JP2019500648A - Optical device for lithographic apparatus and lithographic apparatus - Google Patents

Abstract

The invention relates to an optical device (200) for a lithographic apparatus (100A, 100B), an optical element (204) having positive stiffness (kp) when deformed in at least one direction (δ), and at least one An actuator (306) that deforms the optical element (204) in one direction (δ) and a negative stiffness (kn) that at least partially compensates for the positive stiffness (kp) of the optical element in at least one direction (δ). An optical device (200) for a lithographic apparatus (100A, 100B) comprising a compensation unit (310) having the same is disclosed.

Description

  The present invention relates to an optical device for a lithographic apparatus and a lithographic apparatus.

  The present application claims priority of German Patent No. 10 2015 225 263.9 (filed on 15 December 2015), the entire contents of which are incorporated herein by reference.

  Microlithography is a process used to pattern a portion of a thin film of a substrate body by microfabrication. In particular, microlithography is used in the manufacture of integrated circuits. The lithography process is performed using a lithographic apparatus that includes an illumination system and a projection system. Using light, the geometric pattern is transferred from the reticle to a photochemical solution layer known as a photoresist on the substrate. The reticle is illuminated by an illumination system. The projection system projects a geometric pattern onto a substrate located in the image plane of the projection system.

  Driven by Moore's Law and in particular the pursuit of smaller structures during the production of integrated circuits, EUV lithographic apparatuses are currently under development that use light with wavelengths in the region of 5-30 nm, especially 13.5 nm. . “EUV” indicates “extreme ultraviolet”. As a result of most materials exhibiting high absorbance at this wavelength, such EUV lithographic apparatus requires the use of reflective optical elements, ie mirrors, instead of refractive optical elements, ie lenses, as before.

  The mirror of the EUV lithographic apparatus can be fastened, for example, to a so-called force frame. Each mirror can be operated with up to 6 degrees of freedom. This makes it possible to position the mirrors very accurately relative to each other, for example in the pm region. In this way, changes in optical properties, for example as a result of thermal effects, can be compensated for during operation of the lithographic apparatus.

  More recently, it has been found that more advanced optical error correction can be obtained during operation of the lithographic apparatus, ie by deforming optical elements such as mirrors in real time.

  For example, Patent Document 1 describes a mirror 1 having four posts 2, and refer to FIGS. 1 and 2 of the above document. The actuating device 4 pulls the opposing posts 2 toward the optical axis 3 of the mirror 1 or pushes the opposing posts 2 away from the optical axis 3. As a result, the optical element 1 is deformed.

  Patent Document 2 discloses a deformable mirror 22 in FIG. A plurality of mirror posts 24 are arranged on the rear surface 22 e of the mirror 22. In order to deform the reflecting surface 22d of the mirror 22 by applying a load to the rear surface 22e of the mirror 22, the load applying system 58 displaces the tip of each mirror post 24.

German Patent Application No. 101151919 JP2013-106014A

  An object of the present invention is to provide an improved optical device for a lithographic apparatus.

  This object is achieved by an optical device for a lithographic apparatus comprising an optical element, an actuator and a compensation unit. The optical element has positive rigidity when deformed in at least one direction. The actuator deforms the optical element in at least one direction. The compensation unit has a negative stiffness that at least partially compensates for the positive stiffness of the optical element in at least one direction.

  “Negative stiffness” is defined as a stiffness that tends to deform an optical element in at least one direction and produces a force or moment that increases (or becomes constant) with increasing deformation of the optical element in that at least one direction. The Negative stiffness thus counteracts positive stiffness, thus reducing (or eliminating) the force required to deform the optical element. Another feature of negative stiffness is that it preferably does not require any external energy supply. To be precise, negative stiffness relies on energy stored in the mechanical system or magnetic field and is independent of any external energy supply.

  One concept underlying the present invention consists of dividing the force required to deform the optical element into two components, a quasi-static force and a dynamic force. A quasi-static force is necessary for deformation of the optical element itself. In the present specification, “deformation of an optical element” refers to deformation of the entire optical element or deformation of one or more portions thereof. The quasi-static force mainly depends on the (positive) stiffness of the optical element. The rigidity is determined by the elastic modulus of the optical element manufacturing material, for example, glass or ceramics, and the geometric shape of the optical element. Dynamic forces are necessary to accelerate the mass of the optical element. This force mainly depends on the density of the optical element, the geometric deformation profile, and the deformation trajectory as a function of time.

  The momentum of the optical elements required for optical correction is small, usually in the range of a few nanometers, and at the same time the time window for optical correction is quite large, for example 1/30 second, so the required dynamic force is small. On the other hand, the stiffness of the optical element is relatively large and therefore a quasi-static force much greater than the dynamic force is required for deformation of the optical element.

In a zero (close) stiffness configuration as currently provided, the actuator need only supply the energy necessary to compensate for kinetic energy and friction losses. For example, in order to move a 1 kg mirror mass by 1 μm with a moving time of 10 ms, an acceleration of 10 mm / s ² is required. Thus, a force of 10 mN is required, which can be easily supplied with a power consumption of less than 1 mW, for example by a Lorentz actuator (also known as a voice coil actuator).

The negative stiffness required to compensate for the positive stiffness of the optical element is typically about 10 ⁵ to 10 ⁶ N / m. For a 1 μm excursion, this requires a force of 1N. In the case of this example, this is much larger since it corresponds to 100 times the required dynamic force.

  As a result of this design, the actuator according to the invention only needs to provide a dynamic force and may be small if it provides a quasi-static force. Thus, the total force provided by the actuator is much smaller than known solutions.

  In general, all types of actuators generate significant heat that cannot be extracted without interference such as cooling water vibrations. Nevertheless, additional heat removal is substantially unnecessary since the force required according to the present solution is much reduced.

