Spin-on Metal Oxide Hard Mask as Underlayer for EUV Lithography with Chemically Amplified Resist

With the "first light" of high Numerical Aperture (NA) scanner announced by ASML earlier this year, it has become clear that the inevitable resist thickness shrinkage will pose great challenge to pattern transfer with current chemically amplified resist (CAR), on top of other technical challenges including resolution, line roughness and defects. Historically, through the litho stack optimization, and more critically, the underlayer (UL) optimization, the overall litho performance of a given resist system could be largely improved to meet manufacturing needs. In this paper, we propose the possibility of using spin-on metal-oxide hard mask (SOMHM) materials as EUV lithography UL for CAR. By first validating the excellent etch selectivity at P44 L/S between CAR and SOMHM UL, as well as that between UL and other hard mask layers such as SOC, SiN or SiOx, the following 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 when thinner resist is required to address some litho pattern defects. The possibility of simplifying the standard tri-layer stack is also demonstrated by using SOMHM as the UL as well as direct hard mask for pattern transfer into 60nm SiN.