Soft X-ray interference lithography is a new micro-nano fabrication technology which uses multi beam soft X-ray to form interference field to expose photoresist. Due to the photochemical sensitivity of photoresist, the required fine patterns can be transferred from the mask to the substrate after exposure, development and etching. It is also a technique of frequency doubling of mask period. In this paper, the change of line edge roughness of micro-nano pattern before and after photoresist etching is studied. The results show that the line edge roughness of micro-nano structure after etching is better than that before etching. The line edge roughness of the etched nano pattern is 2.20 nm, which is two thirds the line edge roughness compared with 3.35 nm before etching. The height uniformity of the etched nano pattern is also optimized. This paper provides a reasonable support for soft X-ray interference lithography to fabricate accurate micro-nano patterns by selecting appropriate substrate material, exposure parameters and etching process.
The development of semiconductor industry has made nanometrology more and more important, of which Si/SiO2 multilayer thin-film based critical dimension structures is one of the potential certified reference materials to calibrate measurement instruments. However, in the fabrication process, the quality of the bonding step mainly influences the performance of final structures. In this study, we applied thermocompression bonding method to eliminate the side effect, such as the contamination of adhesive layer and the influence of the adhesive layer on AFM probes caused by the traditional adhesive bonding. Further, thermocompression bonding realized simultaneous observation on both left and right structures in different wafers. On this basis, we also discussed the influence of the size of the silicon wafer, bonding temperature and pressure on bonding performance. The images show that small size is more conducive to improve bonding quality. Besides, the AFM measurement results indicate that Si/SiO2 multilayer thin-film can remain undeformed under higher temperature and pressure (200°C-300°C, 0.6MPa-1.0MPa). This method provides support for Si/SiO2 multilayer thin-film based critical dimension to become high quality certified reference material.
Self-traceable gratings with small scale are much desired in nano-metrology. Atom lithography is the fundamental technique to fabricate self-traceable gratings but the resolution of grating pitch is usually limited by the laser wavelength. To lower down the grating scale, an approach introducing the polarization gradient light field was demonstrated here to achieve the gratings frequency doubling. The influences of polarization gradient standing wave field and cooling light field on the internal atomic structure were first analyzed to illustrate the principle of frequency doubling. And it has been proven that the grating pitch can still perfectly keep traceable to the laser wavelength. Then a quarter-wavelength (λ/4) pitch of 106.4nm self-traceable grating was fabricated experimentally by atom lithography using 425.55nm laser. This approach is hopeful to realize the λ/8 pitch as well, which provides an effective way to fabricate the smaller-scale self-traceable gratings.
The error calibration of the nonlinearity of atomic force microscope (AFM) is the critical step to assure the accuracy during the measurement of microscale structure. In this paper, a new method to calibrate the atomic force microscope is proposed, which is based on the one dimensional self-traceable Chromium nanometre length reference material fabricated by the technique of atomic lithography. The pattern of the Cr grating measured by the metrological AFM present that the pitch is 212.8 nm and the accuracy of the pitch is better than 0.1nm. The number of its pitch is obtained by the centroid method on the data of the grating pattern. The nonlinearity of the commercial AFM is calibrated in the way of measuring the mean pitch of the Cr grating under the several different micron scale. This work offers a flexible solution for calibrating the AFM and meet the calibration need in the activity of nanometre fabrication
One dimensional (1D) Cr nanograting fabricated by laser-focused atomic deposition (LFAD) is suitable for reference materials in nanometrology, owing to its self-traceable to SI meter definition and high accuracy with good uniformity. For further preparing small-scale and traceable reference materials, extremely ultraviolet (EUV) interference lithography with 13.4nm wavelength is utilized to accurately shorten the grating pitch of Cr nanograting (212.8nm). Diffraction efficiency is a key attribute in EUV interference lithography. In this paper, based on rigorous coupled wave analysis (RCWA), diffraction efficiency with EUV light of Cr nanograting was studied. Impacts such as EUV light wavelength, background layer and grating height were mainly taken into consideration. The result shows that Cr background layer has significant influence on diffraction efficiency of Cr nanograting, and an optimized diffraction efficiency of the first diffraction order about 1.4% has been achieved under the practical experimental condition.
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