Plasma FIB speeds failure analysis

Inductively coupled plasma using a xenon ion beam can remove material faster than other FIB technologies.

Ann R. Thryft, Contributing Technical Editor -- Test & Measurement World, 9/1/2011 12:00:00 AM

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Conducting site-specific, cross-sectional failure analysis and fault isolation on complex, highly integrated packaged chips using FIB (focused ion beam) technology is no easy task. Analyzing 3-D IC packages and MEMS (microelectromechanical systems) with existing FIB techniques often requires several hours, instead of the minutes that would be required to make these techniques feasible in high-volume manufacturing environments. Consequently, to date this FIB analysis has been limited to relatively small numbers of samples, which has restricted the amount of development and failure-analysis feedback that can be done with these techniques.

In failure analysis, FIB systems remove material, add material, and form high-resolution images, all with the same beam. FIBs based on a Ga LMIS (gallium liquid metal ion source) have worked well in electronics applications for localized, site-specific sectioning and TEM (transmission electron microscope) sample preparation, said Richard Young, FEI’s FIB technologist. “But in newer, highly integrated 3-D packaging applications, failure-analysis engineers are struggling with much larger volumes of material and larger sections that are hundreds of microns across,” he said. “This can take hours of milling time with FIB systems based on a gallium liquid metal ion source. In particular, the development of TSVs [through-silicon vias] is being hindered by the metrology time required.”

A new FIB source technology, ICP (inductively coupled plasma) using a xenon ion beam, can remove material up to 20 times faster than other FIB technologies, said Young. “ICP technology extends the maximum beam current to more than 1 microamp, compared to only a few tens of nanoamps for gallium liquid metal ion, thus removing material faster. At the same time, it can provide the lower beam currents needed for high-milling precision in final cuts and high-resolution, sub-30-nm cross-section imaging. It can cross-section features in a wide range of diameters, from 50 to 1000 microns.”

This combination of high-speed milling and deposition with precise control and high-quality imaging, realized in FEI’s Vion PFIB (plasma FIB) system, makes the technology appropriate for several tasks. These include defect analysis of 3-D chips and MEMS devices; failure analysis of bumps, wire bonds, TSVs, and stacked die; and site-specific material removal to enable failure analysis and fault isolation on buried die. It’s also possible to introduce different gases so the Vion PFIB can selectively etch certain materials or deposit patterned conductors and insulators. ICP has been used previously for TSV deposition and etching systems, but using it as an ion-beam source in a FIB system is new, said Young.

Not only are the volumes of material to be milled larger, but packaging and failure-analysis engineers are also dealing with new materials, smaller features, and thinner, more fragile samples, said Peter Carleson, FEI’s product marketing manager. “The faster feedback provided by FEI’s Vion PFIB system helps keep the high-volume development and failure analysis of TSVs, MEMS, and 3-D packages on track,” he said. T&MW

Wafer-inspection system uses DUV KLA-Tencor’s latest generation of Surfscan wafer-defect and surface-quality inspection systems for substrate manufacturing and IC process monitoring, the SP3, is designed for extension to the next wafer size of 450 mm and to device nodes of 28 nm and below. The SP3 incorporates DUV (deep-ultraviolet) illumination, providing dramatic advances in sensitivity and throughput over its UV illumination predecessor. www.kla-tencor.com. Frame grabber captures 30 bits/pixel The PIXCI A310 from Epix uses a PCI Express x4 slot for capturing up to 30 bits per pixel of high-resolution RGB video. It acquires images from monochrome or RGB cameras with RS-170, CCIR, RS-343, VGA, SVGA, XGA, WXGA, SXGA, SXGA+, WXGA, WSGA+, and UXGA formats. The card’s 64-bit memory addressing allows it to capture image sequences directly to PC memory. www.epixinc.com. Metrology system examines 3-D ICs The 3DIR (three-dimensional infrared) metrology and defect-review system uses confocal IR laser-scanning microscopy to monitor post-bond parameters of 3-D stacked ICs, measuring alignment points at selected die, storing images, and summarizing results. Correlating overlay-alignment-offset data to electrical yield provides an early indication of bonded wafer yield. www.olympus-ita.com.