Imaging capabilities of proximity X-ray lithography at 70 nm ground rules

This paper discusses the resolution capabilities of proximity X-ray lithography (PXRL) system. Exposure characteristics of features designed at 150 mn pitch size: 75 mn dense lines with 1:1 duty ratio, two-dimensional features at 1:1 and 1.2 duty ratios and isolated lines have been studied. Aerial image simulations were compared to the experimental data. Verification of the aerial image model has been accomplished by measurements of exposure windows of 100 mn and 125 nn nested lines. The PXRL aerial image parameter, equivalent penumbra blur, has been determined from the experimental data. Contributions from the synchrotron radiation X-ray source, stepper and the chemically amplified resist to the degradation of the aerial image have been evaluated. Patterning capability of PXRL at 75 nm feature size is compared to projection optics using the optical hi factor as a common figure of merit. To facilitate the comparison, optical imaging was at pattern sizes currently manufacturable by the mainstream optical tools while the PXRL imaging was at 75 mn pattern size. Requirements for a PXRL system capable of manufacturing VLSI at 70 mn minimum feature sizes with the critical dimension control better than 10% (3 sigma) are also discussed.