Broadband microspectro-reflectometer

Claim 2

In an optical system having a platform for supporting a sample, an apparatus for determining the relative reflectance spectrum of a selected area on the sample, comprising: a light source for emitting a first beam; a beam splitter for splitting said first beam into a reference beam and a sample beam, said beam splitter being a totally reflecting mirror; a focussing means for focussing said sample beam at a focal point, the platform movable with respect to said focussing means; a reference spectroscopic means for detecting a reference spectrum of said reference beam; a sample spectroscopic means for detecting a reflected spectrum of a reflection of said sample beam, said reflection reflecting off the sample over the selected area; and a computation means for comparing said reflected spectrum and said reference spectrum to determine a relative reflectance spectrum.

Claim 3

The apparatus of claim 1, wherein said reference beam illuminates said reference spectroscope means without interacting with said beam splitter.

Claim 4

The apparatus of claim 1, wherein said light source emits light over a spectrum of about 220 nm to about 830 nm.

Claim 5

The apparatus of claim 1, wherein said reference and sample spectroscopic means each comprise: an entrance aperture; a diffraction grating for dispersing light passing through said entrance aperture; and means for detecting a spectrum first order diffraction beam from said diffraction grating, said first order diffraction beam being a diffraction of said light passing through said entrance aperture.

Claim 6

The apparatus of claim 4, wherein said diffraction grating of said reference spectroscopic means and said diffraction grating of said sample spectroscopic means comprise a single diffraction grating.

Claim 7

The apparatus of claim 4, wherein said diffraction grating is an aberration-corrected holographic diffraction grating.

Claim 8

The apparatus of claim 4, wherein said means for detecting a spectrum comprises a linear photodiode array.

Claim 9

The apparatus of claim 1, wherein said beam splitter is placed with an edge offset from an optical centerline, said offset placing said beam splitter in less than half of said first beam and said offset being sufficient to reduce vignetting of said reflection by said edge.

Claim 10

The apparatus of claim 1, wherein said reference spectroscopic means comprises a first photodiode and said sample spectroscopic means comprises a second photodiode.

Claim 11

The apparatus of claim 9, wherein said first photodiode and said second photodiode are sensitive to ultraviolet light.

Claim 12

The apparatus of claim 9, further comprising: a flip-in filtering mirror, flexibly mounted in the optical system to allow placement of said flip-in filtering mirror in at least one spectroscopic light beam and removal therefrom, said flip-in filtering mirror removing visible light from said at least one spectroscopic light beam to form at least one substantially ultraviolet beam, said at least one substantially ultraviolet beam illuminating at least one of said first photodiode and said second photodiode.

Claim 13

The apparatus of claim 9, further comprising: a fixed filtering mirror fixed in a path of at least one spectroscopic light beam, said fixed filtering mirror being substantially transparent to visible light components of said at least one spectroscopic light beam and said fixed filtering mirror reflecting ultraviolet components of said at least one spectroscopic light beam onto at least one of said first photodiode and said second photodiode.

Claim 14

The apparatus of claim 9, further comprising: a flip-in filtering mirror, flexibly mounted in the optical system to allow placement of said flip-in filtering mirror in at least one spectroscopic light beam and removal therefrom, said flip-in filtering mirror removing visible light from said at least one spectroscopic light beam to form at least one substantially ultraviolet beam; a fixed filtering mirror fixed in a path of said at least one substantially ultraviolet beam, said fixed filtering mirror removing visible light from said at least one substantially ultraviolet beam to form at least one ultraviolet beam, said at least one ultraviolet beam illuminating at least one of said first photodiode and said second photodiode.

Claim 15

The apparatus of claim 1, wherein said focussing means comprises an objective lens.

Claim 16

The apparatus of claim 1, further comprising a first aperture formed by a first pupil stop and a second aperture formed by a second pupil stop, wherein said first pupil stop and said second pupil stop are coplanar, wherein said sample beam passes through said first aperture before reaching the selected area, and said reflection of said sample beam passes through said second aperture after being reflected from the selected area, and wherein said second aperture is larger than said first aperture.

Claim 17

The apparatus of claim 1, wherein said light source also provides field illumination to illuminate a viewing field on the sample.

