METHOD AND APPARATUS FOR ATOMIC LAYER DEPOSITION OF A FLUORIDE LAYER, OPTICAL ELEMENT AND OPTICAL ARRANGEMENT

Abstract

A method of depositing at least one fluoride layer comprises: depositing the fluoride layer on a substrate by photoassisted atomic layer deposition, ALD, in a plurality of ALD cycles. The method comprises irradiating the fluoride layer with UV/VIS light at least in some of the plurality of ALD cycles, such as in all ALD cycles, to anneal at least one potential crystal defect in the fluoride layer. The methods can be performed using an apparatus for atomic layer deposition of at least one fluoride layer, thereby producing an optical element comprising a substrate coated with such a fluoride layer, which can be used in an optical arrangement comprising at least one such optical element.

Claims

1. A method, comprising: depositing a fluoride layer on a substrate using photoassisted atomic layer deposition (ALD) in a plurality of ALD cycles, wherein, for at least some of the ALD cycles, the method comprises irradiating the fluoride layer with UV/VIS light to anneal a potential crystal defect in the fluoride layer.

2. The method of claim 1, comprising, for each of the ALD cycles, irradiating the fluoride layer with UV/VIS light to anneal a potential crystal defect in the fluoride layer.

3. The method of claim 1, wherein, in a first reaction step of a respective ALD cycle, the fluoride layer is exposed to a metallic precursor.

4. The method of claim 3, wherein, during the first reaction step of the respective ALD cycle, the fluoride layer is not irradiated with UV/VIS light.

5. The method of claim 3, wherein the metallic precursor comprises a member selected from the group consisting of Al(CH.sub.3).sub.3, AlCl.sub.3, (C.sub.2H.sub.5).sub.3Al, Mg(thd).sub.2, Mg(EtCp).sub.2, Ca(thd).sub.2, La(thd).sub.2, and LiHMDS.

6. The method of claim 3, wherein: in a second reaction step of a respective ALD cycle, the fluoride layer is exposed to a reactive fluorine precursor; and the fluoride layer is irradiated with the UV/VIS light to anneal the potential crystal defect during and/or after the second reaction step.

7. The method of claim 6, wherein the reactive fluorine precursor is generated by photodissociation from a fluorinating active.

8. The method of claim 7, wherein the fluorinating active comprises a member selected from the group consisting of SF.sub.6, NF.sub.3, HF, HF-pyridine, F.sub.2, NH.sub.4F, CF.sub.4, CHF.sub.3, TiF.sub.4, WF.sub.6, MoF.sub.5, and TaF.sub.5.

9. The method of claim 6, further comprising irradiating the fluoride layer with light in a third spectral region to photodissociate the fluorinating active, wherein the third spectral region is in a useful wavelength range of an optical element formed during the deposition of the at least one fluoride layer.

10. The method of claim 6, further comprising irradiating the fluoride layer with VUV light to photodissociate the fluorinating active.

11. The method of claim 1, wherein: in a reaction step of a respective ALD cycle, the fluoride layer is exposed to a reactive fluorine precursor; and the fluoride layer is irradiated with the UV/VIS light to anneal the potential crystal defect during and/or after the reaction step.

12. The method of claim 1, comprising irradiating the fluoride layer with light in a first spectral region to anneal the crystal defect, and the first spectral region comprises the UV/VIS wavelength range.

13. The method of claim 12, comprising irradiating the fluoride layer with light in a second spectral region to mobilize atoms on its surface, wherein the second spectral region is different from the first spectral region.

14. The method of claim 12, wherein the first spectral region is at wavelengths of more than 190 nm.

15. The method of claim 12, wherein at least two fluoride layers having different metallic constituents are deposited on the substrate, and the first spectral region on irradiation of a respective fluoride layer is matched to the respective metallic constituent of the fluoride layer.

16. The method of claim 1, comprising: i) depositing a metal layer on the substrate; ii) after i) disposing the substrate in an ALD chamber; and iii) after ii), depositing the fluoride layer on the substrate.

