Apparatus and method for sensing alignment marks

Abstract

An apparatus and method of sensing an alignment mark in which a still image of the alignment mark is output based on a sensor of a self-reference interferometer, and a camera device is used to capture the image as output by the sensor, and a detector to obtain phase information about the alignment mark as from the image output from the sensor.

Description

[0001] This application is a divisional application of the patent application with application number 202080073644.7 and invention name “Device and method for sensing alignment marks”, which entered the Chinese national phase on April 20, 2022 (international application date is 2020-09-28, international application number is PCT / EP2020 / 077141). Technical Field

[0002] The present disclosure relates to the fabrication of devices 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

[0003] Lithographic equipment can be used, for example, in the manufacture of integrated circuits (ICs). In 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. This pattern can be transferred to a target portion (e.g., a portion including a die, a die, or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually performed via imaging onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are patterned continuously.

[0004] Known lithographic apparatus include so-called steppers, in which each target portion is illuminated by exposing the entire pattern onto the target portion at once, and so-called scanners, in which each target portion is illuminated by scanning the substrate in a given direction (the "scanning" direction) while simultaneously scanning the pattern across a radiation beam parallel or anti-parallel to such direction. The pattern may also be transferred from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0005] ICs are created layer by layer, and a modern IC may have 30 or more layers. Overlay on product (OPO) is a measure of the ability of the system 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 overlay improves device yield and enables printing of smaller product patterns. The overlay error between successive layers formed in or on a patterned substrate is controlled by various components or parts of the exposure equipment of the lithographic apparatus.

[0006] Process-induced wafer errors are a significant impediment to OPO performance. Process-induced wafer errors can be due to the complexity of the printed pattern, and the increase in the number of printed layers. Such errors have a relatively high spatial variation that is different between wafers and within a given wafer.

[0007] In order to control the lithography process to accurately place device features on the substrate, one or more alignment marks are usually set on (for example) the substrate, and the lithography equipment includes one or more alignment sensors that can be used to accurately measure the position of the mark. The alignment sensor can actually be a position measurement device. Different types of marks and different types of alignment sensors are well known from different times and different manufacturers. Measurement of the relative positions of several alignment marks in a field can correct process-induced wafer errors. The alignment error variation in the field can be used to fit a model to correct the OPO in the field.

[0008] It is known that lithographic apparatus use multiple alignment systems to align the substrate relative to the lithographic apparatus. For example, data may be obtained using any type of alignment sensor, such as a SMASH-type or Smart Alignment Sensor Hybrid (SMASH) sensor, as described in U.S. Patent No. 6,961,116, issued on November 1, 2005, and entitled “Lithographic Apparatus, Device Manufacturing Method, and Device Manufactured Thereby,” which is incorporated herein by reference in its entirety, wherein the SMASH sensor uses a self-referencing interferometer with a single detector and four different wavelengths and extracts the alignment signal in software; or an Advanced Technology using High order enhancement of alignment (ATHENA), as described in U.S. Patent No. 6,961,116, issued on October 2, 2001, and entitled “Lithographic Projection Apparatus with an Alignment System for Aligning Substrate on No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector; or an ORION sensor that uses multiple polarizations for each available signal (color).

[0009] 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 text of the documents of which is incorporated herein by reference. EP 1 372 040 A1 describes an alignment system using a self-referencing interferometer that produces two superimposed images of alignment marks. The two images are rotated by up to 180° relative to each other. EP 1 372 040 A1 further describes the detection of 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 this phase difference, which is required for the alignment process. Reference is also made to U.S. Patent No. 8,610,898, issued on December 17, 2013, namely “Self-Referencing Interferometer, Alignment System, and Lithographic Apparatus”, the entire text of the entire contents of which is incorporated herein by reference.

[0010] Existing alignment systems and techniques can produce imperfect measurements due to the inability to distinguish signals originating from the alignment mark from stray inputs from the substrate (known as product crosstalk). In other words, existing sensor systems typically have a single detector that collects all light and has no idea which signal is aberrant light from the product and which signal is from the alignment mark.

[0011] It is also desirable to have a system that measures smaller alignment marks. Typical dimensions for conventional alignment marks may be, for example, 38 μm by 80 μm. However, the footprint, i.e., area occupied, on a wafer is valuable, and being able to use smaller alignment marks so that more wafers can be turned into product would be beneficial. Using smaller alignment marks also allows the use of a larger number of marks, which enables correction of intra-field alignment errors. Summary of the invention

[0012] The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of the embodiments. This summary is not an extensive overview of all contemplated embodiments, and is neither intended to identify key or important elements of all embodiments nor 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 that is presented later.

