Spatial structure of a planar magnetron discharge

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Abstract
In planar magnetron sputter deposition, metal atoms are sputtered from a cathode target by a magnetically confined plasma. The spatial structure of the planar magnetron discharge and the resultant etch track in the cathode depend on gas pressure, discharge voltage V, current I, and magnetic field strength B. We investigate the distribution of discharge current at a cylindrically symmetric cathode. The radial distribution of current at the cathode has been measured for a range of values of the above parameters using a radially staggered array of 1-mm diameter current probes embedded in the cathode plate. The distribution is peaked at the radius at which the magnetic field is tangent to the cathode, and the width of the distribution w̄, is a function of the discharge parameters. We compare this width to two models of the motion of secondary electrons emitted from the cathode. When the cathode sheath is thin compared to the axial range of the secondary electrons, the scaling is w̄∝V1/4/B1/2. We develop a new model of the magnetron discharge when the cathode sheath is thick compared to the energetic electron gyroradius and obtain w̄∝V1/10I1/5/B4/5. We find that the thick sheath model yields the best agreement to the experiment.

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