In the realm of science and technology, the utilization of coherent light sources in the deep ultraviolet (DUV) region has become increasingly vital across a wide range of applications. From lithography to defect inspection, metrology, and spectroscopy, the significance of DUV lasers cannot be overstated. Traditionally, high-power 193-nanometer (nm) lasers have played a crucial role in lithography, providing the precision required for intricate patterning. However, the coherence limitations associated with conventional ArF excimer lasers have posed challenges in applications necessitating high-resolution patterns, like interference lithography.

The Hybrid ArF Excimer Laser

One innovative solution to this issue is the development of the “hybrid ArF excimer laser.” By integrating a narrow linewidth solid-state 193-nm laser seed in place of the ArF oscillator, enhanced coherence and narrow linewidth can be achieved. This advancement not only improves the performance of high-throughput interference lithography but also accelerates lithography speed. The heightened photon energy and coherence of the hybrid ArF excimer laser also allow for the direct processing of various materials, including carbon compounds and solids, with minimal thermal impact. This versatility highlights its potential in a variety of fields, from lithography to laser machining.

To maximize the effectiveness of an ArF amplifier, the linewidth of the 193-nm seed laser must be precisely controlled, ideally below 4 gigahertz (GHz). This level of control is crucial for achieving the coherence length necessary for interference applications, a requirement that can be met through solid-state laser technologies. A recent breakthrough by researchers at the Chinese Academy of Sciences has pushed this field forward significantly. Their achievement of a 60-milliwatt (mW) solid-state DUV laser at 193 nm with a narrow linewidth using a two-stage sum frequency generation process involving LBO crystals is a testament to the progress being made in this area.

Achieving Impressive Results

The process, which utilizes pump lasers at 258 and 1553 nm from a Yb-hybrid laser and an Er-doped fiber laser, respectively, culminates in a 2mm×2mm×30mm Yb:YAG bulk crystal for power scaling. The resulting 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 achievement represents the highest power output for both 193- and 221-nm lasers generated by an LBO crystal, as well as the narrowest linewidth reported for a 193-nm laser.

The impressive conversion efficiency achieved by this research, with values of 27% for 221 to 193 nm and 3% for 258 to 193 nm, sets new benchmarks in efficiency. The study underscores the potential of LBO crystals in generating DUV lasers at power levels ranging from hundreds of milliwatts to watts, paving the way for exploring other DUV laser wavelengths. According to Prof. Hongwen Xuan, the corresponding author for the study, these advancements not only push the boundaries of DUV laser technology but also hold promise for revolutionizing applications across scientific and industrial domains.

The evolution of DUV laser technology, particularly through innovations like the hybrid ArF excimer laser and advancements in solid-state laser technologies, is poised to transform a range of industries. From lithography and metrology to laser machining and beyond, the impact of these developments is far-reaching. As research continues to push the boundaries of what is possible with DUV lasers, the future looks bright for the integration of coherent light sources in the deep ultraviolet region.

Physics

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