When an integrated circuit fails, one of the first questions is: How is the device failing electrically?
A chip may exhibit excessive leakage current, a short circuit, an open connection, abnormal supply current, a parametric shift or a complete functional failure. Before engineers physically cut into the device, they usually want to understand this electrical behavior and narrow the failure to the smallest possible region.
This is the purpose of Electrical Failure Analysis (EFA).
Electrical Failure Analysis is a group of techniques used to characterize, reproduce and localize electrical failures in semiconductor devices. EFA can identify abnormal electrical behavior and help engineers determine where subsequent physical analysis should be focused.
This is particularly important in modern integrated circuits, where a single device may contain millions or billions of transistors. Searching an entire die with physical-analysis equipment would be inefficient. Electrical fault localization can reduce the search from an entire IC to a circuit block, interconnect region or even an individual transistor.
For an overview of semiconductor failure analysis, see:
Semiconductor Failure Analysis: The Complete Guide to IC Failure Analysis
For a comparison of the main FA methods, see:
IC Failure Analysis Techniques: A Complete Guide
Electrical Failure Analysis is the process of electrically characterizing a failing semiconductor device and, when possible, localizing the region responsible for the abnormal behavior.
Its objectives may include:
Electrical analysis is often performed before invasive techniques such as FIB cross-sectioning or TEM sample preparation. JEOL describes nanoprobing-based EFA as being used for semiconductor-device evaluation, identifying failure locations and determining the causes of failures. Individual transistor I-V characteristics can be measured by directly probing transistor electrodes inside an SEM.
Electrical Failure Analysis and Physical Failure Analysis answer different questions.
Electrical Failure Analysis asks:
Physical Failure Analysis asks:
A typical workflow may look like:
Electrical failure detected
↓
Electrical characterization
↓
Fault localization
↓
Physical Failure Analysis
↓
Failure mechanism
↓
Root cause
The two approaches therefore complement each other. EFA identifies where engineers should look, while PFA helps explain what physically happened there.
EFA can be useful whenever a semiconductor device exhibits an electrical or functional abnormality.
Common examples include:
The exact EFA approach depends on the symptom.
For example, excessive leakage may lead to EMMI, OBIRCH or thermal localization, while a suspected transistor-level problem may require nanoprobing.
| Electrical Symptom | Typical EFA Techniques | What the Analysis Can Reveal |
|---|---|---|
| Excessive leakage | I-V testing, EMMI, OBIRCH, thermal imaging | Leakage path or electrically active defect region |
| Power-to-ground short | Curve tracing, thermal localization, OBIRCH | Shorted circuit, interconnect or resistive defect region |
| High supply current | Current measurement, EMMI, thermal imaging | Abnormally active or high-current region |
| Open circuit | Continuity testing, electrical probing, nanoprobing | Broken connection or high-resistance path |
| Parametric shift | I-V characterization, curve tracing, nanoprobing | Abnormal transistor or device characteristics |
| Functional failure | Functional testing, electrical probing, fault isolation | Suspected failing circuit block or signal path |
| Intermittent failure | Dynamic testing, temperature variation, voltage variation | Operating conditions that trigger the failure |
| Transistor-level abnormality | Nanoprobing | Individual transistor I-V, leakage or threshold abnormalities |
| Resistive defect | OBIRCH, nanoprobing | High- or low-resistance defect location |
| Junction breakdown | EMMI, I-V characterization | Electrically active breakdown location |
Before attempting fault localization, the laboratory should confirm that the failure can be reproduced.
This may involve testing the IC under the same or similar conditions in which the failure originally occurred.
Important variables may include:
If the device passes laboratory testing but failed in the application, the difference between the two environments may itself provide important information.
Some failures only appear:
Reproducing the failure is therefore an essential foundation for electrical analysis.
Whenever possible, a failing IC should be compared with a known-good device.
This allows engineers to compare:
Small differences can be easier to identify when a reference device is available. Known-good comparison is particularly useful when the failing device still operates partially and the abnormality is subtle.
