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Abstract

A practical method for greatly enhancing the strength of the modulated signal from laser probing of IC's is described. An IC device under test (DUT) is scanned with two spatially separated laser beams. The output from a single laser source is split into two separate components with each focused on different areas of the DUT. The separation between the beams and their intensity is adjustable to maximize the strength of the modulated return signal. Typically a NIR laser is used with flip-chip IC devices to account for the band-gap (transmission) characteristics of the substrate material. Upon reflection from the DUT, the reflected beams are recombined to interfere with one another. The phase difference of the two beams is adjustable to gain maximum interference. This signal is then processed to obtain the waveforms that correspond to the actions of the active gates and nodes as the chip is electronically cycled through its prescribed test loop. This method significantly improves the signal to noise ratio and reduces the time it takes to acquire a useful voltage waveform.

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First Claim