Nanoscale quantitative thermal imaging of electronic devices

This paper investigates a new method for quantitative nanoscale thermal imaging of electronic devices. Different from previous works that utilized a thermal sensor fabricated on a scanning probe to obtain surface thermal images, the current approach employs a tunneling thermocouple made of a metal tip and an ultra-thin metal film deposited on the sample surface. The metal tip has a negligible Seebeck coefficient; while the metal film can be Bi ₂Te₃ or a semiconducting polymer that has very high Seebeck coefficient and low thermal conductivity. Unlike the probe with a built-in thermal sensor, the measured thermoelectric voltage by the tunneling thermocouple is not affected by the tip-sample contact thermal resistance and air conduction, allowing quantitative temperature measurement with a spatial resolution limited by the metal film thickness, which can be 10-20 nm. We have tested the new approach using Ir or Pt-Ir -coated atomic force microscope (AFM) tips to obtain the surface temperature profiles of interconnect structures coated with a thin Cr film. The measured surface temperature gradient is larger and the maximum measured temperature is 60% higher than the corresponding values obtained by a thermal probe with a builtin thermocouple fabricated at the tip end. The two thermal imaging methods are currently being used to measure temperature distribution on the cross section of a 130 nm-technology silicon-on-insulator field-effect transistor.