Title: The DesignManufacturing Roadmap Andrew B. Kahng UC San Diego CSE
1The Design-Manufacturing RoadmapAndrew B.
KahngUC San Diego CSE ECE Departmentshttp//vl
sicad.ucsd.edu
2Outline
- The Design Roadmap
- DFM Symptoms, Problem, Solution
- DFM Futures Some Examples
3Big 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
4Living 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?
5Design 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)
6Design 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/analys
is, 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)
7Design 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/Cir
cuit, Functional Verification, Test - Key 2003 changes
- Increased analog and circuits content
- Refinement of design cost metrics
- Design system architecture and flow
- SEU and reliability
8Design Technology Crises
Incremental Cost Per Transistor
Test
Manufacturing
Manufacturing
SW Design
NRE Cost
Turnaround Time
Verification
HW Design
- 2-3X more verification engineers than designers
on microprocessor teams - Software 80 of system development cost (and
Analog design hasnt scaled) - Design NRE gt 10s 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
9Challenge 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
10Example 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
11Example Lithography
- 10 CD uniformity requirement causes red bricks
- 10 lt 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?
12Outline
- The Design Roadmap
- DFM Symptoms, Problem, Solution
- DFM Futures Some Examples
13Symptoms 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)
14Symptoms 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
15Example LEF/DEF 5.5, April 2003
16Example LEF/DEF 5.5, April 2003
17Symptoms 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/Yarchitec
ture/ , 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
- gt0.25um width may be wide ? many exceptions
18Symptoms 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 tomorrows IC routers
independently address these issues?
19Corollaries of Moores Law
- Data volume, mask write time explosion
- RET layers explosion
- Design rules explosion
Number of design rules per process node
20Whose 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
21The Problem Evolution
- Conflicting goals
- Designer freedom, reuse, migration
- EDA maintenance mode
- Process/foundry enhance perceived value
( add rules) - ? Prisoners 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)
22DAC-2003 Nanometer Futures PanelWhere should
extra RD be spent?
23The Solution Co-Evolution
- Designer, EDA, and process communities cooperate
and co-evolve to maintain the cost (value)
trajectory of Moores Law - Must escape Prisoners 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
24Example Todays RET Flow
Library (Library Team)
Design Rules Device Models
Litho/Process (Tech. Development)
Layout libs (Corner CaseTiming)
RET
Design (ASIC Chip)
Mask Dataprep (Mask House)
Layout (collection of
polygons ?)
Tapeout
Guardbanding all the way in all stages!! (e.g.
clock ACLV guardband 30)
- What do we lose ?
- Performance ? Too much worst-casing
- Turnaround time ? Huge OPC runtimes, overdesign
- Predictability ? RET is applied post-design
- Mask costs ? Overcorrection
- Designers intent ? RET is not driven by design
25Foundation 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/
26Outline
- The Design Roadmap
- DFM Symptoms, Problem, Solution
- DFM Futures Some Examples
271 Design for Value
- Mask cost trend ? Design for Value (DFV)
- Design for Value Problem
- Given
- Performance measure f
- Value function v(f)
- Selling points fi corresponding to various values
of f - Yield function y(f)
- Maximize Total Design Value ?i y(fi)v(fi)
- or, Minimize Total Cost
- Probabilistic optimization regime
- See "Design Sensitivities to Variability
Extrapolation and Assessments in Nanometer VLSI",
IEEE ASIC/SoC Conference, September 2002, pp.
411-415.
28Obvious 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 - N.B. General RET trajectory rules ? models ?
libraries
29DFV in OPC Regime
- Given Admissible levels of (OPC) correction for
each layout feature, and corresponding delay
impact (mean and variance) - Find Level of correction for each layout
feature, such that a prescribed selling point
delay is attained - Objective Minimize total cost of corrections
30Variation-Aware Library Models
- Each capacitance or delay value replaced by (?,?)
pair - Variation aware .lib
- pin(A)
- direction input
- capacitance (0.002361,0.0003)
-
-
- timing()
- related_pin "A"
- timing_sense positive_unate
- cell_rise(delay_template_7x7)
- index_1 ("0.028, 0.044, 0.076")
- index_2 ("0.00158, 0.004108, 0.00948")
- values ( \
- (0.04918,0.001), (0.05482,0.0015),
(0.06499,0.002)", - .
