Electron beam exposure system

Abstract

The invention relates to an electron beam exposure apparatus for transferring a pattern onto the surface of a target, comprising: a beamlet generator for generating a plurality of electron beamlets; a modulation array for receiving said plurality of electron beamlets, comprising a plurality of modulators for modulating the intensity of an electron beamlet; a controller, connected to the modulation array for individually controlling the modulators, an adjustor, operationally connected to each modulator, for individually adjusting the control signal of each modulator; a focusing electron optical system comprising an array of electrostatic lenses wherein each lens focuses a corresponding individual beamlet, which is transmitted by said modulation array, to a cross section smaller than 300 nm, and a target holder for holding a target with its exposure surface onto which the pattern is to be transferred in the first focal plane of the focusing electron optical system.

The invention claimed is: 
     
       1. A method for transferring a pattern onto a target exposure surface with a multi-beam lithography system, comprising the steps of:
 generating a plurality of beamlets; 
 individually modulating the intensity of each beamlet of said plurality of beamlets by means of a modulator device for blanking or not blanking each beamlet in whole or in part; 
 controlling said modulator device, using control signals, by means of a controller operationally coupled to said modulator; and  
 individually adjusting at least one of said control signals. 
 
     
     
       2. The method according to  claim 1  in which timing of said control signals is adjusted. 
     
     
       3. The method of  claim 1 , in which timing of said control signals is individually adjusted. 
     
     
       4. The method according to  claim 1  in which modulation is performed as an “off” or “on” condition of a beamlet, by either deflecting said beamlet within the system, or by allowing free passage of said beamlet at said modulator, the condition thereby being controlled on the basis of available electronic pattern data, in which timing is adjusted by correcting an instance of deflection or passage of said beamlet, said correction being calculated by the controller. 
     
     
       5. The method of  claim 1 , wherein said control signals having have a timing base, and timing of the control signal of at least one beamlet is adjusted. 
     
     
       6. The method of  claim 1 , further comprising the step of determining a position of a beamlet, storing said position in a memory and comparing said position with a desired position. 
     
     
       7. The method of  claim 6 , wherein said position of a beamlet is the actual position of a beamlet on said exposure surface. 
     
     
       8. The method of  claim 6 , wherein said adjustment of said timing is based on the result of said comparing. 
     
     
       9. The method of claim  1  2, wherein said timing is adjusted locally. 
     
     
       10. The method of claim  1  2, wherein said adjusting of timing of said control signals comprises correcting a timing window. 
     
     
       11. The method of claim  1  2, wherein said control signals have a timing base. 
     
     
       12. The method of  claim 11 , wherein said controller calculates a corrected timing window, and applies said corrected timing window to said timing base. 
     
     
       13. The method of  claim 11 , wherein said controller calculates a corrected timing window, and applies said corrected timing window to said timing base of an individual beamlet. 
     
     
       14. An electron beam exposure apparatus for transferring a pattern onto the surface of a target using a plurality of electron beamlets, comprising:
 a modulator array for receiving said plurality of electron beamlets, comprising a plurality of modulators for modulating the intensity of a beamlet of said plurality of beamlets; 
 a controller, operationally coupled to said modulator array, for controlling each modulator of said plurality modulators on the basis of electronic pattern data to write the pattern, said controller producing a plurality of control signals with at least one control signal for each modulator, and an adjustor for allowing individual adjustment of a control signal. 
 
     
     
       15. The electron beam exposure apparatus according to  claim 14 , wherein said plurality of control signals having have a timing base. 
     
     
       16. The electron beam exposure apparatus according to  claim 14 , wherein said adjustor is adapted for allowing individual adjustment of timing of a control signal. 
     
     
       17. The electron beam exposure apparatus according to  claim 14 , furthermore provided with a measuring device for measuring the actual position of at least one of said beamlets, and wherein the controller is provided with a memory for storing said actual position and a desired position, a comparator for comparing the desired position and the actual position of said at least one of said beamlets, and wherein the adjustor is operationally coupled to the controller for receiving instructions for adjusting a control signal issued to a modulator to compensate for the difference between said desired position and said actual position of said at least one of said electron beamlets. 
     
