Hydrolysis and Condensation of n-BuSnCl₃: Enabling Deposition of Smooth Metal Oxide Photoresist Thin Films

Abstract

Herein, we report hydrolysis and condensation chemistries of C 4 H 9 SnCl 3 to molecular clusters and gel films. Precursor speciation plays a key role in film formation and quality toward realization of atomically smooth surfaces. Density functional theory investigations of C 4 H 9 SnCl 3 and its reactions show that hydrolysis of the dimer (C 4 H 9 Sn) 2 (OH) 2 Cl 4 (H 2 O) 2 has a high energetic penalty in the gas phase and when using a polarizable continuum solvation model based on density. These computations support our observed stability of the dimeric cluster in air, in various solvents, and through initial film deposition. It hydrolyzes and condenses to the [(C 4 H 9 Sn) 12 O 14 (OH) 6 ] 2+ dodecamer on-chip after a post film-deposition bake at 80 °C. Consequently, film surface smoothness is uniquely retained through on-wafer condensation.

High-Resolution Lithographic Patterning with Organotin Films: Role of CO2 in Differential Dissolution Rates

“…Finally, we dissolved each film by immersing the coated wafers in methanol, creating solutions to identify on-wafer species. We have previously described this method to determine the dominant species in films . The electrospray ionization mass spectra (ESI-MS) of the two methanol solutions (Figure S4) reveal dominant peaks centered at ∼1250 and 2500 mass-to-charge ratios ( m / z ).…”

“…The ESI-MS of the two samples is differentiated by varying degrees of peak splitting, which occurs because of partial exchange of −OH for −OCH 3 ligands. , This exchange can only occur during the dissolution process in methanol, as it is the first and only introduction of methoxo ligands into the system. As such, the distinctive peak splittings do not represent differences in on-wafer speciation.…”

“…Among organotin-based resists, the Sn dodecamer with the general formula [(RSn) 12 O 14 (OH) 6 ]­X 2 (R = alkyl ligand, X = hydroxide, chloride, carboxylate) has attracted considerable attention. − , Researchers have also investigated other systems such as a sodium-centered butyltin Keggin, ,, butylhydroxooxostannane, and hexameric organotin carboxylates. , The generally accepted patterning mechanism for these materials initiates with radiolysis of the Sn–C bond under vacuum followed by hydrolysis and condensation reactions in air leading to a tin oxide framework that dissolves more slowly than the unexposed resist. ,,,, Consequently, differential dissolution rates between unexposed and exposed regions of the resist are predicated on the controlled radiolysis of the Sn–C bond. Severe dehydration upon baking and intercluster polymerization via radiation-induced cross-coupling of the organo ligands have also been suggested as contributors to differential dissolution rates and contrast. ,, While the proposed mechanisms describe the basic performance of organotin resists, many details about the chemistry after exposure remain uncertain. This work focuses on this postexposure chemistry.…”

“…Severe dehydration upon baking 36 and intercluster polymerization via radiation-induced cross-coupling of the organo ligands have also been suggested as contributors to differential dissolution rates and contrast. 41,43,44 While the proposed mechanisms describe the basic performance of organotin resists, many details about the chemistry after exposure remain uncertain. This work focuses on this postexposure chemistry.…”

Isomerization of Na‐Centered Alkyltin Keggin Clusters

“…We are interested in alkyltin clusters for nanolithography, due to the radiation sensitivity of the alkyl ligands, high EUV absorption of Sn, and the precise and small features enabled by molecular clusters [25–27] . The family of alkyltin Keggin ions is unique in that only the β and γ isomers have been identified by single‐crystal x‐ray diffraction.…”