TW201732345A - Optical device for a lithography apparatus and lithography apparatus - Google Patents

Abstract

The present invention discloses an optical device (200) for a lithography apparatus (100A, 100B), comprising: an optical element (204) having a positive stiffness (kp) when deformed in at least one direction ([delta]), an actuator (306) for deforming the optical element (204) in the at least one direction ([delta]), and a compensation unit (310) having a negative stiffness (kn) in the at least one direction ([delta]) at least partially compensating the optical element's positive stiffness (kp).

Description

Optical device and lithography device for lithography equipment [Related patent reference]

The priority of the German Patent Application No. DE 10 2015 225 263.9, filed on Dec. 15, 2015, the entire content of which is hereby incorporated by reference.

The present invention relates to an optical device and a lithography apparatus for use in a lithography apparatus.

The lithography is a process for micromachining to pattern portions of the film of the substrate body. In particular, lithography is used in the fabrication of integrated circuits. The lithography process is performed using a lithography device that includes a lighting system and a projection system. Light is used to transfer the geometric pattern from the reticle to a photo-sensitive chemical layer called a photoresist on the substrate. The reticle is illuminated by an illumination system. The projection system projects the geometric pattern onto a substrate that is positioned on the image plane of the projection system.

Driven by Moore's Law and pursuing smaller structures, especially in the manufacture of integrated circuits, EUV lithography equipment is currently being developed, using light having a wavelength of 5 nm to 30 nm, particularly 13.5 nm. "EUV" means "extreme ultraviolet light". Since most materials have high absorption of light at this wavelength, it is desirable to use a reflective optical element (ie, a mirror) in place of the previous refractive optical element (ie, a lens) in such EUV lithography apparatus.

The mirror in the EUV lithography device can for example be fastened to a so-called force frame (force Frame). Each mirror can be manipulated in up to six degrees of freedom. This allows the mirrors to be positioned with high accuracy relative to each other, for example in the pm range. In this manner, changes in optical characteristics (e.g., due to thermal perturbations) can be compensated for during operation of the lithographic apparatus.

More recently, it has been discovered that more advanced optical error correction can be obtained by morphing optical elements (e.g., mirrors) during operation of the lithographic apparatus (i.e., instantaneously).

For example, DE 10151919 A1 describes (cf. Figs. 1 and 2 of this document) a mirror 1 comprising four columns 2. The actuator 4 pulls the opposite column 2 towards the optical axis 3 of the mirror 1 or pushes the opposite column 2 away from the optical axis 3. Therefore, the optical element 1 is deformed.

JP 2013-106014 A describes a deformable mirror 22 in FIG. A plurality of mirror columns 24 are disposed on the rear end surface 22e of the mirror 22. The load supply system 58 is configured to displace the tip of the respective mirror post 24 to introduce a load to the rear end face 22e of the mirror 22 and thereby deform the reflective surface 22d of the mirror 22.

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

This object is achieved by an optical device for a lithography apparatus comprising an optical component, an actuator, and a compensation unit. The optical element has a positive stiffness when deformed in at least one direction. The actuator is configured to deform the optical element in at least one direction. The compensation unit has a negative stiffness in at least one direction to at least partially compensate for the positive stiffness of the optical element.

"Negative stiffness" is defined as the stiffness that produces a force or moment that tends to deform the optical element in at least one direction, and increases (or remains constant) as the deformation of the optical element increases in at least one direction. The negative stiffness thus counteracts the positive stiffness, thus reducing (or even 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. Rather, the negative stiffness relies on energy stored in a mechanical system or magnetic field and does not depend on any external energy supply.

One concept on which the invention is based involves dividing the force required to deform the optical element into two components, a quasi-static force and a dynamic force. The quasi-static force is required for the anamorphic optical element itself. It should be noted that "deformed optical element" herein means that the entire optical element is deformed or one or more portions thereof are deformed. The quasi-static force is primarily dependent on the (positive) stiffness of the optical component. The rigidity is determined by the E-modulus of the material from which the optical element is made, such as glass or ceramic, and the geometry of the optical element. Dynamic forces are required to accelerate the quality of the optical components. This force is primarily dependent on the density of the optical element, the geometric deformation profile, and the deformation trajectory as a function of time.

Since the amount of movement of the optical elements required for optical correction is small (generally in the range of several micrometers), and the time window for optical correction is relatively large (for example, 1/30 second), the required dynamic force is small. On the other hand, the rigidity of the optical element is relatively large, so the static force used to deform the optical element needs to be much larger than the dynamic force.

With the (nearly zero) rigid configuration currently offered, the actuator now only needs to transfer kinetic energy and compensate for the energy required for any frictional losses. For example, an acceleration of 10 mm/s ² is required to move a mirror of 1 kg mass above 1 μm in a moving time of 10 ms. Therefore, a force of 10 mN is required, which can be easily transmitted by, for example, a Lorentz type actuator (also referred to as a voice coil actuator) with a power loss of less than 1 mW.

The negative stiffness required to compensate for the positive stiffness of the optical component will typically be on the order of 10 ⁵ to 10 ⁶ N/m. A force of 1 N will be required for an offset of 1-μm. In this example, this corresponds to 100 times the required dynamic force and is therefore much larger.

Due to this design, the actuator according to the invention only needs to provide dynamic forces and, if available, provide a small static force. Therefore, the total force provided by the actuator is significantly smaller than known solutions.

