Reflective optical element, optical system and EUV lithography device

Abstract

In order to obtain optimal reflectivity on optical elements for the EUV and the soft X-ray range, multilayers constructed of a number of layers are used. Contamination or degradation of the surface leads to imaging defects and transmission losses. In the prior art, it has been attempted to counter a negative change in the surface by providing a cover layer system on the surface of the reflective optical element that should protect the surface. The invention renders the influence of the surface degradation manageable by a targeted selection of the distribution of thickness of the cover layer system, whereby at least one layer of the cover layer system has a gradient that is not equal to zero.

1 . A reflective optical element for the extreme ultraviolet and/or soft x-ray wavelength range comprising: a cover layer system having at least one layer to protect the surface, whose spatial structure can be described in a Cartesian system of coordinates (x, y, z) with z=z(x, y), wherein a thickness distribution d=d(x, y) of at least one layer of the cover layer system as a function of its spatial coordinates has a gradient not equal to zero.  
     
     
         2 . The reflective optical element according to  claim 1 , wherein a maximum change in thickness of the cover layer system is at most 3 nm.  
     
     
         3 . The reflective optical element according to  claim 1 , wherein an overall thickness of the cover layer system is at most 8 nm.  
     
     
         4 . A reflective optical element for the extreme ultraviolet and/or soft x-ray range, comprising: a cover layer system having at least one layer to protect the surface, whose spatial structure can be described in a Cartesian system of coordinates (x, y, z) with z=z(x, y), wherein the cover layer system has at least one outer layer and a layer lying underneath, and a thickness distribution d=d(x, y) of at least the layer of the cover layer system lying underneath, as a function of its spatial coordinates, has a gradient not equal to zero.  
     
     
         5 . A reflective optical element, comprising: a multilayer system for the extreme ultraviolet and/or soft x-ray range with a cover layer system having at least one layer to protect the surface, whose spatial structure can be described in a Cartesian system of coordinates (x, y, z) with z=z(x, y), wherein the gradient of the thickness distribution d=d(x, y) of at least one layer of the cover layer system at the location (x, y) is not equal to the gradient of the thickness distribution of at most ten individual layers of the multilayer system immediately adjacent to the cover layer system.  
     
     
         6 . The reflective optical element according to  claim 5 , wherein a maximum change in thickness of the cover layer system is at most 3 nm.  
     
     
         7 . The reflective optical element according to  claim 5 , wherein an overall thickness of the cover layer system is at most 8 nm.  
     
     
         8 . A reflective optical element, comprising: a multilayer system for the extreme ultraviolet and/or soft x-ray wavelength range with a cover layer system having at least one layer to protect the surface, whose spatial structure can be described in a Cartesian system of coordinates (x, y, z) with z=z(x, y), wherein the cover layer system has at least one outer layer and a layer lying underneath, and the gradient of the thickness distribution d=d(x, y) of at least the layer of the cover layer system lying underneath at the location (x,y) is not equal to the gradient of the thickness distribution of at most ten individual layers of the multilayer system immediately adjacent to the cover layer system.  
     
     
         9 . The reflective optical element according to  claim 1 , wherein at least one layer of the cover layer system has a thickness variation of ≧1 Å over the surface of the optical element.  
     
     
         10 . The reflective optical element according to  claim 1 , wherein the reflective optical element has a shaper and the thickness distribution of the cover layer system is such that the free boundary surface of the reflective optical element reproduces the shape of the shaper in at least one direction relative to the xy-coordinates.  
     
     
         11 . The reflective optical element according to  claim 1 , wherein the thickness distribution of the cover layer system in at least one direction relative to the xy-coordinates varies monotonically with the intensity distribution along the beam cross section of the operating incident radiation.  
     
     
         12 . The reflective optical element according to  claim 1 , wherein the thickness distribution is such that the convolution, in respect of the xy-coordinates, of the intensity distribution along the beam cross section of the operating incident radiation with the electrical field intensity of the standing wave formed by reflection at the free boundary surface and normalized to the incident radiation intensity (the degradation profile) produces a linear distribution.  
     
