Optical arrangement for EUV lithography

Abstract

An optical arrangement for EUV lithography, including: at least one component (23) having a main body (32) with at least one surface region (30) which is exposed to activated hydrogen (H.sup.+, H*) during operation of the optical arrangement. The main body (32) contains at least one material which forms at least one volatile hydride upon contact of the surface region (30) with the activated hydrogen (H.sup.+, H*). At the surface region, noble metal ions (38) are implanted into the main body (32) in order to prevent the formation of the volatile hydride.

Claims

1. An optical arrangement for extreme ultraviolet (EUV) lithography, comprising: at least one component having a main body substrate with at least one surface region which is exposed to activated hydrogen (H.sup.+, H*) during operation of the optical arrangement, wherein the main body substrate contains at least one material which forms at least one volatile hydride upon contact of the surface region with the activated hydrogen, wherein noble metal ions are implanted into the main body substrate at the surface region, and wherein the noble metal ions are implanted into the main body substrate with an implantation depth of between 0.5 nm and 1000 nm.

2. The optical arrangement according to claim 1, wherein the noble metal ions are selected from the group consisting of: Pt, Pd, Au, Rh, Ir.

3. The optical arrangement according to claim 1, wherein the material which forms the volatile hydride is selected from the group consisting of: Si, Ge, Sn, Zn, In.

4. The optical arrangement according to claim 1, wherein the noble metal ions are implanted into the main body substrate with an implantation depth of between 0.5 nm and 100 nm.

5. The optical arrangement according to claim 1, wherein the noble metal ions are implanted into the main body substrate in clusters of not more than 200 atoms.

6. The optical arrangement according to claim 1, wherein boron ions, phosphorous ions, nitrogen ions and/or noble gas ions are additionally implanted into the main body substrate at the surface region.

7. The optical arrangement according to claim 1, wherein the main body substrate forms a substrate of a reflective optical element, and wherein the at least one component further comprises a reflective coating, which is configured to reflect EUV radiation, applied on the main body substrate.

8. The optical arrangement according to claim 7, wherein the main body substrate is formed from quartz glass, from a glass ceramic or from silicon, or wherein the main body substrate further comprises a surface coating containing material forming the volatile hydride.

9. The optical arrangement according to claim 8, wherein the main body substrate is formed from titanium-doped quartz glass or from mono- or polycrystalline silicon.

10. The optical arrangement according to claim 1, wherein the at least one component having the main body substrate is a non-optical component.

11. The optical arrangement according to claim 1, wherein the main body substrate comprises a solid body formed from a metallic material and a surface coating containing material forming the volatile hydride.

12. The optical arrangement according to claim 11, wherein the solid body is formed from nitrogen-containing high-grade steel.

13. The optical arrangement according to claim 1, further comprising at least one shield fitted to the surface region of the main body substrate.

14. The optical arrangement according to claim 1, further comprising: an EUV light source configured to generate EUV radiation for the EUV lithography, an illumination system configured and arranged to illuminate a structured object with the EUV radiation generated by the EUV light source, and a projection lens configured and arranged to image the structured object onto a substrate of semiconductor material.

15. An optical arrangement for extreme ultraviolet (EUV) lithography, comprising: at least one component having a main body substrate with at least one surface region which is exposed to activated hydrogen (H.sup.+, H*) during operation of the optical arrangement, wherein the main body substrate contains at least one material which forms at least one volatile hydride upon contact of the surface region with the activated hydrogen, wherein noble metal ions are implanted into the main body substrate at the surface region, and wherein the noble metal ions are implanted into the main body substrate in clusters of not more than 200 atoms.

16. The optical arrangement according to claim 15, wherein the noble metal ions are selected from the group consisting of: Pt, Pd, Au, Rh, Ir.

17. The optical arrangement according to claim 15, wherein boron ions, phosphorous ions, nitrogen ions and/or noble gas ions are additionally implanted into the main body substrate at the surface region.

18. An optical arrangement for extreme ultraviolet (EUV) lithography, comprising: at least one component comprising a main body forming a substrate of a reflective optical element, wherein the substrate includes a surface region provided with a reflective coating configured to reflect EUV radiation, and at least one surface region which is exposed to activated hydrogen (H.sup.+, H*) during operation of the optical arrangement, wherein the substrate contains at least one material which forms at least one volatile hydride upon contact of the at least one surface region with the activated hydrogen, and wherein the at least one surface region exposed to the activated hydrogen is doped with noble metal ions to form an implanted non-continuous layer of ions in the substrate below the at least one surface region.

