Method for producing a reflective optical component for an EUV projection exposure apparatus and component of this type

Abstract

A method for producing a reflective optical component for an EUV projection exposure apparatus, the component having a substrate having a base body, and a reflective layer arranged on the substrate, wherein the substrate has an optically operative microstructuring, comprises the following steps: working the microstructuring into the substrate, polishing the substrate after the microstructuring has been worked into the substrate, applying the reflective layer to the substrate. A reflective optical component for an EUV projection exposure apparatus correspondingly has a polished surface between the microstructuring and the reflective layer.

Claims

1. A method, comprising: working an optically operative microstructuring into an initial substrate to provide a microstructured substrate; applying a polishing layer to the microstructured substrate; polishing the polishing layer to provide a polished, polishing layer having a surface with a roughness of less than 0.2 nanometer rms; and applying a reflective layer to the polished, polishing layer, wherein: the reflective layer has a surface roughness of less than 0.2 nanometer rms; and the reflective layer is configured to reflect EUV radiation.

2. The method of claim 1, wherein the initial substrate comprises a material selected from the group consisting of metals, metal alloys, semiconductors and the compounds thereof.

3. The method of claim 1, wherein the initial substrate comprises a polymeric material.

4. The method of claim 1, wherein the initial substrate further comprises a base body and an adhesion promoting material is between the base body and the polishing layer.

5. The method of claim 1, wherein: the polishing layer comprises a material that is harder than the microstructured substrate.

6. The method of claim 1, further comprising, after applying the reflective layer to the polished, polishing layer, providing a protective layer which is supported by the reflective layer.

7. A component, comprising: a substrate comprising an optically operative microstructuring; a polishing layer supported by the optically operative microstructuring, the polishing layer having a surface with a roughness of less than 0.2 nanometer rms; and a reflective layer supported by the surface of the polishing layer, wherein a surface of the reflective layer has a roughness of less than 0.2 nanometer rms, and the reflective layer is configured to reflect EUV radiation.

8. The component of claim 7, wherein the initial substrate comprises a material selected from the group consisting of metals, metal alloys, semi-conductors and the compounds thereof.

9. The component of claim 7, wherein the base body comprises a polymeric material.

10. The component of claim 7, wherein the polishing layer comprises a material that is softer than the substrate.

11. The component of claim 7, wherein the polishing layer is harder than the substrate.

12. The component of claim 7, further comprising a protective material supported by the reflective layer.

13. The component of claim 7, wherein the optically operative microstructuring is a wavelength-selective filter.

14. The component of claim 7, wherein the optically operative microstructuring is a diffraction grating comprising ribs and grooves in alternating fashion, each rib and each groove having a surface substantially parallel to a light entrance surface of the component, and the ribs and the grooves having flanks substantially parallel to an optical axis of the component.

15. The component of claim 7, wherein a grating constant locally varies over the diffraction grating.

16. The component of claim 7, wherein the component is a collector mirror.

Description

(1) Further advantages and features are evident from the following description and the accompanying drawing.

(2) It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combination respectively indicated, but also in other combinations or by themselves, without departing from the scope of the present invention.

(3) Exemplary embodiments of the invention are illustrated in the drawing and are described in greater detail hereinafter with reference thereto. In the figures:

(4) FIG. 1 shows a reflective optical component for an EUV projection exposure apparatus in a schematic sectional view in accordance with a first exemplary embodiment;

(5) FIGS. 2a) to d) show a method for producing the reflective optical component in FIG. 1;

(6) FIG. 3 shows a reflective optical component for an EUV projection exposure apparatus in a schematic sectional view in accordance with a further exemplary embodiment;

(7) FIGS. 4a) to e) show a method for producing the reflective optical component in FIG. 3; and

(8) FIGS. 5a) to e) show a further exemplary embodimentmodified relative to the method in FIGS. 2a) to d) and 4a) to e)of a method for producing a reflective optical component illustrated in FIG. 5e);

(9) FIG. 6 a reflective optical component for an EUV projection exposure apparatus in a schematic sectional view in accordance with a further exemplary embodiment;

(10) FIG. 7 a detail of the component in FIG. 6 in an enlarged scale; and

(11) FIG. 8 a detail of the optical component in FIGS. 6 and 7 in a still further enlarged scale and in an intermediate stage of the production of the optical component.

(12) FIG. 1 illustrates a reflective optical component for an EUV projection exposure apparatus, the reflective optical component being provided with the general reference sign 10.

