Wafer chuck with integrated reference sample

• US 6,952,258 B2
• Filed: 05/11/2004
• Issued: 10/04/2005
• Est. Priority Date: 04/30/2001
• Status: Expired due to Fees

• Current Assignee: The Therma-Wave Incorporated (KLA Corporation)
• Original Assignee: The Therma-Wave Incorporated (KLA Corporation)
• Inventors: Ebert, Martin, Traber, Thomas
• Primary Examiner(s): STAFIRA, MICHAEL PATRICK
• Application Number:
  US10/843,159
• Publication Number:
  US 20040207838A1
• Time in Patent Office: 511 Days
• Field of Search: 3562371-2375, 356244-246, 250/225
• US Class Current: 356/244
• CPC Class Codes: G01N 21/01 Arrangements or apparatus for facilitating the optical investigation
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: H01L 21/67253 Process monitoring, e.g. flow or thickness monitoring

Abstract

The subject invention relates to a wafer stage, such as may be used in optical wafer metrology instruments. The stage contains a wafer-chuck that can be connected to translation stages for the purpose of clamping and translating the wafer so that a plurality of sites on the wafer surface may be measured. The chuck includes a holder for mounting a reference sample. The holder is movable between a retracted position where the reference sample is held below the chuck surface and an extended position, such as where the surface of the reference sample is co-planar with the wafer surface. Therefore the holder may be installed within the area of the chuck that is utilized for wafer clamping. By this arrangement, the size of the wafer translation system can be reduced minimizing the stage travel and enabling increased spatial resolution, increased wafer throughput and reduced capital equipment and operating costs.

Claims

1. A wafer support stage that permits the location of a reference sample within a stage area utilized for supporting a wafer, comprising:

a platform for holding the wafer;

a holder supporting a reference sample, said holder being located within a body of the platform at a location within the stage area utilized for supporting the wafer, said holder being movable between a retracted position where the reference sample is below the platform surface and an extended position; and

a mechanism for moving the holder between the retracted and extended positions.

2. A wafer support stage according to claim 1, further comprising:

a wafer motion system coupled to the platform for translating the platform.

3. A wafer support stage according to claim 1, wherein:

the platform is capable of holding the wafer at a measurement position, and the reference sample is raised to be co-planar with the wafer measurement position when the holder is in the extendable position.

4. A wafer support stage according to claim 1, wherein:

the platform is selected from the group consisting of mechanical, electrostatic and vacuum wafer chucking systems.

5. A wafer support stage according to claim 1, wherein:

the mechanism for moving the holder between the retracted and extended positions employs one or more elements selected from the group consisting of mechanical, electro-mechanical, and hydraulic actuators.

6. A wafer support stage according to claim 1, wherein:

the holder is a piston having a support surface for locating and holding the reference sample, said piston being contained within a housing, said piston being free to move between the retracted and extended positions.

7. A wafer support stage according to claim 6, wherein:

the housing includes locating surfaces which limit the extent of the piston motion and determine the retracted and extended positions.

8. A wafer support stage according to claim 6, wherein:

the holder further includes a member fixed to the outer surface of the piston for the purpose of forming a hydraulic seal between the piston and housing, thereby dividing the housing into upper and lower hydraulic chambers, thereby enabling hydraulic actuation of the piston motion within the housing through differential pressurization of the upper and lower hydraulic chambers.

9. A wafer support stage according to claim 8, wherein:

the piston is spring loaded within the housing such that in the absence of differential pressurization of the upper and lower hydraulic chambers the piston locates in the retracted position.

10. A wafer support stage according to claim 8, wherein:

the piston is spring loaded within the housing such that in the absence of differential pressurization of the upper and lower hydraulic chambers the piston locates in the extended position.

11. A wafer support stage according to claim 8, wherein:

differential pressurization of the upper and lower hydraulic chambers is achieved by evacuating the lower hydraulic chamber.

12. A wafer support stage according to claim 8, wherein:

differential pressurization of the upper and lower hydraulic chambers is achieved by pressurizing the lower hydraulic chamber.

13. A wafer support stage according to claim 8, wherein:

differential pressurization of the upper and lower hydraulic chambers is achieved by evacuating the upper hydraulic chamber.