19. The optical arrangement according to claim 18, wherein the noble metal ions in the non-continuous layer of ions are implanted in clusters of not more than approximately 200 atoms.

20. The optical arrangement according to claim 18, wherein the at least one surface region doped with noble metal ions is formed outside the surface region provided with the reflective coating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments are illustrated in the schematic drawing and are explained in the following description. In the figures:

(2) FIG. 1 shows a schematic illustration of an optical arrangement in the form of an EUV lithography apparatus,

(3) FIG. 2A shows a schematic illustration of a surface region of an Si-containing main body which is exposed to activated hydrogen,

(4) FIG. 2B shows a schematic illustration analogous to FIG. 2A in which at the surface region Pt ions are implanted into the main body,

(5) FIGS. 3A and 3B show schematic illustrations of optical elements in which Pt ions are implanted into a main body at various surface regions, namely laterally outside a reflective-coating region (FIG. 3A) or circumferentially on a further surface that adjoins the reflective coating region (FIG. 3B), and

(6) FIG. 4 shows a schematic illustration of a non-optical component in which at two surface regions Pt ions are implanted into a main body composed of nitrogen-containing high-grade steel.

DETAILED DESCRIPTION

(7) In the following description of the drawings, identical reference signs are used for identical or functionally identical components.

(8) FIG. 1 schematically shows the construction of an optical arrangement for EUV lithography in the form of an EUV lithography apparatus 1, specifically of a so-called wafer scanner. The EUV lithography apparatus 1 comprises an EUV light source 2 for generating EUV radiation, which has a high energy density in the EUV wavelength range below 50 nanometers, in particular between approximately 5 nanometers and approximately 15 nanometers. The EUV light source 2 can be configured for example in the form of a plasma light source for generating a laser-induced plasma. The EUV lithography apparatus 1 shown in FIG. 1 is designed for an operating wavelength of the EUV radiation of 13.5 nm. However, it is also possible for the EUV lithography apparatus 1 to be configured for a different operating wavelength in the EUV wavelength range, such as 6.8 nm, for example.

(9) The EUV lithography apparatus 1 furthermore comprises a collector mirror 3 in order to focus the EUV radiation of the EUV light source 2 to form an illumination beam 4 and to increase the energy density further in this way. The illumination beam 4 serves for the illumination of a structured object M with an illumination system 10, which in the present example has five reflective optical elements 12 to 16 (mirrors).

(10) The structured object M can be for example a reflective photomask, which has reflective and non-reflective, or at least much less reflective, regions for producing at least one structure on the object M. Alternatively, the structured object M can be a plurality of micro-mirrors, which are arranged in a one-dimensional or multi-dimensional arrangement and which are, if appropriate, movable about at least one axis, in order to set the angle of incidence of the EUV radiation on the respective mirror.

(11) The structured object M reflects part of the illumination beam 4 and forms a projection beam path 5, which carries the information about the structure of the structured object M and is radiated into a projection lens 20, which produces a projected image of the structured object M or of a respective partial region thereof on a substrate W. The substrate W, for example a wafer, comprises a semiconductor material, for example silicon, and is arranged on a mounting, which is also referred to as a wafer stage WS.

(12) In the present example, the projection lens 20 has six reflective optical elements 21 to 26 (mirrors) in order to produce an image of the structure that is present on the structured object M on the wafer W. The number of mirrors in a projection lens 20 typically lies between four and eight; however, as few as two mirrors can also be used, if configured appropriately.

(13) In addition to the reflective optical elements 3, 12 to 16, 21 to 26, the EUV lithography apparatus 1 also comprises non-optical components, which can be for example carrier structures for the reflective optical elements 3, 12 to 16, 21 to 26, sensors, actuators, etc. FIG. 1 shows by way of example one such non-optical component 27 in the form of a carrier structure, which serves to hold the sixth mirror 26 of the projection lens 20.

(14) The reflective optical elements 3, 12 to 16 of the illumination system 10 and the reflective optical elements 21 to 26 of the projection lens 20 are arranged in a vacuum environment in which a hydrogen plasma prevails. Uncovered surface regions 30 that are exposed to the vacuum environment therefore come into contact with activated hydrogen in the form of hydrogen ions H.sup.+ and hydrogen radicals H*.