[0013] According to one aspect of the embodiment, a system including a combination of multiple detector types is used to obtain a more complete knowledge of the state of an alignment mark. The signal from the alignment mark is split so that part of the signal reaches the detector and another part of the signal reaches the camera. Thus, a component or part of the system (e.g., a single pixel detector) actually "feels" the mark, while at the same time another component of the system (the camera) actually "sees" the mark. The data from these two components enables the identification and rejection of false signals from the substrate.

[0014] According to one aspect of the embodiments, a device for sensing an alignment pattern is disclosed, the device comprising: a sensor, when the alignment pattern is scanned, the sensor is arranged to receive light diffracted by the alignment pattern and is adapted to produce an output including at least one static output image of the alignment pattern; a detector, the detector is adapted to detect a phase signal in the output; a camera, the camera is adapted to capture an image of the output; an optical device, the optical device is arranged to receive the output and is adapted to transmit the output to the detector and the camera. The optical device may be adapted to transmit the output to the detector and the camera simultaneously. The optical device may include a beam splitter. The optical device may be adapted to transmit the output alternately to the detector and the camera. The optical device may include a rotating mirror, i.e., a flip mirror. The sensor may include a self-referencing interferometer. The device may also include a spatially coherent radiation source arranged to illuminate the alignment pattern, the alignment pattern diffracting the spatially coherent radiation to produce light diffracted by the alignment pattern. The device may further comprise a processor arranged to receive data from the camera and adapted to perform image processing on the data. The image processing may comprise setting a digital aperture. The digital aperture may have an arbitrary shape, and or be apodized. The sensor may output a first still output image of the alignment pattern and a second still output image of the alignment pattern, and the image processing may comprise adding the first still image to the second still image. The sensor may output a first still output image of the alignment pattern and a second still output image of the alignment pattern, and the image processing may comprise obtaining a difference between the first still image and the second still image. The sensor may output a first still output image of the alignment pattern and a second still output image of the alignment pattern, and the image processing may comprise adding the first still image to the second still image and obtaining a difference between the first still image and the second still image.

[0015] According to another aspect of the embodiment, a method for sensing an alignment pattern is disclosed, the method comprising the following steps: sensing light diffracted by the alignment pattern when the alignment pattern is scanned and generating an output including at least one still output image of the alignment pattern; splitting the output between a detector and a camera; detecting a phase signal in the output using the detector; and capturing an image of the output using the camera.

[0016] According to another aspect of the embodiment, a method of sensing an alignment pattern is disclosed, the method comprising the steps of: sensing light diffracted by the alignment pattern and generating an output including at least one still output image of the alignment pattern when the alignment pattern is scanned; directing the output to a detector; detecting a phase signal in the output using the detector; directing the output to a camera; and capturing an image of the output using the camera. The steps of directing the output to the detector and directing the output to the camera may be performed simultaneously or alternately. The steps of sensing light diffracted by the alignment pattern and generating an output including at least one still output image of the alignment pattern when the alignment pattern is scanned may be performed by a self-referencing interferometer. The method may also include the step of illuminating the alignment pattern with spatially coherent radiation while sensing light diffracted by the alignment pattern and generating an output including at least one still output image of the alignment pattern when the alignment pattern is scanned. The method may also include the step of performing image processing on the image captured by the camera. The image processing may include setting a digital aperture. The digital aperture may have an arbitrary shape, be adjusted and / or be apodized. The output may include a first still output image of the alignment pattern and a second still output image of the alignment pattern, and the image processing may include adding the first still image to the second still image. The output may include a first still output image of the alignment pattern and a second still output image of the alignment pattern, and the image processing may include obtaining a difference between the first still image and the second still image. The output may include a first still output image of the alignment pattern and a second still output image of the alignment pattern, and the image processing may include adding the first still image to the second still image and obtaining a difference between the first still image and the second still image.

