Reflective optical element for EUV lithography and method of manufacturing a reflective optical element

Patent metadata

Field	Value
Publication number	US-9606446-B2
Application number	US-201514732248-A
Country	US
Kind code	B2
Filing date	Jun 5, 2015
Priority date	Dec 6, 2012
Publication date	Mar 28, 2017
Grant date	Mar 28, 2017

Abstract

A reflective optical element of an optical system for EUV lithography and an associated manufacturing method. The reflective optical element ( 20 ) includes a multilayer system ( 23, 83 ) for reflecting an incident electromagnetic wave having an operating wavelength in the EUV range, the reflected wave having a phase φ, and a capping layer ( 25, 85 ) made from a capping layer material. The method includes determining a dependency according to which the phase of the reflected wave varies with the thickness d of the capping layer, determining a linearity-region in the dependency in which the phase of the reflected wave varies substantially linearly with the thickness of the capping layer, and creating a thickness profile in the capping layer such that both the maximum thickness and the minimum thickness in the thickness profile are in the linearity-region.

First claim

What is claimed is:

1. A method of manufacturing a reflective optical element of an optical system for extreme ultraviolet (EUV) lithography, wherein the reflective optical element comprises a multilayer system configured to reflect an incident electromagnetic wave having an operating wavelength in the EUV range, the reflected wave having a phase φ, and a capping layer made from a capping layer material and having a thickness d, wherein the method comprises:
determining, for the capping layer material, a dependency according to which the phase φ of the reflected wave varies with the thickness d of the capping layer;
determining a linearity-region in the dependency in which the phase of the reflected wave varies substantially linearly with the thickness of the capping layer; and
creating a thickness profile in the capping layer such that both a maximum value of the thickness and a minimum value of the thickness in the thickness profile are in the linearity-region.

2. The method according to claim 1 , wherein creating the thickness profile in the capping layer is performed such that a wavefront aberration in the optical system is at least partially compensated by the reflective optical element.

3. The method according to claim 1 , wherein creating the thickness profile in the capping layer is performed such that the variation in the phase φ relative to the variation in the capping layer thickness d is greater than 25%.

4. The method according to claim 1 , wherein the dependency, according to which the phase of the reflected wave varies with the thickness of the capping layer, is such that the phase φ initially remains substantially constant in the dependency until a thickness d 1 is reached, decreases between the thickness d 1 and a further thickness d 2 , with d 1 <d 2 , and remains substantially constant at a thickness greater than d 2 , wherein creating the thickness profile in the capping layer is performed such that the thicknesses d of the capping layer resulting from the dependency meet the condition d 1 <d<d 2 .

5. The method according to claim 1 , further comprising:
determining, for the capping layer material, a dependency according to which the reflectivity of the reflective optical element varies with the thickness of the capping layer; and
determining a plateau-region in the dependency in which the reflectivity of the reflective optical element is substantially constant;
wherein creating a thickness profile in the capping layer is performed such that both the maximum thickness and the minimum thickness in the thickness profile are located in the plateau-region.

6. A method of manufacturing a reflective optical element of an optical system for extreme ultraviolet (EUV) lithography, wherein the reflective optical element comprises a multilayer system configured to reflect an incident electromagnetic wave having an operating wavelength in the EUV range, and a capping layer made from a capping layer material, wherein the method comprises:
determining, for the capping layer material, a dependency according to which the reflectivity of the reflective optical element varies with the thickness of the capping layer;
determining a plateau-region in the dependency in which the reflectivity of the reflective optical element is substantially constant; and
creating a thickness profile in the capping layer such that both the maximum thickness and the minimum thickness in the thickness profile are located in the plateau-region.

7. The method according to claim 6 , wherein creating the thickness profile in the capping layer is performed such that both the maximum thickness and the minimum thickness in the thickness profile are between 1 nm and 4 nm.

8. The method according to claim 6 , wherein the capping layer material comprises ruthenium, rhodium or silicon nitride.

9. The method according to claim 6 , wherein the multilayer system comprises alternately arranged sub-layers made of silicon and molybdenum.

10. The method according to claim 3 , wherein creating the thickness profile in the capping layer is performed such that the variation in the phase φ relative to the variation in the capping layer thickness d is greater than 35%.

11. The method according to claim 6 , wherein creating the thickness profile in the capping layer is performed such that the variation in the phase φ relative to the variation in the capping layer thickness d is greater than 40%.

12. Reflective optical element for extreme ultraviolet (EUV) lithography, comprising:
a multilayer system configured to reflect an incident electromagnetic wave having an operating wavelength in the EUV range, the reflected wave having a phase φ; and
a capping layer made from a capping layer material and having a thickness d;
wherein the capping layer has a variation in the capping layer thickness d such that the variation in the phase φ relative to the variation in the capping layer thickness is greater than 25%.

13. Reflective optical element according to claim 12 , wherein the capping layer thickness varies such that the variation in the phase φ relative to the variation in the capping layer thickness d is greater than 35%.

14. Reflective optical element according to claim 13 , wherein the capping layer thickness varies such that the variation in the phase φ relative to the variation in the capping layer thickness d is greater than 40%.

15. Optical system for EUV lithography, comprising a reflective optical element according to claim 12 .

16. Optical system according to claim 15 , embodied as a projection system.

17. Optical system according to claim 15 , wherein the reflective optical element is arranged in a given plane of the optical system in which a parameter P(M), which is defined as

P
⁡

(
M
)

=

D
⁡

(
SA
)

D
⁡

(
SA
)

+

D
⁡

(
CR
)

,

is less than 0.2, wherein D(SA) denotes a subaperture diameter and D(CR) denotes a maximum principal ray spacing defined over all field points of the optically used field on the optical surface M in the given plane.

18. Optical system according to claim 17 , wherein P(M) is less than 0.1.

Assignees

• Zeiss Carl Smt Gmbh

Inventors

• Wabra Norbert
• Bittner Boris
• Von Hodenberg Martin
• Enkisch Hartmut
• Muellender Stephan
• Conradi Olaf

Classifications

• G03F7/70308

  Optical correction elements, filters or phase plates for manipulating imaging light, e.g. intensity, wavelength, polarisation, phase or image shift · CPC title

• G03F7/702 Primary

  Reflective illumination, i.e. reflective optical elements other than folding mirrors, e.g. extreme ultraviolet [EUV] illumination systems · CPC title

• G03F7/70316

  Details of optical elements, e.g. of Bragg reflectors, extreme ultraviolet [EUV] multilayer or bilayer mirrors or diffractive optical elements · CPC title

• G02B27/1033

  having a single light modulator for all colour channels · CPC title

• G21K1/062

  Devices having a multilayer structure · CPC title