The use of advanced 3D surface metrology for the characterisation of epi-wafers and Si structures

Over recent years the discipline of surface metrology has advanced greatly both in terms of instrumentation and in terms of techniques for surface characterisation. The advances in instrumentation have entailed the introduction, as an industrial tool, of the atomic force microscope and the widespread use of optical interferometry. Both of these techniques have allowed visualisation of the 3D surface texture of epi-wafers at the micro and nanometer scale. The clear advantage of interferometry is that it is contactless and fast whereas the AFM technique, although it has a better measurement resolution, is still contacting the surface even in tapping mode and could potentially damage or contaminate the surface. A drawback common to both of these instrument types is that despite the "richness" of the data collected it is usually only the average roughness R_a, root mean square roughness R _q or maximum peak to valley roughness R_t, values of the surface texture that are quoted. True surface areal texture information cannot be described by such parameters. Consequently these simple amplitude based roughness parameters are inadequate for describing anything more than very simple epi-structures and as a result differing textures can often yield similar roughness values. This paper outlines the recent advances in 3D surface characterisation and applies this to epi-wafer surface topography.