METHOD FOR PRODUCING AN OPTICAL ELEMENT, OPTICAL ELEMENT, DEVICE FOR PRODUCING AN OPTICAL ELEMENT, SECONDARY GAS AND PROJECTION EXPOSURE SYSTEM

Abstract

A method for producing an optical element (2), in particular for a projection exposure system (400), according to which a protective layer (11) consisting of a protective material is applied to a surface of a main body (7) until a protective layer thickness is obtained. The main body (7) has a substrate (17) and a reflective layer (18) applied to the substrate (17). The protective layer (11) is at least substantially defect-free.

Claims

1. A method of producing an optical element, comprising: forming a capping layer from a capping material by sputtering, with an uninterrupted individualization of particles of a target material at at least one target by bombardment with ions of a working gas, with application of a discharge voltage for at least indirect ionization of the working gas and with formation of the capping layer in conjunction with a defect-preventing method, and applying the capping layer to a surface of a main body until a predetermined capping layer thickness is attained, wherein the main body includes a substrate having a reflection layer applied to the substrate, and wherein the formed capping layer is at least virtually free of defects, wherein the defect-preventing method comprises a facing-targets sputtering operation.

2. The method as claimed in claim 1, wherein the capping layer is formed with sharp boundaries.

3. The method as claimed in claim 1, wherein the capping layer is formed from a capping material having a stoichiometric composition.

4. The method as claimed in claim 1, wherein the particles of the target material form the capping material, move toward the main body and are deposited on the main body to form the capping layer.

5. The method as claimed in claim 1, wherein a reaction gas reacts with the particles of the target material to form particles of the capping material, and the particles of the capping material move toward the main body and are deposited on the main body to form the capping layer.

6. The method as claimed in claim 5, wherein the reaction gas is oxygen.

7. The method as claimed in claim 5, wherein the defect-preventing method comprises reducing a potential of the particles of the target material to cause damage after the individualization and/or of particles of the capping material and/or of ions and/or atoms and/or electrons from the working gas and/or of particles of the reaction gas before hitting the main body and/or the capping layer that forms with regard to at least one damage parameter.

8. The method as claimed in claim 7, wherein the at least one damage parameter comprises a reduced kinetic energy.

9. The method as claimed in claim 1, wherein the forming of the capping layer comprises capturing particles charged in the defect-preventing method in a magnetic trap.

10. The method as claimed in claim 1, wherein the ions of the working gas are formed in the defect-preventing method by a remote plasma source.

11. The method as claimed in claim 1, wherein the ions of the working gas in the defect-preventing method form a pulsed plasma.

12. The method as claimed in claim 1, wherein the at least one target in the defect-preventing method comprises a dual-cathode magnetron with an active anode and/or a passive anode.

13. The method as claimed in claim 1, wherein the ionization of the working gas in the defect-preventing method comprises Penning ionization with a secondary gas.

14. The method as claimed in claim 13, wherein the defect-preventing method comprises using a secondary gas to reduce the discharge voltage.

15. The method as claimed claim 14, wherein an electronic activation energy of the secondary gas is greater than an ionization energy of the working gas.

16. The method as claimed in claim 1, wherein, in the defect-preventing method, the particles of the capping material after the individualization and the ions and/or atoms and/or electrons from the working gas are assimilated in terms of energy by thermalization with the working gas.

17. The method as claimed in claim 16, wherein a pressure of the working gas is adjusted such that thermalization occurs in the defect-preventing method.

18. The method as claimed in claim 1, wherein the defect-preventing method comprises heating and/or melting of the at least one target.

19. The method as claimed in claim 18. wherein the heating and/or melting of the at least one target comprises reducing the discharge voltage.

20. The method as claimed in claim 1, wherein the defect-preventing method comprises decelerating the ions of the working gas by an electrical field in a mesh which is at an electrical potential.

21. The method as claimed in claim 1, wherein the forming of the capping layer comprises providing: zirconium oxide, ZrO.sub.x and/or titanium oxide, TiO.sub.x and/or niobium oxide, NbO.sub.x and/or yttrium oxide, YO.sub.x and/or hafnium oxide, HfO.sub.x and/or cerium oxide, CeO.sub.x and/or lanthanum oxide, LaO.sub.x and/or tantalum oxide, TaO.sub.x and/or aluminum oxide, AlO.sub.x and/or erbium oxide, ErO.sub.x and/or tungsten oxide, WO.sub.x and/or chromium oxide, CrO.sub.x and/or scandium oxide, ScO.sub.x and/or vanadium oxide, VO.sub.x, in pure form and/or as a mixture, as the capping material.

