Device for sensing alignment marks

Abstract

Apparatus and methods for sensing multiple alignment marks, wherein the optical axis of a detector is divided into multiple axes, each of which can detect a separate alignment mark substantially simultaneously to produce a signal that can then be multiplexed and presented to a single detector or multiple detectors, thereby allowing more rapid detection of multiple marks.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 970,481 filed on February 5, 2020, and the entire contents of the U.S. Provisional Patent Application are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to device fabrication using photolithography techniques. In particular, the present disclosure relates to sensing and analyzing alignment marks on a substrate to characterize and control a semiconductor photolithography process. Background Art

[0004] Lithographic equipment can be used in the manufacture of integrated circuits (ICs). For this application, a pattern forming device, alternatively referred to as a mask or reticle, can be used to produce a circuit pattern to be formed on a single layer of the IC. The pattern can be transferred to a target portion (e.g., including a portion of a die, one or several 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 grid of adjacent target portions that are patterned continuously.

[0005] Known lithographic apparatus 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 substrate synchronously parallel or anti-parallel to a given direction (the "scanning" direction) while a radiation beam scans the pattern in this direction. A pattern can also be transferred from a patterning device to a substrate by imprinting the pattern onto the substrate.

[0006] ICs are built up layer by layer, and modern ICs can have 30 or more layers. Overlay on product (OPO) is a measure of the system's ability to accurately print these layers on top of each other. Successive layers or multiple processes on the same layer must be accurately aligned with the previous layer. Otherwise, the electrical contact between the structures will be poor and the resulting device will not perform to specification. Good overlap improves process yield and enables smaller product patterns to be printed. The overlay error between successive layers formed in or on the patterned substrate is controlled by various parts or components of the exposure equipment of the lithographic apparatus.

[0007] Process-induced wafer errors are a significant barrier to OPO performance. Process-induced errors are caused by the complexity of printed patterns and the increasing number of printed layers. Such errors have a relatively high spatial variation: within a given wafer, the variation varies from wafer to wafer. .

[0008] In order to control the lithography process to accurately place device features on the substrate, one or more alignment marks are usually provided, for example, on the substrate, and the lithography equipment includes one or more alignment sensors, which can be used to accurately measure the position of the mark. The alignment sensor can effectively serve as a position measurement device. Different types of marks and different types of alignment sensors are known from different times and different manufacturers. Measuring the relative positions of several alignment marks in the field can correct the wafer errors caused by the process. The alignment error changes in the field can be used to fit the model for correcting the OPO in the field.

[0009] Lithographic apparatus are known to use a number of alignment systems to align a substrate relative to the lithographic apparatus. For example, any type of alignment sensor can be used to obtain data, such as a SMASH (SMart Alignment Sensor Hybrid) sensor, as described in U.S. Pat. No. 6,961,116, entitled “Lithographic Apparatus, Device Manufacturing Method, and Device Manufactured Thereby,” published on November 1, 2005, the entire contents of which are hereby incorporated by reference, which employs a self-referencing interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software; or, an ATHENA (Advanced Technology using Highorder ENhancement of Alignment), as described in U.S. Pat. No. 6,297,876, entitled “Lithographic Projection Apparatus with an Alignment System for Aligning Substrate on Mask,” published on October 2, 2001, the entire contents of which are hereby incorporated by reference, which directs each of the seven diffraction orders to a dedicated detector; or an ORION sensor, which uses multiple polarizations for each available signal (color).

[0010] Reference is made in particular to European application number EP 1 372 040 A1 entitled “Lithographic Apparatus and Device Manufacturing Method”, granted on March 5, 2008, the entire contents of which are hereby incorporated by reference. EP 1 372 040 A1 describes an alignment system using a self-referencing interferometer that produces two superimposed images of an alignment mark. The two images are rotated 180° relative to each other. EP 1 372 040 A1 also describes detecting intensity changes of the interference Fourier transform of the two images in the pupil plane. These intensity changes correspond to the phase difference between the different diffraction orders of the two images, and position information is derived from the phase difference, which is required for the alignment process. Reference is also made to U.S. Patent No. 8,610,898 entitled “Self-Referencing Interferometer, Alignment System, and Lithographic Apparatus” published on December 17, 2013, the entire contents of which are hereby incorporated by reference.

[0011] Alignment sensors (such as SMASH, Athena, and ORION) currently measure alignment marks in the form of scribe marks to find the alignment position. From this alignment position, the wafer grid is determined. An accurate wafer grid reduces the likelihood of overlay errors. A dense sample of alignment marks can help reduce intra-field errors.

[0012] Thus, there is a potential benefit of being able to measure a larger number of markers (such as, for example, the ability to align with in-field problems). However, typically conventional sensors are limited to measuring about forty marker pairs because they measure the markers one by one in succession, and a larger number of pairs results in an unacceptable time penalty, i.e., time loss. The ability to mitigate this time penalty by increasing the scan speed is limited because increasing the scan speed can cause dynamic problems.

[0013] Thus, it would be desirable to be able to measure more alignment marks without having to increase the scanning speed. Summary of the invention

[0014] A simplified overview of one or more embodiments is given below to provide a basic understanding of the embodiments. This overview is not an exhaustive overview of all contemplated embodiments, and is not intended to identify key or important elements of all embodiments, nor is it intended to delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to a more detailed description presented later.

[0015] According to one aspect of the embodiment, the optical axis of the sensor is split so that the sensor can collect information from multiple locations on the wafer simultaneously. The axis of the alignment sensor can be conceptualized as an imaginary line about which the image rotates. The alignment sensors make their measurements relative to this axis. For systems including an interferometer in the form of a self-referencing interferometer (such as SMASH and ORION sensors), this axis can be projected from the self-referencing interferometer back to the wafer through the objective of the optical system used to collect light diffracted by the alignment marks.

[0016] According to an aspect of the embodiment, the axis of the interferometer is split into a plurality of different axes, for example by a beam splitter. The axis can be split into three axes, for example, but this is only an example and the axis can be split into a larger number of axes. Each of the plurality of axes has its own objective lens and can have its own illumination. The signals from the corresponding alignment marks arrive at a common detector. The signals are demultiplexed to separate the alignment information from the three alignment marks on the wafer.

