Design, development, EUVL applications and nano mechanical properties of a new HfO2 based hybrid non-chemically amplified resist

Abstract

A new HfO₂ based hybrid polymer HfO₂–methacrylate–MAPDST (HMM, M_w ∼27 885 g mol⁻¹) was synthesized by reacting the hybrid monomer HfO₂–methacrylate (HM) with (methacryloyloxy)phenyldimethylsulfoniumtriflate (MAPDST) in the presence of azobisisobutyronitrile (AIBN) as a radical initiator in tetrahydrofuran and acetonitrile (2 : 1; v/v) at 60 °C for Extreme Ultraviolet Lithography (EUVL) applications as a non-chemically amplified resist (n-CAR) material. Transmission Electron Microscope (TEM) and Dynamic Light Scattering (DLS) analyses revealed the particle sizes of HM and HMM hybrids as ∼3–5 nm and ∼12 nm respectively. Thin films of thickness ∼53 nm were prepared by spin coating 3% (w/v) solutions of HMM in methanol onto 4′′ p-type Si wafers consisting of a 40 nm hexamethyldisilazane (HMDS) under layer. The films were then subjected to EUV exposure at a dose of 51.7127 mJ cm⁻² on a micro exposure tool (MET) with an Advanced Light Source (ALS) at SEMATECH Berkeley using standard mask IMO228775 with field R4C3 (LBNL low flare bright-field). The EUV E₀ dose used for the exposure was 22 mJ cm⁻². Field Emission Scanning Electron Microscope (FE-SEM) micrographs of the EUV exposed hybrid resist films showed isolated line patterns of 80, 70, 60, 50, 45, 40, 35 and 30 nm for 5 : 1 duty cycle, of which 80 to 50 nm line patterns were well resolved, whereas patterns of 45 to 30 nm or higher resolutions exhibited undesirable traits like bridging, fracturing, de-adhesion, peel-off and pattern collapse. To comprehend the reasons behind these undesirable traits, nano-mechanical properties (modulus and adhesion) of the EUV exposed and developed resist patterns were investigated by using Peak Force-Quantitative Nano-Mechanical (PF-QNM) tapping mode Atomic Force Microscope (AFM). These studies revealed ∼18% and ∼19% reductions in Derjaguin–Müller–Toporov (DMT) modulus and adhesion magnitudes respectively with an increase in isolated line pattern resolution from 80 to 30 nm for 5 : 1 duty cycles. The reduction in modulus and adhesion magnitudes might have caused the observed fracturing, peel-off and collapse of the high resolution line patterns during the pattern development processes.