Method and apparatus for detecting and sizing particles on surfaces

• US 4,967,095 A
• Filed: 09/25/1989
• Issued: 10/30/1990
• Est. Priority Date: 06/28/1989
• Status: Expired due to Term

• Current Assignee: Tencor Instruments (KLA Corporation)
• Original Assignee: Tencor Instruments (KLA Corporation)
• Inventors: Berger, Josef, Neukermans, Armand P., Vaught, John L.
• Primary Examiner(s): Westin, Edward P.
• Application Number:
  US07/411,910
• Time in Patent Office: 400 Days
• Field of Search: 250/222.2, 250/223 R, 250/562, 250/563, 250/571, 250/572, 250/559, 356/37, 356/237, 356/429, 356/430, 356/431
• US Class Current: 250/559.41
• CPC Class Codes: G01N 15/02 Investigating particle size or size distribution by measuring osmotic pressure G01N7/10; investigating sedimentation of particle suspensions G01N15/04; investigating individual particles G01N15/10
• CPC Class Codes: G01N 2015/0681 Purposely modifying particles, e.g. humidifying for growing
• CPC Class Codes: G01N 21/94 Investigating contamination, e.g. dust G01N21/85 takes precedence

Abstract

A method and apparatus for detecting and classifying particles on a surface in which condensation is used to enlarge particles. An apparatus of the present invention includes a heatable wick disposed over a test surface and in fluid communication with a source of volatile liquid. A zone of vapor supersaturation is thus created in which condensation on particles on the surface can occur. A light beam directed onto the surface scans the surface. Droplets are detected by means of light scattered from the droplets. In an alternate embodiment a stream of carrier gas may be provided around the wick or bubbled through a jar of volatile liquid to direct a vapor toward the test surface. In another embodiment, multiple wicks communicate with different sources of volatile liquids. In a method of the invention, mulitple scans are made with either different levels of vapor supersaturation or different vapor compositions. Comparing particles in each scan allows one to classify particles into different size ranges or chemical type.

Claims

1. A particle detection apparatus comprising,

means for supporting an object, a surface of which can be tested,

means for providing a local zone of vapor supersaturation over a portion of said surface, whereby droplets of liquid can condense around any particles on said object in said portion of said surface,

means for directing a light beam adjacent to said local zone of vapor supersaturation toward said surface,

means for providing relative movement of said object with respect to said local zone of vapor supersaturation and said adjacent light beam so as to cause relative movement of said portion of said surface having said droplets into a path of said beam, whereby light from said beam is scattered by said droplets, and

means positioned in scattered light receiving relation to said surface for detecting light scattered by said droplets, whereby particles on said object around which said droplets have condensed are detected.

2. The particle detection apparatus of claim 1 wherein said means for providing a local zone of vapor supersaturation comprises a source of vaporizable liquid material, a wick in fluid communication with said liquid source and disposed over said portion of said surface, and

means for heating said wick so as to vaporize liquid material drawn from said liquid source by said wick.

3. The particle detection apparatus of claim 2 wherein said means for providing a local zone of vapor supersaturation further comprises a source of a carrier gas and means in fluid communication with said carrier gas source and with said heated wick for directing a vapor stream toward said portion of said surface, said vapor stream being composed of vaporized liquid material in said carrier gas.

4. The particle detection apparatus of claim 3 wherein said vapor stream has zero velocity relative to said surface.

5. The particle detection apparatus of claim 1 wherein said means for providing a local zone of supersaturation comprises a source of carrier gas, a bubbler jar having a vaporizable liquid material, means for bubbling said carrier gas through said jar of vaporizable liquid material, and means in communication with said jar and terminating above said surface for directing a vapor stream, composed of vaporized liquid material in said carrrier gas, toward said portion of said surface.

6. The particle detection apparatus of claim 1 wherein said light beam is a laser beam.

7. The particle detection apparatus of claim 1 wherein said means for supporting an object includes means for cooling said object below a temperature in which said droplets of liquid condense.

8. The particle detection apparatus of claim 1 wherein said means for providing a local zone of supersaturation comprises a plurality of sources of vaporizable liquid material of different compositions and means for selecting one of said sources.

9. The particle detection apparatus of claim 8 wherein said means for providing a local zone of supersaturation further comprises a source of carrier gas and a manifold in fluid communication with said carrier gas source, and said means for selecting one of said plurality of vaporizable liquid material sources comprises a plurality of selectably heatable wicks in fluid communication with said liquid material, said manifold partially surrounding said plurality of wicks so as to direct a vapor stream composed of a selected vaporized liquid material and said carrier gas toward said surface.

10. The particle detection apparatus of claim 8 wherein said means for providing a local zone of supersaturation further comprises a source of carrier gas, a plurality of bubbler jars, each jar having a different vaporizable liquid material, means for selectively bubbling said carrier gas through one of said jars of vaporizable liquid material, and a tube in selective communication with said one of said jars and terminating above said surface so as to direct a vapor stream composed of a selected vaporized liquid material and said carrier gas toward said surface.

