Laser-induced gas plasma etching of fused silica under ambient conditions

Elhadj, Selim; Guss, Gabe; Matthews, Manyalibo J.; Bass, Isaac L.

doi:10.1117/12.979814

Cited by 4 publications

(2 citation statements)

References 17 publications

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“…An interesting application of a nanosecond (ns) laserinduced plasma in N 2 and ambient air near SiO 2 surface was reported by Elhadj et al [11] where some interaction between the laser produced plasma and surface was witnessed. In concomitance, material removal due to melting and evaporation was found.…”

Section: Introductionmentioning

confidence: 99%

Dynamics and 2D temperature distribution of plasma obtained by femtosecond laser-induced breakdown

Hossain¹,

Ehrhardt²,

Rudolph³

et al. 2021

J. Phys. D: Appl. Phys.

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Recently, plasma produced by focusing femtosecond laser in gases has been introduced as an etching tool in materials processing. Proper control of the plasma in this application necessitates the apt understanding of the different morphological features of the plasma. In this contribution we show that, the plasma produced in air goes through several stages of morphological development – from ellipsoidal to spherical to toroidal plasma, whereas in argon, axial compression of an ellipsoidal plasma is observed. To explain this dissimilarity, we have quantified the temperature by emission spectroscopy (Planck analysis with Wien’s approximation). The evolution of temperature shows a triple exponential dependence in time which can be correlated with different stages of morphological changes of the plasma. Open Source Field Operation and Manipulation (OpenFOAM) simulations using experimentally determined temperature values show that – (i) the reverse pressure gradient propagates radially inwards and compresses the plasma in both air and argon and forms a localized high pressure zone at the center that generates a secondary pressure wave in air, but not in argon, and (ii) the baroclinic torque that is generated because of the Richtmyer-Meshkov instability, dominates the rate of vorticity in air, whereas effects of flow compressibility and velocity gradients dominate the vortices in argon. Knowledge of the initial state and the dynamics of the subsequent stages of the plasma formation can be utilized for control and optimization of laser-induced plasma applications.

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Section: Introductionmentioning

confidence: 99%

Dynamics and 2D temperature distribution of plasma obtained by femtosecond laser-induced breakdown

Hossain¹,

Ehrhardt²,

Rudolph³

et al. 2021

J. Phys. D: Appl. Phys.

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show abstract

“…Currently, laser-plasma in gases is mainly used for analytic applications such as laser-induced breakdown spectroscopy (LIBS) [21]. Elhadj et al [22] used a nanosecond laser (ND:YAG, λ = 355 nm, t = 7.5 ns, f = 10 Hz) to generate plasma in ambient air or an N 2 stream. The laser-plasma was brought into close proximity of a SiO 2 surface to etch the SiO 2 with the laserinduced plasma.…”

Section: Introductionmentioning

confidence: 99%

Laser-induced reactive microplasma for etching of fused silica

et al. 2020

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The ultra-precise machining (UPM) of surfaces with contact-free, beam-based technologies enables the development of flexible and reliable fabrication methods by non-vacuum processes for future application in advanced industrial fields. Laser machining by laser ablation features limitations for ultra-precise machining due to the depth precision, the surface morphology, and laser-induced defect formation. Contrary to physically-based etching, chemical-based dry and wet processing offer high quality, low damage material removal. In order to take advantage of both principles, a combined laser-plasma process is introduced. Ultra-short laser pulses are used to induce a free-standing microplasma in a CF4 gas atmosphere due to an optical breakdown. CF4 gas, with a pressure of 800–900 mbar, is ionized only near the focal point and reactive species are generated therein. Reactive species of the laser-induced microplasma can interact with the surface atoms of the target material forming volatile products. The release of these products is enhanced by the pulsed, laser-induced plasma resulting in material etching. In the present study, SiO2 surfaces were etched with reactive species of CF4 microplasma generated by their laser-induced break down with 775 nm pulses of an fs-laser (150 fs) at a repetition rate of 1 kHz. The dependency of the depth, the width, and the morphology of the etching pits were analysed systematically against the process parameters used. In particular, a linear increase of the etching depth up to 10 µm was achieved. The etched surface appears smooth without visible cracks, defects, or LIPSS (Laser-induced periodic surface structures).

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Dry Etching of Germanium with Laser Induced Reactive Micro Plasma

Ehrhardt

Lorenz

Bauer

et al. 2021

Lasers Manuf. Mater. Process.

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High-quality, ultra-precise processing of surfaces is of high importance for high-tech industry and requires a good depth control of processing, a low roughness of the machined surface and as little as possible surface and subsurface damage but cannot be realized by laser ablation processes. Contrary, electron/ion beam, plasma processes and dry etching are utilized in microelectronics, optics and photonics. Here, we have demonstrated a laser-induced plasma (LIP) etching of single crystalline germanium by an optically pumped reactive plasma, resulting in high quality etching. A Ti:Sapphire laser (λ = 775 nm, EPulse/max. = 1 mJ, t = 150 fs, frep. = 1 kHz) has been used, after focusing with a 60 mm lens, for igniting a temporary plasma in a CF4/O2 gas at near atmospheric pressure. Typical etching rate of approximately ~ 100 nm / min and a surface roughness of less than 11 nm rms were found. The etching results were studied in dependence on laser pulse energy, etching time, and plasma – surface distance. The mechanism of the etching process is expected to be of chemical nature by the formation of volatile products from the chemical reaction of laser plasma activated species with the germanium surface. This proposed laser etching process can provide new processing capabilities of materials for ultra—high precision laser machining of semiconducting materials as can applied for infrared optics machining.

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Laser-induced gas plasma etching of fused silica under ambient conditions

Cited by 4 publications

References 17 publications

Dynamics and 2D temperature distribution of plasma obtained by femtosecond laser-induced breakdown

Dynamics and 2D temperature distribution of plasma obtained by femtosecond laser-induced breakdown

Laser-induced reactive microplasma for etching of fused silica

Dry Etching of Germanium with Laser Induced Reactive Micro Plasma

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