[0017] According to one aspect of the embodiment, a device for sensing a plurality of alignment marks is disclosed, the device comprising: an illumination system arranged to provide a plurality of light beams to illuminate corresponding alignment marks in the plurality of alignment marks; a diffraction light collection optical system arranged to collect diffracted light from a plurality of diffraction light beams diffracted from corresponding alignment marks in the plurality of alignment marks; an interferometer arranged to receive the diffracted light collected by the light collection system and configured to generate an optical output based on the diffracted light; and a detection system arranged to receive the optical output and configured to generate an electrical signal based on the optical output. The illumination system may include: an illumination source for generating a source light beam; and a plurality of beam splitters arranged to receive the source light beam, transmit a transmitted portion of the source light beam, and redirect a redirected portion of the source light beam toward a corresponding alignment mark in the plurality of alignment marks. The illumination system may be arranged to provide the plurality of light beams to provide coaxial illumination of corresponding alignment marks in the plurality of alignment marks. The illumination system may be arranged to provide the plurality of light beams to provide off-axis illumination of corresponding alignment marks in the plurality of alignment marks. The plurality of alignment marks may include a first pair of alignment marks and a second pair of alignment marks, each alignment mark in the first pair of alignment marks including a first grating having a first pitch, each alignment mark in the second pair of alignment marks including a second grating having a second pitch different from the first pitch, in which case the device may further include a demultiplexer configured to demultiplex light diffracted by the first grating and light diffracted by the second grating based on the second pitch different from the first pitch. The demultiplexer may be configured to demultiplex light diffracted by the first grating and light diffracted by the second grating by offsetting the pupil position of the light diffracted by the first grating relative to the pupil position of the light diffracted by the second grating. A first optical output of light diffracted by the first grating demultiplexer may have a first frequency and a second optical output of light diffracted by the second grating demultiplexer may have a second frequency different from the first frequency, in which case the demultiplexer may be configured to demultiplex the light diffracted by the first grating and the light diffracted by the second grating based on the first frequency and the second frequency. The apparatus may also include: means for causing relative motion of the plurality of alignment marks and the diffracted light collection optical system; and a demultiplexer configured to demultiplex the light diffracted by the plurality of alignment marks based on the timing of receiving the optical signal by the detection system.The diffracted light collection optical system may further comprise an optical component arranged to produce a lateral physical separation between the respective diffracted light beams relative to the propagation direction, in which case the apparatus may further comprise a demultiplexer configured to demultiplex the light diffracted by the plurality of alignment marks based on the lateral position of the light diffracted by the plurality of alignment marks. The illumination system may comprise a plurality of illumination sources arranged to provide respective ones of the plurality of light beams to illuminate respective ones of the plurality of alignment marks. The apparatus may comprise: a control loop arranged to cause a temporal shift between moments when the respective ones of the plurality of illumination sources illuminate respective ones of the plurality of alignment marks; and a demultiplexer configured to demultiplex the light diffracted by the plurality of alignment marks based on the timing of receipt of the optical signal by the detection system. Each of the multiple illumination sources can be suitable for providing multiple light beams to illuminate corresponding alignment marks among the multiple alignment marks using corresponding light beams among the multiple light beams having corresponding wavelengths different from each other, and wherein the device also includes a demultiplexer, which is configured to demultiplex the light diffracted by the multiple alignment marks based on wavelength.

[0018] According to another aspect of the embodiment, a device for sensing alignment marks in an alignment pattern is disclosed, the device comprising: an illumination system, the illumination system being arranged to provide a first light beam for illuminating a first alignment mark, a second light beam for illuminating a second alignment mark, and a third light beam for illuminating a third alignment mark; a diffraction light collecting optical system, the diffraction light collecting optical system being arranged to collect diffracted light from the first alignment mark, the second alignment mark, and the third alignment mark; an interferometer, the interferometer being arranged to receive the diffracted light collected by the light collecting system and being configured to generate an optical output based on the diffracted light; and a detection system, the detection system being arranged to receive the optical output of the self-referencing interferometer and being configured to generate an electrical signal based on the optical output. The illumination system may include: an illumination source for generating a source beam; a first beam splitter arranged to receive the source beam, transmit a first transmitted portion of the source beam, and redirect the first redirected portion of the source beam toward the first alignment mark; a second beam splitter arranged to receive the source beam, transmit a second transmitted portion of the source beam, and redirect the second redirected portion of the source beam toward the second alignment mark; and a third beam splitter arranged to receive the source beam and redirect the third redirected portion of the source beam toward the third alignment mark. The illumination system may be arranged to provide the first beam, the second beam, and the third beam to provide on-axis illumination of a corresponding alignment mark among the first alignment mark, the second alignment mark, and the third alignment mark. The illumination system may be arranged to provide the first beam, the second beam, and the third beam to provide off-axis illumination of a corresponding alignment mark among the first alignment mark, the second alignment mark, and the third alignment mark. The first alignment mark may include a first grating having a first pitch, the second alignment mark may include a second grating having a second pitch different from the first pitch, and the third alignment mark may include a third grating having a third pitch different from the second pitch and the first pitch, and the device may further include a demultiplexer configured to demultiplex the light diffracted by the first grating, the light diffracted by the second grating, and the light diffracted by the third grating based on the first pitch, the second pitch, and the third pitch that are different from each other. The device may further include: a device for causing relative movement of a plurality of alignment marks among the first alignment mark, the second alignment mark, and the third alignment mark and the diffracted light collecting optical system; and a demultiplexer configured to demultiplex the light diffracted by the first alignment mark, the second alignment mark, and the third alignment mark based on the timing of receiving the optical signal by the detection system.The diffracted light collection optical system may further include an optical component arranged to produce a lateral physical separation between the respective diffracted light beams relative to the propagation direction, and the device may further include a demultiplexer configured to demultiplex the light diffracted by the plurality of alignment marks based on the lateral position of the light diffracted by the plurality of alignment marks. The illumination system may include a first illumination source, a second illumination source, and a third illumination source, the first illumination source, the second illumination source, and the third illumination source being arranged to provide a corresponding light beam among the first light beam, the second light beam, and the third light beam to illuminate a corresponding alignment mark among the first alignment mark, the second alignment mark, and the third alignment mark. The device may further include a control loop arranged to cause a time displacement between the moments when the corresponding illumination source among the first illumination source, the second illumination source, and the third illumination source illuminates the corresponding alignment mark among the first alignment mark, the second alignment mark, and the third alignment mark; and a demultiplexer configured to demultiplex the light diffracted by the first alignment mark, the second alignment mark, and the third alignment mark based on the timing of receiving the optical signal by the detection system. The corresponding illumination sources among the first illumination source, the second illumination source, and the third illumination source may be suitable for providing corresponding first light beams, second light beams, and third light beams to illuminate corresponding alignment marks among the first alignment mark, the second alignment mark, and the third alignment mark using corresponding light beams among the first light beams, the second light beam, and the third light beams having corresponding wavelengths different from each other, and the device may also include a demultiplexer configured to demultiplex light diffracted by the first alignment mark, the second alignment mark, and the third alignment mark based on wavelength.

