1. Basic Concepts in Reliability Design - nl3prc

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[2] Designing for Reliability2.4 Factor Analysis TechniquesIn general, the analysis of reliability factors during product design and process design is very effectivefor improving reliability. The main reliability factor analysis techniques are:(1) Design Review (DR)(2) Fault Tree Analysis (FTA)(3) Failure Mode and Effect Analysis (FMEA)DR, in the case of semiconductor devices, means verifying the items shown in Table 2.1 and correctingany problems so as to yield a more robust product. Normally, a design standard is defined to simplifyand guide this process. Design thus proceeds according to the standard and the design is checkedagainst the standard during the DR. If there are any deviations, tests are run to confirm adherence tothe standard and the standard is updated as necessary.FTA analyzes factors contributing to device failure, such as circuit configuration, pattern design,manufacturing process, package design and operation method.The analysis divides the design, manufacturing, packaging and operation phases into well-defineddetailed functional items. The possible failure modes and the effects of such failures are known foreach item. These items are then weighted so that countermeasure priorities can be defined andestablished.An example of the FMEA method is shown in Table 2.6 for a plastic-package MOS LSI manufacturingprocess. Using a scale of 1 to 10, the Failure Index section of the table rates failure information interms of frequency, effect (on the product, equipment or system) and detectability. A failure index iscalculated by multiplying these three rated values together. The larger the index value, the moreserious the failure.The last column in Table 2.6 shows countermeasures for each process-related failure.2-8
[2] Designing for ReliabilityPattern designManufacturing process designPhotoengraving process (PEP)Table 2.1 Design factors affecting reliability (1/2)Design item Related Factors Failure ModeTransistor (bipolar)Size and shape (collector, base, emitter), dopingimpurity concentration, diffusion depthFunctional failureTransistor (MOS) Size and shape (W/L), oxide film thickness Functional failureIsolationWidth, diffusion depth, doping impurity concentrationParasitic transistor, leakage current, insufficientbreakdown voltageResistance(diffusion)Size and shape, diffusion depth, doping impurityconcentrationFunctional failure, insufficient breakdown voltage,shortResistanceSize and shape, doping impurity concentration, film(polysilicon) thicknessFunctional failure, openMetallization(aluminum)Size and shape, film thicknessElectromigration, open, shortMetallization Size and shape, film thickness, doping impurity(polysilicon) concentrationFunctional failure, openMetallization contact Size and shape, contact combination (e.g. Al-silicon,with siliconAl-polysilicon)Open, short (alloy spike)Bonding pad Size and shape, wiring lead shape Improper bonding, openBonding pad layoutBonding pad distance, package, relative bonding Bonding wire open/short, bonding wirepositionsdisplacement (resin mold)I/O protection circuit Protective resistance, protective diode/transistor Electrostatic discharge, surge damagePhotoresist Film thickness, dust, foreign particles, photoresist Improper pattern geometry (open, short,application materialcharacteristic failure), pinholeMask alignment Accuracy of alignment Characteristic failureExposure Time, intensity of illuminationImproper pattern geometry (open, short,characteristic failure)Development Time, developing solutionImproper pattern geometry (open, short,characteristic failure)EtchingTime, temperature, etching solutionImproper pattern geometry (open, short,characteristic failure)Oxidation (thermaloxidation method)Temperature, time, reaction gas, film thickness Functional failure (e.g. V th , h fe )Passivationdeposition (CVD Temperature, time, reaction gas, film thickness Functional failure(e.g. V th , h fe , leakage)method)Diffusion (thermal Temperature, time, doping impurity concentration,diffusion)diffusion depthFunctional failure, insufficient breakdown voltageDiffusion (ion Acceleration voltage, dosage, ion source, implantationimplantation) depthFunctional failureMetal deposition(aluminum)Deposition method, temperature, film thickness Functional failure, open, shortMetal deposition(polysilicon)Temperature, time, reaction gas, film thickness Functional failure, open, shortDie separation Dicing method, wafer thickness Die crack, flaw, shortDie bondingDie bonding method, temperature, die bonding material(Au-Si, epoxy etc.)Characteristic failure (unstable action)Wire bondingWire bonding method (thermal compression, ultrasonicbonding etc.) wire material (Au, Al), wire diameterOpen, shortSealing (hermeticDefective hermetic seal, large leakage current,Sealing method (metal, glass etc.), sealing widthsealing)corrosion breakageEncapsulation (resinmolding)Molding method, temperature, time, materialcharacteristics (thermal expansion coefficient,impurities)Functional failure, die crack, open, short, wirecorrosion breakageLead forming Lead-forming method, size and shapeBroken package, lead shape, abnormality, brokenleadLead finishingTreating method (plating, dipping), protective material(gold, tin, solder etc.)Rusting, contact fault, solder faultMarking Temperature, time, marking method Marking erosion, illegibility2-9
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