[0017] According to yet another aspect of the embodiment, there is disclosed an apparatus for aligning a substrate having an alignment mark, the apparatus comprising: a sensor having a field of view at the substrate that is larger than the alignment mark, the sensor being arranged to receive light diffracted by the alignment mark and being adapted to produce an output including at least one still output image of the alignment mark when the alignment mark is scanned; a detector being adapted to detect a phase signal in the output; a camera being adapted to capture an image of the output; and an optical device being arranged to receive the output and being adapted to transmit the output to the detector and the camera.

[0018] According to yet another aspect of the embodiments, there is disclosed an apparatus for aligning a substrate having at least two alignment marks, the apparatus comprising: a sensor having a field of view at the substrate that is large enough to encompass both of the at least two alignment marks, and being arranged to receive light diffracted by the alignment marks and adapted to include an output of at least one still output image of the alignment marks when the alignment marks are scanned; a detector adapted to detect a phase signal in the output; a camera adapted to capture an image of the output; and an optical device arranged to receive the output and adapted to transmit the output to the detector and the camera.

[0019] According to yet another aspect of the embodiments, there is disclosed an apparatus for aligning a substrate having an alignment mark, the apparatus comprising: a sensor, which is arranged to receive light diffracted by an edge of the alignment mark and is adapted to produce an output including at least one still output image of the edge when the alignment mark is scanned; a detector, which is adapted to detect a phase signal in the output; a camera, which is adapted to capture an image of the output; and an optical device, which is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0020] According to another aspect of the embodiment, a lithography device is disclosed, comprising an arrangement for sensing an alignment pattern, the arrangement comprising: a sensor, which is arranged to receive light diffracted by the alignment pattern when the alignment pattern is scanned and is adapted to produce an output including at least one stationary output image of the alignment pattern; a detector, which is adapted to detect a phase signal in the output; a camera, which is adapted to capture an image of the output; and an optical device, which is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0021] According to another aspect of the embodiment, a lithography device is disclosed, comprising an arrangement for sensing an alignment mark on a substrate, the arrangement comprising: a sensor having a field of view larger than the alignment mark at the substrate, the sensor being arranged to receive light diffracted by the alignment mark and adapted to produce an output including at least one stationary output image of the alignment mark when the alignment mark is scanned; a detector being adapted to detect a phase signal in the output; a camera being adapted to capture an image of the output; and an optical device being arranged to receive the output and adapted to transmit the output to the detector and the camera.

[0022] According to another aspect of the embodiment, a lithography device is disclosed, comprising an arrangement for aligning a substrate having at least two alignment marks, the arrangement comprising: a sensor having a field of view at the substrate that is large enough to cover both of the at least two alignment marks, and when the alignment marks are scanned, the sensor is arranged to receive light diffracted by the alignment marks and is adapted to include an output of at least one still output image of the alignment marks; a detector, the detector is adapted to detect a phase signal in the output; a camera, the camera is adapted to capture an image of the output; and an optical device, the optical device is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0023] According to another aspect of the embodiment, a lithography device is disclosed, comprising an arrangement for aligning a substrate having an alignment mark, the device comprising: a sensor, which is arranged to receive light diffracted by an edge of the alignment mark and is adapted to produce an output including at least one static output image of the edge when the alignment mark is scanned; a detector, which is adapted to detect a phase signal in the output; a camera, which is adapted to capture an image of the output; and an optical device, which is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0024] Further embodiments, features, and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which are incorporated herein and form part of this specification, illustrate the methods and systems of embodiments of the present invention by way of example and not by way of limitation. The drawings, together with the detailed description, further serve to explain the principles of the methods and systems presented herein and to enable those skilled in the relevant art to make and use the methods and systems. In the drawings, like reference numerals indicate identical or functionally similar elements.

[0026] Figure 1 Depicted are selected components or portions of a lithography system such as may be used in accordance with aspects of the embodiments disclosed herein.

[0027] Figure 2 Selected components or portions of the alignment system are depicted to explain the operating principles of known alignment systems.

[0028] Figure 3 A system for analyzing alignment marks according to aspects of the embodiments is depicted.

[0029] Figure 4 A system for analyzing alignment marks according to aspects of the embodiments is depicted.

[0030] Figure 5A Simulated alignment marks are shown.

[0031] Figure 5B and Figure 5C An example of simulated output of a system according to aspects of the embodiments is shown.

[0032] Figure 6 is a flow chart illustrating a method of analyzing an alignment mark according to aspects of an embodiment.

