Comparison to White Light Interferometry

WLI vs Zeta 3D Optical Profilometry

 Read MoreOptical Profiler with ZDot vs WLI.pdf

White Light Interferometry schematic

White Light Interferometry (WLI) has been adopted across multiple industries for 3D measurements.  WLI is capable of measuring surface heights from nanometers to millimeters.  The main advantage of WLI over other optical techniques is that the vertical resolution is independent of magnification or field of view.  This makes it well-suited for applications with low topographic features on smooth, flat surfaces.

However, WLI has some disadvantages for 3D optical profiling of complex surfaces with a range of topographic features. WLI systems are more sensitive to vibration and sample tilt. WLI imaging capability is limited due to the low light throughput design of the optical system. Samples with transparent and multiple layers, low reflectivity, high roughness, large height or large reflectivity variations are generally beyond the capability of WLI systems.

The technology for the Zeta optical profiler overcomes the disadvantages of WLI with an optical design that has high light throughput and is inherently insensitive to vibration and sample tilt. 

High light throughput and optical efficiency are essential for surfaces that have low reflectivity or high aspect ratio features, such as vias or deep trenches. Optical profilers based on WLI have limited light throughput because of their optical design. Zeta optical profilers (right) use a brighter light source and are designed to use the same optical path for focusing and imaging.Zeta optical profiler schematic

White Light Interferometers are inherently sensitive to vibration and sample tilt. Vibration sensitivity is caused by the splitting of the illuminating light into two separate optical paths. Sample tilt narrows the interference fringes, further reducing vertical resolution of interferometers.

The Zeta optical profiler overcomes both of these limitations with its unique optical design that uses a common path for focusing and imaging as well as a patented and proprietary method for sensing the focal plane. The Zeta imaging technology uses a confocal grid structured array illumination (CGSI) to generate contrast that is independent of the sample, enabling robust Z-height measurements on almost any surface. This optical design makes Zeta optical profilers inherently insensitive to vibration and sample tilt.