In general, all types of actuators will produce significant heat that cannot be removed without increasing interference, such as cooling water vibration. However, since the force required for the solution according to the invention is substantially reduced, substantially no additional heat removal is required.

The actuator of the present invention is preferably a Lorentz actuator. Of course However, in some applications, other types of actuators, such as piezoelectric actuators or pneumatic actuators, are also possible.

Another advantage of the Lorentz actuator is its small reaction time, which makes the Lorentz actuator particularly suitable for immediate optical error correction, such as "die to die" or even " Intra-die. "Grade to grain" refers to a morphing optical element in a time window between exposures of two continuous dies on a single wafer. "In-grain" means that the optical element is deformed for optical correction in a time window during scanning of a single die.

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

According to a specific embodiment, the compensation unit is configured to generate a first maximum force on the optical element in at least one direction, and the actuator is configured to generate a second maximum force on the optical element in at least one direction, wherein A maximum force is N times greater than the second maximum force, wherein N > 5, preferably N > 10, more preferably N > 50.

"Maximum force" refers to the maximum force found in the cycle of making a single die or an entire wafer using optical devices. It is found that N > 5, preferably > 10 and more preferably N > 50 will give a sufficiently small actuator force while at the same time having good system stability for open loop control.

According to another embodiment, the compensation unit is configured to generate a first force on the optical element in at least one direction, and the actuator is configured to generate a second force on the optical element in at least one direction, wherein the first The force has a first maximum time derivative, and the second force has a second maximum time derivative, wherein the second maximum time derivative is greater than the first maximum time derivative by M times, wherein M > 10, preferably For M>100

The "maximum time derivative" is the maximum derivative found in a cycle in which a single die or an entire wafer is fabricated using an optical device. It is found that the given value M will give a highly dynamic deformation while keeping the compensation unit simple.

According to another specific embodiment, the negative stiffness of the compensation unit is positive for the optical component It is 0.9 to 0.99 times rigid.

It has been found that this ratio of negative stiffness to positive stiffness gives a small actuator force while giving good dynamic stability. Ideally, it would be desirable to have 100% compensation such that the ratio of negative stiffness to positive stiffness should be equal to one. In this 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 in a force balance in any deformed state and will remain in this deformed state. This may not be desirable because in the event of a fault, it may be desirable to return the mirror to a particular original shape. Therefore, it is preferable to make the negative stiffness compensation slightly less than 100%, for example between 90% and 99%.

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

Therefore, in the neutral state, that is, when the actuator is turned off (no power) or malfunctioning and thus no force is supplied, the state of the optical element, particularly the degree of its deformation, is always defined. The optical element will always return to its original shape.

According to another specific 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" currently refers to bending about one axis perpendicular to the optical axis of the optical component.

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

This type of assembly is also very suitable for obtaining negative rigidity. The spring can be a mechanical spring such as a leaf spring or a coil spring.

According to another specific embodiment, the compensation unit, in particular at least one spring, is configured to preload the optical element in a plane.

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

In accordance with another embodiment, an optical device includes a substrate, wherein the magnet is comprised of a first magnet secured to the optical component and a second magnet and a third magnet respectively secured to the substrate, the first magnet being configurable to the second magnet And moving between the third magnets.

This configuration is also very suitable for obtaining a negative stiffness with zero offset force. When the second magnet and the third magnet are fixed, the first magnet moves with a portion of the optical element to obtain the desired deformation of the optical element.

In accordance with another embodiment, an optical device includes a substrate, wherein the magnet is comprised of a first magnet secured to the optical component and a second magnet secured to the substrate, wherein the first magnet or the second magnet is formed as a ring magnet And another magnet can move along the central axis of the ring magnet.

This particular embodiment describes another configuration of the magnet to achieve a negative stiffness with zero offset force. Likewise, the second magnet is fixed and the first magnet moves with a portion of the optical element as the optical element is deformed.

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

The resonance mode of the optical device may deteriorate due to a decrease in system rigidity. This can result in unacceptable dynamic performance when the actuator is turned off or does not provide the proper force due to a fault. However, this can be counteracted by a switching mechanism that includes turning negative stiffness on or off. This is also advantageous during transmission of, for example, an optical device or a lithography device comprising such a device. Generally, the resonant frequency may cause damage to the optical device during transmission. The inclusion of the adjustment unit now will allow the optical element to have its (normal) positive stiffness or at least substantially positive stiffness which will avoid damaging the optical element during transmission or the like. On the other hand, the adjustment unit can adjust the negative stiffness even on the fly to keep the required actuator force to a minimum during operation of the optical device. The adjustment unit can be configured to continuously adjust the negative stiffness.

According to another embodiment, the adjustment unit is configured to preload at least one spring, adjust the first magnet, the second magnet using at least one electro-permanent magnet a relative position of the iron and/or the third magnet, a magnetic field coupled between the first magnet, the second magnet, and/or the third magnet, or a magnetic field of the first magnet, the second magnet, and/or the third magnet .

Depending on the mechanism by which negative stiffness is obtained, different ways of adjusting the negative stiffness appear to be appropriate. When a spring is used as a source of negative stiffness, the preload applied to the spring can be varied to adjust the negative stiffness. The preload can be carried out, for example, by using a pneumatic cylinder.

When a magnet is used to obtain negative rigidity, the negative rigidity can be changed by changing the relative position of the magnet to change the repulsion and attractive force between the magnets. For this purpose, for example, a fixing screw or the like can be used.

Further, when a magnet is used to obtain negative rigidity, magnetic field coupling between magnets can be changed by, for example, using a moving iron as a short circuit. For example, a horseshoe moving iron can be used.

