Electron optics for multi-beam electron beam lithography tool

Abstract

A charge particle optical column capable of being used in a high throughput, mutli-column, multi-beam electron beam lithography system is disclosed herein. The column has the following properties: purely electrostatic components; small column footprint (20 mm square); multiple, individually focused charge particle beams; telecentric scanning of all beams simultaneously on a wafer for increased depth of field; and conjugate blanking of the charged particle beams for reduced beam blur. An electron gun is disclosed that uses microfabricated, field emission sources and a microfabricated aperture-deflector assembly. The aperture-deflector assembly acts as a perfect lens in focusing, steering and blanking a multipicity of electron beams through the back focal plane of an immersion lens located at the bottom of the column. Beam blanking can be performed using a gating signal to decrease beam blur during writing on the wafer.

What is claimed is:  
     
         1 . An electron optics assembly for a multi-column electron optical system comprising: 
 a multiplicity of separate electron sources, such that there is a corresponding electron source for each column;    a single accelerator structure situated below said electron sources;    a multiplicity of separate scanning deflectors situated below said accelerator structure, such that there is a corresponding scanning deflector for each column; and    a multiplicity of focus lenses situated below said deflectors, such that there is a corresponding focus lens for each column.    
     
     
         2 . An electron optics assembly as in  claim 1 , wherein each of said electron sources comprises a multiplicity of independently operable field emission cathodes.  
     
     
         3 . An electron optics assembly as in  claim 1 , wherein said accelerator structure is comprised of a set of accelerator plates, a multiplicity of accelerator apertures extending fully through said set of accelerator plates, such that there is a corresponding accelerator aperture for each column.  
     
     
         4 . An electron optics assembly as in  claim 1 , wherein said accelerator structure is comprised of a single piece of resistive ceramic material, a multiplicity of accelerator apertures extending fully through said single piece of resistive ceramic material, such that there is a corresponding accelerator aperture for each column.  
     
     
         5 . An electron optics assembly as in  claim 1 , further comprising a multiplicity of alignment deflectors, for precisely steering the electron beams down the centers of corresponding columns, situated between said electron sources and said accelerator structure, such that there is a corresponding alignment deflector for each column.  
     
     
         6 . An electron optics assembly as in  claim 1 , wherein said multiplicity of focus lenses are formed in a single lens plate.