Method for detecting an endpoint for an oxygen free plasma process

• US 6,492,186 B1
• Filed: 11/05/1999
• Issued: 12/10/2002
• Est. Priority Date: 08/05/1999
• Status: Expired due to Term

• Current Assignee: Lam Research Corporation
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Cardoso, Andre, Sakthivel, Palani, Ruffin, Ricky, Han, Qingyan
• Primary Examiner(s): Utech, Benjamin L.
• Assistant Examiner(s): CHEN, KIN CHAN
• Application Number:
  US09/434,617
• Time in Patent Office: 1,131 Days
• Field of Search: 216/60, 216/68, 156/345, 438/723, 438/725, 438/9, 438/14, 438/8, 438/16
• US Class Current: 438/8
• CPC Class Codes: G01N 21/68 using high frequency electric fields
• CPC Class Codes: G03F 7/427 using plasma means only
• CPC Class Codes: H01J 2237/3342 Resist stripping
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge
• CPC Class Codes: H01J 37/32963 End-point detection
• CPC Class Codes: H01L 21/02071 the processing being a delineation, e.g. RIE, of conductive layers
• CPC Class Codes: H01L 21/31138 by dry-etching

Abstract

A method for determining an endpoint for an oxygen free plasma stripping process for use in semiconductor wafer processing. The method comprises exciting a gas composition containing a nitrogen gas and a reactive gas to form the oxygen free plasma. The oxygen free plasma reacts with a substrate having a photoresist and/or residues thereon to produce emitted light signals corresponding to an oxygen free reaction product. The endpoint is determined by optically measuring a primary emission signal of the oxygen free reaction product at a wavelength of about 387 nm. The endpoint is determined when the plasma no longer reacts with the photoresist and/or residues on the substrate to produce the emitted light at about 387 nm, an indication that the photoresist and/or residues have been removed from the wafer. Secondary emission signals of the oxygen free reaction product at about 358 nm and 431 nm can also be monitored for determining the endpoint.

Claims

1. A method for determining an endpoint for an oxygen free plasma ashing process wherein said inethod comprises exciting a gas composition containing a nitrogen gas and a selected one of a hydrogen bearing gas, a fluorine bearing gas and a fluorine-hydrogen bearing gas mixture to form an oxygen free plasma, reactng the oxygen free plasma with a substrate having a photoresist and/or residues thereon to produce emitted light signals corresponding to an oxygen free reaction product;

sequentially recording over a period of time the light emission intensity signals resulting form the reaction product; and

deter said endpoint at a time when the light emission intensity signals of said reaction product are at a threshold level, said level indicating the ashing process is substantially complete.

2. The method according to claim 1 further comprising measuring the light intensity signals at a wavelength of about 387 nm for determining said endpoint.

3. The method according to claim 1 or 2 further comprising measuring secondary light intensity signals at wavelengths of about 358 nm and about 431 nm for determining said endpoint.

4. The method according to claim 1 further comprising using optical emission spectroscopy for measuring said light intensity signals.

5. The method according to claim 4 wherein said optical emission spectroscopy comprises a selected one of a monochromator and a spectrometer.

6. The method according to claim 5 wherein equipment used for said optical emission spectroscopy is a selected one of a spectral filter and light detector combination, a monochromator, a CCD spectrophotometer, a photodetector array and a scanning monochromator.

7. The method according to claim 1 wherein the endpoint is detected when said light emission intensity signals of said reaction are at a threshold intensity value, wherein said threshold intensity value is calculated by experimentation by correlating values of reaction time, light wavelength spectrum and light emission intensity signals, and said value corresponds to a condition wherein the ashing process is substantially complete.

8. The method according to claim 1 wherein said substrate comprises a semiconductor wafer having therein a material having a low k dielectric constant less than about 3.5 and/or exposed copper surfaces.

9. The method according to claim 1 wherein said fluorine bearing gas is selected from the group consisting of NF₃, F₂, SF₆, and C_xH_yF_z wherein x ranges from 1 to 4, y ranges from 0 to 9 and z ranges from 1 to 10.

10. The method according to claim 1 wherein said hydrogen gas mixture comprises a forming gas comprising nitrogen and hydrogen gas wherein said hydrogen gas is in an amount from about 3 percent to about 5 percent by volume of the forming gas.

11. A method for determining an endpoint for an oxygen free plasma asbing process wherein said method comprises exciting a gas composition containing a nitrogen gas and a selected one of a hydrogen bearing gas, a fluorine bearing gas and a fluorine-hydrogen bearing gas mixture to form an oxygen free plasma;

reacting the oxygen free plasma with a substrate having photoresist and/or residues thereon to produce volatile reaction products;

measuring an emission signal of said products at a wavelength of about 387 nm and determining said endpoint in response to an observed change in the monitored emission signal.