     
       18. The electron beam exposure apparatus according to  claim 14 , wherein the adjustor is operationally coupled to the controller for receiving instructions indicating the amount of the adjustments. 
     
     
       19. The electron beam exposure apparatus of  claim 14 , wherein the adjustor is adapted for adjusting timing of each control signal. 
     
     
       20. The electron beam exposure apparatus of  claim 14 , further comprising a beamlet generator, said beamlet generator comprising:
 a source for emitting at least one electron beam, and  
 at least one beamsplitter for splitting said at least one emitted electron beam into said plurality of electron beamlets. 
 
     
     
       21. The electron beam exposure apparatus according to  claim 20 , further comprising a modulation array, comprising a beamlet blanker array comprising a plurality of beamlet blankers for the deflection of a passing electron beamlet and a beamlet stop array, having a plurality of apertures aligned with said beamlet blankers of said beamlet blanker array. 
     
     
       22. The electron beam exposure apparatus according to claim  20  21, further comprising a second electrostatic lens array located between said beamsplitter and said beamlet blanker array to focus said plurality of electron beamlets. 
     
     
       23. The electron beam exposure apparatus according to  claim 22 , wherein said beamlet blanker array is located in the focal plane of said second electrostatic lens array. 
     
     
       24. An electron beam exposure apparatus for transferring a pattern onto the surface of a target using a plurality of electron beamlets, comprising:
 a modulator array for receiving said plurality of electron beamlets, comprising a plurality of modulators for modulating the intensity of a beamlet of said plurality of beamlets; and  
 a controller, operationally coupled to said modulator array, for controlling each modulator of said plurality modulators on the basis of electronic pattern data to write the pattern, said controller producing a plurality of control signals with at least one control signal for each modulator, said controller comprising an adjustor allowing individual adjustment of at least one control signal. 
 
     
     
       25. The electron beam exposure apparatus of  claim 24 , wherein said plurality of control signals having have a timing base. 
     
     
       26. The electron beam exposure apparatus of  claim 24 , said adjustor allowing individual adjustment of timing of at least one control signal. 
     
     
       27. An electron beam exposure apparatus for transferring a pattern onto the surface of a target using a plurality of electron beamlets, comprising:
 a modulator array comprising a plurality of modulators for modulating the intensity of a beamlet of said plurality of beamlets; 
 a scanning deflector for scanning said plurality of electron beamlets over said surface of said target, comprising at least one array of electrostatic deflectors having at least one electrostatic deflector for each beamlet; 
 a controller, operationally coupled to said scanning deflector, for controlling each electrostatic deflector individually using a control signal; and  
 an adjustor for adusting adjusting said control signal. 
 
     
     
       28. The electron electron beam exposure apparatus of  claim 27 , wherein said control signal has a timing base, and said adjustor being adapted for adjusting timing of said control signal. 
     
     
       29. An electron beam exposure apparatus for transferring a pattern onto the surface of a target using a plurality of electron beamlets, comprising:
 a scanning deflector for scanning said plurality of electron beamlets over said surface of said target; 
 a beamlet blanking array, comprising at least one array of electrostatic deflectors having at least one electrostatic deflector for each beamlet for blanking beamlets on the basis of electronic pattern data; 
 a controller, operationally coupled to said scanning deflector beamlet blanking array, for controlling each electrostatic deflector using a control signal, said controller being adapted for adjusting at least one of the control signal signals. 
 
     
     
       30. The electron beam exposure apparatus of  claim 29 , wherein said controller is operationally coupled to said scanning deflector beamlet blanking array for controlling each electrostatic deflector using a control signal having a timing base. 
     
     
       31. The electron beam exposure apparatus of  claim 29 , wherein said controller being adapted for adjusting timing of at least one control signal so that said pattern data is applied when the corresponding beamlet enters a desired area to be written by the beamlet. 
     
     
       32. The electron beam exposure apparatus of  claim 29 , wherein said controller generates a plurality of control signals, at least one control signal for each electrostatic deflector. 
     
     
       33. The electron beam exposure apparatus of  claim 32 , wherein said controller is adapted for adjusting timing of each control signal. 
     
