Electrostatic lens structure

Abstract

An electrostatic lens comprising a first conductive plate with a first aperture, a second conductive plate with a second aperture, the second aperture being substantially aligned with the first aperture, a voltage supply for supplying a first voltage to the first conductive plate and a second voltage to the second conductive plate, the first voltage being lower than the second voltage, and an insulating structure for separating the first conductive plate from the second conductive plate. The insulating structure comprises a first portion in contact with the first conductive plate and a second portion in contact with the second conductive plate, the first portion having an overhanging portion and the second portion having an indented portion at an edge of the insulating structure, so that a gap is formed between the overhanging portion and the second conductive plate.

The invention claimed is: 
     
       1. An electrostatic lens comprising:
 a first conductive plate provided with a first aperture; 
 a second conductive plate provided with a second aperture, the second aperture being substantially aligned with the first aperture; 
 a voltage supply for supplying a first voltage to the first conductive plate and a second voltage to the second conductive plate, the second first voltage being lower than the first second voltage with respect to intended function of the lens; and 
 an insulating structure for separating the first conductive plate from the second conductive plate; 
 wherein the insulating structure comprises a first portion in contact with the first conductive plate and a second portion in contact with the second conductive plate, the first portion having an overhanging portion contacting said first conductive plate and the second portion having an indented portion at an edge of the insulating structure, and wherein a gap is formed between the overhanging portion and the second conductive plate, and 
 wherein a surface of the insulating structure facing the first conductive plate is provided with a conductive layer in electrical contact with the first conductive plate for limiting electric field enhancement between the first conductive plate and the insulating structure. 
 
     
     
       2. The electrostatic lens of  claim 1 , wherein the permittivity of the gap is lower than the permittivity of the insulating structure. 
     
     
       3. The electrostatic lens of  claim 2 , wherein the permittivity of the gap is at least four times lower than the permittivity of the insulating structure. 
     
     
       4. The electrostatic lens of  claim 1 , wherein, in operation, the electric field strength in the gap between the overhanging portion of the insulating structure and the second conductive plate is greater than the electric field strength across the second portion of the insulating structure. 
     
     
       5. The electrostatic lens of  claim 1 , wherein the first portion and the second portion of the insulating structure are of equal thickness. 
     
     
       6. The electrostatic lens of  claim 1 , wherein the first portion and the second portion of the insulating structure comprise separate structures which are bonded together. 
     
     
       7. The electrostatic lens of  claim 1 , wherein a surface of the insulating structure facing the first conductive plate is provided with a conductive layer in electrical contact with the first conductive plate for limiting electric field enhancement between the first conductive plate and the insulating structure. 
     
     
       8. The electrostatic lens of claim  7  1, wherein the conductive layer is deposited on a surface of the insulating structure using a deposition technique. 
     
     
       9. The electrostatic lens of claim  7  1, wherein said conductive layer comprises chromium or tantalum. 
     
     
       10. The electrostatic lens of  claim 1 , wherein a distance between the first conductive plate and the second conductive plate lies in a range from about 100 to 200 μm. 
     
     
       11. The electrostatic lens of  claim 1 , wherein the lens is capable of withstanding a field strength of over 10 V/μm without flashover, and more preferably within a range from 25-50 V/μm without flashover. 
     
     
       12. The electrostatic lens of  claim 1 , wherein the insulating structure comprises borosilicate glass. 
     
     
       13. An electrostatic lens array comprising a plurality of electrostatic lenses according to  claim 1 . 
     
     
       14. The electrostatic lens array of  claim 13 , wherein the insulating structure takes the form of an insulating plate provided with at least one third aperture, the at least one third aperture being arranged such that a projection of its side walls circumscribes multiple first apertures and second apertures. 
     
     
       15. The electrostatic lens array of  claim 13 , wherein the insulating structure takes the form of a plurality of elongated bars, such that between successive bars multiple transmission paths formed by first apertures and second apertures are present. 
     
     
       16. A charged particle beamlet lithography system comprising:
 a source of charged particles for producing a beam of charged particles; 
 an aperture array for producing a plurality of beamlets from the charged particle beam; 
 a beamlet conditioning system for conditioning the plurality of beamlets in accordance with a pattern; and 
 the electrostatic lens array according to  claim 13  for focusing the plurality of beamlets. 
 
