Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
2001-09-26
2004-09-21
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
C356S364000, C356S365000, C356S368000
Reexamination Certificate
active
06795184
ABSTRACT:
TECHNICAL FIELD
The present invention relates to polarization state modifying systems which find application in ellipsometer, polarimeter and the like systems. More particularly the present invention comprises an image rotating system comprised of a sequence of an odd number of reflecting elements, such that a linearly, or partially linearly polarized electromagnetic beam caused to enter, reflectively interacts with the odd number of reflecting elements and exits in a direction which is essentially non-deviated and non-displaced, with an azimuthally rotated, but otherwise substantially unchanged, polarization state.
BACKGROUND
The practice of ellipsometry is well established as a non-destructive approach to determining characteristics of sample systems, and can be practiced in real time. The topic is well described in a number of publications, one such publication being a review paper by Collins, titled “Automatic Rotating Element Ellipsometers: Calibration, Operation and Real-Time Applications”, Rev. Sci. Instrum., 61(8) (1990).
Before proceeding, as it is relevant to the present invention, it is noted that ellipsometer systems generally comprise means for setting a linear or elliptical polarization state, (typically substantially linear).
Continuing, in general, modern practice of ellipsometry typically involves causing a spectroscopic beam of electromagnetic radiation, in a known state of polarization, to interact with a sample system at at least one angle of incidence with respect to a normal to a surface thereof, in a plane of incidence. (Note, a plane of incidence contains both a normal to a surface of an investigated sample system and the locus of said beam of electromagnetic radiation). Changes in the polarization state of said beam of electromagnetic radiation which occur as a result of said interaction with said sample system are indicative of the structure and composition of said sample system. The practice of ellipsometry further involves proposing a mathematical model of the ellipsometer system and the sample system investigated by use thereof, and experimental data is then obtained by application of the ellipsometer system. This is typically followed by application of a square error reducing mathematical regression to the end that parameters in the mathematical model which characterize the sample system are evaluated, such that the obtained experimental data, and values calculated by use of the mathematical model, are essentially the same.
A typical goal in ellipsometry is to obtain, for each wavelength in, and angle of incidence of said beam of electromagnetic radiation caused to interact with a sample system, sample system characterizing PSI and DELTA values, (where PSI is related to a change in a ratio of magnitudes of orthogonal components r
p
/r
s
in said beam of electromagnetic radiation, and wherein DELTA is related to a phase shift entered between said orthogonal components r
p
and r
s
), caused by interaction with said sample system:
PSI=|
r
p
/r
s
|; and
DELTA=(&Dgr;
r
p
−&Dgr;r
s
).
As alluded to, the practice of ellipsometry requires that a mathematical model be derived and provided for a sample system and for the ellipsometer system being applied. In that light it must be appreciated that an ellipsometer system which is applied to investigate a sample system is, generally, sequentially comprised of:
a. a Source of a beam electromagnetic radiation;
b. a Polarizer element;
c. optionally a compensator element;
d. (additional element(s));
e. a sample system;
f. (additional element(s));
g. optionally a compensator element;
h. an Analyzer element; and
i. a Spectroscopic Detector System.
Each of said components b.-i. must be accurately represented by a mathematical model of the ellipsometer system along with a vector which represents a beam of electromagnetic radiation provided from said source of a beam electromagnetic radiation, Identified in a. above)
Various conventional ellipsometer configurations provide that a Polarizer, Analyzer and/or Compensator(s) can be rotated during data acquisition, and are describe variously as Rotating Polarizer (RPE), Rotating Analyzer (RAE) and Rotating Compensator (RCE) Ellipsometer Systems. It is noted, that nulling ellipsometers also exist in which elements therein are rotatable in use, rather than rotating. Generally, use of a nulling ellipsometer system involves imposing a substantially linear polarization state on a beam of electromagnetic radiation with a linear polarizer, causing the resulting polarized beam of electromagnetic radiation to interact with a sample system, and then adjusting an analyzer to an azimuthal azimuthal angle which effectively cancels out the beam of electromagnetic radiation which proceeds past the sample system. The azimuthal angle of the analyzer at which nulling occurs provides insight to properties of the sample system.
Continuing, in use, data sets can be obtained with an ellipsometer system configured with a sample system present, sequentially for cases where other sample systems are present, and where an ellipsometer system is configured in a straight-through configuration wherein a beam of electromagnetic radiation is caused to pass straight through the ellipsometer system without interacting with a sample system. Simultaneous mathematical regression utilizing multiple data sets can allow calibration of ellipsometers and evaluation of sample system characterizing PSI and DELTA values over a range of wavelengths. The obtaining of numerous data sets with an ellipsometer system configured with, for instance, a sequence of sample systems present and/or wherein a sequential plurality of polarization states are imposed on an electromagnetic beam caused to interact therewith, can allow system calibration of numerous ellipsometer system variables.
Patent to Herzinger, U.S. Pat. No. 6,137,618 is disclosed as it describes a Single Brewster Angle Polarizer in the context of multiple reflecting means, and discloses prior art dual Brewster Angle Single Reflective Means Polarizer Systems.
Another Patent, to Herzinger et al., U.S. Pat. No. 6,084,675 describes an adjustable beam alignment compensator/retarder with application to spectroscopic ellipsometry.
U.S. Pat. No. 6,118,537 to Johs et al. describes a multiple Berek plate optical retarder system.
U.S. Pat. No. 6,141,102 to Johs et al. describes a single triangular shaped optical retarder element.
U.S. Pat. No. 5,946,098 to Johs et al., describes dual tipped wire grid polarizers in combination with various compensator/retarder systems.
U.S. Pat. No. 6,100,981 to Johs et al., describes a dual horizontally oriented triangular shaped optical retarder.
U.S. Pat. No. 6,084,674 to Johs et al., describes a parallelogram shaped optical retarder element.
U.S. Pat. No. 5,963,325 to Johs et al., describes a dual vertically oriented triangular shaped optical retarder element.
A Patent to Johs et al., U.S. Pat. No. 5,872,630 is disclosed as it describes an ellipsometer system in which an analyzer and polarizer are maintained in a fixed in position during data acquisition, while a compensator is caused to continuously rotate.
A Patent to Thompson et al. U.S. Pat. No. 5,706,212 is also disclosed as it teaches a mathematical regression based double Fourier series ellipsometer calibration procedure for application, primarily, in calibrating ellipsometers system utilized in infrared wavelength range. Bi-refringent, transmissive window-like compensators are described as present in the system thereof, and discussion of correlation of retardations entered by sequentially adjacent elements which do not rotate with respect to one another during data acquisition is described therein.
Further Patents of which the Inventor is aware include:
U.S. Pat. Nos. 5,757,494; and 5,956,145;
to Green et al., in which are taught a method for extending the range of Rotating Analyzer/Polarizer ellipsometer systems to allow measurement of DELTA'S near zero (0.0) and one-hundred-eighty (180) degrees, and the extension of modulator element ellip
Green Steven E.
Herzinger Craig M.
Johs Blaine D.
Font Frank G.
J.A. Woollam Co. INC
Punnoose Roy M.
Welch James D.
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