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Electron Beam Direct Write (EBDW) lithography is used in the IC manufacturing industry to sustain optical
lithography for prototyping applications and low volume manufacturing. It is also used in R&D to develop advanced
technologies, ahead of mass production. As microelectronics is now moving towards the 32nm node and beyond, the
specifications in terms of dimension control and roughness becomes tighter. In addition, the shrink of the size and pitch
of features significantly reduces the process window of lithographic tools. In EBDW, the standard proximity effects
corrections only based on dose modulation show difficulties to provide the required Energy Latitude for patterning
structures designed below 45nm. A new approach is thus needed to improve the process window of EBDW lithography
and push its resolution capabilities.
In previous papers, a new writing strategy based on multiple pass exposure has been introduced and optimized to
pattern critical dense lines. This new technique consists in adding small electron Resolution Improvement Features
(eRIFs) on top of the nominal structures. Then this new design is exposed in two successive passes with optimized doses.
Previous studies were led to evaluate this new writing technique and establish rules to optimize the design of the eRIF.
Significant improvements have already been demonstrated on SRAM and Logic structures down to the 16nm node.
These results were obtained with a tool dedicated to the 45nm node. The next step of this work is thus to automatically
implement the eRIF to correct large-scale layouts.
In this paper, a new data preparation flow is set up for EBDW lithography. It uses the eRIF solution as a full
advanced correction method for critical structures. The specific correction rules established in our previous studies are
implemented to improve the CD control and the patterning of corners and line ends. Moreover, the dose and shape of the
eRIFs are automatically tuned to best fit the nominal design. This work is done with "INSCALE®", the new data
preparation software from ASELTA Nanographics. This data preparation flow is then applied on layouts down to the
22nm node. Comparisons with the standard dose modulation flow demonstrate that adding eRIFs significantly improves
the process window and thus the resolution of e-beam tools. It also shows that the multiple pass exposure technique can
be used as a specific correction method on large scale layouts.
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