subwavelength optical lithography: challenges and impact on physical design part ii: problem...
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Subwavelength Optical Lithography: Challenges and Impact on Physical Design Part II: Problem Formulations and Tool Integration. Andrew B. Kahng, UCLA CS Department ISPD-99 TUTORIAL April 13, 1999. Forcing Trends in EDA. Silicon complexity and design complexity - PowerPoint PPT PresentationTRANSCRIPT
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Subwavelength Optical Lithography: Challenges and Impact on Physical Design
Part II: Problem Formulations and Tool Integration
Andrew B. Kahng, UCLA CS DepartmentISPD-99 TUTORIAL
April 13, 1999
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Forcing Trends in EDA• Silicon complexity and design complexity
– many opportunities to leave major $$$ on the table– issues: physical effects of process, migratability– design rules more conservative, design waivers – device-level layout opts in cell-based methodologies
• Verification cost increases dramatically• Prevention a necessary complement to checking • Successive approximation = design convergence
– upstream activities pass intentions, assumptions downstream – downstream activities must be predictable– models of analysis/verification == objectives for synthesis
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EDA Awareness of Process
EDA wants to know as little as possible
This talk: The problems that can’t be avoided
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Necessary Formulations, Flows• PD objectives want to capture downstream
layout operations “transparently”• New problem formulations
– PSM: more global phenomena, scalability issues– OPC: mostly local phenomena– function-driven corrections– hierarchical and reuse-centric regimes
• New tool integrations
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Phase Smart Custom LayoutPhase Smart Custom Layout
PhaseConflict
Detection
AnyConflicts?Yes
LayoutEditing
PhaseConflict
Resolution
No
Phase CompliantCells and Cores
PhaseConflictInterface
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Phase Smart Place and Route
Phase Smart Placement Phase Sm art Routing
NoPhase
ConflictDetection
AnyConflicts?
Yes
Placement
PhaseConflict
Resolution
PhaseConflict
Detection
AnyConflicts?
Yes
Routing
PhaseConflict
Resolution
No
Phase CompliantCells and Cores
Phase CompliantLayout
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SubW avelength EnhancedPhysical Verification
OPC
SiliconDRC
SiliconImage
Generator
W ithinTolerance ? Yes
No
PhaseCompliant
LayoutDatabase
Phase ShiftLayout Design
Phase ShiftLayout
VerificationInterface
VAMPIRE
Extraction
LVS
DRC
Phase Smart Verification
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Global phenomena in PSM phase layout
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Phase Assignment in PSM
Features Conflict areas (<B)
0 0180
< B > B
Assign 0, 180 phase regions such that:• (dark field) feature pairs with separation < B have opposite phases• (bright field) features with width < B are induced by adjacent phase regions with opposite phases
b minimum separation or width, with phase shifting B minimum separation or width, without phase shifting
b (Dark field, neg resist)
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Conflict Graph
< B
Vertices: features (or phase regions) Edges: “conflicts” (necessary phase contrasts) (feature pairs with separation < B )
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Odd Cycles in Conflict Graph• Self-consistent phase assignment is not possible if
there is an odd cycle in the conflict graph• Phase-assignable bipartite no odd cycles
0 phase 180 phase
??? phase
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Breaking Odd Cycles
B
• Must change the layout:• change feature dimensions, and/or • change spacings• PSM phase-assignability is a layout, not verification, issue
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blue features
green 180-shift
black boundariesb/w 0 and 180 areas(to be deleted)
red odd degree
Bright-Field (Positive-Resist) Context• Every critical-width feature defined by opposite-phase regions• Regions not defined a priori
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Value Proposition to Designers
• 0.10m feature sizes in production in 1999 2x performance– Higher yield – “Transparent” to designer
Benefit Gate-PSM Full PSMSpeed ++++ ++++Yield ++++ ++++Power ++ ++++Die Size N/A ++++Initial Generation 0.35 m - 0.25 m 0.15 m
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Problem Statements I• Develop efficient algorithms for minimum-cost phase
region definition and phase assignment in bright-field context– open: definition of cost (mfg difficulty, area, …)
• Continuum between sparse, dense criticality– DF Alt PSM + BF binary trim mask approach simple and
elegant for sparse critical features– what about when all features are critical? (full-chip area opt, in addition to gate shrink)– can be treated as a routing problem (of phase edges)
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Problem Statements II
• New logic (mapping) and performance optimization formulations– with phase shifting, gate lengths and wire widths
continuously variable between b and B– without phase shifting, gate lengths and wire widths
must be at least B– not all features can be phase-shifted: function-driven
What is optimal choice of phase-shifted features, and their sizes?
