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The Roadmap for Design and Design for Manufacturing Andrew B. Kahng, UC San Diego CSE & ECE Departments Chair, ITRS Design ITWG, 2001–2003 ISMT Yield Council, September 25, 2003. Outline. The Design Roadmap DFM: Symptoms, Problem, Solution DFM Futures: Some Examples.

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slide1

The Roadmap for Design and Design for Manufacturing Andrew B. Kahng, UC San Diego CSE & ECE DepartmentsChair, ITRS Design ITWG, 2001–2003ISMT Yield Council, September 25, 2003

outline
Outline
  • The Design Roadmap
  • DFM: Symptoms, Problem, Solution
  • DFM Futures: Some Examples
design itwg contributions to itrs
Design ITWG Contributions to ITRS
  • System Drivers Chapter
    • Defines IC products that drive manufacturing and design technologies
    • ORTCs + System Drivers = framework for technology requirements
    • Four System Driver classes
      • SOC (Low-Power, High-Performance, Mixed-Technology)
      • MPU
      • Mixed-Signal
      • Embedded Memory
  • Design Chapter
    • Design cost and productivity models
    • Five technology areas: design process / design system architecture, system-level design, logical/physical/circuit design, design verification, design test
    • Cross-cutting challenges: productivity, power, manufacturing integration, interference, error-tolerance
  • ORTC support
    • Frequency, Power, Density models
big picture
Big Picture
  • Message: Cost of Design threatens continuation of the semiconductor roadmap
    • Design cost model
    • Challenges are now Crises
  • Strengthen bridge from semiconductors to applications, software, architectures
    • Hertz and bits are not the same as efficiency and utility
    • System Drivers chapter, with productivity and power foci
  • Strengthen bridges among ITRS technologies
    • “Shared red bricks” can be solved (or, worked-around) more cost-effectively
    • “Manufacturing Integration” cross-cutting challenge
    • “Living ITRS” framework to promote consistency validation
design manufacturing integration
“Design-Manufacturing Integration”
  • ITRS Design Chapter: “Manufacturing Integration” = one of five Cross-Cutting Challenges
  • Goal: share red bricks with other ITRS technologies
    • Lithography CD variability requirement new Design techniques that can better handle variability
    • Mask data volume requirement  solved by Design-Mfg interfaces and flows that pass functional requirements, verification knowledge to mask writing and inspection
    • ATE cost and speed red bricks  solved by DFT, BIST/BOST techniques for high-speed I/O, signal integrity, analog/MS
    • Does “X initiative” have as much impact as copper?
living itrs framework
“Living ITRS” Framework
  • “Living roadmap”: internally consistent, transparent models as basis of ITRS predictions
  • ORTCs: Models for layout density, system clock speed, total system power in various drivers, circuit fabrics
  • Visualization tool (at Sematech website) for capture, exploration of ITRS models under alternative scenarios
  • “Is --- worth it?”
system drivers chapter
System Drivers Chapter
  • Defines the IC products that drive manufacturing and design technologies
  • Goal: ORTCs + System Drivers = “consistent framework for technology requirements”
  • Starts with macro picture
    • Market drivers
    • Convergence to SOC
  • Main content: System Drivers
    • SOC – focus on low-power “PDA” (and, high-speed I/O)
    • MPU – traditional processor core
    • AM/S – four basic circuits and Figures of Merit
    • Embedded Memory – eDRAM, eSRAM, eNVM (flash)
mpu driver
MPU Driver
  • Two MPU flavors
    • Cost-performance (“mobile”): constant 140 mm2 die
    • High-performance (“server/desktop”): constant 310 mm2 die
  • Stake in ground #1: MPU organization: multiple cores, on-board L3 cache
      • More dedicated, less general-purpose logic
      • More cores helppower management (lower frequency, lower Vdd, more parallelism  overall power savings)
      • Reuse of cores helps design productivity
      • Redundancy helps yield and fault-tolerance
      • MPU and SOC converge (organization and design methodology)
  • Stake in ground #2: No more doubling of clock frequency at each node
fo4 inv delays per clock period
FO4 INV Delays Per Clock Period
  • FO4 INV = inverter driving 4 identical inverters (no interconnect)
  • Half of freq improvement has been from reduced logic stages
soc low power driver model strj
SOC Low-Power Driver Model (STRJ)
  • SOC-LP “PDA” system
    • Composition: CPU cores, embedded cores, SRAM/eDRAM
    • Requirements: IO bandwidth, computational power, GOPS/mW, die size
  • Drives PIDS/FEP LP device roadmap, Design power management challenges, Design productivity challenges
req d performance for multi media processing
Req’d Performance for Multi-Media Processing

