Effect of platen shape on evolution of total thickness variation in single-sided lapping of sapphire wafer

Total thickness variation (TTV) of sapphire wafer is one of the most important geometrical parameters as it is related with the quality of LED. In the wafer manufacturing, single-sided lapping is the final process to correct wafer TTV, but there are few understanding about the mechanism of TTV generation. The authors focused on the effect of platen shape on TTV generation. Because changes of platen shape make changes of pressure distribution on wafer witch is resulted in different material removal rate. For analyzing wafer TTV evolution by platen shape, wafer was projected onto the platen. And then, the distance between platen surface and wafer which related with material removal rate was analyzed. From the analysis on the platen shape, TTV could be calculated. Experiments were conducted with different platen shapes to verify theoretically predicted TTV. Experimental conditions were chosen to exclude effects of the sliding distance on TTV as setting the rotational speed of wafer and platen under the same. Experimental results showed that TTV of lapped wafers were well matched with analyzed TTV considering thermal deformation of platen during lapping process. This novel platen shape model can be helpful to understand mechanisms of TTV generation and to improve TTV.