Direct pattern etching for micromachining applications without the use of a resist mask

The method of direct pattern etching without the use of a conventional resi st mask has been developed. This method takes advantage of the field-shield ing effect of a Faraday cage, inside which the substrate is located. A stai nless-steel stencil mask, constituting the upper plane of the cage fixed on a cathode in a plasma etcher, was used as a pattern mask in reactive ion e tching. A CF4 plasma at 5 mTorr was used to etch the initially bare substra te of a Si wafer covered with a 1-mum-thick blanket SiO2 film. The mask pat terns with the minimal dimension of 40 mum were accurately transferred to t he substrate with the etch profiles vertical to the substrate surface. When the gap distance between the stencil mask and the substrate surface was as small as 0.5 mm, the ratio of the etch rate below an opening to that below a blocking portion of the mask was over 5600. On the other hand, the etch rate ratio fell virtually to unity when the substrate was apart from the ma sk by 10.5 mm. The simulation study of ion trajectories showed that the ion beams were increasingly diverged as ions traveled away from the mask insid e the cage. That is, the beams were well separated from each other in close proximity to the stencil mask, resulting in fine pattern etching. At posit ions sufficiently far from the mask, however, the deviated ion beams extens ively overlapped with each other to yield the uniform ion flux. (C) 2000 Am erican Vacuum Society. [S0734-211X(00)13706-0].