Target for measuring parameters of a lithographic process

Abstract

A target arrangement is disclosed, the target arrangement comprising a first target area and a second target area, the first target area having at least a first pitch and at least a second pitch, the second target area having at least a third pitch, wherein a portion of the first target area having the second pitch overlaps with a portion of the second target area.

Description

[0001] BACKGROUND

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Application 63 / 036,671 filed June 9, 2020, the entirety of which is incorporated herein by reference. TECHNICAL FIELD

[0004] The present invention relates to a target arrangement for metrology of a lithographic process. BACKGROUND

[0005] Lithographic apparatuses are machines that imparts a desired pattern onto a substrate, usually onto a target portion of the substrate. Lithographic apparatuses can be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a pattern formed by a patterning device, which is optionally referred to as a mask or a reticle, can be transferred onto a target portion (e.g., including part of one, or more dies) of the substrate (e.g., a silicon wafer). The pattern can be transferred, for example, via imaging, onto a layer of radiation-sensitive material (resist) provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions each to be imaged with an individually different pattern. In lithographic processes, it is desirable frequently to make measurements of the structures created, e.g., for process control and verification. Various tools for making such measurements are known, including scanning electron microscopes, which are frequently used to measure critical dimension (CD), and specialized tools to measure overlay, i.e. the accuracy of alignment of two layers in a device. Overlay can be described in terms of the degree of misalignment between two layers, e.g. a measured overlay of 1 nm can describe a situation where two layers are misaligned by 1 nm.

[0006] Recently, various forms of scatterometers have been developed for use in the lithographic field. These devices direct a beam of radiation onto a target and measure one or more properties of scattered radiation— e.g., intensity at a single angle of reflection as a function of wavelength; intensity at one or more wavelengths as a function of angle of reflection; or polarization as a function of angle of reflection— to obtain a“spectrum” from which a property of interest of the target can be determined. The determination of the property of interest can be performed by a variety of techniques: e.g., reconstruction of the target by iterative methods such as rigorous coupled wave analysis or finite element methods; library search; and principal component analysis

[0007] Conventional scatterometers use targets that are relatively large, e.g. 40 pm x 40 pm, and the grating and measurement beam generate a spot that is smaller than the grating (i.e. the grating is underfilled). This simplifies the mathematical reconstruction of the target as it can be considered infinite. However, in order to reduce the size of the target (e.g. to 10 pm x 10 pm or less), e.g. so that the target can be positioned in a product feature rather than in a scribe line, metrology has been proposed in which the grating is smaller than the measurement spot (i.e. the grating is overfilled). Typically, dark field scatterometry is used to measure such targets in which the zeroth order diffraction (corresponding to the specular reflection) is blocked and only the higher orders are processed. Examples of dark field metrology can be found in international patent applications WO 2009 / 078708 and WO 2009 / 106279, the contents of which are incorporated herein by reference in their entirety. Further developments of this technique have been described in patent publications US20110027704A, US20110043791A and US20120242970A. Yield enhancing variants of this apparatus are described in US2010201963A1 and US2011102753A1. The contents of all these applications are also incorporated herein by reference. Diffraction based overlay using dark field detection of diffraction orders enables overlay measurements on smaller targets. These targets can be smaller than the illumination spot and can be surrounded by product structures on the wafer. The targets can comprise multiple gratings which can be measured in one image.

[0008] In known metrology techniques, an overlay measurement is obtained by measuring an overlay target twice under certain conditions, while rotating the overlay target or changing the illumination mode or imaging mode to obtain -1 and +1 diffraction order intensities, respectively. Given the intensity asymmetry of the overlay target, i.e. the comparison of these diffraction order intensities, provides a measure of the asymmetry in the target. This asymmetry in the overlay target can be used as an indicator of the overlay (unwanted misalignment of the two layers)

[0009] In another known metrology technique, an alignment measurement is obtained by scanning an alignment target while measuring the scattered radiation, as disclosed for example in US56545553, the contents of which are incorporated herein by reference in their entirety. Alignment targets are disclosed in US6876946, the contents of which are incorporated herein by reference in their entirety.

[0010] It has become apparent that the size and / or placement of metrology targets, overlay and / or alignment, needs to be carefully considered in view of the stringent requirements on real estate on the wafer. Since the lithography process can suffer from unanticipated variations, it is also known that the position on the wafer of the metrology target for alignment and / or overlay can also have variations, which can adversely affect the measured parameter of interest. SUMMARY

[0011] Therefore, it is desirable to have a target arrangement suitable for providing parameters of interest from alignment and / or overlap measurements.

