Simultaneous determination of film uniformity and thickness

• US 3,994,586 A
• Filed: 10/30/1975
• Issued: 11/30/1976
• Est. Priority Date: 10/30/1975
• Status: Expired due to Term

• Current Assignee: Aluminum Company of Egypt
• Original Assignee: Aluminum Company of Egypt
• Inventors: Sharkins, Allen J., Tingle, William H.
• Primary Examiner(s): McGraw, Vincent P.
• Application Number:
  US05/627,214
• Time in Patent Office: 397 Days
• Field of Search: 356/51, 356/73, 356/161, 356/199, 356/200, 250/339, 250/341, 250/349, 250/350
• US Class Current: 356/73
• CPC Class Codes: G01B 11/065 using one or more discrete wavelengths

Abstract

A method and apparatus are disclosed for simultaneously determining thickness and uniformity of a supported film which is at least partially translucent by directing a beam of radiation at the film at an angle thereto, reflecting a portion of the radiation from the interface of the film and substrate back through the film, splitting a portion of the reflected radiation into a first beam portion which is monitored to determine uniformity of film thickness, and a second beam portion which is chopped and split again into a reference beam and a thickness determining beam which are filtered and transduced so that the resulting signals can be compared to determine film thickness.

Claims

1. A method of simultaneously determining thickness and uniformity of a moving film or coating including the steps of:

directing a beam of optical radiation at said film for transmission of the radiation through the film;

splitting the radiation which has been transmitted through the film into a uniformity determinative beam and a thickness determinative beam;

transducing said uniformity dterminative beam to provide an output signal which is a function of the uniformity of the thickness of said film;

chopping said thickness determinative beam to provide chopped radiation;

splitting said chopped radiation into first and second beams;

selecting from said first beam radiation which is absorptive with respect to said film and selecting from said second beam radiation which is non-absorptive with respect to said film; and

transducing said first and second beams of radiation to provide output signals which differ by an amount which is a function of film thickness.

2. A method as set forth in claim 1 in which the film is supported on a metal substrate and the radiation is directed at the film at an angle incident to the surface of the film to be transmitted through the film and reflected from the surface of the metal substrate at the interface between the film and the substrate.

3. A method as set forth in claim 2 in which said radiation is directed at a polarizing medium.

4. A method as set forth in claim 3 wherein said polarizing medium is so oriented that the radiation transmitted therethrough intercepts same at Brewster'"'"'s Angle.

5. A method as set forth in claim 4 in which said radiation intercepts said film at Brewster'"'"'s Angle.

6. A method as set forth in claim 1 in which said beams of radiation are passed through narrow band pass optical filters prior to being transduced to provide wave lengths of the desired frequencies.

7. In a process for measuring parameters of a moving film or coating wherein a beam of optical radiation is directed at the film for transmission of the radiation through the film and thereafter transduced to provide an output signal indicative of film parameters, a method of simultaneously monitoring film thickness and uniformity including the steps of:

splitting the beam of radiation which is transmitted through the film into a uniformity determinative beam and a thickness determinative beam which is chopped and again split into first and second beams which are passed through filters to select from said first beam radiation having a frequency which is absorptive with respect to said film and ffrom said second beam radiation having a frequency which is non-absorptive with respect to the film.

8. A method as set forth in claim 7 in which the film is supported on a metal substrate and the radiation is directed at the film at an angle incident to the surface of the film to be transmitted through the film and reflected from the surface of the metal substrate at the interface between the film and the substrate.

9. A method as set forth in claim 8 in which said radiation is directed through a polarizing medium.

10. A method as set forth in claim 9 wherein said polarizing medium is so oriented that the radiation transmitted therethrough intercepts same at Brewster'"'"'s Angle.

11. A method as set forth in claim 10 in which said radiation intercepts said film at Brewster'"'"'s Angle.

12. A method as set forth in claim 7 in which said beams of radiation are passed through narrow band pass optical filters prior to being transduced to provide wave lengths of the desired frequencies.

13. A method of simultaneously determining thickness and uniformity of a film or coating having first and second at least partially reflective surfaces, including the steps of:

directing a beam of optical radiation into said first surface at a predetermined angle so as to plane polarize any radiation reflected from said first surface, and transmitting at least a portion of the radiation through said film to said second surface;

reflecting the transmitted radiation from said second surface back through said film;

transmitting the radiation through a polarizing medium so oriented as to block any component of said radiation other than that transmitted through said film;

splitting said reflected radiation into a uniformity determinative beam and a thickness determinative beam;

selecting from said uniformity determinative beam radiation having a narrow band width with respect to which said film is absorptive;

transducing said selected radiation to provide an output signal which is a function of the uniformity of thickness of said film;

chopping said thickness determinative beam of radiation to provide chopped radiation;

splitting said chopped radiation into first and second beams which are passed through narrow band pass optical filters to select from said first beam radiation having a frequency which is absorptive with respect to said film and from said second beam radiation which is non-absorptive with respect to said film; and

transducing said first and second beams of radiation to provide output signals which differ by an amount which is a function of film thickness.

