GB1057048A - Method of forming superconducting metallic films - Google Patents

Abstract

A superconducting metallic film of niobium, tantalum or vanadium is formed by vapour depositing the metal at a rate of at least 0.5 microns/ hour on to a substrate (e.g. of copper, aluminium, <PICT:1057048/C6-C7/1> <PICT:1057048/C6-C7/2> quartz, mica or glass) heated to a temperature in excess of 25 DEG C. in a chamber evacuated to a pressure of 1 x 10-5 to 5 x 10-5 mms. of mercury. The initial evaporation getters oxygen and oxygen - containing compounds in the chamber and the metal subsequently deposited forms the superconducting layer. A molybdenum shield may be positioned between the vapour source and substrate during gettering to prevent deposition of oxygen contaminated metal on the substrate. A non-metallic substrate may be heated to above 600 DEG C. during deposition to improve adhesion of the deposited layer. In making superconductive alloys, e.g. of niobium-tin, alternate layers of the metals are deposited and then the temperature of the substrate is raised to alloy the layers by diffusion. Figs. 1 and 5 show apparatus in which the metal to be deposited is heated respectively by electron bombardment and induction. Fig. 1 shows a metal source in the form of a rod 62 with a terminal bead 63, and a substrate 24 on a heating member 22. A heated tungsten wire 41 provides electrons to bombard the bead 63 which is maintained at a positive potential. A molybdenum screen 49 maintained at a negative potential serves to focus the electrons on the bead. Molybdenum shield 83 can be pivoted to shield the substrate from the metal vapour during gettering. A second metal source 73, e.g. of tin, is contained in an heated by a molybdenum wire 72. The substrate may be a wafer or a cylinder, the cylinder being rotated during deposition to ensure the production of a uniform layer over its curved surface. Fig. 5 shows a metal source in the form of a rod 115 with terminal bead 116 heated inductively by a coil 117. A condenser 109 with water inlet 110 and outlet 111 surrounds the top part of the evacuated bell jar 105. Glass rod 119 shadows a portion of the condenser wall to prevent formation of a continuous annular metal deposit thereon, so as to allow effective heating of the metal source.