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2006 LSI Logic Corporation
Semiconductor Design for Manufacturability (DFM)
T. R. RamachandranPrincipal Program ManagerGroup Operations, Custom Solutions Group
Thursday, April 13, 2006 LSI Logic Confidential 2
AcknowledgmentsDiscussions with the following people are gratefully acknowledged: Rich Schultz and Rich Laubhan (Silicon Methodology) Vishy Lakshmanan (Layout and Manufacturability Technology) John Walker (Technology Support/Foundry Technology) Ram Venkatraman and Ruggero Castagnetti (Strategic Planning
and Architecture)
Thursday, April 13, 2006 LSI Logic Confidential 3
Outline Why does DFM matter? Defining DFM
! What is DFM?! Why does it matter how we define DFM?! Characteristics of DFM! DFM: Yield/Reliability as Explicit Goals (Illustration)! DFM Decision Tree! A Framework for Understanding DFM! Defining and Bounding DFM
Charting out a DFM Strategy Key Challenges in DFM Conclusions APPENDIX: Some Examples of DFM implementation at LSI
Logic
Thursday, April 13, 2006 LSI Logic Confidential 4
Why Does DFM Matter? DFM is about yield and reliability Lack of manufacturing access " less knowledge on
process/yield/reliability learning Foundry-engagements often wafer-cost based
! Yield is not guaranteed (even reliability could be a question mark) After-the-fact FA on products is expensive, and sometimes
unsuccessful Growing process technology (and design) complexity usually
means greater uncertainty in scientific understanding! More parametric variation; possibly, greater sensitivity to variations! May lead to more design-specific yield/reliability risk
Manufacturing data is more limited and cost of extracting data (through testchips) is growing rapidly
" DFM, based on accurate manufacturing information, can therefore serve as a form of risk insurance
Thursday, April 13, 2006 LSI Logic Confidential 5
What is DFM? Design for Manufacturability (or Design for Manufacturing)
has been described in different ways. Some examples:! Manufacturing-aware design; design-dependent yield enhancement;
design techniques to optimize manufacturability; design for yield; design through greater design-manufacturing collaboration; design for printability.and so on.
! Another perspective: Everything done in design is for manufacturing; so the term is a misnomer [Nitin Deo, Ponte Solutions]
In some cases, articles about DFM dont clearly define or explain their use of the term! And we have an entire growing industry clustered around this term
Thursday, April 13, 2006 LSI Logic Confidential 6
Why does it matter how we define DFM? You cant effectively solve the DFM problem if you dont know
what DFM means! Vagueness may introduce redundancy, inefficiencies, or errors in judgment,
without clarifying what exactly needs to be done differently Convincing management to fund DFM requires knowing what DFM is
and what it isnt One complaint Ive read is that we sometimes dont know what data is
needed for DFM- We wont know, if we dont know what DFM is
The more well-defined DFM is, the more likely it is that -! The need for it will become transparent ! Companies serving this area will get traction with their customers
Unified DFM definition and structured approach to DFM will not impact product differentiation! DFM is a broad topic with plenty of opportunities to support myriad products! Product differentiation is based on markets served in DFM arena
Thursday, April 13, 2006 LSI Logic Confidential 7
Characteristics of DFM DFM involves Design and Manufacturability
! One cant design for manufacturability, without understandingmanufacturability
! DFM is not just about the D in DFM
Yield is a key part of DFM; Reliability is also integrally linked to DFM! Usually, yield and reliability are linked but acceptable yield may
not always guarantee acceptable reliability
However, none of these four characteristics D, M, Y, R are unique to DFM! They are characteristics of every design and product ever built
So, what makes DFM (somewhat) unique?! Yield and reliability need to be more explicit goals of design! Customer product yield and reliability need to be more explicit goals
of manufacturing
Thursday, April 13, 2006 LSI Logic Confidential 8
DFM: Yield/Reliability as Explicit Goals(An Oversimplified Illustration)
Z = DFM Metric = F (Xdesign, Ydesign)= Yield or Reliability Probability
Mfg/Tech. Requirements, M/R
M/RX = SPICE Model
Tightness (~ 1/)
Y = De
sign R
ule
Tightn
ess (
~ 1/[L
,S])
Mature mfg. process
New, advanced mfg. process
Actual Design, DE
DE
? ??
Product Requirements, P/RP/RSpeed
Area
Thursday, April 13, 2006 LSI Logic Confidential 9
DFM Decision TreeDoes full compliance to product requirements guarantee desired yield and reliability?
Does the manufacturer guarantee desired yield and reliability if you comply 100% with their standard (mandatory) manufacturing requirements?
