OPTICAL ELEMENT AND PELLICLE MEMBRANE FOR A LITHOGRAPHIC APPARATUS

Abstract

An optical element for a lithographic apparatus, the optical element including an anchor layer selected to support a top layer having self-terminating growth in an operating lithographic apparatus or plasma containing environment. Also described is a method of manufacturing an optical element, the method including depositing a top layer on anchor layer via exposure to plasma, preferably electromagnetically induced plasma. Lithographic apparatuses including such optical elements are also described.

Claims

1. An optical element for a lithographic apparatus, the optical element comprising an anchor layer selected to support a top layer having self-terminating growth in an operating lithographic apparatus or plasma containing environment.

2. The optical element according to claim 1, further comprising a substrate layer.

3. The optical element according to claim 1, further comprising a wetting layer.

4. The optical element according to claim 1, including the top layer.

5. The optical element according to claim 1, wherein the anchor layer and the top layer when supported by the anchor layer form a plasma etch barrier.

6. (canceled)

7. The optical element according to claim 1, wherein the top layer comprises one or more elements selected from the group consisting of Si, Ge, Sn, B, P, Mg, and Al.

8. The optical element according to claim 3,wherein the wetting layer comprises one or more elements selected from the group consisting of Cr, Ti, and Mo.

9. The optical element according to claim 1, wherein the anchor layer comprises one or more elements selected from the group consisting of Pt, Ru, Os, Rh, Ir, and Pd.

10. (canceled)

11. The optical element according to claim 1, including an anchor layer-top layer combination selected from the list consisting of: [Ru—SiO.sub.x], [Pt—SiO.sub.x], [Rh—SiO.sub.x], [Ru—GeO.sub.x], [Rh—GeO.sub.x], [Ru—SnO.sub.x], and [Rh—SnO.sub.x].

12. The optical element according to claim 2, wherein the substrate layer comprises carbon nanotubes and a wetting layer.

13. A method of manufacturing an optical element, the method comprising depositing a top layer on an anchor layer via exposure to plasma.

14. The method according to claim 13, wherein the top layer comprises one or more elements selected from the group consisting of Si, Ge, Sn, B, P, Mg, and Al, and/or further comprising a wetting layer that comprises one or more elements selected from the group consisting of Cr, Ti, and Mo; and/or wherein the anchor layer comprises one or more elements selected from the group consisting of Pt, Ru, Os, Rh, Ir, and Pd.

15. (canceled)

16. A pellicle membrane for a lithographic apparatus, the pellicle membrane including a non-volatile sacrificial material.

17. The pellicle membrane according to claim 16, wherein the non-volatile sacrificial material comprises a material having a higher redox potential than at least one other material in the membrane.

18. (canceled)

19. The pellicle membrane according to claim 16, wherein the non-volatile sacrificial material comprises one or more elements selected from the list consisting of silver, gold, platinum, iron, manganese, and tellurium.

20. The pellicle membrane according to claim 19, wherein the non-volatile sacrificial material is an oxidised form.

21. The pellicle membrane according to claim 16, wherein the membrane is configured to have the non-volatile sacrificial material in direct contact with the plasma environment of a lithographic apparatus.

22-26. (canceled)

27. A pellicle assembly for use in a lithographic apparatus, the pellicle assembly including the pellicle membrane of claim 16.

28. (canceled)

29. A lithographic apparatus comprising the optical element of claim 1.

30. The optical element according to claim 1, comprising a pellicle membrane including a non-volatile sacrificial material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawing in which corresponding reference symbols indicate corresponding parts, and in which:

[0060] FIG. 1 depicts a lithographic apparatus according to an embodiment of the invention;

[0061] FIG. 2 is a schematic depiction of an optical element according to an embodiment of the present invention; and

[0062] FIG. 3 is a schematic depiction of a portion of an optical element according to an embodiment of the present invention.

[0063] 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

[0064] FIG. 1 shows a lithographic system including a pellicle 15 (also referred to as a membrane assembly) according to the present invention. The lithographic system comprises 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. 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) 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. In this embodiment, the pellicle 15 is depicted in the path of the radiation and protecting the patterning device MA. It will be appreciated that the pellicle 15 may be located in any required position and may be used to protect any of the mirrors in the lithographic apparatus.

[0065] 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. 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.

[0066] The radiation source SO shown in FIG. 1 is of a type which may be referred to as a laser produced plasma (LPP) source. A laser, which may for example be a CO.sub.2 laser, is arranged to deposit energy via a laser beam into a fuel, such as tin (Sn) which is provided from a fuel emitter. 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 may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region. The laser beam is incident upon the tin at the plasma formation region. The deposition of laser energy into the tin creates a plasma at the plasma formation region. Radiation, including EUV radiation, is emitted from the plasma during de-excitation and recombination of ions of the plasma.

[0067] The EUV radiation is collected and focused by a near normal incidence radiation collector (sometimes referred to more generally as a normal incidence radiation collector). The collector may have a multilayer structure which is arranged to reflect EUV radiation (e.g. EUV radiation having a desired wavelength such as 13.5 nm). The collector may have an elliptical configuration, having two ellipse focal points. A first focal point may be at the plasma formation region, and a second focal point may be at an intermediate focus, as discussed below.

