Strain and Surface Warping Detection of Interconnect Microstructures via Laser Diffraction

As 2.5D/3D interconnect technologies continue to advance, the microstructure environment of a package becoming increasing complex, with structures consisting of different materials packed into regions only a few microns in size. Under such conditions, sub-micron mechanical strain induced by thermal loading must be well understood to prevent failures. Today, the two most common in situ methods of measuring strain fields in microelectronic packages are Digital Image Correlation (DIC) and Moiré Interferometry. A calibrated DIC tool is capable of measuring image displacements of approximately 0.1 pixels. However, its use in the sub-micron regime requires a quality speckle pattern on the sample surface which is often difficult to fabricate. Additionally, the pattern must be resolved at high magnification, limiting the view field. Moiré Interferometry provides a wider view field than DIC, however displacement resolution is on the order of λ/2, where λ is the wavelength of laser light used to generate a Moiré pattern. Due to these limitations, we explore the use of laser diffraction to precisely measure pitch of Au diffraction gratings bonded to a TSV at various temperatures. Improvements to our setup show a tenfold increase in pitch mapping speed and resolution, with the ability to measure surface angle/warpage.