(13) The reflective optical component 10 can be embodied as an EUV collector mirror used in the EUV radiation source. However, the component 10 can also be a mirror used in an EUV projection exposure apparatus in a projection lens or an illumination system of the projection exposure apparatus. The component 10 can also be embodied as a mirror array, in a particular as a micromirror array.

(14) Generally, the optical component 10 has a substrate 12 having a base body 14, into which an optically operative microstructuring 16 is worked. The optically operative microstructuring 16 is embodied here in the form of a schematically illustrated diffraction grating. However, the microstructuring 16 illustrated in FIG. 1 should be understood merely by way of example, and can represent any other optically operative microstructuring which can be used to impart a specific optical property to the optical component 10. In the exemplary embodiment shown, the microstructuring 16 serves as a wavelength-selective filter in order, in the case where the optical component 10 is used in an EUV projection exposure apparatus, to filter out specific wavelengths of the radiation or to ensure that only radiation having a specific wavelength propagates as used light in the projection exposure apparatus.

(15) The base body 14 provided with the microstructuring 16 is adjoined by a reflective layer 20. During the operation of the optical component 10, a surface 22 of the reflective layer 20 represents the surface to which the light or radiation is applied.

(16) In the exemplary embodiment in accordance with FIG. 1, the base body 14 overall is produced from a material suitable for working in the optically operative microstructuring 16 into the material by a conventional method, such as e.g. microlithography, diamond turning or milling, holography or nano-imprint.

(17) In this case, the base body 14 can be produced overall from a metal, a metal alloy, a semiconductor or a compound of the aforementioned materials. By way of example, the base body 14 can be produced from aluminium, an aluminium alloy, copper, a copper alloy, silicon, an aluminium-silicon alloy or from nickel. What is important here is that the material of the base body 14 is well suited to working in firstly the here concavely curved surface shape and secondly the microstructuring 16.

(18) A surface 24 of the microstructuring 16 is a polished surface which meets the requirements made of microroughness, which should typically be less than 0.2 nm rms.

(19) The reflective layer 20 is e.g. a molybdenum/silicon multilayer such as is customary in EUV applications.

(20) Furthermore, cooling lines 28 are present in the base body 14 through which cooling lines e.g. a cooling medium is conducted in order to cool the substrate 12 and hence the optical component 10.

(21) Referring to FIGS. 2a) to d) a method for producing the optical component 10 in FIG. 1 will now be described.

(22) FIG. 2a) shows the step of providing the base body 14. In this case, the base body 14 is produced overall from a material suitable for introducing a microstructuring, as indicated above. By way of example, the base body 14 can be produced from aluminium, an aluminium alloy, copper, a copper alloy, silicon, an aluminium-silicon alloy or from nickel. The cooling lines 28 have already been provided in the base body 14.

(23) In the next step in accordance with FIG. 2b), a surface 30 of the base body 14 is then processed in order to obtain the surface shape of the surface 30 in accordance with FIG. 2b). Conventional machining processing methods can be used for this purpose.

(24) In the next step in accordance with FIG. 2c), the microstructuring 16 is worked into the surface 30 of the base body 14. The microstructuring 16 can be worked by conventional methods such as e.g. microlithography, diamond turning or milling, holography or nano-imprint. In this case, it is not necessary for the method used for working in the microstructuring already to produce the necessary microroughness for the application of the component 10 as an EUV mirror.

(25) Consequently, the surface 24 of the microstructuring 16 does not yet meet the stringent requirements made of microroughness.

(26) In order to meet the stringent requirements made of microroughness, the surface 24 of the microstructuring 16 is polished, in particular superpolished. During the polishing of the surface 24, the surface structure of the microstructuring 16 should be maintained as well as possible in the material of the base body 14.

(27) The surface 24 is polished e.g. via a conventional wet polishing method.

(28) After the surface 24 of the microstructuring 16 has been polished, the reflective layer 20, e.g. in the form of a silicon/molybdenum multilayer is then applied to the polished surface 24 of the microstructuring 16.

(29) The configuration of the optical component 10 wherein the microstructuring 16 is worked into the material of the base body 14 and wherein the surface 24 of the microstructuring 16 is subsequently polished is advantageous particularly when the material of the base body 14 is one which, on the one hand, is sufficiently soft for introducing the microstructuring 16, but sufficiently hard to be subsequently polished. Materials for the base body 14 which are correspondingly suitable are e.g. copper, silicon or nickel.

