A Safer Way to Make Metal Nanoscale Spheres for Calibrating Surface Inspection Instruments

Jul 16, 2004

Tiny surface defects that form during processing can reduce the quality and yield of semiconductor devices, magnetic storage media, and other products. Inspection tools that locate, identify, and characterize surface defects based upon how they reflect or scatter light need to be calibrated with accurate particle size standards in order to work properly. Making metallic standards for such calibrations is typically a hazardous process, but researchers at the National Institute of Standards and Technology (NIST) and the University of Maryland have invented a safer method and apparatus for producing these standards.

Nanoscale spheres typically are used as size standards for calibrating surface inspection instruments. NIST produces a number of Standard Reference Materials (SRMs) used by the semiconductor industry for calibration purposes, including SRM 1963, which consists of 100 nanometer (nm) polystyrene spheres. The new method produces uniformly sized metal nanospheres, which might be used to determine, for example, whether surface inspection systems can differentiate metal contaminants from other defects.

The new method, patented earlier this year and licensed to MSP Corp., makes spheres 50 nm to 300 nm in diameter out of copper, nickel, cobalt, and other metals. The method involves generating aerosol droplets of a solution in an inert gas, and heating the droplets to form metal particles. The solution contains a metal compound, water, and a solvent such as methanol or ethanol. By contrast, the best of current production technologies use hydrogen gas as the solvent, posing a risk of fire or explosion.

The new method resulted from NIST efforts to develop and validate theoretical models for light scattering by polystyrene spheres. Because it is more difficult to predict light scattering by metal spheres than by polystyrene spheres, scientists validated their theories by making metal particles and measuring how they scattered light. This ensured that the models would be highly accurate for polystyrene. Scientists used metal particles made with the new method to validate their theories under a number of conditions and published several papers on the results. For example, they found that oxides grow on the particles at room temperature and limit their useful life as light scattering standards to only a few months.* This increases the value of having a safer way to generate the particles, because laboratories that use them may need to generate new batches of nanospheres on a regular basis.

* J.H. Kim, S.H. Ehrman, and T.A. Germer, “Influence of particle oxide coating on light scattering by submicron metal particles on silicon wafers,” Appl. Phys. Lett. 84, 1278, Feb. 23, 2004.

Source: www.nist.gov/

Explore further: World's smallest propeller could be used for microscopic medicine

add to favorites email to friend print save as pdf

Related Stories

Physicists discuss quantum pigeonhole principle

1 hour ago

The pigeonhole principle: "If you put three pigeons in two pigeonholes at least two of the pigeons end up in the same hole." So where's the argument? Physicists say there is an important argument. While the ...

Giant crater in Russia's far north sparks mystery

3 hours ago

A vast crater discovered in a remote region of Siberia known to locals as "the end of the world" is causing a sensation in Russia, with a group of scientists being sent to investigate.

NASA Mars spacecraft prepare for close comet flyby

4 hours ago

NASA is taking steps to protect its Mars orbiters, while preserving opportunities to gather valuable scientific data, as Comet C/2013 A1 Siding Spring heads toward a close flyby of Mars on Oct. 19.

Giant anteaters kill two hunters in Brazil

4 hours ago

Giant anteaters in Brazil have killed two hunters in separate incidents, raising concerns about the animals' loss of habitat and the growing risk of dangerous encounters with people, researchers said.

Recommended for you

A new way to make microstructured surfaces

14 hours ago

A team of researchers has created a new way of manufacturing microstructured surfaces that have novel three-dimensional textures. These surfaces, made by self-assembly of carbon nanotubes, could exhibit a ...

Tough foam from tiny sheets

Jul 29, 2014

Tough, ultralight foam of atom-thick sheets can be made to any size and shape through a chemical process invented at Rice University.

User comments : 0