The invention relates to an electron beam exposure apparatus for transferring a pattern onto the surface of a target, comprising:
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0. 62. An electron-optical arrangement, comprising:
a first electrostatic lens array for focusing a plurality of beamlets;
a modulation array provided downstream from the first electrostatic lens array, and comprising a plurality of modulators for modulating the beamlets;
a deflector array comprising a plurality of electrostatic deflectors for deflecting a portion of the beamlets in a predetermined direction; and
a second electrostatic lens array for focusing the deflected beamlets.
0. 82. An electron-optical arrangement, comprising:
an electron source for emitting an electron beam;
an illumination system for collimating the electron beam;
a beam splitter for generating beamlets from the electron beam;
an array of electrostatic lenses for focusing the beamlets; and
a demagnifying lens arrangement, receiving the focused beamlets separated at a first pitch d1, directing the beamlets into at least one crossing, and projecting the beamlets on to a target surface at a pitch d2, wherein d2 is smaller than d1.
0. 37. A method of exposing a pattern on a target with a multi-beam lithography system, said pattern divided according to a grid forming grid cells, the method comprising:
providing a plurality of beamlets, the beamlets being arranged in an array;
providing a target to be exposed;
creating relative movement in a first direction between the plurality of beamlets and the target; and
moving the plurality of beamlets in a second direction, the second direction being different than the first direction;
wherein the method further comprises modulating each beamlet of the plurality of beamlets by means of control signals such that an exposure intensity of each grid cell is variable.
0. 49. A maskless lithography system for exposing a pattern in accordance with a grid forming grid cells on a target, comprising:
a beamlet generator for generating a plurality of electron beamlets, the beamlets being arranged in an array;
a target holder for holding a target having a surface for receiving the pattern to be transferred;
an actuator for creating relative movement in a first direction between the plurality of beamlets and the target holder;
a scan deflection array for moving the plurality of beamlets in a second direction, the second direction being different than the first direction;
a modulation array for modulating individual beamlets of the plurality of beamlets; and
a controller arranged to provide control signals to said modulation array such that an exposure intensity of each grid cell is variable.
0. 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;
controlling said modulator device, using control signals, by means of a controller operationally coupled to said modulator;
individually adjusting said control signals.
0. 2. The method according to
0. 3. The method of
0. 4. The method according to
0. 5. The method of
0. 6. The method of
0. 7. The method of
0. 8. The method of
0. 9. The method of
0. 10. The method of
0. 11. The method of
0. 12. The method of
0. 13. The method of
0. 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, 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.
0. 15. The electron beam exposure apparatus according to
0. 16. The electron beam exposure apparatus according to
0. 17. The electron beam exposure apparatus according to
0. 18. The electron beam exposure apparatus according to
0. 19. The electron beam exposure apparatus of
0. 20. The electron beam exposure apparatus of
a source for emitting at least one electron beam,
at least one beamsplitter for splitting said at least one emitted electron beam into said plurality of electron beamlets.
0. 21. The electron beam exposure apparatus according to
0. 22. The electron beam exposure apparatus according to
0. 23. The electron beam exposure apparatus according to
0. 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;
a controller, operationally coupled to said modulator array, for controlling each modulator of said plurality modulators, 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.
0. 25. The electron beam exposure apparatus of
0. 26. The electron beam exposure apparatus of
0. 27. 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, 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 using a control signal;
an adjustor for adusting said control signal.
0. 28. The electron electron beam exposure apparatus of
0. 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, 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 using a control signal, said controller being adapted for adjusting at least one control signal.
0. 30. The electron beam exposure apparatus of
0. 31. The electron beam exposure apparatus of
0. 32. The electron beam exposure apparatus of
0. 33. The electron beam exposure apparatus of
0. 34. The electron beam exposure apparatus of
0. 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.
0. 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.
0. 38. The method according to claim 37, wherein said modulating comprises discretely controlling a dose to be received at a corresponding grid cell.
0. 39. The method according to claim 37, wherein the multibeam lithography system comprises a beamlet stop array, and wherein said modulating comprises deflecting a beamlet of the plurality of beamlets by a variable amount in accordance with a corresponding control signal such that a controlled part of the beamlet passes the beamlet stop array.
0. 40. The method according to claim 39, wherein said deflecting is controlled so that discrete portions of the beamlet pass the beamlet stop array.
0. 41. The method according to claim 40, wherein the discrete parts correspond to 0, ⅓, ⅔ and 1 times a maximum dose provided by a single beamlet.
0. 42. The method according to claim 37, wherein said modulating comprises deflecting a beamlet of the plurality of beamlets by a variable amount in accordance with a corresponding control signal so that the beamlet does not move with respect to the target for a predetermined amount of time.
0. 43. The method according to claim 42, wherein said predetermined time is longer than a minimum control time of the beamlet blanker array.
0. 44. The method according to claim 43, wherein said predetermined time equals a discrete multiple of the control time.
0. 45. The method according to claim 37, wherein providing a plurality of beamlets comprises providing an electron beam to an aperture array so that a plurality of beamlets of different sizes is formed.
