Method for measuring focus performance of a lithographic apparatus, patterning device and apparatus, device manufacturing method

Abstract

A method for focus measurement for a lithographic process is disclosed. The method comprises receiving a substrate on which a metrology pattern has been printed by a lithographic apparatus using an illumination pupil; illuminating the metrology pattern with a metrology tool to measure a signal based on radiation scattered by the metrology pattern; and determining or monitoring a focus of the lithographic process based on the measured signal. A position of at least a portion of the metrology pattern is dependent on the focus. At least a portion of the metrology pattern has been printed by the lithographic apparatus using an angularly asymmetric illumination pupil.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to European Application 20188032.5, filed on 28 July 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to inspection equipment and methods that can be used, for example, to perform measurements during device fabrication using photolithography. The invention also relates to such a method for monitoring focusing parameters during photolithography. Background Technology

[0004] A photolithography apparatus is a machine that applies a desired pattern onto a substrate (typically onto a target portion of the substrate). Photolithography apparatus can be used, for example, in the fabrication of integrated circuits (ICs). In that case, a patterning apparatus (alternatively called a mask or photomask) can be used to generate a circuit pattern to be formed on a single layer of the IC. This pattern can then be transferred onto a target portion (e.g., a portion including a die, a die, or several dies) on a substrate (e.g., a silicon wafer). Pattern transfer is typically performed by 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 patterned sequentially.

[0005] During photolithography, it is desirable to frequently measure the resulting structure (e.g., for process control and verification). Various tools are known for performing these measurements, including scanning electron microscopes, often used to measure critical dimensions (CD), and specialized tools for measuring overlap (the alignment accuracy of two layers in a device). Recently, various forms of scatterers have been developed for use in the field of photolithography. These devices direct a beam of radiation toward a target and measure one or more properties of the scattered radiation—for example, intensity at a single reflection angle as a function of wavelength; intensity at one or more wavelengths as a function of the reflection angle; or polarization as a function of the reflection angle—to obtain a diffraction “spectrum” that can be used to determine the properties of interest of the target.

[0006] Examples of known scatterers include angle-resolved scatterers of the type described in US2006033921A1 and US2010201963A1. The targets used by such scatterers are relatively large (e.g., 40 μm by 40 μm) gratings, and the measurement beam produces a spot smaller than the grating (i.e., grating underfill). Diffraction-based overlap measurement / inspection using dark-field imaging with diffraction order enables the measurement of overlap and other parameters of smaller targets. These targets can be smaller than the illumination spot and can be surrounded by product structures on a substrate. The intensity from the ambient product structure can be effectively separated from the intensity from the overlapping target by dark-field detection in the image plane.

[0007] Examples of dark-field imaging measurements can be found in international patent applications US20100328655A1 and US2011069292A1, the contents of which are hereby incorporated by reference in their entirety. Further developments of the technology have been described in published patent publications US20110027704A, US20110043791A, US2011102753A1, US20120044470A, US20120123581A, US20130258310A, US20130271740A, and WO2013178422A1. These targets can be smaller than the illumination spot and can be surrounded by product structures on the wafer. Composite grating targets can be used to measure multiple gratings in a single image. The contents of all these applications are also incorporated herein by reference.

[0008] One crucial parameter in the photolithography process that needs to be monitored is the focal length. The integration of an ever-increasing number of electronic components into integrated circuits (ICs) is essential. To achieve this integration, it is necessary to reduce the size of the components and, consequently, increase the resolution of the projection system, enabling increasingly smaller details or linewidths to be projected onto the target portion of the substrate. As the critical dimension (CD) in photolithography shrinks, the consistency of the focal length across and between substrates becomes increasingly important. The CD is the dimension of one or more features (such as the gate width of a transistor) whose changes will cause undesirable variations in the physical properties of one or more features.

[0009] Traditionally, optimal settings are determined through "early-send wafers," which are substrates exposed, developed, and measured before production runs. In early-send wafers, test structures are exposed in a so-called focal length energy matrix (FEM), and optimal focal length and energy (exposure dose) settings are determined from inspection of those test structures. In recent years, focal length measurement targets have been incorporated into production designs to allow for continuous monitoring of focusing performance. These measurement targets should allow for rapid focal length measurement to enable rapid performance measurements in high-volume manufacturing. Ideally, the measurement targets should be small enough that they can be placed within product features without undue space loss.

[0010] Current test structure designs and focal length measurement methods have several drawbacks. Known focal length measurement targets require sub-resolution features and / or grating structures with large pitch. These structures may violate the user's design rules for lithography equipment. High-speed measurement equipment (also known as inspection equipment) operating at visible light wavelengths (such as scatterometers) can be used to efficiently measure asymmetries in grating structures. Known focal length measurement techniques utilize the fact that focal length-sensitive asymmetries can be introduced into structures printed in resist layers through the special design of patterns on patterning devices that define the target structure. For extreme ultraviolet (EUV) lithography, generating sub-resolution features becomes even more difficult when printing is performed using radiation with wavelengths less than 20 nm (e.g., 13.5 nm). For EUV lithography, the resist thickness, and therefore the thickness of the target structure, is relatively small. This reduces diffraction efficiency and thus the signal strength available for focal length measurement.

[0011] For these reasons, there is often a need to develop new techniques for measuring focusing performance during lithography (especially in EUV lithography) and for projection-based lithography. Summary of the Invention

[0012] According to one aspect of this disclosure, a method for measuring focal length in a photolithography process is provided. The method includes: receiving a substrate on which a measurement pattern has been printed using a photolithography apparatus with an illumination pupil; illuminating the measurement pattern with a measurement tool to measure a signal based on radiation scattered by the measurement pattern; and determining or monitoring the focal length of the photolithography process based on the measured signal. The position of at least a portion of the measurement pattern is dependent on the focal length. At least a portion of the measurement pattern has been printed by the photolithography apparatus using an angularly asymmetrical illumination pupil.

[0013] Optionally, the measuring tool is a scatterometer, and optionally, the measuring tool is an angle-resolved scatterometer.

[0014] Optionally, the measurement tool measures the dark field imaging.

[0015] Optionally, the measuring tool measures the dark-field image of the diffraction order of the measured pattern.

[0016] Optionally, the step of receiving the substrate includes receiving a substrate on which a measurement pattern has been printed using extreme ultraviolet radiation.

[0017] Optionally, the measurement pattern includes a periodic structure and a periodic intermediate structure, wherein the periodic structure and the periodic intermediate structure are different and form an interlaced pattern.

[0018] Optionally, the signal includes information about at least one of the intensity and phase difference of relatively higher diffraction orders (optionally, -1 diffraction order and +1 diffraction order).

