Mobility measurement and degradation mechanisms of MOSFETs made with ultrathin high-k dielectrics

Accurate measurements and degradation mechanisms of the channel mobility for MOSFETs with HfO/sub 2/ as the gate dielectric have been systematically studied in this paper. The error in mobility extraction caused by a high density of interface traps for a MOSFET with high-k gate dielectric has been analyzed, and a new method to correct this error has been proposed. Other sources of error in mobility extraction, including channel resistance, gate leakage current, and contact resistance for a MOSFET with ultrathin high-k dielectric have also been investigated and reported in this paper. Based on the accurately measured channel mobility, we have analyzed the degradation mechanisms of channel mobility for a MOSFET with HfO/sub 2/ as the gate dielectric. The mobility degradation due to Coulomb scattering arising from interface trapped charges, and that due to remote soft optical phonon scattering are discussed.

I. Introduction

To Fulfill the scaling scenario as projected in the International Technology Roadmap for Semiconductors (ITRS), it is widely believed that a high-k (high permittivity) dielectric is needed to replace as the CMOS gate dielectric to reduce significantly the gate leakage current [1]. After extensive research efforts by numerous groups, several high-k dielectrics have shown promising results [2]. However, there are still many challenges that have held back the actual implementation of these promising candidates. One of the major challenges is the significantly lower channel mobility for the transistors made of high-k gate dielectrics as compare to their counterparts [3], and there is not yet a clear understanding of the causes behind this degraded mobility. Besides the mobility degradation, the accuracy of the mobility measurement is also concern due to high density of interface traps and gate-leakage current. In this paper, we systemically studied the accurate measurement and the degradation mechanism of channel mobility for MOSFET with gate dielectrics.