31Correction Mask Cost CD Control
- 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
32Generic SSTA-Based Cost of Correction Methodology
- Statistical STA (SSTA) provides PDFs of arrival
times at all nodes - Assume variation aware library models (for delay)
are available - Statistical STA currently has runtime and
scalability issues
33MinCorr Parallels to Gate Sizing
- Assume
- Gaussian-ness of distributions prevails
- ? 3? corresponds to 99 yield
- Perfect correlation of variation along all paths
- Die-to-Die variation
- ?12 3?12 ?1 3?1 ?2 3?2
- Resulting linearity allows propagation of (?3?)
or 99 (selling point) delay to primary outputs
using standard Static Timing Analysis (STA) tools - (See DAC-2003 paper)
34MinCorr Parallels to Gate Sizing
Gate Sizing Problem Given allowed areas and
corresponding delays of each cell, minimize total
die area subject to a cycle time constraint
35MinCorr Methodology (DAC-03)
- Mapping of area minimization to RET cost
optimization - Yield library analogous to timing libraries
(e.g., .lib) - Synthesis tool (Design Compiler) performs gate
sizing - Figure counts, critical dimension (CD) variations
derived from Numerical Technologies OPC tool - Restricted TSMC 0.13 ?m library (7 cell masters
BUF, INV, NAND, NOR) - Approach tested on small combinational circuits
- alu128 8064 cells
- c7552 2081 cell ISCAS85 circuit
- c6288 2769 cell ISCAS85 circuit
- Up to 79 reduction in figure complexity without
any parametric yield impact
36Library-Based OPC
- OPC applied post-tapeout
- Overcorrection (matching corners) ? mask cost
- Large runtimes
- Impact of OPC on performance unknown
- Designers intent ? OPC quality metrics
- CD (Poly over active)
- Non-critical poly needs less control
- Contact Coverage
- Perfect corners not needed
- if there is enough contact overlap
37Library Based OPC
- Idea Dataprep each cell once per definition
(during library generation) rather than once per
placement - Model-based OPC very compute-intensive
- reduce runtime and data size by (cell
placements)/(cell definitions) (100s to
millions)
- Radius of influence for 193nm light is about
600nm - Most cells have 200-300nm empty space at the
boundaries ? distance to nearest poly line in any
placement gt 400nm - Small loss in accuracy for fingers at the
periphery of the library cell - Post-OPC GDSII much smaller in size
- Impact of RET predictable during design
characterize library cells post-OPC ?
can prevent a lot of guardbanding, avoid
intricate OPC
640nm
760nm
38Experiments Environment
- Need to emulate a typical environment for the
cell in a placement - Border Poly 160nm from outline
- Affects final CD
- Top-Bottom Poly 70nm from outline
- Affects contact coverage, mask rule violations
- Contact Poly depends on contacts
- Affects contact coverage, mask rule violations
39Results Average CD
CD error Library-OPC vs Full Chip OPC N-i
denotes of devices with less than i error
w.r.t. full-chip OPC Library OPC Runtime is 90
seconds for 10 masters
40CD Error Distribution
41Results Contact Coverage
Contact coverage error Library-OPC vs Full Chip
OPC N-i denotes of contacts with less than i
error w.r.t. full-chip OPC
422 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)
43Systematic ACLV
- ACLV Through-pitch variation (50) Topography
variation (10) Mask variation Etch,
residuals - Current timing analysis (statistical or
deterministic STA) assumes all variation is
random - 50 of ACLV can be predictable by analyzing
layout
- Smile-frown plots indicate
- Through focus variation is systematic
- Corners for timing analysis are derived from
worst-case ACLV tolerance ? instance specific
tolerances are much tighter
Figure courtesy ASML MaskTools
44Taming Pattern and Focus Variation
- Obtain a set of nominal CD (wafer image
simulation) for typical environments of the cell
in a chip ? environment specific timing libs
(typical ASIC libs very limited set of
environments) - Run in-context STA (post-placement) with
context-specific timing libs ? accurate nominal
timing at zero focus condition - Input to output delay modeling based on the
iso-ness and dense-ness of transistors in the
input to output paths ? more accurate delay
variation analysis in STA
45Example of Smile-Frown Aware STA
- If all timing arcs frown, then the path delay
will always decrease through focus ? one corner
is trimmed off ! - If slopes of smile/frown curves are known ?
