edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 27 NO. 2 4 EDFAAO (2025) 2:4-7 1537-0755/$19.00 ©ASM International® SILICON PHOTONIC FAILURE ANALYSIS USING NEAR INFRARED MICROSCOPY Arpan Dasgupta GlobalFoundries, Malta, New York arpan.dasgupta@globalfoundries.com INTRODUCTION Silicon photonics has emerged as a promising solution for on-chip communication to improve computational systems in data centers.[1] High volume manufacturing of functional and reliable photonic integrated circuits (PICs) is key to delivering a co-packaged optics (CPO) solution with compute ICs. GlobalFoundries’ silicon photonics approach provides a monolithic platform using silicon-oninsulator (SOI).[2] Both silicon optics and silicon electronics are realized on the same chip, including a cavity for III-V laser light source to be attached after the wafer fabrication process.[3] The high reflective index of silicon (n = 3.5) or silicon nitride (n = 2.05) waveguides embedded in oxide (n = 1.5) allow for on-chip light distribution with relatively small bending waveguides radii essential for the design of very compact PICs. Electrical-to-optical light conversion is accomplished by using Mach-Zehnder modulators or micro-ring modulators fabricated from silicon wave guides. These junction-based modulators are able to switch the light in a range of up to 50 GHz. Light detection is accomplished by integrating a Ge photodetector in the receiver. Because Ge has a lower band gap than Si, light in the O-band, the C-band, and the L-band is absorbed and converted into an electrical signal.[4] Lastly, the optical I/O from the chip into the fiber and from the fiber into the chip is realized with horizontal edge couplers. Deep trenches with exact dimensions are etched into the silicon wafer forming V-grooves. Single mode fibers can then be placed in the V-grooves, allowing the precise alignment of fiber core and Si waveguide with minimal insertion and return losses.[5] The key elements of GlobalFoundries’ Fotonix offering are illustrated in Fig. 1.[6] Failure analysis techniques are still at their infancy when it comes to silicon photonics.[7] This article focuses on one emerging technique, near infrared microscopy (IR), which is proving to be very useful for isolating unexpected light losses as a first pass. Near IR microscopes are not new to the semiconductor industry. Historically, they have been used to image silicon dies from the backside of the chip, which is externally illuminated by an infrared lamp. One advantage with the near IR range is that unlike mid-range or far-range IR, conventional glass optics work just as well with near IR. This allows the user to utilize conventional microscopes to achieve high magnification optics to isolate and characterize light paths. Most near IR microscopes work with an InGaAs sensor which is Fig. 1 GlobalFoundries Fotonix provides a library with a wide variety of photonic devices that are built on SOI wafers—active and passive photonics components using CMOS-compatible processes, RF-friendly BEOL, and low-loss optical I/O (V-groovespot size converter) for high fiber count. The optical devices are tailored specifically for the near infrared range (C-band and O-band).
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