GOPS

0.01

0.1

1

10

100

Video

MPEG1

Extraction

Compression

MPEG2 Extraction

MP/ML

MP/HL

MPEG4

JPEG

Audio

Voice

Sentence Translation

Dolby-AC3

Voice Auto Translation

MPEG

Word Recognition

Graphics

3D Graphics

10Mpps

100Mpps

2D Graphics

Communication

Recognition

SW Defined Radio

VoIP Modem

Face Recognition

Modem

Voice Print Recognition

Moving Picture Recognition

FAX

GOPS: Giga Operations Per Second

design challenges silicon
Design Challenges - Silicon
  • Silicon Complexity = impact of process scaling, new materials, new device/interconnect architectures
  • Non-ideal scaling (leakage, power management, circuit/device innovation, current delivery)
  • Coupled high-frequency devices and interconnects (signal integrity analysis and management)
  • Manufacturing variability (library characterization, analog and digital circuit performance, error-tolerant design, layout reusability, static performance verification methodology/tools)
  • Scaling of global interconnect performance (communication, synchronization)
  • Decreased reliability (SEU, gate insulator tunneling and breakdown, joule heating and electromigration)
  • Complexity of manufacturing handoff (reticle enhancement and mask writing/inspection flow, manufacturing NRE cost)
design challenges system
Design Challenges - System
  • System Complexity = exponentially increasing transistor counts, with increased diversity (mixed-signal SOC, …)
  • Reuse (hierarchical design support, heterogeneous SOC integration, reuse of verification/test/IP)
  • Verification and test (specification capture, design for verifiability, verification reuse, system-level and software verification, AMS self-test, noise-delay fault tests, test reuse)
  • Cost-driven design optimization (manufacturing cost modeling and analysis, quality metrics, die-package co-optimization, …)
  • Embedded software design (platform-based system design methodologies, software verification/analysis, codesign w/HW)
  • Reliable implementation platforms (predictable chip implementation onto multiple fabrics, higher-level handoff)
  • Design process management (team size / geog distribution, data mgmt, collaborative design, process improvement)
design chapter outline
Design Chapter Outline
  • Introduction
    • Scope of design technology
    • Complexities (silicon, system)
  • Design Cross-Cutting Challenges
    • Productivity
    • Power
    • Manufacturing Integration
    • Interference
    • Error-Tolerance
  • Details of five traditional technology areas: Design Process, System-Level, Logical/Physical/Circuit, Functional Verification, Test
  • Key 2003 changes
    • Increased analog and circuits content
    • Refinement of design cost metrics
    • Design system architecture and flow
    • SEU and reliability
design technology crises
Design Technology Crises

Incremental Cost Per Transistor

Test

Manufacturing

Manufacturing

  • 2-3X more verification engineers than designers on microprocessor teams
  • Software = 80% of system development cost (and Analog design hasn’t scaled)
  • Design NRE > 10’s of $M  manufacturing NRE $1M
  • Design TAT = months or years  manufacturing TAT = weeks
  • Without DFT, test cost per transistor grows exponentially relative to mfg cost

