Optical system

Abstract

The disclosure provides an optical system, having a first optical control loop, which is set up to regulate a position and/or spatial orientation of a first optical element relative to a first module sensor frame, and a first module control loop, which is set up to regulate a position and/or spatial orientation of the first module sensor frame relative to a base sensor frame. Related components and methods are also provided.

Claims

1. An optical system, comprising: optical elements; actuators; a holding frame holding the optical elements so that the optical elements are positionable and/or spatially orientable via the actuators; a sensor frame mechanically decoupled from the holding frame; sensors configured to capture a position and/or spatial orientation of a respective optical element relative to the sensor frame; and an interferometer comprising a measurement section along which electromagnetic radiation is sent and which extends via two reflection points on the sensor frame, wherein: the holding frame encloses a volume; the sensor frame is arranged partially or entirely within the volume; and the interferometer is configured to capture a change in position, a change in spatial orientation, and/or a deformation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

2. The optical system of claim 1, wherein the sensor frame comprises a plurality of arms projecting from a base body, and each of at least two of the arms comprises one of the sensors.

3. The optical system of claim 2, wherein the base body and the projecting arms are configured in one part or in one piece.

4. An inspection system, comprising: an optical system according to claim 1, wherein the inspection system is configured to inspect a photomask.

5. The inspection system of claim 4, wherein the interferometer is configured to capture a change in position of the sensor frame or parts thereof with respect to a reference outside the holding frame.

6. The inspection system of claim 4, wherein the interferometer is configured to capture a change in spatial orientation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

7. The inspection system of claim 4, wherein the interferometer is configured to capture a deformation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

8. A projection system, comprising: an optical system according to claim 1, wherein the projection system is a lithography projection system.

9. The projection system of claim 8, wherein the interferometer is configured to capture a change in position of the sensor frame or parts thereof with respect to a reference outside the holding frame.

10. The projection system of claim 8, wherein the interferometer is configured to capture a change in spatial orientation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

11. The projection system of claim 8, wherein the interferometer is configured to capture a deformation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

12. An apparatus, comprising: an optical system according to claim 1, wherein the apparatus is a lithography apparatus.

13. The apparatus of claim 12, wherein the interferometer is configured to capture a change in position of the sensor frame or parts thereof with respect to a reference outside the holding frame.

14. The apparatus of claim 12, wherein the interferometer is configured to capture a change in spatial orientation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

15. The apparatus of claim 12, wherein the interferometer is configured to capture a deformation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

16. The optical system of claim 1, wherein the interferometer is configured to capture a change in position of the sensor frame or parts thereof with respect to a reference outside the holding frame.

17. The optical system of claim 16, wherein the interferometer is configured to capture a change in spatial orientation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

18. The optical system of claim 17, wherein the interferometer is configured to capture a deformation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

19. The optical system of claim 1, wherein the interferometer is configured to capture a change in spatial orientation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

20. The optical system of claim 19, wherein the interferometer is configured to capture a deformation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

21. The optical system of claim 1, wherein the interferometer is configured to capture a deformation of the sensor frame or parts thereof with respect to a reference outside the holding frame.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the text that follows, the disclosure is explained in more detail on the basis of preferred embodiments with reference to the accompanying figures, in which:

(2) FIG. 1 shows a schematic view of an EUV lithography apparatus;

(3) FIG. 2 shows a schematic view of an optical system in accordance with a first exemplary embodiment;

(4) FIG. 3 shows a schematic view of an optical system in accordance with a second exemplary embodiment;

(5) FIG. 3a shows a section IIIa-IIIa from FIG. 3;

(6) FIG. 4 shows a schematic view of an optical system in accordance with a third exemplary embodiment;

(7) FIG. 5 shows a schematic view of a part of an optical system in accordance with a fourth exemplary embodiment;

(8) FIG. 6 shows a schematic view of a part of an optical system in accordance with a fifth exemplary embodiment;

(9) FIG. 7 shows a schematic view of a part of an optical system in accordance with a sixth exemplary embodiment;

(10) FIG. 8 shows a schematic view of a part of an optical system in accordance with a seventh exemplary embodiment;

(11) FIG. 9 shows a schematic view of a part of an optical system in accordance with an eighth exemplary embodiment;

(12) FIG. 10 shows a schematic view of a part of an optical system in accordance with a ninth exemplary embodiment; and

(13) FIG. 11 shows a flowchart of a method for installing and/or interchanging mirrors of an optical system.

