Chemical mechanical polishing (CMP) is widely adopted in producing excellent local and global planarization of microelectronic devices. However, the fundamental mechanisms of material removal and the interactions of the chemical and mechanical effects are not well understood. In the present paper, the contact area of a pad with a wafer is measured in dry and wet conditions in different pH solutions using optical microscopy and Fourier transform infrared spectroscopy, respectively. Pad surface mechanical properties in dry and wet states are also investigated using atomic force microscopy. The results indicate a significant difference in pad surface mechanical properties between dry and wet states, which could be correlated with the CMP removal rates. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3186032] All rights reserved.