Thermal field emission cathode

Abstract

A thermal field emission cathode which is employed in an electron microscope, a critical dimension examine tool, an electron beam lithograph machine, an electron beam tester and other electron beam related systems as an electron source is disclosed. Embodiments disclose changing coating shape, coating position and shorten emitter length to extend the lifetime of the field emission cathode.

1 . A thermal field emission cathode, comprising:
 an emitter, the emitter comprising an apex wherefrom field emission electrons are released;   a heating filament, the heating filament being attached to the emitter for providing thermal energy to the emitter;   a suppressor electrode, the suppressor electrode being set in a spatial neighborhood of the emitter, with the apex extending through the center bore of the suppressor electrode; and   a coating material reservoir layer formed on the emitter, wherein the thickness of the coating material reservoir is equal to or less than half of the diameter of the emitter.   
     
     
         2 . The thermal field emission cathode of  claim 1 , wherein the location of one end of the coating material reservoir layer is no nearer than 100 micrometers from the apex. 
     
     
         3 . The thermal field emission cathode of  claim 2 , wherein the location of another end of the coating material reservoir layer is no farther than 800 micrometers from the apex. 
     
     
         4 . The thermal field emission cathode of  claim 1 , wherein a predefined portion of the coating layer resides outside of the suppressor electrode with reference to the heating filament material. 
     
     
         5 . The thermal filed emission cathode layer of  claim 1 , wherein the coating material reservoir layer is provided from the group consisting of compounds, such as oxide, nitrides, and carbon compound, of zirconium, titanium, hafnium, yttrium, niobium, vanadium, thorium, scandium, beryllium, or lanthanum. 
     
     
         6 . The thermal field emission cathode of  claim 1 , wherein the coating material reservoir layer is a thin layer coating. 
     
     
         7 . The thermal field emission cathode of  claim 1 , wherein the coating thickness is uniform and not thicker than half of the diameter of the emitter. 
     
     
         8 . The thermal field emission cathode of  claim 1 , wherein a length of the emitter from the apex to the location of a junction is between about 850 to 1350 micrometers. 
     
     
         9 . The thermal field emission cathode of  claim 6 , wherein the thickness of the thin layer coating is in the range of approximately 10-20 micrometers. 
     
     
         10 . The thermal field emission cathode of  claim 8 , wherein a temperature of the location of the heating filament being attached to the emitter is less than 1930K. 
     
     
         11 . The thermal field emission cathode of  claim 10 , wherein a temperature of the location of the heating filament being attached to the emitter is about 1880K. 
     
     
         12 . The thermal field emission cathode of  claim 1 , wherein a length of the coating material reservoir layer is equal or larger than 500 micrometers.