OXYGEN-LOSS RESISTANT TOP COATING FOR OPTICAL ELEMENTS

Abstract

Provided is an optical element for a lithographic apparatus. The optical element includes a capping layer that includes oxygen vacancies therein. The oxygen vacancies prevent attack of the capping layer by preventing hydrogen and other species from penetrating the capping layer and underlying layers. The capping layer provides a low hydrogen recombination rate enabling hydrogen to clean the surface of the optical element. The capping layer may include an alloyed metal, a mixed metal oxide or a doped metal oxide and it may be a ruthenium capping layer that includes one or more dopants therein.

Claims

1. An optical element for a lithographic apparatus, said optical element comprising a capping layer that includes a plurality of oxygen vacancies therein.

2. The optical element according to claim 1, wherein the capping layer comprises a doped zirconium oxide.

3. The optical element according to claim 2, wherein the doped zirconium oxide includes a trivalent cation in its oxidized state as a dopant therein.

4. The optical element according to claim 1, wherein the capping layer comprises zirconium oxide and one or more metal oxides selected from the group consisting of oxides of yttrium, cerium, calcium, magnesium, titanium, and rare-earth metals.

5. The optical element according to claim 1, wherein the capping layer comprises zirconium oxide and yttrium oxide.

6. The optical element according to claim 1, wherein the capping layer comprises yttrium stabilized zirconium oxide.

7. The optical element according to claim 4, wherein the one or more metal oxides comprise from about 1% to about 25%, by mole fraction, of the capping layer.

8. The optical element according to claim 1, wherein the capping layer comprises an alloyed metal or an alloyed metal oxide.

9. The optical element according to claim 8, wherein the alloyed metal or alloyed metal oxide comprises an alloy with a semimetal and/or a non-metal.

10. The optical element according to claim 9, wherein the semimetal and/or non-metal comprises nitrogen.

11. The optical element according to claim 9, wherein the semimetal and/or non-metal comprises boron.

12. The optical element according to claim 11, wherein the alloyed metal or alloyed metal oxide comprises alloyed zirconium oxide.

13. The optical element according to claim 11, wherein the boron comprises from about 1% to about 15% by mole fraction of the capping layer.

14. The optical element according to claim 8, wherein the alloyed metal or alloyed metal oxide comprises alloyed ruthenium.

15. The optical element according to claim 1, wherein the capping layer comprises Mo.sub.(x-y) Ru.sub.xB.sub.y, wherein x+y=1, and wherein 0.01≤y≤0.15.

16. The optical element according to claim 1, wherein said optical element is a collector minor.

17. The optical element according to claim 1, wherein said optical element is a pellicle, a dynamic gas lock membrane, a reticle, or a reticle-stage fiducial marker.

18. The optical element according to claim 1, wherein the capping layer comprises a mixed metal oxide.

19. The optical element according to claim 1, wherein the capping layer comprises yttrium stabilised zirconia.

20. A lithography apparatus including an optical element according to claim 5.

21. An optical element for a lithographic apparatus, said optical element comprising a capping layer comprising two or more metal oxides.

22. The optical element according to claim 21, wherein said capping layer further comprises a metal or semi-metal dopant therein.

23. The optical element according to claim 22, wherein the metal or semi-metal dopant comprises one or more metals selected from the group consisting of yttrium, cerium, calcium, magnesium, titanium, and a rare-earth metal.

24. The optical element according to claim 23, wherein the optical element is a collector mirror of the lithography apparatus.

25. The optical element according to claim 21, wherein the capping layer comprises zirconium oxide and yttrium oxide.

26. An optical element for a lithographic apparatus, said optical element comprising a ruthenium capping layer that includes one or more dopants therein.

27. The optical element according to claim 26, wherein said one or more dopants is selected from the group consisting of boron and nitrogen.

28. The optical element according to claim 27, wherein the one or more dopants are present in an amount ranging from about 1% to about 25%, by mole fraction, of the capping layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0052] FIG. 1 depicts a lithographic apparatus according to an embodiment of the invention;

[0053] FIG. 2 schematically depicts a cross-section through a capping layer according to an embodiment of the invention; and

[0054] FIG. 3 schematically depicts a cross-section through a capping layer according to the present invention.

[0055] The features of the drawings are not necessarily drawn to scale. The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.

DETAILED DESCRIPTION

[0056] FIG. 1 shows a lithographic system. The lithographic system includes a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g. a mask), a projection system PS and a substrate table WT configured to support a substrate W.

[0057] The illumination system IL is configured to condition the radiation beam B before it is incident upon the patterning device MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA to form radiation beam B′) onto the substrate W. The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus aligns the patterned radiation beam B with a pattern previously formed on the substrate W. A pellicle may be located along the path of the radiation for protecting the patterning device MA such as against the patterning device MA. The illumination system IL may include a faceted field minor device 10 and a faceted pupil minor device 11. The faceted field minor device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other minors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.

