Lithographic apparatus

Abstract

A lithographic apparatus is described, the apparatus comprising: a projection system (PS; 200) configured to project a patterned beam of radiation (B) onto a substrate (W); the projection system comprising a plurality of optical elements (200.1, 200.2); a sensor frame (220); a first position measurement system (240) configured to measure positions of the plurality of optical elements relative to the sensor frame; wherein the sensor frame comprises: - N sub-frames (220.1, 220.2), N being an integer greater than 1; - a coupling system (220.3) coupling the N sub-frames; and - a second position measurement system (250) configured to determine relative positions of the N sub-frames.

Description

[0001] This application is a divisional application of Chinese invention patent application No. 201880011274.7, entitled "Method for Manufacturing Photolithography Equipment and Devices" (corresponding PCT international application No. PCT / EP2018 / 050640), filed on January 11, 2018.

[0002] Cross-references to related applications

[0003] This application claims priority to European application 17155563.4, filed on February 10, 2017, the entire contents of which are incorporated herein by reference. Technical Field

[0004] This invention relates to photolithography equipment and methods for manufacturing devices. Background Technology

[0005] A lithography apparatus is a machine that applies a desired pattern onto a substrate (typically a target portion of the substrate). For example, lithography apparatus can be used to manufacture integrated circuits (ICs). In this case, a patterning apparatus, alternatively called a mask or photomask, can be used to generate a circuit pattern to be formed on a single layer of the IC. This pattern can then be transferred onto a target portion (e.g., a portion of a die, one or more dies) on a substrate (e.g., a silicon wafer). Typically, the transfer of the pattern is performed by imaging the pattern onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will contain a network of adjacent target portions patterned sequentially. Known lithography apparatuses include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern with a radiation beam in a given direction (“scanning” direction) while simultaneously scanning the substrate parallel or antiparallel to that direction. Typically, this patterned radiation beam undergoes various transformations (e.g., reduction) between the patterning apparatus and the target portion on the substrate. This transformation is typically achieved using a projection system, which may include various optical elements such as mirrors and / or lenses. If the relative position of these optical elements changes during pattern transfer to the target area, this can cause distortion or displacement of the patterned radiation beam received by the substrate. This distortion or displacement can lead to overlap errors. To avoid or mitigate this effect, it has been suggested to monitor the position of these optical elements using a position measurement system that measures the position of the optical elements relative to a frame, such as an isolation frame, also known as a sensor frame. By monitoring the position of the optical elements relative to this sensor frame, the effects of relative displacement of the optical elements can be determined and accounted for, for example, by adjusting the position of the substrate relative to the projection system.

[0006] However, it has been observed that such isolated sensor frames, which can be used as reference positions for optical elements, can also be subject to deformation, for example, due to forces applied to them. Therefore, an improved sensor frame is needed for monitoring the (relative) position of optical elements in the projection system of a lithography apparatus. Summary of the Invention

[0007] The aim is to provide a lithography apparatus that allows for more precise monitoring of the position of optical components in a projection system.

[0008] According to a first aspect of the present invention, a photolithography apparatus is provided, comprising:

[0009] A projection system configured to project a patterned radiation beam onto a substrate; the projection system includes a plurality of optical elements.

[0010] Sensor frame;

[0011] A first position measurement system is configured to measure the position of the plurality of optical elements relative to the sensor frame; wherein the sensor frame includes:

[0012] -N subframes, where N is an integer greater than 1;

[0013] - A coupled system with N subframes; and

[0014] - A second position measurement system, configured to determine the relative positions of the N sub-frames.

[0015] According to a second aspect of the present invention, a photolithography apparatus is provided, comprising:

[0016] A projection system configured to project a patterned radiation beam onto a substrate; the projection system includes a plurality of optical elements.

[0017] Sensor frame;

[0018] At least one actuator, the at least one actuator being configured to apply a vertically oriented force on the sensor frame;

[0019] A first position measurement system is configured to measure the position of the plurality of optical elements relative to the sensor frame, wherein the sensor frame is supported by M vibration isolators, M being an integer and 1 ≤ M < 3, and the M vibration isolators and the vertically oriented force support the sensor frame at different, non-collinear positions. Attached Figure Description

[0020] Embodiments of the invention will now be described by way of example only with reference to the accompanying schematic drawings, in which corresponding reference numerals indicate corresponding parts, and in the drawings:

[0021] Figure 1 A photolithography apparatus according to a first embodiment of the present invention is described;

