Evolving Preston’s Equation in Chemical Mechanical Planarization

Abstract

The evolution of semiconductor devices necessitates greater control parameters for enhancing CMP process controllability. Historically, CMP engineers have sought to improve polishing process performance by real-time control of time, pressure, and velocity using Preston’s equation. However, Preston’s equation has traditionally addressed blanket-wafer or non-patterned wafer’s vertical or horizontal scale controllability, such as wafer center to edge or the in-wafer non-uniformity expressed by percentage. However, limited control variables cannot determine patterning profile changes.Upon closer examination of the basic Preston’s equation, other factors were considered constant or environmental parameters, excluding pressure and velocity. Current and future scaled-down devices demand additional control parameters to achieve nanometer-scale vertical controllability with patterned wafers. This presentation introduces an extended Preston’s equation by incorporating more control parameters, including temperature and slurry concentration. The study reveals that lowering and controlling the polishing temperature induces slurry selectivity changes by modulating the activation energy between the slurry and wafer. This temperature control also drives pad material changes that impact selectivity. Furthermore, the study evaluates in-situ slurry composition control to assess its real-time impact on wafer performance. When all five active parameters are combined into the extended Preston’s equation, it is demonstrated that real-time nanometer vertical scaling is achievable. The results of this study provide insights into the future design direction of CMP equipment, which will be communicated in this talk along with the concept of future CMP equipment.