Thermal imaging by atomic force microscopy using thermocouple cantilever probes

Thermocouple cantilever probes are used in the atomic force microscope (AFM) to simultaneously obtain thermal and topographical images of surfaces with submicrometer scale spatial resolution. Three designs of thermocouple AFM probes and the thermal images obtained by each of them are presented here. Experiments show that the dominant mechanism for sample-probe heat transfer is gas conduction. If probes are not properly designed, this could lead to image distortion and loss of temperature and spatial resolution. The steady state probe behavior is dominated by the gas thermal conductivity whereas the transient effects are dominated by the thermal mass of the probe. Thermal images of single transistors show their thermal characteristics under different biasing conditions. In addition, hot spots created by short-circuit defects within a transistor can be located by this technique. Efforts are underway to improve the spatial resolution from 0.4 to 0.05 μm by careful probe design. The results suggest that this can be achieved when the size of the thermal sensor at the tip of an AFM cantilever probe is of the order of the tip radius.