Slotted ferromagnetic core polyphase forcer with closed slot design

Abstract

Disclosed is a slotted iron core motor with a novel "closed slot" iron core design for the LiMMS actuator that allows significant drive ripple / cogging reduction without introducing significant penalties on drive force density, thermal performance and manufacturability. In preferred embodiments, the closed slot completely covers the coils placed inside the slots with a thin 5 ferromagnetic layer that may be referred to in this disclosure as a ferromagnetic bridge. The ferromagnetic bridge being made of the same material as the ferromagnetic iron core slotted armature reduces cogging by creating a smooth transition from high permeability to a relative permeability of 1, which eliminates a steep, square-wave style in the magnetic reluctance that is a significant factor in causing cogging. In some embodiments, cogging is reduced by a factor of 2 using this novel design. 0

Description

SLOTTED FERROMAGNETIC CORE POLYPHASE FORCER WITH CLOSED SLOT DESIGNCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 674,271 which was filed on July 22, 2024 and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] This description relates generally to slotted ferromagnetic core forcers.BACKGROUND

[0003] Linear actuators are known. Also known as permanent magnet linear synchronous motors (PMSMs), multi-phase electromagnetic linear actuators have been used as long stroke actuators in lithography apparatuses, metrology systems, and other devices, for example. A lithography (e.g., projection) apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device (e.g., a mask) may contain or provide a pattern corresponding to an individual layer of the IC (“design layout”), and this pattern can be transferred onto a target portion (e.g. comprising one or more dies) on a substrate (e.g., silicon wafer) that has been coated with a layer of radiation-sensitive material (“resist”), by methods such as irradiating the target portion through the pattern on the patterning device. In general, a single substrate contains a plurality of adjacent target portions to which the pattern is transferred successively by the lithographic projection apparatus, one target portion at a time. In one type of lithographic projection apparatus, the pattern on the entire patterning device is transferred onto one target portion in one operation. Such an apparatus is commonly referred to as a stepper. In an alternative apparatus, commonly referred to as a step-and- scan apparatus, a projection beam scans over the patterning device in a given reference direction (the “scanning” direction) while synchronously moving the substrate parallel or anti-parallel to this reference direction. Different portions of the pattern on the patterning device are transferred to one target portion progressively. Various movements of the lithography apparatus may be facilitated by one or more linear actuators.

[0004] There are various kinds of linear actuators, including Lorentz actuators, Linear Motor Motion Systems (LiMMS), and cylindrical linear drive motors. Existing motors each have some drawbacks, while the overall goal may be to improve acceleration capabilities while minimizing unwanted effects. It is desirable to develop new kinds of forcers with higher force densities while reducing negative characteristics. It is also desirable to use less energy to create more efficient performance.SUMMARY

[0005] A closed slot design for a slotted ferromagnetic core polyphase forcer is described.

[0006] According to an embodiment, a linear actuator is disclosed. The linear actuator includes: a ferromagnetic armature core comprising a plurality of ferromagnetic teeth defining a plurality of slots therebetween; a plurality of electric coils, each of which are wound around one of the plurality of ferromagnetic teeth; a plurality of magnets arranged in an array and positioned over the plurality of ferromagnetic teeth along a common axis of motion; and a ferromagnetic bridge cap positioned between the plurality of magnets and the plurality of ferromagnetic teeth and at least partially covering each of the plurality of slots.

[0007] In some embodiments, the ferromagnetic bridge cap entirely covers each of the plurality of slots.

[0008] In some embodiments, the ferromagnetic bridge cap has a thickness of less than 1 mm.

[0009] In some embodiments, the ferromagnetic bridge cap comprises repeating intervals of a thicker strip of ferromagnetic material and a thinner strip of ferromagnetic material.

[0010] In some embodiments, the ferromagnetic bridge cap is configured to reduce cogging when the linear actuator is activated to move along the common axis of motion.

[0011] In some embodiments, the linear actuator further includes one or more cooling plates. In some embodiments, one of the one or more cooling plates is positioned on top of the ferromagnetic bridge cap and in between the ferromagnetic bridge cap and the plurality of magnets. In some embodiments, a second one of the one or more cooling plates is positioned under the plurality of electric coils and between a base of the ferromagnetic armature core and the plurality of electric coils. In some embodiments, one of the one or more cooling plates is positioned within a slot of the plurality of slots and parallel to the ferromagnetic teeth. In some embodiments, the one or more cooling plates are positioned vertically, which would be perpendicular to the ferromagnetic bride cap.

[0012] In some embodiments, a load angle of a commutated electromagnetic excitation is offset by less than half a radian to reduce cogging.

[0013] In some embodiments, a linear actuator is described. The linear actuator includes: a ferromagnetic armature core comprising a first plurality of ferromagnetic teeth defining a plurality of slots therebetween; a ferromagnetic bridge cap comprising a second plurality of ferromagnetic teeth each positioned within a respective one of the plurality of slots; a plurality of electric coils, each of which are wound around one of the ferromagnetic teeth of the second plurality of ferromagnetic teeth of the ferromagnetic bridge cap; and a plurality of magnets arranged in an array and positioned over the ferromagnetic bridge cap and arranged along a common axis of motion with the linear actuator.

