Optical element with multilayer thin film and exposure apparatus with the element

• US 6,574,039 B1
• Filed: 05/30/2001
• Issued: 06/03/2003
• Est. Priority Date: 09/30/1999
• Status: Expired due to Fees

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Murata, Tsuyoshi, Ishizawa, Hitoshi
• Primary Examiner(s): Juba, Jr., John
• Application Number:
  US09/856,971
• Time in Patent Office: 734 Days
• Field of Search: 359/359, 359/360, 359/350, 359/355, 359/586, 355/67, 355/53, 355/71
• US Class Current: 359/359
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: G02B 1/10 Optical coatings produced by application to, or surface treatment of, optical elements G02B1/08 takes precedence
• CPC Class Codes: G02B 1/115 Multilayers
• CPC Class Codes: G02B 5/283 designed for the ultraviolet
• CPC Class Codes: G03F 7/70958 Optical materials or coatings, e.g. with particular transmittance, reflectance or anti-reflection properties
• CPC Class Codes: G03F 7/70983 Optical system protection, e.g. pellicles or removable covers for protection of mask
• CPC Class Codes: G21K 1/062 Devices having a multilayer structure
• CPC Class Codes: G21K 2201/067 Construction details

Abstract

An optical element (1) of the present invention is provided with an optical substrate (10) and a multilayered optical thin film (11-16) formed on the optical substrate (10). An MgF₂ layer (12, 16) of the multilayered optical thin film has a refractive index of 1.10 to 1.35, especially 1.15 to 1.25 with respect to a vacuum ultraviolet light beam having a wavelength of not more than 250 nm. Therefore, when the optical element (1) is used together with an excimer laser light beam having a wavelength of, for example, 248 nm (KrF), 193 nm (ArF), or 157 nm (F₂), excellent optical characteristics are exhibited concerning, for example, the reflectance (anti-reflection), the polarization characteristics, and the dependency on the angle of incidence. The MgF₂ layer (12, 16) can be produced in accordance with the sol-gel method. The optical element is preferably used for a projection lens of an exposure apparatus which uses the excimer laser light beam as a light source.

Claims

1. An optical element comprising:

an optical substrate; and

a multilayered optical thin film which is formed on the optical substrate, wherein;

at least one layer of the multilayered optical thin film is composed of fluoride of alkaline earth metal and is formed by a wet process;

a refractive index of the at least one layer of the multilayered optical thin film with respect to a light beam having a wavelength of not more than 250 nm is not more than 1.35, and

the multilayered optical thin film is an anti-reflection film, and a reflectance is not more than 0.5% with respect to the light beam having a wavelength selected from the group consisting of wavelengths of 157 nm, 193 nm, and 248 nm, provided that an angle of incidence is not more than 50 degrees.

2. An optical element comprising:

an optical substrate; and

a multilayered optical thin film which is formed on the optical substrate, wherein;

at least one layer of the multilayered optical thin film is composed of fluoride of alkaline earth metal and is formed by a wet process,

a refractive index of the at least one layer of the multilayered optical thin film with respect to a light beam having a wavelength of not more than 250 nm is not more than 1.35, and

a reflectance is not more than 0.2% with respect to the light beam having the wavelength selected from the group consisting of the wavelengths of 157 nm, 193 nm, and 248 nm, provided that the angle of incidence is not more than 55 degrees.

3. An optical element comprising:

an optical substrate; and

a muiltilayered optical thin film which is formed on the optical substrate, wherein;

at least one layer of the multilayered optical thin film is composed of fluoride of alkaline earth metal and is formed by a wet process,

a refractive index of the at least one layer of the multilayered optical thin film with respect to a light beam having a wavelength of not more than 250 nm is not more than 1.35, and

the multilayered optical thin film is a reflection film, and a reflectance is not less than 97% with respect to the light beam having a wavelength of 193 nm.

4. An optical element, the optical element being a projection lens to be used for a projection exposure apparatus and comprising:

an optical substrate; and

a multilayered optical thin film which is formed on the optical substrate, wherein;

at least one layer of the multilayered optical thin film is composed of fluoride of alkaline earth metal and is formed by a wet process, and

a refractive index of the at least one layer of the multilayered optical thin film with respect to a light beam having a wavelength of not more than 250 nm is less than 1.35.

5. The optical element according to claim 4, wherein N.A.≧

0.80 is satisfied.

6. An exposure apparatus for exposing a substrate with an image of a pattern on a mask, the exposure apparatus comprising:

an illumination optical system which illuminates the mask with a vacuum ultraviolet light beam;

a projection optical system which includes an optical element and which projects the image of the pattern on the mask onto the substrate; and

a multilayered optical thin film which is formed on a surface of the optical element, wherein;

at least one layer of the multilayered optical thin film is composed of fluoride of alkaline earth metal and is formed by a wet process; and

a refractive index of the at least one layer with respect to a light beam having a wavelength of not more than 250 nm is less than 1.35.

7. The exposure apparatus according to claim 6, wherein the refractive index of the at least one layer of the multilayered optical thin film with respect to the light beam having the wavelength of not more than 250 nm is 1.15 to 1.25.

8. The exposure apparatus according to claim 6, wherein the multilayered optical thin film is an anti-reflection film, and the anti-reflection film has a reflectance which is not more than 0.5% with respect to the light beam having a wavelength selected from the group consisting of wavelengths of 157 nm, 193 nm, and 248 nm, provided that an angle of incidence is not more than 55 degrees.

9. The exposure apparatus according to claim 6, wherein the optical element is a projection lens or a reflecting plate.

10. The exposure apparatus according to claim 6, wherein the vacuum ultraviolet light beam has a wavelength of not more than 250 nm.

11. An exposure apparatus for exposing a substrate with an image of a pattern on a mask, the exposure apparatus comprising:

an illumination optical system which includes an optical element and which illuminates the mask with a vacuum ultraviolet light beam;

a projection optical system which projects the image of the pattern on the mask onto the substrate; and

a multilayered optical thin film which is formed on a surface of the optical element, wherein;

at least one layer of the multilayered optical thin film is composed of fluoride of alkaline earth metal and is formed by a wet process; and

a refractive index of the at least one layer with respect to a light beam having a wavelength of not more than 250 nm is less than 1.35.

12. The exposure apparatus according to claim 11, wherein the projection optical system includes at least one projection lens, a multilayered optical thin film is formed on a surface of the projection lens, and a refractive index of at least one layer of the multilayered optical thin film with respect to a light beam having a wavelength of not more than 250 nm is not more than 1.35.

13. The exposure apparatus according to claim 11, wherein the refractive index of the at least one layer of the multilayered optical thin film with respect to the light beam having the wavelength of not more than 250 nm is 1.15 to 1.25.

14. The exposure apparatus according to claim 11, wherein the multilayered optical thin film is an anti-reflection film, and the anti-reflection film has a reflectance which is not more than 0.5% with respect to the light beam having a wavelength selected from the group consisting of wavelengths of 157 nm, 193 nm, and 248 nm, provided that an angle of incidence is not more than 55 degrees.

15. The exposure apparatus according to claim 11, wherein the vacuum ultraviolet light beam has a wavelength of not more than 250 nm.