17. The method of claim 16, wherein the metal layer comprises an aluminum layer.

18. The method of claim 17, further comprising, after ii), removing an aluminium oxyhydroxide layer from the aluminium layer by atomic layer etching in the ALD chamber.

19. The method of claim 18, wherein removing the aluminium oxyhydroxide layer comprises fluorinating the aluminium oxyhydroxide layer to convert the aluminium oxyhydroxide layer to an aluminium fluoride layer in the ALD chamber.

20. The method of claim 1, wherein the fluoride layer is a fluoride layer of an optical element.

21. The method of claim 20, wherein the optical element is in a VUV lithography apparatus or a wafer inspection system.

22. An apparatus configured for atomic layer deposition (ALD) of a fluoride layer, comprising: an ALD chamber comprising a holder configured to hold a substrate; a gas supply device configured to supply a fluorinating active to the ALD chamber; and a UV/VIS light source configured to irradiate the fluoride layer with UV/VIS light to anneal a potential crystal defect of the fluoride layer.

23. The apparatus of claim 22, further comprising an activation device configured to generate a reactive fluorine precursor from the fluorinating active, wherein the activation device comprises a UV/VIS light source configured to dissociate the fluorinating active.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The figures show:

[0053] FIG. 1 a schematic diagram of an apparatus for atomic layer deposition of fluoride layers on a substrate, having two UV light sources for emission of UV light and an excitation device for excitation of a fluorinating active,

[0054] FIG. 2 a flow diagram of an ALD process for deposition of a fluoride layer on the substrate in the apparatus of FIG. 1,

[0055] FIGS. 3A, 3B flow diagrams of two variants of a photo-ALD process for deposition of the fluoride layer,

[0056] FIGS. 4A, 4B flow diagrams of two variants of a plasma-ALD process for deposition of the fluoride layer,

[0057] FIG. 5 a flow diagram of a process for coating an optical element, in which further layers are deposited in addition to the fluoride layer deposited in the ALD process,

[0058] FIG. 6 a flow diagram of a coating process in which an oxyhydroxide layer is removed in an ALD chamber prior to deposition of the fluoride layer,

[0059] FIG. 7 a flow diagram of an ALD process for deposition of multiple different fluoride layers,

[0060] FIG. 8 a schematic diagram of an optical arrangement for the VUV wavelength range in the form of a VUV lithography apparatus,

[0061] FIG. 9 a schematic diagram of an optical arrangement for the VUV wavelength range in the form of a wafer inspection system, and

[0062] FIG. 10 a schematic diagram of an optical element in the form of a laser chamber window.

DETAILED DESCRIPTION

[0063] In the description of the drawings that follows, identical reference signs are used for components that are the same or have the same function.

[0064] FIG. 1 shows an apparatus 1 for atomic layer deposition of one or more fluoride layers 2 on a substrate 3. For this purpose, the apparatus 1 comprises an ALD chamber 4 in the form of a vacuum chamber, in which is mounted a mount 5 (manipulator) for the substrate 3 in the form of a rotary table. An electrical potential (bias) can be applied to the mount 5, for example in order to accelerate ions from a plasma in the direction of the substrate 3. The mount 5 may also be heated with the aid of a heating device, which is not shown pictorially. A vacuum pump 6 serves to generate a vacuum in an interior of the ALD chamber 4.

[0065] The apparatus 1 also has a gas supply device 7 designed to supply a gaseous fluorinating active FW, a gaseous metallic precursor MP and a purge gas or inert gas IG to the ALD chamber 4, and having multiple gas inlets for this purpose. The gas supply device 7 additionally has a valve arrangement or metering arrangement that enables controlled supply of the gaseous fluorinating active FW, the gaseous metallic precursor MP and the inert gas IG to the interior of the ALD chamber 4. The fluorinating active FW may also be supplied to an activation device 8, and thereby to the interior of the ALD chamber 4, as described in detail further down.