22. The method as claimed in claim 1, wherein the predetermined capping layer thickness is 0.1 nm to 20 nm.

23. An optical element comprising: a main body that has a substrate with a reflection layer applied to the substrate, and a capping layer formed from a capping material by facing-targets sputtering and applied to a surface of the main body, wherein the capping layer has a capping layer thickness, and wherein the capping layer is at least virtually free of defects.

24. The optical element as claimed in claim 23, wherein the capping layer has sharp boundaries.

25. The optical element as claimed in claim 23, wherein the capping material has a stoichiometric composition.

26. The optical element as claimed in claim 23, wherein the capping layer is formed by sputtering in conjunction with Penning ionization.

27. The optical element as claimed in claim 23, wherein the capping layer is formed by sputtering in conjunction with thermalization.

28. The optical element as claimed in claim 23, wherein the capping layer comprises: zirconium oxide, ZrO.sub.x and/or titanium oxide, TiO.sub.x and/or niobium oxide, NbO.sub.x and/or yttrium oxide, YO.sub.x and/or hafnium oxide, HfO.sub.x and/or cerium oxide, CeO.sub.x and/or lanthanum oxide, LaO.sub.x and/or tantalum oxide, TaO.sub.x and/or aluminum oxide, AlO.sub.x and/or erbium oxide, ErO.sub.x and/or tungsten oxide, WO.sub.x and/or chromium oxide, CrO.sub.x and/or scandium oxide, ScO.sub.x and/or vanadium oxide, VO.sub.x, in pure form and/or as a mixture.

29. The optical element as claimed in claim 23, wherein the capping layer thickness is 0.1 nm to 20 nm.

30. An apparatus for producing an optical element, comprising: a target composed of a target material, a coating device configured to individualize particles of the target material with an ionized working gas for coating a main body, wherein the main body has a substrate with a reflection layer applied to the substrate, a working chamber configured to accommodate the main body, a vacuum device configured to form a vacuum in the working chamber, and at least one limiting device comprising two mutually opposing targets and arranged to limit an energy of the particles after the individualizing and/or of the ions and/or electrons and/or atoms of the working gas that coat the main body.

31. The apparatus as claimed in claim 30, wherein the energy is a kinetic energy.

32. The apparatus as claimed in claim 30, wherein the limiting device is configured to alter a density of the working gas in the vacuum.

33. The apparatus as claimed in claim 30, wherein the limiting device is configured as a Penning ionization device such that a secondary gas is fed into the working gas.

34. The apparatus as claimed in claim 33, wherein the limiting device is configured such that an electronic activation energy of the secondary gas is greater than an ionization energy of the working gas.

35. The apparatus as claimed in claim 30, wherein the limiting device comprises a magnetic trap.

36. The apparatus as claimed in claim 30, wherein the limiting device comprises a heating device configured to heat and/or melt the target.

37. The apparatus as claimed in claim 30, wherein the limiting device comprises a mesh at an electrostatic potential.

38. The apparatus as claimed in claim 30, wherein the limiting device comprises an afterglow device.

39. The apparatus as claimed in claim 38, wherein the afterglow device comprises a remote plasma source.

40. The apparatus as claimed in claim 38, wherein the afterglow device comprises a pulsed plasma source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0184] In the figures, functionally analogous or identical elements are given the same reference signs.

[0185] The figures show, in schematic form:

[0186] FIG. 1 an EUV projection exposure apparatus;

[0187] FIG. 2 an illustration in principle of a working example of a device in accordance with the invention;

[0188] FIG. 3 a further illustration in principle of a working example of a device in accordance with the invention;

[0189] FIG. 4 a further illustration in principle of a working example of a device in accordance with the invention;

[0190] FIG. 5 a further illustration in principle of a working example of a device in accordance with the invention;

[0191] FIG. 6 a further illustration in principle of a working example of a device in accordance with the invention;

[0192] FIG. 7 a further illustration in principle of a working example of a device in accordance with the invention; and

[0193] FIG. 8 an illustration in principle of an optical element fabricated in accordance with the invention.

DETAILED DESCRIPTION

[0194] FIG. 1 shows, by way of example, the basic construction of an EUV projection exposure apparatus 400 for semiconductor lithography, for which the invention can preferably be employed. In particular, the invention may be employed in that at least one optical element of the projection exposure apparatus is produced by—as set out hereinafter—applying a capping layer formed from a capping material to a surface of a main body until a capping layer thickness has been attained, with formation of the capping layer in an at least a virtually defect-free manner.

