Ultra-thin (<100 nm) flakes shorting metal lines are difficult to detect and often cause the device to fail after reliability stress or at the customer site. In most cases, the common technique of inspecting the device in an optical microscope followed by conventional low energy (<3.0 kV) scanning electron microscopy (SEM) is often not able to detect this type of defect. In rare cases, where the defect is successfully exposed by the traditional procedure, it is very challenging to perform additional transmission electron microscopy (TEM) characterization of the defect without introducing arifacts during sample preparation of the exposed flake. A new procedure to identify these defects using a combination of face-lapping and high energy (>10 kV) SEM imaging is described in this paper. In this method, the failing device is carefully face-lapped and inspected frequently using a high energy (>10 kV) scanning electron beam. The high energy electron beam penetrates through the oxide layer and detects features embedded below the oxide. This technique greatly incresases the chances of detecting the flake, as the method is capable of detecting the defect at a larger range of oxide thickness as opposed to the traditional method. Additionally, TEM results were improved when the ultra-thin flakes were detected below the surface with the high energy SEM technique. Several examples of ultra-thin flakes found using the high energy SEM vs. low energy SEM will be presented.

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