High-speed observation of pulse energy and pulse width dependences of damage generation in SiC during ultrashort pulse l
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High‑speed observation of pulse energy and pulse width dependences of damage generation in SiC during ultrashort pulse laser drilling Junya Hattori1 · Yusuke Ito1 · Hiroshi Jo1 · Keisuke Nagato1 · Naohiko Sugita1 Received: 4 July 2020 / Accepted: 24 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Ultrashort pulse laser processing is a potential method for microfabricating silicon carbide (SiC). However, it is difficult to precisely process SiC using this method because numerous damages are generated around the processed region. Although various studies have investigated the optimal processing conditions, the effects of the conditions on the high-speed phenomena during processing and the effects of these phenomena on the processed shapes and generated damages remain largely unclear. In this study, we combine a high-speed camera with ultrashort laser probe pulses to visualize the phenomena driven by each pulse irradiation and investigate the pulse energy (50, 100, 200 μJ) and pulse width (180 fs, 1 ps, 10 ps) dependencies. The results clarify that for larger pulse energy, stronger stress waves propagate inside SiC, causing greater damages. In addition, we find that for a pulse width of 10 ps, thermal damage occurs near the hole entrance. The clarified effects of the processing conditions on the stress wave propagation, damage generation, and processed shapes will contribute significantly to developing methods for precision processing of SiC. Keywords Ultrashort pulse laser drilling · SiC · High-speed imaging · Damage generation
1 Introduction Silicon carbide (SiC) has the potential to be used in nextgeneration power semiconductor devices owing to its high dielectric breakdown field strength. To use SiC in applications, a microfabrication technique has to be established. However, it is difficult to microfabricate the material using conventional methods because of its mechanical and optical properties; mechanical machining is difficult to apply because of its high hardness, and laser processing with a long pulse width is not suitable owing to its wide bandgap. As a method for microfabricating wide-bandgap materials, ultrashort pulse laser processing has been attracting attention. Because the peak power of ultrashort pulse lasers is considerably high, the focused beam has extremely high intensity, which induces multiphoton absorption, thus enabling wide-bandgap materials to absorb light energy. Using this nonlinear optical property, microfabrication of SiC has been attempted [1–12]. However, during ultrashort pulse * Yusuke Ito [email protected]‑tokyo.ac.jp 1
Department of Mechanical Engineering, The University of Tokyo, Tokyo 113‑8656, Japan
laser processing of SiC, significant damages are generated around the processed region; therefore, precision processing is inhibited [2, 5, 11]. Many experimental studies have been conducted to determine the optimal processing conditions for precision processing [4, 8, 12–15]. However, these studies discuss the changes in the processed sha
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