Optical band gap analysis and modeling for ultra-thin high-k dielectrics in high-k/metal gate transistors

Abstract

A highly precise band gap measurement based on deep UV spectroscopic ellipsometry along with Bruggeman effective model approximation was developed for high-k/metal gate CMOS with ultrathin EOT (<1.5 nm). By applying and comparing the measurement for HfO2 on SiO2 and SiON interfacial layers with different thicknesses, N%, and annealing conditions, two new sub band gap states corresponding to nitrogen in the film are observed. Together with X-ray photoelectron spectroscopy and electrical measurements, it is found that the band gap energies can be correlated to N% and the leakage current of the high-k films by linear regression (R2 = 0.95). This indicates that the method is capable of quantifying physical and electrical properties of high-k dielectrics, and therefore a time consuming physical analysis or expensive electrical test on fully built devices for gate dielectrics can be avoided.