OPTICAL ELEMENT, OPTICAL ASSEMBLY AND PRODUCTION METHOD

Abstract

An optical element for transmitting radiation includes: a first surface region surrounding an optically used area of the optical element; and a second surface region that adjoins the first surface region. A circumferential edge is formed between the first and second surface regions. The optical element further includes a one-piece film which covers the first surface region, the edge and the second surface region. The film includes a hydrophobic material at least on its side facing away from the first and the second surface regions. An optical assembly includes at least one such optical element. A method produces such an optical element.

Claims

1. An article configured to transmit radiation, the article comprising: an optical element comprising an optically used region, a first surface region surrounding the optically used region, and a second surface region adjoining the first surface region so that a peripheral edge is present between the first and second surface regions; and a one-piece film covering the first surface region, the peripheral edge and the second surface region, wherein: the one-piece film comprises a hydrophobic material at least on a side of the one-piece film facing away from the first and second surface regions; and the one-piece film is preformed.

2. The article of claim 1, wherein the one-piece film has a bend in a region of the peripheral edge.

3. The article of claim 1, further comprising an adhesive layer connecting the one-piece film to the first and second surface regions.

4. The article of claim 3, wherein: the adhesive layer comprises first and second portions; the first portion of the adhesive layer connects the one-piece film to the first surface region; and the second portion of the adhesive layer connects the one-piece film to the second surface region.

5. The article of claim 3, wherein the adhesive layer comprises an adhesive tape.

6. The article of claim 1, further comprising a heat-conducting component between the one-piece film and at least one region selected from the group consisting of the first surface region and the second surface region.

7. The article of claim 6, wherein the heat-conducting component comprises a heat-conducting layer.

8. The article of claim 6, wherein the heat-conducting component extends into the first and second surface regions.

9. The article of claim 6, further comprising first and second adhesive layers, wherein the heat-conducting component is embedded between the first and second adhesive layers.

10. The article of claim 6, wherein the heat-conducting component does not extend to an edge of the one-piece film in at least one region selected from the group consisting of the first surface region and the second surface region.

11. The article of claim 6, wherein the heat-conducting component comprises a material having a thermal conductivity greater than 100 W m.sup.−1 K.sup.−1.

12. The article of claim 1, wherein the one-piece film has a thermal conductivity of more than 100 W m.sup.−1 K.sup.−1.

13. The article of claim 1, wherein the hydrophobic material of the one-piece film comprises at least one material selected from the group consisting of polyolefins, polyacrylates, (poly)vinylchlorides, polystyrenes, polysiloxanes, polycarbonates and epoxy polymers.

14. The article of claim 1, wherein the hydrophobic material is roughened on the side of the one-piece film that faces away from the first and second surface regions.

15. The article of claim 1, wherein the hydrophobic material comprises a coating on the side of the one-piece film facing away from the first and second surface regions.

16. The article of claim 1, wherein the one-piece film has a thickness of less than 500 μm.

17. The article of claim 1, further comprising a radiation-protection layer on at least one region selected from the group consisting of the first surface region and the second surface region.

18. The article of claim 1, wherein the first surface region defines a peripheral lateral surface of a conical volume region of the optical element.

19. The article of claim 18, wherein the second surface region is planar and surrounds the first surface region in an annular manner.

20. The article of claim 1, wherein the second surface region is planar and surrounds the first surface region in an annular manner.

21. An apparatus, comprising: an article according to claim 1, wherein the apparatus is an immersion lithography projection exposure apparatus.

22. The optical assembly of claim 21, further comprising an immersion fluid, wherein an end face of the article is at least partially immersed in the immersion fluid.

23. A method, comprising: forming a one-piece film; connecting the one-piece film to: i) an optically used region of an optical element; ii) a first surface region of the optical element; and iii) a second surface region of the optical element, wherein: the first surface region surrounds the optically used region; the second surface region adjoins the first surface region so that a peripheral edge is present between the first and second surface regions; and the one-piece film comprises a hydrophobic material at least on a side of the one-piece film facing away from the first and second surface regions.

24. The method of claim 23, further comprising: forming a bend in the one-piece film in a region of the peripheral edge; and after forming the bend, connecting the one-piece film to the first and second regions of the optical element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Exemplary embodiments are represented in the schematic drawings and are explained in the following description. In the drawings:

[0044] FIG. 1 shows a schematic representation of a projection exposure apparatus for immersion lithography with an optical element in the form of a lens, which has a conical volume region that is partially immersed into an immersion fluid;

[0045] FIGS. 2a-d show schematic representations of a number of process steps in the production of an optical element according to FIG. 1 that includes a film with a hydrophobic material; and

[0046] FIGS. 3a-d show schematic representations of a number of process steps analogous to FIGS. 2a-d, in which a heat-conducting layer is introduced between the film and a first and second surface region of the optical element.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0047] In the following description of the drawings, identical reference signs are used for identical or functionally identical components.