14. A wafer support stage according to claim 8, wherein:

differential pressurization of the upper and lower hydraulic chambers is achieved by pressurizing the upper hydraulic chamber.

15. A wafer support stage according to claim 8, wherein:

differential pressurization of the upper and lower hydraulic chambers is achieved by evacuating the upper hydraulic chamber and pressurizing the lower hydraulic chamber.

16. A wafer support stage according to claim 8, wherein:

differential pressurization of the upper and lower hydraulic chambers is achieved by evacuating the lower hydraulic chamber and pressurizing the upper hydraulic chamber.

17. A wafer support stage that permits the location of a reference sample within a stage area utilized for supporting a wafer, comprising:

a vacuum-chuck for holding a wafer;

a holder supporting a reference sample, said holder being located within the body of the vacuum-chuck at a location within the stage area utilized for supporting the wafer, said holder being movable between a retracted position where the reference sample is below the vacuum-chuck surface and an extended position where the reference sample is raised to be at least co-planar with the vacuum-chuck surface, said holder comprising;

a piston having a support surface for a reference sample located within and free to move within a housing, said housing containing locating surfaces that limit the range of the piston motion and establish the retracted and extended positions;

a member fixed to the surface of the piston said member forming a hydraulic seal between the piston and housing thereby dividing the housing into upper and lower hydraulic chambers and enabling hydraulic actuation of the piston by differential pressurization of said upper and lower hydraulic chambers; and

a hydro-mechanical actuation mechanism for moving the piston between the extended and retracted position, said actuation mechanism comprising;

a conduit connecting the upper hydraulic chamber to the surface of the vacuum-chuck;

a spring arranged to locate the piston in the retracted position in the absence of differential pressurization of the upper and lower hydraulic chambers and locate the piston in the extended position in the presence of differential pressurization of said upper and lower hydraulic chambers;

a gas manifold that connects the lower hydraulic chamber and vacuum-chuck to both a source of pressurized gas and a vacuum system; and

a check-valve arranged to inhibit differential pressurization of the upper and lower hydraulic chambers during manifold evacuation and enable differential pressurization of the upper and lower hydraulic chambers during manifold pressurization.

18. A wafer support stage according to claim 17, wherein:

a vacuum-chuck is utilized to holding the wafer in an optical metrology instrument selected from the group consisting of reflectometers, ellipsometers, spectroscopic reflectometers, spectroscopic ellipsometers, polarized beam spectroscopic reflectometers and optical CD measurement tools.

19. A wafer support stage that permits the location of a reference sample within a stage area utilized for wafer support, comprising:

a vacuum-chuck for holding the wafer;

a holder supporting a reference sample, said holder being located within the body of the vacuum-chuck at a location within the stage area utilized for wafer support, said holder being movable between a retracted position where the reference sample is below the vacuum-chuck surface and an extended position where the reference sample is raised to be at least partially above the vacuum-chuck surface;

a source of pressure in selective communication with the holder for biasing the holder into the extended position; and

a spring for urging the holder back to the retracted position.

20. A wafer support stage according to claim 19, further comprising:

a vacuum source in selective communication with the holder and also used to urge the holder back to the retracted position.

21. A wafer support stage according to claim 20, further comprising:

a valve for selectively coupling either the source of pressure or the vacuum source to the holder.

22. A wafer support stage according to claim 20, wherein:

said vacuum source is also coupled to the chuck for holding the wafer to the chuck.

23. A method for calibrating an optical metrology instrument, comprising the steps of:

placing a reference sample on a holder, the holder being located within a stage area of a platform utilized for supporting a wafer to be measured by the optical metrology instrument;

raising the reference sample such that a reference surface of the reference sample is located above a surface plane of the platform;

measuring the reference surface using the optical metrology instrument; and

lowering the reference sample below the surface plane such that the wafer to be measured can be placed on the stage area.

24. A method according to claim 23, further comprising:

adjusting the optical measurement instrument in response to the measurement of the reference sample.

25. A method according to claim 23, further comprising:

placing the wafer on the stage area; and

measuring the wafer surface with the optical metrology instrument.

26. A method according to claim 25, further comprising:

removing the wafer from the stage area; and

repeating the steps of raising, measuring, and lowering the reference sample after the step of measuring the wafer surface.