Ligand stabilized metal oxide nanoparticle resists are promising candidates for EUV lithography due to their high
sensitivity for high-resolution patterning and high etching resistance. As ligand exchange is responsible for the
patterning mechanism, we systematically studied the influence of ligand structures of metal oxide EUV nanoparticles on
their sensitivity and dissolution behavior. ZrO2 nanoparticles were protected with various aromatic ligands with electron
withdrawing and electron donating groups. These nanoparticles have lower sensitivity compared to those with aliphatic
ligands suggesting the structures of these ligands is more important than their pka on resist sensitivity. The influence of
ligand structure was further studied by comparing the nanoparticles’ solubility for a single type ligand to mixtures of
ligands. The mixture of nanoparticles showed improved pattern quality.
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/cm2, 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.
This work focuses on the investigation of dual tone patterning mechanism with hybrid inorganic/organic photoresists.
Hafnium oxide (HfO2) modified with acrylic acid was prepared and the influence of electrolyte solutions as well as pH on its
particle size change was investigated. The average particle size and zeta potential of the nanoparticles in different electrolyte
solutions were measured. The results show that addition of different concentrations of electrolytes changed the
hydrodynamic diameter of nanoparticles in water. Increased concentration of tetramethyl ammonium hydroxide (TMAH)
caused the zeta potential of nanoparticles to change from positive to negative and its hydrodynamic diameter to increase from
40 nm to 165 nm. In addition, increasing concentration of triflic acid led to the decrease of particle size and zeta potential.