In the realm of science and technology, the utilization of coherent light sources in the deep ultraviolet (DUV) region has far-reaching implications for various applications such as lithography, defect inspection, metrology, and spectroscopy. Traditionally, the significance of high-power 193-nanometer (nm) lasers in lithography cannot be overstated, playing a crucial role in systems designed for precise patterning. However, the limitations in coherence associated with conventional ArF excimer lasers have often hindered their effectiveness in applications requiring high-resolution patterns, like interference lithography.
The Genesis of the Hybrid ArF Excimer Laser
The introduction of the hybrid ArF excimer laser presents a groundbreaking solution to these challenges. By integrating a narrow linewidth solid-state 193-nm laser seed in place of the ArF oscillator, enhanced coherence alongside a narrow linewidth is achieved. This innovation not only enables improved performance in high-throughput interference lithography but also boosts pattern precision and accelerates lithography speed. Moreover, the heightened photon energy and coherence of the hybrid ArF excimer laser make it ideal for direct processing of various materials, including carbon compounds and solids, with minimal thermal impact. This versatility underscores its potential in a wide range of fields, from lithography to laser machining.
Optimizing Seeding for Enhanced Performance
To maximize the efficiency of an ArF amplifier, meticulous control of the linewidth of the 193-nm seed laser is crucial, ideally below 4 gigahertz (GHz). This specification determines the coherence length essential for interference, a key criterion that can be met through the utilization of solid-state laser technologies. A recent breakthrough by researchers at the Chinese Academy of Sciences has propelled this field forward. Their work, as reported in Advanced Photonics Nexus, showcases the achievement of a remarkable 60-milliwatt (mW) solid-state DUV laser at 193 nm with a narrow linewidth, utilizing a sophisticated two-stage sum frequency generation process employing LBO crystals.
The groundbreaking process involves pump lasers at 258 and 1553 nm, derived from a Yb-hybrid laser and an Er-doped fiber laser, respectively. Through a 2mm×2mm×30mm Yb:YAG bulk crystal for power scaling, impressive results have been demonstrated. The generated DUV laser, along with its 221-nm counterpart, boasts an average power of 60 mW, a pulse duration of 4.6 nanoseconds (ns), and a repetition rate of 6 kilohertz (kHz), with a linewidth of approximately 640 megahertz (MHz). This breakthrough marks the highest power output for both 193- and 221-nm lasers generated by an LBO crystal and the narrowest linewidth reported for a 193-nm laser. Notable achievements include outstanding conversion efficiency rates of 27% for 221 to 193 nm and 3% for 258 to 193 nm, setting new benchmarks in efficiency values.
This research not only highlights the immense potential of LBO crystals in generating DUV lasers at power levels ranging from hundreds of milliwatts to watts but also opens up avenues for exploring other DUV laser wavelengths. According to Prof. Hongwen Xuan, the corresponding author for the work, these advancements demonstrate “the viability of pumping LBO with solid-state lasers for reliable and effective generation of narrow-linewidth laser at 193 nm, and opens a new way to fabricate a cost-effective, high-power DUV laser system using LBO.” The impact of these advancements goes beyond just DUV laser technology, promising to revolutionize applications across scientific and industrial domains.
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