Thermal Imaging Microscope for Semiconductor Device Failure Analysis
Lock-in Thermography Fault Isolation
Lock-in thermography is a process of automatically and repeatedly powering a device at regular intervals using a laboratory power supply and solid-state relays while the temperature response of the device is integrated and analyzed over time. Using this technique, hot spots that heat up less than 1mK (0.001°C) and dissipate below 100 µW can be detected.
In addition to identifying the x, y location of a defect, fault depth within a stacked-die can also be determined by analyzing the phase angle between device power and subsequent surface heating.
True Temperature Mapping
When imaging semiconductor devices, much of the contrast on the image is usually due to emissivity variations, not to temperature variations. Measuring true temperature requires compensating for these emissivity variations according to the following procedure.
First, the unpowered device is placed on the thermal stage so that its temperature can be precisely controlled. After it has reached a stable temperature, the Emissivity Tables software tool is used to automatically create an emissivity map of the device. By applying the emissivity map to thermal images, accurate temperatures can be obtained at any point on a device.
Junction Temperature Measurement
During integrated circuit operation, internal junction self-heating leads to a large concentration of heat at the junction. The peak temperature in a device is at the junction itself and heat conducts outward from the junction into the package. For this reason, accurate junction temperature measurement during device operation is an integral part of thermal characterization. The Emissivity Tables software tool allows accurate temperature measurement of the junction by automatically compensating for emissivity variations across the die surface.
Die Attach Evaluation
Die attach defects can be due to a number of causes such as inadequate or contaminated die attach material, delamination, or voids. Sentris thermal analysis tools like Image Sequence analysis can be used to assess the flow of heat away from a device in order to determine the integrity of the die bond.
Thermal Resistance Evaluation
A common method of characterizing the thermal performance of packaged devices is using the concept of thermal resistance. Thermal resistance is the steady-state temperature rise of a device junction above the temperature of a reference point (device package or heat sink) for each watt of power dissipated in the junction. Once a device's thermal resistance is known, the junction temperature can be readily calculated using temperature measurements on the reference point. Sentris enables accurate measurement of device packaging and heat sinks for reliable thermal resistance evaluation.