Apparatus for detecting defects in patterned substrates

• US 6,509,750 B1
• Filed: 04/30/2001
• Issued: 01/21/2003
• Est. Priority Date: 01/08/1999
• Status: Expired due to Term

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Lo, Chiwoei Wayne, Talbot, Christopher G.
• Primary Examiner(s): Sherry, Michael
• Assistant Examiner(s): KOBERT, RUSSELL MARC
• Application Number:
  US09/846,487
• Time in Patent Office: 631 Days
• Field of Search: 324/750, 324/751, 250/310, 250/311
• US Class Current: 324/754.22
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: H01J 2237/202 Movement
• CPC Class Codes: H01J 2237/221 Image processing
• CPC Class Codes: H01J 2237/24592 Inspection and quality control of devices
• CPC Class Codes: H01J 2237/2485 Electric or electronic means
• CPC Class Codes: H01J 2237/2817 Pattern inspection
• CPC Class Codes: H01J 37/265 Controlling the tube; circuit arrangements adapted to a particular application not otherwise provided, e.g. bright-field-dark-field illumination
• CPC Class Codes: H01J 37/28 with scanning beams H01J37/268, H01J37/292, H01J37/2955 take precedence

Abstract

Defects in a patterned substrate are detected by positioning a charged-particle-beam optical column relative to a patterned substrate, the charged-particle imaging system having a field of view (FOV) with a substantially uniform resolution over the FOV; operating the charged-particle-beam optical column to acquire images over multiple subareas of the patterned substrate lying within the FOV by scanning a charged-particle beam over the patterned substrate while maintaining the charged-particle-beam optical column fixed relative to the patterned substrate; and comparing the acquired images to a reference to identify defects in the patterned substrate. The use of a large-FOV imaging system with substantially uniform resolution over the FOV allows acquisition of images over a wide area of the patterned substrate without requiring mechanical stage moves, thereby reducing the time overhead associated with mechanical stage moves. Multiple columns can be ganged together to further improve throughput.

Claims

1. An apparatus for detecting defects in a patterned substrate, comprising:

a mechanical stage for positioning a charged-particle-beam optical column relative to a patterned substrate;

the charged-particle-beam optical column having a field of view (FOV) greater than approximately 100 microns with a substantially uniform resolution over the FOV, the charged-particle-beam optical column being operable to acquire a plurality of images of a region of the patterned substrate lying within the FOV by scanning a charged-particle beam over the patterned substrate while the mechanical stage maintains the charged-particle-beam optical column fixed relative to the patterned substrate, each image being that of a subarea of the region and acquired at a sub-FOV; and

at least one processor operable to compare the acquired images to a reference to identify defects in the patterned substrate.

2. The apparatus of claim 1, wherein the charged-particle-beam column includes an electron-beam source.

3. The apparatus of claim 2, wherein the electron-beam source includes a thermal-field-emission cathode.

4. The apparatus of claim 2, wherein the electron-beam source includes a zirconium-tungsten cathode.

5. The apparatus of claim 1, wherein the mechanical stage is operable to reposition the charged-particle-beam optical column relative to the patterned substrate, so that images can be acquired from a further region of the patterned substrate.

6. The apparatus of claim 1, further comprising a laser interferometer operable to monitor position of the mechanical stage.

7. The apparatus of claim 1, wherein the charged-particle-beam optical column is operable to acquire images comprises being operable to acquire voltage-contrast images.

8. The apparatus of claim 1, further comprising a source of charged particles operable to pre-charge the patterned substrate prior to operating the charged-particle-beam optical column to acquire images.

9. The apparatus of claim 1, wherein the charged-particle-beam optical column is operable to acquire images comprises being operable to acquire topographic images, and wherein the processor is operable to compare the acquired images comprises being operable to compare the topographic images to the reference to identify topographic defects in the patterned substrate.

10. The apparatus of claim 1, wherein the reference is a reference image that comprises an image of a portion of the patterned substrate.

11. The apparatus of claim 1, wherein the reference is a reference image that comprises a stored reference image.

12. The apparatus of claim 1, wherein the reference is a reference image that comprises an image generated from a computer-aided-design (CAD) database.

13. The apparatus of claim 1, wherein the processor is operable to compare features of the acquired images with features of a reference image to identify defects in the patterned substrate.

14. The apparatus of claim 1, wherein the reference is a reference image comprised of pixels, and wherein the processor is operable to compare the acquired images pixel-by-pixel with the reference image.

15. The apparatus of claim 1, further comprising a flood-beam source operable to apply a flood beam to the patterned substrate prior to acquisition of images with the charge-particle-beam optical column.

16. The apparatus of claim 15, wherein the flood-beam source is operable to apply the flood beam to a sub-region of the FOV.

17. The apparatus of claim 1, wherein the charged-particle-beam optical column comprises a variable-axis immersion lens (VAIL) having a field of view (FOV) with a substantially uniform resolution over the FOV.

18. The apparatus of claim 1, wherein the charged-particle-beam optical column—

includes an in-lens charged-particle detector for collecting and detecting secondary particles substantially uniformly across the FOV.

19. The apparatus of claim 1, further comprising:

a second charged-particle-beam optical column having a field of view (FOV) with a substantially uniform resolution over the FOV, the second charged-particle-beam optical column being operable to acquire further images over multiple subareas of a region of the patterned substrate lying within the FOV by scanning a charged-particle beam over the patterned substrate while the mechanical stage maintains the second charged-particle-beam optical column fixed relative to the patterned substrate; and

at least one processor operable to compare the further acquired images to a reference to identify defects in the patterned substrate.

20. An apparatus for detecting defects in a patterned substrate, comprising:

a mechanical stage for positioning a charged-particle-beam optical column relative to a patterned substrate;

the charged-particle-beam optical column having a field of view (FOV) greater than approximately 100 microns with a substantially uniform resolution over the FOV, the charged-particle-beam optical column being operable to acquire an image of substantially all of the FOV by scanning a charged-particle beam over the patterned substrate while the mechanical stage maintains the charged-particle-beam optical column fixed relative to the patterned substrate; and

at least one processor operable to compare the acquired images to a reference to identify defects in the patterned substrate.

21. An apparatus for detecting defects in a patterned substrate, comprising:

a mechanical stage for positioning at least one charged-particle-beam optical column relative to a patterned substrate;

a first charged-particle-beam optical column having a field of view (FOV) with a substantially uniform resolution over the FOV, the first charged-particle-beam optical column being operable to acquire images over multiple subareas of a region of the patterned substrate lying within the FOV by scanning a charged-particle beam over the patterned substrate while the mechanical stage maintains the first charged-particle-beam optical column fixed relative to the patterned substrate;

at least one first processor operable to compare the acquired images to a reference to identify defects in the patterned substrate;

a second charged-particle-beam optical column having a FOV with a substantially uniform resolution over the FOV, the second charged-particle-beam optical column being operable to acquire further images over multiple subareas of a region of the patterned substrate lying within the FOV by scanning a charged-particle over the patterned substrate while the mechanical stage maintains the second charged-particle-beam optical column fixed relative to the patterned substrate; and

at least one second processor operable to compare the further acquired images to a reference to identify defects in the patterned substrate.