Advanced Manufacturing Laboratory    



Laser Micromachining and Laser Ablative Cleaning


Laser Micro- and Meso-Machinig

Laser micro- and meso-machining (meso refers to a few hundred microns to a few millimeters) are of interest especially for high-strength materials where mechanical methods are not strong enough while etching-based methods are too slow.  When the aspect ratio (depth vs. width) of the features to be machined is high, laser also provides an edge.  Most lasers used for micro- and meso-machining are Q-switched YAG lasers with nanosecond pulse width, especially its third harmonic, that is, 355 nm wavelength (UV), is in widespread use.  Ultra-short pulsed lasers with pico- and femto-second pulse have shown great promise in material processing but are not in widespread use.

UV laser micro- and meso-machining of metallic materials has been used in microelectronic, aircraft engine, and other industries.  Using the Q-Switch techniques, UV lasers (Excimer lasers and especially frequency-tripled Nd:YAG lasers) offer short pulse duration and high peak power, which limits heat affected zone and makes the material removal process dominated by ablation.  While material removal mechanism for polymers by such UV lasers have been well understood, more detailed modeling work is needed for metals to predict optimal process conditions for ablation dominance (in metals, melting cannot be entirely avoided but can be minimized and thus better finished) and to limit heat affected zone.  Models may use enthalpy method to track the solid/liquid interface, Stefan and kinetic boundary conditions be applied at the liquid-vapor interface, property discontinuity across the Knudsen layer be considered, and relevant experimental work be carried out to validate the modeling effort and assist optimization.


Laser Ablative Cleaning for Microelectronics Industry and Art Restoration

One of the mechanisms for laser cleaning is through ablation, which is similar to ablative laser machining.  Laser cleaning has potential applications ranging from oxide removal from copper substrate and nano-particle removal from silicon wafers in microelectronics industry to crust removal from marble or limestone in art restoration.  A number of fundamental issues are being addressed, including effect of laser pulsing characteristics on oxide layer removal, effect of laser fluence on the discoloration of marble, and mechanism and prediction of laser wet cleaning of marble encrustation.