Ultra-Fine Pattern Fabrication by Synchrotron Radiation X-Ray Lithography Using a Shifter-Edge Type Phase-Shifting Mask

This paper reports the feasibility of ultra-fine pattern fabrication using an X-ray phase-shifting mask. Using shifter-edge type phase-shifting masks, less-than-100-nm patterns can be printed without preparing thick precise X-ray absorber patterns. However, it is still important that the shifter not be too thick, because thick shifter patterns are also difficult to fabricate. Shifter thickness is decided by the refractive index n of the shifter and a small n value permits a thin shifter. However, materials with a small n value have large absorption, so the latitude in the shifter transmittance and phase-shifting angle was analyzed. It is clarified that the degradation of shifter transparency is not a serious problem, and the tolerance of phase-shifting angle is very large. It is also demonstrated that SR X-rays with a continuous spectrum can be applied. Patterns almost as fine as 50 nm have been printed.