Adjustable beam alignment compensator/retarder

Abstract: A compensator or retarder system (3) allows adjustment to eliminate introduction of significant deviation and/or displacement into the propagation direction of a beam of electromagnetic radiation (LB) (LB') caused to interact therewith, even when the compensator or retarder system is caused to continuously rotate in a rotating compensator (C1) (C2) (C3) ellipsometer system (1). The system (3) consists of two pivotable reflectors (OS1,OS2) and a totally internally reflecting prism (P2).

Description: The present invention relates to ellipsometer/polarimeter systems, and more particularly to a compensator/retarder system which provides adjustment to eliminate introduction of significant deviation and/or displacement into the propagation direction of a beam of electromagnetic radiation caused to interact therewith, even when, for instance, a compensator/retarder system is caused to continuously rotate in a rotating compensator ellipsometer system. As well, the present invention provides a method of calibration of an ellipsometer/ polarimeter system which comprises a compensator/retarder system that is continuously rotated in use. Polarimeters and ellipsometers are comprised of optical elements such as polarizer and retarder systems. Polarimeter systems allow the polarization state of a polarized beam of electromagnetic radiation to be determined, and ellipsometer systems allow detection of change in polarization state of a polarized beam of electromagnetic radiation resulting from interaction with a sample system to be determined, said change in polarization state being associated with optical and physical properties of said sample system. For general information it is noted that the polarization state of a polarized beam of electromagnetic radiation is determined by: a. ratio of orthogonal components, (related to PSI); b. phase angle between said orthogonal components, (related to DELTA); c. absolute value of one orthogonal component; and d. the direction of rotation, or handedness. It is noted that an ideal polarizer would pass only linearly polarized electromagnetic radiation aligned with the fast axis thereof, and would reject all electromagnetic radiation in an orthogonal orientation. That is, the extinction ration would be essentially infinite. The Mueller Matrix for an ideal polarizer is provided below: An ideal Retarder system would enter a phase retardation between orthogonal components of polarized electromagnetic radiation without preferentially modifying the intensity of either orthogonal component thereof. The Mueller Matrix of an ideal Retarder is: where "r" is the entered retardence. As even very good compensator/retarder systems tend to preferentially modify one orthogonal component of an electromagnetic beam of radiation, (including those presented in this Disclosure), it is necessary to modify said Mueller Matrix to account for said effect. The Mueller Matrix of a Retarder system which accounts for preferential modification of one orthogonal component of a polarized beam of electromagnetic radiation is: where "r" is again the retardence entered. Note that where Retarder system PSI ( ψ) is forty-five (45) degrees, said Mueller Matrix reduces to the ideal Mueller Matrix. It is additionally noted that the value of "r" should be in a range where an ellipsometer system in which it is a component is not severely sensitive to changes therein as, for instance, a function of wavelength. In Rotating Compensator Ellipsometers, it is disclosed that a value of "r" between ninety (90) and one-hundred-fifty (150) degrees is generally acceptable. It is also noted that typical off-the-shelf Retarder systems often exhibit an "r" with a (1/wavelength) response such that "r" values are not within said 90 to 150 degree range, when observed over a wavelength range of say, two-hundred-fifty (250) to one-thousand (1000) nm. It is a requirement of an ideal optical element that a beam of electromagnetic radiation caused to interact therewith not have its direction of propagation deviated or displaced thereby. This is especially critical where an optical element must be rotated in use. It is further desirable that an optical element not exhibit sensitivity of, for instance, extinction ratio, or retardence entered between orthogonal components of an electromagnetic beam of radiation caused to interact therewith, as a function of beam alignment with respect thereto. As well, it is desirable that optical elements be easy to fabricate and that fabrication be from easily obtainable materials. Continuing, the practice of ellipsometry requires that data reflecting change in polarization state of an electromagnetic beam of radiation resulting from interaction with a sample system be obtained and that said data be compared to data generated by use of a proposed mathematical model. Said mathematical model must take into account all nonidealities of optical elements present in the ellipsometer utilized. It is thus preferable to have as few nonidealities present in optical elements as is possible, in order to simplify mathematical model complexity. With an eye to the present invention, a Search of Patents was conducted. Said Search was focused on polarizers, and on compensator/retarder systems which might provide relatively stable retardation over a range of wavelengths without imposing deviation or displacement in a beam of electromagnetic radiation caused to pass therethrough. Regarding compensator/retarder systems, U.S. Patents were found which show elements with geometry somehow similar to geometry of the present invention compensator/retarder systems, but the present invention was not found. In particular, attention is directed to Patent No. 548,495 to Abbe, Patent No. 4,556,292 to Mathyssek et al., Patent No. 5,475,525 Tournois et al., and Patent No. 5,016,980 Waldron. Patent No. 3,817,624 to Martin and Patent No. 2,447,828 to West were also identified. By far the most important Patent describing application of compensators in ellipsometer systems is No. 5,872,630 to Johs et al. Said Patent describes a rotating compensator ellipsometer system in which use of non-achromatic compensators is enabled by a regression based calibration procedure. It is noted that the PCT version of said Patent is Serial No. PCT/US98/02390 and the EPO version thereof is Serial No. 98907397.8. Additional searching of Patents identified a Patent to Dill, No. 4,053,232 which describes a Rotating-Compensator Ellipsometer System, which operates utilizes monochromatic light. Two Patents which identify systems which utilize Polychromatic light in investigation of material systems are described in Patent Nos. 5,596,406 and 4,668,086, to Rosencwaig et al. and Redner, respectively, were also identified. Also identified is a Patent to Woollam et al, No. 5,373,359 as it describes a Rotating Analyzer Ellipsometer System which utilizes white light. Patents continued from the 359 Woollam et al. Patent are, Nos. 5,504,582 to Johs et al. and 5,521,706 to Green et al. Said 582 Johs et al. and 706 Green et al. Patents describe use of polychromatic light in a Rotating Analyzer Ellipsometer System. A Patent to Bernoux et al., No. 5,329,357 is identified as it describes an ellipsometer system in which polarizer rotation is caused during use. A Patent to Chen et al., No. 5,581,350 is identified as it describes the application of regression in calibration of ellipsometer systems. An article by Johs, titled "Regression Calibration Method For Rotating Element Ellipsometers", which appeared in Thin Film Solids, Vol. 234 in 1993 is also identified as it predates the Chen et al. Patent and describes an essentially similar approach to ellipsometer calibration. An article by Jellison Jr. titled "Data Analysis for Spectroscopic Ellipsometry", Thin Film Solids, 234, (1993) is idnetified as it describes a method fo determining the accuracy with which certain data points can be measured, which information allows adding a weighting factor to a curve fitting regression procedure as applied to a multiplicity of data points, said weighting factor serving to emphasize the effect of more accurate and precise data. A book by Azzam and Bashara titled "Ellipsometry and Polarized light" North-Holland, 1977 is disclosed and incorporated herein by reference for general theory. An article by Collins titled "Automated Rotating Element Ellipsometers: Calibration, Operation, and Real-Time Applications", Rev. Sci. Instrum. 