The disclosure relates to an optical device, such as for microlithography, that includes an optical module and a supporting structure. The disclosure also relates to an optical module that includes an optical element and a carrier structure for the optical element. the carrier structure can be connected to the optical element via at least one holding element. The carrier structure can be fixed to the supporting structure and produced, for example, from a material having a coefficient of thermal expansion α<0.2*10−6K−1.
In microlithography, it is often desirable to control the position and geometry of optical modules containing optical elements (e.g., lenses, mirrors or gratings), as well as other elements (e.g., mask, substrate). In certain known microlithography systems, the ceramic material Zerodur® (Schott AG, Mainz, Germany) is used for a supporting structure and a carrier structure of an optical element. Zerodur® has a coefficient of thermal expansion of at most 0.1*10−6K−1 and a thermal conductivity of 1.46 W/mK at 20° C.
In some embodiments, the disclosure provides an optical device which can be made more robust and stiffer and can permit enhanced imaging accuracy.
The disclosure is based, in part at least, on the insight that the imaging accuracy that can be obtained, such as in EUV lithography, can be increased by producing the supporting structure and the carrier structure from different materials. In certain instances, only the carrier structure is concerned with regard to reducing (e.g., minimizing) the coefficient of thermal expansion. With regard to the supporting structure, by contrast, the coefficient of thermal expansion can be greater, and the supporting structure and the carrier structure of the optical module can have different coefficients of thermal expansion.
Optionally, the supporting structure can be made significantly stiffer, which can also be due to the stiffness of the materials used. However, the stiffness is increased by considering (e.g., optimizing) the spatial configuration of the supporting structure as such. This is because the flexibility gained in the material used can give rise to significantly more freedom with regard to the spatial construction of the supporting structure. Moreover, the use of a suitable material for the supporting structure also makes it possible to realize connections between the individual elements of the supporting structure which were not able to be realized previously. This can have positive effects on the spatial configuration of the supporting structure, and can permit a significantly more robust and hence overall stiffer connection of the individual elements of which the supporting structure is essentially composed. An improvement in the stiffness can also achieved via the supporting structure being manufactured in a manner closer to final contours.
Generally, two different thermal expansion properties meet one another in the connection between the carrier structure and the supporting structure, which can lead to increased stresses. Such an effect can be reduced (e.g., avoided), for example, if the carrier structure is mounted via at least one bearing element which compensates for different expansions between the carrier structure and the supporting structure. This can be true even if the carrier structure can no longer contribute to the stiffening of the supporting structure and thus reduces the stiffness of the supporting structure in this respect.
The disclosure is based, in part at least, on the insight that a supporting structure of an optical device despite a significant weakening, can nevertheless be made stiffer overall and ultimately assist in achieveing good imaging accuracies.
In some embodiments, the disclosure provides an optical device, such as for microlithography, that includes an optical module and a supporting structure. The optical module includes an optical element and a carrier structure for the optical element. The carrier structure is connected to the optical element via at least one holding element. The carrier structure is fixed to the supporting structure and is produced from a material having a coefficient of thermal expansion α<0.2*10−6K−1. The carrier structure is fixed to the supporting structure via at least one bearing element which compensates for different expansions between the carrier structure and the supporting structure.
Various embodiments and advantages will become apparent from the disclosure in conjunction with the figures, in which:
The EUV radiation generated by the illumination unit is directed onto a mask 103.1 held by a mask carrier 103. In this case, the mask 103.1 contains a partly transparent pattern, and therefore permits the impinging radiation to pass through the mask 103.1 only at specific locations and to enter into an optical device 104 in the form of a projection device. In this case, the optical device 104 serves for focusing the EUV radiation 105 transmitted through the mask 103.1 onto a substrate 106.1 held in a substrate carrier 106, wherein the substrate is a wafer slice composed of silicon or the like in the exemplary embodiment illustrated.
