Optical emission spectroscopy spatial characterization of a silicon based Micro Hollow Cathode Discharge operating in Helium in DC regime*

Microplasma sources, with at least one dimension below the millimeter scale, have garnered significant attention due to their potential for a broad range of applications [1]. These non-thermal plasma microreactors can operate at atmospheric pressure in DC excitation due to their high surface area volume ratio. Among the typical configurations of microplasma reactors is the Micro Hollow Cathode Discharge (MHCD) reactor, where two electrodes are separated by a thin dielectric layer. At GREMI, we produce MHCD made of silicon from clean room process technology. Some works have been carried out on closed cavity microdischarge devices [2]. We are now producing and investigating Through Silicon Via (TSV) type MHCD.

Spatially resolved Optical Emission Spectroscopy is used as a method to investigate the plasma generated in this type of reactor [3]. With this technique, we are able to map the emission intensity of specific spectral lines across the microplasma. This mapping reveals interesting behavior close to the microreactor walls. For a TSV microplasma ignited in He at 600 mbar with less than 1% of hydrogen, the electron density of the plasma and the gas temperature are estimated to be around 10¹⁵ cm^-3  and 650K respectively for a current of 1.8mA. In the case of closed cavity MHCD, the line profile is substantially modified exhibiting some wings at its edges. This point will be discussed and a comparison will be made between the two types of microreactor.