Theoretical and experimental research on nanosecond laser cleaning of SiO2 particles on silicon wafer surface

In this study, theoretical and experimental research was conducted on the laser cleaning of SiO2 particles on the surface of a silicon substrate via a nanosecond pulsed laser. The adhesion force between SiO2 particles of different sizes and the silicon substrate was obtained via theoretical calculations. Numerical simulations were used to analyze the temperature rise and thermal expansion force of the silicon substrate after absorbing laser energy to quantify the cleaning force on the particles and predict the cleaning threshold of the particles and damage threshold of the silicon substrate. The results showed that the cleaning thresholds of 1-μm and 5-μm SiO2 particles on the silicon surface were 7.69 J/cm2 and 0.342 J/cm2, respectively, and the damage threshold of the silicon substrate was 8.12 J/cm2. The removal rate of SiO2 particles on the silicon surface gradually increased with increases in the laser energy density. Based on the premise of not damaging the silicon substrate, the SiO2 particles with particle size above 1 μm can be completely removed. The surface roughness of the cleaned silicon was 1 nm, which was close to that of the original silicon surface. The surface crystal spacing and lattice constant of the laser-cleaned silicon substrate exceeded those of the original silicon sample. In the nanosecond laser cleaning of SiO2 particles on the surface of silicon, particle removal mechanisms include the silicon substrate thermal absorption expansion and near-field-enhancement effect. The light intensity below the SiO2 particles was approximately 17.45 times the laser input light intensity when the near-field effect occurred. Additionally, the simultaneous removal of particles easily led to the generation of pits.