Measurement of electron energy distribution function in an argon copper plasma for ionized physical vapor deposition

The electron energy distribution function (EEDF) has been measured under a variety of conditions in an Ar/Cu plasma for ionized physical vapor deposit ion. The EEDF is directly measured in a system including a direct-current m agnetron sputter source for copper and a radio frequency (rf) induction pla sma, using a Langmuir probe with a modulated bias voltage in combination wi th a lock-in amplifier. The experimental data indicate that at fixed rf ion ization power, the electron population in the tail of the EEDF is depleted by the introduction of copper vapor, and the electron average energy decrea ses slightly. Observed changes in the EEDF are attributed to inelastic coll isions with copper atoms, which have lower threshold energies for excitatio n and ionization as well as larger cross sections as compared to argon, and the resulting reduction in the measured plasma potential. (C) 1999 America n Vacuum Society. [S0734-2101(99)02203-4].