[0014] In some embodiments, a semiconductor device manufacturing method is described. The method includes: receiving a substrate with a photoresist layer; directing radiation from a radiation source to transfer a pattern from a reticle onto the photoresist layer; actuating the reticle using a linear actuator comprising: a ferromagnetic armature core comprising a plurality of ferromagnetic teeth defining a plurality of slots therebetween; a plurality of electric coils, each of which are wound around one of the plurality of ferromagnetic teeth; a plurality of magnets arranged in an array and positionedover the plurality of ferromagnetic teeth along a common axis of motion; and a ferromagnetic bridge cap positioned between the plurality of magnets and the plurality of ferromagnetic teeth and at least partially covering each of the plurality of slots; and removing a portion of the photoresist layer to form a pattern over the substrate.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0016] FIG. 1 schematically depicts a lithography apparatus, which may include a linear actuator with the present cooling system, according to an embodiment.

[0017] FIG. 2 schematically depicts an embodiment of a lithographic cell or cluster, which may include a linear actuator with the present cooling system in one or more apparatuses of the lithographic cell or cluster, according to an embodiment.

[0018] FIG. 3 shows example winding configurations of electric coils in linear motors that may be used in lithography apparatuses and other kinds of machines that require high acceleration.

[0019] FIG. 4 shows an example slotted polyphase linear motor that minimizes cogging while still providing high force density from a slotted iron core armature, according to some embodiments.

[0020] FIG. 5 shows additional example views of some embodiments of the closed slot iron core design.

[0021] FIGS. 6A and 6B show two example side views of how the bridge cap may be constructed, according to some embodiments.

[0022] FIGS. 7A and 7B show contrasting flux density plots of a standard LiMMS design (FIG.7 A) and a LiMMS with the closed slot design (FIG. 8B) of the present disclosure.

[0023] FIG. 8A shows an alternative embodiment to the closed slot design that includes a partially closed slot. FIG. 8B shows a closed slot design to contrast with FIG. 8A.

[0024] FIG. 9 shows additional measured data about optimizing the design of the closed slot iron core armature, according to some embodiments.DETAILED DESCRIPTION

[0025] Multi-phase ferromagnetic core linear actuators have been used as long stroke actuators in lithography apparatuses, metrology systems, and other devices. For example, Lorentz actuators, linear actuators with magnetic materials present in their armatures with slots or magnetic teeth in the armature, and / or other motion systems, are used in lithography apparatuses. However, these systems produce unwanted vibrations. In particular, there is a periodic reluctance force / attraction force withthe iron core armature that oscillates as a function of velocity, tooth pitch and any harmonics present in the force applied. This causes an unwanted vibration known to those with skill in the art, as cogging. It is desirable to reduce or even eliminate the cogging from linear accelerations, while achieving higher lithography apparatus stage accelerations. Eliminating or reducing cogging allows for more precise movement in the linear motor and reduces degradation in the motor over time.

[0026] In addition, it is desirable to produce higher stage accelerations to increase productivity of a lithography apparatus, resulting in a lower cost per die (or per microchip). To reduce the cost per die for the customer, future high-acceleration systems will require higher throughput (e.g. 220 [wph] to >300 [wph]), which can partially be achieved by increasing the acceleration of the stages to reduce prep time between exposures of each die (e.g. 32Gto around 100G). To achieve higher accelerations, higher force density actuators are needed (e.g., at least 2000 [N / kg] are needed). Additionally, future systems are required to use less energy than is used today (>7 [kWh / waf| to <5 [kWh / waf| per system), and therefore more efficient motors are also desirable for all actuated components. Three- phase LiMMS and Lorentz actuators of both moving magnet and moving coil varieties are presently used in ASML scanners. Lorentz actuators with flat armatures have been recently preferred over slotted ‘iron’-core linear motors (@ ASML referred to as ‘LiMMS’ = Linear Motor Motion Systems) due to the fact that they produce less vibration and feature less prevalent nonlinear behavior. However, Lorentz motors are relatively inefficient due to their larger magnetic gap, requiring more average power from the amplifiers and ultimately resulting in a lower force density (see Fig. 1 for a schematic comparison). For example, ReMa-Y requires a force density >2000 [N / kg] to reach lOOGs, but has < 900 [N / kg] FD. Ideally one would then want to select a LiMMS variant for the reticle stage, linear motors in WS, or possibly ReMa-Y but would need to contend with the ripple effects, and maintain high performance by keeping coils cool (lower resistance means better efficiency).

[0027] A new linear motor that addresses the cogging issues and can provide more efficient cooling to achieve higher acceleration is described below. The invention described enables high force, and high efficiency within reasonable volume limits while suppressing the ripple effects that lead to machine vibrations. Disclosed is a slotted iron core motor with a novel “closed slot” iron core design for the LiMMS actuator that allows significant drive ripple / cogging reduction without introducing significant penalties on drive force density, thermal performance and manufacturability. In preferred embodiments, the closed slot completely covers the coils placed inside the slots with a thin ferromagnetic layer that may be referred to in this disclosure as a ferromagnetic bridge. The ferromagnetic bridge being made of the same material as the ferromagnetic iron core slotted armature reduces cogging by creating a smooth transition from high permeability to a relative permeability of 1, which eliminates a steep, square-wave style in the magnetic reluctance that is a significant factor in causing cogging. In some embodiments, cogging is reduced by a factor of 2 using this novel design.

[0028] The following introductory paragraphs describe general lithography system functionality - as one of many possible use case examples for the linear actuator(s) described herein. Note thatalthough specific reference may be made in this text to the manufacture of integrated circuits (ICs), it should be understood that the described cooling system has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc.