0. 46. The method according to claim 45, wherein the multibeam lithography system further comprises a beamlet blanker array provided with a plurality of modulators controllable by said control signals and a beamlet stop array, and wherein said modulating includes deflecting each beamlet of the plurality of beamlets by means of a corresponding modulator in accordance with a corresponding control signal such that a deflected beamlet is blocked by the beamlet stop array.
0. 47. The method according to claim 45, wherein the aperture array is provided with apertures of three different aperture sizes, a first size arranged to allow passage of a certain current; a second size arranged to allow passage of half the current; and a third size arranged to allow passage of a fourth of the current, and wherein the control signals related to a single grid cell are at least directed to control the current passing through an aperture of the first size, an aperture of the second size and an aperture of the third size.
0. 48. The method according to claim 37, wherein the first direction is perpendicular to the second direction.
0. 50. The system according to claim 49, wherein the control signals provided by the controller discretely control a dose to be received at a corresponding grid cell.
0. 51. The system according to claim 49, wherein the modulation array comprises:
a beamlet blanker array provided with a plurality of modulators controllable by said controller; and
a beamlet stop array.
0. 52. The system according to claim 51, wherein a modulator of the plurality of modulators in said beamlet blanker array is arranged to deflect a corresponding beamlet of the plurality of beamlets in response to receipt of a corresponding control signal so that the deflected beamlet is blocked by the beamlet stop array.
0. 53. The system according to claim 51, wherein a modulator of the plurality of modulators in said beamlet blanker array, in response to receipt of a corresponding control signal, is arranged to deflect a corresponding beamlet of the plurality of beamlets by a variable amount so that a variable part of the beamlet passes the beamlet stop array.
0. 54. The system according to claim 51, wherein a modulator of the plurality of modulators in said beamlet blanker array is arranged to pass discrete portions of the beamlet through the beamlet stop array.
0. 55. The system according to claim 54, wherein the discrete parts correspond to 0, ⅓, ⅔ and 1 times a maximum dose provided by a single beamlet.
0. 56. The system according to claim 51, wherein the scan deflection array comprises a plurality of deflectors, and said controller is further arranged to provide control signals to said plurality of deflectors to deflect the beamlets such that, in use, the beamlets do not move with respect to the target for a predetermined amount of time.
0. 57. The system according to claim 56, wherein said predetermined time is longer than a minimum control time of the beamlet blanker array.
0. 58. The system according to claim 56, wherein said predetermined time equals a discrete multiple of the control time.
0. 59. The system according to claim 49, wherein the beamlet generator comprises an aperture array provided with apertures of different aperture size such that a plurality of beamlets of different sizes is formed.
0. 60. The system according to claim 59, wherein the aperture array is provided with apertures of three different aperture sizes, a first size arranged to allow passage of a certain current; a second size arranged to allow passage of half the current; and a third size arranged to allow passage of a fourth of the current, and wherein the control signals related to a single grid cell are at least directed to control the current passing through an aperture of the first size, an aperture of the second size and an aperture of the third size.
0. 61. The system according to claim 49, wherein the first direction is perpendicular to the second direction.
0. 63. The arrangement according to claim 62, wherein said beam splitter comprises an aperture array having apertures with diameters in the range of about 5-150 μm and with a pitch of about 50 to 500 μm.
0. 64. The arrangement according to claim 62, wherein said beam splitter comprises an aperture array having about 5,000 to 30,000 apertures.
0. 65. The arrangement according to claim 62, 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.
0. 66. The arrangement according to claim 65, wherein each aperture has an area inversely proportional to a current density based on the respective beamlet to be transmitted through said aperture.
0. 67. The arrangement according to claim 62, 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.
0. 68. The arrangement according to claim 62, 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.
0. 69. The arrangement according to claim 68, wherein the first electrostatic lens array comprises two aligned plates with holes.
0. 70. The arrangement according to claim 69, wherein the thickness of the plates is within a range from about 10 to 500 μm.
0. 71. The arrangement according to claim 69, 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.
0. 72. The arrangement according to claim 69, wherein the first electrostatic lens array further comprises insulators for supporting said plates.
0. 73. The arrangement according to claim 68, wherein each electrostatic deflector comprises a first electrode connected to ground, and a second electrode connected to a circuit for receiving control data.
0. 74. The arrangement according to claim 62, 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; and
a beamlet stop array for terminating beamlets deflected by the further electrostatic deflectors of the beamlet blanker array.
0. 75. The arrangement according to claim 74, 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.
0. 76. The arrangement according to claim 74, wherein the beamlet blanker array is located in an electrostatic focal plane of the plurality of electron beamlets.
0. 77. The arrangement according to claim 76, wherein the beamlet stop array is positioned outside a focal plane of the plurality of electron beamlets.
0. 78. The maskless lithography system according to claim 77, wherein the beam splitter comprises an aperture array having apertures with diameters in the range of about 5 to 150 μm and with a pitch of about 50 to 500 μm.
0. 79. The arrangement according to claim 62, further comprising a beam splitter for splitting an incoming electron beam to generate the plurality of beamlets.
