Optical system for microlithography and sensor adapter

Abstract

The invention relates to an optical system for microlithography, in particular a projection objective, comprising: an optical element (128), a manipulator (24) for moving the optical element (128), and at least one sensor (18) for detecting a movement, in particular for detecting a position, of the optical element (128). The sensor (18) is attached to a sensor adapter (12) which has a sensor housing (16) which is installed in the optical system by means of a releasable connection. The invention also relates to a sensor adapter (12) for an optical system for microlithography, in particular for an optical system designed as described above. The sensor adapter (12) comprises a sensor (18) for detecting a movement, in particular for detecting a position, of an optical element (128) and has a sensor housing (16) which is designed for installation in the optical system by means of a releasable connection.

Description

[0001] Optical system for microlithography and sensor adapter

[0002] Reference to related application

[0003] This application claims priority from German patent application DE102023208047.8 filed on August 23, 2023, the entire disclosure of which is incorporated by reference into this application.

[0004] Background of the invention

[0005] The invention relates to an optical system for microlithography, in particular a projection lens for a projection exposure system, comprising: at least one optical element, a manipulator for moving the optical element, and at least one sensor for detecting the movement, in particular for detecting a position, of the optical element. The invention also relates to a sensor adapter.

[0006] The optical system for microlithography can, for example, be a projection lens for a projection exposure system. Projection exposure systems for microlithography are used for the photolithographic production of semiconductor components and other structured parts. A pattern on a mask, also called a reticle, is projected onto a substrate, also called a wafer, which is usually coated with a light-sensitive layer. For this purpose, such a projection exposure system comprises a projection lens having a plurality of optical elements, which can be designed, for example, as lenses, mirrors, gratings, or plane-parallel plates. The optical elements are mounted in a housing of the projection lens via mounts.

[0007] During operation of the optical system, the optical elements heat up, changing the imaging properties of the optical system. This can lead to aberrations in the wavefront propagating in the optical system and thus to a deterioration in imaging quality. It is known to use manipulators for moving and / or deforming optical elements to compensate for imaging errors caused, for example, by heating or the like. Such manipulators are described, for example, in DE 199 01 295 A1 or DE 10 2009 054 868 A1.

[0008] DE 199 10 947 A1 describes a device for displacing an optical element along the optical axis, in particular a lens in a lens. The optical element is supported by a retaining ring, to which an adjustment device with at least one adjustment drive engages. Sensors can be provided that measure or monitor the position or orientation of the retaining ring for the optical element in order to detect tilting of the retaining ring.

[0009] Such sensors typically measure the position or alignment of the optical element directly and are permanently integrated or built into the lens. If such a permanently integrated sensor fails when the optical system has been installed at a customer's site, it is usually necessary to dismantle the entire optical system, e.g. the projection lens, in order to replace the sensor. The replacement cannot usually be carried out at the customer's site; instead, it requires transporting the projection lens to a repair shop, dismantling the projection lens, carrying out the repair itself, subsequent assembly, return transport to the customer, and reinstallation of the projection lens at the customer's site. The entire replacement process is therefore usually very time-consuming and expensive. To reduce the likelihood of replacement, several redundant sensors can be permanently integrated into the optical system.

[0010] To simplify the replacement process, it is possible to use an external sensor that determines the movement of the optical element indirectly using an actuator of the manipulator, for example by measuring the position of an actuator plunger or the like. Replacing such a sensor generally does not require disassembly of the optical system. However, the indirect determination of the position of the optical element using such a sensor is typically not very precise. For example, there may be a path translation between the actuator movement and the stroke during the movement of the optical element, which results in the measuring range of the external sensor being many times larger than the stroke of the movement of the optical element. However, as the measuring range increases, the resolution of the sensor decreases and the noise of the sensor signal increases.Accordingly, the movement of the optical element can only be determined with a comparatively large degree of inaccuracy using such a sensor.

[0011] Object of the invention

[0012] An object of the invention is to provide an optical system for microlithography, in particular a projection lens, with a sensor that enables the position of the optical element to be detected as precisely as possible and is easily replaceable.

[0013] Subject of the invention This object is achieved by an optical system of the type mentioned at the outset, in which the sensor is attached to a sensor adapter which has a sensor housing which is installed or integrated into the optical system by means of a detachable connection.

