Die-related Failure Mechanisms and Attributes  (Page 3 of 3)


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Hot Carrier Effects


The phrases 'hot carriers' and 'hot electrons' refer to highly energetic carriers that result from poor design of the device, high source-drain voltages, and high channel electric fields in MOS devices. 



A high voltage across the source and the drain of a MOS device will accelerate channel carriers into the drain's depletion region, causing them to collide with lattice atoms that result in electron-hole pairs.  This phenomenon is known as impact ionization, with the displaced e-h pairs also gaining enough energy to propel some of them towards the gate oxide of the device and trap them there. A high gate voltage can also pull hot carriers into the gate oxide and trap them there before they even reach the drain region.


Trapped carriers or charges in the gate oxide can shift the threshold voltage and transconductance of the device.  The excess electron-hole pairs created by impact ionization can also increase substrate current, which in gross cases can upset the balance of carrier flow and facilitate latch-up.  


See separate article on hot carrier effects.


Junction Burn-out


Junction burn-out refers to the destruction of a p-n junction as a result of excessive power dissipation from an electrical overstress (EOS) or electrostatic discharge (ESD) event.  It is usually in the form of a silicon meltdown at the junction itself, causing the junction to become open or shorted.


Junction Spiking


See Contact Migration.


Metal Burn-out


Metal burn-out refers to the gross destruction of a metal line from excessive current or power dissipation.  This is the most obvious attribute of gross electrical overstress (EOS) damage, although not all EOS-damaged devices will exhibit a metal burn-out. 


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Metal burn-outs are often accompanied by carbonized plastic, metal reflow, and discoloration of the metal around it. Metal lines that become open after a metal burn-out are said to have 'fused.'  The photo attached to the article on EOS shows metal burn-outs. On the right is another photo of a failure site with metal burn-outs.


Mobile Ionic Contamination


Mobile ionic contamination refers to the presence of mobile ions such as Na+, Cl-, and K+ in the device structures of an integrated circuit.  These mobile ions can come from the environment, humans, wafer processing materials, and packaging materials.


Mobile ionic contamination is commonly observed in the gate oxide of a MOS transistor.  These ions can accumulate and cause charge build-ups that can shift the gate threshold of the MOS transistor.  Inversion channels may also form in MOS transistors.  In bipolar devices, mobile ions can affect carrier concentrations, changing the beta of the transistor.


Mobile ions respond to temperature and voltage, so failures due to mobile ionic contamination can be accelerated by burn-in.  Mobile ionic contamination failures can also be made to recover by subjecting the device to unbiased bake, since this will redistribute the ions by promoting their random movement.   Thus, a device is most likely a mobile ionic contamination failure if it fails after burn-in but recovers after unbiased bake.


Oxide Rupture


See Dielectric Breakdown. 


Silicon Nodules


See separate article on silicon nodules.


Slow Charge Trapping


Slow charge trapping refers to the long-term retention of electrons in the gate oxide of a MOS device due to the presence of imperfections in the gate oxide interface.  These imperfections or 'traps' include structural damage, defects, and impurities in the oxide. Thus, improved oxide growth to minimize trap density will minimize the occurrence of slow trapping.


Slow trapping is prevalent in memory devices that require carrier movement in the oxide for proper operation. Trapped charges in the oxide can shift the threshold voltage of the device.


Time-Dependent Dielectric Breakdown (TDDB)


See Oxide Breakdown and Dielectric Breakdown.


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See Also:  Package FailuresFailure AnalysisBasic FA Flows Reliability Models




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