It has recently been reported that some waviness may affect STI CMP yield. CMP is designed primarily to planarize relatively with large r scale than small topography. However, there may be a range of wafer topographies in which STI patterns are over-polished, depending on peak-to-valley variations and frequencies. Permissible peak-to-valley variations and frequencies are calculated by determining whether the difference in polish quantities between the peak and valley is less than permissible values, such as 10 nm, 20 nm, and 30 nm. Reports indicate that slurry selectivity can decrease this effect, although with certain disadvantages.