Mask for use in lithography, method of making a mask, lithographic apparatus, and device manufacturing method

• US 20030180632A1
• Filed: 03/06/2003
• Published: 09/25/2003
• Est. Priority Date: 03/08/2002
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Dierichs, Marcel Mathijs Theodore Marie, Van Dijsseldonk, Antonius Johannes Josephus, Eurlings, Markus Franciscus Antonius
• Granted Patent: US 6,927,004 B2
• Time in Patent Office: Days
• US Class Current: 430/5
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 40/00 Manufacture or treatment of nanostructures
• CPC Class Codes: G03F 1/24 Reflection masks; Preparation thereof
• CPC Class Codes: G03F 7/70283 Mask effects on the imaging process

Abstract

A reflective mask has a sub-resolution texture applied to absorbing areas to reduce the amount of power in the specular reflection. The texture may form a phase contrast grating or may be a diffuser. The same technique may be applied to the other absorbers in a lithographic apparatus.

Claims

1. A reflective mask for use in a lithographic apparatus, the mask having areas of relatively high reflectance and areas of relatively low reflectance defining a mask pattern having a smallest printing feature size, wherein the areas of low reflectance, comprise a layer having a texture at a scale smaller than the smallest printing feature size such that specular reflection from the areas of low reflectance is reduced.

2. A mask according to claim 1, wherein the texture comprises a phase grating.

3. A mask according to claim 2, wherein the grating comprises lands and recesses such that there is a phase shift of substantially π

radians between exposure radiation reflected from the lands and from the recesses.

4. A mask according to claim 3, wherein the ratio of the total area of the lands to the total area of the recesses is in the range of from ⅔

to {fraction (3/2)}.

5. A mask according to claim 2, wherein the phase grating has a pitch such that first order diffracted beams lie outside a pupil of a projection system of the lithographic apparatus.

6. A mask according to claim 2, wherein the phase grating is two-dimensional.

7. A mask according to claim 1, wherein the texture forms a diffuser for diffusing the reflected radiation into a large solid angle compared to a numerical aperture of a projection system of the lithographic apparatus.

8. A mask according to claim 7, wherein the texture is a surface texture.

9. A mask according to claim 7, wherein the texture is internal and includes a plurality of differently oriented boundaries.

10. A mask according to claim 9, wherein the layer is formed of a granular material.

11. A mask according to claim 1, wherein the layer is formed from at least one of tantalum (Ta) and tantalum-nitride (TaN).

12. A mask according any one of claim 7, wherein the texture has an rms roughness of greater than or equal to 1 nm.

13. A device manufacturing method, comprising:

providing a substrate that is at least partially covered by a layer of radiation-sensitive material;

providing a projection beam of radiation using a radiation system;

using a patterning device to endow the projection beam with a pattern in its cross-section;

projecting the patterned beam of radiation onto a target portion of the layer of radiation-sensitive material using a projection system, wherein using the patterning device comprises;

positioning a mask having areas of relatively high reflectance and areas of relatively low reflectance defining the pattern and the areas of low reflectance comprise a layer having a surface texture at a scale smaller than the smallest printing feature in the pattern resolvable on the substrate by a projection system.

14. A method according to claim 13, wherein the texture comprises a phase grating comprising lands and recesses such that there is a phase shift of substantially π

radians between radiation of the projection beam reflected from the lands and from the recesses.

15. A method according to claim 14, wherein the phase grating has a pitch, p, that satisfies the following inequality:

16. A lithographic projection apparatus, comprising:

a radiation system constructed and arranged to supply a projection beam of radiation;

a support structure constructed and arranged to support a patterning device, the patterning device constructed and arranged to pattern the projection beam according to a desired pattern;

a substrate table constructed and arranged to hold a substrate;

a projection system constructed and arranged to project the patterned beam onto a target portion of the substrate;

an optical element included in the radiation system or the projection system, at least a part of which is provided with an absorbing layer, wherein the absorbing layer of the optical element is provided with a texture at a scale smaller than the smallest feature size resolvable by the projection system such that specular reflection from the absorbing layer is reduced.

17. A device manufacturing method, comprising:

providing a substrate that is at least partially covered by a layer of radiation-sensitive material;

providing a projection beam of radiation using a radiation system;

using a patterning device to endow the projection beam with a pattern in its cross-section;

projecting the patterned beam of radiation onto a target portion of the layer of radiation-sensitive material; and

absorbing a part of the projection beam in an absorbing layer provided on an optical element, the absorbing layer of the optical element being provided with a texture at a scale smaller than the smallest feature size resolvable by the projection system such that specular reflection from the absorbing layer is reduced.