61(8), August 1990 is identified as it provides insight into rotating element ellipsometers. An article by Kleim et al. titled "Systematic Errors in Rotating-Compensator Ellipsometry" published in J. Opt. Soc. Am./Vol. 11, No. 9, Sept 1994 is identified as it describes calibration of rotating compensator ellipsometers. An Article by An and Collins titled "Waveform Analysis With Optical Multichannel Detectors: Applications for Rapid-Scan Spectroscopic Ellipsometer", Rev. Sci. Instrum., 62 (8), August 1991 is also identified as it discusses effects such as Detection System Error Characterization, Stray Light, Image Persistence etc., and calibration thereof. Also disclosed are articles by Schubert et al. which describe "Generalized Ellipsometry". The first thereof is titled "Extension Of Rotating-Analyzer Ellipsometry To Generalized Ellipsometry: Determination Of The Dielectric Function Tensor From Uniaxial TiO2", J. Opt. Soc. Am. A. 13, (1996). The second such article is authored by M. Schubert alone and is titled "Polarization Dependent Parameters Of Arbitrary Anisotropic Homogeneous Epitaxial Systems", Phys. Rev. B 53, (1996). The third such article is titled "Generalized Transmission Ellipsometry For Twisted Biaxial Dielectric Media: Application To Chiral Liquid Crystals", J. Opt. Soc. Am. A/Vol. 13, No. 9 (1996). Further identified for authority regarding regression is a book titled Numerical Recipes in "C", 1988, Cambridge University Press. A compensator/retarder system which can be configured so that it introduces essentially no deviation or displacement into a beam of electromagentic radiation caused to interact therewith, it should then be appreciated, would provide utility. It is an object of the present invention to provide an optical compensator/retarder system which demonstrates acceptably ideal behavior over relatively large wavelength ranges, and which can be applied to usage in stating compensator ellipsometer systems. According to the present invention in a first aspect, there is provided a compensator or retarder system comprising: first and second orientation adjustable elements having reflective surfaces; and a third element which presents first and second sides which project at an angle with respect to one another from a common point, said third element being made of material which provides reflective interfaces on said first and second sides inside thereof; said third element being oriented with respect to said first and second orientation adjustable elements and such that in use an input electromagnetic beam of radiation caused to approach said first orientation adjustable element, is caused to reflect therefrom and enter said third element and substantially totally internally reflect from said first side thereof, then substantially totally internally reflect from said second side and then proceed to and reflect from said second orientation adjustable element and proceed along a propagation direction which is substantially undeviated and undisplaced from that of said input electromagnetic beam of radiation, the arrangement being such that retardation is entered between orthogonal components of said input electromagnetic beam of radiation. Preferably said first and second orientation adjustable elements are mirrored elements and said electromagnetic radiation is caused to reflect externally therefrom. The invention has particular application where the system further comprises means for causing said system to rotate during use about the propagation direction of said input beam of electromagnetic radiation. In one convenient arrangement the system is arranged such that as viewed in upright side elevation, said third element presents said first and second sides thereof projecting to the left and right and downward from said upper point; said third element being oriented with respect to said first and second orientation adjustable elements such that in use said input electromagnetic beam of radiation is caused to approach said first orientation adjustable element along a substantially horizontally oriented direction, is caused to reflect therefrom and travel along a direction which is substantially upwardly vertically oriented, then enter said third element and substantially totally internally reflect from said first side thereof, then proceed along a substantially horizontal direction and substantially totally internally reflect from said second side and proceed along a substantially downward vertically oriented direction, then reflect from said second orientation adjustable element and proceed along a substantially horizontally oriented propagation direction which is substantially undeviated and undisplaced from the substantially horizontally oriented propagation direction of said input beam. There may be provided in accordance with the invention a spectroscopic ellipsometer or polarimeter system including one or more compensator or retarder systems as set out above. In particular there may be provided a spectroscopic ellipsometer or polarimeter system comprising in sequence: a source of electromagnetic radiation; a polarizer system; one or more compensator or retarder systems as set out above; an analyzer; and a detector system; the arrangement being such that in use a beam of electromagnetic radiation is provided by said source of electromagnetic radiation and is caused to pass through said polarizer system, then interact, in a functional sequence; with a sample system and said compensator or retarder system; or with said compensator or retarder and a sample system; and then pass through said analyzer and enter said detector system. It is to be appreciated that where features of the invention are set out herein with regard to an apparatus or system according to the invention, such features may also be provided with regard to a method according to the invention, and visa versa. In particular, there is provided in accordance with one aspect of the invention a method of operating a spectroscopic ellipsometer or polarimeter system which sequentially comprises: a source of electromagnetic radiation; a polarizer; a compensator or retarder system; an analyzer system; and a detector system; the method comprising the steps of: placing a sample system into said spectroscopic ellipsometer or polarimeter system; causing said source of electromagnetic radiation to provide a beam of electromagnetic radiation to said sample system; and detecting said beam of electromagnetic radiation after interaction thereof with said sample system; said beam of electromagnetic radiation being arranged to pass through said compensator or retarder system by steps in which said electromagnetic beam of radiation is caused to approach a first orientation adjustable reflective element, is caused to reflect therefrom and enter a third element, and substantially totally internally reflect from a first side thereof, then substantially totally internally reflect from a second side thereof, and then proceed to and reflect from a second orientation adjustable reflective element and proceed along a propagation direction which is substantially undeviated and undisplaced from that of said electromagnetic beam of radiation approaching said first reflective element. The method may further comprise the step of causing said compensator or retarder system to rotate during use about the propagation direction of said input beam. In accordance with yet a further aspect of the invention there may be provided a method of calibrating a spectroscopic rotating compensator material system investigation system comprising the steps of: a. providing a spectroscopic rotating compensator material system investigation system comprising: a source of electromagnetic radiation; a polarizer; a compensator or retarder system as set out above; a stage for supporting a material system; an analyzer system; and a detector system; b. developing a mathematical model of said spectroscopic rotating compensator material system investigation system which comprises as calibration parameter variables polarizer azimuthal angle orientation, present material system, present material system DELTA, compensator azimuthal angle orientation(s), matrix components of said compensator or retarder system, analyzer azimuthal angle orientating, and optionally detector element image persistence and Readout non-idealities, which mathematical model is effectively a transfer function which enables