Nano-lithography Alignment Based On Moiré Fringe In Complex Environment

The progress of nanofabrication technology, mainly lithography, is dependent on the rapid development of microelectronic and nano technologies. As one of the critical technologies in the process of lithography, the alignment, whose accuracy has a direct influence on the overlay result, should meet at least 1/10 of critical dimension. Nowadays, the resolution of latest lithography tools could reach about 10 nm,resulting to the attention on high-precision alignment approaches. The alignment method with moiré fringes is considered to be a promising technology for the high-end lithography, due to its high precision and good robustness. Although several studies have been performed on this approach, most of them are about the method to increase sensitivity and accuracy, resulting in a lack of research on the environmental influences on alignment precision. In fact, the spatial attitude of alignment mark, the collimation of illuminate light and the phase extracting algorithm are all closely connected to the measurement accuracy. Herein, this dissertation mainly studies how the environmental factors affect its phase distribution and then the alignment accuracy.The main contents of this dissertation are summarized as follows:1. The advantage and disadvantage of the existing alignment methods are analyzed; the nano-lithography alignment approach based on moiré fringe is proposed. Based on optical interference and diffraction theory, the amplification effect of moiré fringe on a small displacement and the relationship between the phase information and misalignment displacement are given. At last, we design a set of grating alignment marks for lithography alignment, and obtain the misalignment displacement by demodulating it with the image processing and phase extracting algorithms.2. In order to meet the high-precision and real-time requirements of fine alignment, a windowed fast Fourier transform(FFT) method based on phase spectrum is proposed to extract the phase extraction of the moiré fringe. And the numerical simulation is performed on the Matlab2012 b Window Design & Analysis Tool platform to test the performance of proposed algorithm, including the ability to restrain spectrum leakage and the performance of window function.3. We will mainly study how the tilted moiré fringe affects its phase distribution and then the alignment accuracy. On this basis, the method for error correction is proposed and confirmed. The results show that, the accuracy of the correcting method for tiled moiré fringes could reach to 10-6rad.4. The relationship between the phase distribution of moiré fringe and the collimation of illuminated light is established and verified. On this basis, the method for error correction is proposed and confirmed. For the key parameter, the collimation of incident light, we proposed the collimation measuring method with differential grating and Talbot interferometry, whose detection capability is proved to be 10-8rad.5. Based on those theoretical researches above, the mask-wafer alignment experiment system is constructed. With this platform, stepping and repetitive experiments are performed to verify this proposed alignment method. The experimental results show 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).