Optical system with aperture stop

Abstract

The invention relates to an optical system, in particular a lithography system (100A), comprising: an aperture stop (202) having an aperture (204) with an edge (206) for defining an outer perimeter (200a) of an optical path (200) of the optical system (100A); and a thermal stop (208) arranged upstream of the aperture stop (202) for partially obscuring the aperture stop (202), wherein the edge (206) of the aperture stop (202) is not obscured.

Description

[0001] Reference to relevant applications

[0002] This application claims priority to German patent application DE 102020208007.0 dated June 29, 2020, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention relates to an optical system, particularly a photolithography system, including an aperture stop having an aperture with an edge for defining the outer perimeter of the optical path of the optical system. Background Technology

[0004] A lithography system can be a lithography device used to expose wafers or other microlithography optical systems, such as inspection systems, for example, systems used to measure or inspect lithographic masks, wafers, etc. A lithography system can particularly be an EUV lithography device or a DUV lithography device. EUV stands for "Extreme Ultraviolet," describing the radiation wavelengths used from 0.1 nm to 30 nm. DUV stands for "Deep Ultraviolet," describing the radiation wavelengths used from 30 nm to 250 nm.

[0005] Numerical aperture is a crucial parameter in photolithography systems, especially photolithography equipment. In photolithography systems, the numerical aperture is set or modified using a so-called aperture stop. An aperture stop is understood as an aperture that (clearly) defines the outer perimeter of an optical path. Therefore, an aperture stop has an aperture with a (circumferential) edge. Here, the geometry of the aperture or edge defines the geometry of the outer perimeter of the cross-section of the aperture, optical path, or beam passing through that aperture stop.

[0006] Besides aperture stops, so-called obscuration stops are also used in optical systems. These stops are arranged within the optical path of the optical system and block the inner portion of the light path or beam cross-section. It is known that the obscuration stop is held in the center of the optical path by means of a thin rod or other methods. Heat is introduced into the obscuration stop due to radiation that inevitably strikes it. The corresponding thermal load can only be dissipated through the thin rod. Therefore, the obscuration stop receives more heat than the aperture stop. Thus, during the exposure process of a photolithography device, the obscuration stop can be heated to temperatures exceeding approximately 120°C or 190°C, while the aperture stop reaches temperatures as high as approximately 30°C-40°C.

[0007] The high temperature of the light-shielding aperture causes its associated thermal expansion and / or the associated thermal expansion of the rod used to attach the light-shielding aperture to the support. Thermal expansion in the rod can induce radial stress, which can cause the light-shielding aperture to deflect in the direction of the optical path or laterally. This leads to undesirable changes in the optical parameters of the lithography equipment, such as its telecentricity.

[0008] DE 10 2015 201 253 A1 describes a projection exposure apparatus with a light-shielding aperture having an outer aperture ring and an inner aperture located inside the aperture ring, the inner aperture being used to block the inner region of a working laser beam. In one exemplary embodiment, the inner aperture has a cooling device configured to allow for a defined reduction in heat within the inner aperture. In another exemplary embodiment, the inner aperture has a reflective surface for reflecting the working light.

[0009] DE 10 2016 221 823 A1 describes an optical system having a light-shielding aperture and a support. In one exemplary embodiment, a decoupling device is provided, which is configured to decouple the thermal expansion of the light-shielding aperture from the support. In another exemplary embodiment, a thermal aperture is arranged upstream of the light-shielding aperture in the direction of light in the optical path, and the thermal aperture is configured to partially shield the light-shielding aperture, wherein the light-determining edge of the light-shielding aperture is not shielded. Summary of the Invention

[0010] Purpose of the invention

[0011] The purpose of this invention is to provide an optical system, particularly a photolithography system, whose optical parameters, especially its numerical aperture, change as little as possible during operation.

[0012] Invention Theme

[0013] This objective is achieved by an optical system of the type mentioned in the introduction, in which a thermal stop is arranged upstream of the aperture stop (outside the optical path) to partially shield the aperture stop, wherein the edge of the aperture stop is not shielded.

[0014] The inventors have recognized that it is not only the (large) heat load incident on the diaphragm that may exist, but also the heat load incident on the aperture stop, that can significantly affect the optical parameters of the optical system. This effect is due to the fact that, during the operation of the optical system, the aperture stop material heats up dramatically to the point of thermal expansion under a typically considerable heat load (e.g., several watts) caused by the absorption of blocked radiation. This thermal expansion causes the aperture stop's edge to deviate from its nominal position. The result is a failure to adhere to the aperture stop's positional tolerances, which can lead to significant variations in the numerical aperture during the operation of the optical system.