[0019] According to another aspect of the embodiment, a method for sensing a plurality of alignment marks is disclosed, the method comprising the steps of providing a plurality of light beams to illuminate corresponding alignment marks of the plurality of alignment marks; collecting diffracted light from a plurality of diffracted light beams diffracted from corresponding alignment marks of the plurality of alignment marks; receiving the diffracted light collected by a light collection system using an interferometer and generating an optical output based on the diffracted light; and generating an electrical signal based on the optical output. The step of providing a plurality of light beams to illuminate corresponding alignment marks of the plurality of alignment marks of an illumination system may include: generating a source light beam; and providing a plurality of beam splitters, the plurality of beam splitters being arranged to receive the source light beam, transmit a transmitted portion of the source light beam, and redirect a redirected portion of the source light beam toward a corresponding alignment mark of the plurality of alignment marks. The step of providing a plurality of light beams to illuminate corresponding alignment marks of the plurality of alignment marks of an illumination system may include providing on-axis illumination of corresponding alignment marks of the plurality of alignment marks. The step of providing a plurality of light beams to illuminate corresponding alignment marks of the plurality of alignment marks of an illumination system may include providing off-axis illumination of corresponding alignment marks of the plurality of alignment marks. The plurality of alignment marks may include a first pair of alignment marks and a second pair of alignment marks, each alignment mark of the first pair of alignment marks including a first grating having a first pitch, each alignment mark of the second pair of alignment marks including a second grating having a second pitch different from the first pitch, and the method may further include the step of demultiplexing light diffracted by the first grating and light diffracted by the second grating based on the second pitch different from the first pitch. The demultiplexer may demultiplex the light diffracted by the first grating and the light diffracted by the second grating by shifting a pupil position of the light diffracted by the first grating relative to a pupil position of the light diffracted by the second grating. A first optical output of the light diffracted by the first grating demultiplexer may have a first frequency and a second optical output of the light diffracted by the second grating demultiplexer may have a second frequency different from the first frequency, and the demultiplexer may demultiplex the light diffracted by the first grating and the light diffracted by the second grating based on the first frequency and the second frequency. A diffraction light collecting optical system can be used to perform the step of collecting diffracted light from multiple diffraction light beams diffracted from corresponding alignment marks among the multiple alignment marks, and the method can also include the following steps: causing relative movement between the multiple alignment marks and the diffraction light collecting optical system; and demultiplexing the light diffracted by the multiple alignment marks according to the timing of generating an electrical signal based on the optical output.Collecting diffracted light from a plurality of diffracted light beams diffracted from respective ones of the plurality of alignment marks may include creating a lateral physical separation between the respective diffracted light beams relative to a propagation direction, and the method may further include demultiplexing the light diffracted by the plurality of alignment marks based on the lateral position of the light diffracted by the plurality of alignment marks. Providing a plurality of light beams to illuminate respective ones of the plurality of alignment marks; the illumination system may include using a plurality of illumination sources, the plurality of illumination sources being arranged to provide respective ones of the plurality of light beams to illuminate respective ones of the plurality of alignment marks. Providing a plurality of light beams to illuminate respective ones of the plurality of alignment marks may include causing a temporal shift between the moments when the respective ones of the plurality of illumination sources illuminate the respective ones of the plurality of alignment marks, and the method may further include demultiplexing the light diffracted by the plurality of alignment marks based on the timing of the optical output. The step of providing multiple light beams to illuminate corresponding alignment marks among the multiple alignment marks may include providing multiple light beams to illuminate corresponding alignment marks among the multiple alignment marks using corresponding light beams among the multiple light beams having corresponding wavelengths different from each other, and the method may also include demultiplexing light diffracted by the multiple alignment marks based on wavelength.

[0020] According to another aspect of the embodiment, a device for sensing multiple alignment marks is disclosed, the device comprising: an illumination system, the illumination system being arranged to provide multiple light beams to illuminate corresponding alignment marks among the multiple alignment marks; a diffraction light collecting optical system, the diffraction light collecting optical system being arranged to collect diffracted light from multiple diffraction light beams diffracted from corresponding alignment marks among the multiple alignment marks; a single interferometer, the single interferometer being arranged to receive the diffracted light collected by the light collecting system and being configured to generate an optical output based on the diffracted light; and a detection system, the detection system being arranged to receive the optical output and being configured to generate an electrical signal based on the optical output.

[0021] According to another aspect of the embodiment, a method for sensing multiple alignment marks is disclosed, the method comprising the following steps: providing multiple light beams to illuminate corresponding alignment marks among the multiple alignment marks; collecting diffracted light from multiple diffraction light beams diffracted from corresponding alignment marks among the multiple alignment marks; using a single interferometer to receive the diffracted light collected by a light collection system and generate an optical output based on the diffracted light; and generating an electrical signal based on the optical output.

[0022] Further embodiments, features, and advantages of the present invention as well as the structure and operation of various embodiments are described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate the methods and systems of the embodiments of the present invention by way of example and not limitation. Together with the detailed description, the drawings are also used to explain the principles and enable those skilled in the relevant art to make and use the methods and systems proposed herein. In the accompanying drawings, similar reference numerals represent the same or functionally similar elements.

[0024] Figure 1 Depicted are selected portions of a lithography system, such as a lithography system that may be used in accordance with aspects of the embodiments disclosed herein.

[0025] Figure 2 Selected portions or components of known alignment systems are depicted to explain the principles of operation of known alignment systems.

[0026] Figure 3 A system for analyzing alignment marks according to an aspect of the embodiments is depicted.

[0027] Figure 4A An alignment mark adapted to be measured is depicted according to an aspect of the embodiments.

[0028] Figure 4B Describe according to Figure 5 An aspect of the embodiment shown in FIG. 1 is an alignment mark suitable for being measured.

[0029] Figure 5 A system for analyzing alignment marks according to an aspect of the embodiments is depicted.

[0030] Figure 6 A system for analyzing alignment marks according to an aspect of the embodiments is depicted.

[0031] Figure 7 A system for analyzing alignment marks according to an aspect of the embodiments is depicted.

[0032] Figure 8 A system for analyzing alignment marks according to an aspect of the embodiments is depicted.

[0033] The structure and operation of the various embodiments of the present invention and other features and advantages of the present invention are described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein only for illustrative purposes. Based on the teachings contained herein, those skilled in the relevant art will understand additional embodiments. DETAILED DESCRIPTION

[0034] Various embodiments are now described with reference to the accompanying drawings, in which similar reference numerals are used to refer to similar elements. In the following description, for the purpose of explanation, many specific details are set forth to facilitate a thorough understanding of one or more embodiments. However, it may be apparent in some or all cases that any embodiment described below can be put into practice without adopting the specific design details described below. In other examples, well-known structures and devices are shown in block diagram form to facilitate description of one or more embodiments. A simplified overview of one or more embodiments is provided below to provide a basic understanding of the embodiments. This overview is not an exhaustive overview of all contemplated embodiments, and is not intended to identify the key or important elements of all embodiments, nor is it intended to describe the scope of any or all embodiments.

[0035] Embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium that can be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include a solid-state memory, a read-only memory (ROM), a random access memory (RAM), a disk storage medium, an optical storage medium, a flash memory device; electrical, optical, acoustic or other forms of propagation signals (e.g., carrier waves, infrared signals, digital signals, etc.), etc. In addition, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are merely for convenience, and that these actions are actually generated by a computing device, a processor, a controller, or other devices that execute firmware, software, routines, instructions, etc.

[0036] Figure 1 A lithographic apparatus is schematically depicted. The apparatus comprises an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or other suitable radiation), a support structure (e.g. mask table) MT configured to support a patterning device (e.g. mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters, a substrate table (e.g. wafer stage) WT configured to hold a substrate (e.g. a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate according to certain parameters, and a projection system (e.g. refractive projection lens system) PL configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0037] 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.