  The actuator of the present invention is preferably a Lorentz actuator. However, depending on the application, other types of actuators such as piezoelectric actuators or pneumatic actuators may be feasible.

  Another advantage of Lorentz actuators is a short response time, which makes them particularly suitable for real-time optical error correction, eg “die to die” or even “intra-die” It will be a thing. “Die-to-die” refers to deforming an optical element with a time window between the exposure of two consecutive dies on a single wafer. “In-die” refers to deforming an optical element for optical correction in a time window during scanning of a single die.

  Yet another advantage of a Lorentz actuator over a piezoelectric actuator, for example, is that it can be operated in an open loop control system because it exhibits little or no hysteresis, drift, or other inaccuracies.

  According to one embodiment, the compensation unit generates a first maximum force on the optical element in at least one direction, and the actuator generates a second maximum force on the optical element in at least one direction; The first maximum force is N times greater than the second maximum force, where N is greater than 5, preferably greater than 10 and more preferably greater than 50.

  “Maximum force” refers to the maximum force found in a single die or finished wafer manufacturing cycle using an optical device. If N is greater than 5, preferably greater than 10 and more preferably greater than 50, a sufficiently small actuator force for easy open loop control can be obtained and at the same time good system stability can be obtained. I understood.

  According to yet another embodiment, the compensation unit generates a first force on the optical element in at least one direction, and the actuator generates a second force on the optical element in at least one direction; The first force has a first maximum time derivative, the second force has a second maximum time derivative, the second maximum time derivative is M times greater than the first maximum time derivative, and M is greater than 10. , Preferably greater than 100.

  “Maximum time derivative” is the maximum derivative found in a single die or finished wafer manufacturing cycle using an optical device. It has been found that a given value of M keeps the compensation unit simple while giving a highly dynamic deformation.

  According to yet another embodiment, the negative stiffness of the compensation unit is 0.9 to 0.99 times the positive stiffness of the optical element.

  This ratio of negative to positive stiffness has been found to give good dynamic stability as well as small actuator forces. Ideally, 100% compensation should be desired so that the negative to positive stiffness ratio is equal to one. In such a case, the positive stiffness due to the elasticity of the optical element is completely compensated by the negative stiffness of the compensation unit. However, this also means that the mirror is force balanced in any deformation state and remains in such a deformation state. This may not be desirable because in the event of a malfunction it would be desirable to return the mirror to a specific original shape. Therefore, it is desirable that the negative stiffness compensation is slightly lower than 100%, for example, 90% to 99%.

  According to yet another embodiment, the difference between the positive stiffness of the optical element and the negative stiffness of the compensation unit is greater than zero.

  Thus, in the neutral state, i.e. when no force is provided because the actuator is off (no power) or malfunctions, the state of the optical element, in particular its degree of deformation, is always determined. The optical element will always return to its original form.

  According to yet another embodiment, the deformation of the optical element in at least one direction is obtained by out-of-plane bending of the optical element.

  “Out-of-plane bending” here refers to bending with respect to an axis perpendicular to the optical axis of the optical element.

  According to yet another embodiment, the compensation unit comprises a magnet, in particular a permanent magnet, or at least one spring.

  Such a component is suitable for obtaining negative stiffness. The spring may be a mechanical spring such as a leaf spring or a helical spring.

  According to yet another embodiment, the compensation unit, in particular at least one spring, preloads the optical element in a plane.

  “In-plane” means that the force generated by the compensation unit acts in a direction parallel to the extended plane of the optical element. Therefore, negative rigidity is obtained using the buckling effect.

  According to still another embodiment, the optical device includes a base, and the magnet includes a first magnet fastened to the optical element and a second magnet and a third magnet fastened to the base, respectively. It is movable between the second magnet and the third magnet.

  This configuration is suitable for obtaining a negative stiffness having a zero offset force. While the second and third magnets are fixed, the first magnet moves with a portion of the optical element to obtain the required deformation of the optical element.

  According to still another embodiment, the optical device includes a base, and the magnet includes a first magnet fastened to the optical element and a second magnet fastened to the base, and any of the first magnet and the second magnet One of them is formed as a ring magnet, and the other magnet is movable along the central axis of the ring magnet.

  This embodiment represents yet another configuration of a magnet for obtaining negative stiffness with zero offset force. Also in this case, the second magnet is fixed, and the first magnet moves together with a part of the optical element as the optical element is deformed.

  According to yet another embodiment, the optical device comprises an adjustment unit for adjusting the negative stiffness of the compensation unit.

  By reducing the stiffness of the system, the resonant mode of the optical device can be degraded. This can lead to unacceptable dynamic performance if the actuator is off or does not provide adequate force due to malfunction. However, this can be countered by including a switching mechanism that can turn the negative stiffness on or off. This is also advantageous, for example, during transport of an optical device or a lithographic apparatus equipped with such a device. Normally during transportation, the resonant frequency can damage the optical device. Here, by including the adjusting unit, the optical element can have its (normal) positive rigidity or at least substantially positive rigidity, thereby preventing the optical element from being damaged during transportation. On the other hand, the adjustment unit can even adjust the negative stiffness in real time to keep the actuator force required during operation of the optical device to a minimum. The adjustment unit can continuously adjust the negative stiffness.

  According to yet another embodiment, the adjustment unit applies preload to at least one spring, adjusts the relative position of the first magnet, the second magnet, and / or the third magnet, The magnetic coupling between the two magnets and / or the third magnet is adjusted, or the magnetic field of the first magnet, the second magnet, and / or the third magnet is adjusted using at least one permanent electromagnet.

  Depending on the mechanism that obtains the negative stiffness, a suitable method for adjusting the negative stiffness may vary. When a spring is used as a negative stiffness source, the preload acting on the spring can be changed to adjust the negative stiffness. The preload can be applied using, for example, a pneumatic cylinder.

