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

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

Nitride Deposition

The STI Process

Etch

Oxide Deposition

Nitride Strip

CMP

CMP in STI is a dual-material polish

Models: Effective Density from Pad Bending

Derivations for CMP in STI

Li

Lii

Lj

Ljj

jjiifjidji' '

)','()','(),(

Models: Local Pad Compression

Derivations for CMP in STI

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

Models: Dual-Material Polish

Derivations for CMP in STI

Polish rates are similar to local pad compression Different blanket polish rate for different materials Intersection depends on contact height and density

Assumptions:

Derivations for CMP in STI

Two stages identified for CMP in STI Overburden oxide removal Dual-material polish of nitride and oxide

Results:

)',',,(0),( jijiHtHd xx

Dummy Feature Placement for STI

jijixjixjijijijit

jijiHjijiHjijitjiHjijitjiH

a

M

ni

ox

,),,(),(0',',,),',',,(0

',',,,)',',,(,,0)),(),,((,,0)),(),,((

2

1

MH

Formulations as NLP Problems

Min

S.T.ji

jix,

),(Min

S.T.

jijixjixjijijijitjijijijiHjijitjiHjijitjiH

a

ni

ox

,),,(),(0',',,),',',,(0',',,,)',',,(,,0)),(),,((,,0)),(),,((

2

1

Min-Fill Formulation Min-Var Formulation

Dummy Feature Placement for STI

Iterative Approaches

Computational Experience

Computational ExperienceDensity and Post-CMP Topography Simulations for L3:

Original Tiled

Density

Topography

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