[0048] In FIG. 1, an optical assembly 10 in the form of a microlithographic projection exposure apparatus, to be more precise in the form of a wafer scanner, for the production of large-scale-integrated semiconductor components is schematically shown. The optical assembly 10 includes as a light source an excimer laser 11 for generating radiation 2 with a used wavelength λ.sub.B of 193 nm, other used wavelengths, for example 248 nm, also being possible. A downstream illumination system 12 generates in its exit plane a large, sharply delimited image field adapted to the desired telecentricity properties of a downstream projection lens 13.

[0049] A device 14 for holding and manipulating a photomask (not shown) is arranged after the illumination system 12 such that the mask lies in the object plane 15 of the projection lens 13 and is movable in this plane for scanning operation in a traveling direction indicated by an arrow 16.

[0050] Following after the plane 15, which is also referred to as the mask plane, is the projection lens 13, which projects an image of the photomask at a reduced scale, for example at a scale of 4:1 or 5:1 or 10:1, onto a wafer 17 coated with a photoresist layer. The wafer 17 used as a light-sensitive substrate is arranged such that the plane substrate surface 18 with the photoresist layer substantially coincides with the image plane 19 of the projection lens 13. The wafer 17 is held by a device 20, which includes a scanner drive, in order to move the wafer 17 synchronously in relation to the photomask and parallel to it. The device 20 also includes manipulators for moving the wafer both in the z direction parallel to an optical axis 21 of the projection lens 13 and in the x and y directions perpendicular to this axis.

[0051] The projection lens 13 has as a final element adjacent to the image plane 19 an optical element 1 in the form of a plano-convex lens with a conical volume region 3, the end face 4 of which forms the last optical face of the projection lens 13 and is arranged at a working distance above the substrate surface 18. Arranged between the end face 4 and the substrate surface 18 is an immersion fluid 22, in the present case water, to be more precise ultrapure water, in order to increase the output-side numerical aperture of the projection lens 13. Via the immersion fluid 22, the imaging of structures on the photomask can take place with a higher resolution and depth of field than is possible if the intermediate space between the optical element 1 and the wafer 17 is filled with a medium with a lower refractive index, for example air. The gap that forms the intermediate space is generally between 2 mm and 4 mm.

[0052] In the example shown, the lens element 1 consists of synthetic, amorphous quartz glass (SiO.sub.2) and has the conical volume region 3 described further above, on the underside of which the end face 4 of the lens element 1 is formed. The radiation 2 produced by the light source 11 passes in a directed manner through the end face of the lens element 1 that forms or delimits an optically used region 4 of the lens element 1. A first surface region 5 in the form of a peripheral lateral surface of the conical lens part 3 surrounds the optically used region 4 and is partially wetted by the immersion fluid 22. The conical, radially inward lens part 3 or the conical lateral surface 5 is adjoined radially outwardly by a plane, second surface region 6. Formed between the conical first surface region 5 and the plane second surface region 6 is an annularly peripheral edge 7, i.e. the first and second surface regions 5, 6 are aligned in relation to one another in the radial direction by an angle which in the example shown is more than about 100°.

[0053] The radiation 2 of the light source 11 does not pass in a directed manner through either the first surface region 5 in the form of the lateral surface or the plane second surface region 6, i.e. these two surface regions 5, 6 are outside the beam path of the radiation 2 generated by the light source 11.

[0054] Droplets of the immersion fluid 22 may remain on the surface regions 5, 6 of the lens element 1 that are not immersed or only partially immersed in the immersion fluid 22. When these droplets evaporate, there is locally a cooling down of the quartz glass material of the lens element 1, which leads to a local change in the refractive index and also leads to the lens element 1 being deformed locally as a result of the thermal expansion. Both effects can lead to image errors, and are therefore undesired.

[0055] In order to prevent local cooling down of the lens element 1 by the evaporating immersion fluid 22, or to minimize the local temperature gradients thereby occurring, a film 8 that includes a hydrophobic material is applied to the lens element 1, as described below on the basis of FIGS. 2a-d.