[0038] The support structure supports the pattern forming device, i.e., carries the weight of the pattern forming device. It holds the pattern forming device in a manner that depends on the orientation of the pattern forming device, the design of the lithographic apparatus and other conditions such as, for example, whether the pattern forming device is maintained in a vacuum environment. The support structure can hold the pattern forming device using mechanical, vacuum, electrostatic or other clamping techniques. The support structure can be a frame or a table, for example, which can be fixed or movable as required. The support structure can ensure that the pattern forming device is in a desired position (e.g. relative to the projection system). Any term "reticle" or "mask" used herein may be considered to be synonymous with the more general term "pattern forming device".

[0039] The term "patterning device" as used herein should be broadly interpreted as referring to any device that can be used to impart a pattern in the cross-section of the radiation beam so as to produce a pattern in the target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate (for example if the pattern includes phase-shifting features or so-called assist features). Typically, the pattern imparted to the radiation beam will correspond to a specific functional layer in a device (such as an integrated circuit) produced in the target portion.

[0040] The pattern forming device can be transmissive or reflective. Examples of pattern forming devices include masks, programmable mirror arrays, and programmable LCD (liquid crystal display) panels. Masks are well known in lithography and include mask types such as binary mask types, alternating phase shift mask types, attenuated phase shift mask types, and various hybrid mask types. An example of a programmable mirror array uses a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam reflected by the mirror matrix.

[0041] The term "projection system" as used herein should be broadly interpreted to include any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation used, or other factors such as the use of immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system".

[0042] As depicted here, the device is of the transmissive type (eg, employing a transmissive mask). Alternatively, the device may be of the reflective type (eg, using a programmable mirror array of the type mentioned above, or using a reflective mask).

[0043] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more mask tables). In such a "multi-stage" machine, the extra 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.

[0044] The lithographic apparatus may also be of a type in which at least a portion of the substrate may also be covered by a liquid having a relatively high refractive index (e.g., water) so as to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, such as the space between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of a projection system. The term "immersion" as used herein does not mean that structures such as substrates must be immersed in liquid, but rather "immersion" only means that liquid is located between the projection system and the substrate during exposure.

[0045] Reference again Figure 1 , the illuminator IL receives a radiation beam 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 a case, the source is not considered to constitute a part of the lithographic apparatus, and the radiation beam is transferred from the source SO to the illuminator IL by means of a beam delivery system BD comprising, for example, suitable directional mirrors and / or a beam expander. In other cases, the source may be an integral part of the lithographic apparatus (for example, when the source is a mercury lamp). The source SO and the illuminator IL, together with the beam delivery system BD provided when necessary, may be referred to as a radiation system.

[0046] The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer radial extent and / or the inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. Furthermore, the illuminator IL may comprise various other components, such as an integrator IN and a condenser CO. The illuminator may be used to adjust the radiation beam so as to have a desired uniformity and intensity distribution in its cross-section.

[0047] refer to Figure 1, the radiation beam B is incident on and patterned by the pattern forming device (e.g. mask MA), which is held on the support structure (e.g. mask table MT). Having traversed the mask MA, the radiation beam B passes through the projection system PL, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and a position sensor IF (e.g. an interferometer device, a linear encoder, a 2D encoder or a capacitive sensor), the substrate table WT can be accurately moved (e.g. to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and the further position sensor ( Figure 1 The first positioner PM is not explicitly depicted in the figure for accurately positioning the mask MA relative to the path of the radiation beam B. Typically, movement of the mask table MT may be achieved with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning) forming part of the first positioner PM. Similarly, movement of the substrate table WT may be achieved using a long-stroke module and a short-stroke module forming part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT may be connected only to a short-stroke actuator, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks occupy dedicated target portions, they may be located in the spaces between multiple target portions (these are referred to as scribe alignment marks). Similarly, in the case where more than one die is disposed on the mask MA, the mask alignment marks M1, M2 may be located between these dies. The wafer may also include additional marks, such as, for example, marks that are sensitive to variations in a chemical mechanical planarization (CMP) process as a step in wafer fabrication.

[0048] The targets P1 and / or P2 on the substrate W may be, for example, (a) a resist layer grating printed so that after development, the grating stripes consist of solid resist lines; or (b) a product layer grating; or (c) a composite grating stack in an overlapping target structure, comprising a resist grating overlapped or staggered on a product layer grating. The grating stripes may alternatively be etched into the substrate.

[0049] Figure 2A schematic overview of a known alignment system 10 is shown. A light source 11 emits a spatially coherent radiation beam which illuminates an alignment mark WM on a substrate (e.g. a wafer), which reflects the radiation as positive diffraction orders +n and negative diffraction orders -n. These diffraction orders are collimated by an objective lens 12 and enter a self-referencing interferometer (SRI) 13. The self-referencing interferometer outputs two images of the input rotated 180° relative to each other, which are superimposed and can therefore interfere. In a pupil plane 14, the superimposed Fourier transforms of these images (in which the different diffraction orders are separated) can be seen and can interfere. A detector 15 in the pupil plane detects the interfered diffraction orders to provide position information. Based on this position information, the substrate can be accurately aligned relative to the lithographic equipment. Figure 2 The right part of shows the formation of two superimposed images in the pupil plane 14; for one image, +n′ and -n′ are rotated +90° relative to the input diffraction orders +n and -n; for the other image, +n″ and -n″ are rotated -90° relative to the input diffraction orders +n and -n. In the pupil plane, the (+n′ and -n″)-order and (+n″ and -n′)-order interferences are respectively present.

[0050] The output of a sensor (such as just described) is typically relayed to a detector that detects the pattern of intensities in the sensor output. In the alignment sensor, the output sensor (single pixel detector) detects the intensity changes resulting from the interference between the + order and the - order. This interference produces two channels, the SUM channel, in which the electric field is added and the DIFF channel, in which the electric field is subtracted. The phases of these two channels are 180 degrees different from each other. The alignment position of the mark is calculated by measuring the phase of the signal in the case of the DIFF or SUM channel or a combination of these two channels. In such a system, all light is directed to the detector.

[0051] As noted above, according to one aspect of the embodiment, in order to measure multiple marks substantially simultaneously, the optical axis of the sensor is split so that the sensor can collect information from multiple locations on the wafer simultaneously. The axis of alignment of the sensor can be conceptualized as an imaginary line about which the image rotates. The alignment sensor measures relative to this axis. For a system that includes an interferometer in the form of a self-referencing interferometer, this axis can be projected from the self-referencing interferometer through the objective of the optical system back to the wafer to collect light diffracted by the alignment marks.

[0052] As described below, the axis of the interferometer can be split into a plurality of different axes, for example by a beam splitter. The axis can, for example, be split into three axes. The three axes will be described below for the purpose of a specific example, but it will be apparent that the axis can be split into a greater number of axes. Each of the plurality of axes has its own objective lens and can have its own separate illumination. The signals from the corresponding alignment marks can reach a common detector or a plurality of separate detectors. The signals are demultiplexed to separate the alignment information from the three alignment marks on the wafer.