     
       34. The electron beam exposure apparatus of  claim 32 , wherein said controller is adapted for adjusting timing of each control signal individually. 
     
     
       35. An electron beam exposure apparatus for transferring a pattern onto the surface of a target using a plurality of electron beamlets, comprising:
 a blanking deflection means for effectively realising an off/on condition for individual beamlets at said target surface, by deflecting such individual beamlets within the system; 
 a controller, operationally coupled to said blanking deflection means, for individually controlling electrostatic deflectors of said blanking deflection means, said controller using an individual control signal for each deflector of said deflection means, thereby determining said on and off condition for individual beamlets; 
 correction means, part of, or operationally associated with said controller for individually correcting a timing window of a beamlet adjusting the control signal of the blanking deflector for said beamlet. 
 
     
     
       36. An electron beam exposure apparatus for transferring a pattern onto the surface of a target using a plurality of electron beamlets, comprising:
 a blanking deflection device for effectively realising an off/on condition for individual beamlets at said target surface, comprising a plurality of deflectors for deflecting such individual beamlets within the system for realising said off/on condition; 
 a controller, operationally coupled to said blanking deflection device, for individually controlling electrostatic deflectors of said blanking deflection device, said controller using an individual control signal for each deflector of said deflection device, thereby determining said on and off condition for individual beamlets; 
 a correction device, part of, or operationally associated with said controller for individually correcting a timing window of a beamlet adjusting the control signal of the blanking deflector for said beamlet. 
 
     
     
       37. The method according to claim 4, wherein said modulation is controlled on the basis of available electronic pattern data in which timing is adjusted by correcting an instance of deflection or passage of said beamlet, said correction being calculated by the controller. 
     
     
       38. A maskless lithography system for transferring a pattern onto the surface of a target, comprising:
 an electron beam generator for generating an electron beam;   an optical system and beam splitter for generating a plurality of separate beamlets from the electron beam;   a modulation array for modulating individual beamlets on the basis of electronic pattern data to write the pattern; and   a focusing electron optical system for projecting the beamlets onto the target and reducing the cross section of the individual beamlets;   wherein said beamlets projected onto the target are maintained separate to each other until projection of said beamlets on to said target.   
     
     
       39. The system according to claim 38, wherein said system further includes, downstream of said beam splitter, a condensor lens array for focusing individual beamlets within said plurality of beamlets. 
     
     
       40. The system according to claim 39, wherein said individual beamlets are focused to a diameter in a range from about 0.1 to 1 μm. 
     
     
       41. The system according to claim 39, wherein the condensor lens array comprises two aligned plates with holes. 
     
     
       42. The system according to claim 41, wherein the thickness of the plates is within a range from about 10 to 500 μm. 
     
     
       43. The system according to claim 41, wherein the condensor lens array comprises a plate with holes of a diameter within a range from 50 to 200 μm, and a pitch within a range from about 50 to 500 μm. 
     
     
       44. The system according to claim 41, wherein the system further comprises insulators for supporting said plates. 
     
     
       45. The system according to claim 38, wherein said modulation array includes a beamlet blanker array and a beamlet stop array. 
     
     
       46. The system according to claim 45, wherein said modulation means is included between said beam splitter and said projection lenses. 
     
     
       47. The system according to claim 45, wherein the beam diameter is within the range from about 0.1 to 5 μm at the beamlet blanker array. 
     
     
       48. The system according to claim 45, wherein the transversal energy at said beamlet blanker array is within the range from about 1 to 20 meV. 
     
     
       49. The system according to claim 45, wherein the beamlet blanker array comprises an array of electrostatic deflectors, each electrostatic deflector comprising a first electrode connected to ground and a second electrode connected to a circuit receiving control data. 
     
     
       50. The system according to claim 49, wherein each electrostatic deflector is controlled individually. 
     
     
       51. The system according to claim 45, wherein the beamlet blanker array is located in an electrostatic focal plane of the plurality of beamlets. 
     
     
       52. The system according to claim 51, wherein the beamlet stop array is positioned outside an electrostatic focal plane of the plurality of beamlets. 
     