calculation of electromagnetic beam intensity as a function of wavelength detected by a detector element, given intensity as a function of wavelength provided by said source of a polychromatic beam of electromagnetic radiation, said mathematical model optionally providing equations for coefficients of terms in said transfer function, said coefficients of terms being functions of calibration parameters; c. causing a polychromatic beam of electromagnetic radiation produced by said source of a polychromatic beam of electromagnetic radiation, to pass through said polarizer, interact with a material system caused to be in the path thereof, 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, with said polychromatic beam of electromagnetic radiation also being caused to pass through said compensator or retarder system positioned at a location selected from the group consisting of: (before said stage for supporting a material system and after said stage for supporting a material system and both before and after and/or said stage for supporting a sample system); d. obtaining an at least two dimensional data set of intensity values vs. wavelength and a parameter selected from the group consisting of: (angle-of-Incidence of said polychromatic beam of electromagnetic radiation with respect to a present material system, and azimuthal angle rotation of one element selected from the group consisting of: (said polarizer and said analyzer)), over time, while said compensator or retarder system is caused to continuously rotate and, optionally, from said data set calculating numerical values for coefficients of terms in the transfer function for said spectroscopic rotating compensator material system investigation system; e. performing a mathematical regression of said mathematical model onto said at least two dimensional data set and/or onto values for coefficients of terms in the transfer function to evaluate said calibration parameters; said regression based calibration procedure evaluated calibration parameters serving to compensate said mathematical model for non-achromatic characteristics and non-idealities of said compensator or retarder system, and for azimuthal angle orientations of said polarizer, analyzer and compensator or retarder system. In accordance with a yet further aspect of the invention there may be provided a method of practising ellipsometry/polarimetry comprising the steps of: a. providing a spectroscopic ellipsometer/polarimeter system sequentially comprising: a source of electromagnetic radiation; a polarizer; a compensator or retarder system comprising: as viewed in upright side elevation, first and second orientation adjustable mirrored elements which each have reflective surfaces; said compensator or retarder system further comprising a third element which, as viewed in upright side elevation, presents with first and second sides which project to the left and right and downward from an upper point, said third element being made of material which provides reflective interfaces on first and second sides inside thereof; said third element being oriented with respect to said first and second orientation adjustable mirrored elements such that in use an input electromagnetic beam of radiation caused to approach one of said first and second orientation adjustable mirrored elements along an essentially horizontally oriented locus, is caused to externally reflect therefrom and travel along a locus which is essentially upwardly vertically oriented, then enter said third element and essentially totally internally reflect from one of said first and second sides thereof, then proceed along an essentially horizontal locus and essentially totally internally reflect from the other of said first and second sides and proceed along an essentially downward vertically oriented locus, then reflect from the other of said first and second orientation adjustable mirrored elements and proceed along an essentially horizontally oriented propagation direction locus which is essentially undeviated and undisplaced from the essentially horizontally oriented propagation direction locus of said input beam of essentially horizontally oriented electromagnetic radiation even when said compensator or retarder system is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation; an analyzer system; and a detector system; b. placing a sample system into said spectroscopic ellipsometer/polarimeter system; c. causing said source of electromagnetic radiation to provide a beam of electromagnetic radiation to said sample system; and d. detecting said beam of electromagnetic radiation after interaction thereof with said sample system. The method may further comprise the step of adjusting the orientation of said and second orientation adjustable mirrored elements so that an electromagnetic beam which is caused to exit from said compensator or retarder system is undeviated and undisplaced from the locus of said input beam of electromagnetic radiation, even when said compensator or retarder system is caused to rotate. In accordance with another feature, the method may further include the step of changing the orientation of said spectroscopic ellipsometer/polarimeter system so that a beam of electromagnetic radiation entered thereto is not oriented horizontally with respect to an external frame of reference, but so that relative relationships between said first and second orientation adjustable mirrored elements and said third element are maintained. The method may further comprise the step of causing said compensator or retarder system to rotate during use about the propagation direction locus of said input beam of electromagnetic radiation which is no longer oriented horizontally with respect to said external frame of reference. There will now be set out a number of preferred and/or optional features and arrangements which may be provided in accordance with embodiments of the invention. There may be provided a compensator/retarder system comprising, as viewed in upright side elevation, first and second orientation adjustable mirrored elements which each have reflective surfaces. Said compensator/retarder system further comprises a third element which, as viewed in upright side elevation, presents with first and second sides which project to the left and right and downward from an upper point and said third element is made of material which provides reflective interfaces on first and second sides inside thereof. Said third element is oriented, with respect to said first and second orientation adjustable mirrored elements, such that in use an input electromagnetic beam of radiation caused to approach one of said first and second orientation adjustable mirrored elements along an essentially horizontally oriented locus, is caused to externally reflect therefrom and travel along a locus which is essentially upwardly vertically oriented, then enter said third element and essentially totally internally reflect from one of said first and second sides thereof, then proceed along an essentially horizontal locus and essentially totally internally reflect from the other of said first and second sides and proceed along an essentially downward vertically oriented locus, then reflect from the other of said first and second orientation adjustable mirrored elements and proceed along an essentially horizontally oriented propagation direction locus which is essentially undeviated and undisplaced from the essentially horizontally oriented propagation direction locus of said input beam of essentially horizontally oriented electromagnetic radiation. This is the case even when said compensator/retarder is caused to rotate about the propagation direction locus of said beam of essentially horizontally oriented electromagnetic radiation. The result of use of said compensator/retarder is that retardation is entered between orthogonal components of said input electromagnetic beam of radiation. Said compensator/retarder system can also comprise means for imparting at least one of: translational; and rotational; motion, in at least one dimension, to at least one of said first and second orientation adjustable mirrored elements. It is noted that said translational motion of said at least one of said first and second orientation adjustable mirrored elements can be in any X-Y-Z direction, and rotational motion thereof can be likewise be in three dimensions, as can be enabled by a ball-joint type means. However, as said