DETAILED DESCRIPTION

(14) Unless otherwise indicated, the same reference signs in the figures denote elements that are the same or functionally the same. It should also be noted that the illustrations in the figures are not necessarily to scale.

(15) FIG. 1 shows a schematic view of an EUV lithography apparatus 100 according to one embodiment, which includes a beam shaping system 102, an illumination system 104 and a projection system 106. The beam shaping system 102, the illumination system 104 and the projection system 106 are respectively provided in a vacuum housing, which is evacuated with the aid of an evacuation device that is not depicted in any more detail. The vacuum housings are surrounded by a machine room (not depicted in any more detail), in which the drive apparatuses for mechanically moving or adjusting the optical elements are provided. Moreover, electrical controllers and the like can also be provided in this machine room.

(16) The beam shaping system 102 has an EUV light source 108, a collimator 110 and a monochromator 112. A plasma source or a synchrotron, which emit radiation in the EUV range (extreme ultraviolet range), that is to say for example in the wavelength range from 0.1 nm to 30 nm, may for example be provided as the EUV light source 108. The radiation emitted by the EUV light source 108 is first focused by the collimator 110, after which the desired operating wavelength is filtered out by the monochromator 112. Consequently, the beam shaping system 102 adapts the wavelength and the spatial distribution of the light emitted by the EUV light source 108. The EUV radiation 114 generated by the EUV light source 108 has a relatively low transmissivity through air, for which reason the beam guiding spaces in the beam shaping system 102, in the illumination system 104 and in the projection system 106 are evacuated.

(17) In the depicted example, the illumination system 104 includes a first mirror 116 and a second mirror 118. These mirrors 116, 118 may for example be formed as facet mirrors for pupil shaping and conduct the EUV radiation 114 to a photomask 120.

(18) The photomask 120 is likewise formed as a reflective optical element and may be arranged outside the systems 102, 104, 106. The photomask 120 has a structure which is imaged onto a wafer 122 or the like in a reduced fashion via the projection system 106. For this purpose, the projection system 106 has in the beam guiding space for example a third mirror 124 and a fourth mirror 126. It should be noted that the number of mirrors of the EUV lithography apparatus 100 is not restricted to the number represented. A greater or lesser number of mirrors can also be provided. Furthermore, the mirrors, as a rule, are curved on their front side for beam shaping.

(19) FIG. 2 shows a schematic view of an optical system 200 in accordance with a first exemplary embodiment. The optical system 200 is, for example, part of the EUV lithography apparatus 100 illustrated in FIG. 1 or, more specifically, part of the projection system 106 illustrated in FIG. 1. Alternatively, the optical system 200 can also be part of the illumination system 104 illustrated in FIG. 1.

(20) The optical system 200 has a holding frame 202 (in the present case also base holding frame), a sensor frame 204 (in the present case also base sensor frame) and, by way of example, optical elements in the form of the two mirrors 124, 126. The optical system 200 furthermore has two sensors 206a, 206b. A corresponding modular sensor frame 208a, 208b and a corresponding modular holding frame 210a, 210b are provided for each of the two mirrors 124, 126.

(21) A sensor 206a, 206b has a transmitting and receiving unit 212 and a corresponding measurement object 214, which sends an optical signal back to the transmitting and receiving unit 212. The position and/or spatial orientation of one of the mirrors 124, 126 can be determined on the basis of the signal that is sent back. The transmitting and receiving unit 212 of the sensor 206a, 206b is preferably attached to the sensor frame 204. In this case, the measurement object 214, which sends the signal back to the transmitting and receiving unit 212, is arranged at the respective modular sensor frame 208a, 208b, which is associated with the corresponding mirror 124, 126. Alternatively, the measurement object 214 can also be attached to the sensor frame 204. The transmitting and receiving unit 212 is then attached to the modular sensor frame 208a, 208b, which is associated with the corresponding mirror 124, 126. At least part of a respective sensor 206a, 206b is accordingly attached to the sensor frame 204.

