Atomic Layer Deposition of Tungsten(Ⅲ) Oxide Thin Films from W_2(NMe_2)_6 and Water: Precursor-Based Control of Oxidation State in the Thin Film Material

摘要

In thin film growth from molecular precursors, the nature and chemical reactivity of the precursors affect the material that is deposited as well as its properties. In deposition processes leading to oxide and nitride phases, a common approach is to employ a metal precursor in combination with an oxygen source such as water or dioxygen or a nitrogen source such as ammonia. In these procedures, the metal-containing precursors fall into one of the following classes: (1) the precursor is in its highest accessible oxidation state and leads to a phase in which the metal is in the same oxidation state, (2) a mid- or low-valent precursor is oxidized during the deposition process to afford a phase in a higher oxidation state, or (3) the precursor is in its highest accessible oxidation state, but an additional reducing agent is added to yield a phase in a lower oxidation state. In the chemical vapor deposition (CVD) growth of tungsten oxide films to date, WO_3 is selectively deposited regardless of the oxidation state of the tungsten precursor employed. Many other oxide and nitride depositions show similar preferred oxidation states in the film material. Growth processes in which a mid- or low-valent precursor affords oxide or nitride materials without change in the oxidation state of the metal are very rare and are limited to the CVD growth of SnO films from Sn(OCH(CF_3)_2)_2(HNMe_2) and water, PbO films from various Pb-(Ⅱ) precursors, and tantalum(Ⅳ) nitride films from Ta(NEt_2)_2-(N(C_6H_(11))_2)_2 and ammonia.