DIELECTRIC FILM THICKNESS MONITORING AND CONTROL SYSTEM AND METHOD

• US 3,612,692 A
• Filed: 11/21/1968
• Issued: 10/12/1971
• Est. Priority Date: 11/21/1968
• Status: Expired due to Term

• Current Assignee: Ernest S. Ward, Robert W. Kruppa
• Original Assignee: Ernest S. Ward, Robert W. Kruppa
• Inventors: Kruppa, Robert W., Ward, Ernest S.
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Clark, Conrad
• Application Number:
  US04/777,556
• Time in Patent Office: 1,055 Days
• Field of Search: 356/106-113
• US Class Current: 356/492
• CPC Class Codes: G01B 11/0675 using interferometry
• CPC Class Codes: G05D 5/03 characterised by the use of electric means

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.

Claims

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. A system according to claim 1 wherein said light-sensitive means is responsive only to a narrow reflected beam.

7. A system according to claim 6 wherein the light-sensitive means is responsive only to light of selected wavelengths.

8. 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.

9. 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.