Process-Aware 1-D Standard Cell Design

1. Process-Aware 1-D Standard Cell Design Hongbo Zhang and Martin D. F. Wong Dept. of Electrical and Computer Engineering University of Illinois at Urbana-Champaign hzhang27@illinois.edu Theme/Task: 1821.001

2. Dense Line Printing and 1-D Cell Design • More regular geometric patterns are required in advanced cell design • Based on dense line printing technology, 1-D patterns can be printed by specialized dipole or annular light source • Good for cell composition/decomposition 2D patterns Hard to decompose Hard to print 1D patterns Easy to decompose Easy to print Techcon 2009,Session 5.5

3. Dense line printing (gap free) • EPE: 1.224nm (-0.1um~0.1um defocus) Dense line printing with gaps Dense Line Printing • Dry, dipole, 0.93NA, 193nm, σ= 0.9, 115nm pitch, 32nm width T.A. El-Moselhy et. al, A capacitance solver for incremental variation-aware extraction, ICCAD 2008 Techcon 2009,Session 5.5

4. Gap Size Matters • Increase of gap size will degrade printability • Increase EPE • Reduce Process windows • One direct way: insert dummies into large gaps Techcon 2009,Session 5.5

5. Defocus = 0nm Defocus = 100nm Gap Pattern Matters • Certain gap patterns will destroy printability Techcon 2009,Session 5.5

6. a b c d e f g I II III IV V VI Test Structures for Different Gap Distributions Techcon 2009,Session 5.5

7. Small difference between a and b at 100nm defocus Simulation Results for Test Structure I and II • Process windows have slight difference between test I and test II • Gap has small impact on adjacent wire b a I II Techcon 2009,Session 5.5

8. Not much difference Simulation Results for Test Structure II, III, IV and V • Process windows have not much difference • Gaps can be aligned together to reduce the impact on printability c b II III e d IV V Techcon 2009,Session 5.5

9. g f e • Huge difference Simulation Results for Test Structure V and VI • Process windows have huge difference • A bad distribution will destroy the process window V VI Techcon 2009,Session 5.5

10. Gap Classification • Regular gap • When a gap is adjacent to a real wire • Critical gap • When a gap is adjacent to a real wire’s line-end regular gap critical gap real wire real wire or dummy Techcon 2009,Session 5.5

11. Rules for 1-D Cell Design • Insert dummies into empty space • Make gap size small and uniform • But more work can be done • Extend line-end to adjust gap distribution • Adjacent to a real wire • Align gaps together to reduce the impact • Reduce the number of regular gaps • Avoid certain gap patterns • Avoid critical gaps Techcon 2009,Session 5.5

12. An Example • On-grid cell design • Properly extend wire and insert dummy wire segment to reduce # of regular and critical gaps A typical example of AOI21 Techcon 2009,Session 5.5

13. Wire Extension Methodology • Wires can be represented by intervals • Only local region is concerned when judging a regular/critical gap • Wire end can be extended until a regular gap is removed or it cannot be extended any more. • Only the original wires rather than extension parts are concerned for gap hazard. • The remaining empty space will be filled with dummy in order to keep the uniform pitch Techcon 2009,Session 5.5

14. A A A Algorithm I • A simplified algorithm without considering critical gaps • Sensitive region is limited to 2 continuous grids and 2 adjacent tracks • Regular gap is detected on case a and b • Extension sequence is not important • Always extend one side of line-ends first and then do the other side next a b c √ √ Techcon 2009,Session 5.5

15. Real Wire Extension Dummy Algorithm I • Wire extension and dummy insertion Original Extend left end Dummy insertion Extend right end Techcon 2009,Session 5.5

16. a b A A B B Algorithm II • A more complete version for considering critical gaps • Two forbidden patterns of critical gaps • In case of line-end A & B • Line-ends should be push far apart (a) or aligned together (b) • Only real wire’s line-end is concerned • Extension will help to prevent forbidden patterns, but dummy insertion will not Techcon 2009,Session 5.5

17. Algorithm II: Initialization • Initialization is required to remove all critical gaps in the beginning • Case I: • Solution: • Do the left/right line-end extension to every wire first • One of A or B will be automatically extended • Case II: • Solution: • No more room can be applied for extension • Redesign is needed Techcon 2009,Session 5.5

18. Algorithm II: Initialization • Case III: • Solution: • Before regular line-end extension is started, extend the line-end A • Critical gaps are removed initially Techcon 2009,Session 5.5

19. Algorithm II • Always start extending the left line-end from the left most ones • Once a line-end is extended, the corresponding critical gap will be removed • Avoid misjudgement of the forbidden patterns • Extend the line-end until the gap is no longer adjacent to a real wire or it can not be extended any more • Critical gap should not be created during extension Techcon 2009,Session 5.5

20. Optimality • Theorem: Algorithm II guarantees # of critical gaps is minimized. Moreover, among all solutions with minimum # of critical gaps, algorithm II produces minimum # of regular gaps. Techcon 2009,Session 5.5

21. Experimental Results • Compare EPE between 1-D circuits with and without wire extension • 33.8% is saved for 32nm, 47.9% is saved for 45nm 45nm process: Pitch = 115nm, NA = 0.92 32nm process: Pitch = 75nm, NA = 1.40 Techcon 2009,Session 5.5

22. Experimental Results • Algorithm I • Run time • Algorithm II Techcon 2009,Session 5.5

23. Conclusion • Gap distribution is an important factor on 1-D cell design • Extension and dummy insertion is an effective way to rearrange gaps and benefit printing • Adjacent cells would interact with each other, but this extension and dummy insertion will help • Great improvement on printability has been shown Techcon 2009,Session 5.5

24. Ongoing work • Study impact on circuit performance • Consider more constraints on wire extension: • Cross talk/noise • Limited extension • Explore wire permutation to obtain better cell structure Techcon 2009,Session 5.5

25. TechTransfer • Liaison Interactions • Publications/presentations • H. Zhang, M. D. F. Wong, On Process-Aware 1-D Standard Cell Design, ASPDAC 2010 (to appear) • H. Zhang, M. D. F. Wong, K.-Y. Chao, L. Deng, and S.-H. Choi. Uniformity-aware standard cell design with accurate shape control. Proc. SPIE 7275, 72751G (2009) Techcon 2009,Session 5.5