In situ investigations of the chemical and mechanical mechanisms during CMP processes require analytical access to the wafer surface while interacting with the slurry and the pad under polishing conditions. In this study me make use of novel, specifically prepared, and self-designed Si wafer called microstructured single reflection elements (mSRE) utilizing the IR transparency of silicon [1]. The mSRE's enable in and ex situ attenuated total reflection (ATR) Fourier transform infrared (FTIR) investigations at the interface between silicon and the ambient with an enhanced usable spectral range. So, a thin silicon oxide layer or the polishing slurry can be investigated in the entire mid and far infrared spectral region. These mSRE wafers were placed at a simple reflection accessory of a FTIR spectrometer and either wet etched by a buffered oxide etch or polished using a CMP equivalent polishing configuration. During CMP the change of typical vibration bands of SiO2 layers and slurry constituents are observed. It was shown that the sensitivity as well as the surface selectivity of the experimental setup enables slurry and thin-film characterisations within the thickness range of monolayers. Surprisingly, the spectral features of the pad have not been observed during the polishing investigations.