Mechanism Of A Surface Profiler

By Author: Vishal Khosla
Total Articles: 19
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Surface profiler finds usage for data storage and optics in several industries. The equipment is used for measurement of the slope of diffraction gratings of binary lenses, volume and radius of curvature. Precise measurement is done by ensuring that adequate light from the surface returns to the material.

Surface profiler is an instrument that uses light wavelength to perform the measurement of surface shapes, finishes and roughness. It deploys the properties of light wave for evaluation of the optical pathway variation between the examination surface and reference surface. When a light beam is dispersed in the profiler, half of it is reflected from the test object, while the other is reflected from the reference mirror.

When the beam splitter distance to the reference mirror equalizes the distance of the light splitter to the test surface, constructive interference and destructive interference is created. Split beams with variation in the length of beam light rejoin, resulting in creation of interference fringes.

Flat reference mirror makes sure that the optical pathway variation is the outcome of altering ...
... height in the test side. Role of digital camera is to differentiate the focused interference beam. Appearance of destructive interference is darker, while constructive interference appears lighter.

The instrument scans the object vertically. As the object moves via the focal plane, it causes interference. The mechanism is such that every height level of the test object does not reach optimum focus at the same time. The instrument provides precise measurements, which allows it to be used when micro-measurement of surface difference is required.

Surface profiler is used for data storage and optics in several industries. It is used for measuring the volume, radius of curvature and slope of diffraction gratings of binary lenses. The technology focuses on the surface outline of the disk at the edging, surface finish roughness and the geometry of laser-textured bumps.

Precise measurement in surface profiler is done by ensuring that adequate light from the surface returns to the material. The technology fails in high slopes where light is reflected past the material. It is suitable for measuring ink, plastic, metals, paper, paint, glass and epoxies. The technology is also used for analyzing cumulative effects of sawing, polishing and grinding. It can also be used for measurement when three dimensional picture of a surface is required, or you need to find the average heights of various parts.

Optical profiling simply means that nothing touches the surface when surface measurements are being made other than light. Yet, three dimensional profiles produced by surface profilers is accurate. Height variations in the measurement are plotted with sensitivity of a sub-nanometer. The technology can be very successful on measuring fragile and soft surfaces as well as for measuring roughness modeled three dimensionally such as geometric structures and regular textures.

Techniques used in surface profiler include non-contact, three-dimensional, scanning white light and optical phase-shifting interferometry. Vertical resolution is usually 0.1 nm, while Minimum lateral resolution is 0.11 µm. Several image zoom options are available. It is easy to find ‘fringes’ when there is a flat surface on the sample. In case the surface is transparent to wavelength, you should coat the wafer with a thin film of reflecting material for precise measurement.

The instrument features excellent surface profiling process repeatability and reproducibility. It provides sufficient vertical range for large variations in topography.

Author of this article is associated with Rtec Instruments, a California based company that deals in surface profiler, ball on disk tester, high temperature tribometer, nano indentation, atomic force microscope and other instruments.