Substrate etching by means of Ar-mixed graphite-cathodic-arc plasma beam was investigated in a newly-developed compact-type mu T-FAD. The surface level and roughness change were measured as a function of the Ar gas flow rate, when Ar gas was introduced into the arc generation zone and in the vicinity of the substrate. When Ar gas was introduced to the arc generation zone, the etching rate was lower but the surface was relatively not roughened. When Ar gas was introduced in the vicinity of the substrate, the etching rate was higher but the surface was roughened. At the same gas flow rate (and pressure), the substrate was etched more than three times faster when Ar gas was introduced into the arc generation zone than to the vicinity of the substrate. After measuring the discharge and plasma conditions, the results were considered to be caused by the difference in the amount of plasma transported to the substrate. (C) 2009 Elsevier B.V. All rights reserved.