Scanning white light interferometry

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Scanning white light interferometry
SWLI objectives.jpg
Interferometric Objective Diagrams[1]
Technology Details
Other Names SWLI,  Optical profilometry
Technology Metrology
Equipment Zygo NewView 5000

Scanning white light interferometry (SWLI) is a technology used for optical 3D profiling of topography and surface roughness of samples.

Equipment

Zygo NewView 5000

Main article: Zygo NewView 5000

The Zygo 3D optical profiler is located in the LNF main cleanroom.


Method of operation

SWLI uses a white light source with interferometric objectives in order to map surface topography of samples. Light from the source passes through a beam splitter to generate a measurement beam and reference beam. The reference beam travels along the reference beam path length and reflects from a mirror. The measurement beam reflects off of the sample and is recombined with the reference beam. The interferometer scans it's focus or Z-height through a height range and the intensity of reflected light versus focus height is captured by a CCD (charge coupled device) array (camera). When the distance traveled by the light reflected off of the sample matches the distance that the reference beam travels, it produces intensity interference fringing. This intensity fringing data is analyzed to produce a 3D contour map of the sample surface.


Applications

  • SWLI is most frequently used for measuring the depth of high aspect ratio trenches etched using the Deep Reactive Ion Etch (DRIE) tools. Trench profiles from DRIE are often beyond the capability of stylus profilometry where the maximum aspect ratio of ~1 and maximum step height of 150um are limited by the physical dimensions of the stylus and scanning technique.
  • SWLI is also useful for measuring sample surface roughness. This technique is preferred rather than stylus profilometry for surface roughness analysis since the physical dimensions of the stylus (25 μm tip radius) can limit accuracy of the measurement.
  • This technique does have a disadvantage for surfaces that have different (dissimilar) materials on them. If material in one area is different than material in another area within the analysis region, there will be a different phase shift in reflected light due to the difference in optical properties of the two materials. SWLI will interpret this phase shift difference as a height difference. Stylus profilometry and Confocal laser optical profilometry do not have this limitation.

References

Further reading