High-NA EUV lithography required for continued extreme downscaling of Si devices demands ultrathin photoresists with high EUV patterning performance and etch resistance. This talk briefs our current efforts on synthesizing new organic-inorganic hybrid resists based on atomic layer deposition (ALD) techniques and characterizing their electron beam and EUV patterning characteristics. Two distinctive approaches are discussed–vapor-phase infiltration (VPI) and molecular ALD (MALD), where the former utilizes an infiltration of gaseous inorganic precursors into existing organic resists and the latter a cyclic layering of organic and inorganic moieties. Featured systems include an indium-oxide-infiltrated PMMA and a MALD hybrid resist comprising trimethylaluminum (TMA) and hydroquinone (HQ). Given the facile implementablility and control of resist composition and characteristics, the ALD-based hybrid resist synthesis has a potential for enabling high-performance EUV photoresist systems.
Infiltration synthesis of vapor-phase precursors is ex-situ route of converting established polymeric resists into hybrids. The concept initially modelled over polymethylmethacrylate (PMMA)-AlOx hybrid has been expanded to infiltrating several metal oxide moieties into high sensitivity resist (HSR). Beyond implementing single metal oxide species, alloyed infiltration is explored as a means to limit pattern roughness originating from granular crystallites. Lithography performance of these new generation of hybrid positive tone resists is assessed towards contact-hole patterning.
Herein, we investigated the chemical reactions associated with low-energy electron exposures on an inorganic-organic hybrid thin film system deposited using molecular atomic layer deposition (MALD) for EUV photoresist applications. Using the hybrid thin films consisting of trimethylaluminum (TMA) and hydroquinone (HQ), we determined the critical doses and thickness contrast of the hybrid materials at various electron energies (up to 400 eV). The custom-built in-situ Fourier-Transform Infrared (FTIR) spectroscopy system, equipped with an electron flood gun and gas residual analyzer (RGA), was employed to monitor the chemical changes induced by low-energy electrons in the hybrid thin films. Based on the in-situ FTIR and RGA results, potential chemical reaction mechanisms responsible for the change in solubility of the TMA/HQ material are proposed.
We investigated the hydroquinone (HQ)/trimethylaluminum (TMA) hybrid thin film synthesized by molecular atomic layer deposition (MALD) as a potential extreme ultraviolet (EUV) photoresist. The patterning characteristics of the resist was studied using electron beam lithography (EBL) and low-energy electron microscopy (LEEM), identifying energy-dependent critical exposure dose and contrast under wet development. Also identified were the reactive ion etching (RIE) characteristics, demonstrating a dry development parameter window, achieving the maximum etch contrast of ~10 nm between the regions with and without electron exposure. The results suggest the MALD approach as a viable synthesis route for developing new hybrid EUV photoresists.
High-NA EUV lithography–scheduled to be implemented in a few years for high-volume manufacturing of extremely downscaled Si devices with 2 nm node and beyond–demands ultrathin organic-inorganic hybrid photoresists with high EUV sensitivity and etch resistance. In this work, we synthesized a positive-tone hybrid photoresist composed of PMMA infiltrated with molecular network of indium oxide by vapor-phase infiltration (VPI), an ex-situ inorganic hybridization method derived from atomic layer deposition, and evaluated its patterning characteristics by electron-beam and EUV lithography (EBL and EUVL). The hybrid resist featured significantly enhanced etch resistance under dry etching but also the critical doses of 300 uC/cm2 for EBL and 60 mJ/cm2 for EUVL, both largely comparable to those of PMMA. Unlike alumina infiltration in PMMA that has been demonstrated previously, it was found that the weak binding nature of trimethyl indium (TMIn), the gaseous precursor used to infiltrate indium oxide in PMMA matrix, to the carbonyl group in PMMA enabled a uniform distribution of the oxide content across the PMMA thickness. However, it also led to undesired residue in the developed regions due to the strong interaction between the Lewis-basic hydroxyl groups on the surface of starting Si substrate with infiltrated TMIn. The residue issue could be mitigated by passivating the Si surface by hexamethyldisilizane (HMDS) and combining the acid/base rinse and oxygen plasma descum. The results not only hint at the potential of VPI-based ex-situ hybridization in developing novel hybrid EUV photoresists but also highlight the technological details that must be addressed to enable high EUVL performance in the infiltrated hybrid resist system.
Infiltration synthesis is an emerging material hybridization technique. Starting with a brief dive into infiltration synthesis mechanism, I will present our pioneering work on ex-situ conversion of conventional organic photoresists into hybrid EUV resists as well as the generation of mechanically resilient hybrids with one of the highest storage elastic strain energy capacities for potential applications in MEMS technologies. I will also overview the use of infiltration synthesis approach for hybridizing nanopatterned polymer templates and self-assembled block copolymer thin films to form robust dry etch masks for pattern transfer as well as direct-writing oxide nanostructures for optoelectronic device applications.
We have developed an organic-inorganic hybrid resist platform featuring versatile ex-situ control of its performance by incorporating inorganic elements using vapor-phase infiltration (VPI) into standard organic resists. With poly(methyl methacrylate) (PMMA)-AlOx hybrid as a model composition we unveiled controllability of the critical exposure dose, contrast (as high as ~30), and etch resistance; estimated Si etch selectivity over ~300, demonstrating high aspect ratio ~17 with ~30 nm resolution Si fin-structures. Building upon the demonstration of PMMA-AlOx hybrid resist, we expanded our material portfolio to a high sensitivity resist and other inorganic moieties. We present preliminary results obtained from the extreme ultraviolet (EUV) lithography dose tests conducted on corresponding infiltrated hybrids and optimization of infiltration with the help of transmission electron microscopy (TEM).
We demonstrate a simple ex-situ inorganic infiltration route for transforming standard organic resists into high-performance positive tone hybrid resist platform. A model thin film PMMA-AlOx hybrid resist system has been synthesized by hybridization of PMMA with AlOx and investigated for electron beam lithography. The approach possesses full controllability of the resist performance in terms of critical does, patterning contrast reaching up to 30 and etch resistance for plasma-based pattern transfer processes. The high selectivity Si etching capability demonstrated using a low-temperature cryo-Si etch process, based on the controlled infiltration outperforms commercial resists and typical hard mask material thermal SiO2, with estimated achievable selectivity in excess of ~300. Si nanostructures down to ~30 nm with aspect ratio up to ~17 are also transferred into the Si substrate. Easy implementation and adaptability for different inorganic infiltrations, this platform is well capable of potentially delivering the resist performance and throughput necessary for EUV lithography.
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