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Ruiqi Tian 1,2 , Xiaoping Tang 1 , D. F. Wong 1

Dummy Feature Placement for Chemical-mechanical Polishing Uniformity in a Shallow Trench Isolation Process. Ruiqi Tian 1,2 , Xiaoping Tang 1 , D. F. Wong 1. 1. Dept. of CS, University of Texas at Austin, Austin, TX 78712 2. Motorola Inc., 3501 Ed Bluestein Blvd., Austin, TX 78721

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Ruiqi Tian 1,2 , Xiaoping Tang 1 , D. F. Wong 1

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  1. Dummy Feature Placement for Chemical-mechanical Polishing Uniformity in a Shallow Trench Isolation Process Ruiqi Tian1,2, Xiaoping Tang1, D. F. Wong1 1. Dept. of CS, University of Texas at Austin, Austin, TX 787122. Motorola Inc., 3501 Ed Bluestein Blvd., Austin, TX 78721 {ruiqi, tang, wong}@cs.utexas.edu

  2. Outline • The STI Process • Derivations for CMP in STI • Models used (a review) • Assumptions and results • Dummy Feature Placement • Problem formulation • Iterative Approach • Computational Experience • Conclusion

  3. The STI Process CMP in STI is a dual-material polish Nitride Deposition Etch Oxide Deposition CMP Nitride Strip

  4. Derivations for CMP in STI Models: Effective Density from Pad Bending

  5. Derivations for CMP in STI Models: Local Pad Compression • Polish rates of high and low areas are related by step height due to pressure re-distribution • Initial contact height decreases with increasing density, no consideration for spacing

  6. Derivations for CMP in STI Models: Dual-Material Polish • Polish rates are similar to local pad compression • Different blanket polish rate for different materials • Intersection depends on contact height and density

  7. Derivations for CMP in STI Assumptions: • Two stages identified for CMP in STI • Overburden oxide removal • Dual-material polish of nitride and oxide Results:

  8. Dummy Feature Placement for STI Formulations as NLP Problems • Min-Fill Formulation • Min-Var Formulation Min Min S.T. S.T.

  9. Dummy Feature Placement for STI Iterative Approaches

  10. Computational Experience

  11. Computational Experience Density and Post-CMP Topography Simulations for L3: Density Topography Original Tiled

  12. Conclusion • Formulation for CMP in STI • Models for pad bending, pad compression, and dual-material polish are considered • Dummy feature placement as an NLP problem • Solution for dummy feature placement • Iterative approaches proposed • Experimental results are good • Future studies needed • Contact height dependence on feature spacing

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