UV Optical Metrology

Customer Needs
Accurate measurement methods and standards for characterizing DUV detectors and optical materials are critical in a number of photolithography applications. We work closely with industry to develop standards, new technology, and appropriate measurement techniques for DUV wavelength measurements. These efforts include development work in the following areas: characterization measurements of optical materials, standards development, detector studies, calibration services, and advising customers on in-house measurements. In particular, accurate DUV measurements of optical materials properties, such as the index of refraction, dispersion, and temperature dependence, are critical to the design of DUV photolithography projection systems.

Technical Strategy
There is an urgent need in the industry for evaluation of stability of VUV detectors to be used for transfer standards or for other applications in various manufacturing processes. Using synchrotron radiation in conjunction with an excimer laser we measure the stability of these detectors over a wide range in wavelength. We also intend to extend the characterization of photodetectors at 157 nm to include evaluation of the stability of photodiodes as a function of the intensity of the irradiation excimer pulse. This will provide important information regarding non-linear effects in the response towards excimer radiation. We also plan to characterize pyroelectric detectors using synchrotron radiation and measure the stability of such detectors towards excimer radiation.

Accomplishments

• Detector damage testing and characterization at 157 nm. We have evaluated the stability of semiconductor diodes under irradiation from an excimer laser operating at 157 nm. A new facility at SURF III has been built that allows simultaneous exposure of photodiodes to excimer radiation and synchrotron radiation. Measurements of the spectral responsivity can be made in the spectral range from 120 nm to 320 nm with a standard uncertainty of 0.5%. The intense, pulsed laser radiation was used to expose the photodiodes for varying amounts of accumulated irradiation whereas the low intensity, continuously-tunable cw radiation from the synchrotron source was used to characterize the photodiodes. The changes in the spectral responsivity of different kinds of diodes such as UV silicon, GaP, GaAsP, PtSi, diamond, and GaN were measured for a large range of total accumulated dose from an F2 excimer laser operating at 157 nm. Differing amounts of changes were seen in different diodes depending on the total excimer irradiation dose and they showed different spectral changes in the responsivity as well.

  Significance: Yields important information about the mechanism responsible for the degradation of photodiodes and also for the suitability of use of various kinds of detectors for different industrial applications.
  
  

  Study of Photodiode Damage by 157 nm Laser
  



• Development of DUV irradiance meter We have also constructed and characterized a probe that is suitable for accurate measurements of irradiance in the vacuum ultraviolet spectral range. The probe consists of a PtSi detector behind a precision 5 mm aperture. The probe was characterized at various wavelengths ranging from 157 nm to 325 nm, encompassing many of the important industrial application wavelengths. The principle of measurement of the irradiance is based on scanning the probe in a light field and measuring the spectral responsivity on a grid with regular spacing. Measurement of the spectral responsivity in the center of the probe along with the integrated total responsivity yields the spectral irradiance. This method can alternatively be used to calculate aperture areas as well by measuring the ratio of the total responsivity and the responsivity in the center.

  Significance: Many industrial applications such as UV curing, photolithography, or semiconductor chip fabrication require accurate measurement of the irradiance and would benefit from having such a stable, accurate UV probe.
  
  

  Spatial responsivity scan of an irradiance meter with
  157 nm pencil beam from SURF III
  

Files for this document are noted by   and require a reader to be loaded for viewing.

Publications

Optical Properties of Materials, T.A. Germer, Rajeev Gupta, Leonard Hanssen, and Eric Shirley, Optics and Photonics News, 12, 38, (2001).

The New Ultraviolet Spectral Responsivity Scale Based on Cryogenic Radiometry at SURF III (190KB) , Ping-Shine Shaw, Thomas C. Larason, Rajeev Gupta, Steven W. Brown, Robert E. Vest, and Keith R. Lykke, Review of Scientific Instruments, 72, 2242 (2001).

Improved Near-Infrared Spectral Responsivity Scale (260KB) , Ping-Shine Shaw, Thomas C. Larason, Rajeev Gupta, Steven W. Brown, and Keith R. Lykke, J. Res. Natl. Inst. Stand. Technol., 105, 689 (2000).

Material Characterization using UV radiometric beamline at SURF III (182KB) , P.S. Shaw, R. Gupta, T.A. Germer, U. Arp, T. Lucatorto, and K.R. Lykke, Metrologia, 37, 551 (2000).

The New UV Radiometry Facility at SURF, P.S. Shaw, K.R. Lykke, R. Gupta, U. Arp, and T.B. Lucatorto, SRI99: Eleventh US National Conference, AIP Conference Proceedings 521, 81 (1999).

Detector and Material Characterization for Lithography in the VUV Spectral Range, Rajeev Gupta, John Burnett, and Vladimir Liebermann, Future Fab International, July 2000.

Index of Refraction and Temperature Coefficients of 157 nm Optical Materials, John Burnett, Rajeev Gupta, and Ulf Griesmann, SPIE Proceedings 4000, 1503 (2000)

Material and Detector Characterization for DUV and VUV Lithography, Rajeev Gupta, Lambda Physik Highlights, 56, 6 (2000)

UV radiometry using synchrotron radiation and absolute cryogenic radiometer (186KB) , P.S. Shaw, K.R. Lykke, R. Gupta, T.R. O’Brian, U. Arp, H.H. Hunter, T.B. Lucatorto, J.L. Dehmer, and A.C. Parr, Applied Optics 38, 18 (1999).

The New UV Radiometry Facility at SURF, P.S. Shaw, K.R. Lykke, R. Gupta, U. Arp, and T.B. Lucatorto, SRI99: Eleventh US National Conference, AIP Conference Proceedings 521, 81 (1999).

Measurements of the Index of Refraction in the Deep and Vacuum Ultraviolet, R. Gupta, J.H. Burnett, and U. Griesmann, SPIE Proceedings (1998).

Fourier Transform Refractometry, S. Kaplan, L.M. Hanssen, U. Griesmann, and R. Gupta, SPIE Proceedings (1998).

Index of Refraction and Thermal Coefficients of Optical Materials Near 193 nm. R. Gupta, J.H. Burnett, U. Griesmann, SPIE Proceedings 3334-118, 445 (1998).

Absolute Refractive Indices and Thermal Coefficients of Fused Silica and Calcium Fluoride Near 193 nm (81.9KB) , R. Gupta, J.H. Burnett, U. Griesmann, and M. Walhout, Applied Optics, 37, 5964 (1998).

New Ultraviolet Radiometry Beamline at the Synchrotron Ultraviolet Radiation Facility at NIST (223KB) , P.S. Shaw, K.R. Lykke, R. Gupta, T.R. O’Brian, U. Arp, H.H. White, T.B. Lucatorto, J.L. Dehmer, and A.C. Parr, Metrologia, 35, 301 (1998).

OTD Home Page   |   Technical Inquiries   |   Site Comments
Online: July 1997   -   Last updated: November 2003