(30) FIG. 3 illustrates a further exemplary embodiment of a reflective optical component for an EUV projection exposure apparatus, the reflective optical component being provided with the general reference sign 10a.

(31) The optical component 10a has a substrate 12a having a base body 14a, into which an optically operative microstructuring 16a is worked as in the previous exemplary embodiment.

(32) In contrast to the previous exemplary embodiment, the surface 24a of the microstructuring 16a is not a polished surface, rather the base body 14a provided with the microstructuring 16a is adjoined by a polishing layer 18a, which is then adjoined by the reflective layer 20a.

(33) This configuration of the optical component 10a with the additional polishing layer 18a enables a higher flexibility in the selection of the material of the base body 14a. This is because the material of the base body 14a, in this configuration, only has to be suitable for enabling the microstructuring 16a to be introduced easily into the material of the base body 14a by conventional methods, but the material does not also have to be suitable for polishing, in particular superpolishing, in order to obtain the required microroughness. Consequently, for the material of the base body 14a it is possible to choose particularly soft materials, such as aluminium or copper or even polymeric materials such as PMMA and other plastics.

(34) Specifically, the polishing layer 18 can be chosen from a material harder than the material of the base body 14a, e.g. quartz, amorphous or crystalline silicon, but other amorphous, crystalline or polycrystalline layers are also conceivable as polishing layer 18. Metals such as copper or metal compounds such NiP are also suitable as materials for the polishing layer 18. The polishing time can be reduced by a suitable choice of the material of the polishing layer 18a.

(35) FIGS. 4a) to e) now illustrate a method for producing the optical component 10a in FIG. 3.

(36) In accordance with FIG. 4a), firstly the base body 14a is provided. In this case, the base body 14a is produced overall from a material which is suitable for introducing, i.e. working in a microstructuring, the material being correspondingly soft. By way of example, the base body 14a can be produced from a particularly soft material, as already explained above. The cooling lines 28a have already been provided in the base body 14a.

(37) In the next step in accordance with FIG. 4b), a surface 30a of the base body 14a is then processed in order to obtain the surface shape of the surface 30a in accordance with FIG. 4b).

(38) In the next step in accordance with FIG. 4c), the microstructuring 16a is worked into the surface 30a of the base body 14a. On account of the softness of the material, the process of introducing the microstructuring 16a can be carried out by conventional methods, as described above.

(39) In the next step in accordance with FIG. 4d), the polishing layer 18a is applied to the surface 24a of the microstructuring 16a, and the polishing layer 18a is subsequently polished, in particular superpolished, in order thus to obtain a polished surface 26a.

(40) The polishing layer 18a is applied with a thin layer thickness. The polishing layer 18 can be e.g. a quartz layer or an amorphous or crystalline silicon layer.

(41) The polishing layer 18a is polished by a conventional wet polishing method, such that the surface shape of the surface 24a of the microstructuring 16a is maintained, but on the other hand the required microroughness is obtained. The polishing layer 18 is typically not polished to such an extent that the layer 18a disappears, rather the latter remains on the surface 24a of the microstructuring 16a and thus serves as an actual substrate surface for the further application of the reflective layer 20a in accordance with FIG. 4e.

(42) The thickness of the polishing layer 18a is e.g. in a range of from approximately 0.5 m to approximately 100 m. The polishing layer 18a is present continuously across the area of the substrate 12 after polishing.

(43) In the exemplary embodiment of the optical component 10a, therefore, the base body 14a is optimized with regard to the process of working in the microstructuring 16a, while the polishing layer 18a is optimized with regard to its polishability, in order thus to achieve a microroughness of less than 0.2 nm rms.

(44) FIGS. 5a) to e) illustrate a methodmodified relative to the method in accordance with FIGS. 2a) to d) and the method in accordance with FIGS. 4a) to e)for producing a reflective optical component 10b in accordance with FIG. 5e).

(45) In accordance with FIG. 5a), the first step again involves providing a base body 14b, having a surface 30b and cooling lines 28b that have already been worked into the base body 14b.

(46) In contrast to the base body 14 or 14a, the base body 14b can be produced from any desired material, in particular also one which is not suitable for working in a microstructuring 16b (see FIG. 5e)). Consequently, the base body 14b can also be composed of a hard and/or brittle material, e.g. composed of a ceramic or glass ceramic (e.g. ULE, Zerodur). Nevertheless, however, the base body 14b can also be produced from one of the abovementioned materials for the base body 14 or 14a. In addition to the abovementioned materials for the base body 14 or 14a, the appropriate materials include e.g. silicon carbide, SiSiC, molybdenum, tungsten, AlN, AlSiC, Si.sub.3N.sub.4, AlSiC alloys.

