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fluorescence microscopy
integrated-circuits
2-photon excitation
Physics
Abstract:
Optical beam induced current (OBIC) imaging through the backside of integrated circuits was investigated in the wavelength lambda region from 1.15 to 1.26 mu m. With a subpicosecond excitation source and approximately 1 mW at the sample, the two-photon contribution to the generated photocurrent dominates at lambda = 1.25 mu m but becomes negligible for lambda < 1.18 mu m. One-photon- (1P-) and two-photon- (2P-) OBIC images are very different. In the 1P case a strong contribution by scattered light to the carrier generation leads to an edge enhancement effect that is entirely missing when 2P excitation dominates. 2P-OBIC images often show supply-voltage dependent intensity steps that are much sharper than the optical resolution permits. The advantages of 2P-OBIC lie in the spatial confinement of the free carrier generation, a more relevant contrast mechanism, and the promise of a substantial increase in spatial resolution because of the quadratic intensity dependence and the possibility of using silicon solid immersion lenses, which could eventually provide resolution sufficient for circuits made by deep UV lithography. (C) 1999 American Institute of Physics. [S0021-8979(99)07316-8].
