Tod F. Schiff

Design review of a high-accuracy UV to near-IR scatterometer

A unique broadband scatterometer has been designed, built and tested for NASA Goddard. One use of the instrument will be to accurately measure the BRDF of calibration standards used by shuttle astronauts in experiments to measure atmospheric ozone. BRDF accuracy is better than 1% except for angles of incidence and scatter greater than 80 degrees. The source employs a high intensity xenon arc and programmable monochromator that allows measurements to be made anywhere from 0.23 to 0.9 micrometers over adjustable bandwidths as small as four nanometers. The goniometer allows out-of-plane measurements to be made in either transmission or reflection from horizontal samples.

Design Review Of A Complete Angle Scatter Instrument

An instrument has been designed and built to measure plane of incidence scatter at multiple wavelengths including .6328μm, from reflective, transmissive, specular, diffuse, flat and curved optics. An extensive software package accompanies the instrument and is used both to control the measurement process and to analyze the measurement data. Techniques employed in the design and development of this instrument are described. An error analysis for the measured BSDF is provided and calibration of the instrument is discussed.

Comparison Of Wavelength Scaling Data To Experiment

Wavelength scaling is the process of using scatter data at one wavelength to predict scatter at a different wavelength from the same optical component. The economic advantages of avoiding scatter measurements at all wavelengths of interest are obvious; however, the subtleties involved in making accurate wavelength scaling predictions are not. The requirements of the vector perturbation theory that the optic be a clean, smooth, front surface reflector are not always easily met for all desired wavelengths and materials. Furthermore, the experiments themselves are not trivial because they often involve all the complexities of instrument comparison measurements. This paper presents data for one dimensional (grating like) and two dimensional (polished) reflectors at wavelengths of 1.06, .86, .63, and .49 microns. The results show excellent correlation for both cases.

Design review of a unique out-of-plane polarimetric scatterometer

This paper reviews a scatterometer which is capable of measuring scatter throughout most of the sphere surrounding the sample. The instrument can be configured to operate at many different laser wavelengths, or with a broadband source, at virtually any angle of incidence. Automated polarization control of both source and receiver has been accomplished, which allows calculation of incident and scattered Stokes vectors as well as the Mueller matrix associated with either reflective or transmissive samples. This paper forms the background material for the two papers that follow it in this proceeding.

Maximum And Minimum Limitations Imposed On Bsdf Measurements

A lot of confusion exists within the optical community about the definition of Bidirectional Scatter Distribution Function (BSDF), how it should be measured, and how it should be specified. This paper defines BSDF, and then explores the practical factors that limit the measurable upper and lower values of BSDF. The upper value, which is limited by detector aperture size, can take on values exceeding 107 sr-1 in practical cases. The lower limit, sometimes called the electronic noise equivalent BSDF, is determined by the incident power and the detector solid angle as well as the system electronic noise, and needs to be specified with all three values. For systems that are noise limited by the detector, the minimum BSDF can be expressed in terms of the detector parameters (responsivity, noise, active area, and detectivity). The upper and lower limit for several systems has been explored and these results are presented.

Mueller matrix measurements of scattered light

This paper includes a very brief review of Stokes vectors and Mueller matrices. Matrix characteristics are reviewed for a number of different samples--i.e.: isotropic, anisotropic, diffuse, etc. Measurements are given for a number of different samples at both 633 and 1060 nm. This paper relies on hardware descriptions presented in the previous paper in this document.

Mueller matrix measurements of several optical components

The Stokes/Mueller approach provides complete characterization of sample induced polarization changes to both specular and scattered light that is reflected or transmitted from optical components. Ellipsometry is a subset of this more complete approach to polarization analysis. In this paper, Mueller matrices of several samples are found and compared to the matrix of ideal elements. Samples include optical mirrors that scatter both topographically and non-topographically, waveplates, and optical windows.

Measurement Of Very Near Specular Scatter

Scatterometer optics create near specular scatter (instrument signature) that complicates the process of measuring near specular scatter from samples. In order to achieve measurements within one degree of specular, the instrument signature must be compared to (or subtracted from) the scatter measured from the sample/instrument combination. Because sample scatter is independent of instrument signature, high scatter samples will separate from signature closer to specular than low scatter samples. This paper reports the results of an effort to measure down to few thousandths of a degree from specular. The samples are Bragg cells designed for use in RF spectrometers and the data is taken at 0.86 microns. Data from several materials are presented. The inherent physical limitations imposed on such measurements are also discussed.

TIS uniformity maps of wafers, disks, and other samples

Total integrated scatter measurements, the earliest well defined measurement relating light scatter to surface roughness, is now being used in modern production facilities as a means of monitoring product surface roughness. The two applications reviewed here are computer disks, where the issue is a well defined roughness (as opposed to the smoothest possible surface) and an emerging issue with roughness specifications for the backsides of silicon wafers. The paper describes a scanning instrument that allows sample uniformity to be revealed and thus the manufacturing process investigated.

Retroreflections on a low-tech approach to the measurement of opposition effect

This paper reviews a simple (economical) technique for measuring retro-scatter. Noise floors below 10-5 sr-1 have been achieved. The technique relies on a unique Stokes/Mueller method of characterizing sample polarization characteristics. Data is presented for several samples. This paper relies on material presented in the preceding two papers of this document.