Thermal Stability and Electrical Characteristics of Tungsten Nitride Gates in Metal–Oxide–Semiconductor Devices

Abstract

Tungsten nitride (WN x) was investigated to be used as a metal gate of metal-oxide-semiconductor field effect transistors (MOSFETs). WN x films with various N/W atomic ratios were deposited on SiO 2 and HfO 2 by reactive sputter deposition at different N 2 /Ar ratio flows. Nitrogen concentration in WN x films increases rapidly with the N 2 /Ar gas ratio and tends to saturate. WN x films with nitrogen atomic ratio higher than 44% have a main phase of WN, and the WN phase is stable up to 800 C. The higher-order WN x phase does not form even if the nitrogen concentration is as high as 61%. Many of the excess nitrogen atoms in WN x films are desorbed at temperatures below 766 C. The excess nitrogen in WN x films can cause effective work function lowering. A weak Fermi-level pinning effect is observed on the HfO 2 film. In this case, WN x is not suitable to be metal gate of bulk p-channel MOSFETs. Fully depleted silicon-on-insulator (FD SOI) devices require a work function of 0.2 eV from the midgap of the Si energy band. Therefore, a WN x /HfO 2 gate stack can be applied to p-channel FD SOI devices. The good integrity of the WN x /HfO 2 gate stack also suggests that WN x is a promising gate material.

Synthesis and Mechanical Character of Hexagonal Phase δ−WN

“…δ−WN shows excellent conductive characteristics with a low electrical resistivity of 9.964 × 10 –7 Ω·m. It is reported that tungsten nitride has attracted considerable attention in modern very large scale integrated circuits (VLSI) as a diffusion barrier between Cu and Si substrate because of its low resistivity, easy patterning, and compatibility with conventional complementary metal-oxide-semiconductor (CMOS) technology. , The low electrical resistivity of δ−WN suggests that δ−WN is a promising candidate for use as a diffusion barrier.…”

Thermal stability of copper nitride thin films: The role of nitrogen migration

“…We can speculate that these bumps correspond to bubbles filled with nitrogen gas, in accordance with previous results reported for similar metal nitrides. 32 The bubbles are more clearly visible for the sample annealed at 300°C right underneath ͑B͒ as well as, on the film surface ͑A͒ ͓see Fig. 6͑a͔͒.…”

Low Temperature Deposition of WNxCyDiffusion Barriers Using WN(NEt2)3as a Single-Source Precursor

“…Due to their low resistivity, appropriate work function, and thermal stability, refractory metal nitrides have been proposed for a number of applications, ranging from wafer level hermetic sealing 1 to field effect transistor (FET) gate electrodes. 2 In particular, the tungsten-based materials WN x and WN x C y have been considered as an alternative for both diffusion barriers 3,4 and gate electrodes 5 due to their low resistivity, appropriate and tunable work function (4.39-5.01 eV 6 ), thermal and mechanical stability, good barrier performance, and processing simplicity. 7,8 Depositions of WN x and WN x C y typically use ammonia and WCl 6 , WF 6 or W(CO) 6 as co-reactants.…”