[0015] When an aperture stop is positioned within the projection system of a lithography system, another problem arises: the operator of the lithography system can adapt the illumination setup to the application, making it difficult to predict the heat load incident on the aperture stop. Therefore, it is impossible to adapt the aperture size to the expected heat load. The heat load can also be dissipated through the aperture stop's support, but the aperture stop is typically not well cooled because it is only indirectly connected to a cooling device, such as those used in EUV lithography equipment to cool the so-called "microenvironment" (see below).

[0016] Therefore, this invention proposes using another aperture stop, also known as a thermal aperture stop, to reduce the thermal load on the aperture stop. The thermal aperture stop acts as a shield for the aperture stop and is located upstream of the aperture stop (outside the optical path). Being located outside the optical path is understood to mean that the aperture of the thermal aperture stop, more specifically, the edge of the aperture, does not define the optical path peripherally along its outer perimeter; that is, the thermal aperture stop does not have a light-limiting edge. Therefore, the thermal aperture stop does not perform the task of adjusting the optical path peripherally, but only serves to prevent thermal expansion of the aperture stop as much as possible, thereby allowing compliance with tolerances regarding the aperture stop position. In this way, it can be observed that the positioning tolerances of the aperture stop are more stringent than in the case where no thermal aperture stop is present.

[0017] In one embodiment, the edge of the thermal stop's aperture is spaced apart from the outer perimeter of the optical path. As mentioned above, it is advantageous if the thermal stop does not perform the function of an actual aperture stop defining the optical path at its periphery. To prevent the edge of the thermal stop from becoming a light-limiting edge during thermal expansion, the edge of the thermal stop is kept at a safe distance from the outer perimeter of the optical path.

[0018] In a further improvement, when the optical system is operating, the edge of the thermal stop's aperture is located at a (minimum) distance of at least 50 μm, and particularly at least 1 μm, from the outer periphery of the optical path. The cross-sectional area of ​​the thermal stop's aperture is larger than the cross-sectional area of ​​the optical path at the location of the thermal stop by a specific amount, i.e., a gap is formed between the outer periphery of the optical path and the edge of the thermal stop's aperture. The size of this distance or gap is determined such that even under the impact of maximum thermal load and therefore at its maximum operating temperature, the thermal stop will not expand to the point that the edge of the thermal stop's aperture reaches the outer periphery of the optical path.

[0019] To achieve this, it is necessary to position each point on the aperture edge of the optical system at its maximum operating temperature (including tolerances, such as those due to manufacturing, location, etc.) at least 1 μm from the optical path, and particularly at least 50 μm. This prevents changes in the shape of the thermal stop from affecting the optical path or the volume of light used in any way before the light beam enters the aperture stop. This ensures that the thermal stop does not function as an aperture stop.

[0020] The expansion of a thermal aperture depends not only on the maximum heat load but also on the coefficient of thermal expansion of the aperture material. For example, if the aperture material is an Invar alloy with a low coefficient of thermal expansion, the aperture can be mounted at a shorter distance from the optical path compared to materials with a larger coefficient of thermal expansion. During installation (at room temperature (22°C), the distance between the aperture edges is selected based on the coefficient of thermal expansion of the aperture material, ensuring that the aforementioned distance condition is met when the optical system operates at the aperture's typically maximum operating temperature of approximately 40°C.

[0021] When the optical system is operating, the (maximum) distance between the aperture edge and the outer perimeter of the optical path should preferably not exceed 2 mm, and particularly not exceed 1 mm. The greater the distance between the aperture edge and the outer perimeter of the optical path of the thermal stop, the less the aperture stop is blocked by the thermal stop. Therefore, when the optical system is operating, the distance between the aperture edge and the outer perimeter of the optical path should not be too large. In this way, as much radiation as possible can be absorbed by the thermal stop and no longer reach the aperture stop.

[0022] When the cross-section of the optical path between the thermal stop and the aperture stop changes only slightly, the values ​​given above regarding the distance from the outer perimeter of the optical path are correspondingly applicable to the distance from the outer perimeter of the aperture stop's aperture. That is, when the optical system is operating under maximum thermal load, the distance between the aperture edge of the thermal stop (when projected onto a plane perpendicular to the optical axis of the optical system) and the aperture edge of the aperture stop (when projected onto the same plane) is at least 50 μm or at least 1 μm.

