Characterization of ultrathin gate dielectrics formed by in-situ steam generation with nitrogen postprocessing

Abstract

We examined ultrathin films produced by in-situ steam generation (ISSG), ISSG with NO anneal, ISSG with remote plasma nitridation (RPN), and rapid thermal oxidation (RTO). Capacitance-voltage measurements performed on these films indicated an equivalent oxide thickness (EOT) in the range of 1.6-2.5 nm. The nitrogen postprocessing made it possible to achieve thinner EOTs while keeping the leakage current density below 10-2 A/cm2 at Vg = -1.5 V. Total x-ray fluorescence (TXRF) analysis on the films yielded a transition metal concentration less than 5 × 1010 atoms/cm2. Atomic force microscopy (AFM) measurements yielded microroughness values of 0.18-0.2 nm, which were conformal to the starting material surface microroughness. High-resolution transmission electron microscopy (HRTEM) images showed physical thicknesses ranging from 2.0-3.0 nm, which were used, in conjunction with the EOTs, to calculate effective dielectric constants for the films. Low energy (500 eV) secondary ion mass spectrometry (SIMS) measurements performed on the ISSG + NO and ISSG + RPN films showed sharply different [N] profiles.