14. Apparatus for simultaneously determining thickness and uniformity of a moving film or coating including:

means for directing a beam of optical radiation at said film for transmission of at least a portion of the radiation through the film;

means for splitting the radiation which has been transmitted through the film into a uniformity determinative beam and a thickness determinative beam;

means for transducing said uniformity determinative beam to provide an output signal which is a function of the uniformity of the thickness of said film;

means for chopping said thickness determinative beam to provide chopped radiation;

means for splitting said chopped radiation into first and second beams which are passed through filters to select from said first beam radiation having a frequency which is absorptive with respect to said film and from said second beam radiation which is non-absorptive with respect to said film; and

means for transducing said first and second beams of radiation to provide output signals which differ by an amount which is a function of film thickness.

15. Apparatus as set forth in claim 14 in which the film is supported on a metal substrate and the radiation is directed at the film at an angle incident to the surface of the film to be transmitted through the film and reflected from the surface of the metal substrate at the interface between the film and the substrate.

16. Apparatus as set forth in claim 15 which includes a polarizing medium at which said radiation is directed to block any radiation except that which is transmitted through said film.

17. Apparatus as set forth in claim 16 wherein said polarizing medium is so oriented that the radiation directed thereat intercepts same at Brewster'"'"'s Angle.

18. Apparatus as set forth in claim 17 in which said radiation intercepts said film at Brewster'"'"'s Angle.

19. Apparatus as set forth in claim 14 which includes optical filters through which said beams of radiation are passed prior to being transduced to provide wave lengths of the desired frequencies.

20. In an apparatus for measuring parameters of a moving film or coating wherein a beam of optical radiation is directed at the film to be transmitted therethrough and thereafter transduced to provide an output signal indicative of film parameters, apparatus for simultaneously monitoring film thickness and uniformity including:

means for splitting the beam of radiation which is transmitted through the film into a uniformity determinative beam and a thickness determinative beam and means for chopping and again splitting said thickness determinative beam into first and second beams which are passed through means for selecting from said first beam radiation having a frequency which is absorptive with respect to said film and from said second beam radiation which is non-absorptive with respect to the film.

21. Apparatus as set forth in claim 20 in which the film is supported on a metal substrate and the radiation is directed at the film at an angle incident to the surface of the film to be transmitted through the film and reflected from the surface of the metal substrate at the interface between the film and the substrate.

22. Apparatus as set forth in claim 21 which includes a polarizing medium at which said radiation is directed prior to reaching the surface of the film.

23. Apparatus as set forth in claim 22 wherein said polarizing medium is so oriented that the radiation directed thereat intercepts same at Brewster'"'"'s Angle.

24. Apparatus as set forth in claim 23 in which said radiation intercepts said ffilm at Brewster'"'"'s Angle.

25. Apparatus as set forth in claim 20 which includes optical filters through which said beams of radiation are passed prior to being transduced to provide wave lengths of the desired frequencies.

26. Apparatus for simultaneously determining thickness and uniformity of a film or coating having first and second at least partially reflective surfaces, including:

means for directing a beam of optical radiation onto said first surface at a predetermined angle so as to plane polarize any radiation reflected from said first surface, and transmitting at least a portion of the radiation through said film to said second surface;

means for reflecting a portion of the transmitted radiation from said second surface back through said film;

means for transmitting the radiation through a polarizing medium so oriented as to block any component of said radiation other than that transmitted through said film;

means for splitting said reflected radiation into a uniformity determinative beam and a thickness determinative beam;

means for selecting from said uniformity determinative beam radiation having a narrow band width with respect to which said film is absorptive;

means for transducing the selected radiation to provide an output signal which is a function of the uniformity of thickness of said film;

means for chopping said thickness determinative beam of radiation to provide chopped radiation;

means for splitting said chopped radiation into first and second beams;

means for selecting from said first beam radiation having a frequency which is absorptive with respect to said film;

means for selecting from said second beam radiation which is non-absorptive with respect to said film; and

means for transducing said first and second beams of radiation to provide output signals which differ by an amount which is a function of film thickness.