[0066] The metallic precursor MP supplied from a gas reservoir may, for example, be Al(CH.sub.3).sub.3, AlCl.sub.3, (C.sub.2H.sub.5).sub.3Al, Mg(thd).sub.2, Mg(EtCp).sub.2, Ca(thd).sub.2, La(thd).sub.2 or LiHMDS. The fluorinating active FW is chosen depending on the metallic constituent of the fluoride layer 2, which, in the example shown, is a metal fluoride layer. The fluorinating actives FW described here are capable of depositing a fluoride layer 2 in the form of an AlF.sub.3 layer, an MgF.sub.2 layer or an LaF.sub.3 layer in an ALD process. In the example shown, trimethylaluminium, i.e. Al(CH.sub.3).sub.3, is used as the metallic precursor MP.

[0067] The inert gas IG may, for example, be a noble gas, for example argon, which may serve purposes including ventilation of the ALD chamber 4 prior to opening and establishment of a pressure in the interior of the ALD chamber 4, and in particular may serve as purge gas for purging of the interior of the ALD chamber 4 between reaction steps A and B of the ALD process; cf. FIG. 2.

[0068] The fluorinating active FW may be, for example: SF.sub.6, NF.sub.3, HF, HF-pyridine, F.sub.2, NH.sub.4F, CF.sub.4, CHF.sub.3, TiF.sub.4, WF.sub.6, MoF.sub.5 or TaF.sub.5. In the example shown, the fluorinating active used is gaseous SF.sub.6. For the performance of a (partial) reaction step of the ALD process, it is desirable to use the fluorinating active FW to create a reactive fluorine precursor FP to which the surface of the fluoride layer 2 or substrate 3 is exposed. This purpose is served by the activation device 8.

[0069] For this purpose, the activation device 8 shown in FIG. 1 has a (third) light source 9c in the form of a photodissociation light source for photodissociation of the fluorinating active FW, and a plasma source 11. If the fluorinating active FW is activated by the UV light source 9c, it is introduced directly into the interior of the ALD chamber 4 via a gas inlet of the gas supply device 7. In this case, the activation is effected by photodissociation of the fluorinating active FW by light 10c which is generated by the third light source 9c. The light 10c generated by the third light source 9c has at least one wavelength here that has greater photon energy than the dissociation energy of the fluorinating active FW. The third light source 9c, or the light 10c generated thereby, is thus matched to the fluorinating active FW used. In the example shown, the light 10c from the third light source 9c is radiated onto the fluoride layer 2. The light 10c of the third light source is light 10c of a third spectral region within the useful wavelength range of an optical element, which is formed on deposition of the fluoride layer 2 onto the substrate 3. In the example shown, the third spectral region is within the VUV wavelength range.

[0070] If the reactive fluorine precursor FP is generated from the fluorinating active FW by the formation of a plasma, the fluorinating active FW is supplied to the plasma source 11, is activated thereby and forms the reactive fluorine precursor FP, which may include, for example, fluorine radicals or fluorine in an excited electron state. It will be apparent that the activation device 8 need not necessarily include both the plasma source 11 and the photodissociation light source 9c: In general, one of these two sources is sufficient to generate the reactive fluorine precursor FP.

[0071] The apparatus 1 shown in FIG. 1 also has a first and second UV light source 9a, 9b, which serve to generate UV light 10a, 10b incident on the surface 2a of the fluoride layer 2. In the example shown in FIG. 1, the first UV light source 9a is designed to emit UV light 10a in a first spectral range which serves to anneal potential crystal defects during deposition of the fluoride layer 2 in the atomic layer deposition process. The first spectral region may be at wavelengths of more than 190 nm. The second UV light source 9b is designed to emit UV light 10b in a second spectral range which serves to mobilize atoms at the surface 2a of the fluorine layer 2. The two spectral regions are not shown pictorially and are selected depending on the deposited material, where the selection may be made, for example, in the manner described in DE 10 2021 203 505 A1, cited at the outset.