Further, when a magnet is used to obtain negative rigidity, the attraction and repulsive force between the magnets can be changed by adjusting the magnetic field of the corresponding magnet. For this purpose, an electrically permanent magnet can be used. An "electric permanent magnet" is currently defined as a magnetic unit that includes at least one first magnet having an adjustable permanent magnetization and a means for adjusting the permanent magnetization of at least one of the magnets.

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

"Permanent magnetization" means that when a device for adjusting permanent magnetization does not generate a magnetic field, at least one magnet loses its magnetization (for example, expressed in A/m) per year, and is not more than 5%, preferably not more than 2 %, more preferably no more than 0.5%.

Permanent magnetization is adjustable. That is to say, for example, the means for permanent magnetization of at least one magnet can be switched between two states of magnetization. These two states may include, for example, a demagnetization state (magnetization is zero) and a magnetization state. In other embodiments, this means that the means for permanent magnetization can switch between more than two, preferably more than ten, magnetization states. Switching can also be performed continuously. The means for permanent magnetization can be formed as a coil. The external magnetic field used to magnetize the at least one magnet can be adjusted by adjusting the current in the coil.

In one example, at least one magnet has a medium coercive field strength (coercivity field strength). "Coercive magnetic field strength" means the field strength required to completely demagnetize the material after magnetic saturation of the magnetic material of at least one of the magnets. Medium coercivity materials are known in the art and include, for example, iron, aluminum, cobalt, copper and/or nickel. For example, the medium coercive field strength 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 medium coercive material is AlNiCo. AlNiCo refers to an alloy of iron, aluminum, nickel, copper and cobalt.

Furthermore, the magnetic unit may comprise another magnet whose permanent magnetization is not altered by the means for changing the permanent magnetization. This feature can be obtained by using a high coercive material as another magnet (second magnet). The first magnet and the second magnet together can produce the desired negative stiffness. In other embodiments, the first magnet alone produces the desired negative stiffness.

The negative rigidity can be appropriately adjusted by controlling the means for adjusting the permanent magnetization of the first magnet.

In accordance with another embodiment, the optical element has a first positive stiffness when deformed in the first direction and a second positive stiffness when deformed in the second direction, wherein the actuator is configured to be in the first direction and the second direction Up deforming the optical element, and wherein the compensation unit has a first negative stiffness in the first direction to at least partially compensate for the positive stiffness of the optical element in the first direction and a second negative stiffness in the second direction to The positive stiffness of the optical element is at least partially compensated in the direction.

In this manner, the basic principles of the invention are applicable to multi-axis systems. The response of such systems can be described by a rigid matrix in which the non-diagonal terms describe the coupling between the axes. If the system is significantly coupled, the local negative stiffness described in the previous paragraph will no longer be sufficient to compensate for all of the stiffness forces and an equivalent negative stiffness matrix needs to be established to compensate for the positive stiffness matrix. That is, not only the diagonal (local) stiffness needs to be compensated, but the crosstalk between adjacent actuators is also compensated. Depending on the geometry, the resulting mechanical system is typically a slightly ribbon-like rigid matrix in which adjacent actuators will have some coupling rigid and remote actuators that will have (near) zero coupling stiffness. Equation 1 below gives a typical negative rigidity matrix, where k _p is a partial negative rigidity of the actuator, and k _c is a rigid coupling between the degrees of freedom. δ ₁ ... δ _{i are} given deformations in the respective directions, and F ₁ ... F _i give the negative rigid forces generated by the respective actuators.

For example, a negative stiffness matrix having the characteristics described in Equation 1 can be obtained using a suitable magnet topology.

According to another specific embodiment, the actuator is configured to deform the optical element for optical correction.

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

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

The λ plate is also referred to as a wave plate or a dam, that is, an optical device that changes the polarization state of light waves passing therethrough.

The mirror can be flat or curved. In addition, the mirror can be a facet of a mirror comprising a plurality of facets.

Further, a lithography apparatus including the above optical device is provided.

The lithography device can be an EUV or DUV lithography device. EUV stands for "extreme ultraviolet light" and indicates that the wavelength of the exposure light is between 0.1 nm and 30 nm. DUV stands for "deep ultraviolet light" and indicates that the wavelength of the exposure light is between 30 nm and 250 nm.

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

Other exemplary embodiments will be explained in more detail with reference to the accompanying drawings.

