Abstract A hemispherical silicon solid immersion lens (SIL) was used to improve the spatial resolution of front-side thermal IR imaging in lock-in mode. The bottom of the SIL was coneshaped to reduce the footprint of the SIL to the size of the imaged region. Caused by the lock-in operation mode, the detection limit improves by 2-3 orders of magnitude, and scattered light does not limit the image contrast. By using this SIL in combination with an IR camera working in the 3-5 μm wavelength range, a spatial resolution of 1.4 μm was obtained for thermal IR imaging. An automatic SIL positioning facility was constructed to place the SIL exactly in the center of the imaged region and to easily remove it after the detailed investigation.

Abstract Lock-in thermography based on an infrared camera has proven to be a useful tool for failure analysis of integrated circuits (ICs). This article discusses four novel technical developments of lock-in thermography. These developments are blackening the IC surface with colloidal bismuth, the synchronous undersampling technique allowing the use of higher lock-in frequencies, displaying the 0deg/-90deg signal as a novel high resolution emissivity corrected image type, and removing the thermal blurring effect by mathematically deconvoluting the 0deg/-90deg; signal. The effect of these techniques is demonstrated by using a regularly working operational amplifier (pA 741) and a damaged capacitor as test devices. It is shown that blackening the IC surface improves the detection sensitivity in metallized regions by up to a factor of 10, whereas the other methods allow improvement of the effective spatial resolution. The article also discusses which of the spatial resolution improvement techniques is most appropriate in different situations.