An Evaluation of Ti-Based Metal Gate Electrodes on Hf-Silicate Dielectrics for Dual-Metal-Gate Applications

Abstract

An evaluation of Ti-based gate metals ͑Ti, TiN, and TiB 2 ͒ on Hf-silicate gate dielectric prepared by atomic layer deposition has been reported. The effective metal work functions, calculated by taking an interface layer and interface charge into consideration, were 4.27, 4.56, and 5.08 eV for Ti, TiN, and TiB 2 , respectively. Regardless of gate electrodes, the conduction mechanism of the samples was fitted with the Poole-Frenkel model, which is related to oxygen vacancies in the film. A Ti gate electrode was found to be more favorable for n-channel metal oxide semiconductor ͑MOS͒ devices, and TiB 2 gate electrode can be used for p-channel MOS devices with Hf-silicate dielectrics.Many high-k materials are currently being considered as a potential replacement for SiO 2 -based dielectrics in future complementary metal oxide semiconductor ͑CMOS͒ technology. 1-7 Among the many candidate materials, nitrogen-incorporated hafnium silicate has received intense attention as a new gate dielectric material due to its reasonable permittivity ͑15-25͒, relatively large bandgap ͑5.68 eV͒, and thermodynamic stability with Si. 1-11 Nitrided Hf-silicate is also more resistant to boron diffusion from poly-Si gate through the dielectric. 12 However, the incompatibility between the poly-Si gate electrode and the Hf-based dielectric, such as poly Si depletion effect, Fermi energy pinning, and sheet resistance constraint, limit its usefulness in advanced CMOS devices, especially beyond the 45 nm technology node. 13-15 Therefore, advanced high-performance devices require high-dielectric-constant ͑high-k͒ gate dielectrics and dual work function metal gate electrodes. 13 Dual metal gate CMOS integration requires two different metals with work functions near the Si bandedges, around 4.0 eV for n-channel metal oxide semiconductors ͑NMOS͒ and 5.0 eV for p-channel metal oxide semiconductors ͑PMOS͒. 13 Consequently, the evaluation of various single metal and/or metal alloys on nitrogen-incorporated Hf-silicate dielectric could be advantageous for future advanced CMOS technology development.Because of good thermal stability and minimal interaction with high-k films, titanium-based materials could be an attractive candidate for metal gate applications. 16,17 Ti-based refractory materials such as TiN and TiB 2 have been previously considered as diffusion barriers in metal contact formation due to their high electrical conductivity and excellent chemical inertness at high temperature. 18 In this article, the electrical characteristics of metal oxide semiconductor ͑MOS͒ devices with Ti-based metal gates ͑Ti, TiN, and TiB 2 ͒ on nitrogen-incorporated Hf-silicate dielectric are investigated. The effective metal work functions are extracted in order to examine their compatibility with NMOS or PMOS devices. In addition, the conduction mechanism of Ti-based metal/Hf-silicate dielectric/p-type Si MOS devices is investigated.HfSiO x films were deposited directly on p-type ͑100͒ precleaned ͑SC1, 1% HF solution and deionized water rinse͒ 8 in. Si substrat...

Synthesis and Characterization of Ether Adducts of Thorium Tetrahydroborate Th(BH4)4 and Chemical Vapor Deposition of Thorium Boride Thin Films

“…The CVD apparatus we employed has been described elsewhere. 25 The precursor reservoir was maintained at a temperature above ambient (typically, 60 °C), the hot zone was maintained at the desired temperature (200−350 °C), and the base pressure in the apparatus was 10 −4 Torr. Depositions were carried out over 8 h; over this period, opaque silver-black films were deposited on the substrates.…”

“…There has long been interest in the chemical vapor deposition of metal boride coatings, owing to their highly attractive properties, such as hardness, infusibility, moderate strength, resistance to wear and corrosion, chemical inertness, and excellent electrical conductivity. − In general, metal diborides have considerable potential as diffusion barriers for copper interconnects and as contact metals and gate electrode materials for silicon metal-oxide semiconductor field effect transistors (MOSFETs). − …”