[0023] In a further embodiment, the geometry of the thermal aperture matches the geometry of the aperture stop. Generally, geometry is understood to mean circular, oval, elliptical, rectangular, square, polygonal, etc., but can also be free-form. Matching geometry is understood to mean, for example, that the apertures or aperture edges of the aperture stop and thermal aperture have oval or elliptical shapes or free-form shapes, and their geometric configurations match (possibly in addition to proportions, see below). In the case of the thermal aperture, the corresponding geometry or aperture size is typically larger than that of the aperture stop. The same geometry is also understood to mean that the two apertures can be scaled differently in two mutually perpendicular directions, for example, if the ratio of the principal axis lengths of the apertures with oval or elliptical geometries of the thermal aperture and aperture stop are different from each other. This is typically the case when the aperture stop and thermal aperture are not parallel but at an angle to each other (see below). When the aperture stop and the thermal stop are oriented at a certain angle to each other, the aperture of the thermal stop is projected onto the plane of the aperture stop to compare the geometry of the aperture of the thermal stop and the geometry of the aperture of the aperture stop.

[0024] In one embodiment, the thermal stop is oriented at a non-0° angle relative to the aperture stop. This angle is typically greater than 1°, preferably greater than 3°, and particularly preferably greater than 5°. In particular, the angle can be from about 8° to about 20°. While the aperture stop is typically arranged in or near a defined plane (the pupil plane), this is not necessary for the thermal stop, as it does not perform any optical function. The thermal stop can be conveniently set in a defined orientation, for example, in a horizontal plane, while the aperture stop is tilted, i.e., its orientation is at an angle relative to that plane. The possibility that the thermal stop can be oriented in almost any way in space can be particularly useful for simplifying the cooling of the thermal stop. Moreover, when the aperture stop is oriented at an angle to the thermal stop, the available mounting space can be better utilized.

[0025] For example, the orientation of a thermal stop in a horizontal plane can also be used as a reference surface for the aperture module, in which the aperture stop and other stops (e.g., a light-shielding stop or a light-shielding stop frame) are integrated, and the aperture stop is positioned within the aperture module. The thermal stop can be fixed or positioned laterally by an end stop on a suitable interface. With the aid of spacers, the aperture module can be held in the desired position relative to the optical path within the optical system, but this is not always necessary.

[0026] In a further embodiment, the optical system includes a light-shielding stop for blocking an inner portion of the optical path. As described above, the light-shielding stop is designed to block or shield an inner portion of the cross-section of the optical path. Light-shielding stops are typically used to cover openings in a shield, such as a mirror, through which the optical path of the optical system passes. Shields or shielding designs can be particularly useful in EUV lithography projection systems or projection lenses with high numerical apertures. In projection systems with shielding designs, a small portion of the exit pupil remains dark, but this design can provide significant advantages in transmission. For example, a projection system with a shielding optical design is described in WO2006 / 069725 A1, and more specifically, a projection system with a shielded pupil, which is incorporated herein by reference in its entirety.

[0027] An aperture stop can be used as a support for a light-blocking stop, as described in, for example, DE 10 2016 221 823 A1, which is incorporated herein by reference in its entirety.

[0028] In a further improvement, a light-blocking stop is positioned in the optical path between the aperture stop and the thermal stop. In this case, the light-blocking stop is typically positioned at a small distance from the aperture stop and is generally oriented substantially parallel to the aperture stop. This is advantageous because both the aperture stop and the light-blocking stop are typically positioned in or near the pupil plane of the optical system. In this case, the aperture stop does not serve as a support for the light-blocking stop, which is attached to its own support, for example, by a rod. The support can be a support frame for the optical system or an aperture module to which the aperture stop is typically also attached.

[0029] In a further embodiment, the optical system includes a support for holding a light-shielding aperture in the optical path, and preferably includes a decoupling device designed to decouple the thermal expansion of the light-shielding aperture from the support. The light-shielding aperture forms an aperture element, which is attached to the support, for example, via a web. As described in DE 10 201 6221 823 A1 cited in the introduction, the optical system may have a decoupling device to decouple the thermal expansion of the light-shielding aperture from the support. For this purpose, the decoupling device may have, for example, one or more springs arranged, for example, between the light-shielding aperture and the support, or between a corresponding rod and the support. The support for the light-shielding aperture may be a support frame of the optical system to which the aperture stop is typically also attached, or it may be a component connected to the support frame, such as an aperture module.

[0030] Because the distance between the aperture stop and the shading stop is usually very small, the heating of the aperture stop causes thermal radiation to diffuse, resulting in a potentially large amount of heat being input into the shading stop. The thermal load on the aperture stop is reduced by the aforementioned thermal stop, resulting in less thermal radiation from the aperture stop reaching the shading stop, and its thermal load is also reduced.