  When obtaining negative rigidity using a magnet, the repulsive force and attraction force between the magnets, and the negative rigidity caused thereby, can be changed by adjusting the relative positions of the magnets. For this purpose, for example, a set screw or the like can be used.

  Furthermore, when obtaining negative rigidity using a magnet, the magnetic coupling between magnets can be changed by using a movable iron piece as a short circuit. For example, a U-shaped movable iron piece can be used.

  Furthermore, when obtaining negative rigidity using a magnet, the repulsive force and attractive force between magnets can be changed by adjusting the magnetic field of each magnet. Permanent electromagnets can be used for this purpose. A “permanent electromagnet” is currently defined as a magnetic unit comprising at least a first magnet having adjustable permanent magnetization and means for adjusting the permanent magnetization of at least one magnet.

  The at least one magnet can be made of, for example, a ferromagnetic or ferrimagnetic material.

  “Permanent magnetization” means that when the means for adjusting the permanent magnetization does not generate a magnetic field, the magnetization (e.g. expressed as A / m) that at least one magnet loses per year is 5% or less, preferably 2% or less, and even more Preferably it says 0.5% or less.

  Permanent magnetization can be adjusted. This means, for example, that the permanent magnetization means of at least one magnet can be switched between two magnetization states. These two states may include, for example, one demagnetized state (magnetization is zero) and one magnetized state. In other embodiments, this means that the permanent magnetization means can be switched between 3 or more, preferably 11 or more magnetization states. Switching can also be performed continuously. The permanent magnetizing means can be formed as a coil. By adjusting the current of the coil, the external magnetic field for magnetizing at least one magnet can be adjusted.

  In one example, the at least one magnet has a coercivity field strength. “Coercive field strength” refers to the magnetic field strength required to completely demagnetize a magnetic material of at least one magnet after magnetic saturation. Medium coercivity is known in the art and includes, for example, iron, aluminum, cobalt, copper, and / or nickel. For example, the intermediate coercivity corresponds to a magnetic field strength of 10 to 300 kA / m, preferably 40 to 200 kA / m, more preferably 50 to 160 kA / m. In particular, the material with medium coercivity is AlNiCo. AlNiCo refers to an alloy of iron, aluminum, nickel, copper, and cobalt.

  Further, the magnetic unit may include an additional magnet that cannot change permanent magnetization by means of changing permanent magnetization. This characteristic can be obtained by using a high coercive force material for the additional magnet (second magnet). The first magnet and the second magnet can jointly provide the necessary negative stiffness. In other embodiments, the first magnet alone provides the necessary negative stiffness.

  By controlling the means for adjusting the permanent magnetization of the first magnet, the negative stiffness can be adjusted appropriately.

  According to yet another embodiment, the optical element has a first positive rigidity when deforming in the first direction and a second positive rigidity when deforming in the second direction, and the actuator includes the optical element The compensation unit is deformed in the first direction and the second direction, and the compensation unit at least partially compensates the positive stiffness of the optical element in the first direction and the positive stiffness of the optical element in the second direction. And a second negative stiffness in the second direction that at least partially compensate for.

Thus, the basic principle of the present invention can be applied to a system having a plurality of axes. The response of such a system can be described using a stiffness matrix whose off-diagonal terms represent coupling between axes. If the system is significantly coupled, the local negative stiffness as described in the previous paragraph is not sufficient to compensate for the total stiffness force, and an equivalent negative to compensate for the positive stiffness matrix. It is necessary to create a stiffness matrix. That is, it is necessary to compensate not only diagonal (local) stiffness but also crosstalk between adjacent actuators. Depending on the geometry, the resulting mechanical system is usually a band-like stiffness matrix, actuators that are close to each other have some coupling stiffness, and actuators that are spaced apart from each other have (nearly) zero coupling stiffness. Have A normal negative stiffness matrix is shown in Equation 1 below, where k _p is the local actuator negative stiffness and k _c is the coupling stiffness between the degrees of freedom. δ ₁ . . . δ _i indicates the deformation in each direction, and F ₁ . . . F _i indicates the negative rigidity force generated by each actuator.

(Formula 1)

  For example, a negative stiffness matrix having characteristics as described in Equation 1 can be obtained by using an appropriate magnet topology.

  According to yet another embodiment, the actuator deforms the optical element for optical correction.

  In general, optical correction may include any type of image error correction, particularly with overlay and / or focus correction.

  According to yet another embodiment, the optical element is a mirror, lens, diffraction grating, or lambda plate.

  Lambda plates are also known as wave plates or retarders, i.e. optical devices that change the polarization state of light waves passing through them.

  The mirror may be flat or curved. Further, the mirror may be a facet of a mirror that includes a plurality of facets.

  Further provided is a lithographic apparatus comprising the above-described optical device.

  The lithographic apparatus can be an EUV or DUV lithographic apparatus. EUV is an abbreviation for “extreme ultraviolet” and refers to the wavelength of exposure light of 0.1 nm to 30 nm. DUV is an abbreviation for “deep ultraviolet rays” and refers to the wavelength of exposure light of 30 nm to 250 nm.

  The optical device can be incorporated into an objective lens of the lithographic apparatus. The objective lens can be immersed in a liquid (immersion lithography) at least during exposure of the wafer (waver).

  Still other exemplary embodiments will be described in more detail with reference to the accompanying drawings.

