ALD2023 Session EM-WeM: EUV Litho Materials

Continued extreme downscaling of semiconductor devices and their high-volume manufacturing hinge on EUV lithography (λ=13.5 nm, EUVL), especially the soon-planned implementation of high numerical aperture (NA) EUVL. Photoresist (PR) materials are a crucial area that demands significant improvement for the high NA EUVL, particularly in achieving ultrathin thickness, uniform composition and high patterning performance (e.g., EUV sensitivity, pattern resolution, critical dimension uniformity), as well as increased etch resistance.

In this talk, we will introduce an innovative synthesis route for organic-inorganic hybrid photoresists, which leverages the molecular atomic layer deposition (MALD) of ultrathin films comprised of organic and inorganic components. Specifically, we will discuss the fabrication of a hybrid resist system, which is composed of trimethylaluminum (TMA) and hydroquinone (HQ), and its characteristics under exposure using a low energy electron beam to mimic expensive and rare EUV lithography. Most importantly, we will focus on the low-energy electron exposure characteristics, investigated using an in-situ infrared spectroscopy system. The TMA-HQ hybrid resists not only exhibited a comparable 100 kV EBL performance to that of HSQ (hydrogen silsesquioxane), a commercial negative-tone EBL resist but also sustained the negative tone under low-energy electron exposures down to ~100 eV and lower electron energy (evaluated in diluted AZ 300 MIF solution). Furthermore, the dose-dependent characteristics of the MALD hybrid resists were also investigated at various low electron energies via EBL and electron flood gun system. The post-development remaining thickness of the exposure dose matrices was determined using atomic force microscopy (AFM), in which the required dose to maintain 50% of resist thickness (critical dose) was estimated to be approximately 8.4 mC/cm² at 100 eV. The obtained in-situ IR absorbance spectra suggested that chemical reactions involving aromatic rings of HQ as well as the reduction of C–O bonding are contributed to the formation of a crosslinking network within the TMA-HQ hybrid resist. We will also briefly go over the dry etching characteristics of the resist, identifying a potential process window for dry development.

This study is supported by the GRC-NMP program (task# 3035.001) through SRC.

The development of new resist materials is required to enable extreme ultraviolet (EUV) lithography for next-generation microelectronics. Inorganic resists are a promising class of materials because compared to traditional organic resists, they have higher etch resistance, are more impervious to pattern collapse, and are more absorbing of EUV radiation. However, there is limited understanding about how they behave under irradiation as well as what chemical and structural properties of the resist are most beneficial. In this work, we study the molecular layer deposition (MLD) of Hf- and Al-based hybrid thin film resists, known as “hafnicone” and “alucone.” These materials are grown at 100 ºC using the metal precursors tetrakis(dimethylamido)hafnium(IV) and trimethylaluminum together with ethylene glycol as the organic counterreactant. Both alucone and hafnicone are tested against electron beam exposure to inform their behavior under EUV, and results show that they behave as negative tone resists. Hafnicone exhibits a sensitivity of 400 µC/cm² and the ability to resolve 50 nm line widths. Alucone’s line patterns are more sharply defined than those of hafnicone, suggesting higher resolution. However, whereas alucone’s sensitivity is 4800 μC/cm² using 0.125 M HCl as the developer, hafnicone’s sensitivity is 400 μC/cm² using 3 M HCl. The MLD resists are additionally characterized via X-ray photoelectron and infrared spectroscopy to investigate the patterning mechanism, which is described in the context of classical nucleation theory. This study of hafnicone and alucone hybrid MLD offers new insight into structural features of an MLD film that can lead to desired EUV-responsive behavior. This insight may accelerate the development of vapor-deposited inorganic resists for use in electron-beam and EUV lithography.