Surface chemical characteristics of CMP polyurethane pads

Attenuated total reflection FT-IR spectroscopy coupled with a hydrogen-deuterium exchange technique is employed to investigate the surface chemistry of two polishing pads, a thermoplastic polyurethane (TPU) pad and a commercial cast urethane (PU) pad. A time/temperature-dependent reduction of nitrogen-hydrogen stretching modes (v(N-H)) was observed when the pads were immersed in deuterium oxide (D2O). Compared to TPU pads, the PU pads showed an ambiguous correlation between dependence of the band intensity changes and D2O-immersion time/temperature. For both types of pads, a sharp decrease in v(N-H) band intensity and an unexpected rebound in v(N-H) band intensity were observed within 24 hrs after immersing the pads in D2O. However, a comparable rebound in v(N-H) band intensity was not observed for conditioned TPU pad samples. This phenomenon is proposed to be due to a rearrangement of polar groups at the pad surface when the pad is immersed in water, which may influence pad performance on the asperity level.