Global Failure Site Isolation: Thermal Techniques

Abstract

The need for techniques that would produce high spatial and thermal resolution images of microelectronic devices has existed for many years. This became particularly true with the advent of multiple level metallization on integrated circuits (ICs). The addition of a second and subsequent levels of metallization significantly reduced defect observability and node access. Many defect types result in higher power supply currents, which generate heat during operation. This is due to the power dissipation associated with the excess current flow at the defect site. Systems to detect this power dissipation can be characterized by their sensitivity to thermal changes and spatial resolution. Infrared (IR) thermal techniques were the earliest available that calculated the temperature of an object from it’s infrared emission. While IR techniques have excellent temperature range and resolution, they have a fundamental spatial resolution limitation. Liquid crystals have been used with great success since the mid-1960’s. Liquid crystals provide a binary response, indicating if the hot area is above the crystal’s transition temperature or not. Two factors have contributed to a recent reduction in the effectiveness of liquid crystals. Smaller feature sizes have made the spatial resolution of liquid crystal a factor. In addition, the reduction in power supply voltages and hence power dissipation have served to make the thermal sensitivity of liquid crystals an issue. The fluorescent microthermal imaging technique (FMI) was developed to overcome these issues. This chapter reviews the background material, operating principles, and image characteristics for these three thermal imaging techniques.