     
       53. The system according to claim 38, wherein the focusing electron optical system comprises an array of electrostatic lenses for focusing each individual beamlet within said plurality of beamlets with a corresponding electrostatic lens. 
     
     
       54. The system according to claim 53, wherein the array of electrostatic lenses comprises two or more plates, each plate having a thickness within a range from about 10 to 500 μm. 
     
     
       55. The system according to claim 53, wherein the array of electrostatic lenses comprises two or more plates, the distance between consecutive plates being within a range from 50 to 800 μm. 
     
     
       56. The system according to claim 53, wherein the array of electrostatic lenses comprises three or more plates, the distance between consecutive plates being different from plate to plate. 
     
     
       57. The system according to claim 38, wherein the focusing electron optical system comprises a lens array of the magnetic type. 
     
     
       58. The system according to claim 45, wherein the focusing electron optical system comprises a lens array of the magnetic type and an array of electrostatic lenses, the lens array of the magnetic type being located between the beamlet stop array and the array of electrostatic lenses. 
     
     
       59. The system according to claim 57, wherein the lens array of the magnetic type is included for enhancing the focusing properties of the projection system. 
     
     
       60. The system according to claim 38, wherein the beam splitter is formed by a spatial filter. 
     
     
       61. The system according to claim 58, wherein the spatial filter is formed by an aperture array. 
     
     
       62. The system according to claim 61, wherein the apertures of the aperture array are arranged in a hexagonal structure. 
     
     
       63. The system according to claim 61, wherein each aperture of the aperture array has an area inversely proportional to the current density of a beamlet that is, in use, transmitted through said aperture. 
     
     
       64. The system according to claim 38, wherein the beam splitter comprises an electrostatic quadruple lens array. 
     
     
       65. The system according to claim 38, wherein the beam splitter comprises a number of aperture arrays in series along the path of the electron beam or plurality of beamlets, the aperture arrays having mutually aligned apertures, each subsequent aperture array along the path from electron beam generator to target having apertures being smaller than corresponding apertures of the previous array. 
     
     
       66. The system according to claim 38, wherein, along a beamlet path from electron beam generator to target, an electrostatic lens array is located immediately after said beam splitter. 
     
     
       67. The system according to claim 38, the system further comprising:
 a beamlet blanker array for controllably deflecting individual beamlets of said plurality of beamlets; and   a beamlet stop array for obstructing deflected beamlets and letting through undeflected beamlets.   
     
     
       68. The system according to claim 67, wherein the beamlet blanker array is located in a focal plane of an electrostatic lens array for focusing said plurality of beamlets. 
     
     
       69. The system according to claim 38, wherein said beamlets projected onto the target are maintained parallel to one another. 
     
     
       70. A deflection system for deflecting a plurality of electron beamlets with respect to a target surface, the deflection system comprising:
 a first deflector array for deflecting the beamlets in a first direction; and   a second deflector array for deflecting the beamlets in a second direction, the second direction being opposite to the first direction.   
     
     
       71. The deflection system according to claim 70, wherein, in use, combined deflection of a beamlet by said first deflector array and said second deflector array results in displacement of the beamlet at the target surface without changing an orientation of the beamlet with respect to the target surface. 
     
     
       72. The deflection system according to claim 71, wherein said orientation of the beamlet is perpendicular to the target surface. 
     
     
       73. A maskless lithography system for transferring a pattern onto a surface of a target, comprising:
 a beamlet generator for generating a plurality of electron beamlets;   a modulation array for modulating an intensity of electron beamlets of the plurality of electron beamlets;   a deflection system according to claim 70 for deflecting the modulated electron beamlets;   a target holder for holding a target having a surface for receiving the pattern to be transferred.   
     
     
       74. The system according to claim 73, wherein the system further comprises an electron optical system for focusing the modulated electron beamlets on the surface of the target. 
     
     
       75. The system according to claim 73, wherein the deflection system is positioned within the electron optical system such that deflection occurs in a front focal plane of the electron optical system. 
     
