Laser generation of nano-bumps below 2 nm height on silicon for debris-free marking/patterning

By rapidly scanning a 532 nm diode pumped Nd : YVO4 laser beam at nano-second pulses below the ablation threshold, a uniform array of nano-bumps of less than 2 nm in height (diameter of around 20 μm) was generated on a p-type (1 0 0) Si wafer. This height is two orders of magnitude lower than previously reported values. The array was produced at 30 000 bumps per second. The effect of laser fluence (energy density) and scanning speed on the characteristics of the nano-bumps was investigated and the wettability of the laser nano-textured surfaces was examined. The mechanisms of nano-bump formation are discussed. Also presented are the application of the technique for debris free, invisible marking/texturing of silicon and the recognition of such marks/patterns.