A group from the University of Science and Technology of China (USTC), under the direction of Prof. Haiding Sun, created a vertically integrated micro-scale light-emitting diode (micro-LED) array in a study that was published in Laser & Photonics Reviews. This array was used for the first time in a deep ultraviolet (DUV) maskless photolithography system.
Schematic diagram of self-stabilizing luminescence system built with vertically integrated devices. Image Credit: Images by Prof. Sun’s team
Photolithography is essential to producing integrated circuit chips, one of the fundamental technologies in the semiconductor and microelectronics industries. Since the 1990s, the low-cost, high-resolution maskless photolithography system has been a hotspot in advanced lithography research. However, there are major technological barriers because the United States, Japan, South Korea, and Europe hold most of the patents for this cutting-edge technology.
In this context, Prof. Sun's iGaN team has conducted extensive research on DUV micro-LEDs over the years and has proposed a novel maskless photolithography system that uses a DUV micro-LED array as a light source.
They carefully designed and optimized the DUV micro-LED’s epitaxial structure, device dimensions, sidewall profile, and geometric shape, significantly increasing its power efficiency, modulation bandwidth, and multifunctionality in UV light detection, imaging, and sensing. Building on this, the team successfully created an array system using these DUV micro-LEDs.
In this study, the team proposed and built a DUV display integrated chip that takes advantage of DUV micro-LED’s ultra-small size and ultra-high brightness. They proposed a three-dimensional vertically integrated device architecture that includes an AlGaN-based DUV micro-LED array and a zinc oxide (ZnO)-based photodetector (PD) connected via a transparent sapphire substrate.
UV photons emitted by the DUV micro-LED array can pass through the transparent sapphire substrate and be captured by the PD on the backside, allowing for efficient optical signal transmission.
Using the vertically integrated device, the team also created a self-stabilizing luminescence system with closed-loop feedback control. This system can monitor fluctuations in the output light intensity of the micro-LED array while also providing continuous feedback to ensure stable output power.
Using the vertically integrated device, the researchers developed a self-stabilizing luminescence system with closed-loop feedback control. This system can detect fluctuations in the output light intensity of the micro-LED array while also providing continuous feedback to ensure consistent output power.
Following the maskless DUV photolithography, the team successfully displayed a distinct pattern on a silicon wafer and demonstrated a DUV micro-LED array with a high pixel density of 564 pixels-per-inch (PPI) using the feedback system, suggesting potential in high-resolution photolithography technology. This is the first time that DUV maskless photolithography using a DUV micro-LED active matrix has been demonstrated.
This study created a unique integrated device that combines PD and a DUV micro-LED array, demonstrating important potential uses for upcoming maskless photolithography systems. Additionally, it establishes the groundwork for the subsequent advancement of multifunctional and highly integrated 3D optoelectronic integration systems.
To increase the density and integration of arrays per unit area, the team will concentrate on further shrinking the size of individual micro-LEDs and PDs in the upcoming phase. Additionally, they will improve the efficiency of individual devices and the consistency of large wafers, opening the door for more precise maskless photolithography technology.
Journal Reference:
Yu, H. et. al. (2024) Vertically Integrated Self-Monitoring AlGaN-Based Deep Ultraviolet Micro-LED Array with Photodetector Via a Transparent Sapphire Substrate Toward Stable and Compact Maskless Photolithography Application. Laser & Photonics Reviews. doi.org/10.1002/lpor.202401220