     
       76. An electron-optical arrangement for use in a maskless lithography system, the arrangement comprising:
 a deflector system according to claim 70 for deflecting a plurality of beamlets; and   an electrostatic lens array for focusing said plurality of deflected beamlets;   wherein the deflector array is positioned in a front focal plane of the electrostatic lens array.   
     
     
       77. The arrangement according to claim 76, wherein the electrostatic lens array comprises two or more plates, and the deflector array is formed by deposition of electrostatic scan deflectors on a target surface side of one of the two or more plates of the electrostatic lens array. 
     
     
       78. The arrangement according to claim 76, wherein the electrostatic lens array comprises two or more plates, each plate having a thickness within a range from about 10 to 500 μm. 
     
     
       79. The arrangement according to claim 76, wherein the electrostatic lens array comprises two or more plates, the distance between consecutive plates being within a range from about 50 to 800 μm. 
     
     
       80. The arrangement according to claim 76, wherein the electrostatic lens array comprises three or more plates, the distance between consecutive plates being different from plate to plate. 
     
     
       81. A method of displacement of a plurality of beamlets with respect to a target surface, the method comprising:
 deflecting the beamlets in a first direction by means of a first deflector array;   deflecting the beamlets in a second, opposite direction by means of a second deflector array.   
     
     
       82. The method according to claim 81, wherein the combined deflection in the first direction and the second direction results in displacement of the beamlet at the target surface without changing an orientation of the beamlet with respect to the target surface. 
     
     
       83. The method according to claim 82, wherein the orientation of the beamlet after the combined deflection is perpendicular to the target surface. 
     
     
       84. The method according to claim 81, wherein the plurality of beamlets are parallel with respect to each other before the first deflecting step and after the second deflecting step. 
     
     
       85. The method according to claim 81, further comprising
 providing an electrostatic lens array positioned so that the deflector arrays are in a front focal plane of the electrostatic lens array; and   focusing the plurality of beamlets with the electrostatic lens array.   
     
     
       86. A maskless lithography system for transferring a pattern onto the surface of a target, comprising:
 an electron beam generator for generating an electron beam;   a beam splitter for splitting the electron beam into a plurality of electron beamlets;   a modulation array for modulating the plurality of beamlets on the basis of electronic pattern data in accordance with the pattern to be transferred;   an array of electrostatic scan deflectors for deflecting electron beamlets to scan the target surface, wherein the array of electrostatic scan deflectors comprise scan deflection electrodes, each scan deflection electrode being arranged to deflect a group of electron beamlets in the same direction;   an optical system for focusing the plurality of beamlets;   a target holder for holding a target with its surface onto which the pattern is to be transferred in a focal plane of the optical system.   
     
     
       87. The maskless lithography system according to claim 86, wherein the deflection electrodes are electrodes deposited on a plate. 
     
     
       88. The maskless lithography system according to claim 87, wherein the deflection electrodes are deposited on the side of the plate facing the target holder. 
     
     
       89. The maskless lithography system according to claim 86, wherein the deflection electrodes comprise strips. 
     
     
       90. The maskless lithography system according to claim 86, wherein the modulation array comprises an array of apertures, and the deflection electrodes are positioned close to said apertures. 
     
     
       91. The maskless lithography system according to claim 90, wherein the deflection electrodes are positioned in a front focal plane of the electrostatic lenses. 
     
     
       92. The maskless lithography system according to claim 86, wherein the scan deflection electrodes comprise a first group of strips and a second group of strips, the first group of strips being arranged to scan in a first direction, the second group of strips being arranged to scan in a second direction. 
     
     
       93. The system according to claim 86, wherein the deflection electrodes are in the form of strips. 
     
     
       94. The system according to claim 93, wherein alternating voltages are located on consecutive strips. 
     
     
       95. The maskless lithography system according to claim 92, wherein the direction is opposite to the second direction. 
     
     
       96. A maskless lithography system for transferring a pattern onto the surface of a target, comprising:
 an electron beam generator for generating an electron beam;   an electron-optical arrangement; and   a target holder for holding a target provided with a surface for receiving the pattern to be transferred;   wherein the electron-optical arrangement comprises:
 a beam splitter for splitting the electron beam into a plurality of beamlets; 
 a first electrostatic lens array for focusing the beamlets; 
 a modulation array comprising a plurality of modulators for modulating the beamlets on the basis of electronic pattern data to write the pattern; 
 a deflector array comprising a plurality of electrostatic deflectors for deflecting a portion of the beamlets in a predetermined direction; 
 a second electrostatic lens array for focusing the deflected beamlets. 
   
