Multi-layered mirror

• US 20010033421A1
• Filed: 05/30/2001
• Published: 10/25/2001
• Est. Priority Date: 09/08/1998
• Status: Active Grant

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Murakami, Katsuhiko, Shiraishi, Masayuki
• Granted Patent: US 6,441,963 B2
• Time in Patent Office: Days
• US Class Current: 359/584
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: G03F 7/70058 Mask illumination systems
• CPC Class Codes: G03F 7/70233 Optical aspects of catoptric systems, i.e. comprising only reflective elements, e.g. extreme ultraviolet [EUV] projection systems
• CPC Class Codes: G21K 1/062 Devices having a multilayer structure

Abstract

A multi-layered mirror has a substrate, a first layer of a first substance, a second layer of a second substance. The refractive index of the first substance in a utilized wavelength region is different from that of the second substance. The first and second layers are laminated alternately on the substrate. To obtain a high reflectivity and superior optical characteristics, a multi-layered structure is formed within either the first layer or the second layer using at least two substances whose real parts of the complex indices of refraction in the utilized wavelength region are approximately the same. Alternatively, a layer surface is smoothed before forming a next layer thereon. An exposure apparatus that uses multi-layered mirrors of the present invention uses light with higher efficiency.

Claims

1. A multi-layered mirror comprising:

a substrate;

at least one first layer of a first substance; and

at least one second layer of a second substance,

wherein the at least one first layer and the at least one second layer are alternately laminated on the substrate, and

wherein a difference between a refractive index of the first substance in a utilized wavelength and that in a vacuum is large, and a thickness of the first layer is determined based on the utilized wavelength and the refractive index of the first substance, and

wherein a difference between a refractive index of the second substance in the utilized wavelength and that in a vacuum is small, and a thickness of the second layer is determined based on the utilized wavelength and the refractive index of the second substance, and

wherein for at least one pair comprising two adjacent first and second layers, at least one of the layers within the pair has a multi-layered structure formed by alternately laminating to the thickness of that layer, at least two substances whose real parts of complex indices of refraction in the utilized wavelength are approximately the same.

2. The multi-layered mirror according to

claim 1

, wherein the first substance is molybdenum, the second substance is silicon, and at least one of the first layers contains a layer of ruthenium.

3. A multi-layered mirror comprising:

a substrate;

at least one first layer of a first substance;

at least one second layer of a second substance; and

at least one stress-relief layer formed in at least one of the at least one first layer or the at least one second layer,

wherein the at least one first layer and the at least one second layer are alternately laminated on the substrate, and

wherein a difference between a refractive index of the first substance in the soft X-ray wavelength region and that in a vacuum is large, and a difference between a refractive index of the second substance in the soft X-ray wavelength region and that in a vacuum is small, and

wherein when the at least one stress-relief layer is formed within the at least one first layer, it has approximately a same real part of a complex index of refraction in the soft X-ray wavelength region as the first substance, and when the at least one stress-relief layer is formed within the at least one second layer, it has approximately a same real part of a complex index of refraction in the soft X-ray wavelength region as the second substance.

4. The multi-layered mirror according to

claim 3

, wherein the first substance is molybdenum, the second substance is silicon, and the at least one stress-relief layer is formed using ruthenium within the at least one first layer.

5. A multi-layered mirror comprising:

a substrate;

at least one layer of silicon;

at least one layer of molybdenum; and

at least one layer of ruthenium formed in at least one of the molybdenum layers,

wherein the at least one layer of silicon and the at least one layer of molybdenum are alternately laminated on the substrate.

6. A multi-layered mirror comprising:

a substrate;

at least one first layer of a first substance with a small refractive index; and

at least one second layer of a second substance with a large refractive index,

wherein the at least one first layer and the at least one second layer are alternately laminated on the substrate by sputtering, and

wherein an interface between the at least one first and the at least one second layers of the multi-layered mirror has been irradiated by an ion beam and smoothed.

7. The multi-layered mirror according to

claim 6

, wherein the interface between the at least one first and the at least one second layers is smoothed so that for d≧

5 nm, σ

_int−

σ

_sub<

0.2 nm, and for d<

5 nm, σ

_int−

σ

_sub<

0.5 nm, where d is a periodic length defined as a sum of the first substance layer thickness and the second substance layer thickness, σ

_sub is an RMS value of surface roughness of the substrate, and σ

_int is an RMS value of roughness of the interface.