[0012] The present invention provides a target arrangement in a first aspect, the target arrangement including a first target region and a second target region, the first target region having at least a first pitch and at least a second pitch, the second target region having at least a third pitch, wherein a portion of the first target region having the second pitch overlaps with a portion of the second target region.

[0013] Other features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It should be noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Other embodiments will be apparent to those skilled in the art based on the teachings included herein. Attached Figure Description

[0014] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0015] Figure 1 A photolithography apparatus according to an embodiment of the present invention is shown;

[0016] Figure 2 A photolithography unit or cluster according to an embodiment of the present invention is shown;

[0017] Figures 3(a) to 3(d) Including: Figure 3(a) is a schematic diagram of a dark field scatterer for measuring a target using the first pair of illumination apertures; Figure 3(b) shows details of the diffraction spectrum of a target grating for a given illumination direction; Figure 3(c) shows the second pair of illumination apertures providing an additional illumination mode when performing diffraction-based overlap measurements using the scatterer; and Figure 3(d) shows a third pair of illumination apertures combining the first pair of apertures and the second pair of apertures.

[0018] Figure 4 The known form of the contours of multiple grating targets and measurement points on the substrate is depicted;

[0019] Figure 5 The image obtained from the scatterer in Figure 3 is depicted. Figure 4 The image of the target;

[0020] Figure 6 An example of a target arrangement according to an embodiment of the present invention is depicted;

[0021] Figure 7(a) depicts the target arrangement, and Figure 7(b) depicts an image obtained from a portion of the target arrangement depicted in Figure 7(a). Detailed Implementation

[0022] Before describing the embodiments of the invention in detail, it is beneficial to present example environments in which the embodiments of the invention can be implemented. Figure 1 A lithography apparatus LA is schematically depicted. The apparatus includes: an illumination optics system (illuminator) IL configured to modulate a radiation beam B (e.g., UV or DUV radiation); a patterning apparatus support or support structure (e.g., mask stage) MT configured to support a patterning apparatus (e.g., mask) MA and connected to a first positioner PM configured to precisely position the patterning apparatus according to certain parameters; a substrate stage (e.g., wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to precisely position the substrate according to certain parameters; and a projection optics system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the radiation beam B by the patterning apparatus MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0023] Irradiation optical systems may include various types of optical or non-optical components for guiding, shaping or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of components, or any combination thereof.

[0024] The patterning apparatus support holds the patterning apparatus in a manner that depends on the orientation of the patterning apparatus, the design of the lithography equipment, and other conditions such as whether the patterning apparatus is kept in a vacuum environment. The patterning apparatus support can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning apparatus. The patterning apparatus support can be a frame or a stage, which may be fixed or movable as needed. The patterning apparatus support can ensure that the patterning apparatus is, for example, in a desired position relative to a projection system. Any use of the terms "intermediate mask" or "mask" herein is to be considered synonymous with the more general term "patterning apparatus".

[0025] The term "patterning apparatus" as used herein should be interpreted broadly as any apparatus that can be used to impart a pattern across the cross-section of a radiation beam to form a pattern in a target portion of a substrate. It should be noted that, for example, if the pattern includes phase-shifting features or so-called auxiliary features, the pattern imparted to the radiation beam may not precisely correspond to the desired pattern in the target portion of the substrate. Typically, the pattern imparted to the radiation beam will correspond to a specific functional layer in a device formed in the target portion, such as an integrated circuit.

[0026] Pattern forming apparatuses can be transmissive or reflective. Examples of pattern forming apparatuses include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in photolithography and include mask types such as binary, alternating phase-shift, and attenuation phase-shift, as well as various hybrid types. Examples of programmable mirror arrays employ a matrix arrangement of small mirrors, each of which can be individually tilted to reflect incident radiation beams in different directions. The tilted mirrors impart a pattern to the radiation beams reflected by the mirror matrix.

[0027] As depicted herein, the device is transmissive (e.g., employing a transmissive mask). Alternatively, the device may be reflective (e.g., employing a programmable mirror array of the type described above, or employing a reflective mask).

[0028] Photolithography apparatuses can also be of the type in which at least a portion of the substrate can be covered by a liquid (e.g., water) with a relatively high refractive index to fill the space between the projection system and the substrate. Immersion liquids can also be applied to other spaces within the photolithography apparatus, such as 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 imply that structures such as the substrate must be submerged in the liquid, but simply that the liquid is located between the projection system and the substrate during exposure.

