Junichi Kosugi

Latest performance of immersion scanner S620D with the Streamlign platform for the double patterning generation

Currently, it is considered that one of the most favorable options for the 32 nm HP node is pitch-splitting double patterning, which requires the lithography tool to achieve high productivity and high overlay accuracy simultaneously. In the previous work [1], we described the concepts and the technical features of Nikons immersion scanner based on our newly developed platform, Streamlign, designed for 2nm overlay, 200wph throughput, and short setup time. In this paper, we present the latest actual performance of S620D with the Streamlign platform. Owing to the high repeatability of our new encoder metrology system, Birds Eye Control, and Stream Alignment, S620D achieves less than 2 nm overlay accuracy, less than 15nm focus accuracy, and successful 32 and 22 nm L/S pitchsplitting double patterning exposures. Furthermore, the results at high scanning speed up to 700 mm/s are fine and we have successfully demonstrated over 4,000 wpd throughput, which confirms the potential for high productivity. Nikon has developed this Streamlign as an optimized long life platform based on the upgradable Modular2 structure for upcoming generations. The performance of S620D indicates the possibility of immersion extension down through the 22 nm HP node and beyond.

High-productivity immersion scanner enabling 1xnm hp manufacturing

NSR-S622D, Nikon’s new ArF immersion scanner, provides the best and practicable solutions to meet the escalating requirement from device manufactures to accommodate the further miniaturization of device pattern. NSR-S622D has various additional functions compared to the previous model such as the newly developed illumination system, new projection lens, new AF system new wafer table in addition to the matured Streamlign platform. These new features will derive the outstanding performance of NSR, enabling highly controlled CD uniformity, focus accuracy and overlay accuracy. NSR-S622D will provide the adequate capabilities that are demanded from a lithography tool for production of 1x nm hp node and beyond.

Process window control using CDU Master

As double patterning techniques such as spacer double/quadruple patterning mature, ArF water immersion lithography is expected to be applied down to the 1x nm hp node or beyond. This will necessitate precise process control solutions to accommodate extremely small process windows. In the case of spacer double/quadruple patterning in particular, CD uniformity of the final feature is strongly related to the lithography performance of the initial pre-spacer feature. CD uniformity of the resist image is affected by many sources. In the case of the exposure tool, CD error on the reticle, as well as exposure dose and focus errors are the key factors. For the resist process, heterogeneity of the stacked resist film thickness, post exposure bake (PEB) plate temperature, and development all have an impact. Furthermore, the process wafer also has error sources that include under-layer non-uniformities or wafer flatness. Fortunately, the majorities of these non-uniformities are quite stable in a volume production process. To improve and maintain the CD uniformity, a technique to calculate exposure dose and focus correction values simultaneously using the measured resist image feature was reported previously [1]. Further, a demonstration of a correction loop using a neural network calculation model was reported in SPIE 2010 [2], and the corrected CD uniformity was less than 1.5 nm (3 sigma) within a wafer. For further improvement, a demonstration of precise dose and focus control using high order field-by-field correction was then reported at SPIE 2011[3]. In that work, the interand intra-field CD uniformities reported were less than 1 nm (3 sigma) respectively. A key aspect of this method is the simultaneous compensation of dose and focus offsets, which successfully maximizes the process margin of a target pattern. The Nikon CDU Master then derives the optimal control parameters for each compensation function in the scanner using the exposure dose and focus correction data, with the NSR-S620 scanner having the capabilities to also control higher order dose and focus distribution. This high degree of controllability ultimately enables precise correction of the complicated CD error distribution that is caused by heterogeneities in the process. In this work, this correction concept was expanded to include contact hole CD uniformity optimization and quick correction method using the AMI-3500 auto macro inspection tool. A 3D contour analysis method is used for contact hole CDs measured by CD-SEM. The contact hole CD is then corrected directly without using any other monitor pattern features. Further, using the Nikon AMI-3500 system, it is possible to successfully extract the adjustment components using the optical diffraction image. Since the AMI measurement time is very quick (just a few minutes), a regular correction loop using the AMI may be a promising solution for system auto correction in an IC manufacturing facility.

Advanced CDU improvement for 22nm and below

ArF water immersion lithography is expected to be used down to the 22nm hp node or below. However, such advancements in technology nodes have led to extremely small process margins. This necessitates more accurate means of process control. CD uniformity of the photo-resist (PR) image is affected by many sources. In the case of the exposure tool-CD error on the reticle, as well as exposure dose and focus errors are the key factors. For the PR process, heterogeneity of the stacked PR film thickness, post exposure bake (PEB) plate temperature, and development have an impact. Further, the process wafer also has error sources that include under-layer uniformity and wafer flatness. Fortunately, the majority of these factors is quite stable in a volume production process and can be compensated for by adjusting exposure dose and focus in the scanner. A technique to calculate exposure dose and focus correction values simultaneously from the measured PR image feature was reported previously [1]. In addition, a demonstration of a correction loop using a neural network calculation model was reported in SPIE 2010 [2], and the corrected CD uniformity was less than 1.5 nm (3-sigma) within the wafer. In this paper, we will report the latest CD uniformity correction results achieved with the NSR-S620D ArF immersion scanner using correction values estimated by scatterometry and CD-SEM. The method of correction using CD-SEM is newly developed. A maximum of nine parameters extracted from the PR profile are used in this correction. In general, the CD variation of an isolated line pattern caused by focus error is more sensitive than that of a dense pattern. Thus, we estimate the focus error from the isolated pattern, with the dose error estimated using both isolated and dense patterns. The Nikon CDU Master then derives the optimal control parameters for each compensation function in the scanner using the exposure dose and focus correction data, and the NSR-S620D is able to control higher order dose and focus distribution. This advanced level of control capabilities enables precise correction of the complicated CD error distribution that is caused by heterogeneities in the process.