Thermal and radiation chemistry of butyltin oxo hydroxo: A model inorganic photoresist

We have investigated the thermal and radiation chemistry of an organotin-based model photoresist to elucidate patterning mechanisms related to extreme ultraviolet (EUV) lithography. Butyltin oxide hydroxide (BuSnOOH) was dissolved in organic solvents and spin-coated to form uniform thin films. The thermal stability and radiation sensitivity of the thin films were characterized by temperature programmed desorption (TPD), electron stimulated desorption (ESD), and X-ray photoelectron spectroscopy (XPS). From the TPD studies, we determined that decomposition of BuSnOOH occurs at ~653 K through cleavage of the butyl-tin bond. Low kinetic energy electron (E_kin = 80 eV) and X-ray (1486.6 eV) exposure also resulted in cleavage of the butyl-tin bond with the resulting desorption of butyl ligands from the film. From the ESD data, we estimated that the butyl ligand desorption cross section was ~4.3 × 10⁻¹⁴ cm² for electrons with 80 eV kinetic energy. From the XPS results, we found a significant reduction in C 1s intensity for extended X-ray exposures, which corresponds to butyl ligand loss. There were also changes in the O 1s spectra indicating loss of hydroxyl groups and tin oxide network formation during radiation exposure. These results indicate the preferential dissociation and desorption of butyl ligands that can occur through either thermal or radiation induced processes, and that butyl ligand loss leads to the solubility contrast.