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Problem Statements III• Understand PSM implications for custom layout
– define a taxonomy of phase conflict– no set of traditional design rules can handle all phase
conflicts what are “good layout practices”?• “no T’s on poly”• “fingered transistors should have even-length fingers”• etc.
• Address PSM as a multi-layer problem– e.g., conflict can be solved by re-routing a connection to
another layer
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Layer Assignment
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Problem Statements IV• Unified theory of PSM design: Can bright- and dark-field,
positive and negative resist contexts all be addressed by a single graph-algorithmic framework?
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dotted matching line
green 180-shift
red conflicts
any path matching odd nodes of dual graph should go through features - split into different phases
Near-Duality for Dark Field
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Local phenomena in OPC
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Problem Statements V• Pass functional intent down to OPC insertion
– OPC insertion is for predictable circuit performance, function
– Problem: make only corrections that win $$$, reduce perf variation (i.e., link to performance analysis, optimization) ?
• Pass limits of mask verification up to layout– Problem: avoid making corrections that can’t be
manufactured or verified
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Problem Statements VI• Minimize data volume
– Problem: make corrections that win $$$, reduce perf variation up to some limit of data volume for resulting layout (== mask complexity, cost)
• Layout needs models of OPC insertion process– Problem: taxonomize implications of layout geometry on
cost of the OPC that is required to yield function or “faithfully” print the geometry
– find a realistic cost model for breaking hierarchy (including verification, characterization costs)
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Hierarchical and Reuse-Centric Contexts
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Problem Statements VII• Given a cell library, what is its flexibility (i.e.,
composability with respect to PSM) ?• Given a standard-cell layout and allowed increase in
hierarchical layout data volume, what is the maximum reduction in area obtainable by creating new cell masters with different phase layout solutions?
• Given a standard-cell layout with phase-solution instantiations that induce conflicts, what is minimum-cost removal of phase conflicts?– DOF’s: change instance, shift, space, mirror, ...
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Integrated Layout Flow, 1• Gate-level netlist, performance constraint budgeting,
early context (mask/litho technology, area density...)• Standard-cell placement with integrated compatibility
awareness (composable PSM layouts)• Global and detailed routing, cell resynthesis on fly
– delay, noise, reliability assumptions = constraints– OPC- and PSM-aware min-cost layout synthesis subject to
constraints (e.g., minimize costs of breaking hierarchy, follow “good practices”, etc.)
– fill abstractions (for parasitic extraction) in constraint-driven routing
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Integrated Layout Flow, 2
• Density analysis, CMP-fill estimation based on detailed routing
• Post-detailed routing performance analysis• PSM phase assignability check for all layers
– new compaction constraints as necessary– layout compaction or incremental detailed routing– until pass phase assignability, performance analysis– note: integration with full-chip geometric compaction!
• Actual dummy fill insertion– issues: data volume
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Integrated Layout Flow, 3
• Detailed physical verification (geom, conn, perf)• Full-chip OPC insertion
– issues: min-cost OPC that achieves required function– issues: data volumes, metrics, intermediate formats– issues: tools stepping on each other (line extensions in
DSM router rules are “zeroth-order OPC”, for example)• Full-chip printability check• Silicon-level DRC/LVS/performance analysis
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Conclusions• New problem formulations
– PSM: layout practices, automated full-chip and standard-cell compatible solutions
– OPC: taxonomy of local phenomena, data reduction– function-driven corrections (can filter complexity)– hierarchy, data volume, reuse concerns
• New tool integrations– compaction, on-the-fly cell synthesis, incremental detailed
routing– graph-based (verification-type) layout analyses– new performance opts, even logic opts