[0031] In a further embodiment, the optical system has at least one beam trap for absorbing radiation reflected at the light-shielding aperture. As mentioned above, a portion of the radiation incident on the light-shielding aperture is typically reflected at the light-shielding aperture. To capture the reflected radiation, and more specifically, to absorb it, the optical system may have (at least) a beam trap having or being made of a radiation-absorbing material. It is advantageous if the radiation reflected at the light-shielding aperture can pass through the aperture of the thermal aperture before it enters the beam trap, as this provides more freedom in the arrangement of the beam trap within the optical system. To ensure that the radiation reflected back at the light-shielding aperture passes completely through the aperture of the thermal aperture, it is advantageous if the light-shielding aperture and the aperture stop, which is typically oriented parallel to it, are oriented at an angle to each other.

[0032] The beam trap can be installed, for example, inside the vacuum enclosure of the optical system (see below), which can be temperature-controlled, particularly cooled, by means of a temperature control device.

[0033] In a further embodiment, the optical system includes a temperature control device, particularly a cooling device, for controlling the temperature of the thermal stop, especially for cooling the thermal stop. Since the thermal stop bears most of the heat load that would otherwise be incident on the aperture stop, it is advantageous if the heat load can be dissipated quickly and easily by the thermal stop. This ensures that the thermal expansion of the edge or contour of the thermal stop is not excessive during the heating process during operation of the optical system, resulting in the aperture edge of the thermal stop being positioned closer to the outer perimeter of the optical path. Therefore, the heat load incident on the aperture stop can be reduced because a larger portion of the heat load is absorbed by the thermal stop.

[0034] The temperature control device can be designed to directly cool the thermal aperture or indirectly cool it, for example, by cooling the support of the thermal aperture. The temperature control device can also be used to heat the thermal aperture. The temperature control device may include, for example, Peltier elements for heating and / or cooling, or fluid and / or gas cooling. In the case of fluid cooling, for example, the thermal aperture itself, the support of the thermal aperture, or other components preferably in extensive contact with the thermal aperture or support can be cooled by means of a cooling fluid, such as cooling water. The thermal aperture can also be heated in this manner.

[0035] In one improvement, the thermal aperture contacts the surface of the vacuum housing of the optical system, and a temperature control device is designed to control the temperature of the vacuum housing, particularly for cooling it. Due to the preferred large-scale contact between the surface of the vacuum housing and the thermal aperture, which is typically a plate-like component, effective temperature control, and especially effective cooling, of the thermal aperture can be achieved.

[0036] The vacuum enclosure can, in particular, be an enclosure defining a so-called "microenvironment" in which at least one optical element is arranged, as described, for example, in WO2008 / 034582 A1, which is incorporated herein by reference in its entirety. Temperature control devices can be configured as cooling devices to cool the vacuum enclosure, for example, by fluid cooling, particularly by water cooling. For this purpose, cooling channels can be provided in the vacuum enclosure or in components in contact with the vacuum enclosure.

[0037] In a further embodiment, the aperture stop and / or thermal stop are formed of a metallic material, preferably selected from the group consisting of aluminum, copper, and steel. The aperture stop, thermal stop, and / or shading stop that may be present are preferably formed in a plate shape and made of a metallic material, such as a metal sheet. The use of metallic materials with high thermal conductivity, particularly aluminum or copper, has proven advantageous for cooling the aperture. However, even when aluminum or copper is used as the aperture material, positional deviations due to thermal expansion are significant without the use of a thermal stop.

[0038] In a further embodiment, the optical system includes a projection system for imaging a mask master onto a wafer, wherein an aperture stop is arranged in a region of the pupil plane of the projection system. In this case, the optical system is configured as a photolithography apparatus and includes a beam shaping and illumination system in addition to the projection system. The illumination settings of the beam shaping and illumination system vary depending on the structure to be imaged on the mask, which affects the radiation power and the thermal load at the aperture stop. As described above, if desired, a light-shielding stop can also be arranged in or adjacent to the pupil plane.

[0039] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention with reference to the accompanying drawings, which illustrate essential details of the invention. In variations of the invention, each individual feature may be implemented individually or in any combination. Attached Figure Description

[0040] Exemplary embodiments are shown in the schematic drawings and explained in the following description. In the drawings:

[0041] Figure 1a A schematic diagram of an EUV lithography apparatus is shown.

[0042] Figure 1b A schematic diagram of a DUV lithography equipment is shown.

[0043] Figure 2 A schematic diagram is shown of an aperture stop used to define the outer perimeter of the optical path of the EUV lithography system in Figure 1 and a thermal stop used to partially shield the aperture stop.

[0044] Figures 3a-3b A schematic plan view of an aperture stop or an aperture stop with a thermal stop placed in front of it is shown.