8. The multi-layered mirror according to

claim 6

, wherein a region over which the first substance of the first layer and the second substance of an adjacent second layer diffuse into each other is less than or equal to 1 nm.

9. A multi-layered mirror comprising:

a substrate;

at least one first layer of a first substance with a small refractive index; and

at least one second layer of a second substance with a large refractive index,

wherein the at least one first layer and the at least one second layer are alternately laminated on the substrate by sputtering, and

wherein an interface between the first layer and the second layer is smoothed so that a region over which the first substance of the first layer and the second substance of an adjacent second layer diffuse into each other is less than or equal to 1 nm.

10. A multi-layered mirror comprising:

a substrate;

a first layer of a first substance formed on the substrate;

a second layer of a second substance formed on the first layer;

a third layer of the first substance formed on the second layer;

a fourth layer of the second substance formed on the third layer; and

a fifth layer of a third substance formed within a layer made with the first or the second substance,

wherein a difference in a refractive index in a utilized wavelength and a refractive index in a vacuum is large, and a difference in a refractive index in a utilized wavelength and a refractive index in a vacuum of the other substance is small, and

wherein thicknesses of the first and the third layers are determined based on the utilized wavelength and a refractive index of the first substance, and thicknesses of the second and the fourth layers are determined based on the utilized wavelength and a refractive index of the second substance, and

wherein the third substance has approximately a same real part of a complex index of refraction in the utilized wavelength region as that of the layer within which the fifth layer is formed.

11. The multi-layered mirror according to

claim 10

, wherein the first substance is molybdenum, the second substance is silicon, the third substance is ruthenium, and the fifth layer is formed within one of the molybdenum layers.

12. The multi-layered mirror according to

claim 10

, wherein the first substance is silicon, the second substance is molybdenum, the third substance is ruthenium, and the fifth layer is formed within one of the molybdenum layers.

13. A multi-layered mirror comprising;

a substrate;

a first layer of a first substance formed on the substrate by sputtering;

a second layer of a second substance formed on the first layer by sputtering;

a third layer of the first substance formed on the second layer by sputtering; and

a fourth layer of the second substance formed on the third layer sputtering,

wherein a refractive index of the first substance is different from that of the second substance.

14. The multi-layered mirror according to

claim 13

, wherein the first substance is molybdenum and the second substance is silicon.

15. The multi-layered mirror according to

claim 13

, wherein the first substance is silicon and the second substance is molybdenum.

16. The multi-layered mirror according to

claim 13

, wherein at least one of interfaces between two adjacent layers has been irradiated by an ion beam.

17. The multi-layered mirror according to

claim 16

, wherein the interfaces of two adjacent layers is smoothed so that for d≧

5 nm, σ

_int−

σ

_sub<

0.2 nm, and for d<

5 nm, σ

_int−

σ

_sub<

0.5 nm, where d is a periodic length defined as a sum of the first substance layer thickness and the second substance layer thickness, σ

_sub is an RMS value of surface roughness of the substrate, and σ

_int is an RMS value of roughness of the interface.

18. The multi-layered mirror according to

claim 16

, wherein a region over which the first substance of the first layer and the second substance of an adjacent second layer diffuse into each other is less than or equal to 1 nm.

19. A method for manufacturing a multi-layered mirror upon a substrate comprising:

alteratively laminating by sputtering upon the substrate a first layer of a first substance with a small refractive index and a second layer of a second substance with a large refractive index; and

smoothing at least one of the first or the second layer by irradiation using an ion beam prior to forming another layer on top of that layer.

20. The method according to

claim 19

, wherein an ion type of the ion beam used in the smoothing step is an inert gas.

21. The method according to

claim 19

, wherein energy of the ion beam used in the smoothing step is greater than 50 eV and less than 1000 eV.

22. The method claim according to

claim 20

, wherein the energy of the ion beam used in the smoothing step is greater than 50 eV and less than 1000 eV.

23. The method claim according to

claim 19

, wherein the substrate is either electrically grounded or a DC bias voltage is imparted to the substrate.

24. The method claim according to

claim 20

, wherein the substrate is either electrically grounded or a DC bias voltage is imparted to the substrate.

25. The method claim according to

claim 21

, wherein the substrate is either electrically grounded or a DC bias voltage is imparted to the substrate.

