Speaker
Description
Production test hardware for manufacturing semiconductor devices enables the assurance of quality and performance as part of the semiconductor manufacturing process, strongly required for providing defect-free and reliable high-performance products in challenging and safety-relevant application areas such as automotive, data centers, consumer devices and industrial machinery and automation. The production test of high-power semiconductor devices is particularly demanding for test hardware since high currents in fast switching scenarios are to be applied to semiconductor devices on wafer level via miniscule contacting needles in probe-cards ass front-end connecting equipment in high throughput production testers. The high electrical currents applied via probe card needles lead to extremely high current densities thus challenging thermal conditions, since such needles for power devices have a typical diameter of only 63 µm (2.5 milli-inch) and a contact area to the device surface to be tested of about 20 µm. As heavily required for high throughput high volume production tests the used probe card needles must reliably conduct high currents without a damage of overheating in ten to hundred thousand of contacts and current tests without degradation and service.
The contribution of this work is the thermal investigation of high speed high current loads on probe card needles via active thermography in order to assess the thermal load, the related thermal distribution and flow conditions in typical and extreme application conditions. We demonstrate high speed microscopic thermal investigations at frame rates above 1500 Hz with an optical resolution below 5µm. The requirement is on one hand to carry several short consecutive high DC currents pulses: as e.g. 2 A for several pulses with 3 ms duration. On the other hand, for longer time duration lower DC currents, as e.g. 0.8 A are applied. Previous simulations showed that the temperature of the contact region increases already during the couple of ms heating pulse up to 500 K, but afterwards it cools down quickly. On the other hand, in the body of the probe needle the heat accumulates and it becomes warmer and warmer after several heating pulses.
In order to be able to investigate this thermal behavior a test setup has been prepared for infrared microscopy. The test wafer has been cut so, that the contacted needles are at the surface. Additionally, they have been blackened to increase the emissivity. A cooled IR camera with microscopic lens has been used (IRcam Velox 1310SM) with a spatial resolution of 2 µm/pixel. The test setup was positioned below the microscope lens and the electrical current was applied to the needles. The electrical current application and the recording the IR images were synchronized.
Several experiments with different window sizes have been carried out: large windows to measure the temperature increase of the probe bodies after several seconds and small windows to inspect the probe heads close to the contacting region. With decreasing the window size the recorded frame rate was increased up to 1600Hz, providing a sufficient temporal resolution even during the 3 ms heating pulses.
The mid-wave IR camera records in the wavelength range of 3-5 µm. Due to diffraction of the IR waves and the given MTF of the used lens, the blurring of the IR images with 2µm/pixel resolution could not be avoided, but even so, the experiments show very good agreement with the simulations.