[0019] Optionally, the measurement pattern includes a first sub-target and a second sub-target, wherein the first sub-target and the second sub-target are printed by a photolithography device using different angularly asymmetrical illumination pupils.

[0020] Optionally, the measurement pattern includes a first part and a second part, wherein the positions of the first part and the second part have different defocus offsets.

[0021] Optionally, the measurement pattern includes a first sub-target and a second sub-target, wherein the first sub-target and the second sub-target are printed by a photolithography device using the same angularly asymmetrical illumination pupil.

[0022] Optionally, the measurement pattern and the periodic structure at least partially overlap, wherein the periodic structure is located on a layer on the substrate that is different from the layer of the measurement pattern.

[0023] Optionally, the measurement pattern includes an angularly symmetrical structure.

[0024] The present invention further provides a computer program that, when executed on a suitable processor-controlled device, makes the processor-controlled device operable to execute processor-readable instructions of the first aspect.

[0025] The present invention further provides a photolithography unit operable to perform the first aspect.

[0026] The present invention further provides a substrate having a structure. The structure is a measurement pattern for determining or monitoring the focal length of a photolithography process based on a signal obtained by measuring radiation scattered by a measurement pattern and measured by a measurement tool, wherein the position of at least a portion of the measurement pattern depends on the focal length; wherein at least a portion of the measurement pattern has been printed by a photolithography apparatus using an angularly asymmetrical illumination pupil.

[0027] The present invention further provides a pattern forming apparatus having a structure. The structure enables the generation of a measurement pattern when printed onto a substrate, wherein the measurement pattern is adapted for focal length measurement or monitoring according to the photolithography process of the first aspect.

[0028] The present invention further provides a measurement pattern for determining or monitoring the focal length of a photolithography process based on a signal measured by a measurement tool, wherein the position of at least a portion of the measurement pattern depends on the focal length; wherein at least a portion of the measurement pattern has been printed by a photolithography apparatus using an angularly asymmetrical illumination pupil.

[0029] 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. These embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the art based on the teachings contained herein. Attached Figure Description

[0030] Embodiments of the invention will now be described with reference to the accompanying illustrative drawings, which are by way of example only, in which corresponding reference numerals indicate corresponding parts, and in the drawings:

[0031] Figure 1 A lithography apparatus having a reflective pattern forming device;

[0032] Figure 2 The lithography equipment and measurement equipment can be used to perform lithographic elements or lithographic clusters according to the method of the present invention;

[0033] Figures 3(a) and 3(b) schematically illustrate the inspection equipment adapted to perform angle-resolved scattering measurement and dark-field imaging inspection methods;

[0034] Figure 4 A schematic representation depicting overall photolithography, illustrating the collaboration between three key technologies used to optimize semiconductor manufacturing;

[0035] Figure 5 The three different illumination pupils of the photolithography apparatus are schematically shown: (a) a dipole; (b) and (c) are monopoles with relative illumination distributions.

[0036] Figure 6 A top view schematically showing a portion of an example of a measurement pattern;

[0037] Figure 7 A schematic cross-sectional view showing two parts of an example measurement pattern and the position offset from the defocus;

[0038] Figure 8A cross-sectional view schematically showing two parts of another example of a measurement pattern and the positional offset of the defocus point;

[0039] Figure 9 A top view schematically showing a portion of another example of a measurement pattern and the positional offset of the defocus;

[0040] Figure 10 A cross-sectional view schematically showing a portion of another example of a measurement pattern and the positional offset of the defocus point;

[0041] Figure 11 It is a graph showing the experimental results of positional offset relative to the focal length of the lithography equipment used for the structure;

[0042] Figure 12 This is a flowchart of a method according to an embodiment of the present invention. Detailed Implementation

[0043] Before describing the embodiments of the invention in detail, it is instructive to present an example environment that can be used to implement the embodiments of the invention.

[0044] Figure 1 A lithography apparatus 100 including a source module SO is schematically depicted according to an embodiment of the present invention. The apparatus includes:

[0045] An irradiation system (irradiator) IL, which is configured to modulate a radiation beam B (e.g., EUV radiation).

[0046] A support structure (e.g., a mask stage) MT, which is configured to support a pattern forming apparatus (e.g., a mask or a mask plate) MA and is connected to a first positioner PM configured to accurately position the pattern forming apparatus.

[0047] A substrate stage (e.g., a wafer stage) WT, configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate; and

[0048] A projection system (e.g., a reflective projection system) PS, which is configured to project a pattern, which is imparted to the radiation beam B by the pattern forming apparatus MA, onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0049] Irradiation systems may include various types of optical components for guiding, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

[0050] The support structure MT holds the patterning apparatus in a manner dependent on the orientation of the patterning apparatus MA, the design of the lithography equipment, and other conditions such as whether the patterning apparatus is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning apparatus. The support can be, for example, a frame or stage, which may be fixed or movable as needed. The support structure ensures that the patterning apparatus is, for example, in the desired position relative to the projection system.

[0051] The term "patterning apparatus" should be interpreted broadly as any apparatus that can be used to impart a pattern to a radiation beam in the cross-section of the beam in order to generate a pattern in a target portion of a substrate. The pattern imparted to the radiation beam may correspond to a specific functional layer in a device (such as an integrated circuit) generated in the target portion.

[0052] Typically, patterning apparatuses used in photolithography can be either transmissive or reflective. Examples of patterning 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 attenuating phase-shift masks, as well as various hybrid mask types. Examples of programmable mirror arrays employ a matrix configuration of small mirrors, each of which can be individually tilted to reflect the incident radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam reflected by the mirror matrix.

[0053] Similar to an illumination system, a projection system may include various types of optical components suitable for the exposure radiation used or for other factors such as the use of a vacuum, including refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof. It may be desirable to use a vacuum for EUV radiation because other gases may absorb excessive radiation. Therefore, a vacuum environment can be provided throughout the beam path by means of vacuum walls and a vacuum pump.

[0054] As described herein, the apparatus is of the reflective type (e.g., employing a reflective mask). The focal length measurement technique disclosed herein was developed specifically for use with reflective pattern forming apparatuses (masks), where illumination is not in a direction perpendicular to the plane of the pattern forming apparatus surface, but at a slightly angled angle. In principle, the same technique can be applied to transmissive pattern forming apparatuses if illumination introduces asymmetry for some reason. Conventionally, the illumination of a mask is designed to be symmetrical, but this is generally not possible in the case of reflective masks.

[0055] Some embodiments of this disclosure use reflective pattern forming apparatus to take advantage of asymmetry in a projection system. Other embodiments are applicable to any type of projection system.

[0056] Photolithography equipment can be of the type with two (dual-platform) or more upper substrate stages (and / or two or more mask stages). In such a “multi-platform” machine, additional stages can be used in parallel, or preparatory steps can be performed on one or more stages while one or more other stages are used for exposure.

