(Invited) Structural Evolution of Hafnium Methacrylate Nanoclusters Following Electron-Beam Irradiation from in Situ ir Spectroscopy

Abstract

High absorption metal and main group oxide nanoclusters have recently become the subject of intense investigation due to their potential as alternatives to conventional organic chemically amplified photoresists for negative tone patterning in the extreme ultraviolet (EUV) range. It is believed that the low energy secondary electrons generated from photoionization of the nanoclusters are responsible for the chemistry that occurs following irradiation. Despite their potential, little is known about many aspects of their function as resist materials; in particular, the role of high absorption elements in the absorption/photoionization process, the role of electrons of different energies, the formation of radicals and chemically reactive species and the overall structural changes that occur at each stage of processing. Thus, the precise atomic mechanism underlying solubility switching upon irradiation remains unknown. We have investigated one such class of materials: nanoclusters based on a hafnium oxide core decorated with methacrylic acid ligands (HfMAA) , using a combination of in situ infrared (IR) spectroscopy and x-ray photoemission spectroscopy (XPS). Thin films (10-30 nm) of the HfMAA nanoclusters deposited onto SiO2 from solution are characterized by XPS and IR spectroscopy in conjunction with density functional calculations. The mechanisms of solubility switching following EUV exposure are investigated using irradiation with low energy electrons to emulate the photoexcited carriers generated in the EUV absorption process. Using in situ IR spectroscopy, we are able to monitor the structural evolution of the nanoclusters at each stage of processing, beginning from the initial deposition to post application bake (PAB), electron irradiation, post exposure bake (PEB) and development. Monochromatic electron beams with energies ranging from 5 eV up to the typical EUV wavelength of 92 eV enable a correlation between the role of secondary electron energy with chemistry and functional character. In conjunction with XPS analysis, these measurements detail the structural evolution of the films under typical processing conditions, providing insight into the solubility switching mechanism of this emerging class of inorganic photoresists.