OBIRCH (Optical Beam Induced Resistance Change) is a laser-based fault-localization technique used in semiconductor failure analysis to identify electrically abnormal regions such as resistive shorts, leakage paths, defective vias and interconnect problems.
The technique works by scanning a focused laser across an electrically biased semiconductor device. Local laser heating changes the resistance of conductive or semiconductor structures beneath the beam. If the heated structure forms part of an abnormal current path, that local resistance change produces a measurable change in device current.
Typical OBIRCH applications include:
→ Resistive short localization
→ Abnormal leakage-path localization
→ Defective via identification
→ Interconnect defect localization
→ Internal power-distribution faults
→ Frontside and backside IC fault localization
→ Memory-device failure analysis
→ Advanced-package electrical fault localization
Once OBIRCH identifies a suspect region, the location can be correlated with the IC layout and examined using targeted physical-analysis techniques such as FIB cross-sectioning, SEM or TEM.
What Is OBIRCH?
OBIRCH stands for Optical Beam Induced Resistance Change.
It belongs to a broader family of laser-based semiconductor fault-localization techniques. These methods use a scanning laser microscope to perturb a very small region of an operating or electrically biased device while monitoring the electrical response.
The basic OBIRCH process is:
Electrically bias the failing device
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Scan a focused laser across the IC
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Laser produces localized heating
↓
Local electrical resistance changes
↓
Device current changes
↓
Electrical response is mapped to laser position
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Suspect failure location is identified
The important point is that OBIRCH does not simply create a thermal image. The laser acts as a controlled local thermal stimulus, while the electrical measurement determines whether that location is participating in the failure.
How OBIRCH Works
Electrical resistance depends on temperature. When a focused laser heats a very small region of an integrated circuit, the resistance of the material in that region changes.
If the heated region lies on an electrically significant current path, this resistance change affects the total current flowing through the device.
The measurement therefore links three things:
→ Laser position
→ Local temperature change
→ Electrical current response
By raster-scanning the laser across the semiconductor and measuring the electrical response at each location, an image can be produced showing where the device is most sensitive to the thermal stimulus.
An anomalous response can reveal a region containing a resistive short, defective interconnect, via problem or another electrically active resistance-related defect.
Why Local Heating Changes Resistance
The electrical response to heating depends on the material involved.
Metallic Conductors
For many metallic conductors, resistance increases as temperature increases.
If a metallic defect forms part of a short or resistive path, heating that location can increase its resistance and alter the current flowing through the device.
Semiconductor Structures
Semiconductor structures can respond differently. Under some conditions, their resistance decreases as temperature rises.
In either case, the key requirement is that the laser-induced temperature change modifies the electrical resistance enough to produce a measurable change in device current.
OBIRCH Electrical Configuration
In a conventional OBIRCH configuration, the device under test is biased using a constant-voltage source.
A current amplifier is connected in series with the device to detect small changes in current as the laser scans across the circuit.
The measurement concept is therefore:
Constant voltage applied to device
↓
Laser heats local structure
↓
Local resistance changes
↓
Device current changes
↓
Current amplifier detects the response
The resulting electrical signal is synchronized with the X-Y position of the laser to form a fault-localization image.
What Is CC-OBIRCH?
CC-OBIRCH stands for Constant Current Optical Beam Induced Resistance Change.
Instead of applying a constant voltage and measuring current changes, CC-OBIRCH uses a constant-current bias and monitors the resulting change in voltage.
The basic distinction is:
OBIRCH: constant voltage → measure current change
CC-OBIRCH: constant current → measure voltage change
The appropriate configuration depends on the electrical characteristics of the failing device and the noise associated with the biasing and detection system.
Why Biasing Method Matters
OBIRCH signals can be very small. The quality of the measurement therefore depends strongly on electrical noise from both the bias source and the detection electronics.
For a failing IC with a relatively high resistance, a voltage-source configuration may be more appropriate.
For a relatively low-resistance leakage path, a constant-current configuration may reduce some of the noise associated with the biasing arrangement.
Signal sensitivity can also be improved in suitable systems through techniques such as lock-in detection, which helps extract small laser-induced signals from background electrical noise.
OBIRCH for Short-Circuit Localization
Short localization is one of the most important applications of OBIRCH.
Consider an unintended conductive path between two circuit nodes. If a voltage exists across the short, current flows through that path.
When the scanning laser passes over the defective region, the localized temperature rise changes the resistance of the short.
