X-Ray Radiation Hazard using Vacuum Deposition Plant

Abstract

IT has been shown in a recent report by Strachan and Harris¹ that a sputtering plant operated at voltages as low as 8–10 kV. can give rise to X-radiation which can be dangerous to the operator. This observation was made with an apparatus different from the two-electrode system used for the deposition of thin films. Their apparatus consisted of a glass vessel in which positive ions formed in a discharge between an oxide-coated cathode and iron anode were accelerated to a target used for sputtering. It was shown that the X-rays arose from secondary electrons emitted from the target bombarding the walls of the glass envelope. It was possible to operate the main sputtering chamber at a lower gas pressure than normal because the ions were formed in an auxiliary discharge. Thus, the secondary electrons were able to reach voltages comparable to that of the ion-accelerating potential because of their long mean free-path. In a glow discharge the secondary electrons are required for ionizing the gas molecules and their final voltage is not that of the applied potential. Thus it is uncertain whether the results of Strachan and Harris would be directly applicable to a normal two-electrode system with a cold cathode operated at 8–10 kV.