[0056] Shown in FIG. 2a is a one-piece film 8 with a three-dimensional geometry which is adapted to the geometry of the optical element 1, to be more precise to the geometry of the first and second surface regions 5, 6. In the example shown, only on its side facing the immersion fluid 22 is the film 8 formed from a hydrophobic material, which has been applied to the film 8 in the form of a coating 34. The coating 34 may be applied to the film 8 before or possibly after the preforming. In the example shown, the film 8 consists of a metallic material, for example of silver, and consequently serves at the same time as a heat-conducting component. In the example shown, the film 8 has a typically constant thickness D, which is less than 500 μm, preferably less than 350 μm, and generally does not go below a thickness D of 50 μm.

[0057] The coating 34 of the hydrophobic material may for example contain hydrophobic molecules with fluoroalkyl groups and/or hydrocarbon groups. The application of colloidal SiO.sub.2 nanoparticles or SiO.sub.2 soot provided with a fluorosilane coating is also possible to form the hydrophobic material. Alternatively, a layer of colloidal silicon may be provided with a hydrocarbon layer in order to form the hydrophobic coating 34. It goes without saying that the hydrophobic coating 34 of the film 8 may also be formed in a way other than that described here.

[0058] In the example shown in FIG. 2a, the film 8 is preformed, i.e. it has a first, conical film portion 8a and a second, plane film portion 8b, between which there is formed a bend 8c or a rounding, which forms a continuous transition between the film portions 8a, 8b. If appropriate, the transition between the film portions 8a, 8b may also take place discontinuously, i.e. the bend 8c forms a kink. The preformed film 8 may for example be produced by embossing or thermoforming an annular or circular plane film that is suitably cut to shape. If appropriate, the three-dimensionally shaped film 8 may be produced in a generative layer building process, for example via a 3D printer. The preforming of the film 8 facilitates the application of the film 8 to the first and second surface regions 5, 6 of the optical element 1.

[0059] FIG. 2b shows the preformed film 8, to which an adhesive layer 30 in the form of an adhesive tape has been applied. In the example shown, the adhesive layer 30 has a first adhesive layer portion 30a, which has been applied to the conical film portion 8a in order to connect the film 8 to the first surface region 5. A second adhesive layer portion 30b has been applied to the plane, annular film portion 8b of the film 8 and serves for connecting the film 8 to the second, plane surface region 6 of the optical element 1. In the example shown, the adhesive layer 30 is formed in two parts, so that the region of the bend 8c is not provided with an adhesive layer 30. The desire for the adhesive layer 30 to be preformed, as is the case with the film 8, can be avoided by the use of two adhesive layer portions 30a, 30b.

[0060] It may be possible to dispense with the provision of the first adhesive layer portion 30a, i.e. the film 8 is only connected to the second, plane surface region 6 of the optical element 1 by way of the second adhesive layer portion 30b. In this case, the immersion fluid 22 can penetrate into the gap formed between the first surface region 5 and the film 8, which however has virtually no effects on the imaging quality of the optical element 1 as a result of the heat-conducting properties of the film 8 shown in FIGS. 2a, b, which brings about a homogenization of the temperature in the region of the gap.

[0061] FIG. 2c shows the film 8 from FIG. 2b during the attachment to the optical element 1. Applied to the optical element 1 in the first and second surface regions 5, 6 is a radiation-protection layer 33, which consists of a material that has absorbent properties at wavelengths of less than 250 nm, in particular at the used wavelength λ.sub.B, or is substantially non-transmissive to radiation at these wavelengths. An oxidic material may serve for example as the radiation-protection layer 33, for example titanium dioxide (TiO.sub.2), tantalum pentoxide (Ta.sub.2O.sub.5), hafnium dioxide (HfO.sub.2), zirconium dioxide (ZrO.sub.2) etc.

[0062] As can be seen in FIG. 2c, the first adhesive layer portion 30a on the conical film portion 8a of the preformed film 8 is connected to the first, conical surface region 5 of the optical element 1. Correspondingly, the second adhesive layer portion 30b on the plane film portion 8b is connected to the second, plane surface region 6 of the optical element 1. For this purpose, the film 8 is placed onto the first and second surface regions 5, 6 of the optical element 1, as indicated in FIG. 2c by arrows. FIG. 2d shows the optical element 1 after the completion of the connection process. Since the first and second adhesive layer portions 30a, 30b in each case run around in an annular manner, no immersion fluid 22 can penetrate into the intermediate space between the film 8 and the first and second surface regions 5, 6.

