Chemical-mechanical polishing is not optimized as a commercial semiconductor process. Especially, to succeed in the high yields, uniformity of polishing rate is very important. A new technology is proposed to obtain the uniform polishing rate all over the wafer.
PETEOS oxide wafers were polished by orbital type polisher for 2 minutes. The oxide thickness was measured pre-CMP and post-CMP, using the 62 points mapping with 6mm edge exclusion. The polishing rate is the thickness difference averaged over the 62 points and normalized by the polishing time.
To find the reason of bump on the wafer, we examined the three factors; linear velocity, stress distribution, and slurry effect. First, dependence of polishing rate on the linear velocity was examined by experiments. In addition, simulation on the linear velocity profile was performed in orbital type CMP. As a result of experiments and simulations, we could find that the bump was not concerned in velocity.
Second, effect of download was investigated. Using the finite-element method, stress distribution was simulated on the wafer surface. Stress concentration was not found on the wafer surface at which bump is occurred. However, polishing rate profile was changed under various retainer ring download.
For the last time, effect of flow rate was examined. Polishing rate was not sensitive to flow rate.
Using the fact that polishing rate is proportional to traveling distance, experiments were performed on the various widths of channel to decrease the traveling distance. Dependence on the retainer ring download was also examined to improve the uniformity of the polishing rate on the wafer edge.