Optical emission end point detector

• US 4,491,499 A
• Filed: 03/29/1984
• Issued: 01/01/1985
• Est. Priority Date: 03/29/1984
• Status: Expired due to Term

• Current Assignee: AT&T Teleholdings Incorporated (AT&T, Inc.)
• Original Assignee: AT&T Teleholdings Incorporated (AT&T, Inc.)
• Inventors: Lory, Earl R., Muething, Kevin A., Tsou, Len Y., Jerde, Leslie G.
• Primary Examiner(s): Powell, William A.
• Application Number:
  US06/594,629
• Time in Patent Office: 278 Days
• Field of Search: 156/626, 156/627, 156/643, 156/646, 156/656, 156/659.1, 156/665, 156/345, 204/164, 204/192 E, 204/298, 356/345, 356/381, 356/437, 356/218, 356/222, 356/229
• US Class Current: 216/60
• CPC Class Codes: C23F 4/00 Processes for removing metallic material from surfaces, not provided for in group C23F1/00 or C23F3/00
• CPC Class Codes: G01N 21/62 Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge

Abstract

A method for determining the optimum time at which a plasma etching operation should be terminated. The optical emission intensity (S₁) of the plasma in a narrow band centered about a predetermined spectral line, indicative of the gas phase concentration of a plasma etch product or reactant species. The optical emission intensity (S₂) of the plasma in a wide band centered about the predetermined spectral line, indicative of a background emission signal is also monitored. The intensity (S_1L) of the spectral line is then determined in accordance with the equation S_1L =S₁ -k (αS₂ -S₁). The etching process is terminated when the monitored signal intensity (S_1L) or its time derivative reaches a predetermined value.

Claims

1. A method for determining the time at which a plasma etching operation should be terminated, comprising the steps of:

monitoring the optical emission intensity (S₁) of the plasma, in a narrow band centered about a predetermined spectral line, indicative of the gas phase concentration of a plasma etch product or reactant species;

monitoring the optical emission intensity (S₂) of the plasma, in a wide band centered about the predetermined spectral line, indicative of an optical background emission signal;

determining the intensity (S_1L) of the spectral line in accordance with the equation;

space="preserve" listing-type="equation">S.sub.1L =S.sub.1 -k (α

S.sub.2 -S.sub.1)

where;

k=a constant set to a value to give optimum results; and

α

=a constant determined by optical and electrical responses of the two signal amplification channels; and

terminating the etching process when (S_1L) achieves a predetermined value.

2. The method as set forth in claim 1, wherein:

the material being etched is aluminum.

3. The method as set forth in claim 1, wherein:

the wide band is approximately three times wider than the narrow band.

4. The method as set forth in claim 1, wherein:

the plasma etching process is terminated when the time derivative of (S_1L) achieves a predetermined value.

5. The method as set forth in claim 2, wherein:

the narrow band is 1 nm and the wide band is 3 nm; and

both bands are centered at 396.1 nm.

6. The method as set forth in claim 1, comprising the step of:

determining the value of the constant k when S_1L =0 using the following formula;

##EQU5##

7. An apparatus for determining the time at which a plasma etching operation should be terminated, comprising:

means for monitoring the optical emission intensity (S₁) of the plasma, in a narrow band centered about a predetermined spectral line, indicative of the gas phase concentration of a plasma etch product or reactant species;

means for monitoring the optical emission intensity (S₂) of the plasma, in a wide band centered about the predetermined spectral line, indicative of an optical background emission signal;

means for determining the intensity (S_1L) of the spectral line in accordance with the equation;

space="preserve" listing-type="equation">S.sub.1L =S.sub.1 -k (α

S.sub.2 -S.sub.1)

where;

k=a constant set to a value to give optimum results; and

α

=a constant determined by optical and electrical responses of the two signal amplification channels; and

means for terminating the etching process when (S_1L) achieves a predetermined value.

8. The apparatus as set forth in claim 7, wherein:

the material being etched is aluminum.

9. The apparatus as set forth in claim 7, wherein:

the wide band is approximately three times wider than the narrow band.

10. The apparatus as set forth in claim 7, wherein:

the plasma etching process is terminated when the time derivative of (S_1L) achieves a predetermined value.

11. The apparatus as set forth in claim 8, wherein:

the narrow band is 1 nm and the wide band is 3 nm; and

both bands are centered at 396.1 nm.

12. The apparatus as set forth in claim 7, comprising:

means for determining the value of the constant k when S_1L =0 using the following formula;

##EQU6##