RESOLUTION LIMITATION OF PROXIMITY X-RAY-LITHOGRAPHY DETERMINED BY WAVE-GUIDE EFFECT

In proximity X-ray lithography, the thickness of mask patterns is 500 to 1000 times greater than the X-ray wavelength. This is expected to induce a new physical phenomenon such as interaction between X-rays within the mask patterns. Taking into account such X-ray wave interaction, the resolution limitation of proximity X-ray lithography is reexamined by a new simulation method treating the mask pattern as a kind of waveguide and directly solving Maxwell's equations, instead of Fresnel's approximation. It is recently discovered that the waveguide effect severely deteriorates the resolution, particularly in the sub-100-nm range, by interference of propagated X-rays in the microgap range. Furthermore, this result makes the mask-wafer gap latitude for pattern replication smaller, and may limit the resolution of proximity X-ray lithography, at most, to 70 nm, which is worse than so far expected. Thus, more attention should be focused on gap control or mask design, taking the waveguide effect into account in order to minimize degradation caused by this effect.