Comprehensive study of NBTI under compressive and tensile strain

In this paper, we have experimentally investigated the effects of all types of strains, including uniaxial tensile strain, uniaxial compressive strain, biaxial tensile strain and biaxial compressive strain, on the negative bias temperature instability (NBTI) of Si pMOSFETs. Strain is applied by using a wafer bending system to avoid processing effects on the NBTI characteristics that result from strain engineering. We confirm experimentally, for the first time, that both uniaxial and biaxial compressive strain in Si pMOSFETs is advantageous as demonstrated by suppressed NBTI. On the other hand, NBTI is enhanced under both uniaxial and biaxial tensile strains. Differences in measured in gate current (I_g) can be attributed to the varying NBTI degradation under different types of strains. The experimental results are partly explained by strain induced band structure modulation and hole repopulation among the heavy hole and light hole subbands.