edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 25 NO. 2 8 SIMS is critical to broad ion beam delayering because it enables the etch to be stopped on a specific layer. As the substrate is etched, a time series is produced containing the signal from different masses corresponding to the expected etch products (Cu, Al, Ta, W). Si from Si or SiO2 is difficult to observe because the peak, at 28 AMU, overlaps with background N2, which is a stronger signal. An example trace is shown in Fig. 7a, with a cross section of a chip of the same design shown in 7b. As the ion beam etches the chip, from top to bottom in Fig. 7b, the time series is produced showing a periodic rise and fall of the Cu signal from the metal layers and the Ta signal from the vias. In this case, the whole chip was etched to produce this time series. However, the SIMS signal can be used to stop at a precise point. For instance, knowing that the chip has seven metal layers that are all Cu, one can pre-program the tool to stop at the third rise of the Cu signal, corresponding to M5. The chip can then be removed, imaged at M5, and then placed back for further delayering. An example of this is shown in Fig. 7c, where the second rise is identified as the stop point. CONCLUSION As demonstrated above, broad ion beam delayering is a versatile technique for whole-chip failure analysis. The large area of uniformity coupled with the ability to precisely stop at the layer of interest enables rapid wholechip defect detection. Because this is a fully computercontrolled process with SIMS endpoint detection, the process is completely repeatable from device to device and technician to technician. ABOUT THE AUTHORS David Douglass has a B.S. in engineering physics and a Ph.D. in physics from the University of Virginia. He has many years of experience in laser development, as well as technical marketing for capital equipment in photonics and semiconductor applications. He is currently at Denton Vacuum, managing both applications development and technical marketing. Kyle Godin graduated with a B.S. in physics from Rose-Hulman with a specialization in semiconductor devices, an M.S. in microelectronics-photonics from the University of Arkansas, and Ph.D. in interdisciplinary engineering from Stevens Institute of Technology. After doing research in 2D materials and photonics, doing end-to-end fabrication and characterization of simple devices, he has worked in ion beam sputtering and ion sources for five years. He is currently at Denton Vacuum in Moorestown, New Jersey. (a) (b) (c) Fig. 7 SIMS signals and end points. Advertise in Electronic Device Failure Analysis magazine! For information about advertising in Electronic Device Failure Analysis: Kelly Johanns, Business Development Manager 440.671.3851, kelly.johanns@asminternational.org Current rate card may be viewed online at asminternational.org/mediakit.
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