The development of ultra small electromagnetic motor by micromachining (2nd report, etching conditions of insulation layer)

Etching conditions of SiO2 were investigated in order to fabricate the insulation layer of coils used for electromagnetic micro motors. The effects of cooling temperature of substrate, pressure, RF power, and the amount of reactive gases on the shape of insulation layer were examined using ECR-RIE method. CF4 and CHF3 gases were selected as reactive gases, and 18 μm thick insulation layer was processed. In coil fabrication process, Cu is electroplated after the etching of the insulation layer. The additional etching conditions of the insulation layer were investigated to get the uniform electroplated Cu film. From these experiments, the following conclusions were obtained. (1) The amount of side etching of the insulation layer was minimized under the conditions of RF power of 125 W and the flow rate of CF4 and CHF3 gases of 30 SCCM. (2) The selectivity of SiO2 and Cu metal mask reached 20.6, and the aspect ratio of 9 (18 μm in height and 2 μm in width) was obtained. (3) During the etching process, ion bombarded the electrode film that was used for electroplating. The material etched by bombarded ion adhered on the surface of the insulation layer, and as a result, Cu was not electroplated uniformly in the cavity of the insulation layer. It was clarified that the electroplated Cu film grew uniformly after the cleaning process by O2 gas.