Claim 20

The method of claim 17, wherein the step of measuring said reflected spectrum comprises measuring a single sample value, and wherein the step of measuring said reference spectrum comprises measuring a single reference value.

Claim 21

The method of claim 17, wherein a spectrum comprises values at each of n wavelengths, where n is a positive integer greater than zero, wherein the step of measuring said reflected spectrum comprises measuring a sample value at each of said n wavelengths, wherein the step of measuring said reference spectrum comprises measuring a reference value at each of said n wavelengths, and wherein the step of comparing comprises the steps of dividing, for each wavelength, said sample value by said reference value for each of said n wavelengths, said relative reflectance spectrum comprising n reflectance values.

Claim 22

In an optical system, including a movable platform for supporting a sample, an objective lens and a means for moving the movable platform such that a selected area on said sample can be brought into focus with respect to the objective lens, means for autofocusing comprising: an illumination source which emits a beam of light comprising at least visible light; a beam shaper for forming a circularly asymmetric beam from said beam of light, said circularly asymmetric beam illuminating and reflecting off the sample near the selected area; a position sensitive detector for detecting a centroid of at least a portion of said reflected circularly asymmetric beam, said position sensitive detector including an output indicating a separation distance value and a separation direction value between said centroid and a focus point, said focus point being a point on said position sensitive detector where said centroid is located when the sample is in focus with respect to the objective lens; and a signal means, for providing said separation distance value and said separation direction value to the means for moving the movable platform, the means for moving the movable platform responding to said separation distance value and said separation direction value by moving the movable platform to a coarse-focus position 3.

Claim 23

In an optical system, including a movable platform for supporting a sample, an objective lens and a means for moving the movable platform such that a selected area on said sample can be brought into focus with respect to the objective lens, means for autofocusing comprising: an illumination source which emits a beam of light comprising at least visible light; a beam shaper for forming a circularly asymmetric beam from said beam of light, said circularly asymmetric beam illuminating and reflecting off the sample near the selected area; a position sensitive detector for detecting a centroid of at least a portion of said reflected circularly asymmetric beam, said position sensitive detector including an output indicating a separation distance value and a separation direction value between said centroid and a focus point, said focus point being a point on said position sensitive detector where said centroid is located when the sample is in focus with respect to the objective lens; and a signal means, for providing said separation distance value and said separation direction value to the means for moving the movable platform, the means for moving the movable platform responding to said separation distance value and said separation direction value by moving the movable platform to a coarse-focus position 3.

Claim 24

The autofocus means of claim 20, wherein said circularly asymmetric beam comprises a beam with a half annular cross section.

Claim 25

The autofocus means of claim 20, wherein said illumination source includes an aperture means for limiting light reaching said beam shaper.

Claim 26

The autofocus means of claim 20, wherein said illumination source includes a radial uniformer.

Claim 27

The autofocus means of claim 20, wherein said illumination source comprises a lamp, an off-axis parabolic mirror for forming a non-diverging beam, and a radial uniformer comprising a silica fiber.

Claim 28

The autofocus means of claim 20, wherein said illumination source provides a field illumination beam comprising visible light for illuminating a viewing field on the sample.

Claim 29

The autofocus means of claim 20, further comprising means for fine-focusing, wherein said illumination source is limited by a first aperture, wherein said reflected circularly asymmetric beam is reflected off a mirror with an second aperture therein, wherein said first and second apertures are at different conjugate focal points of the objective lens, wherein light reflecting off said mirror is collected by a light intensity detector, and wherein said light intensity detector controls the position of the sample with respect to the objective lens and positions the sample so as to minimize said light collected by said light intensity detector, the sample being substantially in focus when said light collected be said light intensity detector is minimized.

Claim 30

The autofocus means of claim 26, wherein said position sensitive detector is also said light intensity detector.

Claim 31

The autofocus means of claim 20, further comprising a beam splitter cube, comprising a partially reflecting surface, for deflecting a portion of said circularly asymmetric beam to form a viewing beam, said beam splitter cube mounted at an angle offset from a perpendicular angle to said circularly asymmetric beam.

Claim 32

The autofocus means of claim 28, wherein said angle is between about 3 degrees and about 5 degrees.

Claim 33

The autofocus means of claim 28, wherein a first coating of black glass is attached to unused surface areas of said beam splitter cube, for absorbing unwanted reflections in said beam splitter cube.

