EUV light source components and methods for producing, using and refurbishing same
View Patent ↗A method is disclosed for in-situ monitoring of an EUV mirror to determine a degree of optical degradation. The method may comprise the steps/acts of irradiating at least a portion of the mirror with light having a wavelength outside the EUV spectrum, measuring at least a portion of the light after the light has reflected from the mirror, and using the measurement and a pre-determined relationship between mirror degradation and light reflectivity to estimate a degree of multi-layer mirror degradation. Also disclosed is a method for preparing a near-normal incidence, EUV mirror which may comprise the steps/acts of providing a metallic substrate, diamond turning a surface of the substrate, depositing at least one intermediate material overlying the surface using a physical vapor deposition technique, and depositing a multi-layer mirror coating overlying the intermediate material.
1. A method for in-situ monitoring of an EUV mirror to determine a degree of optical degradation, the method comprising the acts of:
irradiating at least a portion of the mirror with light having a wavelength outside the EUV spectrum while the EUV mirror is in an operational position in a photolithography apparatus;
measuring at least a portion of the light after the light has reflected from the mirror; and
using the measurement and a pre-determined relationship between mirror degradation and light reflectivity to estimate a degree of multi-layer mirror degradation.
2. A method as recited in claim 1 wherein the mirror is operationally positioned in an EUV light source portion of the photolithography apparatus.
3. A method as recited in claim 1 wherein the mirror is a near-normal incidence multi-layer mirror.
4. A method as recited in claim 3 wherein the irradiating act is performed with a point source of visible light.
5. A method as recited in claim 4 wherein the point source is selected from the group of point sources consisting of a light emitting diode and a light source in combination with an aperture.
6. A method as recited in claim 3 wherein the mirror has an ellipsoidal shape defining a first focus and a second focus, and wherein the irradiating act is performed with a point source of visible light positioned at the first focus and the measuring act is performed with a detector positioned at a location closer to the second focus than the first focus.
7. A method as recited in claim 3 wherein the irradiating act is performed with a laser beam and the measuring act is performed with a detector positioned to detect diffuse reflected light.
8. A method as recited in claim 1 wherein the mirror has an ellipsoidal shape defining a first focus and a second focus, and wherein the irradiating act is performed with a point source positioned at the first focus generating a cone of reflected light having an apex at the second focus and diffuse reflected light and the measuring act is performed with a detector positioned at a distance from the second focus to detect diffuse reflected light.
9. A method for producing EUV light, said method comprising the acts of:
providing an EUV mirror having a substrate, a first multi-layer coating stack, a stop layer overlying the first multi-layer coating stack and a second multi-layer coating stack overlying said stop layer;
using the mirror to reflect EUV light produced by an EUV light emitting plasma, the plasma generating debris which degrades the second multi-layer coating stack; and thereafter;
etching said mirror to expose at least a portion of said stop layer; and thereafter;
using the mirror to reflect EUV light produced by an EUV light emitting plasma.
10. A method as recited in claim 9 wherein said stop layer comprises a material selected from the group of materials consisting of Si 3 N 4 , SiB 6 , SiC, C, Cr, B 4 C, Mo 2 C, SiO 2 , ZrB 2 , YB 6 and MoSi 2 , and said etching step employs an etchant selected from the group of materials consisting of Cl 2 , HCl, CF 4 , and mixtures thereof.
11. A method as recited in claim 10 wherein said second multi-layer coating stack comprises a plurality of bi-layers, each bi-layer having a layer of Mo and a layer of Si.
12. A method as recited in claim 11 wherein said second multi-layer coating stack comprises a plurality of Mo layers, a plurality of Si layers and a plurality of diffusion barrier layers separating Mo layers from Si layers.
13. A method as recited in claim 9 wherein said second multi-layer coating stack comprises more than forty bi-layers.
14. A method as recited in claim 9 wherein said stop layer has a thickness selected to maintain the periodicity of the mirror from the second multi-layer coating stack to the first multi-layer coating stack.
15. A method as recited in claim 9 wherein said stop layer is a first stop layer and said mirror comprises a second stop layer overlying said second multi-layer coating stack and a third multi-layer coating stack overlying said second stop layer.
16. A system for in-situ monitoring of an EUV mirror to determine a degree of optical degradation, the system comprising:
a light source irradiating at least a portion of the mirror with light having a wavelength in the visible spectrum while the EUV mirror is in an operational position in a photolithography apparatus; and
a detector measuring an intensity of at least a portion of the light after the light has reflected from the mirror, the detector generating an output signal for use in estimating a degree of multi-layer mirror degradation.