Study On The Theory And Application Of Nano Lithography Alignment Based On Moire Fringe

In recent years, nanotechnology has undergone a rapid development, which shows broad application prospects in microelectronics, materials preparation, aerospace and biomedicine, and thus becomes one of three core technologies for the future revolution of science and technology in the 21 st century. Among them, the integrated circuit industry as the core field of nanotechnology development has become an important symbol to measure the sustainable development level of national economy and information industry.According to the "the development law of a generation technology, a generation equipment and a generation device", the shrinking feasibility size of integrated circuit puts forward higher request to the resolution of lithography. Optical projection lithography by increasing the numerical aperture and shortening the exposure wavelength to improve the resolution, has been playing a central role in the integrated circuit manufacturing, at the same time also faces many technical bottlenecks and increasing costs. In such a situation, the emerging nanoimprint lithography technology as the representative of close/contact lithography technology due to its low cost, high resolution, easy operation and many other advantages, compared with the traditional optical projection lithography shows great advantages, which is thus classed by the international technology roadmap for semiconductors(ITRS) as one of the most potential candidate technologies for the next generation lithography at the 22 nm technology node below. However, current optical projection alignment methods are very difficult to adapt to the next generation lithography characterized by improving resolution. As one of the most important techniques in lithography process, alignment accuracy is closely related to overlay accuracy, which requires at least 1/10 of lithography resolution. Therefore, the research on next generation alignment method with nanoscale accuracy will be imminent.Based on current situation of lithography alignment technologies and combined the characteristics of the next generation of close/contact lithography like nanoimprint and surface plasma lithography technology, this dissertation will explore an alignment method based moiré fringe. The main contents include the design of alignment mark,the extraction algorithm of misalignment and many problems faced in practical applications, which are summarized as follows:1. Traditional alignment methods using light intensity signal combining the workpiece table scan mode and video image have many deficiencies. By refining their advantages, the optical interferometry is introduced into the mask-wafer alignment. Based on optical interference and diffraction theory combined with the amplification effect of Moiré fringe on a small displacement, the misalignment is modulated in the phase information of Moiré fringe. By demodulating it, the misalignment can be directly obtained. The four quadrant tiled grating alignment mark is designed, and the physical model of mask-wafer alignment are also established;2. The relationship among the tilted Moiré fringe, the alignment mark and CCD camera is established. And the impact of tilted alignment marks on the alignment accuracy is studied. On this basis, two correction methods based on the phase slope and spatial frequency decomposition are proposed, and their basic principles and algorithm processes are introduced. Furthermore, their scope of application and performance are compared by simulation study. The results show that the latter with a accuracy of 10-4°(10-6rad) is more suitable for the correction of tiled moiré fringe in lithography alignment;3. In order to meet the real-time requirements of alignment, a windowed fast Fourier transform(FFT) method based on phase spectrum is proposed to extract the misalignment between mask and wafer. And the implementation process of this method is introduced in detail. The cause for spectrum leaking using FFT to process a signal is analyzed. Furthermore, the windowing algorithm is introduced into the phase extraction of the moiré fringe signals. Various candidate window functions are comparatively studied based on Matlab2012 b Window Design & Analysis Tool platform, and the results show that Blackman-Harris window is theoretically best suitable to the proposed alignment method;4. According to the Talbot effect theory, the relationship between the moiré fringe contrast and Talbot effect is analyzed, and the optimization model for the gap control between mask and wafer is established. Through the Wolfram Mathematica 9.0.1 software programming, the best alignment gap can be easily found, and the experiments validate its correctness;5. Followed by a large number of theoretical researches above, the mask-wafer alignment experiment system is built. By referring to the piezoelectric micro positioner, different grating periods and step distances are used to demonstrate the performance of this proposed alignment method. The experimental results indicate that the maximum error is less than 10 nm, the standard deviation of error is less than 5nm and the repeatability alignment precision is less than ± 30nm(3σ);6. Finally, the moiré fringe-based alignment method is extended to the mask-stage alignment in projection lithography. Based on these given system parameters, its feasibility and alignment accuracy are preliminary analyzed.