Method and apparatus for detecting a planarized outer layer of a semiconductor wafer with a confocal optical system

• US 6,354,908 B2
• Filed: 01/04/2001
• Issued: 03/12/2002
• Est. Priority Date: 10/22/1998
• Status: Expired due to Term

• Current Assignee: Bell Semiconductor, LLC (Hilco Inc. (d/b/a Hilco Global))
• Original Assignee: LSI Logic Corporation (Broadcom, Inc.)
• Inventors: Daniel, David W., Allman, Derryl D. J., Gregory, John W.
• Primary Examiner(s): BANKS, DERRIS HOLT
• Application Number:
  US09/754,429
• Publication Number:
  US 20010021622A1
• Time in Patent Office: 432 Days
• Field of Search: 451/5, 451/6, 451/41, 451/285, 451/287, 451/288, 250/559.27, 250/559.14, 250/559.22, 250/559.33, 356/381, 356/375, 356/376
• US Class Current: 451/6
• CPC Class Codes: B24B 37/013 Devices or means for detecting lapping completion
• CPC Class Codes: B24B 49/04 involving measurement of the workpiece at the place of grinding during grinding operation
• CPC Class Codes: B24B 49/12 involving optical means
• CPC Class Codes: H01L 21/67253 Process monitoring, e.g. flow or thickness monitoring

Abstract

A method of planarizing a first side of a semiconductor wafer with a polishing system includes the step of polishing the first side of the wafer in order to remove material from the wafer. The method also includes the step of moving a lens of a confocal optical system between a number of lens positions so as to maintain focus on the first side of the wafer during the polishing step. The method further includes the step of determining a rate-of-movement value based on movement of the lens during the moving step. Moreover, the method includes the step of stopping the polishing step if the rate-of-movement value has a predetermined relationship with a movement threshold value. An apparatus for polishing a first side of a semiconductor wafer is also disclosed.

Claims

1. A method of planarizing a first side of a semiconductor wafer with a polishing system, comprising the steps of:

polishing said first side of said wafer in order to remove material from said wafer;

moving a lens of a confocal optical system between a number of lens positions so as to maintain focus on said first side of said wafer during said polishing step;

determining a rate-of-movement value based on movement of said lens during said moving step; and

stopping said polishing step if said rate-of-movement value has a predetermined relationship with a movement threshold value.

2. The method of claim 1, wherein said stopping step includes the step of stopping said polishing step if said rate-of-movement value is less than said movement threshold value.

3. The method of claim 1, wherein:

said polishing step includes the step of rotating said wafer with a wafer motor, and

said stopping step includes the step of idling said wafer motor if said rate-of-movement value has said predetermined relationship with said movement threshold.

4. The method of claim 1, wherein:

said polishing step includes the step of rotating a wafer carrier so as to urge said wafer into contact with a polishing platen, and

said confocal optical system is positioned such that an incident light beam emitting therefrom is directed through an opening defined in said polishing platen so as to impinge upon said first side of said wafer.

5. The method of claim 1, wherein said moving step includes the step of moving an objective lens of said confocal optical system between said number of lens positions so as to maintain focus on said first side of said wafer during said polishing step.

6. A method of planarizing a first side of a semiconductor wafer, comprising the steps of:

polishing said first side of said wafer in order to remove material from said wafer;

transmitting a first incident light beam from a confocal optical system during a first time period, wherein said first incident light beam impinges on said first side of said wafer during said polishing step so as to form a first reflected light beam which is reflected from said first side of said wafer;

analyzing said first reflected light beam so as to determine if said confocal optical system is focused on said first side of said wafer during said first time period;

transmitting a second incident light beam from said confocal optical system during a second time period, wherein said second incident light beam impinges on said first side of said wafer during said polishing step so as to form a second reflected light beam which is reflected from said first side of said wafer;

analyzing said second reflected light beam so as to determine if said confocal optical system is focused on said first side of said wafer during said second time period; and

stopping said polishing step if said confocal optical system is focused on said first side of said wafer during both said first time period and said second time period.

7. The method of claim 6, wherein:

said polishing step includes the step of rotating said wafer with a wafer motor, and

said stopping step includes the step of idling said wafer motor if said confocal optical system is focused on said first side of said wafer during both said first time period and said second time period.

8. The method of claim 6, wherein:

said polishing step includes the step of rotating a wafer carrier so as to urge said wafer into contact with a polishing platen, and

said confocal optical system is positioned such that both said first and said second incident light beams are directed through an opening defined in said polishing platen.

