X-ray Reflectivity Study on Depth Profile of Acid Generator Distribution in Chemically Amplified Resists

Abstract

In the sub-100-nm mass production of semiconductor devices, thin-film resists dispersing acid generator molecules, referred to as chemically amplified resists, have been used. Feature sizes in lithography are approaching the molecular scale with the rapid progress in miniaturization. With reductions in lateral dimensions, a decrease in resist thickness is inevitable and the effects of interfaces become significant. A requirement for ultrafine fabrication is the uniformity of resist components. In this work, the depth profile of the acid generator distribution was investigated by X-ray reflectivity measurement at SPring-8. The depth profile in thin resist films was clarified. It was found that the depth profile varies with acid generator concentration.

Requirement for Suppression of Line Width Roughness in Fabrication of Line-and-Space Patterns with 7 nm Quarter-Pitch Using Electron Beam Lithography with Chemically Amplified Resist Process

“…The main reason for the lower limit of LER is that the concentration of acid generator is finite [32]. ) [27] Thermalization distance (nm) [14] Acid generator concentration (wt%) Reaction radius of acid generator (nm) [14] Effective reaction radius for neutralization (nm) Effective reaction radius for deprotection (nm) [7] Protection ratio (%) Deprotonation efficiency of proton source [28] Deprotonation efficiency of nonproton source [15] Diffusion constant of acids (nm for the acid generator concentration of 10, 20, and 30 wt%, respectively. The maximum normalized chemical gradient can be increased, by increasing the acid generator concentration.…”

“…The effective reaction radius for deprotection was set to be 0.1-0.3 nm [7]. The parameters used in the simulation are summarized in Table 1 [7,14,15,27,28].…”

Challenges in Development of Sub-10 nm Resist Materials

“…If the electron reached a radical cation within the distance of r + , the electron was regarded to be lost through the recombination. If the electron reached an acid generator molecule within the distance of r AG , the electron was regarded to induce ) [31] Thermalization distance (nm) Acid generator concentration (wt%) Reaction radius of acid generator (nm) [22] Acid diffusion constant (nm Effective reaction radius for neutralization (nm) Effective reaction radius for deprotection (nm) Protection ratio (%) Deprotonation efficiency of proton source [32] Deprotonation efficiency of nonproton source [23] the dissociation of that acid generator molecule. r AG of TPS-Tf has been determined to be 0.70 ± 0.08 nm [22].…”

“…The effective reaction radius for deprotection was changed from 0.1 to 1.0 nm. The parameters used in the simulation are summarized in Table 1 [22,23,31,32]. The other details in the reaction mechanisms have been reported elsewhere [14,33].…”

Resist Materials and Processes for Extreme Ultraviolet Lithography

“…The inhomogeneous distribution of acid generators is a serious concern in ultrafine patterning. 54,55) Therefore, the lower limit cannot be infinitely reduced by increasing the acid generator concentration. Note that acid generators capable of solubility changes are under development.…”