[0057] refer to Figure 1 The irradiator IL receives an extreme ultraviolet radiation beam from the source module SO. Methods for generating EUV light include, but are not limited to, converting a material having at least one element (e.g., xenon, lithium, or tin) into a plasma state using one or more emission lines in the EUV range. In one such method (often referred to as laser-generated plasma "LPP"), the desired plasma can be generated by irradiating a fuel (such as droplets, streams, or clusters of material having the desired spectral emission element) with a laser beam. The source module SO may include a laser ( Figure 1 (Not shown) This is part of an EUV radiation system, where the laser is used to provide a laser beam for exciting the fuel. The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector disposed in the source module. For example, when a CO2 laser is used to provide a laser beam for fuel excitation, the laser and the source module can be separate entities.

[0058] In this case, the laser is not considered a component forming the lithography apparatus, and the radiation beam is delivered from the laser to the source module by means of a beam delivery system including, for example, suitable directional mirrors and / or beam expanders. In other cases, such as when the source is a discharge-generated plasma EUV generator (often referred to as a DPP source), the source can be a component of the source module.

[0059] An irradiator IL may include adjusters for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer radial range and / or inner radial range (often referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the illumination pupil plane of the irradiator can be adjusted. Additionally, the irradiator IL may include various other components, such as faceted field mirror assemblies and faceted pupil mirror assemblies. The irradiator IL can be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0060] A radiation beam B is incident on a patterning apparatus (e.g., a mask) MA held on a support structure (e.g., a mask stage) MT and patterned by the patterning apparatus. After reflection from the patterning apparatus (e.g., the mask) MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. The substrate stage WT can be accurately moved, for example, to position the different target portions C within the path of the radiation beam B, by means of a second locator PW and a position sensor PS2 (e.g., an interferometer, a linear encoder, or a capacitive sensor). Similarly, a first locator PM and another position sensor PS1 can be used to accurately position the patterning apparatus (e.g., the mask) MA relative to the path of the radiation beam B. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the patterning apparatus (e.g., the mask) MA with the substrate W.

[0061] The described device can be used in at least one of the following modes:

[0062] 1. In step mode, the support structure (e.g., mask stage) MT and substrate stage WT are kept substantially stationary (i.e., single static exposure) while the entire pattern to be applied to the radiation beam is projected onto the target portion C in one go. Then, the substrate stage WT is shifted in the X and / or Y directions to allow different target portions C to be exposed.

[0063] 2. In scanning mode, the support structure (e.g., mask stage) MT and the substrate stage WT are scanned synchronously, while the pattern applied to the radiation beam is projected onto the target portion C (i.e., single dynamic exposure). The velocity and orientation of the substrate stage WT relative to the support structure (e.g., mask stage) MT can be determined by the magnification (reduction ratio) and image inversion characteristics of the projection system PS.

[0064] 3. In another mode, while projecting the pattern applied to the radiation beam onto the target portion C, the support structure (e.g., mask stage) MT holding the programmable patterning apparatus is kept substantially stationary, and the substrate stage WT is moved or scanned. In this mode, a pulsed radiation source is typically used, and the programmable patterning apparatus is updated as needed after each movement of the substrate stage WT or between successive radiation pulses during scanning. This mode of operation can be readily applied to maskless lithography utilizing programmable patterning apparatuses (such as programmable mirror arrays of the type mentioned above).

[0065] Alternatively, combinations and / or variations of the usage patterns described above, or entirely different usage patterns, may be employed.

[0066] It should be understood that photolithography equipment in Figure 1The representation is in a highly illustrative form, but such form is all that is necessary for this disclosure.

[0067] like Figure 2 As shown, the lithography equipment LA forms part of the lithography unit LC (sometimes also referred to as a lithography cell or lithography cluster), which also includes equipment for performing pre-exposure and post-exposure processes 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 transport device or robot RO picks up the substrate from input / output ports I / O1, I / O2, moves the substrate between different process units, and subsequently delivers the substrate to the lithography equipment's feed stage LB. These devices (often collectively referred to as a track or coating / developing system) are controlled by a track or coating / developing system control unit TCU, which itself 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.

[0068] To ensure accurate and consistent exposure of the substrate W exposed by the lithography equipment, it is desirable to inspect the exposed substrate to measure properties such as overlap error between subsequent layers, line thickness, critical dimension (CD), etc. Therefore, the manufacturing facility with the lithography unit LC also includes a metrology system (MET), which receives some or all of the substrates W that have been 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, the exposure of subsequent substrates can be adjusted, especially when inspection can be performed quickly enough so that other substrates in the same batch are still awaiting exposure. Furthermore, exposed substrates can be stripped and reworked to improve yield or discarded, thereby avoiding further processing of substrates known to be defective. In cases where only some target portions of the substrate are defective, additional exposure can be performed only on the good target portions.

[0069] Within a metrology system (MET), inspection equipment is used to determine the properties of a substrate, and specifically, how the properties of different substrates or different layers of the same substrate vary between different layers. Inspection equipment can be integrated into a lithography unit (LA) or a lithography cell (LC), or it can be a separate device. For the fastest possible measurement, it is desirable to have the inspection equipment measure the properties in the exposed resist layer immediately after exposure. However, latent images in resist have very low contrast—there is 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 such a stage, the image in the resist can be referred to as a semi-latent image. It is also possible to measure the developed resist image—in which case the exposed or unexposed portions of the resist have been removed—or after a pattern transfer step such as etching. The latter possibility limits the likelihood of reworking defective substrates, but can still provide useful information.

[0070] Figure 3(a) schematically illustrates the key components of an inspection apparatus for performing so-called dark-field imaging measurements. The apparatus can be a standalone device or incorporated into, for example, a lithography apparatus LA or a lithography unit LC at a measurement station. The optical axis with several branches running through the apparatus is indicated by the dashed line O. Figure 3(b) illustrates the target grating structure T and diffraction rays in more detail.

[0071] As described in the previous application cited in the introduction, the dark-field imaging apparatus of FIG3(a) can be part of an alternative to a spectral scatterer or a multi-purpose angle-resolved scatterer used in addition to a spectral scatterer. In this type of inspection apparatus, the radiation emitted by the radiation source 11 is modulated by an illumination system 12. For example, the illumination system 12 may include a collimating lens system, a color filter, a polarizer, and an aperture device 13. The modulated radiation follows an illumination path IP, in which the modulated radiation is reflected by a partially reflective surface 15 and focused by a microscope objective 16 onto a spot S on the substrate W. A measurement target T can be formed on the substrate W. The lens 16 has a high numerical aperture (NA), preferably at least 0.9 and more preferably at least 0.95. An immersion fluid may be used as needed to obtain a numerical aperture greater than 1.

