Magnetically enhanced sputter source

Abstract

A circular magnetron sputter source employs a central anode surrounded by an annular cathode of generally inverted conical configuration. The anode structure forms a composite anode and inner magnetic pole piece which is operated at or near ground potential. An outer magnetic pole piece concentrically surrounds the annular cathode. This outer pole piece is electrically isolated from the cathode, and held at or near ground potential. The cathode is operated at a potential of several hundred volts negative with respect to ground. The cathode is held in place by a novel retainer means and has a novel cross section configuration. Magnetic flux is provided either by permanent magnets or by electromagnets or by a combination of both located externally of the vacuum chamber in which the sputter source is operated. Magnetic field lines pass from the outer pole piece and through the cathode, exiting the sputter surface near the outer edge of the cathode. These magnetic field lines form an arch over the cathode by passing directly to the central anode without reentering the uneroded sputter surface of the cathode. In a circular geometry, these arching magnetic field lines form an endless tunnel for confining a glow discharge. The tunnel thus formed is a novel and modified magnetic tunnel in which electrons are reflected electrostatically from the cathode surface near the outer edge of the cathode and reflected by magnetic mirroring near the inner edge. Use of this modified magnetic tunnel leads to improved electrical impedance characteristics of the glow discharge and to improved uniformity in cathode erosion.