Laser micromachining & surface treatment
Laser cleaning and surface modification
Laser cleaning technology to remove particles from surfaces has long been an issue of practical and scientific importance due to its potential to removal sub-micrometer-scale contaminant particles. Various laser cleaning processes based on different physical mechanisms have been proposed depending on industry needs, e.g., dry laser cleaning (DLC), steam laser cleaning (SLC), laser shock cleaning (LSC), and laser-induced spray jet cleaning (LSJC).
SEM images of silicon wafer contaminated with 300nm sized PSL particles
Adhesion force:
The particle adhesion forces are in general linearly proportional to particle size (~d). On the other hand, the forces that are involved in the cleaning process are typically proportional to the square of the particle size (~d2). Consequently, particle removal becomes more challenging as the size decreases.
Laser shock cleaning(LSC):
In the LSC process, the strong shock wave induced by laser induced breakdown (LIB) is used to remove the contaminated particles. The cleaning force is provided by the pressure difference across the shock front and the dynamic pressure associated with the high-speed flow behind the shock.
Concept of laser shock cleaning
Steam laser cleaning(SLC):
Practical issues of excimer laser cleaning techniques for submicron contaminants removal are investigated. As a part of them, a novel steam laser cleaning(SLC) method assisted by thin vapor film ablation process is being developed.
Concept of steam laser cleaning
Laser-induced spray jet cleaning(LSJC):
We proposed a novel laser-induced spray jet cleaning (LSJC) technique based on laser-induced breakdown (LIB) of a liquid droplet. High-speed liquid spray jets composed of atomized micro droplets are produced and can remove various particles.
Concept of laser-induced spray jet cleaning
- Laser cleaning is a noncontact method for cleaning and free from chemical reactions.
- Using laser cleaning, we can perform an environmentally clean process.
- There is little to worry about mechanical damages to the cleaning object.
- Laser cleaning can perform effectively for submicron to macroscopic-sized contaminants.
- Selective cleaning is another merit of laser cleaning