Lithographic apparatus and lithographic apparatus cleaning method

Abstract

An immersion lithographic projection apparatus having a megasonic transducer configured to clean a surface and a method of using megasonic waves to clean a surface of an immersion lithographic projection apparatus are disclosed.

1 . An immersion lithographic projection apparatus, comprising: 
 a substrate table constructed and arranged to hold a substrate;    a projection system configured to project a patterned beam of radiation onto the substrate;    a megasonic transducer configured to clean a surface; and    a liquid supply system constructed and arranged to supply liquid between the megasonic transducer and the surface to be cleaned.    
   
   
       2 . The apparatus of  claim 1 , wherein the megasonic transducer has a frequency of above 750 Hz.  
   
   
       3 . The apparatus of  claim 1 , wherein the liquid supply system comprises a barrier member which surrounds a lower end of the megasonic transducer and which forms a seal between the barrier member and the surface to be cleaned, thereby to contain liquid between the megasonic transducer and the surface to be cleaned.  
   
   
       4 . The apparatus of  claim 3 , wherein the barrier member, the transducer, or both, is moveable relative to the surface.  
   
   
       5 . The apparatus of  claim 3 , wherein the contactless seal is a gas seal.  
   
   
       6 . The apparatus of  claim 3 , wherein the surface is a top surface of the substrate table.  
   
   
       7 . The apparatus of  claim 1 , wherein the liquid supply system is constructed and arranged to provide a flow of liquid over the surface.  
   
   
       8 . The apparatus of  claim 1 , wherein the megasonic transducer is positioned, in a cleaning mode, to face the surface such that sonic waves are directed in a line of sight path to the surface to be cleaned.  
   
   
       9 . The apparatus of  claim 1 , wherein the surface is a surface of the substrate table, a surface of a liquid confinement system constructed to provide liquid between the projection system and a substrate to be exposed, or both.  
   
   
       10 . The apparatus of  claim 1 , wherein the liquid supply system comprises a bath and a controller configured to fill the bath with liquid to a certain level.  
   
   
       11 . The apparatus of  claim 10 , wherein the megasonic transducer is positioned in a bottom of the bath to induce sonic waves, directed away from the bottom of the bath, in liquid in the bath.  
   
   
       12 . The apparatus of  claim 10 , wherein the bath is moveable to a cleaning position under the projection system and to at least partly enclose a liquid confinement system constructed to provide, in use, liquid between the projection system and a substrate to be exposed, and the certain level is below the bottom of the projection system but above a bottom surface of the liquid confinement system.  
   
   
       13 . The apparatus of  claim 1 , wherein the liquid supply system comprises a barrier which surrounds a top surface of the substrate table, such that liquid can be provided on the top surface and be prevented from escaping by the barrier.  
   
   
       14 . The apparatus of  claim 13 , wherein the barrier is moveable between a cleaning position and a non-cleaning position.  
   
   
       15 . The apparatus of  claim 1 , wherein the megasonic transducer is moveable relative to the surface.  
   
   
       16 . The apparatus of  claim 1 , further comprising a shield to shield an optical element of the projection system from megasonic waves, liquid, or both.  
   
   
       17 . The apparatus of  claim 1 , further comprising a gas supply configured to introduce gas into the liquid.  
   
   
       18 . The apparatus of  claim 17 , wherein the gas comprises N 2 , CO 2 , O 2 , O 3 , H 2  containing water or a mixture of two or more of these gases.  
   
   
       19 . The apparatus of  claim 1 , further comprising a surfactant supplier to supply surfactant to the liquid and/or a hydrogen oxide supplier to supply H 2 O 2  to the liquid.  
   
   
       20 . The apparatus of  claim 1 , further comprising a pump configured to create a flow of the liquid between the megasonic transducer and the surface to be cleaned.  
   
   
       21 . The apparatus of  claim 1 , wherein the liquid supply apparatus comprises a controller configured to control the pH of the liquid and/or concentration of electrolyte in the liquid.  
   
   
       22 . An immersion lithographic projection apparatus, comprising: 
 a substrate table constructed and arranged to hold a substrate;    a projection system configured to project a patterned beam of radiation onto the substrate;    a megasonic transducer configured to clean a surface, the megasonic transducer being moveable relative to the surface such that, in a cleaning mode, a direct straight path through liquid exists between the megasonic transducer and the surface; and    a liquid supply system configured to provide liquid between the transducer and the surface.    
   
   
       23 . The apparatus of  claim 22 , wherein, in the cleaning mode, the megasonic transducer and the surface face each other at a distance of less than 50 mm.  
   
   
       24 . The apparatus of  claim 22 , wherein, in the cleaning mode, the megasonic transducer and the surface face each other at a distance of less than 50 mm, and wherein the surface is a surface of a liquid confinement system constructed to provide liquid between the projection system and a substrate to be exposed.  
   
   
       25 . The apparatus of  claim 22 , further comprising a gas supply configured to introduce gas into the liquid.  
   
   
       26 . The apparatus of  claim 25 , wherein the gas is selected from the group: N 2 , CO 2 , O 2 , O 3 , H 2  containing water or a mixture of two or more of these gases.  
   
   
       27 . The apparatus of  claim 22 , further comprising a surfactant supplier configured to supply surfactant to the liquid.  
   
   
       28 . A method of cleaning a surface of an immersion lithographic projection apparatus, comprising: 
 covering at least a part of the surface to be cleaned in liquid; and    introducing megasonic waves into the liquid.    
   
   
       29 . The method of  claim 28 , wherein the megasonic transducer has a frequency of above about 750 kHz.  
   
   
       30 . The method of  claim 28 , wherein the megasonic waves are introduced using a megasonic transducer and comprising moving the megasonic transducer relative to the surface to be cleaned.  
   
   
       31 . The method of  claim 28 , wherein the megasonic waves impinge perpendicularly to the surface to be cleaned.  
   
   
       32 . The method of  claim 28 , wherein the megasonic waves impinge at an angle to the surface to be cleaned.  
   
   
       33 . The method of  claim 28 , comprising moving the liquid covering at least part of the surface to be cleaned over the surface.  
   
   
       34 . The method of  claim 28 , comprising positioning a megasonic transducer, in a cleaning mode, to face the surface such that the megasonic waves are directed in a line of sight path to the surface to be cleaned.  
   
   
       35 . The method of  claim 28 , further comprising introducing gas into the liquid.  
   
   
       36 . The method of  claim 28 , further comprising introducing a surfactant into the liquid.  
   
   
       37 . The method of  claim 28 , further comprising moving the liquid between the surface to be cleaned and the megasonic transducer.  
   
   
       38 . The method of  claim 28 , further comprising providing the liquid at a certain pH and/or with a certain concentration of an electrolyte.  
   
   
       39 . The method of  claim 38 , wherein the certain pH and/or concentration is such that the zeta potential of the surface to be cleaned and particles on the surface to be removed is not of different polarity.