  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.
