EUV LITHOGRAPHY SYSTEM COMPRISING A GAS-BINDING COMPONENT IN THE FORM OF A FOIL

Abstract

An EUV lithography system (1) including: a housing (26), at least one reflective optical element (M1, M2) disposed within an interior (27) of the housing (26), and at least one gas-binding component (31a-c) having a gas-binding material for binding gaseous contaminating substances (29) present in the interior (27). The gas-binding component is formed as a foil (31a-c) and a coating (33, 33a,b) containing the gas-binding material is applied on at least one side (32a, 32b) of the foil (31a-c).

Claims

1. An extreme ultraviolet (EUV) lithography system, comprising: a housing having an interior, at least one reflective optical element disposed within the interior of the housing, and at least one gas-binding component having a gas-binding material for binding of gaseous contaminating substances present in the interior, wherein the gas-binding component is configured as a foil, wherein a coating containing the gas-binding material is applied on at least one side of the foil, and wherein the foil has a thickness between 1 ?m and 1 mm.

2. The EUV lithography system as claimed in claim 1, wherein the foil contains the gas-binding material.

3. The EUV lithography system as claimed in claim 1, wherein the coating has a thickness between 1 nm and 10 ?m.

4. The EUV lithography system as claimed in claim 1, wherein the gas-binding material is selected from the group consisting of: Ta, Nb, Ti, Zr, Th, Ni, Ru, Rh.

5. The EUV lithography system as claimed in claim 1, wherein the foil is a polymer foil or a metal foil.

6. The EUV lithography system as claimed in claim 5, wherein the polymer foil is a polyimide foil.

7. The EUV lithography system as claimed in claim 1, wherein the foil is connected to a surface of the housing and/or to at least one surface of at least one component disposed in the interior of the housing.

8. The EUV lithography system as claimed in claim 7, wherein the foil is detachably connected to the surface of the housing and/or to the at least one surface of the at least one component disposed in the interior of the housing.

9. The EUV lithography system as claimed in claim 7, wherein an adhesive layer for connecting the foil to the surface of the housing and/or to the at least one surface of the at least one component disposed in the interior of the housing is applied to one side of the foil.

10. The EUV lithography system as claimed in claim 9, wherein the adhesive layer detachably connects the foil to the surface of the housing and/or to the at least one surface of the at least one component disposed in the interior of the housing.

11. The EUV lithography system as claimed in claim 7, wherein the foil is connected by electrostatic attraction to the surface of the housing and/or to the at least one surface of the at least one component disposed in the interior of the housing.

12. The EUV lithography system as claimed in claim 7, wherein the component disposed in the interior of the housing forms a casing encapsulating a beam path of the EUV lithography system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Working examples are shown in the schematic drawing and are described in detail in the description which follows. The figures show:

[0032] FIG. 1 a schematic meridional section through a projection exposure apparatus for EUV projection lithography,

[0033] FIG. 2 a schematic diagram of a detail of the beam path of the projection exposure apparatus of FIG. 1 with a casing for encapsulating the beam path and with gas-binding foil components, and

[0034] FIGS. 3A-C schematic diagrams of a detail of a gas-binding component in the form of a foil which is adhesively bonded to a surface (FIG. 3A), is freely positioned in space (FIG. 3B) or is retained on a surface by electrostatic attraction (FIG. 3C).

DETAILED DESCRIPTION

[0035] In the following description of the drawings, identical reference signs are used for identical, functionally identical or analogous components.

[0036] The salient components of an optical arrangement for EUV lithography in the form of a microlithographic projection exposure apparatus 1 are described by way of example below with reference to FIG. 1. The description of the basic setup of the projection exposure apparatus 1 and the components thereof should not be considered to be restrictive here.

[0037] One embodiment of an illumination system 2 of the projection exposure apparatus 1 has, in addition to a light or radiation source 3, an illumination optical unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 may also be provided in the form of a module separate from the rest of the illumination system. In this case, the illumination system does not include the light source 3.