[0029] refer to Figure 1 The irradiator IL receives the radiation beam from the radiation source SO. For example, when the source is an excited excimer laser, the source and the lithography apparatus can be separate entities. In this case, the source is not considered part of the lithography apparatus, and the radiation beam is transmitted from the source SO to the irradiator IL by means of a beam delivery system BD, which includes, for example, suitable guiding mirrors and / or beam expanders. In other cases, such as when the source is a mercury lamp, the radiation source can be an integral part of the lithography apparatus. The source SO, the irradiator IL, and the beam delivery system BD, if necessary, can be collectively referred to as the radiation system.

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

[0031] A radiation beam B is incident on a pattern forming apparatus (e.g., a mask) MA held on a pattern forming apparatus support (e.g., a mask stage MT) and patterned by the pattern forming apparatus. After passing through the pattern forming apparatus (e.g., the mask) MA, the radiation beam B passes through a projection optics system PS, which focuses the beam onto a target portion C of the substrate W, thereby projecting an image of the pattern onto the target portion C. The substrate stage WT can be precisely moved, for example, to position different target portions C within the path of the radiation beam B, by means of a second positioner PW and a position sensor IF (e.g., an interferometer, a linear encoder, a 2-D encoder, or a capacitive sensor). Similarly, for example, after mechanical retrieval from a mask library, or during scanning, a first positioner PM and another position sensor (…) can be used… Figure 1 The pattern forming device (e.g., mask) MA is precisely positioned relative to the path of the radiation beam B by another position sensor (not explicitly shown).

[0032] The patterning apparatus (e.g., mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks shown occupy dedicated target portions, they can be located in the space between the target portions (these substrate alignment marks are referred to as scribing alignment marks). Similarly, when more than one die is provided on the patterning apparatus (e.g., mask) MA, the mask alignment marks can be located between the dies. Smaller alignment marks can also be included within the dies in device features, in which case it is desirable that the marks be as small as possible and that no imaging or process conditions different from those of adjacent features are required. An alignment system for detecting alignment marks is further described below.

[0033] In this example, the lithography apparatus LA is a so-called dual-platform type, which has two substrate stages WTa and WTb and two stations—an exposure station and a measurement station—that allow for the exchange of substrate stages between the exposure and measurement stations. While one substrate on one stage is being exposed at the exposure station, another substrate can be loaded onto the other substrate stage at the measurement station, and various preparatory steps can be performed. These preparatory steps may include: mapping the surface control of the substrate using a level sensor LS; and measuring the position of alignment marks on the substrate using an alignment sensor AS. This enables a significant increase in the apparatus's throughput.

[0034] The depicted apparatus can be used in a variety of modes, including, for example, stepping mode or scanning mode. The construction and operation of lithography apparatus are well known to those skilled in the art and require no further description for understanding the invention.

[0035] like Figure 2As shown, the lithography equipment LA forms part of a lithography system called a lithography unit LC or lithography cell or cluster. The lithography unit LC may also include equipment for performing pre-exposure and post-exposure processing on the substrate. Typically, these devices include: a spin coater SC for depositing a resist layer; a developer DE for developing the exposed resist; a chiller CH; and a baking plate BK. A substrate manipulator or robot RO picks up the substrate from input / output ports I / O1, I / O2, moves the substrate between different processing devices, and then transfers the substrate to the feed stage LB of the lithography equipment. These devices, generally referred to collectively as tracks, are controlled by a track control unit TCU, which in turn is controlled by a management control system SCS, which in turn controls the lithography equipment via the lithography control unit LACU. Therefore, different devices can be operated to maximize throughput and processing efficiency.

[0036] To ensure accurate and consistent exposure of substrates exposed by lithography equipment, it is desirable to inspect the exposed substrates to measure characteristics such as overlap error between subsequent layers, line thickness, and critical dimension (CD). Therefore, the manufacturing facility where the lithography unit (LC) is located also includes a metrology system (MET), which receives some or all of the substrates (W) already processed in the lithography unit. The measurement results are provided directly or indirectly to the management and control system (SCS). If an error is detected, especially if the inspection can be performed quickly and sufficiently so that other substrates in the same batch still need to be exposed, the exposure of subsequent substrates can be adjusted. Furthermore, exposed substrates can be stripped and reworked to increase yield or discarded, thus avoiding further processing of known defective substrates. In cases where only some target portions of the substrate are defective, further exposure can be performed only on those good target portions.