[0053] As described more fully below, demultiplexing of the signals may be performed using any of a variety of methods. For example, each of the three different marks on the wafer (which has a grating with a given pitch) may have a different pitch. In this case, the signals may be separated spatially or by frequency, for example using Fourier decomposition. Demultiplexing the signals may also be achieved by using optical devices (such as optical mirrors and prisms in the pupil plane at the detector) that can guide the signals from each channel and separate them spatially. Here, the signals are separated laterally (i.e., in a direction lateral to the direction of propagation of the light). Multiple separate detectors may be used for this configuration. Alternatively, the illumination of the marks may be multiplexed in time, and the signals may be separated by gating the time intervals of the detectors. Alternatively, the alignment marks may be illuminated with light of different wavelengths, and the signals from the alignment marks may be separated by frequency.

[0054] In these arrangements, a single self-referencing interferometer can be used to measure multiple alignment marks.

[0055] Figure 3 An example of a system according to an aspect of the embodiment is shown in FIG. Figure 3 As shown in FIG. 3 , an alignment pattern 300 consisting of alignment marks 302, 304 and 306 is provided on a substrate 310. The light source 320 generates a light beam 330. A first beam splitter 340 splits the beam 330 into a first component directed toward the alignment mark 302 in the alignment pattern 300 and a second portion that propagates forward. It will be appreciated that such a beam splitter and other beam splitters described herein may advantageously include an objective lens. The second portion arrives at a second beam splitter 350, which directs a portion of the beam toward the alignment mark 304 and another portion toward a third beam splitter 360. The third beam splitter 360 directs the portion of the beam it receives to a third alignment mark 306.

[0056] In each case, the portion of the beam that reaches the alignment mark is diffracted by the alignment mark. The diffracted light propagates backward through these beam splitters. The light 370 diffracted by the alignment mark 302 hits the folding mirror 380 and is directed toward the splitter 390. Similarly, the light 400 diffracted by the second alignment mark 304 is relayed to the splitter 390, and the light 410 is relayed to the splitter 390 by the folding mirror 420. The output of the splitter 390 reaches the self-referencing interferometer 430. The optical output of the self-referencing interferometer 430 is supplied to the detector 440. In this embodiment, the lights 370, 400 and 410 are a pair of beams, that is, these numbers do not represent a single beam, but rather the path of the pair of diffraction orders.

[0057] Various methods can be used to separate the signal from each alignment mark. For example, Figure 3 The alignment marks 302, 304 and 306 in may be gratings with different pitches. Figure 4A Shown in Figure 3 390 of the diffraction order in the pupil after. Because the pitches 302, 304 and 306 are different, they diffract to show different order pairs, namely pairs 302a and 302b, pairs 304a and 304b, and pairs 306a, 306b. In this way, the signals from these paired alignment marks can be distinguished. These signals can also be separated spectrally, for example, by Fourier decomposition.

[0058] The signals can also be separated in time. Figure 4B and Figure 5 An apparatus for achieving this is shown in FIG. Figure 4B In the direction indicated by arrow A, the substrate 310 carrying the alignment marks 302a and 302b and collecting the diffracted light and including Figure 5 There is relative motion between the optical systems of the beam splitter shown in FIG. Figure 5 The arrangement further comprises a light valve 450 which allows the optical output to pass to the detector 440 of the optical output of the self-referencing interferometer 430 only when it is known that the alignment marks 302a, 302b are located in a region where they diffract light from the source 320. By synchronizing this activity, the alignment marks that cause the optical signal to reach the detector 440 can be identified.

[0059] Alternatively, if Figure 6As shown in , demultiplexing the signals can also be achieved by using an optical device 460 (such as an optical mirror and prism located in the pupil plane) that can guide the signals from each channel and spatially separate the signals. Here, the signals are separated laterally (i.e., in a direction lateral to the direction of propagation of the light). Multiple separate detectors 442, 446 and 448 can be used in this configuration as shown, or a single camera with multiple detectors can be used.

[0060] Each of the individual alignment marks may be provided with a separate illuminator, such as Figure 7 As shown in Figure 7 , illuminator 322 illuminates alignment mark 302. Similarly, illuminator 324 illuminates alignment mark 304 and illuminator 326 illuminates alignment mark 306. This allows for temporal separation of the signals arriving at the detector 440. In other words, if only one of the illuminators illuminates an alignment mark, the optical signal arriving at the detector 440 at that time is the signal resulting from the illumination of the alignment mark. In addition, the illuminators can be configured to provide illumination with different wavelengths. Spectral filters can then be used at the detector to distinguish between such illumination of different wavelengths. Alternatively, multiple detectors can be employed, one for each wavelength.

[0061] In the examples described above, coaxial illumination was used to illuminate the alignment marks. Figure 8 An apparatus is shown in which off-axis illumination is used. In other words, the illumination is incident at an angle to the alignment mark and the optical axis of the detector. The incident light strikes the photomask at an oblique angle rather than perpendicular to the photomask, i.e., the incident light is not parallel to the axis of the optical system. This allows the measurement of marks with a smaller pitch. Off-axis illumination can be used for any arrangement of the apparatus described above. As shown, the off-axis illumination is bilaterally symmetrical, so that illuminators 322 and 323 illuminate the alignment mark 302. Similarly, illuminators 324 and 325 illuminate the alignment mark 304 and illuminators 326 and 327 illuminate the alignment mark 306.

[0062] Other aspects of the invention are set forth in the following numbered aspects:

[0063] 1. A device for sensing a plurality of alignment marks, the device comprising:

[0064] an illumination system arranged to provide a plurality of light beams to illuminate respective alignment marks of the plurality of alignment marks;

[0065] a diffraction light collecting optical system arranged to collect diffracted light from a plurality of diffracted light beams diffracted from corresponding alignment marks among the plurality of alignment marks;

[0066] an interferometer arranged to receive the diffracted light collected by the light collection system and configured to generate an optical output based on the diffracted light; and

[0067] A detection system is arranged to receive the optical output and is configured to generate an electrical signal based on the optical output.

[0068] 2. The apparatus according to claim 1, wherein the illumination system comprises:

[0069] an illumination source for generating a source beam; and

[0070] A plurality of beam splitters are arranged to receive the source beam, transmit a transmitted portion of the source beam, and redirect the redirected portion of the source beam toward a corresponding alignment mark of the plurality of alignment marks.

[0071] 3. The apparatus of clause 1, wherein the illumination system is arranged to provide the plurality of light beams to provide coaxial illumination of respective alignment marks of the plurality of alignment marks.

[0072] 4. The apparatus of clause 1, wherein the illumination system is arranged to provide the plurality of light beams to provide off-axis illumination of respective alignment marks of the plurality of alignment marks.

[0073] 5. An apparatus according to aspect 1, wherein the plurality of alignment marks include a first pair of alignment marks and a second pair of alignment marks, each alignment mark in the first pair of alignment marks includes a first grating having a first pitch, each alignment mark in the second pair of alignment marks includes a second grating having a second pitch different from the first pitch, and wherein the apparatus further includes a demultiplexer configured to demultiplex light diffracted by the first grating and light diffracted by the second grating based on the second pitch different from the first pitch.