[0045] In the following description of the accompanying drawings, the same reference numerals are used for the same or functionally identical parts. Detailed Implementation

[0046] Figure 1aThe structure of an EUV lithography apparatus 100A is schematically shown, which includes a beam shaping and illumination system 102 and a projection system 104. Each of the beam shaping and illumination system 102 and the projection system 104 is configured with... Figure 1a In the vacuum enclosures shown, each vacuum enclosure is evacuated by means of a vacuum pumping device (not shown). The vacuum enclosure is surrounded by a mechanical chamber (not shown), in which a drive device for mechanically moving or setting optical elements is installed. In addition, electrical control devices and the like may also be installed in this mechanical chamber.

[0047] EUV lithography equipment 100A has an EUV light source 106A. For example, a plasma source (or synchrotron) can be used as the EUV light source 106A, emitting radiation 108A in the EUV range, such as radiation with wavelengths from 5 nm to 20 nm. The EUV radiation 108A is focused in the beam shaping and illumination system 102, and the desired operating wavelength is filtered from this EUV radiation 108A. The EUV radiation 108A generated by the EUV light source 106A has relatively low transmittance in air, which is why the beam guiding space in the beam shaping and illumination system 102 and the projection system 104 is evacuated.

[0048] Figure 1a The beam shaping and illumination system 102 shown has five mirrors 110, 112, 114, 116, and 118. After passing through the beam shaping and illumination system 102, EUV radiation 108A is guided onto a mask master 120. The mask master 120 is also configured as a reflective optical element and can be arranged outside systems 102 and 104. Furthermore, EUV radiation 108A can be guided onto the mask master 120 via mirror 122. The mask master 120 has a structure that projects a reduced image onto a wafer 124, etc., via a projection system 104.

[0049] The projection system 104 (also called the projection lens) has six mirrors M1-M6 for imaging the mask master 120 onto the wafer 124. It should be noted that the number of mirrors in the EUV lithography apparatus 100A is not limited to the number shown. More or fewer mirrors can also be provided. Furthermore, for beam shaping purposes, the mirrors are typically curved on their front side.

[0050] Figure 1b A schematic diagram of a DUV lithography apparatus 100B is shown, which includes a beam shaping and illumination system 102 and a projection system 104. (As already referenced...) Figure 1a As described, the beam shaping and illumination system 102 and the projection system 104 can be arranged in a vacuum enclosure and / or surrounded by a mechanical chamber with corresponding drive mechanisms.

[0051] The DUV lithography equipment 100B has a DUV light source 106B. For example, an ArF excimer laser can be set as the DUV light source 106B, which emits radiation 108B in the DUV range, such as radiation at 193 nm.

[0052] Figure 1b The beam shaping and illumination system 102 shown directs DUV radiation 108B onto a mask master 120. The mask master 120 is configured as a transmission optical element and can be arranged outside of systems 102 and 104. The mask master 120 has a structure that projects images onto a wafer 124 or the like in a reduced form via a projection system 104.

[0053] The projection system 104 has multiple lens elements 128 and / or mirrors 130 for imaging the mask master 120 onto the wafer 124. In this case, the individual lens elements 128 and / or mirrors 130 of the projection system 104 can be arranged symmetrically about the optical axis 126 of the projection system 104. It should be noted that the number of lens elements and mirrors in the DUV lithography apparatus 100B is not limited to the number shown. More or fewer lens elements and / or mirrors can also be provided. Furthermore, for beam shaping purposes, mirrors are typically curved on their front side.

[0054] The air gap between the last lens element 128 and the wafer 124 can be replaced by a liquid medium 132 with a refractive index > 1. The liquid medium can be, for example, high-purity water. This configuration is also known as immersion lithography and has increased resolution when the mask master 120 is imaged onto the wafer 124.

[0055] Figure 2 It shows Figure 1a Details of the EUV lithography equipment 100A, and more specifically, details of the projection system 104. Figure 2 The first reflecting mirror M1 and the second reflecting mirror M2 shown (see Figure 1a The aperture stop 202 defines a portion of the optical path 200 of the projection system 104 or the EUV lithography apparatus 100A. The aperture stop 202 is disposed between the first reflector M1 and the second reflector M2. This aperture stop has an aperture 204 with a perimeter 206 for defining the outer perimeter 200a of the optical path 200 of the EUV lithography apparatus 100A. The aperture stop 202 is used to adjust or precisely define the optical path 200 on the periphery to define the (incident side) numerical aperture of the projection system 104.

