Atomic Layer Deposition of TaN, NbN and MoN films for Cu metallization

Petra Alen
Abstract & Cover

Transition metal nitrides, metal silicides, and metal-silicon-nitrides are considered the most promising diffusion barrier materials for next generation ultra large scale integration (ULSI) microelectronics. The semiconductor industry has long used Ti, Ta, and W based materials, and their material properties have been very well studied. Recently, tantalum-based materials have been attracting particular interest. The barrier properties of materials based on other transition metals have been little studied. In this work, tantalum nitride films were deposited, with four new reducing agents used to reduce tantalum and obtain the desired TaN phase. As well, the deposition of niobium and molybdenum nitride films was investigated. All films were deposited by the atomic layer deposition (ALD) method, which ensures excellent conformality and large area uniformity of the films.

The problem in depositing TaN films by ALD is that in volatile tantalum precursors the tantalum usually exists in oxidation state +V which is difficult to reduce to the +III state needed in cubic TaN. The new reducing agents examined in this study were trimethylaluminum (TMA), tert-butylamine (tBuNH2), allylamine (allylNH2), and tris(dimethylamino)silane (TDMAS). In addition to reducing tantalum, TMA also acted as a carbon and aluminum source, tBuNH2 and allylNH2 as nitrogen sources, and TDMAS as a silicon precursor.

ALD of niobium nitride and molybdenum nitride films was studied at lower temperatures than reported earlier. Both NbNx and MoNx films were deposited from the corresponding metal chloride precursors (NbCl5 and MoCl5, respectively) using ammonia as nitrogen source. No additional reducing agent was required.

The deposition parameters, compositions, crystallinity, and electrical properties were studied for all deposited films. Barrier characteristics were investigated for Ta(Al)N(C), NbNx, and MoNx films. The work function values were measured for Ta(Si)N films deposited at two different temperatures.

Source of Information
FinALD40 exhibition material,
University of Helsinki, Department of Chemistry, Laboratory of Inorganic Chemistry
(Helsinki, Finland)
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