[0033] The following describes in detail the additional features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention 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, additional embodiments will be apparent to those skilled in the relevant art. DETAILED DESCRIPTION

[0034] Various embodiments are now described with reference to the accompanying drawings, wherein the same reference numerals are used throughout to represent the same 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 is apparent in some or all instances that any embodiment described below can be put into practice without adopting the specific design details described below. In other instances, 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 presented below to provide a basic understanding of the embodiments. This overview is not an exhaustive review of all contemplated embodiments, and is not intended to illustrate 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, which may 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; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.), etc. In addition, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be understood that such description is merely for convenience, and such actions are actually caused by a computing device, processor, controller, or other device that executes firmware, software, routines, instructions, etc.

[0036] Figure 1 A lithographic apparatus is schematically depicted. The lithographic apparatus comprises an illumination system (illuminator) 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. resist-coated wafer) 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 via 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 for directing, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

[0038] The support structure supports the pattern forming device, i.e. bears the weight of the pattern forming device. The way in which it holds the pattern forming device 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 held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the pattern forming device. The support structure can be, for example, a frame or a table that can be fixed or moved as required. The support structure can ensure that the pattern forming device is in a desired position, for example relative to the projection system PS. Any use of the term "reticle" or "mask" herein may be considered 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 radiation beam with a pattern in its cross-section, for example to create a pattern in a target portion of a 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) created in the target portion.

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

[0041] The term "projection system" as used herein should be broadly interpreted to include any type of projection system, including refractive, reflective, refractive-reflective, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate, applicable to the exposure radiation being used or other factors such as the use of an 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 transmissive (eg, using a transmissive mask). Alternatively, the device may be reflective (eg, using a programmable mirror array, 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 performed 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 be covered by a liquid having a relatively high refractive index, such as 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, for example, between the mask and the projection system. It is well known in the art that immersion techniques are used to increase the numerical aperture of the projection system. The term "immersion" as used herein does not mean that structures such as the substrate must be immersed in the liquid, but only means that the liquid is located between the projection system and the substrate during exposure.

[0045] Refer again Figure 1 The illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In this case, the source is not regarded as forming part of the lithographic apparatus, and the radiation beam is delivered 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 (where necessary), may be referred to as a radiation system.

[0046] The illuminator IL may include 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 include various other components, such as an integrator In and a condenser CO. The illuminator IL may be used to condition the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0047] The radiation beam B is incident on a patterning device (e.g. a mask MA) held on a support structure (e.g. a mask table MT) and is patterned by the patterning device. After having passed through the mask MA, the radiation beam B passes through a projection system PL which focuses the beam B onto a target portion C of the substrate W. With the aid of a second positioning device PW and a position sensor IF (e.g. an interferometric device, a linear encoder, a two-dimensional encoder or a capacitive sensor), the substrate table WT can be precisely moved, for example, in order to position a different target portion C in the path of the radiation beam B. Similarly, the first positioning device PM and a further position sensor (not shown) are provided. Figure 1The first positioner PM may be provided with a long-stroke module (rough 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 provided 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 mask table MT may be connected to a short-stroke actuator only, or may be fixed. The mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as shown occupy dedicated target portions, they may be located in the spaces between target portions (these are referred to as scribe lane alignment marks). Similarly, in the case where more than one die is provided on the mask MA, the mask alignment marks may be located between the dies. The wafer may also include additional marks, such as, for example, marks sensitive to variations in a chemical mechanical planarization (CMP) process used 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 which is printed so that after development the bars are formed by solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlaid or interlaced on a product layer grating. The bars may alternatively be etched into the substrate.

[0049] Figure 2 A schematic overview of a known alignment system 10 is shown. A light source 11 emits a spatially coherent beam of radiation that illuminates an alignment mark WM located on a substrate (e.g. a wafer), which reflects the radiation into 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 that are relatively rotated by 180° and superimposed and can therefore cause interference. In the pupil plane 14, the superimposed Fourier transforms of these images can be seen, as well as the different diffraction orders that are separated and can be caused to interfere. The 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 2The right part of the diagram shows the formation of two superimposed images in the pupil plane 14; for one image, +n' and -n' are rotated +90° with respect to the input diffraction orders +n and -n; for the other image, +n'' and -n'' are rotated -90° with respect to the input diffraction orders +n and -n. In the pupil plane, the orders (+n' and -n'') and (+n'' and -n') interfere, respectively.