     
         13 . The reflective optical element according to  claim 1 , wherein the thickness distribution is such that the convolution, in respect of the xy-coordinates, of the intensity distribution along the beam cross section of the operating incident radiation with the electrical field intensity of the standing wave formed by reflection at the free boundary surface and normalized to the incident radiation intensity (the degradation profile) produces a rotationally symmetrical distribution.  
     
     
         14 . The reflective optical element according to  claim 1 , wherein the thickness distribution is such that the convolution, in respect of the xy-coordinates, of the intensity distribution along the beam cross section of the operating incident radiation with the electrical field intensity of the standing wave formed by reflection at the free boundary surface and normalized to the incident radiation intensity (the degradation profile) produces a superpositioning of a linear and a rotationally symmetrical distribution.  
     
     
         15 . The reflective optical element according to  claim 12 , wherein the distribution resulting from the convolution in terms of the xy-coordinates is such that the magnitude of this distribution decreases at every point (x, y) of the surface with increasing thickness of the cover layer system.  
     
     
         16 . The reflective optical element according to  claim 1 , wherein the thickness distribution is such that the weighted product, in respect of the xy-coordinates, of the intensity distribution along the beam cross section of the operating incident radiation and the electrical field intensity of the standing wave formed by reflection at the free boundary surface and normalized to the incident radiation intensity (the degradation profile) yields a linear distribution.  
     
     
         17 . The reflective optical element according to  claim 1 , wherein the thickness distribution is such that the weighted product, in respect of the xy-coordinates, of the intensity distribution along the beam cross section of the operating incident radiation and the electrical field intensity of the standing wave formed by reflection at the free boundary surface and normalized to the incident radiation intensity (the degradation profile) yields a rotationally symmetrical distribution.  
     
     
         18 . The reflective optical element according to  claim 1 , wherein the thickness distribution is such that the weighted product, in respect of the xy-coordinates, of the intensity distribution along the beam cross section of the operating incident radiation and the electrical field intensity of the standing wave formed by reflection at the free boundary surface and normalized to the incident radiation intensity (the degradation profile) yields a superpositioning of a linear and a rotationally symmetrical distribution.  
     
     
         19 . The reflective optical element according to  claim 16 , wherein the distribution resulting from the weighted product in terms of the xy-coordinates is such that the magnitude of this distribution decreases at every point (x, y) of the surface with increasing thickness of the cover layer system.  
     
     
         20 . An optical system with at least two reflective optical elements for the extreme ultraviolet and/or soft x-ray wavelength range, at least one reflective optical element of which is an element according to  claim 1 .  
     
     
         21 . An optical system, comprising: at least two reflective optical elements for the extreme ultraviolet and/or soft x-ray wavelength range each with a cover layer system, wherein the cover layer systems have different materials, or different thickness distributions in the z-direction as a function of the x or y-coordinates, or x and y-coordinates, or a combination thereof, and the thickness distribution of at least one layer of one cover layer system has a gradient not equal to zero.  
     
     
         22 . The optical system according to  claim 21 , wherein a maximum change in thickness of the cover layer system is at most 3 nm.  
     
     
         23 . The optical system according to  claim 21 , wherein an overall thickness of the cover layer system is at most 8 nm.  
     
     
         24 . An optical system, comprising: at least two reflective optical elements for the extreme ultraviolet and/or soft x-ray wavelength range each with a cover layer system, wherein the cover layer systems have different materials, or different thickness distributions in the z-direction as a function of the x or y-coordinates, or x and y-coordinates, or a combination thereof, and the cover layer system has at least one outer layer and a layer lying underneath, and the thickness distribution d=d(x, y) of at least the layer of the cover layer system lying underneath has a gradient not equal to zero.  
     
