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.
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 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.
KEYWORDS: Etching, Multilayers, Wet etching, Ultrasonics, Signal processing, Line edge roughness, Scanning electron microscopy, Transmission electron microscopy, Calibration, Reactive ion etching
Background: The multilayer gratings are considered as the potential length-standard-traceable lateral scales for calibrating the next-generation critical dimension scanning electron microscope (CD-SEM) magnification. As a key step in the fabrication of multilayer gratings, selective wet etching determines the final grating structure formation. However, the effects of the etching process parameters on the multilayer gratings in several nanometer scales have not been reported in detail. Aim: By optimizing the process of selective wet etching, we should fabricate high-aspect-ratio and uniform multilayer gratings to obtain high-contrast secondary electron signals and stable secondary electron images while also obtaining measurement accuracy from the small line edge roughness. Approach: Based on the analysis of the important factors in the etching process and SEM and TEM measurement results, we evaluate the effects of ultrasonic agitation, HF acid concentration, etch time, and linewidth scale on the aspect-ratio and uniform of multilayer gratings. Results: We recommend to etching the multilayer films with an HF acid concentration of about 2% during the ultrasonic agitation for uniformity. Moreover, selective wet etching reaction is limited by scale when the linewidth is below 20 nm. Despite the fact that the grating structure is fragile and easy to be broken down, for linewidths of about 10 and 5 nm, the aspect ratio of multilayer gratings can reach about 3 and 2, respectively. Conclusions: By focusing on the optimum conditions of ultrasonic agitation, HF acid concentration, and linewidth scale in the selective wet etching, selective wet etching can be used to fabricate high-aspect-ratio and uniform multilayer gratings with linewidth below 20 nm.
KEYWORDS: Metrology, Chromium, Atomic force microscopy, Calibration, Chemical species, Laser stabilization, Scanning electron microscopy, Standards development, Manufacturing, Atomic force microscope
Nanometric lateral standards are essential to nanometrology. Using laser-focused atomic deposition, a one-dimensional (1D) grating has been manufactured. The pitch of the grating is 212.8 nm, which can be traced to the laser wavelength that is accurately locked to the 52Cr atomic resonance transition 7S3 →7P40. In this paper, the uniformity rather than the pitch accuracy of the 1D grating was evaluated using atomic force microscope (AFM). Based on the center-of-gravity method, the average pitch and the nonuniformity of the grating pitch were calculated. The results show that the average pitch of the grating is 213.2 nm which deviates from the design pitch due to the calibration of AFM, and the nonuniformity of the grating is 0.1 nm. The results preliminarily prove that 1D grating fabricated by laser-focused atomic deposition has good uniformity, and has great potential to become nanometric reference material for AFM and scanning electron microscope (SEM) calibration.
Atom lithography is a novel technique for nanofabrication which can be used to grow periodic arrays of highly uniform nanometer-scale structures. The pitch standard of Cr nano-grating is 212.8±0.1 nm, which coincides with λ/2 of the standing wave, in correspondence with the 52Cr atomic resonance transition: 7S3 → 7P40, λ= 425.55 nm. With the utilization of the material removal ability by AFM scratching, the Cr nanostructures have been transferred to an InP substrate for replication and subdivision. The uncertainty analysed based on gravity centre (GC) method is better than 0.5% for both replicated and subdivided nano-gratings. AFM lithography method expands the application of atom lithography in metrology to a smaller scale with high precision.
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