Method and apparatus for using optical reflection data to obtain a continuous predictive signal during CMP

• US 6,491,569 B2
• Filed: 04/19/2001
• Issued: 12/10/2002
• Est. Priority Date: 04/19/2001
• Status: Active Grant

• Current Assignee: Novellus Systems Incorporated (LAM Research Corporation)
• Original Assignee: SpeedFam-Ipec Corporation
• Inventors: Bibby, Thomas Frederick Allen Jr., Adams, John A.
• Primary Examiner(s): Eley, Timothy V.
• Assistant Examiner(s): NGUYEN, DUNG V
• Application Number:
  US09/838,980
• Publication Number:
  US 20020155788A1
• Time in Patent Office: 600 Days
• Field of Search: 451/6, 451/5, 451/8, 451/41, 451/285, 451/286, 451/287, 451/288, 451/289, 156/345, 438/692
• US Class Current: 451/6
• CPC Class Codes: B24B 37/013 Devices or means for detecting lapping completion
• CPC Class Codes: B24B 49/04 involving measurement of the workpiece at the place of grinding during grinding operation
• CPC Class Codes: B24B 49/12 involving optical means

Abstract

A method and apparatus to generate an endpoint signal to control the polishing of thin films on a semiconductor wafer surface includes a through-bore in a polish pad assembly, a light source, a fiber optic cable, a light sensor, and a computer. The light source provides light within a predetermined bandwidth, the fiber optic cable propagates the light through the through-bore opening to illuminate the surface as the pad assembly orbits, and the light sensor receives reflected light from the surface through the fiber optic cable and generates reflected spectral data. The computer receives the reflected spectral data and calculates an endpoint signal by comparing the reflected spectral data with previously collected reference data. The comparison involves calculating an evaluation time based on the comparison, and calculating a difference time utilizing correlation to account for over polish/under polish. The endpoint is predicted utilizing the evaluation time and the difference time.

Claims

1. A method for determining an endpoint during polishing of a semiconductor wafer, the method comprising:

sampling a reference wafer surface at time intervals to determine reference spectra at each time interval;

sampling a production wafer surface at time intervals to determine reflectance spectra at each time interval;

calculating an evaluation time based upon analysis of the spectra sampled;

calculating a difference time based upon analysis of the spectra sampled; and

predicting a wafer polishing endpoint time based on the evaluation time and the difference time.

2. The method of claim 1, wherein the step of calculating the evaluation time comprises:

calculating a magnitude of a difference between the reflectance spectrum and the reference spectrum for each sampled time interval;

using paired data comprising calculated magnitudes and corresponding time intervals to determine a best straight line curve fit; and

determining an evaluation time value when the magnitude difference is zero, based on the best curve fit.

3. The method of claim 1, wherein the step of calculating the difference time comprises:

comparing a reflectance spectrum sampled at a specific time with a file of reference spectra correlated with time to determine a difference time shift between a closest match of spectra;

analyzing differences between closest matching spectra; and

determining the time difference based on the analysis of the differences.

4. The method of claim 1, wherein the step of predicting the endpoint time comprises:

calculating a sum of the evaluation time and the difference time.

5. The method of claim 1, wherein the step of sampling a production wafer is performed throughout the entire polishing process.

6. An apparatus to generate an endpoint during polishing of films on a semiconductor wafer for use in a chemical mechanical polishing system comprising:

a light source providing light to reflect from a film;

a light sensor receiving a spectrum of light reflected from the film, the light sensor including a processor generating, in digital form, spectral reflective data based on the reflected spectrum of light; and

a computer in communication with the light sensor and programmed to generate an endpoint calculated from the spectral reflectance data, wherein the generation of the endpoint comprises;

calculating an evaluation time based upon data collected;

calculating a difference time based upon data collected; and

predicting the wafer polishing endpoint time based on the evaluation time and the difference time.

7. The apparatus of claim 6, wherein the computer is programmed to calculate the evaluation time through steps comprising:

sampling the wafer surface at time intervals to determine reference spectra at each time interval;

sampling the wafer surface at time intervals to determine reflectance spectra at each time interval;

calculating a magnitude of a difference between a reflectance spectrum and a reference spectrum for each sampled time interval;

using paired data comprising calculated magnitudes and corresponding time intervals to determine a best straight line curve fit; and

determining an evaluation time value corresponding to when the magnitude difference is zero, based on the best curve fit.

8. The apparatus of claim 6, wherein the computer is programmed to calculate the difference time through steps comprising:

comparing a reflectance spectrum sampled at a specific time with a file of a reference spectra correlated with time to determine a time difference shift between the closest matching spectra;

analyzing differences between closest matching spectra; and

determining the time difference based on the analysis of the differences.

9. The apparatus of claim 6, wherein the computer is programmed to predict the endpoint time through steps comprising:

calculating a sum of the evaluation time and the difference time.

10. The apparatus of claim 6, wherein the data collected is collected throughout the entire polishing process.

11. A method for detecting an endpoint during chemical mechanical polishing of a wafer surface of a wafer, the method comprising:

producing reference spectrum data corresponding to a spectrum of light reflected from the surface of a reference wafer during polishing;

producing reflectance spectrum data corresponding to a spectrum of light reflected from the surface of a production wafer during polishing;

comparing the reflected spectrum data with the reference spectrum data;

calculating an evaluation time based upon data collected;

calculating a difference time based upon the data collection; and

predicting the endpoint time with the evaluation time and the difference time.

12. The method of claim 11, wherein the comparing step comprises calculating the sum of the square of the differences between the reflected spectrum data and the reference spectrum data at each sampled time interval.

13. The method of claim 11, wherein the step of calculating the evaluation time comprises:

using paired data comprising calculated magnitudes and corresponding time intervals to determine a best straight line curve fit; and

determining an evaluation time value when the magnitude difference is zero, based on the best curve fit.

14. The method of claim 11, wherein the step of calculating the difference time comprises:

comparing a reflectance spectrum sampled at a specific time with a file of a reference spectra correlated with time to determine a time difference shift between the closest matching spectra;

analyzing differences between closest matching spectra; and

determining the time difference based on the analysis of the differences.

15. The method of claim 11, wherein the step of predicting the endpoint time comprises:

calculating the sum of the evaluation time and the difference time.

16. The method of claim 11, wherein the steps of collecting data samples are preformed throughout the entire polishing process.