[0072] In this example, objective lens 16 is also used to collect radiation scattered by the target. The collection path CP for this returned radiation is schematically shown. A multi-purpose scatterer may have two or more measurement branches in the collection path. An example illustrated as a pupil imaging branch includes a pupil imaging optics system 18 and a pupil image sensor 19. Imaging branches are also shown, and will be described in more detail below. Additionally, other optical systems and branches will be included in the actual device, for example, to collect reference radiation for intensity normalization, for coarse imaging of the target, for focusing, etc. Details of these optical systems and branches can be found in the previously published materials mentioned above.

[0073] When the measurement target T is set on the substrate W, this can be a 1-D grating, which is printed such that, after development, the grating strips are formed from solid resist lines. The target can also be a 2-D grating, which is printed such that, after development, the grating is formed from solid resist pillars or vias in the resist. The grating strips, pillars, or vias can alternatively be etched into the substrate. Each of these gratings is an example of a target structure whose properties can be studied using inspection equipment.

[0074] Various components of the illumination system 12 can be adjustable to implement different measurement “configurations” within the same device. Besides selecting wavelength (color) and polarization as characteristics of the illumination radiation, the illumination system 12 can also be adjusted to implement different illumination profiles. The plane of the aperture device 13 is conjugate to the illumination pupil plane of the objective lens 16 and the plane of the pupil image detector 19. Therefore, the illumination profile defined by the aperture device 13 defines the angular distribution of light incident on the substrate W in the spot S. To implement different illumination profiles, the aperture device 13 can be positioned in the illumination path. The aperture device can include different holes mounted on a movable slider or wheel. Alternatively, the aperture device can include a programmable spatial light modulator. As another alternative, optical fibers can be positioned at different locations in the illumination pupil plane and can be selectively used to transmit light or not transmit light at their corresponding locations. These variations are discussed and illustrated in the literature cited above.

[0075] In the first example illumination mode, aperture 13N is used and ray 30a is provided, such that the angle of incidence is at “I” in Figure 3(b) as shown. The path of the zeroth-order ray reflected by the target T is labeled “0” (not to be confused with the optical axis “O”). In the second illumination mode, aperture 13S is used, such that ray 30b is provided, in which case the angle of incidence and the angle of reflection are reversed compared to the first mode. In Figure 3(a), the zeroth-order rays of the first example illumination mode and the second example illumination mode are labeled 0 (13N) and 0 (13S), respectively. Both of these illumination modes will be identified as off-axis illumination modes. Many different illumination modes can be implemented for different purposes, including coaxial illumination modes.

[0076] As shown in more detail in Figure 3(b), the target grating T, as an example of the target structure, is positioned such that the substrate W is perpendicular to the optical axis O of the objective lens 16. In the case of off-axis illumination profile, the illumination ray I, which is irradiated onto the grating T at an angle deviating from the axis O, produces one zero-order ray (solid line 0) and two first-order rays (dotted line +1 and double-dotted line -1). It should be remembered that, in the case of using an overfilled small target grating, these rays are merely one of many parallel rays covering the area of ​​the substrate including the measurement target grating T and other features. Since the beam of illumination ray 30a has a finite width (required to receive a useful amount of light), the incident ray I will actually occupy an angular range, and the diffracted rays 0 and +1 / -1 will be slightly dispersed. According to the point spread function of the small target, each order +1 and -1 will be further dispersed over the angular range, rather than a single ideal ray as shown.

[0077] In the branch of the collection path used for dark-field imaging, the imaging optics system 20 forms an image T′ of the target on the substrate W on the sensor 23 (e.g., a CCD or CMOS sensor). An aperture stop 21 is positioned in a plane within the imaging branch of the collection path CP, conjugate to the illumination pupil plane of the objective lens 16. The aperture stop 20 may also be referred to as the pupil stop. The aperture stop 21 can take different forms, just as the illumination aperture can take different forms. The aperture stop 21, combined with the effective aperture of the lens 16, determines which portions of the scattered radiation will produce the image on the sensor 23. Typically, the aperture stop 21 is used to block the zero-diffraction-order beam, so that the image of the target formed on the sensor 23 is formed by only a first-order beam. In an example where two first-order beams are combined to form an image, this image would be a so-called dark-field image, equivalent to dark-field microscopy. As an example of the aperture stop 21, an aperture 21a that only allows coaxial radiation can be used. When using off-axis illumination in combination with aperture 21a, only one of these first-order images is imaged at a time.

[0078] The image captured by sensor 23 is output to an image processor and controller PU, the functionality of which depends on the specific type of measurement being performed. For this purpose, measurements of the asymmetry of the target structure are performed. These asymmetry measurements can be combined with knowledge of the target structure to obtain measurements of performance parameters for the photolithography process used to form the target structure. Performance parameters that can be measured in this way include, for example, overlap, focal length, and dose. A specific design of the target is provided to allow these measurements of different performance parameters via the same underlying asymmetry measurement method.

[0079] Referring again to Figure 3(b) and the first example illumination mode with ray 30a, a +1 diffraction order ray from the target grating enters the objective lens 16 and contributes to an image recorded at the sensor 23. When using the second illumination mode, ray 30b is incident at the opposite angle to ray 30b, and therefore a -1 diffraction order ray enters the objective lens and contributes to the image. When using off-axis illumination, the aperture stop 21a blocks zero-order radiation. As described in previously published materials, the illumination mode can be defined using off-axis illumination in the X and Y directions.

[0080] Asymmetric measurements can be obtained by comparing images of the target grating under these different illumination modes. Alternatively, asymmetric measurements can be obtained by maintaining the same illumination mode but rotating the target. Although off-axis illumination is shown, coaxial illumination of the target is used instead, and approximately only one first order of diffraction light can be transmitted to the sensor using a modified off-axis aperture 21. In another example, a pair of off-axis prisms 21b are used in combination with a coaxial illumination mode. These prisms have the effect of directing the +1 and -1 orders to different positions on the sensor 23, allowing these prisms to be detected and compared without two consecutive image capture steps. This technique is disclosed in the published patent application US2011102753A1 mentioned above, the contents of which are incorporated herein by reference. Instead of a first-order beam or other than a first-order beam, second-order, third-order, and higher-order beams (not shown in FIG3) can also be used for measurements. As another variation, the off-axis illumination mode can be kept constant while the target itself is rotated 180 degrees below the objective lens 16 to capture an image using relative diffraction orders.

