Shallow Trench Isolation Stress Effect on 45 Degree Rotated MOSFET Layout

Abstract

This paper describes the Shallow Trench Isolation (STI) stress effect on 45 degree rotated MOSFET layouts. 45 degree rotated PMOS layout with large Sa (active space) shows 15% increase in saturation drain current (I dsat) as compared to the non-rotated ones. On the other hand, PMOS layout with minimum Sa and same rotation show 3.8% I dsat enhancement only. This is because when rotated 45 degree, the channel orientation changes from to axis. This enhances the PMOS I dsat with large Sa. At minimum Sa, the I dsat enhancement is small because the PMOS is at high STI stress. For or non-rotated layouts, the STI stress is observed to increase the I dsat by 14 %. The impact of STI stress effect on PMOS with minimum Sa is negligible at or rotated. For NMOS, no Idsat enhancement or degradation is observed on 45 degree rotated layouts. Finally, we have studied the effect of using 45 degree rotated PMOS in ring oscillator circuit.