[0029] As an introduction, prior to transferring a pattern from a patterning device such as a mask to a substrate, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures (“post-exposure procedures”), such as a post-exposure bake (PEB), development, a hard bake and measurement and / or other inspection of the transferred pattern. This array of procedures is used as a basis to make an individual layer of a device, e.g., an IC. The substrate may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemical mechanical polishing, etc., all intended to finish an individual layer of the device. If several layers are required in the device, then the whole procedure, or a variant thereof, is repeated for each layer. Eventually, a device will be present in each target portion on the substrate. These devices are then separated from one another by a technique such as dicing or sawing, and then the individual devices can be mounted on a carrier, connected to pins, etc.

[0030] Manufacturing devices, such as semiconductor devices, typically involves processing a substrate (e.g., a semiconductor wafer) using a number of fabrication processes to form various features and multiple layers of the devices. Such layers and features are typically manufactured and processed using, e.g., deposition, lithography, etch, chemical mechanical polishing, ion implantation, and / or other processes. Multiple devices may be fabricated on a plurality of dies on a substrate and then separated into individual devices. This device manufacturing process may be considered a patterning process. A patterning process involves a patterning step, such as optical and / or nanoimprint lithography using a patterning device in a lithographic apparatus, to transfer a pattern on the patterning device to a substrate and typically, but optionally, involves one or more related pattern processing steps, such as resist development by a development apparatus, baking of the substrate using a bake tool, etching using the pattern using an etch apparatus, etc. One or more metrology processes are typically involved in the patterning process. Lithography apparatuses, metrology systems, and other equipment used to fabricate semiconductor devices may use one or more linear actuators having the described cooling system.

[0031] Lithography is a step in the manufacturing of device such as ICs, where patterns formed on substrates define functional elements of the devices, such as microprocessors, memory chips, etc. Similar lithographic techniques are also used in the formation of flat panel displays, micro-electro mechanical systems (MEMS) and other devices.

[0032] FIG. 1 schematically depicts an embodiment of a lithographic apparatus LA that may include and / or be associated with one or more linear actuators and corresponding cooling systems. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiationbeam B (e.g. UV radiation, DUV radiation, or EUV radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT (e.g., WTa, WTb or both) configured to hold a substrate (e.g. a resist-coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies and often referred to as fields) of the substrate W. The projection system is supported on a reference frame (RF). As depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask).

[0033] The illuminator IL receives a beam of radiation from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising for example suitable directing mirrors and / or a beam expander. In other cases, the source may be an integral part of the apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0034] The illuminator IL may alter the intensity distribution of the beam. The illuminator may be arranged to limit the radial extent of the radiation beam such that the intensity distribution is non-zero within an annular region in a pupil plane of the illuminator IL. Additionally or alternatively, the illuminator IL may be operable to limit the distribution of the beam in the pupil plane such that the intensity distribution is non-zero in a plurality of equally spaced sectors in the pupil plane. The intensity distribution of the radiation beam in a pupil plane of the illuminator IL may be referred to as an illumination mode.

[0035] The illuminator IL may comprise adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Generally, at least the outer and / or inner radial extent (commonly referred to as o-outer and o-inncr. respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be operable to vary the angular distribution of the beam. For example, the illuminator may be operable to alter the number, and angular extent, of sectors in the pupil plane wherein the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes may be achieved. For example, by limiting the radial and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multi-pole distribution such as, for example, a dipole, quadrupole or hexapole distribution. A desired illumination mode may beobtained, e.g., by inserting an optic which provides that illumination mode into the illuminator IL or using a spatial light modulator.

[0036] The illuminator IL may be operable to alter the polarization of the beam and may be operable to adjust the polarization using adjuster AD. The polarization state of the radiation beam across a pupil plane of the illuminator IL may be referred to as a polarization mode. The use of different polarization modes may allow greater contrast to be achieved in the image formed on the substrate W. The radiation beam may be unpolarized. Alternatively, the illuminator may be arranged to linearly polarize the radiation beam. The polarization direction of the radiation beam may vary across a pupil plane of the illuminator IL. The polarization direction of radiation may be different in different regions in the pupil plane of the illuminator IL. The polarization state of the radiation may be chosen in dependence on the illumination mode. For multi-pole illumination modes, the polarization of each pole of the radiation beam may be generally perpendicular to the position vector of that pole in the pupil plane of the illuminator IL. For example, for a dipole illumination mode, the radiation may be linearly polarized in a direction that is substantially perpendicular to a line that bisects the two opposing sectors of the dipole. The radiation beam may be polarized in one of two different orthogonal directions, which may be referred to as X-polarized and Y-polarized states. For a quadrupole illumination mode, the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as XY polarization. Similarly, for a hexapole illumination mode the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as TE polarization.

[0037] In addition, the illuminator IL generally comprises various other components, such as an integrator IN and a condenser CO. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. Thus, the illuminator provides a conditioned beam of radiation B, having a desired uniformity and intensity distribution in its cross section.

[0038] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system.

[0039] The lithographic apparatus may be of a type having two (dual stage) or more tables (e.g., two or more substrate tables WTa, WTb, two or more patterning device tables, a substrate table WTa and a table WTb below the projection system without a substrate that is dedicated to, for example,facilitating measurement, and / or cleaning, etc.). In such “multiple stage” machines, the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. For example, alignment measurements using an alignment sensor AS and / or level (height, tilt, etc.) measurements using a level sensor LS may be made.