(47) Firstly, in accordance with FIG. 5b), the surface 30b of the base body 14b is processed in order to obtain the desired surface shape, which is illustrated here once again as concave.

(48) Since the material of the base body 14b is possibly too hard or brittle for producing the microstructuring 16b, a structuring layer 32b composed of a material suitable for working in the microstructuring 16b by conventional methods, as described above, is subsequently applied to the surface 30b. The structuring layer 32b is therefore preferably once again a layer composed of a metal, a metal alloy, a semiconductor or the compounds thereof, in particular NiP, copper, aluminium, gold, silver, platinum metals, amorphous silicon, or quartz or composed of a polymer, such as e.g. cured photoresist, PMMA and the like.

(49) The structuring layer 32b can be applied by vapour deposition or sputtering, plating or chemical coating and, in the case where the structuring layer 32b is produced from a polymeric material, also by spraying, spin-coating or resist coating.

(50) For the case where the structuring layer 32b is intended to be applied galvanically, for example, but the material of the base body 14b is not or not sufficiently conductive, an adhesion promoting layer, e.g. composed of aluminium, chromium or the like, can be applied prior to the process of applying the structuring layer 32b to the surface 30b of the base body 14b. The structuring layer 32b can, for example, then be composed of a metal or a metal alloy, a metal compound, e.g. NiP, be applied galvanically to the base body 14b. However, not only for the case where the structuring layer 32b is applied galvanically, but also in the case of other methods for applying the structuring layer 32b, the prior application of an adhesion promoting layer may be advantageous depending on the materials used.

(51) In accordance with FIG. 5c), a microstructuring 16b is then worked into the structuring layer 32b as described with reference to FIG. 2c) or 4c).

(52) Afterwards, a polishing layer 18b can be applied to the microstructuring 16b and can be polished, as described with reference to FIG. 4d), and a reflective layer 20b is subsequently applied.

(53) In a departure therefrom, however, it is possible, if the material of the structuring layer 32b is suitable for this purpose, to omit the polishing layer 18b and in return to polish the surface 24b of the structuring layer 32b as has been described above with reference to the optical component 10 and the method for producing the latter. If the structuring layer 32b is formed e.g. from NiP or copper or silicon, the surface 24b of the microstructuring 16b can also be polished directly.

(54) In all of the exemplary embodiments described above, a final protective layer can be applied to the reflective layer 20, 20a or 20b.

(55) In the exemplary embodiment in accordance with FIG. 1 and FIGS. 2a) to d) and in the exemplary embodiment in accordance with FIG. 3 and FIGS. 4.a) to e), it is likewise possible to mould the base body 14 or 14a), if appropriate together with the optically active microstructuring 16, in a moulding method from a mouldable material, e.g. a metal or a polymer, or to produce the base body 14 or 14a together with the microstructuring 16 or 16a in an injection-moulding method.

(56) What is common to all the exemplary embodiments mentioned above is that the microstructuring 16, 16a or 16b is worked into the substrate 12, 12a, 12b before the substrate 12, 12a or 12b is polished, and the reflective layer 20, 20a or 20b is implemented after the microstructuring 16, 16a or 16b has been worked in and after the substrate 12, 12a or 12b has been polished.

(57) With reference to FIGS. 6 through 8, a further exemplary embodiment of a reflective optical component 10c for an EUV projection exposure apparatus will be described. The reflective component 10c is a modification of the optical component 10 in FIG. 1 with respect to the configuration of the microstructuring of the component 10c.

(58) The reflective optical component 10c has a substrate 12c having a base body 14c into which an optically operative microstructuring 16c is worked. The base body 14c is adjoined by a reflective layer 20c, a surface 22c of which represents the surface of the optical component 10c to which light or radiation is applied during the operation of the optical component 10c.

(59) With respect to the selection of the material of the base body 14c and the production of the optical component 10c, reference can be made to the corresponding description of the optical component 10, wherein only the differences of the optical component 10c and of its production with respect to the optical component 10 will be described in the following.

(60) The microstructuring 16c of the optical component 10c is embodied in form of a diffraction grating which has ribs 40 and grooves 42 in alternating fashion.