[0022] Figure 2 A portion of a photolithography apparatus according to a second embodiment of the present invention is depicted;

[0023] Figure 3a and Figure 3b A portion of a photolithography apparatus according to the third and fourth embodiments of the present invention is depicted;

[0024] Figure 4 The sensor frame and support components of the photolithography equipment are depicted;

[0025] Figure 5 A sensor frame and support that can be applied in a lithography apparatus according to the present invention are described;

[0026] Figure 6 Two embodiments of a sensor frame and support that can be applied in a lithography apparatus according to the present invention are described. Detailed Implementation

[0027] Figure 1 A lithography apparatus according to an embodiment of the present invention is schematically illustrated. The lithography apparatus includes an illumination system IL, a support structure MT, a substrate stage WT, and a projection system PS. The illumination system IL is configured to adjust a radiation beam B. The support structure MT is configured to support a pattern forming apparatus MA and is connected to a first positioning device PM configured to precisely position the pattern forming apparatus MA according to certain parameters. The substrate stage WT is configured to hold a substrate W (e.g., a wafer coated with resist) and is connected to a second positioning device PW configured to accurately position the substrate W according to certain parameters. The projection system PS is configured to project a pattern imparted by the radiation beam B by the pattern forming apparatus MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0028] An irradiation system (IL) may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, to guide, shape, or control radiation.

[0029] The irradiator IL receives the radiation beam B from the radiation source SO. For example, when the radiation source SO is an excimer laser, the radiation source SO and the lithography apparatus can be separate entities. In this case, the radiation source SO is not considered as part of forming the lithography apparatus, and the laser beam B is transmitted from the radiation source SO to the irradiation system IL with the help of a beam delivery system BD, including, for example, suitable guiding mirrors and / or beam expanders. In other cases, for example, when the radiation source SO is a mercury lamp, the radiation source SO can be a component of the lithography apparatus. The radiation source SO, the irradiation system IL, and the beam delivery system BD (if desired) can be referred to as the radiation system.

[0030] The illumination system IL may include an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial ranges (generally referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the pupil plane of the illumination system IL can be adjusted. Additionally, the illumination system IL may include various other components, such as an integrator IN and a concentrator CO. The illumination system IL can be used to adjust the radiation beam B to have the desired uniformity and intensity distribution in its cross-section.

[0031] The term “radiation beam” as used herein encompasses all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having wavelengths equal to or about 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having wavelengths in the range of 5 nm to 20 nm) as well as particle beams such as ion beams or electron beams.

[0032] A support structure MT supports the patterning apparatus MA, i.e., bears the weight of the patterning apparatus MA. The support structure MT holds the patterning apparatus MA in a manner dependent on the orientation of the patterning apparatus MA, the design of the lithography equipment, and other conditions such as whether the patterning apparatus MA is kept in a vacuum environment. The support structure MT can hold the patterning apparatus MA using mechanical, vacuum, electrostatic, or other clamping techniques. The support structure MT can be a frame or a stage, for example, it can be fixed or movable as needed. The support structure MT ensures that the patterning apparatus MA is positioned in the desired location (e.g., relative to the projection system PS).

[0033] The term "patterning apparatus" as used herein should be broadly understood to refer to any apparatus capable of imparting a pattern across the cross-section of a radiation beam to form a pattern on a target portion C of the substrate W. It should be noted that the pattern imparted by the radiation beam B may not perfectly correspond to the desired pattern in the target portion C of the substrate W, for example, if the pattern includes phase-shifting features or so-called auxiliary features. Typically, the pattern imparted by the radiation beam B will correspond to a specific functional layer in the device formed on the target portion C, such as an integrated circuit.

[0034] The pattern forming apparatus MA can be transmissive or reflective. Examples of pattern forming apparatuses include masks, programmable mirror arrays, and programmable liquid crystal display (LCD) panels. Masks are well known in photolithography and include mask types such as binary masks, alternating phase-shift masks, attenuation phase-shift masks, and various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be independently tilted to reflect the incident radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam B reflected by the mirror matrix.

[0035] The term “projection system” as used herein should be understood broadly to include any type of projection system suitable for the exposure radiation or other factors used (such as the use of immersion liquid or vacuum), including refractive, reflective, reflective-refractive, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof.

[0036] As shown here, the lithography apparatus is transmissive (e.g., using a transmissive mask). Alternatively, the lithography apparatus may be reflective (e.g., using a programmable mirror array of the type described above, or using a reflective mask).