[0081] Typically, the patterning process in the photolithography equipment 100 (LA) is one of the most critical steps in the process, requiring high accuracy in the dimensional calibration and placement of the structures on the substrate W. To ensure this high accuracy, three systems can be combined... Figure 4The diagram schematically depicts a so-called "holistic" control environment. One of these systems is a lithography apparatus (LA), which is (in effect) connected to a metrology tool (MT) (the second system) and a computer system (CL) (the third system). The key to this "holistic" environment is optimizing the collaboration between these three systems to enhance the overall process window and provide a tight control loop, thereby ensuring that the patterning performed by the lithography apparatus (LA) remains within the process window. The process window defines a set of process parameters (e.g., dose, focal length, overlap) within the defined result produced by a particular manufacturing process (e.g., a functional semiconductor device)—typically allowing variations in process parameters during the lithography or patterning process.

[0082] The computer system CL can use the design layout (partial) to be patterned to predict which resolution enhancement techniques to use and perform computational lithography simulations and calculations to determine which mask layout and lithography equipment settings will enable the patterning process. The maximum overall process window (defined by the double arrows in the first scale SC1) is shown in the image. Figure 4 (Depicted in the image). Typically, resolution enhancement techniques are configured to match the patterning possibilities of the lithography equipment LA. A computer system CL can also be used to detect where the lithography equipment LA is currently operating within the process window (e.g., using input from a metrology tool MT) to predict whether defects might exist due to, for example, suboptimal processing (in...). Figure 4 (This is depicted by the arrow pointing to "0" in the second scale SC2).

[0083] The measurement tool (MT) can provide input to the computer system (CL) for accurate simulation and prediction, and can provide feedback to the lithography equipment (LA) to identify possible drifts in, for example, the calibration status of the lithography equipment (LA). Figure 4 (The middle is depicted by multiple arrows in the third scale SC3).

[0084] The following disclosure illustrates techniques for measuring the focusing performance of a photolithography process using tilted illumination on a reflective patterning apparatus. These techniques are particularly applicable to EUV lithography, where reflective optics in a near-vacuum environment are required. Simultaneously with printing product features, measurement targets, including certain focal length measurement patterns, are printed on a substrate. A diffraction-based technique, such as that shown in Figure 3, will be used to measure the asymmetry of these printed patterns. To allow for the use of small targets, it will be assumed that the dark-field imaging branch of the apparatus will be used to perform these asymmetry measurements. However, a pupil imaging branch can also be used for diffraction-based measurements of asymmetry. Of course, the apparatus shown in Figure 3 is merely one example of an inspection apparatus and method that can be used to measure asymmetry.

[0085] In the context of lithography equipment operating in the DUV wavelength range, targets based on diffraction-based focal length (DBF) measurements have been successfully designed and used. Known types of DBF targets are generated by including sub-segmented features in a grating pattern on a mask. These features, adjacent to more solid-state features, have dimensions smaller than the imaging resolution of the lithography equipment. Therefore, dimensions smaller than the imaging resolution of the lithography equipment are not printed as separate features in the resist layer on the substrate, but they affect the printing of solid-state features in a way that is sensitive to focal length errors. Specifically, the presence of these features creates an asymmetric resist profile for each line in the grating within the DBF measurement target, where the degree of asymmetry depends on the focal length. Therefore, a measurement tool such as that of an inspection apparatus like Figure 3 can measure the degree of asymmetry based on the target formed on the substrate and translate the degree of asymmetry into the scanner focal length.

[0086] Unfortunately, known DBF measurement target designs are not suitable for all situations. In EUV lithography, the resist film thickness is significantly lower than that used in DUV immersion lithography, resulting in low diffraction efficiency and difficulty in extracting accurate asymmetry information from the diffracted radiation in the scatterometer. Furthermore, due to the inherently higher resolution of the imaging system in EUV lithography, features with smaller printing resolutions than those in DUV immersion lithography become “solid” features that can be printed using EUV lithography. Setting similar sub-resolution features on an EUV mask is quite impractical and / or may violate semiconductor manufacturers’ “design rules.” Such rules are typically established as a way to constrain feature design to ensure that the printed features meet their process requirements. In any case, working outside the design rules makes it difficult to simulate the process performed on the DBF target, turning optimal target design and focal length measurement calibration into a trial-and-error problem. The expectation of conforming to design rules applies to DBF targets in DUV lithography, not just EUV lithography.

[0087] The focal length (DBF) measurement target should possess a unique, preferably monotonic, asymmetric signal that varies depending on the target's defocus. In such a context, the asymmetric signal can describe the difference (e.g., intensity difference and / or phase difference) between relatively higher diffraction orders (e.g., +1 diffraction order versus -1 diffraction order). High accuracy and sensitivity are also important. Other considerations include minimizing dose and (e.g., from processing effects) other crosstalk effects, and ensuring good tool-to-tool matching between instruments.

[0088] Scattermeters can be used to measure several different aspects of photolithography equipment, such as focal length and dose. The focal length and dose of radiation used in photolithography equipment directly affect the parameters of the pattern or structure exposed on the substrate. Parameters that can be measured using a scattermeter are the physical properties of the structure that has been printed onto the substrate, such as, for example, the critical dimension (CD) or sidewall angle (SWA) of a stripe structure. For example, depending on the structure being measured, the critical dimension is actually the average width of the structure, such as a stripe, gap, dot, or hole. The sidewall angle is the angle between the surface of the substrate and the rising or falling portion of the structure.

[0089] Focal length and dose have been determined simultaneously by scattering measurements or scanning electron microscopy based on the structure in the mask pattern, which generates the structure on the substrate, from which measurements are obtained, as described in U.S. Patent Application US 20110249244A1, which is incorporated herein by reference in its entirety. A single structure can be used as long as it has a unique combination of critical size measurements and sidewall angle measurements for each point in the focal length energy matrix (FEM) when exposed and processed. If these unique combinations of critical dimensions and sidewall angles are available, the focal length and dose values ​​can be uniquely determined based on these measurements.

[0090] The properties of reflected radiation are compared with mathematical models or libraries based on previous measurements or simulations and extrapolation of the relationship between these properties (reflected radiation, CD, SWA) and the focal length and / or dose-related properties of the exposure equipment.

[0091] The focal length and / or dose-related properties of an exposure apparatus can be focal length offsets (e.g., focal length offsets can be caused by lens misalignment) or dose offsets (e.g., dose offsets can be caused by fluctuations in the intensity of the radiation beam). The focal length and / or dose-related properties of an exposure apparatus can also be other focus-related parameters, such as astigmatism, contrast, or lens aberrations (typically expressed as Zernike coefficients). Alternatively, the focal length and / or dose-related properties of an exposure apparatus can be irradiation (i.e., radiation) parameters, such as dose or intensity variations. Also alternatively, the measured properties can be parameters that affect the resist in a manner similar to those caused by dose, such as localized bake plate temperature (which produces variations in reflected radiation or CD or SWA on the substrate surface, similar to variations in dose on the substrate surface) and resist variations (again, variations in resist thickness or density, etc., will produce variations in CD and SWA, etc., in a manner similar to variations in dose).