[0050] The output of a sensor such as the one 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 (a single pixel detector) detects the intensity changes caused by interference between the + order and the - order. This interference produces two channels: a sum (SUM) channel in which the electric fields are added, and a difference (DIFF) channel in which the electric fields are subtracted. The two channels are 180 degrees out of phase with each other. The alignment position of the mark is calculated by measuring the phase of the signal at the difference (DIFF) channel, or the sum (SUM) channel, or a combination of the two channels.

[0051] In such a system, all light is directed to the detector, and the detector cannot distinguish light from the marker from light from the wafer as an artifact of a wafer anomaly. According to aspects of the embodiments, optics are introduced to pick up a portion of the signal from the detector and direct it to the camera. The image on the camera is an image of the field at the wafer. In the case where the detector is an SRI, there will be two images that have been rotated 180 degrees relative to each other. As used herein, the term "camera" means any device or system for capturing an image, no matter how configured.

[0052] Figure 3 1. As can be seen in said figure, a light source 100 generates a spatially coherent radiation beam which passes through a beam splitter 110 and illuminates a wafer mark WM on a wafer W. Light from the wafer mark WM then passes through the beam splitter 110 to a sensor 120. The output of the sensor 120 is then divided by a beam splitter 130. A portion of the output of the sensor 120 is passed to a detector 140. Another portion of the output of the sensor 120 is passed to a camera 150.

[0053] This arrangement of optical elements is not the only possible arrangement. Figure 4 As shown in FIG. 1 , a flip mirror 160 may be used to alternatively direct the output of the sensor 120 to the detector 140 or the camera 150. Thus, although Figure 3 The arrangement spatially divides the sensor output, but Figure 4 The arrangement divides the sensor output in time. For example, in Figure 4In the embodiment of the present invention, the flip mirror 160 can be used to direct the signal to the camera 150 when only in-field marks are measured.

[0054] Figure 5A A simulation of microdiffraction-based overlay (μDBO or micro-DBO) labeling is shown. Figure 5B shows the result of taking the difference between the signals from the sensors (the difference (diff) channel, ie the difference between two images that have been rotated 180 degrees relative to each other), and Figure 5C The result of adding the signals from the sensors (sum channel) is shown. As the marker moves (in this case in the y direction), the still image from the interferometer adjusts in terms of total intensity. The sum channel and the difference (diff) channel can be combined electronically to always have a good signal at the camera.

[0055] The marks may have such a small pitch that the signal resulting from diffraction from the mark pattern exceeds the numerical aperture of the objective lens used to collect the light. However, diffraction from the edges of the marks may still be captured and will then show the marks.

[0056] When the image is captured, all pixels identified as light from the product (i.e., as product interference pixels) can be eliminated from the image processing used for alignment. This is effectively an actively addressable aperture or digital aperture. Such an aperture can be electronically adjusted (e.g., apodized) to enable more robust sensing relative to tilt or defocus, or both, of the mark.

[0057] According to another aspect of the embodiment, Figure 6 The method for analyzing alignment marks is shown in the flow chart. Figure 6 As shown in FIG. 1 , in step S100, the mark is illuminated. In step S110, light reflected from the mark is directed to a sensor. Here, the term "reflected" is used to include light diffracted by the mark. This light is then sent to a detector in step S120 and / or a camera in step S130. Steps 120 and S130 may be performed simultaneously or alternately, as described above.

[0058] The embodiments may be further described using the following aspects:

[0059] 1. A device for sensing an alignment pattern, the device comprising:

[0060] a sensor arranged to receive light diffracted by the alignment pattern and adapted to produce an output comprising at least one still output image of the alignment pattern when the alignment pattern is scanned;

[0061] a detector adapted to detect a phase signal in the output;

[0062] a camera adapted to capture an image of the output; and

[0063] An optical device is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0064] 2. Apparatus according to aspect 1, wherein the optical arrangement is adapted to deliver the output to the detector and the camera simultaneously.

[0065] 3. An apparatus according to clause 2, wherein the optical device comprises a beam splitter.

[0066] 4. Apparatus according to aspect 1, wherein the optical arrangement is adapted to deliver the output alternately to the detector and the camera.

[0067] 5. The apparatus of clause 4, wherein the optical device comprises a flip mirror.

[0068] 6. Apparatus according to any one of clauses 1 to 5, wherein the sensor comprises a self-referencing interferometer.

