Improvements in stribeck curves for copper and tungsten chemical mechanical planarization on soft pads

Understanding the tribology of polishing processes using an improved Stribeck curve (i.e. referred as Stribeck+ curve) elucidates the essential factors governing the mechanical aspects of chemical mechanical planarization. This study investigated tribological and thermal aspects of copper and tungsten blanket wafer polishing on the Politex soft pad with a multitude of gradual yet continuous changes in polishing pressure and sliding velocity. This work also attempted to understand the frictional and thermal transients associated with such dynamic processes. Results showed that polishing with the Politex pad produced stable COF values that indicated a “boundary lubrication” regime throughout. In contrast, copper polishing on hard pads produced tremendous spread of data clusters having a trend in COF that started with “boundary lubrication” and then transitioned to the “mixed lubrication” mode. Regarding temperature effects, the plots between average pad surface temperature and the product of COF, velocity and downward pressure showed a linear relationship between the two parameters for all copper and tungsten polishing used in conjunction with Politex and hard pads.