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Very low supply voltage room temperature test to screen minus temperature soft blown fuse fails which result in a Resistive bridges

Automotive, Reliability and Test Workshop

Peter Sarson CMgr MCMI SMIEEE

17th – 18th November 2016

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AgendaIntroduction to the productProblem HypothesisDesign of ExperimentsResultsCorrelationTest EscapeConclusion

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IntroductionAutomotive, battery operated wireless device

Digital Subsystem + OTP control

Voltage Regulator

(1.7V)

Analog Circuitry + Fuses

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Fuses

The NVM block used in this application used antifuse technology and was stated as automotive qualified by the IP provider.

Lessons learned – nothing is for free in this world

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AgendaIntroduction to the productProblem HypothesisDesign of ExperimentsResultsCorrelationTest EscapeConclusion

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What problem are we solving

Issue with this product was that system critical fuses that were being blown at 35 degrees were being seen unblown at minus temperature on a large scale

Looking into the technology and the physics of the cell this is not uncommon Usually this technology is used for consumer products

We can extend the state of the art if we can make antifuse technology really automotive qualified with no temperature screen

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OTP Failure at minus temperature

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However …….This is not an issue of the technology but of the process

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Step field issue

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High Volume product ramping

• But this is a product with a sharp rampup• For the automotive business segment• Devices need to ship • With no quality risks

• Otherwise there is the risk to loose the end customer and reputation• Also known as a complete nightmare

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AgendaIntroduction to the productProblem HypothesisDesign of ExperimentsResultsCorrelationTest EscapeConclusion

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Problem 1 – Antifuse

• Antifuse technology blows through an oxide • Increase the leakage compared to non blown• Comparison is done with a sense amp with a certain tolerance • Which changes over temperature• Hence multiple effects that compound the tolerance of the

detection of a blown fuse• Result is high defect rate across temperature – OK for consumer• For Automotive requires a second temperature stage

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Equivalent circuit

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Description of problem

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Problem 2 - Layout

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AgendaIntroduction to the productProblem HypothesisDesign of ExperimentsResultsCorrelationTest EscapeConclusion

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How to increase the coverage at 35 degreesReduce VDD (2V) at what the fuses are verified at – decreases the current

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But ….Electronically inked die shown to be quality risk at customer

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Voltage shmooCharacterization – device passed at 2V @ 35 degrees

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Finding where the device flips

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Minus failure correlation at 1.8V

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AgendaIntroduction to the productProblem HypothesisDesign of ExperimentsResultsCorrelationTest EscapeConclusion

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Using a step field issue wafer for verification1.8V screen @ 35 degrees

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Minus probe correlation1.8V screen is more aggressive at finding the issues

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AgendaIntroduction to the productProblem HypothesisDesign of ExperimentsResultsCorrelationTest EscapeConclusion

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New Inking strategy

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New material – 40 degrees sortNo step field

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35 degrees sortPurely randomly as expected

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AgendaIntroduction to the productProblem HypothesisDesign of ExperimentsResultsCorrelationTest EscapeConclusion

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Stack map – 3ppm

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AgendaIntroduction to the productProblem HypothesisDesign of ExperimentsResultsCorrelationTest EscapeConclusion

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Conclusion

It has been shown that by using a very low supply voltage screen for parameters sensitive to cold temperature, a reliable and most effective technique can be developed to remove such problem devices resulting either from process issues or from randomly expected defects. In combination with an intelligent nearest neighbor removal one can have a high degree of confidence in shipping high quality and reliable dice even when suspect wafers have been produced.

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Thank you

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