Every semiconductor device generates heat. The device’s ability to dissipate this heat dictates its performance and reliability. For this reason, thermal testing plays an important role in both the design of new devices and quality control for manufactured chips. Thermal resistance measurements can help accurately specify operating limits, screen out defective products, and engineer cooling solutions.
But not all thermal resistance data are created equal! In this blog, we explain why.
Important Considerations When Interpreting Thermal Resistance Data from Semiconductor Testing
Thermal stress testing is employed extensively in semiconductor manufacturing to help screen out components that are likely to fail prematurely (a wide variety of different manufacturing defects can cause a component to fail under thermal stress). We take a deeper look at thermal failure in semiconductor components in our article here. Centered on extensive accelerated temperature cycling, thermal stress testing plays a valuable role in the manufacturing process, but it is not capable of generating the precise thermal resistance data which are so crucial to predicting and limiting thermal failure.
Generating this data for some semiconductor devices, however, is a genuine metrology challenge. Sensors such as thermocouples or resistive thermometers may be employed to record temperature changes as heat is applied to a material, but increasingly thin semiconductor materials have limited the utility of these traditional measurement techniques. In short, micron-scale thin films are thinner than the sensors traditionally used to record thermal resistance data, causing the sensors themselves to exert too much influence on the recorded measurements (we provide an explanation of thickness and thermal conductivity measurements in our blog here).
Why do the assumptions underpinning traditional thermal metrology data not hold for thin films?
In semiconductor thermal testing, temperature measurements are not read at the device or hot spot, but from some distance away. The actual device/hotspot temperature must then be inferred based on the thermal resistances of each material between the measurement device and the chip. Reliable data on thin film thermal resistance, however, is not widely available. This limitation is crucial to understand because estimating the thermal resistance of thin films based on bulk properties is most likely not applicable, especially at sub-micron length scales. Defects and interfaces can arise during growth and heterogeneous integration of thin film materials can ultimately result in far lower thermal conductivity for the thin film variant of bulk material.
If these issues are not recognized, incorrect assumptions about the thermal resistance of thin film materials risk becoming baked into the analytical models used in device design, driving incorrect results and chronic errors in temperature measurements. For semiconductor manufacturers, these errors can lead directly to device and package designs with inadequate power handling requirements and a tendency to fail due to overheating. For this reason, more accurate thermal resistance data for the materials and interfaces in a device can play a direct role in enabling sufficient designs (including geometry, materials, cooling systems, etc.) for accommodating power requirements and regulating temperature.
How does SSTR-F address the limitations of traditional thermal metrology techniques?
Laser Thermal’s Steady-State Thermoreflectance in Fiber Optics (SSTR-F) is a novel thermal resistance testing technique that overcomes the limitations of traditional approaches to generate much more accurate data.
SSTR-F is a non-contact laser-based pump-probe technique that can measure the thermal conductivity and interfacial thermal resistance of thin films. Laser Thermal’s patented design of the SSTR-F tool allows for turnkey, fully automated thermal conductivity measurements, with high throughput batch testing that is ideal for screening thermal resistance changes in materials. SSTR-F provides accurate (+/- 10 %), repeatable (+/- 0.5 %), and reproducible (+/- 1.0 %) measurements of the thermal resistances of thin films and interfaces.
If you’re interested in learning more about SSTR-F, how it works, and how it can help provide more precise thermal property measurements for challenging materials such as semiconductors, our video playlist here is a great place to start. Or, you can find a selection of results generated using SSTR-F in our database here.