Real-Time Monitoring for Laser Surface Cleaning
- PDF / 382,381 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 49 Downloads / 244 Views
ABSTRACT Real-time monitoring of surface cleanness in laser dry cleaning was investigated by monitoring the acoustic waves emitted from the substrate surface under pulsed laser irradiation. It is found that the acoustic wave from the surface under laser irradiation can reflect the surface condition, i.e., the surface cleanness. Besides the surface condition, the acoustic waveforms also depend on the substrate materials and laser pulse energies (intensities). The frequency spectrum obtained from the Fourier transform can provide clear indication for different surface cleanness. Removing of surface contaminants can generally result in weaker laser-induced acoustic wave and change in the frequency spectrum. The surface cleanness, therefore, can be monitored in real-time by detecting the amplitude and frequency of the acoustic wave during the laser cleaning process. This phenomenon provides the laser cleaning technique a real-time feedback during the cleaning process.
INTRODUCTION Laser surface cleaning is a new technology that is chemical free and environment friendly.[1,2] It has great potential in removing various contaminants from different substrates, such as semiconductors, magnetic materials, metals, and glasses. However, laser cleaning has its own disadvantages. For example, overexposure to the laser pulse may result in substrate damage whereas underexposure can leave residual contamination on the surface. For a substrate much larger than the laser spot, the whole surface has to be cleaned by scanning the laser beam. In most cases, the contamination is not uniformly distributed on the whole substrate. Some areas of the substrate may suffer damage while others still have residual contamination if the same laser irradiation conditions are applied on the whole surface. Therefore, a feedback is required in the laser cleaning process. Although the surface contamination can be monitored by CCD camera or surface reflectivity, these methods have certain limitations. For example, they are not sensitive to transparent contaminants and are limited to monitor smooth and bright surfaces. Detection of acoustic waves in laser cleaning can be a good solution because laser pulse interactions with solids[3], particles[4] and even liquids[5] can produce acoustic emission. In this article, we report a real-time monitoring method based on the acoustic wave emission in the laser cleaning process.
EXPERIMENTAL Figure 1 shows the schematic diagram of the experimental setup for the real-time acoustic monitoring of laser cleaning processes. A KrF excimer laser (Lambda Physik LPX 100) is used as light source for laser cleaning. The beam has a wavelength of 248 nm and 483 Mat. Res. Soc. Symp. Proc. Vol. 354 01995 Materials Research Society
a pulse width of around 20 ns. The beam profile is flattened by a beam homogenizer. The beam after passing through the homogenizer is focused (or defocused) by a quartz lens (plano-convex lens) with a diameter of 50 mm and a focal length of 800 mm. The position of the lens is adjusted to change the
Data Loading...
