Characterization of a multipolar electron cyclotron resonance microwave plasma source

Abstract

A microwave-cavity plasma applicator with multicusp electron cyclotron resonance (ECR) used as an ion beam source and for oxidation and etching of semiconductor materials has been characterized over its range of operating conditions. Single and double Langmuir probe measurements of electron density, ion density, and electron energy distribution functions have been made in the downstream region and as a function of power (120-250 W) and pressure (0.5-15.5 mtorr) in argon and oxygen. In addition, Faraday cup measurements of ion energies and optical emission data have been made. The plasma applicator is a 17.8 cm-diameter, 2.45 GHz cylindrical resonator with one end terminated by a sliding short and the other end by an overdense disk-shaped plasma. Processing of materials or ion extraction occurs at the field-free lower face of the plasma disk. Ion densities are typically 10/sup 11/-10/sup 12/ cm/sup -3/ at this point and decrease exponentially with distance downstream from the discharge. The electron energy distribution functions are Maxwellian and below 3 mtorr more closely follow a Druyvesteyn distribution with average energies of 5-8.5 eV. Ion energies to a grounded substrate are typically 10-25 eV with few, if any high-energy (>25 eV) ions.<>