Metal oxide nanomaterials have shown promise for use as EUV resists. Recently, significant efforts have focused on tinoxo clusters that have high absorption coefficient Sn centers and radiation sensitive organic ligands. In our studies, we have investigated a β-Keggin butyl-Sn cluster (β-NaSn13), which is charge-neutral and allows studying radiation induced chemistries without interference from counterions. We have used ambient pressure X-ray photoelectron spectroscopy (APXPS) to investigate the contrast properties of the β-NaSn13 in ultrahigh vacuum (UHV) and in the presence of ambient oxygen. These contrast studies indicate that ambient oxygen reduces the dose requirements for the solubility transition of the β-NaSn13 photoresists. APXPS spectra collected before and after the solubility transition shows that ambient oxygen causes a greater loss of butyl ligands from the samples and the formation of more tin oxide for larger doses, suggesting the presence of reactive oxygen species. APXPS was also used to study processes during the post exposure bake, where we compared the differences in film chemistries in ambient oxygen or in UHV. There were only very small differences in the APXPS spectra before exposure and after exposure and the post exposure bake. However, ambient oxygen resulted in some changes for unexposed regions during the post exposure bake; there was a greater ratio of tin oxide to other oxygen species (alkoxy ligands, hydroxyls) for samples annealed in oxygen. These results have significance for EUV and e-beam lithography processing parameters, as well as implications for cluster design and ligand chemistries.
Inorganic resists are of interest for nanomanufacturing due to the potential for high resolution, low line width roughness, and high sensitivity. The combination of high absorption coefficient elements and radiation sensitive ligands can improve inorganic resist sensitivity while still allowing high contrast for extreme ultraviolet (EUV) lithography. A prototypical resist is Hf(OH)4-2x-2y(O2)x(SO4)y·qH2O (HafSOx), which has both high absorption coefficient elements (Hf) and radiation sensitive ligands (peroxides). Herein, we evaluate the use of electron stimulated desorption (ESD) to characterize HafSOx. These results indicate that the peroxo species are extremely radiation sensitive, even for low kinetic energy electrons that approximate the range of electron energies expected during EUV exposures. The primary desorption products from HafSOx are O2 and H2O, where the time evolution suggest much faster desorption kinetics for O2. These data provide insight into the radiation-induced changes responsible for the solubility transition upon exposure and dissolution during development, and the role of low kinetic energy electrons in these processes. The following describes our experimental methodology for the ESD studies, and the specific kinetic model used to extract total desorption cross sections from the ESD data.
Inorganic resists are of considerable interest for advanced lithography at the nanoscale due to the potential for high resolution, low line width roughness (LWR), and high sensitivity. Historically inorganic resists suffered from low sensitivity, however approaches have been identified to increase sensitivity while maintaining high contrast. An aqueous precursor of Hf(OH)4-2x-2y(O2)x(SO4)y·qH2O (HafSOx) has been demonstrated with excellent sensitivity to EUV and electrons, while still obtaining high resolution and low LWR. In this work, we characterize both HafSOx precursor solutions and spin-coated thin films using high-resolution transmission electron microscopy (HR-TEM) with energy-dispersive X-ray spectroscopy (EDS) elemental analysis. HR-TEM of precursor solutions drop cast onto TEM grids confirmed the presence of nanoscale particles. HR-TEM cross sectional images showed that spin-coated HafSOx films are initially uniform in appearance and composition for thin (12 nm) films, however thicker (30 nm) films display segregation of species leading to multilayer structures. Regardless of film thickness, extended exposure to the high energy TEM electron beam induces significant migration of oxygen species to the Si interface. These species result in the formation of SiOx layers that increase in thickness with an increase in TEM electron beam dose. Sulfate is also very mobile in the films and likely assists in the significant condensation exhibited in completely processed films.