Quantitative Makyoh topography

When a collimated beam of light is reflected by an approximately flat, mirror polished object and a screen is placed in the reflected beam some distance away for the object, a 'mirror image' or Makyoh topogram of the object is formed on the screen. For objects with surface height variations, the topogram will not have a uniform intensity distribution, but even small height variations will show up strongly amplified as dark or bright patches/lines. Makyoh topography has now been used for a number of years as a sensitive tool for the inspection of mirror polished surfaces, and in particular, semiconductor wafer surfaces. The main drawbacks of conventional Makyoh topography are: 1) Ambiguity of interpretation because almost identical Makyoh topograms can result from an object with some given surface height profile and constant reflectivity, an object with constant surface height and a given non-uniform reflectivity profile, or an object with both height variations and a non- uniform reflectivity profile. 2) Lack of quantitative interpretation, for example surface height values cannot be obtained from the contrast in conventional topograms.