Thermal decomposition mechanisms of tungsten nitride CVD precursors on Cu(111)

Abstract

Chemisorption and thermal decomposition of metallorganic chemical vapor deposition precursors, (t-BuN)(2)W(NHBu-t)(2), bis(tertbutyl imido) bis(tert-butylamido) tungsten (BTBTT) and (t-BuN)(2)W(NEt2)(2), bis(tert-butylimido)bis(diethylamido)tungsten (BTBDT), on Cu(111) have been investigated by means of thermal desorption spectroscopy (TDS) and synchrotron-based X-ray photoelectron spectroscopy (SR-XPS) under ultrahigh vacuum conditions. The precursors remain intact upon chemisorption on Cu(111) at 100 K, and at 300 K both precursors decompose readily via the characteristic hydride abstraction/elimination pathways to produce two stable surface intermediates for each precursor. For BTBTT, one species is W(=NBu-t)(3) and the other is proposed to be a bridged amido complex, [(t-BuN)(2)W(mu-NBu-t)](2). In comparison, a W-imine complex and a W-N-C metallacycle are two intermediates produced from BTBDT, Annealing toward 800 K further decomposes the intermediates and the detectable desorption species are completely derived from the ligands. The desorption products from BTBTT include t-butylamine generated from alpha-H abstraction, isobutylene from gamma-H elimination, acetonitrile from beta-methyl elimination.. and molecular hydrogen. In addition to these desorption species, BTBDT produces hydrogen cyanide and imine (EtN = CHMe) via beta-H elimination, not possible with BTBTT due to the absence of beta-H in the ligands. Eventually, tungsten nitrides incorporating oxygen atoms and a small amount of graphitic carbons are formed and the stoichiometry is approximated as WN1.5O0.1. Oxygen incorporation, driven by a large oxide formation enthalpy, is sensitively dependent on the moisture exposure in UHV environment. (c) 2005 Elsevier B.V. All rights reserved.