100A‧‧‧EUV lithography equipment

100B‧‧‧DUV lithography equipment

102‧‧‧Lighting 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‧‧‧Photomask

122‧‧‧ wafer

124‧‧‧ Optical axis

126‧‧‧Mirror

132‧‧‧ lens

134‧‧‧Mirror

136‧‧‧Liquid medium

200‧‧‧Optical device

202‧‧‧Base

204‧‧‧Mirror

206‧‧‧ hole

208‧‧‧ optical axis

210‧‧‧ front face

300‧‧‧Support

302‧‧‧Support

304‧‧‧ rear end face

306‧‧‧Actuator

308‧‧‧ Controller

310‧‧‧Compensation unit

310a-310b‧‧‧compensation subunit

500‧‧‧ spring

502‧‧‧ pneumatic cylinder

504‧‧‧ side

600‧‧‧First magnet

600a-600c‧‧‧first magnet

602‧‧‧Connect

602a-602c‧‧‧Connector

604‧‧‧second magnet

604a-604c‧‧‧second magnet

606‧‧‧ Third magnet

606a-606c‧‧‧3rd magnet

608‧‧‧ center axis

610‧‧‧Axis of symmetry

700‧‧‧Adjustment unit

702‧‧‧ Controller

704‧‧‧ sensor

706‧‧‧Electric permanent magnet

708‧‧‧First electric permanent magnet

710‧‧‧ coil

712‧‧‧Second electric permanent magnet

714‧‧‧ iron core

F, F ₁ , F ₂ , F ₃ ‧ ‧ force

F _c ‧‧‧Preload force

F _D ‧‧‧ Dynamic force

F _n ‧‧‧negative rigidity

F _p ‧‧‧正正力力

F _Q ‧‧‧Static force

F _r ‧‧‧heli

k _r ‧‧‧acquired rigidity

k _n ‧‧‧negative rigidity

k _p ‧‧‧正 rigidity

M1-M6‧‧‧Mirror

δ, δ ₁ , δ ₂ , δ ₃ ‧‧‧ directions

1A shows a schematic view of an EUV lithography apparatus; FIG. 1B shows a schematic view of a DUV lithography apparatus; FIG. 2 shows a perspective view of an optical apparatus integrated into a micro-infrared apparatus such as that of FIG. 1A or 1B; FIG. 3 schematically shows the Section III-III; FIG. 3A shows a force diagram associated with FIG. 3; FIG. 4A shows a diagram according to the first embodiment, which depicts a force versus displacement diagram of the optical device of FIG. 3; FIG. 4B is based on a second embodiment. The force versus displacement diagram of the optical device of Figure 3 is depicted; Figures 5A-5C depict, in schematic side views, optical devices using a mechanical compensation system to obtain negative stiffness, respectively; Figure 6A shows in schematic side view the use of a magnetic compensation system to achieve negative stiffness Figure 6B shows a variation of the embodiment of Figure 6A; Figures 7A-7D show different embodiments to obtain an optical device with adjustable negative stiffness; and Figure 8 shows the included side in a schematic side view A negatively rigid compensated optical device for multiple axes.

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

1A shows a schematic diagram of an EUV lithography apparatus 100A that includes a lighting system 102 and projection system 104 (also referred to as "POB"). EUV stands for "extreme ultraviolet light" and indicates that the wavelength of the exposure light is between 0.1 nm and 30 nm. The illumination system 102 and projection system 104 are integrated into a vacuum enclosure that is evacuated by a vacuuming device (not shown). The vacuum enclosure is surrounded by a machine room (not shown). The machine room contains means for positioning the optical elements. In addition, the machine room can contain control devices and other electronic devices.

The EUV lithography apparatus 100A includes an EUV light source 106A. The EUV light source 106A can be formed as a plasma source or as a synchrotron emitting light 108A in the EUV range, such as light having a wavelength between 0.1 nm and 30 nm. EUV light 108A is concentrated within illumination system 102 and the desired operating wavelength will be filtered out. EUV light 108A has low transmission in air, which is why illumination system 102 and projection system 104 are to be evacuated.

The illumination system 102 shown in FIG. 1A has, for example, five mirrors 110, 112, 114, 116, 118. After passing through the illumination system 102, the EUV light 108A is directed to the reticle 120. The reticle 120 is also configured as a reflective optical element and can be disposed outside of the systems 102,104. Additionally, EUV light 108A can be directed to reticle 120 using mirrors 126 external to any of systems 102, 104. The reticle 120 includes a structure that projects a smaller image of the structure to the wafer 122 or the like by the projection system 140.

Projection system 140 can include, for example, six mirrors M1-M6 for projecting structures onto wafer 122. A portion of the mirrors M1-M6 of the projection system 104 can be symmetrically disposed relative 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. Furthermore, the mirrors can be of different shapes, for example some can be formed as curved mirrors, while others can be formed as facet mirrors.

FIG. 1B shows a schematic diagram of DUV lithography apparatus 100B, which also includes illumination system 102 and projection system 104. DUV means "deep ultraviolet" and means that the wavelength of the exposure light is between 30 nm and 250 nm. As explained with reference to FIG. 1A, illumination system 102 and projection system 104 can be disposed in a vacuum enclosure and/or machine room.

The DUV lithography apparatus 100B includes a DUV light source 108B. DUV light source 108B can ArF excimer laser emitting light 108B having a wavelength of, for example, 193 nm is configured.

The illumination system 102 directs the DUV light 108B onto the reticle 120. The reticle 120 is configured as a transmissive optical element and can be disposed separately from the systems 102, 104, respectively. Similarly, reticle 120 has a structure that projects a smaller image of the structure to wafer 122 or the like by projection system 140.

Projection system 104 can include a plurality of lenses 132 and/or mirrors 134 for projecting the structure of reticle 120 to wafer 122. Lens 132 and/or mirror 134 may be symmetrically disposed relative to optical axis 124 of projection system 104. Likewise, 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 gap between the last lens 132 and the wafer 122 may be replaced by 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 enhanced optical lithography resolution.

2 shows the optical device 200 in a perspective view, comprising a substrate 202 supporting an optical element 204, which may be formed, for example, as a mirror.

Optical device 200 can be integrated into one of the lithography devices shown in Figures 1A and 1B. Optical element 204 may, for example, correspond to one of mirrors Ml through M6 (FIG. 1A) or to one of lenses or mirrors 132, 134 (FIG. 1B). In other embodiments (not shown), the optical element 204 is configured as a grating or a λ plate.

