Niobium Nitride Thin Films Deposition using Radical Beam Assisted Deposition
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IVAN H. MURZIN*, NOBUYUKI HAYASHIf*, ISAO SAKAMOTO** AND MATSATAKA OHKUBO** *Metallurgy Department and Institute of Materials Science, The University of Connecticut, Storrs, CT 06268 "*Electrotechnical
Laboratory, Applied Radiation Physics Section, 1-1-4 Umezono, Tsukuba-shi,
Ibaraki, 305 Japan
ABSTRACT We have employed a radical beam assisted deposition technique to prepare singlecrystalline niobium nitride thin films on MgO (100) substrates. The radical beam containing excited species of nitrogen was produced by an ECR plasma source and used to irradiate the growing Nb film, which was simultaneously deposited by an electron-gun vapor source. The nitride film was found to grow epitaxially on the substrates heated to 600 - 650'C. It has resulted in the formation of NbN having predominantly B I structure, resistivity of 44 ltQ)cm at 20 K, and almost equiatomic composition.
INTRODUCTION The niobium and niobium nitride are the promising materials for use in various cryogenic devices such as high resolution X-ray detectorsl or superconducting quantum mixers 2. NbN has a superconducting transition temperature T, up to 16.5 K, high energy gap (E. = 5.4 meV), and large values of critical field Hc2. Furthermore, since it can be easily fabricated in thin film form, NbN is an alloy with potential application in various microdevices. Preparation of this material in a single-crystal form could improve such its properties as electronic scattering, penetration depth, surface flatness, coherent length and others. The deposition techniques that have been used most often by now to form this material are rf and dc magnetron sputtering when the pressure during deposition is in the range from 10-2 to 10-3 Torr although the deposition rate is high3' 4 . To produce niobium nitride thin films, we have applied a new deposition technique that utilizes a beam of nitrogen radicals at relatively low pressures, typically 10-5 Torr. Recently, ECR microwave source has proved to be a versatile tool for materials synthesis and modification. Missert et al. 5 and O'Keeffe et al. 6 succeeded in producing superconducting YBCO films that have sharp transitions and high critical currents by using an oxygen radical beam. It has been reported that oxygen concentration in the high T, superconductors can be precisely controlled by means of ECR plasma source6.6 This paper reports our very first results obtained as an attempt to grow epitaxially thin films of single-crystalline niobium nitride using a combined method of Nb evaporation and radical beam gun deposition.
Mat. Res. Soc. Symp. Proc. Vol. 354 01995 Materials Research Society
EXPERIMENTAL The UHV deposition system used for this study consists of an electron gun evaporator and an ECR plasma source with 2.45 GHz microwave that can produce both radical and ion fluxes. The experimental configuration is shown schematically in Fig. 1. The typical flow rate of N 2 gas fed to the source was kept about 1.0 ccm providing the pressure of about 5xl0 5 Torr in the chamber during nitride deposition. The pri
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