first and second orientation adjustable mirrored elements have a depth dimension, translational motion in a depth oriented direction is typically unnecessary. A primary application of the present invention compensator/retarder is in spectroscopic ellipsometer/polarimeter systems which comprise, in sequence: a source of electromagnetic radiation; a polarizer system; a compensator/retarder; an analyzer; and a detector system. A method of practicing ellipsometry/polarimetry may comprise the steps of: a. providing a spectroscopic ellipsometer/polarimeter system sequentially comprising: a source of electromagnetic radiation; a polarizer; a present invention compensator/retarder system as described infra herein; an analyzer system; and a detector system; b. placing a sample system into said spectroscopic ellipsometer/polarimeter system; c. causing said source of electromagnetic radiation to provide a beam of electromagnetic radiation to said sample system; and d. detecting said beam of electromagentic radiation after interaction thereof with said sample system. Said method of practicing ellipsometry/polarimetry can further comprise the step of causing said compensator/retarder system to rotate during use about the propagation direction locus of said input beam of essentially horizontally oriented electromagnetic radiation. Said method of practicing ellipsometry/polarimetry can further comprise the step of adjusting the orientation of said first and second orientation adjustable mirrored elements so that an electromagentic beam which is caused to exit from said compensator/retarder system is undeviated and undisplaced from the locus of said input beam of electromagnetic radiation, even when said compensator/retarder system is caused to rotate. Said method of practicing ellipsometry/polarimetry can further include the step of changing the orientation of said spectroscopic ellipsometer/polarimeter system so that a beam of electromagentic radiation entered thereto is not oriented horizontally with respect to an external frame of reference, but so that relative relationships between said first and second orientation adjustable mirrored elements and said third element are maintained. And said method of practicing ellipsometry/polarimetry can further comprise the step of causing said compensator/retarder system to rotate during use about the propagation direction locus of said input beam of electromagnetic radiation which is no longer oriented horizontally with respect to said external frame of reference. An alternative form of an embodiment of a present invention compensator/retarder system may provide for first and second orientation adjustable mirrored elements which each have reflective surfaces. Said compensator/retarder system further comprises a third element which presents with first and second sides which project at an angle with respect to one another from a common point and said third element is made of material which provides reflective interfaces on first and second sides inside thereof. Said third element is oriented with respect to said first and second orientation adjustable mirrored elements such that in use an input electromagnetic beam of radiation caused to approach one of said first and second orientation adjustable mirrored elements, is caused to externally reflect therefrom and enter said third element and essentially totally internally reflect from one of said first and second sides thereof, then essentially totally internally reflect from the other of said first and second sides and then proceed to and reflect from the other of said first and second orientation adjustable mirrored elements and proceed along a propagation direction locus which is essentially undeviated and undisplaced from that of said input electromagentic beam of radiation, even when said compensator/retarder is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation. And again, said compensator/retarder system can further comprise means for imparting at least one of: translational; and rotational; motion, in at least one dimension, to at least one of said first and second orientation adjustable mirrored elements. And said compensator/retarder system can further comprise means for causing said compensator/retarder system to rotate during use about the propagation direction locus of said input beam of electromagnetic radiation. Continuing, to provide insight to a particularly relevent application of the present invention compensator/retarder system, it is noted that it is generally considered that while Rotating Compensator Material System Investigation Systems, (eg. Rotating Compensator Ellipsometers), provide many benefits, (eg. Material System PSI and DELTA investigation limiting "dead-spots" are not present), that in the absence of essentially Achromatic "ideal" Compensators it would be prohibitively difficult and expensive to build, calibrate and utilize a "Spectroscopic" Rotating Compensator Material System Investigating System. This is to be understood in light of the fact that Compensators which are essentially Achromatic, (ie. provide essentially constant retardation over a large range of Wavelengths, such as 190 - 1000 nanometers), are not generally and economically available as off-the-shelf items. Embodiments of the present invention compensator/retarder system can be, however, applied in an affordable, easy to calibrate and utilize 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 Photo Array Detector Element System which contains a multiplicity of Detector Elements, which Spectroscopic Rotating Compensator Material System Investigation System further comprises at least one Compensator(s) positioned at a location selected from the group consisting of: (before said stage for supporting a sample system and after said stage for supporting a sample system and both before and after said stage for supporting a sample system). While it is known that generally available Compensators do not provide an exact Ninety (90) Degrees of Retardation at all wavelengths over a relatively large range of Wavelengths, the present invention, as described supra herein, utilizes a Regression based Calibration procedure which compensates for said non-ideal Compensator Retardation characteristics. And while it is true that the sensitivity and accuracy of a Rotating Compensator Material System Investigation System degrades as the Retardance provided by a utilized Compensator approaches zero (0.0) or one-hundred-eighty (180) degrees, it has been found that Compensators which demonstrate Retardation, over a range of utilized Wavelengths, of from forty (40) to one-hundred-seventy (170) degrees, are acceptable for use in the present invention, and allow achieving very impressive results over a demonstrated relatively large range of wavelengths, (eg. at least two-hundred-fifty (250) to one-thousand (1000) nanometers). When an embodiment of the present invention 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/are 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 is 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 Detector System Photo Array. A method of calibrating a Spectroscopic Rotating Compensator Material System Investigation System embodying the present invention can comprise the steps of: a. providing a Spectroscopic Rotating Compensator Material System Investigation System embodying the present invention as just described infra herein. b. developing a Mathematical Model of said Spectroscopic Rotating Compensator Material System Investigation System which comprises as Calibration Parameter variables Polarizer Azimuthal Angle Orientation, present Material System PSI, present Material System DELTA, Compensator Azimuthal Angle Orientation(s), Matrix Components of said Compensator(s), Analyzer Azimuthal Angle Orientation, and optionally Detector Element Image Persistance and Readout non-Idealities, which Mathematical Model is effectively a Transfer Function which enables calculation of Electromagnetic Beam Intensity as a function of Wavelength detected by a Detector Element, given Intensity as a function of wavelength provided by said Source of a Polychromatic Beam of Electromagnetic Radiation, said Mathematical Model optionally providing equations for Coefficients of Terms in said Transfer Function, said Coefficients of terms being functions of Calibration Parameters; c. causing a Polychromatic Beam of Electromagnetic Radiation produced by said Source of a Polychromatic Beam