Mapping wafer flatness changes in chemical mechanical planarization

Effects of Film Stress on the Chemical Mechanical Polishing Process

“…It was found in one study that the mean removal rate decreases while the WIWNU increases as the compressively stressed thermal oxide on one side of Si substrate (i.e., convex wafer shape) was thinned down by the continuous polish process (i.e., decreasing wafer bow). 3 Conversely, in another study, 4 both the removal rate and WIWNU were found to decrease with increasing prepolish wafer bow, from negative (concave, tensile stress) to positive (convex, compressive stress). Neither of the two studies above has given a proper physical model to account for the observed wafer curvature effects on the CMP process, although both speculated that the existence of the wafer bow makes it difficult to flatten the wafer when the carrier was pressed against it, giving rise to polish nonuniformity.…”

“…x ϭ a cos ϭ a cos [4] where x is the horizontal distance between center and point C (O and (O 2 -F -). Expanding both sides of Eq.…”

Impact of Wafer Geometry on CMP for Advanced Nodes

“…15 Attempts have been made to address the effect of lower frequency wafer topography components such as shape. 11,12,16 Notably, Zhang et al presented experiments that showed that local curvatures of wafer shape might affect CMP removal rate uniformity. 16 The previous work has established approaches to modeling CMP processes and made comparisons between models and experiments.…”

“…11,12,16 Notably, Zhang et al presented experiments that showed that local curvatures of wafer shape might affect CMP removal rate uniformity. 16 The previous work has established approaches to modeling CMP processes and made comparisons between models and experiments. While wafer geometry issues have been addressed to some extent in previous work, the role of backside NT and wafer shape have not been adequately addressed.…”