Ablation and cleaning of wafer surface by excimer laser

The importance of surface cleaning is an essential factor in VLSI technology, flat panel display, and data storage devices. The results of laser cleaning technology were studied using KrF excimer laser (248 nm) irradiation in cleanroom environment. The applied energy density was 200 - 800 mJ/cm(2) at a repetition rate of 10 - 40 Hz with various focused beam widths. Results of photoresist stripping were made before and after laser irradiation with PR covered wafers and comparison of laser cleaning results were investigated as well with bare wafers. The atomic force microscopy (AFM) images of laser cleaning results were also presented and compared before and after laser irradiation. The surface roughness of AFM image of contaminated wafer surface before laser irradiation was 192 Angstrom and that of after laser irradiation was 16.2 A. The mechanism of laser cleaning and ablation is rapid thermal expansion of substrate surface induced by an instantaneous temperature rising due to laser irradiation. It is found that the temperature rising of the substrate surface was about 297 degreesC with a fluence of 400 mJ/cm(2) at 300K. Laser dry cleaning technology easily removed fingerprints, submicron Al2O3 and SiO2 particulates intentionally contaminated on the top of the wafer surface without aids of toxic chemicals and deionized water.