Full-chip correction of implant layer accounting for underlying topography
2012
Photolithography for the formerly "non-critical" implant blocking layers is becoming more challenging as edge
placement control budgets for junction definition shrink with each node. In addition to the traditional proximity
effects associated with the implant layer mask, the underlying active and gate layers can interact through a variety of
mechanisms to influence the edge placement of the developed implant layer. These mechanisms include bulk
reflectivity differences, resist thickness thin film interference effects, reflective notching from pattern sidewalls,
reflections from curved surfaces, focus differences, and more. While the use of organic developable bottom
antireflection coating (dBARC) can be effective in minimizing these influences, it does represent an added
complexity and cost, and processes are still relatively immature. Without such a dBARC, the CD variation due to
underlying layers can easily exceed 50 nm, or more than 25% of the target dimension. We propose here a
framework for modeling and correcting for these underlayer effects. The approach is based upon calibration of an
optical model representing only implant mask proximity effects and two additional optical models which represent
the effects of the underlayer topography. Such an approach can be effective in delivering much improved CD
control for complex layouts, and represents only a small impact to full-chip correction runtime.
Keywords:
- Correction
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