RETICLE ENHANCEMENT TECHNOLOGY IN THE SUBWAVELENGTH ERA IMPLICATIONS FOR DESIGN TO SILICON • Design CD << Wavelength • Variants of RET Pervasively Increasing • Design Size Is Explosive • GDS is an Inadequate PD Data Format Consequently: • Mask Data Prep Resources Are a Big Cost Adder • PD to Si Equivalence Verification is A Major Issue • Mask Manufacturability Drives Cost/Cycle Time Issues ISPD 2001 - Resources, Verification W. Grobman Mask Making
Subwavelength RET: An Increasingly Important Post Tapeout Flow Behavioral & Logic Synthesis Formal & Func. Verification Phase Shift Complient Rules DFT, DFM, DFD, DFR Library Creation Floorplanning , Place&Route Noise, Power, Delay Extraction Layout , Parasitics A (GDSII) Phase Shift Methodology Mask. Prep OPC Tile Mask Data Reticle Mfg Reticle Litho Process Si Process ISPD 2001 - Resources, Verification W. Grobman Mask Making Si IC B (Post-RET GDSII)
RET Mini-Review ISPD 2001 - Resources, Verification W. Grobman Mask Making
Motorola Digital & RF Systems Roadmaps for Gate Length Extend Below Native Stepper Resolution Industry Roadmap Motorola Roadmap Stepper Wavelength Chart Courtesy of Numerical Technologies, Inc. ISPD 2001 - Resources, Verification W. Grobman Mask Making
Summary - Reticle Enhancement Technology Optical Proximity Correction (OPC) Add shapes to design data (GDS II) Corrects for litho optics & process Rule based OPC - one mode fits all Model-based OPC - customized to shape neighborhood Phase-Shift “Strong” PSM - Phase mask + binary (“cut”) mask Used for gate printing CD, sheet rho, control “Weak” PSM - Via clear areas include attenuator Tiling Rule based tiling - Doesn’t guarantee global planarity Model-based tiling - POR for future reticles ISPD 2001 - Resources, Verification W. Grobman Mask Making
OPTICAL PROXIMITY CORRECTION IMPROVES PRINTING (ADDS SHAPES TO MASK) MASK WAFER No OPC With OPC Photo downloaded from Micro. Unity (now ASML Mask. Tools) web site ISPD 2001 - Resources, Verification W. Grobman Mask Making
Rule-Based OPC Fig. 1 A Fig. 1 B ISPD 2001 - Resources, Verification W. Grobman Mask Making
Phase-Shifting • Uses phase-modulation at the mask level to further the resolution capabilities of optical lithography Mask 180 o phase-shifter • Benefits: – Smaller feature sizes – Improved yield (process latitude) – Dramatically extended useful life of current equipment – Performance Boost – Chip Area/Cost Advantage for Embedded Systems ISPD 2001 - Resources, Verification W. Grobman Mask Making 0. 11 mm Printed using a ~0. 18 mm nominal process
Phase Shift - Simple Idea, Complex EDA Challenge Chrome Etch Routing poly (phase plate) Legend: Grey= Opaque Color= Clear 180 Phase Etch (phase plate) ISPD 2001 - Resources, Verification W. Grobman Mask Making Gate Binary Mask Clear Area
Rule-Based Tiling + • Done with Boolean operations • Only density of the template is variable • Not adequate for arbitrary design ISPD 2001 - Resources, Verification W. Grobman Mask Making
Model-Based Tiling • Different amount of tiles at different locations • Uses Linear Programming and in-house software ISPD 2001 - Resources, Verification W. Grobman Mask Making
Model-Based Tiling - Large Manuafacturability Enhancement Untiled reticle (768 A) (unmanufacturable) Conventional Rule-Based Tiling (702 A) (9% uniformity improvement) 193 nm ASML Stepper N. A. = 0. 85!!! Model-Based Tiling (152 A) (80% uniformity improvement) ISPD 2001 - Resources, Verification W. Grobman Mask Making
RET is Increasingly Driving New Issues Design Release Data Prep Resources • Computation Time • CPU Time • Storage Requirements PD to Si Equivalence Verification • Design Changes AFTER DRC/LVS/Timing/Power Mask Manufacturability • Mask Fabrication Cycle Time & Cost ISPD 2001 - Resources, Verification W. Grobman Mask Making
RET Methods Pervasively Expand as Technology Nodes Evolve “Prototypical” Scenario 0. 25 um 0. 18 um 0. 13 um 0. 10 um 0. 07 um Rule-based OPC Model-based OPC Scattering Bars AA-PSM Number Of Layers Increases / Generation Weak PSM Rule-based Tiling Optimization-driven MB Tiling 248 nm 248/193 nm ISPD 2001 - Resources, Verification 193 W. Grobman Mask Making nm