[0058] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B′ is generated. The projection system PS is configured to project the patterned EUV radiation beam B′ onto the substrate W. For that purpose, the projection system PS may include mirrors 13, 14 which are configured to project the patterned EUV radiation beam B′ onto the substrate W held by the substrate table WT. In some embodiments, the projection system PS may apply a reduction factor to the patterned EUV radiation beam B′, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied in some embodiments. Although the projection system PS is illustrated as having only two minors 13, 14 in FIG. 1, the projection system PS may include a different number of mirrors (e.g., six or eight mirrors) in other embodiments.

[0059] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B′, with a pattern previously formed on the substrate W.

[0060] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and/or in the projection system PS.

[0061] The radiation source SO, illumination system IL, and projection system PS may all be constructed and arranged such that they can be isolated from the external environment. A gas at a pressure below atmospheric pressure (e.g. hydrogen) may be provided in the radiation source SO. A vacuum may be provided in illumination system IL and/or the projection system PS. As mentioned, a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL and/or the projection system PS.

[0062] The radiation source SO shown in FIG. 1 may be of a type referred to as a laser produced plasma (LPP) source. A laser system 1 which may be a CO.sub.2 laser in various embodiments, is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn) which is provided from a fuel emitter 3. The energy is directed along laser beam 2 to the fuel. Although tin is referred to in the following description, any suitable fuel may be used. The fuel may for example be in liquid form, and may for example be a metal or alloy. The fuel emitter 3 may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident upon the tin at the plasma formation region 4. The deposition of laser energy into the tin creates a plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during de-excitation and recombination of ions of the plasma.

[0063] The EUV radiation is collected and focused by a near normal incidence radiation collector 5 (sometimes referred to more generally as a normal incidence radiation collector or collector minor). The collector 5 may have a multilayer structure which is arranged to reflect EUV radiation. The EUV radiation may have a wavelength in the range of about 4 nm to about 20 nm, and in some embodiments, the EUV radiation may have a wavelength such as 13.5 nm. In some embodiments, collector 5 may have an elliptical configuration, having two ellipse focal points. A first focal point may be at the plasma formation region 4, and a second focal point may be at an intermediate focus 6, as discussed below.

[0064] The laser system 1 may be separated from the radiation source SO. Where this is the case, the laser beam 2 may be passed from the laser system 1 to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing minors and/or a beam expander, and/or other optics. The laser system 1 and the radiation source SO may together be considered to be a radiation system.

[0065] Radiation that is reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at a point to form an image of the plasma formation region 4, which acts as a virtual radiation source for the illumination system IL. The point at which the radiation beam B is focused may be referred to as the intermediate focus 6. The radiation source SO is arranged such that the intermediate focus 6 is located at or near to an opening 8 in an enclosing structure of the radiation source SO.

[0066] The radiation beam B passes from the radiation source SO into the illumination system IL, which is configured to condition the radiation beam. The illumination system IL may include a facetted field minor device 10 and a facetted pupil minor device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B passes from the illumination system IL and is incident upon the patterning device MA held by the support structure MT. The patterning device MA reflects and patterns the radiation beam B. The illumination system IL may include other mirrors or devices in addition to or instead of the faceted field mirror device 10 and faceted pupil mirror device 11.

[0067] Following reflection from the patterning device MA the patterned radiation beam B′ enters the projection system PS. The projection system comprises a plurality of minors 13, 14 which are configured to project the radiation beam B′ onto a substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the radiation beam, forming an image with features that are smaller than corresponding features on the patterning device MA. A reduction factor of 4 may for example be applied. Although the projection system PS has two minors 13, 14 in FIG. 1, the projection system may include any number of mirrors (e.g. six minors).

[0068] The radiation sources SO shown in FIG. 1 may include components which are not illustrated. For example, a spectral filter may be provided in the radiation source. The spectral filter may be substantially transmissive for EUV radiation but substantially blocking for other wavelengths of radiation such as infrared radiation.

[0069] If the patterning device MA is left unprotected, the contamination can require the patterning device MA to be cleaned or discarded. Cleaning the patterning device MA interrupts valuable manufacturing time and discarding the patterning device MA is costly. Replacing the patterning device MA also interrupts valuable manufacturing time. As such a pellicle may be used to cover or otherwise protect patterning device MA.