This produces:
Laser heating at short location
↓
Resistance of short changes
↓
Current through device changes
↓
OBIRCH system detects electrical response
↓
Short location appears in fault-localization image
This can reduce a potentially die-wide search to a small region suitable for targeted physical analysis.
OBIRCH for Resistive Interconnect Defects
Not every interconnect failure is a complete open or a low-resistance short.
A defective interconnect can develop abnormal resistance because of problems such as a damaged connection, poor contact or a partially defective conductive path.
If the resistance of that path responds to localized heating, OBIRCH can potentially identify its position.
Typical candidates include:
→ Resistive metal paths
→ Defective contacts
→ Abnormal interconnect regions
→ Local current-carrying defects
→ Resistive leakage structures
After localization, the suspect interconnect can be investigated using FIB cross-sectioning followed by SEM or TEM where appropriate.
OBIRCH for Defective Vias
Vias provide electrical connections between different interconnect levels within an integrated circuit.
A defective via can produce abnormal electrical resistance without necessarily creating an obvious visible defect at the surface.
Because OBIRCH responds to thermally induced resistance changes, defective vias are an important application of the technique.
A typical FA sequence may be:
Abnormal resistance measured
↓
OBIRCH scan performed
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Localized response identified
↓
Location correlated with via structure
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FIB cross-section through suspect via
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SEM / TEM physical examination
This is a good example of how fault localization and physical analysis work together rather than competing with each other.
OBIRCH and Leakage Current
Leakage current is another failure signature that may lead to OBIRCH analysis, particularly when the leakage is associated with a resistive current path.
Electrical testing may establish that excessive current exists but provide little information about where the current is flowing on the die.
A laser scan can then perturb local resistance across the circuit and identify regions where heating causes a measurable change in the leakage current.
The investigation can therefore narrow from:
Excessive device leakage
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Unknown physical location
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OBIRCH laser scan
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Localized electrically sensitive region
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Targeted physical analysis
OBIRCH and Internal Power Networks
A semiconductor device can exhibit excessive power consumption because of a local defect in its internal supply network.
Current measurements may clearly show the abnormal power consumption while providing little or no direct physical localization.
Laser-based resistance-change techniques such as OBIRCH can help bridge this gap by identifying where the local electrical network responds abnormally to thermal stimulation.
Frontside OBIRCH
OBIRCH can be performed from the front side of a semiconductor die when sufficient optical access to the target region is available.
The laser is focused through the microscope optics and scanned across the exposed IC while the electrical response is monitored.
Frontside access can be useful when the metal structure or defect of interest is sufficiently accessible from above.
However, modern ICs may contain many interconnect layers that restrict direct access to underlying structures. In these cases, backside analysis may become advantageous.
Backside OBIRCH and IR-OBIRCH
IR-OBIRCH uses infrared laser access and can support backside fault localization through the silicon substrate.
Backside access is important for advanced ICs because it avoids much of the obstruction created by the frontside metal stack.
A backside analysis arrangement can be represented as:
Infrared laser
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Backside silicon surface
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Laser energy reaches target region
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Localized heating changes resistance
↓
Electrical response is measured
Depending on device construction and substrate properties, backside preparation may be needed to provide suitable optical access and focus.
OBIRCH as a Laser Signal Injection Technique
OBIRCH belongs to a broader group of techniques often described as Laser Signal Injection Microscopy (LSIM).
In LSIM, a focused laser is raster-scanned across the device while the analyst monitors a laser-induced electrical change.
Different laser wavelengths and electrical configurations can produce different physical effects.
Broadly:
→ Shorter optical wavelengths can generate electron-hole pairs
→ Longer wavelengths can create localized thermal stimulation
OBIRCH primarily uses the second mechanism: micro-local thermal heating followed by measurement of an electrical resistance response.
OBIRCH vs. EMMI
OBIRCH and Emission Microscopy are both important semiconductor fault-localization techniques, but they detect fundamentally different physical effects.
EMMI
EMMI detects photons naturally produced by electrically active semiconductor structures and can be particularly useful for:
→ Junction leakage
→ Avalanche breakdown
→ Latch-up
→ Abnormal transistor activity
→ Certain gate-dielectric failures
OBIRCH
OBIRCH actively scans a laser across the IC and measures the electrical response to localized heating. It is particularly useful for:
→ Resistive shorts
→ Resistive leakage paths
→ Defective vias
→ Interconnect resistance anomalies
A failure that produces little or no detectable photon emission may still respond clearly to OBIRCH if a thermally sensitive resistive path exists.
