Essential cogs in our digitized economies and the development of new technologies, semiconductors and their manufacturing methods are at the heart of a global strategic battle.
A team from the Lasers, Plasmas and Photonic Processes laboratory has developed a three-dimensional laser writing technology inside silicon chips. Published in
Nature Communications, their approach exploits microplasmas to achieve unprecedented resolution and could transform the design of integrated circuits.
3D Eiffel Tower engraved beneath the surface of a silicon wafer with a precision only accessible by plasma etching. Observations are made by transmission lateral and dark-field infrared microscopy (top view). The structure is designed from engraved voxels, spaced 2 µm (about 0.00008 inches) apart. Scale: 20 µm.
© Wang, A., Das, A., Fedorov, V.Y. et al. Three-dimensional laser writing with ultrashort pulses has already transformed many manufacturing technologies like microelectronics or quantum photonics. It allows structuring the interior of transparent materials like glass to create miniaturized optical components and precise microstructures without thermal damage. However, this technique is rarely used for the fabrication of semiconductors like silicon, due to constraining optical properties. Its high refractive index and strong non-linearities prevent sufficiently localizing the light energy to write precisely.
The team of Andong Wang and David Grojo, from the Lasers, Plasmas and Photonic Processes laboratory (
LP3, Aix-Marseille University/CNRS), has developed a solution inspired by plasma optics. The concept relies on synchronized double ionization. The first pulse, one femtosecond, in silicon generates the microplasma (pre-ionization). The second, slower pulse then deposits the energy necessary to modify the material. The microplasma acts as a guide by concentrating the energy deposition on its wavefront. To validate their approach, the scientists managed to "write" an Eiffel Tower less than 200 micrometres (about 0.008 inches) tall, a few micrometres beneath the surface of a silicon wafer.
The work showed a very relevant resolution for this technique, but also the presence, in the modified zones, of amorphous domains of silicon. This local amorphization, long sought by the industry, opens the possibility of refractive index engineering for integrated photonics (to control light propagation). Furthermore, this research also demonstrated the reversibility of the process. The modifications made to the materials can be erased locally by new laser irradiation, and this up to more than 100 writing and erasing cycles on the same substrate. This capability allowed creating QR codes inside silicon wafers, written, erased, and rewritten in the same location. Among the potential applications: unforgeable marking and traceability in the semiconductor industry.
The fabrication of reconfigurable devices is a long-term goal for quantum photonics. The technology developed by the LP3 team offers an alternative to current solutions based on thermal or electromechanical stimulation. It could also be extended to other semiconductor materials besides silicon. The researchers have patented their approach and are considering transforming the way integrated circuits are designed. A strategic challenge in a global market valued at over 600 billion dollars in 2024, and still largely under Asian dominance.