[0014] The inventors propose using a sensor to detect the movement of the optical element. The sensor is arranged within a housing of the optical system, in particular within an outer mount of the optical element. To enable easy replacement of the sensor, the sensor is attached to a sensor adapter whose sensor housing is integrated or built into the optical system via a detachable connection. By releasing the connection, the sensor can be removed from the optical system together with the sensor adapter and can be easily replaced in the event of a sensor failure. In the simplest case, the sensor adapter can comprise only the sensor and the sensor housing. The sensor adapter usually has additional components, for example electrical lines or the like, to transmit a measurement signal generated by the sensor or to supply the sensor with energy.

[0015] The optical system can, for example, be a projection lens for microlithography. The sensor adapter described here can, in particular, be incorporated into a component of an optical system, for example such a projection lens. The projection lens can be designed for different wavelengths, for example for a wavelength of 365 nm, which corresponds to the i-line of a mercury vapor lamp, for the DUV wavelength range, or for the VUV wavelength range with or without immersion. The optical element can, in particular, be a lens. The sensor can, for example, be used to measure a movement of the optical element in the form of a displacement of the optical element along its optical axis, a deformation of the optical element, or—when using multiple sensors—a tilting movement of the optical element.

[0016] The inventors have recognized that, despite the generally small stroke in the order of magnitude of 1 mm or less, which is typically generated when the optical element is moved by means of the manipulator, no fixed integration or installation of the sensor in the optical system is required: Even when the sensor is attached to a sensor housing of a sensor adapter that is detachably attached or built into the optical system, sufficient precision in detecting the movement of the optical element is possible, ie the sensor can be positioned precisely enough even when attached to a sensor adapter to enable the movement of the optical element to be detected as precisely as possible.

[0017] In one embodiment, the sensor housing has a connecting section that is detachably connected to an outer side of a preferably annular outer mount of the optical element. The detachable connection can be, for example, a screw connection. Other types of detachable connections are also possible, e.g., bayonet locks, plug-in or clamp connections, etc. The connecting section is a housing section of the single-part or multi-part sensor housing of the sensor adapter.

[0018] The connection at the connecting section determines the orientation of the sensor adapter relative to the outer mount. The connecting section can protrude laterally beyond, for example, a rod-shaped guide section of the sensor adapter and can, for example, have several openings for the passage of screws or the like in order to firmly but detachably connect the sensor adapter to the outer mount. To remove the sensor from the optical system, the sensor adapter can be detached by an operator from the outside of the outer mount without having to access the inside of the outer mount, which would typically require disassembly of the optical system.

[0019] In a further development, the outer mount has a preferably radially extending, continuous channel for introducing a measuring section of the sensor housing, to which the sensor is attached, into an interior of the outer mount. The sensor adapter, or more precisely a generally rod-shaped guide section of the sensor housing extending from the connecting section, is inserted into the channel in order to position the measuring section with the sensor in the interior of the outer mount and in this way enable the detection of the movement of the optical element arranged in the outer mount. The sensor adapter can be sealed off from the channel using a seal, e.g., an O-ring, but this is not absolutely necessary.

[0020] In a further development, the measuring section of the sensor adapter protrudes beyond the inner surface of the outer mount. In this case, the measuring section of the sensor adapter extends into the interior of the outer mount to position the sensor appropriately for detecting the movement of the optical element. For detecting the movement of the optical element, the sensor can be arranged, for example, at a short distance from a target surface (see below).

[0021] In one embodiment, the sensor is designed as a non-contact sensor, in particular as a non-contact position sensor. In principle, the movement of the optical element can be measured using different types of sensors. A non-contact measurement, in particular a non-contact position measurement, is advantageous in order to simplify the removal of the sensor from the optical system using the sensor adapter. The non-contact position sensor is typically a distance sensor. In this case, the position of the optical element is determined based on the distance between a sensor surface of the distance sensor and a target surface. The position sensor or distance sensor can be, for example, an optical sensor.

