Optical and mechanical characterization of chemical mechanical planarization pad surfaces

Both contact and non-contact methods are used to analyze surface properties of three types of chemical mechanical planarization (CMP) pads: plain, XY grooved, and concentrically grooved. Optical interferometry is used to probe the pad surface without contact and to produce a surface height probability density function (PDF). The right hand contacting tail of the PDF is often found to be exponential for CMP pads and a decay length (λ) as a measure of pad surface abruptness can be extracted. An incremental loading device is developed and used to measure the pad surface mechanical response. A pad-wafer contact model based on Greenwood and Williamson theory is used to interpret the nonlinear features of the pad surface compression data, which, furthermore, enables independent calculation of λ from mechanical data. Surface abruptness (λ) extracted from both methods (optical and mechanical) is found to be consistent for all three types of pads. No significant difference is observed in the pad surface abruptness among the three types of pads.