[0037] Within a metrology system (MET), inspection equipment is used to determine the properties of a substrate, specifically how the properties of different substrates or different layers of the same substrate vary from layer to layer. The inspection equipment can be integrated into a photolithography (LA) unit or a lithography (LC) unit, or it can be a standalone device. For the fastest possible measurement, it is desirable for the inspection equipment to measure the properties of the exposed resist layer immediately after exposure. However, latent images in resist have very low contrast—only a very small difference in refractive index between the exposed and unexposed portions of the resist—and not all inspection equipment has sufficient sensitivity to make useful measurements of latent images. Therefore, measurements can be performed after a post-exposure baking (PEB) step, which is typically the first step performed on the exposed substrate and increases the contrast between the exposed and unexposed portions of the resist. At this stage, the image in the resist can be referred to as a semi-latent image. Measurements of developed resist images—where both exposed and unexposed portions of the resist have been removed—can also be performed, or after pattern transfer steps such as etching. While the latter possibility limits the likelihood of repairing the faulty substrate, it can still provide useful information.

[0038] The measurement device is shown in Figure 3(a). The target T and diffracted rays of the measurement radiation used to illuminate the target are shown in more detail in Figure 3(b). The measurement device shown is of a type known as a dark-field measurement device. The measurement device depicted herein is purely exemplary to provide an explanation of dark-field measurement. The measurement device can be a standalone device or integrated into a lithography apparatus LA, for example, integrated into a measurement station or lithography unit LC. In this device, an optical axis with several branches is indicated by the dashed line O. In this device, light emitted by a light source 11 (e.g., a xenon lamp) is guided onto the substrate W via a beam splitter 15 through an optical system including lenses 12, 14 and objective lens 16. These lenses are arranged in a double sequence of 4F. Different lens arrangements can be used as long as different lens arrangements still provide an image of the substrate to the detector and simultaneously allow access to the intermediate pupil plane for spatial frequency filtering. Therefore, the range of angles at which radiation is incident on the substrate can be selected by defining a spatial intensity distribution in a plane that presents the spatial spectrum of the substrate plane, referred to herein as the (conjugate) pupil plane. Specifically, this can be achieved by inserting a suitably shaped aperture plate 13 between lenses 12 and 14 in a plane that is the back-projected image of the objective pupil plane. In the example shown, the aperture plate 13 has different forms, labeled 13N and 13S, allowing for the selection of different illumination modes. The illumination system in this example forms an off-axis illumination mode. In the first illumination mode, aperture plate 13N provides off-axis illumination from a direction designated "north" only for descriptive purposes. In the second illumination mode, aperture plate 13S is used to provide similar illumination, but from the opposite direction, labeled "south." Other illumination modes are possible by using different apertures. Because any unwanted light outside the desired illumination mode will interfere with the desired measurement signal, the remainder of the pupil plane is ideally dark.

[0039] As shown in Figure 3(b), the target T is placed together with a substrate W perpendicular to the optical axis O of the objective lens 16. The substrate W may be supported by a support (not shown). The ray of measurement radiation I, which is incident on the target T at an angle deviating from axis O, produces a zero-order ray (solid line 0) and two first-order rays (dotted chain line +1 and double dotted chain line -1). It should be remembered that for small, overfilled targets, these rays are only a batch of many parallel rays covering the area of ​​the substrate that includes the measurement target T and other features. Because the aperture in plate 13 has a finite width (to allow for a useful amount of light), the incident ray I will actually occupy a certain range of angles, and the diffracted rays 0 and +1 / -1 will extend slightly. Depending on the point spread function of the smaller target, each order +1 and -1 will extend further within a certain angular range, rather than a single ideal ray as shown. It should be noted that the grating pitch and illumination angle of the target can be designed or adjusted so that the first-order rays entering the objective lens are closely aligned with the central optical axis. The rays shown in Figures 3(a) and 3(b) are shown slightly off-axis, simply to make the rays easier to distinguish in the figures.

[0040] At least the 0th and +1st order diffracted by the target T on the substrate W are collected by the objective lens 16 and guided back through the beam splitter 15. Returning to Figure 3(a), the first and second illumination modes are shown by specifying radially opposite apertures labeled North (N) and South (S). When the incident ray I for measuring radiation comes from the north side of the optical axis, i.e., when the first illumination mode is applied using aperture plate 13N, the +1st order diffracted ray, labeled +1(N), enters the objective lens 16. Conversely, when the second illumination mode is applied using aperture plate 13S, the -1st order diffracted ray (labeled -1(S)) is the ray entering the lens 16.

