Optical Profilometry

Zeta 3D optical profiler images

Profilometry

Profilometry is a technique used to extract topographical data from a surface.  This can be a single point, a line scan or even a full three dimensional scan.  The purpose of profilometry is to get surface morphology, step heights and surface roughness.  This can be done using a physical probe or by using light.

Metrology is the science of measurement. How rough is the sample? How high are the features? How much of the area has voids or particles? What is the defect density? Answers to these questions are often quantified using profilometry.

Stylus vs Optical Profilometry

There are two types of profilometers: stylus vs optical. Stylus or contact profilometry is the earliest form of profilometry. Stylus profilometers use a probe to detect the surface. The probe is typically made of a very hard material like diamond and has the ability to alter the sample, i.e. scratch or indent. Lateral resolution is limited by the stylus tip geometry. Because the probe is physically scanning the surface, diamond stylus probes need periodic replacement followed by system calibration. Data is typically a line profile due to time constraints. 

The benefit of an optical profilometer is that it uses a light source instead of a physical probe to detect the surface. Therefore, optical profilometry is considered a non-contact technique. Data are point, line or 3D measurements. The light source and instrument design impact vibration sensitivity and light throughput. Optical profilometry is faster than contact profilometry with sacrifices in lateral resolution.  It is completely non-destructive to samples that are not sensitive to light and can scan soft surfaces.

 

Grid Confocal
Grid Confocal

Combination of pattern projection and focus detection

Stylus Profilometer
Stylus Profilometer

Basics of stylus and optical profilometry

White Light Interferometry
White Light Interferometry

Principles and schematic of white light interferometry

Confocal Profilometry
Confocal Profilometry

Principles and schematic of confocal profilometry

Laser Interferometry
Laser Interferometry

Principles and schematic of laser interferometry