of Electromagnetic Radiation, to pass through said Polarizer, interact with a Material System caused to be in the path thereof, 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, with said Polychromatic Beam of Electromagnetic Radiation also being caused to pass through said Compensator(s) positioned at a location selected from the group consisting of: (before said Stage for Supporting a Material System and after said Stage for Supporting a Material system and both before and after said Stage for Supporting a Sample System); d. obtaining an at least Two Dimensional Data Set of Intensity Values vs. Wavelength and a parameter selected from the group consisting of: (Angle-Of-Incidence of said Polychromatic Beam of Electromagnetic Radiation with respect to a present Material System, and Azimuthal Angle Rotation of one element selected from the group consisting of: (said Polarizer and said Analyzer)), over time, while at least one of said at least one Compensator(s) is caused to continuously rotate and, optionally, from said data set calculating numerical values for Coefficients of Terms in the Transfer Function for said Spectroscopic Rotating Compensator Material System Investigation System; e. performing a Mathematical Regression of said Mathematical Model onto said at least Two Dimensional Data Set and/or onto values for Coefficients of Terms in the Transfer Function to evaluate said Calibration Parameters; said Regression based Calibration Procedure evaluated Calibration Parameters serving to compensate said Mathematical Model for non-Achromatic characteristics and non-Idealities of said Compensator(s), and for Azimuthal Angle Orientations of said Polarizer, Analyzer and Compensator(s). In addition, evaluation of Detector System Detector Element Image Persistance and Readout non-Ideality compensation Calibration Parameters also included in the Mathematical Model, can simultaneously be carried out in the Mathematical Regression Procedure. It is noted that where two Compensators are present, each can be rotated at essentially the same, or different speeds. It is therefore a purpose of embodiments of the present invention to provide a compensator/retarder system which allows adjustment to eliminate introduction of significant deviation and/or displacement into the propagation direction of a beam of electromagnetic radiation caused to interact therewith. It is another purpose of embodiments of the present invention to provide use of a compensator/retarder in an ellipsometer/polarimeter systems in which it is caused to continuously rotate during use. It is yet another purpose of embodiments of the present invention to provide a method of calibration of an ellipsometer/ polarimeter system which includes a compensator/retarder system embodying the present invention. Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 diagrammatically shows a general ellipsometer system; Figure 2a demonstrates a "displacement" in a beam of electromagnetic radiation (LB') as compared to electromagnetic beam (LB) of radiation; Figure 2b demonstrates a "deviated" electromagnetic beam (LB') of radiation as compared to electromagnetic beam (LB) of radiation; Figure 3 shows, in upright side elevation, the present invention retarder system (3) which can be any of the compensator/retarders (C1) (C2) (C3) shown in Figure 1; and Figure 4 shows an enlarged version of Figure 3, with some additional attributes included. Turning now to the Drawings, there is diagramatically shown in Fig. 1 a general ellipsometer system (1). Shown in functional sequence are: a source of electromagnetic radiation (LS); a polarizer (P); at least one compensator (C1) (C2) (C3); an analyzer (A); and a detector system (DET); where said polarizer, compensator and analyzer can each be variously, stationary, rotatable or rotating in use. Fig. 1 shows that a beam of electromagnetic radiation (LBI), (after interaction with said Polarizer (P) and if present compensator (C1)), is caused to interact with a sample system (SS) and either reflect off thereof (LBO), or be transmitted therethrough (LBO') said sample system (SS) and enter a Detector (DET). Multiple compensators (C1) (C2) and (C3) are shown in dashed lines to indicate that only one, or more than one can be present. Electromagnetic radiation beam (EPCLB) is also shown exiting shown Analyzers (A) (A') and entering a Detector (DET). An embodiment of the present invention provides a new compensator/retarder system which can be applied at (C1) and/or (C2) and/or (C3) as shown located in the Fig. 1 system. Before presenting the present embodiment of the invention compensator/retarder system, to aid understanding as to why the present embodiment compensator/retarder system has utility, Fig. 2a is included to demonstrate a "displacement" in a beam of electromagnetic radiation (LB') as compared to electromagnetic beam (LB) of radiation. Fig. 2b is included to demonstrate a "deviated" electromagnetic beam (LB') of radiation as compared to electromagnetic beam (LB) of radiation. It should be appreciated then that the terms "displaced" and "deviated" indicate a change in the propagation direction of a beam of electromagnetic radiation. An important aspect of the present embodiment compensator/retarder system is that it is manufacturer, or user, adjustable to allow setting a condition wherein deviation or displacement between exit and incident beams of electromagnetic radiation do not exist, but rather said exit and incident beams of electromagnetic radiation are directly alligned with one another in a direction of propagation after interaction with the present embodiment compensator/retarder system. This is a very important result, particularly where a compensator/retarder system is caused to continuously rotate in use, as in rotating compensator ellipsometer or polarimeter systems. Continuing, Fig. 3 shows that, in side elevation, the present embodiment compensator/retarder system (3) comprises a first element (P1), which as viewed in upright side elevation presents with first (OS1) and second (OS2) orientation adjustable mirrored elements which project at an angle with respect to one another. Said first element (P1) first (OS1) and second (OS2) orientation adjustable mirrored elements have reflective surfaces. Said compensator/retarder system (3) further comprises a nominally triangular shaped element (P2) which as viewed in side elevation presents with first (IS1) and second (IS2) sides which project to the left and right and downward from an upper point (UP2), said esssentially triangular shaped element (P2) is made of material which provides internally reflective, phase delay introducing, interfaces on first (IS1) and second (IS2) sides inside thereof. Said nominally triangular shaped element (P2) is oriented with respect to the first (OS1) and second (OS2) orientation adjustable mirrored elements such that in use an input electromagnetic beam of radiation (LB) caused to approach said first (OS1) orientation adjustable mirrored element along an essentially horizontally oriented propagation direction locus, is shown as being caused to reflect from, typically, an outer surface thereof and travel along as electromagnetic beam of radiation (R1) which is essentially upwardly vertically oriented. Next said electromagnetic beam of radiation (R1) is caused to enter said nominally triangular shaped element (P2) and essentially totally internally reflect from said first (IS1) side thereof, then proceed along an essentially horizontal locus and essentially totally internally reflect from the second (IS2) side thereof and proceed along an essentially downward vertically oriented electromagnetic beam of radiation (R3). This is followed by reflection from, typically, an outer surface of said second orientation adjustable mirrored element (OS2) of said first element (P1), such that said electromagnetic beam (LB') of radiation proceeds along an essentially horizontally oriented propagation direction locus, undeviated and undisplaced from the essentially horizontally oriented propagation direction locus of said input beam (LB) of essentially horizontally oriented electromagnetic radiation. This is the case even when said compensator/retarder system (3) is caused to rotate. The result of said described compensator/retarder system (3) application being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation (LB), where it is caused to interact with the second (P2) element. Further, said