Cold cathode electron beam sources for high-rate PVD

Electron beams (EB) are known to be powerful and versatile tools for materials evaporation and physical vapor deposition (PVD) of thin films. Regardless the beneficial technological features of the EB?PVD, established designs of high-power electron beam sources based upon thermionic emitters as well as their supply and control systems are complex and expensive. Hence, business economics prevent their application in many thin film processes. Alternative EB sources with cold cathodes have nowadays attracted enhanced interest because of their prospects as economic beam sources for a broader spectrum of applications, including PVD. A simple but efficient high-power, cold cathode electron source has been developed and tested recently. Inside this EB gun, a high-voltage glowdischarge (HVGD) is sustained. Ions from the plasma are accelerated in the cathode fall and hit the cathode thus releasing secondary electrons. These electrons gain energy on the reverse path. Beside to the greatly simplified mechanical design and electric supply circuitry, cost reductions result also from the facts that the HVGD beam source does not require differential high-vacuum pumping and that it can be operated in a wide range of acceleration voltages without the need for movable electrodes. Particle-in-cell (PIC) simulations of the HVGD and of the beam formation in a simple geometry have been carried out to study the effects of the electrodes' geometry and of several discharge parameters on the electron-optical characteristics. Understanding the interaction of cathode material and plasma work gas as well as the handling of arc phenomena are crucial for stable operation of the EB source and have been addressed by experimental investigations therefore. Finally, a compact, cost efficient compound evaporator with an integrated beam bending system and a specially shaped vapor aperture will be introduced. It was successfully tested together with a 30 kV / 60 kW HVGD EB gun in evaporation of copper for high-rate metallization of plastics