An infrared scanning technique for the determination of temperature profiles in microcircuits

Circuit reliability and performance, particularly in high-density microcircuits, are affected by temperature. Therefore, a knowledge of the heat transfer paths and temperature distribution are of prime importance in topological design for efficient circuit performance. The method of thermal profiling described uses infrared scanning. The method is direct, rapid, and nondestructive, and the temperature profile is unaffected by the measurement. The effects of heat sinks, heat sources, and unusual geometrical patterns are automatically taken into account. The "heart" of the infrared scanning system is a photosensitive element of single-crystal indium antimonide with a long wave cutoff near 6 microns. The system has successfully determined isothermal patterns from 55°C to >250°C in thin-film tantalum microcircuits having linewidth patterns as small as 2 mils. Isothermal patterns of various geometries are shown to illustrate how the area and shape of resistors affect the thermal pattern and the temperature of the hottest part. Life data correlating the temperatures at the hottest parts with operating stability of thin-film resistive networks is presented. Through the correlation of temperature profiles with storage life tests, the potential exists for greatly reducing the amount of costly life testing of microcircuits for every new bias condition and circuit. Although emphasis is placed on thin-film microcircuits, a thermal profile of a solid silicon microcircuit is presented to indicate usefulness of the infrared scanning technique for temperature profiling of other types of microsystems.