Direct Measurement of the Reaction Front in Chemically Amplified Photoresists

Abstract

The continuing drive by the semiconductor industry to fabricate smaller structures using photolithography will soon require dimensional control at length scales comparable to the size of the polymeric molecules in the materials used to pattern them. The current technology, chemically amplified photoresists, uses a complex reaction-diffusion process to delineate patterned areas with high spatial resolution. However, nanometer-level control of this critical process is limited by the lack of direct measurements of the reaction front. We demonstrate the use of x-ray and neutron reflectometry as a general method to measure the spatial evolution of the reaction-diffusion process with nanometer resolution. Measuring compositional profiles, provided by deuterium-labeled reactant groups for neutron scattering contrast, we show that the reaction front within the material is broad rather than sharply defined and the compositional profile is altered during development. Measuring the density profile, we directly correlate the developed film structure with that of the reaction front.

Photoresist Latent and Developer Images as Probed by Neutron Reflectivity Methods

“…[ 31 ] By using a deuterium-labeled protection group after the reaction the volatile products leave the fi lm and provide the change in contrast necessary to measure the deuterium profi le with nanometer resolution. Therefore, the ideal line-edge was blurred by photoacid diffusion to form a smooth composition profi le from an initial sharp edge.…”

“…The loss of volatile protection groups changes the polarity of the polymer fi lm such that above an average deprotection level (solubility switch) the fi lm becomes soluble in an aqueous hydroxide developer. The model line-edge approach (Figure 4 ) developed by Lin et al [ 31 ] fi rst demonstrated neutron refl ectivity as a general method to probe the reaction front of photoresists for 248 nm lithography. The loss of the deuterium-labeled tert -butoxycarbonyl (tBOC) groups provided the change in scattering length density contrast, such that the deuterium profi le accurately represents the chemical latent image.…”

Mechanism of UV Photoreactivity of Alkylsiloxane Self-Assembled Monolayers

“…[17][18][19][20][21] A molecular level understanding of how the photoresist reacts will be increasingly important in high-resolution photoresist micropatterning since the resolution may begin to be limited by the size of the resist and spatial extent of the photochemical reactions, as the feature sizes approach nanometer scales. 22 The mechanisms of photooxidation of organic materials in the condensed phase is much more complex than in the gas phase. 19,23 SAMs afford the opportunity to systematically vary the structure and composition of organic layers to understand from a molecular level how these factors affect the reactivity.…”

Towards X-ray induced transient grating methods for nanometer scale dynamics: Diffraction on transient structures induced by extreme ultraviolet radiation from FLASH

“…Here the spatial resolution (structure size 32 nm) and the line edge roughness is not only determined by the fundamental diffraction limit but by the diffusive processes within the photo-resist materials after EUV irradiation [15]. As the initial EUV photochemical reaction creates radicals and acids, which are the starting point of chemical amplification within the illuminated resist material during post-exposure baking [16][17][18], their initial spatial distribution, ultra fast dynamics as well as their collective dynamics and diffusion within the photoresist determine the achievable structure size and line edge roughness [15]. 2.…”