the results. As shown in the figure, the SiC removal rate is higher for the 1 wt % Fe and 3 wt % Al\({}_{2}\)O\({}_{3}\)-impregnated pads (Pad D) than that for the conventional polyurethane pad. The MRR for the 1 wt % Fe impregnated pad was \(\sim\)0.33 \(\upmu\)m/h, which is higher than that for the 1 wt % Al\({}_{2}\)O\({}_{3}\) impregnated pad (\(\sim\)0.18 \(\upmu\)m/h). The highest removal rate of \(\sim\)0.74 \(\upmu\)m/h was obtained by using the impregnated pad containing 1 wt % Fe and 3 wt % Al\({}_{2}\)O\({}_{3}\). SiC polishing typically involves the formation of an oxide layer due to a chemical reaction, and this layer is removed by the abrasive particles present on the surface of the pad. Thus, the materials on the SiC surface are removed by the combination of chemical reactions and mechanical processes. According to these observations, the Fe-impregnated pad can increase the MRR due to the Fe catalytic reaction in H\({}_{2}\)O\({}_{2}\) on the surface of the Fe catalyst. Initially, Fe is immersed in H\({}_{2}\)O\({}_{2}\) solution and ionizes to form ferrous ions (Fe\({}^{2+}\)). Then, Fe\({}^{2+}\) reacts with H\({}_{2}\)O\({}_{2}\) to generate OH radicals (OH-), a strong oxidation species. These OH radicals react with the top-surface of the SiC substrate to form an oxide layer when the Fe catalyst comes into contact with SiC. This oxide layer (SiO\({}_{2}\)) is mechanically and chemically removed [10]. The Fe and Al\({}_{2}\)O\({}_{3}\)-impregnated pads tend to increase the propensity for two-body contact interactions, as shown in Figure 4. When the two-body contact dominates the polishing process, the polishing rate of the wafer will be high. For the two-body contact interactions to occur, the abrasive layer must be firmly retained by the pad. The MRRs from the three-body abrasion are lower than those obtained from two-body abrasion because of the presence of loose abrasive particles between the abraded solid surfaces for only \(\sim\)10% of the time, while they spend \(\sim\)90% of the time in rolling. Figure 2: Experimental setup for the polishing system used in this work. Figures 5 and 6 show the surface roughness (Ra) of SiC wafers polished by pads impregnated with 1 wt % Fe particles, 1 wt % Al\({}_{2}\)O\({}_{3}\) particles, 1 wt % Fe and 1 wt % Al\({}_{2}\)O\({}_{3}\) particles, and 1 wt % Fe and 3 wt % Al\({}_{2}\)O\({}_{3}\) particles. The surface roughness was measured by Zygo with a measuring window of 42 \(\mu\)m \(\times\) 42 \(\mu\)m. The results showed that the average Ra values of the SiC samples after polishing were 5.59 A, 4.66 A, 2.61 A and 1.59 A. Moreover, the surface roughness of the samples polished using the impregnated pads consisting of 1 wt % Fe and 3 wt % Al\({}_{2}\)O\({}_{3}\) particles was better than that of the samples polished using the other pads. Following Pad E polishing, the average Ra value was determined to be \(\sim\)1.21 A. Note that the Ra obtained using Pad D polishing is almost identical to that for Pad E polishing, shown in Figure 6. The MRR for the nanoparticle-impregnated pads is significantly better than that for the polyurethane polishing pad. Hence, pads impregnated with 1 wt % Fe and 3 wt % Al\({}_{2}\)O\({}_{3}\) particles can result in a higher MRR while yielding a defect-free surface. After numerous experiments, [PERSON] _et al._[12] deduced the critical depth expression for brittle-ductile transition, as given in Equation (1). \[d_{c}=\varphi\frac{E}{H}{(\frac{K_{\mathrm{c}}}{H})}^{2} \tag{1}\]  
where \(d_{\mathrm{c}}\) is the critical depth, \(\psi\) is a dimensionless quantity, \(K_{\mathrm{c}}\) is the fracture toughness, \(E\) is the material's Young modulus of elasticity, and \(H\) is the hardness.