[0022] In a further development of this embodiment, the contactless sensor is designed as a capacitive distance sensor. A capacitive distance sensor detects the distance between a sensor surface, which typically forms a first electrode, and a target surface, which typically forms a second electrode. It is advantageous for distance measurement if the sensor surface and the target surface are flat surfaces, but this is not absolutely necessary. Distance measurement using a capacitive distance sensor is also possible precisely if the sensor surface is arranged at a small distance from the target surface, e.g., 1 mm or less.

[0023] In a further development, the optical element is accommodated in a preferably annular holder, and the position sensor is designed to determine a distance between a sensor surface of the sensor and a target surface of the holder or of a component attached to the holder, in particular a spacer. The holder is typically a retaining ring that carries the optical element. When the optical element moves, the retaining ring is typically also moved, which is why the movement of the optical element can be detected by determining the distance between the retaining ring or a component attached to the retaining ring, usually fastened, and the sensor surface. The component attached to the holder can, for example, be a spacer that compensates for an undesired offset in the longitudinal direction of the optical system during the initial assembly of the optical system.However, the component that has the target surface of the sensor can also be another component attached to the holder.

[0024] In a further embodiment, the manipulator is designed to move the optical element along a longitudinal direction of the optical system, in particular of the projection lens. The longitudinal direction of the optical system can, in particular, be the direction of gravity, which is also referred to below as the Z-direction. The longitudinal direction of the optical system typically coincides with the optical axis of the optical system or runs parallel to the optical axis of the optical system.

[0025] The manipulator can be used to move the optical element with a linear movement in the longitudinal direction of the optical system or along the optical axis. However, it is also fundamentally possible for the manipulator to additionally tilt the optical element during the movement along the longitudinal direction. For this purpose, the manipulator can have several adjusting elements that act on the optical element and can be moved independently of one another along the longitudinal direction of the optical system. For this purpose, the manipulator can, for example, have one or more adjusting elements that act on the holder described above in order to move it in the longitudinal direction of the optical system.

[0026] The actuating element(s) of the manipulator can be attached to a typically annular support element, which forms part of the outer casing or is attached to the outer casing, usually on the inner side of the outer casing. A multitude of possibilities exist for the specific design of the manipulator. Reference is made, merely by way of example, to DE 199 01 295 A1, DE 10 2009 054 868 A1, and DE 199 10 947 A1 cited above, which are incorporated into this application in their entirety by reference.

[0027] In a further embodiment, the sensor adapter has a connector for electrically contacting the sensor. The connector is typically attached to the end of the sensor adapter where the connecting section is formed. The connector is in signal communication with the sensor, for example, via electrical lines running through the sensor adapter. The connector can be used to easily establish electronic contact with the sensor in order to read the sensor and / or supply it with power.

[0028] In a further embodiment, the optical system has at least three sensors, each attached to a sensor adapter, for detecting the movement of the optical element. The three or more sensors are typically arranged distributed over the circumference of the optical element and make it possible to detect the position of the optical element in the longitudinal direction of the optical system or along the optical axis. Based on the three or more positions detected by the sensors, a tilt of the optical element relative to a plane perpendicular to the longitudinal direction of the optical system can be determined. In the event that the manipulator has several independently controllable actuating elements, the tilt can be corrected if it is undesirable, or the tilt can be adjusted accordingly.

[0029] The invention also relates to a sensor adapter for an optical system, in particular for an optical system which is designed as described above, comprising: a sensor for detecting a movement, in particular for detecting a position, of the optical element, wherein the sensor adapter has a sensor housing which is designed for installation in the optical system by means of a detachable connection.

[0030] The sensor adapter can be designed in particular in the manner described above in connection with the optical system.

[0031] In one embodiment, the sensor housing has a connecting portion for detachable connection to an outer side of a preferably annular outer mount of the optical element. The detachable connection can be, for example, a screw connection.

[0032] The sensor housing preferably has a guide section designed for insertion into a preferably radially extending, continuous channel of the outer socket, in order to insert a measuring section of the sensor adapter, to which the sensor is attached, into an interior of the outer socket. The connecting section, the typically rod-shaped guide section, and the measuring section form three sections of a one- or multi-part sensor housing of the sensor adapter.

[0033] In a further embodiment, the sensor is designed as a contactless sensor, preferably as a contactless position sensor, in particular as a capacitive distance sensor. As described above, the use of a contactless sensor facilitates the replacement of the sensor adapter.