1 shows a schematic diagram of an EUV lithographic apparatus. 1 shows a schematic diagram of a DUV lithographic apparatus. FIG. 2 shows a perspective view of an optical device incorporated in the lithographic apparatus of FIG. 1A or FIG. Fig. 3 schematically shows a section III-III from Fig. 2; FIG. 4 shows a power diagram related to FIG. FIG. 4 shows a force versus displacement diagram of the optical device of FIG. 3 according to the first embodiment. FIG. 4 shows a force versus displacement diagram of the optical device of FIG. 3 according to a second embodiment. FIG. 2 shows a schematic side view of an optical device that obtains negative stiffness using a mechanical compensation system. FIG. 2 shows a schematic side view of an optical device that obtains negative stiffness using a mechanical compensation system. FIG. 2 shows a schematic side view of an optical device that obtains negative stiffness using a mechanical compensation system. 1 shows a schematic side view of an optical device that obtains negative stiffness using a magnetic compensation system. FIG. 6B shows a variation of the embodiment of FIG. 6A. 1 illustrates one embodiment for obtaining an optical device with adjustable negative stiffness. 1 illustrates one embodiment for obtaining an optical device with adjustable negative stiffness. 1 illustrates one embodiment for obtaining an optical device with adjustable negative stiffness. 1 illustrates one embodiment for obtaining an optical device with adjustable negative stiffness. FIG. 4 shows a schematic side view of an optical device including negative stiffness compensation along multiple axes.

  In the drawings, similar reference signs indicate similar or functionally equivalent elements unless otherwise indicated.

  FIG. 1A shows a schematic diagram of an EUV lithographic apparatus 100A comprising an illumination system 102 and a projection system 104 (also referred to as “POB”). EUC is an abbreviation for “extreme ultraviolet” and indicates the wavelength of exposure light of 0.1 nm to 30 nm. The illumination system 102 and the projection system 104 are incorporated into a vacuum housing that is evacuated by an exhaust device (not shown). The vacuum housing is surrounded by a machine room (not shown). The machine room includes devices for positioning the optical elements. In addition, the machine room may include control devices and other electrical equipment.

  The EUV lithography apparatus 100A includes an EUV light source 106A. The EUV light source 106A can be formed as a plasma source or synchrotron that emits light 108A in the EUV region, for example, light having a wavelength of 0.1 nm to 30 nm. The EUV light 108A is focused in the illumination system 102 and the desired operating wavelength is extracted. Since the EUV light 108A has a low transmittance in the air, the illumination system 102 and the projection system 104 are evacuated.

  The illumination system 102 illustrated in FIG. 1A includes, for example, five mirrors 110, 112, 114, 116, and 118. After passing through the illumination system 102, the EUV light 108A is guided to the reticle 120. The reticle 120 is also configured as a reflective optical element and can be placed outside the systems 102, 104. Further, the EUV light 108A can be directed to the reticle 120 using the mirror 126 outside either system 102, 104. The reticle 120 includes a structure in which a much smaller image is projected onto the wafer 122 and the like by the projection system 104.

  Projection system 104 may comprise, for example, six mirrors M1-M6 to project the structure onto wafer 122. Some of the mirrors M <b> 1 to M <b> 6 of the projection system 104 can be arranged symmetrically with respect to the optical axis 124 of the projection system 104. Of course, the number of mirrors of the EUV lithography apparatus 100A is not limited to the number shown in FIG. 1A. Further, the mirrors may have different shapes, for example, some may be formed as curved mirrors, and some may be formed as facet mirrors.

  FIG. 1B shows a schematic diagram of a DUV lithographic apparatus 100B that also includes an illumination system 102 and a projection system 104. DUV refers to “deep ultraviolet” and indicates the wavelength of exposure light of 30 nm to 250 nm. The illumination system 102 and the projection system 104 may be placed in a vacuum housing and / or machine room as described with reference to FIG. 1A.

  The DUV lithography apparatus 100B includes a DUV light source 108B. The DUV light source 108B may be configured as an ArF excimer laser that emits light 193b having a wavelength of 193 nm, for example.

  The illumination system 102 guides the DUV light 108B to the reticle 120. Reticle 120 is configured as a transmissive optical element and may be located outside each of systems 102 and 104. Also in this case, the reticle 120 has a structure in which a much smaller image is projected onto the wafer 122 or the like by the projection system 104.

  Projection system 104 may include a plurality of lenses 132 and / or mirrors 134 to project the structure of photomask 120 onto wafer 122. The lens 132 and / or the mirror 134 may be arranged symmetrically with respect to the optical axis 124 of the projection system 104. Also in this case, the number of lenses or mirrors of the DUV lithography apparatus 100B is not limited to the number of lenses and mirrors shown in FIG. 1B.

  The air gap between the final lens 132 and the wafer 122 can be replaced with a liquid medium 136 having a refractive index greater than one. For example, high purity water can be used as the liquid medium. This setting is called immersion lithography and is characterized by high photolithography resolution.

  FIG. 2 illustrates in perspective view an optical device 200 with a base 202 that supports an optical element 204 that may be formed, for example, as a mirror.

  The optical device 200 can be incorporated into one of the lithographic apparatus shown in FIGS. 1A and 1B. The optical element 204 corresponds to, for example, one of the mirrors M1 to M6 (FIG. 1A) or one of the lenses or mirrors 132 and 134 (FIG. 1B). In other embodiments (not shown), the optical element 204 is configured as an optical grating or lambda plate.

  The base 202 can be fastened to a fixed structure of the lithographic apparatuses 100A, 100B, for example, to a force frame (not shown). For this purpose, a fastening hole 206 or the like can be provided in the base 202. Base 202 may comprise a rectangle or any other suitable shape.

  Mirror 204 (referred to below for ease of understanding, but should not be construed as a mirror-only limitation; any other suitable optical element can be used) is used for incident light 108A, 108B is reflected. The corresponding optical axis of the mirror 204 is indicated by reference numeral 208. The front surface 210 that reflects at least the light 108A, 108b, or the entire mirror 204 can be curved (shown) or straight.

  FIG. 3 shows a section III-III from FIG. The mirror 204 is shown in an undeformed state (solid line) and a deformed state (dotted line). The mirror 204 is shown to have a planar shape in the undeformed state. Nevertheless, the mirror 204 can have any shape, such as a curved shape, in an undeformed state.

