Finding rough spot in surface measurement

Jul 14, 2005

For makers of computers, disk drives and other sophisticated technologies, a guiding principle is the smoother the surfaces of chips and other components, the better these devices and the products, themselves, will function.

So, some manufacturers might be surprised to learn that a fast and increasingly popular method for measuring surface texture can yield misleading results. As reported at recent conferences and in an upcoming issue of Applied Optics,* a team of National Institute of Standards and Technology researchers has found that roughness measurements made with white light interferometric microscopes, introduced in the early 1990s, differed by as much as 80 percent from those obtained with two other surface-profiling methods.

Interferometric microscopes are used to measure surface heights, lengths and spaces by analyzing the interference patterns created by two light beams--one reflected by a reference specimen and the other by the object of interest.

To date, the team has evaluated a total of five white light instruments from three different vendors. They compared roughness measurements of gratings with both wavelike surfaces and random surfaces.

White light interferometers were compared with "phase shifting" interferometers, which use specialized single-color light sources, and with accurate, but sometimes destructive, stylus profiling instruments that trace a sharp probe over a surface. The latter two tools were in agreement across the spectrum of test samples within the expected measurement range of the phase shift interferometers. For measurements of relatively rough surfaces, white light interferometers also yielded results that corresponded closely. But for measurements of surfaces with an average roughness between 50 and 300 nanometers, results diverged significantly, peaking at about 100 nanometers.

"The discrepancy seems to be unrelated to the specific white light instrument used or to the randomness of the surface profile," explains Ted Vorburger, head of NIST's Surface and Microform Metrology Group.

The comparative study was carried out as part of an effort to develop international standards for three-dimensional measurements of surface texture. NIST researchers are now evaluating theoretical explanations for the observed discrepancies.

* H.G. Rhee, T.V. Vorburger, J.W. Lee and J. Fu, Discrepancies between roughness measurements obtained with phase shifting interferometry and white-light interferometry. Applied Optics, 2005.

Source: NIST

Explore further: Understanding the source of extra-large capacities in promising Li-ion battery electrodes

add to favorites email to friend print save as pdf

Related Stories

Fermi finds a 'transformer' pulsar

3 hours ago

(Phys.org) —In late June 2013, an exceptional binary containing a rapidly spinning neutron star underwent a dramatic change in behavior never before observed. The pulsar's radio beacon vanished, while at ...

A global view of oceanic phytoplankton

Jul 18, 2014

University of Maine oceanographer Ivona Cetinic is participating in a NASA project to advance space-based capabilities for monitoring microscopic plants that form the base of the marine food chain.

NASA's ten-year-old Aura satellite tracks pollutants

Jul 17, 2014

(Phys.org) —NASA's Aura satellite, celebrating its 10th anniversary on July 15, has provided vital data about the cause, concentrations and impact of major air pollutants. With instruments providing key ...

Comet ISON's dramatic final hours

Jul 16, 2014

(Phys.org) —A new analysis of data from the ESA/NASA Solar and Heliospheric Observatory (SOHO) spacecraft has revealed that comet 2012/S1 (ISON) stopped producing dust and gas shortly before it raced past ...

NASA mission to reap bonanza of earth-sized planets

Jul 15, 2014

Set to launch in 2017, NASA's Transiting Exoplanet Survey Satellite (TESS) will monitor more than half a million stars over its two-year mission, with a focus on the smallest, brightest stellar objects.

Recommended for you

Graphene surfaces on photonic racetracks

13 hours ago

In an article published in Optics Express, scientists from The University of Manchester describe how graphene can be wrapped around a silicon wire, or waveguide, and modify the transmission of light through it.

Simulating the invisible

14 hours ago

Panagiotis Grammatikopoulos in the OIST Nanoparticles by Design Unit simulates the interactions of particles that are too small to see, and too complicated to visualize. In order to study the particles' behavior, he uses ...

Building 'invisible' materials with light

15 hours ago

A new method of building materials using light, developed by researchers at the University of Cambridge, could one day enable technologies that are often considered the realm of science fiction, such as invisibility ...

User comments : 0