[0074] 6. A device according to aspect 5, wherein the demultiplexer is configured to demultiplex the light diffracted by the first grating and the light diffracted by the second grating by offsetting the pupil position of the light diffracted by the first grating relative to the pupil position of the light diffracted by the second grating.

[0075] 7. An apparatus according to aspect 5, wherein a first optical output of light diffracted by the first grating demultiplexer has a first frequency and a second optical output of light diffracted by the second grating demultiplexer has a second frequency different from the first frequency, and wherein the demultiplexer is configured to demultiplex the light diffracted by the first grating and the light diffracted by the second grating based on the first frequency and the second frequency.

[0076] 8. The apparatus according to aspect 1, further comprising:

[0077] means for causing relative movement of the plurality of alignment marks and the diffraction light collecting optical system; and

[0078] A demultiplexer is configured to demultiplex light diffracted by the plurality of alignment marks based on a timing at which the optical signal is received by the detection system.

[0079] 9. The apparatus of clause 1, wherein the diffracted light collection optical system further comprises an optical component arranged to produce a lateral physical separation between the respective diffracted light beams relative to the propagation direction,

[0080] And wherein the apparatus further comprises a demultiplexer configured to demultiplex the light diffracted by the plurality of alignment marks based on the lateral position of the light diffracted by the plurality of alignment marks.

[0081] 10. The apparatus of clause 1, wherein the illumination system comprises a plurality of illumination sources arranged to provide respective ones of the plurality of light beams to illuminate respective ones of the plurality of alignment marks.

[0082] 11. Apparatus according to aspect 10, further comprising a control loop arranged to cause a temporal shift between times when a corresponding plurality of illumination sources illuminate corresponding alignment marks of the plurality of alignment marks; and

[0083] A demultiplexer is configured to demultiplex light diffracted by the plurality of alignment marks based on a timing at which the optical signal is received by the detection system.

[0084] 12. An apparatus according to aspect 10, wherein corresponding illumination sources among the multiple illumination sources are suitable for providing multiple light beams to illuminate corresponding alignment marks among the multiple alignment marks using corresponding light beams among the multiple light beams having corresponding wavelengths different from each other, and wherein the apparatus further comprises a demultiplexer configured to demultiplex light diffracted by the multiple alignment marks based on wavelength.

[0085] 13. An apparatus for sensing an alignment mark in an alignment pattern, the apparatus comprising:

[0086] an illumination system arranged to provide a first light beam for illuminating the first alignment mark, a second light beam for illuminating the second alignment mark, and a third light beam for illuminating the third alignment mark;

[0087] a diffraction light collecting optical system arranged to collect diffraction light from the first alignment mark, the second alignment mark, and the third alignment mark;

[0088] an interferometer arranged to receive the diffracted light collected by the light collection system and configured to generate an optical output based on the diffracted light; and

[0089] A detection system is arranged to receive the optical output of the self-referencing interferometer and is configured to generate an electrical signal based on the optical output.

[0090] 14. The apparatus of clause 13, wherein the illumination system comprises:

[0091] an illumination source, the illumination source being used to generate a source beam;

[0092] a first beam splitter arranged to receive the source beam, transmit a first transmitted portion of the source beam, and redirect the first redirected portion of the source beam toward the first alignment mark;

[0093] a second beam splitter arranged to receive the source beam, transmit a second transmitted portion of the source beam, and redirect a second redirected portion of the source beam toward the second alignment mark; and

[0094] A third beam splitter is arranged to receive the source beam and redirect a third redirected portion of the source beam towards the third alignment mark.

[0095] 15. The apparatus of clause 13, wherein the illumination system is arranged to provide the first light beam, the second light beam, and the third light beam to provide coaxial illumination of corresponding alignment marks among the first alignment mark, the second alignment mark, and the third alignment mark.

[0096] 16. The apparatus of clause 13, wherein the illumination system is arranged to provide the first light beam, the second light beam, and the third light beam to provide off-axis illumination of respective ones of the first alignment mark, the second alignment mark, and the third alignment mark.

[0097] 17. The apparatus of clause 13, wherein the first alignment mark comprises a first grating having a first pitch, the second alignment mark comprises a second grating having a second pitch different from the first pitch, and the third alignment mark comprises a third grating having a third pitch different from the second pitch and the first pitch, and

[0098] The apparatus further includes a demultiplexer configured to demultiplex the light diffracted by the first grating, the light diffracted by the second grating, and the light diffracted by the third grating based on the first pitch, the second pitch, and the third pitch which are different from each other.

[0099] 18. The apparatus according to aspect 13, further comprising

[0100] means for causing relative movement of a plurality of alignment marks among the first alignment mark, the second alignment mark, and the third alignment mark and the diffraction light collecting optical system; and

[0101] A demultiplexer is configured to demultiplex light diffracted by the first alignment mark, the second alignment mark, and the third alignment mark based on a timing at which the optical signal is received by the detection system.

[0102] 19. The apparatus of clause 13, wherein the diffracted light collection optical system further comprises an optical component arranged to produce a lateral physical separation between the respective diffracted light beams relative to the propagation direction,

[0103] And wherein the apparatus further comprises a demultiplexer configured to demultiplex the light diffracted by the plurality of alignment marks based on the lateral position of the light diffracted by the plurality of alignment marks.

[0104] 20. An apparatus according to aspect 13, wherein the illumination system includes a first illumination source, a second illumination source, and a third illumination source, and the first illumination source, the second illumination source, and the third illumination source are arranged to provide corresponding beams of the first light beam, the second light beam, and the third light beam to illuminate corresponding alignment marks of the first alignment mark, the second alignment mark, and the third alignment mark.

[0105] 21. The apparatus of clause 20, further comprising a control loop arranged to cause a temporal shift between times at which respective ones of the first, second, and third illumination sources illuminate respective ones of the first, second, and third alignment marks; and

[0106] A demultiplexer is configured to demultiplex light diffracted by the first alignment mark, the second alignment mark, and the third alignment mark based on a timing at which the optical signal is received by the detection system.

[0107] 22. An apparatus according to aspect 20, wherein corresponding ones of the first illumination source, the second illumination source, and the third illumination source are suitable for providing corresponding first light beams, second light beams, and third light beams to illuminate corresponding ones of the first alignment mark, the second alignment mark, and the third alignment mark using corresponding ones of the first light beams, the second light beam, and the third light beams having corresponding wavelengths different from each other, and wherein the apparatus further comprises a demultiplexer configured to demultiplex light diffracted by the first alignment mark, the second alignment mark, and the third alignment mark based on wavelength.

[0108] 23. A method for sensing a plurality of alignment marks, the method comprising the steps of:

[0109] providing a plurality of light beams to illuminate corresponding alignment marks among the plurality of alignment marks;

[0110] collecting diffracted light from a plurality of diffracted light beams diffracted from corresponding alignment marks among the plurality of alignment marks;

[0111] receiving the diffracted light collected by the light collection system using an interferometer and generating an optical output based on the diffracted light; and

[0112] An electrical signal is generated based on the optical output.

