NIST logo
*
Bookmark and Share

Nano-Structured Optics and Optical Surface Metrology

Summary:

Aspheric, free-form, and nano-structured surfaces are indispensable in high-performance optical systems. The ability to accurately manufacture these surfaces and achieve the required optical performance depends on the ability to measure them. Our project focuses on innovative applications of diffractive optics and nano-structured optics with sub-wavelength features in precision surface metrology and advanced optical systems. We develop and characterize interferometric measurement methods for optical figure of ultra-precise surfaces and for light fields generated by diffractive and nano-structured optics.

Description:

The project addresses metrology needs of U.S. industry and other agencies for the manufacture and application of ultra-precision surfaces and optical elements possessing high added-value. Ultra-precision surfaces and optical elements are essential to product innovations in many high-tech areas, such as semiconductor manufacturing, medical technology, defense, homeland security, consumer products, office automation, information technology, and science. Product examples range from an enormous variety of imaging systems to hard-drive platters, automotive lighting, laser beam shapers, and x-ray focusing optics. Advanced optical elements boost competitiveness and technological leadership in a broad range of manufacturing sectors. "Light is the tool of the future", as evidenced by the growth in optical inspection, machine vision, and laser systems for welding and additive manufacturing. Advances in nano-scale and semiconductor manufacturing fundamentally rely on advances in ultra-precision surfaces and high-performance optical elements, such as wafers, photomasks and the lenses and mirrors used in optical projection lithography.

Advanced optical elements incorporate features that yield vastly improved performance but pose significant measurement challenges. Examples of such features are complex surfaces, i.e., surfaces that are neither flat nor spherical, micro- and nano-scale surface structures, extreme accuracies, special materials and coatings, and adaptive technologies. The development and manufacture of these advanced features depend strongly on advances in traceable metrology for optical figure and wavefront. In many high-impact applications, such as semiconductor lithography, the required form accuracies are at the (sub-) nanometer level. No general, widely-recognized, validated way exists to calibrate complex and nano-structured (optical) surfaces, and the application range and uncertainty of existing methods are poorly understood. This is a persistent measurement barrier to the widespread manufacture and adoption of these elements, despite their high potential for product innovations.

The project addresses these measurement challenges through the following objectives:

  • Development and characterization of diffractive and nano-structured optics with properties traceable to the international system of units (SI) and known wavefront uncertainty.
  • Development and application of metrology holograms to measure advanced aspheric and freeform surfaces.
  • Innovative calibration methods and measurement services with sub-nanometer uncertainty for ultra-precise surfaces and optical reference artifacts.
  • Procedures and standards for characterizing the uncertainty of interferometric inspection methods.

Major Accomplishments:

  • Nano-structured Optics Laboratory at NIST for research and development of advanced diffractive and nano-structured optics with properties traceable to the international system of units (SI), and their application to the metrology of complex surfaces and optical wavefronts.
  • New bi-focal zone lens solves the challenge of measuring, with low uncertainty, the radius of precision spherical surfaces having a large radius of curvature.
  • Improved the calibration uncertainty for spherical reference surfaces that are used in the optics industry by an order of magnitude.
  • New method for deformation-free flatness measurements of thin optics, such as photomask blanks for extreme ultraviolet (EUV) lithography. The test part is floated on a liquid with a high specific gravity to eliminate mounting induced deformation.
  • Fabricated novel mirrors with phase relief patterns to assess the spatial instrument response function of surface measurement interferometers.
Figure 1. Form error of a 1 kg silicon sphere. The form error was obtained from 138 overlapping images.
Figure 1. Form error of a 1 kg silicon sphere. The form error was obtained from 138 overlapping images.

Lead Organizational Unit:

pml

Facilities/Tools Used:

  • Nano-structured Optics Laboratory with a dedicated maskless lithography system for the fabrication of diffractive optics and sub-wavelength nano-structured optics with traceability to the international system of units (SI) on optical quality substrates.
  • "eXtremely accurate CALIBration InterferometeR" (XCALIBIR), a multi-configuration phase-shifting interferometry system, housed in a temperature controlled cleanroom, with an aperture of 300 mm for form measurements of  ultra-precise flat, spherical, and free-form surfaces with uncertainties at the nanometer level. Commercial phase shifting interferometers for less demanding form measurements.

 

Figure 2. Application of the NIST XCALIBIR interferometer to measure the form of a single-crystal silicon sphere with a mass of 1 kg.
Figure 2. Application of the NIST XCALIBIR interferometer to measure the form of a single-crystal silicon sphere with a mass of 1 kg.

Figure 3. Zone Plate Array Lithography (ZPAL) tool for the fabrication of diffractive optics on optical quality substrates.
Figure 3. Zone Plate Array Lithography (ZPAL) tool for the fabrication of diffractive optics on optical quality substrates.

Staff:

Ulf Griesmann, Project Co-Leader
Johannes A. Soons, Project Co-Leader
Quandou Wang

Related Programs and Projects:

  • Dimensional Measurement Services (in 683.01)
Contact

Physical Measurement Laboratory (PML)
Semiconductor & Dimensional Metrology Division (683)

General Information:
301-975-5609 Telephone
301-869-0822 Facsimile

100 Bureau Drive, M/S 8220
Gaithersburg, Maryland 20899-8220