     
     
       97. The maskless lithography system according to claim 96, wherein the beam splitter comprises an aperture array having apertures arranged in a hexagonal pattern. 
     
     
       98. The maskless lithography system according to claim 96, wherein said beam splitter comprises an aperture array having about 5,000 to 30,000 apertures. 
     
     
       99. The maskless lithography system according to claim 96, wherein said beam splitter comprises an aperture array having apertures with a size adjusted to compensate for non-uniform current density of said electron beam. 
     
     
       100. The maskless lithography system according to claim 99, wherein each aperture has an area inversely proportional to a current density based on the respective beamlet to be transmitted through said aperture. 
     
     
       101. The maskless lithography system according to claim 96, wherein said beam splitter comprises a number of aperture arrays in series along a path of the electron beam or plurality of beamlets, the aperture arrays having mutually aligned apertures, each subsequent aperture array along the path towards the first electrostatic lens array having apertures that are smaller than the apertures of a previous aperture array. 
     
     
       102. The maskless lithography system according to claim 96, wherein said first electrostatic lens array is arranged to focus individual beamlets within the plurality of beamlets to a diameter in a range from about 0.1 to 1 μm. 
     
     
       103. The maskless lithography system according to claim 102, wherein the first electrostatic lens array comprises two aligned plates with holes. 
     
     
       104. The maskless lithography system according to claim 103, wherein the thickness of the plates is within a range from about 10 to 500 μm. 
     
     
       105. The maskless lithography system according to claim 103, wherein the holes have a diameter within a range from about 50 to 200 μm, and a pitch within a range from 50 to 500 μm. 
     
     
       106. The maskless lithography system according to claim 103, wherein the first electrostatic lens array further comprises insulators for supporting said plates. 
     
     
       107. The maskless lithography system according to claim 96, wherein the modulation array comprises:
 a beamlet blanker aperture array provided with said modulators, said modulators being further electrostatic deflectors for deflecting beamlets in a further predetermined direction;   a beamlet stop array for terminating beamlets deflected by the further electrostatic deflectors of the beamlet blanker array.   
     
     
       108. The maskless lithography system according to claim 107, wherein the first electrostatic lens array is arranged to focus individual beamlets within the plurality of beamlets to a diameter in a range from about 0.1 to 5 μm at the beamlet blanker array. 
     
     
       109. The maskless lithography system according to claim 107 wherein the beamlet blanker array is located in an electrostatic focal plane of the plurality of electron beamlets. 
     
     
       110. The maskless lithography system according to claim 109, wherein the beamlet stop array is positioned outside a focal plane of the plurality of electron beamlets. 
     
     
       111. The maskless lithography system according to claim 107, wherein each further electrostatic deflector comprises a first electrode connected to ground, and a second electrode connected to a circuit for receiving control data. 
     
     
       112. The maskless lithography system according to claim 96, wherein the second electrostatic lens array comprises two or more plates, each plate having a thickness within a range from about 10 to 500 μm. 
     
     
       113. The maskless lithography system according to claim 96, wherein the second electrostatic lens array comprises two or more plates, the distance between consecutive plates being within a range from 50 to 800 μm. 
     
     
       114. The maskless lithography system according to claim 96, wherein the second electrostatic lens array comprises three or more plates, the distance between consecutive plates being different from plate to plate. 
     
