Developed at Sandia National Laboratories, the technique uses thermally induced voltage alteration (TIVA) and Seebeck effect imaging (SEI) to quickly find failures in ICs. The ability to scan the front and back of an IC is important because state-of-the-art ICs have up to seven layers of metal interconnections. This prevents direct observation of deeper structures from the front of the device. Additionally, flip chip or upside down packaging denies direct access to the front surface.
In the technique, the beam from an infrared laser, operating at wavelengths for which silicon is transparent, is focused on the device. The laser heats only a small part of the IC at a time. The localized heating produces a voltage change on the IC, which is biased with constant current source.
An image of the IC's response is generated by rastering the laser spot over the circuit with a laser-scanning microscope while recording changes in the power requirements. The laser-scanning optics also generate a reflected light image. When registered with the TIVA image, this reflected image clearly shows IC defects.
Faults and failures within the circuit react differently to heat stimulation than operational components. In an unflawed device, the effects produced by the heat don't change the circuit's operation. However, if the power demands of the chip change due to the local heating, the chip has flaws.
Sandia has licensed the technology to OptoMetrix Inc. (Renton, WA), an optical instrumentation company specializing in failure analysis techniques for ICs. For more information, call Sandia at 505-844-1421 or OptoMetrix at 425-251-6363.