  The mirror 204 can be supported by, for example, the supports 300 and 302 at two places. The supports 300 and 302 can support the mirror 204 or a part thereof on the rear surface 304. In this simple support configuration, the support 300 can be configured to allow relative rotation of the mirror 204, but connects and fixes the mirror 204 to the base 202 in a direction perpendicular to the optical axis 208. On the other hand, support 302 allows relative rotation of mirror 204 and allows movement of mirror 204 perpendicular to optical axis 208. As used herein, “vertical” may include a deviation from exactly vertical of up to 10 °, preferably up to 5 °, more preferably up to 1 °.

  However, any other type of support for the mirror 204 or part thereof is possible. For example, the mirror 204 may be supported at 3 or more locations, for example, 5 locations, 10 locations, or 20 locations, or more locations. Further, the support may generate a force and / or moment where it connects to the mirror 204.

Furthermore, the optical device 200 includes an actuator 306. The actuator 306 deforms the optical element 204 (or a part thereof) between the two states shown in FIG. Actuator 306 is fastened to mirror 204 on the one hand and to base 202 or any other suitable reference on the other hand. The actuator 306 is, for example, Lorentz type, i.e. the resultant force on the mirror 204 to deform the mirror 204 (Resulting force) F r voice coil to generate a _(see Figure 3A illustrating a force diagram associated with FIG. 3) ( It can be configured as an actuator including a magnet (not shown) and a magnet (not shown). The direction in which the force F _r acts is denoted by δ.

  Instead of the Lorentz actuator, in principle any other actuator, for example a piezoelectric actuator or a pneumatic actuator, may be used. However, using a Lorentz actuator, particularly when used in an open loop control system, can result in a less complex system, which can be cost effective.

  When using a Lorentz actuator, the magnet can be fastened to the mirror 204, specifically the rear face 304, and the voice coil can be fastened to the base 202. Other arrangements in which the voice coil 306 is fastened to the mirror 204 and the magnet is fastened to the base 202 are also conceivable.

  The actuator 306 can be controlled by the controller 308. The controller 308 may control the actuator 306 to deform the mirror 204 to perform optical correction. That is, by changing the mirror 204, the incident angles of the light 108A and 108B are changed. Optical correction may include image error correction with overlay or focus correction. “Image” refers to the image projected onto the wafer 122 (see FIGS. 1A and 1B).

  The controller 308 may deform the mirror 204 in real time, for example, within a time window between the exposure of two different dies on the wafer 122, or even within a die, ie during a single die scan on the wafer 122. The scanning of each die on the wafer 122 can be performed at 30 Hz, for example. Thus, the time window for changing the deformation of the mirror 204 can be less than 1/30 second.

  In the example of FIG. 3, deformation of the mirror 204 in the direction δ is obtained by out-of-plane bending of the mirror 204. This is a result of the actuator 306 acting on the mirror 204 in a direction δ parallel to the optical axis 208 at a location between the two supports 300, 302. “Parallel” may include a deviation from exactly parallel of up to 10 °, preferably up to 5 °, more preferably up to 1 °.

When the mirror 204 is deformed by a force acting in the direction δ, this force is generally composed of two components. The first is the quasi-static force F _Q (see FIG. 3A) necessary to deform the mirror 204 itself. This quasi-static force is a function of the elastic modulus of the material of the mirror 204 and its geometry, and therefore corresponds to the (positive) stiffness of the mirror 204. On the other hand, the force consists of dynamic force F _D required to accelerate the mass of the mirror 204. This dynamic force varies depending on the density of the mirror 204, the geometric deformation profile, and the deformation trajectory (as a function of time). In order to reduce the resultant force F _r that the actuator 306 needs to spend on deformation of the mirror 204, the positive stiffness of the mirror is combined with the corresponding negative stiffness. For this purpose, the optical device 200 comprises a compensation unit 310 having a negative stiffness in the direction δ and at least partially compensating for the positive stiffness of the mirror 204.

FIG. 3A shows a schematic diagram of the forces acting on the mirror 204 at the location of the actuator 306 and the compensation unit 310. When the mirror 204 is deformed in the direction δ, a positive force F _p is obtained from the positive rigidity k _{p of the} mirror. This is also shown in FIG. 4A, which shows a diagram of force F versus deformation δ. On the other hand, when the mirror is deformed in a direction δ that opposes the force F _p , the force F _n is obtained from the negative rigidity of the compensation unit 310. The resultant force is a force F _Q that is a quasi-static force necessary to deform the mirror 204 in the direction δ. In addition to the force F _Q is a quasi-static force, the actuator 306, it is necessary to accelerate the mirror 204 by adding a dynamic force F _D on the mirror 204. The sum of the forces _{F Q} and the force _{F D} is equal to the resultant force _{F r} of the actuator 306 is added. Since F _n and F _p are much larger than F _Q , F _D , and F _r , they are not drawn to scale in FIG. 3A and are shown as dotted lines, respectively.

The amount of deformation of the mirror 204 in the direction δ is usually small, for example in the micrometer range, and at the same time the time window for deformation is quite large, for example 1/30 second (see the description for the scanning trajectory above), which is necessary The dynamic force F _D is small compared to the quasi-static force F _Q. Furthermore, with proper system design, the resultant force F _r (= F _Q + F _D ) is much smaller than the force F _n generated by the compensation unit. Obviously, the force _{F p, F n, F D} can vary over time during the production of the die or wafer. However, it can be seen that these forces are typically periodic in the manufacture of a single die or the entire wafer. When looking at a single cycle, the system can be designed such that the negative stiffness force F _n has a maximum value N times greater than the maximum resultant force F _r that the actuator 306 needs to generate, where N is preferably 5 Greater than, more preferably greater than 10 and even more preferably greater than 50.

  This type of system design provides an actuator 306 with low energy consumption. This further reduces thermal expansion problems and corresponding cooling problems by reducing the corresponding heat losses.