[0037] The lithography apparatus can be of the type having two (dual-platform) or more substrate stages (and / or two or more mask stages). In such a "multi-platform" machine, additional stages can be used in parallel, or one or more other stages can be used for exposure while preparatory steps are performed on one or more stages. The additional stages can be arranged to hold at least one sensor, rather than holding the substrate W. The at least one sensor can be a sensor for measuring properties of the projection system PS, a sensor for detecting the position of a mark on the patterning apparatus MA relative to the sensor, or can be any other type of sensor. The additional stages can include cleaning devices, such as cleaning devices for cleaning a portion of the projection system PS or any other part of the lithography apparatus.

[0038] The lithography apparatus may also be of the type in which at least a portion of the substrate W may be covered by a liquid (e.g., water) having a relatively high refractive index to fill the space between the projection system and the substrate. Immersion liquids may also be applied to other spaces within the lithography apparatus, such as the space between the patterning apparatus MA and the projection system PS. Immersion techniques are known in the art for increasing the numerical aperture of a projection system. The term "immersion" as used herein does not imply that a structure such as the substrate W must be submerged in a liquid, but only that the liquid is located between the projection system PS and the substrate W during exposure.

[0039] A radiation beam B is incident on a patterning apparatus MA held on a support structure MT and patterned by the patterning apparatus MA. After traversing the support structure MT, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. The substrate stage WT can be accurately moved, for example, to position different target portions C within the path of the radiation beam B, by means of a second positioning device PW and a position sensor IF (e.g., an interferometric measuring device, a linear encoder, or a capacitive sensor). Similarly, a first positioning device PM and another position sensor (which is not in...) Figure 1 The pattern forming apparatus MA (exactly described in the diagram) can be used (e.g., after mechanical acquisition from a mask library or during scanning) to accurately position itself relative to the path of the radiation beam B. Generally, movement of the support structure MT can be achieved by means of long-stroke and short-stroke modules, which form part of a first positioning device PM. The long-stroke module provides movement of the support structure MT over a wide range with limited accuracy (coarse positioning), while the short-stroke module provides movement of the support structure MT over a small range relative to the long-stroke module with high accuracy (fine positioning). Similarly, movement of the substrate stage WT can be achieved using long-stroke and short-stroke modules, which form part of a second positioning device PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected only to the short-stroke actuator, or it may be fixed.

[0040] The pattern forming apparatus MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2, as shown in the figure, occupy dedicated target portions, they can be located in the space between the target portions C. When the substrate alignment marks P1, P2 are located in the space between the target portions C, the substrate alignment marks P1, P2 are known as scribing alignment marks. Similarly, in cases where more than one die is disposed on the pattern forming apparatus MA, the mask alignment marks M1, M2 can be located between the dies.

[0041] The described device can be used in at least one of the following modes:

[0042] In the first mode (stepping mode), while keeping the support structure MT and substrate stage WT essentially stationary, the entire pattern imparted by the radiation beam B is projected onto the target portion C in a single exposure (i.e., a single static exposure). The substrate stage WT is then moved along the X and / or Y directions, allowing exposure of different target portions C. In stepping mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.

[0043] In the second mode (scanning mode), while the support structure MT and the substrate stage WT are scanned synchronously, the pattern imparted by the radiation beam B is projected onto the target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate stage WT relative to the support structure MT can be determined by the (reduced) magnification and image inversion characteristics of the projection system PS. In scanning mode, the maximum size of the exposure field limits the width of the target portion C (in the non-scanning direction) in a single dynamic exposure, while the length of the scanning motion determines the height of the target portion C (in the scanning direction).

[0044] In the third mode, the support structure MT used to hold the programmable patterning apparatus MA is kept essentially stationary, and the pattern imparted by the radiation beam B is projected onto the target portion C while the substrate stage WT is moved or scanned. In this mode, a pulsed radiation source is typically used, and the programmable patterning apparatus MA is updated as needed after each movement of the substrate stage WT or between consecutive radiation pulses during scanning. This operating mode is readily applicable to maskless lithography utilizing a programmable patterning apparatus (e.g., a programmable mirror array of the type described above).

[0045] The lithography equipment also includes a control unit that controls the described actuators and sensors. The control unit also includes signal and data processing capabilities to perform the necessary calculations related to the operation of the lithography equipment. In practice, the control unit will be implemented as a system of many sub-units. Each sub-unit can handle real-time data acquisition, processing, and / or control of components within the lithography equipment. For example, one sub-unit may be dedicated to the servo control of the second positioning device (PW). Individual sub-units may handle short-stroke and long-stroke modules, or different axes. Another sub-unit may be dedicated to the readout position sensor (IF). The overall control of the lithography equipment can be controlled by a central processing unit that communicates with these sub-units, as well as with the operators and other equipment involved in the lithography process.