NO
Are you satisfied that the manufacturer has done sufficient due diligence and collected the
data needed for them to make this guarantee?
[requires some in-house process expertise!]
YES
Has the manufacturer provided a guarantee that
planned process / manufacturing
improvements will definitely address the assessedyield/reliability gaps?
NO
NO
YES
Consider DFM a requirement
NO
Consider DFM an option
YES
Thursday, April 13, 2006 LSI Logic Confidential 10
A framework for understanding DFM (1)Terms Used: The term Perturbations refers to deviations from nominal expectations
Unavoidable perturbations are highly unlikely to be eliminated in a mature process and require design intervention
Avoidable perturbations are those that manufacturing has the responsibility to eliminate as the process matures
The term Model or Modeled is used loosely to also encompass design rules
B = Nominal process and known perturbations with acceptable variation that are modeled accurately [Desired Baseline]
UB = Known perturbations with unacceptable variation that are modeled accurately [Undesirable Baseline]
KU = Known perturbations with unknown variation that are modeled inaccurately [Known Unknowns]
UU = Unknown perturbations with unknown variation that are not modeled at all [Unknown Unknowns]
Thursday, April 13, 2006 LSI Logic Confidential 11
A framework for understanding DFM (2):Illustrative (hypothetical) example
UU KU UB BBetter knowledge of process and better modeling of variations/perturbations
Avoidable perturbation? Manufacturing should take responsibility to eliminate perturbation
Advanced mfg. pr
ocess at introduct
ion
Advanced mfg. process a
t maturity without DFM
" The first step of DFM, then, is to develop an accurate understanding of unavoidable manufacturing perturbations, including their expected time evolution
Unavoidable perturbation? Manufacturing to shift perturbation to UB/B, working with design if appropriate
Advanced mfg. process at maturity, with DFM
Count
Thursday, April 13, 2006 LSI Logic Confidential 12
A framework for understanding DFM (3) Once the yield/reliability impacts of unavoidable manufacturing
perturbations are accurately understood, manufacturing may decide to account for them in one of two ways:
! Update the standard manufacturing requirements (e.g., standard design rules, SPICE models, etc.)
The designer would be responsible for complying 100%- This is the traditional design/foundry engagement model
[or]
! Issue (optional) DFM requirements that are not addressed by the standard manufacturing and product requirements
Designer would have to adequately account for them based on design-specific trade-offs (ROI)
" The second step of DFM, then, is to adequately account forunavoidable manufacturing perturbations that are not addressed by the standard manufacturing and product requirements
Thursday, April 13, 2006 LSI Logic Confidential 13
Defining and Bounding DFM DEFINITION: Two completely equivalent definitions are offered
below. They are intentionally worded differently to call out the design and manufacturing aspects of DFM:
! DFM involves the accurate understanding of, and adequate accounting for, the time-dependent yield/reliability impact of unavoidable manufacturing perturbations which are not addressed by the standard manufacturing and product requirements
! DFM involves the identification and quantification of the design sensitivity of manufacturing yield and reliability, and the modification of design features to improve the yield or reliability of manufactured IP, without compromising on the standard manufacturing and product requirements
SCOPE: The scope of DFM extends to design-related (not just design) activities that go above and beyond complying with standardmanufacturing and product requirements, in order to improve yield or reliability
Thursday, April 13, 2006 LSI Logic Confidential 14
Charting out a DFM StrategyDFM Drivers
Yield
Reliability
Broad Areas of Focus
Process Variation
Killer Defects
Mask-making
Possible Nature of Problems
Process Modeling Gaps
Defectivity Modeling Gaps
Design Verification Gaps
Design Rule Gaps
Device and Interconnect Modeling Gaps
How Problems will be Identified
EDA Vendor models, expertise, roadmap
Mfg. DFM rules, models, expertise, roadmap
Internal expertise and learning
Industry/academic research
Yield Reliability
Defining Solution Paths (Models, Tools, Utilities,
Libraries, Decks, etc.)