Current-voltage characterization, commonly called I-V testing, is one of the fundamental tools in electrical failure analysis. The voltage applied to a terminal is varied while the resulting current is measured.
The shape of the resulting I-V curve can provide information about:
A failing device can be compared with a known-good part to identify differences.
For example, if a pin that normally exhibits extremely low leakage suddenly draws significant current, the I-V behavior can help determine whether the problem resembles:
At transistor level, JEOL notes that nanoprobing can be used to directly measure transistor I-V characteristics inside an SEM.
Curve tracing is closely related to I-V characterization. A curve tracer applies controlled voltage or current conditions to device terminals and plots the resulting electrical relationship.
Curve tracing can be useful for identifying:
For semiconductor failure analysis, curve tracing is particularly useful because the resulting electrical signature can quickly indicate whether a device terminal behaves differently from a known-good unit.
It can help answer questions such as:
Leakage current is one of the most common electrical symptoms investigated during semiconductor failure analysis.
Unexpected leakage can occur because of:
The challenge is that measuring leakage only confirms that a problem exists. The next question is:
Where is the leakage coming from?
This is where fault-localization techniques such as EMMI, OBIRCH, thermal analysis and nanoprobing become valuable.
A common workflow is:
Measure excessive leakage
↓
Determine which terminals or power domains are involved
↓
Use fault-localization technique
↓
Identify region of interest
↓
Perform physical analysis
Abnormally high power-supply current can indicate many different IC problems.
Potential causes include:
Measuring current while different circuit functions are activated can help narrow the problem. For example, if current remains normal until a particular functional block is enabled, the failure may be associated with that block.
This reduces the area requiring subsequent analysis.
IDDQ testing measures the quiescent supply current of CMOS circuits. In an ideal static CMOS circuit, supply current should generally be very low when the circuit is not switching.
Certain defects can increase this quiescent current. IDDQ testing can therefore help detect defects associated with:
IDDQ has historically been particularly useful in CMOS defect testing and can also provide useful information during failure analysis. AnySilicon already has related content: IDDQ Testing
Some semiconductor failures are electrically straightforward:
Continuity and resistance measurements can help identify these conditions. However, finding an open or short at package pins does not necessarily reveal the physical location inside the semiconductor device. Additional localization may still be required.
For example, an apparent open could originate from:
Electrical testing identifies the failure mode; physical analysis determines where the physical discontinuity exists.
Once engineers understand the electrical signature, the next challenge is localizing the defect. This is one of the most important stages of EFA. Several technologies may be used depending on the problem and semiconductor architecture.
Common electrical fault-localization techniques include:
The objective is to move from:
“The IC leaks current”
to:
“The abnormal current appears to originate from this specific region.”
That region can then be investigated using SEM, FIB, TEM or other Physical Failure Analysis methods.
Emission Microscopy, commonly called EMMI, is an optical fault-localization technique. Certain electrically active semiconductor defects emit very small amounts of light when the IC is powered. A sensitive optical detector can capture this photon emission and correlate it with the physical layout of the chip.
EMMI may help identify:
The method detects photons emitted from operating semiconductor circuitry to provide information about electrical activity.
The value of EMMI is primarily localization. It tells the analyst where to investigate next. It does not automatically identify the physical cause.
For example:
EMMI identifies emission location
↓
FIB exposes the region
↓
SEM examines the structure
↓
Physical defect is identified
Read more:
Emission Microscopy (EMMI) for IC Failure Analysis
OBIRCH stands for Optical Beam Induced Resistance Change. The technique scans a powered semiconductor device using a focused laser while monitoring changes in electrical resistance.
The laser produces highly localized heating. If the beam passes over an abnormal resistive region, the resulting electrical response can help identify the defect location.
OBIRCH can be useful for locating:
A commercial failure-analysis laboratory describes OBIRCH as being used for high- and low-resistance analysis, current-leak analysis and locating defects such as voids in metal lines or beneath vias. OBIRCH is especially useful when the defect produces a resistance-related electrical signature that is difficult to locate using conventional testing.