[0038] A reticle 7 arranged in the object field 5 is illuminated through the illumination system 2. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable, in particular in a scanning direction, by way of a reticle displacement drive 9.

[0039] FIG. 1 shows a Cartesian xyz coordinate system in which the x direction extends perpendicularly into the plane of the drawing, the y direction extends horizontally, and the z direction extends vertically. The scanning direction extends in the y direction in FIG. 1, and the z direction extends perpendicularly to the object plane 6.

[0040] The projection exposure apparatus 1 also includes a projection system 10. The projection system 10 is used to image the object field 5 into an image field 11 in an image plane 12. A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable, in particular in the y direction, by way of a wafer displacement drive 15. The displacement of the reticle 7 on the one hand by way of the reticle displacement drive 9 and the displacement of the wafer 13 on the other hand by way of the wafer displacement drive 15 may be synchronized with one another.

[0041] The radiation source 3 is an EUV radiation source. The radiation source 3 emits, in particular, EUV radiation 16, which is also referred to below as used radiation, illumination radiation or illumination light. In particular, the used radiation has a wavelength in the range between 5 nm and 30 nm. The radiation source 3 may be a plasma source, for example an LPP source (Laser Produced Plasma) or a GDPP source (Gas Discharge Produced Plasma). It may also be a synchrotron-based radiation source. The radiation source 3 may be a free electron laser (FEL).

[0042] The illumination radiation 16 emanating from the radiation source 3 is focused by a collector mirror 17. The collector mirror 17 may be a collector mirror with one or more ellipsoidal and/or hyperboloidal reflection surfaces. The illumination radiation 16 may be incident on the at least one reflection surface of the collector mirror 17 with grazing incidence (GI), which is to say at angles of incidence of greater than 45?, or with normal incidence (NI), which is to say at angles of incidence of less than 45?. The collector mirror 17 may be structured and/or coated, firstly to optimize its reflectivity for the used radiation and secondly to suppress extraneous light.

[0043] The illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18 downstream of the collector mirror 17. The intermediate focal plane 18 may constitute a separation between a radiation source module, comprising the radiation source 3 and the collector mirror 17, and the illumination optical unit 4.

[0044] The illumination optical unit 4 comprises a deflection mirror 19 and, arranged downstream thereof in the beam path, a first facet mirror 20. The deflection mirror 19 may be a plane deflection mirror or, alternatively, a mirror with a beam-influencing effect that goes beyond the purely deflecting effect. As an alternative or in addition, the deflection mirror 19 may be in the form of a spectral filter that separates a used light wavelength of the illumination radiation 16 from extraneous light at a wavelength deviating therefrom. The first facet mirror 20 comprises a plurality of individual first facets 21, which are also referred to below as field facets. FIG. 1 depicts only some of said facets 21 by way of example. In the beam path of the illumination optical unit 4, a second facet mirror 22 is arranged downstream of the first facet mirror 20. The second facet mirror 22 comprises a plurality of second facets 23.

[0045] The illumination optical unit 4 thus forms a double-faceted system. This fundamental principle is also referred to as a fly's eye integrator. The individual first facets 21 are imaged into the object field 5 with the aid of the second facet mirror 22. The second facet mirror 22 is the last beam-shaping mirror or indeed the last mirror for the illumination radiation 16 in the beam path upstream of the object field 5.

[0046] The projection system 10 comprises a plurality of mirrors Mi, which are consecutively numbered in accordance with their arrangement in the beam path of the projection exposure apparatus 1.

[0047] In the example illustrated in FIG. 1, the projection system 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or any other number of mirrors Mi are likewise possible. The penultimate mirror M5 and the last mirror M6 each have a through opening for the illumination radiation 16. The projection system 10 is a doubly obscured optical unit. The projection optical unit 10 has an image-side numerical aperture that is greater than 0.4 or 0.5 and may also be greater than 0.6, and may, for example, be 0.7 or 0.75.

