Researchers at Bilkent University have developed a groundbreaking technique for creating tiny structures deep inside silicon, the key material in electronics, solar panels, and photonics.
Previously, making such small structures inside silicon was very difficult due to the limitations of current methods, which either couldn’t penetrate the surface without causing damage or were restricted by the resolution of laser lithography.
Inspired by Richard Feynman’s idea that “There’s plenty of room at the bottom,” this new method allows scientists to manipulate matter at an incredibly small scale.
The innovative technique surpasses these limitations, enabling the controlled creation of nanostructures buried deep within silicon wafers.
The research, published in Nature Communications, addresses two main challenges: the complex optical effects within the wafer and the natural limit of laser light’s resolution.
The team overcame these obstacles by using a special type of laser pulse created through spatial light modulation.
This laser pulse, which doesn’t spread out as it travels, overcomes optical scattering effects that previously hindered precise energy placement, creating extremely small, localized voids inside the wafer.
The process starts with forming small voids inside the silicon, which then act as seeds for further nanostructure creation. This new approach is ten times better than current methods, achieving feature sizes as small as 100 nanometers.
“Our technique focuses the laser’s energy into a very small volume within the silicon, exploiting field enhancement effects similar to those in plasmonics.
This allows us to create nanostructures with sub-wavelength precision directly inside the material,” explained Prof. Tokel. “We can now fabricate nanophotonic elements buried in silicon, such as high-efficiency nanogratings with spectral control.”
The researchers used spatially-modulated laser pulses, technically known as Bessel beams, created with advanced holographic projection techniques. These special beams enable precise energy localization, leading to high temperatures and pressures that can modify the material in a small volume.
Once the initial field enhancement is established, it sustains itself through a seeding mechanism. Essentially, the creation of earlier nanostructures helps in fabricating later ones.
By adjusting the laser’s polarization, the team could control the alignment and symmetry of the nanostructures, creating diverse nano-arrays with high precision.
“By using the anisotropic feedback mechanism in the laser-material interaction system, we achieved polarization-controlled nanolithography in silicon,” said Dr. Asgari Sabet, the study’s first author. “This capability allows us to guide the alignment and symmetry of the nanostructures at the nanoscale.”
The research team demonstrated large-area volumetric nanostructuring with features smaller than the diffraction limit, creating proof-of-concept buried nano-photonic elements. These advancements have significant implications for developing nano-scale systems with unique architectures.
“We believe this new design freedom in silicon, one of the most important technological materials, will lead to exciting applications in electronics and photonics,” said Tokel.
“The ability to create features beyond the diffraction limit and control them in multiple dimensions suggests future advancements, such as metasurfaces, metamaterials, photonic crystals, numerous information processing applications, and even 3D integrated electronic-photonic systems.”
Prof. Tokel concluded, “Our findings introduce a new way to fabricate silicon at the nano-scale, opening up possibilities for further integration and advanced photonics. We can now start exploring complete three-dimensional nano-fabrication in silicon. Our study is the first step in that direction.”