[0072] In a departure from the illustration in FIG. 1, the apparatus 1 may have a single UV light source which emits UV light 10a, 10b both in the first spectral range and in the second spectral range. The apparatus may also have only the first UV light source 9a, which emits UV light 10a in the first spectral range. The apparatus 1 may also have more than two UV light sources 9a, 9b.

[0073] In the example shown, both the first UV light source 9a and the second UV light source 9b are designed to respectively emit UV light 10a, 10b in a fixed first and second spectral range. However, it is also possible for the first and/or the second UV light source 9a, 9b to be tunable in order to be able to set or tune the first and/or the second spectral range. In the example shown in FIG. 1, the first UV light source 9a is an excimer laser having a wavelength of 193 nm, and the second UV light source 9b is a D.sub.2 lamp that emits light e.g. in a wavelength range from 115 nm to 122 nm.

[0074] Alternatively, one or both light sources 9a, 9b may be designed to generate light in the visible wavelength region (VIS light). In this case, the light sources 9a, 9b may be designed to respectively emit VIS light in a defined first and second spectral range, or the light sources 9a, 9b may be designed to be tunable. Moreover, a single VIS light source may be designed to generate VIS light both in the first spectral range and in the second spectral range. It is also possible to provide one or more UV light sources and one or more VIS light sources.

[0075] There follows a description of the method of atomic layer deposition of a fluoride layer, more specifically an AlF.sub.3 layer, in the apparatus 1 from FIG. 1 with reference to the flow diagram shown in FIG. 2. In the method, in a first step, the substrate 3, for example in the form of a glass substrate or crystal, is secured on the mount 5 and a purge step is conducted, and the ALD chamber 4 is evacuated. Subsequently, a first (partial) reaction step A of an ALD cycle Z is conducted, in which the substrate 3 or the surface of the already deposited portion of the fluoride layer 2 is exposed to the metallic precursor MP, and a first surface reaction of the ALD process proceeds on the surface of the fluoride layer 2. After a subsequent purge step, in which residues of the metallic precursor MP and volatile reaction products from the first reaction step A are pumped out of the interior of the ALB chamber 4, a second (partial) reaction step B of the ALD cycle Z is conducted.

[0076] In the second reaction step B, the surface 2a of the fluoride layer 2 is exposed to the reactive fluorine precursor FP. This is generated in the manner described in association with FIG. 1, either by photodissociation or by formation of a plasma from the fluorinating active, which is SF.sub.6 in the example disclosed. The surface reactions that proceed in the two reaction steps A, B are described in the article cited at the outset by M. F. J. Vos et al. The two reaction steps A, B and the respectively subsequent purge steps form an ALD cycle Z in which one or more layers of AlF.sub.3 are deposited. The ALD cycle Z is repeated n times until the fluoride layer 2 has its predetermined thickness. The number n of ALD cycles Z, depending on the thickness of the fluoride layer 2, may, for example, be between about 10 and 500. After the fluoride layer 2 has been grown on with the desired thickness, the substrate 3 is removed from the mount and from the ALD chamber 4.

[0077] As likewise apparent in FIG. 2, in the second reaction step B, the substrate 3 or surface 2a of the fluoride layer 2 is exposed to the UV light 10a from the first UV light source 9a in order to anneal at least one potential crystal defect in the fluoride layer 2, as described above in association with FIG. 1.

[0078] FIG. 3A, 3B show two variants of a photo-ALD process for deposition of the fluoride layer 2, of which the first variant shown in FIG. 3A corresponds to the variant shown in FIG. 2 in which the fluorinating active FW is activated by photodissociation. In the variant shown in FIG. 3B, in addition to the irradiation of the fluoride layer 2 with UV light 10a in the second reaction step B, a bleaching step is conducted in a further, subsequent process step of a respective ALD cycle Z, in which the surface 2a of the fluoride layer 2 is likewise irradiated with UV light 10a in order to anneal potential crystal defects in the fluoride layer 2. Alternatively, the bleaching can be conducted solely after the second reaction step B. As likewise shown in FIG. 3B, in the bleaching step, a fluorinating active FW may additionally be supplied in the interior of the ALD chamber 4 in order to bring about refluorination of the fluoride layer 2, for example when a layer of an oxyfluoride/hydroxyfluoride has formed on the surface 2a of the fluoride layer 2.

