METHOD FOR PRODUCING A MAIN BODY OF AN OPTICAL ELEMENT FOR SEMICONDUCTOR LITHOGRAPHY, AND MAIN BODY OF AN OPTICAL ELEMENT FOR SEMICONDUCTOR LITHOGRAPHY

Abstract

A method for producing a main body (33) of an optical element for semiconductor lithography includes: —producing a blank (32), —introducing at least one fluid channel (36.x) into the blank (32), then —producing the main body (33) by shaping the blank (32) onto a mold (42). Furthermore, the disclosure describes a main body (33) of an optical element that includes at least one fluid channel (36.x), the fluid channel (36.x) being embodied such that the distance between the fluid channel (36.x) and the surface (40) of the main body (33) provided for an optically active area (41) varies by less than 1 mm, preferably less than 0.1 mm and particularly preferably less than 0.02 mm.

Claims

1. A method for producing a main body of an optical element for semiconductor lithography, comprising: producing a blank with an optical side, introducing at least one fluid channel into the blank, and thereafter producing the main body by shaping the blank onto a mold.

2. The method as claimed in claim 1, wherein said shaping of the blank comprises heating the blank.

3. The method as claimed in claim 1, wherein said introducing comprises introducing the at least one fluid channel at a constant distance from the optical side of the blank.

4. The method as claimed in claim 1, wherein said introducing comprises introducing the fluid channel such that the fluid channel defines a constant distance between the fluid channel and an optical surface of the main body after the main body has been shaped onto the mold.

5. The method as claimed in claim 1, wherein a cross section of the at least one fluid channel changes in response to the shaping.

6. The method as claimed in claim 1, wherein the at least one fluid channel has a circular cross section after said shaping.

7. The method as claimed in claim 1, wherein said shaping of the blank comprises cooling a material surrounding the at least one fluid channel.

8. The method as claimed in claim 7, wherein said cooling comprises setting a temperature of the material surrounding the at least one fluid channel to permit the material to bend.

9. The method as claimed in claim 1, further comprising finishing the main body by forming an optically active area on the optical side of the main body.

10. The method as claimed in claim 9, wherein the optically active area of the optical element is formed to be spherical or aspherical during said finishing.

11. The method as claimed in claim 10, wherein the at least one fluid channel runs at a constant distance from the aspherical optically active area after said finishing.

12. The method as claimed in claim 1, wherein the optical side of the blank comprises depressions.

13. The method as claimed in claim 12, wherein parameters for said shaping of the blank are set so that the depressions rest against the mold during said shaping.

14. An optical element comprising: a main body having an optical side, and at least one fluid channel in the main body, wherein a distance between the at least one fluid channel and the optical side of the main body varies by less than 1 mm.

15. The optical element as claimed in claim 1, wherein the distance between the at least one fluid channel and the optical side of the main body varies by less than 0.02 mm.

16. The optical element as claimed in claim 14, wherein two fluid channels are arranged at two different distances from the optical side of the main body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Exemplary embodiments and variants of the invention are explained in more detail below with reference to the drawing, in which:

[0029] FIG. 1 shows a basic structure of an extreme ultraviolet (EUV) projection exposure apparatus in which embodiments of the invention can be implemented,

[0030] FIG. 2 shows a basic structure of a deep ultraviolet (DUV) projection exposure apparatus in which embodiments of the invention can be implemented,

[0031] FIGS. 3A-C show, in a plan view and two sections, respectively, a schematic illustration of the arrangement of the fluid channels in the blank before shaping,

[0032] FIGS. 4A and 4B show schematic illustrations for explaining two respective points in the production of a convex mirror surface,

[0033] FIG. 5A-C show schematic illustrations for explaining the production of a concave and aspheric optically active area, with reference to a blank with a depression (FIG. 5A), the blank after shaping (FIG. 5B) and the blank after subsequent removal of material (FIG. 5C), and

[0034] FIG. 6 shows a flowchart for a production method according to the invention.

DETAILED DESCRIPTION

[0035] FIG. 1 shows by way of example the basic construction of a microlithographic EUV projection exposure apparatus 1 in which embodiments of the invention can be implemented. An illumination system of the projection exposure apparatus 1 has, in addition to a light source 3, an illumination optical unit 4 for the illumination of an object field 5 in an object plane 6. EUV radiation 14 in the form of optical used radiation generated by the light source 3 is aligned by via a collector, which is integrated in the light source 3, so that it passes through an intermediate focus in the region of an intermediate focal plane 15 before it is incident on a field facet mirror 2. Downstream of the field facet mirror 2, the EUV radiation 14 is reflected by a pupil facet mirror 16. With the aid of the pupil facet mirror 16 and an optical assembly 17 having mirrors 18, 19 and 20, field facets of the field facet mirror 2 are imaged into the object field 5.

