Atomic Layer Deposition and Superconducting Properties of NbSi Films

Abstract

INTRODUCTIONNiobium silicide-based alloys have a wide range of applications including tunnel barriers for Josephson junctions, 1 superconductors for particle detection (bolometers), 2,3 and low friction and high temperature corrosion resistant coatings for engines. 4 Thin films of Nb x Si 1Àx compounds with various compositions can be deposited using a variety of methods including electron beam evaporation 5,6 (Nb 5 Si 3 and NbSi 2 ), RF magnetron sputtering, 7 explosive or arc melting and chill-casting 8À10 (NbSi 3 ), chemical vapor deposition, 11 direct laser fabrication, 12 or ion-induced formation. 13 In contrast with these line-of-sight techniques, atomic layer deposition (ALD) offers many advantages. ALD is a thin film deposition technique that uses alternating, self-limiting chemical reactions between gaseous precursors and a solid surface to deposit materials in an atomic layer-by-layer fashion. 14 The self-terminating chemistry coupled with gaseous diffusion of the precursor vapors allows an excellent control of both the composition and the thickness uniformity on arbitrary complexshaped objects. ALD has been used previously to deposit a wide range of materials including metals, metal oxides, and metal nitrides, but only metal silicides have received relatively little attention. 15 To our knowledge this is the first reported in-depth growth study for the ALD of a pure silicide.There has been only one previous report for the ALD of superconducting materials. 16 Despite the fact that very little effort has been invested in the growth study of superconductors by ALD, this unique technique could clearly beneficiate a variety of low-temperature superconductor-based applications that are currently limited by line-of-sight deposition techniques. Bolometers are one example. 2,3 Another example is superconducting radio frequency (SRF) accelerating niobium cavities 17 used is almost all particle accelerators around the world.This study pursues dual goals: first, to develop a low temperature, reliable ALD process to synthesize NbSi with a high growth rate that can open the way to other transition metal silicide or NbSi-based alloys growth study by ALD and, second, to characterize and optimize the superconducting properties of the NbSi films. In this study we use alternating exposures to NbF 5 and Si 2 H 6 to deposit NbSi films by ALD. In-situ quartz crystal microbalance (QCM) and quadrupole mass spectrometer (QMS) measurements are used to explore the mechanism for the NbSi ALD. A variety of ex-situ techniques are used to determine the physical properties of the films. X-ray reflectivity (XRR) measurements are used to evaluate the thickness, roughness, and density of the films while Rutherford backscattering spectroscopy (RBS) is employed to determine the density and stoichiometry of the films. The composition and impurity content of the films are evaluated using X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) is utilized to examine the uniformity and conformality of the coatings on no...

Optical Properties of Vanadium Pentoxide Deposited by ALD

“…The types of materials which can be deposited by ALD span almost all material classes, from single elements [70][71][72][73][74] to oxides [75][76][77][78], nitrides [79][80][81][82][83][84], phosphates [85][86][87], silicides [88], carbides [89], sulphides [90][91][92], selenides [93], tellurides [93,94] and fluorides [95][96][97][98][99][100].…”

Atomic layer deposition of 2D and 3D standards for synchrotron-based quantitative composition and structure analysis methods

“…al. 37 to be 0.46x10 15 sites/cm 2 , the thickness of the TEM window is 50 nm, H is 611.1 kJ/mol, and the density and speci c heat of Si 3 N 4 are 3.44 g/cm 3 and 800 J/(kg.K) respectively. Using equation 5 yields a T of 80°C.…”

Superconductivity in amorphous Re Zr (x≈6) thin films

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