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| Growing need for advanced PSM Metrology |
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The Advanced Lithography Symposium in San Jose has just finished and although EUV has a made a lot of progress, it became clear that it will not be ready for high-volume production before 2011. Furthermore, it was emphasised that there will be no hyper NA scanners available, as the development of high index lens material has been stopped. This means that the industry will stay with 1.35NA scanners for the next technology nodes.
Lithographers are forced to print at lower k1 which leads to shrinking process windows and makes getting to high lithographic yield more challenging than ever before. At the same time mask complexity increases and mask specification tighten which makes process control extremely important. With feature sizes going beyond the lithographic wavelength and pushing lithography to extreme low k1 factors the mask itself becomes more and more an optical element in the printing process and its performance needs to be characterized precisely. Concluding from the ITRS roadmap PSM remain the key solution to stay with single exposure at low k1. Therefore precise phase measurement becomes of high importance to ensure correct phase and good phase linearity and uniformity across mask for Alternating PSM and Attenuated PSM as well....
Especially for Alternating PSM the ITRS 2007 shows that the phase uniformity stays at ± 1° for 45nm and 32nm node. The challenging part however is that the minimum feature size on mask decreases down to 85nm. In these regions imaging effects as well as topography effects impact the phase significantly.
Phame®, the phase measurement system developed by Carl Zeiss SMS, addresses the phase measurement for all types of PSM including imaging effects, polarization effects and 3D mask effects and helps the mask maker to understand and control any phase related imaging effect.
With the recent investigation we have worked out the viability of Phame® to control phase linearity and phase signatures and optimize process window. It was shown that:
Phase shift shows a strong correlation to process window
Largest process window is achieved at 180°
Dry etch process impacts phase distribution
Dry etch process impacts absolute phase value across feature sizes
Phase off-set between small and large features is not constant
Furthermore we have demonstrated that Phame® enables measurement of phase shift over a wide range of feature sizes, addressing phase linearity, and phase uniformity across the plate. By optimizing the etch process the phase distribution across plate can be improved. Additionally it was verified that the absolute phase value of small features can be adapted as well by tuning the etch process. It was shown that there is an off-set between the phase values of large features and small features which is not constant. This makes a calibration impossible and underlines the importance of in-die phase measurement.
Phame® enables the industry to measure, understand and control phase related printing effects and to optimize the mask for perfect printing.
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