(22) The optical system 200 has a module control loop 216a, 216b for each of the two mirrors 124, 126. Each of the module control loops 216a, 216b depicted in FIG. 2 includes actuators 218a, 218b and the sensors 206a, 206b. The module control loops 216a, 216b can be used to position and/or spatially orient the respective mirror 124, 126 together with the modular sensor frame 208a, 208b and the modular holding frame 210a, 210b relative to the sensor frame 204. The modular holding frames 210a, 210b are here connected to the holding frame 202 via the actuators 218a, 218b.

(23) The optical system 200 depicted in FIG. 2 furthermore has an optical control loop 233a, 233b for each of the two mirrors 124, 126. Each of the two optical control loops 233a, 233b illustrated includes actuators 222a, 222b and sensors 224a, 224b. The optical control loops 233a, 233b can be used to position and/or spatially orient the respective mirror 124, 126 relative to the modular sensor frame 208a, 208b. The mirrors 124, 126 are here connected to the modular holding frame 210a, 210b via the second actuators 222a, 222b.

(24) The sensor 224a, 224b has a transmitting and receiving unit 226 and a corresponding measurement object 228, which sends a signal back to the transmitting and receiving unit 226. The position and/or spatial orientation of one of the mirrors 124, 126 relative to the modular sensor frame 208a, 208b can be determined on the basis of the signal that is sent back. The transmitting and receiving unit 226 is preferably attached to the modular sensor frame 208a, 208b. In this case, the measurement object 228 is arranged at the mirror 124, 126. Alternatively, the arrangement can also be the other way around. At least part of the sensor 224a, 224b is accordingly attached to the modular sensor frame 208a, 208b.

(25) One of the mirrors 124, 126, the corresponding modular sensor frame 208a, 208b and/or the corresponding modular holding frame 210a, 210b can in each case form a module 232a, 232b. The respective module 232a, 232b can be installed and removed from the optical system 200 as a component.

(26) Alternatively, the optical system 200 does not have a modular holding frame 210a, 210b and/or a modular sensor frame 208a, 208b for each mirror 124, 126 (or for no mirror 124, 126). Positioning and/or spatial orientation of the mirrors 124, 126 is performed for the mirrors 124, 126 without associated modular holding frame 210a, 210b and modular sensor frame 208a, 208b only via the optical control loops 233a, 233b.

(27) The mirrors 124, 126 are always capable of being positioned and spatially oriented in six degrees of freedom. This ability to be positioned and spatially oriented can be achieved by way of the module and/or optical control loop 216a, 216b, 233a, 233b. In the sum, the ability to be positioned and spatially oriented in six degrees of freedom, i.e. the ability to be positioned and spatially oriented in three spatial directions and at three angles, is always achieved by way of the control loops 216a, 216b, 233a, 233b.

(28) The actuators 218a, 218b and the actuators 222a, 222b form a cascaded system. By way of example, the module control loop 216a, 216b can increase the actuation range of the mirror 124, 126 and thus ideally complement the optical control loop 233a, 233b, which is highly precise but in turn limited in the actuation range. This permits both coarse and fine adjustment.

(29) The sensor frame 204 is arranged partially or completely within a volume V (see FIGS. 3 and 3a, wherein the latter depicts a section IIIa-IIIa from FIG. 3) which is enclosed by the holding frame 202. By way of example, the holding frame 202 can enclose an at least partially cylindrical, in particular circular-cylindrical volume V, as can be seen from FIGS. 3 and 3a together. As a result, a mirror 124, 126 of the optical system 200 can be easily installed or interchanged. This advantage is achieved because no closed sensor frame is present anymore which would surround the holding frame 202 and impede the introduction of a mirror 124, 126 into the optical system 200 or removal of a mirror 124, 126 from the optical system 200. The sensor frame 204 can furthermore be arranged between the mirrors 124, 126. It is possible in this way for the sensor frame 204 to be guided into the vicinity of each mirror 124, 126 or of each modular sensor frame 208, which is associated with a mirror 124, 126. As a result, the mirrors 124, 126 can be positioned and spatially oriented on the basis of the sensor frame 204.

