Performance of radio frequency hollow cathodes at low gas pressures

Typical hollow cathodes (HC) have distances between opposite inner walls in a millimeter range and can operate at gas pressures of approximately 0.1–10 Torr (13.3–1333 Pa). This is because the pressure and the cathode geometry must fulfill the condition for the hollow cathode effect, based on electron exchange between opposite walls. In this paper, we report on the performance of the radio frequency powered cylindrical and linear HC, with the gas flowing through the cathode, at the mTorr (0.1 Pa) pressure range typical for magnetron sputters or arc evaporators. Operation of simple cylindrical HC with inner diameters exceeding 10 mm was possible at pressures down to 0.9 mTorr (0.12 Pa) in argon. The plasma ion density did not exceed magnitude of 109 cm−3. However, a plasma density as high as 5×1011 cm−3 was measured 15 cm below 16 cm long linear Magnets-in-Motion (M-M) HC in mTorr pressure range. The M-M cathodes can be used as an efficient sputtering/evaporation source for large area PVD of films or incorporated into different hybrid PVD and PE CVD plasma systems with conventional sources for production of new quality coatings.