[0092] The irradiator IL of the lithography apparatus 100 can adjust the radiation beam B to generate various radiation intensity distributions in the irradiated pupil plane using components such as faceted field mirror devices and pupil mirror devices. The radiation beam B can be off-axis or coaxial, similar to that discussed with respect to the scatterer in Figure 3.

[0093] Two examples of projecting an image from a patterning apparatus MA onto an off-axis pattern on a substrate W are as follows: Figure 5 The image shows dipoles and monopoles.

[0094] In dipole mode, the radiation distribution of the radiation beam B in the illumination pupil 510 includes two off-axis regions, for example, as Figure 5 501 and 502 are shown in (a). Optionally, these two distinct regions 501 and 502 are located at or near the edge of the illumination pupil 510. Optionally, the two distinct regions are located on opposite sides of the pupil and have angular (or rotational) symmetry about the center of the pupil. The intensity distribution in the pupil may also have angular symmetry.

[0095] When the intensity distribution of the irradiation beam B in the irradiation pupil plane is angularly asymmetrical, or so-called rotationally asymmetrical, the position of at least a portion of the printed structure can be focal length dependent. This means that, while other lithography parameters remain constant, the focal length at which the lithography apparatus prints the structure is related to the position of the structure on the wafer. This effect can be used for focal length measurement, which determines the focal length value and / or monitors the focal length of the lithography apparatus by measuring the printed structure using a measuring tool during the lithography process. In one embodiment, within a structure (e.g., a focus target / marker), different substructures can have different designs, such as different pitches and / or critical dimensions (CD), and the positional offset from defocus can be pitch / CD dependent. In another embodiment, within a structure, different substructures can be printed using different irradiation modes (i.e., different radiation intensity distributions in the irradiation pupil plane, optionally, different pupil angular asymmetries), and the positional offset of the different substructures can also differ due to defocus. Features of the two embodiments can also be combined and used simultaneously.

[0096] An example of a mode with pupil angular asymmetry is the monopole. A monopole can be a radiation setting mode in which radiation is focused onto a single off-axis region within the illumination pupil. An example of an illumination pupil is... Figure 5 (b) shows a monopole pupil 520 with only one left-side region 503, which can be referred to as a left-side monopole. Axes TC and NTC represent two orthogonal directions in the pupil plane, respectively. Figure 5(c) shows a second example of a monopole pupil, which has a right region 504 at a relative position to the left region 503. The second example may be referred to as a right monopole.

[0097] Another example of a mode with angular asymmetry in the pupil is a dipole mode with angular asymmetry in the plane of illumination pupil, for example, having different intensities and / or different shapes for the left monopole and the right monopole.

[0098] The transverse cross-sectional shape of monopole radiation is conventionally circular, but it can also be any other distribution concentrated around the sigma center: for example, a circle, a square, a leaf, a line, etc. The intensity distribution of monopole radiation does not need to be uniform. The intensity distribution of monopole radiation can be a top-hat distribution. However, the intensity distribution of monopole radiation can also be a collection of discrete or pixelated individual spots within a given shape.

[0099] Figure 6 A measurement pattern 1600 is schematically shown in a top view of a substrate. The measurement pattern 1600 may have periodicity in the Xt direction, and the repeating units of such a pattern include line structures or features 610 spaced apart in the periodic direction. Optionally, the periodicity, which may be referred to as the pitch, is 1 μm. The line structure 610 may be a straight line extending in the Yt direction. When the measurement pattern 1600 is printed using a photolithography apparatus, the periodic direction may correspond to... Figure 5 The NTC direction in this example can be the X-direction of the patterning apparatus and the substrate, while the line feature can extend along the Y-direction. Optionally, the Xt and Yt directions are perpendicular. Optionally, each line structure in the line structure can be segmented in one or more directions. For example, at least a portion of line structure 610 is segmented in both the Yt and Xt directions. The segments can be the same or different in different directions. Line structure 610 can be the same or different in one or more of its length, width, or segments.

[0100] exist Figure 6 In one example of this embodiment shown, a portion of the measurement pattern 600 is shown as an enlarged view of the portion indicated by the dashed rectangle. All or part of the line feature 610 is further segmented into a first segment feature 601 and a second segment feature 602 along the same direction Yt. Segment features 601 and 602 may be periodic in the same direction in different design configurations. For example, segment features 601 and 602 may differ in one or more aspects of pitch, duty cycle, space width, and line width. The duty cycle is defined by dividing the space width by the pitch. Segment features 601 and 602 form an interlaced pattern in their periodic direction. All features shown in the figure can be visualized through pupils with the same angular asymmetry (e.g., Figure 5(b) The left monopole pupil shown in the photolithography equipment is used to print it.

[0101] Segmented features 601 and 602 can be as follows: Figure 7 The left portion shows different positional shifts with defocus in the periodic direction. Figure 7 This is a schematic side view (or cross-sectional view). In one embodiment, the position of the first segment feature 601 is not out of focus, while the position of the second segment feature 602 is out of focus. Figure 7 The example shown in the left-hand portion depicts a gradual change in focal length from (a) to (e), with the second segment feature 602 gradually shifting to the right, i.e., further away from the first segment feature 601. The focal length of c in this example can be referred to as the optimal focal length.

[0102] like Figure 7 As visible in the right-hand portion, the measurement pattern 600 may optionally include pupils similar to or equivalent to the line feature 610, but with different angular asymmetry (e.g., Figure 5 The second line feature 620 is printed using a photolithography apparatus (as shown in (c) of the right monopole pupil). Regarding Figure 6 One or more of the features of the line structure 610 may also be presented in the second line feature 620 as needed. In this embodiment, the line feature 610 and the second feature 620 may be referred to as the first sub-target and the second sub-target, respectively. When the focal length is the optimal focal length c, the distance between the line feature 610 and the second feature 620 is the same as the distance between the first segmented line feature 603 and the second segmented line feature 604, while as the focal length is gradually changed from (a) to (e), the second segmented line feature 604 in the second line feature 620 gradually shifts to the left (i.e., in the opposite direction to the positional offset of the second segmented line feature 602 in the first line feature 610). Although the first sub-target and the second sub-target are referred to as line features in this embodiment, it should be noted that other features may also work as long as at least a portion of the first sub-target and at least a portion of the second sub-target are printed by a photolithography apparatus with different angularly asymmetrical pupils and have different defocus positional offsets.