[0070] FIG. 2 depicts a stack formed over substrate 20, including a capping layer 16. The illustrated layers are provided on a surface of substrate 20 which may be one or more of the optical elements described in the present application. For example, in some embodiments, the optical element with the illustrated capping layer may be collector 5 of FIG. 1. Alternatively or additionally, the illustrated layers may be provided on a surface of substrate 20 which may be a pellicle or dynamic gas lock membrane or on various other optical elements. There may be optional layers 17 and 18 underneath the capping layer 16. These optional layers 17, 18 may serve to reduce the lattice mismatch between the materials of the multilayer 19 and the capping layer 16 or may serve as, for example, diffusion barriers. The multilayer 19 may comprise alternating layers of silicon and molybdenum in some embodiments. Although FIG. 2 depicts four layers in the multilayer 19, it will be appreciated that there may be any suitable number of layers in the multilayer 19 and the present invention is not limited by the number of layers in the multilayer, nor to silicon and molybdenum as the multilayers. Capping layer 16, optional layers 17, 18 and multilayer 19 are disposed on a substrate 20 which may represent any of the optical elements described herein. Any suitable substrate may be used and the invention is not limited to a particular substrate nor a particular optical element. The disclosed capping layer according to the present invention may be any of the capping layers described herein and may comprise a plurality of oxygen vacancies therein. In an embodiment, the capping layer 16 comprises zirconium oxide and yttrium oxide in a mole fraction of from about 70:1 to about 5:1.

[0071] FIG. 3 is similar to FIG. 2, but the stack includes a sub-capping layer 16a below the capping layer 16. The sub-capping layer 16a may comprise a material which does not include a plurality of oxygen vacancies. As such, the capping layer 16 which includes a plurality of oxygen vacancies and may be any of the capping layers described herein, may be positioned on the sub-capping layer 16a. In this way, the capping layer comprising a plurality of oxygen vacancies may be in addition to a capping layer material which is already used on optical elements for lithography apparatus.

[0072] Although specific reference has been made to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. Where applicable, the disclosure herein may be applied to optical elements used such manufacturing tools as well as in various other types of wafer or other processing tools.

[0073] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the various layers may be replaced by other layers that perform the same function.

[0074] Other aspects of the invention are set out in the following numbered clauses.

1. An optical element for a lithographic apparatus, said optical element comprising a capping layer that includes a plurality of oxygen vacancies therein.
2. The optical element according to clause 1, wherein the capping layer comprises a doped zirconium oxide.
3. The optical element according to clause 2, wherein the zirconium oxide includes a trivalent cation in its oxidized state as a dopant therein.
4. The optical element according to clause 1, wherein the capping layer comprises zirconium oxide and one or more metal oxides selected from the group consisting of oxides of yttrium, cerium, calcium, magnesium, titanium, and rare-earth metals.
5. The optical element according to clause 1, wherein the capping layer comprises zirconium oxide and yttrium oxide.
6. The optical element according to clause 1, wherein the capping layer comprises yttrium stabilized zirconium oxide.
7. The optical element according to clause 4, wherein the one or more metal oxides comprise from about 1% to about 25%, by mole fraction, of the capping layer.
8. The optical element according to clause 1, wherein the capping layer comprises an alloyed metal or an alloyed metal oxide.
9. The optical element according to clause 8, wherein the alloyed metal or alloyed metal oxide comprises an alloy with a semimetal and/or a non-metal.
10. The optical element according to clause 9, wherein the semimetal and/or non-metal comprises boron.
11. The optical element according to clause 9, wherein the semimetal and/or non-metal comprises nitrogen.
12. The optical element according to clause 10 or 11, wherein the alloyed metal or alloyed metal oxide comprises alloyed zirconium oxide.
13. The optical element according to clause 10 or 11, wherein the alloyed metal or alloyed metal oxide comprises alloyed ruthenium.
14. The optical element according to clause 10, wherein the boron comprises from about 1% to about 15% by mole fraction of the capping layer.
15. The optical element according to clause 1, wherein the capping layer comprises Mo.sub.(x-y)Ru.sub.xB.sub.y, wherein x+y=1, and wherein 0.01≤y≤0.15.
16. The optical element according to any preceding clause, wherein said optical element is a collector mirror.
17. The optical element according to any of preceding clauses 1 to 15, wherein said optical element is a pellicle, a dynamic gas lock membrane, a reticle, or a reticle-stage fiducial marker.
18. The optical element according to clause 1, wherein the capping layer comprises a mixed metal oxide.
19. The optical element according to clause 1, wherein the capping layer comprises yttrium stabilised zirconia.
20. A lithography apparatus including an optical element according to any preceding clause.
21. An optical element for a lithographic apparatus, said optical element comprising a capping layer comprising two or more metal oxides.
22. The optical element according to clause 21, wherein said capping layer further comprises a metal or semi-metal dopant therein.
23. The optical element according to clause 22, wherein the metal dopant comprises one or more metals selected from the group consisting of yttrium, cerium, calcium, magnesium, titanium, and a rare-earth metal.
24. The optical element according to clause 21, wherein the capping layer comprises zirconium oxide and yttrium oxide.
25. An optical element for a lithographic apparatus, said optical element comprising a ruthenium capping layer that includes one or more dopants therein.
26. The optical element according to clause 25, wherein said one or more dopants is selected from the group consisting of boron and nitrogen.
27. The optical element according to clause 26, wherein the one or more dopants are present in an amount ranging from about 1% to about 25%, by mole fraction, of the capping layer.
28. The optical element according to any of clauses 21 to 27, wherein the optical element is a collector minor of a lithography apparatus.

[0075] The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.