[0036] A reticle 7 arranged in the object field 5 and held by a schematically illustrated reticle holder 8 is illuminated. A merely schematically illustrated projection optical unit 9 serves for imaging the object field 5 into an image field 10 in an image plane 11. A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 12, which is arranged in the region of the image field 10 in the image plane 11 and held by a likewise partly represented wafer holder 13. The light source 3 can emit used radiation in particular in a wavelength range of between 1 nm and 120 nm.

[0037] FIG. 2 illustrates an exemplary projection exposure apparatus 21 in which embodiments of the invention can be applied. The projection exposure apparatus 21 serves for imaging structures onto a substrate which is coated with photosensitive materials, and which generally consists predominantly of silicon and is referred to as a wafer 22, for the production of semiconductor components, such as computer chips.

[0038] The projection exposure apparatus 21 in this case substantially comprises an illumination device 23, a reticle holder 24 for receiving and exactly positioning a mask provided with a structure, a so-called reticle 25, by which the subsequent structures on the wafer 22 are determined, a wafer holder 26 for holding, moving and exactly positioning the wafer 22 and an imaging device, specifically a projection lens 27, with a plurality of optical elements 28, which are held with mounts 29 in a lens housing 30 of the projection lens 27.

[0039] The basic functional principle in this case provides for the structures introduced into the reticle 25 to be imaged onto the wafer 22, the imaging generally reducing the scale.

[0040] The illumination device 23 provides a projection beam 31 in the form of electromagnetic radiation, which is required for the imaging of the reticle 25 onto the wafer 22, the wavelength range of this radiation lying between 100 nm and 300 nm, in particular. The source used for this radiation may be a laser, a plasma source or the like. Optical elements in the illumination device 23 are used to shape the radiation such that, when incident on the reticle 25, the projection beam 31 has the desired properties with regard to diameter, polarization, form of the wavefront and the like.

[0041] An image of the reticle 25 is produced by the projection beam 31 and transferred from the projection lens 27 onto the wafer 22 in an appropriately reduced form, as already explained above. In this case, the reticle 25 and the wafer 22 can be moved synchronously, so that regions of the reticle 25 are imaged onto corresponding regions of the wafer 22 virtually continuously during what is called a scanning operation. The projection lens 27 has a multiplicity of individual refractive, diffractive and/or reflective optical elements 28, such as for example lens elements, mirrors, prisms, terminating plates and the like, wherein these optical elements 28 can be actuated for example with one or more actuator arrangements (not shown here).

[0042] FIG. 3A shows a plan view of a schematic illustration, in which a blank 32 of a subsequent main body of an optical element designed as a mirror, for example, is shown. In this case, the blank 32 is a plane-parallel plate and, according to the method described in FIGS. 4A and 4B, becomes the main body of the subsequent mirror. The blank 32 is traversed by fluid channels 36.x which are produced by drilling, for example, and are arranged in two planes 37, 38 (cf. FIGS. 3B and 3C) in the example shown. In this case, the fluid channels 36.1 of a first plane 37 are formed at right angles to the fluid channels 36.2 of the second plane 38 and the planes are at different distances from the optical side 40 of the blank 32. In this case, the optical side 40 of the blank 32 is that surface which is provided for the subsequent optically active area, that is to say that surface of the subsequent optical element through which its optical effect on incident electromagnetic radiation is achieved.

[0043] FIG. 3B shows a side view of the blank 32, in which the fluid channels 36.1 of the first plane 37 are arranged at a distance A from the optical side 40 of the blank 32.

[0044] FIG. 3C shows a further side view of the blank 32, in which the fluid channels 36.2 of the second plane 38 are arranged at a distance B from the optical side 40 of the blank 32. The distance A of the first plane shown in FIG. 3B is smaller than the distance B in this case. The arrangement of the fluid channels 36.x in the blank 32 is arbitrary and, in addition to the arrangement shown, can also be designed in a meandering shape, for example. A meandering fluid channel 36.x can be produced by selective etching, for example. Alternatively, the fluid channels 36.x can also be arranged in three or more planes and parallel to one another.