[0195] An illumination system 401 of the projection exposure apparatus 400 comprises, as well as a radiation source 402, an optical unit 403 for the illumination of an object field 404 in an object plane 405. A reticle 406 disposed in the object field 404, held by a schematically illustrated reticle holder 407, is illuminated. A projection optical unit 408, illustrated merely schematically, serves to image the object field 404 into an image field 409 in an image plane 410. A structure on the reticle 406 is imaged onto a light-sensitive layer of a wafer 411 which is disposed in the region of the image field 409 in the image plane 410 and which is held by a wafer holder 412 that is likewise illustrated in part.

[0196] The radiation source 402 can emit EUV radiation 413, in particular in the range of between 5 nanometers and 30 nanometers, in particular 13.5 nm. Optically differently designed and mechanically adjustable optical elements are used for controlling the radiation path of the EUV radiation 413. In the case of the EUV projection exposure apparatus 400 illustrated in FIG. 1, the optical elements are in the form of adjustable mirrors in suitable embodiments that are mentioned merely by way of example hereinafter.

[0197] The EUV radiation 413 generated by the radiation source 402 is aligned with a collector 402a integrated in the radiation source 402 such that the EUV radiation 413 passes through an intermediate focus in the region of an intermediate focal plane 414 before the EUV radiation 413 arrives at a field facet mirror 415. Downstream of the field facet mirror 415, the EUV radiation 413 is reflected by a pupil facet mirror 416. With the aid of the pupil facet mirror 416 and an optical assembly 417 having mirrors 418, 419, 420, field facets of the field facet mirror 415 are imaged into the object field 404.

[0198] FIG. 2 in conjunction with FIG. 8 shows an illustration in principle of an apparatus 1 for production of an optical element 2, especially for a projection exposure apparatus 400, comprising a target 3 composed of a target material, a coating device 4 configured to individualize particles 5 of the target material via an ionized working gas 6 for coating of a main body 7, where the main body 7 has a substrate 17 with a reflection layer 18 applied to the substrate 17, and a working chamber 8 for accommodating the main body 7 and a vacuum device 9 for forming a vacuum in the working chamber 8. The apparatus further comprises a limiting device 10 in order to limit an energy of the particles 5 after individualization and/or of the ions and/or of electrons and/or of atoms of the working gas 6 that hit the main body 7.

[0199] The optical element 2 may especially be an optical element 2, 402a, 415, 416, 418, 419, 420 of the projection exposure apparatus 400.

[0200] In particular, the optical element 2 may also be a collector mirror 402a of the EUV projection exposure apparatus 400.

[0201] The main body 7 is formed here by a substrate 17 to which the reflection layer 18 composed of one or more materials has been applied, to which a barrier layer 19 has been applied in turn (see FIG. 8).

[0202] In another embodiment (not shown), it may be the case that the main body 7 is formed by a substrate 17, to which a reflection layer 18 composed of one or more materials has been applied, to which multiple barrier layers 19 have been applied in turn.

[0203] The apparatus 1 shown in FIG. 2 is suitable, for example, for performance of a method of producing an optical element 2, especially for a production exposure apparatus 400. This involves applying a capping layer 11 formed from a capping material to a surface of the main body 7 until a capping layer thickness is attained, where the main body 7 includes a substrate 17 having a reflection layer 18 applied to the substrate 17. The capping layer 11 here is formed at least virtually without defects.

[0204] In the working example shown for the apparatus 1, the method of producing the optical element 2 may be implemented such that the capping layer 11 is formed by sputtering. This involves constant individualization of particles 5 of the target material at the at least one target 3 by bombardment with ions of the working gas 6. In addition, a discharge voltage is applied for at least indirect ionization of the working gas 6, and the capping layer 11 is formed in conjunction with a defect-preventing method.

[0205] The capping layer 11, in the present working example, is formed from a capping material having a stoichiometric composition. In addition, in the present working example, the capping layer 11 is formed such that sharp boundaries are formed between the capping layer and the main body.

[0206] In the method implemented in the working example, the particles 5 of the target material form a capping material, move toward the main body 7, are deposited on the main body 7 and hence form the capping layer 11.

[0207] It may be the case that the particles 5 of the target material react with a reaction gas and hence form particles 5 of the capping material, and the particles 5 of the capping material subsequently move toward the main body 7 and are deposited on the main body 7 and hence form the capping layer 11.

[0208] In the present working example, it may be the case that the reaction gas is oxygen.

