Radiation source, lithographic apparatus, and device manufacturing method

Abstract

A radiation source unit is provided that includes an anode and a cathode that are configured and arranged to create a discharge in a substance in a space between said anode and cathode and to form a plasma so as to generate electromagnetic radiation. The substance may comprise xenon, indium, lithium, tin or any suitable material. To improve conversion efficiency, the source unit may be constructed to have a low inductance, and operated with a minimum of plasma. To, for example, improve heat dissipation, a fluid circulation system can be created within the source volume and a wick by using a fluid in both its vapor and liquid states. To, for example, prevent contamination from entering a lithographic projection apparatus, the source unit can be constructed to minimize the production of contamination, and a trap can be employed to capture the contamination without interfering with the emitted radiation.

1 . A radiation source comprising an anode and a cathode that are configured to create a discharge in a discharge space between the anode and cathode and to form a plasma so as to generate electromagnetic radiation, wherein a vapor in the discharge space is created by directing an energetic beam onto a liquid, a solid target, or both, proximate the discharge space.  
     
     
         2 . The radiation source of  claim 1 , wherein the vapor would comprise one or more elements selected from the group consisting of: xenon (Xe), tin (Sn), lithium (Li), indium (In) and iridium (Ir).  
     
     
         3 . The radiation source of  claim 1 , wherein the energetic beam would comprise a beam of charged particles.  
     
     
         4 . The radiation source of  claim 1 , wherein the energetic beam would comprise a beam of radiation.  
     
     
         5 . The radiation source of  claim 1 , wherein the radiation source is configured to vary a concentration of the vapor using one or more parameters of the energetic beam selected from the group of parameters consisting of: wavelength, energy per impulse, and pulse length.  
     
     
         6 . The radiation source of  claim 1 , wherein the solid target would comprise a wire.  
     
     
         7 . The radiation source of  claim 1 , further comprising a wicking surface area of a wall defining the discharge space, the wicking surface area configured to transport a liquid towards the discharge space from a liquid reservoir in contact with the wicking surface area.  
     
     
         8 . The radiation source of  claim 7 , wherein the wicking surface area is provided on the anode, the cathode, or both.  
     
     
         9 . The radiation source of  claim 7 , wherein the anode, the cathode, or both, is substantially vertically located above the liquid reservoir.  
     
     
         10 . The radiation source of  claim 1 , further comprising a hollow receptacle arranged on an optical axis of the radiation source, an open end of the receptacle directed to the discharge space to capture contamination emitted from the discharge space.  
     
     
         11 . The radiation source of  claim 1 , further comprising an aperture provided in the anode, the cathode, or both, through which the electromagnetic radiation is emitted, the aperture comprising a plurality of electrically-conductive structures arranged so as to leave the aperture substantially open to the radiation but to substantially close the aperture electrically.  
     
     
         12 . The radiation source of  claim 1 , further comprising an isolator configured to electrically separate the anode and cathode and a cooler located near the isolator and configured to condense vapor to reduce contact of the vapor onto the isolator.  
     
     
         13 . The radiation source of  claim 1 , wherein the cathode and the anode are substantially concentric and the anode is disposed at least in part around and outside the cathode.  
     
     
         14 . A method for generating vapor in a discharge space between an anode and a cathode of a radiation source, the radiation source configured to form a plasma so as to generate electromagnetic radiation, the method comprising directing an energetic beam onto a liquid, a solid target, or both, proximate the discharge space to generate the vapor.  
     
     
         15 . The method of  claim 14 , wherein the vapor comprises one or more elements selected from the group consisting of: xenon (Xe), tin (Sn), lithium (Li), indium (In) and iridium (Ir).  
     
     
         16 . The method of  claim 14 , wherein the energetic beam comprises a beam of charged particles.  
     
     
         17 . The method of  claim 14 , wherein the energetic beam comprises a beam of radiation.  
     
     
         18 . The method of  claim 14 , further comprising varying a concentration of the vapor using one or more parameters of the energetic beam selected from the group of parameters consisting of: wavelength, energy per impulse, and pulse length.  
     
     
         19 . The method of  claim 14 , wherein the solid target comprises a wire.  
     
     
         20 . The method of  claim 14 , further comprising transporting the liquid towards the discharge space from a liquid reservoir using a wicking surface area of a wall defining the discharge space.  
     
     
         21 . The method of  claim 20 , wherein the wicking surface area is provided on the anode, the cathode, or both.  
     
     
         22 . The method of  claim 20 , wherein the anode, the cathode, or both, is substantially vertically located above the liquid reservoir.  
     
     
         23 . The method of  claim 14 , further comprising capturing contamination emitted from the discharge space using a hollow receptacle arranged on an optical axis of the radiation source, an open end of the receptacle directed to the discharge space.  
     
     
         24 . The method of  claim 14 , further comprising emitting the electromagnetic radiation through an aperture provided in the anode, the cathode, or both, the aperture comprising a plurality of electrically-conductive structures arranged so as to leave the aperture substantially open to the radiation but to substantially close the aperture electrically.  
     
     
         25 . The method of  claim 14 , wherein the cathode and the anode are substantially concentric and the anode is disposed at least in part around and outside the cathode.  
     
     
         26 . A lithographic projection apparatus, comprising: 
 a radiation system comprising an anode and a cathode that are configured to create a discharge in a discharge space between the anode and cathode and to form a plasma so as to generate a beam of radiation, wherein a vapor in the discharge space is created by directing an energetic beam onto a liquid, a solid target, or both, proximate the discharge space;    a support structure configured to hold a patterning device, the patterning device configured to impart the beam of radiation with a pattern to form a patterned beam;    a substrate table configured to hold a substrate; and    a projection system configured to project the patterned beam onto a target portion of the substrate.    
     
     
         27 . The apparatus of  claim 26 , wherein the vapor would comprise one or more elements selected from the group consisting of: xenon (Xe), tin (Sn), lithium (Li), indium (In) and iridium (Ir).  
     
     
         28 . The apparatus of  claim 26 , wherein the energetic beam would comprise a beam of charged particles.  
     
     
         29 . The apparatus of  claim 26 , wherein the energetic beam would comprise a beam of radiation.  
     
     
         30 . The apparatus of  claim 26 , wherein the radiation system is configured to vary a concentration of the vapor using one or more parameters of the energetic beam selected from the group of parameters consisting of: wavelength, energy per impulse, and pulse length.