Read more:
OBIRCH Analysis for Semiconductor Failure Analysis
Electrical defects often generate heat.
Examples include:
Thermal analysis can help identify these locations.
Infrared cameras can identify relatively strong temperature differences across a powered device. A localized hotspot may point to the region responsible for excessive current.
Lock-in thermography uses synchronized electrical excitation and thermal detection to improve sensitivity. This can allow much weaker heat-generating defects to be detected.
Thermal methods can be useful because they are generally used before destructive physical analysis. Once the thermal hotspot has been identified, the region can be targeted with techniques such as FIB or SEM.
Lasers can also be used to stimulate semiconductor devices and observe changes in electrical behavior. Depending on the method, laser stimulation may produce:
The device response can help identify areas associated with the failure. Several specialized laser-based techniques are used within semiconductor fault isolation.
The exact method depends on the semiconductor structure and whether front-side or backside access is available.
As semiconductor devices have become more complex, accessing active circuitry from the front side can become difficult because many interconnect layers may cover the transistors. For some advanced devices, fault-localization techniques are therefore performed through the backside of the silicon die. Silicon is transparent to certain infrared wavelengths, allowing optical techniques to interact with or observe active circuitry through the substrate.
Backside analysis can be particularly valuable for devices with many metal interconnect layers. However, sample preparation may be required to thin the silicon substrate and improve access.
For transistor-level analysis, nanoprobing is one of the most powerful EFA techniques. A nanoprobing system uses extremely small probes inside a scanning electron microscope.
The probes can directly contact:
By probing transistor electrodes, individual transistor I-V characteristics can be evaluated. Nanoprobing can therefore help determine whether an individual transistor behaves normally or abnormally.
Possible measurements include:
As semiconductor dimensions shrink, locating a failure to a general circuit region may no longer be sufficient. The analyst may need to determine which individual transistor is failing.
Nanoprobing provides a bridge between:
Circuit-level electrical analysis
and
Nanometer-scale physical analysis
A workflow may look like:
Electrical failure
↓
Fault localization
↓
Nanoprobing identifies abnormal transistor
↓
FIB prepares site-specific sample
↓
TEM analyzes physical structure
Thermo Fisher notes that nanoprobing can electrically characterize individual transistors and complex interconnect structures and can improve subsequent TEM analysis by ensuring that the correct device is selected.
Voltage contrast is another electrical-analysis approach commonly associated with electron microscopy. Different electrical potentials within semiconductor structures can produce changes in electron-emission behavior and image contrast.
This can help identify:
Voltage-contrast methods can therefore assist in identifying electrical abnormalities within exposed semiconductor circuitry.
The technique is particularly useful when the physical feature appears structurally normal but its electrical state differs from surrounding circuitry.
Intermittent failures can be among the most difficult semiconductor problems to analyze.
A device may function normally during laboratory testing but fail only under certain conditions.
Potential triggers include:
For intermittent problems, EFA may involve deliberately changing operating conditions until the failure is reproduced.
The investigation might record electrical behavior while varying:
Only once the trigger condition is understood can the defect be effectively localized.
EFA is not limited to packaged customer-return devices. It can also be applied during:
Suppose wafer test identifies repeated failures in the same functional block. Engineers may select representative failing dies and perform additional electrical characterization.
The results can then be correlated with:
This can help determine whether the failure is associated with a systematic semiconductor process defect.
EFA is also important when devices fail accelerated reliability testing.
Examples include devices exposed to:
Electrical characterization can show how the device changed during the reliability test.
For example:
The electrical signature helps determine which physical mechanisms should subsequently be investigated.
Electrostatic discharge and electrical overstress can create electrically active defects. Possible symptoms include:
EFA methods such as I-V characterization and emission microscopy can help identify the damaged region. However, identifying damage consistent with ESD or EOS is not necessarily the same as identifying the root cause.
