As semiconductor technology continues advancing toward the nanometer and even angstrom scale, chip integration is steadily increasing, and internal structures are becoming more complex. Throughout the entire lifecycle of a chip, failures are inevitable, and Hot Spot technology has become a crucial tool for product engineers to unravel the mysteries of chip failures. This technology focuses on regions within the chip where local overheating or abnormal current density is caused by various defects, enabling precise localization of potential failure points and laying a solid foundation for further in-depth analysis.
1. Core Concept and Key Value of Hot Spot
1.1 Precise Definition
A Hot Spot refers to a localized high-temperature area within a chip under normal operation or specific testing conditions caused by defects. These defects stem from various causes, including short circuits, leakage, excessive power consumption, and interconnect electromigration. For example, in chips using advanced processes, as transistor sizes shrink, even minute manufacturing defects can cause short circuits between adjacent components, forming a Hot Spot.
1.2 Irreplaceable Significance
Efficient Defect Localization: Traditional electrical testing is like “feeling an elephant blindfolded”—it can detect that a fault exists but struggles to pinpoint its exact location. Hot Spot technology functions as a precise “locator,” narrowing the suspicious area down to a few micrometers or even nanometers, significantly improving fault localization efficiency.
Significant Time Savings in Analysis: In highly integrated chips, blind decapsulation and layer-by-layer analysis without Hot Spot localization is time-consuming and costly. By leveraging Hot Spot technology, the target area can be quickly locked in, greatly enhancing the efficiency and cost-effectiveness of failure analysis.
Effective Prevention of Potential Failures: In reliability analysis, Hot Spot detection acts as a “security guard,” identifying potential high-temperature areas early, helping engineers reduce failure risks by optimizing processes and improving design.
2. Typical Causes of Hot Spots
2.1 Short Circuits and Leakage Paths
Minor defects in the manufacturing process or electrostatic discharge (ESD) damage may lead to unexpected short circuits between MOSFETs, metal interconnects, or vias. Abnormal increases in current rapidly raise the local temperature, resulting in Hot Spots. For instance, a smartphone chip once experienced severe heating and performance degradation due to a via manufacturing defect causing a short circuit.
2.2 Electromigration
In metal interconnect structures, high current density drives metal atoms to migrate, forming voids or accumulations. This not only increases interconnect resistance abnormally but may even cause open circuits—key contributors to Hot Spot formation. As chip processes continue to shrink, electromigration becomes increasingly prominent, posing a major reliability risk.
2.3 Latch-up Effect
In CMOS processes, once the parasitic P-N-P-N bipolar structure is triggered, it creates a persistent high-current path, leading to localized overheating. This phenomenon easily occurs during power supply fluctuations or ESD events and seriously threatens chip operation.
2.4 Device Aging and Material Defects
Prolonged chip operation leads to device degradation, while material defects such as microcracks and stress concentration points formed during manufacturing may evolve into Hot Spots over time. For example, in automotive electronics, where harsh environments prevail, failure caused by aging and material defects is particularly common.
3. Diverse Detection Methods and Technical Features
3.1 Infrared Thermography
Principle: Infrared thermal imaging is a non-contact temperature measurement method that visualizes and analyzes the temperature distribution on the chip surface using thermal radiation captured by an infrared camera.
Advantages: Easy to operate; does not require physical contact with the chip; effective in analyzing short circuits and leakage currents; offers 0.03℃ temperature resolution and 20 μm spatial resolution; detects power as low as μW.
Limitations: Spatial resolution is limited by detector pixel size and optics; less effective in detecting small or deep-layer Hot Spots.
3.2 Lock-in Thermography
Principle: Lock-in Thermography (LIT) is a dynamic infrared technique involving periodic modulation of a heat source. Defects in the chip induce periodic changes in surface temperature, creating amplitude and phase contrasts captured by infrared cameras. Lock-in techniques isolate weak useful signals from background noise, greatly improving sensitivity.
Advantages:
- High Sensitivity: Capable of detecting extremely small thermal signals—two to three orders of magnitude more sensitive than traditional steady-state thermography. Detects micro-leakage currents or micro-short circuits as low as μA.