[0113] 24. The method of sensing a plurality of alignment marks according to aspect 23, wherein the step of providing a plurality of light beams to illuminate corresponding alignment marks of the plurality of alignment marks of the illumination system comprises:

[0114] generating a source light beam; and

[0115] A plurality of beam splitters are provided, and the plurality of beam splitters are arranged to receive the source light beam, transmit a transmitted portion of the source light beam, and redirect the redirected portion of the source light beam toward a corresponding alignment mark of the plurality of alignment marks.

[0116] 25. A method for sensing multiple alignment marks according to aspect 23, wherein the step of providing multiple light beams to illuminate corresponding alignment marks among the multiple alignment marks of the illumination system includes providing coaxial illumination of corresponding alignment marks among the multiple alignment marks.

[0117] 26. A method for sensing multiple alignment marks according to aspect 23, wherein the step of providing multiple light beams to illuminate corresponding alignment marks among the multiple alignment marks of the illumination system includes providing off-axis illumination of corresponding alignment marks among the multiple alignment marks.

[0118] 27. A method for sensing multiple alignment marks according to aspect 23, wherein the multiple alignment marks include a first pair of alignment marks and a second pair of alignment marks, each alignment mark in the first pair of alignment marks includes a first grating having a first pitch, each alignment mark in the second pair of alignment marks includes a second grating having a second pitch different from the first pitch, and wherein the method also includes a step of demultiplexing light diffracted by the first grating and light diffracted by the second grating based on the second pitch different from the first pitch.

[0119] 28. A method for sensing multiple alignment marks according to aspect 27, wherein the demultiplexer demultiplexes the light diffracted by the first grating and the light diffracted by the second grating by offsetting the pupil position of the light diffracted by the first grating relative to the pupil position of the light diffracted by the second grating.

[0120] 29. A method for sensing multiple alignment marks according to aspect 27, wherein a first optical output of light diffracted by the first grating demultiplexer has a first frequency and a second optical output of light diffracted by the second grating demultiplexer has a second frequency different from the first frequency, and wherein the demultiplexer demultiplexes the light diffracted by the first grating and the light diffracted by the second grating based on the first frequency and the second frequency.

[0121] 30. The method of sensing a plurality of alignment marks according to aspect 23, wherein the step of collecting diffracted light from a plurality of diffracted light beams diffracted from corresponding alignment marks among the plurality of alignment marks is performed using a diffraction light collecting optical system, and wherein the method further comprises the steps of:

[0122] causing relative movement between the plurality of alignment marks and the diffraction light collecting optical system; and

[0123] Light diffracted by the plurality of alignment marks is demultiplexed according to a timing of generating an electrical signal based on the optical output.

[0124] 31. The method of sensing a plurality of alignment marks according to clause 23, wherein collecting diffracted light from a plurality of diffracted light beams diffracted from respective ones of the plurality of alignment marks comprises creating a lateral physical separation between the respective diffracted light beams relative to a propagation direction, and

[0125] And wherein the method further comprises demultiplexing light diffracted by the plurality of alignment marks based on a lateral position of the light diffracted by the plurality of alignment marks.

[0126] 32. A method for sensing multiple alignment marks according to aspect 23, wherein multiple light beams are provided to illuminate corresponding alignment marks among the multiple alignment marks; the illumination system includes using multiple illumination sources, and the multiple illumination sources are arranged to provide corresponding light beams among the multiple light beams to illuminate corresponding alignment marks among the multiple alignment marks.

[0127] 33. A method of sensing a plurality of alignment marks according to aspect 23, wherein the step of providing a plurality of light beams to illuminate corresponding ones of the plurality of alignment marks comprises causing a temporal shift between times when corresponding ones of the plurality of illumination sources illuminate corresponding ones of the plurality of alignment marks, and

[0128] Wherein the method further comprises demultiplexing light diffracted by the plurality of alignment marks based on the timing of the optical output.

[0129] 34. A method for sensing multiple alignment marks according to aspect 23, wherein the step of providing multiple light beams to illuminate corresponding alignment marks among the multiple alignment marks includes providing multiple light beams to illuminate corresponding alignment marks among the multiple alignment marks using corresponding light beams among the multiple light beams having corresponding wavelengths different from each other, and wherein the method also includes demultiplexing light diffracted by the multiple alignment marks based on wavelength.

[0130] 35. An apparatus for sensing a plurality of alignment marks, the apparatus comprising:

[0131] an illumination system arranged to provide a plurality of light beams to illuminate respective alignment marks of the plurality of alignment marks;

[0132] a diffraction light collecting optical system arranged to collect diffracted light from a plurality of diffracted light beams diffracted from corresponding alignment marks among the plurality of alignment marks;

[0133] a single interferometer arranged to receive the diffracted light collected by the light collection system and configured to produce an optical output based on the diffracted light; and

[0134] A detection system is arranged to receive the optical output and is configured to generate an electrical signal based on the optical output.

[0135] 36. A method for sensing a plurality of alignment marks, the method comprising the steps of:

[0136] providing a plurality of light beams to illuminate corresponding alignment marks among the plurality of alignment marks;

[0137] collecting diffracted light from a plurality of diffracted light beams diffracted from corresponding alignment marks among the plurality of alignment marks;

[0138] using a single interferometer to receive the diffracted light collected by the light collection system and to generate an optical output based on the diffracted light; and

[0139] An electrical signal is generated based on the optical output.

[0140] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns of magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc. It will be understood by those skilled in the art that in the context of such alternative applications, any term "wafer" or "die" used herein may be considered synonymous with the more general term "substrate" or "target portion", respectively. The substrate referred to herein may be processed before or after exposure, for example in a track or coating development system (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. In addition, the substrate may be processed more than once, for example for the production of a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0141] Although specific reference has been made above using embodiments in the context of optical lithography, it will be appreciated that embodiments of the invention may be used in other applications, such as imprint lithography, and are not limited to optical lithography where the context permits. In imprint lithography, the topography in a patterning device defines the pattern produced on a substrate. The topography of the patterning device may be imprinted into a layer of resist supplied to the substrate, whereby the resist is cured by application of electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist, leaving a pattern therein.

[0142] The terms "radiation" and "beam" as used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of or about 365 nm, 355 nm, 248 nm, 593 nm, 557 nm, or 526 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 nm to 20 nm), as well as particle beams, such as ion beams or electron beams.

[0143] Although specific reference may be made herein to the use of the apparatus according to the invention in the manufacture of ICs, it should be clearly understood that such an apparatus may have many other possible applications. For example, such an apparatus may be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. One of ordinary skill in the art will understand that in the context of such alternative applications, any use of the terms "reticle", "wafer" or "die" in this context should be considered to be replaced by the more general terms "mask", "substrate" and "target portion", respectively.

[0144] The present invention has been described above by means of functional building blocks illustrating the implementation of the specified functions and their relationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined in this article. As long as the specified functions and their relationships are properly performed, the boundaries of the replacements can be defined.

