Plasma amplified photoelectron process endpoint detection apparatus

• US 4,846,920 A
• Filed: 12/09/1987
• Issued: 07/11/1989
• Est. Priority Date: 12/09/1987
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Keller, John H., Selwyn, Gary S., Singh, Jyothi
• Primary Examiner(s): Lacey, David L.
• Assistant Examiner(s): DANG, THI D
• Application Number:
  US07/130,573
• Time in Patent Office: 580 Days
• Field of Search: 204/298, 204/192.33, 204/192.32, 156/643, 156/646, 156/345, 156/626, 156/627, 118/665, 118/620, 427/10, 427/34
• US Class Current: 156/345.25
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge

Abstract

A plasma processing apparatus and process endpoint detection method including a plasma chamber for processing an item that has a first portion of a first material and a second portion of a second material, with the first and second materials having different work functions, and a structure for generating a plasma in the plasma chamber, with the plasma generating structure including at least a pair of RF-power electrodes with one of them being excited by an RF excitation frequency. The apparatus further includes a structure for generating and ejecting electrons from the second material only when the second material is exposed to the plasma, and a structure for increasing the energies of these generated electrons and accelerating these electrons into the etching plasma with sufficient energy to generate secondary electrons in the plasma. The apparatus further includes a structure for receiving a plasma discharge voltage signal, a structure for filtering the discharge electrical voltage signal to remove the RF excitation frequency and any DC components therein, and a structure for amplifying the natural frequencies of excitation and decay of the plasma discharge voltage perturbation signal, to thereby detect the processing endpoint.

In a preferred embodiment, the electron energy increasing and accelerating structure includes a structure for generating an electrode voltage sheath, and a structure for generating the electrons within this voltage sheath to thereby accelerate the electrons into the plasma. The electron generating structure includes a structure for directing a beam of photons in a selected energy range onto the item to be processed, which energy range is not sufficient to eject photoelectrons from the first material, but is high enough to generate photoelectrons from areas of exposed second material.

Claims

1. A plasma processing apparatus comprising:

a plasma generation chamber for processing an item that includes a first portion of a first material and a second portion of a second material, with said first and second materials having different work functions;

means for generating a plasma in said plasma generation chamber and a plasma RF discharge voltage signal which has natural frequencies of excitation and decay as well as an RF excitation frequency, said plasma generating means including an RF-powered electrode, said plasma for exposing an amount of second material or for covering an amount of any exposed second material,

means for directing a beam of energy in a selected energy range of impinge onto said item, which energy range is not sufficient to eject electrons from said first material, but is high enough to generate electrons from any exposed areas of second material;

means for increasing the energies of said generated electrons and accelerating said generated electrons into said plasma with sufficient energy to thereby generate secondary electrons in said plasma;

means for receiving said plasma RF discharge voltage signal;

means for filtering said plasma RF discharge voltage signal to remove said RF excitation frequency therefrom; and

means connected to said filtering means for receiving said filtered RF discharge voltage signal and for amplifying the natural frequencies of excitation and decay in the filtered plasma discharge voltage signal in the plasma discharge to thereby detect the process endpoint or surface condition.

2. An apparatus as defined in claim 1, wherein said electron energy increasing and accelerating means comprises

means for generating an electrode voltage sheath;

and

means for generating said generated electrons within said voltage sheath to thereby accelerate said generated electrons into said plasma.

3. An apparatus as defined in claim 2, wherein said electron generating means comprises means for directing a beam of photons in a selected energy range on to said item, which energy range is not sufficient to eject electrons from said first material, but is high enough to generate electrons from areas of exposed second material.

4. An apparatus as defined in claim 3, wherein said beam directing means comprises a laser.

5. An apparatus as defined in claim 3, wherein said beam directing means comprises a pulsed laser.

6. An apparatus as defined in claim 2, further comprising means for integrating said filtered and amplified signal.

7. An apparatus as defined in claim 6, further comprising:

means connected to said integrating means for generating a control signal to control a process parameter in said plasma chamber in response to said integrated signal.

8. An apparatus as defined in claim 1, wherein said filtering means comprises

a capacitor;

and

notch filter means for removing any RF excitation signal harmonics from said discharge voltage signal.

9. An apparatus as defined in claim 8, wherein said amplifying means includes means for amplifying said filtered signal in the frequency range of 0.3-7 MHz.

10. An apparatus as defined in claim 1, wherein said plasma generation chamber is a dry etching chamber;

and wherein said plasma generating means comprises means for generating an etching plasma.

11. An apparatus as defined in claim 1, wherein said plasma generation chamber is a deposition chamber;

and wherein said plasma generating means comprises means for generating a deposition plasma.

12. A plasma etching apparatus comprising:

a dry etching chamber for etching a wafer, said wafer including a top layer of a first material and a second layer of a second material, with said first and second materials having different work functions;

means for generating an etching plasma in said etching chamber to etch said wafer, said means including at least a pair of electrodes, with at least one of said at least a pair of electrodes being excited by an RF excitation frequency, with at least one of said at least a pair of electrodes receiving a discharge voltage signal from said plasma, which discharge voltage signal has natural frequencies of excitation and decay as well as said RF excitation frequency, so that said etching plasma etches said first material to thereby expose at least a portion of said second material;

means for directing a beam of photons in a selected energy range onto said wafer, which energy range is not sufficient to eject photoelectrons form one of said first or second materials on the wafer, but is high enough to eject photoelectrons from the other of the first or second materials, to thereby change the number of photoelectrons ejected when said other material is exposed;

means for generating a sheath field adjacent to one of said at least a pair of electrodes to accelerate said ejected photoelectrons into said etching plasma with sufficient energy to thereby generate secondary electrons;

means for filtering the discharge voltage signal at one of said at least a pair of electrodes to remove the RF excitation frequency therefrom; and

means for amplifying the natural frequencies of excitation and decay of the plasma discharge for detecting the etching endpoint.

