Detection of NM-Scale Scratches on High Gloss Metal Sheets by a Light Scattering Method Available to Purchase

This paper discusses a promising method to investigate high gloss finished metal surfaces. The main aim is to detect very shallow scratches on such surfaces. The method must be simple in its applicability, insensitive to external disturbances and sufficiently fast for application in monitoring industrial processes. To achieve this, the principle of light scattering is used by scanning a surface with a compact scattering light sensor using an LED as a light source (λ = 632.8nm). The reflected light is scattered into a specular part and a diffuse part, and collected by a one dimensional CCD-Array. The detected intensity distribution of the scattered light depends on the topography of the reflecting surface. Significant variations in the intensity profile will permit to identify the surface defects. With this system we were able to detect scratches on high gloss metal sheets with a typical width of 1 μm and a depth as small as 40 nm.