The X-ray mask is the most critical and most challenging element of a proximity X-ray lithography system, because the mask's dimensions must equal the final device dimensions and the mask's membrane film, which is only about 2 mm thick, must support a heavy metal absorber pattern. In NTT, we have developed fabrication technologies for highly accurate and defect-free masks, such as multiple exposure and distortion compensation methods in the electron-beam writing step, highly accurate dry etching, and inspection and repair of mask defects. In addition, the feasibility of proximity X-ray lithography was confirmed by fabricating a device. This article describes the current status of and issues with X-ray mask technology.
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