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Proceedings Paper

Implementation of assist features in EUV lithography
Author(s): Fan Jiang; Martin Burkhardt; Ananthan Raghunathan; Andres Torres; Rachit Gupta; James Word
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Paper Abstract

The introduction of EUV lithography will happen at a critical feature pitch which corresponds to a k1 factor of roughly 0.45. While this number seems not very aggressive compared to recent ArF lithography nodes, the number is sufficiently low that the introduction of assist features has to be considered. While the small NA makes the k1 factor larger, the depth of focus still needs to be scaled down with wavelength. However the exposure tool's focus control is not greatly improved over the ArF tools, so other solutions to improve the depth of focus, e.g. SRAFs, are needed. On the other hand, sub-resolution assist features (SRAFs) require very small mask dimensions, which make masks more costly to write and inspect. Another disadvantage of SRAFs is the fact that they may cause pattern-dependent best focus shift due to thick mask effects. Those effects can be predicted, but the shift of best focus and the associated tilt of Bossung curves make the process more difficult to control. We investigate the impact of SRAFs on printing in EUV lithography and evaluate advantages and disadvantages. By using image quality parameters such as best focus (BF), and depth of focus (DOF), respectively with and without SRAFs, we will answer the question if we can gain a net benefit for 1D and 2D patterns by adding SRAFs. SRAFs will only be introduced if any net improvement in process variation (PV) outweighs the additional expense of assist patterning on the mask. In this paper, we investigate the difference in printing behavior of symmetric and asymmetric SRAF placement and whether through slit effect needs to be considered in SRAF placement for EUV lithography.

Paper Details

Date Published: 16 March 2015
PDF: 10 pages
Proc. SPIE 9422, Extreme Ultraviolet (EUV) Lithography VI, 94220U (16 March 2015); doi: 10.1117/12.2085946
Show Author Affiliations
Fan Jiang, Mentor Graphics Corp. (United States)
Martin Burkhardt, IBM Corp. (United States)
Ananthan Raghunathan, IBM Corp. (United States)
Andres Torres, Mentor Graphics Corp. (United States)
Rachit Gupta, Mentor Graphics Corp. (United States)
James Word, Mentor Graphics Corp. (United States)

Published in SPIE Proceedings Vol. 9422:
Extreme Ultraviolet (EUV) Lithography VI
Obert R. Wood; Eric M. Panning, Editor(s)

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