Endpoint detection for photomask etching

Abstract

Apparatus and method for endpoint detection are provided for photomask etching. The apparatus provides a plasma etch chamber with a substrate support member. The substrate support member has at least two optical components disposed therein for use in endpoint detection. Enhanced process monitoring for photomask etching are achieved by the use of various optical measurement techniques for monitoring at different locations of the photomask.

1 . A method for etching a substrate, comprising:
 (a) providing an etch chamber having a substrate support member, the substrate support member comprising at least a first window in a center region and a second window in a peripheral region;   (b) providing a substrate on the substrate support member;   (c) introducing a process gas into the etch chamber;   (d) generating a plasma from the process gas for etching the substrate;   (e) detecting a first optical signal through the first window and a second optical signal through the second window using an endpoint detection system; and   (f) terminating the plasma based on information obtained from at least one of the detected first and second optical signals.   
   
   
       2 . The method of  claim 1 , wherein each of the first and second optical signals is one of reflectance, transmittance, interferometric signal, or optical emission signal. 
   
   
       3 . The method of  claim 1 , wherein (e) further comprises:
 (e1) providing a light source and a photodetector in the endpoint detection system;   (e2) directing an incident optical beam from the light source through at least one of the first and second windows onto one or more predetermined locations of the substrate; and   (e3) coupling at least one return optical beam from the one or more predetermined locations of the substrate through at least one of the first and windows to the photodetector.   
   
   
       4 . The method of  claim 3 , wherein one of the predetermined locations is in a peripheral region and another of the predetermined locations is in a central region of the substrate. 
   
   
       5 . The method of  claim 1 , wherein at least one of the first and second signals is an emission signal from the plasma. 
   
   
       6 . The method of  claim 1 , wherein the first optical signal is an emission signal from the plasma. 
   
   
       7 . The method of  1 , further comprising:
 providing a wavelength dispersive element and a photodetector in the endpoint detection system; and   coupling emission from the plasma to the photodetector via the wavelength dispersive element.   
   
   
       8 . The method of  claim 1 , further comprising:
 providing a third window in the peripheral region of the substrate support member for coupling a third optical signal to the photodetector;   wherein the second and third windows are disposed respectively at a corner and along a side of the peripheral region.   
   
   
       9 . The method of  claim 1 , further comprising:
 providing a plurality of windows in the center region of the substrate support member.   
   
   
       10 . The method of  claim 9 , further comprising:
 detecting a plurality of optical signals through the plurality of windows in the center region of the substrate support; and   selecting one optical signal from the plurality of optical signals for use in endpoint detection.   
   
   
       11 . The method of  claim 9 , further comprising:
 detecting a plurality of optical signals through the plurality of windows in the center region of the substrate support; and   obtaining an average from at least two of the plurality of optical signals for use in endpoint detection.   
   
   
       12 . The method of  claim 8 , further comprising:
 determining a center to edge etch uniformity based on the first optical signal and at least one of the second and third optical signals.   
   
   
       13 . The method of  claim 8 , further comprising:
 providing a third window in the peripheral region of the substrate support member for coupling a third optical signal to the photodetector;   wherein the second window is disposed along a first direction with respect to the first window, and the third window is disposed along a second direction with respect to the first window, the second direction being perpendicular to the first direction; and   determining a center to edge etch uniformity for the first and second directions based on the first, second and third optical signals.   
   
   
       14 . A method for etching a substrate, comprising:
 (a) providing an etch chamber having a substrate support member, the substrate support member comprising a first window and a second window;   (b) providing a substrate on the substrate support member;   (c) generating a plasma from a process gas for etching the substrate;   (d) providing an endpoint detection system comprising a photodetector;   (e) monitoring at least one optical signal through at least one of the first window and the second window using the photodetector; and   (f) terminating the plasma based on information obtained from the at least one optical signal.   
   
   
       15 . The method of  claim 14 , further comprising:
 (g) providing a light source in the endpoint detection system;   (h) coupling an output from the light source to incident on the substrate through at least one of the first window and the second window;   (i) operating the light source in a pulsed mode and obtaining two optical spectra during etching of the substrate;   (j) subtracting the two optical spectra to generate a different spectrum; and   (k) terminating the etching of the substrate based on information obtained from the difference spectrum.   
   
   
       16 . The method of  claim 1 , further comprising:
 (g) providing a third window in a wall of the etch chamber; and   (h) detecting an optical emission signal from the plasma.   
   
   
       17 . A computer readable medium containing instructions, that when executed by the controller, cause an etch chamber to perform a method comprising:
 (a) providing an etch chamber having a substrate support member, the substrate support member comprising a first window in a center region and a second window in a peripheral region;   (b) providing a substrate on the substrate support member;   (c) introducing a process gas into the etch chamber;   (d) generating a plasma from the process gas for etching the substrate;   (e) detecting a first optical signal through the first window and a second optical signal through the second window using an endpoint detection system; and   (f) terminating the plasma based on information obtained from at least one of the detected first and second optical signals.   
   
   
       18 . A method for etching a substrate, comprising:
 (a) providing an etch chamber having a substrate support member, the substrate support member comprising at least a first window in a center region;   (b) providing a second window in a wall of the chamber;   (c) providing a substrate on the substrate support member;   (d) generating a plasma from a process gas for etching the substrate;   (e) providing an endpoint detection system comprising a photodetector;   (f) monitoring at least one optical signal through at least one of the first window and the second window using the photodetector; and   (g) terminating the plasma based on information obtained from the at least one optical signal.