Paper TF+PS+SE-MoA5
Plasma Enhanced Atomic Layer Deposition of Superconducting Nb_xTi_yN Films

Monday, November 7, 2016, 3:00 pm, Room 102B

NbN, TiN, and their mixtures have been studied for their use in superconducting applications. These materials are commonly deposited via sputtering techniques, but a lack of thickness control limits this technique from applying thin, uniform films. Atomic Layer Deposition (ALD) has been widely recognized for its ability to coat substrates with uniform film thicknesses ranging from a few Ångstroms to 100’s of nanometers. Plasma Enhanced ALD (PEALD) extends the capabilities of the ALD technique, improving the properties of certain films, particularly nitrides deposited at low temperatures. PEALD of NbTiN has previously demonstrated superconducting properties¹ and PEALD NbN has been previously reported with a critical temperature of 10.4K ².

In this work, Nb_xTi_yN (0 ≤ x, y ≤ 1) has been deposited using PEALD in an Ultratech/CNT Fiji system at substrate temperatures between 100 and 300°C. Stoichiometry was controlled by adjusting the ratio of NbN:TiN cycles during the film deposition. Precursors utilized for this study were (t-butylimido) tris(diethylamido) niobium (TBTDEN) and tetrakis(dimethylamido) titanium (TDMAT). A mixture of N₂ and H₂ was used as the plasma gas for the NbN cycles while TiN was deposited with an N₂ plasma. Films were analyzed for thickness and optical properties through spectroscopic ellipsometry. Room temperature resistivity was derived from four point probe measurements. Samples were analyzed with X-ray photoelectron spectroscopy to determine stoichiometry and impurity levels. Superconductivity characteristics of the films will also be presented.

A 20nm, 300°C deposition of NbN, which had a room temperature resistivity of 282μΩ-cm, was shown to have a critical temperature of 12.4K and a critical field greater than 12 Tesla.