13. An apparatus as defined in claim 12, wherein said beam directing means includes means for generating laser pulses.

14. An apparatus as defined in claim 13, wherein said filtering means comprises

a capacitor;

and

notch filter means for removing an RF excitation signal harmonics.

15. An apparatus as defined in claim 14, wherein said amplifying means includes means for amplifying said filtered signal in a frequency range of 0.3-7 MHz.

16. An apparatus as defined in claim 15, further comprising means for integrating said filtered signal.

17. An apparatus as defined in claim 16, wherein said integrating means includes means for detecting said filtered signal a predetermined time period after the occurrence of each laser pulse and integrating a plurality of said detected filtered signals.

18. An apparatus as defined in claim 16, further comprising means connected to said integrating means for generating a control signal to control an etch parameter in said dry etch chamber in response to said integrated signal.

19. A method for detecting the endpoint in a plasma process comprising the steps of:

disposing an item to be processed in a plasma chamber, said item including a first portion of a first material and a second portion of a second material, with said first material having a greater work function than said second material;

generating by means of an RF electrode excited by an RF excitation frequency a plasma in said plasma chamber to process said item to change the amount of second material which is exposed, with the plasma having a plasma discharge voltage signal thereacross having natural frequencies of excitation and decay as well as said RF excitation frequency;

directing a beam of photons in a selected energy range to impinge onto said item, which energy range is not sufficient to eject electrons from said first material, but is high enough to eject electrons from areas of exposed second material;

accelerating said generated electrons into said plasma with a sufficient energy to thereby generate secondary electrons in said plasma;

receiving said plasma discharge voltage signal;

filtering and amplifying the plasma discharge voltage signal so that the natural frequencies of excitation and decay of the plasma are detectable; and

detecting any perturbations in said filtered and amplified plasma discharge voltage signal that indicate the appearance or disappearance of said second material to thereby determine the process endpoint.

20. A method as defined in claim 19, wherein said accelerating step comprises the steps of

generating a voltage sheath adjacent to said RF electrode;

and

generating and ejecting said generated electrons within said voltage sheath to thereby accelerate said generated electrons.

21. A method as defined in claim 20, wherein said filtering and amplifying step includes the steps of filtering out said RF excitation frequency from said plasma discharge voltage signal and amplifying a band of frequencies containing the natural frequencies of excitation and decay of the plasma discharge.

22. A method as defined in claim 21, wherein said amplifying step comprises the step of amplifying a band of frequencies in the range 0.3-7 MHz.

23. A method as defined in claim 19, wherein said detecting step comprises the step of electrically integrating said filtered signal.

24. A method as defined in claim 23, wherein said integrating step comprises the step of:

detecting said filtered signal in a time interval occurring a predetermined time period after the occurrence of each photon pulse, and integrating a plurality of said detected filtered signals.

25. A method as defined in claim 23, further comprising the step of generating a control signal to control a process parameter in said plasma chamber in response to said integrated signal.

26. A method as defined in claim 19 wherein said beam directing step comprises the step of directing a pulsed photon beam at said item to be processed.

27. A method as defined in claim 19, wherein said disposing step comprises the step of disposing said item in a dry etching chamber;

and wherein said plasma generating step comprises the step of generating an etching plasma.

28. A method as defined in claim 19, wherein said disposing step comprises the step of disposing said item in a deposition chamber;

and wherein said plasma generating step comprises the step of generating a deposition plasma.

29. A method for detecting the endpoint in a plasma etching process comprising the steps of:

disposing an item to be etched in a dry etching chamber, said item including a top layer of a first material disposed over a second layer of a second material, with said first and second materials having different work functions;

generating by means of an RF excitation frequency an etching plasma in said etching chamber to etch said item to change the amount of second material which is exposed, said etching plasma having a discharge voltage signal thereacross having natural frequencies of excitation and decay as well as said RF excitation frequency;

directing a beam of energy in a selected energy range onto said item, which energy range is not sufficient to eject photoelectrons from one of said first or second materials on said item, but is high enough to eject photoelectrons into said plasma from the other of said first or second materials;

ejecting photoelectrons by means of said beam of energy when said other material is exposed by said etching process;

accelerating said ejected photoelectrons into said plasma with a sufficient energy to thereby generate secondary electrons in said plasma;

receiving said plasma discharge voltage signal;

filtering said plasma discharge voltage signal to remove said RF excitation frequency;

amplifying the natural frequencies of excitation and decay of the filtered plasma voltage discharge signal; and

detecting any perturbations in the amplified natural frequencies of excitation and decay in this voltage signal that indicate the appearance or disappearance of second material to thereby detect the etch endpoint.

30. A method as defined in claim 29,

wherein said filtering step comprises the step of filtering out any RF excitation frequency harmonics and any D.C. components from said plasma discharge voltage signal.

31. A method as defined in claim 30, wherein said beam directing step includes the step of directing laser pulses at said item to be etched.

32. A method as defined in claim 31, wherein said detecting step includes the step of electrically integrating said filtered signal.

33. A method as defined in claim 32, wherein said integrating step comprises the step of

detecting said filtered signal in a time-interval occurring a predetermined time period after the occurrence of each laser pulse and integrating a plurality of said detected filtered signals.

34. A method as defined in claim 29, further comprising the step of generating a control signal to control an etch parameter in said dry etching chamber in response to said integrated signal.

35. A method as defined in claim 29, wherein said amplifying step comprises the step of amplifying a band of frequencies in the range 0.3-7 MHz.