Fluorine-free Plasma Enhanced Atomic Layer Deposited Ultrathin Tungsten Nitride Thin Films for Dual Diffusion Barrier Performance

Abstract

A vacuum deposition technique in a highly narrow device is a critical issue for fabricating barrier layers in semiconductor devices. Though tungsten nitride (WN x ) thin films’ uniform and conformal thickness control can be achieved via atomic layer deposition (ALD), most ALD-WN x processes use fluorine-based precursors, resulting in high resistivity with low growth rate and corrosive and toxic F-containing impurities. This study underscores the importance of the plasma-enhanced ALD (PEALD) process for WN x films via a fluorine-free inorganic WCl 5 precursor and critically optimizes the counter reactant ratio (N 2 + H 2 ratio of 1:1 to 1:10), temperature ranges (200∼325 °C), plasma mixture, plasma power, and postannealing condition process parameters. The as-grown WN x film properties and the impact of the plasma ratio on the WN phase, crystallinity, and stoichiometry were confirmed comprehensively by advanced transmission electron microscopy, spectroscopy, and diffraction techniques. Notably, secondary ion mass and photoelectron spectroscopies ensure uniformity and fewer impurity contents of O/Cl throughout the thickness of the WN x film. Significantly, the parent nanocrystalline hexagonal WN phase at a N 2 + H 2 ratio of 1:3 at 250 °C transformed to a crystalline cubic W 2 N phase with decreasing resistivity as the H 2 ratio of total N 2 + H 2 mixture plasma gas increased. The postannealed (500 °C) deposited WN x film demonstrated the formation of a stable cubic phase, lowering the sheet resistance with increasing deposition temperature (film thickness) and plasma ratio. The as-deposited film’s diffusion barrier performance against Cu and Ru (∼4 nm) was evaluated to withstand up to 850 °C, revealing a promising dual diffusion barrier capability as interconnects in challenging shrinking semiconductor device structures.

Topics & Concepts