Sub-0.15 μm pattern replication using a low-contrast X-ray mask

Mask contrast optimization is essential for replicating sub-0.15-µ m patterns with relatively large mask-to-wafer gaps, e.g., larger than 20 µ m, which is strongly desired for industrial production. We have confirmed that decreasing the mask contrast to around 4 is very effective for increasing the exposure latitude for the grating patterns with pitch around 0.24 µ m, without deteriorating the exposure quality of larger patterns. The obtained exposure latitude for 0.12 µ m lines and spaces at the gap of 20 µ m was ±8.7% for ±10% replicated line-width change. How the mask pattern bias affects the replicated pattern was checked using the 0.24-µ m-pitch grating patterns. It was revealed that the dependence of the absorber width bias on the replicated pattern width is weaker than the linear correlation, as is suggested from the calculation of the Fresnel diffraction feature. It seems that when applying the larger mask-to-wafer gap to resolve a given pitch of grating patterns, the replicated pattern width becomes less sensitive to the line/space ratio on the mask.