OBIRCH vs. TIVA
OBIRCH and TIVA (Thermally Induced Voltage Alteration) use similar localized thermal stimulation but differ in their electrical biasing and detection configurations.
Conventional OBIRCH uses constant-voltage bias and monitors current changes.
TIVA commonly uses constant-current bias and monitors changes in voltage.
Simplified:
OBIRCH: thermal stimulation → resistance change → current response
TIVA: thermal stimulation → electrical change → voltage response under constant-current bias
Both techniques can be useful for locating electrically active resistance-related defects.
OBIRCH vs. OBIC
OBIC stands for Optical Beam Induced Current.
Although the names are similar, OBIC and OBIRCH rely on different dominant mechanisms.
OBIC primarily uses laser-generated photo-carriers and can reveal semiconductor junction-related behavior.
OBIRCH primarily uses localized thermal heating to reveal resistance-related electrical anomalies.
OBIC: optical excitation → photo-carriers → current response
OBIRCH: optical heating → resistance change → current response
OBIRCH for Memory Failure Analysis
Memory devices can contain failures that electrical bitmapping does not physically localize with sufficient accuracy.
For example, a broad block failure may be caused by a defect in an internal power-distribution structure rather than by one directly identifiable memory cell.
Current and leakage measurements can characterize the electrical symptom, while OBIRCH can help identify the physical region associated with the abnormal current path.
A possible workflow is:
Memory test identifies failure pattern
↓
Electrical characterization indicates current anomaly
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OBIRCH localizes resistive region
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Location correlated with layout
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FIB / SEM / TEM investigation
What OBIRCH Cannot Localize Well
OBIRCH is not the correct technique for every semiconductor failure.
Its strongest applications involve failures where local heating modifies a resistance or current path that can be measured electrically.
A purely functional logic failure may behave differently.
If the failure depends on an internal switching state rather than the device’s analog supply resistance or leakage behavior, conventional OBIRCH may not produce useful localization.
Examples that may require other techniques include:
→ Marginal timing failures
→ Frequency-dependent logic failures
→ Functional failures visible only during specific test patterns
→ Failures without a measurable thermally sensitive current path
Tester-assisted laser techniques or other fault-localization methods may be more suitable in those situations.
OBIRCH for 2.5D and 3D Semiconductor Packages
Advanced semiconductor packages create complex electrical paths through dies, substrates, bumps, interposers and other interconnected structures.
Electrical characterization is important before choosing the next localization technique.
A continuity failure characterized as resistive or non-linear may be a candidate for techniques including thermal imaging or OBIRCH, depending on physical access and the electrical structure involved.
This makes OBIRCH part of a broader diagnostic process rather than an isolated measurement.
For example:
Package electrical failure
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I-V characterization
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Failure identified as resistive / non-linear
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Fault-localization method selected
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OBIRCH if suitable optical and electrical access exists
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Targeted destructive analysis
OBIRCH and MEMS Failure Analysis
Laser signal injection methods can also be useful for certain MEMS failures when the failure creates electrical contact between structures.
Examples can include:
→ Stiction causing structures to touch
→ Particles electrically shorting structures
→ EOS or ESD-related welded contacts
Care is particularly important because released MEMS structures may be more thermally isolated than bulk silicon structures.
Excessive laser power can therefore overheat or damage the structure being analyzed. Laser power must be selected carefully so that the fault-localization process does not create a new defect.
Laser Power and OBIRCH Sensitivity
The laser must produce enough localized heating to create a measurable electrical response, but excessive heating can alter or damage the device.
The analyst must therefore balance:
→ Laser power
→ Spot size
→ Device thermal properties
→ Electrical sensitivity
→ Required spatial resolution
→ Risk of modifying the failure
The objective is not simply to maximize signal strength. The objective is to obtain enough signal to localize the original failure while preserving the evidence needed for subsequent analysis.
Noise and Signal Detection
The laser-induced electrical signal can be small compared with the total current flowing through the device.
Electrical noise can therefore limit OBIRCH sensitivity.
Important considerations include:
→ Stability of the voltage or current source
→ Current-amplifier noise
→ Device resistance
→ Magnitude of laser-induced resistance change
→ Background electrical fluctuations
Careful biasing and signal detection are therefore central to successful OBIRCH fault localization.