(61) FIG. 7 shows a detail of the optical component 10c in an enlarged scale. The ribs 40 of the microstructuring 16c each have a surface 44 substantially parallel to a light entrance surface 22c of the optical component 10c, and the grooves 42 each have a surface 46 which is also substantially parallel to the light entrance surface 22c. Substantially parallel is to be understood here such that the surfaces 44 and 46 are adapted to the curved surface 22c of the optical component 10c as shown in the exemplary embodiment by providing the surfaces 44 and 46 with a corresponding curvature. If such an optical component is configured plane instead of concavely curved as shown, the microstructuring 16c has, in a strict sense, the shape of a rectangular profile.

(62) The ribs 40 and the grooves 42 each have flanks 48, 50 which are substantially parallel to an optical axis 52 of the optical component 10c.

(63) The microstructuring 16c of the optical component 10c is also denoted as binary grating.

(64) Such a binary grating is particularly suited for suppressing a wavelength or a wavelength range of perturbing electromagnetic radiation, for example infrared or near infrared radiation which is used for generating EUV radiation, and which impinges on the optical component 10c.

(65) The ribs 40 have a rib width w.sub.1, and the grooves 42 have a groove width w.sub.2. The rib width w.sub.1 and the groove width w.sub.2 are equal at least portionwise over the diffraction grating. A grating constant d is the sum of the rib width w.sub.1 and the groove width w.sub.2.

(66) A depth of the grooves 42 or a height of the ribs 40 is labelled with h in FIG. 7.

(67) The depth h of the grooves 42 or the height of the ribs 40, respectively, at least approximately meets the condition: h=n.Math./4, wherein is the wavelength of electromagnetic radiation which is to be suppressed, and n is an odd integer.

(68) For perpendicular incidence of the electromagnetic radiation which is to be suppressed, the depth h or the height h is at least approximately chosen such that the condition h=n.Math./4 is met, while the depth h or the height h of the binary grating structure is to be chosen higher, accordingly, for non-perpendicular incidence of the electromagnetic radiation which is to be suppressed.

(69) Ideally, the height h or depth h can locally vary over the diffraction grating in order to take into account the local different angles of incidence of the electromagnetic radiation which is to be suppressed.

(70) The rib width w.sub.1 and the groove width w.sub.2 can be equal at least portion-wise, but can also locally vary. Preferably, in particular the grating constant d varies locally, in order to direct the electromagnetic radiation which is to be suppressed in different directions so that the electromagnetic radiation which is suppressed and diffracted out can be directed onto different impact sites of one or more cooling bodies (not shown), in order to avoid a too high local heat load of this cooling body or these cooling bodies.

(71) FIG. 8 shows a detail of the microstructuring 16c of the optical component 10c in a still further enlarged scale, before the reflective layer 20c is applied.

(72) A solid line 54 shows the ideal contour of the microstructuring 16c as it should be present after the polishing process, so that, after applying the reflective layer 20c, the surface 22c of the reflective layer 20c follows this contour, too.

(73) However, the polishing process, in particular if the surface 24c of the microstructuring 16c is directly polished, i.e. without previously applying a polishing layer, results in a removal of material of the surface of the microstructuring 16c.

(74) If the microstructuring 16c would be already worked in with the ideal contour according to the solid line 54 and then polished, it can happen that the microstructuring 16c has a contour after the polishing, as, for example, shown by the broken line 56 in FIG. 8. In particular, the edges of the binary grating structure can be rounded off in undesired fashion as indicated by the broken line 56. In order to take into account the expected removal of material, the microstructuring 16c therefore is worked in with a structure reserve as illustrated in exemplary fashion in FIG. 8 by a broken line 58. The structure reserve according to the line 58 substantially is opposite to the contour 56 which is to be expected after the polishing process if the microstructuring would be already worked in with the ideal contour 54. In case the microstructuring 16c is worked in with a structure reserve according to the contour 58, the microstructuring 16c has the ideal contour 54 after the polishing.

(75) It is to be understood that the broken line 58 is only an example of a structure reserve when working in the microstructuring 16c.

(76) For example, a structure reserve can be furthermore carried out by working in the grooves 42 or the ribs 40 with a greater depth or height h as shown by a broken line 60 in FIG. 8

(77) Finally, arbitrary other structure reserves can be taken into consideration in order to take into account the expected removal of material by the polishing of the microstructuring 16c.

(78) It is to be understood that the microstructuring 16c described with reference to the optical component 10c can also be applied to the optical components 10a or 10b, i.e. regardless whether the microstructuring is directly worked into the base body or into a structuring layer, or regardless whether a polishing layer is additionally applied to the microstructuring, as described above with reference to the other exemplary embodiments.