NIL patterns frequently suffer from the presence of defects such as missing lines or dots which degrade their properties and functionality. Due to their low density and nanosize, the measurement of their fraction is challenging nanometrology trade-off between resolution and measurement range. In this paper, we focus on the use of range-limited SEM images and explore the benefits of a computational modeling approach to simulate the measurement process and estimate the statistics and accuracy of the measurement of missing lines in patterns. The main questions we address have to do with the choice of the parameters available in the measurement process such as the number of acquired images, their magnification defining the lines included in images and the position (overlapped or not) at line pattern. The missing lines can have both uncorrelated and correlated positions in pattern. In the case of positive correlations, the defects are aggregated whereas in the opposite case of negative correlations they are arranged in periodic-like positions. We found that for uncorrelated defects, the critical parameter is the total number of lines included in the measurement process while the image position do not have any impact on the measurement accuracy. On the contrary, when correlations in defect positions are considered, the number of images and the number of lines per image differentiate their effects on the accuracy of the result while the arrangement of images along pattern also plays a crucial role in the measurement process.
Multilevel controllable nanoimprint driven molecular orientation has been obtained in thin films of block copolymer <i>polystyrene-b-polyethylene oxide</i>( PS-b-PEO) by means of solvent vapours assisted nanoimprint lithography (SAIL). The NIL setup using solvent vapours was capable of imprinting nanoscale features over a large area and simultaneously annealing PS-b-PEO thin films. A line pattern stamp was replicated in the BCP film in over a large area with a high resolution registry, and was also observed that the PS-b-PEO film exhibited microphase segregation in the residual layer exhibits a nanodot array from showing hexagonally packed PEO dots in the PS matrix, with a diameter of 20 nm with 40 nm pitch. The order of the hexagonally arranged nanodot lattice seen in the nanodots array was quantified from SEM images using by the opposite partner method from SEM images analysis and compared with to conventionally solvent annealed BCP films, demonstrating an improvement of the ordering of up to 50%. Grazing-incidence small-angle X-ray scattering (GISAXS) study demonstrates the excellent fidelity of the pattern transfer and confirms the periodicity of the BCP in the mesas. In addition, applying the SAIL methodology to BCP thin films in nanopatterned silsequioxane substrates, it was possible to obtain multilevel structures decorated with the BCP microphase segregation. The SAIL technique is a versatile and robust platform to obtain complex high density periodic nanostructures, particularly for second generation block copolymers directed self-assembly.
We report on the use of two original techniques for the quality evaluation of nanoimprint lithography with 50
nm feature size: sub-wavelength blazed diffraction gratings and photoacoustic metrology. Sub-wavelength diffraction
has been used to characterise nanoscale structures by studying the diffraction patterns of visible wavelengths of light
from gratings which are made up of features below the diffraction limit. Diffraction efficiencies of the diffracted orders
are related to the nanoscale line-widths, heights and defects of the gratings. A stamp of a sub-wavelength blazed grating
was fabricated by electron beam lithography and reactive ion etching in silicon and imprinted by NIL with different
tools. Measured diffraction efficiencies agree with those from finite difference time domain simulations and we
demonstrated the possibility to distinguish diffraction patterns from successfully imprinted gratings and those with a
defect. The photoacoustic method has been used for the first time to study nanoimprint polymers. Signals were obtained
from the top and bottom interfaces of polymer layers with aluminium and silicon, respectively, and thicknesses
calculated from the time of flight of the acoustic wave and modelling physical parameters of the polymers, agree well
with those measured by profilometry.
Nanoimprint lithography (NIL), with its apparent simplicity and resolution down to 6 nm, has become an attractive flexible and low-cost technique for nanopatterning of thin films, which themselves act as a mask for further nanofabrication steps, or which can be used as-printed thanks to the functionality of the thin film itself. In this work, we focus on the latter approach and report on our experiments carried out to fabricate organic photonic devices. Silicon stamps, with figures down to 100 nm, are fabricated using electron beam lithography and reactive ion etching. Different fabricated stamps include waveguides, gratings, splitters and interferometers. New fabrication techniques are investigated, namely the combination of NIL with optical lithography and reverse NIL. These two techniques allow producing three-dimensional structures. For the combination of NIL with optical lithography, an original approach is used consisting of a polymer stamp on top of a quartz + metal optical mask. In the case of reverse imprint and multilevel structures, particular attention is paid to adhesion between the stamp, the polymer and the substrate on which the layer is reported. These two techniques are very promising for the fabrication of complex polymer optical devices, like distributed feedback structures, in one step.