[0041] The second beam splitter 17 divides the diffracted beam into two measurement branches. In the first measurement branch, the optical system 18 uses the zeroth-order and first-order diffracted beams to form the diffraction spectrum (pupil plane image) of the target on the first sensor 19 (e.g., a CCD or CMOS sensor). Each diffraction order illuminates a different point on the sensor, allowing image processing to compare and contrast the orders. The pupil plane image captured by the sensor 19 can be used for focusing measurement devices and / or normalizing the intensity measurements of the first-order beam. The pupil plane image can also be used for many measurement purposes, such as reconstruction.

[0042] In the second measurement branch, optical systems 20 and 22 form an image of the target T on sensor 23 (e.g., a CCD or CMOS sensor). In this second measurement branch, an aperture stop 21 is provided in a plane conjugate with the pupil plane. Aperture stop 21 blocks the zero-order diffraction beam, ensuring that the image of the target formed on sensor 23 is formed only by either a -1st or +1st order beam. The image captured by sensors 19 and 23 is output to a processor PU that processes the image; the functionality of the processor PU will depend on the specific type of measurement being performed. Note that the term "image" is used broadly here. If only one of the -1st and +1st orders is present, such an image of grating lines will not be formed.

[0043] The specific forms of the aperture plate 13 and field stop 21 shown in Figure 3 are merely examples. In another embodiment of the invention, on-axis illumination of the target is used, and an aperture stop with an off-axis aperture is used to deliver essentially only one first-order diffracted light to the sensor. In other examples, two quadrant apertures can be used. This allows for the simultaneous detection of the plus and minus orders, as described in US2010201963A1 mentioned above. Embodiments with optical wedges (segmented prisms or other suitable elements) in the detection branches can be used to separate multiple orders for spatial imaging in a single image, as described in US2011102753A1 mentioned above. In still some embodiments, second-, third-, and higher-order beams (not shown in Figure 3) can be used in the measurement instead of or in addition to the first-order beam. In other embodiments, a segmented prism can be used instead of aperture stop 21, such that the +1 and -1 orders can be captured simultaneously at spatially separated locations on the image sensor 23.

[0044] To enable the measurement of radiation to be adapted to these different types of measurements, the orifice plate 13 may include a plurality of aperture patterns formed around a disk that rotates to bring the desired pattern into place. Note that the orifice plates 13N or 13S may be used only for measuring gratings oriented in one direction (depending on the setup, X or Y). For measurements of orthogonal gratings, the target can be rotated by 90° and 270°. Different orifice plates are shown in Figures 3(c) and 3(d). The use of these devices, as well as many other variations and applications of the device, are described in the previously disclosed applications mentioned above.

[0045] Figure 4An overlapping target or composite overlapping target formed on a substrate according to known practices is depicted. In this example, the overlapping target comprises four sub-targets (e.g., gratings) 32 to 35 closely positioned together, such that all four sub-targets 32 to 35 are within a measurement point 31 formed by the measurement radiation beam from the measurement device. Therefore, all four sub-overlapping targets are simultaneously illuminated and imaged onto sensor 23. In an example specifically for measuring overlap, the sub-targets 32 to 35 are themselves composite structures formed by overlapping gratings patterned in different layers of a semiconductor device formed on substrate W. The sub-targets 32 to 35 may have different overlapping offsets to facilitate measurements of overlap between layers forming different portions of the composite sub-target. As shown, the sub-targets 32 to 35 may also have different orientations to diffract incident radiation in the X and Y directions. In one example, sub-targets 32 and 34 are X-direction sub-targets with offsets of +d and d, respectively. Sub-targets 33 and 35 are Y-direction sub-targets with offsets of +d and d, respectively. Individual images of these sub-targets can be identified within the images captured by sensor 23. This is just one example of overlapping targets. Overlapping targets may include more or fewer than four sub-targets.

[0046] Figure 5 This demonstrates that the orifice plates 13NW or 13SE from Figure 3(d) can be used in the device of Figure 3. Figure 4 An example of an image formed on and detected by sensor 23 of overlapping targets. Although the pupil plane image sensor 19 cannot distinguish different individual sub-targets 32 to 35, the image sensor 23 can. The shaded area 40 represents the field of the image on the sensor, in which the illumination spot 31 on the substrate is imaged into the corresponding circular area 41. Here, the rectangular areas 42 to 45 represent images of smaller overlapping targets (sub-targets 32 to 35). If the overlapping targets are located in the product area, product features can also be seen in the periphery of this image field. The image processor and controller PU use pattern recognition to process these images to identify the individual images 42 to 45 of the sub-targets 32 to 35. In this way, the images do not have to be aligned very precisely at a specific location within the sensor frame, which greatly improves the productivity of the entire measuring device.