SW Design

NRE Cost

Turnaround Time

Verification

HW Design

design cost model
Design Cost Model
  • Engineer cost per year increases 5% / year ($181,568 in 1990)
  • EDA tool cost per year (per engineer) increases 3.9% per year
  • Productivity due to 8 major Design Technology innovations
    • RTL methodology
    • Large-block reuse
    • IC implementation suite
    • Intelligent testbench
    • Electronic System-level methodology
  • Matched up against SOC-LP PDA content:
    • SOC-LP PDA design cost = $15M in 2001
    • Would have been $342M without EDA innovations
challenge manufacturing integration
Challenge: “Manufacturing Integration”
  • Goal: share red bricks with other ITRS technologies
    • Lithography CD variability requirement new Design techniques that can better handle variability ?
    • Mask data volume requirement  new Design-Mfg interfaces and flows that pass functional requirements, verification knowledge to mask writing and inspection ?
    • ATE cost and speed red bricks  new DFT, BIST/BOST techniques for high-speed I/O, signal integrity, analog/MS ?
  • Can technology development reflect ROI (value / cost) analysis: Who should solve a given red brick?
    • Shared Red Bricks
example manufacturing test
Example: Manufacturing Test
  • High-speed interfaces (networking, memory I/O)
    • Frequencies on same scale as overall tester timing accuracy
  • Heterogeneous SOC design
    • Test reuse
    • Integration of distinct test technologies within single device
    • Analog/mixed-signal test
  • Reliability screens failing
    • Burn-in screening not practical with lower Vdd, higher power budgets  overkill impact on yield
  • Design Challenges: DFT, BIST
    • Analog/mixed-signal
    • Signal integrity and advanced fault models
    • BIST for single-event upsets (in logic as well as memory)
    • Reliability-related fault tolerance
example lithography
Example: Lithography
  • 10% CD uniformity requirement causes red bricks
  • 10% < 1 atomic monolayer at end of ITRS
  • This year: Lithography, PIDS, FEP agreed to relax CD uniformity requirement (but we still see red bricks)
  • Design challenge: Design for variability
    • Novel circuit topologies
    • Circuit optimization (conflict between slack minimization and guardbanding of quadratically increasing delay sensitivity)
    • Centering and design for $/wafer
  • Design challenge: Design for when devices, interconnects no longer 100% guaranteed correct
    • Can this save $$$ in manufacturing, verification, test costs?
outline20
Outline
  • The Design Roadmap
  • DFM: Symptoms, Problem, Solution
  • DFM Futures: Some Examples
symptoms routing rules 1
Symptoms: Routing Rules (1)
  • Minimum area rules and via stacking
    • Stacking vias through multiple layers can cause minimum area violations (alignment tolerances, etc.)
    • Via cells can be created that have more metal than minimum via overlap (used for intermediate layers in stacked vias)
  • Multiple-cut vias
    • Use multiple-cut vias cells to increase yield and reliability
      • Can be required for wires of certain widths
    • Multiple via cut patterns have different spacing rules
      • Four cuts in quadrilateral; five cuts in cross; six cuts in 2x3 array; …
      • With wide-wire spacing rules, complicates pin access
    • Cut-to-cut spacing rules  check both cut-to-cut and metal-to-metal when considering via-to-via spacing
  • Line-end extensions
    • Vias or line ends need additional metal overlap (0th-order OPC)
slide22

Symptoms: Routing Rules (2)

  • Width- and Length-dependent spacing rules
    • Width-dependent rules: domino effects
    • Variant: “parallel-run rule” (longer parallel runs  more spacing)
    • Measuring length and width: halo rules affect computation
  • Influence rules or stub rules
    • A fat wire, e.g., power/ground net, will influence the spacing rule within its surroundings  any wire that is X um away from the fat wire needs to be at least Y um away from any other geometry.
    • Example: fat wire with thin tributaries
      • bigger spacing around every wire within certain distance of the thin tributaries
      • ECO insertion of a tributary causes complications
      • Strange jogs and spreading when wires enter an influenced area
slide24

Symptoms: Routing Rules (3)

