Direct micro-structuring of Si(111) surfaces through nanosecond laser Bessel beams
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Direct micro‑structuring of Si(111) surfaces through nanosecond laser Bessel beams Erkan Demirci1 · Elif Turkan Aksit Kaya1 · Ramazan Sahin2 Received: 17 March 2020 / Accepted: 6 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We present a nanosecond laser ablation of Si(111) surfaces with diffraction-free (BesselJ0 ) beams. Experimental results compared with theoretical predictions show that Bessel beams give possibility of straightforward micro-structuring of Si(111). Only central spot could damage the surface provided that the laser pulse energy is in the energy range we confirmed in our experiments. Moreover, our results clearly indicate that reduced heat-affected zone area due to thermal expansion in ns pulse regime is natural outcome of Bessel beams as opposed to Gaussian beams. This method is open to be improved by using high-quality Gaussian beams ( M 2 ≈ 1 ) while the size of structures can be much reduced by using larger base angle of the Axicon (such as 𝛼 = 40◦). Keywords Bessel beam · Nanosecond laser · Si wafer · Ablation · Micro-structuring
1 Introduction The laser treatment of surfaces has attracted numerous attentions not only from the research community [1] but also from the industry applications [2] due to its ability of contactless structuring of the target surfaces. In addition, this method does not require any chemical pre-treatment [3]. However, both resolution and quality of generated structures depend on the pulse duration. Although there are many different types of lasers to be involved in laser ablation processes (such as high-power continuous lasers and pulsed or ultrashort pulsed lasers), ultra-short pulsed lasers provide better aspect ratio profiles while resulting in minimal side effects during micro-structuring of surfaces [4–8]. It is generally assumed that there are two different ablation mechanisms for these lasers addressed in the literature. When the pulse duration of laser source is similar to heat diffusion time, the thermal ablation regime occurs as the material is locally heated by laser as its local temperature increases until this melts and vaporizes [9–11]. On the other hand, a very hot * Ramazan Sahin [email protected] 1
Informatics and Information Security Research Center, BILGEM, TUBITAK, 41470 Gebze, Turkey
Department of Physics, Akdeniz University, 07058 Antalya, Turkey
2
plasma of electrons is created by the ultra-short pulsed laser source. When the energy of this hot plasma reaches to a level enough to break molecular bonding, material removal takes place through a direct sublimation process. Because of the short interaction time, a minimal thermal damage occurs [12–14]. Patterned silicon (Si) surfaces are very popular for electronic and photonic applications [15–17]. In addition, the quality of devices and their response to optical or electrical excitations are directly based on the quality of the fabricated structures [18–21]. Although ultrafast lasers (femtosecond or picosecond) yield straightforward micro-structuring
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