Crystal on crystal growth: mastering a complex art​

At CEA-Leti, researchers work on a variety of materials based on Si, Ge and Sn or on Nitrides of Ga, Al and In. The crux of the problem for an epitaxy specialist is to grow a crystal on another crystal while minimizing the strain of the layers and avoiding the formation of defects. To enable innovative devices, CEA-Leti researchers grow complex stacks of various materials to create single or multiple layers with thicknesses up to several hundred nanometers.​

​“In the case of Nitrides, we’re aiming to develop power and radio-frequency transistors as well as micro-LEDs for a variety of sectors such as the automotive industry, communications and micro-displays” says Amélie Dussaigne, researcher, expert in III-N materials, at CEA-Leti. “One of our challenges in the field of micro-displays is to grow three pixels (red, green and blue) on the same substrate with high quantum efficiency. We recently achieved blue and green pixels on the same substrate. We also achieved homogeneous active zones that emitted in the red range thanks to an innovative epitaxy approach that incorporates up to 45% In.”​

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Epitaxy to boost FD-SOI applications​

CEA-Leti is internationally recognizedfor its pioneering development of FDSOI technology on 300mm silicon wafers. One of the key elements behind the success of this technology is the creation of an optimized electrical conduction that reduces leakage currents. In order to achieve an efficient contact, researchers had to understand how to selectively thicken the source and drain regions of N-MOS transistors using in-situ doped silicon phosphorous (Si:P) through epitaxy.​

“The use of Si:P reduces the resistance of the junction and greatly enhances the intensity of the electrical current. In 2023, we significantly optimized the properties of Si:P material through epitaxy and were able to improve transistor performance by 50%!” highlights Joël Kanyandekwe, Epitaxy Research Engineer at CEA-Leti. “A new generation of low-temperature Si:P epitaxy is currently under development in our research laboratories in order to incorporate even more ionized phosphorous in the source and drain regions of interest.”​

In addition to work on N-MOS transistors, CEA-Leti researchers are innovating to improve the performance of P-MOS transistors. Instead of using Si:P, researchers are developing an epitaxy process that relies on boron-doped Silicon-Germanium (SiGe:B). This approach will ensure future generations of epitaxy processes are ready to meet the needs of FD-SOI 10nm technology.