Investigation and Modeling of Stress Interactions on 90 nm SOI CMOS with Various Mobility Enhancement Approaches

Abstract

The interactions of STI stress and various mobility enhancement approaches on SOI CMOS has been systematically studied. Strong interactions between STI stress and CESL (Contact Etch Stop Layer) stress on channel mobility was observed and attributed to the amplification of CESL channel tensile-stress under the reduced LOD (Length of Diffusion). In addition, an almost completely reversed PMOS mobility-LOD trend on <110>/(100) and <100>/(100) orientated SOI wafers was observed, which is induced by the reversed polarity of piezo-resistance coefficients. On the other hand, charge pumping leakage was increased by post-gate oxide stress (such as CESL stress) only, and did not be affected by any stress prior to gate oxidation step (such as STI stress). This observation implies that processes must be integrated very carefully while pursuing any mobility enhancement scheme via post-gate oxide stress.