SURFACE TOPOGRAPHY OF LARGE AREA MIRROR-LIKE SURFACES BY THE MAKYOH (MAGIC MIRROR) METHOD

摘要

Makyoh or magic mirrors have been used in the Far East for centuries, they were large seeminglyflat polished bronze disks, hanged usually on the walls of temples. These devices exhibit no noticeable structure on the front face, but when illuminated by the sun, the reflected image on the wall shows the strains, undulations of the mirror. Concave and convex distortions are represented by variations in intensity where convex distortions appear darker and concave ones brighter. These intensity variations are related directly to the radius of curvature of the corresponding irregularities. Unfortunately, similar darker and lighter patches can be produced by non-uniform irradiation or by the variation of the reflectivity. Therefore, in general a surface height profile can not be obtained from such a topogram of an arbitrary surface i.e. the method lacks quantitavity. Even by nonuniform irradiation quantitavity can be achieved by applying the Makyoh method modified by a projection of a grid to the wafer, where the grid nods mark the surface positions. The distorted image of this grid is analyzed to gain information on the flatness of the wafer. The method is applicable to any mirror like moderately distorted surface, among others to semiconductor wafers. The present paper discusses this technique.