[0063] Shown in FIGS. 3a-d is a method for producing an optical element 1 that differs from the method described in conjunction with FIGS. 2a-d firstly in that the film 8 itself consists of a hydrophobic material, to be precise in the example shown of PTFE. It goes without saying that other hydrophobic materials that can be produced in the form of a film 8 can also be used, for example other polyolefins, for example polypropylene, polyacrylates, for example (poly)methylmethacrylate, (poly)vinylchlorides, polystyrenes, polysiloxanes, polycarbonates, epoxy polymers, etc.

[0064] In the example shown in FIGS. 3a-d, a heat-conducting component in the form of a heat-conducting metallic layer 32 has been introduced between the preformed film 8 and the first and second surface regions 5, 6. As can be seen in FIG. 3b, for this purpose the metallic layer 32 is placed onto a first adhesive layer 30, which as in FIG. 2b has a first and second adhesive layer portion 30a, 30b. A second adhesive layer 31, which likewise has a first adhesive layer portion 31a and a second adhesive layer portion 31b, covers the heat-conducting layer 32, so that the latter is embedded between the first and second adhesive layers 30, 31.

[0065] To improve the adhesion of the film 8 to the first adhesive layer 30, it may be desired or advantageous to subject the hydrophobic material of the film 8 to a surface treatment, for example an etching process, a plasma treatment and/or a machining operation. The hydrophobic material of the film 8 may alternatively or additionally also be structured and/or roughened on the side facing the immersion fluid 22, in order to increase its hydrophobicity. For this purpose, the film 8 may be subjected to a surface treatment on the side facing the immersion fluid 22, for example an etching process, a plasma treatment and/or a machining operation. It goes without saying that such a treatment may also be carried out on the film 8 described in FIGS. 2a-d, to be more precise on its hydrophobic coating 34.

[0066] As can likewise be seen in FIG. 2b, the metallic layer 32 is formed as one part and extends both into the first surface region 5 and into the second surface region 6 of the optical element 1, i.e. the heat-conducting layer 32 covers the bend 8c of the film 8 or the edge 7 between the first and second surface regions 5, 6. In this way, the heat-conducting layer 32 can produce a heat transfer between the first and second surface regions 5, 6.

[0067] Suitable as materials for the heat-conducting layer 32 are in particular metals that have a high thermal conductivity of for example more than 100 W m.sup.−1 K.sup.−1, for example silver, which has a thermal conductivity of 429 W m.sup.−1 K.sup.−1, but also other metals, such as for example Ag, Cu, Au, Al, Mo, Zn, Mg, tungsten, alloys such as for example brass and also nonmetallic materials such as carbon (for example graphite, nanotubes, diamond), SiC, AlN, Si, NiP, . . . . The heat-conducting layer 32 may be formed in one piece, without having to be preformed for this purpose, since the heat-conducting layer 32 is applied to the first adhesive layer 30. The heat-conducting layer 32 may alternatively be preformed before it is applied to the first adhesive layer 30.

[0068] As can be seen in particular in FIG. 3b, the heat-conducting layer 32 extends neither up to the inner edge of the first surface region 5, or up to the inner edge of the film 8, nor up to the outer edge of the second surface region 6, or up to the outer edge of the film 8, but is at a distance from it of more than about 1 mm or more than about 2 mm. In this way the immersion fluid 22 can be prevented from being able to penetrate into the region between the film 8 and the first and second surface regions 5, 6. If appropriate, the heat-conducting layer 32 may also extend up to the edge of the first and/or second surface region 5, 6, as long as sufficient impermeability of the connection between the film 8 and the first and/or second surface region 5, 6 is ensured.

[0069] Unlike the situation shown in FIGS. 2a-d and in FIGS. 3a-d, the film 8 may cover not only the second surface region 6 of the optical element 1 but possibly also further components, for example a mount or the like, on which the optical element 1 is fastened in the projection lens 13. In this case the film 8, to be more precise its plane surface region 8b, has a diameter that is greater than the diameter of the optical element 1 or the diameter of the second, plane surface region 6. If appropriate, the second surface region 6 may be adapted in the portion projecting over the optical element 1 to the geometry of components that are present there, in that in this portion the film 8 is preformed or suitably cut to shape.

[0070] It goes without saying that optical elements for immersion lithography do not necessarily have to have the plano-convex geometry described further above; however, a conically shaped volume region 3 is typical for such optical elements. In particular instead of amorphous quartz glass, the optical element 1 or its main body may consist of some other material that is transparent above a wavelength of about 250 nm or about 193 nm, for example of crystalline quartz glass (SiO.sub.2), barium fluoride (BaF.sub.2) or germanium dioxide (GeO.sub.2).