New developments in ligand-stabilized metal oxide nanoparticle photoresists for EUV lithography

Abstract

The introduction of EUV lithography to manufacturing requires the development of both new EUV exposure tools and photoresists. The main challenges for photoresists are to achieve high resolution, and low roughness patterning at very high sensitivity given the limited intensity of current sources. A new class of photoresist formed from ligand-stabilized metal oxide nanoparticles shows extraordinary sensitivity for EUV lithography. These nanoparticles are processed in traditional organic solvents for both deposition and development as negative tone resist; positive tone images are possible if the aqueous base developer is used in addition to a post-exposure bake step. This paper presents new developments in the study of ligand-stabilized nanoparticle photoresists for EUV lithography. It is our current understanding that a key aspect of the solubility change of these photoresists during exposure involves ligand displacement by anions generated from photoactive compounds such as sulfonic acid photoacid generators. Both positive and negative tone patterning are possible and depend on thermal treatment history and choice of developer. On the basis of a non-chemically amplified ligand exchange mechanism, new resist structures were created. Both aromatic and aliphatic carboxylic acids with different functional groups have been studied in the formation of the nanoparticles and include dimethylacrylic acid, isobutyric acid, toluic acid. It has been shown that those nanoparticles with higher binding affinity ligands show better resolution and line edge roughness under EUV exposure. Some formulations demonstrate EUV sensitivity as high as 1.4 mJ/cm 2 , while other formulations demonstrate that improved LER values of 3-5nm. The overall resolution, sensitivity and roughness tradeoff has been evaluated and provides an understanding of structure -property relationships. In this paper, we also discuss major efforts on the further understanding of the patterning mechanism. By testing the dissolution rate and plotting it in Hansen interaction triangles, we can compare the differences between different formulations and choose a suitable developer for each formulation. We also used the dissolution rate study to confirm the important role of PAG and ligand exchange for pattern formation. In addition, aspects of the EHS properties of these new photoresists have been investigated and will be discussed.

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

“…By choosing the right metalcomponent, they can meet the desired properties for EUV photon absorption while offering intrinsically small and homogeneous size (monodisperse) due to their molecular nature. 10,13,22 In the present contribution, the elucidation of a simple and versatile preparation method of a new Zn-based metal oxocluster, as well as the stability and sensitivity of the resulting material toward EUV radiation are explored. Recently, molecular materials based on Zn have been investigated and have shown promising results.…”

Stochastic simulation and calibration of organometallic photoresists for extreme ultraviolet lithography

“…6 The investigation of stochastic effects during the development requires a more detailed description of the dissolution mechanism. Several experimental investigations [23][24][25][26][27] demonstrated that the photoresist dissolution behavior depends on the behavior of the ligands on the metal cores. Our stochastic development model tracks the substitution of the ligand and oxo-bond sites by the solvent molecules based on balance equations.…”

Partial decarboxylation of hafnium oxide clusters for high resolution lithographic applications

“…Soluble metal oxide complexes have found very important applications in materials chemistry because of their great potential as photoresists in EUV (extreme ultraviolet, 13.5 nm wavelength) lithography. 1–4 The EUV scanner is an indispensable lithography tool to produce modern semiconductors with 20 nm half pitch (HP) for 7 nm or smaller nodes. One major reason is that the efficiency of EUV absorptions of transition metal complexes such as Zn, 5–7 Sn, 8–11 Hf, 12–18 Zr, 19–24 Co 25 and In 26 is much higher than those of polymer-based photoresists by 2–3 fold.…”