Method of endpoint detection of plasma etching process using multivariate analysis

Patent metadata

Field	Value
Publication number	US-9330990-B2
Application number	US-201314056059-A
Country	US
Kind code	B2
Filing date	Oct 17, 2013
Priority date	Oct 17, 2012
Publication date	May 3, 2016
Grant date	May 3, 2016

Abstract

Disclosed is a method for determining an endpoint of an etch process using optical emission spectroscopy (OES) data as an input. Optical emission spectroscopy (OES) data are acquired by a spectrometer attached to a plasma etch processing tool. The acquired time-evolving spectral data are first filtered and demeaned, and thereafter transformed into transformed spectral data, or trends, using multivariate analysis such as principal components analysis, in which previously calculated principal component weights are used to accomplish the transform. A functional form incorporating multiple trends may be used to more precisely determine the endpoint of an etch process. A method for calculating principal component weights prior to actual etching, based on OES data collected from previous etch processing, is disclosed, which method facilitates rapid calculation of trends and functional forms involving multiple trends, for efficient and accurate in-line determination of etch process endpoint.

First claim

What is claimed is:

1. A method for determining etch process endpoint data, comprising:
in a plasma etch processing tool, performing k plasma etch process runs, where k is an integer greater than zero, each of the k plasma etch process runs comprising steps of:
loading a substrate to be processed into the plasma etch processing tool, the plasma etch processing tool comprising a spectrometer having a detector comprising m pixels, each pixel corresponding to a different light wavelength;
igniting a plasma in the plasma etch processing tool;
collecting n optical emission spectroscopy (OES) data sets sampled at equal time intervals during each of k plasma etch process runs, each of the n optical emission spectroscopy (OES) data sets comprising m pixel intensities corresponding to m pixels of the spectrometer;
forming an n×m optical emission spectroscopy (OES) data matrix [X] for each of k plasma etch process runs, each time sample occupying a row of the optical emission spectroscopy (OES) data matrix [X], the columns of the optical emission spectroscopy (OES) data matrix [X] corresponding to pixels of the spectrometer;

computing an n×m average optical emission spectroscopy (OES) data matrix [X] avg , wherein each element of the average optical emission spectroscopy (OES) data matrix [X] avg is computed as an average of corresponding elements of optical emission spectroscopy (OES) data matrices [X] for the k etch process runs;
filtering noise from the average optical emission spectroscopy (OES) data matrix [X] avg ;
truncating each optical emission spectroscopy (OES) data matrix [X] to eliminate optical emission spectroscopy (OES) data acquired during plasma startup and for times beyond an etch process endpoint;
truncating the average optical emission spectroscopy (OES) data matrix [X] avg to eliminate averaged optical emission spectroscopy (OES) data acquired during plasma startup and for times beyond the etch process endpoint;
calculating an n×m mean optical emission spectroscopy (OES) data matrix [S avg ], wherein each element of the mean optical emission spectroscopy (OES) data matrix [S avg ] is computed as an average value of n elements of the corresponding column of the average optical emission spectroscopy (OES) data matrix [X] avg ;
subtracting the mean optical emission spectroscopy (OES) data matrix [S avg ] from optical emission spectroscopy (OES) data matrices [X], to de-mean the optical emission spectroscopy (OES) data, and performing a principal component analysis [T]=([X] [i] −[S avg ])[P] on the de-meaned and non-normalized subtraction results, to obtain a transformed optical emission spectroscopy (OES) data vector [T] and principal component weights vector [P];
storing the mean optical emission spectroscopy (OES) data matrix [S avg ] for later use in in-situ determination of an etch process endpoint;
storing the principal component weights vector [P] for later use in in-situ determination of the etch process endpoint.

2. The method of claim 1 , further comprising:
selecting a functional form f(T i ) involving elements of the transformed optical emission spectroscopy (OES) data vector [T] as a trend variable for in-situ determination of the etch process endpoint.

3. The method of claim 2 , wherein the selected functional form f(T i ) of the trend variable is a single element of the transformed optical emission spectroscopy (OES) data vector [T].

4. The method of claim 3 , wherein the selected functional form f(T i ) of the trend variable contains a ratio of two elements of the transformed optical emission spectroscopy (OES) data vector [T], wherein twice a minimum value min(T i ) of each of the elements of the transformed optical emission spectroscopy (OES) data vector [T] has been subtracted from the respective elements of the transformed optical emission spectroscopy (OES) data vector [T] prior to computing the ratio.

5. The method of claim 4 , wherein the selected functional form f(T i ) of the trend variable involves a second and third element of the transformed optical emission spectroscopy (OES) data vector [T], and is of the form f(T i )=(T 2 −2·min(T 2 )) 2 /(T 3 −2·min(T 3 )) 2 .

6. The method of claim 2 , further comprising:
computing a time evolution of at least one element of the transformed optical emission spectroscopy (OES) data vector [T];
determining at least one minimum value min(T i ) of the transformed optical emission spectroscopy (OES) data vector [T] from the computed time evolution of the at least one element of the transformed optical emission spectroscopy (OES) data vector [T];
storing the at least one determined minimum value min(T i ) of an element of the transformed optical emission spectroscopy (OES) data vector [T] for later use in in-situ determination of the etch process endpoint.

7. The method of claim 6 , wherein the selected functional form f(T i ) of the trend variable is an element of the transformed optical emission spectroscopy (OES) data vector [T] from which the twice the minimum value min(T i ) of the same element of the transformed optical emission spectroscopy (OES) data vector [T] has been subtracted.

8. The method of claim 2 , wherein the selected functional form f(T i ) of the trend variable contains a ratio of two elements of the transformed optical emission spectroscopy (OES) data vector [T].

9. The method of claim 1 , wherein the step of filtering noise comprises applying a moving average filter.

10. The method of claim 1 , wherein the step of filtering noise comprises applying a filter whose characteristics are specific to the plasma etch processing tool.

Assignees

• Tokyo Electron Ltd

Inventors

• Chen Yan
• Komarov Serguei
• Vuong Vi

Classifications

• H10P72/0421

  for drying etching · CPC title

• H10P50/242

  of Group IV materials · CPC title

• H10P74/238 Primary

  comprising acting in response to an ongoing measurement without interruption of processing, e.g. endpoint detection or in-situ thickness measurement · CPC title

• H01J37/32963 Primary

  End-point detection · CPC title

• G06F17/16

  Matrix or vector computation {, e.g. matrix-matrix or matrix-vector multiplication, matrix factorization (matrix transposition G06F7/78)} · CPC title