An advanced apparatus for ion beam assisted sputter coating of the inner walls of tubes

An apparatus for ion beam sputter coating of the inner walls of tubes is described. A sputter target is moved through the tube parallel to its axis. A beam of ions enters the tube along its axis, impinges onto the target and sputters material onto the tube inner wall. As a model system, tubes of aluminium were coated with copper by means of a conical sputter target which was bombarded with argon ions. Rutherford backscattering measurements both along the tube axis and along the inner circumference show that a homogeneous coating is hardly possible, unless ion beam, sputter target and tube are extremely carefully aligned. The situation can be greatly improved when the tube is rotated along its axis during deposition. The features of this advanced apparatus for homogeneous coating are described. Results of the dependence of film thickness and homogeneity on the process parameters are given. They show that the described set-up allows to coat the entire tube with a homogeneous film with a variation in thickness of less than 5%