X-RAY PHASE-SHIFTING MASK FOR 0.1-MU-M PATTERN REPLICATION UNDER A LARGE PROXIMITY GAP CONDITION

The effects of Fresnel diffraction on the patterning characteristics in synchrotron radiation lithography are greatly influenced by X-ray phase shift in the absorber, especially when a low-contrast X-ray mask is used. We show that the resolution in sub-quarter-micron region can be markedly improved without reducing the proximity gap by utilizing the phase-shifting effects in the absorber. By controlling the absorber thickness within a suitable range (1.5 less-than-or-equal-to mask contrast less-than-or-equal-to 4.0, - 30-degrees greater-than-or-equal-to phase shift phi greater-than-or-equal-to - 120-degrees), fine patterns as small as 0. 1 mum can be replicated with a large exposure latitude at a large proximity gap of 30 mum. Based on these results, we propose a novel X-ray phase-shifting mask with shallowly etched patterns (L in width) at the absorber edge as a phase shifter. This mask can be fabricated by a simple self-alignment process and also offers the possibility of 0. 1 -mum pattern replication at the 30-mum proximity gap by using 0.02 less-than-or-equal-to L less-than-or-equal-to 0. 1 mum.