Heating effect of the radiation chemistry of polyhydroxystyrene-type chemically amplified resists

Abstract

The photomask used in the lithography process has the important role of transferring circuit pattern images onto the photoresist. To meet the demand for increased photomask manufacturing throughput, the current density of electron beam (EB) writers has been increased. EB exposure locally increases the resist temperature on the mask substrate depending on various factors, including current density, shot size, and writing order. Resist sensitivity increases with irradiated resist temperature, a phenomenon known as “heating effect”. In this study, we reported the cause of the temperature-dependent sensitivity increase in a polyhydroxystyrene-type chemically amplified resist. The experimental results, including acid generation efficiency measurements and pulse radiolysis with changing temperature, suggest that the heating effect is mainly caused by the deprotonation efficiency associated with the radical cation of the base polymer.

Resist Thickness Dependence of Latent Images in Chemically Amplified Resists Used for Electron Beam Lithography

“…The thermalization distance of secondary electrons in PHS has been reported to be 3.2 nm. [30] The deprotonation efficiency of tert-butoxycarbonyl protected unit radical cations was set to 0.59 [32]. The trajectories of secondary electrons and the reaction of thermalized electrons with acid generators were calculated by a Monte Carlo method.…”

“…Parameters used in the simulation. Acceleration voltage of electron beam (kV) Beam blur (σb) (nm) Backscattering coefficient [38] Half-pitch (nm) Initial resist film thickness (nm) Stopping power (eV/nm) Resist film density (g/cm 3 ) [21] Thermalization distance (nm) [30] Acid generator concentration (/nm 3 ) Quencher concentration (/nm 3 ) Reaction radius of acid generator (nm) [30,31] Effective reaction radius for neutralization (nm) Effective reaction radius for deprotection (nm) Protection ratio (%) Deprotonation efficiency of proton source [39] Deprotonation efficiency of nonproton source [32] Diffusion constant of acids (nm of the calculation procedure have been reported elsewhere [36]. The effective reaction radius for neutralization was set to 0.5 nm.…”

“…The backscattering coefficient was assumed to be 0.31 [38]. The parameters used in the simulation are summarized in Table I [21,[30][31][32]38,39]. The validity of the simulation method has been examined by comparison with the experimental results obtained by using EBM-9000 of NuFlare [37].…”

Bayesian optimization-based estimation of effective reaction radius of chemically amplified resist in acid catalyzed deprotection reaction

“…The parameters used in the simulation was listed in Table I. [13][14][15][16][17] Table I. Parameters used in simulation.…”

“…Resist thickness (nm) Stopping power (eV nm −1 ) 13 Resist film density (g cm −3 ) 14 Thermalization distance (nm) 15 PAG concentration (nm −3 ) TOA concentration (nm −3 ) Reaction radius of PAG (nm) 15 Effective reaction radius for neutralization (nm) Effective reaction radius for deprotection (nm) Protection ratio (mol%) Deprotonation efficiency of proton source 16 Deprotonation efficiency of nonproton source 17 Acid generation efficiency 17) Diffusion constant of acids (nm 2 s −1 ) Diffusion constant of quenchers (nm 2 s −1 ) Diffusion constant of protected units (nm 2 s −1 ) PEB time (s) HP (nm) Dose (μC cm −2 ) 0.87 1.0 1.0 0.0 90 35-60 192-320…”