Infrared optical probing techniques that have significant applications to and continued development for silicon physical debug have existed for decades. More recently, resolution enhancement achieved by improving numerical aperture, etc. have reached fundamental limits and the ability for resolution to match node scaling with radiation transparent to silicon (photon energy < silicon bandgap) becomes diffraction limited for some 10nm and many future process nodes. Decreasing the wavelength used for imaging and signal acquisition can improve resolution; however, it is well documented that absorption increases sharply for photons with energy greater than the bandgap of the bulk substrate material. Significant reduction in the thickness of the backside substrate material can be performed to achieve acceptable transmission through the absorbing substrate, but the requirement for very thin sample preparation significantly modifies the thermal system surrounding active circuitry. Here, high aspect ratio trenches are shown to offer a unique method to take advantage of thick silicon (> 100µm) for lateral heat dissipation as well as thin silicon (< 2µm) for minimally absorbing optical path in close proximity to enable case-by-case preparation methods for postsilicon labs faced with visible light resolution requirements on high power density circuits.

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