(15) FIGS. 2A and 2B show such an uncovered surface region 30 formed at a main body 32 comprising a silicon-containing material which is present in the form of an (abstract) chemical compound Si.sub.mX.sub.nY.sub.pZ.sub.q having other chemical elements X, Y, Z. As is illustrated in FIG. 2A, both the hydrogen radicals H* and the hydrogen ions H.sup.+ adsorb on the surface region 30 and form with the silicon a chemical compound in the form of a hydride, e.g. in the form of SiH.sub.3 or SiH.sub.4. Since SiH.sub.3 and SiH.sub.4 are volatile chemical compounds, these desorb into the gas phase and leave behind an etched surface region 30 of the main body 32. The desorbed hydrides, e.g. in the form of SiH.sub.3 or SiH.sub.4, can deposit at the optical surfaces of the reflective optical elements 3, 12 to 16, 21 to 26 of the EUV lithography apparatus 1 and cause a loss of reflection there. A cross-contamination by desorbed hydrides thus occurs in the EUV lithography apparatus 1.

(16) FIG. 2B shows a surface region 30 of a main body 32 which, in contrast to that shown in FIG. 2A, is doped with Pt ions. The Pt ions are implanted into the main body 32 at the surface region 30 or below the surface region 30. The Pt ions serve as a catalyst for a recombination reaction of the activated hydrogen H.sup.+, H* into molecular hydrogen (H.sub.2) at the surface region 30. The molecular hydrogen H.sub.2 desorbs from the surface region 30 and transitions to the gas phase, thereby preventing the formation of volatile hydrides such as e.g. SiH.sub.4. In addition, the surface region 30 or the main body 32 is not altered, that is to say that an etching process does not occur.

(17) It is therefore advantageous, at surface regions 30 exposed to hydrogen ions H.sup.+ and/or hydrogen radicals H* and containing at least one material which forms a readily volatile hydride with activated hydrogen H*, H.sup.+, e.g. Si, Ge, Sn, Zn or In, to implant Pt ions or other types of ions that form a catalyst for the recombination to form molecular hydrogen H.sub.2. Said ions can be in particular Pt or other noble metal ions, for example Pd, Au, Rh or Ir.

(18) FIG. 3A shows a sectional illustration of the fifth optical element 16 of the illumination system 10, which comprises a main body 32 formed from a solid body 33 composed of aluminium, and further comprises a surface coating 34 composed of silicon applied on the solid body. The solid body 33 can also be formed from copper or from some other metallic material. The main body 32 serves as a substrate for a reflective coating 35 applied on a planar front side 36a of the main body 32, in particular to the Si surface coating 34. The main body 32, at its likewise planar rear side 36b, is applied area-ly on a mount (not illustrated pictorially in FIGS. 3A and 3B). The reflective optical element 16 is illustrated in a greatly simplified manner in FIGS. 3A and 3B, even though said reflective optical element in actuality has a more complex geometry in practice.

(19) In the examples shown in FIGS. 3A and 3B, the reflective coating 35 is configured for reflecting EUV radiation 37 incident with grazing incidence on the front side 36a of the main body 32, i.e., for EUV radiation 37 incident on the front side 36a of the main body 32 at an angle of incidence of more than approximately 60°. In the example shown, the reflective coating 35 is formed by a single layer, but can also be formed by a multilayer system.

(20) While the front side 36a of the main body 32 is protected against the activated hydrogen H.sup.+, H* in the region of the reflective coating 35, this is not the case for a ring-shaped surface region 30 surrounding the reflective coating 35 at the front side 36a of the main body 32, that is to say that the ring-shaped surface region 30 is exposed to the hydrogen plasma H*, H.sup.+.

(21) In order to prevent the formation of volatile Si hydrides at the uncovered surface region 30 of the reflective optical element 16, Pt ions 38 are implanted into the main body 32, in particular into the Si surface coating 34 of the main body 32. The implanted Pt ions 38 are restricted to the Si surface coating 34, specifically to an implantation depth T in a value range of between approximately 0.5 nm and approximately 1000 nm, preferably between 0.5 nm and 100 nm, proceeding from the ring-shaped surface region 30. By contrast, the Si surface coating 34 has a thickness D in the range of a number of millimeters, that is to say that the implanted Pt ions 38 are restricted to a near-surface volume region of the Si surface coating 34. As can likewise be discerned in FIG. 3A, the Pt ions 38 are implanted only at or below the ring-shaped surface region 30, but not at or below the reflective coating 35. The solid body 33—consisting of Al—of the main body 32 does not have to be protected against the reactive hydrogen H.sup.+, H* since Al generally does not form volatile hydrides with the activated hydrogen H*, H.sup.+.