0. 80. The arrangement according to claim 62, for use in a maskless lithography system for transferring a pattern onto the surface of a target.
0. 81. The arrangement according to claim 80, 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.
0. 83. The arrangement according to claim 82, wherein the beam splitter comprises an aperture array having apertures arranged in a hexagonal pattern.
0. 84. The arrangement according to claim 82, wherein the beam splitter comprises an aperture array having apertures with diameters in the range of about 5-150 μm and with a pitch of about 50 to 500 μm.
0. 85. The arrangement according to claim 82, wherein the beam splitter comprises an aperture array having about 5,000 to 30,000 apertures.
0. 86. The arrangement according to claim 82, wherein the beam splitter comprises an aperture array having apertures with a size adjusted to compensate for non-uniform current density of the electron beam.
0. 87. The arrangement according to claim 86, wherein each aperture has an area inversely proportional to a current density based on the respective beamlet to be transmitted through said aperture.
0. 88. The arrangement according to claim 82, wherein the 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.
0. 89. The arrangement according to claim 82, wherein the 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.
0. 90. The arrangement according to claim 89, wherein the electrostatic lens array comprises two aligned plates with holes.
0. 91. The arrangement according to claim 90, wherein the thickness of the plates is within a range from about 10 to 500 μm.
0. 92. The arrangement according to claim 90, 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.
0. 93. The arrangement according to claim 90, wherein the electrostatic lens array further comprises insulators for supporting the plates.
0. 94. The arrangement according to claim 82, wherein the modulation array comprises:
a beamlet blanker aperture array provided with the modulators, the modulators being further electrostatic deflectors for deflecting beamlets in a further predetermined direction; and
a beamlet stop array for terminating beamlets deflected by the further electrostatic deflectors of the beamlet blanker array.
0. 95. The arrangement according to claim 94, wherein the 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.
0. 96. The arrangement according to claim 94, wherein the beamlet blanker array is located in an electrostatic focal plane of the plurality of electron beamlets.
0. 97. The arrangement according to claim 94, wherein the beamlet stop array is positioned outside a focal plane of the plurality of electron beamlets.
0. 98. The arrangement according to claim 94, wherein each electrostatic deflector comprises a first electrode connected to ground, and a second electrode connected to a circuit for receiving control data.
0. 99. The arrangement according to claim 82, further comprising a second electrostatic lens array for projecting the beamlets onto the target surface, the second electrostatic lens array comprising two or more plates, each plate having a thickness within a range from about 10 to 500 μm.
0. 100. The arrangement according to claim 82, further comprising a second electrostatic lens array for projecting the beamlets onto the target surface, the second electrostatic lens array comprising two or more plates, and the distance between consecutive plates being within a range from 50 to 800 μm.
0. 101. The arrangement according to claim 82, further comprising a second electrostatic lens array for projecting the beamlets onto the target surface, the second electrostatic lens array comprising three or more plates, and the distance between consecutive plates being different from plate to plate.
0. 102. The arrangement according to claim 82, further comprising:
a modulation array comprising a plurality of modulators for modulating the beamlets;
a deflector array comprising a plurality of electrostatic deflectors for deflecting a portion of the beamlets in a predetermined direction; and
a second electrostatic lens array for focusing the deflected beamlets.
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Notice: More than one reissue application has been filed for the reissue of U.S. Pat. No. 7,091,504. These reissue applications are application Ser. No. 12/189,817 filed on Aug. 12, 2008 and reissued as U.S. Pat. No. Re. 44,240 E (the parent of this application), and Ser. No. 13/343,038 filed on Jan. 4, 2012 (this application) and Ser. No. 13/343,036 filed on Jan. 4, 2012 (filed currently with this application) which are divisional reissues of U.S. Pat. No. 7,091,504.
The present patent application is a Divisional of application Ser. No. 10/699,246 filed Oct. 30, 2003, now U.S. Pat. No. 6,897,458 which is a Non-Provisional of Provisional Application No. 60/422,758 filed Oct. 30, 2002.
Several kinds of electron beam exposure systems are known in the art. Most of these systems are provided to transfer very precise patterns onto an exposure surface of a substrate. Since lithography features are pushed to become smaller and smaller following Moore's law, the high resolution of electron beams could be used to continue the drive to even smaller features than today.
A conventional electron beam exposure apparatus has a throughput of about 1/100 wafer/hr. However, for lithography purposes a commercially acceptable throughput of at least a few wafers/hr is necessary. Several ideas to increase the throughput of an electron beam exposure apparatus have been proposed.
U.S. Pat. No. A1-5,760,410 and U.S. Pat. No. A1-6,313,476, for instance, disclose a lithography system using an electron beam having a cross section, which is modified during the transferring of a pattern to an exposure surface of a target. The specific cross section or shape of the beam is established during operation by moving the emitted beam inside an aperture by using electrostatic deflection. The selected aperture partially blanks and thereby shapes the electron beam. The target exposure surface moves under the beam to refresh the surface. In this way a pattern is written. The throughput of this system is still limited.
