CEA‑Leti's strain‑mapping service uses transmission electron microscopy (TEM) to carry out precession electron diffraction (PED). In ordinary electron diffraction the beam hits the crystal at a fixed angle, often producing complex patterns because of dynamical scattering. PED solves that by rotating the beam in a conical sweep, recording a more complete diffraction pattern over dozens of orientations. The result is higher-quality diffraction data that can be turned into strain maps.
“TEM is the ideal technique to measure these deformations at the nanometric scale," says Nicolas Bernier, research engineer‑electron microscopy.
Avoiding Unintended Material Deformation
The workflow starts with ultra‑thin lamellae - cross‑sections of a chip that are roughly 80 nm thick - prepared using focused ion beam (FIB) milling.
“FIB is the only technique that provides precise localization on a wafer and also prevents unintended material deformation," explains Audrey Jannaud, the sample-preparation specialist.
Once the specimen is ready, it is inserted into a TEM equipped with a PED module. Scanning diffraction allows the lab to measure the lattice parameters of the crystal with high spatial resolution in different regions of a device
“A precession motion is applied to the electron beam, causing it to rotate around its axis. This significantly improves the quality of our diffraction patterns. Over the past ten years, we have pushed the limits of precession to make it robust and, above all, quantitative," says Matthew Bryan, research engineer-data scientist.
Numbers That Speak Volumes
The technique delivers strain maps with 1 nm spatial resolution and ~ 0.02 % precision - which places CEA-Leti among the world's leaders in nanoscale metrology.
“PED represents a unique and highly relevant area of expertise for our partners. We have around 80 publications on this topic," Bernier notes, underscoring the depth of expertise behind the offering.
The technique has been simplified and accelerated where possible to enable higher throughput, and make better use of the instruments. The result is a faster turnaround time for characterization requests.
“The processing of the generated data has been optimized and simplified to enable near-real‑time analysis," Jannaud says.
Three TEMs are now equipped to perform PED measurements, allowing CEA-Leti to handle a larger volume of samples and making the service accessible to more qualified microscopists.
Collaboration Across Institutions
The project didn't happen in isolation. Bernier emphasizes the combined expertise of the team members that made it possible:
“I was really impressed by the complementarity between CEA-IRIG, especially with Jean‑Luc Rouvière, who was developing the fundamental aspects and the algorithmic side, and our team at CEA-Leti, notably with David Cooper, where we were really focused on applications. We were able to develop the technique on a broad range of microelectronic devices."
That partnership between fundamental research and application‑driven engineering helped turn an experimental methodology into a practical, routine characterization service.