[0040] In operation of the lithographic apparatus, a radiation beam is conditioned and provided by the illumination system IL. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g., an interferometric device, linear encoder, 2-D encoder, or capacitive sensor), the substrate table WT can be moved accurately, e.g. to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Fig. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0041] The depicted apparatus may be used in at least one of the following modes: 1. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while a pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. 2. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a singledynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. 3. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed, and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0042] A substrate may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology or inspection tool. Any or all of these tools may include linear actuators with corresponding cooling systems. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already includes multiple processed layers.

[0043] The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) or deep ultraviolet (DUV) radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0044] Various patterns on or provided by a patterning device may have different process windows, i.e., a space of processing variables under which a pattern will be produced within specification. Examples of pattern specifications that relate to potential systematic defects include checks for necking, line pull back, line thinning, critical dimension (CD), edge placement, overlapping, resist top loss, resist undercut and / or bridging. The process window of the patterns on a patterning device or an area thereof may be obtained by merging (e.g., overlapping) process windows of each individual pattern. The boundary of the process window of a group of patterns comprises boundaries of process windows of some of the individual patterns. In other words, these individual patterns limit the process window of the group of patterns.

[0045] As shown in FIG. 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to a lithocell or cluster, which also includes apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include one or more spin coaters SC to deposit one or more resist layers, one or more developers to develop exposed resist, one or more chill plates CH and / or one or more bake plates BK. A substrate handler, or robot, RO picks up one or more substrates from input / output port I / Ol, I / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus. These apparatuses, which areoften collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0046] In order that a substrate that is exposed by the lithographic apparatus is exposed correctly and consistently and / or in order to monitor a part of the patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., an optical lithography step), it is desirable to inspect a substrate or other object to measure or determine one or more properties such as alignment, overlay (which can be, for example, between structures in overlying layers or between structures in a same layer that have been provided separately to the layer by, for example, a double patterning process), line thickness, critical dimension (CD), focus offset, a material property, etc.

[0047] The one or more measured parameters may include, for example, alignment, overlay between successive layers formed in or on the patterned substrate, critical dimension (CD) (e.g., critical linewidth) of, for example, features formed in or on the patterned substrate, focus or focus error of an optical lithography step, dose or dose error of an optical lithography step, optical aberrations of an optical lithography step, etc. This measurement may be performed on a target of the product substrate itself and / or on a dedicated metrology target provided on the substrate. The measurement can be performed after-development of a resist but before etching, after-etching, after deposition, and / or at other times.

[0048] There are various techniques for making measurements of the structures formed in the patterning process, including the use of a scanning electron microscope, an image-based measurement tool and / or various specialized tools. Any or all of these tools may include linear actuators with corresponding cooling systems. A fast and non-invasive form of specialized metrology tool is one in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered (diffracted / reflected) beam are measured. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. This may be termed diffraction-based metrology. One such application of this diffraction-based metrology is in the measurement of feature asymmetry within a target. This can be used as a measure of overlay, for example, but other applications are also known. For example, asymmetry can be measured by comparing opposite parts of the diffraction spectrum (for example, comparing the -1st and +lstorders in the diffraction spectrum of a periodic grating).

[0049] Metrology results may be provided directly or indirectly to the supervisory control system SCS. If an error is detected, an adjustment may be made to exposure of a subsequent substrate (especially if the inspection can be done soon and fast enough that one or more other substrates of the batch are still to be exposed) and / or to subsequent exposure of the exposed substrate. Also, an already exposed substrate may be stripped and reworked to improve yield, or discarded, thereby avoidingperforming further processing on a substrate known to be faulty. In a case where only some target portions of a substrate are faulty, further exposures may be performed only on those target portions which meet specifications.

[0050] The lithographic apparatus LA and radiation source SO described herein can be used in a method for manufacturing a semiconductor device. A semiconductor device manufacturing method comprises receiving a substrate W with a photoresist layer. The method further comprises directing a radiation beam from radiation source SO to transfer a pattern from a mask onto the photoresist layer. This could be achieved by a patterning device which is configured to form a patterned radiation beam, imparting the patterned radiation beam onto the photoresist layer. The method for manufacturing a semiconductor device further comprises the step of removing a portion of the photoresist layer to form the pattern over the substrate W.

[0051] The substrate W may be made of silicon or other semiconductor materials. Alternatively or additionally, the substrate W may include other semiconductor materials such as germanium (Ge) or carbon (C). In some embodiments, the semiconductor substrate is made of a compound semiconductor such as III-V compound semiconductors, II- V compound semiconductors, and / or any suitable integration of Group IV materials. In some embodiments, the substrate W may be a silicon-on- insulator (SOI) or a germanium-on-insulator (GOI) substrate.

[0052] The semiconductor device made from the substrate W may have various device elements. Examples of semiconductor device elements that are formed over the substrate W include transistors (e.g., planar or non-planar metal oxide semiconductor field effect transistors (MOSFET), bipolar junction transistors (BJT), high-voltage transistors, high-frequency transistors, etc.), diodes, CMOS image sensors, passive devices, and / or other applicable elements. Various processes may be performed to form the semiconductor device elements, such as deposition, etching, implantation, epitaxial growth, polishing, thermal treatment, and / or other suitable processes. In some embodiments, the substrate W is coated with a photoresist layer sensitive to the EUV light.

