X-Ray Diffraction Measurements of Lithographically Defined Nanostructures

Abstract

The most sophisticated integrated circuits, such as memory chips and microprocessors, are patterned with projection lithography. The performance of semiconductor electronics is coupled to the resolution of the lithographic process. Next-generation nanopatterning requires imaging processes that can achieve sub-20 nm resolution in ultrathin films. Current manufacturing practices are based on projection lithography with chemically-amplfi ed (CA) resists; however, such as "top-down" lithographic processes are approaching their intrinsic resolution limits, so alternative techniques like "bottom-up" block copolymer (BCP) self-assembly are increasingly attractive. The physicochemical parameters that control imaging in top-down and bottom-up lithography are very different, but improving either technique requires accurate feedback for the structure of the "latent chemical image. The objectives of this work are to acquire feedback for image formation using advanced X-ray diffraction techniques, and use this data to construct lithography models that include interfacial interactions. Image formation in CA resists is governed by a coupled reaction-diffusion mechanism. The bulk deprotection kinetics of a glassy poly(hydroxystyrene-co-tertbutylacrylate) resin was examined with infrared spectroscopy and stochastic simulations. Experimental data were interpreted with a model based on non-Fickian catalyst transport (subdiffusive behavior), providing strong evidence that reaction front propagation is controlled by polymer dynamics. Thin films were nanopatterned with electron beam lithography, and the depth dependent shape of the reaction front was measured with variable-incident-angle small-angle X-ray scattering. The image resolution varies with distance from the free surface and substrate interface, where a broader reaction front is detected at the film surface. This behavior is consistent with a surface excess of catalyst, depth dependent polymer dynamics, or both of these factors.

Image formation in BCP self-assembly is controlled by thermodynamics. Thin films of a lamellar poly(styrene-b-methyl methacrylate) copolymer were cast on chemo-epitaxial templates, and their depth dependent structure was measured with variable-incident-angle small-angle X-ray scattering. The shape is signi ficantly deformed near the substrate interface. Simulations based on self-consistent fi eld theory suggest that these deformations are associated with copolymer penetration into the underlying template. This data demonstrates that controlling the structure of the copolymer-template interface is critical for implementation of bottom-up lithography.