[0056] A portion of the EUV radiation 108A incident on the region adjacent to the aperture stop 202 and edge 206 of the EUV lithography apparatus is absorbed by the material of the aperture stop 202, resulting in the aperture stop becoming hot. Figure 2In the example shown, aperture stop 202 is plate-shaped and made of a metallic material, i.e., it is a metal sheet. In particular, metallic materials with high thermal conductivity, such as aluminum, copper, or steel, have proven advantageous as materials for aperture stop 202 (and for thermal stop 208 (see below)) because this allows for direct cooling.

[0057] It has been shown that, although the aperture stop 202 is formed of a material with high thermal conductivity, it may heat up significantly during the operation of the EUV lithography apparatus 100A as it is exposed to a heat load of possibly several watts, causing it to heat up to temperatures exceeding approximately 30°C–40°C. Due to this heating during operation of the EUV lithography apparatus 100A, the aperture stop 202 expands (potentially unevenly), which may lead to incorrect positioning and / or changes in geometry of the aperture 204 relative to the optical path 200, particularly a reduction in the size of the aperture 204. This results in optical errors when the mask master 120 is imaged onto the wafer 124.

[0058] To reduce the heat load on the aperture stop 202, a thermal stop 208 is positioned upstream of the aperture stop 202 in the optical path of the EUV radiation 108A. The thermal stop 208 partially shields the aperture stop 202 relative to the EUV radiation 108A, ensuring that the edge 206 of the aperture stop 202 is not obscured. This ensures that only the aperture stop 202, and not the thermal stop 208, performs the function of defining the numerical aperture of the projection system 104. To achieve this, the thermal stop 208 has an aperture 210 with an edge 212 spaced apart from the outer perimeter 200a of the optical path 200.

[0059] EUV radiation 108A illuminates the thermal stop 208. This radiation propagates within the projection system 104 but outside the optical path 200, and therefore contributes nothing to imaging. The EUV radiation 108A incident on the thermal stop 208 can also be scattered at components of the EUV lithography apparatus 100A located outside the optical path 200. Figure 2 As can be seen, the thermal aperture 208 is completely outside the optical path 200 used for radiation, that is, outside the optical path 200 that helps to image the mask master 120 onto the wafer 124. However, when so-called external light shines on the thermal aperture 208, the external light does not reach the wafer 124, but is absorbed by the thermal aperture 208.

[0060] exist Figure 2In the example shown, during the operation of the EUV lithography apparatus 100A, at the maximum possible operating temperature of approximately 40°C for the thermal stop 208, the edge 212 of its aperture 210 has a (minimum) distance A of at least 50 μm, and particularly at least 1 μm, from the outer periphery of the optical path 200a. This distance A is large enough that even under the expected maximum thermal load, the thermal stop 208 will not expand so much that its edge 212 reaches the outer periphery 200a of the optical path 200, while simultaneously being small enough that the aperture stop 202 is maximally shielded by the thermal stop 208. The distance A between the edge 212 of the aperture 210 of the thermal stop 208 and the outer periphery 200a of the optical path 200 need not be constant; rather, it can vary in the circumferential direction of the edge 212. In the plane of the thermal stop 208, the typical value of the distance A between the edge 212 of the thermal stop 208 and the outer perimeter 200a of the optical path 200 is about 1 μm to about 2 mm, and particularly about 50 μm to about 1 mm.

[0061] exist Figure 2 In the example shown, aperture stop 202 is arranged in or adjacent to the pupil plane 132 of the optical path 200 of projection system 104. This arrangement requires aperture stop 202 to be tilted at an angle α relative to a horizontal plane that forms the XY plane of the XYZ coordinate system. Compared to aperture stop 202, thermal stop 208 is horizontally oriented, i.e., parallel to the XY plane. The orientation angle α of aperture stop 202 relative to thermal stop 208 is typically greater than 1°, greater than 3°, or greater than 5°. The typical value of the angle α between aperture stop 202 and thermal stop 208 is approximately 8° to approximately 20°, where the magnitude of angle α depends particularly on the design of projection system 104.

[0062] Figure 3a It shows Figure 1a A plan view of the aperture stop 202 along the optical axis 126 of the projection system 104 or the EUV lithography equipment 100A. Figure 3b A plan view of the aperture stop 202 and the thermal stop 208 is shown along or in the direction of the optical axis 126 in the propagation direction of EUV radiation 108A. Figure 3a , 3b As shown, the aperture 204 of aperture stop 202 and the larger aperture 210 of thermal stop 208 both have an oval geometry. However, the aperture 204 of aperture stop 202 can also have any other geometric configuration (circular or non-circular), including free-form geometric configurations. The aperture 210 of thermal stop 208 is generally adapted to or corresponds to the geometry of the aperture of aperture stop 202.