[0053] Referring to FIG. 3, shown are example winding configurations of electric coils in linear motors that may be used in lithography apparatuses and other kinds of machines that require high acceleration. Example linear motor 300 is a LiMMS with three phases. There are electrical coils wrapped around slots of an iron core armature and a series of magnets lined on the top. Illustration 305 shows just the iron core armature with slots that serves as the support structure for the LiMMS motor. Illustration 310 is a closer view of the LiMMS that illustrates a small gap 312 between the top of the slots of the iron core armature and the series of magnets. The iron slots being close to the magnets constituting just a small gap in between provides a strong attractive force between the two materials, and thus provides a highest force per unit moving-mass, volume, and current. The slots in the iron core armature therefore provide an efficient structure to achieve high acceleration. One drawback in this structure, however, is that the slots in the iron core armature cause high force rippledisturbances that those with skill in the art refer to as cogging. This creates strong and unwanted vibrations that limit the potential of the LiMMS motor.

[0054] As another example, illustration 315 shows a standard Lorentz linear motor with three phases, where the iron core armature lacks the slots or teeth. Illustration 320 shows just the iron core armature of this structure, where no slots are present. Since there are no slots present, there is low cogging that needs to be addressed. However, one drawback in this structure is that there is a larger gap 327 between the position of the iron and the magnets. This provides a less attractive force between the magnets and the iron when activated by the electrical coils, which produces a less efficient linear forcer. Thus, for the same reason that there may be less cogging, this type of motor is less effective at providing stronger acceleration.

[0055] In general, it is desirable to develop a linear forcer that can combine the benefits of both the LiMMS and Lorentz designs. In other words, it is desirable to achieve high force density while also reducing the cogging that is typically present with a slotted iron core armature.

[0056] Referring to FIG. 4, shown is an example slotted polyphase linear motor that minimizes cogging while still providing high force density from a slotted iron core armature, according to some embodiments. Shown in illustration 400 is a novel “closed slot” iron core design that results in significant drive ripple / cogging reduction without introducing significant penalties on drive force density, thermal performance, or manufacturability. This closed slot iron core design features the electrical coils and iron core armature structure 445, now with a ferromagnetic bridge 405 that covers the ferromagnetic teeth 420 and the slots defined therebetween. The electrical coils 415 are still wrapped around the ferromagnetic teeth 420 and still fill the slots, although now they are covered by the ferromagnetic bridge 405. Like in the examples of FIG. 3, the electrical coils provide three phases: a, a’; b, b’, and c, c’. In some embodiments, cooling surfaces 410 are included in the design at any or all of the disclosed positions of reference 410. The presence of more or fewer cooling surfaces does not reduce the effectiveness of the ferromagnetic bridge 405. The closed slot design of FIG. 4 also shows the magnet array 440 with the same small gap with the ferromagnetic teeth 420. The slots that fit the electrical coils are typically rounded at the corners, as shown by the rounded bridge contour 435 and the rounded base contour 430. These features would contribute to cogging as well but have their impacts reduced by the addition of the ferromagnetic bridge 405.

[0057] The addition of the ferromagnetic bridge 405 reduces cogging by creating a smooth transition in permeability, like a controlled saturation state. In some embodiments, the material of the ferromagnetic bridge 405 may be the same as the rest of the iron core armature 425 in order to provide the smooth transition from high permeability to relative permeability of 1. This uniform bridge over the slots with the same material as the iron teeth 420 may reduce cogging by a factor of 2, according to some embodiments. In other cases, some parts may be made of different materials. For example, the teeth may be made of SiFe while the bridge may be made of CoFe. A change in materials for somecomponents may be easier to manufacture, or certain components may be more beneficial when they are stiffer or more malleable.

[0058] Referring to FIG. 5, shown are additional example views of some embodiments of the closed slot iron core design. Illustration 500 shows an exploded view of components of one example design of the closed slot linear actuator, according to some embodiments. The closed slot design is not intuitive because it would be normally impractical to form the closed slot design from a single piece of iron. This is because the electric coils, and possibly other components like cooling plates, need to be fitted into the slots. It is much more impractical to snake electric coils and other components into the slots if the slot is already closed on top. To address this issue, the embodiment in illustration 500 features a ferromagnetic bridge cap 505 that is precisely manufactured to touch evenly the top of the iron teeth of the iron core armature 520 so that airgaps in between are minimized. The bridge cap 505 is placed over the other components once the cooling plates 510 and electric coils 515 are fitted into the slots first. In this example, the electric coils 515 are sandwiched between two layers of cooling plates 510. Other embodiments can include multiple layers of electric coils sandwiched between even more layers of cooling plates before the bridge cap is placed on top, and embodiments are not so limited. The bridge cap 505 may be a thin layer of ferromagnetic material with intervals of thicker strips designed to touch the iron core teeth of the iron core armature 520 in the configuration where the electric coils and / or cooling plates are stacked higher than the top of the iron teeth.

[0059] Illustration 550 shows an example of the assembly of the pieces from illustration 500. This set of components shows just one section of a three phase linear motor, and the overall linear actuator may be modularized to include multiple sets of this three-repeating section. In other cases, the iron core armature may be manufactured in longer pieces with more slots, as may be the cooling plates and the bridge cap. In another example, illustration 560 shows an assembled view of a similar design but with the cooling plates oriented vertically, which is to say orthogonal to the axis of linear motion.

