Profilometer is an instrument used to measure a surface’s profile, in order to quantify its roughness. The profilometer measures the vertical depth of a material across a specified horizontal length. The profile is displayed on a printable graphical interface. Uses for this equipment include measuring etch depth, deposited film thickness, and surface roughness. the most advanced laser profilometers are also available to measure the overall thickness of a surface and is used widely in several domains starting from construction work for buildings, to road work for asphalt and pavement projects and also for fine procedures regarding millimeter accuracy.

Types & Technologies of Profilometers

  • Non-Contact Optical Profilometers
    • Vertical Scanning Interferometry/White-light interferometer
    • Phase Shifting Interferometry
    • Differential interference contrast microscopy (Nomarski Microscopy)
    • Focus Detection Profilometer Technologies using Intensity Detection, Focus variation, Differential Detection, Critical Angle Method, Astigmatic Method, Focault Method, and Confocal microscopy
    • Pattern Projection Profilometer Technologies using Fringe projection, Fourier Profilometry, and Moire Profilometry
  • Contact and Pseudo-contact Profilometers
    • Stylus profilometer (mechanical profilometer)
    • Atomic Force Microscopy
    • Scanning Tunneling Microscopy

Contact (Stylus) Profilometers

A diamond stylus is moved vertically in contact with a sample and then moved laterally across the sample for a specified distance and specified contact force. A profilometer can measure small surface variations in vertical stylus displacement as a function of position. A typical profilometer can measure small vertical features ranging in height from 10 nanometres to 1 millimetre. The height position of the diamond stylus generates an analog signal which is converted into a digital signal stored, analyzed and displayed. The radius of diamond stylus ranges from 20 nanometres to 25 μm, and the horizontal resolution is controlled by the scan speed and data signal sampling rate. The stylus tracking force can range from less than 1 to 50 milligrams. Advantages of contact profilometers are:

  • Acceptance: Most of the world’s surface finish standards are written for contact profilometers.
  • Surface Independence: Contacting the surface is often an advantage in dirty environments where non-contact methods can end up measuring surface contaminants instead of the surface itself. However, because the stylus is in contact with the surface, this method is not sensitive to surface reflectance or color.
  • Resolution: The stylus tip radius can be as small as 20 nanometres, significantly better than white-light optical profiling.
  • Direct Technique: No software modeling required.

Non-contact Optical Profilometers

An optical profilometer is a non-contact method for providing much of the same information as a stylus based profilometer. There are many different techniques which are currently being employed, such as laser triangulation (triangulation sensor), confocal microscopy (used for profiling of very small objects), low coherence interferometry and digital holography. Advantages of optical profilometers are:

  • Resolution: Vertical resolution is usually in the nanometre level, lateral resolution is usually poorer, limited by the wavelength of the light.
  • Speed: Because the non-contact profilometer does not touch the surface the scan speeds are dictated by the light reflected from the surface and the speed of the acquisition electronics.
  • Reliability: optical profilometers do not touch the surface and therefore cannot be damaged by surface wear or careless operators.
  • Spot size: The spot size, or lateral resolution, of optical methods ranges from a few micrometres down to sub micrometre.
  • Flexibility: Thanks to the small diameter of certain probes, surfaces can be scanned even inside hard-to-reach spaces, such as narrow crevices or small-diameter tubes.
  • Ruggedness: Scanning can take place in hostile environments, including very hot or cryogenic temperatures, or in radioactive chambers, while the detector is located at a distance, in a human-safe environment.
  • Ease of incorporating into industrial processes: fiber-based probes are easily installed in-process, such as above moving webs or mounted onto a variety of positioning systems.