Simulations on attenuated phase-shift masks (att PSM) for EUV have shown that these novel mask absorbers can strongly boost optical contrast. The optimum EUV imaging mask does not only need to balance the diffraction order amplitudes (as in DUV imaging), it also needs to mitigate the strong mask 3D effects that are present in EUV lithography. The latter is very important and strongly relies on material properties. Here, we present an overall progress update on our att PSM work, including the first experimental lithography results on an EUV att PSM test mask and guidelines needed for optimum performance from diffraction point of view.
The purpose of pellicles is to protect reticles from particle contamination, thus reducing the number of defects and increasing yield. In this paper we show how recent progress in pellicle technology has succeeded in solving the main challenges in imaging with EUV pellicles. We demonstrate this using the recent results of imaging tests in scanner, EUV reflectivity measurements, and lifetime testing. EUV light reflectivity of pellicles is one of the effects that have negatively impacted imaging with pellicles in the past. Light reflected from pellicles leads to the overexposure of neighboring fields in the corners and edges. Tests with pellicles produced using a new process show EUV reflectivity within specification of 0.04%, and measured impact on critical dimension in the corners below 0.15nm for multiple pellicles. Lifetime performance was tested by exposing up to 3000 wafers with a pellicle while periodically assessing the stability of imaging metrics. The lithometrics studies include: critical dimension (CD) and critical dimension uniformity (CDU), and contrast (via line width roughness). DoseMapper, which is an EUV scanner application developed to improve CDU, was applied during the lifetime test. Here we show that it can successfully reduce the pellicle-induced CDU and CDU over lifetime (previously shown to be dominated by pellicle EUV transmission drift). Our results using DoseMapper show that whilst intrafield CDU 3sigma increases over lifetime, it stays comfortably within the 1.1nm NXE3400 ATP specification using DoseMapper.