Fabrication of Three Dimensional X-ray Mask using MEMS Technology

The authors fabricated silicon microstructures with inclined sidewalls on the SOI wafer by using tapered-RIE technique. Then, this wafer was processed to an X-ray mask that made the silicon structure an X-ray absorber. The inclined angle of the sidewall of silicon X-ray absorbers has been changed from 60 to 71 degrees by adjusting the pressure of the mixed gas in the process chamber of the ICP-RIE system. The thickness distribution of the X-ray absorber is different according to the difference of the inclined angle of the X-ray absorber. As a result, the transmission intensity of X-rays is locally changed, and the energy distribution of X-rays irradiated on a resist can be controlled. The authors experimented on the X-ray lithography using this X-ray gray mask and the beamline BL-4 in the synchrotron radiation facility TERAS of AIST. As a result, we succeeded in fabrication of three-dimensional PMMA microstructures by only one X-ray exposure without scanning and rotating the X-ray exposure stage.