- Non-Destructive Testing: Precise imaging without damaging the sample, suitable for various packaging types, including unopened chips and PCBA.
- 3D Visualization: Phase information allows micrometer-level depth localization, enabling blind-spot-free reconstruction of internal chip structures.
- Rapid Localization: Locates Hot Spots faster than other techniques, shortening failure analysis time.
Limitations: Time-consuming testing process; strict environmental requirements such as temperature and humidity control.
3.3 Scanning Thermal Microscopy (SThM)
Principle: Using a micro-cantilever probe, this technique detects small temperature variations across the chip surface in a point-by-point manner, similar to an atomic force microscope. A thermocouple-equipped tip scans the sample, producing thermal and topographical images simultaneously, with quantitative temperature and qualitative thermal conductivity distribution.
Advantages:
- Submicron resolution, ideal for nanoscale process failure analysis.
- Nano-precision temperature measurement.
- Ultra-high spatial resolution of thermal properties.
- Sensitive to both temperature and thermal conductivity.
- Supports various scanning modes (tapping, contact, peak-force, etc.).
Limitations: Slow scanning speed; requires ultra-clean, constant-temperature and constant-humidity environments.
3.4 Other Advanced Techniques
TIVA: Applies localized heating to the chip using a laser or thermal source and observes voltage changes to pinpoint defects such as opens and poor contacts. By scanning the surface with a laser, impedance variations can be detected and mapped.
TIVA Principle: A small current I1 is applied to the circuit; a laser scans the chip surface while voltage V changes are monitored to locate leakage.
OBIRCH: Optical Beam Induced Resistance Change is a high-resolution defect localization technique that quickly and accurately identifies failure sites in chips with leakage. A voltage V is applied, and a laser scans the chip surface while current I1 changes are monitored.
OBIRCH Principle: A laser beam scans the chip surface under constant voltage. If defects are present, heat accumulation occurs due to poor thermal conduction, altering metal resistance and current. Mapping these changes to laser position pinpoints failure locations. Widely used for high- and low-impedance path analysis and leakage path detection.
Laser Localization Advantages: High-energy laser can penetrate multi-layer metal and silicon substrates. Backside probing saves 1–2 days of wire bonding time. Applicable to both silicon and III-V chips. Enables localization of leakage, short circuits, transistor, capacitor, resistor issues, as well as ESD and EOS faults.
4. Technical Challenges and Future Trends
4.1 Pushing Resolution and Sensitivity Limits
As chip processes enter the nanometer and angstrom scale, Hot Spot sizes shrink, demanding unprecedented detection resolution and sensitivity. Techniques like Scanning Thermal Microscopy and OBIRCH will continue to improve through better probe design and laser focusing to meet these demands.
4.2 Addressing Packaging Complexity
With widespread adoption of multi-layer packaging, internal Hot Spot detection becomes more difficult. Future advancements will include new infrared penetration and local de-packaging techniques, as well as integration with 3D imaging for comprehensive internal chip analysis.
4.3 Precise Adaptation to Complex Testing Scenarios
Many Hot Spots only manifest under specific voltages, temperatures, or loads, requiring Hot Spot detection to adapt to diverse environments and simulate realistic conditions. Future test equipment will integrate multiple modules to simulate various scenarios and ensure detection accuracy and reliability.
4.4 Synergistic Multi-Technology Integration
Single Hot Spot detection techniques have limitations. Future trends will see deep integration of Hot Spot technology with EMMI, X-ray, CSAM, and more, forming comprehensive failure diagnosis solutions. This synergy enhances fault analysis efficiency and accuracy.
5. Conclusion and Outlook
Hot Spot technology plays an irreplaceable role in chip failure analysis, especially in locating localized overheating caused by short circuits, leakage, and other defects. A variety of detection methods offer flexible solutions for diverse failure analysis needs. By enabling engineers to quickly pinpoint faults, Hot Spot technology shortens analysis time and improves localization precision.
Looking ahead, as semiconductor innovation continues, Hot Spot technology will also evolve. Breakthroughs in resolution, packaging adaptability, scenario simulation, and multi-tech integration will provide stronger technical support for high-quality development in the chip industry. These advances will help engineers overcome chip failure challenges and improve product reliability and competitiveness.
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