Huabin Yu, Jikai Yao, Muhammad Hunain Memon, Yuanmin Luo, Zhixiang Gao, Dongyang Luo, Rui Wang, Zixun Wang, Wei Chen, Linjun Wang, Shuiqing Li, Jinjian Zheng, Jiangyong Zhang, Sheng Liu, Haiding Sun
First published: 26 September 2024
DOI:10.1002/lpor.202401220
Abstract
Drawing inspiration from modern integrated circuit systems composed of various electronic components built on a single silicon platform, the emerging integrated photonics can also follow a similar trend in the pursuit of expanded optical functionalities in constructing compact optoelectronic systems. Herein, vertically integrated a micro-scale light-emitting diode (micro-LED) array with a photodetector (PD) side-by-side through a transparent sapphire substrate is proposed. The downward emitted photons from the micro-LEDs can easily transmit through the transparent sapphire and then be captured by the PD fabricated on the backside of the sapphire. Additionally, by integrating a feedback electrical circuit, a self-stabilized light output power is demonstrated from the micro-LED array in such vertically integrated LED/PD architecture, which cannot only monitor the fluctuation of light intensity from the micro-LED array over time but also provide a constant output feedback to ensure a stable light output power. Such a compact and stable DUV light source composed of micro-LED array is then employed for constructing a DUV maskless photolithography system. To best of our knowledge, this is the first demonstration of maskless photolithography based on DUV micro-LED active matrix. The proposed vertically-stacked optical device architecture by leveraging the transparent substrate offers a new path toward the realization of future integrated photonic systems.
Introduction to the Innovative Technology
Recently, Professor Sun Haiding‘s iGaN laboratory at the University of Science and Technology of China has developed a three-dimensional vertically integrated deep ultraviolet (UV) light-emitting device array. This device features self-monitoring, self-calibrating, and adaptive capabilities, achieved by fabricating micro-LED arrays and photodetectors on either side of a transparent sapphire substrate. This groundbreaking research proposes using deep UV micro-LED arrays as a light source in maskless deep UV photolithography technology for the first time. By leveraging the high energy density, high resolution, high integration, and low energy consumption of each micro-LED, this technology offers a new pathway for achieving high-precision deep UV lithography.
The research, titled “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,” was published in Laser & Photonics Reviews. Various funding programssupported this work, including the National Key Research and Development Program, the National Natural Science Foundation, and research grants from the University of Science and Technology of China.
The Importance of Photolithography in Semiconductor Manufacturing
Photolithography plays a vital role in the manufacturing process of integrated circuit chips and is one of the key core technologies of modern semiconductor, microelectronics, and information industries. Compared with the high cost and complex system structure of traditional photolithography machines, low-cost, high-resolution maskless photolithography has become one of the frontier hotspots of photolithography research since the 1990s. However, the related technical patents that have been developed are mainly concentrated in Europe, the United States, Japan, South Korea, and other countries, and the technical barriers are relatively high. In this context, Professor Sun Haiding’s iGaN team innovatively proposed and implemented a maskless deep ultraviolet photolithography technology based on deep ultraviolet micro-LED arrays as light sources. Through years of research and accumulation in ultraviolet micro-LEDs, the team has systematically designed and optimized the epitaxial structure [Optics Letters 47: 4187, 2022], device size [Optics Letters, 46: 3271, 2021], sidewall morphology [Optics Letters, 46: 4809, 2021] and geometric shape [IEEE Electron Device Letters 44: 1520, 2024] of deep ultraviolet micro-LEDs, greatly improving the luminous efficiency, luminous power, modulation bandwidth of each microLED, as well as their versatility and superior chip performance in day-blind ultraviolet light detection, imaging and sensing, and successfully constructed an array system based on deep ultraviolet micro-LEDs [Journal of Semiconductors 43: 062801, 2022; IEEE Electron Device Letters 44: 472, 2023]. Furthermore, by constructing an on-chip optoelectronic integrated chip that integrates light emission and detection, the application of on-chip and inter-chip optical communication systems has been realized [Laser & Photonics Reviews, 18: 2300789, 2024; Advanced Optical Materials, 2400499, 2024].