In US A1-20010028042, US-A1-20010028043 and US-A1-20010028044 an electron beam lithography system is disclosed using a plurality of electron beams by using a plurality of continuous wave (CW) emitters to generate a plurality of electron beamlets. Each beamlet is then individually shaped and blanked to create a pattern on the underlying substrate. As all these emitters have slightly different emission characteristics, homogeneity of the beamlets is a problem. This was corrected by levelling every individual beam current to a reference current. Correction values for the mismatch are extremely difficult to calculate and it takes a significant amount of time, which reduces the throughput of the system.
In Journal of Vacuum Science and Technology B18 (6) pages 3061-3066, a system is disclosed which uses one LaB6-source for generating one electron beam, which is subsequently, expands, collimated and split into a plurality of beamlets. The target exposure surface is mechanically moved relatively to the plurality of beamlets in a first direction, the beamlets are switched on and off using blanking electrostatic deflectors and at the same time scanning deflectors sweep the beamlets which have passed the blanker array over the target exposure surface in a direction perpendicular to the first direction, thus each time creating an image. In this known system, electrostatic and/or magnetic lenses are used to reduce the image before it is projected on the target exposure surface. In the demagnification process at least one complete intermediate image is created, smaller than the one before. When the entire image has the desired dimensions, it is projected on the target exposure surface. A major disadvantage of this approach is that the plurality of electron beamlets together has to pass through at least one complete crossover. In this crossover, Coulomb interactions between electron in different beamlets will disturb the image, thus reducing the resolution. Moreover, due to the strong demagnification of the image, the area that is exposed at one time is rather small, so a lot of wafer scans are needed to expose a die: 16 scans are needed to expose one die, requiring a very high stage speed for reaching a commercially acceptable throughput.
In GB-A1-2.340.991, a multibeam particle lithography system is disclosed having an illumination system, which produces a plurality of ion sub-beams. The illumination systems use either a single ion source with aperture plates for splitting a beam in sub-beams, or a plurality of sources. In the system using a single ion source, the aperture plate is projected (demagnified) on a substrate using a multibeam optical system. The system furthermore uses a deflection unit of electrostatic multipole systems, positioned after the multibeam optical system, for correcting individual imaging aberrations of a sub-beam and positioning the sub-beam during writing. The publication does not disclose how each sub-beam is modulated. Furthermore, controlling individual sub-beams is a problem, and maintaining inter-sub-beam uniformity.
In Jpn. J. Appl. Phys. Vol. 34 (1995) 6689-6695, a multi-electron beam (‘probes’) lithography system is disclosed having a specific ZrO/W-TFE thermal emission source with an emitter tip immersed in a magnetic field. A disadvantage of such a source is its limited output. Furthermore, this source needs a crossover. The mutual homogeneity of the ‘probes’ is not further discussed. Furthermore, the intensity of the source is a problem.
The article furthermore in a general way mentions a writing strategy in which a stage is moved in one direction, and deflectors move the ‘probes’ concurrently through the same distance perpendicular to the direction of the stage movement. A further problem, not recognised in this publication, is correction of deviation of electron beamlets from their intended positions.
It is an objective of the current invention to improve the performance of known electron beam exposure apparatus.
Another objective is to improve the resolution of known electron beam exposure apparatus.
Yet another objective of the current invention is to improve throughput of known electron beam exposure apparatus.
Yet another objective of the current invention is to overcome the problems related to Coulomb interactions and the demagnification methods in the prior art.
Another objective of the current invention is to simplify controlling uniformity of beamlets, especially during writing.
The invention relates to an electron beam exposure apparatus for transferring a pattern onto the surface of a target, comprising:
In this apparatus, electron crossover could be avoided, as it does not demagnify a complete (part of) an image. In this way, resolution and writing speed increases. Furthermore, it avoids the needs to control the current in each individual beamlet. The apparatus is less complex as the position correction and modulation are integrated.
In an embodiment of an electron beam exposure apparatus according to the present invention, said modulation array comprises:
In this way, it is possible to avoid crossover of electron beamlets in one single focal point, and make high-speed modulation possible. In an embodiment, substantially every beamlet blanker is aligned with an electron beamlet, in order to make it possible to individually modulate every beamlet. Furthermore, the beamlet stop array comprises at least one plane of apertures, substantially every aperture being aligned with one beamlet, preferably with an aperture centred with respect to a beamlet. In this way, a beamlet passes an aperture when an electron beamlet is not deflected, and a beamlet is blocked or stopped when the beamlet is deflected. In an embodiment of this modulation array, the controller is operationally connected to said beamlet blankers.
In an embodiment, the electron beam exposure apparatus is furthermore provided with measuring means for measuring the actual position of at least one of said beamlets, and the controller is provided with memory means for storing said actual position and a desired position, a comparator for comparing the desired position and the actual position of said beamlets, and wherein the adjustor is operationally connected to the controller for receiving instructions for adjusting the control signals issued to the modulators to compensate for the measured difference between said desired position and said actual position of said electron beamlets. In this way, by adjusting control signals, positioning of the beamlets can be corrected in an easy way. Measurement of the actual positions can for instance be done as described in U.S. Pat. No. A1-5,929,454.
