Two-/Multi-Photon Imaging for Characterization of Fine Line Features and Microvias in Advanced Packaging

This paper demonstrates the application of non-destructive two-/multi-photon imaging for the characterization of high density interconnects including fine lines and spaces and small microvias (d10 μm diameter). Scaling of microvia critical dimensions (CDs) to approach the L/S which is required to achieve very high density interconnects is a major challenge in panel scale packaging. However, the characterization of fine lines and spaces as well as microvias become very challenging, of particular concern is the determination of the formation of microvias. In this paper we present two-photon imaging technique which uses femtosecond laser with a tunable wavelength in the range of 700-800 nm and has the ability to measure the feature sizes of not only the lines and spaces but also the microvias. Moreover, we illustrate the use of this technique to clearly recognize whether the microvias drilled are through-hole vias compared to the vias having left over residues. In the absence of two-photon excited fluorescence from the materials, one can continue to make use of three-photon and multi-photon imaging techniques for the characterization of vias and L/S.