[0046] Alternatively, combinations and / or variations of the above usage patterns, or entirely different usage patterns, may be used.

[0047] According to the invention, a patterned radiation beam passes through a projection system PS, thereby performing various transformations (e.g., reduction) between a pattern forming apparatus MA and a target portion C on a substrate W. This transformation is typically achieved by means of a projection system PS, which may include various optical elements, such as mirrors and / or lenses. If the relative positions of these optical elements change during pattern transfer to the target portion, this can cause deformation or displacement of the patterned radiation beam received by the substrate. Such deformation or displacement can lead to overlap errors. To avoid or mitigate such errors, the lithography apparatus according to the invention further includes a sensor frame and a position measurement system for measuring the position of the optical elements relative to the sensor frame. Note that in this arrangement, the sensor frame can therefore serve as a reference position for the optical elements. By monitoring the position of the optical elements, the difference between the actual position and the desired position can be detected, and appropriate actions can be taken in response. As an example, in cases where a known difference causes displacement of the patterned radiation beam, this displacement can be taken into account by a positioning device PW that controls the position of the substrate W. Optionally or additionally, the position of the optical elements can be controlled (e.g., by applying a force to the optical elements) to reduce the positional error of one or more optical elements. The inventors of this invention have observed that the above-described method may still have its drawbacks. In particular, it has been observed that it can be difficult to hold the entire sensor frame in a reference position. It has been observed that sensor frames used in known devices can deform due to the forces transmitted to them. Note that such sensor frames are typically mounted to a base or a separate frame using vibration isolators. However, such isolators still allow some vibration to be transmitted, causing deformation of the sensor frame. One way to mitigate this effect is to use multiple separate sensor frames, each equipped with a position measurement system to monitor the position of various optical elements of the projection system. However, this arrangement may require a relatively large number of vibration isolators.

[0048] Alternatively, according to a first aspect of the invention, an arrangement is proposed to subdivide the sensor frame into N sub-frames, where N is an integer greater than 1, whereby the sub-frames are coupled together by a coupling system. Furthermore, the relative positions of the N sub-frames are monitored by means of a position measurement system.

[0049] Figure 2 A portion of a photolithography apparatus according to a first aspect of the present invention is schematically depicted. Figure 2 The projection system 200, comprising two optical elements 200.1 and 200.2, is shown schematically. Figure 2A force frame 210 configured to support optical elements 200.1 and 200.2 is also shown. This support can be achieved, for example, using one or more vibration isolators 210.1 or actuators 210.2. In the illustrated embodiment, the lithography apparatus also includes a sensor frame 220 comprising a first subframe 220.1 and a second subframe 220.2, the second subframe 220.2 being coupled to the first subframe 220.1 via a coupling system 220.3, schematically represented as a damper-spring combination. In the illustrated embodiment, the lithography apparatus further includes a first position measurement system 240 for measuring the position of optical elements 200.1 and 200.2 relative to the sensor frame 220; and a second position measurement system 250 for measuring the relative positions of the subframes 220.1 and 220.2. In the illustrated embodiment, the force frame 210 is mounted to the base frame 260 of the apparatus via a vibration isolator 270. Furthermore, it can be seen that the sensor frame 220 is mounted on the force frame via the vibration isolator 280.

[0050] In the illustrated embodiment, the displacement of optical elements 200.1 and / or 200.2 relative to the sensor frame 220 can be monitored by means of a position measurement system 240. Such a position measurement system may, for example, include an interferometer-based measurement system or an encoder-based measurement system. Capacitance or inductance measurement systems are also contemplated.

[0051] In the embodiment shown, sensor frame 220 includes two sub-frames coupled together by coupling system 220.3. In one embodiment, the coupling system may include, for example, a spring and a damper. Coupled sub-frames together offer one or more advantages compared to systems with multiple independent sensor frames:

[0052] - By coupling the sensor subframe, the position measurement system 250 can maintain a relatively small measurement range for the relative position of the monitoring subframe. Typically, a measurement range of less than 1 μm, usually around 10 nm, is sufficient.

[0053] - By keeping the subframes connected together, the sensor frame 220 as a whole can be supported by the same number of vibration isolators 280 required to support the essentially rigid sensor frame.

