Recently, Margaux Chanal, a scientist from France, Qatar, Russia and Greece, published a paper entitled Crossing the threshold of ultrafast laser writing in bulk silicon in the latest issue of Nature Communications. In previous attempts to write ultra-fast lasers in silicon, femtosecond lasers have made breakthroughs in the structural inability to process bulk silicon. The use of extreme NA values allows laser pulses to achieve sufficient ionization to destroy chemical bonds in silicon, leading to permanent structural changes in silicon materials.
Since the late 1990s, researchers have been writing ultrashort pulses of femtosecond lasers into bulk materials with wide bandgap, which are usually insulators. But up to now, for materials with narrow bandgap, such as silicon and other semiconductor materials, precise ultra-fast laser writing can not be achieved. People have been working to create more conditions for the application of 3D laser writing in Silicon Photonics and the study of new physical phenomena in semiconductors, so as to expand the huge market of silicon applications.
In this experiment, scientists found that even if femtosecond lasers increase the laser energy to the maximum pulse intensity technically, the bulk silicon can not be processed structurally. However, when femtosecond lasers are replaced by ultrafast lasers, there is no physical limitation in the operation of inductor silicon structures. They also found that laser energy must be transmitted in a fast way in the medium in order to minimize the loss of non-linear absorption. The problems encountered in previous work originated from the small numerical aperture (NA) of the laser, which is the angle range in which the laser can be projected when it is transmitted and focused. The researchers solved the problem of numerical aperture by using silicon sphere as solid immersion medium. When the laser is focused at the center of the sphere, the refraction of the silicon sphere is completely suppressed and the numerical aperture is greatly increased, thus solving the problem of silicon photon writing.
In fact, in silicon photonics applications, 3D laser writing may greatly change the design and fabrication methods in the field of silicon photonics. Silicon photonics is regarded as the next revolution of microelectronics, affecting the final data processing speed of laser at chip level. The development of 3D laser writing technology opens the door to a new world for microelectronics.