[0079] FIG. 4A, 4B show two variants of a plasma ALD process for deposition of the fluoride layer 2, of which the first variant shown in FIG. 4A corresponds to the variant shown in FIG. 2 in which the fluorinating active FW is activated by a plasma or plasma cracking to form the reactive fluorine precursor FP. In FIG. 4B, analogously to FIG. 3B, in a dedicated bleaching step conducted after the second reaction step B, the surface 2a of the fluoride layer 2 is irradiated with UV/VIS light 10a. Unlike in FIG. 3B, in the variant shown in FIG. 4B, no bleaching is conducted during the second reaction step B. But it will be apparent that this is also possible in the plasma ALD process described in FIG. 4B.

[0080] For the production of an optical element, it is typically not only the fluoride layer 2 that is deposited on the substrate 3, but generally further layers. FIG. 5 shows a flow diagram of a method in which, in two preceding steps, first an aluminium layer and subsequently a fluoride layer or fluoride coating are deposited on the substrate 3, before the coated substrate 3 is introduced into the ALD chamber 4, and a fluoride layer 2 is deposited on the coated substrate 3 by atomic layer deposition in the manner described above. The deposition of the aluminium layer and of the fluoride layer prior to introduction into the ALD chamber 4 is effected not by atomic layer deposition but rather, for example, by a thermal evaporation process.

[0081] FIG. 6 shows a process sequence analogous to FIG. 5, in which, after deposition of the aluminium layer under ambient air, a native thin Al.sub.xO.sub.y layer or more generally an Al.sub.xO.sub.yOH.sub.z layer has formed on the surface of the aluminium layer. In order to remove this, an atomic layer etching process may be conducted in the ALD chamber 4 before the at least one fluoride layer 2 is deposited by the atomic layer deposition process (variant (a) in FIG. 6). The apparatus 1 in this case is designed not just for atomic layer deposition but additionally also for atomic layer etching.

[0082] Alternatively, the Al.sub.xO.sub.yOH.sub.2 layer may be removed from the surface of the aluminium oxide layer by converting it to an aluminium fluoride layer (variant (b) in FIG. 6). The conversion is accomplished using a fluorinating active FW, to which the surface of the aluminium layer is exposed and active fluorine species are generated therefrom by photo dissociation or by a plasma, as described above in association with the ALD process. After conversion to the aluminium fluoride layer, in the manner described above, at least one fluoride layer 2 may be deposited by atomic layer deposition on the substrate 3, or more specifically on the aluminium fluoride layer formed by the conversion.

[0083] It is also possible to conduct the fluorination described above in connection with the aluminium oxyhydroxide layer on the fluoride layer deposited by atomic layer deposition in the ALD chamber 4 in order to undertake post-fluorination or refluorination of the deposited fluoride layer 2. This may be favourable, for example, if a layer of an oxyfluoride/hydroxyfluoride has formed on the surface of the fluoride layer 2. For the fluorination, the surface 2a of the fluoride layer 2 is exposed to a fluorinating active FW. This is typically converted by photodissociation using UV/VIS light 10c or using a plasma to active fluorine species that bring about refluorination of the fluoride layer 2.

[0084] FIG. 7 shows a process sequence in the deposition of multiple dielectric functional fluoride layers that are applied alternately to the substrate 3 in order to create a functional coating, for example in the form of a reflective or antireflective dielectric coating, which in the example shown has a number n of alternating layers of AlF.sub.3 and LaF.sub.3. In the deposition of a respective fluoride layer 2, the bleaching light, or more specifically the spectral range of the UV light 10.sub.a emitted by the first UV light source 9a, is matched to the metallic material of the fluoride layer 2 that is to be deposited. More specifically, in the example shown, the first spectral range is switched from a wavelength range between about 170 nm and 190 nm for atomic layer deposition of AlF.sub.3 to a wavelength of about 260 nm for atomic layer deposition of MgF.sub.2.

