Surface wave microplasma for localized etching

Abstract

A microwave re-entrant cavity is applied to create a miniature beam of plasma species. A miniature microwave plasma discharge is created using 2.45 GHz microwave energy to generate a discharge inside 1-2 mm inner diameter (i.d.) tubes with a micromachined aperture on the end. Through this aperture the plasma stream for materials processing is formed. The diameter of the plasma stream considered in this study ranges from 2 millimeters down to 10's microns. The I/V characteristics obtained from probe measurements show that the plasma ions pass through the aperture with a aperture hole diameter as small as 14 microns. Additional measurements of the microplasma generated in the discharge tube are performed to determine the electron temperature and gas temperature. Langmuir probe measurements give an electron temperature of approximately 2 eV when the pressure is in the range of 1 - 5 Torr. Optical emission spectroscopy measurements of argon/nitrogen discharge mixtures at 1 Torr in a 2 mm tube with 33 W microwave power give a temperature of 600K - 1200K dependent on the percent argon and nitrogen. The plasma discharge in the tube discharge region is modeled using both a global model and a surface wave discharge model. The flow of the plasma discharge/beam from the source, through the aperture, and down to the substrate surface is also modeled. The modeling results will be compared to experimental results for the size and shape of the region processed by the plasma discharge/beam. A CAD-guided automated path generation system is developed to assist manufacturing micro-structures/patterns automatically using the microplasma applicator. An argon/SF feed gas mixture is used to create a plasma stream with radicals for silicon etching. Also, the etching of Ultra- nanocrystalline Diamond (UNCD) is performed using an argon/oxygen plasma. Data will be reported on the etch results including etch rate and pattern profile for both gas chemistries.