Apparatus and method of rapidly measuring hemispherical scattered or radiated light

• US 5,313,542 A
• Filed: 11/30/1992
• Issued: 05/17/1994
• Est. Priority Date: 11/30/1992
• Status: Expired due to Fees

• Current Assignee: Breault Research Organization Inc.
• Original Assignee: Breault Research Organization Inc.
• Inventors: Castonguay, Raymond J.
• Primary Examiner(s): Lee, John D.
• Application Number:
  US07/983,470
• Time in Patent Office: 533 Days
• Field of Search: 250/227.11, 250/227.26, 250/227.28, 250/227.29, 351/206, 351/207, 351/209-212, 356/337, 356/340, 356/341, 356/343, 356/445-448, 385/115, 385/116, 385/120, 385/121
• US Class Current: 385/115
• CPC Class Codes: G01N 2021/4719 using a optical fibre array
• CPC Class Codes: G01N 2021/4742 comprising optical fibres
• CPC Class Codes: G01N 21/00 Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light G01N3/00 - G01N19/00 take precedence
• CPC Class Codes: G01N 21/474 Details of optical heads therefor, e.g. using optical fibres
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G02B 6/02 Optical fibres with cladding with or without a coating
• CPC Class Codes: G02B 6/04 formed by bundles of fibres G02B6/24 takes precedence
• CPC Class Codes: G06F 18/00 Pattern recognition

Abstract

A portable scatterometer and/or an angular radiated light measurement instrument that uses a measurement head which includes a double tapered fiber optic bundle with a concave front face to simultaneously collect partial or full hemispherically scattered light reflected from a point on a surface illuminated by a depolarized, telescopically focused, laser diode source, the light rays being received by each fiber normal to its face. The image of the collected light beams is minified and coupled by the fiber optic bundle into an anti-blooming CID camera with an x-y scanning area array which converts the light beams to electrical signals. In a unique real time, computer-controlled, data acquisition and reconstruction process, a frame grabber and a unique algorithm are used to collect over 200,000 points of light, reconstruct the data into a 2D or 3D scatter profile and display the results, all within one second. Multiple embodiments of the tapered fiber optic bundle collector include a full hemispherical version with the laser source directed through the boule, a unitary boule fused from two tapered halves, a linear in-plane tapered bundle and a partial taper with imaging lens mode. Alignment mechanisms provide z-translation, azimuth, and focus adjustments. The measurement unit is in a compact, rugged aluminum housing which is adapted to be secured to a production line machine for a variety of services, such as, a quality control inspection device.

Claims

1. A scatterometer for measuring light reflected angularly from a point comprising:

a power controlled laser light source for illuminating the point,

a fiber optic bundle having a plurality of individual fiber optic elements having a common field of view which is the point for collecting light beams reflected therefrom,

a camera for converting the reflected light beams into electrical signals,

the signal level of the collected light beams being raised above the dark current noise level of the camera by predetermined amounts to form sequential images stored in a frame grabber, and

the frame grabber also sequentially digitizing and storing images and reconstructing therefrom a single scatter profile of light emanating from the point while simultaneously scaling out the signal level increases.

2. A scatterometer for measuring light reflected angularly from a point, as recited in claim 1, wherein the fiber optic bundle further comprises:

a plurality of optical fibers the one ends of each of which are fixed in spaced relation to each other in a curved surface having a radius of curvature such that the longitudinal axis of each of the fibers at the one end substantially converges at a common light source that radiates light normal to each fiber and the other ends of each of which are arranged in an indexed array,

whereby light radiating angularly from the point is received simultaneously at the one end by each fiber and is transmitted to the other end.

3. A scatterometer for measuring light reflected angularly from a point, as recited in claim 2, wherein the curved surface is a full hemisphere and the single scatter profile is a three dimensional profile.

4. A scatterometer for measuring light reflected angularly from a point, as recited in claim 3, wherein the full hemisphere further comprises:

a rigid hemi-dome which has a plurality of openings in each one of which is secured the one end of one of the optical fibers.

5. A scatterometer for measuring light reflected angularly from a point, as recited in claim 2, wherein the curved surface is a spherical segment and the single scatter profile is a three-dimensional profile.

6. A scatterometer for measuring light reflected angularly from a point, as recited in claim 2, wherein the curved surface is a segment fixing the ends of the optical fibers in a single plane containing their longitudinal axes and the single scatter profile is a three-dimensional profile.

7. A scatterometer for measuring light reflected angularly from a point, as recited in claim 2, wherein the indexed array is adapted to be mated to a CID camera for converting the collected light to electrical signals.

