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In this study, we investigate a maskless fine etching technology using a He/O2 atmospheric pressure plasma jet (APPJ) assisted by a scanning probe microscope (SPM). The APPJ is localized in the submicrometer range by a nanopipette, which is also used as the probe of the SPM. We improve the rate of submicrometer-scale etching by adding O2 gas to the He source gas. The depth and full width at half maximum of a typical etched dot on a polymethylmethacrylate film were 475 nm and 235 nm, respectively. The etching rate was found to be six times faster with the added gas than without it. We also demonstrate line patterning; the width of the line was found to be 281 nm.

We developed a local irradiation system for atmospheric pressure inductively coupled plasma (ICP) using a quartz capillary nozzle (nanopipette) with a sub-micrometer diameter tip aperture for fine processing of material surface. Using this system, a polymethyl methacrylate (PMMA) film coated on a glass substrate was etched at the micrometer scale. Fine etching was achieved by the ICP localized by the nanopipette precisely placed near the surface, using the positioning capability of a homemade scanning probe microscope. The locally etched surface of the PMMA film was confirmed by imaging immediately after the etching process by scanning the nanopipette. For quantitative evaluation, the topographical image of the same location of the surface was then acquired using an atomic force microscope. The etching rate of the ICP was 20 times higher than that of the low-frequency atmospheric pressure plasma jet. The depth of the etched holes increased with increasing applied power and irradiation time and decreasing irradiation distance. In addition, line groove patterning with sub-micrometer width was successfully achieved. The proposed system is expected to be used in various applications such as processing and repairing of microdevices.

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