CAD Correlation After OBIRCH
An OBIRCH image becomes much more useful when the localized electrical response is correlated with the physical IC layout.
The analyst may compare the fault location with:
→ Metal routing
→ Via locations
→ Power-distribution networks
→ Transistor regions
→ Circuit blocks
→ Suspect nets
This can transform an optical fault-localization spot into a specific hypothesis about which interconnect or circuit structure is responsible for the failure.
OBIRCH Followed by FIB, SEM and TEM
OBIRCH is primarily a fault-localization technique. It normally does not provide the final physical root cause by itself.
Once the failure site has been localized, physical analysis can be concentrated on the suspect region.
A common investigative logic is:
Electrical anomaly confirmed
↓
OBIRCH localizes suspect region
↓
Location correlated with layout
↓
FIB exposes or cross-sections structure
↓
SEM examines physical morphology
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TEM used if nanoscale structural analysis is required
↓
Failure mechanism established
↓
Root cause determined
The major advantage is that destructive physical analysis can be directed at a specific Region of Interest rather than searching blindly across the die.
Advantages of OBIRCH
→ Localizes resistance-related electrical failures
→ Effective for many resistive shorts
→ Useful for defective vias and interconnects
→ Can investigate leakage paths
→ Can operate from frontside or backside in suitable devices
→ Produces location-specific information
→ Can be correlated with IC layout data
→ Helps target FIB and physical analysis
→ Can reduce destructive-analysis search area
Limitations of OBIRCH
The Failure Must Respond to Thermal Stimulation
If local heating does not produce a measurable change in the electrical behavior, OBIRCH may provide little or no useful contrast.
A Voltage Gradient Is Important
A resistance change is useful only when it affects an electrically active path. A defect with no meaningful electrical bias across it may be difficult to detect.
Electrical Noise Limits Sensitivity
Weak resistance-change signals can be obscured by noise in the bias or measurement electronics.
Optical Access Is Required
Frontside metal layers or package structures may restrict laser access. Backside preparation may be required.
Laser Heating Can Alter the Device
Excessive laser power can change or damage sensitive semiconductor or MEMS structures.
Not Every Functional Failure Is Suitable
Failures that depend mainly on internal digital switching, timing or marginal logic behavior may require tester-assisted laser techniques rather than conventional OBIRCH.
OBIRCH Is Localization, Not Final Root Cause
The localized response must normally be followed by physical examination to establish the exact defect and root cause.
Common Semiconductor Failures Investigated With OBIRCH
| Failure Signature |
How OBIRCH Can Help |
| Resistive short |
Local heating changes short-path resistance and device current |
| Leakage path |
Identifies regions where heating modifies leakage current |
| Defective via |
Localizes abnormal resistance associated with via structures |
| Resistive interconnect |
Maps thermally sensitive interconnect resistance anomalies |
| Internal supply-network fault |
Helps physically localize electrically measured power or current anomalies |
| Memory block failure |
Can localize resistance-related defects not sufficiently localized by fail addresses |
| Advanced-package resistive failure |
Can support localization after electrical characterization identifies a resistive or non-linear path |
Typical OBIRCH Failure Analysis Workflow
1. Verify the Electrical Failure
Reproduce and document the failure condition, including:
→ Applied voltage
→ Device current
→ Leakage characteristics
→ Resistance
→ Temperature dependence
→ Relevant device state
2. Determine Whether the Failure Is Suitable for OBIRCH
The analyst determines whether the failure appears to involve a resistive short, leakage path, interconnect resistance or another thermally sensitive electrical anomaly.
3. Select Frontside or Backside Access
The access direction depends on device construction, package configuration, metal-layer density and target depth.
4. Prepare the Device if Necessary
Package opening or backside preparation may be required while preserving the ability to electrically reproduce the failure.
5. Establish Stable Electrical Bias
A low-noise biasing arrangement is established so that small laser-induced current or voltage changes can be detected.
6. Scan the Laser
The focused laser is raster-scanned across the Region of Interest or, if necessary, a larger part of the die.
7. Detect the Electrical Response
The system records changes in device current or voltage corresponding to each laser position.
8. Identify Suspect Sites
Regions producing anomalous thermal response are identified as possible fault locations.
9. Correlate With Layout
The OBIRCH location is compared with the IC layout to identify suspect interconnects, vias, power structures or circuit elements.