[0103] exist Figure 7 In the illustrated embodiment, any two of the segmented line features 601, 602, 603, and 604 may be referred to as the first and second portions of the measurement pattern 1600, and the positions of the first and second portions have different defocus offsets. When the second segmented line feature 602 in the first line feature 610 and the second segmented line feature 604 in the second line feature 620 are referred to as the first and second portions of the measurement pattern 1600, the positions of the first and second portions have opposite defocus offsets.

[0104] The first and second piecewise linear features can be printed close enough to each other that they are not distinguishable from the measurement tool. In this way, the measurement tool treats the piecewise linear features as an asymmetric structure and infers the focal length based on the detected signal (optionally, the detected intensity asymmetry, optionally, the intensity difference between the +1 and -1 diffracted orders). A computer can then be used to extract the focal length from the detected signal.

[0105] Figure 8 A schematic cross-sectional view of two portions of another example of a measurement pattern 800 having a focal length that gradually changes from (a) to (e) is shown. Optionally, regarding... Figure 6 and 7 One or more features of the measurement pattern 1600 may also be present in the measurement pattern 800. The first line feature or sub-target 801 and the second line feature or sub-target 802 of the measurement pattern 800 at least partially overlap with periodic structures 803 and 804, respectively, wherein the periodic structures are located on a layer on the substrate different from the layer of the measurement pattern 800. The first sub-target 801 and the second sub-target 802 may be periodic structures. In this embodiment, the line features 801 and 802 may be gratings at the top layer, which may be referred to as top gratings, and the periodic structures 803 and 804 are gratings at the bottom layer, which may be referred to as bottom gratings. A pitch-dependent pattern offset relative to the bottom grating will introduce a pattern position offset proportional to defocus. The first sub-target 801 and the second sub-target 802 may be printed using a photolithography apparatus with photolithography pupils having different angular asymmetric pupils. Optionally, the top grating may have one or more of the same periodicity as the bottom grating. Optionally, the top grating may have a different periodicity than the bottom grating. Optionally, the top grating is printed using left and right monopoles respectively. Therefore, the defocus position offsets of the first sub-target 801 and the second sub-target 802 have opposite directions. In an embodiment, the first sub-target 801 and the second sub-target 802 may be referred to as the first portion and the second portion of the measurement pattern 800.

[0106] Focal length variations can introduce opposite overlap between the top and bottom gratings of the structures printed by the left and right monopoles. The intensity asymmetry ΔI measured by the left and right monopoles, respectively, is... L ΔI R It can be expressed as

[0107] ΔI L =K(OV) focus +OV c )

[0108] ΔIR =K(-OV) focus +OV c )

[0109]

[0110] Among them, OV focus The sign of the overlap caused by focal length can be reversed when the illumination setting is switched to the opposite setting (e.g., from the left monopole to the right monopole), OV c This is a common overlap error introduced through other means. The difference ΔI L -ΔI R It scales linearly with the focal length drift, proportional to the pattern position offset and with small focal length changes.

[0111] OV focus The overlap caused by defocus is proportional to the focal length. K can be obtained with the help of the deviation d, which is the overlap introduced between the top and bottom gratings.

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118] In another embodiment, instantaneous focal length measurements can be printed via a photolithography process using only one type of exposure (i.e., using only a single monopole or dipole with angular asymmetry within the plane of the illumination pupil). In one embodiment, each line feature 610 includes two distinct pitches. A defocus duty cycle variation exists. The intensity of the diffraction order measured by the scatterometer varies with the duty cycle.

[0119] Figure 9 A top view schematically showing a portion of another example of a measurement pattern 900 and its defocus position offset. Optionally, regarding... Figure 6 , Figure 7 and Figure 8One or more features of the measurement pattern 1600 may also exist in the measurement pattern 900. The measurement pattern 900 includes a first part, a first sub-target 901, and a second part, a second sub-target 902. The first part, the first sub-target 901, and the second part, the second sub-target 902 can be printed by a photolithography apparatus using the same or different angularly asymmetrical illumination pupils. The positions of the first part and the second part have different defocus offsets due to different designs. Each line feature 910 of the measurement pattern 900 includes two parts, optionally a top structure 9101 and a bottom structure 9102 printed in a single layer, such as by... Figure 9 The dashed lines delineate the area. Line feature 910 is an angularly symmetrical structure that enables focal length measurement using only one type of exposure (optionally, a single monopole exposure or an angularly asymmetrical dipole within the illumination pupil plane). An angularly symmetrical structure with one type of exposure can provide absolute focal length information using the signal difference between the top and bottom structures.

[0120] Figure 10 A cross-sectional view of a portion of another example of a measurement pattern 1000 with a focal length that gradually changes from (a) to (e) is schematically shown. Regarding Figure 6 , Figure 7 , Figure 8 and Figure 9 One or more features of the measurement pattern may also exist in the measurement pattern 1000 as needed. The measurement pattern 1000 includes a first segmentation feature 1001 and a second segmentation feature 1002, which can be combined with... Figure 6 and Figure 7 The segmentation features 601 and 602 shown in the figure are the same or similar. Figure 10The feature in (c) is printed at a reference focal length, which may be the optimal focal length for the photolithography process. For example, in the cases shown in (a) and (e), large defocus in an uncorrelated imaging system can introduce an image reversal effect, and the image reversal appears as a half-pitch-related pattern shift. When features with different pitches are printed out of focus, some features with pitches exhibit the image reversal effect while others do not. In this example, the first segmented feature 1001 with a first pitch does not exhibit the image reversal effect within the focal length regions (a) to (e), while the second segmented feature 1002 with a second pitch exhibits the reversal effect within focal lengths (a) and (e), thus producing a half-pitch-related pattern shift compared to (c), indicated by the dashed line. Since the focal length of the image reversal effect can be calculated if certain photolithography and / or feature parameters are known (e.g., the periodicity of the segmented features is known), the image reversal effect can be measured by a scatterometer and used for focal length measurement. In this embodiment, the first segment feature 1001 and the second segment feature 1002 may be referred to as the first part and the second part of the measurement pattern 800. The cross-sectional shape of the structure can vary with different focal lengths, such as... Figure 10 As shown, the cross-sectional shape of all structures is rectangular at focal length c and trapezoidal at focal lengths a, b, d, and e. Note that the cross-sectional shapes presented herein are for illustrative purposes only, and the actual cross-sectional shapes may differ.

[0121] Figure 11 This is a graph showing the experimental results relating the positional offset (Y-axis) to the focal length (X-axis) of the periodic feature, with the left monopole (a) and right monopole (b), respectively. As can be seen, opposite monopoles will result in opposite positional offsets of the periodic structure at different focal lengths. Combinations of pitches can be used to amplify the focal length capture range. Based on the sensitivity and practical measurement accuracy from recent experimental data, the embodiments discussed are expected to result in high accuracy.

