Abstract
In this work, we demonstrate the importance of laser pulse overlap in controlling the ablation process of a thin film just above the single pulse material ablation threshold. A 532 nm, 15 ps ultrafast diode pump solid-state (DPSS) laser has been employed to pattern a gold alloy source–drain layer during the production of organic thin film transistor (OTFT) for flexible display applications. Maintaining the laser fluence constantly above and in proximity of the ablation threshold value, different process windows are identified by varying the pulse overlap. With less than four overlapping pulses per area, a debris-free removal process is achieved with almost no edge delamination. By increasing the number of pulses per area up to 20, edge delamination progressively grows stronger and eventually ablation terminates altogether. If the pulse overlap increases further, ablation starts again but with more evidence for thermal, cumulative irradiation effects. This behavior can be attributed to the progressive transition from initially a photomechanical stress-assisted ablation process, dominant at low pulse overlap to increasingly a more thermally driven removal process, at higher pulse overlaps.
Highlights
Ultrafast diode pump solid-state (DPSS) lasers present great potential for material functionalization when three-dimensional high precision and accuracy processing is needed
Such “cold” ablation regime makes ultrafast lasers an ideal tool for selective thin film patterning where material removal needs to be well controlled to typically few tens of nanometres only [5]
The role of spatial laser pulse overlap was studied by scribing straight lines and analyzing a matrix of incident laser fluence F versus pulse overlap
Summary
Ultrafast DPSS lasers (ps and fs) present great potential for material functionalization when three-dimensional high precision and accuracy processing is needed. Ablation can be assisted by laser-induced photomechanical stress [3] In such a regime, ablation usually takes place at low temperature and material removal is energetically more efficient, compared to evaporative ablation, and any collateral damage inflicted to the material is greatly reduced [4]. When photomechanical stress-assisted ablation applies, strong delamination or even ablation termination was observed by increasing the pulse overlap Such effects must be taken into account in an industrial production environment because they can greatly influence the usual tradeoff between process speed and quality
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