[0054] - By subdividing the sensor frame 220 into multiple subframes and connecting them, an arrangement is achieved that makes it easier to control or monitor the deformation of the sensor frame. Subdividing the sensor frame and connecting the subframes allows the sensor frame to deform in a more controllable or predictable manner, for example, due to vibrational forces transmitted from the force frame 210. In particular, by introducing a certain degree of flexibility into the coupling system 220.3, the subframes 220.1 and 220.2 will exhibit essentially rigid body behavior, meaning they will be allowed to shift (e.g., translation and rotation) without deforming substantially. In other words, due to the coupling system connecting the subframes, any deformation of the sensor frame can be concentrated in the coupling system 220.3. As a result, the behavior of the sensor frame as a whole can be more predictable and therefore controllable. According to a first aspect of the invention, a position measurement system 250 is provided to measure the relative positions of the subframes of the sensor frame 220. Since the subframes are coupled by means of the coupling system, the position measurement system 250 only needs to have a small operating range. Suitable position measurement systems may include encoder-based measurement systems, capacitance or inductance measurement systems. In one embodiment, the position measurement system 250 is configured to measure the relative position of the subframe in multiple degrees of freedom, including, for example, rotational degrees of freedom. In one embodiment, the position measurement system 250 is configured to measure the relative position of the subframe in six degrees of freedom (6DOF). When the relative position of the subframe is known, the positions of optical elements 200.1 and 200.2 can be accurately determined based on the measurements of the position measurement system 240, which measures the position of the optical elements relative to the subframe. If these positions or relative positions deviate from the desired positions, appropriate control actions can be taken. Such control actions may, for example, include the controlled displacement of one or more optical elements and / or one or both platforms (i.e., the support MT or the substrate stage WT).

[0055] Thus, in embodiments of the invention, the lithography apparatus includes a control unit 300 configured to control the operating parameters or state of the apparatus. Such a control unit 300 can be, for example, a controller, microprocessor, computer, etc. In the embodiment shown, the control unit 300 includes an input terminal 300.1 for receiving input signals 310. In one embodiment, the input terminal 300.1 can be configured, for example, to receive position measurement signals from position measurement systems 240 and 250, thereby allowing the control unit 300 to determine the positions of the optical elements 200.1 and 200.2 of the projection system 200 based on the received measurement signals. Based on this position information, the control unit can, for example, generate a control signal and output the control signal 320 through the output terminal 300.2 of the control unit 300. Such a control signal 320 can, for example, be a control signal for controlling the operation of actuator 210.2, thereby controlling the positions of the optical elements 200.1 and 200.2. Alternatively or additionally, the control unit 300 used in embodiments of the invention may be configured to determine control signals for controlling the positioning of a substrate in a lithography apparatus, particularly the positioning of the substrate relative to a patterned radiation beam projected onto the substrate by the projection system 200. By doing so, displacement of the patterned radiation beam caused by displacement of one or more optical elements of the projection system 200 can be corrected.

[0056] In one embodiment, the coupling system 220.3 includes a mechanical spring and a passive damper.

[0057] According to the invention, the coupling system between the subframes should preferably be rigid enough to allow the sensor frame to be supported by a limited number of supports, for example, three or four supports. Simultaneously, the coupling between the subframes should be at a frequency lower than the lowest intrinsic frequency of the subframes. Typically, the first intrinsic frequency of a single sensor frame can be, for example, 200 Hz or higher. By subdividing the frame as described above, for example, into two subframes, the first intrinsic frequencies of the two subframes are 250 Hz or higher. On the other hand, the suspension of the combined frame by vibration isolators will be designed, for example, between 3 and 15 Hz. Taking these values ​​into account, the intrinsic frequency of the coupling system between the two subframes can typically be designed in the range of 20 to 250 Hz, for example, between 50 and 150 Hz. To avoid undamped resonant behavior at this frequency, damping of at least a few percentage points, typically about 5%, is preferred.

[0058] In one embodiment of the invention, the coupling system applied to the subframe connecting the sensor frame includes an active damping system. This active damping system may, for example, include a displacement sensor configured to determine the relative displacement of the subframes connected by the coupling system, and an actuator for applying a force on the subframe to counteract the displacement. In one embodiment, both the displacement sensor and the actuator are implemented using piezoelectric components. Alternatively, the active damping system may consist only of an actuator that receives a control signal from a control unit 300, whereby the control unit is configured to determine the control signal based on position measurements performed by a position measurement system 250.

