Mask error factor in proximity X-ray lithography

Many estimations have shown that an increase in mask-error factor (MEF) will be a serious issue for deep ultraviolet lithography in the 130- and 100-nm device generations. For proximity X-ray lithography (PXL), reduction of the MEF has already been reported. The MEF reduction is advantageous for PXL because it allows larger error in the critical dimension (CD) on 1X X-ray masks. To define the characteristics of the MEF in PXL, we used the CNTech Toolset lithography simulator to calculate the MEFs for line-and-space (L/S), isolated-line, and isolated-hole patterns with feature sizes as low as 70 nm. We also made exposure experiments with an XS-1 X-ray stepper at the Association of Super Advanced Electronics Technologies (ASET) to verify the simulation results.