Back side thermal imaging of integrated circuits at high spatial resolution

In integrated circuits, most of the heating is produced in the active layers below the surface, making thermal measurements extremely difficult. The authors demonstrate that near infrared thermoreflectance can provide thermal imaging inside the circuit, through its silicon substrate. The use of an InGaAs camera with a noncoherent illumination in the 1.1–1.7μm band allows fast thermal imaging with a diffraction-limited resolution of 1.7μm. A silicon solid immersion lens was then used to further improve the resolution to 440nm, corresponding to an effective numerical aperture of 2.36.