[0069] 7. The apparatus of any one of aspects 1 to 6, further comprising a spatially coherent radiation source arranged to illuminate the alignment pattern, the alignment pattern diffracting the spatially coherent radiation to produce light diffracted by the alignment pattern.

[0070] 8. Apparatus according to clause 1, further comprising a processor arranged to receive data from the camera and adapted to perform image processing on the data.

[0071] 9. The apparatus of clause 8, wherein the image processing comprises setting a digital aperture.

[0072] 10. The apparatus of clause 9, wherein the digital aperture has an arbitrary shape.

[0073] 11. The apparatus of clause 9, wherein the digital aperture is adjusted.

[0074] 12. The apparatus of clause 9, wherein the digital aperture is apodized.

[0075] 13. The apparatus of clause 8, wherein the sensor outputs a first still output image of the alignment pattern and a second still output image of the alignment pattern, and wherein the image processing comprises adding the first still image to the second still image.

[0076] 14. The apparatus of clause 8, wherein the sensor outputs a first still output image of the alignment pattern and a second still output image of the alignment pattern, and wherein the image processing comprises obtaining a difference between the first still image and the second still image.

[0077] 15. An apparatus according to aspect 8, wherein the sensor outputs a first still output image of the alignment pattern and a second still output image of the alignment pattern, and wherein the image processing includes adding the first still image to the second still image and obtaining a difference between the first still image and the second still image.

[0078] 16. A method for sensing an alignment pattern, the method comprising the following steps:

[0079] sensing light diffracted by the alignment pattern as the alignment pattern is scanned and generating an output including at least one still output image of the alignment pattern;

[0080] splitting the output between a detector and a camera;

[0081] detecting a phase signal in the output using the detector; and

[0082] An image of the output is captured using the camera.

[0083] 17. A method for sensing an alignment pattern, the method comprising the following steps:

[0084] sensing light diffracted by the alignment pattern as the alignment pattern is scanned and generating an output including at least one still output image of the alignment pattern;

[0085] directing the output to a detector;

[0086] detecting a phase signal in the output using the detector;

[0087] directing the output to a camera; and

[0088] An image of the output is captured using the camera.

[0089] 18. A method according to clause 17, wherein the step of directing the output to a detector and the step of directing the output to a camera are performed simultaneously.

[0090] 19. A method according to clause 17, wherein the step of directing the output to a detector and the step of directing the output to a camera are performed alternately.

[0091] 20. The method of clause 17, wherein the steps of sensing light diffracted by the alignment pattern as the alignment pattern is scanned and producing an output comprising at least one stationary output image of the alignment pattern are performed by a self-referencing interferometer.

[0092] 21. The method according to aspect 17 also includes the step of illuminating the alignment pattern with spatially coherent radiation while sensing light diffracted by the alignment pattern when scanning the alignment pattern and generating an output including at least one still output image of the alignment pattern.

[0093] 22. The method of clause 17, further comprising the step of performing image processing on the image captured by the camera.

[0094] 23. The method of clause 22, wherein the image processing comprises setting a digital aperture.

[0095] 24. The method of clause 22, wherein the digital aperture has an arbitrary shape.

[0096] 25. The method of aspect 22, wherein the digital aperture is adjusted.

[0097] 26. The method of clause 22, wherein the digital aperture is apodized.

[0098] 27. A method according to clause 21, wherein the output comprises a first still output image of the alignment pattern and a second still output image of the alignment pattern, and wherein the image processing comprises adding the first still image to the second still image.

[0099] 28. A method according to clause 21, wherein the output comprises a first still output image of the alignment pattern and a second still output image of the alignment pattern, and wherein the image processing comprises obtaining a difference between the first still image and the second still image.

[0100] 29. A method according to aspect 21, wherein the output includes a first still output image of the alignment pattern and a second still output image of the alignment pattern, and wherein the image processing includes adding the first still image to the second still image and obtaining the difference between the first still image and the second still image.