[0048] Just like the mirrors of the illumination optical unit 4, the mirrors Mi may have a highly reflective coating for the illumination radiation 16.

[0049] FIG. 2 shows a detail of the projection optical unit 10 from FIG. 1 with a beam path 25 that proceeds from the reticle 7 and passes through an opening in a housing 26 in which the projection optical unit 10 is disposed. Within the housing 26 is an interior 27 in which there exists a vacuum environment which is produced with the aid of vacuum pumps (not shown in the figure). There are six mirrors Mi disposed in the interior 27, of which FIG. 2 shows the first mirror M1 and the second mirror M2.

[0050] As likewise apparent in FIG. 2, there is a casing 28 disposed in the interior 27, which essentially surrounds or encapsulates the beam path 25 in the projection system 10, as described in U.S. Pat. No. 8,382,301 B2 or in U.S. Pat. No. 8,585,224 B2 for example, which are incorporated into this application in their entireties by reference. The casing 28 is a vacuum housing which is composed of multiple housing parts and consists essentially of stainless steel in the example shown. As likewise apparent in FIG. 2, the geometry of the casing 28 is matched to the geometry of the beam path 25, meaning that the geometry of the casing 28 follows the geometry of the beam path, meaning that the cross section thereof increases or decreases when the size of the cross section of the beam path 25 increases or decreases.

[0051] There are contaminating gaseous substances 29 in the interior 27 of the housing 26, which are indicated by dotted lines in FIG. 2. The volume within the casing 28 is typically purged by a purge gas, such that there is generally a smaller amount of contaminating gaseous substances 29 within the casing 28 than outside the casing 28. Likewise shown in FIG. 2 is a component 30, for example a sensor, actuator or the like, which outgases the contaminating gaseous substances 29 when the component 30 comes into contact with hydrogen present in the interior 27, especially with activated hydrogen. The activated hydrogen is formed from molecular hydrogen present in the interior 27 by an interaction with the illumination radiation or EUV radiation 16.

[0052] The contaminating substances 29 that outgas from component 30 are what are called HIO elements or HIO compounds, for example compounds of phosphorus, zinc, tin, sulfur, indium, magnesium or silicon. If the gaseous contaminating substances 29 reach the optical surfaces of the mirrors M1 to M6, these are deposited on the surfaces of the mirrors M1 to M6 and reduce the transmission thereof. The HIO compounds deposited on the surfaces of the mirrors M1 to M6 can additionally be removed only with great difficulty, if at all, from the surfaces of the mirrors M1 to M6.

[0053] In order to prevent the gaseous contaminating substances 29 from reaching the mirrors M1 to M6, FIG. 2 shows, by way of example, three gas-binding components 31a-c in the interior 27, which take the form of foils and are each shown in respective section diagrams in FIGS. 3A-C.

[0054] In the gas-binding component in the form of a foil 31a which is shown in FIG. 3A, a gas-binding coating 33 is applied to a first side 32a of the foil 31a. An adhesive layer 34 is applied to a second side 32b of the foil 31a, which serves to two-dimensionally connect the foil 31a on its second side 32b to a surface 26a on the inside of the housing 26, as shown in FIG. 2. The two-dimensional adhesive connection of foil 31a to surface 26a on the inside of housing 26 is a preferably detachable adhesive connection. In this way, the gas-binding component in the form of the foil 31a can be detached in a simple manner from the surface 26a of the housing 26 and exchanged for a new foil 31a when the gas-binding effect of the gas-binding material of the coating 33 has decreased to such an extent as to require exchange of the foil 31a.

