Three-dimensional X-ray lithography using a silicon mask with inclined absorbers

We proposed a new fabrication method of an X-ray gray mask using MEMS technologies, and we also succeeded in fabricating three-dimensional microstructures on a PMMA sheet by using only a single X-ray exposure. Silicon can be diagonally etched by optimizing the etching condition in a RIE process. We thought X-ray absorbers of an X-ray mask were processed to three-dimensional shape, and a gray mask for the X-ray lithography was fabricated by using a taperedtrench-etching technique. Then, we experimented on the X-ray lithography using the beamline BL-4 in the synchrotron radiation facility TERAS of AIST. The total dose energy was 150 mA·h and the development was performed at the room temperature for 16 h using a GG developer, Sidewalls in the upper part of the PMMA resist structure were inclined and rounded. Especially, the shape of the PMMA resist structure of the line width 20 μm was able to be processed to shape like the target. Thus, the effectiveness of the gray mask that adjusted the thickness of absorber was confirmed by X-ray lithography experiments. Moreover, we experimentally showed that the final shape of PMMA resist structures after the X-ray lithography was predictable by the calculation.