Moving boundary transport model for acid diffusion in chemically amplified resists

Abstract

Polymer structure effect on dissolution characteristics and acid diffusion in chemically amplified deep ultraviolet resists J.We propose a general model for latent image formation in chemically amplified resists. The model is based on a moving boundary acid transport concept that incorporates transient free volume generation and densification. It is based on experimental observation of negligible acid diffusion in polyhydroxysterene below T g . The model offers insight into the post exposure bake ͑PEB͒ reaction mechanism that governs the relief image formation in chemically amplified resists. During PEB, there is a thermally induced deprotection catalyzed by the photogenerated acid that produces volatile by-products thereby generating free volume in the resist polymer. The free volume enhances local diffusivity of the acid. The rapid loss of the volatile products is followed by relaxation of the polymer matrix which eliminates the transient free volume and densifies the polymer. The densified polymer inhibits the diffusion of any acid trapped in the deprotected sites. We present cases where the model reduces to Fickean and case II type reaction driven diffusion models under some simplifying assumptions. The model was implemented in simulation tools for resist models to simulate one-dimensional and two-dimensional profiles. The results imply that the relief image formation depends strongly on both the mechanical the chemical properties of the resist. This model provides new directions for resist process optimization.

Photosensitive polynorbornene based dielectric. II. Sensitivity and spatial resolution

“…The evaporation of the solvent generates transient free volume in the polymer film during the soft bake and post-exposure bake steps. 5 The bake temperatures were below the glass transition temperature of the polymer film. Glassy polymers do not respond immediately to a change in their equilibrium state.…”

Simulation of the Postexposure Bake Process of Chemically Amplified Resists by Reaction–Diffusion Equations

“…Second, the reaction-diffusion models involve both reaction and diffusion mechanisms [7][8][9][10][11]. Third, the moving boundary transport models include the volatility of deprotection by-products and the relaxation of free volume [12,13]. Among the three PEB models, the moving boundary transport model is the most general and complicated one.…”

“…Among the three PEB models, the moving boundary transport model is the most general and complicated one. The reaction-diffusion model and the diffusionless model may be considered special cases of the moving boundary transport model [12].…”

Measurement of the spatial evolution of the deprotection reaction front with nanometer resolution using neutron reflectometry

“…Additionally, the acid is subsequently trapped in the deprotected polymer matrix leading to a net reduction in the available acid for deprotection. Numerical calculations based upon this model show that the reaction front propagates as a sharply defined interface into the protected polymer layer [14]. Other successful modeling approaches include the use of a simulation incorporating in detail the deprotection reaction kinetics as well as diffusion mechanisms.…”

“…Differences between the models largely lie in the description of the acid diffusion process and the detail in which the reaction kinetics are incorporated. Predictions from reaction-diffusion models have been compared with the total extent of reaction with FTIR data before development in several systems [7,8,[12][13][14]. Top loss deprotection experiments and comparison with different acid diffusion descriptions showed that Fickian diffusion cannot explain the experimental results [11].…”