9. The method of claim 8, wherein:

said first incident light beam includes a first incident laser beam,

said second incident light beam includes a second incident laser beam,

said step of transmitting said first incident light beam includes the step of generating said first incident laser beam with a laser source unit,

said step of transmitting said second incident light beam includes the step of generating said second incident laser beam with said laser source unit, and

said laser source unit is positioned such that both said first and second incident laser beams are directed through said opening defined in said polishing platen so as to impinge on said first side of said wafer during said polishing step.

10. An apparatus for polishing a first side of a semiconductor wafer, comprising:

a polishing system which operates to polish said wafer, said polishing system having (i) a polishing platen which includes a polishing surface, and (ii) a wafer carrier which is configured to (a) engage said wafer by a second side of said wafer, and (b) apply pressure to said wafer in order to press said wafer against said polishing surface of said polishing platen;

a confocal optical system having a movable objective lens, said confocal optical system being configured to move said objective lens between a number of lens positions so as to maintain focus on said first side of said wafer during polishing of said wafer; and

a controller electrically coupled to said confocal optical system, wherein said controller is configured to (i) determine a rate-of-movement value based on movement of said objective lens during polishing of said wafer, and (ii) terminate operation of said polishing system so as to cease polishing of said wafer in response to determination that said rate-of-movement value has a predetermined relationship with a movement threshold value.

11. The apparatus of claim 10, further comprising a wafer motor, wherein:

said wafer motor is operable in (i) a polishing mode of operation in which said wafer motor rotates said wafer carrier, and (ii) an idle mode of operation in which said wafer motor is idle, and

said wafer motor is positioned in said idle mode of operation if said rate-of-movement value has said predetermined relationship with said movement threshold.

12. The apparatus of claim 10, wherein:

said polishing platen has an opening defined therein, and

said confocal optical system is positioned such that an incident light beam emitting therefrom is directed through said opening defined in said polishing platen so as to be impinged upon said first side of said wafer.

13. The apparatus of claim 12, wherein:

said confocal optical system includes a confocal laser system,

said incident light beam includes an incident laser beam generated by said confocal laser system, and

said confocal laser system is positioned such that said incident laser beam is directed through said opening defined in said polishing platen so as to impinge said incident laser beam on said first side of said wafer.

14. The apparatus of claim 10, wherein said controller is further configured to terminate operation of said polishing system so as to cease polishing of said wafer in response to determination that said rate-of-movement value is less than said movement threshold value.

15. An apparatus for polishing a first side of a semiconductor wafer, comprising:

a polishing system which operates to polish said wafer, said polishing system having (i) a polishing platen which includes a polishing surface, and (ii) a wafer carrier which is configured to (a) engage said wafer by a second side of said wafer, and (b) apply pressure to said wafer in order to press said wafer against said polishing surface of said polishing platen;

a confocal optical system positioned such that (i) a first incident light beam transmitted by said confocal optical system is impinged upon said first side of said wafer during a first period of time so as to form a first reflected light beam which is reflected from said first side of said wafer, (ii) a second incident light beam transmitted by said confocal optical system is impinged upon said first side of said wafer during a second period of time so as to form a second reflected light beam which is reflected from said first side of said wafer, and (iii) said first and second reflected light beams are received with said confocal optical system; and

a controller electrically coupled to said confocal optical system, wherein said controller is configured to (i) analyze said first reflected light beam so as to determine if said confocal optical system is focused on said first side of said wafer during said first time period, (ii) analyze said second reflected light beam so as to determine if said confocal optical system is focused on said first side of said wafer during said second time period, and (iii) terminate operation of said polishing system so as to cease polishing of said wafer in response to determination that said confocal optical system is focused on said first side of said wafer during both said first time period and said second time period.

16. The apparatus of claim 15, further comprising a wafer motor, wherein:

said wafer motor is operable in (i) a polishing mode of operation in which said wafer motor rotates said wafer carrier, and (ii) an idle mode of operation in which said wafer motor is idle, and

said wafer motor is positioned in said idle mode of operation in response to determination that said confocal optical system is focused on said first side of said wafer during both said first time period and said second time period.

17. The apparatus of claim 15, wherein:

said polishing platen has an opening defined therein, and

said confocal optical system is positioned such that (i) said first and second incident light beams are directed through said opening defined in said polishing platen so as to be impinged upon said first side of said wafer, and (ii) said first and second reflected light beams are directed through said opening so as to be received with said confocal optical system.

18. The apparatus of claim 17, wherein:

said confocal optical system includes a confocal laser system,

said first and second incident light beams include first and second incident laser beams generated by said confocal laser system,

said first and second reflected light beams include first and second reflected laser beams reflected from said first side of said wafer, and

said confocal laser system is positioned such that (i) said first and second incident laser beams are directed through said opening defined in said polishing platen so as to impinge said first and second incident laser beams on said first side of said wafer, and (ii) said first and second reflected laser beams are received by said confocal laser system.