Quantitative in-situ measurement of asperity compression under the wafer during polishing

The interaction of the wafer, slurry and pad determines the material removal rate during Chemical Mechanical Planarization (CMP). Dual emission laser induced fluorescence (DELIF) provides a means to measure the slurry layer thickness between the wafer and a Fruedenbergy FX9 pad during CMP with high spatial (4.3 μm/pixel) and temporal resolution (2 Hz). In this paper we present some preliminary measurements of pad compression using DELIF to measure the standard deviation of asperity height. Static slurry layer images were captured at high (70 kPa) and low (0 kPa) down-force applied to the wafer. In-situ, dynamic images at 10 kPa down-force applied to etched wafers were imaged. Two wafers were etched such that they contain square wells, one wafer with 27 μm and the other will 14.5 μm deep wells. In the static case, asperity compression is directly related the amount of fluid displaced. In the dynamic case, asperity compression is 35% greater under the 27 μm wells than the 14.5 μm wells.