Cathode Dark-Space Measurements and Deposition Rates of Tantalum in a Sputtering System

Measurements of the cathode dark-space distance have been made, both visually and electrically, for an argon discharge in a dc diode sputtering system fitted with a tantalum cathode. The values are fitted by Aston's dark-space equation and have been used to calculate the dependence of sputtering rates on discharge conditions. These calculated values are in good agreement with the deposition rates measured for films deposited on glass substrates. The variation of discharge voltage with current does not fit Aston's cathode-fall equation, which must be modified slightly. A change of slope observed in the current-voltage relationship may be due to heating of the system by the discharge. The modified Aston's equation also fitted the current-voltage curve for a platinum cathode and the same change of slope was observed.