Suppression of x-ray radiation during sputter-etching

Abstract

An attenuating member comprising a plurality of passages like a tube nest, is positioned between the electrodes of a diode sputter-etching system and close or next to the anode. The passages of the attenuating member are parallel to the direct path between the electrodes and have a length appreciably greater than their maximum width. A bias on the attenuating member tends to cause secondary electrons emitted by ion bombardment at the cathode to pass through the attenuating member with a minimum of collisions. Upon striking the anode, X-rays generated at the anode by the collision of the secondary electrons are inhibited from traveling back to the workpiece by the interposition of the attenuating member. The arrangement is important in the fabrication of surface-sensitive devices such as MOS devices in which the impingement of even low energy X-rays may affect critical operating parameters, in particular, the threshold voltage.