Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
2001-05-24
2002-09-24
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
Reexamination Certificate
active
06456376
ABSTRACT:
TECHNICAL FIELD
The present invention relates to rotating compensator ellipsometer systems, and more particularly to spectroscopic rotating compensator ellipsometer systems which comprise spatial filters before and/or after an investigated sample system.
BACKGROUND
Not limited to, but particularly in the case where an electromagnetic beam is utilized to investigate a sample system which presents with a varying depth surface topology, it is important to provide an electromagnetic beam of a known lateral dimension and which presents with a relatively simple cross-sectional intensity profile.
It is noted that often electromagnetic beams present with a substantially arbitrary intensity profile, with the highest intensity being located centrally, which intensity generally decreasing as with increasing radius. While an arbitrary beam intensity profile is typically acceptable for use in ellipsometry and related practices, it has been found that once the intensity of a substantially arbitrary profile beam of electromagnetic radiation has decreased to, as an arbitrary example, say 10% of its peak, it does not always continue to decay directly to essentially zero (0.0). Instead, it often presents irregularly as a function of radius, (eg. easily visualized as being generally similar to the Fourier transform of a square wave), and such irregular intensity content can adversely affect ellipsometer performance. The cause of said irregular intensity profile can include such as optical element wavelength dependent diffraction, surface roughness or other non-idealities, and where electromagnetic radiation is provided via an aperture or via the end of a light fiber contained in a cladding, electromagnetic radiation falling outside a geometric image thereof is often of an irregular intensity content.
It would be of benefit, as regards obtaining accurate data from application of ellipsometers and the like systems, if the intensity of an electromagnetic beam could be forced to decay quickly to zero (0.0), rather than demonstrate an irregular intensity profile as a function of radius in an outer annulus region.
With an eye to the present invention, a Search of Patents was conducted. Perhaps the most relevant Patent identified is U.S. Pat. No. 5,517,312 to Finarov. Said 312 Patent describes application of a scattered light reducing system at the entry to a Detector in a Rotating Analyzer or Rotating Polarizer Ellipsometer System, which scattered light reducing system consists of two lenses with a pin-hole containing diaphram located midway therebetween, and at the focal lengths of said lenses. Said scattered light reducing system is present after a sample system and processes electromagnetic radiation after it interacts with said sample system. The pinhole is described as serving to reduce scattered light and providing high spatial resolution. Another Patent identified is that to Campbell et al., U.S. Pat. No. 5,148,323. Said 323 Patent describes a Spatial Filter in which a pinhole is located other than at the focal length of a converging lens. U.S. Pat. No. 3,905,675 to McCraken describes a Spatial Filter containing system which enables observation of a weak source of electromagnetic radiation in the presence of strong sources thereof. U.S. Pat. No. 5,684,642 to Zumoto et al., describes an optical transmission system for use in fashioning an electromagnetic beam for use in machining materials which combines a Spatial Filter and an Optical Fiber. U.S. Pat. No. 4,877,960 to Messerschmidt et al. is identified as it describes masking energy from outside the target area in a microscope having dual remote image masking.
Continuing, Spectroscopic Rotating Compensator Ellipsometer Systems are also known in the art. And, as mentioned, application a Spatial Filters near a Detector, in the context of Rotating Polarizer and Rotating Analyzer Ellipsometer Systems has been reported, (see U.S. Pat. No. 5,517,312 to to Finerov). However, the application of Spatial Filters in Rotating Compensator Ellipsometer Systems, such as the Rotating Compensator Ellipsometer System Claimed in co-owned U.S. Pat. No. 5,872,630, has not here-to-fore been known. Said 630 Patent, which is incorporated by reference hereinto and which is co-owned with this Application, 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 at least one compensator is caused to continuously rotate.
A Patent to Dill et al., U.S. Pat. No. 4,053,232 is disclosed as it describes a Rotating-Compensator Ellipsometer System which operates utilizing monochromatic light.
A Patent to Aspnes et al., U.S. Pat. No. 5,877,859 is disclosed as it 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 said wavelength range has a retardation imposed which is outside that retardation range.
A Patent, U.S. Pat. No. 5,329,357 to Bernoux et al. is also identified as it Claims use of fiber optics to carry electromagnetic radiation to and from an ellipsometer system which has at least one polarizer or analyzer which rotates during data acquisition. It is noted that if both the polarizer and analyzer are stationary during data acquisition that this Patent is not controlling where electromagnetic radiation carrying fiber optics are present.
Further Patents of general interest of which the Inventors are aware include those to Woollam et al, U.S. Pat. No. 5,373,359, Patent to Johs et al. U.S. Pat. No. 5,666,201 and Patent to Green et al., U.S. Pat. No. 5,521,706, and Patent to Johs et al., U.S. Pat. No. 5,504,582 are disclosed for general information as they pertain to ellipsometer systems.
A Patent to He et al., U.S. Pat. No. 5,963,327 is also disclosed as it describes a laterally compact ellipsometer system which enables providing a polarized beam of electromagnetic radiation at an oblique angle-of-incidence to a sample system in a small spot area.
In addition to the identified Patents, certain Scientific papers are also identified.
A paper by Johs, titled “Regression Calibration Method for Rotating Element Ellipsometers”, Thin Solid Films, 234 (1993) is also disclosed as it describes a mathematical regression based approach to calibrating ellipsometer systems.
A Review paper by Collins, titled “Automatic Rotating Element Ellipsometers: Calibration, Operation and Real-Time Applications”, Rev. Sci. Instrum., 61(8) (1990), is identified for general information.
Even in view of the known art, in the context of rotating compensator ellipsometer systems, a need remains for a system and methodology of its use, which adds spatial filter means before and/or after a sample sytem, to, for instance, fashion a beam with a radially essentially arbitrary Profile which directly approaches zero intensity. The present invention meets said need.
DISCLOSURE OF THE INVENTION
Rotating Compensator Ellipsometer Systems provide many benefits, (eg. Sample System PSI and DELTA investigation limiting “dead-spots” are not present), but until a co-owned Patent to Johs et al., U.S. Pat. No. 5,872,630 taught otherwise, it was generally believed that in the absence of essentially Achromatic “ideal” Compensators, it would be prohibitively difficult and expensive to build, calibrate and utilize a “Spectroscopic” Rotating Compensator Ellipsometer System. This is to be understood in light of the fact that Compensators which are essentially Achromatic, (ie. provide essentially constant retardation over a large range of Wavelengths, such as 190-1000 nanometers), are not generally and economically available as off-the-shelf items. The present invention expands on the utility available from the Spectroscopic Rotating Compensator Ellipsometer System previously taught in the 630 Patent. In very general terms the present invention is a rotating compensator ellipsometer system whi
He Ping
Herzinger Craig M.
Johs Blaine D.
Liphardt Martin M.
J.A. Woollam Co. Inc.
Pham Hoa Q.
Welch James D.
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