circuit sensitivity to focus variation can be
computed
46Taming.. Timing Results
473 Intelligent MDP Mask 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
484 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
49Self-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
505 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
B
A
C
Active lines
3
w
fill grid pitch
D
E
4
5
buffer distance
F
G
6
51Min-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)
526 Analog Rules
- We dont 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
537 Restricted Layout
- Soft reset 1-time hit on Moores Law density
scaling - Restricted Design Rules (RDR) can be
compensated many ways - embedded 1-T SRAM fabric, stacking, I/O circuit
design, - N.B. Moores Law is a meta Law!
Dual Exposure Result
Islands
Checkerboard
Example PhasePhirst! (Levenson et al.)
0?
180?
Transparent
Opaque
Trim Mask Exposure
First Exposure
Dark-Field PSMs
or
M. D. Levenson, 2003
54Pre-Made Mask Blanks
- PhasePhirst!
- Levenson/Petersen/Gerold/Mack, BACUS-2000
- Idea mask blanks can be mass-produced and stored
to reduce average cost (e.g., 10K), then
customized on demand
M. D. Levenson, 2003
55Notes on Regular Layout
- 65 nm has high likelihood for layouts to look
like regular gratings - Uniform pitch and width on metal as well as poly
layers - ? Predictable layouts even in presence of focus
and dose variations - More manufacturable cell libraries with regular
structures - New layout challenges (e.g., preserving
regularity in placement) - Caveats
- Non-minimum width poly is less susceptible to
variation ? larger devices (with same W/L) may
lead to more robust designs (so, selective
upsizing may be an alternative to regular
layouts) - 180nm node is a sweet spot for cost,
analog/mixed-signal integration, etc. ? more and
more technology nodes will tend to coexist
56Restricted Design Rule Investigative Flow
OPC
Std cells
Basic design rules
Recipe
Netlist
Auto Layout
Generation
GDSII for Cells
Changes in
Cap Extraction
Restricted Design
HSPICE Simulation
Rule List
.lib files associated with
different design rule set
Standard PR
GDSII for Testbench
Area, Power, Delay, EPE,
and Feature Count Extraction
Electrical Performance
vs. Restrictive Design Rules, Cost
577 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 (x1), 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?
588 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
599 Data Compression
- Today RET complexity ? exploding data volume
- Partitioning of compression and decompression?
- Equipment architecture question where to put
engines, I/Fs, storage? - Largely orthogonal to design considerations
- Procedural compression largely unexplored? (Ex
Verilog SPR 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)
60Choice 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 repetition represents an
array of (polygon) records, enabling
compression of layout data.
equivalent to GDSII AREF
Other OASIS repetition types
6110 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
62Leakage 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 in critical path delay
63Multi-Lgate Design for Leakage?
- Lgate biasing from 130nm to 140nm
- Leakage benefit 29
- Delay overhead 5 Dynamic power overhead
3.5 - Potential alternative/supplement to multi-Vt
design - Avoid high variability in low Vt and
manufacturing overheads of multi-Vt - The CD variability (as a ) is less for larger
Lgate design
64Conclusions
- Designer, EDA, and mask communities must
co-evolve to maintain the cost (value) trajectory
of Moores 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
- ? Much (valuable) work is ahead of us !
65THANK YOU !