Evaluation of the New OASIS Format for Layout Fill Compression

1ICECS 2004

Evaluation of the New OASIS Format

for Layout Fill Compression

Yu Chen, Andrew B. Kahng, Gabriel Robins, Yu Chen, Andrew B. Kahng, Gabriel Robins,

Alexander Zelikovsky and Yuhong ZhengAlexander Zelikovsky and Yuhong Zheng

UCLA, UCSD, UVA, GSUUCLA, UCSD, UVA, GSU

vlsicad.ucsd.eduvlsicad.ucsd.edu

Supported by Cadence Design Systems Inc.,Supported by Cadence Design Systems Inc.,U.S. National Science Foundation, U.S. National Science Foundation,

and the Packard Foundationand the Packard Foundation

2ICECS 2004

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

3ICECS 2004

CMP and Interlevel Dielectric Thickness

Chemical-Mechanical Planarization (CMP) = wafer surface planarization

Uneven features cause polishing pad to deform

Interlevel-dielectric (ILD) thickness feature density Insert dummy features to decrease variation

Post-CMP ILD thicknessFeatures

Area fillfeatures

Post-CMP ILD thickness

4ICECS 2004

Motivation

Dummy features grow layout size to terabytes Need in more compressible format

New format: OASIS = Open Artwork System Interchange Standard

Our focus: How to exploit new compression capabilities of OASIS? How to improve proposed OASIS for further fill compression?

5ICECS 2004

Repetition Operators in GDSII

AREF = array reference SREF = structure reference

6ICECS 2004

Repetition Operators in OASIS

Type 1

Type 7

Type 4

Type 3Type 2 Type 5

Type 8

Type 6

7ICECS 2004

Compression Ratio of OASIS Repetitions

Compression Ratio CR=

size flat OASIS / size compressed OASIS

CR ( , ) = Θ(MN)

CR ( , , ) = Θ(M)

8ICECS 2004

Compression Ratio of OASIS Repetitions

Compression Ratio of Types 4,5 and 8

CR ( , ) = 7

CR ( ) = 3.5

9ICECS 2004

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 Filled layout with 82 area features

Filled layout with area features in 9 operators

10ICECS 2004

Greedy Compressible Fill Generation

11ICECS 2004

Compressible Fill Generation & GZIP

GZIP applied to compressible fill compress slower and worse than native generator GCF

GZIP and GCF are orthogonal to each otherC_Ratio(GCF+GZIP) =C_Ratio(GCF)×C_Ratio(GZIP)

12ICECS 2004

Compressible Fill Generation Results

I = Restricted OASIS (= GDSII)II = Full OASISIII = Types 1,2,3,4,5 IV = Types 4,5

13ICECS 2004

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

14ICECS 2004

15ICECS 2004

Exhaustive Search Greedy Fill Compression

16ICECS 2004

Fill Compression Results

Rest = GDSIIFull = Full OASISESBG = Exhaustive searchRSBG = Regularity search

17ICECS 2004

Fill Compression Results

18ICECS 2004

Conclusions & Suggestions

Contributions: New algorithms for compressible fill generation

New fill compression algorithms for OASIS format

Comparison of GDSII and OSIS formats

Suggestions to enhance OASIS 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