Development of coaxial ECR plasma source for tube inner coating

Abstract

We developed an electron cyclotron resonance (ECR) plasma source with a coaxial microwave mode which has no cut-off length for coating inside a metallic tube of small diameter and shorter than the cut-off length for the microwaves used. In a discharge with a narrow gap less than the wavelength of the microwaves, both the magnetic field and the electron loss to the boundary play an important role in the condition for breakdown. We theoretically and experimentally investigated the gaseous breakdown conditions for microwave power in the presence of an external crossed magnetic field. Using a new calculation method to treat the effects of electron collisions in a wide range of gas pressures the result indicates that the ECR condition ( ω = ω ce where ω is the microwave frequency and ω ce is the electron cyclotron frequency) has significant advantages for such a narrow-gap microwave discharge. The plasma is found to be produced at B of around 875 Gauss for the pressure range from 1 × 10 −4 to 5 × 10 −3 Torr. The discharge area broadened with increasing gas pressure. Good agreement is found between the calculated and measured discharge area. The typical electron density n e and electron temperature T e were also measured to be 8 × 10 10 cm −3 and 10 eV, respectively, which parameters are suitable for reactive sputtering or plasma chemical vapour deposition.