Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
2001-12-28
2004-11-23
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
Reexamination Certificate
active
06822738
ABSTRACT:
TECHNICAL FIELD
This invention relates to ellipsometers and polarimeters and the like, and more particularly is a Spectroscopic Rotating Compensator Ellipsometer System including a Pseudo-Achromatic Compensator providing, over a range of wavelengths, a range of retardations, (ie. maximum retardance minus minimum retardance), of less than 90 degrees, said range of retardations being bounded by a minimum of preferably at least 30 degrees, to a maximum of less than 135 degrees. Said System also comprises a detector means for simultaneously detecting a Multiplicity of Wavelengths, which Spectroscopic Rotating Compensator Ellipsometer System is calibrated by a Mathematical Regression based technique involving, where beneficial and desired, Parameterization of Calibration Parameters. Prefered embodiments provide a preferred fast axes offset, dual or triple zero-order, or dual or triple effective zero-order, or combination zero-order and effective zero-order waveplate compensator means system; alternative use of D.C. or A.C, and combination A.C. and D.C. data normalizing bases in various calibration steps and use of un-normalized signals to determine reflectance, as well as use of various samples during calibration data acquisition. Said invention system can be realized utilizing off-the-shelf, non-ideal, waveplates combined to provide a compensator which presents a fast axis azimuth which varies with wavelength.
BACKGROUND
Ellipsometry is a well known means by which to monitor material systems, (samples). In brief, a polarized beam of electromagnetic radiation of one or more wavelengths is caused to impinge upon a material system, (sample), along one or more angles of incidence and then interact with a material system, (sample). Beams of electromagnetic radiation can be considered as comprised of two orthogonal components, (ie. “P” and “S”), where “P” identifies a plane which contains both an incident beam of electromagnetic radiation, and a normal to an investigated surface of a material system, (sample), being investigated, and where “S” identifies a plane perpendicular to the “P” plane and parallel to said surface of said material system, (sample). A change in polarization state in a polarized beam of electromagnetic radiation caused by said interaction with a material system, (sample), is representative of properties of said material system, (sample). (Note Polarization State basically refers to a magnitude of a ratio of orthogonal component magnitudes in a polarized beam of electromagnetic radiation, and a phase angle therebetween.) Generally two well known angles, (PSI and DELTA), which characterize a material system, (sample), at a given Angle-of-Incidence, are determined by analysis of data which represents change in polarization state. Additional sample identifying information is often also obtained by application of ellipsometry, including layer thicknesses, (including thicknesses for multilayers), optical thicknesses, sample temperature, refractive indicies and extinction coefficients, index grading, sample composition, surface roughness, alloy and/or void fraction, parameter dispersal and spectral dependencies on wavelength, vertical and lateral inhomogenieties etc.
Continuing, Ellipsometer Systems generally include a source of a beam of electromagnetic radiation, a Polarizer means, which serves to impose a linear state of polarization on a beam of electromagnetic radiation, a Stage for supporting a material system, (sample), and an Analyzer means which serves to select a polarization state in a beam of electromagnetic radiation after it has interacted with a material system, (sample), and pass it to a Detector System for analysis therein. As well, one or more Compensator(s) can be present and serve to affect a phase angle change between orthogonal components of a polarized beam of electromagnetic radiation.
It is noted that Spectroscopic Ellipsometer Systems utilize a Source which simultaneously provides a plurality of Wavelengths, which Source can be termed a “Broadband” Source of Electromagnetic radiation.
A number of types of ellipsometer systems exist, such as those which include rotating elements and those which include modulation elements. Those including rotating elements include Rotating Polarizer (RP), Rotating Analyzer (RA) and Rotating Compensator (RC). The presently disclosed invention comprises a Rotating Compensator Ellipsometer System. It is noted that Rotating Compensator Ellipsometer Systems do not demonstrate “Dead-Spots” where obtaining data is difficult. They can read PSI and DELTA of a Material System, (Sample), over a full Range of Degrees with the only limitation being that if PSI becomes essentially zero (0.0), one can't then determine DELTA as there is not sufficient PSI Polar Vector Length to form the angle between the PSI Vector and an “X” axis. In comparison, Rotating Analyzer and Rotating Polarizer Ellipsometers have “Dead Spots” at DELTA's near 0.0 or 180 Degrees and Modulation Element Ellipsometers also have “Dead Spots” at PSI near 45 Degrees. The utility of Rotating Compensator Ellipsometer Systems should then be apparent. Another benefit provided by fixed Polarizer (P) and Analyzer (A) positions is that polarization state sensitivity to input and output optics during data acquisition is essentially non-existent. This enables relatively easy use of optic fibers, mirrors, lenses etc. for input/output.
A Search for relevant Patents has Identified very little. Most important is a Patent to Johs et al., U.S. Pat. No. 5,872,630, from which the present Application is derived as a CIP. Said 630 Patent describes:
A spectroscopic rotating compensator material system investigation system comprising a source of a polychromatic beam of electromagnetic radiation, a polarizer, a stage for supporting a material system, an analyzer, a dispersive optics and at least one detector system which contains a multiplicity of detector elements, said spectroscopic rotating compensator material system investigation system further comprising at least one compensator(s) positioned at a location selected from the group consisting of:
before said stage for supporting a material system;
after said stage for supporting a material system; and
both before and after said stage for supporting a material system;
such that when said spectroscopic rotating compensator material system investigation system is used to investigate a material system present on said stage for supporting a material system, said analyzer and polarizer are maintained essentially fixed in position and at least one of said at least one compensator(s) is caused to continuously rotate while a polychromatic beam of electromagnetic radiation produced by said source of a polychromatic beam of electromagnetic radiation is caused to pass through said polarizer and said compensators, said polychromatic beam of electromagnetic radiation being also caused to interact with said material system, pass through said analyzer and interact with said dispersive optics such that a multiplicity of essentially single wavelengths are caused to simultaneously enter a corresponding multiplicity of detector elements in said at least one detector system.
Said 630 Patent also, amongst other disclosure, describes a Mathematical Regression based Calibration procedure which makes possible the use of essentially any compensator regardless of non-achromatic characteristics.
Another Patent to Johs, from which the 630 Patent was Continued-in Part, is U.S. Pat. No. 5,666,201, filed Sep. 20, 1995. The focus in said 201 Patent comprises a detector arrangement in which multiple orders of a dispersed beam of electromagnetic radiation are intercepted by multiple detector systems. However, Claim 8 in the 201 Patent, in combination with a viewing the Drawings therein, provide conception of the Spectroscopic Rotating Compensator Ellipsometer, as Claimed in Claim 1 of the JAW 630 Patent and, in fact, the the 630 Patent issued in view of a Terminal Disclaimer based upon the 201 Patent.
Also disclosed is U.S. Pat. No. 5,706,212, Issued Ja
Herzinger Craig M.
Johs Blaine D.
J.A. Woollam Co. Inc.
Pham Hoa Q.
Welch James D.
LandOfFree
Spectroscopic rotating compensator ellipsometer system with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spectroscopic rotating compensator ellipsometer system with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spectroscopic rotating compensator ellipsometer system with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3333682