Characteristics of DC discharges of high pressure micro gas jet in vacuum*

We have been proposing material processing using microplasma in SEM with \textit{in-situ} observation. It is necessary to produce a small-size and locally confined plasma on the surface of specimen in the vacuum environment. The microplasma processing in SEM is expected to be used for fabrication of MEMS (Micro Electro Mechanical Systems) devices and for local restoration of microelectronics devices such as large scaled integrated circuits (LSIs). It has been confirmed that a micro orifice is suitable to introduce local high pressure micro gas jet into vacuum. Characteristics of DC gas discharges with the micro gas jet were investigated by applying negative or positive DC voltage to the orifice and supplying almost atmospheric pressure of Ar gas to the orifice. A stable DC discharge was observed when the orifice was positively biased. The observed plasma size was the minimum when anode jet was operated at 50 kPa Ar pressure and 1.2mm-gap between the orifice and a counter electrode.