10. Perform Targeted Physical Analysis
Follow-up techniques may include:
→ FIB cross-sectioning
→ SEM
→ TEM
→ Nanoprobing
→ Additional electrical characterization
Frequently Asked Questions About OBIRCH
What does OBIRCH stand for?
OBIRCH stands for Optical Beam Induced Resistance Change.
What is OBIRCH used for in semiconductor failure analysis?
OBIRCH is primarily used to localize electrical defects whose resistance changes when locally heated. Important applications include resistive shorts, leakage paths, defective vias and interconnect resistance problems.
How does OBIRCH detect a semiconductor defect?
A focused laser locally heats the device. If the illuminated region forms part of an electrically active resistive path, its resistance changes. That produces a measurable current change that can be correlated with the laser position.
Does OBIRCH use a laser?
Yes. OBIRCH is a laser-scanning fault-localization technique. The laser provides localized thermal stimulation.
Can OBIRCH detect shorts?
Yes. Resistive short localization is one of the principal applications of OBIRCH.
Can OBIRCH detect defective vias?
Yes. Defective vias with abnormal electrical resistance can be candidates for OBIRCH localization.
Can OBIRCH detect leakage?
OBIRCH can help localize leakage when the leakage follows a thermally sensitive resistive path that produces a measurable electrical change during laser scanning.
What is IR-OBIRCH?
IR-OBIRCH uses infrared laser access and is particularly relevant to backside semiconductor fault localization through silicon.
What is the difference between OBIRCH and EMMI?
EMMI detects photons naturally emitted by electrically active semiconductor structures. OBIRCH actively heats the device with a scanning laser and measures the resulting resistance-related electrical response.
What is the difference between OBIRCH and TIVA?
Both use localized thermal stimulation. Conventional OBIRCH uses constant-voltage bias and detects current changes, while TIVA commonly uses constant-current bias and monitors voltage changes.
Is OBIRCH destructive?
The laser fault-localization measurement itself does not require destructive cross-sectioning. However, package opening or backside sample preparation may be required to obtain optical access. Excessive laser power can also damage sensitive structures, so analysis conditions must be controlled.
Does OBIRCH identify the root cause?
Usually not by itself. OBIRCH localizes the electrically abnormal region. Techniques such as FIB, SEM or TEM are often used afterward to identify the actual physical defect and determine root cause.
Can OBIRCH analyze functional logic failures?
Not all functional logic failures are suitable for conventional OBIRCH. If a failure depends primarily on switching activity, timing or a marginal digital operating condition rather than an analog resistance or leakage path, tester-assisted laser techniques may be more appropriate.
OBIRCH as Part of Semiconductor Failure Analysis
The main value of OBIRCH is its ability to convert an electrical resistance anomaly into a physical location on the semiconductor device.
Without fault localization, a resistive failure may exist anywhere among millions of interconnects, contacts and vias.
OBIRCH can narrow the investigation:
Device fails electrical test
↓
Resistance / leakage abnormality identified
↓
OBIRCH laser scan performed
↓
Thermally sensitive electrical site detected
↓
Failure location correlated with layout
↓
FIB targets Region of Interest
↓
SEM / TEM reveals physical structure
↓
Failure mechanism identified
↓
Root cause established
For resistance-related failures, this can significantly reduce the amount of destructive searching required and improve the probability that the physical analysis intersects the actual defect.
OBIRCH therefore occupies an important position between electrical characterization and physical failure analysis.
Looking for an OBIRCH Failure Analysis Lab?
If your semiconductor device exhibits unexplained leakage, a resistive short, abnormal supply current, a suspected defective via or another resistance-related electrical failure, an OBIRCH-capable failure analysis laboratory may be able to localize the defect before destructive physical analysis begins.
Typical requirements may include:
→ OBIRCH fault localization
→ IR-OBIRCH
→ Backside laser fault localization
→ Resistive short localization
→ Leakage-path localization
→ Via and interconnect analysis
→ Laser Signal Injection Microscopy
→ CAD correlation
→ Follow-up FIB / SEM / TEM analysis
When requesting OBIRCH analysis, provide information about the device technology, package type, electrical failure signature, resistance or leakage measurements, required bias conditions, failure reproducibility and any previous fault-localization results.
The appropriate semiconductor failure analysis provider can then be selected according to the required OBIRCH equipment, frontside or backside capability, electrical biasing capability, device expertise and follow-up physical-analysis resources.
