10 April 1995 Femtosecond-pulse laser processing of metallic and semiconducting thin films
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Abstract
Femtosecond-pulse laser processing in the visible spectral range ((tau) approximately equals 300 fs; 615 nm) allows precise microstructuring of metallic and semiconducting thin films on metal and glass substrates without disruption and delamination of the remnant material. Laser light couples into geometrical surface defects differently than into homogeneous surface regions. The heat affected zone (HAZ) is not controlled by the laser pulse duration, when (tau) < 0.5 ps, but by the electron-phonon relaxation time (tau) e approximately equals 0.5-1 ps. A model is proposed which allows to calculate the ablation threshold fluence for the application of ultra-short laser pulses. Experimental results for the ablation of platinum and amorphous silicon thin films on gold and glass substrates are presented. Visible femtosecond-laser pulses can ablate metal films by a one-photon mechanism, and the indirect semiconductor silicon due to a nonlinear process. In the latter case, self-induced multiphoton absorption limits the laser interaction with the target to a small volume. Laser structuring of silicon thin films on glass substrates is supported by a intrinsic etch stop because the ablation threshold of glass (Fth approximately equals 1.2 J cm-2) is greater than that of the amorphous silicon film (Fth approximately equals 0.2 J cm-2). Barium borosilicate glass starts ablating by visible femtosecond-laser pulses after several incubation pulses which generate sufficient defects for efficient light coupling.
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Joerg Krueger, Joerg Krueger, Wolfgang Kautek, Wolfgang Kautek, } "Femtosecond-pulse laser processing of metallic and semiconducting thin films", Proc. SPIE 2403, Laser-Induced Thin Film Processing, (10 April 1995); doi: 10.1117/12.206276; https://doi.org/10.1117/12.206276
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