Duoplasmatron ion beam source for vacuum sputtering of thin films

Abstract

A variation of the von Ardenne type of a duoplasmatron ion source is described. Here the arc discharge is maintained between the cathode in the high pressure and the anode in the vacuum chamber, as opposed to the conventional arrangement in which the arc discharge is confined primarily to the high pressure chamber. This modification allows the extraction, through apertures, of a well defined ion beam of current up to 500 mA over an area ˜1 cm² into a vacuum chamber at a pressure of ˜10^-5 Torr. The ion beam is accelerated and made to impinge on a target material for sputtering. Sequential sputtering of different targets inside the vacuum chamber is possible with the help of suitable magnetic fields. The ion beam has been used to sputter conducting, semiconducting, and insulating target materials. Typical rate of deposition of silver films at a distance of 8 cm from the target with a 50 mA, 2 kV ion beam of 8 mm diam is ˜400 Å/min. Deposition rates of ˜50 Å /min are obtained for SiO₂ and TiO films. Vacuum sputtered films adhere to the subtrates much more strongly than the evaporated films do. Gold and silver films grow epitaxially on rock salt substrates at ambient or lower temperatures. This vacuum sputtering process has been found to induce and stabilize new structures. For example, sputtered films of molybdenum, tantalum, tungsten (normally bcc), and hafnium, rhenium and zirconium (normally hcp) have been observed to exist in an fcc phase. Fcc structure films as thick as 2μ have been prepared. Epitaxial growth of the fcc structures on rock salt substrates at temperatures of ˜400°C are observed.