8. A scatterometer for measuring light reflected angularly from a point comprising:

a power controlled laser light source for illuminating the point,

a fiber optic bundle for collecting light beams reflected from the point and having a plurality of optical fibers of unequal length the one ends of each of which are fixed in spaced relation to each other in a curved surface having a radius of curvature such that the longitudinal axis of each of the fibers at the one end substantially converges at a common light source that radiates light normal to each fiber and the other ends of each of which are arranged in an indexed array, whereby light radiating angularly from the point is received simultaneously at the one end by each fiber and is transmitted to the other end,

a camera for converting the reflected light beams into electrical signals,

the signal level of the collected light beams being raised above the dark current noise level of the camera by predetermined amounts to form sequential images stored in a frame grabber, and

the frame grabber also sequentially digitizing and storing images and reconstructing therefrom a single scatter profile of light emanating from the point while simultaneously scaling out the signal level increases.

9. A scatterometer for measuring light reflected angularly from a point, as recited in claim 8, wherein the curved surface is a full hemisphere.

10. A scatterometer for measuring light reflected angularly from a point, as recited in claim 9, wherein the full hemisphere further comprises:

a rigid hemi-dome which has a plurality of openings in each one of which is secured the one end of one of the optical fibers.

11. A scatterometer for measuring light reflected angularly from a point, as recited in claim 8, wherein the curved surface is a spherical segment.

12. A scatterometer for measuring light reflected angularly from a point, as recited in claim 8, wherein the curved surface is a segment fixing the ends of the optical fibers in a single plane containing their longitudinal axes.

13. A scatterometer for measuring light reflected angularly from a point, as recited in claim 8, wherein the indexed array is adapted to be mated to a CID camera for converting the collected light to electrical signals.

14. A scatterometer for measuring light reflected angularly from a point comprising:

a power controlled laser light source for illuminating the point,

a tapered fiber optic bundle for collecting light beams reflected from the point and having a plurality of optical fibers the one ends of each of which are fixed in spaced relation to each other in a curved surface which is a spherical segment in the tapered portion of the bundle having a radius of curvature such that the longitudinal axis of each of the fibers at the one end substantially converges at a common light source that radiates light normal to each fiber and the other ends of each of which are arranged in an indexed array, whereby light radiating angularly from the point is received simultaneously at the one end by each fiber and is transmitted to the other end,

a camera for converting the reflected light beams into electrical signals,

the signal level of the collected light beams being raised above the dark current noise level of the camera by predetermined amounts to form sequential images stored in a frame grabber, and

the frame grabber also sequentially digitizing and storing images and reconstructing therefrom a single scatter profile of light emanating from the point while simultaneously scaling out the signal level increases.

15. A scatterometer for measuring light reflected angularly from a point, as recited in claim 14, wherein the curved surface is in the one end and the other end is the narrow end of the bundle.

16. A scatterometer for measuring light reflected angularly from a point, as recited in claim 14, wherein the tapered fiber optic bundle is a unitary bundle which has a wide central portion, a first tapered portion in which the surface is located at the one end and a second tapered portion which terminates at the other end.

17. A scatterometer for measuring light reflected angularly from a point comprising:

a power controlled laser light source for illuminating the point,

a tapered fiber optic bundle having

a plurality of individual fiber optic elements having a common field of view which is the point for collecting light beams reflected therefrom,

a concave face on the tapered portion at one end, and

the other end formed as an indexed array adapted for transmitting the collected light beams,

a CID camera having a scannable area array for receiving the transmitted light beams and for converting the reflected light beams into electrical signals,

the signal level of the collected light beams being raised above the dark current noise level of the camera by predetermined amounts to form sequential images stored in a frame grabber, and

the frame grabber also sequentially digitizing and storing images and reconstructing therefrom a single scatter profile of light emanating from the point while simultaneously scaling out the signal level increases.

18. A scatterometer for measuring light reflected angularly from a point, as recited in claim 17, further comprising:

an imaging lens intermediate the bundle and the camera for imaging the collected light beams onto the scannable area array.

19. A scatterometer for measuring light reflected angularly from a point, as recited in claim 17, further comprising:

the bundle having a narrow end and a wide end,

the one end is the wide end, and

the other end is the narrow end.

20. A scatterometer for measuring light reflected angularly from a point, as recited in claim 19, further comprising:

a spring biased housing, encapsulating the narrow end of the taper, and positioning the narrow end in relation to the area array.

21. A scatterometer for measuring light reflected angularly from a point, as recited in claim 20, further comprising:

a fiber optic face plate intermediate the bundle and the array.

