KEYWORDS: Directed self assembly, Image processing, Signal processing, Electron beam lithography, Lithography, Annealing, Thin films, Epitaxy, Data modeling, 3D modeling
Directed self-assembly (DSA) of block copolymers (BCPs) is a lithographic technique that is expected to be mutually complimentary with ArF immersion lithography, EUV lithography, electron beam direct writing, or nanoimprint for sub-15 nm line patterning and sub-20 nm contact hole patterning. Defect mitigation is the primary challenge behind the use of DSA lithography in practical applications in advanced semiconductor device manufacturing. Therefore, resolve this issue, defect dynamics needs to be clarified using in-situ measurements of self-assembling processes of BCPs in conjunction with modeling approaches.
In this work, the evolution of a surface morphology in self-assembling processes of BCPs during annealing was investigated using in-situ atomic force microscope (AFM).5 A JPK NanoWizard ULTRA Speed AFM (JPK Instruments AG) under AC mode (lock-in phase signal image) was employed to carry out in-situ measurements of self-assembling of symmetrical polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) thin films with a thickness of 40 nm, and a domain spacing 30 nm domain spacing (L0) of 30 nm on a 5 nm thick neutral layer (PS-r-PMMA) during the thermal annealing process starting from a disordered as-cast state. The COOrdinated Line epitaxy (COOL) process was applied to provide DSA line multiplication patterns as hybrid guide patterns which act as chemical and physical epitaxy process.
The in-situ observation approach of the surface morphology during micro-phase separation process revealed the defect generation and rectification processes in DSA thin films. A combination of the time development data in the in-situ AFM and grazing-incidence small-angle X-ray scattering (GI-SAXS) will also be discussed to develop a kinetic modeling for predicting dynamical changes in the three-dimensional nanostructures.
Directed self-assembly (DSA) of block copolymers (BCPs) has been expected to become one of the most promising next generation lithography candidates for sub-15 nm line patterning and sub-20 nm contact hole patterning. In order to provide the DSA lithography to practical use in advanced semiconductor device manufacturing, defect mitigation in the DSA materials and processes is the primary challenge. We need to clarify the defect generation mechanism using in-situ measurement of self-assembling processes of BCPs in cooperation with modeling approaches to attain the DSA defect mitigation.
In this work, we thus employed in-situ atomic force microscope (AFM) and grazing-incidence small angle X-ray scattering (GI-SAXS) and investigated development of surface morphology as well as internal structure during annealing processes.
Figure 1 shows series of the AFM images of PMAPOSS-b-PTFEMA films during annealing processes. The images clearly show that vitrified sponge-like structure without long-range order in as-spun film transforms into lamellar structure and that the long range order of the lamellar structure increases with annealing temperature. It is well-known that ordering processes of BCPs from disordered state in bulk progress via nucleation and growth. In contrary to the case of bulk, the observed processes seem to be spinodal decomposition. This is because the structure in as-spun film is not the concentration fluctuation of disordered state but the vitrified sponge-like structure. The annealing processes induce order-order transition from non-equilibrium ordered-state to the lamellar structure. The surface tension assists the transition and directs the orientation.
Figure 2 shows scattering patterns of (a) vicinity of film top and (b) whole sample of the GI-SAXS. We can find vertically oriented lamellar structure in the vicinity of film top while horizontally oriented lamellar structures in the vicinity of film bottom, indicating that the GI-SAXS measurement can clarify the variation of the morphologies in depth direction and that the surface tension affects the orientation of the lamellar structure. Finally a combination of the time development data in the in-situ AFM and the GI-SAXS is used to develop a kinetic modeling for prediction of dynamical change in three-dimensional nano-structures.
A part of this work was funded by the New Energy and Industrial Technology Development Organization (NEDO) in Japan under the EIDEC project.
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