The substrate 202 can be fastened to a fixed structure of the lithography apparatus 100A, 100B, such as to a force frame (not shown). To this end, the substrate 202 can be equipped with fastening holes 206 or the like. Substrate 202 can comprise a rectangle or any other suitable shape.

Mirror 204 (for ease of understanding, reference will be made below to the mirror, but this should not be construed as being limited to mirrors, but any other suitable optical element may be used) to reflect incident light 108A, 108B. The corresponding optical axis of mirror 204 is indicated by element symbol 208. At least the front end face 210 where the light 108A, 108B is reflected, or the entire mirror 204 can be curved (as shown) or straight.

Figure 3 shows section III-III of Figure 2. The mirror 204 is shown in an undeformed state (solid line) and in a deformed state (dotted line). Mirror 204 is shown to be flat in its undeformed state Face shape. However, the mirror 204 may have any shape, such as a curved shape, in its undeformed state.

The mirror 204 can be supported, for example, at two locations by, for example, supports 300, 302. The supports 300, 302 can support the mirror 204 or portions thereof at the rear end face 304 of the mirror 204. In this simple support configuration, the support 300 can be configured to allow relative rotation of the mirror 204, but still fixedly connect the mirror 204 to the substrate 202 in a direction perpendicular to the optical axis 208. On the other hand, the support 302 allows relative rotation of the mirror 204 and allows vertical movement of the mirror 204 relative to the optical axis 208. As used herein, "vertical" may include a deviation from an accurate vertical of 10°, preferably 5°, more preferably 1°.

However, any other type of support of mirror 204 or portions thereof is possible. For example, mirror 204 can be supported at more than two locations, such as five, ten, twenty or more locations. Additionally, the support can be configured to generate a force or moment or both at a location where it is coupled to the mirror 204.

Additionally, optical device 200 includes an actuator 306. Actuator 306 is configured to deform optical element 204 (or a portion thereof) between the two states shown in FIG. The actuator 306 is fastened to the mirror 204 on the one hand and to the substrate 202 or any other suitable reference on the other hand. The actuator 306 may be configured as, for example Lorentz actuator, i.e. comprising a voice coil (not shown) and a magnet (not shown) to produce a resultant force F _r on the reflecting mirror 204 (refer to FIGS. 3A, It shows the force diagram with respect to Figure 3 to deform the mirror 204. The direction in which the force F _r acts is indicated as δ.

In principle, any other actuator, such as a piezoelectric actuator or a pneumatic actuator, can be used in place of the Lorentz actuator. However, the use of Lorentz actuators, when used in open circuit control systems, can provide a cost effective low complexity system.

When a Lorentz actuator is used, the magnet can be fastened to the mirror 204 (especially to its rear side 304) and the voice coil can be fastened to the base 202. Other configurations in which the voice coil 306 is fastened to the mirror 204 and the magnets are fastened to the substrate 202 are also possible.

Actuator 306 can be controlled by controller 308. Controller 308 can be configured to control Actuator 306, with anamorphic mirror 204, provides optical correction. That is, by deforming the mirror 204, the angle of the incident light 108A, 108B will change. Optical correction can include image error correction, such as overlap or focus correction. "Image" refers to an image projected onto wafer 122 (see Figures 1A and 1B).

The controller 308 can be configured to instantly deform the mirror 204, such as between two different dies on the exposed wafer 122 or even within the dies (i.e., during a single granule scan on the wafer 122) Within the time window. Scanning of the respective dies on wafer 122 can be performed, for example, at 30 Hz. Therefore, the time window for changing the deformation of the mirror 204 can be less than 1/30 second.

In the example of FIG. 3, the deformed mirror 204 in the direction δ can be obtained by out-of-plane bending of the mirror 204. This is because the actuator 306 acts on the mirror 204 at a position between the two supports 300, 302 in a direction δ parallel to the optical axis 208. "Parallel" may comprise a deviation of up to 10°, preferably up to 5°, and more preferably up to 1°.

When the mirror 204 is deformed by a force acting in the direction δ, this force will generally consist of two component forces. First, it is the quasi-static force F _Q required to deform the mirror 204 itself (refer to FIG. 3A). This static force is a function of the E-modulus of the material of the mirror 204 and its geometry, and thus corresponds to the (positive) stiffness of the mirror 204. On the other hand, the force will be formed by the dynamic force F _D required to accelerate the mass of the mirror 204. This dynamic force depends on the density of the mirror 204, the geometric deformation profile, and the deformation trajectory (as a function of time). In order to reduce actuator 306 of the deformable mirror 204 takes the required force F _r, n corresponding to the negative rigidity of the rigidity of the mirror pair. To this end, the optical device 200 includes a compensation unit 310 that has a negative stiffness in the direction δ to at least partially compensate for the positive stiffness of the mirror 204.

FIG. 3A shows a schematic diagram of the forces acting on the mirror 204 at the position of the actuator 306 and the compensation unit 310. When the mirror 204 is deformed in the direction δ, the positive stiffness k _{p of the} mirror results in a positive force F _p . This is also shown in Figure 4A, which shows a plot of force F versus deformation δ. On the other hand, when the deformation of the mirror δ force F _p opposite direction, the compensation unit 310 will result in a negative rigidity a force F _n. The force generated is the force F _Q , which is the static force required to deform the mirror 204 in the direction δ. In addition to static forces F _Q, the actuator 306 needs to exert a dynamic force F _D on the mirror 204 to be accelerated. The sum of the forces F _Q and F _D is equal to the resultant force F _r applied by the actuator 306. Since F _n and F _{p are} much larger than F _Q , F _D and F _r , they are not shown to scale in FIG. 3A and are respectively indicated by broken lines.