[0063] fromFigure 3b As can be seen, the distance A between the edge 206 of the aperture stop 202 and the edge 212 of the thermal stop 208 in the projection along the optical axis 126 of the projection system 104 is at least 50 μm, and particularly at least 1 μm, as described above. The distance A, or the gap width between the edge 206 of the aperture stop 202 and the edge 212 of the thermal stop 208 (in a plane perpendicular to the optical axis 126), is approximately 1 μm to 2 mm, and particularly approximately 50 μm to approximately 1 mm, in the example shown.

[0064] The projection system 104 includes a shield (not shown), such as an opening in one of the mirrors M1-M6, through which the optical path 200 of the projection system 104 passes. This shield is covered by a light-blocking aperture 214, specifically to reduce the field dependence of the corresponding shield (in the plane of wafer 124). The light-blocking aperture 214 is configured to cover or block an inner portion 200b of the optical path 200. This means that a portion of the EUV radiation 108A is reflected or absorbed by the light-blocking aperture 214 during its journey through the optical path 200 from the first mirror M1 to the second mirror M2. The light-blocking aperture 214 is located entirely within or near the pupil plane 132 of the optical path 200, more specifically, between the aperture stop 202 and the thermal stop 208. The light-blocking aperture 214 may have a reflective coating (not shown) to reduce heat entering the light-blocking aperture 214. In the example shown, the light-shielding aperture 214 is configured as an oval or elliptical plate and has an outer perimeter that acts as a light-shielding edge to shield the inner portion region 200b of the light path 200.

[0065] The projection system 104 also includes a bracket 216 that holds the light-shielding aperture 214 within the optical path 200. In the example shown, the bracket 216 is attached to the aperture module 228 of the projection system 104, and more specifically, to the sidewall of the aperture module 228. The bracket 216 may also form part of the aperture module 228 itself, or the bracket 216 may be configured as a support frame for the projection system 104 for holding the mirrors M1-M6. The mirrors M1-M6 may be held, in particular, by actuators (e.g., gravity compensators and / or Lorentz actuators). Figure 2 As an alternative to the example shown, aperture stop 202 itself can serve as a support for light-shielding stop 214.

[0066] exist Figure 2In the example shown, the light-shielding aperture 214 is attached to the support 216 via a rod 218. To thermally decouple the thermal expansion of the light-shielding aperture 214 from that of the support 216, the projection system 104 in the example shown has a decoupling device 220. The decoupling device 220 is arranged between the support 216 and the light-shielding aperture 214, and in the example shown, is configured as a resilient rod 218. The decoupling device 220 may also have other configurations; for example, it may include one or more springs mounted between the respective rod 218 and the support 216, as described in more detail, for example, in DE 10 2016 221 823 A1 cited in the introduction.

[0067] from Figure 2 As can be seen, the aperture stop 202, the light-blocking stop 214, and the thermal stop 208 are housed in a common stop module 228, which is itself part of a vacuum housing (not shown) that surrounds or encapsulates the (vacuum) environment of the second mirror M2 (see Figure 1a The aperture module 228 is mounted on top of the vacuum housing 224, as shown. Figure 2 As shown, the vacuum housing 224 surrounds or encapsulates the first reflector M1.

[0068] The bottom surface of the aperture module 228, more specifically the thermal aperture 208, rests extensively on surface 226 or the vacuum housing 224, which extends horizontally on the top of the vacuum housing 224. The temperature of the vacuum housing 224 is controlled by means of a temperature control device 222, i.e., heating and / or cooling. In the example shown, the temperature control device is a cooling device configured for water cooling of the vacuum housing 224. For this purpose, cooling channels (not shown) are attached to or within the vacuum housing 224. The extensive contact between the thermal aperture 208 and the vacuum housing 224 simplifies its cooling. To enable efficient cooling, the thermal aperture 208, like the aperture stop 202, is formed of a metallic material with high thermal conductivity, such as aluminum, copper, or steel. Due to its horizontal orientation, the thermal aperture 208 is also suitable as a reference or initial position for holding the aperture aperture 202 and the light-shielding aperture 214 within the aperture module 228. A temperature control device 222 may also be provided, which allows for selective cooling or heating of the vacuum housing 224. For this purpose, the temperature control device 222 may be configured as, for example, a Peltier element or having at least one Peltier element.

