NH_3-RTP grown ultra-thin oxynitride layers for MOS gate applications

摘要

Ultra-thin oxynitrides can serve as gate dielectrics for the technology nodes 100 nm and below. In this work, we present the properties of ultra-thin oxynitride gate dielectrics prepared by RTF nitridation of Si in NH_3 followed by post-grown oxidation in O_2 or in steam (post nitridation anneal, PNA). The layers show excellent barrier properties including significantly lower leakage current compared to SiO_2 of identical equivalent oxide thickness (EOT). For the same EOT, the tunnel current density of the RTF oxynitride layers were about four orders of magnitude lower compared to SiO_2. With optimised, the interface state density (At) of the RTF-grown oxynitride layer is in the region of a good SiO_2 layer (D_(it) approx 1E11 eV~(-1) cm~2). X-ray photoelectron spectroscopy (XPS) data of selected oxynitride layers indicate that a nitrogen concentration of as high as 31 percent can be achieved by RTF process. RTF grown oxynitride layers were applied to NMOS transistors as gate dielectrics and their device performances were compared with those prepared by RF plasma nitridation (RF-PN). Transistors with RTF-grown oxynitride gate show a significantly better uniformity in threshold voltage on 200 mm wafers than those oxynitride layers grown by RF-PN. It was also found that the leakage currents of the RTF and RF-PN gate oxynitrides obey the same trend from the 1.5 nm EOT regime down to the 1.0 nm EOT regime. This observation indicates that the leakage current barrier quality of the RTF oxynitride is at least as good as the RF-PN oxynitrides.