second (P2) element is typically a right triangle, (with a ninty (90) degree angle at (UP2)), in side elevation as shown in Fig. 3, but it is noted that the bottom side IS3 can be other than a simple straight surface, (eg. see IS3'), and the outer surfaces of first (OS1) and second (OS2) orientation adjustable mirrored elements are typically, but not necessarily, made reflective by the presence of a coating of metal thereupon. A coating of metal serves assure a high reflectance and good electromagnetic beam radiation intensity throughput. Also, assuming accurately manufactured right angle (P2) nominally triangular shaped element is utilized, this compensator/retarder design provides inherent compensation of both angular and translational misalignments of the input light beam (LB), particularly where the first (OS1) and second (OS2) orientation adjustable mirrored elements are rotated as necessary about pivot points (PP1) and (PP2), respectively. It is specifically noted that while the essentially totally internal reflections from said first (IS1) and second (IS2) sides of said esssentially triangular shaped element (P2) provides the retardation entered between orthogonal components of said electromagnetic beam (LB) of radiation, retardation can be entered by reflections from the first (OS1) and second (OS2) orientation adjustable mirrored elements. As well, the total retardence provided is compensated for angular misalignments of the input electromagnetic radiation beam. That is, if the input electromagnetic radiation beam (LB) is not aligned so as to form an angle of incidence of forty-five (45) degrees with the first outer surface (OS1), the reflected electromagnetic beam (R1) will internally reflect at the first internal surface (IS1)of the nominally triangular shaped element (P2) at a larger (smaller) angle than would be the case if said angle of incidence were forty-five (45) degrees. This effect, however, is directly compensated by a smaller (larger) angle of incidence of electromagnetic beam (R2) where it internally reflects from inner surface (IS2) of the second triangular shaped element (P2). As another comment it is to be understood that because of the oblique angles of incidence of the reflections from the outer surfaces (OS1) and (OS2) of the orientation adjustable mirrored elements of (P1) a polarimeter/ellipsometer in which said compensator/retarder (3) is present will require calibration to characterize the PSI-like component thereof. Fig. 4 shows a larger version of Fig. 3, with some additional indications of acceptable variations on the shape of the the lower side of the nominally triangular shaped element (P2), (EG. (IS3) (IS3'), (IS3'') & (IS3''')). Also indicated are adjustable modules (P1') & (P1'') which are in place of (P1) in Fig. 3. The nominally triangular shaped element (P2) and the adjustable modules (P1') & (P1'') are affixed to the (BACK SUPPORT) in generally acceptable locations. It is noted that Fig. 4 shows an angle Theta ( 1 ) at the top of the nominally triangular shaped element (P2), and it is noted that while said angle is typically ninty (90) degrees, it need not be so and it is to be understood that any functional angle is within the scope of the present invention. Adjustable Modules (P1') & (P1'') have exemplary, (not limiting), provision to allow location of orientation adjustable mirrored elements (OS1) & (OS2) pivot points, ((PP1) and (PP2) respectively, about which (OS1) and (OS2) can rotate in at least one plane), to be adjusted within slots ((S1) & (S2)) or ((S1') & (S2')), respectively. (It is noted that the pivots (PP1) and/or (PP2) can provide rotational motion capability in one or more planes) and functional equivalents which allow described and exemplified translational or rotational motion are to be considered within the scope of the present invention. The adjustment provided by basic placement of (P1') and (P1'') and (P2) on said (BACK SUPPORT), in combination with available translational and rotational adjustment of (OS1) & (OS2) within (P1') and (P1''), respectively, allows a user to very accurately align the present embodiment compensator/retarder system (3) such that that electromagnetic beam (LB') of radiation exits the present invention compensator/retarder (3) in the essentially same propagation direction as does electromagnetic beam (LB) of radiation enter thereinto. Fig. 4 also shows Rotation Means (RM) at right and left sides thereof which are shown to represent that the present embodiment compensator/retarder system (3) has the functional capability of being rotated about the propagation direction of said undeviated and undisplaced exit and incident beams of electromagnetic radiation (LB) & (LB'). It is noted that while Figs. 3 and 4 show electromagnetic beams (LB) & (LB') of radiation as externally reflecting from an "external" surface of adjustable mirrored elements (OS1) & (OS2), such is to be broadly interpreted to include a functionally equivalent system in which the mirrored surface is "internal", thereby requiring at least one of said electromagnetic beams (LB) & (LB') of radiation to transverse the depth of an adjustable mirrored elements (OS1) & (OS2), reflect from the "internal" "back" surface thereof, and transverse the depth of an adjustable mirrored elements (OS1) & (OS2) as it propagates. The present embodiment compensator/retarder system as shown in Figs. 3 and 4 is preferred because in addition to the Present Rotating Compensator Material System Investigation System being Spectroscopic, (ie. simultaneously operates on a number of Wavelengths in a Beam containing many Electromagnetic Wavelengths, over a range of, for instance, 190 - 1000 nanometers, and a Compensator (C), (C'), (C'') utilized therein can provide a Retardance which, for instance, varies inversely with Wavelength and still be usable), a Compensator (C), (C'), (C'') embodying the present invention must allow passage of a Polychromatic Electromagnetic Beam therethrough without causing significant Attenuation, Deviation or Displacement in the Direction of Propagation thereof. If this is not the case, difficult to compensate complexities are caused in Detector Elements (DE's) containing Photo Array Detector System (DET) Detector Element Output Signals. Continuing, the reason the Present Embodiment can operate with a Compensator (C), (C'), (C'') that does not provide even close to a Constant Ninety (90) Degree Retardance over a range of Wavelengths, (which would constitute Ideal Characteristics), is that a Regression based Calibration Procedure utilized, (see the Introduction of this Specification), provides Wavelength dependent Compensation effecting values for Calibration Parameters as required in a developed Mathematical Model of the present embodiment Rotating Compensator Material System Investigation System as described in pending EPO Application No. 98907397.8 as entered via PCT/US98/02390. It is also noted that Polychromatic Electromagnetic Beam Source can be comprised of a combined plurality/multiplicity of Laser Sources, and that Polychromatic Electromagnetic Beam Source can include an effective Polarizer therewithin, thereby eliminating the need for a separate Polarizer. Such cases are to be considered within the scope of the Claims. It is also to be understood that the terminology "Achromatic" is to be understood to mean that an uncertianty in Retardance provided by a Compensator of One (1.0) Degree will effect an uncertianty of One-Quarter (1/4) Degree in a measured Sample System (PSI), and an uncertianty of One-Half (1/2) Degree in a measured Sample System (DELTA). As alluded to infra herein, embodiments of the present invention compensator/retarder system finds particulary relevant, but not limiting, application in rotating compensator ellipsometer and polarimeter systems, which, it is noted, do not demonstrate "blind-spots" at DELTA'S of zero (0.0) and one-hundred-eighty (180) degrees, (as characteristic of rotating polarizer or analyzer systems), or PSI of forty-five (45) degrees, (as characteristic of modulation element systems). Having hereby disclosed embodiments of the present invention, it should be apparent that many modifications, substitutions, and variations of the present invention are possible in light thereof. It is to be understood that the present invention can be practiced other than as specifically described and should be limited in scope and breadth only by the appended Claims.

