US3873209A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Measurement of thin films by optical waveguiding technique
Assignee: AT&T Inc
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Filing: 1973-12-10
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Granted: 1975-03-25
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Expires: 1993-12-10
Abstract
Abstract In order to measure the thickness and refractive index of a transparent thin film on a substrate of higher refractive index, such as a film of silicon oxide on a substrate of silicon, an optical wave is coupled into and guided through the film. The guided wave is coupled into the film by means of the phenomenon of the tunneling into the film of an evanescent wave from a beam of light incident on the surface of an adjacent coupling medium at an angle greater than the critical angle for total internal reflection in the medium. The intensity minima of the optical radiation which can be coupled out of the film back into the coupling medium (overall reflection), as a function of angle, yields data from which the desired thickness and refractive index can be determined.
Inventors
- 👤 David Paul Schinke
- 👤 Richard Grant Smith
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 09:47
CPC Classifications
G; G01; G01N; G01N21/00; G01N21/17; G01N21/41; G01N21/43; G01B; G01B11/00; G01B11/02; G01B11/06; G01B11/0616; G01B11/0625; G01B11/0633
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
163 words
The method of testing a thin film on a substrate of higher refractive index than the film at a given wavelength of optical radiation which comprises the steps of a. launching an evanescent wave of the optical radiation containing said wavelength in an air gap between a portion of an exposed major surface of the thin film and a first medium, said evanescent wave being produced in the air gap by means of a beam of optical radiation at said wavelength propagating at an angle greater than the critical angle in the first medium, whereby the optical wave in the first medium is coupled into the thin film; and b. determining the angle of incidence at which the intensity of the optical wave beam reflected from the thin film on the substrate undergoes a relative minimum of intensity, said beam being reflected from the film as radiation coupled out of the film arising from the evanescent wave''s having been coupled into the film.
Claim 2
Independent Claim
163 words
The method of testing a thin film on a substrate of higher refractive index than the film at a given wavelength of optical radiation which comprises the steps of a. launching an evanescent wave of the optical radiation containing said wavelength in an air gap between a portion of an exposed major surface of the thin film and a first medium, said evanescent wave being produced in the air gap by means of a beam of optical radiation at said wavelength propagating at an angle greater than the critical angle in the first medium, whereby the optical wave in the first medium is coupled into the thin film; and b. determining the angle of incidence at which the intensity of the optical wave beam reflected from the thin film on the substrate undergoes a relative minimum of intensity, said beam being reflected from the film as radiation coupled out of the film arising from the evanescent wave''s having been coupled into the film.
Claim 3
Dependent Claim
33 words
The method recited in claim 1 which further comprises the step of applying a compressive force between the first medium and the thin film while said measurements are being made in step (b).
Claim 4
Dependent Claim
143 words
Apparatus for testing a thin film on a substrate of higher refractive index at a given wavelength, which comprises: a. a source of essentially monochromatic beam of optical radiation of said wavelength; b. an optical coupler medium having a major surface defining an air gap with respect to a portion of an exposed major surface of the film, such that the beam is incident in the coupler medium at said surface thereof at an angle greater than the critical angle, such that an evanescent optical radiation wave is generated in the air gap, at least some of the radiation in the evanescent wave entering the thin film and thence being coupled out of the film whereby at least some of the radiation in the film is absorbed in the substrate when the beam is directed at certain angles of incidence in the medium.
Claim 5
Dependent Claim
143 words
Apparatus for testing a thin film on a substrate of higher refractive index at a given wavelength, which comprises: a. a source of essentially monochromatic beam of optical radiation of said wavelength; b. an optical coupler medium having a major surface defining an air gap with respect to a portion of an exposed major surface of the film, such that the beam is incident in the coupler medium at said surface thereof at an angle greater than the critical angle, such that an evanescent optical radiation wave is generated in the air gap, at least some of the radiation in the evanescent wave entering the thin film and thence being coupled out of the film whereby at least some of the radiation in the film is absorbed in the substrate when the beam is directed at certain angles of incidence in the medium.
Claim 6
Dependent Claim
37 words
Apparatus according to claim 3 which further includes means for varying the angle of incidence in the medium whereby the overall reflected radiation from the film goes through a relative minumum in response to varying said angle.
Claim 7
Dependent Claim
25 words
Apparatus according to claim 4 which further includes means for applying a force to compress the coupling medium against the exposed surface of the film.
Claim 8
Dependent Claim
13 words
Apparatus according to claim 5 in which the coupler is an optical prism.
Claim 9
Dependent Claim
13 words
Apparatus according to claim 3 in which the coupler is an optical prism.
Claim 10
Dependent Claim
40 words
Apparatus according to claim 3 which further includes means for applying a force to compress the coupling medium against the exposed surface of the film, thereby to limit the width of the air gap to less than one-half said wavelength.
Claim 11
Dependent Claim
18 words
Apparatus according to claim 3 in which the thin film is silicon dioxide and the substrate is silicon.
Claim 12
Dependent Claim
26 words
Apparatus according to claim 9 in which the coupler medium is gadolinium gallium garnet and the beam of optical radiation is supplied by a helium-neon laser.
Claim 13
Dependent Claim
140 words
Apparatus for measuring a thin film on a substrate of higher refractive index at a given optical wavelength which comprises: a. an optical prism; b. means for compressing a face of the prism against the exposed surface of the film, to define an air gap therebetween of width less than one-half the optical wavelength; and c. means for detecting optical radiation at said wavelength which is overall reflected as a reflected output beam by the thin film by virtue of optical input radiation''s being incident thereon from the prism at an angle in said prism which is greater than the critical angle for total internal reflection, whereby the input radiation is coupled into the thin film from an evanescent wave produced in the air gap and consequently optical radiation is coupled ouT of the film as the reflected output beam.
Claim 14
Dependent Claim
140 words
Apparatus for measuring a thin film on a substrate of higher refractive index at a given optical wavelength which comprises: a. an optical prism; b. means for compressing a face of the prism against the exposed surface of the film, to define an air gap therebetween of width less than one-half the optical wavelength; and c. means for detecting optical radiation at said wavelength which is overall reflected as a reflected output beam by the thin film by virtue of optical input radiation''s being incident thereon from the prism at an angle in said prism which is greater than the critical angle for total internal reflection, whereby the input radiation is coupled into the thin film from an evanescent wave produced in the air gap and consequently optical radiation is coupled ouT of the film as the reflected output beam.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-03-24 | 1978-09-23 | 1979-03-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-03-24 | 1982-09-23 | 1983-03-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-03-24 | 1986-09-23 | 1987-03-25 | $7700.00 | Window Closed / Lapsed |