[0085] FIG. 8 shows an optical arrangement for the VUV wavelength range in the form of a VUV lithography apparatus 21. The VUV lithography apparatus 21 comprises two optical systems, namely an illumination system 22 and a projection system 23. The VUV lithography apparatus 21 additionally has a radiation source 24, which may be an excimer laser, for example.

[0086] The radiation 25 emitted by the radiation source 24 is conditioned with the aid of the illumination system 22 such that a mask 26, also called a reticle, is illuminated thereby. In the example shown, the illumination system 22 has a housing 32, in which there are disposed both transmissive and reflective optical elements. In a representative manner, the illustration shows a transmissive optical element 27, which focuses the radiation 25, and a reflective optical element 28, which deflects the radiation.

[0087] The mask 26 has, on its surface, a structure which is transferred to an optical element 29 to be exposed, for example a wafer, with the aid of the projection system 23 for the purpose of producing semiconductor components. In the example shown, the mask 26 is designed as a transmissive optical element. In alternative embodiments, the mask 26 can also be designed as a reflective optical element.

[0088] The projection system 23 has at least one transmissive optical element in the example shown. The example shown illustrates, in a representative manner, two transmissive optical elements 30, 31, which serve, for example, to reduce the structures on the mask 26 to the size desired for the exposure of the wafer 29.

[0089] Both in the illumination system 22 and in the projection system 23, a wide variety of transmissive, reflective or other optical elements can be combined with one another as desired, including in a more complex manner. Optical arrangements without transmissive optical elements can also be used for VUV lithography.

[0090] FIG. 9 shows an optical arrangement for the VUV wavelength range in the form of a wafer inspection system 41, but a mask inspection system may also be involved. The wafer inspection system 41 has an optical system 42 with a radiation source 54, from which radiation 55 is directed onto a wafer 49 via the optical system 42. For this purpose, the radiation 55 is reflected onto the wafer 49 by a concave mirror 46. In the case of a mask inspection system, it would be possible to replace the wafer 49 with a mask to be examined. The radiation reflected, diffracted and/or refracted by the wafer 49 is directed onto a detector 50 for further evaluation by a further concave mirror 48, which is likewise associated with the optical system 42, via a transmissive optical element 47. The wafer inspection system 41 additionally has a housing 52, in which there are disposed the two mirrors 46, 48 and the transmissive optical element 47. The radiation source 54 may, for example, be exactly one radiation source or a combination of a plurality of individual radiation sources in order to provide a substantially continuous radiation spectrum. In modifications, one or more narrowband radiation sources 54 can also be used.

[0091] At least one of the optical elements 27, 28, 30, 31 of the VUV lithography apparatus 21 shown in FIG. 8 and at least one of the optical elements 46, 47, 48 of the wafer inspection system 41 shown in FIG. 9 are designed here as described above. They are thus coated with at least one fluoride layer 2, where the at least one fluoride layer 2 has been deposited by the method described above and/or via the apparatus 1 described above.

[0092] FIG. 10 shows an optical element for transmitting radiation in the VUV wavelength range in the form of a laser chamber window 60 of a laser chamber 61 of an excimer laser 62. The laser beam emitted by the excimer laser 62 passes to the outside through the laser chamber window 60. The exterior of the laser chamber window 60 is coated with a fluoride layer 2 which has been deposited by the method described above and/or via the apparatus 1 described above. The fluoride layer 2 was irradiated with UV/VIS light 10a during atomic layer deposition to anneal potential crystal defects and therefore simultaneously has a high density and a low extinction coefficient. Sealing with such a layer 2 counteracts degradation of the laser chamber window 60 and thus prolongs the lifetime thereof.