A team of scientists from the University of Tokyo, SIGMA KOKI, and the National Institute of Information and Communications Technology (NICT), has developed a non-contact self-organized method of near-field etching that can reduce surface roughness, Ra, to 1.36 Å. This represents a significant advance in the state of the art, as surface roughness below 2 Å has not been demonstrated using conventional chemical-mechanical polishing. More recently, the team performed real-time monitoring of surface roughness during its optical near-field etching process by measuring the intensity of light scattered from the sample.

To their surprise, this method can detect changes in surface roughness with angstrom resolution. Furthermore, it yields in-plane information about the surface as well as the surface roughness. Comparison of the etching-time dependence of the surface roughness and the power spectrum revealed that near-field etching not only decreased the surface roughness, but also increased the number of scatterers, which was confirmed using AFM. Because the intensity of scattered light decreases with decreasing surface roughness, it should be noted that the flattened substrate has a higher laser-damage threshold due to the reduction of scattered loss at the surface.

As this non-contact method does not require a polishing pad, it can be applied not only to flat substrates but also to three-dimensional substrates, which can have convex or concave surfaces, such as micro-lenses and the inner-wall surfaces of cylinders. Further optimization of the etching parameters (wavelength, power density and etching time) should provide scope for an additional reduction in surface roughness. The scientists believe that their latest results, published in the journal Nanotechnology, will accelerate commercialization of this new technique.