Gwangju, South Korea – As the artificial intelligence (AI) era accelerates, the demand for highly integrated, high-performance semiconductor packaging is skyrocketing. Glass substrates have emerged as the "dream material" for next-generation advanced packaging due to their superior thermal, electrical, and dimensional properties compared to conventional organic substrates. However, fabricating 3D interconnected electrodes—such as Through-Glass Vias (TGV) and Redistribution Layers (RDL)—on complex 3D glass structures remains a critical bottleneck, as traditional 2D lithography requires extensive, multi-step masking and etching processes.
Now, a global joint research team has elegantly solved this challenge. Led by Prof. Seunghwoi Han at Chonnam National University and Prof. Young-Jin Kim at KAIST, in collaboration with researchers from KIMM, KITECH, and Texas A&M University, the team has successfully developed a novel 3D direct-write patterning technology.
Published in the world-renowned optics journal PhotoniX (IF: 19.1), the researchers introduced Ultrafast Laser Chemical Vapor Deposition (ULCVD). By utilizing a 1040 nm femtosecond laser, the team demonstrated the maskless patterning of highly crystalline, conductive carbon circuits on various transparent glass substrate (quartz). The key differentiation of this technique is its true "All-Surface" capability; by simply shifting the optical focal point, circuits can be seamlessly drawn on the front, rear, inside through-holes, and highly curved 3D surfaces of the glass.
The secret lies in the nonlinear multi-photon absorption triggered by the femtosecond laser. "Unlike conventional continuous-wave lasers that suffer from extensive thermal diffusion and parasitic soot deposition, our femtosecond laser approach creates a remarkably steep temperature gradient with an in-situ thermal annealing effect," explained Prof. Seunghwoi Han. "This allows us to achieve perfectly clean, highly graphitic circuitry that rivals the electrical conductivity of the highest-performing laser-induced graphene (LIG) reported to date."
To demonstrate its immense potential and real-world applicability, the team successfully fabricated a photothermal carbon heater on the surface of a 3D cuboidal atomic vapor cell. This conceptual demonstration of non-contact heating provides a fundamental solution for magnetic-noise-free operation, which is highly critical for advanced quantum sensors.
Looking ahead, the researchers are setting their sights on the ultimate goal of semiconductor metallization. "By overcoming the limitations of conventional 2D lithography, we have secured a fundamental technology for 3D spatial wiring," Prof. Han added. "Our next step is to expand this ULCVD process beyond carbon to pattern essential packaging metals such as copper (Cu) and gold (Au). We believe this will be a driving force in securing a competitive edge in the global advanced semiconductor packaging supply chain."