[0059] In the embodiment shown, the sensor frame 220 is supported by the force frame 210 via the vibration isolator 280. It can be noted that alternative arrangements may also be considered.

[0060] exist Figure 3a and Figure 3b Two such alternative arrangements are schematically shown. As a first alternative, such as... Figure 3a As shown, the sensor frame 220 can be mounted to the base frame 260 in a similar manner to how the force frame 210 is mounted to the base frame 260. As a second alternative, such as Figure 3b As shown, the sensor frame 220 is mounted to a separate frame 290, which is separate from the force frame, via a vibration isolator 280. This separate frame, also referred to as the intermediate frame 290, is mounted via a vibration isolator 272, which can be, for example, similar to the vibration isolator 270 supporting the force frame. With the aid of the intermediate frame 290 and the vibration isolators 272 and 280, Figure 3b The sensor frame 220 shown can be used with Figure 2 Similar methods are used for isolation, as shown in the diagram. Figure 3b Another advantage of this arrangement is that it provides improved isolation between the force frame 210 and the sensor frame 220, since the sensor frame 220 is no longer directly supported by the force frame 210. This results in less interference for the sensor frame 220. Regarding the embodiment shown, it can also be noted that the intermediate frame 290 can be additionally used to mount a position measurement system for positioning devices, for example... Figure 1 The positioning device PW is shown. As an example, an interferometric system can be mounted to the intermediate frame 290. The interferometric system is configured, for example, to emit a laser beam toward the substrate stage, such as... Figure 1 The substrate stage WT shown is positioned by the positioning device PW. Alternatively, in the case of an encoder-based measurement system, a one-dimensional or two-dimensional encoder grating can be mounted to the intermediate frame 290, the grating being configured to cooperate with an optical encoder sensor mounted on the substrate stage WT positioned by the positioning device PW.

[0061] In such Figure 2 , Figure 3a and Figure 3b In the embodiment shown, the sensor frame 220 is subdivided into N sub-frames, thus enabling better control over the deformation of the sensor frame 220 caused by vibrations applied to the frame.

[0062] The inventors have observed other possible causes for sensor frame deformation. In the embodiment shown, the sensor frame 220 is mounted to the force frame 210 by means of a vibration isolator. Figure 2 ), base frame ( Figure 3a ) or intermediate frame ( Figure 3b Such vibration isolators can be, for example, mechanical systems comprising mechanical springs. Such spring-based systems can be designed to have specific stiffness in the translational directions (X, Y, Z), which is selected to obtain the desired suspension frequency of the sensor frame. Ideally, it is desirable for such vibration isolators to have zero stiffness with respect to rotation and no crosstalk between directions of motion. However, in practice, such crosstalk and non-zero stiffness with respect to rotation may be difficult (if not impossible) to achieve. Within the meaning of this invention, such crosstalk and non-zero stiffness are referred to as parasitic stiffness. It is desirable to minimize this parasitic stiffness, as it can lead to additional deformation of the sensor frame. As those skilled in the art will understand, in the event of deformation or movement of the supporting frame (force frame, base frame, or intermediate frame), this deformation will also lead to deformation of the sensor frame due to parasitic stiffness. This effect is particularly likely to occur when the sensor frame is supported in an overdetermined manner, for example, by more than three vibration isolators or by vibration isolators with parasitic stiffness. Regarding the occurrence of parasitic stiffness, it should be noted, for example, that such parasitic stiffness can also be referred to by a stiffness matrix having non-zero elements in off-diagonal positions.

[0063] Regarding the mounting or support of the sensor frame, it can be noted that over-determined support may be required due to the physical constraints imposed by the layout of the lithography equipment. As an example, in the case of EUV-based lithography equipment, the projection system may include multiple mirrors whose positions need to be monitored. The specific layout, such as the size and orientation of the mirrors, is determined by the optical design of the projection system. The sensor frame used to monitor the optical elements must be designed in such a way that it does not interfere with the optical design, including the trajectory of the patterned radiation beam. Figure 4A sensor frame 420, which can be applied in an EUV-based lithography apparatus, is schematically shown. The sensor frame 420, as shown, has a generally rectangular shape and an aperture 420.1 through which a patterned radiation beam can pass. In the embodiment shown, the sensor frame 420 is supported by four vibration isolation systems or vibration isolators 430. The vibration isolators 430 can be, for example, mechanical isolators configured to support the sensor frame at a suspension frequency ranging from 3 Hz to 15 Hz, preferably about 6 Hz. Due to the parasitic stiffness described above, such a sensor frame arrangement may therefore be subject to induced deformation, thus compromising the application of the sensor frame as a positional reference for optical elements. In addition to the effects of parasitic stiffness, deformation forces can also be transmitted to the sensor frame when it is mounted in an overdetermined manner and the supporting frame itself deforms. For example, when the sensor frame is supported by four isolators, even without parasitic stiffness in the isolators, the torsional shape of the supporting frame will result in forces on the sensor frame.

