FULL SPECTRUM ADAPTIVE FILTERING (FSAF) FOR LOW OPEN AREA ENDPOINT DETECTION

• US 20080291428A1
• Filed: 05/24/2007
• Published: 11/27/2008
• Est. Priority Date: 05/24/2007
• Status: Active Grant

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: TARABOUKHINE, MIKHAIL
• Granted Patent: US 7,746,473 B2
• Time in Patent Office: Days
• US Class Current: 356/72
• CPC Class Codes: G01N 21/68 using high frequency electric fields
• CPC Class Codes: H01J 37/32963 End-point detection
• CPC Class Codes: H01L 22/26 Acting in response to an ongoing measurement without interruption of processing, e.g. endpoint detection, in-situ thickness measurement endpoint detection arrangements in CMP apparatus B24B37/013, in discharge apparatus H01J37/32

Abstract

A method for precise endpoint detection during etch processing of a substrate based on adaptive filtering of the optical emission spectrum (OES) data, even in low open area etching, is provided. Endpoint detection performed in this manner offers the benefits of increased signal-to-noise ratio and decreased computation costs and delay when compared to conventional endpoint detection techniques.

Claims

1. A method of detecting a desired etch state while etching a substrate, the method comprising:

(a) providing first and second reference spectrums;

(b) detecting optical emissions during etching of the substrate to generate a runtime optical emission spectrum (OES);

(c) comparing the runtime OES with the first and second reference spectrums using adaptive filtering to generate a comparator output; and

(d) repeating (b) and (c) until the desired etch state is detected based on the comparator output.

2. The method of claim 1, wherein the desired etch state is an etch endpoint just before over etching.

3. The method of claim 2, further comprising stopping the etching of the substrate immediately or after a predetermined amount of time has passed after the etch endpoint is detected.

4. The method of claim 1, wherein the first reference spectrum is a main etch OES vector and the second reference spectrum is an over etch OES vector.

5. The method of claim 1, wherein comparing the runtime OES with the first and second reference spectrums comprises:

comparing the runtime OES with the first reference spectrum in a first adaptive filter having a first error output;

comparing the runtime OES with the second reference spectrum in a second adaptive filter having a second error output;

compressing the first error output to for a first compressed error value;

compressing the second error output to form a second compressed error value;

comparing the first and second compressed error values in a third adaptive filter having a third error output; and

buffering the third error output with a fourth adaptive filter having a fourth error output used for the comparison.

6. The method of claim 1, wherein detecting the optical emissions comprises using a charge-coupled device (CCD)-based optical sensor or a Fabray-Perot interferometer.

7. A computer-readable medium containing a program for detecting a desired etch state while etching a substrate, which, when executed by a processor, performs operations comprising:

(a) providing first and second reference spectrums;

(b) detecting optical emissions during etching of the substrate to generate a runtime optical emission spectrum (OES);

(c) comparing the runtime OES with the first and second reference spectrums using adaptive filtering to generate a comparator output; and

(d) repeating (b) and (c) until the desired etch state is detected based on the comparator output.

8. The computer-readable medium of claim 7, wherein the desired etch state is an etch endpoint just before over etching.

9. The computer-readable medium of claim 7, wherein the first reference spectrum is a main etch OES vector and the second reference spectrum is an over etch OES vector.

10. A digital filter for detecting a desired etch state while etching a substrate, comprising:

a runtime input;

a first reference input;

a second reference input;

a first adaptive filter coupled to the runtime input and the first reference input and having a first filter output;

a second adaptive filter coupled to the runtime input and the second reference input and having a second filter output;

a third adaptive filter coupled to a compressed version of the first filter output and a compressed version of the second filter output and having a third filter output; and

a fourth adaptive filter coupled to the third filter output and having a fourth filter output used as the output of the digital filter for desired etch state detection.

11. The digital filter of claim 10, wherein at least one of the first, second, third, and fourth adaptive filters is a least mean squares (LMS) adaptive filter.

12. The digital filter of claim 10, wherein data input to the runtime, the first reference, and the second reference inputs are optical emission spectrum (OES) vectors.

13. The digital filter of claim 10, wherein at least one of the runtime input, the first reference input, and the second reference input is normalized before being coupled to the first or the second adaptive filters.

14. The digital filter of claim 13, wherein at least one of the runtime, the first reference, and the second reference inputs is normalized by taking a logarithm of each element of the at least one of the inputs and dividing each logarithm by a sum of the elements of the same at least one of the inputs.

15. The digital filter of claim 10, wherein at least one of the runtime input, the first reference input, and the second reference input are resized to match a size of the runtime input, the first reference input, and the second reference input having the largest size.

16. The digital filter of claim 10, wherein the compressed version of the first filter output is generated by summing absolute values of elements of the first filter output.

17. The digital filter of claim 10, wherein the first and the second adaptive filters have the same filter order.

18. The digital filter of claim 17, wherein the first and the second adaptive filters have the filter order of 10.

19. The digital filter of claim 10, wherein the first and the second adaptive filters have the same adaptation speed.

20. The digital filter of claim 10, wherein the third adaptive filter has a minimum filter order of 1.

21. The digital filter of claim 10, wherein the fourth adaptive filter has a filter order of 1.

22. The digital filter of claim 10, wherein an adaptation speed of the fourth adaptive filter is calculated by taking a reciprocal of a square of a maximum of an absolute value of the third filter output over a plurality of iterations through the digital filter.