Selective laser ablation of metal thin films using ultrashort pulses

TL;DR

This paper introduces a novel ultrafast laser ablation technique using sub-picosecond pulses and a transition metal interlayer to selectively remove metal thin films with minimal substrate damage, advancing microfabrication precision.

Contribution

It demonstrates a new ultrafast laser ablation method that minimizes thermal damage through a transition metal interlayer and is validated both analytically and experimentally.

Findings

Selective removal of metal films achieved with sub-picosecond laser pulses.

Minimal thermal damage to substrates demonstrated.

Method validated through analytical modeling and experimental micropatterning.

Abstract

Selective thin-film removal is needed in many microfabrication processes such as 3-D patterning of optoelectronic devices and localized repairing of integrated circuits. Various wet or dry etching methods are available, but laser machining is a tool of green manufacturing as it can remove thin films by ablation without use of toxic chemicals. However, laser ablation causes thermal damage on neighboring patterns and underneath substrates, hindering its extensive use with high precision and integrity. Here, using ultrashort laser pulses of sub-picosecond duration, we demonstrate an ultrafast mechanism of laser ablation that leads to selective removal of a thin metal film with minimal damage on the substrate. The ultrafast laser ablation is accomplished with the insertion of a transition metal interlayer that offers high electron-phonon coupling to trigger vaporization in a picosecond timescale. This contained form of heat transfer permits lifting off the metal thin-film layer while blocking heat conduction to the substrate. Our ultrafast scheme of selective thin film removal is analytically validated using a two-temperature model of heat transfer between electrons and phonons in material. Further, experimental verification is made using 0.2 ps laser pulses by micropatterning metal films for various applications.