Spin-on metal-oxide underlayer for EUV patterning

As the industry enters Extreme Ultraviolet (EUV) era, like every technology generation in history, there are constant demands for new materials to solve the emerging challenges accompanying with the continuous scaling effort. Although Chemically Amplified Resist (CAR) resist and conventional tri-layer stack that were established for DUV lithography have been successfully extended to EUV, challenges such as limited etch budget associated with further resist thickness shrinking needed for high Numerical Aperture (NA) EUV, increased line wiggling in SOC layer resulting from larger aspect ratio, etc., are expected to bring CAR EUV lithography to it's end soon. While new resist platform such as Metal Oxide Resist (MOR) is expected to provide the needed solution for future, other approaches such as further optimization of the underlayer (UL) could also offer an alternate solution by extending the utilization of CAR. In this paper, we explored the possibility of using spin-on metal-oxide hard mask (SOMHM) materials as UL for CAR EUV lithography. We first demonstrated excellent etch selectivity between CAR and SOMHM UL, as well as that between UL and other hard mask layers such as SOC, SiN or SiOx, in P44 pattern transfer study. Further P32 full wafer investigation allowed us to examine the critical parameters such as LER and LWR. Studies of even smaller pitches of 28nm and 24nm showed more advantages of SOMHM UL due to the etch budget limit of CAR. The possibility of simplifying the standard tri-layer stack is also demonstrated by using SOMHM as the direct hard mask for pattern transfer into 60nm SiN.