     
         25 . An optical system comprising: at least two reflective optical elements for the extreme ultraviolet and/or soft x-ray wavelength range each with a cover layer system, wherein the cover layer systems have different materials, or different thickness distributions in the z-direction as a function of the x or y-coordinates, or x and y-coordinates, or a combination thereof, and the gradient of the thickness distribution d=d(x, y) of at least one layer of one cover layer system at the location (x, y) is unequal to all gradients of at most ten individual layers of the multilayer system immediately adjacent to the cover layer system.  
     
     
         26 . The optical system according to  claim 25 , wherein a maximum change in thickness of the cover layer system is at most 3 nm.  
     
     
         27 . The optical system according to  claim 25 , wherein an overall thickness of the cover layer system is at most 8 nm.  
     
     
         28 . An optical system, comprising: at least two reflective optical elements for the extreme ultraviolet and/or soft x-ray wavelength range each with a cover layer system, wherein the cover layer systems have different materials, or different thickness distributions in the z-direction as a function of the x or y-coordinates, or x and y-coordinates, or combinations thereof, and the gradient of the thickness distribution d=d(x, y) of at least the layer of one cover layer system lying underneath at the location (x, y) is unequal to all gradients of at most ten individual layers of the multilayer system immediately adjacent to the cover layer system.  
     
     
         29 . An EUV lithography appliance, comprising: at least two reflective optical elements for the extreme ultraviolet and/or soft x-ray wavelength range with at least one cover layer system, at least one reflective optical element of which is an element according to  claim 1 .  
     
     
         30 . An EUV lithography appliance, comprising: at least two reflective optical elements for the extreme ultraviolet and/or soft x-ray wavelength range with at least one cover layer system, wherein the cover layer systems have different materials, or different thickness distributions in the z-direction as a function of the x or y-coordinates, or x and y-coordinates, or a combination thereof, and the thickness distribution of at least one layer of one cover layer system has a gradient not equal to zero.  
     
     
         31 . The EUV lithography appliance according to  claim 30 , wherein an overall thickness of the cover layer system is at most 8 nm.  
     
     
         32 . The EUV lithography appliance according to  claim 30 , wherein a maximum change in thickness of the cover layer system is at most 3 nm.  
     
     
         33 . An EUV lithography appliance, comprising: at least two reflective optical elements for the extreme ultraviolet and/or soft x-ray wavelength range with at least one cover layer system, wherein the cover layer system has at least one outer layer and one layer lying underneath, and the cover layer systems have different materials, or different thickness distributions in the z-direction as a function of the x or y-coordinates, or x and y-coordinates, or a combination thereof, and the thickness distribution of at least the layer of a cover layer system lying underneath has a gradient not equal to zero.  
     
     
         34 . A semiconductor component produced with an optical element according to  claim 1 .  
     
     
         35 . The reflective optical element according to  claim 9 , wherein at least one layer of the cover layer system has a thickness variation of ≧3 Å over the surface of the optical element.  
     
     
         36 . The reflective optical element according to  claim 9 , wherein at least one layer of the cover layer system has a thickness variation of ≧5 Å over the surface of the optical element.  
     
     
         37 . The reflective optical element according to  claim 13 , wherein the distribution resulting from the convolution in terms of the xy-coordinates is such that the magnitude of this distribution decreases at every point (x, y) of the surface with increasing thickness of the cover layer system.  
     
     
         38 . The reflective optical element according to  claim 14 , wherein the distribution resulting from the convolution in terms of the xy-coordinates is such that the magnitude of this distribution decreases at every point (x, y) of the surface with increasing thickness of the cover layer system.  
     
     
         39 . The reflective optical element according to claims  17 , wherein the distribution resulting from the weighted product in terms of the xy-coordinates is such that the magnitude of this distribution decreases at every point (x, y) of the surface with increasing thickness of the cover layer system.  
     
     
         40 . The reflective optical element according to claims  18 , wherein the distribution resulting from the weighted product in terms of the xy-coordinates is such that the magnitude of this distribution decreases at every point (x, y) of the surface with increasing thickness of the cover layer system.