A comparison of the reaction-diffusion kinetics between model-EUV polymer and molecular-glass photoresists

Abstract

It has been recently postulated that sub-22 nm photolithography with polymeric photoresists has reached a materials design barrier due to its large molecular mass and distribution. In this argument, the "pixel" size, which is related to the smallest molecular unit, determines the feature fidelity and resolution of the lithographic process. This hypothesis remains unproven, but molecular glass photoresists can provide a test because they can share similar chemical functionality to polymer resists, but with low molecular mass and a monodisperse molecular mass distribution. The low molecular mass leads to the smaller pixel size compared to the radius of gyration of the polymer photoresist. In this work, we compare the deprotection reaction-diffusion kinetics of a common photoacid generator in a polymer and molecular glass resist with similar resist chemistry to elucidate effects of molecular architecture on photoresist performance. We determine the mechanism of reaction, photoacid trapping behavior, and diffusivity by measuring and comparing the reaction kinetics parameters as a function of temperature and exposure dose. These results permit an analysis of the latent image formation which is a crucial factor in resolution and line-edge roughness. Further, knowledge of the reaction-diffusion parameters of each type of resist provides a quantitative approach to predict linespace features, crucial for design for resolution-enhancement features.

Photoresist Latent and Developer Images as Probed by Neutron Reflectivity Methods

“…The L d may be estimated without neutron refl ectivity, [ 46,47 ] however, the shape of the profi le is critical, in particular, as the feature size approach the diffusion length. This is the ultimate challenge in photoresists and the effect is controlled by the polymer chemistry as shown next.…”

Ion Diffusion in Chemically Amplified Resists

“…It was proposed that this enhancement, which is observed in several CAR resins with volatile protecting groups, arises from a short-lived increase in free volume upon reaction. ,,− However, this concept is inconsistent with measurements of PBOCSt deprotection, which show the same timescales for reaction and polymer densification . Another common approach in reaction–diffusion models is the inclusion of additional processes describing an acid loss. ,, Acid loss is often presented as a “trapping process” attributed to either contaminants or strong local interactions with the polymer, such as hydrogen bonding, and has been used in models of several CAR chemistries. ,,,− …”

Extending the scope of poly(styrene)-block-poly(methyl methacrylate) for directed self-assembly

“…A key aim for the development of photoresists and associated processes is to simultaneously improve RLS. Many gains can be made by optimisation of resist formulations, although more disruptive technologies include the redesign of the resists and such approaches include: polymer bound PAG resists, [1][2][3][4][5][6][7] molecular glass resists [8][9][10][11][12][13][14][15][16] and chain scissioning resists. [17][18][19][20][21][22][23][24][25][26] In particular, polymer bound PAG resists have achieved a great deal of success as EUVL platforms, although improvements are still required for achieving the ITRS goals.…”