22. A scatterometer for measuring light reflected angularly from a point comprising:

a housing,

a power controlled laser diode light source supported within the housing for illuminating the point,

a tapered fiber optic bundle supported within the housing and having

a plurality of individual fiber optic elements having a common field of view which is the point for collecting light beams reflected therefrom,

a concave face on the tapered portion at one end, and

the other end being formed as an indexed array adapted for transmitting the light beams reflected from the point,

a CID camera supported within the housing and having a scannable area array for receiving the transmitted light beams and for converting the reflected light beams into electrical signals,

the signal level of the collected light beams being raised above the dark current noise level of the camera by predetermined amounts to form sequential images stored in a frame grabber, and

the frame grabber also sequentially digitizing and storing images and reconstructing therefrom a single scatter profile of light emanating from the point while simultaneously scaling out the signal level increases.

23. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

a diode controller for controlling the laser power.

24. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

a fold mirror for reflecting the light from the laser diode to the point.

25. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

a depolarizer for the laser light source.

26. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

a set of lenses for focusing the light emitted by the laser diode at a point on the surface of the fiber optic bundle.

27. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

a beam dump for blocking the specular beam reflected from the point.

28. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

an imaging lens intermediate the bundle and the camera for imaging the collected light onto the scannable area array.

29. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

the bundle having a wide end and a narrow end,

the one end is the narrow end, and

the other end is the wide end.

30. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

the bundle having a narrow end and a wide end,

the one end is the wide end, and

the other end is the narrow end.

31. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

a camera controller for controlling the integration time of the array.

32. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

a shutter mounted on the housing for protecting the housing interior from outside contaminants.

33. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

a window in the housing for protecting the housing interior from outside contaminants.

34. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

the housing, laser light source, fiber optic bundle, and CID camera being a measurement unit, and

an alignment mechanism for adjusting the measurement unit.

35. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

a reference sample adapter plate removably attached to the housing for calibrating the apparatus.

36. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, and having an x-y scannable array camera for the light reflected from the point further comprising:

a) means for measuring the ambient light and storing the measurement in a reference frame,

b) means for illuminating the point with a laser diode light source for a predetermined time period,

c) means for collecting the light beams reflected from the point during the on period and transmitting the beams to the array,

d) means for digitizing the collected data by x-y scanning the array and converting the light beams to electrical data,

e) means for storing the digitized data in a next frame, and

f) means for repeating steps (b) to (e) while increasing the on time of the laser diode by a predetermined amount during each repetition,

whereby a reference frame and four data frames are collected and stored in five sequential frames.

37. A scatterometer for measuring light reflected angularly from a point, as recited in claim 22, further comprising:

means for reconstructing the scatter profile within one second.

38. A scatterometer for measuring light reflected angularly from a point and having means for reconstructing a single data profile from data stored in a plurality of sequential x-y oriented memory frames of a computer frame grabber the first frame of which is a reference frame in which the data represents a factor common to all frames in the sequence and the remaining frames of which are data frames, comprising:

a power controlled laser light source for illuminating the point,

a fiber optic bundle having a plurality of individual fiber optic elements having a common field of view which is the point for collecting light beams reflected therefrom,

a camera for converting the reflected light beams into electrical signals,

the signal level of the collected light beams being raised above the dark current noise level of the camera by predetermined amounts to form sequential images stored in a frame grabber, and

the frame grabber also sequentially digitizing and storing images and reconstructing therefrom a single scatter profile of light emanating from the point while simultaneously scaling out the signal level increases,

and further comprising;

a) means for setting an x-y oriented array in memory and filling the array with zeros,

b) means for computing a scale factor,

c) means for subtracting the common factor data in the reference frame from the data in each of the data frames in the sequence,

d) means for scaling the data in the first data frame by the scale factor and adding the scaled data to the profile array,

e) means for scaling and adding the data stored in each x-y point in the next succeeding data frame to its corresponding x-y location in the profile array only if it has not been previously stored in that location, and if

(1) the data already in the x-y point in the profile array is zero, and

(2) the data in that x-y point in the current and any prior data frame is less than T, where T is a threshold level representing a level above which the data is invalid, and

f) means for repeating step (e) separately in sequence for each subsequent data frame in the sequence.

39. A method for measuring light reflected angularly from a point in a scatterometer comprising the steps of:

power controlling a laser light source for illuminating the point,

collecting the light beams reflected from the point in a fiber optic bundle having a plurality of individual fiber optic elements having a common field of view which is the point,

converting the reflected light beams into electrical signals in a camera,

raising the signal level of the collected light beams above the dark current noise level of the camera by predetermined amounts to form sequential images stored in a frame grabber,

sequentially digitizing the stored images in the frame grabber, and

reconstructing therefrom a single scatter profile of light emanating from the point while simultaneously scaling out the signal level increases.

40. A method of measuring light reflected angularly from a point in a scatterometer, as recited in claim 39, further comprising the step of:

reconstructing the scatter profile within one second.