[0034] In one embodiment, the sensor adapter has a connector for electrically contacting the sensor. The connector is typically mounted in the region of the connecting section of the sensor adapter to enable contact with the connector from the outside of the outer socket. Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can be implemented individually or in groups in any desired combination in a variant of the invention.

[0035] drawing

[0036] Examples of embodiments are shown in the schematic drawing and are explained in the following description.

[0037] Fig. 1 is a schematic representation of a DUV lithography system with an illumination device and a projection lens,

[0038] Fig. 2a, b a schematic representation of a plan view of an annular outer mount of an optical element of the projection lens with one or with three sensor adapters,

[0039] Fig. 3a, b schematic sectional views of the outer socket and a sensor adapter during insertion and after insertion into a channel of the outer socket, as well as

[0040] Fig. 4a, b perspective views of two sensor adapters with different geometries.

[0041] In the following description of the drawings, identical reference numerals are used for identical or functionally equivalent components. Fig. 1 shows a schematic view of a DUV projection exposure system 100, which comprises a beam-shaping and illumination device 102 and a projection lens 104. DUV stands for "deep ultraviolet" (DUV) and denotes a wavelength of the working light between 30 nm and 370 nm. The DUV projection exposure system 100 has a DUV light source 106. The DUV light source 106 can be, for example, an ArF excimer laser, which emits radiation 108 in the DUV range at, for example, 193 nm.

[0042] The beam-shaping and illumination device 102 shown in Fig. 1 directs the DUV radiation 108 onto a photomask 129. The photomask 129 is designed as a transmissive optical element and can be arranged outside the beam-shaping and illumination device 102 and the projection lens 104. The photomask 129 has a structure that is imaged in a reduced size onto a wafer 124 or the like by means of the projection lens 104.

[0043] The projection lens 104 has a plurality of lenses 128, 140 and / or mirrors 130 for imaging the photomask 129 onto the wafer 124. Individual lenses 128, 140 and / or mirrors 130 of the projection lens 104 can be arranged symmetrically to the optical axis 126 of the projection lens 104. It should be noted that the number of lenses and mirrors of the DUV projection exposure system 100 is not limited to the number shown. More or fewer lenses and / or mirrors can also be provided. Furthermore, the mirrors are typically curved at their front side for beam shaping.

[0044] An air gap between the last lens 140 and the wafer 124 can be replaced by a liquid medium 132 having a refractive index > 1. The liquid medium 132 can be, for example, ultrapure water. Such a setup is also referred to as immersion lithography and features increased photolithographic resolution.

[0045] The optical elements 128, 130, 140 of the projection lens 104 are each housed in an outer mount. In Fig. 1, such an outer mount 10 for receiving an optical element in the form of a lens 128 is shown in dashed lines. The annular outer mount 10 is shown in a plan view in Fig. 2a, b and serves in Fig. 2a for mounting a sensor adapter 12 and in Fig. 2b for mounting three sensor adapters 12a-c. During assembly, the sensor adapters 12, 12a-c are each inserted radially into the outer mount 10, as indicated by arrows in Fig. 2a, b.

[0046] Fig. 3a shows the sensor adapter 12 and the outer housing 10 of Fig. 2a in a longitudinal section. As can be seen in Fig. 3a, during assembly, the sensor adapter 12 is inserted in the direction of the arrow, which corresponds to the radial direction, into a continuous channel 14 extending radially in the outer housing 10 until the sensor adapter 12 reaches a measuring position shown in Fig. 3b. In the example shown, the radially extending channel 14 is designed in the form of a cylindrical through-bore, but this is not mandatory.

[0047] The sensor adapter 12 has a sensor housing 16, which has a rod-shaped or cylindrical guide section 16b, a connecting section 16a adjacent to the guide section 16b at a first end of the sensor adapter 12, and a measuring section 16c adjacent to the guide section 16b at a second end of the sensor adapter 12, as shown in Fig. 4a, b. A sensor 18 is attached to the measuring section 16c of the sensor adapter 12.

