Using the plasma that we developed to generate a low-temperature plasma at atmospheric pressure, we have investigated the etching possibility of tin oxide $(SnO_2)$ thin films. Hydrogen and methane radicals generated from the plasma were observed and their intensity was found to be dependent on the cathode material by an analysis with optical emission spectroscopy as well as by the plasma impedance. The etching ability of this plasma was evaluated by an emission intensity as well as by the evaluation of impedance using a plasma I-V curve.