[0101] 30. An apparatus for aligning a substrate having an alignment mark, the apparatus comprising:

[0102] a sensor having a field of view at the substrate that is larger than the alignment mark, the sensor being arranged to receive light diffracted by the alignment mark and adapted to produce an output including at least one still output image of the alignment mark when the alignment mark is scanned;

[0103] a detector adapted to detect a phase signal in the output;

[0104] a camera adapted to capture an image of the output; and

[0105] An optical device is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0106] 31. An apparatus for aligning a substrate having at least two alignment marks, the apparatus comprising:

[0107] a sensor having a field of view at the substrate large enough to encompass both of the at least two alignment marks and arranged to receive light diffracted by the alignment marks and adapted to include an output of at least one still output image of the alignment marks as the alignment marks are scanned;

[0108] a detector adapted to detect a phase signal in the output;

[0109] a camera adapted to capture an image of the output; and

[0110] An optical device is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0111] 32. An apparatus for aligning a substrate having alignment marks, the apparatus comprising:

[0112] a sensor arranged to receive light diffracted by an edge of the alignment mark and adapted to produce an output including at least one still output image of the edge when the alignment mark is scanned;

[0113] a detector adapted to detect a phase signal in the output;

[0114] a camera adapted to capture an image of the output; and

[0115] An optical device is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0116] 33. A lithographic apparatus comprising an arrangement for sensing an alignment pattern, the arrangement comprising:

[0117] a sensor arranged to receive light diffracted by the alignment pattern and adapted to produce an output comprising at least one still output image of the alignment pattern when the alignment pattern is scanned;

[0118] a detector adapted to detect a phase signal in the output;

[0119] a camera adapted to capture an image of the output; and

[0120] An optical device is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0121] 34. A lithographic apparatus comprising an arrangement for sensing an alignment mark on a substrate, the arrangement comprising:

[0122] a sensor having a field of view at the substrate that is larger than the alignment mark, the sensor being arranged to receive light diffracted by the alignment mark and adapted to produce an output including at least one still output image of the alignment mark when the alignment mark is scanned;

[0123] a detector adapted to detect a phase signal in the output;

[0124] a camera adapted to capture an image of the output; and

[0125] An optical device is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0126] 35. A lithographic apparatus comprising an arrangement for aligning a substrate having at least two alignment marks, the arrangement comprising:

[0127] a sensor having a field of view at the substrate large enough to encompass both of the at least two alignment marks and arranged to receive light diffracted by the alignment marks and adapted to include an output of at least one still output image of the alignment marks as the alignment marks are scanned;

[0128] a detector adapted to detect a phase signal in the output;

[0129] a camera adapted to capture an image of the output; and

[0130] An optical device is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0131] 36. A lithographic apparatus comprising an arrangement for aligning a substrate having alignment marks, the apparatus comprising:

[0132] a sensor arranged to receive light diffracted by an edge of the alignment mark and adapted to produce an output including at least one still output image of the edge when the alignment mark is scanned;

[0133] a detector adapted to detect a phase signal in the output;

[0134] a camera adapted to capture an image of the output; and

[0135] An optical device is arranged to receive the output and is adapted to transmit the output to the detector and the camera.

[0136] The systems and methods disclosed herein capture an image of the mark downstream of a self-referencing interferometric sensor and make it possible to combine information from the image with information from a phase signal measured by a detector. As opposed to having to pause scanning to obtain an image, the stationary image pattern output by the self-referencing sensor allows scanning of the mark while collecting the image. Combining the difference (diff) channel and the sum (sum) channel can be used to ensure sufficient signal for the image. The ability to apply a digital aperture of arbitrary shape with or without adjustment / apodization allows measurement of features less than 20 microns and helps distinguish signals from the mark from signals originating from the product as background, leakage or crosstalk. The subject matter disclosed herein provides a method for checking the integrity of a mark and can reduce overlap errors caused by damaged marks.

[0137] Systems arranged according to aspects of the embodiments as described herein can achieve several potential benefits. For example, they enable the ability to measure small marks that underfill the field of view at the wafer. They also enable the ability to simultaneously measure multiple small marks within the field of view using digital aperture and image processing techniques available by aspects of the embodiments. They also generate or enhance the ability to align edge diffraction of the marks.

[0138] The system as described above can be used not only to improve overlay alignment, but also to diagnose, monitor and / or adjust scanner performance in general. The scan signal can be analyzed to correlate with key performance indicators for the stepper / scanner. The results of the analysis can be presented and / or stored in any number of ways, such as being instantaneously displayed on a monitoring device or compiled in a report.

