Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
2000-03-21
2003-03-18
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
C356S367000, C356S364000
Reexamination Certificate
active
06535286
ABSTRACT:
TECHNICAL AREA
The present invention relates to detector systems, and more particularly to sequentially positionable, multiple detector systems in spectrophotometer, ellipsometer and polarimeter systems. The present invention also includes methods of use wherein different detector systems are utilized during different data acquisition, system calibration and/or component alignment procedures.
BACKGROUND
Spectrophotometers are well known systems for monitoring polychromatic electromagnetic beam intensity change as function of interaction with material systems, without concern to measurement of orthogonal component magnitudes, and/or phase angle therebetween. Ellipsometer systems, on the other hand, monitor change in phase between orthogonal components in a beam of electromagnetic radiation, in combination with a change in the magnitude of a ratio of the magnitudes of the orthogonal components. It is further noted that polarimeter systems generally comprise the Polarization State Detector System portion of an Ellipsometer system and are employed to detect a partial, or full polarization state of a beam of electromagnetic radiation as can be presented by a Stokes Vector, whereas, again, ellipsometer systems are typically applied to detect change in polarization state of a beam of electromagnetic radiation as a result of interaction with a material system, which change is inherently represented by ellipsometric PSI and ellipsometric DELTA. A change in the polarization state of a beam of electromagnetic radiation which results from said interaction with a material system provides insight to characteristics of the material system.
(Note: It should be appreciated that Ellipsometry measures change in Polarization State of an Electromagnetic Beam which results from interaction with a Sample. Said change in Polarization State is generally expressed In terms of “Ellipsometric PSI” and “Ellipsometric DELTA”, which are related by the well known Equation:
tan(PSI)exp(
i
DELTA)=
R
p
/R
s
;
which is often written:
&rgr;=tan(&PSgr;)
e
i&Dgr;
=R
p
/R
s
where R
p
and R
s
are Complex Fresnel Coefficients for the case where said Electromagnetic Beam reflects from a sample. Similar T
p
and T
s
Transmission Fresnel Coefficients apply where an Electromagnetic Beam transmits through a sample).
Conventional ellipsometer systems typically comprise a source of electromagnetic radiation, a polarization state modifier, a stage for supporting a material system to be investigated, a polarization state analyzer, and a detector system. Further, the combination of a source of electromagnetic radiation and a polarization state modifier, is often termed a Polarization State Generator System, and the combination of a polarization state analyzer and a detector system, is often termed a Polarization State Detector System, or polarimeter. In use a beam of electromagnetic radiation which is produced by the source thereof, is caused to pass through said polarization state modifier, interact with a material system which is placed on said stage for supporting a material system to be investigated, and then pass through said polarization state analyzer, then enter said detector system. (Note that said interaction with a sample system can involve reflection from and/or transmission therethrough).
It is further to be appreciated that there are many functionally different types of electromagnetic radiation detectors available, (eg. Photo-Diode, Photo-Diode Array, Charge Coupled Device (CCD), Photo Multiplier Tubes, Photo-Resistive Elements, Photo-Conductive Elements, Thermo-Piles, Bolemeters etc.), and that the present invention detector system can be configured to make a number of such functionally different types of detectors easily sequentially available in use. This is beneficial because electromagnetic radiation detectors which operate on different scientific principals provide different capabilities as regards wavelength ranges measurable and single to noise (S/N) ratios achievable etc.
With the foregoing in mind, it is disclosed that when practicing spectrophotometry, ellipsometry and/or polarimetry, it at times occurs that a detector system being utilized is inadequate to detect information present in an electromagnetic beam being intercepted. It is often necessary to remove said detector system and replace it with another of a different functional basis type. Such detector system change can be tedious, difficult and time consuming. Utility would obviously be provided by a system which enabled simply moving another detector system into position. A need is thus identified for a system which, for instance, allows a user to select and easily, sequentially, position more than one functional basis type of detector system, without removing any detector system(s).
A search of Patents produced very little. A Patent to Briggs, U.S. Pat. No. 3,405,270 describes a system containing slots which allow positioning of a source and detector relative to one another. A Patent to Rayton et al., U.S. Pat. No. 1,773,436 describes a polarization photometer system with a bracket arm rotatable secured to a post, which is used to support a table and test specimen. U.S. Pat. No. 4,242,581 to Crow, describes a system of four laser energy detectors arranged to allow simultaneous energy monitoring, which system can be easily positioned with respect to a laser beam source aperture. Patent U.S. Pat. No. 3,630,621 to Liskowitz provides a system for measurement of visibility through a fluid using polarized light wherein a source and a detector which are easily positioned with respect to one another. Other Patents identified, but not felt to be particularly relevant are U.S. Pat. No. 4,938,602 to May et al., and U.S. Pat. No. 5,494,829 to Sandstrom et al.
The present invention meets the identified need(s) in the form of providing spectrophotometer, ellipsometer and polarimeter systems which are comprised of multiple detector systems, wherein selected detector systems therein can be easily, sequentially, positioned to receive electromagnetic radiation as desired by a user during, for instance, system component alignment, actual reflection or transmission sample system investigation data acquisition, and/or during calibration data acquisition etc. procedures. The present invention finds particularly relevant application where it is desired to quickly, sequentially, acquire both spectrophotometric and ellipsometric data.
DISCLOSURE OF THE INVENTION
The primary embodiment of the present invention is an ellipsometer system, comprising:
a source system comprising:
a source of electromagnetic radiation: and
a polarization state modifier system:
a stage for supporting a material system;
a plurality of polarization state detector systems, each of which comprises:
a polarization state analyzer: and
a detector system.
During use, a beam of electromagnetic radiation is produced by said source of electromagnetic radiation and caused to pass through said polarization state modifier system, interact with a material system placed on said stage for supporting a material system, pass through a polarization state analyzer and enter a detector system in the pathway thereof. The present invention improvement is found in the mounting of said plurality of polarization state detector systems in a manner which allows easily, sequentially, placing any thereof so as to receive said beam of electromagnetic radiation, during use, without required removal of any of said polarization state detector systems from said ellipsometer system.
The present invention also includes a polarimeter system comprising a plurality of polarization state detector systems, each of which comprises:
a polarization state analyzer: and
a detector system.
During use, a beam of electromagnetic radiation which originates otherwise than in said polarimeter system is caused to pass through a polarization state analyzer in the pathway thereof, then enter a detector system in the pathway thereof. As in the case of the ellipsometer system, the present invention improvement is found in t
Cooney Gerald
Green Steven E.
Font Frank G.
J.A. Woollam Co. Inc.
Punnoose Roy M.
Welch James D.
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