Methods and systems for lithographic gray scaling

• US 20060139597A1
• Filed: 12/29/2004
• Published: 06/29/2006
• Est. Priority Date: 12/29/2004
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: De Smit, Joannes Theodor, Lof, Joeri, De Jager, Pieter Willem Herman
• Granted Patent: US 7,253,881 B2
• Time in Patent Office: Days
• US Class Current: 355/55
• CPC Class Codes: G03F 7/70283 Mask effects on the imaging process

Abstract

Improved gray scaling imaging methods and systems include a group of elements within an array of individually controllable elements that project a part of a radiation beam onto a lens in an array of microlenses, and are individually controllable so that any number of the individually controllable elements may be switched on or off to generate a gray scale.

Claims

1. A lithographic apparatus comprising:

an illumination system that conditions a radiation beam;

an array of individually controllable elements that modulates a cross-section of the radiation beam;

a substrate table that supports a substrate; and

a projection system that projects the modulated radiation beam onto a target portion of the substrate, the projection system including an array of focusing elements arranged in a plane such that each focusing element transmits a different part of the radiation beam onto a spot on the substrate;

wherein elements within a group of the individually controllable elements are controlled to selectively direct a part of the radiation beam through a focusing element in the array of focusing elements, thereby providing gray scaling.

2. The lithographic apparatus according to claim 1, further comprising a modifying element arranged between the array of individually controllable elements and the array of focusing elements in the path of the radiation beam, the modifying element increasing the area of the focusing element through which part of the radiation beam is selectively directed by one individually controllable element.

3. The lithographic apparatus according to claim 2, wherein the modifying element increases the area through which part of the radiation beam is directed for each of the focusing elements in the array of focusing elements.

4. A lithographic apparatus according to claim 2, wherein the modifying element comprises a common modifying element for all focusing elements.

5. The lithographic apparatus according to claim 2, wherein the modifying element comprises a diffusor.

6. The lithographic apparatus according to claim 2, wherein the modifying element comprises a second array of focusing elements arranged in a plane such that each focusing element transmits a different part of the radiation beam.

7. A lithographic apparatus according to claim 2, wherein the modifying element is comprises at least one of a quartz rod and a Flies eye lens.

8. A lithographic apparatus according to claim 2, wherein the modifying element increases the numerical aperture of the projection system.

9. The apparatus according to claim 1, further comprising a controller that controls the selection of at least one of (a) the elements within the group of the individually controllable elements to maximize an exposure moment defined by the area of the focusing element traversed by the radiation beam, and (b) the individually controllable elements in the group to maximize an exposure moment defined by the area of the focusing element traversed by the radiation beam, multiplied by the distance from the center of the focusing element summed over the focusing element.

10. A lithographic method, comprising:

outputting a radiation beam using an illumination system;

modulating a cross section of the radiation beam using an array of individually controllable elements;

providing an array of focusing elements arranged in a plane such that each focusing element transmits a different part of the radiation beam onto a spot on the substrate, a group of the individually controllable elements selectively directing a part of the radiation beam onto a single focusing element in the array of focusing elements; and

projecting the modulated beam of radiation onto a target portion of a substrate;

wherein the selection of individually controllable elements in the group used to direct part of the radiation beam through the single focusing element is controlled to provide gray scaling to the substrate.

11. The lithography method according to claim 10, wherein the selection of individually controllable elements in the group used to direct part of the radiation beam through the single focusing element is controlled to maximize an exposure moment of the single focusing element defined by the area of the focusing element traversed by the radiation beam multiplied by the distance from the center of the single focusing element summed over the focusing element.

12. A method according to claim 11, further comprising maximizing the area of the focusing element traversed by the radiation beam.

13. A method according to claim 12, further comprising changing the modulation of the radiation beam by a single controllable element during the exposure of a point on the substrate.

14. A method according to claim 13, wherein for a given exposure dose over a given period of time a number of individually controllable elements in the group are used to direct the radiation beam through the focusing element for a fraction of the period of time, the number of individually controllable elements being used being larger than equivalent number used for the whole of the period for the same exposure dose.

15. A method according to claim 14, further comprising maximizing the distance between the individually controllable elements in the group directing the radiation beam through a single focusing element.

16. A method according to claim 10, further comprising maximizing the distance between the individually controllable elements in the group directing the radiation beam through a single focusing element.

17. A method according to claim 10, wherein each group of controllable elements projecting onto an individual focusing element is controlled to direct a pattern through a single focusing element that is symmetrical.

18. The lithographic method according to claim 10, further comprising increasing the area of the single focusing element through which part of the radiation beam is directed using an additional modifying element arranged between the array of individually controllable elements and the array of focusing elements in the path of the radiation beam.

21. A flat panel display manufactured according to the method of claim 10.

19. A lithographic method, comprising:

receiving a beam of radiation at an array of individually controllable elements;

directing portions of the beam of radiation from corresponding groups of the individually controllable elements to a substrate through corresponding focusing elements; and

selectively controlling elements within the groups of the individually controllable elements to provide gray scaling to the substrate.

20. The lithographic method according to claim 19, further comprising selectively controlling at least one of (a) elements within the groups of the individually controllable elements to provide a desired spot size, (b) elements within the groups of the individually controllable elements to provide a desired numerical aperture, (c) elements within the groups of the individually controllable elements to switch on symmetrically, and (d) elements within the groups of the individually controllable elements to maximize an illuminated portion of a corresponding focusing element.

22. A flat panel display manufactured according to the method of claim 19.