(30) The respective modular sensor frame 208a, 208b can be connected to the respective modular holding frame 210a, 210b via in particular oscillation-decoupling connecting elements 230 (see FIG. 2). The sensors 206a, 206b, 224a, 224b can be in the form of optical sensors. The optical system 200 can also have lens elements or other optical elements instead of or in addition to the mirrors 124, 126.

(31) FIG. 3 shows a schematic view of an optical system 200 in accordance with a second exemplary embodiment. In this exemplary embodiment, the sensor frame 204 is arranged entirely within the holding frame 202. The EUV radiation in the holding frame 202 passes via holes 300 to the mirrors 124, 126 and out of the holding frame 202. As opposed to the exemplary embodiment from FIG. 2, the exemplary embodiment of FIG. 3 has no modular holding frames 210a, 210b for the mirrors 124, 126. FIG. 3 does not depict cascaded actuators either. It does show the actuators 222a, 222b for the optical control loop 233a, 233b. It would alternatively also be possible to provide the actuators 218a, 218b for the module control loop 216a, 216b. The mirror 124, 126 can thus be positioned and/or spatially oriented relative to the sensor frame 204 and/or relative to the respective modular sensor frame 208a, 208b.

(32) The sensor frame 204 has a base body 301 and, projecting therefrom, a first arm 302, a second arm 304, and a third arm 306. Consequently, the sensors 206a, 206b can be arranged near the modular sensor frames 208a, 208b. Alternatively, the sensor frame can also be configured in the form of a scaffold. In a further alternative, a plurality of arms of the sensor frame 204 can form a star shape. The arms 302, 304, 306 and the base body 301 are configured in one part or in one piece.

(33) The measurement distance, or the measurement section, 308 is the distance between the transmitting and receiving unit 212 and the measurement body 214 and is less than 8 mm, preferably less than 4 mm and with further preference less than 1 mm. A small measurement distance 308 permits very accurate measurement of the position and/or of the spatial orientation of the modular sensor frame 208 and thus of the mirror 124, 126. The small measurement distance 308 is achieved by way of the arms 302, 304, 306 having the sensors 206a, 206b and reaching to the modular sensor frames 208a, 208b.

(34) The sensor frame 204 shown in FIG. 3 is attached to the holding frame 202, possibly via a mechanical insulation (flexible connection) (not illustrated). Attachment can be effected by way of an interface ring (not shown).

(35) FIG. 4 shows a schematic view of an optical system 200 in accordance with a third exemplary embodiment. The third exemplary embodiment differs from the second exemplary embodiment in that no modular sensor frame 208a, 208b is associated with the mirrors 124, 126. An optical control loop 233a, 233b can be used to position and/or spatially orient a mirror 124, 126 relative to the sensor frame 204. Here, the optical control loop 233a, 233b has actuators 222a, 222b and sensors 206a, 206b.

(36) FIG. 5 shows a schematic view of a part 500 of an optical system 200 in accordance with a fourth exemplary embodiment. Mirrors 124, 126 are not shown. Illustrated are the holding frame 202 and the sensor frame 204. The sensor frame 204 is measured using a phase-shifting interferometer 502. The phase-shifting interferometer 502 has an interferometer component 504, which is positioned in a defined manner with respect to a reference 501 outside the holding frame 202, a measurement mirror 506 and an optical component 508. The interferometer component 504 is arranged outside the holding frame 202. Electromagnetic radiation, illustrated by way of a first ray 512 and a second ray 514, is directed through an opening 510 via a deflection mirror 516 onto the measurement mirror 506. In the process, the first ray 512 and the second ray 514 pass through the optical component 508.

