Thermal-induced voltage acceleration (TIVA) is a technique used in failure analysis, specifically to isolate and identify the root cause of failure in integrated circuits (ICs) by subjecting them to thermal stresses. Here’s a more detailed breakdown of how TIVA is applied to IC failure analysis:
What is TIVA?
TIVA is a method where an IC is heated to accelerate the failure mechanism, allowing for the identification of weak spots or defective areas within the IC. The principle behind TIVA is that many failure modes in semiconductor devices, such as shorts, opens, or degradation of material properties, are temperature-dependent. By increasing the temperature of the IC, these failures can be induced more quickly or at a lower stress threshold, making them easier to observe and analyze.
Key Steps in TIVA for IC Failure Analysis:
- IC Failure Selection:
- A failed IC is first identified and removed for analysis. The failure may not always be immediately obvious, so visual inspections, electrical testing, or functional testing might be done initially to confirm that there is indeed a failure.
- Controlled Heating:
- The IC is then subjected to controlled thermal cycling or a temperature ramp. This can be done using a thermal test chamber, laser-induced heating, or even hot plates, depending on the specific equipment available. The temperature is typically increased gradually and monitored to prevent damage from excessive heat.
- Voltage Monitoring:
- During the thermal cycling, the voltage across the IC (or specific parts of the IC) is monitored continuously. As the temperature increases, weak spots such as faulty interconnects, delamination, or other defect mechanisms may cause voltage changes, leaks, or failure of the IC to operate properly.
- This allows for observation of voltage fluctuations that correlate with certain failure modes, such as the breakdown of gate oxides or the failure of intermetallics.
- Failure Mode Isolation:
- By carefully analyzing the temperature-dependent behavior of the IC, the failure mode can be isolated. For example, if the failure occurs due to a thermal expansion mismatch between materials, you might observe cracks or delaminations that become more apparent at higher temperatures.
- Alternatively, if a specific area of the chip heats up faster and shows voltage anomalies, it might point to localized defects like a weakened transistor or a faulty metal trace.
- Post-Analysis Examination:
- After the failure has been induced or accelerated, a more detailed inspection is done using tools like electron microscopy (SEM), X-ray imaging, or other advanced failure analysis techniques to pinpoint the exact cause of failure (e.g., stress-induced fractures, metal migration, or contamination).
Benefits of TIVA in Failure Analysis:
- Faster Failure Identification: By accelerating failure mechanisms with heat, TIVA allows analysts to identify the root cause of failure more quickly than if relying on normal operating conditions.
- Improved Understanding of Failure Modes: TIVA helps uncover failure modes that are temperature-sensitive and may not be apparent during standard testing.
- Non-destructive Testing: In many cases, TIVA can be performed in a non-destructive manner, meaning the IC can still be analyzed after the test, which is important for further investigation or validation of the failure cause.
Applications:
- Design Debugging: TIVA is often used in the design phase to identify potential weaknesses in ICs before mass production.
- Reliability Testing: TIVA can help simulate real-world operating conditions and environmental stresses, allowing manufacturers to improve product reliability.
- Defect Localization: The technique helps locate failure hotspots, particularly in complex ICs where the exact cause of failure might be difficult to pinpoint.
Challenges:
- Accuracy: TIVA depends on accurate temperature control and monitoring. Improper heating or temperature gradients could lead to false results.
- Complexity in Failure Mechanism: Some failure modes may not respond well to thermal acceleration, so TIVA may not always isolate the failure mode on its own.
