Stability studies on a sensitive EUV photoresist based on zinc metal oxoclusters

Abstract

Background: Hybrid inorganic-organic materials have emerged as promising candidates for EUV resists. However, knowledge on their stability when deposited as thin films is essential for their performance in EUV lithography. Aim: We investigate whether the molecular structure of Zn-based metal oxoclusters is preserved upon thin film deposition and study aging processes of the thin film under different atmospheres, since these chemical changes affect the solubility properties of the material. Approach: A hybrid cluster that combines the high EUV photon absorption cross-sections of zinc and fluorine with the reactivity of methacrylate organic ligands was synthesized. The structural modifications upon thin film formation and after aging in air, nitrogen, and vacuum were studied using a combination of spectroscopic techniques. Preliminary studies on the lithographic performance of this material were performed by EUV interference lithography. Results: The Zn-based compound undergoes structural rearrangements upon thin film deposition as compared to the bulk material. The thin films degrade in air over 24 h, yet they are found to be stable for the duration and conditions of the lithography process and show high sensitivity. Conclusions: The easy dissociation of the ligands might facilitate hydrolysis and rearrangements after spincoating, which could affect the reproducibility of EUV lithography.

Mixed-ligand zinc-oxoclusters: efficient chemistry for high resolution nanolithography

“…The Zn(MA)(TFA) compound was synthesized by ligand exchange from a commercial Zn-oxocluster as precursor having the same tetranuclear oxo-core unit and six TFA ligands, Zn 4 O(OOCCF 3 ) 6 , following the protocol in ref. 43 and as shown in Fig. 1a.…”

“…12 It should be noticed that a good control in the Zn(MA)(TFA) composition is crucial for reproducibility in the sensitivity of this resist. 43 Table 1 below summarises the performance of some inorganic and hybrid inorganic-organic EUV photoresist when exposed using the EUVL-IL tool at PSI.…”

“…This compound has previously shown to have a high linear absorption coefficient at 13.5 nm (12.4 mm À1 ) and high sensitivity. 43 Here, we used EUV interference lithography (EUV-IL) 44,45 to achieve dense line/space (L/S) patterns of half-pitch (HP) down to 22 nm at low doses (B20 mJ cm À2 ) on this material, a response that is close to commercial EUV resists. 12,13,17 The lithography experiments were also combined with several ex situ spectroscopic techniques, which allowed to elucidate a novel mechanism behind the nanopattern formation involving C-F bond cleavage in the TFA ligands and cross-linking of the double bond of MA ligands initiated by different radical species (Scheme 1).…”

High Sensitivity Resists for EUV Lithography: A Review of Material Design Strategies and Performance Results

“…Thakur et al prepared Zn-based oxoclusters having trifluoroacetate (TFA) and methacrylate (MA) ligands. The Zn(MA)TFA photoresist displays appreciable sensitivity toward EUV radiation [111].…”

“…On the other hand for energies above 2 eV the material was crosslinked providing a denser final film. [111]. The mechanisms in all the above materials are still not adequately understood.…”