[0048] During assembly, the sensor adapter 12 is inserted into the channel 14 of the outer socket 10 with the measuring section 16c facing forward. The rod-shaped guide section 16b is circularly cylindrical in the example shown and serves to guide the sensor adapter 12 during insertion into the channel 14 of the outer socket 10. The connecting section 16a projects laterally beyond the guide section 16b and is designed to detachably connect the sensor adapter 12 to an outer side 10a of the outer socket 10. For this purpose, the connecting section 16a has two through-bores 20 in the sensor adapter 12 shown in Fig. 4a and four through-bores 20 in the sensor adapter 12 shown in Fig. 4b. The through-bores 20 each serve to accommodate a screw that is screwed to the outer socket 10. It is understood that the connecting section 16a can also be designed in a different way than that shown in Fig. 4a, b.

[0049] As described above, the sensor adapter 12, or more precisely the sensor housing 16, is fastened or fixed to the connecting section 16a on the outer side 10a of the outer socket 10 by means of a screw connection and is aligned in the radial direction. Centering holes or centering pins, which are not shown, can be used to center the sensor adapter 12 in the channel 14 of the outer socket 10. It is possible to seal the sensor adapter 12 to the channel 14 using a seal, e.g., an O-ring, in order to seal off an interior space 22 of the outer socket 10, shown in Fig. 2a, b, from the environment. However, such a seal is not absolutely necessary.

[0050] In the measuring position shown in Fig. 3b, the sensor 18 protrudes beyond an inner side 10b of the outer mount 10 and projects into the interior space 22 of the outer mount 10. In the example shown, the sensor 18 is designed as a position sensor and serves to detect the movement of the lens 128 in the Z direction. The Z direction runs parallel to the optical axis 126 of the projection lens 104 and forms the longitudinal direction of the projection lens 104. The movement of the lens 128 in the Z direction is generated with the aid of a manipulator 24 indicated in Fig. 3a, b. In the example shown, the manipulator 24 serves to move the lens 128 in the longitudinal direction Z of the projection lens 104 without causing a tilt of the lens 128. The manipulator 24 can be designed in different ways, for example as described in the DE 199 01 295 A1 cited at the beginning, the DE 10 2009 054 868 A1 or the DE 199 10 947 A1.The manipulator 24 may alternatively be designed to produce a tilt of the lens 128.

[0051] In the example shown, the manipulator 24 has an actuating element 26 that acts on an annular holder or retaining ring 28, by which the lens 128 is carried. The actuating element 26 of the manipulator 24 is attached to a support 30 that is fastened to the inner side 10b of the outer mount 10. The actuating element 26 can be designed in different ways and effects a linear movement of the lens 128 in the Z direction, i.e., a change in the Z position Pz of the lens 128, as indicated in Fig. 1 by a double arrow. The maximum stroke when moving the lens 128 in the Z direction with the aid of the manipulator 24 is on the order of approximately + / - 1 mm.

[0052] The sensor 18 serves to detect the Z position Pz of the lens 128 and is designed as a non-contact distance sensor, more precisely as a capacitive distance sensor. In the example shown, the sensor 18 is designed to detect a distance A in the Z direction between a flat sensor surface 18a of the sensor 18 and a flat target surface 32a, which forms the upper side of a spacer 32 that is attached or fastened to the retaining ring 28. The spacer 32 is used during the initial assembly of the projection lens 104 to compensate for an undesired offset of the lens 128 or the mechanics (outer mount, mechanisms, etc.) in the Z direction. The spacer 32 is moved by the manipulator 24 together with the retaining ring 28 in the Z direction, so that the Z position P zthe lens 128 can be detected based on the distance A in the Z direction between the sensor surface 18a and the target surface 32a. It is understood that, unlike as shown in Fig. 3a, b, the sensor 18 can also be designed to determine the distance A to a target surface on the retaining ring 28.

[0053] The sensor 18 directly detects the movement or displacement of the annular holder 28 in the Z direction. This is advantageous because the maximum stroke when moving the lens 128 in the Z direction with the aid of the manipulator 24 is very small, and the sensor 18 must therefore detect the Z position Pz of the lens 128 very precisely. For the direct measurement of the Z position Pz, the sensor 18 is positioned in the interior 22 of the outer mount 10. With the aid of the sensor adapter 12, the sensor 18 can be removed from the interior 22 of the outer mount 10 without having to disassemble the projection lens 104 for this purpose.