The projection device 104 has a supporting structure 107 including an outer housing 107.1 and inner supporting elements 107.2, of which, for the sake of clarity, only one supporting element 107.2 is illustrated and moreover only purely schematically in
Optical modules 108.1, 108.2, 108.3 with their carrier structures 109 are fixed to the supporting structure 107 illustrated in
A schematic illustration of an optical module 108 of the optical device 104, the optical module being connected to the supporting structure 107, is illustrated in
In the exemplary embodiment illustrated, the holding element 111 is embodied in the form of schematically illustrated actuators that are coordinated with one another. In the exemplary embodiment illustrated, the actuators of the holding element 111 form a static bearing of the optical element 110 relative to the carrier structure 109. The actuators can be driven electrically, whereby the length of the actuators is varied depending on the situation in order to ensure an exact orientation of the optical element. In the exemplary embodiment illustrated, the holding element 111 ultimately serves for the fine alignment of the optical element. This can also be achieved by the holding element 111 being embodied as an aligning device which enables an exact positioning of the optical element 110 in a purely mechanical manner. In the simplest case, however, the holding element 111 serves as a receptacle for the optical element 110, which, consequently, is not fixed directly to the carrier structure 109.
In order to keep disturbing external influences away from the optical element 110, which influences can be temperature-induced stresses, for instance, the carrier structure 109 is produced from a material having a relatively small coefficient of thermal expansion. In the exemplary embodiment illustrated, the coefficient of thermal expansion is not greater than 0.1*10−6K−1. The material is a glass ceramic which is produced by Schott AG and bears the product name Zerodur. In principle, however, other glass ceramic materials or other ceramic materials are also appropriate. Optionally, these materials have a coefficient of thermal expansion α<0.2*10−6K−1.
The supporting structure 107, only a portion of which is illustrated in
In the exemplary embodiment illustrated in
The material used in the exemplary embodiment illustrated is a metal having a so-called Invar effect. This involves a group of alloys for which a very small coefficient of thermal expansion occurs given a specific composition in specific temperature ranges. Even though other alloys are possible, the metal used is an iron-nickel alloy including a nickel content of 30 to 40% by weight, which can be FeNi36 or Fe65Ni35. Alloys having an Invar effect can have coefficients of thermal expansion of α≧0.5*10−6K−1.
As an alternative to a metallic material of the type described above, it is also possible to use a ceramic material for the supporting structure 107 as such. The ceramic components of the supporting structure 107 are then predominantly connected to one another via non-ceramic connecting elements. Such ceramic materials can belong to the group of silicon carbides, in which case, depending on the intended use, high-purity, hot-pressed, sintered, recrystallized or hot-isostatically pressed silicon carbide can be used. These ceramic materials also lead to a higher configurational freedom and, on account of the materials used, however, also on account of the use of a stiffer connecting technique, to stiffer supporting structures 107.
With the use of ceramic materials, those having a coefficient of thermal expansion of α≧0.4*10−6K−1 are appropriate. Typically, the coefficient of thermal expansion does not exceed a value of 3.0*10−6K−1, however. The silicon carbide compounds that can enable coefficients of thermal expansion of α≧2.6*10−6K−1. The same also applies to the use of ceramic fiber composite materials, which likewise enable stiffer supporting structures to be provided. These materials have a ceramic matrix into which either ceramic or non-ceramic fibers such as carbon fibers, for instance, are introduced. The material properties of the ceramic fiber composite materials are highly dependent on the (preferred) fiber directions. In this respect, the material properties can be set overall, on the one hand, but also with regard to a very specific preferred direction, on the other hand. Thus, in the case of ceramic fiber composite materials, the thermal expansion in the fiber direction can be set to α<0.5*10−6K−1.
In addition, the use of a metallic material instead of the glass ceramic mentioned also leads to a high thermal conductivity of the supporting structure 107, which is then λ>10 W/mK (e.g., λ>40 W/mK), while the thermal conductivity of the carrier structure 109 is significantly lower and does not exceed 1.5 W/mK in the exemplary embodiment illustrated. If desired, the supporting structure 109 could also have a thermal conductivity of λ>40 W/mK. If the carrier structure 109 is produced by resorting to a different material rather than Zerodur, then this can also involve a ceramic material having a thermal conductivity of λ≦3.0 W/mK.