Claims: A compensator or retarder system comprising: first (OS1) and second (OS2) orientation adjustable elements having reflective surfaces; and a third element (P2) which presents first (IS1) and second (IS2) sides which project at an angle with respect to one another from a common point (UP2), said third element (P2) being made of material which provides reflective interfaces on said first (IS1) and second (IS2) sides inside thereof; said third element (P2) being oriented with respect to said first and second orientation adjustable elements (OS1 and OS2) such that in use an input electromagnetic beam (LB) of radiation caused to approach said first orientation adjustable element (OS1), is caused to reflect therefrom and enter said third element (P2) and substantially totally internally reflect from said first side (IS1) thereof, then substantially totally internally reflect from said second side (IS2) and then proceed to and reflect from said second orientation adjustable element (OS2) and proceed along a propagation direction (LB') which is substantially undeviated and undisplaced from that of said input electromagnetic beam (LB) of radiation, the arrangement being such that retardation is entered between orthogonal components of said input electromagnetic beam of radiation. A system according to Claim 1 in which said first and second orientation adjustable elements (OS1 and OS2) are mirrored elements and said electromagnetic radiation is caused to reflect externally therefrom. A system according to Claim 1 or 2 which further comprises means (RM) for causing said system (3) to rotate during use about the propagation direction of said input beam (LB) of electromagnetic radiation. A system according to any preceding claim arranged such that, as viewed in upright side elevation, said third element (P2) presents said first and second sides thereof projecting to the left (IS1) and right (IS2) and downward from said upper point (UP2); said third element (P2) being oriented with respect to said first (OS1) and second (OS2) orientation adjustable elements such that in use said input electromagnetic beam (LB) of radiation is caused to approach said first orientation adjustable element (OS1) along a substantially horizontally oriented direction, is caused to reflect therefrom and travel along a direction (R1) which is substantially upwardly vertically oriented, then enter said third element (P2) and substantially totally internally reflect from said first side (IS1) thereof, then proceed along a substantially horizontal direction (R2) and substantially totally internally reflect from said second side (IS2) and proceed along a substantially downward vertically oriented direction (R3), then reflect from said second orientation adjustable element (OS2) and proceed along a substantially horizontally oriented propagation direction (LB') which is sabstantially undeyiated and undisplaced from the substantially horizontally oriented propagation direction of said input beam (LB) A spectroscopic ellipsometer or polarimeter system including a compensator or retarder system according to any preceding claim. A spectroscopic ellipsometer or polarimeter system comprising in sequence: a source (LS) of electromagnetic radiation; a polarizer system (P); one or more compensator or retarder systems (C1) (C2) (C3) as set out in any of Claims 1 to 5; an analyzer (A); and a detector system (DET); the arrangement being such that in use a beam (LBI) of electromagnetic radiation is provided by said source of electromagnetic radiation and is caused to pass through said polarizer system (P), then interact, in a functional sequence; with a sample system (SS) and said compensator or retarder system (3); or with said compensator or retarder (C1) (C2) (C3) and a sample system; and then pass through said analyzer (A) and enter said detector system (DET). A method of operating a spectroscopic ellipsometer or polarimeter system (1) which sequentially comprises: a source (LS) of electromagnetic radiation; a polarizer (P); a compensator or retarder system (3); an analyzer system (A); and a detector system (DET); the method comprising the steps of:- placing a sample system (SS) into said spectroscopic ellipsometer or polarimeter system (1); causing said source (LS) of electromagnetic radiation to provide a beam (LBI) of electromagnetic radiation to said sample system (SS); and detecting said beam of electromagnetic radiation after interaction thereof (LBO) (LBO') with said sample system (SS); said beam of electromagnetic radiation being arranged to pass through said compensator or retarder system by steps in which said electromagnetic beam (LB) of radiation is caused to approach a first orientation adjustable reflective element (OS1), is caused to reflect therefrom and enter a third element (P2), and substantially totally internally reflect from a first side (IS1) thereof, then substantially totally internally reflect from a second side (IS2) thereof, and then proceed to and reflect from a second orientation adjustable reflective element (OS2) and proceed along a propagation direction (LB') which is substantially undeviated and undisplaced from that of said electromagnetic beam (LB) of radiation approaching said first reflective element (OS1). A method according to Claim 7 further comprising the step of causing said compensator or retarder system (3) to rotate during use about the propagation direction of said input beam (LBI). A method of calibrating a spectroscopic rotating compensator material system investigation system (1) comprising the steps of: a. providing a spectroscopic rotating compensator material system investigation system (1) comprising: a source (LS) of electromagnetic radiation; a polarizer (P); a compensator or retarder system (C1) (C2) (C3) according to any of Claims 1 to 5; a stage for supporting a material system (SS); an analyzer system (A); and a detector system (DET); b. developing a mathematical model of said spectroscopic rotating compensator material system investigation system (1) which comprises as calibration parameter variables polarizer (P) azimuthal angle orientation, present material system (SS) PSI, present material system (SS) DELTA, compensator (C1) (C2) (C3) azimuthal angle orientation(s), matrix components of said compensator or retarder system (3), analyzer (A) azimuthal angle orientating, and optionally detector element (DET) image persistence and Readout non-idealities, which mathematical model is effectively a transfer function which enables calculation of electromagnetic beam intensity as a function of wavelength detected by a detector (DET) element, given intensity as a function of wavelength provided by said source (LS) of a polychromatic beam of electromagnetic radiation, said mathematical model optionally providing equations for coefficients of terms in said transfer function, said coefficients of terms being functions of calibration parameters; c. causing a polychromatic beam (LBI) of electromagnetic radiation produced by said source (LS) of a polychromatic beam of electromagnetic radiation, to pass through said polarizer (P), interact with a material system (SS) caused to be in the path thereof, pass through said analyzer (A), and interact with said dispersive optics such that a multiplicity of essentially single wavelengths are caused to simultaneously enter a corresponding multiplicity of detector (DET) elements in said at least one detector (DET) system, with said polychromatic beam of electromagnetic radiation also being caused to pass through said compensator or retarder system (3) positioned at a location selected from the group consisting of: (before (C1) said stage for supporting a material system (SS) and after (C2) (C3) said stage for supporting a material system (SS) and both before and after (C1) and (C2) and/or (C3) said stage for supporting a sample system (SS)); d. obtaining an at least two dimensional data set of intensity values vs. wavelength and a parameter selected from the group consisting of: (angle-of-Incidence of said polychromatic beam of electromagnetic radiation with respect to a present material system, and azimuthal angle rotation of one element selected from the group consisting of: (said polarizer and said analyzer)), over time, while said compensator or retarder system (3) is caused to continuously rotate and, optionally, from said data set calculating numerical values for coefficients of terms in the transfer function for said spectroscopic rotating compensator material system investigation system; e. performing a mathematical regression of said mathematical model onto said at least two dimensional data set and/or onto values for coefficients of terms in the transfer function to evaluate said calibration parameters; said regression based calibration procedure evaluated calibration parameters serving to compensate said mathematical model for non-achromatic characteristics and non-idealities of said compensator or retarder system (3), and for azimuthal angle orientations of said polarizer (P), analyzer (A) and compensator or retarder system (3). A compensator or retarder system (3) comprising: first (OS1) and second (OS2) orientation adjustable mirrored elements which each have reflective surfaces; said compensator or retarder system (3) further comprising a third element (P2) which presents with first (IS1) and second (IS2) sides which project at an angle with respect to one another from