Laser lift-off initiated by direct induced ablation of different metal thin films with ultra-short laser pulses

Abstract

Molybdenum thin films on glass substrates play an important role as contact layer for thin film solar cells. They can be ablated by picosecond laser pulses irradiated from the substrate side at low laser fluences of less than 1 J cm−2, while structured trenches remain free from thermal damage and residues. The fluence for that so-called direct induced ablation from the substrate side is in contrast to metal side ablation reduced by approximately one order of magnitude and is far below the thermodynamic limit for heating, melting and evaporating the complete layer. For an extended investigation of the direct induced laser ablation and the underlying mechanism, further thin film materials, chromium, titanium and platinum, with thicknesses between 200 nm and 1 µm were examined. Finally, a simple thermo-dynamical model is able to connect the observed ablation energetics with the mechanical ductility and stress limit of the metal thin films.

Impact of scribe width reduction on the back-contact insulation process for the series connection of thin-film silicon solar cells

“…One additional parameter is the so-called onset peak fluence F p;on ¼ 2E p;on =px 0 2 [22,23]. This value marks the onset for proper ablation from the substrate side.…”

Atomistic Simulation Study of Short Pulse Laser-Induced Generation of Crystal Defects in Metal Targets

“…The effect of spatial confinement on laser-induced structural and phase transformation in [215,216,218], laser-induced forward transfer [219][220][221], thin film patterning/scribing [222,223], and the generation of highquality surface structures [57,239].…”

“…The physical understanding of the effect of the spatial confinement on laser-induced processes is largely based on the results of theoretical analysis of the evolution of pressure generated under conditions of spatially-confined laser ablation [216,223] and continuum-level modeling of thermo-elastic deformation of metal films irradiated through transparent substrates [218,226,227]. These studies have recently been complemented by atomistic molecular dynamics (MD) simulations of short pulse laser interactions with bulk metal substrate covered by a transparent overlayer [56].…”

“…The spatial confinement is realized when a metal target (a film or a bulk substrate) is covered by a transparent overlayer and the laser irradiation is focused on the metal surface through the overlayer. This setup has been shown to be advantageous for a number of practical applications, from laser shock peening [215][216][217][218] to laser-induced forward transfer [219][220][221] and thin film patterning/scribing, [222,223] and to the generation of high-quality surface nanostructures [57]. In particular, a substantial increase in pressure generated in laser ablation confined by a glass overlayer [215,216,224] has been utilized in material processing by laser-induced shock waves [215][216][217][218] and has enabled design of "exotic targets" with enhanced momentum transfer for laser propulsion applications [225].…”

“…The analytical description and computer modeling of laser-induced processes under conditions of spatial confinement have been largely focused on thermodynamic analysis of the evolution of pressure exerted on the metal target by the vapor/plasma plume expansion and evaluation of the momentum transfer to the irradiated target [216,[223][224][225]. In several recent numerical simulations of thin film removal by backside femtosecond pulse irradiation through a transparent substrate, the dynamics of the relaxation of thermo-elastic stresses and the mechanical deformation of the metal film are considered [218,226,227] and found to play the dominant role in the separation and ejection of the film fragments at laser fluences close to the ablation threshold [226].…”