(37) The measurement mirror 506 and the optical component 508 are fixedly connected to the sensor frame 204. The optical component 508 has, on its side facing the measurement mirror 506, a reference surface 518. The reference surface 518 is inclined relative to the measurement mirror 506. The radiation reflected at the measurement mirror 506, illustrated by way of a third ray 520 and a fourth ray 522, is directed via the deflection mirror 516 and through the opening 510 back into the interferometer component 504. In the process, the radiation passes for a second time through the optical component 508. Owing to the reference surface 518 being inclined relative to the measurement mirror 506, the third and fourth rays 520, 522 have different optical paths and phases. As a consequence, an interferogram 524 can be seen in the interferometer component 504. The different optical paths and phases of the third and fourth rays 520, 522 are symbolized by way of the returning fourth ray 522 starting only at the reference surface 518.

(38) A measurement section 526 is located between the measurement mirror 506 and the optical component 508. If the length of the sensor frame 204 changes, the length of the measurement section 526 will also change. This change in length can be read in the interferogram 524.

(39) FIG. 6 shows a schematic view of a part 500 of an optical system 200 in accordance with a fifth exemplary embodiment. As opposed to the fourth exemplary embodiment shown in FIG. 5, the fifth exemplary embodiment shows the modular sensor frame 208a and the modular holding frame 210a. If the position of the modular sensor frame 208a and/or the position of the modular holding frame 210a changes, the length of the measurement section 526 will also change. This change in length can be read in the interferogram 524.

(40) FIG. 7 shows a schematic view of a part 500 of an optical system 200 in accordance with a sixth exemplary embodiment. Mirrors 124, 126 are not shown. Illustrated are the holding frame 202 and the sensor frame 204. The sensor frame 204 is measured using an interferometer 600 with moir measurement technology. The interferometer 600 with moir measurement technology has a camera 602, a concave mirror 604 and a grating 606. The camera 602 is arranged outside the holding frame 202. A light source 608 is likewise arranged outside the holding frame 202. Electromagnetic radiation from the light source 608 is directed through an opening 510, via a deflection mirror 516, onto the left-hand part 610 of the grating 606. The left-hand part 610 of the grating 606 is imaged, by way of the concave mirror 604, onto the right-hand part 612 of the grating 606. This gives a moir pattern, which is recorded, via the deflection mirror 516 and an observation optical unit 614, by the camera 602.

(41) The concave mirror 604 is fixedly connected to the sensor frame 204 using a connecting element 616. The grating 606 is likewise fixedly connected to the sensor frame 204. If the sensor frame 204 bends, the concave mirror 604 will be tilted. This is symbolized by way of the curved double-headed arrow 618. As a result, the moir measurement section 620 is lengthened or shortened, and the image of the left-hand part 610 of the grating 606 will be shifted to the right-hand part 612 of the grating 606. This effects a change in the moir pattern, which is detected by way of the camera 602.

(42) FIG. 8 shows a schematic view of a part 500 of an optical system 200 in accordance with a seventh exemplary embodiment. As opposed to the sixth exemplary embodiment shown in FIG. 7, the seventh exemplary embodiment shows the modular sensor frame 208a and the modular holding frame 210a. If the position and/or the spatial orientation of the modular sensor frame 208a and/or the position and/or the spatial orientation of the modular holding frame 210a changes, then the length of the moir measurement section 620 will also change and the image of the left-hand part 610 of the grating 606 will be shifted onto the right-hand part 612 of the grating 606. This effects a change in the moir pattern, which is detected by way of the camera 602.

(43) FIG. 9 shows a schematic view of a part 500 of an optical system 200 in accordance with an eighth exemplary embodiment. The eighth exemplary embodiment differs from the sixth exemplary embodiment in FIG. 7 in that a plane mirror 700 is provided on the sensor frame 204 in the eighth exemplary embodiment. In the eighth exemplary embodiment, once again a left-hand part 610 of a grating 606 is imaged onto a right-hand part 612 of the grating 606, and the resulting moir pattern is detected. However, the radiation is deflected via the plane mirror 700. Hereby, a twisting measurement section is produced using the moir measurement technique. The main idea is here that the obliquely illuminated plane mirror 700 rotates the image of the left-hand part 610 of the grating 606 if it is tilted about an axis located in the plane of incidence.

