METHOD OF DETERMINING THE THICKNESS OF CONTIGUOUS THIN FILMS ON A SUBSTRATE

• US 3,824,017 A
• Filed: 03/26/1973
• Issued: 07/16/1974
• Est. Priority Date: 03/26/1973
• Status: Expired due to Term

• Current Assignee: George Tipton Galyon
• Original Assignee: George Tipton Galyon
• Inventors: Galyon, George Tipton
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Clark, Conrad
• Application Number:
  US05/344,804
• Time in Patent Office: 477 Days
• Field of Search: 356/114,115,118,108 250/219TH 350/164,166,152
• US Class Current: 356/504
• CPC Class Codes: G01B 11/0641 with measurement of polarization
• CPC Class Codes: G01N 21/211 Ellipsometry optical thickness measurement G01B11/06

Abstract

A method of determining the thickness of each of a plurality of contiguous films on a substrate, the films having known indices of refraction and being transparent to at least some portions of the electromagnetic spectrum. The process disclosed comprises the steps of scanning, at various wavelengths the surface of the composite film with a beam of light within the portion of the spectrum in which the films are transparent, and preferably at an angle of incidence greater than 0*. Either the incident or reflected beam is polarized (in a conventional manner) first in a plane either parallel or perpendicular to the plane of incidence and then in the other plane. The intensity of the reflected polarized beam in each of the perpendicular planes is then measured as the surface is scanned. A trace may then be made of the measured or observed intensity and wavelength and compared with a trace of calculated results of various intensity and wavelengths for various film thicknesses until an approximate coincidence is obtained between the trace of the observed measurements and the trace of the calculated results whereby the thickness of each of the films is established.

Claims

1. A method of determining the thickness of a plurality of superimposed films, said films being transparent to at least some portion of the electromagnetic spectrum, comprising the steps of:

illuminating the composite film with varying wave length electromagnetic radiation and polarizing one of the incident and reflected beams perpendicular to the plane of incidence;

illuminating the composite film with varying wavelength electromagnetic radiation and polarizing one of the incident or reflected beams parallel to the plane of incidence or reflectance; and

measuring the intensity of said reflected polarized beam during said illuminating steps to provide a trace of intensity versus wave length of each of said illuminating steps;

matching said observed traces to calculated polarized beam traces of the composite film for varying thicknesses of composite films until an approximation of said observed and calculated traces are obtained.

2. A method in accordance with claim 1 wherein said first and second illuminating steps occur at the same angle of incidence.

3. A method in accordance with claim 1 wherein said angle of incidence is greater than zero for each illuminating step.

4. A method in accordance with claim 3 wherein the angle of incidence is between 20* and 90*.

5. A method in accordance with claim 3 including the step of maintaining in substantial uniformity the angle of incidence for each illuminating step.

6. A method in accordance with claim 3 wherein said angle of incidence is set at Brewster'"'"''"'"'s angle of the upper surface of the composite film.

7. A method of determining the thickness of a plurality of contiguous films having known indices of refraction and which are transparent to at least some portion of the electromagnetic spectrum, comprising the steps of:

illuminating the surface of one of the films with two beams of electromagnetic radiation of varying frequency, one beam Polarized in a plane perpendicular to the plane of incidence and the other beam polarized in a plane parallel to the plane of incidence;

measuring the intensity of the reflected radiation;

making a representation of the intensity and wavelength of said measured reflected radiation of each of said polarized beams, comparing said representation with a like theoretical representation of intensity and wavelengths to thereby determine the thickness of each of said films.

8. A method in accordance with claim 7 wherein said first and second illuminating steps occur at the same angle of incidence.

9. A method in accordance with claim 8 wherein said angle of incidence is set at Brewster'"'"''"'"'s angle of the upper surface of said one of the films.

10. A method of determining the thickness of each of a plurality of contiguous films on a substrate, said films having known relative indices of refraction and being transparent to at least some portion of the electromagnetic spectrum, comprising the steps of:

illuminating at various wavelengths the surface of said composite film with a beam of light within said portion of said spectrum and at an angle of incidence greater than zero. polarizing one of the incident or reflected beams in a plane parallel to the plane of incidence and in a plane perpendicular to the plane of incidence, measuring the intensity of the reflected polarized beam in each of said perpendicular planes as said surface is illuminated, comparing the observed measurements of intensity and wavelengths with calculated results of intensity and wavelength for various thicknesses until an approximate coincidence is obtained between the observed measurements and the calculated results whereby the thickness of each of said films may be determined.

11. A method in accordance with claim 10 wherein said first and second illuminating steps occur at the same angle of incidence.

12. A method in accordance with claim 11 wherein said angle of incidence is set at Brewster'"'"''"'"'s angle of the upper surface of said composite film.

13. A method of determining the thickness of each of a pair of contiguous films on a silicon substrate, said films and substrate having known relative indices of refraction and being transparent to at least some portion of the electromagnetic spectrum, comprising the steps of:

providing a beam of electromagnetic radiation at an angle of incidence to the surface of the upper film substantially greater than 0*, and at various wavelengths;

polarizing either the incident or reflected beam in one of a plane perpendicular to the plane of incidence and plane parallel to the plane of incidence and then polarizing in the other of said planes;

measuring the intensity of the reflected polarized beam in each of said planes as said beam impinges upon said surface of said upper film;

comparing the observed measurements of intensity and wavelength with calculated results of intensity and wavelength for various thicknesses until an approximate coincidence is obtained between the observed measurements and the calculated results whereby the thickness of each of said films may be determined.