Claim 34

The autofocus means of claim 28, further comprising a penta prism in said viewing beam, for deflecting said viewing beam through a right angle with a non-mirrored image, said penta prism mounted at an angle offset from a perpendicular to said viewing beam of between about 3 degrees and about 5 degrees.

Claim 35

The autofocus means of claim 31, wherein a first coating of black glass is attached to unused surface areas of said penta prism, for absorbing unwanted reflections in said penta prism.

Claim 36

In an optical system having a housing for supporting optical elements and a platform movable relative to the housing for supporting a sample, an apparatus for determining the relative reflectance spectrum of a selected area on the sample, comprising: a light source for emitting a first beam, said light source comprising a lamp and a radial uniformer comprising a silica fiber, said lamp emitting light with a spectrum of about 220 nm to about 830 nm; a beam splitter for splitting said first beam into a reference beam and a sample beam, said beam splitter being a totally reflecting mirror; an objective lens for focussing said sample beam at a focal point, wherein said focal point is within a range of movement of the platform such that the selected area on the sample can be brought into focus with respect to said objective lens; a reference spectroscopic means for detecting a reference spectrum of said reference beam; a sample spectroscopic means for detecting a reflected spectrum of a reflection of said sample beam, said reflection reflecting off the sample over the selected area; a computation means for comparing said reflected spectrum and said reference spectrum to determine a relative reflectance spectrum; a beam shaper for forming a circularly asymmetric beam from said beam of light, said circularly asymmetric beam illuminating and reflecting off the selected area; a position sensitive detector for detecting a centroid of at least a portion of said reflected circularly asymmetric beam, said position sensitive detector including an output indicating a separation distance value and a separation direction value between said centroid and a focus point, said focus point being a point on said position sensitive detector where said centroid is located when the sample is in focus with respect to said objective lens; a signal means, for providing said separation distance value and said separation direction value to the means for moving the platform, the means for moving the platform responding to said separation distance value and said separation direction value by moving the platform to a coarse-focus position; means for fine-focussing, wherein said light source is limited by a first aperture, wherein said reflected circularly asymmetric beam is reflected off an mirror including a second aperture, wherein said first and second apertures are at different conjugate focal points of the objective lens, wherein light reflecting off said mirror is collected by a light intensity detector, and wherein said light intensity detector controls the position of the sample with respect to the objective lens though movements of the platform and positions the sample so as to minimize said light collected by said light intensity detector, the sample being substantially in focus when said light collected be said light intensity detector is minimized; a beam splitter cube, comprising a partially reflecting surface, for deflecting a portion of said circularly asymmetric beam to form a viewing beam, said beam splitter cube mounted at an angle of between about 3 degrees and about 5 degrees from perpendicular to said circularly asymmetric beam; a first coating of black glass attached to unused surface areas of said beam splitter cube, for absorbing unwanted reflections in said beam splitter cube; a penta prism in said viewing beam, for deflecting said viewing beam through a right angle with a non-mirrored image, said penta prism mounted at an angle of offset from perpendicular to said viewing beam by an angle of between about 3 degrees and about 5 degrees; and a second coating of black glass attached to unused surface areas of said penta prism, for absorbing unwanted reflections in said penta prism.

