A 20-nm-thick pad oxide layer is thermally grown on a 6-in, p-type [100] Si wafer, and is followed by the deposition of a 315-nm-thick low pressure chemical vapor deposition nitride layer for the trench isolation formation. Nitride and oxide layers are etched and Si is then etched away for trench formation. Initially, CF4/Ar was used to etch the 20 nm/315-nm-thick oxide/nitride layers, after which the wafers were transferred to a different etcher, AME5000 MXP polysilicon etcher, for the Si etch. The Si etch consists of two steps: first, the breakthrough step was performed to remove either the remaining oxide layer from the previous step or the native oxide layer using 35 seem of CF4 for 15 s. In a second step, the main etch was performed to etch Si using 90 seem of HBr, 30 seem of Cl-2, and 7 seem of He-O-2 for 250 s. After the Si etch, surface defects on the order of 1000-1600/wafer were observed on the Si surfaces using the Tencor AIT pattern inspection tool. The surface defects are caused by polymer-related micromasking. Instead of employing CF4/Ar for the removal of the oxide/nitride layers, 30 seem of NF3 and 5 seem of O-2 were used for the main etch step, and 10 seem of CHF3 and 40 seem of N-2 were used for the overetch step. The Si etch was continued in the AME5000 MXP polysilicon etcher using the original parameters. The use of NF3/O-2, which does not polymerize the Si surface, resulted in an almost defect-free surface. More experiments were conducted for the overetch step after the removal of nitride layer because NF3 etches the Si surface quickly once it is exposed. The combination of the NF3/O-2 main etch step by endpoint algorithm and the 25 s CHF3/N-2 overetch step, resulted in fewer surface defects than using CF4/Ar for both main and overetch steps.