In an embodiment, the controller is operationally connected to the beamlet blankers, in an embodiment via the adjustor.
In an embodiment, the adjustor is operationally connected to the controller for receiving instructions indicating the amount of the adjustments. The amount of the adjustments can be determined based a resulting value of the above-mentioned comparator.
In a further embodiment, the adjustor is adapted for individually adjusting timing of each control signal. In this very easy way, correction can be accomplished.
In an embodiment of the electron beam exposure apparatus according to the present invention, the beamlet generating means comprise:
In this way, a uniform intensity distribution among the beamlets is easily achieved if the source emits uniformly in all relevant directions. In an embodiment, the electron beam exposure apparatus further comprising a second electrostatic lens array located between said beam splitting means and said beamlet blanker array to focus said plurality of electron beamlets. In this embodiment, substantially every electrostatic lens is aligned and focuses one electron beamlet. In a further embodiment thereof, the beamlet blanker array is located in the focal plane of said second electrostatic lens array.
In an embodiment of the electron beam exposure apparatus of the current invention with beamsplitter, the beamsplitter comprise a spatial filter, preferably an aperture array. In this way, one source with one beam, or, when source intensity is insufficient or intensity fluctuates across the beam, several sources, are easily split into a plurality of beamlets.
When source intensities are high, the splitting means can comprise a number of aperture arrays in a serial order along the path of the electron beam or plurality of beamlets, the aperture arrays having mutually aligned apertures, each next aperture array along the path from the source to the target having apertures that are smaller than the apertures of the previous aperture array. This reduces heat load.
In an embodiment of the aperture array, the apertures of each aperture array are arranged in a hexagonal structure, which makes it possible to obtain close integration.
In a further embodiment of the electron beam exposure apparatus comprising splitting means comprising an aperture array, each aperture of the aperture array has an area inversely proportional to the current density based on the beamlet that is transmitted through that same aperture.
In a further embodiment of the electron beam exposure apparatus comprising a beamsplitter, the beamsplitter comprises an aperture array, wherein the aperture sizes in the aperture array are adapted to create a discrete set of predetermined beamlet currents.
These embodiments improve the uniformity of the electron beamlets.
In yet a further embodiment of the electron beam exposure apparatus comprising the beamsplitter, the beamsplitter comprises an electrostatic quadrupole lens array.
In an embodiment, the electron beam exposure apparatus according to the present invention comprises a thermionic source. In an embodiment, the thermionic source is adapted for being operated in the space charge limited regime. It was found that space charge has a homogenising effect, which is favourable in this specific application. Furthermore, in certain settings, the space charge may have a negative lens effect.
In a further embodiment with the thermionic source, the thermionic electron source has a spherical cathode surface. In an embodiment, the thermionic source comprises at least one extractor electrode. In another embodiment, the extractor electrode is a planar extractor electrode. In an embodiment thereof, the extractor is located after the space charge region and provided with a positive voltage for inducing a negative lens effect. These voltages can be set at a predefined value for creating a negative lens effect for the emitted electron beam.
In an alternative embodiment, the extractor electrode has a spherical surface with through holes. All these embodiments serve to create a negative lens influence on the electron beam, thus avoiding a crossover in the electron beam.
In another embodiment of the electron beam exposure apparatus of the current invention, the apparatus further comprises an illumination system that transforms the electron beam, emitted by said source, into a collimated electron beam before it reaches said splitting means.
In yet another embodiment of the electron beam exposure apparatus said beamlet generator comprises an array of sources of which each source is responsible for the generation of an electron beamlet. In a further embodiment thereof, the electron beam exposure apparatus further comprising a second electrostatic lens array located between said array of sources and said beamlet blanker array to focus said plurality of electron beamlets.
In an embodiment of the electron beam exposure apparatus with beamlet blanking means, said beamlet blanker comprise electrostatic deflectors.
In yet another embodiment of the electron beam exposure apparatus according to the invention, it further comprising scanning deflection means provided between the modulation array and the focusing electron optical system for deflecting the electron beamlets to scan said target exposure surface. In an embodiment thereof, the scanning deflection means comprises electrostatic scan deflectors. In a further embodiment thereof, the electron beam exposure apparatus is further provided with actuating means for moving said electrostatic scan deflectors and said means for holding the target relatively to each other in the plane of the surface onto which the pattern is to be transferred in a direction that differs from the direction of the deflection performed by said electrostatic scan deflectors.
In an embodiment, the adjustor or a time shifter are adapted for shifting a timing base of the scanning deflection means and the actuators with respect to each other. In an embodiment thereof, the control signals of the modulators have a timing base and the actuators of the target holder have a second timing base, and there timing bases can be shifted with respect to one another. This can for instance be used to have a critical component, which has to be written on the target surface and which would lay between two beamlets, written using only one beamlet.