Systematic Design and Optimization of Micro-LEDs
In this study, the team took advantage of the ultra-small size, high light energy density, long life, and low power consumption of deep ultraviolet micro-LEDs, and further developed a deep ultraviolet display optoelectronic integrated chip that integrates self-monitoring, self-calibration, and adaptive functions, and applied it to a maskless deep ultraviolet lithography system, realizing the international exploration of maskless lithography technology using this new ultraviolet light source. Based on the research on the pursuit of high-efficiency, small-size deep ultraviolet micro-LEDs and their arrays, the team proposed a three-dimensional vertical integrated chip architecture that integrates deep ultraviolet micro-LED array light emission and photodetectors, as shown in Figure 1 (a)-(b). In this three-dimensional vertical integration architecture, the UV photons emitted downward by the deep ultraviolet micro-LED array can penetrate through the transparent sapphire substrate and be captured by the UV detector on the back of the substrate to achieve “photon interconnection and integration” between the LED and the detector, thereby achieving efficient optical signal transmission. In addition, by building an external circuit feedback system, as shown in Figure 1 (c), the team demonstrated the spontaneous stabilization and automatic calibration of the light output energy density of the deep ultraviolet micro-LED array. Ultimately, the system can not only monitor the fluctuations in the light output energy density of the array device over time but also continuously provide feedback signals to ensure constant light output power and light power density, which provides a light source foundation for the ultimate realization of compact, portable and low-cost maskless deep ultraviolet lithography technology.
As shown in Figure 2 (a), based on the constructed circuit feedback system, it can be observed that the luminous intensity of the deep ultraviolet micro-LED array without system feedback gradually decreases over time; on the other hand, the device with self-monitoring and self-calibration feedback function still maintains a high luminous intensity and can achieve long-term stable operation. At the same time, based on the feedback system, an integrated deep ultraviolet micro-LED array with a high pixel density of 564 PPI was demonstrated. The letter “U” was continuously and stably displayed using the integrated array, and the silicon wafer spin-coated with SPR955 photoresist was exposed to a deep ultraviolet maskless lithography process. After development, a clear “U”-shaped pattern was successfully displayed on the silicon wafer, as shown in Figures 2 (b)-2 (d). As we all know, the current gallium nitride-based microLED technology has played an important role in the field of high-definition display, and this study further demonstrated their application potential in the field of high-resolution and high-precision lithography technology.
Future Directions and Applications
In addition, the study proposed a three-dimensional vertical integrated chip architecture that integrates deep ultraviolet micro-LED array light-emitting and photodetectors, realizing vertical optoelectronic integration of wide bandgap semiconductor aluminum gallium nitride (AlGaN)-based light-emitting array and photodetectors through transparent sapphire substrates, and demonstrated the possibility of vertical photonic interconnection on a single chip. This integrated system is not only conducive to overcoming the limitations of most traditional monolithic optoelectronic integrated systems that can only be optically interconnected and integrated into the horizontal direction or on the same crystal plane of the substrate (silicon, sapphire, etc.) but also with the help of this new light-emitting device array architecture with constant output power, it demonstrates its application potential in maskless lithography technology. It provides a new path for the future development of highly integrated and multifunctional three-dimensional optoelectronic integrated systems.
In the next step, the team will focus on how to further reduce the device size and geometric morphology of single micro-LEDs and detectors, improve the density and integration of device arrays per unit area, and optimize the single performance of devices and the uniformity of performance on large wafers, laying the foundation for the next step of realizing higher-precision maskless ultraviolet lithography technology. At the same time, the team’s proposal to cleverly use transparent sapphire substrates to construct a three-dimensional vertical integrated chip architecture that integrates light emission and detection also provides a new path and method for the development of highly integrated photonic chips, making it widely applicable to various application scenarios including three-dimensional integrated optoelectronic systems and maskless lithography.
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