[0055] The gas-binding foil component 31b shown in FIG. 3B, in addition to a gas-binding coating 33a applied on a first side 32a of the foil 31b, has a second gas-binding coating 33b on a second, opposite side 32b of the foil 31b. The foil 31b shown in FIG. 3B may be freely positioned in space and, in the example shown in FIG. 2, is merely punctiform adhesively connected to the surface 26a on the inside of the housing 26. FIG. 2 shows, by way of example, two adhesive bonding points 35a,b at which the foil 31b is connected to the housing 26. The punctiform connection of the foil 31b to the housing 26 can likewise be detached without any great difficulty when the foil 31b is to be exchanged. As likewise apparent in FIG. 2, the foil 31b serves to shield the component 30 that outgases contaminating substances from the rest of the interior 27 as substantially as possible, in order in this way to bind a maximum proportion of the gaseous contaminating substances 29 produced by the outgassing component 30. The first coating 33a on the first side 32a of the foil 31b binds these contaminating substances 29 outgassed by component 30; the second coating 33b on the second side 32b of the foil 31b binds these gaseous contaminating substances 29 present in the rest of the interior 27.

[0056] The foil 31c shown in FIG. 3C is formed in accordance with the foil 31a shown in FIG. 3a, but this has no adhesive layer, and is instead applied directly to a surface 28a on the inside of the housing 28, as apparent in FIG. 2. The foil 31c shown in FIG. 3C is held by electrostatic interaction on the surface 28a on the inside of the casing 28, meaning that it is detachably connected to the surface 28a on the inside of the housing 28. It is favorable for the holding of the foil 31c by electrostatic interaction that the casing 28 consists essentially of stainless steel (see above). The use of a foil 31c with a gas-binding coating 33 on a first side 32a of the foil 31c for lining of the inside of the casing 28 is favorable since this can be exchanged in a simple manner. Moreover, there is generally only a small amount of build space available within the casing 28, and it is therefore virtually impossible to arrange gas-binding components in the form of metal sheets or the like within the casing 28.

[0057] In the three examples shown in FIGS. 3A-C, the gas-binding material is present in the coating 33, 33a,b, or the gas-binding material forms the coating 33, 33a,b. The gas-binding material in the example shown is a metallic material selected from the group comprising: Ta, Nb, Ti, Zr, Th, Ni, Ru, Rh. But it will be apparent that it is also possible to use other materials for the coating of the foils 31a-c that have a gas-binding effect in respect of the contaminating gaseous substances 29 in the interior 27. The coating 33, 33a,b is deposited onto the foil 31a-c with the aid of a conventional coating method, for example by sputtering, by evaporating, by chemical vapor deposition (CVD), by galvanic processes, etc.

[0058] By contrast with what is shown in FIGS. 3A-C, the foil 31a-c may itself have a gas-binding effect. In that case, the foil 31a-c itself is produced from a gas-binding material. For example, the foil 31a-c in this case may be a ruthenium foil. It is generally possible in this case to dispense with the provision of the coating 33, 33a,b shown in FIGS. 3A-C.

[0059] The foil 31a-c typically consists of a non-gas-binding material. The foil 31a-c may be a polymer foil, for example a polyimide foil, or a metal foil, for example an aluminum foil, provided with a gas-binding coating 33, 33a,b. The foil 31a-c typically has a thickness D between 1 ?m and 1 mm. Especially if the build space is very limited, it is possible to use a comparatively thin foil 31a-c having a thickness D in the order of magnitude of a few micrometers. The coating 33 that is applied to the first side 32a of the foils 31a,c shown in FIG. 3A and FIG. 3C respectively has a thickness d between 1 nm and 10 ?m. The same applies to the respective thicknesses d1, d2 of the coatings 33a,b that are applied to the two sides 32a,b of the foil 31b shown in FIG. 3B.

[0060] Gas-binding components in the form of foils 31a-c may be disposed not only in the interior 27 of the housing 26 of the projection system 10 of the projection exposure apparatus 1, but also in the interiors of corresponding housings of the illumination system 2, the light source 3 or a housing surrounding the illumination system 2 and the projection system 10. Gas-binding components in the form of foils 31a-c may be used not only in the projection exposure apparatus 1 shown in FIG. 1 but also in other EUV lithography systems, in order to bind contaminating gaseous substances 29.