12. The method according to claim 11 further comprising measuring emission signals at wavelengths of about 358 nm and 431 nm wherein said endpoint is determined in response to the observed change in the monitored emission signals.

13. The method according to claim 11 further comprising using optical emission spectroscopy for measuring said emission signals.

14. The method according to claim 13 wherein equipment used for said optical emission spectroscopy is a selected one of a spectral filter and light detector combination, a monochromator, a CCD spectrophotometer, a photodetector array and a scanning monochromator.

15. The method according to claim 13 wherein said optical emission spectroscopy is a selected one of a monochromator and a spectrometer.

16. A method for determining an endpoint of an oxygen free plasma ashing process used for stripping photoresist and/or residues from a substrate, said method comprising the steps of:

generating an oxygen free plasma from a gas composition containing a nitrogen gas and at least one reactive gas;

measuring a first emission signal at a wavelength of about 387 nm;

placing a coated substrate having the photoresist and/or residues thereon into the reaction chamber;

exposing the coated substrate to said plasma;

reacting a substantially electrically neutral species of said oxygen free plasma with said photoresist and/or said residues;

measuring a second emission signal at a wavelength of about 387 nm; and

determining said endpoint of the plasma ashing process by comparing said first signal with said second signal wherein said endpoint is detected when said first and second signals are about the same.

17. The method according to claim 16 wherein the first emission signal further comprises wavelengths at about 358 nm and about 431 nm and the second emission signal further comprises wavelengths at about 358 nm and about 431 nm.

18. The method according to claim 16 further comprising subtracting the first signal from the second signal wherein said endpoint is detected when said second signal reaches a steady state having about a zero emission intensity.

19. The method according to claim 16 further comprising placing at least one uncoated substrate into the reaction chamber for measuring the first emission signal.

20. The method according to claim 16 further comprising detecting an endpoint when said second emission signal intensity is at a threshold intensity value, wherein said threshold intensity value is calculated by experimentation by correlating values of reaction time, light wavelength spectrum and light emission intensity signals, and said value corresponds to a condition wherein the ashing process is substantially complete.

21. The method according to claim 16 further comprising using optical emission spectroscopy for measuring said light intensity signals.

22. The method according to claim 21 wherein said optical emission spectroscopy is a monochromator.

23. The method according to claim 16 further comprising step-wise heating said substrate from a range of about 80°

C. to about 350°

C. during said exposure to said plasma.

24. The method according to claim 16 wherein said substrate comprises a low k dielectric material less than about 3.5 and/or an exposed copper surface.

25. An ashing step for removing photoresist and/or residues from a substrate comprising:

placing the substrate having the photoresist and/or residues thereon into a reaction chamber;

generating an oxygen free plasma from a gas composition containing nitrogen gas and at least one reactive gas;

exposing said photoresist and/or residues to a substantially electrically neutral species of said oxygen free plasma;

reacting said photoresist and/or post etch residues with the neutral species to produce byproducts having emission signals at about 358 nm, 387 nm, and 431 nm;

optically measuring said emission signals of said byproducts; and

stopping the ashing step when the emission signals from said reaction byproducts are no longer detectable.

26. The method according to claim 25 wherein optically measuring said emission signals is by optical emission spectroscopy.

27. The method according to claim 26 wherein said optical emission spectroscopy comprises a selected one of a monochromator and a spectrometer.

28. A method for determining an endpoint of an oxygen free plasma ashing process used for stripping photoresist and/or residues from a substrate having low k dielectric layers having a dielectric constant less than about 3.5, said method comprising the steps of:

placing the substrate having the photoresist and/or residues thereon into a reaction chamber;

generating an oxygen free plasma from a gas composition including nitrogen and a reactive gas;

reacting a substantially electrically neutral reactive species of said oxygen free plasma with said photoresist and/or said residues to produce an emission light;

recording an emission intensity spectrum of said emitted light during said reaction wherein said emission intensity spectrum includes a wavelength of about 387 nm; and

determining said endpoint of the plasma stripping process from said emission intensity spectrum wherein said endpoint is detected in response to an observable change at about 387 nm.

29. The method according to claim 28 further comprising using optical emission spectroscopy for measuring said light intensity signals.

30. The method according to claim 29 wherein said optical emission spectroscopy comprises a spectrometer.

31. The method according to claim 29 wherein said emission intensity spectrum further includes wavelengths of about 358 nm and about 431 nm.

32. A method for determining an endpoint for an oxygen free plasma ashing process wherein said method comprises exciting a gas composition containing nitrogen gas and a selected one of a hydrogen bearing gas, a fluorine bearing gas and a fluorine-hydrogen bearing gas mixture to form an oxygen free plasma;

reacting the oxygen free plasma with a substrate having photoresist and/or residues thereon to produce volatile reaction products, measuring a selected one of an emission signal of said products at wavelengths of about 358 nm, about 387 nm and about 431 nm, and determining said endpoint in response to an observed change in the monitored emission signal.