[0209] The limiting device 10, which, in the working example shown in FIG. 2, is part of the apparatus 1, is suitable for implementation of a defect-preventing method. In the defect-preventing method, a potential of particles 5 of the target material to cause damage after individualization and/or of particles 5 of the capping material and/or of ions and/or atoms and/or electrons of the working gas 6 and/or of particles of the reaction gas before they hit the main body 7 and/or before they hit the capping layer 11 that forms is reduced with regard to at least one damage parameter.

[0210] In particular, in the present working example, the at least one damage parameter is a kinetic energy which is preferably above a threshold. The limiting device 10 reduces the maximum kinetic energy that occurs.

[0211] The energy limited by the limiting device 10 is accordingly kinetic energy.

[0212] The limiting device 10, which, in the working example shown in FIG. 2, is part of the apparatus 1, is configured here such that a density of the working gas 6 in the vacuum is altered. An elevated collision frequency between the particles of the working gas 6 assimilates or limits the kinetic energy thereof.

[0213] The density of the working gas 6 in the present working example is increased by the limiting device 10 in that the limiting device supplies the working chamber 8 with working gas 6. In particular, it may be the case that the limiting device 10 takes the form of a metering device and/or valve device. Furthermore, it may also be the case in the present working example that the limiting device 10 supplies the working chamber 8 with a thermalization gas, which does not act as a working gas, but the particles of the working gas 6 collide with the particles thereof and hence the kinetic energy thereof is assimilated.

[0214] With the limiting device 10 detailed as part of the apparatus 1 shown in FIG. 2, it is possible to conduct a method in which the capping layer 11 is formed by sputtering, and, in the defect-preventing method, the particles 5 of the capping material after individualization and the ions and/or atoms and/or electrons from the working gas 6 are assimilated in terms of energy by thermalization with the working gas 6. In particular, with the limiting device 10 configured as a metering device, it is possible to adjust a pressure of the working gas 6 such that thermalization occurs in the defect-preventing method.

[0215] It may be the case that the limiting device 10 takes the form of an afterglow device. It may especially be the case that the afterglow device takes the form of a remote plasma source. The plasma source forms the working gas at a spatial distance from the target 3 and/or the capping layer 11 and subsequently moves it toward the target 3.

[0216] Individualization of the particles 5 of the target material takes place here via a plasma afterglow.

[0217] It may likewise be the case that the afterglow device takes the form of a pulsed plasma source. In this case, the working gas 6 is ionized merely in pulses over time. Individualization of the particles 5 of the target material is accordingly brought about for the most part via a plasma afterglow.

[0218] If the limiting device 10 takes the form of an afterglow device and especially of a remote plasma source, the device 1 is suitable for implementing a method by which the ions of the working gas 6 are formed by a remote plasma source in the defect-preventing method.

[0219] If the afterglow device takes the form of a pulsed plasma source, it is possible to implement a method whereby ions of the working gas 6 form a pulsed plasma in the defect-preventing method. In particular, it may be the case that, in the defect-preventing method, the at least one target takes the form of a dual-cathode magnetron.

[0220] FIG. 3 shows an apparatus 1 in which the limiting device 10 is configured as a Penning ionization device 12 such that a secondary gas 13 is fed into the working gas 6. The Penning ionization device 12 is configured here such that an electronic activation energy of the secondary gas 13 is greater than an ionization energy of the working gas 6.

[0221] An apparatus 1 configured as per the working example shown in FIG. 3 enables the performance of a method wherein the capping layer 11 is formed by sputtering in conjunction with a defect-preventing method. The defect-preventing method comprises ionizing the working gas 6 by Penning ionization with a secondary gas 13.

[0222] In order to prevent defects, it is possible here to reduce the discharge voltage if a secondary gas 13 is used.

[0223] For this purpose, an electronic activation energy of the secondary gas 13 is greater than the ionization energy of the working gas 6.

[0224] FIG. 4 shows an illustration in principle of a further working example of the apparatus 1. The limiting device 10 here takes the form of a magnetic trap 14. The magnetic trap 14 here forms a magnetic field such that charged particles having high kinetic energy are steered away from the capping layer 11.

[0225] In particular, the magnetic trap 14 is configured such that, in particular, ions of the working gas 6 having a high kinetic energy are held within a limited region of the working chamber 8 and especially do not interact with the capping layer 11.

[0226] The apparatus 1 shown in FIG. 4 can be used, for example, to perform a method wherein the capping layer 11 is formed by sputtering and wherein particles charged in the defect-preventing method, especially ions of the working gas, are trapped in a magnetic trap 14.

