Pulsed Laser Assisted Particulate Cleaning of Solid Surfaces
- PDF / 1,692,229 Bytes
- 5 Pages / 414.72 x 648 pts Page_size
- 80 Downloads / 234 Views
475 Mat. Res. Soc. Symp. Proc. Vol. 477 ©1997 Materials Research Society
could also etch the part; furthermore, particles can be deposited onto the part when the plasma is turned off. It is in this context that laser laser assisted cleaning of solid surfaces is acquiring significant importance. Recently, several groups have reported the removal of small particles from solid surfaces using lasers [5-11 ]. Free from wetability limitations, laser assisted cleaning of solid surfaces is an environment-friendly as the method does not involve any chemical and no hazardous waste is generated during the cleaning process. In this paper, we have investigated the use of excimer laser to clean submicron sized particles from semiconductor surfaces. The most important feature of the present work is the realization higher cleaning efficiency by mean of line beam laser which has not been used till date in laser assisted cleaning experiments. EXPERIMENTAL (100) silicon wafers were first contaminated with 0.05- 0.3 jim sized A12 0 3 particles using suspension of alumina in ethanol and water. The samples with uniform particle distribution on the surfaces were irradiated with laser beams at 248 nm. The beam was focused onto the sample surfaces using spherical and cylindrical lenses. Spherical lens was used to KrF Excimer Laser focus the original laser beam (L=3.5 cm., W=l.5cm) to smaller spot sizes with Sample reduction in both length and width while the an cylindrical lens was used to focus the original laser beam only along its width. The sample Mirror Focusing Lens Stage was constantly moved in X-Y plane in oder Fig. I. Schematic of experimental set-up for to expose the whole sample surface to the laser cleaning of sloid surfaces. laser beam. The schematic of the experimental set-up we have used for the cleaning experiment is shown in Fig. 1. The laser was operated at energy density and repetion rate ranging from 200-600 mJ/cm 2 and 1-20 Hz, respectively. The number of particles on the sample surfaces were counted from scanning electron microscopy (SEM) measurements. RESULTS AND DISCUSSION Figure 2 shows distribution of 0.1-0.3 gm alumina particles on (100) silicon surfaces which were obtained using suspension in water and ethanol. The pH of both the suspensions was maintained at 4. It is clear from these micrographs that alumina suspension in ethanol provides better coating of silicon surfaces than that in water as in the case of use of former not only the coating is more uniform but the degree of agglomeration of chosen particles is also significantly less. The realization of samples with more uniform particle distribution on surfaces and less agglomeration of particles using alumina suspension in ethanol can be explained on the basis of
476
better wetability of silicon surfaces by ethanol and lower surface tension. In order to avoid the melting effect, we determined the minimum energy density required to cause melting of solid silicon surfaces. The experimental and simulated results are shown in Fig. 3 according to which the
Data Loading...