  • Density
    • Grounded metal fills (dummy fill*)
    • Via isodensity rules and via farm rules (via layers must be filled and slotted, have width-dependent spacing rule analogs, etc.)
  • Non-rectilinear (-geometry) routing
    • X-Architecture: http://www.xinitiative.org/
      • Y-Architecture: http://vlsicad.ucsd.edu/Yarchitecture/ , LSI Logic patents
    • Landing pad shapes (isothetic rectangle vs. octagon vs. circle), different spacings (~1.1x) between diagonal and Manhattan wires, etc.
  • More exceptions
    • More non-default classes (timing, EM reliability, …)
      • Not just power and clock
    • >0.25um width may be “wide”  many exceptions
symptoms routing rules
Symptoms: Routing Rules
  • Degrade completion rates, runtime efficiency
  • “Postprocessing” likely no longer suffices
    • E.g., antennas
  • There is no chip until the router is done
  • Must / Should / Can tomorrow’s IC routers “independently” address these issues?
slide26

Whose Job Is It To Solve:

  • Mask NRE cost ( runtimes  shapes complexity)
  • BEOL catastrophic yield loss
    • Deposited copper  can infer yield loss mechanisms
      • Open faults more prevalent than short or bridging faults
      • High-resistance via faults
      • Cf. “non-tree routing” for reliability and yield?
    • Variability budget for planarization
      • Copper is soft dual-material polish mechanisms
      • Oxide erosion and copper dishing  cross-sectional variability, inter-layer bridging faults, …
  • Low-k: thermal properties, anisotropy, nonuniformity
  • Resistivity at small conductor dimensions
the problem evolution
The Problem: Evolution
  • Conflicting goals
    • Designer: “freedom”, “reuse”, “migration”
    • EDA: “maintenance mode”
    • Process/foundry: “enhance perceived value” (= add rules)
    •  Prisoner’s Dilemma: who will invest in change?
  • Fiddling: Incremental, linear extrapolation of current trajectory
    • “GDS-3”
    • Thin post-processing layers (decompaction, RET insertion, …)
    • Leads to “dark future” (12th Japan DA Show keynote)
the solution co evolution
The Solution: Co-Evolution
  • Designer, EDA, and process communities cooperate and co-evolve to maintain the cost (value) trajectory of Moore’s Law
    • Must escape Prisoner’s Dilemma
    • Must be financially viable
    • At 90nm to 65nm transition, this is a matter of survival for the worldwide semiconductor industry
  • Example Focus Areas:
    • Explicit manufacturability and cost/value optimization
    • Restricted layout
    • Intelligent mask data prep
    • “Analog” (not binary) rules
    • (Many layout and design optimizations)
    • Disclaimer: Not a complete listing
foundation of the dfm solution
Foundation of the (“DFM”) Solution
  • Bidirectional design-manufacturing data pipe
    • Fundamental drivers: cost, value
  • Pass functional intent to manufacturing flow
    • Example: RET for predictable timing slack, leakage, yield
    • RETs should win $$$, reduce performance variation
    •  cost-driven, parametric yield constrained RET
  • Pass limits of manufacturing flow up to design
    • Example: avoid corrections that cannot be manufactured or verified  e.g., design should be aware of metrology

N.B.: 1998-2003 papers/tutorials: http://vlsicad.ucsd.edu/~abk/TALKS/

outline31
Outline
  • The Design Roadmap
  • DFM: Symptoms, Problem, Solution
  • DFM Futures: Some Examples
1 design for value
#1: Design for Value*
  • Mask cost trend Design for Value (DFV)

Design for Value Problem:

Given

      • Performance measure f
      • Value function v(f)
      • Selling points ficorresponding to various values of f
      • Yield function y(f)

MaximizeTotal Design Value = i y(fi)*v(fi)

[or,MinimizeTotal Cost]

  • Probabilistic optimization regime

* See "Design Sensitivities to Variability: Extrapolation and Assessments in Nanometer VLSI", IEEE ASIC/SoC Conference, September 2002, pp. 411-415.

obvious step function aware opc
Obvious Step: Function-Aware OPC
  • Annotate features with “required amount” of OPC
    • E.g., why correct dummy fill?
    • Determined by design properties such as setup and hold timing slacks, parametric yield criticality of devices and features
  • Reduce total OPC inserted (e.g., SRAF usage)
    • Decreased physical verification runtime, data volume
    • Decreased mask cost resulting from fewer features
  • Supported in data formats (OASIS, IBM GL-I, OA/UDM)
    • Design through mask tools need to make, use annotations
  • (General RET trajectory: rules  models  libraries!)
mincorr minimum mask complexity
MinCorr: Minimum Mask Complexity
  • Levels of RET = Levels of CD control
  • Levels of RET = levels of CD control