(22) FIG. 3B shows a reflective optical element 23 arranged in the projection lens 20 of the EUV lithography apparatus 1. The reflective optical element 23 has a reflective coating 35 at its front side 36a, which reflective coating, in the example shown, is a multilayer coating for reflecting EUV radiation 37 incident with normal incidence on the reflective optical element 23. For this purpose, the reflective multilayer coating 35 has a plurality of layers having alternately a high and a low real part of the refractive index.

(23) The reflective optical element 23 shown in FIG. 3B is also exposed to activated hydrogen H.sup.+, H* during operation of the EUV lithography apparatus 1. In order to prevent the material of the solid main body 32, which is SiO.sub.2 in the example shown, from being exposed to the surrounding hydrogen plasma H.sup.+, H*, Pt ions 38 are implanted at a circumferential lateral surface region 30 of the main body 32. In order to intensify the catalytic effect of the Pt ions 38, nitrogen ions 39 are additionally implanted at the circumferential lateral surface region 30. Other ions that intensify the catalytic effect of the Pt ions 38 can also be implanted into the main body 32 at the lateral surface region 30, for example noble gas ions, e.g. Ar ions or Kr ions, boron ions or phosphorous ions. In the example shown in FIG. 3B, the rear side 36b of the main body 32 is secured area-ly to a carrier component (not illustrated pictorially) and, therefore, just like the front side 36a of the main body 32 that is covered area-ly by the reflective coating 35, is not exposed to the activated hydrogen H.sup.+, H*.

(24) In order additionally to protect the lateral surface region 30 of the main body 32 against an etching effect of the activated hydrogen H.sup.+, H*, in the example shown in FIG. 3B, a shield in the form of a stop 40 is provided at the reflective optical element 23. For this purpose, the stop 40 covers the lateral surface region 30 of the reflective optical element 23 at a defined distance with the formation of a gap 41, the gap width of which is less than approximately 5 mm in the example shown. Other measures for shielding the lateral surface region 30 against the activated hydrogen H.sup.+, H* can also be provided; by way of example, a shield in the form of a coating or a protective film can be applied on the lateral surface region 30.

(25) FIG. 4 shows highly schematically the non-optical component 27 from FIG. 1, which, in the example shown, is formed from a solid main body 32 composed of high-grade steel, in particular composed of nitrogen-containing high-grade steel (Nitronic®). This type of high-grade steel typically contains a small proportion of silicon, such that the main body 32, in particular the front side forming a first surface region 30a and also a circumferential side surface forming a second surface region 30b of the main body 32, has to be protected against activated hydrogen H.sup.+, H*. For this purpose, noble metal ions are implanted into the main body 32 both at the first and at the second surface region 30a, 30b. The rear side 36b of the non-optical component 27 in the form of the carrier component is secured area-ly to a further component (not illustrated pictorially), such that this does not have to be protected against the activated hydrogen H.sup.+, H*.

(26) In all of the examples described further above, the noble metal ions 38 do not form a continuous layer, but rather are implanted into the main body 32 in clusters of not more than approximately 200 atoms. This can be achieved by suitably selecting the parameters in the implantation of the noble metal ions 38. By way of example, it has proved to be advantageous if the ion dose during the ion implantation, which can be carried out for example by a plasma immersion ion implantation or an ion implantation with a linear accelerator, is chosen not to be too high. The ion dose during the implantation of the noble metal ions 38 should typically lie between approximately 10.sup.11/cm.sup.2 and 10.sup.17/cm.sup.2, preferably between 10.sup.11/cm.sup.2 and 10.sup.15/cm.sup.2.

(27) Main bodies 32 which are formed from materials different from those described further above can also be protected against the formation of volatile hydrides by the implantation of noble metal ions 38. Said materials can for example be glass ceramics, e.g. Zerodur®, mono- or polycrystalline silicon, etc.