Subwavelength Lithography and Its Impact on Design

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Subwavelength Lithography and Its Impact on Design

• Donovan Sung
• EE235 Student Presentation
• 2/13/08

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Outline

1. Introduction
2. Corrective Methods
3. Optical proximity correction (OPC)
4. Phase-shifting masks (PSM)
5. Scattering bars
6. Tool Changes
7. Conclusion

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Subwavelength Lithography
Problem ? scales slower than the minimum
feature size!
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Disappearance of WYSIWYG regime

• Problems
• Line end shortening
• Corner rounding
• Context-dependent linewidth variation

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Optical Proximity Correction

• Issues
• Rule-based OPC vs. Model-based OPC
• Hierarchical Reuse Methodology
• Integration of Functional Knowledge
• Integration of Mask Verifiability

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Phase-Shifting Masks

• Layout Design
• Hierarchical Reuse Methodology
• Two-color conflict graph
• Layout perturbations for phase assignability
• Re-routing interconnect
• Verification Challenges
• Design Rule Checking (DRC)
• Parasitic Extraction
• Layout-vs-Schematic Checking (LVS)

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Scattering bars

• Benefits
• Reduce maximum light intensity in open areas
• More consistent edge biases
• Increased process window

• Problems
• Creates forbidden pitches
• Process window varies widely with spacing of lines

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Tool Changes

• New CAD restrictions
• All transistors must be in the same orientation
• All wrong way routing must not be minimum width.
• All preferred direction routing must be a subset
  of a uniform width, uniform spacing grating
• Issue
• Will this hurt cell density?

Source L.W. Lieberman, Resolution enhancement
techniques in optical lithography, its not just
a mask problem, 2001.
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Conclusion

• Flow changes
• Upstream and downstream tools must exchange more
  information
• Switch from checking-centric to
  prevention-centric mindset