Optical Profilometry

Optical profilometry is a rapid, nondestructive, and noncontact surface metrology technique. An optical profiler is a type of microscope in which light from a lamp is split into two paths by a beam splitter. One path directs the light onto the surface under test, the other path directs the light to a reference mirror. Reflections from the two surfaces are recombined and projected onto an array detector. When the path difference between the recombined beams is on the order of a few wavelengths of light or less interference can occur. This interference contains information about the surface contours of the test surface. Vertical resolution can be on the order of several angstroms while lateral resolution depends upon the objective and is typically in the range of 0.3-8 microns.

Technique Advantages

  • True imaging (area measurement, not serially point by point)
  • Fast data acquisition over large areas
  • Noncontact and nondestructive
  • Large Z-axis range, from several nanometers up to feature heights as great as 7mm
  • Variable field of view, 90um up to 6mm (stitching is available)
  • Critical dimension measurements (X, Y, and Z)

Typical Applications

  • surface topography
  • step height
  • characterizing wear of mechanical parts
  • coating thickness of transparent films with known refractive index (at least 1um thick)

Instrumentation

Zygo Nexview 3D Optical Surface Profiler

  • 2.5x, 10x, 20x, 50x objectives with 0.5x, 1x, 2x internal magnification
  • automated image stitching
  • 200mm XY stage and 100mm Z clearance with capacity for up to 10lbs
Patterned grid on silicon surface: using analysis regions tool to separate surfaces at different heights.
Tracking surface topography changes on the interior surface of ostrich eggshells during embryonic development (stitched 1mm FoV)