Incidence surfaces and optical windows that are solvophobic to immersion liquids

Abstract

Optical windows are provided that transmit light such as deep-UV (DUV) light. An exemplary window includes a window substrate that is transmissive to at least one wavelength of the light. The window substrate has an incidence surface decorated with sub-wavelength asperities arranged so as to render the incidence surface solvophobic to the light-transmissive liquid. The arrangement of sub-wavelength asperities can be configured to render the incidence surface super-solvophobic to the liquid. The sub-wavelength asperities can have any of various shapes and combinations thereof, and can be regularly or irregularly arranged.

1 . An optical window for transmitting a beam of DUV light, comprising a substrate that is transmissive to at least one wavelength of the DUV light, the substrate having an incidence surface that is decorated with sub-wavelength asperities arranged so as to render the incidence surface solvophobic to a DUV-transmissive liquid. 
   
   
       2 . The optical window of  claim 1 , wherein the arrangement of sub-wavelength asperities is configured to render the incidence surface super-solvophobic to the DUV-transmissive liquid. 
   
   
       3 . The optical window of  claim 1 , wherein at least some of the asperities comprise interconnecting ridges. 
   
   
       4 . The optical window of  claim 1 , wherein the asperities are arranged in a regular, irregular, or random array. 
   
   
       5 . The optical window of  claim 1 , wherein the asperities are identical to each other. 
   
   
       6 . The optical window of  claim 1 , wherein:
 the asperities have respective top surfaces that are substantially not transmissive to the at least one wavelength;   the asperities are separated from one another by hollows; and   the hollows are transmissive to the at least one wavelength.   
   
   
       7 . The optical window of  claim 1 , wherein each asperity has a top surface having a dimension no greater than λ/10, wherein λ is a wavelength of the DUV light. 
   
   
       8 . The optical window of  claim 1 , wherein the arrangement of sub-wavelength asperities is configured to provide solvophobicity to the incidence surface according to a Wenzel model. 
   
   
       9 . The optical window of  claim 1 , wherein the arrangement of sub-wavelength asperities is configured to provide solvophobicity to the incidence surface according to a Cassie model. 
   
   
       10 . The optical window of  claim 1 , wherein the arrangement of sub-wavelength asperities is configured according to a fakir state to provide solvophobicity to the incidence surface. 
   
   
       11 . The optical window of  claim 1 , configured to be substantially non-refractive to light passing through the optical window. 
   
   
       12 . The optical window of  claim 1 , configured to be refractive to light passing through the optical window. 
   
   
       13 . The optical window of  claim 1 , wherein:
 the substrate comprises a first material; and   the asperities on the incident surface of the substrate comprise a second material different from the first material.   
   
   
       14 . The optical window of  claim 13 , wherein the second material is more solvophobic than the first material. 
   
   
       15 . The optical window of  claim 13 , wherein:
 the asperities have respective surfaces; and   the surfaces of the asperities comprise at least one layer of the second material.   
   
   
       16 . The optical window of  claim 15 , wherein the second material is more solvophobic than the first material. 
   
   
       17 . The optical window of  claim 15 , wherein:
 the asperities include intervening hollows having respective surfaces; and   the surfaces of the hollows comprise at least one layer of the second material.   
   
   
       18 . The optical window of  claim 13 , wherein:
 the asperities include intervening hollows having respective surfaces; and   the surfaces of the hollows comprise at least one layer of the second material.   
   
   
       19 . A surface contacted by a liquid that is transmissive to at least one wavelength of light, the surface being transmissive to the at least one wavelength and decorated with an arrangement of sub-wavelength asperities configured to render the surface solvophobic to the light-transmissive liquid. 
   
   
       20 . The surface of  claim 19 , configured as at least a portion of an optical window. 
   
   
       21 . The surface of  claim 19 , wherein the surface that is transmissive to the at least one wavelength and decorated with the asperities is a surface of a solvophobic material on at least a portion of a substrate. 
   
   
       22 . The surface of  claim 21 , wherein the substrate comprises a first material different from the solvophobic material. 
   
   
       23 . The surface of  claim 22 , wherein the first material is less solvophobic than the solvophobic material. 
   
   
       24 . The surface of  claim 21 , wherein:
 the asperities have respective surfaces; and   the surfaces of the asperities comprise at least one layer of the solvophobic material.   
   
   
       25 . The surface of  claim 24 , wherein:
 the asperities include intervening hollows having respective surfaces; and   the surfaces of the hollows comprise at least one layer of the solvophobic material.   
   
   
       26 . The surface of  claim 21 , wherein:
 the asperities include intervening hollows having respective surfaces; and   the surfaces of the hollows comprise at least one layer of the second material.   
   
   
       27 . An optical sensor, comprising:
 a light sensor having a sensitivity to a sensor light; and   an optical window through which a beam of the sensor light is transmitted to the light sensor, the optical window comprising a window substrate that is transmissive to at least one wavelength of the sensor light, the window substrate having an incidence surface that is decorated with sub-wavelength asperities arranged so as to render the incidence surface solvophobic to a sensor-light-transmissive liquid.   
   
   
       28 . The optical sensor of  claim 27 , wherein the sensor light is DUV light. 
   
   
       29 . The optical sensor of  claim 27 , further comprising an optical system situated between the optical window and the light sensor. 
   
   
       30 . The optical sensor of  claim 27 , wherein the optical system comprises:
 a first lens having a Fourier plane; and   an aperture stop situated at the Fourier plane, the aperture stop defining an aperture that is sized to transmit a lower order of diffracted light from the optical window while blocking a higher order of diffracted light from the optical window.   
   
   
       31 . The optical sensor of  claim 30 , further comprising at least a second lens situated between the Fourier plane and the light sensor. 
   
   
       32 . The optical sensor of  claim 30 , wherein the aperture stop further includes at least one diffraction-order stop within the aperture.