[0060] Referring to FIGS. 6A and 6B, shown are example side views of how the bridge cap may be constructed, according to some embodiments. Illustration 600 in FIG. 6A shows the side view of the linear actuator consistent with the embodiments in FIG. 5. The bridge cap 602 is made of a thin layer of ferromagnetic material and includes intervals of thin strips of additional ferromagnetic material 604 to touch the teeth of iron core armature 610. Before the bridge cap 602 is placed down, the electric coils 608 are slotted into the iron core armature 610 and wrapped around the teeth. As previously mentioned, there may be one or more cooling plates positioned contiguous to the electric coils 608, not shown here. The completed configuration of the linear actuator is shown in illustration 620, where the bridge cap 602 covers the slots entirely and the ferromagnetic material seamlessly connects with the rest of the iron core armature via connection with the teeth. In this way, cogging is significantly reduced by creating a smooth transition from high permeability to a permeability of 1 that effectively smooths out the force ripples.

[0061] Illustration 630 in FIG. 6B shows an alternative configuration for manufacture, which includes a bridge cap 632 that is connected with the ferromagnetic teeth, instead of the iron core armature 636 including them. The electric coils 634 are therefore fitted around the teeth of the bridge cap 632 instead of the iron core armature 636. Illustration 640 shows the completed view of the bridge cap 632 placed into iron core armature 636. Here, there are gaps shown at the bottom between the bridge cap 632 and the iron core armature 636. However, the pieces are effectively contiguous due to the electric coils 634 touching both pieces of ferromagnetic material. This maintains the smooth transition from high permeability to a permeability of 1.

[0062] Referring to FIGS. 7A and 7B, shown are contrasting flux density plots of a standard LiMMS design (FIG. 7A) and a LiMMS with the closed slot design of the present disclosure. The plots illustrate how much more effective the closed slot design is compared to a typical LiMMS design available today. In FIG. 7A, shown is a flux density plot 700 of a side view of a typical LiMMS motor with an iron core with teeth 702. The plot is inverted, so the teeth are facing downward. The gradient in the plot represents a degree of permeability or flux density. It is desirable to have more areas that are shaded with the darker gradient. However, where the magnets 704 are in close proximity 706 to the iron teeth 702, the shades are much lighter, indicating that the transition from a high permeability region to a low permeability region in the iron core is abrupt. This contributes heavily to creating the force ripples that causes cogging.

[0063] In contrast, in FIG. 7B, flux density plot 750 shows the effect of the bridge cap in the closed slot design. Here, the areas of 752 where the bridge cap is placed over the slots show the significantly darker shade in the flux density. This indicates that the transition from the high permeability region to a low permeability region in the iron core is continuous. This reduces the force ripples which will reduce cogging.

[0064] Referring to FIGS. 8A and 8B, shown is an alternative embodiment to the closed slot design that includes a partially closed slot in FIG. 8A, contrasted with the closed slot design in FIG. 8B. Illustration 800 of FIG. 8A shows a partially closed design that has been analyzed and researched to determine what design achieved the most effective cogging reduction. Here, a cross-sectional view of the iron core armature is shown, with a portion of the iron core armature 810 highlighted for emphasis. The sections on the side in illustration 800 repeat the same pattern shown in the middle highlighted area of the iron core armature 810. In the slots between the teeth of the iron core armature are electric coils 812 wrapped around each tooth. The comers 808 of the slots may be smoothed to have a curved contour, and may shaped in other various ways to be optimized for various effects, like cogging and cooling effectiveness. The partial bridge cover 802 is a ferromagnetic layer constructed to only partially cover the slot of the iron core armature 810. As shown, there is still a gap or opening in the bridge cover 802, though the gap is significantly smaller than without any bridge cap like in traditional slotted iron core designs. After analyzing the effectiveness on force ripple reduction, it hasbeen found that the partial design does reduce cogging, but less so than a full bridge cover like the designs described in FIGS. 4, 5, and 6.

[0065] Illustration 850 in FIG. 8B emphasizes the preferred embodiment with the full bridge cap 806 over the entirety of the slot and the electric coils 812. The bridge cap may be made of a minor amount of ferromagnetic material to produce just a small thickness 804 over the slots. After analyzing the effects of the thickness of the bridge cap 804, it was found that the thickness of the bridge did have an effect on the cogging reduction effectiveness. For example, given a particular ferromagnetic material, it was found that the lowest drive ripple as a percentage of drive force was achieved when the bridge thickness was about 0.8mm, for a fully closed slot design.

[0066] Referring to FIG. 9, shown are additional measured data about optimizing the design of the closed slot iron core armature, according to some embodiments. After performing some sensitivity analysis, it was determined that the cogging may be reduced even further with a change in the load angle of the commutate electromagnetic excitation. Shown in illustration 900 is an effect on the cogging as a function of change of the load angle of the commutation offset in radians. Shown are ten different plots, each for a different width of the closed slot interval. While the key 950 shows ten plots with varying widths, from 1 mm to 10 mm, since the width of the slot is 10mm, it can be extrapolated that each varying width of the closed slot shown can represent a percentage of how closed the slot is, rather than just the width itself. For example, a first plot showing a partially closed width of 1 mm in the key 950 can also be interpreted as showing the effects of cogging for a bridge closing the slot by 10%, and another plot showing a fully closed width of 10 mm in the key 950 can also be interpreted as showing the effects of cogging for a bridge closing the slot by 100%, and so on.

