Atomic Layer Deposition of Molybdenum and Tungsten Oxide Thin Films Using Heteroleptic Imido-Amidinato Precursors: Process Development, Film Characterization, and Gas Sensing Properties

Abstract

Heteroleptic bis(tert-butylimido)bis(N,N'-diisopropylacetamidinato) compounds of molybdenum and tungsten are introduced as precursors for atomic layer deposition (ALD) of tungsten and molybdenum oxide thin films using ozone as the oxygen source. Both precursors have similar thermal properties, but exhibit different growth behavior. With the molybdenum precursor, high growth rates up to 2 Å/cycle at 300 °C and extremely uniform films are obtained, although the surface reactions are not completely saturative. The corresponding tungsten precursor enables saturative film growth with a lower growth rate of 0.45 Å/cycle at 300 °C. Highly pure films of both metal oxides are deposited and their phase as well as stoichiometry can be tuned by changing the deposition conditions. The WOx films crystallize as -WO3 at 300 °C and above while the films deposited at lower temperatures are amorphous. Molybdenum oxide can be deposited as either amorphous ( 250 °C), crystalline suboxide (275 °C), a mixture of suboxide and α-MoO3 (300 °C), or pure α-MoO3 films ( 325 °C). MoOx films are further characterized by synchrotron photoemission spectroscopy and temperaturedependent resistivity measurements. A suboxide MoOx film deposited at 275 °C is demonstrated to serve as an efficient hydrogen gas sensor at a low operating temperature of 120 °C.

Thermal Stability and Decomposition Pathways in Volatile Molybdenum(VI) Bis-Imides

“…Molybdenum-containing films have a wide array of applications including: microelectronic manufacturing, [1] highsurface area heterogeneous catalysis, [2] gas-sensing, [3] optical materials, [4] and lubricants. [5] Chemical vapor deposition (CVD) and atomic layer deposition (ALD) are two popular methods to prepare Mo-containing films; CVD is a continuous technique while ALD is a stepwise layer-by-layer method.…”

Ligand-Assisted Volatilization and Thermal Stability of Bis(imido)dichloromolybdenum(VI) ([(t-BuN═)2MoCl2]2) and Its Adducts

“…21,22 Others have treated 1 with anionic N,N'-chelating ligands, such as guanidinates (which have yet to find success for Mo ALD), 23 and amidinates, which have recently been used, in conjunction with O3, to prepare MoO3 films. 24 Deposition of Mo metal from such compounds appears challenging, possibly due to the high nitrogen content in the ligands.…”

Nickel nanoparticle-decorated reduced graphene oxide/WO3 nanocomposite – a promising candidate for gas sensing

“…The major disadvantages of MOS are their poor selectivity and high operating temperatures of 200 to 400 °C, which means a high power consumption [4]. WO 3 is a wide-bandgap [12,13] n-type semiconductor [14,15] with good sensitivity towards NO 2 [16] and CO [17].…”