In a further embodiment thereof, the electron beam exposure apparatus furthermore comprises an additional aperture plate between the modulation array and the focussing electron optical system, the additional aperture plate having one surface directed to and substantially parallel to the exposure surface of the target, wherein said electrostatic scan deflectors are conducting strips deposited on the side of the additional aperture plate facing the exposure surface of the target located between said blanker array and the electrostatic lens array of the focusing electron optical system. In another embodiment thereof, the electrostatic scan deflectors are conducting strips deposited at the target exposure surface side of any of the lens plates present in the focusing electron optical system. In an embodiment thereof, the conducting strips alternatively have a positive or negative potential.
In an embodiment of the electron beam exposure apparatus with the blanking electrostatic deflectors, these deflectors deflect the electron beamlets in such a way that a predetermined section of the beamlet is stopped by the beamlet stop array.
In a further embodiment of the electron beam exposure apparatus according to the present invention, it further comprises a post-reduction acceleration stage, located between the electrostatic lens array of the focusing electron optical system and said protective means, for accelerating the electrons in the plurality of transmitted electron beamlets.
In an embodiment of the controller, it is furthermore provided with correction means to compensate for the incorrect positioning of the electron beamlets on the target exposure surface by
In an embodiment of the electron beam exposure apparatus according to the present invention, it further comprising protective means to prevent particles released by impinging electrons to reach any one of the aperture arrays, lens arrays or blanker arrays, preferably located between the electrostatic lens array of the focusing electron optical system and the exposure surface of a target, preferably comprising an aperture array wherein the apertures have a size smaller than 20 μm.
In an embodiment of the electron beam exposure apparatus according to the present invention, all lens arrays, aperture arrays and blanker arrays are connected to a power supply, which, when gas is admitted into the system, creates a plasma that cleans the plates and removes all contaminants.
In a further embodiment, the electron beam exposure apparatus according to the present invention, the system is operated at an elevated temperature of about 200-600° C. to keep the apparatus clean.
The invention further relates to an electron beam exposure apparatus for transferring a pattern onto the surface of a target, comprising:
Using such a specific beamlet generator makes it possible to provide uniform beamlets with a sufficient current to provide a high throughput.
In an embodiment thereof, said extractor electrode is located after said space charge region and is provided with a positive voltage for inducing a negative lens effect to said electron beam.
The invention furthermore pertains to an electron beam generator for generating a plurality of electron beamlets, wherein said beamlet generator comprises at least one thermionic source, said source comprising at least one extractor electrode adapted for being operated in a space charge limited region, said source adapted for generating an electron beam, and said beamlet generator furthermore provided with a beamsplitter for splitting said electron beam up into a plurality of electron beamlets.
The invention furthermore pertains 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 plurality of modulators for modulating each electron beamlet, and a controller for providing each modulator with a control signal, said control signal having a timing base, wherein the controller is adapted for individually adjusting the timing base of a control signal with respect to the other control signals.
In this apparatus, the problem of positioning and modulating is solved in a very simple and elegant way, reducing the number of components and providing a robust apparatus.
The invention further pertains to a method for transferring a pattern onto a target exposure surface with an electron beam, using an electron beam exposure apparatus described above, and to a wafer processed using the apparatus of the current invention. The apparatus can furthermore be used for the production of mask, like for instance used in state-of-the-art optical lithography systems.
The invention will be further elucidated in the following embodiments of an electron beam exposure apparatus according to the current invention, in which:
An embodiment of the present invention is schematically shown in
A remarkable aspect of the configuration shown in
In the present invention the method shown in
The electron source 1 of
The extractor electrodes 2 usually, but not necessarily, focus the beam. The illumination lenses 3-4 create a parallel beam of electrons 5 on the aperture array 6. The lenses 3-4 are optimised to limit the beam energy spread as a result of Coulomb interactions, i.e. the opening angle of the beam is made as large as possible. Furthermore lenses 3-4 are optimised to limit the beam blur created by chromatic and spherical aberration effects. For the latter it may be advantageous to use the aperture array 6 as a lens electrode, because this may create negative chromatic and spherical aberrations, resulting in a compensation of the aberrations of lenses 3-4. Furthermore, it is possible to use lens 4 for magnification of the pattern by slightly focusing or defocusing it.
In such an embodiment, however, the electron beam emitted from the single emitter is focussed in a small crossover x before it is expanded. Within this crossover x there is a large energy spread due to electron-electron interactions in this crossover x. In the end the crossover x will be imaged demagnified on the target exposure surface. Due to the Coulomb interactions the desired resolution is not achieved. A method to expand and collimate the expanded beam without a crossover is therefore desirable.
In a first embodiment, shown in
The electrons can be extracted with a spherical extractor that comprises large holes. The main advantage of the spherical shape of the extractor is the more homogeneous field that is created.
In an alternative embodiment, shown in
By tuning V1 it is possible to let the source 1 operate in its space charge limited emission mode. The main advantage of this emission mode is the significant increase of homogeneity of the emission. The increase of the total current can be limited by selecting a source with a confined emission area.