Since the amount of deformation of the mirror 204 in the direction δ is generally small (for example, in the micrometer range), and the time window of the deformation is relatively large (for example, 1/30 second) (refer to the explanation of the scanning trajectory in the foregoing), The dynamic force F _D is smaller than the static force F _Q . Furthermore, the resultant force F _r (=F _Q +F _D ) is given by the appropriate system design to be much smaller than the force F _n generated by the compensation unit. Obviously, when a die or wafer, the force F _p, F _n, F _D may change over time. However, forces will generally appear to be cyclic in the fabrication of a single die or monolithic wafer. The system may be designed such that it has been found when viewed with a single period, a negative stiffness forces F _n having a maximum value, which is greater than the maximum required force F generated by the actuator of 306 _r N times, preferably wherein N> 5, more Good for N>10, further better for N>50.

This type of system design allows the actuator 306 to have low energy consumption. This in turn causes the corresponding heat loss to be small, thus avoiding thermal expansion problems and corresponding cooling problems.

To further improve the system design, the "big" force F _p and F _n can be designed with a dynamic force F _D "small" compared to small changes. To this end, the maximum time derivative of the dynamic force F _D on a cycle (refer to the foregoing explanation) may be M times greater than the maximum time derivative of the negative stiffness force F _n , where M is preferably greater than 1, more preferably greater than 2, and More preferably, it is greater than 10.

To further improve the energy efficiency of the system, the actuator 306 can be designed to restore dynamic energy in the mirror 204. In other words, when the mirror 204 needs to be decelerated, the work done by the mirror 204 on the actuator 306 is converted to electrical energy, which is returned to the electrical energy storage. Therefore, the heat loss of the actuator 306 can be further reduced.

Returning now to Figure 4A, it can be seen that the positive stiffness force F _p , the negative stiffness force F _n and the resultant force F _r depend on the stiffness k _p (positive stiffness), k _n (negative stiffness), k _r (the resulting stiffness), respectively. And deformation δ. Preferably, the resulting stiffness k _r and the corresponding resultant force F _r are designed to be positive and not equal to zero. For example, the negative stiffness k _n can be equal to 0.9 to 0.99 times the positive stiffness k _p . This will ensure that when the actuator 306 is not generating a force (eg, when the actuator 306 is off (no power), such as during transmission of the optical device 200 or the lithography apparatus 100A, 100B) or when the actuator 306 is present In the event of an unforeseen failure, the deformation of the mirror 204 in the direction δ will be limited. By selecting the resulting stiffness k _r to be positive, the mirror 204 will return to its undeformed state without the action of the actuator 306 (actuator 306 is off or malfunctioning).

FIG. 4B shows a force versus deformation map in accordance with another embodiment of optical device 200. In this particular embodiment, the negative stiffness force _Fn can be turned on or off, as explained further below with reference to Figures 7A through 7D. Thus, when closing the negative rigidity k _n, corresponding to the rigidity of the resulting positive rigidity k _p, which is large enough to avoid, for example, due to vibration or other movement of the mirror 204 from being damaged during transport. Thus, the stiffness _kr produced during normal operation of the optical device 200 (i.e., during fabrication of the wafer) can be designed to be smaller (or equal to zero) than in the particular embodiment illustrated in Figure 4A. For example, in the particular embodiment of FIG. 4B, the negative rigidity k _n may be designed to positive from 0.99 to 0.999 times the rigidity k _p.

Example: If the mirror mass is assumed to be 1 kg and moves over 1 μm within 10 ms of movement time, an acceleration of 10 mm/s ² is required. The corresponding dynamic force F _D is equal to 10 mN, which can be transmitted by a Lorentz actuator at a power loss of less than 1 mW.

The negative stiffness k _p required to compensate for the mirror's positive stiffness k _{n is} on the order of 10 ⁵ to 10 ⁶ N/m. For a 1 μm offset, this would therefore require a negative stiffness force _{Fn of} 1N. This corresponds to a dynamic force F _{D of} 100 times. In order to be of the same order of magnitude as the dynamic force F _D , the negative stiffness force F _n needs to be very accurate. Preferably, the negative stiffness force is instantly adjustable, i.e., dynamically adjusted during operation of the optical device 200. The manner of adjusting the negative rigidity will be explained later with reference to Figs. 7A to 7D.

A specific embodiment of an optical device 200 that uses mechanical compensation to achieve a desired negative stiffness k _n will now be explained with reference to Figures 5A through 5C.

The compensation unit 310 of FIG. 5A includes, for example, a mechanical spring 500 (eg, a leaf spring or a coil spring) and a preload unit 502 (eg, a pneumatic cylinder) configured to preload the spring 500. The spring 500 acting on, for example, the side 504 of the mirror 204 is preferably configured to be relatively long. When the deformable mirror 204, the spring length of about 500 to ensure a constant preload force F _c, so this will also cause deformation of the mirror 204 is moved laterally, i.e. in a direction perpendicular to the optical axis 208. In addition to the use of pneumatic cylinders 502, spring 500 may be attached to the base 202 in its compressed state to produce a force F _c. In other embodiments, for example by using a magnet or a pneumatic cylinder directly (without using a mechanical spring) applies a force F _c.

