US3612692A
Expired / Lapsed
US
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Dielectric film thickness monitoring and control system and method
Assignee: International Business Machines Corp
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Filing: 1968-11-21
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Granted: 1971-10-12
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Expires: 1988-11-21
Abstract
Abstract An automatic thickness monitoring and control system and method for monitoring the growth of a dielectric film on a reflective substrate such as a silicon wafer during an RF sputtering deposition process and for stopping the deposition process when the film reaches a predetermined thickness. The successive minima (or maxima) in the interference pattern of light reflected from the wafer are counted to determine the film thickness and the sputtering is stopped at a predetermined count. In another embodiment, sputtering is stopped by interpolation between counts.
Inventors
- 👤 Robert W Kruppa
- 👤 Ernest S Ward
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 13:11
CPC Classifications
G; G05; G05D; G05D5/00; G05D5/02; G05D5/03; G01; G01B; G01B11/00; G01B11/02; G01B11/06; G01B11/0616; G01B11/0675
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
184 words
An optical thickness-monitoring system for determining the thickness of a transparent film situated on the surface of a reflective substrate while the thickness of said film is being varied by an RF sputtering process comprising: a. means for directing an incident beam of collimated light onto said surface, to produce a reflected beam of ligHt having parallel and perpendicular polarization components and an intensity which varies with time in a cyclic pattern according to the optical interference effect caused by the variation in thickness of said film, said cyclic pattern including periodic instants of intensity at each of two types of extrema points, b. polarization analyzer means for transmitting only the perpendicularly polarized component of said reflected beam. c. light-sensitive means receiving said polarized reflected beam for generating an electrical signal having a magnitude varying according to said intensity, and d. indicator means responsive to said electrical signal for indicating the total number of said instants of intensity at at least one type of said two types of extrema points which have occurred since the variation in the thickness of said film was initiated.
Claim 2
Dependent Claim
184 words
An optical thickness-monitoring system for determining the thickness of a transparent film situated on the surface of a reflective substrate while the thickness of said film is being varied by an RF sputtering process comprising: a. means for directing an incident beam of collimated light onto said surface, to produce a reflected beam of ligHt having parallel and perpendicular polarization components and an intensity which varies with time in a cyclic pattern according to the optical interference effect caused by the variation in thickness of said film, said cyclic pattern including periodic instants of intensity at each of two types of extrema points, b. polarization analyzer means for transmitting only the perpendicularly polarized component of said reflected beam. c. light-sensitive means receiving said polarized reflected beam for generating an electrical signal having a magnitude varying according to said intensity, and d. indicator means responsive to said electrical signal for indicating the total number of said instants of intensity at at least one type of said two types of extrema points which have occurred since the variation in the thickness of said film was initiated.
Claim 3
Dependent Claim
40 words
A control system including the monitoring system according to claim 1 and further comprising: means responsive to said indicator means for causing the variation in the thickness of said film to cease when said total number reaches a predetermined number.
Claim 4
Dependent Claim
115 words
A control system including the monitoring system according to claim 1 and further comprising: a. means responsive to the time interval between two successive ones of said periodic instants for generating a first time signal proportional to said time interval, b. means for generating a last count signal when said total number reaches a predetermined number, c. means responsive to said last count signal proportional to elapsed time since said last count signal, and d. means for comparing said second time to said last count signal with a predetermined part of said first time signal and responsive to the results of the comparison for causing the variation in the thickness of said film to cease.
Claim 5
Dependent Claim
25 words
A system according to claim 1 wherein said instants of intensity at at least one type of said two types of extrema points are minima.
Claim 6
Dependent Claim
27 words
A system according to claim 4 wherein: a. said film is a dielectric film transparent to said collimated light, and b. said substrate is a semiconductor wafer.
Claim 7
Dependent Claim
18 words
A system according to claim 1 wherein said light-sensitive means is responsive only to a narrow reflected beam.
Claim 8
Dependent Claim
18 words
A system according to claim 6 wherein the light-sensitive means is responsive only to light of selected wavelengths.
Claim 9
Dependent Claim
38 words
A monitoring system as claimed in claim 1 wherein said means for directing an incident beam directs said incident beam onto said surface at an angle greater than 75 degrees when measured from the normal to said surface.
Claim 10
Dependent Claim
94 words
A monitoring system as claimed in claim 8 wherein said light-sensitive means comprises: a. a bundle of optical fibers arranged to form a single input and a plurality of outputs for said polarized light, b. a plurality of optical filters, one associated with each of said plurality of outputs, each of said filters having a different peak wavelength response, and c. a plurality of photocells, one associated with each of said filters, for generating electrical signals of a magnitude proportional to the intensity of received light, whereby, substantially continuous discrete thickness indications are obtained.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-10-11 | 1975-04-12 | 1975-10-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-10-11 | 1979-04-12 | 1979-10-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-10-11 | 1983-04-12 | 1983-10-12 | $7700.00 | Window Closed / Lapsed |