System and method for aerial image sensing

• US 6,906,305 B2
• Filed: 01/07/2003
• Issued: 06/14/2005
• Est. Priority Date: 01/08/2002
• Status: Expired due to Term

• Current Assignee: ASML Netherlands BV (ASML Holding NV), Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Original Assignee: Brion Technologies Incorporated (ASML Holding NV)
• Inventors: Ye, Jun, Pease, R. Fabian W.
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US10/337,510
• Publication Number:
  US 20030128870A1
• Time in Patent Office: 889 Days
• Field of Search: 250/208.1, 250/201.3, 250/548, 250/559.3, 250/492.24, 250/311, 250/306, 382/144, 382/145
• US Class Current: 250/208.1
• CPC Class Codes: G03F 1/84 Inspecting
• CPC Class Codes: G03F 7/70591 Testing optical components
• CPC Class Codes: G03F 7/7065 Defects, e.g. optical inspection of patterned layer for defects
• CPC Class Codes: G03F 7/70666 Aerial image, i.e. measuring the image of the patterned exposure light at the image plane of the projection system
• CPC Class Codes: G03F 7/7085 Detection arrangement, e.g. detectors of apparatus alignment possibly mounted on wafers, exposure dose, photo-cleaning flux, stray light, thermal load
• CPC Class Codes: G03F 9/7069 Alignment mark illumination, e.g. darkfield, dual focus

Abstract

A system to sense an aerial image produced by optical equipment used in, for example, semiconductor fabrication. In one embodiment, the system includes a photo-electron emission device which, in response to an aerial image projected thereon, emits electrons in a pattern corresponding to the light intensity distribution produced by the aerial image. Electron optics provides an enlarged pattern of the pattern in which the electrons are emitted. A sensing unit senses the enlarged pattern. In another embodiment, the system employs a photo-conducting layer to project the aerial image thereon. The photo-conducting layer, in response to the projection of the aerial image thereon, produces local charge depletion corresponding to the light intensity distribution. A steering device delivers electrons to the photo-conducting layer to produce local re-charging currents in proportion to the local charge depletion. A pattern corresponding to the aerial image may be obtained from the re-charging currents.

Claims

1. A system for sensing, at an increased resolution, an aerial image exhibiting a light intensity distribution at a primary resolution, the system comprising:

a photo-electron emission unit to sense the aerial image and, in response, emit electrons in a pattern corresponding to the light intensity distribution of the aerial image;

electron optics to project an enlarged pattern of the pattern of electrons emitted by the photo-electron emission unit;

a sensing unit to sense the enlarged pattern; and

an image analysis unit, coupled to the sensing unit, to digitize the enlarged pattern.

2. The system of claim 1 further comprising:

an object;

a light source to provide light;

condensing optics to illuminate the object with the light; and

an optical imaging and projection unit, wherein the optical imaging and projection unit projects the aerial image on the photo-electron emission unit.

3. The system of claim 2 wherein the photo-electron emission unit, electron optics and optical imaging and projection unit are disposed in or are a part of a photolithographic system.

4. The system of claim 3 wherein the photolithographic system is a stepper or a scanner.

5. The system of claim 4 wherein the object is a photolithographic mask.

6. The system of claim 5 further includes a computer to inspect the photolithographic mask using the digitized aerial image.

7. The system of claim 6 wherein the computer inspects the photolithographic mask using die-to-die inspection, die-to-database inspection, or image self-analysis techniques.

8. The system of claim 4 further includes a controller, coupled to the image analysis unit, to adjust the operation of the photolithographic stepper or the photolithographic scanner using at least a portion of the digitized aerial image.

9. The system of claim 4 wherein the light source provides a light that has a wavelength that is substantially equal to a wavelength of light that is used to expose a resist on a product wafer.

10. The system of claim 4 further includes a mechanical positioning unit wherein, the mechanical positioning unit, in response to an operator input, positions the photo-electron emission unit at an image plane.

11. The system of claim 4 further includes a mechanical positioning unit to position the photo-electron emission unit at an image plane to allow for in-situ aerial image sensing.

12. The system of claim 4 wherein the light has a wavelength in the UV range.

13. The system of claim 1 wherein the photo-electron emission unit includes an electron-multiplying cathode for amplifying the electrons.

14. The system of claim 13 wherein the electron-multiplying cathode allows the emission of substantially thermalized electrons.

15. The system of claim 1 wherein the photo-electron emission unit and the electron optics have a higher resolution than the resolution of the optical imaging and projection unit.

16. A system for sensing an aerial image exhibiting a light intensity distribution at a primary resolution, the system comprising:

a photo-conducting layer for projecting the aerial image thereon, wherein in response to the aerial image, the photo-conducting layer produces a depletion pattern corresponding to the light intensity distribution of the aerial image;

an electron source for providing electrons;

a steering device to direct the electrons to the photo-conducting layer to produce local re-charging currents in proportion to the local charge depletion;

amplifier circuitry coupled to the steering device, wherein the amplifier circuitry determines a pattern corresponding to the serial image using the re-charging currents; and

an image analysis unit, coupled to the sensing unit, to digitize the pattern.

17. The system of claim 16 further comprising:

an object;

a light source to provide light;

condensing optics to illuminate the object with the light; and

an optical imaging and projection unit to produce the aerial image on the photo-conducting layer.

18. The system of claim 17 wherein the photo-conducting layer, electron source, steering device and the optical imaging and projection unit are disposed in or are a part of a photolithographic system.

19. The system of claim 18 wherein the photolithographic system is a photolithographic stepper or a photolithographic scanner.

20. The system of claim 19 wherein the object is a photolithographic mask.

21. The system of claim 20 further includes a computer to inspect the photolithographic mask using the digitized aerial image.

22. The system of claim 21 wherein the computer inspects the photolithographic mask using die-to-die inspection, die-to-database inspection, or image self-analysis techniques.

23. The system of claim 19 further includes a controller, coupled to the image analysis unit, to adjust the operation of the photolithographic stepper or a photolithographic scanner using at least a portion of the digitized aerial image.

24. The system of claim 19 wherein the light source provides a light that has a wavelength that is substantially equal to a wavelength of light that is used to expose a resist on a product wafer.

25. The system of claim 19 further includes a mechanical positioning unit wherein, the mechanical positioning unit, in response to an operator input, positions the photo-electron emission unit at the an image plane.

26. The system of claim 19 further includes a mechanical positioning unit to position the photo-electron emission unit at the an image plane to allow for in-situ aerial image sensing.

27. The system of claim 19 wherein the light has a wavelength in the UV range.