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Proceedings Paper

Through-focus image balancing of alternating phase-shifting masks
Author(s): Song Peng
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Paper Abstract

Image imbalance refers to the phenomenon that printed image sizes are different between etched and unetched openings if the effective phase and transmission of an alternating phase shifting mask (PSM) are not ideal. The root cause of the phenomenon is the presence of a 0-th diffraction order. When the 0-th order interacts with plus or minus 1 orders, depending on location, it constructively or destructively interferes with the ideal sinusoidal fields generated by the plus or minus 1 orders, causing aerial image difference between the etched and unetched openings. Furthermore, the image imbalance affect changes through focus because optical path length of the 0-th order differs from that of the plus or minus order. An analytical solution of the aerial image has been derived to quantitatively understand the phenomenon. It can be shown that the contributions of phase error and transmission error are orthogonal, thus both errors must be eliminated to eliminate the 0-th diffraction order. The biased etchback approach proposed by Ferguson et al. has been shown to be effective in correcting transmission errors. Detailed implementation of the technique are explored in this presentation. The technique consists of multiple steps of uniform wet etch coupled with aerial image measurements after each etch step. After transmission error is corrected, a phase trimming process may be necessary to improve through-focus image balance.

Paper Details

Date Published: 30 December 1999
PDF: 9 pages
Proc. SPIE 3873, 19th Annual Symposium on Photomask Technology, (30 December 1999); doi: 10.1117/12.373328
Show Author Affiliations
Song Peng, IBM Microelectronics Div. (United States)


Published in SPIE Proceedings Vol. 3873:
19th Annual Symposium on Photomask Technology
Frank E. Abboud; Brian J. Grenon, Editor(s)

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