Homogeneous coatings inside cylinders

Abstract

The creation of homogeneous, thin films inside small cylindrical parts, for example, pipes, is a significant challenge. In particular, uniform properties over the whole surface area to be covered by the thin film are very difficult to obtain with a physical vapour deposition (PVD) process. A physical limit leads to a minimum distance between the cathode and the thin film growth zone. A pin-shaped metal cathode, in combination with a specially designed outlet port for the argon gas, makes it possible to deposit a thin metal film inside an aluminium pipe. The metal cathode was 4 mm in diameter and the aluminium pipe 30 mm in length and 12 mm or 20 mm, respectively, in diameter. A PVD process was used for plating the thin film. Under vacuum conditions, argon ions are used to evaporate the target. The metal atoms and ions are transported to the substrate surface where the growth layer is deposited. In our experiments, copper was used as the cathode material. The average thickness of the metal coating is approximately 250 nm. The advantage of this process is a low substrate temperature and the relatively good homogeneity of the thin film. X-ray fluorescence measurements were used to measure the thickness distribution over the whole surface of the coating. The film structure has also been evaluated in other investigations. It is the intention of this work to allow functional films to be produced requiring low process temperatures during the coating phase. Niobium films for superconductors are eligible for potential applications.