There are numerous analytical methods for establishing the surface roughness as well as the visualization of surface texture. Each of these methods has its own advantages and disadvantages. The following list briefly compares and contrasts these techniques.
Optical Methods Optical methods have the advantage that they can measure surface properties very rapidly. However, the horizontal resolution of all optical methods is limited to the resolution of optical techniques, typically greater than ½ micron. Another limitation of optical methods is that they require an optically opaque sample. The following is a summary of optical methods:
Microscopes - Optical microscopes are excellent for visualization of surface texture but they do not allow direct measurement of quantitative surface roughness parameters.
Optical profilers - Optical profilers are ideal for rapidly measuring surface roughness parameters with a horizontal resolution that is greater than a 1/2 micron. Large areas can be analyzed with optical profilers.
Scatterometry - Like other optical methods, scatterometry gives rapid surface roughness parameters of a surface area that is greater than 1 micron. However, this optical method is not a direct measure of surface topography and does not allow visualization of surface texture.
Electron/Ion Beam Methods
Electron and Ion beam techniques are capable of visualizing surface texture with horizontal resolutions of less than a nanometer. However, the beam techniques do not give quantitative three-dimensional surface topograms so it is difficult to get quantitative surface texture information. Also, because the contrast in beam techniques relies on the differing emission of electrons, beam techniques do not give contrast on flat homogeneous materials.
It is possible to get accurate surface roughness values using beam methods by cross sectioning a sample. However, cross sectioning can be difficult and the value may be changed by the cross sectioning process.
Mechanical Profilers
AFM technology is derived from the surface profiler. The primary difference between a profiler and an AFM is the loading force on the scanned probe. Because the loading force on an AFM is substantially smaller than a profiler, smaller probes can be used in an AFM. It is possible to visualize much smaller surface structure with a smaller probe in an AFM than in with a profiler. Often an image from an AFM shows more detail than a profiler and the surface roughness can be much greater.
