Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
2000-05-30
2004-10-12
Smith, Zandra V. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
Reexamination Certificate
active
06804004
ABSTRACT:
TECHNICAL FIELD
The present invention relates to ellipsometry and polarimetry, and more particularly comprises quasi-achromatic multi-element lens(es) and the application thereof in focusing, and optionally re-colliminating), a spectroscopic electromagnetic beam into a very small, chromatically relatively undispersed, area spot on a material system, said achromatic multi-element lens(es) providing relatively constant focal length at each wavelength in a large range of wavelengths, including into the deep UV; and said present invention is further a method for breaking correlation between, and evaluating parameters in parameterized equations for calculating retardance entered to, or between, orthogonal components in a beam of spectroscopic electromagnetic radiation by quasi-achromatic multi-element input and/or output optical elements, (eg. lens(es)), and a typically ellipsometrically indistinguishable, adjacently located, investigated material system with which the spectroscopic beam of electromagnetic radiation is caused to interact.
BACKGROUND
The practice of ellipsometry is well established as a non-destructive approach to determining characteristics of material systems, and can be applied in real time process control. The topic is generally well described in a number of publication, 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).
In general, modern practice of ellipsometry typically involves causing a spectroscopic beam of electromagnetic radiation, in an imposed, known, state of polarization, to interact with a material system at one or more angle(s) 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 material 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 material system are indicative of the structure and composition of said material system. The practice of ellipsometry utilizes said changes in polarization state by proposing a mathematical model of the ellipsometer system and the material system investigated by use thereof, obtaining experimental data by application of the ellipsometer system, and applying square error reducing mathematical regression, (typically), to the end that parameters in the mathematical model which characterize the material system are evaluated so that the obtained experimental data, and values calculated by use of the mathematical model have a “best match” relationship.
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 material system, material 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 material system;
PSI
=
&LeftBracketingBar;
r
p
/
r
s
&RightBracketingBar;
;
and
DELTA
=
(
∠
r
p
-
∠
r
s
)
.
As alluded to, the practice of ellipsometry requires that a mathematical model be derived and provided for a material 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 material 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) such as lens(es), beam directing means, and/or windows such as in vacuum chambers);
e. a material system;
f. (additional element(s) such as lens(es), beam directing means, and/or windows such as in vacuum chambers);
g. optionally a compensator element;
h. an Analyzer element; and
i. a 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 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.
Where an ellipsometer system is applied to investigate a small region of a material system present, it must be appreciated that the beam of electromagnetic radiation can be convergently entered thereto through an input lens, and, optionally, exit via a re-collimating output lens. In effect this adds said input, go (and output), lenses as elements in the ellipsometer system as “additional elements”, (eg. identified in d. and f. above), which additional elements must be accounted for in the mathematical model. If this is not done, material system representing parameters determined by application of the ellipsometer system and mathematical regression, will have the effects of said input, (and output), lenses at least partially correlated thereinto, much as if the input and, (output lenses), were integrally a part of the material system.
It is emphasized that where two sequentially adjacent elements in an ellipsometer system are held in a static positon with respect to one another while experimental ellipsometric data is acquired, said two sequentially adjacent elements generally appear to be a single element. Hence, a beam directing element adjacent to a lens can appear indistinguishable from said lens as regards the overall effect of said combination of elements. In that light it is to be understood that present input and output lenses are normally structurally fixedly positioned and are not rotatable with respect to a material system present in use, thus preventing breaking correlation between parameters in equations for sequentially adjacent input and output lenses and an investigated material system by an element rotation technique. While correlation of parameters in mathematical equations which describe the effects of groupings of elements, (such as a compensator and an optional element(s)), can be tolerable, correlation between parameters in the mathematical model of an investigated material system and other elements in the ellipsometer system must be broken to allow obtaining accurate material system representing PSI and DELTA values, emphasis added. That is to say that correlation between parameters in equations in a mathematical model which describe the effects of a stationary compensator and a sequentially next located lens element, (eg. correllation between effects of elements c. and d. or between f. and g. identified above), in a beam of electromagnetic radiation might be tolerated to the extent that said correlation does not influence determination of material system describing PSI and DELTA values, but the correlation between parameters in equations which describe the effects of ellipsometer system components (eg. a., b., c., d., f., g., h. and i.), and equations which describe the effects of a present material system (eq. element e. above), absolutely must be broken to allow the ellipsometer system to provide accurate PSI and DELTA values for said material system. Application of ellipsometry to investigation of a material system present can then present a challenge to users of ellipsometer systems in the form of providing a mathematical model for each of an input and output lens, and providing a method by which the effects of said input and output lenses can be separated from the effects of an investigated material system.
Thus is identified an example of a specific problem, solution of which is the topic of the present invention.
One typical
He Ping
Herzinger Craig M.
Johs Blaine D.
Liphardt Martin M.
J. A. Woollam Co., Inc
Smith Zandra V.
Welch James D.
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