[0064] According to a second aspect of the invention, by reducing the number of vibration isolators with such parasitic stiffness and introducing at least one controlled actuator force into the sensor frame, deformation of the sensor frame due to the parasitic stiffness of the vibration isolator (vibration isolator 430) can be avoided or mitigated, whereby the controlled actuator force and the vibration isolator are arranged in different, non-collinear positions.

[0065] Figure 5 A first embodiment of a suspended sensor frame that can be applied in a lithography apparatus according to a second aspect of the present invention is schematically depicted. Figure 5 The sensor frame 520 is schematically shown, which is supported by two vibration isolators 530 and controlled by two actuator forces 540 applied thereon.

[0066] In one embodiment, the actuator force applied to the sensor frame is essentially a unidirectional force, for example, oriented in the vertical direction (Z direction).

[0067] In one embodiment, the actuator for generating the actuator force is a permanent magnet actuator. This actuator can be configured to generate unidirectional forces in both the actuation direction and a direction perpendicular to the actuation direction while possessing low stiffness. In this arrangement, the actuator may, for example, include a coil assembly configured to cooperate with the permanent magnet assembly to generate the desired force. (Reference) Figure 2 The coil assembly of this actuator device can be mounted, for example, on the force frame 210, while the permanent magnet assembly can be mounted on the sensor frame 220.

[0068] Such electromagnetic actuators, such as permanent magnet actuators, are generally interpreted as contactless actuators, meaning that the coil assembly and the permanent magnet assembly are separated by a gap, such as an air gap. These actuators are typically well-suited for generating unidirectional forces with virtually no crosstalk or parasitic stiffness. More specifically, permanent magnet actuators can be designed to generate the desired force over a 3D operating range, whereby the generated force remains substantially the same regardless of the relative positions of the coil assembly and the permanent magnet assembly within the operating range.

[0069] In one embodiment, the actuator that generates the actuator force is configured to stabilize the sensor frame. In another embodiment, the actuator may be configured to apply a force to the sensor frame such that the sensor frame is suspended at a desired frequency. By applying one or more controlled actuator forces, the number of vibration isolators can be reduced, thereby reducing the effect of the parasitic stiffness of the vibration isolators.

[0070] This can be achieved, for example, by measuring the relative displacement of the subframe and providing that relative displacement as feedback to a controller of one or more actuators, which can then control one or more actuators to apply forces on the subframe to counteract the relative displacement. By doing so, “electronic” stiffness of the desired magnitude can be achieved.

[0071] In one embodiment, the sensor frame is supported by only two vibration isolators and controlled by one or more actuators. In such an embodiment, the two vibration isolators can be arranged to support the sensor frame in a substantially balanced manner. By doing so, the required control force applied to the sensor frame by the actuators can be minimized. This can be achieved by positioning the vibration isolators such that the projection of the center of gravity of the sensor frame onto the horizontal plane lies on the projection of the line connecting the support positions of the vibration isolators onto the horizontal plane. Figure 6 Two possible arrangements of the vibration isolators and actuators according to the invention are schematically depicted to support and control a sensor frame. In the embodiment on the left, the sensor frame 620 is supported by two vibration isolators 630 arranged along the longitudinal axis of the frame. The position of the frame 620 is further controlled by two actuator forces applied to the frame at position 640 marked “X”. In the embodiment on the right, the vibration isolators are located on an axis perpendicular to the longitudinal axis. Note that in both embodiments, the vibration isolators 630 are positioned such that the projection of the center of gravity 650 of the sensor frame 620 onto the horizontal plane (i.e., the XY plane) lies on the projection of the line 660 connecting the vibration isolator support positions 630.1 onto the horizontal plane.

[0072] In one embodiment, the first and second aspects of the invention can be combined. In such an arrangement, the sensor frame can be subdivided into N sub-frames, where N is an integer greater than 1, and is supported by M vibration isolators (M is an integer and 1 ≤ M < 3) and at least one vertically oriented actuator force.

