Selective Laser Ablation of Metal Thin Films Using Ultrashort Pulses
- PDF / 4,753,741 Bytes
- 12 Pages / 595.276 x 790.866 pts Page_size
- 34 Downloads / 216 Views
Online ISSN 2198-0810 Print ISSN 2288-6206
REGULAR PAPER
Selective Laser Ablation of Metal Thin Films Using Ultrashort Pulses Byunggi Kim1 · Han Ku Nam1 · Shotaro Watanabe2 · Sanguk Park1 · Yunseok Kim3 · Young‑Jin Kim1 · Kazuyoshi Fushinobu2 · Seung‑Woo Kim1 Received: 15 June 2020 / Revised: 6 September 2020 / Accepted: 14 September 2020 © Korean Society for Precision Engineering 2020
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. Keywords Selective thin film ablation · Electron-phonon coupling · Thin metal film · Laser ablation · Ultrashort pulse laser
1 Introduction Laser ablation is preferably used for clean machining of material without use of toxic chemicals, but special care is required to minimize thermal damage caused by excessive heat input. Ultrashort lasers of sub-picosecond pulse duration are now emerging as an enabling tool of micromachining with a potential of non-thermal ablation by ultrafast control of pulse energy and timing [1–4]. In view of microscopic heat transfer, the intense ultrashort light pulse is instantly absorbed by electrons in a picosecond timescale, provoking ultrafast electron-to-electron heat transfer
* Seung‑Woo Kim [email protected] 1
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak‑ro, Yuseong‑gu, Daejeon 34141, Republic of Korea
2
Department of Mechanical Engineering, Tokyo Institute of Technology, 2‑12‑1 Ookayama, Meguro‑ku, Tokyo 152‑8550, Japan
3
Lasernics Co., KAIST ICC, 193 Munji‑ro, Yuseong‑gu, Daejeon 34051, Republic of Korea
before a thermal equilibrium is reached between electrons and lattices of material. The ultrafast energy absorption by photoelectrons consequently reduces the heat affected zone by ablating material with extr
Data Loading...
