Temperature-Oriented Mobility Measurement and Simulation to Assess Surface Roughness in Ultrathin-Gate-Oxide (∼1 nm) nMOSFETs and Its TEM Evidence

On a 1.27-nm gate-oxide nMOSFET, we make a comprehensive study of SiO2/Si interface roughness by combining temperature-dependent electron mobility measurement, sophisticated mobility simulation, and high-resolution transmission electron microscopy (TEM) measurement. Mobility measurement and simulation adequately extract the correlation length lambda and roughness rms height Delta of the sample, taking into account the Coulomb-drag-limited mobilities in the literature. The TEM measurement yields the apparent correlation length lambda(m) and roughness rms height Delta(m). It is found that the following hold: 1) lambda approximate to lambda(m) for both the Gaussian and exponential models, validating the temperature-oriented extraction process; 2) the extracted Delta (similar to 1.3 angstrom for the Gaussian model and 1.0 angstrom for the exponential one) is close to that (similar to 1.2 angstrom) of Delta(m), all far less than the conventional values (similar to 3 angstrom) in thick-gate-oxide case; and 3) the TEM 2-D projection correction coefficient Delta(m)/Delta is approximately 1.0, which cannot be elucidated with the current thick-gate-oxide-based knowledge.