Are There Economic Benefits in DFM ? - a Fabless Design House Perspective - Riko Radojcic Matt Nowak
What IS DFM to Qualcomm ? So …. ? • DFM = everything that a designer can do to ensure that the product meets its performance, power and cost targets • Tight design to process coupling for : • Litho effects = to get what you see in x-y plane • CMP effects = to get what you see in z-plane • Variability = to get what you simulate electrically • Random effects = to get the yield that you modeled • Act of God effects = to get the operating margins you need • DFM = everything that the foundry partner tells you to do ? • DFM = everything that the EDA supplier says you can do ? • DFM = everything that the ‘DFM Start Ups’ say you should do ? • DFM = everything that the designer thinks he should do ? • DFM = business as before and hope for the best ?
CONCERN / ISSUE METRIC / TOOL DESIGN CONSIDERATIONS • DFM issues are not a discontinuity • However there is a challenge with metrics • Area used to be a metric, but…. • Yield is the obvious new metric but … • Designer has no way of designing for it without a way of quantifying it SPICE & STA ~Gate Delays RC Extractors etc.. ~Wire Delays Simulators & Vt selectors ~Power AREA ???? ~Cost & Yield What is the Big Deal about DFM ? • Process windows are getting awfully tight • Ergo, need to tighten up the design : as always !!!
QUALCOMM Perspective Why go to next generation of Technology ? • Higher Performance • New features • Cut-over as soon as possible • Allow for de-bug, system integration • Yield is Boss ! • DFM very important • Lower Cost • Existing (mostly) features • Cut-over when cost is better • Allow for system re-qual time • Die Size is Boss ! • DFM desirable & optional DFM seems to be ‘the right thing to do’, but… Does it really make money for a Fabless COT House?
So, ARE there Economic Benefits in DFM ? • Don’t Really Know : • The commercial DFM space is fuzzy and confusing • The economic value of a DFM technology is confusing • The business case for DFM is unclear • The relative benefit of a DFM methodology is unclear • What we do know : • DFM is done to Optimize Costs and is hence a Business Decision • Any designer should be able to deal with the DFM trade offs
process design Process Characterization Models & Simulators Post GDS Transformation Pre GDS Transformation • Test chip • Measurements • Data massage • Validation • …. • Litho • CMP • Yield • Parametric • …. • Hot Spots • DRC/MRC • Edge Massage • Comps • ….. • P&R • Timing • Synthesis • Architecture • ….. Need to Segment DFM Universe • Segregate DFM activities into 4 types For this segment need a 3 way relationship • Qualcomm role is that of a ‘champion’ or a ‘promoter’ • Principal differentiator is accuracy. • Qualcomm role is that of a ‘client’ • Principal differentiator is use mode and integration. Qualcomm has a different role with each ‘bucket’
Benefit Assessment $ Yes/No Process maturity Benefit of DFM Parameter 1 e.g. minimum die size - typically constant or slight ‘linear’ improvement with maturity Benefit of DFM Parameter 2 e.g. parametric yield or forbidden pitch compliance - typically high at ramp and saturates at maturity ? Need to Monetize DFM Technical Value • DFM is Design to Optimize vs. Pass Go-No Go Checks • Function of process characteristics and maturity • Function of design technology and trade off vs. other variables • Function of product volume and ASP ramp EDA Tools DFM Design Decisions Process Design Kit
Need a DFM Business Case • Business Model for Sharing Costs and Benefits • Foundry should reap the benefits for process improvements • Fabless design house should reap some benefit for DFM improvements • With Wafer Business the BENEFITS are mostly with Fabless side • not entirely: foundry gets larger virtual capacity 2 1 • With Die Business BENEFITS are mostly on the Foundry side • not entirely fabless gets larger capacity Wafer Business • The incremental COST of DFM is mostly on the Fabless side • not entirely: foundry does more characterization Die Business 3 4 • The challenge is a Business Case for DFM in a Fabless House using a Die Priced Business Mode Foundry Fabless
Need a Metric for DFM Benefits • Yield or Project Cost is too Complicated • Retroactive direct measurements • Many compounding and confounding factors • Feedback loops long & often cloaked in economic factors • Need some Relative DFM “Score” • Arbitrary normalized number • Simple and non controversial • Not necessarily a direct measures of yield or cost • but intuitively related to those • Usable without a dedicated process-specific test chip • Perhaps Use Separate Scores, as makes sense ? • e.g. systematic vs. random vs. parametric phenomena
In fact Need Two DFM Metrics Match 2 kinds of costs • “Cost of Design” • measure the efficiency of implementing a given DFM optimization at various steps in the design flow • e.g. routing, or (expensive) polishing, or (more expensive) OPC/RET • “Cost of Si” • measure the net effectiveness of a given DFM optimization • e.g. percentage of redundant vias Being a high volume shop, these are the key metrics that Qualcomm is very sensitive to These metrics are important to Qualcomm but will not make or break a product
DFM Metrics for Cost of Design ? Even un-weighted numbers would be useful as it would allow comparing a design before and after some DFM transformation • e.g. frequency of occurrence of undesirable constructs ? • ‘Bucketed’ in groups and Weighted by : • Dimensions (e.g. at Design Rule vs. at DFM Guideline) • Phenomenon (e.g. OPC unfriendly jog vs. notch vs. …. ) • Or something like this ?
DFM Metrics for Cost of Si ? • e.g. frequency of occurrence of given features • ‘Bucketed’ in groups and Weighted by : • Phenomenon (e.g. via vs. CA vs. …) • Layout configuration (e.g. bordered vs. borderless via…) • Or something like this ? Even un-weighted numbers would be useful as it would allow comparing a design before and after some DFM transformation
So, ARE there Economic Benefits in DFM ? • Can’t Really Know – and will not know until : • The DFM buzz is clarified • Need a clear definition of client-supplier relationships • Tool ROI is clarified • Need a way of estimating the benefits • DFM cost vs. benefit is clarified • Need ability to simulate and share benefit vs. time • Process data and ownership is clarified • Need standard Design Kits • What we do know : • We need DFM Score metrics • We need Process Design Kits