CMP process run-to-run control to adjust margin in control limit

This paper describes a run-to-run control method based on within-wafer distribution of film-thickness and removal rate. The main feature of this method incorporates adjusting the lower and upper margin of the film-thickness after CMP. The margins represent the differences of the minimum and maximum film-thickness values from the lower and upper control limits, respectively. In order to realize this concept, (1) the removal-rate within-wafer distribution is modeled as a polygonal line profile using the results of blanket-wafer polishing, (2) the removal rate at measurement sites of the product wafer is derived from the profile to adjust for differences between product types, (3) the profile is updated with the results of product wafer polishing in the work sequence, and (4) polishing time is calculated so that it satisfies the condition wherein the margin on the upper side equals the margin on the lower side within control limits to prevent film-thickness failure due to run-to-run variations. A capability index based on the margins is suggested and actual production results are shown using this index, which indicates a 71.6% improvement in accuracy and precision.