[0227] FIG. 5 shows an illustration in principle of an apparatus 1 wherein the limiting device 10 takes the form of two mutually opposing targets 3. Such an apparatus 1 can be used, for example, to conduct a method wherein the defect-preventing method is configured as a facing-targets sputtering operation. In particular, the targets 3 face one another such that, in particular, very high-speed ions of the working gas 6 cannot directly hit the main body 7 beneath the capping layer 11.

[0228] Instead, there is a high probability that very high-speed particles, especially ions of the working gas 6, will hit the respective opposing target 3.

[0229] FIG. 6 shows a further working example of the apparatus 1 wherein the limiting device 10 takes the form of a heating device 15 for heating and/or for melting the target 3. Such an apparatus 1 enables, for example, performance of a method whereby the capping layer 11 is formed by sputtering, and wherein the at least one target 3 is heated and/or melted in the defect-preventing method.

[0230] Melting of the target 3 requires lower energy for individualization of the particles 5 of the target material. Hereby, it is envisaged in the working example disclosed that the discharge voltage is reduced when the at least one target 3 is being heated and/or melted.

[0231] FIG. 7 shows an illustration in principle of a working example of the apparatus 1 wherein the limiting device 10 takes the form of a mesh 16 at an electrostatic potential. With such an apparatus, it is possible, for example, to conduct a method wherein the capping layer 11 is formed by sputtering, with deceleration of the ions of the working gas 6 by an electrical field in a mesh 16 which is at an electrical potential in the defect-preventing method.

[0232] Deceleration of charged particles, especially of the ions of the working gas 6, advantageously reduces the potential damage caused by ions of the working gas 6.

[0233] FIG. 8 shows an illustration in principle of an optical element 2, especially of a mirror of a projection exposure apparatus 400, having a main body 7, where the main body 7 has a substrate 17 with a reflection layer 18 applied to the substrate 17, and a capping layer 11 formed from a capping material that has been applied to a surface of the main body 7 and has a capping layer thickness, wherein the capping layer 11 is at least virtually free of defects.

[0234] The main body 7 is formed by a substrate 17 to which a reflection layer 18 composed of one or more materials has been applied, to which a barrier layer 19 has been applied in turn.

[0235] The capping layer 11 here has sharp boundaries both on the side facing the barrier layer 19 and on the side remote from the barrier layer 19.

[0236] In addition, the capping material that forms the capping layer 11 in the present working example has a stoichiometric composition. In the present working example, the capping layer 11 may be formed by facing-targets sputtering and/or by sputtering in conjunction with Penning ionization and/or by sputtering in conjunction with thermalization and/or by further methods that have been disclosed in the context of the invention.

[0237] The formation of the main body 7 from a substrate 17 with a reflection layer 18 applied to the substrate 17 should at first be interpreted broadly in the context of the invention in that the main body 7 has a substrate 17 with a reflection layer 18 applied to the substrate 17. The main body 7 may then especially, as shown in FIG. 8, also still have a barrier layer 19, as described above.

[0238] In a narrow interpretation, the main body 7 in the context of the invention should be considered to be formed solely from a substrate 17 with a reflection layer 18 applied to the substrate 17 and optionally one or more barrier layers 19 applied to the reflection layer 18, optionally over only part of the area.

LIST OF REFERENCE SIGNS

[0239] 1 Apparatus [0240] 2 Optical element [0241] 3 Target [0242] 4 Coating device [0243] 5 Particles of the target material [0244] 6 Working gas [0245] 7 Main body [0246] 8 Working chamber [0247] 9 Vacuum device [0248] 10 Limiting device [0249] 11 Capping layer [0250] 12 Penning ionization device [0251] 13 Secondary gas [0252] 14 Magnetic trap [0253] 15 Heating device [0254] 16 Mesh [0255] 17 Substrate [0256] 18 Reflection layer [0257] 19 Barrier layer [0258] 400 Projection exposure apparatus [0259] 401 Illumination system [0260] 402 Radiation source [0261] 402a Collector [0262] 403 Optical unit [0263] 404 Object field [0264] 405 Object plane [0265] 406 Reticle [0266] 407 Reticle holder [0267] 408 Projection optical unit [0268] 409 Image field [0269] 410 Image plane [0270] 411 Wafer [0271] 412 Wafer holder [0272] 413 EUV radiation [0273] 414 Intermediate focal plane [0274] 415 Field facet mirror [0275] 416 Pupil facet mirror [0276] 417 Optical assembly [0277] 418 Mirror [0278] 419 Mirror [0279] 420 Mirror