a common point (UP2), said third element (P2) being made of material which provides reflective interfaces on first (IS1) and second (IS2) sides inside thereof; said third element (P2) being oriented with respect to said first (OS1) and second (OS2) orientation adjustable mirrored elements such that in use an input electromagnetic beam (LB) of radiation caused to approach one of said first (OS1) and second (OS2) orientation adjustable mirrored elements, is caused to externally reflect therefrom and enter said third element (P2) and essentially totally internally reflect from one of said first (IS1) and second (IS2) sides thereof, then essentially totally internally reflect from the other of said first (IS1) and second (IS2) sides and then proceed to and reflect from the other of said first (OS1) and second (OS2) orientation adjustable mirrored elements and proceed along a propagation direction locus (LB') which is essentially undeviated and undisplaced from that of said input electromagnetic beam (LB) of radiation, even when said compensator or retarder system (3) is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation. A method of practising ellipsometry/polarimetry comprising the steps of: a. providing a spectroscopic ellipsometer/polarimeter system (1) sequentially comprising: a source (LS) of electromagnetic radiation; a polarizer (P); a compensator or retarder (3) system comprising: as viewed in upright side elevation, first and second orientation adjustable mirrored elements (OS1) (OS2) which each have reflective surfaces; said compensator or retarder system (3) further comprising a third element (P2) which, as viewed in upright side elevation, presents with first and second sides which project to the left (IS1) and right (IS2) and downward from an upper point (UP2), said third element (P2) being made of material which provides reflective interfaces on first (IS1) and second (IS2) sides inside thereof; said third element (P2) being oriented with respect to said first (OS1) and second (OS2) orientation adjustable mirrored elements such that in use an input electromagnetic beam (LB) of radiation caused to approach one of said first (OS1) and second (OS2) orientation adjustable mirrored elements along an essentially horizontally oriented locus, is caused to externally reflect therefrom and travel along a locus (R1) which is essentially upwardly vertically oriented, then enter said third element (P2) and essentially totally internally reflect from one of said first (IS1) and second (IS2) sides thereof, then proceed along an essentially horizontal locus (R2) and essentially totally internally reflect from the other of said first (IS1) and second (IS2) sides and proceed along an essentially downward vertically oriented locus (R3), then reflect from the other of said first (OS1) and second (OS2) orientation adjustable mirrored elements and proceed along an essentially horizontally oriented propagation direction locus (LB') which is essentially undeviated and undisplaced from the essentially horizontally oriented propagation direction locus of said input beam (LB) of essentially horizontally oriented electromagnetic radiation even when said compensator or retarder system (3) is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam (LB) of radiation; an analyzer system (A); and a detector system (DET); b. placing a sample system (SS) into said spectroscopic ellipsometer/polarimeter system (1); c. causing said source (LS) of electromagnetic radiation to provide a beam (LBI) of electromagnetic radiation to said sample system (SS); and d. detecting said beam of electromagnetic radiation after interaction thereof (LBO) (LBO') with said sample system (SS). A method of calibrating a spectroscopic rotating compensator material system investigation system (1) comprising the steps of: a. providing a present invention spectroscopic rotating compensator material system investigation system (1) comprising: a source (LS) of electromagnetic radiation; a polarizer (P); a compensator or retarder system (C1) (C2) (C3) comprising: as viewed in upright side elevation, first and second orientation adjustable mirrored elements (OS1) (OS2) which each have reflective surfaces; said compensator or retarder system (3) further comprising a third element (P2) which, as viewed in upright side elevation, presents with first and second sides which project to the left (IS1) and right (IS2) and downward from an upper point (UP2), said third element (P2) being made of material which provides reflective interfaces on first (IS1) and second (IS2) sides inside thereof; said third element (P2) being oriented with respect to said first (OS1) and second (OS2) orientation adjustable mirrored elements such that in use an input electromagnetic beam (LB) of radiation caused to approach one of said first (OS1) and second (OS2) orientation adjustable mirrored elements along an essentially horizontally oriented locus, is caused to externally reflect therefrom and travel along a locus (R1) which is essentially upwardly vertically oriented, then enter said third element (P2) and essentially totally internally reflect from one of said first (IS1) and second (IS2) sides thereof, then proceed along an essentially horizontal locus (R2) and essentially totally internally reflect from the other of said first (IS1) and second (IS2) sides and proceed along an essentially downward vertically oriented locus (R3), then reflect from the other of said first (OS1) and second (OS2) orientation adjustable mirrored elements and proceed along an essentially horizontally oriented propagation direction locus (LB') which is essentially undeviated and undisplaced from the essentially horizontally oriented propagation direction locus of said input beam (LB) of essentially horizontally oriented electromagnetic radiation even when said compensator or retarder system (3) is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam (LB) of radiation; a stage for supporting a material system (SS); an analyzer system (A); and a detector system (DET); b. developing a mathematical model of said spectroscopic rotating compensator material system investigation system (1) which comprises as calibration parameter variables polarizer (P) azimuthal angle orientation, present material system (SS) PSI, present material system (SS) DELTA, compensator (C1) (C2) (C3) azimuthal angle orientation(s), matrix components of said compensator or retarder system (3), analyzer (A) azimuthal angle orientation, and optionally detector element (DET) image persistence and Readout non-idealities, which mathematical model is effectively a transfer function which enables calculation of electromagnetic beam intensity as a function of wavelength detected by a detector (DET) element, given intensity as a function of wavelength provided by said source (LS) of a polychromatic beam of electromagnetic radiation, said mathematical model optionally providing equations for coefficients of terms in said transfer function, said coefficients of terms being functions of calibration parameters; c. causing a polychromatic beam (LBI) of electromagnetic radiation produced by said source (LS) of a polychromatic beam of electromagnetic radiation, to pass through said polarizer (P), interact with a material system (SS) caused to be in the path thereof, pass through said analyzer (A), and interact with said dispersive optics such that a multiplicity of essentially single wavelengths are caused to simultaneously enter a corresponding multiplicity of detector (DET) elements in said at least one detector (DET) system, with said polychromatic beam of electromagnetic radiation also being caused to pass through said compensator or retarder system (3) positioned at a location selected from the group consisting of: (before (C1) said stage for supporting a material system (SS) and after (C2) (C3) said stage for supporting a material system (SS) and both before and after (C1) and (C2) and/or (C3) said stage for supporting a sample system (SS)); d. obtaining an at least two dimensional data set of intensity values vs. wavelength and a parameter selected from the group consisting of: (angle-of-Incidence of said polychromatic beam of electromagnetic radiation with respect to a present material system, and azimuthal angle rotation of one element selected from the group consisting of: (said polarizer and said analyzer)), over time, while said compensator or retarder system (3) is caused to continuously rotate and, optionally, from said data set calculating numerical values for coefficients of terms in the transfer function for said spectroscopic rotating compensator material system investigation system; e. performing a mathematic regression of said mathematical model onto said at least two dimensional data set and/or onto values for coefficients of terms in the transfer function to evaluate said calibration parameters; said regression based calibration procedure evaluated calibration parameters serving to compensate said mathematical model for non-achromatic characteristics and non-idealities of said compensator or retarder system (3), and for azimuthal angle orientations of said polarizer (P), analyzer (A) and compensator or retarder system (3).

Inventors: HERTZINGER CRAIG M, JOHS BLAINE D, HERTZINGER, CRAIG M., JOHS, BLAINE D.
Applicants: J A WOOLLAM CO INC, J.A. WOOLLAM CO. INC.
Application year: 1999
Main classification: G01N21
IPC codes: G01J3, G01J4, G01N21