[0054] As can be seen in Fig. 4a, b, the sensor adapter 12 has a connector 34 that enables electrical contact with the sensor 18. To establish the electrical connection between the connector 34 and the sensor 18, electronic lines (not shown) are mounted in the sensor housing 16 of the sensor adapter 12. The sensor 18 can be supplied with power via the connector 34, and the distance A or the capacitance detected by the distance sensor 18 between the sensor surface 18a and the target surface 32a can be read via the connector 34. The provision of a connector 34 on the sensor adapter 12 is not mandatory.

[0055] With the help of the three sensor adapters 12a-c shown in Fig. 2b, to which three sensors (not shown) are attached, a Z position can be determined at three positions in the circumferential direction of the lens 128. Based on this information, a tilt of the lens 128, i.e. a deviation of the alignment of the lens 128 from a plane perpendicular to the Z direction, can be calculated or determined. It is understood that for this purpose the three sensor adapters 12a-c do not necessarily have to be arranged at equal distances in the circumferential direction, as shown in Fig. 2b, but can also be arranged at different distances in the circumferential direction.

Claims

Patent claims 1 . Optical system for microlithography, in particular a projection lens (104), comprising: an optical element (128), a manipulator (24) for moving the optical element (128), at least one sensor (18) for detecting a movement, in particular for detecting a position (Pz), of the optical element (128), characterized in that the sensor (18) is attached to a sensor adapter (12) which has a sensor housing (16) which is installed in the optical system by means of a detachable connection.

2. Optical system according to claim 1, wherein the sensor housing (16) has a connecting portion (16a) which is detachably connected to an outer side (10a) of a preferably annular outer mount (10) of the optical element (128).

3. Optical system according to claim 2, wherein the outer frame (10) has a preferably radially extending, continuous channel (14) for introducing a measuring section (16c) of the sensor housing (16), to which the sensor (18) is attached, into an interior space (22) of the outer frame (10).

4. Optical system according to claim 3, wherein the measuring section (16c) of the sensor housing (16) projects beyond an inner side (10b) of the outer frame (10).

5. Optical system according to one of the preceding claims, wherein the sensor is designed as a contactless sensor, in particular as a contactless position sensor (18).

6. Optical system according to claim 5, wherein the non-contact sensor is designed as a capacitive distance sensor (18).

7. Optical system according to one of claims 5 or 6, in which the optical element (128) is accommodated in a preferably annular holder (28) and the position sensor (12) is designed to determine a distance (A) between a sensor surface (18a) of the position sensor (12) and a target surface (32a) of the holder (28) or of a component attached to the holder (28), in particular a spacer (32).

8. Optical system according to one of the preceding claims, wherein the manipulator (24) is designed to move the optical element (128) along a longitudinal direction (Z) of the optical system, in particular of the projection lens (104).

9. Optical system according to one of the preceding claims, wherein the sensor adapter (12) has a connector (34) for electrically contacting the sensor (18).

10. Optical system according to one of the preceding claims, which has at least three sensors each attached to a sensor adapter (12a-c) for detecting the movement of the optical element (128).

11. Sensor adapter (12) for an optical system for microlithography, in particular for an optical system according to one of the preceding claims, comprising: a sensor (18) for detecting a movement, in particular for detecting a position (Pz), of an optical element (128), wherein the Sensor adapter (12) has a sensor housing (16) which is designed for installation in the optical system by means of a detachable connection.

12. Sensor adapter according to claim 11, wherein the sensor housing (16) has a connecting portion (16a) which is detachably connectable to an outer side (10a) of a preferably annular outer mount (10) of the optical element (128).

13. Sensor adapter according to claim 12, wherein the sensor housing (16) has a guide section (16b) which is designed for insertion into a preferably radially extending, continuous channel (14) of the outer socket (10) in order to insert a measuring section (16c) of the sensor housing (16), to which the sensor (18) is attached, into an interior space (22) of the outer socket (10).

14. Sensor adapter according to one of claims 11 to 13, wherein the sensor (18) is designed as a contactless sensor, preferably as a contactless position sensor, in particular as a capacitive distance sensor.

15. Sensor adapter according to one of claims 11 to 14, which has a connector (34) for electrically contacting the sensor (18).

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