Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
2000-02-01
2002-03-05
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
Reexamination Certificate
active
06353477
ABSTRACT:
TECHNICAL FIELD
The present invention relates to ellipsometers and polarimeters and the like, and more particularly is a Spectroscopic Rotating Compensator Material System Investigation System including a Pseudo-achromatic Compensator, and Photo Array for simultaneously detecting a Multiplicity of Wavelengths, which Spectroscopic Rotating Compensator Material System Investigation System is calibrated by a Mathematical Regression based technique involving, where beneficial and desired, Parameterization of Calibration Parameters. The present invention provides a preferred fast axes offset, dual zero-order, or effective zero-order, or combination zero-order and effective zero-order waveplate compensator system, alternative use of D.C. and A.C and combination A.C. and D.C. data normalizing bases in various calibration steps, as well as use of various material systems during calibration data acquisition. The present invention system can be realized utilizing off-the-shelf, non-ideal, waveplates.
BACKGROUND
Ellipsometry is a well known means by which to monitor material systems. In brief, a polarized beam of electromagnetic radiation of one or more wavelengths is caused to impinge upon a material system along one or more angles of incidence and then interact with a material system. 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 being investigated, and where “S” identifies a plane perpendicular to the “P” plane and parallel to said surface of said material system. A change in polarization state in a polarized beam of electromagnetic radiation caused by said interaction with a material system, is representative of properties of said material system. (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 at a given Angle-of-Incidence, are determined by analysis of data which represents change in polarization state.
Continuing, Ellipsometer Systems generally include a source of a beam of electromagnetic radiation, a Polarizer, which serves to impose a linear state of polarization on a beam of electromagnetic radiation, a Stage for supporting a sample system, and an Analyzer which serves to select a polarization state in a beam of electromagnetic radiation after it has interacted with a material system 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 between orthogonal components of a polarized beam 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 present invention is, in its primary embodiment, 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 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 of Patents relevant to the present invention has identified very little. Most important, is a Patent to Johs et al, U.S. Pat. No. 5,872,630, from which the present invention is derived. Said 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 compensator(s), 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 Jan. 6, 1998, and Filed Mar. 20, 1996 for an Infrared Ellipsometer System Regression based Calibration Procedure. Said 212 Patent describes use of an Achromatic Rotating Compensator and application of Mathematical Regression in a Calibration procedure which evaluates calibration parameters in both rotating and stationary components. Said 630 Patent was Continued-in-Part therefrom.
A recent Patent to Aspnes, is U.S. Pat. No. 5,877,859. This Patent describes a Broadband Spectroscopic Rotating Compensator Ellipsometer System wherein the Utility is derived from selecting a Wavelength Range and Compensator so that at least one wavelength in said wavelength Range has a retardation imposed of between 135 and 225 Degrees, and another wavelength in the wavelength Range has a retardation imposed which is outside that retardation Range. The entire Utility of the Therma-wave Patent derives from that condition being met so that coefficients of two-omega and four-omega terms at various wavelengths provide information, even when other such coefficients do not.
Another Patent, U.S. Pat. No. 4,053,232 to Dill et al. describes a Rotating-Compensator Ellipsometer System, which operates uti
Herzinger Craig M.
Johs Blaine D.
J. A. Woollam Co. Inc.
Pham Hoa Q.
Welch James D.
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