# US 7,746,473 B2 · Full spectrum adaptive filtering (FSAF) for low open area endpoint detection

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- Number: US 7,746,473 B2
- Document ID: US7746473B2
- Status: Granted
- Kind: B2
- Application number: 11/753,563
- Filed: 2007-05-24
- Published: 2008-11-27
- Granted: 2010-06-29
- Earliest claimed: 2007-05-24
- Assignees: Applied Materials, Inc.
- Inventors: Mikhail Taraboukhine
- Web page: https://patentgrep.com/patent/US7746473B2

## CPC

- G01N 21/68: using high frequency electric fields
- H01J 37/32963: {End-point detection}
- H10P 74/238: {comprising acting in response to an ongoing measurement without interruption of processing, e.g. endpoint detection or in-situ thickness measurement}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10

## 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

### Claim 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.

### Claim 2 (depends on 1)

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

### Claim 3 (depends on 2)

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.

### Claim 4 (depends on 1)

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.

### Claim 5 (depends on 1)

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.

### Claim 6 (depends on 1)

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.

### Claim 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.

### Claim 8 (depends on 7)

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

### Claim 9 (depends on 7)

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.