The complete investigation should still ask:
Why did the device experience the damaging electrical condition?
That may involve examining:
Electrical Failure Analysis is usually not the final stage. Its most important output is often a well-defined Region of Interest. Once this region has been identified, Physical Failure Analysis can begin.
Typical PFA techniques include:
SEM is a major tool in semiconductor defect and failure analysis. FIB can then be used to expose buried structures or prepare site-specific TEM samples, while TEM provides higher-resolution structural analysis when required. The complete investigation might therefore look like:
Abnormal electrical behavior
↓
I-V characterization
↓
EMMI / OBIRCH / thermal localization
↓
Nanoprobing
↓
FIB
↓
SEM / TEM
↓
Failure mechanism
↓
Root cause
Consider an IC returned because it consumes substantially more current than expected.
Supply-current testing confirms the excessive current.
I-V measurements show an abnormal conductive path not present in known-good samples.
EMMI identifies abnormal photon emission in one circuit region.
Nanoprobing identifies a transistor with abnormal leakage behavior.
FIB is used to prepare the transistor region for examination.
SEM or TEM identifies the physical defect.
The physical evidence is correlated with design, process and application data.
This illustrates an important point:
Electrical Failure Analysis narrows the search. Physical Failure Analysis explains the physical cause.
If the electrical failure has not been localized first, destructive analysis may target the wrong region.
A device may fail only under specific voltage, temperature or functional conditions.
Without a reference part, subtle electrical abnormalities can be difficult to interpret.
A short is an electrical failure mode. It does not explain why the short developed.
Repeated testing at excessive voltage or current can modify the original defect and create additional damage.
Not every electrical symptom originates within the semiconductor die.
The package, PCB or application can also contribute to the observed behavior.
Useful information includes:
The more accurately the electrical failure is described, the more efficiently the laboratory can select appropriate EFA methods.
EFA stands for Electrical Failure Analysis.
It is the process of electrically characterizing and localizing failures in semiconductor devices before or alongside physical analysis.
The main purpose is to understand how a semiconductor device is failing electrically and narrow the failure to a specific region, circuit or device.
This helps subsequent physical analysis target the correct location.
Common techniques include:
Yes.
Emission Microscopy is commonly used as an electrical fault-localization technique because electrically active defects can produce photon emission that reveals the location of abnormal activity.
OBIRCH is useful for localizing resistance-related electrical abnormalities such as leakage paths, resistive shorts and high-resistance interconnect or via defects.
Nanoprobing uses microscopic probes to electrically contact individual semiconductor structures inside an SEM.
It can measure characteristics of individual transistors and help identify the device responsible for a failure.
Many EFA techniques are non-destructive or minimally invasive.
However, sample preparation may be required for some advanced methods, particularly when the circuitry must be exposed or accessed from the backside.
Once the failure has been electrically localized, Physical Failure Analysis typically investigates the suspected region using methods such as SEM, FIB and TEM.
Electrical Failure Analysis converts a broad failure symptom into a specific target for physical investigation.
The process may begin with something as general as:
“The IC consumes too much current.”
Electrical characterization may change this to:
“There is abnormal leakage between these two supply domains.”
Fault localization may then refine the conclusion further:
“The abnormal current originates from this circuit region.”
Nanoprobing might narrow it to:
“This transistor has abnormal electrical characteristics.”
Only then does physical analysis need to examine the transistor.
This progression makes EFA one of the most important components of an efficient semiconductor failure-analysis process.
If you have a semiconductor device exhibiting leakage, abnormal current, shorts, opens, parametric problems or another electrical failure, AnySilicon can help connect you with companies providing Electrical Failure Analysis and semiconductor fault-localization services.
Capabilities may include:
Find a Semiconductor Failure Analysis Company
When requesting support, include the device type, package, electrical symptoms, operating conditions, available samples and any testing already performed. This can help identify the most appropriate EFA laboratory and analysis method.