     
     
       17. The charged particle beamlet lithography system of  claim 16 , wherein said electrostatic lens array is positioned between said aperture array and said beamlet conditioning system. 
     
     
       18. The charged particle beamlet lithography system of  claim 16 , wherein said charged particle beamlet lithography system further comprises a support unit for supporting a substrate to be patterned and said electrostatic lens array is positioned downstream of said beamlet conditioning system for focusing a plurality of conditioned beamlets on a target surface of the substrate. 
     
     
       19. A method of manufacturing an insulating structure for use in an electrostatic lens, the method comprising:
 providing a first insulating plate; 
 manufacturing at least one first through hole in said first insulating plate, said at least one first through hole having a first diameter; 
 depositing a conductive layer on a surface of the first insulating plate; 
 providing a second insulating plate; 
 manufacturing at least one second through hole in said second insulating plate, said at least one second through hole having a second diameter, said second diameter being larger than said first diameter; and 
 combining the first insulating plate and the second insulating plate to form an insulating structure with the at least one first through hole and the at least one second through hole aligned such that said insulating structure has at least one aperture formed by said at least one first and second through holes, and such that the conductive layer is provided on a surface of the insulating structure. 
 
     
     
       20. The method of  claim 19 , wherein the first insulating plate and the second insulating plate are made of the same insulating material. 
     
     
       21. The method of  claim 19 , wherein at least one of the first insulating plate and the second insulating plate comprises borosilicate glass. 
     
     
       22. The method according to  claim 19 , wherein at least one of the manufacturing the at least one first through hole and the manufacturing the at least one second through hole is performed by power blasting. 
     
     
       23. An insulating structure for use in an electrostatic lens manufactured according to the method of  claim 19 . 
     
     
       24. An electrostatic lens array comprising:
 a first conductive plate provided with a plurality of first apertures;   a second conductive plate provided with a plurality of second apertures, the second apertures being substantially aligned with the first apertures;   a voltage supply for supplying a first voltage to the first conductive plate and a second voltage to the second conductive plate, the first voltage being lower than the second voltage with respect to intended function of the lens; and   an insulating structure for separating the first conductive plate from the second conductive plate,   wherein the insulating structure is provided with a third aperture, the third aperture comprising side walls, wherein the third aperture is arranged such that a projection of the side walls circumscribes multiple of said first apertures and said second apertures,   and wherein the insulating structure comprises a first portion in contact with the first conductive plate and a second portion in contact with the second conductive plate, the first portion having an overhanging portion contacting said first conductive plate and the second portion having an indented portion at an edge of the insulating structure, and wherein a gap is formed between the overhanging portion and the second conductive plate.   
     
     
       25. Electrostatic lens array according to claim 24, wherein the surface of the insulating structure facing the first conductive plate is provided with a conductive layer in electrical contact with the first conductive plate for limiting electric field enhancement between the first conductive plate and the insulating structure. 
     
     
       26. The electrostatic lens array of claim 25, wherein the conductive layer is deposited on a surface of the insulating structure using a deposition technique. 
     
     
       27. The electrostatic lens array of claim 25, wherein said conductive layer comprises chromium or tantalum. 
     
     
       28. The electrostatic lens array according to claim 24, wherein the edges of the first apertures facing the second apertures are rounded. 
     
     
       29. The electrostatic lens array of claim 24, wherein the permittivity of the gap is lower than the permittivity of the insulating structure. 
     
     
       30. The electrostatic lens array of claim 24, wherein, in operation, the electric field strength in the gap between the overhanging portion of the insulating structure and the second conductive plate is greater than the electric field strength across the second portion of the insulating structure. 
     
     
       31. The electrostatic lens array of claim 24, wherein the first portion and the second portion of the insulating structure are of equal thickness. 
     
     
       32. The electrostatic lens array of claim 24, wherein a distance between the first conductive plate and the second conductive plate lies in a range from about 100 to 200 μm. 
     
     
       33. The electrostatic lens array of claim 24, wherein the lens is capable of withstanding a field strength of over 10 V/μm without flashover. 
     
     
       34. The electrostatic lens array of claim 24, wherein the insulating structure comprises borosilicate glass.