[0047] Once individual images of overlapping targets have been identified, the intensity of those individual images can be measured, for example, by averaging or summing the intensity values ​​of selected pixels within the identified regions. The intensity and / or other properties of the images can be compared to each other. These results can be combined to measure different parameters of the lithography process. Overlap performance is an important example of such a parameter.

[0048] The overlap error (i.e., undesirable and unintentional overlap misalignment) between two layers within sub-targets 32 to 35 is measured using methods described in applications such as US20110027704A mentioned above. Such methods may be referred to as overlap-based micro-diffraction (μDBO). This measurement can be accomplished through overlapping target asymmetry, as revealed by comparing the intensities in +1 and -1 order dark-field images (and possibly comparing other corresponding higher-order intensities, such as +2 and -2 orders), to obtain a measure of intensity asymmetry.

[0049] Using such Figure 4 In known methods for multi-grating targets, the overlapping OV can be determined using the following equation:

[0050]

[0051] in:

[0052] - It is the +1 diffraction order (e.g., intensity value) from the positively offset target;

[0053] - It is the -1 diffraction order from a positively offset target;

[0054] - It is the +1 diffraction order from the negative offset target;

[0055] - It is the -1 diffraction order from the negative offset target;

[0056] - (For example, the asymmetry in the +1 and -1 intensities from a positive offset target); and

[0057] - (For example, the asymmetry in the +1 and -1 intensities from a negative offset target).

[0058] Equation 1 can be reformulated based on the sensitivity coefficient K, which is a stack-dependent parameter with special properties that are independent of overlap (assuming a perfect target):

[0059] A +d +A -d =K·OV (Equation 2)

[0060] in:

[0061]

[0062] Equation 2 is a simple linear equation based on the assumption of smaller offset values ​​and overlap errors compared to the pitch of the grating that forms the sub-targets. However, the dependence of asymmetry on overlap errors and offsets over a wider range has a substantially sinusoidal form, and a sinusoidal model can also be used instead of the linear model of Equation 2.

[0063] Known methods using four different sub-objectives require circumventing each sub-objective ( Figure 4 and Figure 5 (not shown in the image) boundaries are used to make them distinguishable in image 40. This means that a portion of the pattern-forming region is unavailable due to edge effects. Furthermore, the above assumption of linearity is imposed using only two specific offsets, which may lead to inaccuracies when the true relationship is non-linear.

[0064] Besides being suitable for measuring the overlap between two semiconductor processing layers, wafer alignment is also known to provide useful information for the photolithography process. As is known to the art, the size of the alignment target can be larger than the size of the overlapping target.

[0065] A common problem in semiconductor process measurements is that the measurement target is affected by variations in processing conditions, whether for alignment or overlap purposes. Furthermore, reducing the size of the space occupied by the specific measurement target is a continuous objective for measurements used in photolithography processes.

[0066] This invention discloses a target arrangement comprising a first target region and a second target region. The first target region has at least a first pitch and at least a second pitch, and the second target region has at least a third pitch, wherein a portion of the first target region having the second pitch overlaps with a portion of the second target region. In an embodiment, the first target region is a portion of an alignment target having a pitch in a first direction and another pitch in a second direction. In an embodiment, the two directions are perpendicular. In another embodiment, the second target region is a portion of a measurement target suitable for measuring overlap, focus, dose, or physical parameters (e.g., tilt, sidewall angle, and / or critical dimensions) of a device structure existing on a lithographic wafer. The third pitch is a pitch of the measurement target suitable for measuring overlap, focus, dose, or physical parameters (e.g., tilt, sidewall angle, critical dimensions) of a device structure existing on a lithographic wafer. In an embodiment, a portion of the alignment target having the second pitch overlaps with the measurement target, which is suitable for measuring overlap, focus, dose, or physical parameters (e.g., tilt, sidewall angle, critical dimensions) of a device structure existing on a lithographic wafer. In an embodiment, depending on the state of the art, the first pitch of the aligned target makes alignment measurement possible.

[0067] Figure 6A portion of the target arrangement is described. The target arrangement is formed by a first arrangement located in a first layer and a second target arrangement located in a second layer. In an embodiment, the first target arrangement is a top grating (GT), and the second target arrangement is a bottom grating (GB). The grating GT includes a grating with a pitch pt, such as... Figure 6 As shown, the pitch pt is the third pitch in the second target region of the target arrangement. These gratings can have a single pitch pt. ​​In an embodiment, the grating forming arrangement GT can have portions with different pitches pt1, pt2, pt3, such as Figure 6 As depicted in the diagram. The GT (Ground Tolerancing) can be placed in the first layer. The GB (Ground Block) can be placed in the second layer. On the wafer, the GT can cover the GB.