To further improve the system design, the “large” forces F _p and F _n can be designed to be almost unchanged compared to the “small” dynamic forces F _D. For this purpose, it is possible to increase M times than the maximum time derivative maximum time derivative of the negative rigidity (see above description) F _n of dynamic force F _D in one cycle, M is more preferably 1 Greater than 2, more preferably greater than 2, even more preferably greater than 10.

  In order to further improve the energy efficiency of the system, the actuator 306 can be designed to recover the dynamic energy of the mirror 204. In other words, if the mirror 204 needs to be decelerated, the work that the mirror 204 does for the actuator 306 is converted to electrical energy, which is returned to electrical energy storage. Therefore, the heat loss of the actuator 306 can be further reduced.

Next, returning to FIG. 4A, the positive stiffness force F _p , the negative stiffness force F _n , and the resultant force F _r are the stiffness k _p (positive stiffness), k _n (negative stiffness), k _r (resulting stiffness). )), And changes according to the deformation δ. Preferably, the composite stiffness k _r and the corresponding resultant force F _r are designed to be non-zero positive. For example, the negative stiffness _{k n} can be equal to from 0.9 to 0.99 times the positive stiffness _{k p.} Thereby, when the actuator 306 is not generating a force, for example, when the optical device 200 or the lithographic apparatuses 100A and 100B are being transported, the actuator 306 is turned off (the power is not turned on), or the actuator is unexpected. In the event of a failure, it is ensured that the deformation of the mirror 204 in the direction δ is determined. By selecting the positive synthetic force k _r, the mirror 204, without action of the actuator 306 (in the off or malfunction of the actuator 306) returns to the undeformed state.

FIG. 4B shows a force versus deformation view according to another embodiment of the optical device 200. In this embodiment, as with reference to FIG. 7A~ to 7D will be described in more detail below, it is possible to switch the negative rigidity F _n on or off. Therefore, turning off the negative stiffness k _n, synthetic rigidity becomes to correspond to the positive stiffness k _p, which, for example, enough to prevent damage to the mirror 204 during transport by vibration or other movement large. As a result, during normal operation of the optical device 200, i.e., the synthetic stiffness k _r during the manufacture of the wafer, can be designed even smaller (or equal to zero) so as than the embodiment described in Figure 4A. For example, in the embodiment of FIG. 4B, the negative stiffness _{k n} may be designed to be from 0.99 to 0.999 times the positive stiffness _{k p.} Example: Assuming the mirror mass is 1 kg moved 1 μm with a 10 ms travel time, this requires an acceleration of 10 mm / s ² . Therefore, the corresponding dynamic force F _D is equal to 10 mN, which can be supplied by Lorentz actuator power consumption of less than 1 mW.

Negative stiffness _{k n} needed to compensate for the positive stiffness _{k p} of the mirror is approximately ¹⁰ 5 ^~10 6 N / m. Thus, for a 1 μm bias, this requires a negative stiffness force F _n of 1N. This corresponds to 100 times the dynamic force _{F D.} To dynamic forces F _D of the same order, the negative rigidity F _n must be very accurate. Preferably, the negative stiffness force can be adjusted dynamically in real time, i.e. during operation of the optical device 200. A method for adjusting the negative stiffness is described below with respect to FIGS. 7A-7D.

Next, an embodiment of the optical device 200 to obtain the desired negative stiffness k _n with mechanical compensation will be described with reference to FIGS 5A~ Figure 5C.

The compensation unit 310 of FIG. 5A includes, for example, a mechanical spring 500, such as a leaf spring or a spiral spring, and a preload unit 502, such as a pneumatic cylinder that preloads the spring 500. For example, the spring 500 acting on the side 504 of the mirror 204 is preferably quite long. When the mirror 204 is deformed, this deformation also mirror 204 in the horizontal direction, i.e., it moved in a direction perpendicular to the optical axis 208, a long spring 500 is to ensure a more or less constant preload force F _c. Instead of using a pneumatic cylinder 502 can be attached to the base 202 of the spring 500 in a compressed state in order to generate the force F _c. In other embodiments, for example, by a pneumatic cylinder, or by using a magnet, (without a mechanical spring) directly the force F _c may be added.

The mirror 204 of FIG. 5A is preloaded with a compensation force F _c in a plane, ie perpendicular to the optical axis 208. Force _{F c} is the mirror 204 to buckle, thus the mirror 204 tends to bend out of plane. The force _{F c} can be for example applied by a mechanical spring 500.

  Since the mirror 204 is symmetrical, half of the mirror 204 can be considered as a simple cantilever that receives forces at the ends as shown in FIG. 5B.

  The deflection is given by:

(Formula 2)

Where L corresponds to the width of the mirror 204 between the supports 300, 302 as shown in FIG. 5A, F _p corresponds to the positive stiffness required to overcome the positive stiffness of the mirror 204, and E is the mirror Corresponding to the elastic modulus of 204 material (eg glass or ceramic), I corresponds to the moment of inertia (depending on the geometrical shape of the cross section of the mirror 204).

Therefore, the positive rigidity k _p of the mirror 204 is given by the following equation.

(Formula 3)

A bending moment of magnitude F _c × δ is obtained from the compressive force F _c (preload) applied to the cantilever (FIGS. 5B and 5C) by the deflection δ. This moment results in a deflection δ ′ as follows:

(Formula 4)

For [delta] = [delta] '(corresponding to zero rigidity, that is, when the positive stiffness k _p is equal to negative stiffness k _n), the required compressive force F _c is given by the following equation.

(Formula 5)

Thus, what has been shown above is that a constant preload F _c is suitable to provide a negative or substantially negative stiffness that compensates for the positive stiffness of the mirror 204. For example, a substantially constant compensation force F _c can be provided by a long spring 500 with preload.

  6A and 6B show first and second embodiments of a compensation unit 310 comprising a magnet.

