Feb 15 2006
Topics Covered
Background
Optical Methods
Microscopes
Optical Profilers
Scatterometry
Electron/Ion Beam Methods
Mechanical Profilers
Background
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.
The following information was supplied by Pacific Nanotechnology