Main Drivers of RET Issues 0. 25 um 0. 18 um 0. 13 um 0. 10 um 0. 07 um Rule-based OPC Model-based OPC Data File Size, Computation Time, Mask Mfgbility Scattering Bars AA-PSM Design Constraints, Mask Mfgbility, Mfg Complexity Weak PSM Rule-based Tiling Optimization-driven MB Tiling Computation Time, File Size, Timing/Power Reverification 248 nm 248/193 nm ISPD 2001 - Resources, Verification 193 W. Grobman Mask Making nm
RET RESOURCES BLOAT (1997=1) 1000 Data Size/ Level Hours/design 100 # CPU’s # Layers 10 Mask Production (Days) 1 1997 1998 1999 ISPD 2001 - Resources, Verification W. Grobman Mask Making 2000 2001 (Est. )
Mask / Si Dimensions (Source: ITRS) 1000 Dimension (nm) MPU Lpoly (nm) Mask Min. Image Mask OPC Feature 200 100 50 10 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 ISPD 2001 - Resources, Verification W. Grobman Mask Making Year
Mask Metrology Dimensions for RET Implementation Are Significantly Smaller than Predicted by ITRS Roadmaps 1000 Dimension (nm) MPU Lpoly (nm) Mask Min. Image Mask OPC Feature 200 100 ITRS Mask Min. Feature Assumption 50 10 RET-Driven Mask Min. Feature 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 ISPD 2001 - Resources, Verification W. Grobman Mask Making Year
Solutions • Reticle Delivery Cycle - Model-Driven Mask Inspection • PD to Si Integrity - Model Si AND Mask Process - Use to Drive Si vs. PD Virtual Validation • Intelligent OPC - ID Critical Design Features - Apply MB-OPC With Discrimination • Use Parallel Processing - Recapture Hierarchy For Compaction and Functional Validation (e. g. Timing) • Retain Design Data in PD Representation - GDS Replacement Open Standard ISPD 2001 - Resources, Verification W. Grobman Mask Making
RETICLE INSPECTION ISSUES t t t Defectivity is the most serious problem affecting reticle delivery More acute with the introduction of OPC features do not resolve as drawn in the design on reticle When inspected, OPC results in vast numbers of false defect detections Worst case (currently typical), the mask cannot be inspected at all Standard practice: n De-sense reticle inspection tool so partially resolved OPC shapes do not cause errors n De-sensing for OPC also de-senses the tool to legitimate defects Original Data with Serifs Reticle Image on Inspection Tool From Kling, Lucas Motorola Patent Overlay of sample design data (red), OPC data (yellow), and reticle image on inspection tool (white)
OPC RETICLE INSPECTION INNOVATIONS t Create a data set separate from the design to mimic shrinkage and rounding of OPC structures on reticle t The only change from written data is that OPC structures are altered for inspectability t The altered data set is presented to the inspection tool t Essentially we are inspecting to an image that depicts the reticle as it is expected to appear after exposure transformations and chemical processing Original data with serifs Data with inspection shapes From Kling, Lucas Motorola Patent Database image with inspection shapes on inspection tool Reticle image on inspection tool
RET Must Incorporate Virtual Stepper AND Virtual Maskwriter PD No OPC With Mask-Model Based OPC ISPD 2001 - Resources, Verification W. Grobman Mask Making MASK WAFER
Si ~ Layout - Separate Mask and Wafer Process Models Improve Manufacturability / Flexibility Layout to Si Common Today MASK process model Courtesy: Numerical Technologies, Inc. = This Paper’s Suggested strategy ISPD 2001 - Resources, Verification W. Grobman Mask Making Improve Mask Inspection Fix Linearity Bias (Small vs. large feature) (Esp. bad at metal: xtalk, intralevel shorts… ) Fix E-beam writer artifacts
Model-Driven (MD) RET - MD Data Processing - MD Verification Phase Shift Complient Rules Behavioral & Logic Synthesis Formal & Func. Verification DFT, DFM, DFD, DFR Library Creation Floorplanning , Place&Route Noise, Power, Delay Extraction Layout , Parasitics A (GDSII) Phase Shift Methodology Mask. Prep OPC Tile Mask Data Reticle Mfg MODELS Reticle Litho Process Si Process ISPD 2001 - Resources, Verification W. Grobman Mask Making Si IC B (Post-RET GDSII)