[0068] Figure 6 The target arrangement is further described as part of the bottom grating GB. This part includes an intermediate region formed by gratings having pitches pb1, pb2, or pb3. In one embodiment, the region having pitch pt1 overlaps with the region having pitch pb1. In another embodiment, the regions having pitches pb1, pb2, or pb3 overlap with the region having a single pitch pt. ​​In yet another embodiment, the arrangement GB includes a structure defining dimensions Aleft and Aright. (See reference...) Figure 6 The structure depicted in GB and, by way of example only, the structure defined by Aleft and Aright can form a grating having a pitch in a direction perpendicular to the pitches pb1, pb2, or pb3, which is a pitch suitable for allowing the measurement of alignment information, as described in the art.

[0069] In an embodiment, such as Figure 6The target arrangement described herein can be used as follows: the arrangement GT overlaps with the middle portion of the GB defined by pitches pb1, pb2, and pb3. In an embodiment, pb1, pb2, and pb3 may be identical. In an embodiment, the arrangement GT comprises a single pitch pt. ​​In an embodiment, pt, pb1, pb2, and pb2 are identical pitches. In an embodiment, pb3 is identical to pb1. Pb2 is identical to pt1, and pb1 is identical to pt2. When measured with a metrology tool (a metrology tool that provides illumination radiation and means for detecting radiation reflected from the target arrangement formed by the overlapping GT and GB), methods known in the art can be used to extract information about overlap, focus, dose, or physical parameters (e.g., tilt, sidewall angle, critical dimensions) of the device structure present on the lithographic wafer. The metrology tool can be a diffraction-based overlap metrology tool (DBO) or an image-based metrology tool (IBO). Furthermore, alignment-related measurement parameters can be extracted when all or only a portion of region GB is measured using a measurement tool suitable for alignment measurement (such as measurements known in the art). Therefore, the overall advantage of the current target arrangement is that it provides both measurement information about the wafer's position (such as that provided from alignment-related measurement processes) and / or information about the relative alignment between two or more layers during the measurement process (such as that provided from overlap or correlation parameter measurement processes). Alignment and overlap or correlation parameters are measurement processes known in the prior art.

[0070] Figure 7 further depicts the target arrangement in Figure 7(a) and an image obtained for a portion of the target arrangement in Figure 7(a). Regions AUL, AUR, ABL, and ABR are the target arrangements found in the so-called bottom layer, which includes Figure 6 The layout of GB, with regions UL, UR, BL, and BR being the target layout found in the so-called top layer, includes... Figure 6 The arrangement of the GT structure. There is overlap between regions AUL, AUR, ABL, and ABR and regions UL, UR, BL, and BR. In the example, region AUL overlaps with region UL, region AUR overlaps with region UR, region ABL overlaps with BL, and region BR overlaps with ABR. Regions AUL, AUR, ABL, and ABR can be used for alignment measurements. As mentioned above, the overlapping portions can be used for alignment and overlap, focus, dose, or other physical parameters of the grating, as understood in the prior art using DBO or IBO measurement tools whenever possible.

[0071] Figure 7(b) illustrates an image formed on the detector of a DBO or IBO measurement tool. The image ImageUL is formed by illuminating at least the region UL, which overlaps with a portion of region AUL, with the irradiation radiation and detecting the scattered radiation. In the example, the grating forming the region UL and AUL is...Figure 2 The arrangement. For measurement applications, the measurement tool (based on the alignment of the measurement tool or DBO or IBO) may include software in a computer carrier that can identify regions of interest relating to the overlap between gratings arranged in GB and GT. In an embodiment, ROIP3 is formed by the overlap between pb3 and pt grating, ROIP2 is formed by the overlap between pb2 and pt grating, and ROIP1 is formed by the overlap between pb1 and pt grating.

[0072] In another embodiment of the invention, the pitch of the target region can be continuous, i.e., the distance between the centroids of each grating varies in a manner described by a function. In this embodiment, the function can be a sine function or a cosine function. The advantage of having a continuous variation in pitch in the region of the measurement or alignment target is that negative effects are minimized due to the presence of discontinuities in the pitch at the edges of the target region. In this embodiment, referring to FIG7(a), the alignment pitch of region AUL can vary continuously toward the measurement pitch of region UL. In this embodiment, the continuous variation in pitch can be controlled by a 2D function that will be described by variations in the x or y direction.