Owing to the higher thermal conductivity of the supporting structure 107, heat can be drawn from the optical device 104 more rapidly and more uniformly via a corresponding cooling. In this way, the temperature gradients of the optical device 104 can be kept very small. This ultimately leads to lower stresses and to higher accuracies during the EUV lithography. The same also correspondingly holds true when using supporting structures 107 composed of a ceramic material instead of a metallic material. The thermal conductivity of the material can then readily be λ≧40 W/mK or even λ≧100 W/mK. This holds true for example in principle for the material silicon carbide having a thermal conductivity of 150 W/mK.
Lower thermal conductivities are provided if the supporting structure 107 is constructed from a ceramic fiber composite material, in which case the corresponding thermal conductivities are regularly at least 15 W/mK, however. In contrast to the thermal expansion, the thermal conduction parallel to the fiber direction of the ceramic fiber composite materials is significantly greater than in a direction perpendicular to the fibers.
The use of two different materials for the supporting structure 107, on the one hand, and the carrier structure 109 for the optical element 110, on the other hand, becomes practicable, owing to the different thermal expansion behavior of the carrier structure 109 and of the supporting structure 107, only by using a suitable bearing 112 of the carrier structure 109 on the supporting structure 107.
Bearings 112 including bearing elements which can compensate for expansion differences—which occur on account of the temperature difference with respect to a desired temperature—between the carrier structure 109 and the supporting structure 107 are appropriate here, in principle. For dynamic reasons, a relatively stiff connection between the supporting structure 107 and the carrier structure 109 of the optical module 108 is additionally desired in order to enable a highly accurate alignment of the optical element 110 and to avoid an excitation of oscillations as a result of a high natural frequency. In the case of the optical module illustrated in
The use of a different material for the supporting structure 107 in comparison with the carrier structure 109 becomes practicable only by using a suitable bearing 112 for the carrier structure 109 which is stiff enough to fix the carrier structure 109 and to compensate for different thermal length-specific expansions between carrier structure 109 and supporting structure 107 if the temperature of the carrier structure 109 and/or of the supporting structure 107 deviates from a desired temperature or operating temperature by a certain magnitude. This enables not only compensation of the thermal expansion but also greater configurational freedoms that are attributed to the material of the supporting structure 107, but to the connecting techniques that are possible as a result. In addition, the proposed bearing 112 is more tolerant of damage with regard to the carrier structure 109 and the supporting structure 107 since mounting and production tolerances can be compensated for. Stresses which can lead to inaccuracies but also to fracture damage of the materials used are ultimately avoided.
The bearing 112—which is only illustrated schematically in FIG. 2—of the carrier structure 109 on the supporting structure 107 includes bearing elements 112.1, which are illustrated in greater detail in
The bearing element 112.1 additionally also has two portions for weakening the stiffness of the bearing element 112.1 in the transverse direction (y direction), the portions constituting cross-sectional taperings 118.1, 118.2 relative to a cross section perpendicular to the longitudinal direction of the bearing element 112.1. In principle, just one corresponding tapering or else still further corresponding taperings could also be provided. The cross section of the bearing element 112.1 illustrated in
As a further difference between the bearing elements 112.1, 112.2 illustrated in
The construction of the bearing elements 112.1, 112.2 illustrated in
The bearing elements 112.3 have two mutually perpendicular preferred directions which lie in a plane defined by the respective bearing element 112.3 and are characterized by a very high stiffness. Perpendicular to this plane, the bearing element 112.3 has a significantly lower stiffness on account of a configuration that is thin or overall planar in this direction. The holding element 111 is configured in the same way as the holding element 111 illustrated in
The components of the optical module illustrated in
This application claims the benefit of U.S. Application Ser. No. 61/032,128, filed Feb. 28, 2008, which is incorporated by reference herein.
Number | Date | Country | |
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61032128 | Feb 2008 | US |