Langmuir probe measurements of electron temperature and density scaling in multidipole radio frequency plasmas

We have constructed a multidipole rf plasma system in a bell jar with a single planar rf powered electrode inserted at one end of a ‘‘magnetic bucket.’’ Capacitive probe measurements revealed that the rf fluctuations are particularly large in these capacitively coupled plasmas. A Langmuir probe has been developed, in which a large shunting capacitor and several self-resonant inductors are used to allow the probe tip to follow the rf fluctuations. With this new probe, we are able to adequately suppress the effect of these large rf fluctuations and measure time averaged plasma densities and electron temperatures or electron energy distribution functions (EEDFs). We report here a series of experiments in argon with the Langmuir probe fixed at the center of the plasma. The EEDFs were found to be Maxwellian with temperatures from 2 to 5 eV. The value of Te depends primarily on pressure, which was varied from 0.5 to 2.5 mTorr. The plasma density exhibited an approximately linear relationship with AelVrf/Te, where Ael is the area of the powered electrode, and Vrf is the rf voltage on the powered electrode.