[0045] FIG. 4A shows the initial situation during the production of a mirror, for example, illustrating a mold 42 and a blank 32 which has not yet been shaped. The mold 42 already exhibits the geometry of the subsequent mirror surface. The blank 32 with the fluid channels 36.x arranged at a distance A from the optical side 40 is placed with the shaping surface 39, which is opposite the optical side 40, onto the mold 42 and then heated together with the latter. Alternatively, the blank 32 and the mold 42 can also be heated to a temperature that allows the blank 32 to be shaped onto the mold 42, before the blank 32 is placed on the mold 42. The temperature is chosen so that, as a result of the gravitational force, the material of the blank 32 rests against the shaping surface 39, that is to say changes the shape without changing the thickness, for example.

[0046] FIG. 4B shows the mirror main body 33 created from the blank 32 after it has been shaped onto the mold 42. The distance A of the fluid channels 36.x from the optical surface 40 is identical or almost identical to the distance A in the blank 32, as a result of which the fluid channels 36.x are arranged at a constant distance A from the optical side 40. The subsequent removal for the creation of an optically active area on the optical side 40 and, optionally, the application of a coating are negligible in relation to the effect on the heat conduction to the cooling fluid flowing through the fluid channels 36.x.

[0047] FIGS. 5A to 5C show the production process of a concave aspherical main body 33 (cf. FIG. 5C) for a subsequent mirror, which comprises two bulges 45 as parts of its aspherization in the example shown. A special design of the blank 32 is advantageous in order to be able to ensure that the fluid channels 36.3 and 36.4 are at the same distance from the optically active area 41 (cf. FIG. 5C) for such geometries as well.

[0048] FIG. 5A shows a blank 32 with fluid channels 36.3, 36.4 and a cutout 44 formed in the optical side 40. In this case, the depression 44 is only formed in the region of the optical side 40 from which there is no further removal during the following process for producing the subsequent optically active area 41. It is quite evident from FIG. 5A that the distance C of the fluid channel 36.3 from the optical side 40 is less than the distance D of the fluid channel 36.4.

[0049] FIG. 5B shows the blank 32 after shaping onto the mold 42, with the shaping surface 39 shown there now corresponding to the optical surface 40, in contrast with the production method described in FIGS. 4A and 4B. During shaping, the material in the region of the depression 44 sinks onto the mold 42, with the fluid channel 36.3 arranged in the region of the depression 44 likewise being displaced in the direction of the mold 42. The distance C of the fluid channel 36.3 in the region of the depression 44 and the distance D of the fluid channels 36.4 in the region without depressions 44 in relation to the optical surface 40 has not changed significantly after the shaping.

[0050] FIG. 5C shows the main body 33 created from the blank 32 after the formation of aspheres 45 in the optically active area 41 then created, the aspheres 45 being formed by removing material from those regions of the main body 33 in which no depressions 44 are formed in the blank 32 shown in FIG. 5A. As a result, the two fluid channels 36.3, 36.4 are at the same distance C from the optically active area 41 then created, whereby uniform heat conduction to the fluid channels 36.3, 36.4 is ensured.

[0051] FIG. 6 shows a flowchart of a feasible method for producing a main body 33 of an optical element for semiconductor lithography.

[0052] A blank is produced in a first method step 51. At least one fluid channel 36.x is introduced into the blank 32 in a second method step 52. Then, in a third method step 53, the main body 33 is produced by shaping the blank 32 onto a mold 42.

LIST OF REFERENCE SIGNS

[0053] 1 Projection exposure apparatus [0054] 2 Field facet mirror [0055] 3 Light source [0056] 4 Illumination optical unit [0057] 5 Object field [0058] 6 Object plane [0059] 7 Reticle [0060] 8 Reticle holder [0061] 9 Projection optical unit [0062] 10 Image field [0063] 11 Image plane [0064] 12 Wafer [0065] 13 Wafer holder [0066] 14 EUV radiation [0067] 15 Intermediate field focal plane [0068] 16 Pupil facet mirror [0069] 17 Assembly [0070] 18 Mirrors [0071] 19 Mirrors [0072] 20 Mirrors [0073] 21 Projection exposure apparatus [0074] 22 Wafer [0075] 23 Illumination optical unit [0076] 24 Reticle holder [0077] 25 Reticle [0078] 26 Wafer holder [0079] 27 Projection lens [0080] 28 Optical element [0081] 29 Mounts [0082] 30 Lens housing [0083] 31 Projection beam [0084] 32 Blank [0085] 33 Main body [0086] 36.1-36.4 Fluid channel [0087] 37 Fluid channel plane 1 [0088] 38 Fluid channel plane 2 [0089] 39 Shaping surface [0090] 40 Mirror surface [0091] 41 Optically effective surface [0092] 42 Mold [0093] 44 Depression [0094] 45 Asphere [0095] 51 Method step 1 [0096] 52 Method step 2 [0097] 53 Method step 3 [0098] A, B, C, D Distance between fluid channel and surface