(44) FIG. 10 shows a schematic view of a part 500 of an optical system 200 in accordance with a ninth exemplary embodiment. As opposed to the eighth exemplary embodiment shown in FIG. 9, the ninth exemplary embodiment shows the modular sensor frame 208a and the modular holding frame 210a. The plane mirror 700 is here arranged on the modular sensor frame 208a. If the position and/or the spatial orientation of the modular sensor frame 208a and/or the position and/or the spatial orientation of the modular holding frame 210a changes, the moir pattern will also change.

(45) FIG. 11 shows a flowchart of a method for installing and/or interchanging mirrors 124, 126 of an optical system 200. In a first step S1, one of the mirrors 124, 126 is inserted into the optical system 200. In a second step S2, the position and/or spatial orientation of the mirror 124, 126 relative to a sensor frame 204 is measured. The sensor frame 204 is here arranged at least partially within a holding frame 202. In a third step S3, the mirror 124, 126 is positioned and/or spatially oriented relative to the sensor frame 204 in accordance with the measurement result according to step 2. In a fourth step S4, the positioned and/or spatially oriented mirror 124, 126 is secured.

(46) The measurement of the position and/or spatial orientation of the mirror 124, 126 in step S2 can be effected in a contact-free manner. Furthermore, the measurement of the position and/or spatial orientation of the mirror 124, 126 in step S2 can be effected using one or more optical sensors 206a, 206b, 224a, 224b.

(47) Exemplary embodiments for an optical system 200 of an EUV lithography apparatus with a wavelength of the operating light of between 0.1 and 30 nm have been explained. However, the disclosure is not restricted to EUV lithography apparatuses and may also be applied to other lithography apparatuses. A DUV (deep ultraviolet) lithography apparatus having a wavelength of the operating light of between 30 and 250 nm is mentioned here by way of example. The optical system 200 can furthermore also be used in a photomask inspection system for inspecting a photomask 120.

(48) Although the disclosure has been described on the basis of various exemplary embodiments, it is not in any way restricted to them but rather can be modified in a wide variety of ways.

LIST OF REFERENCE SIGNS

(49) 100 EUV lithography apparatus

(50) 102 Beam shaping system

(51) 104 Illumination system

(52) 106 Projection system

(53) 108 EUV light source

(54) 110 Collimator

(55) 112 Monochromator

(56) 114 EUV radiation

(57) 116 First mirror

(58) 118 Second mirror

(59) 120 Photomask

(60) 122 Wafer

(61) 124 Third mirror

(62) 126 Fourth mirror

(63) 200 Optical system

(64) 202 Holding frame

(65) 204 Sensor frame

(66) 206a, 206b Sensor

(67) 208a, 208b Modular sensor frame

(68) 210a, 210b Modular holding frame

(69) 212 Transmitting and receiving unit

(70) 214 Measurement object

(71) 216a, 216b Module control loop

(72) 218a, 218b Actuator

(73) 222a, 222b Actuator

(74) 224a, 224b Sensor

(75) 226 Transmitting and receiving unit

(76) 228 Measurement object

(77) 230 Connecting element

(78) 232a, 232b Module

(79) 233a, 233b Optical control loop

(80) 300 Hole

(81) 301 Base body

(82) 302 First arm

(83) 304 Second arm

(84) 306 Third arm

(85) 308 Measurement distance

(86) 500 Part

(87) 501 Reference

(88) 502 Phase-shifting interferometer

(89) 504 Interferometer component

(90) 506 Measurement mirror

(91) 508 Optical component

(92) 510 Opening

(93) 512 First ray

(94) 514 Second ray

(95) 516 Deflection mirror

(96) 518 Reference surface

(97) 520 Third ray

(98) 522 Fourth ray

(99) 524 Interferogram

(100) 526 Measurement section

(101) 600 Interferometer with moir measurement technology

(102) 602 Camera

(103) 604 Concave mirror

(104) 606 Grating

(105) 608 Light source

(106) 610 Part of the grating

(107) 612 Part of the grating

(108) 614 Observation optical unit

(109) 616 Connecting element

(110) 618 Curved double-headed arrow

(111) 620 Moir measurement section

(112) 700 Plane mirror

(113) V Volume