| Summary: | 博士 === 國立交通大學 === 電子研究所 === 99 === This dissertation provides a comprehensive study on the impact of process-induced uniaxial strain on the carrier mobility considering various scattering mechanisms. First, we introduce a BSIM-based method for the Rsd extraction. This BISM-based method is more accurate than the conventional Channel-Resistance and Shift & Ratio method because it considers the gate-length dependence of mobility caused by local uniaxial stress and laterally non-uniform channel doping. This method was verified using samples with different process conditions and good agreement with experimental data has been obtained. The accuracy of BSIM Rsd extraction method has also been verified by TCAD simulations.
In addition, the short channel mobility extraction method by using split-CV is introduced to investigate the strain impact on short channel mobility. Then the uniaxial strain dependence of Coulomb mobility extracted by Matthiessen’s rule is experimentally investigated for both nMOSFETs and pMOSFETs under various temperatures. Our study indicates that the stress sensitivity of the Coulomb mobility shows strong temperature dependence. It is due to the competition result of the stress sensitivity between bulk charge scattering and interface charge (Nit) scattering. Therefore, in order to optimize the strain efficiency on Coulomb mobility, it is necessary to suppress the formation of Nit.
Besides, through He-based low temperature measurement, the uniaxial strain dependence on surface roughness mobility (mSR) of pMOSFETs is also studied. Moreover, we compare the strain sensitivity between mPH and mSR. Our measured data indicates that mSR can be significantly enhanced by the uniaxial compressive strain. Furthermore, the mSR has higher strain dependence mPH. Our experimental results confirm the previously reported simulation results. In addition, a wavefunction penetration perspective is proposed to explain the possible physical origin of the uniaxial strain dependence of mSR.
Moreover, we experimentally assess the impact of process-induced uniaxial strain on the temperature dependency of carrier mobility in nanoscale pMOSFETs. Our study indicates that the strain sensitivity of hole mobility becomes less with increasing temperature and it is consistent with previous uniaxial mechanical bending result. It is because the less hole repopulations at energy band edge induce less strain sensitivity as temperature increases. Furthermore, through decoupling mSR and mPH, we investigate the impact of uniaxial strain on the temperature dependence of phonon-scattering limited mobility in nanoscale PMOSFETs. The vertical electric field dependence (EEFF) and temperature dependence of the extracted mSR and mPH are consistent with the reported data in the literature. The temperature sensitivity of the extracted phonon mobility becomes higher when compressive strain is applied. It is contributed by the higher optical phonon energy induced by uniaxially-compressive strain. Our new findings also explain the higher temperature sensitivity of drain current presented in uniaxial strain PMOSFETs.
|
|---|