Compensation 310 in FIG. 6A includes a first magnet 600 that is fastened to the mirror 204 to generate a negative rigidity _{F n.} A connection 602 between the first magnet 600 and the mirror 204 is indicated. The magnet 600 is disposed between the second and third magnets 604 and 606 that are fixed. For this purpose, the second and third magnets 604, 606 can be fastened to the base 202. The first magnet 600 can be mechanically guided in the direction δ. The magnets 600, 604, 606 may be configured as block magnets and may have the same polarization (designated “N” for north and “S” for south) with respect to direction δ. Accordingly, when the first magnet 600 is positioned in the middle between the second magnet and the third magnets 604 and 606, the first magnet 600 generates a zero offset force with respect to the mirror 204. Also, as the deformation of the mirror 204 increases in the direction δ, the force F _n increases accordingly. Accordingly, the negative stiffness _{k n} occurs.

In the example of FIG. 6B, the compensation 310 includes a first magnet 600 connected to the mirror 204 by a connection unit 602. Furthermore, the compensation unit 310 includes a second magnet 604 configured as a ring magnet. Ring magnet 604 has a central axis 608. The first magnet 600 is mechanically guided so as to move along the central axis 608 when the mirror 204 is deformed in the direction δ, for example. The first magnet 600 and the second magnet 604 have opposite polarities along the axis 608. When the first magnet 600 is disposed on the symmetry axis 610 of the second magnet 604 along the axis 608, the first magnet 600 generates a zero offset force on the mirror 204. When the deformation of the mirror 204 is increased in the direction [delta], the first magnet 600 is so displaced from its position in the axis of symmetry 610, also increases the negative rigidity F _n to the first magnet 600 is generated.

  7A-7D show four different embodiments of the adjustment unit 700. FIG.

In the example of FIG. 7A, the adjustment unit has a pneumatic cylinder 700 that switches on and off. In the “off” state, the pneumatic cylinder 700 does not generate a preload F _c for the spring 500. On the other hand, can the controller 702 is provided to control the preload force F _c (continuously even) based on the input. For example, a sensor 704 that senses an optical error that requires correction may be provided. The controller 702 can control the pneumatic cylinder 700 to receive a corresponding input signal from the sensor 704 and generate a pre-pressure F _c that results in deformation of the mirror 204 that leads to proper optical correction.

Setting the desired preload force F _c by the controller 702, for example, it can be carried out by measuring the current in the low speed deformation movement in the (Lorentz) actuator 306. This is a slow, acceleration forces are negligible, the Lorentz force is due only to the residual stiffness k _r. If both F _r and δ are measured, _kr can be determined and F _c adjusted accordingly until the desired _kr value is reached.

The embodiment of FIGS. 7B-7D may also include a controller 702 and possibly a sensor 704. They differ only in the way in which the negative stiffness force _Fn is adjusted.

  In the embodiment of FIG. 7B, the adjustment unit 700 moves the second magnet 604 along the central axis 608 from an initial position P1 to a second position P where the first magnet 600 generates an initial offset force against the mirror 204. May include other means such as set screws. Instead of the set screw or the like, the position of the second magnet 604 may be adjusted using, for example, electromagnetic means.

  In the embodiment of FIG. 7C, the adjustment unit 700 adjusts the magnetic field coupling between the first magnet 600 and the second magnet 604. For this purpose, the adjustment unit 700 can include, for example, a U-shaped mover magnet, which is moved perpendicular to the central axis 608 to change the magnetic field coupling between the magnets 600, 604. . In the position P1, the magnets 600 and 604 are disposed in the mover magnet 700. Thus, there is maximum magnetic field coupling between the magnets 600,604. In the position P <b> 2, the mover magnet 700 is moved to a position where the magnets 600 and 604 are disposed outside the mover magnet 700. Thus, there is no (further) magnetic field coupling between the magnets 600,604. Thereby, when the magnet 600 moves along the central axis 608 when the mirror 204 is deformed, the force acting between the first magnet and the second magnet 600 604 is changed.

In the example of FIG. 7D, the adjustment unit 700 includes a permanent electromagnet 706. The permanent electromagnet 706 includes at least a first magnet 708 made of a medium coercive force material and a coil 710 that changes the magnetization of the magnet 708 in accordance with an input signal received from, for example, the controller 702 (see FIG. 7A). Furthermore, the adjustment unit 700 may comprise a second magnet 712 of high coercivity material and an iron core 712 that additionally or alternatively increases the total magnetic field strength. Magnet 708 and, if provided, magnet 712 form second magnet 604 described in FIG. 6B. By adjusting the magnetization of the first magnet 708 may be the second magnet 604 is to adjust magnetic field generated, thus a negative stiffness F _n.

  FIG. 8 shows an optical device 200 having a plurality of axes δ1, δ2, δ3 where deformation can occur. The mirror 204 is connected to the first magnets 600a, 600b, and 600c via, for example, three connectors 602a, 602b, and 602c. The first magnets 600a, 600b, and 600c are disposed between the first and second magnets 604a, 604b, and 604c and 606a, 606b, and 606c, respectively. Each first, second, and third magnet 604a-606c associated with each connector 602a, 602b, 602c forms a compensation subunit 310a, 310b, 310c. Compensation subunits 310a, 310b, 310c together form compensation unit 310.

  The negative stiffness of the compensation unit 310 in FIG. 8 is described by the following negative stiffness matrix.

  The stiffness matrix should not be created just to produce the required diagonal (local) stiffness, but the crosstalk term of the mirror 204 by generating the appropriate negative crosstalk between adjacent magnets 604a-606c. There is also a need to compensate.

  Although the present invention has been described with respect to particular embodiments, many variations and modifications are possible and the results are still within the scope of the invention. No limitation with respect to the specific embodiments disclosed herein is intended or inferred.

