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

Chemisorption and thermal decomposition of metallorganic chemical vapor deposition precursors, (t-BuN)2W(NHBu-t)2, bis(tertbutylimido)bis(tert-butylamido)tungsten (BTBTT) and (t-BuN)2W(NEt2)2, bis(tert-butylimido)bis(diethylamido)tungsten (BTBDT), on Cu(111) have been investigated bymeans of thermal desorption spectroscopy (TDS) and synchrotron-basedX-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 isW(=NBu-t)3 and the other is proposed to be a bridged amido complex, [(t-BuN)2W(lNBu-t)]2. In comparison, aW-imine complex and aW–N–Cmetallacycle are two intermediates produced fromBTBDT. 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 a-H abstraction, isobutylene from c-H elimination, acetonitrile from bmethyl elimination, and molecular hydrogen. In addition to these desorption species, BTBDT produces hydrogen cyanide and imine (EtN = CHMe) via b-H elimination, not possible with BTBTT due to the absence of b-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. 2005 Elsevier B.V. All rights reserved.