[0145] The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can easily modify and / or adapt various applications such as these specific embodiments by applying knowledge within the technical scope of the art without departing from the general concept of the invention and without undue experimentation. Therefore, based on the teachings and guidance set forth herein, such adaptations and modifications are intended to fall within the meaning and range of equivalents of the disclosed embodiments. It should be understood that the words or terms herein are for descriptive and non-limiting purposes, so that the terms or terms of this specification should be interpreted by those skilled in the art in accordance with the teachings and guidance.

[0146] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A device for sensing a plurality of alignment marks, the device comprising: an illumination system arranged to provide a plurality of light beams to illuminate respective alignment marks of the plurality of alignment marks; a diffraction light collecting optical system arranged to collect diffracted light from a plurality of diffracted light beams diffracted from corresponding alignment marks among the plurality of alignment marks; an interferometer arranged to receive the diffracted light collected by the diffracted light collecting optical system and configured to generate an optical output based on the diffracted light; as well as a detection system arranged to receive the optical output and configured to generate an electrical signal based on the optical output; The device also includes: means for causing relative movement between the plurality of alignment marks and the diffraction light collecting optical system; and A demultiplexer is configured to demultiplex the light diffracted by the plurality of alignment marks based on a timing at which the electrical signal is received by the detection system.

2. The device according to claim 1, wherein The irradiation system comprises: an illumination source for generating a source beam; and A plurality of beam splitters are arranged to receive the source beam, transmit a transmitted portion of the source beam, and redirect the redirected portion of the source beam toward a corresponding alignment mark of the plurality of alignment marks.

3. The device according to claim 1, wherein: The illumination system is arranged to provide the plurality of light beams to provide coaxial illumination of respective alignment marks of the plurality of alignment marks.

4. The device according to claim 1, wherein: The illumination system is arranged to provide the plurality of light beams to provide off-axis illumination of respective alignment marks of the plurality of alignment marks.

5. The device according to claim 1, wherein: The plurality of alignment marks include a first pair of alignment marks and a second pair of alignment marks, each alignment mark of the first pair of alignment marks including a first grating having a first pitch, each alignment mark of the second pair of alignment marks including a second grating having a second pitch different from the first pitch, and wherein the demultiplexer is configured to demultiplex light diffracted by the first grating and light diffracted by the second grating based on the second pitch different from the first pitch.

6. The device according to claim 5, wherein: The demultiplexer is configured to demultiplex the light diffracted by the first grating and the light diffracted by the second grating by shifting a pupil position of the light diffracted by the first grating relative to a pupil position of the light diffracted by the second grating.

7. The device according to claim 5, wherein: A first optical output of light diffracted by the first grating has a first frequency and a second optical output of light diffracted by the second grating has a second frequency different from the first frequency, and wherein the demultiplexer is configured to demultiplex the light diffracted by the first grating and the light diffracted by the second grating based on the first frequency and the second frequency.

8. The device according to claim 1, wherein: The diffracted light collecting optical system further comprises an optical component arranged to produce a lateral physical separation between the respective diffracted light beams with respect to the propagation direction, And wherein the demultiplexer is configured to demultiplex the light diffracted by the plurality of alignment marks based on the lateral position of the light diffracted by the plurality of alignment marks.

9. The device according to claim 1, wherein: The illumination system comprises a plurality of illumination sources arranged to provide respective ones of the plurality of light beams to illuminate respective ones of the plurality of alignment marks.

10. The apparatus of claim 9, further comprising a control loop arranged to cause a temporal shift between times when respective ones of the plurality of illumination sources illuminate respective ones of the plurality of alignment marks; and The demultiplexer is configured to demultiplex light diffracted by the plurality of alignment marks based on a timing at which the electrical signal is received by the detection system.

11. The device according to claim 9, wherein: Respective ones of the plurality of illumination sources are adapted to provide a plurality of light beams to illuminate corresponding ones of the plurality of alignment marks with corresponding ones of the plurality of light beams having corresponding wavelengths different from each other, and wherein the demultiplexer is configured to demultiplex light diffracted by the plurality of alignment marks based on the wavelengths.

12. An apparatus for sensing an alignment mark in an alignment pattern, the apparatus comprising: an illumination system arranged to provide a first light beam for illuminating the first alignment mark, a second light beam for illuminating the second alignment mark, and a third light beam for illuminating the third alignment mark; a diffraction light collecting optical system arranged to collect diffraction light from the first alignment mark, the second alignment mark, and the third alignment mark; an interferometer arranged to receive the diffracted light collected by the diffracted light collecting optical system and configured to generate an optical output based on the diffracted light; as well as a detection system arranged to receive the optical output of the interferometer and configured to generate an electrical signal based on the optical output; The device also includes: means for causing relative movement between a plurality of alignment marks among the first alignment mark, the second alignment mark, and the third alignment mark and the diffraction light collecting optical system; and A demultiplexer is configured to demultiplex the light diffracted by the first alignment mark, the second alignment mark, and the third alignment mark based on the timing at which the electrical signal is received by the detection system.

13. The device according to claim 12, wherein: The irradiation system comprises: an illumination source, the illumination source being used to generate a source beam; a first beam splitter arranged to receive the source beam, transmit a first transmitted portion of the source beam, and redirect the first redirected portion of the source beam toward the first alignment mark; a second beam splitter arranged to receive the source beam, transmit a second transmitted portion of the source beam, and redirect a second redirected portion of the source beam toward the second alignment mark; and A third beam splitter is arranged to receive the source beam and redirect a third redirected portion of the source beam towards the third alignment mark.

14. The apparatus according to claim 12, wherein: The illumination system is arranged to provide the first light beam, the second light beam, and the third light beam to provide coaxial illumination of respective ones of the first alignment mark, the second alignment mark, and the third alignment mark.

15. The apparatus according to claim 12, wherein: The illumination system is arranged to provide the first light beam, the second light beam, and the third light beam to provide off-axis illumination of respective ones of the first alignment mark, the second alignment mark, and the third alignment mark.

16. The apparatus according to claim 12, wherein: The first alignment mark includes a first grating having a first pitch, the second alignment mark includes a second grating having a second pitch different from the first pitch, and the third alignment mark includes a third grating having a third pitch different from the second pitch and the first pitch, and wherein the demultiplexer is configured to demultiplex the light diffracted by the first grating, the light diffracted by the second grating, and the light diffracted by the third grating based on the first pitch, the second pitch, and the third pitch that are different from each other.

17. The apparatus according to claim 12, wherein: The diffracted light collecting optical system further comprises an optical component arranged to produce a lateral physical separation between the respective diffracted light beams with respect to the propagation direction, And wherein the demultiplexer is configured to demultiplex the light diffracted by the plurality of alignment marks based on the lateral position of the light diffracted by the plurality of alignment marks.

18. The apparatus according to claim 12, wherein: The illumination system includes a first illumination source, a second illumination source, and a third illumination source, and the first illumination source, the second illumination source, and the third illumination source are arranged to provide corresponding light beams among the first light beam, the second light beam, and the third light beam to illuminate corresponding alignment marks among the first alignment mark, the second alignment mark, and the third alignment mark.

Images