26. The method claim according to

claim 22

, wherein the substrate is either electrically grounded or a DC bias voltage is imparted to the substrate.

27. A method of manufacturing a multi-layered mirror on a substrate comprising;

alternately laying at least one first layer of a first substance and at least one second layer of a second substance on the substrate;

forming at least one stress relief layer within at least one of the at least one first layer or the at least one second layer; and

applying particle beam irradiation after formation of at least one of the at least one first layer, the at least one second layer, or the least one stress relief layer,

wherein a difference between a refractive index of the first substance in the soft X-ray wavelength region and that in a vacuum is large, and a difference between a refractive index of the second substance in the soft X-ray wavelength region and that in a vacuum is small, and

wherein each of the at least one stress-relief layer consists of a substance that has approximately a same size of a real part of a complex index of refraction in the soft-X-ray region as the substance of the layer within which it is formed.

28. A method for controlling stress of a multi-layered mirror formed upon a substrate comprising;

laminating a first layer of a first substance on the substrate;

applying particle beam irradiation upon the surface of the first layer; and

laminating a second layer of a second substance on the first layer that has been treated by particle beam irradiation,

wherein the first and second substances are different.

29. An exposure apparatus comprising;

an X-ray source for generating X-rays;

an illumination optical system capable of directing X-rays from the X-ray source to an X-ray mask; and

a projection optical system capable of directing X-rays from the X-ray mask to a photo-sensitive substrate so that a pattern of the X-ray mask is copied to the photo-sensitive substrate,

wherein the illumination optical system and the projection optical system are equipped with multi-layered mirrors, and

wherein at least one of the multi-layered mirrors includes a substrate, at least one first layer of a first substance, and at least one second layer of a second substance, wherein the at least one first layer and the at least one second layer are alternately laminated on the substrate, a difference between a refractive index of the first substance in a utilized wavelength and that in a vacuum is large, a thickness of the first layer is determined based on the utilized wavelength and the refractive index of the first substance, a difference between a refractive index of the second substance in the utilized wavelength and that in a vacuum is small, a thickness of the second layer is determined based on the utilized wavelength and the refractive index of the second substance, and for at least one pair comprising two adjacent first and second layers, at least one of the layer within the pair has a multi-layered structure formed by alternately laminating to the thickness of that layer, at least two substances whose real parts of complex indices of refraction in the utilized wavelength region are approximately the same.

30. An exposure apparatus comprising;

an X-ray source for generating X-rays;

an illumination optical system capable of directing X-rays from the X-ray source to an X-ray mask; and

a projection optical system capable of directing X-rays from the X-ray mask to a photo-sensitive substrate so that a pattern of the X-ray mask is copied to the photo-sensitive substrate,

wherein the illumination optical system and the projection optical system are equipped with multi-layered mirrors, and

wherein at least one of the multi-layered mirrors includes a substrate, at least one first layer of a first substance, at least one second layer of a second substance, and at least one stress-relief layer formed in at least one of the at least one first layer and the at least one second layer, wherein the at least one first layer and the at least one second layer are alternately laminated on the substrate, a difference between a refractive index of the first substance in the soft X-ray wavelength region and that in a vacuum is large, a difference between a refractive index of the second substance in the soft X-ray wavelength region and that in a vacuum is small, the at least one stress-relief layer, when formed within the at least one first layer, has approximately a same real part of a complex index of refraction in the soft X-ray wavelength region as the first substance, and the at least one stress-relief layer, when formed within the at least one second layer, has approximately a same real part of a complex index of refraction in the soft X-ray wavelength region as the second substance.

31. An exposure apparatus comprising;

an X-ray source for generating X-rays;

an illumination optical system capable of directing X-rays from the X-ray source to an X-ray mask; and

a projection optical system capable of directing X-rays from the X-ray mask to a photo-sensitive substrate so that a pattern of the X-ray mask is copied to the photo-sensitive substrate,

wherein the illumination optical system and the projection optical system are equipped with multi-layered mirrors, and

wherein at least one of the multi-layered mirrors includes a substrate, at least one layer of silicon, at least one layer of molybdenum, and at least one layer of ruthenium formed within at least one of the molybdenum layers, wherein the at least one layer of silicon and the at least one layer of molybdenum are alternately laminated on the substrate.