## 4 Results and Discussion
### Experimental Results  
The fresh slurry supplied into the pad-wafer interface increased with the number of pad grooves [16]. More pad grooves allow the newly injected slurry to flow through the interface faster and prevent the used slurry from flowing back with the wafer rotation, as discussed in the numerical simulation results. The global pad/wafer contact ratio also decreased when the original land area was occupied by the radial grooves. The local pad-abrasive-wafer pressure can then be increased, leading to a slightly larger single silica particle indentation depth and higher MRR. The 300 mm wafer polisher had a faster relative velocity between the pad and wafer. To confirm the results, the experiment was run with a 300 mm wafer polisher. In the scaled-up experiment, an additional R8 pad was added. As shown in Figure 11a, the MRR of the 300 mm polisher was higher and NU was lower in the R32 pad than in the R0 pad. The R8 pad showed almost the same MRR as the R32 pad but was slightly lower. The NU of the polished wafer was improved with the increased radial grooves on the pad. Brief MRR profiles across the wafer are shown in Figure 11b. The NU value decreased with increasing numbers of radial grooves (4.65%, 2.67%, and 1.56% for rR0, R8, and R32, respectively), and the MRR was more stable at the wafer edges than at the wafer center. Regarding the resolved unstable pressure distribution observed for more radial grooves, the wafer edge contact was stabilized and the MRR increased.  
Figure 11: (**a**) The material removal rate and non-uniformity of 300 mm wafers polished with the R0, R8, and R32 pads. (**b**) Profiles of wafer surfaces polished with the different pads.  
Despite the improvements in MRR and NU with increasing numbers of grooves, there was not an obvious change when the radial groove count was increased from 8 to 32, especially in the MRR. The pressure distribution of the pad-wafer interface was expected to improve even with only a few radial grooves. The changes of the R0 pad to R8 and R8 to R32 were a qualitative change and a quantitative change, illustrating the diminishing marginal effect.  
Figure 12 shows the COF curves and COF slopes of the polishing processes. The SST was determined using the same method used in the simulation, but the first SST point was chosen within a 3% margin of error compared to the average COF value from 50 to 60 s. As a result, the R0 and R32 pads required 21.52 s and 16.06 s, respectively, for slurry saturation, which is defined as the time when DIW was fully replaced by fresh slurry and the COF reached a stable state.  
The SSTs of different pads were quantitatively analyzed and proved with the simulation and COF convergence. The slurry consumption efficiency is only around 10%, and most was wasted because of the high centrifugal force and narrow flow channel [44]. Since insufficient slurry transportation, the bow wave can form around the retainer ring and CMP pad interface, as shown in Figure 13. Moreover, the thickness is sensitively dependent on the pad groove pattern [21]. To qualitatively compare the slurry transportation ability, the slurry bow wave near the retainer ring was recorded with a high-speed camera. As  
Figure 12: The measured COF, relevant slope, and slurry saturation time in the (**a**) coupon wafer polished by the 100 mm wafer polisher, and (**b**) 300 mm wafer polished by the 300 mm wafer polisher with R0 pads and R32 pads.  
shown in Figure 14, the bow wave on the R32 pad was significantly reduced, and the gap between the retainer ring and pad was more clearly visible than on the R0 pad. It proves that the R32 pad owns the enhanced ability to transport slurry into the pad-wafer interface than the R0 pad, and the SST is also shorter.