Supported by Cadence Design Systems Inc. , U. S. National Science Foundation, and the Packard Foundation Evaluation of the New OASIS Format for Layout Fill Compression Yu Chen, Andrew B. Kahng, Gabriel Robins, Alexander Zelikovsky and Yuhong Zheng UCLA, UCSD, UVA, GSU vlsicad. ucsd. edu ICECS 2004 1
Overview § CMP and Interlevel Dielectric Thickness § Motivation § Repetition Operators in GDSII § Repetition Operators in OASIS & their Compression Ratios § Compressible Fill Generation: algorithms and results § Fill Compression Problem: algorithms and results § Conclusions & Suggestions ICECS 2004 2
CMP and Interlevel Dielectric Thickness § § Chemical-Mechanical Planarization (CMP) = wafer surface planarization Uneven features cause polishing pad to deform Features § § Post-CMP ILD thickness Interlevel-dielectric (ILD) thickness feature density Insert dummy features to decrease variation Area fill features ICECS 2004 Post-CMP ILD thickness 3
Motivation § § Dummy features grow layout size to terabytes Need in more compressible format § New format: OASIS = Open Artwork System Interchange Standard § Our focus: l l How to exploit new compression capabilities of OASIS? How to improve proposed OASIS for further fill compression? ICECS 2004 4
Repetition Operators in GDSII AREF = array reference ICECS 2004 SREF = structure reference 5
Repetition Operators in OASIS Type 1 Type 2 Type 3 Type 5 Type 4 Type 6 Type 7 Type 8 ICECS 2004 6
Compression Ratio of OASIS Repetitions § Compression Ratio CR= size flat OASIS / size compressed OASIS CR ( , CR ( ICECS 2004 ) = Θ(MN) , , ) = Θ(M) 7
Compression Ratio of OASIS Repetitions § Compression Ratio of Types 4, 5 and 8 CR ( ICECS 2004 , )= 7 ) = 3. 5 8
Compressible Fill § Compressible Fill Generation Problem (CFGP) Given a design rule-correct layout, create the minimum number of OASIS operators to represent area fill features that keep window density variation within the given bounds (L, U) Original layout ICECS 2004 Filled layout with area Filled layout featuresarea features with 82 in 9 operators 9
Greedy Compressible Fill Generation ICECS 2004 10
Compressible Fill Generation & GZIP applied to compressible fill compress slower and worse than native generator GCF GZIP and GCF are orthogonal to each other C_Ratio(GCF+GZIP) =C_Ratio(GCF)×C_Ratio(GZIP) ICECS 2004 11
Compressible Fill Generation Results I = Restricted OASIS (= GDSII) II = Full OASIS III = Types 1, 2, 3, 4, 5 IV = Types 4, 5 ICECS 2004 12
Fill Compression Problem § OASIS Fill Data Compression Problem Given a layout containing are fill features, represent these area fill features using OASIS repetition operators in a way that minimizes the resulting data volume Finding regularities ICECS 2004 13
ICECS 2004 14
Exhaustive Search Greedy Fill Compression ICECS 2004 15
Fill Compression Results Rest Full ESBG RSBG ICECS 2004 = GDSII = Full OASIS = Exhaustive search = Regularity search 16
Fill Compression Results ICECS 2004 17
Conclusions & Suggestions § Contributions: l l New fill compression algorithms for OASIS format l § New algorithms for compressible fill generation Comparison of GDSII and OSIS formats Suggestions to enhance OASIS l l Add irregular array OASIS repetition = combination of 4 & 5 Include pseudo-random number generator in OASIS, for fast and simple generation of irregular area fill ICECS 2004 18
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