A team led by Prof. SUN Haiding from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences developed a vertically integrated micro-scale light-emitting diode (micro-LED) array, which was then applied in deep ultraviolet (DUV) maskless photolithography system for the first time. The study was published in Laser & Photonics Reviews.

Photolithography plays a crucial role in the manufacture of integrated circuit chips and is one of the key core technologies in the semiconductor and microelectronics industries. Since the 1990s, low-cost, high-resolution maskless photolithography system has emerged as a hotspot in advanced lithography research.

Prof. SUN's team has conducted extensive research on DUV micro-LED over the years, and has proposed a maskless photolithography system using DUV micro-LED array as the light source. Based on the DUV micro-LED, the team developed an array system.

In this study, the researchers proposed and fabricated a DUV display integrated chip, leveraging the advantages of DUV micro-LED’s ultra-small size and ultra-high brightness. They proposed a three-dimensional vertically integrated device architecture with a AlGaN-based DUV micro-LED array and zinc oxide (ZnO)-based photodetector (PD) side-by-side via a transparent sapphire substrate. In this architecture, the UV photons emitted from the DUV micro-LED array can penetrate the transparent sapphire substrate and be captured by the PD on the backside of the substrate, enabling efficient optical signal transmission.

Furthermore, the researchers developed a self-stabilizing luminescence system with a closed-loop feedback control based on the vertically integrated device. This system can not only monitor fluctuations of the output light intensity of the micro-LED array, but also provide continuous feedback to ensure stable output power. Test results showed that the device with self-stabilizing system maintains high light intensity and long-term stability while the light intensity of the device without feedback gradually decreased over time.

Using the feedback system, the researchers demonstrated a DUV micro-LED array with a high pixel density of 564 pixels-per-inch (PPI) and successfully displayed a clear pattern on a silicon wafer after the maskless DUV photolithography, showing the potential in high-resolution photolithography technology. This is the first demonstration of DUV maskless photolithography based on a DUV micro-LED active matrix.

This study lays the foundation for the development of highly integrated and multifunctional three-dimensional optoelectronic integration systems. In the next phase, the team will focus on reducing the size of individual micro-LED and PD, thereby increasing the density and integration of arrays per unit area, and will also optimize the performance of individual devices and the uniformity across large wafers, paving the way for higher precision in maskless photolithography technology.