Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
2000-01-07
2001-07-31
Font, Frank G. (Department: 2879)
Optics: measuring and testing
By polarized light examination
Of surface reflection
C356S329000, C250S225000
Reexamination Certificate
active
06268917
ABSTRACT:
TECHNICAL FIELD
The present invention relates to material system investigation systems, such as ellipsometers, spectrophotometers and polarimeters which comprise a polychromatic source of electromagnetic radiation, and more particularly to a source of polychromatic electromagnetic radiation which, via beam combiner means, combines beams of polychromatic electromagnetic radiation from a plurality of sources, to provide a relatively broad and flat intensity characteristic vs. wavelength output spectrum.
BACKGROUND
The use of material system investigation systems, (such as ellipsometer systems), to investigate material systems, (such as substrates with thin films present thereupon), is well known.
As insight, an ellipsometer system is, for instance, comprised of a source of electromagnetic radiation, a polarization state setting system, a means for supporting a material system, and a polarization state detecting system comprised of an analyzer and a detector system. In addition compensators(s) can be present between the source of electromagnetic radiation and the detector system, often as part of a polarization state setting system.
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). In particular 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. Another benefit provided by fixed Polarizer (P) and Analyzer (A) positions in rotating compensator ellipsometer systems 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.
Continuing, it is generally known that a source of electromagnetic radiation can provide a monochromatic, (eg. a laser system), or a polychromatic output. In spectroscopic ellipsometer systems, a polychromatic source of electromagnetic radiation is utilized to enable obtaining data at numerous wavelengths simultaneously. Typically available sources of polychromatic electromagnetic radiation, however, do not provide similar intensity output at all wavelengths, let alone a relatively broad and flat magnitude vs. wavelength spectra. As a result, data can not be obtained at all wavelengths over a wide range thereof.
A need is thus identified for a source of polychromatic electromagnetic radiation which can combine wavelength spectra from multiple polychromatic electromagnetic radiation sources, to provide a relatively broad and flattened intensity vs. wavelength spectra in material system investigation systems.
With the present invention in mind, a Search of Patents for sources of broad band polychromatic electromagnetic radiation was conducted, and said Search has identified Patents which describe systems which combine wavelengths from a plurality of laser sources to provide a single output beam of electromagnetic radiation that contains wavelengths provided by all said sources. In particular said Search revealed numerous Patents wherein a beam of electromagnetic radiation comprising wavelengths present in a plurality of laser sources is achieved by use of electromagnetic beam combining dichroic mirrors as an enabling means. U.S. Pat. No. 5,179,462 to Kageyama et al. for instance, provides a sequence of three such electromagnetic beam combining dichroic mirrors in an arrangement which produces an output beam of electromagnetic radiation that contains wavelengths from each of four sources of electromagnetic radiation. Each electromagnetic beam combining dichroic mirror is arranged so as to transmit a first input beam of electromagnetic radiation, comprising at least a first wavelength content, therethrough so that it exits a second side of said electromagnetic beam combining dichroic mirror, and to reflect a second beam of electromagnetic radiation, comprising an additional wavelength content, from said second side of said electromagnetic beam combining dichroic mirror in a manner that a single output beam of electromagnetic radiation is formed which contains the wavelength content of both sources of electromagnetic radiation. The sources of electromagnetic radiation are described as lasers in said 462 Patent. Another Pat. No. 5,296,958 to Roddy et al., describes a similar system which utilizes Thompson Prisms to similarly combine electromagnetic beams for laser source. Pat. Nos. 4,982,206 and 5,113,279 to Kessler et al. and Hanamoto et al. respectively, describe similar electromagnetic electromagnetic beam combination systems in laser printer and laser beam scanning systems respectively. Another Pat., No. 3,947,688 to Massey, describes a method of generating tuneable coherent ultraviolet light, comprising use of an electromagnetic electromagnetic beam combining system. A Patent to Miller et al., No. 5,155,623, describes a system for combining information beams in which a mirror comprising alternating regions of transparent and reflecting regions is utilized to combine transmitted and reflected beams of electromagnetic radiation into a single output beam. A Patent to Wright, No. 5,002,371 is also mentioned as describing a beam splitter system which operates to separate “P” and “S” orthogonal components in a beam of polarized electromagnetic radiation.
Patents assigned to the J. A. Woollam Co. Inc., which describe material system investigation systems such as ellipsometers, spectrophotometers and polarimeters include No. 5,373,359 to Woollam et al., Nos. 5,872,630 and 5,666,201 and 5,805,285 to Johs et al., Nos. 5,521,706 and 5,504,582 to Green et al and Johs et al. respectively, No. 5,706,212 to Thompson et al. In addition a modulation element ellipsometer system is described in Patent No. 5,416,588 to Ducharme et al. Said just recited Patents are hereby included herein by reference.
Said 359 Patent describes a Rotating Analyzer ellipsometer system, and the 201 Patent comprises a detector arrangement in which multiple orders of a dispersed beam of electromagnetic radiation are intercepted by multiple detector systems. 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 and describes a particularly relevant ellipsometer system in which the present invention can be beneficially applied. In particular 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.
Another, and recent, Patent to Aspnes, is 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 va
Font Frank G.
J.A. Woollam Co. Inc.
Ratliff Reginald A.
Welch James D.
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