[0073] While specific references may be made herein to the use of lithography equipment in IC manufacturing, it should be understood that the lithography equipment described herein may have other applications, such as the fabrication of integrated optical systems, patterning for guiding and detecting magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc. Those skilled in the art will understand that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered synonymous with the more general terms “substrate” or “target portion,” respectively. The substrate W referred to herein may be processed before or after exposure in, for example, a track (a tool typically used to apply a resist layer to the substrate and develop the exposed resist), metrology tools, and / or inspection tools. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Furthermore, the substrate W may be processed more than once, for example, to produce a multilayer IC, such that the term substrate W as used herein may also refer to a substrate that already contains multiple processed layers.

[0074] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it should be understood that the invention can be used in other applications, such as imprint lithography, and is not limited to optical lithography where the context permits. In imprint lithography, the morphology in the patterning apparatus MA defines a pattern produced on a substrate. The morphology of the patterning apparatus can be imprinted into a resist layer provided to the substrate, and the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist has cured, the patterning apparatus MA is removed from the resist, thereby leaving the pattern.

[0075] While specific embodiments of the invention have been described above, it should be understood that the invention may be practiced in ways other than those described. For example, the invention may take the form of a computer program comprising one or more machine-readable sequences of instructions describing the methods disclosed above, or a data storage medium (e.g., semiconductor memory, magnetic disk, or optical disk) in which such a computer program is stored.

[0076] The above description is intended to illustrate and not limit. Therefore, it will be apparent to those skilled in the art that modifications can be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A lithographic apparatus comprising: - a projection system configured to project a patterned beam of radiation onto a substrate; the projection system comprising a plurality of optical elements; - a sensor frame comprising N sub-frames and a coupling system coupling the N sub-frames, N being an integer larger than 1 ; - at least one actuator configured to exert a substantially vertically oriented force on the sensor frame; - a first position measurement system configured to measure a position of the plurality of optical elements relative to the sensor frame; - a second position measurement system configured to determine a relative position of the N sub-frames relative to each other, and - a force frame, wherein the force frame is configured to connect and support the plurality of optical elements using a plurality of first vibration isolators, wherein the sensor frame is supported on the force frame by M vibration isolators, M being an integer and 1 < M < 3, the M vibration isolators and the substantially vertically oriented force supporting the sensor frame at different, non-collinear locations.

2. The lithographic apparatus according to claim 1, further comprising a base frame, wherein the force frame is supported on the base frame by means of a plurality of second vibration isolators.

3. The lithographic apparatus of claim 2, wherein, The sensor frame is supported by the force frame by means of a plurality of vibration isolators.

4. The lithographic apparatus of claim 2, wherein, The sensor frame is supported by the base frame by means of a plurality of vibration isolators.

5. The lithographic apparatus of any of claims 1 to 4, wherein, The coupling system comprises a spring-damper system.

6. The lithographic apparatus of claim 5, wherein, The spring-damper system comprises an active damper.

7. The lithographic apparatus of any of claims 1 to 6, wherein, The second position measurement system comprises an encoder-based measurement system.

8. The lithographic apparatus according to any one of claims 1 to 7, further comprising: - a substrate table configured to hold a substrate; - a positioning device configured to position the substrate table; and - a control unit configured to: - receive a first position measurement signal of the first position measurement system; - receive a second position measurement signal of the second position measurement system; - determine a position of the plurality of optical elements based on the first position measurement signal and the second position measurement signal; and - generate a control signal for the positioning device based on the determined position.

9. The lithographic apparatus according to claim 2, further comprising: - an actuator assembly configured to position at least one optical element of the plurality of optical elements; - a control unit configured to: - receive a first position measurement signal of the first position measurement system; - receive a second position measurement signal of the second position measurement system; - determine a position of the plurality of optical elements based on the first position measurement signal and the second position measurement signal; and - generate a control signal for the positioning device based on the determined position.

10. The lithographic apparatus according to claim 1, further comprising: - at least one actuator configured to exert a vertically oriented force on the sensor frame.

11. The lithographic apparatus of claim 1, wherein, M = 2。 12. The lithographic apparatus of claim 1, wherein, The vibration isolators are positioned to substantially keep the sensor frame in balance. The sensor frame is supported by the force frame by means of a plurality of vibration isolators. The sensor frame is supported by the base frame by means of a plurality of vibration isolators. The coupling system comprises a spring-damper system. The spring-damper system comprises an active damper. The second position measurement system comprises an encoder-based measurement system.

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