[0139] Although the use of lithographic equipment may be specifically mentioned in the manufacture of ICs herein, it should be understood that the lithographic equipment described herein may have other applications, such as manufacturing integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film heads, etc. Those skilled in the art will understand that in the context of such alternative applications, any use of the term "wafer" or "die" herein is considered to be synonymous with the more general term "substrate" or "target portion", respectively. The substrates referred to herein may be processed before or after exposure, such as in a track or coating and developing system (i.e., a tool that typically applies a resist layer to a substrate and develops the exposed resist), a measurement tool, and / or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. In addition, for example, the substrate may be processed more than once in order to manufacture a multi-layer IC, so that the term "substrate" used herein may also refer to a substrate that already contains multiple processed layers.

[0140] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it should be understood that the invention may be used in other applications, such as imprint lithography, and is not limited to optical lithography where the context permits. In imprint lithography, the topography in the patterning device defines the pattern produced on the substrate. The topography of the patterning device may be imprinted into a layer of resist provided to the substrate, and the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is removed from the resist, leaving the pattern behind after the resist is cured.

[0141] As used herein, the terms "radiation" and "beam" encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of or about 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 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.

[0142] Although specific reference may be made herein to the use of the apparatus according to the invention in the manufacture of integrated circuits, it should be clearly understood that such apparatus has many other possible applications. For example, it may be used to manufacture integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. Those skilled in the art will appreciate that in the context of such alternative applications, any use of "template", "wafer" or "chip" herein should be considered to be replaced by the more general terms "mask", "substrate" and "target portion", respectively.

[0143] The present invention has been described above by means of functional building blocks that illustrate the implementation of specific functions and their relationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined here. As long as the specified functions and their relationships are properly performed, other boundaries can be defined.

[0144] The foregoing description of the specific embodiments will fully reveal the general nature of the invention, and by applying knowledge within the technical scope of the art, others can easily modify and / or adapt such specific embodiments for various applications without excessive experimentation, without departing from the general concept of the invention. Therefore, based on the teachings and guidance given herein, these changes and modifications are intended to fall within the meaning and scope of the equivalents of the disclosed embodiments. It should be understood that the wording or terminology here is for the purpose of describing by example rather than limiting, so that the terms or wording of this specification will be interpreted by the technician according to the teachings and guidance.

[0145] 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 method for sensing an alignment pattern, the method comprising the following steps: sensing light diffracted by the alignment pattern as the alignment pattern is scanned and generating an output including at least one still output image of the alignment pattern; splitting the output between a detector and a camera; detecting a phase signal in the output using the detector; as well as An image of the output is captured using the camera.

2. A method for sensing an alignment pattern, the method comprising the following steps: sensing light diffracted by the alignment pattern as the alignment pattern is scanned and generating an output including at least one still output image of the alignment pattern; directing the output to a detector; detecting a phase signal in the output using the detector; directing the output to a camera; as well as An image of the output is captured using the camera.

3. The method of claim 2, wherein the step of directing the output to a detector and the step of directing the output to a camera are performed simultaneously.

4. The method of claim 2, wherein the step of directing the output to a detector and the step of directing the output to a camera are performed alternately.

5. The method of claim 2, wherein the steps of sensing light diffracted by the alignment pattern as the alignment pattern is scanned and producing an output including at least one stationary output image of the alignment pattern are performed by a self-referencing interferometer.

6. The method of claim 2 further comprising the step of illuminating the alignment pattern with spatially coherent radiation while sensing light diffracted by the alignment pattern as it is scanned and generating an output including at least one still output image of the alignment pattern.

7. The method of claim 2, further comprising the step of performing image processing on the image captured by the camera. The method of claim 7 , wherein the image processing comprises setting a digital aperture.

9. The method of claim 7, wherein the digital aperture has an arbitrary shape.

10. The method of claim 7, wherein the digital aperture is adjusted. The method of claim 7 , wherein the digital aperture is apodized.

12. The method of claim 6, wherein the output comprises a first still output image of the alignment pattern and a second still output image of the alignment pattern, and wherein the image processing comprises adding the first still image to the second still image.

13. The method of claim 6, wherein the output comprises a first still output image of the alignment pattern and a second still output image of the alignment pattern, and wherein the image processing comprises taking a difference between the first still image and the second still image.

14. A method according to claim 6, wherein the output includes a first still output image of the alignment pattern and a second still output image of the alignment pattern, and wherein the image processing includes adding the first still image and the second still image and obtaining the difference between the first still image and the second still image.

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