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Thursday, April 13, 2006 LSI Logic Confidential 15
Key Challenges in DFM (1) Focus on addressing design aspect of DFM often results
in under-emphasis on understanding manufacturability
! Its not just about the D in DFM
! D and M " joint responsibility for DFM
! Meaningful DFM not possible without an accurate understanding of unavoidable manufacturing perturbations that impact yield/reliability
Quantitative information, interdependencies, time evolution Inaccuracies could result in under- or over-compensation
! Need to press manufacturing partners on this consistently. If we dont:
The value of DFM will remain nebulous, except in the most obvious of cases
Foundries may be tempted to outsource their basic manufacturing and characterization responsibilities to their customers, for a fee
Thursday, April 13, 2006 LSI Logic Confidential 16
Key Challenges in DFM (2) Wafer-cost business models are not naturally conducive to
DFM
! Incentives for foundries to make yield/reliability (DFM) a key focus? Competition and Customer Service/Partnerships are two
possibilities- Foundry customers should press foundries on product quality
expectations (esp. yield/reliability)- Foundries should recognize that product yield/reliability can make
or break customers success
! Incentives for designers to make yield/reliability (DFM) a key focus? Visible improvements in product yield and reliability
- However, need accurate manufacturing information- Recommended rules alone dont help convince designers
! Recent developments (on the foundry front) are promising but its too early to make any judgments
Thursday, April 13, 2006 LSI Logic Confidential 17
Key Challenges in DFM (3) Lack of common, open standards
! Is it really premature to talk standards for DFM? No.
! Standards for manufacturing information Companies should work together in consortia to define minimum
acceptable manufacturing information and data/model formats OAC/Si2 could drive standards on formats
! Standards for design tools Embrace Open Access for application development Adopt minimum acceptable standards for tool calibration Ensure minimum acceptable standards for model robustness
! Standards for design companies Consider consortia-enabled collaboration on shared test vehicles
for manufacturing and design tool benchmarking- Sometimes even basic silicon guarantees may not be met by
manufacturer due to inadequate characterization
Thursday, April 13, 2006 LSI Logic Confidential 18
Key Challenges in DFM (4) Circuit-Impact awareness of DFM design tools
! Lack of interoperability " circuit-impact of DFM enhancements likely cannot be determined in real-time
Routing-friendliness of DFM design tools! DFM verification tools are sometimes not integrated into existing
P&R flow! Some are not auto-correct and may or may not offer specific
recommendations on fixes
Manufacturing awareness of DFM design tools! Accurate interpretation of manufacturing information is important
Options for DFM fixes linked to manufacturing knowledge Manufacturing variations - across die, reticle, wafer, lots, and
time - not easily simplified into a single model! Holistic approach preferred to piecemeal approach
Tools that cant make tradeoffs between different DFM requirements are of limited value
! DFM applications most often focus on the BEOL of the process Significant effects and issues in FEOL (and increasingly so)
Thursday, April 13, 2006 LSI Logic Confidential 19
Key Challenges in DFM (5) TAT and Database Size
! Lack of parallel processing, incremental processing, and user-defined or circuit-property-dependent actions, will result in significant barriers to tool acceptance
! Database size explosion and massive TAT for even a single pass of DFM enhancement could be major roadblocks to adoption
Dealing with Recommended Rules and Non-Traditional Rule Checks! Dealing with non-black-and-white rules, rules dependent on voltage
domain or circuit intent, etc., not easy! Need data-based, effective solutions that also allow proper trade-off
analysis
Multiplicity of tools makes adoption challenging! The more (DFM) tools in the design flow, the greater the complexity
and TAT and barrier to adoption
Thursday, April 13, 2006 LSI Logic Confidential 20
Conclusions DFM involves the accurate understanding of, and adequate
accounting for, the time-dependent yield/reliability impact of unavoidable manufacturing perturbations which are not addressed by the standard manufacturing and product requirements
DFM requires:! Significant and accurate manufacturing information to make the
design activity meaningful! Unprecedented collaboration between foundries, EDA vendors and
design companies, using appropriate open standards (but encrypted data)
! Design tools that are efficient, more holistic, fast, user-friendly, standards-based, well-calibrated, platform-independent (or interoperable) and built using an informed interpretation of manufacturing data
! Adequate incentives for all parties to make it viable
The future of the DFM industry depends on our being able to replace hype and fuzziness with sharp focus and clarity
2006 LSI Logic Corporation
APPENDIX: Some Examples of DFM Implementation at LSI Logic
Thursday, April 13, 2006 LSI Logic Confidential 22
Some Examples of DFM Implementation at LSI Logic Analysis of OPC/litho process variations and library optimization
for OPC/litho effects Development of more accurate device/interconnect models to fill
gaps and inaccuracies in standard models from manufacturing! Extensive Si to Simulation analysis to expose potential problem
areas! Accurate modeling and accounting of LOD effect, WPE, etc.
DFM rule prioritization to help IP design, based on process knowledge and Si learning
Adoption of select DFM rules for library design! Electrical analysis of impact of deviation from key DFM rules! Extensive use of key DFM rules and accurate models for
analog/MXS IP Proprietary DFM testchip for defect and process sensitivity
analysis Adoption of routing optimization for DFM (redundant via, metal
extensions, etc.)! Based on yield sensitivity analysis and design tradeoffs
Etc.