     
       115. A method of cleaning an electron optical system comprising an electron beam generator for generating an electron beam, a target holder for holding a target on to which one or more beamlets are to be projected, and at least one of:
 a beam splitter for splitting the electron beam into a plurality of beamlets;   one or more electrostatic lens arrays for focusing the beam or beamlets;   a modulation array comprising a plurality of modulators for modulating the beam or beamlets;   a deflector array comprising a plurality of electrostatic deflectors for deflecting the beam or a portion of the beamlets in a predetermined direction; and   a second electrostatic lens array for focusing the deflected beamlets;   the system further comprising a power supply connected to at least one of the beam splitter, the first electrostatic lens array, the modulation array, the deflector array, and the second electrostatic lens array;   wherein the method comprises:   admitting a gas into the electron optical system;   supplying power by means of the power supply to the electron optical system for creating a plasma therein;   terminating said supplying of power; and   removing said gas from the electron optical system.   
     
     
       116. The method according to claim 115, wherein said gas comprises oxygen. 
     
     
       117. The method according to claim 116, the method further comprising:
 adding a further gas for removal of oxides into the maskless lithography system;   resupplying power to the maskless lithography system;   terminating said resupplying of power; and   removing said further gas from the maskless lithography system.   
     
     
       118. The method according to claim 117, wherein said further gas comprises HF. 
     
     
       119. A method for transferring a pattern onto the surface of a target, comprising:
 generating a plurality of electron beamlets;   modulating the plurality of beamlets on the basis of electronic pattern data in accordance with the pattern to be transferred;   providing an array of electrostatic scan deflectors having electrodes in the form of strips;   deflecting the electron beamlets using the array of electrostatic scan deflectors to scan the target surface; and   focusing the plurality of beamlets onto the target surface onto which the pattern is to be transferred.   
     
     
       120. The method according to claim 119, further comprising: creating relative movement in a first direction between the plurality of beamlets and the target; and wherein the step of providing an array of electrostatic scan deflectors comprises providing strips oriented in a direction corresponding to the first direction. 
     
     
       121. The method according to claim 119, further comprising: creating relative movement in a first direction between the plurality of beamlets and the target; and wherein the step of deflecting the electron beamlets comprises deflecting the beamlets in a direction different from the first direction. 
     
     
       122. The method according to claim 119, wherein the step of deflecting the electron beamlets comprises applying alternating voltages on consecutive strips of the electrostatic scan deflector electrodes. 
     
     
       123. The method according to claim 119, wherein the step of providing an array of electrostatic scan deflectors comprises providing a first group of strips and a second group of strips, the first group of strips being arranged to scan in a first direction, the second group of strips being arranged to scan in a second direction. 
     
     
       124. The method according to claim 123, wherein the first direction is opposite to the second direction. 
     
     
       125. A method of operating an electron optical system comprising an electron beam generator for generating an electron beam, a target holder for holding a target on to which one or more beamlets are to be projected, and at least one of:
 a beam splitter for splitting the electron beam into a plurality of beamlets;   one or more electrostatic lens arrays for focusing the beam or beamlets;   a modulation array comprising a plurality of modulators for modulating the beam or beamlets;   a deflector array comprising a plurality of electrostatic deflectors for deflecting the beam or a portion of the beamlets in a predetermined direction; and   a second electrostatic lens array for focusing the deflected beamlets;   the method comprising operating the system at an elevated temperature.   
     
     
       126. The method according to claim 125, wherein oxygen is admitted to the system. 
     
     
       127. The method according to claim 125, wherein operating the system is performed at a temperature above 150 C. 
     
     
       128. The method according claim 125, wherein operating the system is performed at a temperature below 400 C. 
     
     
       129. The method according to claim 125, wherein the operating temperature is elevated sufficiently to effect a reduction of contamination of the system. 
     
     
       130. The method according to claim 129, further comprising preheating the electron optical system at a temperature between 1000 and 1500 C. 
     
     
       131. A method of operating an electron optical system comprising an electron beam generator for generating an electron beam, a target holder for holding a target on to which one or more beamlets are to be projected, and at least one of:
 a beam splitter for splitting the electron beam into a plurality of beamlets;   one or more electrostatic lens arrays for focusing the beam or beamlets;   a modulation array comprising a plurality of modulators for modulating the beam or beamlets;   a deflector array comprising a plurality of electrostatic deflectors for deflecting the beam or a portion of the beamlets in a predetermined direction; and   a second electrostatic lens array for focusing the deflected beamlets;   the method comprising the step of admitting oxygen to the system during operation.