Atomic Layer Deposition of Superconductive Niobium Carbonitride Thin Films

Abstract

Transition metal carbonitrides (TMCN) are stable materials with excellent catalytic and superconductive properties. Atomic layer deposition (ALD) stands out as the optimal method for the fabrication of these materials, enabling their use in future applications. In this study, we deposit ALD NbC _x N _y films at 250-450 °C with NbF₅ and 1,4-bis-(trimethylsilyl)-1,4-dihydropyrazine on Si, Ru, TiN, and soda lime glass. We analyze the film growth characteristics, composition, and phase. The films show substrate-enhanced growth on Si with a growth per cycle (GPC) of 1.3 Å. Additionally, the films were superconductive as-deposited and had a superconducting critical temperature (T _c ) of 14.5 K after annealing at 950 °C. This work expands the range of TMCNs deposited by ALD and demonstrates the applicability of ALD for thin film materials with a high T _c .

1

Suggested mechanisms for the deposition of NbC _x N _y films with NbF₅ and (Me₃Si)₂DHP at 425 °C.

2

SDTA curve measured for (Me₃Si)₂DHP using a hermetically sealed high-pressure stainless-steel pan. A heating rate of 10 °C/min was applied.

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Photograph of a NbC _x N _y film deposited on glass at 425 °C (a). The white stripe is cast on the film from the lighting fixture above it. Elemental composition of NbC _x N _y films deposited at different temperatures (b). Resistivities of NbC _x N _y films deposited at different temperatures (c).

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NbC _x N _y film GPCs as a function of NbF₅ (a) and SiDHP (b) pulse lengths and deposition temperature. NbC _x N _y film GPC as a function of deposition temperature on Si substrates (c). NbC _x N _y film thicknesses as a function of the number of ALD cycles on Si, TiN, and Ru substrates at 425 °C (d).

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SEM images of NbC _x N _y films deposited on Si at 425 °C.

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Top-down and cross-sectional SEM images of NbC _x N _y films deposited on Ru, Si, and TiN substrates at 425 °C.

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ToF-ERDA elemental depth profiles of a 62 nm NbC _x N _y film deposited at 425 °C (a). GIXRD diffractograms of a film deposited at 425 °C and after annealing in a N₂ atmosphere at different temperatures. The reference peaks correspond to cubic NbC_0.5N_0.5 (b).

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XPS Nb 3d, C 1s, and N 1s measurements of a NbC _x N _y film deposited at 425 °C after Ar⁺ sputtering.

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Raman spectrum of a 62 nm NbC _x N _y film deposited at 425 °C.

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Resistance as a function of temperature for films deposited at 425 °C before annealing and after annealing at 550, 650, 750, 850, and 950 °C (a). T _c of the films as a function of the annealing temperature obtained from (a). The deposition temperature of 425 °C is shown with a dashed line (b).

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Top-down and cross-sectional SEM images of NbC _x N _y films deposited on Si annealed at 550, 750, and 950 °C in N₂.

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Cross sectional SEM images of a NbC _x N _y film deposited on a Ru film deposited on silicon as-deposited and after annealing at 950 °C in N₂ (top) and diffractogram of the film after the annealing (bottom).