11. A particle detection apparatus comprising,

means for supporting an object with a surface to be tested,

a source of vaporizable liquid material,

a wick in fluid communication with said source and disposed over a portion of said surface, said wick being heatable so as to cause liquid material drawn by said wick to vaporize,

means for heating said wick, whereby a local zone of vapor supersaturation is provided over said portion of said surface, droplets of liquid being thereby capable of condensing on any particles in said portion,

a light beam source for producing a beam,

means in a path of said beam for directing said beam in a scanning motion toward said surface, said beam scanning a path adjacent to said local zone of vapor supersaturation,

means associated with said support for moving said object relative to said wick and said scanning beam path, whereby any droplets which condense are moved into said beam path so as to scatter said light beam,

a light detector positioned to receive light scattered by any said droplets, whereby particles around which said droplets have condensed are detected.

12. The apparatus of claim 11 wherein said means for heating a wick comprises means for providing an electric current through said wick.

13. The apparatus of claim 11 wherein said light beam source is a laser.

14. The apparatus of claim 11 further comprising,

a source of a carrier gas, and

a manifold partially surrounding said wick and in fluid communication with said gas source so as to provide a gas stream around said wick directed toward said surface.

15. The apparatus of claim 11 further comprising,

additional sources of vaporizable liquid material, each material having a different composition, and

additional wicks, each wick capable of being in fluid communication with one of said additional sources, and disposed over said surface, each wick being selectably heatable.

16. The apparatus of claim 15 further comprising,

a source of carrier gas, and

a manifold partially surrounding said wick and said additional wicks in fluid communication with said gas source so as to provide a gas stream around said wicks directed toward said surface.

17. The apparatus of claim 11 wherein said means for moving said object moves said object in a first direction and said means for directing said beam produces a beam path in a second direction substantially perpendicular to said first direction.

18. A method of detecting and classifying particles on a surface comprising,

(a) providing a first supersaturated vapor over a test surface, whereby droplets condense on a first set of particles on said surface,

(b) scanning said surface so as to detect said droplets,

(c) repeating steps (a) and (b) a predetermined number of times with other supersaturated vapors, whereby droplets condense on other sets of particles on said surface and are subsequently detected, and

(d) comparing said droplet detections from the repeated scans and classifying said particles on said surface according to the scan or scans in which their corresponding droplets are detected.

19. The method of claim 18 wherein said first supersaturated vapor is supersaturated to a first level, droplets condensing on particles of at least a first minimum size, and said other supersaturated vapors are supersaturated at other levels, droplets condensing on particles of at least other minimum sizes, said particles being classified into a plurality of relative size ranges corresponding to the supersaturation levels needed for their droplet detection.

20. The method of claim 18 wherein said first supersaturated vapor is composed of material of a first chemical characteristic, other supersaturated vapors being composed of materials of other chemical characteristics, said particles being classified according to the vapor material or materials for which they act as precipitation centers.

21. The method of claim 20 wherein said first supersaturated vapor is composed of a polar material, droplets of said material tending to condense on ionic salt particles on said surface, a second supersaturated vapor being composed of a non-polar material, droplets of said nonpolar material tending to condense on particles of nonionic material.

22. The method of claim 20 wherein one of said supersaturated vapors is composed of a photoresist solvent, particles around which droplets of said solvent condense being classified as photoresist residue.

23. The method of claim 18 wherein comparing said droplets includes counting the number of droplets detected in each scan and obtaining the number of particles in each class.

24. The method of claim 18 wherein comparing said droplets includes locating the position of detected droplets in each scan and matching any common positions in the plurality of scans, droplets detected in different scans which are determined to have matching common positions being designated as corresponding to a single particle.

25. The method of claim 18 wherein scanning said surface comprises,

directing a beam toward said surface, said beam being adjacent to a local zone of vapor supersaturation over said surface,

providing relative movement of said surface with respect to said beam and said local zone so as to cause relative movement of a local surface portion having said droplets into a path of said beam, said beam being scattered by any such droplets, and

detecting and measuring said scattered beam.

26. The method of claim 25 wherein a laser beam is directed toward said surface.

27. The method of claim 18 wherein providing a supersaturated vapor comprises,

providing a source of vaporizable liquid material,

disposing a wick in fluid communication with said liquid source over a local portion of said surface, the wick drawing said liquid material from said source, and

heating said wick so as to vaporize said liquid material drawn by said wick.

28. The method of claim 27 wherein providing a supersaturated vapor further comprises,

directing a stream of carrier gas for said vaporized liquid material around said wick toward said surface.

29. The method of claim 28 wherein said stream is directed so as to have zero velocity relative to said surface.

30. The method of claim 18 wherein providing a supersaturated vapor comprises,

providing a source of vaporizable liquid material,

bubbling a carrier gas through said liquid material, whereby said gas becomes saturated with said liquid material, and

directing a stream of said vapor saturated carrier gas toward said surface, said gas being warmer than said surface.