The aperture array 6 has apertures of typically 5-150 μm in diameter with a pitch of about 50-500 μm. The apertures are preferably arranged in a hexagonal pattern. The aperture array 6 splits the incoming parallel beam of electrons 5 in a plurality of electron beamlets, typically in the order of about 5,000-30,000. The size of the apertures is adjusted to compensate non-uniform current density of the illumination. Each aperture has an area inversely proportional to the current density based on the individual beamlets that is transmitted through that same aperture. Consequently the current in each individual beamlet is the same. If the heat load on the aperture plate becomes too large, several aperture arrays are arranged in a serial order with decreasing aperture diameters along the path of the electron beam or plurality of electron beamlets. These aperture arrays have mutually aligned apertures.
Another possible way to split the collimated electron beam 5 into a plurality of electron beamlets is the use of a quadrupole lens array. A possible configuration of such an array is disclosed in U.S. Pat. No. 6,333,508, which document is referenced here as if fully set forth.
The modulation array comprises a beamlet blanker array 8 and a beamlet stop array 10. At the beamlet blanker array 8, the typical beam diameter is about 0.1-5 μm while the typical transversal energy is in the order of a 1-20 meV. Beamlet blanking means 17 are used to switch the electron beamlets on and off. They include blanking electrostatic deflectors, which comprise a number of electrodes. Preferably at least one electrode is grounded. Another electrode is connected to a circuit. Via this circuit control data are sent towards the blanking electrostatic deflectors. In this way, each blanking deflector can be controlled individually. Without the use of the beamlet blanking means 17 the electron beamlet will pass the beamlet stop array 10 through the apertures. When a voltage is applied on a blanking electrostatic deflector electrode in the beamlet blanker array 8, the corresponding electron beamlet will be, deflected and terminate on the beamlet stop array 10.
In an embodiment, the beamlet blanker array 8 is located in the electrostatic focal plane of the electron beamlets. With the blanker array in this position, the system is less sensitive for distortions. In this embodiment, the beamlet stop array is positioned outside a focal plane of the electron beamlets.
The transmitted beamlets now have to be focused on the target exposure surface 14. This is done by a focusing electron optical system 13 comprising at least one array with electrostatic lenses. Each individually transmitted electron beamlet is focused on the target exposure surface by a corresponding electrostatic lens. The lens array comprises two or more plates 13a and 13b, both having a thickness of about 10-500 μm and apertures 13c with a diameter of about 50-250 μm. The distance between two consecutive plates is somewhere between 50-800 μm and may be different from plate to plate. If necessary, the focusing electron optical system may also comprise a lens array of the magnetic type. It is then located between the beamlet stop array 10 and the objective lens array of the electrostatic type 13, to further enhance the focusing properties of the electron optical system.
A major problem in all electron beam lithography systems patterning a wafer or a mask is contamination. It reduces the performance of the lithography system significant due to the interaction between electrons and particles in the resist layer, the resist degrades. In a polymeric resist, molecules are released due to cracking. The released resist particles travel through the vacuum and can be absorbed by any of the structures present in the system.
In order to cope with the contamination problem, in a particular embodiment protective means are located in close proximity of the target exposure surface, i.e. between the target exposure surface and the focusing electron optical system. Said protective means may be a foil or a plate. Both options are provided with apertures with a diameter smaller than 20 μm. The protective means absorb the released resist particles before they can reach any of the sensitive elements in the lithography system. In some cases it is necessary to refresh the protective means after a predetermined period, e.g. after every processed wafer or mask. In the case of a protective plate the whole plate can be replaced. In a particular embodiment, the foil is wound around the coil winders. A small section of the foil is tightened just above the entire target exposure surface 14. Only this section is exposed to the contaminants. After a certain period the protective capacity of the foil rapidly degrades due to the absorbed particles. The exposed foil section then needs to be replaced. To do this the foil is transported from one coil winder to the other coil winder, thus exposing a fresh foil section to the contamination particles.
The entire system that is described above operates at relatively low voltages. In operations in which high-energy electrons are needed, an additional acceleration stage is positioned between the electrostatic lens array of the focusing electron optical system 13 and the protective means. This acceleration stage adds energy to the passing electrons. The beam may be accelerated additional tens of kiloelectronvolts, e.g. 50 keV.
As explained earlier in
In one embodiment, the electrostatic scan deflectors 18 are deposited on the target exposure surface side of one of the plates of the objective electrostatic lens array 13, such that the deflection essentially occurs in the front focal plane of the objective lenses. The desired result is that the deflected beamlets impinge perpendicularly on the target surface.
In another embodiment there are two deflector arrays, one deflecting in a first direction and the other deflecting in a second, opposite direction. The combined deflection causes displacement of the beamlets a displacement of the beamlets at the target surface location, without changing the perpendicular axis of a beamlet with respect to the target surface.
In a second embodiment, the electrostatic scan deflectors 18 are located on the protective means.