[0069] Similarly, Figure 2 As shown, a beam trap 230 (“beam collector”) is mounted on the inside of the vacuum enclosure 224. The beam trap 230 is used to absorb EUV radiation 232 reflected at the light-shielding aperture 214. Similarly, from... Figure 2As can be seen, the reflected EUV radiation 232 passes through the aperture 210 of the thermal stop 208 before being incident on the bundle trap 230 of the cooled vacuum housing 244 and absorbed by the bundle trap 230. To allow the reflected EUV radiation 232 to pass through the opening 210 of the thermal stop 208 without being (partially) blocked by the thermal stop 208, it is advantageous if the aperture stop 202 (especially the light-blocking stop 214 parallel to the orientation of the aperture stop 202) is oriented at an angle α relative to the thermal stop 208, such as... Figure 2 The situation is shown in the example.

[0070] It goes without saying that, not only in the EUV lithography apparatus 100A described further above, but also in other optical systems, the aperture stop 202 can be shielded by the thermal stop 208 to reduce the heat load. This optical system can be particularly... Figure 1b The DUV lithography apparatus 100B shown is an example. The optical system can also be a microscope, particularly an electron microscope. Specifically, the optical system can also be... Figure 1a EUV lithography equipment 100A or Figure 1b This refers to a part of the DUV lithography equipment 100B, specifically the arrangement of its various components. It goes without saying that the aperture stop 202 does not necessarily have to be placed in the optical path 200 between the two mirrors M1 and M2, but can also be placed in the optical path between other optical elements, which are basically lens elements, delay films, gratings, etc.

Claims

1. An optical system, comprising: An aperture stop (202) having an aperture (204) with an edge (206) defines the outer perimeter (200a) of the optical path (200) of the optical system. Its features are, A thermal stop (208) is disposed upstream of the aperture stop (202) to partially shield the aperture stop (202), wherein the edge (206) of the aperture stop (202) is not shielded, wherein the thermal stop (208) has an aperture (210) with an edge (212), the edge (212) of the aperture (210) of the thermal stop (208) being spaced apart from the outer periphery (200a) of the optical path (200), and wherein, during operation of the optical system, the distance (A) between the edge (212) of the aperture (210) of the thermal stop (208) and the outer periphery (200a) of the optical path (200) is not greater than 2 mm. The thermal aperture (208) is oriented at an angle (α) relative to the aperture aperture (202).

2. The optical system as claimed in claim 1, wherein, The optical system is a photolithography device (100A, 100B).

3. The optical system as claimed in claim 1, wherein, During the operation of the optical system, the distance (A) between the edge (212) of the aperture (210) of the thermal stop (208) and the outer perimeter (200a) of the optical path (200) is at least 50 µm.

4. The optical system as claimed in claim 3, wherein, The distance (A) is at least 1 µm.

5. The optical system as claimed in any one of claims 1 to 4, wherein, During the operation of the optical system, the distance (A) between the edge (212) of the aperture (210) of the thermal stop (208) and the outer perimeter (200a) of the optical path (200) is not greater than 1 mm.

6. The optical system as claimed in any one of claims 1 to 4, wherein, The geometry of the aperture (210) of the thermal stop (208) corresponds to the geometry of the aperture (204) of the aperture stop (202).

7. The optical system as claimed in any one of claims 1 to 4, further comprising: A light-blocking aperture (214) is used to block the inner part of the light path (200b).

8. The optical system of claim 7, wherein, The light-blocking aperture (214) is arranged in the optical path (200) between the aperture aperture (202) and the thermal aperture (208).

9. The optical system of claim 7, further comprising: At least one beam trap (230) is used to absorb radiation (232) reflected at the light-shielding aperture (214).

10. The optical system of claim 7, further comprising: A bracket (216) is used to hold the light-shielding aperture (214) in the optical path (200), and A decoupling device (220) is configured to decouple the thermal expansion of the light-shielding aperture (214) from the support (216).

11. The optical system as claimed in any one of claims 1 to 4, further comprising: Temperature control device (222) is used to control the temperature of the thermal aperture (208).

12. The optical system of claim 11, wherein, The temperature control device is a cooling device used to cool the thermal aperture (208).

13. The optical system of claim 11, wherein, The thermal aperture (208) contacts the surface (226) of the vacuum housing (224) of the optical system, and the temperature control device (222) is configured to control the temperature of the vacuum housing (224).

14. The optical system as claimed in any one of claims 1 to 4, wherein, The aperture stop (202) and / or the thermal stop (208) are formed of metallic material.

15. The optical system of claim 14, wherein, The metallic material is selected from the group consisting of aluminum, copper, and steel.

16. The optical system of any one of claims 1 to 4, further comprising: A projection system (104) is used to image a mask master (120) onto a wafer (124), wherein the aperture stop (202) is arranged in the region of the pupil plane (132) of the projection system (104).

Images