Sandra began her academic journey with a preparatory course in mathematics and physics before going on to engineering school. She enrolled at Polytech Grenoble in a program specializing in materials science, a field that has long interested her, particularly because of its connection to semiconductors.
Following her work experience at STMicroelectronics, Sandra decided to build on the knowledge she had gained during her work-study program and explore the field of academic research. She then applied to CEA-Leti to pursue a Ph.D., drawn by the opportunity to work at the intersection of fundamental research and industrial applications. Her work on GaN etching for micro-LEDs, presented at the AVS under the title “CH4/H2 etching of N-polar GaN for micro-LED application," earned her the first student prize.
When LED miniaturization brings new challenges
In her work, Sandra focuses on the physicochemical characterization of pixel sidewalls, a topic that has received little attention in scientific literature. In fact, analyses generally focus on the study of the etch bottom. Her goal is to test a new etching chemistry to limit etch-induced defects in the material at the pixel edges. This would improve the electro-optical properties of GaN micro-LEDs.
A major challenge lies in the miniaturization of LEDs: as their size decreases, electro-optical efficiency declines, becoming critical below 10 µm (microns). Indeed, the impact of micro-LED sidewalls surfaces damaged by plasma etching is no longer negligible and leads to a significant drop in the LED's electro-optical efficiency. Thus, it is essential to develop new etching methods that limit the degradation of micro-LED sidewalls. The chemistry Sandra is studying had already been addressed in the scientific literature, but without any specific mechanism having been proposed.
At the 71st AVS Conference, Sandra proposed a mechanism to explain the etching of GaN using a CH₄/H₂/Ar plasma: this chemical mixture tends to react at the GaN surface to form a polymer layer, the presence of which is essential to the etching process. Without it, the material is simply sputtered, rendering plasma etching ineffective. However, when it becomes too thick, it can also act as an obstacle by screening the GaN to be etched. To control this phenomenon, Sandra's team defined specific parameters that allow the material to be etched while controlling the deposition of a polymer layer on the surface, thereby ensuring a better balance between GaN degradation at the pixel sidewalls and etch rate.
Toward Etching for Industrial Applications
Sandra's work has applications in the field of micro-display technology, such as virtual and augmented reality devices, but that's not all. In fact, micro-LEDs also offer an attractive solution for fiber-optic data transmission in demanding systems, such as high-performance computing, artificial intelligence and data centers.
From an industrial perspective, the main challenge is to develop an etching process that does not damage the material. It is in this context that Sandra is collaborating through a joint development program with the equipment manufacturer LAM Research, with the aim of strengthening the link between its research and its practical applications in the semiconductor industry.