Efficient Picosecond-Laser Lift-Off of Copper Oxide from Copper: Modelling and Experiment

TL;DR

This paper develops a theoretical model for optimizing laser lift-off processes, specifically demonstrating that maximum lift-off area occurs at a lower fluence than traditional ablation, validated through experiments on copper oxide.

Contribution

The authors introduce a new theoretical framework for laser lift-off, deriving closed-form expressions for optimal parameters, and validate it with experiments on copper oxide from copper.

Findings

Maximum lift-off area at fluence e times lower than ablation threshold.

Derived formulas for optimal beam radius, focus, and maximum lift-off area.

Experimental validation shows excellent agreement with the model.

Abstract

Laser-induced lift-off of functional surface layers is a key process in micro- and nano-fabrication; however, optimization criteria for maximizing the lifted-off area remain insufficiently defined. In analogy to the well-established theory of efficient laser ablation, where the maximum ablated volume per pulse is achieved at a peak fluence of F_0^{\mathrm{opt}} = e^{2} F_{\mathrm{th}}, we develop a theoretical framework for efficient laser lift-off driven by Gaussian beams. By analytically describing the lift-off area as a function of peak fluence, beam radius, and focus position, we demonstrate that the maximum lifted-off area is achieved at a substantially lower optimal fluence, namely F_0^{\mathrm{opt}} = e^{1} F_{\mathrm{th}}. Closed-form expressions for the optimal beam radius, maximal lift-off area, and optimal focus position are derived and validated by numerical modeling. The theory is applied to picosecond laser lift-off of copper oxide from copper, showing excellent agreement between experimental observations and model predictions. The results reveal fundamental differences between ablation- and lift-off-dominated material removal and provide practical guidelines for maximizing process efficiency in laser-assisted delamination, selective coating removal, and surface functionalization.