Spectroscopic measurement of a compact helium ECR discharge produced in a simple cusp field

In the plasma-based chemical and physical vapor deposition processes, the enhanced ionization degree of up to more than several tens of percent enables better controllability of the homogeneity, composition, and chemical structure of deposited films. For this purpose, pulsed power discharge techniques have been utilized to produce highly ionized plasmas. The pulsed power discharges are, however, limited in duty ratio, and the production of a large volume and uniform plasma is an ongoing research topic. As an alternative approach, an increase in ionization in an ECR discharge by imposing a simple cusp field has been proposed. The cusp field can confine electrons within the ECR surface by magnetic mirror force enhanced by the ECR heating and ions by the ambipolar electric field. Although better confinement can be obtained using a combination of the mirror and multi-cusp fields, the simple cusp field has better plasma accessibility, which would be an important advantage for industrial applications. We constructed a compact device with approximately 30 cm on each side and evaluated plasma parameters and ionization degree of helium plasmas using optical emission spectroscopy.