Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
2001-09-10
2002-11-19
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
Reexamination Certificate
active
06483586
ABSTRACT:
TECHNICAL FIELD
The present invention relates to Rotating Compensator Sample System Investigation Systems and more particularly to use of Beam Splitting Analyzer means therein to simultaneously provide two electromagnetic beams, each thereof having a different effective Analyzer Azimuthal angle imposed thereupon. In use each of said two beams of electromagnetic radiation is directed to a separate detector such that two corresponding data sets are simultaneously, rather than sequentially as required where conventional Rotatable Analyzer means are utilized, obtained.
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).
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, in which elements therein are rotatable rather than rotating, and that ellipsometers containing modulation elements also are known.
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 the 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. 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 and/or analyzer azimuthal angle states are imposed on an electromagnetic beam caused to interact with one or more sample systems, can allow system calibration of numerous ellipsometer system variables. It is noted, however, that it is often inconvenient to have to sequentially reconfigure an ellipsometer system to obtain multiple data sets. It is that problem to which the present invention provides an answer.
As it is relevant to the present invention it is noted at this point that polarizer and analyzer elements often comprise rotatable elements which serve to provide, or detect, a single beam of linearly polarized electromagnetic radiation, and that multiple data sets can correspond to multiple azimuthal angle rotation positions of said analyzer.
With the present invention in mind it is disclosed that relevant Patents include U.S. Pat. No. 5,872,630 to Johs et al., (said 630 Patent being incorporated by reference hereinto), which describes a Rotating Compensator Ellipsometer System. Said 630 Patent rotating compensator ellipsometer is described as being a sample system investigation system comprising a source of a beam of electromagnetic radiation, a polarizer, a stage for supporting a sample system, an analyzer, and a detector system, said rotating compensator sample 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;
such that when said rotating compensator sample system investigation system is used to investigate a sample system present on said stage for supporting a sample system, said polarizer means and analyzer means are maintained essentially fixed in position and at least one of said at least one compensator(s) is caused to continuously rotate while a beam of electromagnetic radiation produced by said source of a beam of electromagnetic radiation is caused to pass through said polarizer means and said at least one compensator(s), said beam of electromagnetic radiation being also caused to interact with said sample system and pass through said analyzer means and enter said detector system.
Further disclosed is a U.S. Pat. No. 5,416,588 to Ducharme which describes use of a Wollaston Prism as an Analyzer beam splitting means in said Modulation Element Ellipsometer System.
U.S. Pat. No. 5,946,098 to Johs et al. is disclosed as providing numerous designs for compensators which can be used in a present invention system. Said 098 Patent is incorporated by reference herewithin.
As the present invention includes regression calibration, 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
Green Steven E.
Hale Jeffrey S.
Herzinger Craig M.
Johs Blaine D.
J. A. Woollam Co. Inc.
Pham Hoa Q.
Welch James D.
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