Claim 37

In an optical system having a housing for supporting optical elements and a platform movable relative to the housing for supporting a sample, an apparatus for determining the relative reflectance spectrum of a selected area on the sample, comprising: a light source for emitting a first beam, said light source comprising a lamp and a radial uniformer comprising a silica fiber, said lamp emitting light with a spectrum of about 220 nm to about 830 nm; a beam splitter for splitting said first beam into a reference beam and a sample beam, said beam splitter being a totally reflecting mirror; an objective lens for focussing said sample beam at a focal point, wherein said focal point is within a range of movement of the platform such that the selected area on the sample can be brought into focus with respect to said objective lens; a reference spectroscopic means for detecting a reference spectrum of said reference beam; a sample spectroscopic means for detecting a reflected spectrum of a reflection of said sample beam, said reflection reflecting off the sample over the selected area; a computation means for comparing said reflected spectrum and said reference spectrum to determine a relative reflectance spectrum; a beam shaper for forming a circularly asymmetric beam from said beam of light, said circularly asymmetric beam illuminating and reflecting off the selected area; a position sensitive detector for detecting a centroid of at least a portion of said reflected circularly asymmetric beam, said position sensitive detector including an output indicating a separation distance value and a separation direction value between said centroid and a focus point, said focus point being a point on said position sensitive detector where said centroid is located when the sample is in focus with respect to said objective lens; a signal means, for providing said separation distance value and said separation direction value to the means for moving the platform, the means for moving the platform responding to said separation distance value and said separation direction value by moving the platform to a coarse-focus position; means for fine-focussing, wherein said light source is limited by a first aperture, wherein said reflected circularly asymmetric beam is reflected off an mirror including a second aperture, wherein said first and second apertures are at different conjugate focal points of the objective lens, wherein light reflecting off said mirror is collected by a light intensity detector, and wherein said light intensity detector controls the position of the sample with respect to the objective lens though movements of the platform and positions the sample so as to minimize said light collected by said light intensity detector, the sample being substantially in focus when said light collected be said light intensity detector is minimized; a beam splitter cube, comprising a partially reflecting surface, for deflecting a portion of said circularly asymmetric beam to form a viewing beam, said beam splitter cube mounted at an angle of between about 3 degrees and about 5 degrees from perpendicular to said circularly asymmetric beam; a first coating of black glass attached to unused surface areas of said beam splitter cube, for absorbing unwanted reflections in said beam splitter cube; a penta prism in said viewing beam, for deflecting said viewing beam through a right angle with a non-mirrored image, said penta prism mounted at an angle of offset from perpendicular to said viewing beam by an angle of between about 3 degrees and about 5 degrees; and a second coating of black glass attached to unused surface areas of said penta prism, for absorbing unwanted reflections in said penta prism.

Claim 40

The method of claim 34, said splitting including directing the beam to a mirror placed less than completely across said light beam.

Claim 41

The method of claim 34, said splitting including deflecting less than all of said light beam to form the sample beam, the undeflected portion of said light beam defining a reference light beam.

Claim 42

The method of claim 34, said splitting including forming a circularly asymmetric beam from said beam of light, said asymmetric beam illuminating and reflecting from the sample.

Claim 43

The method of claim 37, further comprising detecting a position of the reflected circularly asymmetric beam relative to a reference position.

Claim 44

The method of claim 38, further comprising moving the sample in response to said position of the reflected circularly asymmetric beam relative to the reference position.

Claim 45

The method of claim 38, said detecting including determining a relative position of a centroid of at least a portion of said reflected circularly asymmetric beam relative to a reference position of said centroid.

Claim 46

The method of claim 34, said light beam and said reflected and reference spectra including multiple wavelengths.

Claim 47

The method of claim 41, said multiple wavelengths within a range from about 220 nm to about 830 nm.

Claim 50

The apparatus of claim 43, said beam splitter including a totally reflecting mirror placed less than completely across said light beam.

Claim 51

The apparatus of claim 43, said beam splitter deflecting less than all of said light beam to form the sample beam, the undeflected portion of said light beam defining a reference light beam.

Claim 52

The apparatus of claim 43, said beam splitter forming a circularly asymmetric beam from said beam of light, said circularly asymmetric beam illuminating and reflecting from the sample.

Claim 53

The apparatus of claim 46, further comprising a position sensitive detector detecting a position of the reflected circularly asymmetric beam relative to a reference position.

Claim 54

The apparatus of claim 47, further comprising means for moving the sample in response to said position of the reflected circularly asymmetric beam relative to the reference position.

Claim 55

The apparatus of claim 47, said detector detecting a relative position of a centroid of at least a portion of said reflected circularly asymmetric beam relative to a reference position at the detector.

Claim 56

The apparatus of claim 43, said light beam and said reflected and reference spectra including multiple wavelengths.

Claim 57

The apparatus of claim 50, said multiple wavelengths within a range from about 220 nm to about 830 nm.

Claim 60

The method of claim 52, wherein said directing directs a light beam containing visible light to the sample.

Claim 63

The apparatus of claim 54, wherein said source supplies visible light to the sample.

Claim 64

The apparatus of claim 54, said detector being a position sensitive detector.

Claim 65

The apparatus of claim 54, wherein said source supplies a beam with a half annular cross-section.