Improvements on Electrical Characteristics of p-Channel Metal-Oxide-Semiconductor Field Effect Transistors with HfO_2 Gate Stacks by Post Deposition N_2O Plasma Treatment

摘要

In this work, we found that employing a post deposition N_2O plasma treatment following the deposition of HfO_2 film can effectively improve the electrical characteristics of p-type channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) with a HfO_2 gate stack in terms of lower gate leakage current, lower interface state density, superior subthreshold swing, higher normalized transconductance and enhanced driving current even though it had led to a slightly higher equivalent oxide thickness (EOT) value of the HfO_2 gate stack by around 0.3 nm. In order to clarify the attributes of the improvements, we used charge pumping (CP) measurement to analyze the densities of interface states and bulk traps in the HfO_2 gate stacks. The improvements are then ascribed to the higher interface quality offered by the post deposition N_2O plasma treatment. Moreover, we found that to more accurately estimate the bulk traps from the CP measurement, the leakage should be taken into account especially at low frequencies. Finally, it was found that the levels of the bulk traps and interface states can be reduced by the N_2O plasma treatment, which also helps significantly eliminate the degradation of the gate stack during the subsequent voltage stress.