[0073] It is understood that all the specific arrangements shown are purely illustrative, and there exists a nearly infinite number of possible target arrangements falling within the scope of this disclosure. For example, a target arrangement may consist only of a target area for measurement in a single direction. Spacing may also be added between pads to counteract crosstalk and / or parallax issues. The target arrangement shown is designed for measuring overlap. However, the concepts herein also apply to target arrangements designed for measurement of another parameter of interest. For example, a focal arrangement (e.g., forming a region with focal-sensitive asymmetry) may also benefit, as focal-dependent asymmetry will also change the sign in the measurement and thus decouple it from distortion offsets dependent on the measurement tool.

[0074] Associated with a physical grating structure of a target realized on a substrate and a patterning apparatus, embodiments may include a computer program comprising one or more machine-readable instruction sequences describing methods for measuring the target on the substrate and / or analyzing measurements to obtain information about the photolithography process. This computer program may, for example, be in the unit PU and / or... ​ The calculation is performed within the LACU (Label Control Unit). A data storage medium (e.g., semiconductor memory, magnetic disk, or optical disk) containing such a computer program may also be provided. Where existing metrology equipment (e.g., of the type shown in Figure 3) is already in production and / or use, the invention can be implemented by providing an updated computer program product for causing the processor to perform the steps required to calculate the overlap error.

[0075] The program can optionally be arranged to control the optical system, substrate support, etc., to perform the steps required to calculate the overlap error for measuring asymmetry on multiple suitable targets.

[0076] Therefore, a target arrangement is disclosed, which is suitable for measuring a photolithography process including at least two targets positioned within the target arrangement, such that the target arrangement has rotational symmetry. The at least two targets can be positioned within the target arrangement such that the measured properties of the at least two targets have rotational symmetry. A method for measuring parameters of a photolithography process is also disclosed, the method comprising: measuring at least two targets of a measurement target arrangement by irradiating the targets with radiation and detecting the radiation scattered by the targets; and determining a measured property of the targets, wherein the property has rotational symmetry.

[0077] Although the use of embodiments of the invention has been specifically referenced above in the context of optical lithography, it will be understood that the invention can be used in other applications, such as imprint lithography, and wherein, where the context permits, the invention is not limited to optical lithography. In imprint lithography, the morphology in the patterning apparatus defines a pattern produced on a substrate. The morphology of the patterning apparatus can be pressed into a resist layer supplied to the substrate, and the resist is then cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist has cured, the patterning apparatus is removed from the resist, thereby leaving a pattern in the resist.

[0078] As used herein, the terms “radiation” and “beam” include all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having wavelengths of 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm, or about 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having wavelengths in the range of 5 nm to 20 nm) as well as particle beams, such as ion beams or electron beams.

[0079] Where the context allows, the term "lens" can refer to any one or a combination of various types of components, including refractive, reflective, magnetic, electromagnetic, and electrostatic components.

[0080] Without departing from the general concept of the invention, the foregoing description of specific embodiments will fully disclose the general characteristics of the invention, enabling others to easily modify and / or adapt it to various applications, such as the specific embodiments, by applying knowledge within the art, without excessive experimentation. Therefore, based on the teachings and guidance set forth herein, such modifications and variations are intended to fall within the meaning and scope of equivalents of the disclosed embodiments. It will be understood that the wording or terminology used herein is for descriptive purposes, and not for limiting purposes, such that the terminology or terminology of this specification will be interpreted by those skilled in the art based on the teachings and guidance.

[0081] The breadth and scope of this invention should not be limited by any of the exemplary embodiments described above, but should be defined solely by the appended claims and their equivalents.

Claims

1. A target arrangement, comprising: A first target region, wherein the first target region has at least a first pitch and at least a second pitch; The second target region, the second target region having at least a third pitch. Wherein, the portion of the first target region with the second pitch overlaps with a portion of the second target region.

2. The target arrangement according to claim 1, wherein, The first pitch and the second pitch of the first target region are in the vertical direction.

3. The target arrangement according to claim 1, wherein, The second target area is suitable for measuring the overlap, focus, dose, physical parameters of the lithography devices present on the wafer, tilt, sidewall angle and / or critical dimensions.

4. The target arrangement according to claim 1 or claim 2, wherein, The first target area is suitable for alignment measurement.

5. The target arrangement according to claim 1 or claim 3, wherein, The second target region includes multiple regions, each with a different pitch.

6. The target arrangement according to claim 5, wherein, The second target region includes overlapping areas.

7. The target arrangement according to claim 6, wherein, The overlapping regions have different pitches.

8. The target arrangement according to claim 6, wherein, The overlapping regions have the same pitch.

9. The target arrangement according to claim 1, wherein, The pitch variation is described by a continuous function.

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