Keiko T. Hattori

Impact of acid/quencher behavior on lithography performance

To describe complex acid/quencher interaction and their mutual diffusion in imaging with chemically amplified resist films, our acid-quencher mutual diffusion/quenching model is implemented to the fast resist image simulator. Accuracy better than 10-nm was obtained over wide varieties of 0.13- node metal-level pattern features. The model also suggested that diffusion of quencher, as well as that of acid, significantly degrades proximity effects and MEF.

Accuracy of simulation based on the acid-quencher mutual diffusion model in KrF processes

The accuracy of the acid-quencher mutual diffusion model was examined for three commercial resists (acetal-type resists for use with KrF exposure), by comparing results for real wafer CDs with simulated results as obtained by using the model with best-fit parameters (diffusion length for acid/quencher, and relative concentration of quencher). Utilizing our model reduced the deviation between simulated and measured CDs for a wide range of patterns to 6 nm in terms of standard deviation and +/- 10 nm in terms of p-v range. Best-fit Parameters are in the following ranges; acid-diffusion length equals 7 - 13 nm, quencher-diffusion length equals 150 - 200 nm, and relative quencher concentration equals 0.16 - 0.175 (all for two-iteration calculation). The best-fit diffusion length dependence on number of iterations in diffusion/quenching calculation implied agreement with Ficks law and the dependence of the best-fit relative quencher concentration on exposure dose suggested the validity of this model. Quencher diffusion into an organic bottom anti-reflective coating (BARC) was also observed by carrying out a simple experiment.

Quasi-physical model for fast resist contour simulation: importance of lens aberrations and acid diffusion in LSI pattern design

The aberration in optics and acid diffusion in resist films have a great influence on proximity effects in optical lithography. Our analysis clarified that (1) a local (random) pupil-phase variation (higher-order aberration) degrades imaging performance under highly coherent illumination often used with periodic phase-shifting masks, and (2) in some positive-tone chemically amplified resists, the non-Fickean diffusion process changes effective image distributions, depending on the patterns features and mask tonality. Although the latter has a potential to achieve high resolution capability for isolated bright features, these effects generally pronounce proximity effects and make their correction difficult. Simple modeling of these effects and their simulation implementation are also discussed.

Negative resists for i-line lithography utilizing acid-catalyzed intramolecular dehydration reaction

Chemical amplification negative resist system composed of a novolak resin, a carbinol and an acid generator is investigated for i-line phase-shift lithography. The reaction in this resist is based on an acid-catalyzed intramolecular dehydration reaction. The dehydration products act as aqueous-base dissolution inhibitors, and carbinol compounds in unexposed areas work as dissolution promoters. The resist composed of a novolak resin, 1,4-bis((alpha) -hydroxyisopropyl) benzene (DIOL-1) and 2- naphthoylmethyltetramethylenesulfonium triflate (PAG-2) gives the best lithographic performance in terms of sensitivity and resolution. Line-and-space patterns of 0.275 micrometers are obtained using an i-line stepper (NA:0.45) in conjunction with a phase shifting mask.

Suppression of resist pattern deformation on SiON bottom antireflective layer in deep-UV lithography

The interaction between a chemical amplification (CA) resist and a bottom anti-reflective layer (BARL) was clarified to find ways to suppress the resist pattern deformation in the BARL. A SiON film, which is a candidate for use as a BARL material, was analyzed by Fourier transform IR attenuated total reflection spectroscopy, thermal desorption spectroscopy, and x-ray photoelectron spectroscopy (XPS). The Si-NHx, Si-NSi2, Si-OH and Si-OSi groups were identified as the interaction sites on SiON. The effects of those sites on the acid that catalyzes the in-resist reactions were estimated with the partial charge and the at of formation calculated by a molecular-orbital method. The calculation results indicated that the Si-NHx groups completely decompose the acid, and the Si-OH groups decompose it to some extent. The other groups only trap the acid. The strong acid has high affinity and reactivity with those sites. However, a strong acid making a weak bond with the sites on SiON is likely to have a high catalytic ability. This advantage of the strong acid was confirmed by pattern delineation with a resist including onium-salt- generating CF3SO3H.