The electrostatic scan deflectors 18 comprise scan deflection electrodes, which are arranged to deflect an assembly of electron beamlets in the same direction. The scan deflection electrodes may be deposited in the form of strips 19 on a suitable plate 20 at the target exposure surface side as is shown in
In one embodiment the first assembly is scanned in one direction while the next one is scanned in the opposite direction, by putting alternating voltages on the consecutive strips 19 as is shown in
As already mentioned there are two scan directions, a mechanical scan direction M and a deflection scan direction S, both depicted in
When the mechanical scan length is a throughput-limiting factor, an assembly of electron beam exposure apparatuses as described above is used to expose the entire wafer at the same time.
It is assumed that an ideal grid exists on the wafer and that the electron beamlets can be positioned exactly on the grid coordinates. Say that a correct pattern is created when the electron beamlet can be positioned within 1/30th of the minimum feature size. Then to write one pixel, 30 scan lines and thus 30*30=900 grid points are needed. For the 45 nm-mode the positioning should be controllable within a range of 1.5 nm. The data path should therefore be able to handle an enormous amount of data.
The writing strategy described above is based on the assumption that the beamlet can only be switched on or off. To reduce the amount of data by less grid lines, and thus less grid cells seems a logical approach. However, the dimension control of the desired pattern suffers considerably. An approach to circumvent this problem is to pattern the target exposure surface 14 with discrete dose control. Again the pattern is divided according to a rectangular grid. However, the number of grid lines is much smaller e.g. 2-5 per dimension, which results in a number of grid points of about 4-25. In order to get the same pattern reliability as for the finer grid, the intensity of each grid cell is variable. The intensity is represented by a so-called gray value. In case of a 3 bit gray value representation, the values are 0, 1/7, 2/7, 3/7, 4/7, 5/7, 6/7 and 1 times the maximum dose. The number of data required for the position of the beamlet reduces, although each cell is represented with more information due to the controlled dose variation.
In the present invention gray scale writing can be introduced in several ways. First of all the deflection of the beams may be controlled in such a way that part of the beam passes the beamlet stop array 10, while part of the beam continues traveling towards the target exposure surface 14. In this way for instance ⅓ or ⅔ of the beam can be stopped, resulting in 4 possible doses on the target exposure surface, namely 0, ⅓, ⅔ and 1 times the maximum dose, corresponding to a 2 bit gray value representation.
Another method to create gray levels is to deflect the beamlets in such a way that they do not move with respect to the target surface for a predetermined amount of time T, which amount of time T is longer than a minimum on/off time of the blankers. During time T, the modulator can now deposite 1, 2, 3, etc. shots on one position, thus creating gray levels.
Another method to create these 4 so-called gray values is to change the aperture size in the aperture array 6. If there are for instance three aperture sizes, the original size, a size that permits half the original current to pass and apertures with an area such that only a fourth of the original current passes, the same discrete dose values as mentioned before an be created. By switching the beamlets on and off with the deflection electrodes 17 of the beamlet blanker array 8 the desired dose can be deposited on the target exposure surface 14. A disadvantage of the latter method is the fact that more beamlets are needed to write one pixel. Most, including aforementioned methods for discrete dose control can also be used to create more than 4 gray values, e.g. 8, 16, 32 or 64.
The positions of the beamlets on the target exposure surface most often do not exactly correspond with the desired positions. This is for instance due to misalignment of the different arrays with respect to each other. Additionally, manufacturing errors may also contribute to the offset of the individual beamlets. To transfer the correct pattern from the controller onto the exposure surface of the target, corrections have to be made. To this end, in a particular embodiment, first the position of all beamlets is measured and stored. Each position is then compared to the position the beamlet should have. The difference in position is then integrated in the pattern information that is sent to the modulation means.
Since changing the signal sequence that is sent towards the modulation means takes a lot of time, the measured difference in position is integrated in the pattern information by transforming it into a corresponding difference in timing in the beamlet modulation control.
The current electron beam exposure system is thus capable of dynamically adjusting the position of a scanned line using timing corrections. This allows for critical components in a pattern to be written in one scan line instead of using two halves of two scan lines, which would spread the critical component over two scan lines. This correction can also be done locally, i.e. the timing can be corrected over a small time window. The controller should thus identify critical components, which would normally be spread over two scan lines. Subsequently, the controller should calculated a corrected timing window, and apply the corrected timing window to the timing base used for scanning an electron beamlet.
All lens plates, aperture plates and blanker plates can be connected to a power supply, which, when gas is admitted into the system, creates a plasma. The plasma cleans the plates and removes all contamination. If one plasma does not clean thorough enough, two gases may be admitted into the system in series. For instance oxygen may be admitted first to remove all hydrocarbons residing in the system. After the removal of the oxygen plasma, a second plasma, for instance comprising HF, is created to remove all present oxides.
Another possibility to reduce the contamination is to perform all operations at elevated temperatures, i.e. 150-400° C. A pretreatment at 1000-1500° C. may be necessary. At these temperatures hydrocarbons get no chance to condense on any of the elements in the system. Allowing a fraction of oxygen into the system can further enhance the cleaning process.
It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. The scope of the invention is to be limited only by the following claims. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the spirit and scope of the present invention.
Wieland, Marco Jan-Jaco, Van Veen, Alexander Hendrik Vincent, Kampherbeek, Bert Jan, Kruit, Pieter
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