100A EUV lithography apparatus 100B DUV lithography apparatus 102 Illumination system 104 Projection system 106A EUV light source 106B DUV light source 108A EUV light 108B DUV light 110 Mirror 112 Mirror 114 Mirror 116 Mirror 118 Mirror 120 Reticle 122 Wafer 124 Optical axis 126 Mirror 132 Lens 134 Mirror 136 Fluid 200 Optical device 202 Base 204 Mirror 206 Hole 208 Optical axis 210 Front surface 300 Support body 302 Support body 304 Rear surface 306 Actuator 308 Controller 310 Compensation unit 310a-310b Compensation subunit 500 Spring 502 Pneumatic cylinder 504 Side surface 600 First magnet 600a-600c 1st magnet 602 connection part 602a-6002c connection part 604 2nd magnet 604a-604c 2 magnet 606 third magnet 606a~606c third magnet 608 central axis 610 of symmetry axis 700 adjusting unit 702 controller 704 sensor 706 electro-permanent magnet 708 the first permanent magnet 710 the coil 712 second permanent magnet 714 iron core _F, F 1, _{F 2} , _{F 3} force _{F c} preload _{F D} dynamic forces _{F n} negative rigidity _{F p} positive rigidity _{F Q} quasi static force _{F r} force _{k r} synthetic stiffness _{k n} negative stiffness _{k p} positive stiffness M1~M6 mirror δ, δ ₁ , δ ₂ , δ ₃ displacement / direction

Claims (15)

An optical device (200) for a lithographic apparatus (100A, 100B) comprising:
An optical element (204) having positive stiffness (k _p ) when deformed in at least one direction (δ);
An actuator (306) for deforming the optical element (204) in the at least one direction (δ);
Said at least one direction ([delta]), the positive stiffness _{(k p)} lithographic apparatus that includes a compensation unit (310) having a negative stiffness _{(k n)} to at least partially compensate for (100A of the optical element, 100B) optical device. The optical device according to claim 1, wherein the compensation unit (310) generates a first maximum force (F _n ) on the optical element (204) in the at least one direction (δ). (306) generates a second maximum force (F _r ) on the optical element (204) in the at least one direction (δ), and the first maximum force (F _n ) is the second maximum force. An optical device that is N times greater than (F _r ), where N is greater than 5, preferably greater than 10 and more preferably greater than 50. The optical device according to claim 1 or 2, wherein the compensation unit (310) generates a first force (F _n ) against the optical element (204) in the at least one direction (δ), The actuator (306) generates a second force (F _r ) with respect to the optical element (204) in the at least one direction (δ), and the first force (F _n ) has a first maximum time derivative. The second force (F _r ) has a second maximum time derivative, the second maximum time derivative being M times greater than the first maximum time derivative, and M being greater than 10, preferably An optical device greater than 100. 4. The optical device according to claim 1, wherein the negative rigidity (k _n ) of the compensation unit is 0.9 to 0.99 times the positive rigidity (k _p ) of the optical element. An optical device that is. The optical device according to claim 1, wherein the positive stiffness (k _p) and the negative stiffness (k _n) with larger optical device than the difference zero of the compensation unit of the optical element .   The optical device according to any one of claims 1 to 5, wherein the deformation of the optical element (204) in the at least one direction (δ) is obtained by out-of-plane bending of the optical element (204). device.   Optical device according to any one of the preceding claims, wherein the compensation unit (310) comprises a magnet (600, 604, 606), in particular a permanent magnet, or at least one spring (500). .   The optical device according to any one of the preceding claims, wherein the compensation unit (310), in particular at least one spring (500), preloads the optical element (204) in a plane.   The optical device according to any one of claims 1 to 8, further comprising a base (202), wherein the magnet comprises a first magnet (600) fastened to the optical element (204) and the base (202). An optical device comprising a second magnet and a third magnet (604, 606) fastened to each other, wherein the first magnet (600) is movable between the second magnet and the third magnet (604, 606).   The optical device according to any one of claims 1 to 8, further comprising a base (202), wherein the magnet comprises a first magnet (600) fastened to the optical element (204) and the base (202). The first magnet (600) and the second magnet (604) are formed as ring magnets, and the other magnet is the central axis of the ring magnet. An optical device movable along (608). The optical device according to any one of claims 1 to 10, further comprising an optical device wherein the negative stiffness _{(k n)} adjusting unit for adjusting (700) of the compensation unit (310). The optical device of claim 11, wherein the adjustment unit (700), or changing the preload _{(F c)} of at least one spring (500), first magnet, second magnet, and / or third magnet ( 600, 604, 606), or the magnetic coupling between the first magnet, the second magnet, and / or the third magnet (600, 604, 606), or at least one. An optical device that adjusts the magnetic field of the first magnet, the second magnet, and / or the third magnet (600, 604, 606) using two permanent electromagnets (706). The optical device according to any one of claims 1 to 12,
It said optical element (204) includes a first positive stiffness when deformed in a first direction ([delta] _{1) (k p),} a second rigid when deformed in a second direction ([delta] ₁₎ and _{(k p)} Have
The actuator (306) deforms the optical element (204) in the first direction and the second direction (δ1, δ2),
The compensation unit (310), the positive stiffness (k _p) at least partially the first negative stiffness in the first direction to compensate ([delta] ₁₎ (k of said optical element in the first direction ([delta] ₁₎ and _n), and said second direction ([delta] ₂₎ the second negative stiffness of the optical element positive stiffness _{(k p)} to at least partially compensate for the second direction ([delta] ₂₎ of the _{(k n)} Optical device having.   14. The optical device according to any one of the preceding claims, wherein the actuator (306) deforms the optical element (204) for optical correction, particularly in overlay and / or focus correction, and The optical element (204) is an optical device that is a mirror, a lens, a diffraction grating, or a lambda plate.   A lithographic apparatus (100A, 100B) comprising the optical device (200) according to any one of the preceding claims.