August_EDFA_Digital

edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 22 NO. 3 18 DEFECT CHARACTERIZATION OF ADVANCED PACKAGES USING NOVEL PHASE AND DARK FIELD X-RAY IMAGING S.H. Lau, Sheraz Gul, Guibin Zan, David Vine, Sylvia Lewis, and Wenbing Yun Sigray Inc., Concord, California shlau@sigray.com EDFAAO (2020) 3:18-25 1537-0755/$19.00 ©ASM International ® INTRODUCTION New heterogeneous integration schemes require improvements to packaging components, including continuing miniaturization, new materials and material integration schemes, and reliability under environments such as higher temperature and mechanical stress. The heterogeneous implementations are driving demand for substantive changes to metrology, diagnostics, process control, and physical failure analysis (PFA). Real time x-ray imaging and computed tomography have become key workhorses in PFA, driven by developments in 3D x-ray microscopy [1,2] through improved resolution and throughput. Notwithstanding the continually shrinking features and new material integration, there are ever- increasing needs for even better resolution, contrast, and throughput. Currently, gaps in nondestructive 2D and 3D imaging in PFA exist due to lack of resolution to resolve sub-micron defects, as in the case of most cracks or voids in microbumps within packages less than 30 microns in diameter. Furthermore, other categories of defects that are challenging in x-ray imaging are those within low Z materials. These include sidewall delamination between Si die and underfill; bulk cracks in the underfill, in organic substrates, or redistribution layer (RDL); Si die cracks; and voids within the underfill and in the epoxy. Most of these categories of defects cannot be detected nondestruc- tively by other existing PFA tools either, such as confocal scanning acoustic microscopes (C-SAM). Consequently, innovations inmetrology are needed to enable the imple- mentationof newtechnologies andmaterials for advanced packaging aswell as to control the respectivemanufactur- ing processes. One promising solution is the development of a novel laboratory-based x-ray system that provides phase contrast and dark field/scattering contrast using a Talbot-Lau interferometer. Examples of the application of this system to analyze advanced semiconductor pack- ages, lowZ organic components, and porous samples are discussed. CONVENTIONAL NONDESTRUCTIVE INSPECTION: X-RAY AND ACOUSTIC MICROSCOPY Nondestructive inspection of electronic packages is an important process for metrology, diagnostics, process control, and PFA in the semiconductor industry. Two- dimensional x-ray radiography (2D real time x-ray) has excellent penetrating power and can inspect many parts and electronic components in real time making it an indispensable tool for most laboratories and for quality inspection lines. In recent years, microtomography (micro-CT) or x-ray microscopy (XRM) has increasingly been used in failure analysis laboratories because of their ability to image in 3D to nondestructively isolate faults with spatial information necessary for further analysis. This has improved substantially in the past decade with developments achieving resolution of < 1 micron and shorter imaging times. With tomography, a virtual cross section of complex advanced packages can be made in any orientation to reveal failure mechanisms. Advanced packages consist of various components such as semiconductor chips (silicon based), metal wires, solder joints, copper vias, intermetallic layer plus underfill, andmolding compounds, whichareorganicmaterials. The inspection of heavy-elemental components such asmetal wires, solder, and copper vias requires the use of highly energetic x-rays for absorption contrast imaging. However, defects in low Z materials, such as silicon, underfill, and epoxy encapsulants are almost invisible in the x-ray