Structural Analysis of PS-b-PMMA Block Copolymer Thin Films with Grazing Incidence Small-Angle X-ray Scattering

Pohang University of Science and Technology* Department of Chemical Engineering, Pohang University of Science and Technology**
‚óčJinhwan Yoon* Byeongdu Lee* Sangwoo Jin* Kyeong Sik Jin* Seung-Yun Yang* Won-Chul Joo** Jin Kon Kim** Moonhor Ree*

Thin films of block copolymer with well defined nanostructure have recently received considerable attention for their potential nano-fabrication application. In these applications, controlling the morphology of the block copolymer thin film, particularly the orientation and ordering of the phase-separated microdomain, is essential. For characterizing the structures and observing the morphology and orientation of the block copolymer thin films, microscopy tools such as transmission electron microscopy, scanning electron microscopy and atomic force microscopy are commonly used. With these tools, images such as those that show local structures near the surface have been obtained, thus enabling discussion of the underlying physics. From the viewpoint of fabrication, this approach is often sufficient, but from the scientific point of view, X-ray scattering & Diffraction results are required, because only they provide information on a larger scale at high resolution. Grazing incidence small-angle X-ray scattering (GISAXS) has emerged as a powerful technique for characterizing internal structure of thin film. The X-ray beam impinges at a grazing angle onto the sample slightly above the critical angle, so that the film is still fully penetrated by X-ray. Analytical solutions of GISAXS patterns based on the distorted wave Born approximation have been developed to describe the complicated reflection and refraction effects, which are not found in conventional Transmission SAXS. Here, we attempted the quantitative analysis of the two-dimensional GISAXS patterns of polystyrene-b-polymethylmethacrylate (PS-b-PMMA) diblock copolymer films deposited on silicon substrates with derived GISAXS formula for hexagonal cylinder with preferred orientation, which were obtained with synchrotron radiation sources. The analysis of the GISAXS patterns was successfully carried out, and we found that PS-b-PMMA thin films deposited on silicon substrates contain cylinder microdomain perfectly oriented normal to the substrate surface.