Chemical-Mechanical Polishing, CMP, as its name implies involves the combination of chemical and mechanical interactions to polish the surface of the wafer. This planarization occurs after the deposition of films over a patterned structure and is required to prepare the surface prior to the next step in the device fabrication process.

CMP is an increasingly critical step in advanced chip processes. This s driven by the move to complex 3D structures coupled with the very small depth of focus available with EUV and High NA EUV. This requires the planarisation of the chip across the wafer to be consistently within a few 10s of nano-meters. The uniformity of the polishing can be influenced by the pattern density which can result in yield limiting ‘hot spots’ within the chip.

Measuring the planarisation has typically required optical systems, either using white light interferometry which can be sensitive to thin film interference effects or Scatterometry which requires special targets that lack information on within chip pattern effects.

The RPM is ideally suited to this application as it can measure high speed intra-die polishing uniformity and flatness metrology to < 0.5nm 3 sigma.