OPC solutions due to K. Wampler, MaskTools, March 2003

CD studies due to D. Pramanik, Numerical Technologies, December 2002

mincorr methodology dac 03
MinCorr Methodology (DAC-03)
  • Mapping of area minimization to RET cost optimization
  • “Yield library” analogous to timing libraries (e.g., .lib)
  •  Off-the-shelf synthesis tool performs OPC “sizing”
  • Up to 79% reduction in figure complexity without any parametric yield impact
2 process aware design
#2: Process-Aware Design
  • Anisotropy in H vs. V bias
    • Features in one direction (scanning, raster write, …) may be better controllable than those in the orthogonal direction
    • Single orientation throughout layout is preferred
    • Dominant (critical-feature) orientation in layout design should match write direction
  • Wafer symmetries (e.g., etch gradient due to spin-on)
  • Iso-Dense balancing (imaging through focus)
3 intelligent mdp write
#3: Intelligent MDP+Write
  • MDP driven by (write error * MEEF) = wafer CD error
    • Partitioning into multiple gray-scale writing passes
    • Apertures, beam currents, dwell times, shot ordering, …
  • EDA tools define stripe, major field, subfield boundaries!
  • Electrical / functional defect criteria
4 mask write optimizations
#4: Mask Write Optimizations
  • Conflicting goals: resolution, CD control, throughput
  • Resist heating = large contributor to mask CD variation
    • Knobs: beam current, flash size, idle times, grayscale passes
  • Subfield writing order = example new knob
    • Reduced heating  increased beam current density
    • Reduced dwell time compensates for travel and settling time

Ordering #1

Ordering #2

  • Ordering #2 is “self-avoiding”  lower pre-flash temps
slide39

Max

48.85C

Mean

27.59C

Sequential schedule

“Self-Avoiding” Subfield Order for Mask Write

  • SPIE Microlithography ’03, Photomask Japan ’03
  • Simulation of subfield temperatures within a main deflection field for sequential vs. greedily optimized writing schedules

Max

32.68C

Mean

16.07C

Greedily optimized schedule

5 fill parametric yield impact
#5: Fill Parametric Yield Impact
  • Performance Impact Limited Fill (PIL-Fill), DAC-2003
  • Fill adds capacitance, hurts timing and SI closure
    • Plain capacitance minimization objective is not sufficient
    • CMP modeling  layout density vs. dimensions built into RLCX

1

top view

Active

lines

2

A

B

C

Active

lines

3

w

fill grid

pitch

D

E

4

5

buffer distance

F

G

6

min slack fill constrained pil fill
Min-Slack, Fill-Constrained PIL-Fill
  • Inputs: LEF/DEF, extracted RSPF, STA (slack) report
  • Drive ILP and greedy PIL-Fill methods by estimated lateral coupling and Elmore delay impact
  • Baseline comparison = LP/Monte-Carlo methods
  • Iterated greedy method for MSFC PIL-Fill reduces timing slack impact of fill by 80% (average over all nets), 63% (worst net)
6 analog rules
#6: Analog Rules
  • We don’t need no $#(*&(! “rules”
    • Rules just make lithographers feel better (?)
  • Ultimately, bottom line is cost of ownership, TCOG
  • Given adequate models of MDP, RET and Litho flows, design tools can and should optimize parametric yield, $/wafer, profits
    • More examples: critical-area reduction by decompaction, introducing redundancy (vias, wires), …
  • Automated learning of models and “implicit rules”
    • Current approach: test wafers, test structures, second-hand understanding
    • Future: machine learning techniques
7 restricted layout

Phase Shifters

180

0

#7: Restricted Layout

Dual Exposure Result

Islands

Checkerboard

  • “Soft reset” = 1-time hit on Moore’s Law density scaling
  • Restricted Design Rules (“RDR”) can be compensated many ways
    • embedded 1-T SRAM fabric, stacking, I/O circuit design, …
    • N.B.: Moore’s Law is a “meta” Law!