FIG 5A mirror 204 in a plane (i.e., at right angles to the optical axis 208) to compensate for the preload force F _c. The force F _c tends to bend the mirror 204, the mirror 204 and thus bend out of plane. This force F _c can be applied, for example, by a mechanical spring 500.

Because the mirror 204 is symmetrical, half of the mirror 204 can be considered a simple cantilever with a force at its end, as shown in Figure 5B.

The offset is given by: Wherein 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 rigidity required to overcome the positive rigidity of the mirror 204, and E corresponds to the material of the mirror 204 (for example, glass) The E modulus of the ceramic or I corresponds to the moment of inertia (which depends on the geometry of the cross section of the mirror 204).

Therefore, the positive stiffness k _{p of the} mirror 204 is given by:

Compressive force F _c is applied to the cantilever (preload) (refer to FIG. 5B and 5C) will result in an offset size δ of the F _c. The bending moment of δ. This moment produces an offset δ' such that:

When δ = δ' (corresponding to zero stiffness, also when positive stiffness k _p is equal to negative stiffness k _n ), the required compensation force F _c is given by:

Thus, the display has been previously constant preload force F _c is adapted to provide a negative or near negative stiffness, which will compensate for the rigidity of the mirror 204 is positive. For example, a long spring 500 may be preloaded to provide a near constant compensation force F _c.

6A and 6B depict first and second embodiments of a compensation unit 310 including a magnet.

The compensation unit 310 of FIG. 6A includes a first magnet 600 that is secured to the mirror 204 to create a negative stiffness force _Fn . The connection between the first magnet 600 and the mirror 204 is indicated at 602. The magnet 600 is disposed between the stationary second and third magnets 604, 606. To this end, the second and third magnets 604, 606 can be fastened to the substrate 202. The first magnet 600 can be mechanically guided in the direction δ. The magnets 600, 604, 606 can be configured as block magnets and can have the same polarity as the direction δ (indicated by "N" for the north and "S" for the south). Therefore, when the first magnet 600 is positioned in the middle of the second and third magnets 604, 606, the first magnet 600 produces a zero offset force on the mirror 204. Likewise, as the deformation of the mirror 204 increases in the direction δ, the force _Fn also increases accordingly. Therefore, a negative rigidity k _{n is} generated.

In the example of FIG. 6B, the compensation unit 310 includes a first magnet 600 that is coupled to the mirror 204 through a connection 602. Furthermore, the compensation unit 310 comprises a second magnet 604 configured as a ring magnet. The ring magnet 604 has a central axis 608. When the mirror 204 is deformed in the direction δ, the first magnet 600 is, for example, mechanically guided to move along the central axis 608. The first magnet 600 and the second magnet 604 have opposite polarities along the axis 608. When the first magnet 600 is disposed along the axis 608 on the axis of symmetry 610 of the second magnet 604, the first magnet 600 produces a zero offset force on the mirror 204. As the deformation of the mirror 204 increases in the direction δ, the negative stiffness force _Fn produced by the first magnet 600 will also be such that the first magnet 600 is offset from its position on the axis of symmetry 610.

Figures 7A through 7D show four different embodiments of the adjustment unit 700.

In the example of Figure 7A, the adjustment unit has a pneumatic cylinder 700 that is configured to open or close. In the "closed" state, the pneumatic cylinder 700 will not preload force F _c on the spring 500. On the other hand, the controller 702 can be configured as an input to the controller 702 based on the control of preload force F _c (or even continuous). For example, a sensor 704 can be provided that senses the optical error that needs to be corrected. The controller 702 may receive input signals from the respective sensors 704 and controls the pneumatic cylinder 700 generates a preload force F _c, which would generate an appropriate optical correction lead to deformation of the mirror 204.

It can be performed by the controller 702 to set the desired preload force F _c in the measured current slow deformation during the movement, for example, (Lorentz) of the actuator 306. Since this is slow, the acceleration is negligible and the Lorentz force is only due to the residual stiffness k _r . If both F _r and δ are measured, then k _r can be determined and F _c adjusted accordingly until the desired k _r value is reached.

The particular embodiment of Figures 7B through 7D may also include a controller 702, and may also include a sensor 704 as appropriate. They differ only in the way the negative stiffness force F _n is adjusted.

In the particular embodiment of FIG. 7B, adjustment unit 700 can include mechanical means (eg, set screws) to move second magnet 604 from initial position P1 to position P2 along central axis 608, wherein first magnet 600 produces an initial offset Forced on the mirror 204. For example, in addition to a set screw or the like, an electromagnetic device can be used to adjust the position of the second magnet 604.

In the particular embodiment of FIG. 7C, adjustment unit 700 is configured to adjust the magnetic field coupled between first magnet 600 and second magnet 604. To this end, the adjustment unit 700 can include a U-shaped moving magnet that moves perpendicular to the central axis 608 to change the magnetic field coupled between the magnets 600, 604. At the position P1, the magnets 600 and 604 are disposed in the moving magnet 700. Therefore, there is a maximum field between the magnets 600, 604. At the position P2, the moving magnet 700 moves to a position where the magnets 600, 604 are disposed outside the moving magnet 700. Therefore, there is no (extra) field coupling between the magnets 600, 604. This changes the force acting between the first magnet 600 and the second magnet 604 as the magnet 600 moves along the central axis 608 as the mirror 204 deforms.