Proper Models -> Local Design Integrity Identify Critical Design Features Apply OPC With Discrimination & Verify Si=PD Layout with OPC Verification Wafer Image Simulation Printed Wafer Courtesy: Numerical Technologies
Intelligent MB-OPC is Desirable Add Vertices Only for Manufacturability e. g. Apply OPC With Discrimination 44 Vertices Today Critical Requires MBOPC Better 20 Vertices Simply Must Avoid Pullback ISPD 2001 - Resources, Verification W. Grobman Mask Making
Partitioning for Parallel Processing Use Hierarchy (Library Cells) AND/OR Flatten and use explicit proximity effect range (Global Wire / Custom) Calculate OPC In Here Keep Solution in Here ISPD 2001 - Resources, Verification W. Grobman Mask Making
PROCESSING THROUGHPUT AND COST RET Today’s Model N-Way Processor Shared Memory Full-chip Hours -> Days / Run ~ $500 K System Not Easily Scaleable Conventional License Model Cluster N Linux Nodes Distributed Memory Loose Multithreading (Optical / EM Effects are Short Range Compared to Compute Cell Size) Hours / Run ~ N X $2000 System Simple to Scale --> Need New License Model ISPD 2001 - Resources, Verification W. Grobman Mask Making
Storage / Data Transmission “Explosion” It’s Desirable to Compress Data Post RET MB-OPC Breaks Hierarchy Recapture Hierarchy by One or Both of: 1. Hierarchical Data Incorporated in Design Shapes • GDS Is an Interchange Format • Need Representation which Couples Physical with Other Design Attributes • Examples: SI 2 Open Library API, Cadence Genesis 2. Use Pattern Extraction Heuristics to Identify Arrays of Shapes • Can be Computationally Very Efficient - O(N) CPU time where N is the Number of Shapes • Available Now - Here’s a Quick Demo ISPD 2001 - Resources, Verification W. Grobman Mask Making
Example: Pattern Extraction Heuristic to Regain Hierarchy Start With Flat Data File of Sequential Records, Sort to Get Contiguous Records Of Same Shape, Different x, y Positions opcode 1 x y Shape Attributes Opcode-k x y Shape Attributes Opcode-L x y Shape Attributes ISPD 2001 - Resources, Verification Sort 1 W. Grobman Mask Making . . Shape Attributes Sort 2
Example: Pattern Extraction Heuristic to Regain Hierarchy ISPD 2001 - Resources, Verification W. Grobman Mask Making 2000 Random Points + 9 X 7 Array
Example: Pattern Extraction Heuristic to Regain Hierarchy ISPD 2001 - Resources, Verification W. Grobman Mask Making After 1 Pass of Heuristic
Example: Pattern Extraction Heuristic to Regain Hierarchy ISPD 2001 - Resources, Verification W. Grobman Mask Making After Second Pass of Heuristic
Post-Parallel Processing Compaction and Verification • Pattern Recognition Heuristics Can Be Very Effective for Compaction • This is Important for Efficient Data Delivery to Mask Shop BUT • Timing, Power, … Checking for Tiled Design Requires An Even Better Connection of PD Data to Design • Global Nets May Need Timing Verification after Tiling • Consequently, RET Could Drive Industry to More Quickly Adopt a New Standard Useful for PD Re-Timing After RET ISPD 2001 - Resources, Verification W. Grobman Mask Making
Open Library API (OLA) - SI 2 ISPD 2001 - Resources, Verification W. Grobman Mask Making
Example RET Design Flow Scenario Workstation Hierarchical PD Rule-based OPC c: PSM Si vs PD (mask and litho models) Flatten & Partition • Smart MB-OPC • Tiling Partitioned Flat PD for Parallel Computation (OLA-like PD Data Representation) Parallel Processors Timing/Power Verify Data Compaction Mask Data ISPD 2001 - Resources, Verification W. Grobman Mask Making Mask Inspect Data Create Mask Inspect Data
Robust, Implementable RET Design Requires New Paradigms • RET Requires Models of New Types - Closer to Fabrication • Accurate PD -> Mask -> Si Models • Drive Design Reverification • Drive Mask Inspect Data for Mask Cycle Reduction • Parallel Computation Can Shrink Compute Resources • Recapture of Hierarchy Shrinks Data Size • Recapture of Design Structure Drives Global Timing Verification ISPD 2001 - Resources, Verification W. Grobman Mask Making
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