Model for Designing Planar Magnetron Cathodes

摘要

Planar magnetron cathodes have arching magnetic field lines which concentrate plasma density to enhance ion bombardment and sputtering. Typical parameters are: helium at 1 to 300 milli-torr, 200 to 2000 gauss at the cathode, 200 to 800 volts, and plasma density decreasing by up to ten times within 2 to 10 cm from the cathode. A 2D, quasineutral, fluid model yields formulas for the plasma density: n(x,y), current densities: j(x,y), j(sub e)(x,y), j(sub +)(x,y), the electric field: E(sub y)(y), and the voltage between the cathode surface and a distant plasma. An ion sheath develops between the cathode and the quasineutral flow. The thickness of this sheath depends on processes in the quasineutral flow. Experiments shows that T(sub e) (3 (yields) 8 eV) adjusts to ensure that (alpha)(sub 0)(tau) (approx) 2.5 in helium, for ionization rate (alpha)(sub 0) (10(sup 4) (yields) 10(sup 5) s(sup -1)), and electron transit time to the unmagnetized plasma (tau) (10 (yields) 100 (micro)s). Helium glow discharge cathode fall (alpha)(sub 0)(tau) is about 2.5, though this occurs at much higher voltage.