In the particular embodiment of FIG. 7D, adjustment unit 700 includes an electrically permanent magnet 706. The electrically permanent magnet 706 includes at least a first magnet 708 formed of a medium coercive material and a coil 710 configured to vary the magnetization of the magnet 708 in accordance with an input signal received, for example, from the controller 702 (refer to FIG. 7A). Additionally, adjustment unit 700 can include a second magnet 712 formed of a high coercivity material, and can additionally or alternatively include a core 714 to increase the overall field strength. Magnet 708 and magnet 712 (if provided) form second magnet 604 as depicted in Figure 6B. By adjusting the magnetization of the first magnet 708, the magnetic field generated by the second magnet 604 can be adjusted, and thus the negative stiffness _Fn can be adjusted.

Figure 8 shows an optical device 200 having multiple axes δ ₁ , δ ₂ , δ ₃ in which deformation can occur along the axes δ ₁ , δ ₂ , δ ₃ . The mirror 204 is connected to the first magnets 600a, 600b, 600c via, for example, three connectors 602a, 602b, 602c. The first magnets 600a, 600b, and 600c are disposed between the second and third magnets 604a, 604b, and 604c and 606a, 606b, and 606c, respectively. Each of the first, second, and third magnets 604a...606c associated with the respective connector 602a, 602b, 602c forms a compensation subunit 310a, 310b, 310c. The compensation subunits 310a, 310b, 310c together form a compensation unit 310.

The negative stiffness of the compensation unit 310 of Figure 8 is described by the following negative stiffness matrix:

The rigid matrix should be established to not only produce the desired diagonal (local) stiffness, but also to compensate for the crosstalk term of mirror 204 by creating a suitable negative crosstalk between adjacent magnets 604a...606c.

Although the present invention has been described in terms of specific embodiments, many modifications and variations are possible and the results are still within the scope of the invention. It is intended or inferred that there are no limitations of the specific embodiments disclosed herein.

202‧‧‧Base

204‧‧‧Mirror

208‧‧‧ optical axis

210‧‧‧ front face

300‧‧‧Support

302‧‧‧Support

304‧‧‧ rear end face

306‧‧‧Actuator

308‧‧‧ Controller

310‧‧‧Compensation unit

Δ‧‧‧ Direction

Claims (15)

An optical device for a lithography apparatus, comprising: an optical element having a positive stiffness when deformed in at least one direction, an actuator for deforming the optical component in the at least one direction, and a compensation unit It has a negative stiffness in the at least one direction to at least partially compensate for the positive stiffness of the optical element. The optical device of claim 1, wherein the compensation unit is configured to generate a first maximum force on the optical element in the at least one direction, and the actuator is configured to be in the at least one direction A second maximum force is generated on the optical component, wherein the first maximum force is N times greater than the second maximum force, wherein N>5, preferably N>10, more preferably N>50. The optical device of claim 1 or 2, wherein the compensation unit is configured to generate a first force on the optical element in the at least one direction, and the actuator is configured to be in the at least one Generating a second force to the optical element, wherein the first force has a first maximum time derivative, and the second force has a second maximum time derivative, wherein the second maximum time derivative is greater than the first maximum The time derivative is M times, where M > 10, preferably M > 100. The optical device according to any one of claims 1 to 3, wherein the compensation unit has a negative rigidity of 0.9 to 0.99 times the positive rigidity of the optical element. The optical device according to any one of the preceding claims, wherein the difference between the positive rigidity of the optical element and the negative rigidity of the compensation unit is greater than zero. The optical device according to any one of claims 1 to 5, wherein the deformation of the optical element in the at least one direction is obtained by out-of-plane bending of the optical element. The optical device according to any one of claims 1 to 6, wherein the compensation unit comprises a magnet, in particular a permanent magnet, or at least one spring. The optical device of any one of clauses 1 to 7, wherein the compensating unit, in particular the at least one spring, is configured to preload the optical element in a plane. The optical device according to any one of claims 1 to 8, further comprising a substrate, wherein the magnet is a first magnet fastened to the optical component and one fastened to the substrate The second magnet and the third magnet are configured to move between the second magnet and the third magnet. The optical device according to any one of claims 1 to 8, further comprising a substrate, wherein the magnet is a first magnet fastened to the optical component and a first one fastened to the substrate The second magnet is composed of a first magnet or a second magnet formed as a ring magnet and the other magnet is movable along a central axis of the ring magnet. The optical device according to any one of claims 1 to 10, further comprising an adjusting unit for adjusting the negative rigidity of the compensating unit. The optical device of claim 11, wherein the adjusting unit is configured to change a preload of the at least one spring, adjust the first magnet, the second magnet, and/or using at least one electric permanent magnet. Or the relative position of the third magnet is adjusted to the first magnet and the second magnet And/or a magnetic field coupled between the third magnets or a magnetic field of the first magnet, the second magnet, and/or the third magnet. The optical device according to any one of claims 1 to 12, wherein the optical element has a first positive rigidity when deformed in a first direction and has a deformation when deformed in a second direction a second positive stiffness, the actuator configured to deform the optical element in the first direction and the second direction, and the compensation unit has a first negative stiffness in the first direction to be at the first The positive stiffness of the optical element is at least partially compensated in the direction and has a second negative stiffness in the second direction to at least partially compensate for the positive stiffness of the optical element in the second direction. The optical device of any one of clauses 1 to 13, wherein the actuator is configured to deform the optical component for optical correction, particularly in overlay and/or focus correction, and / or wherein the optical component is a mirror, a lens, a grating or a λ plate. A lithography apparatus comprising one of the optical devices according to any one of claims 1 to 14.