In its essence, silicon photonics brings together two separate but parallel-evolving technologies: integrated circuits and optical communications. Each technology boasts unique advantages. Silicon-based IC fabrication enables the integration of billions of transistors onto a single substrate. On the other hand, laser-driven optical communications deliver exceptional bandwidth and low-loss signal transmission across extensive distances. Through the synergy of Silicon Photonics (SiPh), these technologies present novel prospects in terms of transmission speed, scalability, energy efficiency, and cost reduction. We’re fast approaching the time when SiPh is set to transition from data center applications to interconnections within individual chips.

Photonics testing is still in its nascent stages, with broad volume production yet to be realized. The development of test equipment and techniques is ongoing. Currently, the landscape comprises a fusion of established semiconductor testing methods tailored to accommodate the distinct requirements of photonics. To establish robust production testing, the key lies in cultivating a comprehensive ecosystem encompassing testers, handlers, and complementary components aimed at minimizing testing expenses. The emergence of this ecosystem is still in its early stages.

Dan Rishavy, Strategic Market Development Director at FormFactor focused on Silicon Photonics, stated in a Semiconductor Engineering article – Testing Silicon Photonics in Production, “In the silicon world, our customers like to test as early as possible to initially understand their devices and eventually avoid investing too much into devices that will never work.”

Typically, Silicon Photonics (SiPh) entails the incorporation of on-chip I/O components, manifested as etched diffraction gratings or edge edge facets. These gratings and edge facets serve to guide light from off-chip optical fibers into waveguides within the chip. Within these waveguides, various functions such as filtering and conversion to digital data streams are executed.

This introduction of optical I/O, in conjunction with electrical components, introduces an entirely novel aspect to wafer testing methodologies. The necessity to capture and manipulate modulated light beams necessitates the development of innovative probing approaches that cater to a fresh set of mechanical prerequisites. The conventional challenge of maintaining precise physical probe contact with pads on the wafer surface gives way to a new paradigm where optical fibers must be intricately aligned to facilitate the coupling of light into and out of a wafer, all without physical contact.

FormFactor addresses this challenge through the implementation of an optical positioning solution that leverages FormFactor’s machine vision technology to calibrate it to the probe station for highly accurate and repeatable measurements.  Using uniquely designed fixtures, FormFactor’s industry leading solutions can accommodate both single fibers and fiber arrays (FAU’s) in both surface and edge coupling applications.. The system allows for precise adjustments across six degrees of freedom – encompassing three translational and three rotational motions. In essence, it enables scanning comparable to the maximum-power-point tracking (MPPT) utilized for configuring the orientation of solar cells.

There’s a big push in Europe currently – specifically the “photonixFAB project” – that aims to establish a European value chain and initial industrial manufacturing capabilities dedicated to silicon photonics devices. The overarching goal is to pave the way for high-volume production in this domain.

FormFactor adopts a comprehensive perspective in formulating effective strategies for SiPh wafer level testing. We have established collaborative partnerships with essential test technology providers, leveraging the unique strengths of each participant. In this specific context, our collaboration involves Preferred Partners such as Keysight Technologies for measurement instrumentation and Physik Instrumente (PI) and others for positioning technology. Drawing upon our skilled and innovative team, along with these strategic partnerships, FormFactor is equipped to deliver impactful solutions.