Electron beam sources with cold cathodes based on DC high-voltage glow-discharges for PVD applications

Summary form only given. Electron beams are known to be powerful and versatile tools for evaporation of various kinds of materials. Because of the high sophistication of conventional electron beam technology based on thermionic emitters, its costs may be too high for some applications. A simple but efficient alternative electron source with a cold cathode has been developed, tested and optimized for industrial applications. Inside this electron gun, a high-voltage-glow-discharge is sustained. Ions from the plasma are accelerated in the cathode fall and hit the cathode releasing secondary electrons. These electrons gain high energy on the reverse path, and the plasma acts as a transparent anode. The shape of the cathode and of the plasma sheath ensures formation of a convergent electron beam. The cross-over can be projected towards the process site employing conventional electron-optical devices. Besides the greatly simplified mechanical design and electric supply circuitry, cost reductions result also from the fact, that the beam source does not require differential high-vacuum pumping. Very important for the operation are the features of the cathode. A high coefficient of secondary electron emission gamma is usually desired and provided by a thin oxide layer on the cathode's surface. Because the cathode experiences a constant sputtering by the ion bombardment, this layer has to be constantly renewed. The interaction of cathode material and plasma work gas is therefore critical and has been one subject of our investigations. At the same time, the insulating layers on the cathode also promote the onset of arcing. This problem had to be analyzed and resolved by various means. Several solutions on the way towards a stable industry-ready tool will be presented. As an example for utilizing the new EB sources in high-rate PVD applications, the coating of plastic substrates with copper will be reported. The work principle of the new electron sources holds promise for gaining benefits also in other EB applications beyond PVD. Some of them will be shortly introduced as a survey of ongoing research.