High density plasma activated by resonance properties of metamaterials and measurements of spatial distribution of plasma parameters

Microwave metamaterials in low-power levels are currently introduced into the industrial wireless communication devices, for instance, for antenna miniaturization activated by their resonance properties. When we increase the level of microwaves, metamaterials are expected to be applicable to plasma generation with high efficiency arising from their inherent resonances. In one previous study [1], microwave plasma generation was observed in a waveguide, where profiles of detected electron densities are nonuniform, depending on local shapes of a metamaterial unit. In this study, we aim at microwave plasma generation assisted by an inserted metamaterial for semiconductor plasma processing. The metamaterial consists of split ring resonators as a unit structure, and its two-dimensional array structure is regularly arranged in the disk configuration. The working frequency for plasma generation is 2.45 GHz, where the resonance frequency of the metamaterial ranges from 2.40 to 2.55 GHz. According to experimental results by a movable Langmuir probe with a three-dimensional scanner, generated plasma is homogeneous over the measurement space with electron density of 2-3 x 10¹⁷ m^-3, which indicates that the plasma media is equivalent to the negative permittivity space. [1] A. Iwai et al., Plasma Sources Sci Technolo. 29, 035012 (2020).