[0068] The laser may be separated from the radiation source SO. Where this is the case, the laser beam may be passed from the laser to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and/or a beam expander, and/or other optics. The laser and the radiation source SO may together be considered to be a radiation system.

[0069] Radiation that is reflected by the collector forms a radiation beam B. The radiation beam B is focused at a point to form an image of the plasma formation region, 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. The radiation source SO is arranged such that the intermediate focus is located at or near to an opening in an enclosing structure of the radiation source.

[0070] 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 mirror device 10 and a facetted pupil mirror 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.

[0071] Following reflection from the patterning device MA the patterned radiation beam B enters the projection system PS. The projection system comprises a plurality of mirrors 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 mirrors 13, 14 in FIG. 1, the projection system may include any number of mirrors (e.g. six mirrors).

[0072] 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.

[0073] In an embodiment the membrane assembly 15 is a pellicle for the patterning device MA for EUV lithography. The membrane assembly 15 of the present invention can be used for a dynamic gas lock or for a pellicle or for another purpose. In an embodiment the membrane assembly 15 comprises a membrane formed from the at least one membrane layer configured to transmit at least 90% of incident EUV radiation. In order to ensure maximized EUV transmission and minimized impact on imaging performance it is preferred that the membrane is only supported at the border.

[0074] 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.

[0075] FIG. 2 depicts an embodiment of a pellicle membrane according to the present invention. The pellicle assembly 15 includes a pellicle membrane generally depicted as 16. The pellicle membrane 16 include a substrate 17. The substrate 17 is generally thicker than the other layers which make up the pellicle membrane 16. The depiction of FIG. 2 is exemplary and is not indicative of the true relative thicknesses of the various layers. The substrate 17 is generally silicon or carbon, which may be in the form of carbon nanotubes. A wetting layer 18 is disposed on the substrate 17. The wetting layer 17 serves to reduce or eliminate dewetting of the overlying anchor layer 19. A self-limiting top layer 20 is disposed on anchor layer 19. The hashed lines between anchor layer 19 and self-limiting top layer 20 depict the strong bond between the two layers which serves to prevent etching of the self-limiting top layer 20.

[0076] FIG. 3 depicts an embodiment of a pellicle membrane according to the present invention. In particular, FIG. 3 depicts a portion of a pellicle membrane comprising a carbon nanotube (CNT) substrate 22. The carbon nanotube 22 has a hollow core 26. The depicted embodiment is a single wall carbon nanotube, although it will be appreciated that double- and multi-walled carbon nanotubes are also possible substrates. In the depicted embodiment, the CNT has a diameter of around 10 nm, although the invention is not particularly limited to this diameter and other diameters may be used. Disposed on the CNT substrate 22, there is a wetting layer 23 of molybdenum. The thickness of the molybdenum layer is from around 0.1 nm to around 1 nm in thickness. The molybdenum layer functions as a wetting layer to prevent or substantially reduces the tendency of the overlying anchor layer 24 to dewet. In the depicted embodiment, the anchor layer 24 comprises ruthenium. The thickness of the ruthenium layer is from around 2 nm to around 4 nm. A self-terminating non-etchable top layer 25 is provided on the anchor layer 24. In the depicted embodiment, the self-terminating non-etchable top layer 25 comprises silicon oxide. The thickness of the silicon oxide layer is from around 1 nm to around 2.5 nm in thickness. A pellicle membrane having such a configuration displays almost complete resistance to etching in a lithographic apparatus and also has EUV transmissivity of over 90% as well as a thermal emissivity of over 50%. As such, a pellicle apparatus comprising such a membrane has advantageous mechanical lifetime in a lithography apparatus, particularly an EUV lithography apparatus, as well as improved etch resistance to plasmas.

EXAMPLES

[0077] The following examples provide specific embodiments of the present invention. These examples are not intended to be limiting to the scope of the invention.

[0078] The following table includes combinations of anchor layer and self-limiting top layer which are particularly suitable in resisting etching in a lithographic apparatus.

TABLE-US-00001 Anchor Layer Self-limiting top layer (and oxides thereof) Ruthenium Si, Ge, Sn, B, P, Mg, or Al Platinum Si, Ge, Sn, B, P, Mg, or Al Rhodium Si, Ge, Sn, B, P, Mg, or Al Osmium Si, Ge, Sn, B, P, Mg, or Al Iridium Si, Ge, Sn, B, P, Mg, or Al Palladium Si, Ge, Sn, B, P, Mg, or Al

[0079] It has been found that combinations of ruthenium anchor layers with silicon oxide top layers, and platinum anchor layers with silicon oxide top layers are particularly stable to etching in a lithographic apparatus.

[0080] On the other hand, it has been found that a copper of aluminium anchor layer does not offer the same self-limiting growth top layer with resistance to etching.

[0081] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0082] 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.