Example: PhasePhirst! (Levenson et al.)

0

180

Transparent

Opaque

Trim Mask Exposure

First Exposure

Dark-Field PSMs

or

M. D. Levenson, 2003

7 charging and antennas
#7: Charging and Antennas
  • Process steps use plasmas, charged particles
    • Electrical fields over gate oxides induce damage (Vt shift) or breakdown
  • Limit antenna ratio = (Apoly + AM1 + …) / Agate-ox
    • AMx = metal(x) area that is electrically connected to node without using metal (x+1), and not connected to an active area
    • Bridging (break antenna by hopping to higher layer)
      • Extra wiring, vias, congestion
    • Reverse-biased diode or source-drain contact near gate
      • Leakage, area, timing penalties
  • Will antenna ratios continue to decrease?
    • High-k gate dielectrics  increased physical Tox  less leaky, hard failure modes?
  • More preemption (no post-processing, or dioded cells)?
  • Tradeoff unfixed antenna yield penalty for fixed antenna yield loss?
8 pattern collapse
#8: Pattern Collapse
  • Pr(pattern collapse) = f(length)

 Length-dependent spacing rules

  • Limits wire AR, packing density
  • Standardized embedding of long wires for manufacturability and physical reliability
  • becomes
  • ???

Cao et al. U. Wisconson

9 data compression
#9: Data Compression
  • Today: RET + complexity  exploding data volume
  • Partitioning of compression and decompression?
    • Equipment architecture question – where to put engines, I/F’s, storage?
    • Largely orthogonal to design considerations
    • Procedural compression largely unexplored? (Ex: Verilog + SP&R binaries + runscripts = representation of detail-routed layout)
  • Design for compressibility? (DATE ’03, SPIE ML ’03)
    • What is ROI of relaxing constraints on layout? Of +k bytes of data?
    • How context-sensitive must patterning be? (Lessons from RET…)
  • Use of lossy compression? (SPIE ML ’03)
    • What design features can be “lost”? (Ex: dummy fill)
choice of geometric compression operators

TYPE 2

TYPE 8

TYPE 1

TYPE 4

TYPE 3

TYPE 7

TYPE 5

TYPE 6

Choice of Geometric Compression Operators
  • Who is using compression, at what stages of design-mfg flow?
  • Is there synergy between manufacturing flow and GDSII-OASIS-UDM?

OASIS Format (recent SEMI standard) defines eight repetition types.

A repetitionrepresents an “array” of (polygon) records, enabling compression of layout data.

equivalent to “GDSII AREF”

Other OASIS repetition types

10 leakage management
#10: Leakage Management
  • Huge parametric yield loss
  • Subthreshold leakage current varies exponentially with threshold voltage: I  exp(-Vth)
  • Vth = f(channel length, oxide thickness, doping)
    • Most affected by variations in gate length

±100% Isub

±10% Ld

Dennis Sylvester, U. Michigan

leakage understanding control
Leakage: Understanding + Control
  • Understanding: variation in chip-level leakage due to intra- and inter-die Leff variation
    • cost-benefit of controlling relevant variation sources
  • Control: Multi-everything (threshold, supply, sizing)
  • New control: can use selective Lgate bias (~2 nm) to reduce leakage by 60% with no loss in critical path delay
    • Draft in preparation
conclusions
Conclusions
  • Designer, EDA, and mask communities must co-evolve to maintain the cost (value) trajectory of Moore’s Law
    • Wakeup call: Intel 157nm announcement
  • Basic goal: bidirectional design-mfg data pipe
    • Drivers: cost, value
    • Pass functional intent to mask and foundry flows
    • Pass limits of mask and foundry flows up to design
  • Several examples given
    • Manufacturability and cost/value optimization
    • Leakage power
    • Restricted layout
    • Intelligent mask data prep
    • Analog rules
  • Please pay someone to do this!