[0067] Here, for a given partially or fully closed slot, in illustration 900, the effect on cogging was also analyzed for a given commutation offset, measured in radians. It can be seen in illustration 900 that an offset of 0 actually did not produce the least drive cogging for all widths of the partially or fully closed slot designs. Rather, at plot 902, the optimization that produced the least drive cogging as a percentage of drive force was the fully closed slot design with a commutation offset of about 0.25 radians. Therefore, in some embodiments, the closed slot design also includes a commutation offset to further reduce the cogging.

[0068] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses. In the following, further features, characteristics, and exemplary technical solutions of the present disclosure will be described in terms of clauses that may be optionally claimed in any combination:1. A linear actuator comprising: a ferromagnetic armature core comprising a plurality of ferromagnetic teeth defining a plurality of slots therebetween; a plurality of electric coils, each of which are wound around one of the plurality of ferromagnetic teeth; a plurality of magnets arranged in an array and positioned over the plurality of ferromagnetic teeth along a common axis of motion; anda ferromagnetic bridge cap positioned between the plurality of magnets and the plurality of ferromagnetic teeth and at least partially covering each of the plurality of slots.2. The linear actuator of clause 1, wherein the ferromagnetic bridge cap entirely covers each of the plurality of slots.3. The linear actuator of any of the previous clauses, wherein the ferromagnetic bridge cap has a thickness of less than 1 mm.4. The linear actuator of any of the previous clauses, wherein the ferromagnetic bridge cap comprises repeating intervals of a thicker strip of ferromagnetic material and a thinner strip of ferromagnetic material.5. The linear actuator of any of the previous clauses, wherein the ferromagnetic bridge cap is configured to reduce cogging when the linear actuator is activated to move along the common axis of motion.6. The linear actuator of any of the previous clauses, further comprising one or more cooling plates.7. The linear actuator of any of the previous clauses, wherein one of the one or more cooling plates is positioned on top of the ferromagnetic bridge cap and in between the ferromagnetic bridge cap and the plurality of magnets.8. The linear actuator of any of the previous clauses, wherein a second one of the one or more cooling plates is positioned under the plurality of electric coils and between a base of the ferromagnetic armature core and the plurality of electric coils.9. The linear actuator of any of the previous clauses, wherein one of the one or more cooling plates is positioned within a slot of the plurality of slots and parallel to the ferromagnetic teeth.10. The linear actuator of any of the previous clauses, wherein a load angle of a commutated electromagnetic excitation is offset by less than half a radian to reduce cogging.11. A linear actuator comprising: a ferromagnetic armature core comprising a first plurality of ferromagnetic teeth defining a plurality of slots therebetween; a ferromagnetic bridge cap comprising a second plurality of ferromagnetic teeth each positioned within a respective one of the plurality of slots; a plurality of electric coils, each of which are wound around one of the ferromagnetic teeth of the second plurality of ferromagnetic teeth of the ferromagnetic bridge cap; and a plurality of magnets arranged in an array and positioned over the ferromagnetic bridge cap and arranged along a common axis of motion with the linear actuator.12. The linear actuator of any of the previous clauses, wherein a portion of the ferromagnetic bridge cap that covers each of the plurality of electric coils has a thickness of less than 1 mm.13. The linear actuator of any of the previous clauses, wherein the ferromagnetic bridge cap is configured to reduce cogging when the linear actuator is activated to move along the common axis of motion.14. The linear actuator of any of the previous clauses, further comprising one or more cooling plates.15. The linear actuator of any of the previous clauses, wherein one of the one or more cooling plates is positioned on top of the ferromagnetic bridge cap and in between the ferromagnetic bridge cap and the plurality of magnets.16. The linear actuator of any of the previous clauses, wherein a second one of the one or more cooling plates is positioned under the plurality of electric coils and between a base of the ferromagnetic armature core and the plurality of electric coils.17. The linear actuator of any of the previous clauses, wherein a load angle of a commutated electromagnetic excitation is offset by less than half a radian to reduce cogging.18. A semiconductor device manufacturing method, the method comprising: receiving a substrate with a photoresist layer; directing radiation from a radiation source to transfer a pattern from a reticle onto the photoresist layer; actuating the reticle using a linear actuator comprising: a ferromagnetic armature core comprising a plurality of ferromagnetic teeth defining a plurality of slots therebetween; a plurality of electric coils, each of which are wound around one of the plurality of ferromagnetic teeth; a plurality of magnets arranged in an array and positioned over the plurality of ferromagnetic teeth along a common axis of motion; and a ferromagnetic bridge cap positioned between the plurality of magnets and the plurality of ferromagnetic teeth and at least partially covering each of the plurality of slots; and removing a portion of the photoresist layer to form a pattern over the substrate.19. The semiconductor device manufacturing method of clause 18, wherein the ferromagnetic bridge cap entirely covers each of the plurality of slots.20. The semiconductor device manufacturing method of any of the previous clauses, wherein the ferromagnetic bridge cap has a thickness of less than 1 mm.21. The semiconductor device manufacturing method of any of the previous clauses, wherein the ferromagnetic bridge cap comprises repeating intervals of a thicker strip of ferromagnetic material and a thinner strip of ferromagnetic material.22. The semiconductor device manufacturing method of any of the previous clauses, wherein the ferromagnetic bridge cap is configured to reduce cogging when the linear actuator is activated to move along the common axis of motion.23. The semiconductor device manufacturing method of any of the previous clauses, wherein the ferromagnetic bridge cap further comprises one or more cooling plates.24. The semiconductor device manufacturing method of any of the previous clauses, wherein one of the one or more cooling plates is positioned on top of the ferromagnetic bridge cap and in between the ferromagnetic bridge cap and the plurality of magnets.25. The semiconductor device manufacturing method of any of the previous clauses, wherein a second one of the one or more cooling plates is positioned under the plurality of electric coils and between a base of the ferromagnetic armature core and the plurality of electric coils.26. The semiconductor device manufacturing method of any of the previous clauses, wherein one of the one or more cooling plates is positioned within a slot of the plurality of slots and parallel to the ferromagnetic teeth.27. The semiconductor device manufacturing method of any of the previous clauses, wherein a load angle of a commutated electromagnetic excitation is offset by less than half a radian to reduce cogging.

