US4660980A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Apparatus for measuring thickness of object transparent to light utilizing interferometric method
Assignee: Anritsu Corp
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Filing: 1984-12-10
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Granted: 1987-04-28
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Expires: 2004-12-10
Abstract
Abstract An apparatus for measuring a thickness of an object transparent to light utilizing an interferometric method includes a light source for generating a coherent light beam to which an object to be measured is transparent, an illumination unit for radiating onto the object the incident light beam as scanned over a range of angle of incidence varying from a predetermined angle of incidence θ A to another predetermined angle of incidence θ B , and a photosensor unit for detecting light intensity changes resulting from changing of the optical path difference between two light beams reflected by the upper and lower surfaces of the object. A count circuit receives an output signal from the photosensor unit and counts the difference between an order of interference fringes obtained for one scan of incident light beam having the predetermined angle of incidence θ A to that having the other predetermined angle of incidence θ B , and a calculating circuit converts the output from the count circuit into a value corresponding to the thickness of the object.
Inventors
- 👤 Hitoshi Takabayashi
- 👤 Takahiro Nakamura
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 14:46
CPC Classifications
G; G01; G01B; G01B11/00; G01B11/02; G01B11/06
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
204 words
An apparatus for measuring the thickness of an object transparent to light utilizing an interferometric method, comprising: light-emitting means for generating a coherent light beam to which the object to be measured is transparent; deflecting means for scanning the light beam in a predetermined angle range and generating a deflected light beam; illuminating means for irradiating on the object to be measured the deflected light beam which is substantially parallel and which scans continuously a range of incident angle from θ A to θ B ; light-receiving means for detecting light intensity changes caused by scanning of the incident angle and changing of the optical path difference between two light beams reflected from upper and lower surfaces of the object; counting means for receiving an output signal from said light-receiving means and counting a difference in an order of interference fringes obtained for one scanning cycle of said deflecting means, said incident angles θ A and θ B being determined such that the difference in the order of interference fringes obtained for one scanning cycle of said deflecting means is at least two; and calculating means for converting an output from said counting means into a value corresponding to the thickness of the object.
Claim 2
Independent Claim
204 words
An apparatus for measuring the thickness of an object transparent to light utilizing an interferometric method, comprising: light-emitting means for generating a coherent light beam to which the object to be measured is transparent; deflecting means for scanning the light beam in a predetermined angle range and generating a deflected light beam; illuminating means for irradiating on the object to be measured the deflected light beam which is substantially parallel and which scans continuously a range of incident angle from θ A to θ B ; light-receiving means for detecting light intensity changes caused by scanning of the incident angle and changing of the optical path difference between two light beams reflected from upper and lower surfaces of the object; counting means for receiving an output signal from said light-receiving means and counting a difference in an order of interference fringes obtained for one scanning cycle of said deflecting means, said incident angles θ A and θ B being determined such that the difference in the order of interference fringes obtained for one scanning cycle of said deflecting means is at least two; and calculating means for converting an output from said counting means into a value corresponding to the thickness of the object.
Claim 3
Dependent Claim
41 words
An apparatus according to claim 1, wherein said deflecting means comprises: a tuning fork having a mirror at a distal end thereof so as to deflect the light beam from said light-emitting means; and driving means for driving said tuning fork.
Claim 4
Dependent Claim
13 words
An apparatus according to claim 1, wherein said light-emitting means comprises a laser.
Claim 5
Dependent Claim
12 words
An apparatus according to claim 1, wherein said light-emitting means comprises LED.
Claim 6
Dependent Claim
15 words
An apparatus according to claim 1, wherein said coherent light beam comprises an s-polarized light.
Claim 7
Dependent Claim
22 words
An apparatus according to claim 1, wherein said light-receiving means comprises a photo-diode whose output is proportional to an incident light intensity.
Claim 8
Dependent Claim
145 words
An apparatus according to claim 1, wherein said counting means includes: a wave-forming circuit for forming an output signal from said light-receiving means into a rectangular wave signal; a differentiating circuit for converting the rectangular wave signal to positive- and negative-going pulses; an angle-detecting circuit for monitoring a phase of said deflecting means and detecting a difference between angles respectively corresponding to first and last pulses from said differentiating circuit during one scanning cycle and a total pulse number during said one scanning cycle; a first calculating circuit for calculating an average angle of interference fingers in accordance with an output signal from said angle-detecting circuit; and a second calculating circuit for calculating a difference in an order of interference fringes in accordance with the average angle of the interference fringes and a range of angle from said deflecting means during said one scanning cycle.
Claim 9
Dependent Claim
41 words
An apparatus according to claim 7, wherein said deflecting means comprises: a tuning fork having a mirror at a distal end thereof so as to deflect the light beam from said light-emitting means; and driving means for driving said tuning fork.
Claim 10
Dependent Claim
38 words
An apparatus according to claim 1, wherein said illuminating means includes means for setting the average angle of incidence of the light beam such that a maximum number of interference fringes is produced per unit angle of incidence.
Claim 11
Dependent Claim
72 words
An apparatus according to claim 1, wherein said illuminating means includes: means for splitting the light beam into two beam components which are incident on the surface of the object symmetrically about a normal thereto, said light-receiving means and said counting means being provided for each of the two beam components; and average value means for averaging output signals from said counting means and supplying an average value to said calculating means.
Claim 12
Dependent Claim
42 words
An apparatus according to claim 1, wherein said illuminating means includes a cylindrical lens arranged in an incident optical path and forming a line-focussed light beam waist on the surface of the object in a direction perpendicular to the plane of incidence.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1990-04-27 | 1990-10-27 | 1991-04-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1994-04-27 | 1994-10-27 | 1995-04-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1998-04-27 | 1998-10-27 | 1999-04-28 | $7700.00 | Window Closed / Lapsed |