[0069] While the concepts disclosed herein may be used for a linear actuator associated with wafer manufacturing on a substrate such as a silicon wafer, it shall be understood that the disclosed concepts may be used with any type of manufacturing system that may include a linear actuator, e.g., those used for manufacturing on substrates other than silicon wafers. In addition, the combination and subcombinations of disclosed elements may comprise separate embodiments. For example, the cooling system, and an associated lithography apparatus that includes the cooling system may comprise separate embodiments, and / or these features may be used together in the same embodiment.

[0070] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. A linear actuator comprising: a ferromagnetic armature core comprising a plurality of ferromagnetic teeth defining a plurality of slots therebetween; a plurality of electric coils, each of which are wound around one of the plurality of ferromagnetic teeth; a plurality of magnets arranged in an array and positioned over the plurality of ferromagnetic teeth along a common axis of motion; and a ferromagnetic bridge cap positioned between the plurality of magnets and the plurality of ferromagnetic teeth and at least partially covering each of the plurality of slots.

2. The linear actuator of claim 1, wherein the ferromagnetic bridge cap entirely covers each of the plurality of slots.

3. The linear actuator of claim 1, wherein the ferromagnetic bridge cap has a thickness of less than 1 mm.

4. The linear actuator of claim 1, wherein the ferromagnetic bridge cap comprises repeating intervals of a thicker strip of ferromagnetic material and a thinner strip of ferromagnetic material.

5. The linear actuator of claim 1, wherein the ferromagnetic bridge cap is configured to reduce cogging when the linear actuator is activated to move along the common axis of motion.

6. The linear actuator of claim 1, further comprising one or more cooling plates, wherein: one of the one or more cooling plates is positioned on top of the ferromagnetic bridge cap and in between the ferromagnetic bridge cap and the plurality of magnets; and a second one of the one or more cooling plates is positioned under the plurality of electric coils and between a base of the ferromagnetic armature core and the plurality of electric coils.

7. The linear actuator of claim 6, wherein one of the one or more cooling plates is positioned within a slot of the plurality of slots and parallel to the ferromagnetic teeth.

8. The linear actuator of claim 1, wherein a load angle of a commutated electromagnetic excitation is offset by less than half a radian to reduce cogging.

9. A linear actuator comprising:a ferromagnetic armature core comprising a first plurality of ferromagnetic teeth defining a plurality of slots therebetween; a ferromagnetic bridge cap comprising a second plurality of ferromagnetic teeth each positioned within a respective one of the plurality of slots; a plurality of electric coils, each of which are wound around one of the ferromagnetic teeth of the second plurality of ferromagnetic teeth of the ferromagnetic bridge cap; and a plurality of magnets arranged in an array and positioned over the ferromagnetic bridge cap and arranged along a common axis of motion with the linear actuator.

10. The linear actuator of claim 9, wherein a portion of the ferromagnetic bridge cap that covers each of the plurality of electric coils has a thickness of less than 1 mm.

11. The linear actuator of claim 9, wherein the ferromagnetic bridge cap is configured to reduce cogging when the linear actuator is activated to move along the common axis of motion.

12. The linear actuator of claim 9, further comprising one or more cooling plates, wherein one of the one or more cooling plates is positioned on top of the ferromagnetic bridge cap and in between the ferromagnetic bridge cap and the plurality of magnets.

13. The linear actuator of claim 12, wherein a second one of the one or more cooling plates is positioned under the plurality of electric coils and between a base of the ferromagnetic armature core and the plurality of electric coils.

14. The linear actuator of claim 9, wherein a load angle of a commutated electromagnetic excitation is offset by less than half a radian to reduce cogging.

15. A semiconductor device manufacturing method, the method comprising: receiving a substrate with a photoresist layer; directing radiation from a radiation source to transfer a pattern from a reticle onto the photoresist layer; actuating the reticle using a linear actuator comprising: a ferromagnetic armature core comprising a plurality of ferromagnetic teeth defining a plurality of slots therebetween; a plurality of electric coils, each of which are wound around one of the plurality of ferromagnetic teeth; a plurality of magnets arranged in an array and positioned over the plurality of ferromagnetic teeth along a common axis of motion; anda ferromagnetic bridge cap positioned between the plurality of magnets and the plurality of ferromagnetic teeth and at least partially covering each of the plurality of slots; and removing a portion of the photoresist layer to form a pattern over the substrate.

Images