[0122] It has been found that the measurement offset caused by different angular asymmetric illumination pupils matches the simulation offset very well. Therefore, if different illuminations are used for exposure, the focal length can also be inferred from the simulation results using different illuminations.

[0123] Position offset can depend on many parameters of the measurement pattern. A pitch that is less critical to the imaging parameters of the photolithography process can be chosen, but still demonstrates a significant difference in the offset performance of defocused patterns printed with different pupils having angular asymmetry. For example, different pupils with angular asymmetry can be different monopoles. Alternatively, different pupils with angular asymmetry can be different dipoles with asymmetrical pupils.

[0124] All the embodiments mentioned above can be used in the method for focal length measurement in the photolithography process, such as Figure 12 As depicted, the first step 120 involves receiving a substrate on which a measurement pattern has been printed using a photolithography apparatus with an illumination pupil. This measurement pattern can be one of the embodiments mentioned above. Optionally, the position of at least a portion of the measurement pattern depends on the focal length. Optionally, at least a portion of the measurement pattern has been printed by the photolithography apparatus using an angularly asymmetrical illumination pupil. A second step 121 may be present, in which the measurement pattern is illuminated using a measurement tool to measure a signal based on radiation scattered by the measurement pattern. Optionally, the measurement tool is a scatterometer, which may be an angle-resolved scatterometer. Optionally, the measurement tool measures dark-field imaging. A third step 122 may be present, in which the focal length of the photolithography process is determined or monitored based on the measured signal. Further details regarding methods for measuring the focal length of a photolithography process are provided in the above description.

[0125] In addition to lithography equipment calibration and setup, this invention can be applied to products for focal length measurement and / or control. The overlap (or focal length) baseline control loop is a method used during the lithography process to reduce overlap (or focal length) variations caused by stabilizing the overlap (or focal length) identification flag of the lithography equipment at a defined baseline via feedback or feedforward control. Figure 8 The embodiments shown enable the conversion of focal length measurements into overlap measurements and provide the opportunity to combine overlap with a focal length baseline control loop. This means that both overlap and focal length can be monitored during the lithography process based on overlap measurements. The methods mentioned above can also be computer programs comprising processor-readable instructions that, when executed on a suitable processor-controlled device, cause the processor-controlled device to perform the methods described above.

[0126] An example of the present invention is a substrate having a first structure, wherein the first structure is a measurement pattern suitable for focusing performance of a photolithography process of any of the measurement patterns mentioned above.

[0127] Another example of the invention is a patterning apparatus having a second structure, such as a mask or stencil, wherein the second structure causes the first structure to be formed on the substrate when printed onto the substrate by a photolithography apparatus. For photolithography apparatus that utilizes extreme ultraviolet radiation, a reflective patterning apparatus can be used, while for photolithography apparatus that utilizes deep ultraviolet radiation, a transmissive mask can be used instead.

[0128] In summary, the method of manufacturing devices using a photolithography process can be improved by performing a focal length measurement method as disclosed herein, using the focal length measurement method to measure the performance parameters of the photolithography process on the processed substrate, and adjusting the parameters of the process (especially the focal length) to improve or maintain the performance of the photolithography process for subsequent substrate processing.

[0129] While the target structures and measurement patterns described above are measurement targets specifically designed and formed for measurement purposes, in other embodiments, target measurement properties can be provided for functional parts of devices formed on a substrate. Many devices have regular grating-like structures. Terms such as "measurement pattern" and "measurement target" as used herein do not necessarily require a structure specifically provided for the measurement being performed.

[0130] Further embodiments are disclosed in the following sections:

[0131] 1. A method for measuring focal length in a photolithography process, the method comprising:

[0132] The receiving substrate has had a measurement pattern printed on it using a photolithography apparatus and an illumination pupil.

[0133] The measurement pattern is illuminated using a measurement tool to measure the signal based on the radiation scattered by the measurement pattern.

[0134] The focal length of the photolithography process is determined or monitored based on the measured signals;

[0135] The position of at least a portion of the measurement pattern depends on the focal length;

[0136] At least a portion of the measurement pattern has been printed by the photolithography equipment using an angularly asymmetrical illumination pupil.

[0137] 2. The method according to aspect 1, wherein the measuring tool is a scattering instrument, and optionally, the measuring tool is an angle-resolved scattering instrument.

[0138] 3. The method according to any of the foregoing aspects, wherein the measuring tool measures dark-field imaging.

[0139] 4. The method according to aspect 3, wherein the measuring tool measures the dark-field imaging of the diffraction order diffracted by the measuring pattern.

[0140] 5. The method according to any of the foregoing aspects, wherein the step of receiving the substrate includes receiving the substrate on which the measurement pattern has been printed using extreme ultraviolet radiation.

[0141] 6. The method according to any of the foregoing aspects, wherein the measurement pattern comprises a periodic structure and a periodic intermediate structure, wherein the periodic structure and the periodic intermediate structure are different and form an interlaced pattern.

[0142] 7. The method according to any of the foregoing aspects, wherein the signal includes information about at least one of the intensity and phase difference of relatively higher diffraction orders (optionally, -1 diffraction order and +1 diffraction order).

[0143] 8. The method according to any of the foregoing aspects, wherein the measurement pattern includes a first sub-target and a second sub-target, wherein the first sub-target and the second sub-target are printed by the photolithography apparatus using different angularly asymmetrical illumination pupils.

[0144] 9. The method according to any one of aspects 1 to 7, wherein the measurement pattern comprises a first portion and a second portion, wherein the positions of the first portion and the second portion have different defocus offsets.

[0145] 10. The method according to any one of aspects 1 to 7, wherein the measurement pattern includes a first sub-target and a second sub-target, wherein the first sub-target and the second sub-target have different designs, and wherein the first sub-target and the second sub-target are printed by the photolithography apparatus using the same angularly asymmetrical illumination pupil.

[0146] 11. The method according to any of the foregoing aspects, wherein the measurement pattern at least partially overlaps with the periodic structure, wherein the periodic structure is located on the substrate at a layer different from the layer of the measurement pattern.

[0147] 12. The method according to any of the foregoing aspects, wherein the measurement pattern comprises an angularly symmetrical structure.

[0148] 13. A method for measuring focal length in a photolithography process, the method comprising:

[0149] The receiving substrate has had a measurement pattern printed on it using a photolithography apparatus and an illumination pupil.

[0150] The measurement pattern is illuminated using a measurement tool to measure the signal based on the radiation scattered by the measurement pattern.

[0151] The focal length of the photolithography process is determined or monitored based on the measured signals;

[0152] The measurement pattern includes a first part and a second part;

[0153] Wherein, the first part has a first position offset from focus and the second part has a second position offset from focus;

[0154] The first position offset and the second position offset are different.

[0155] 14. The method according to aspect 18, wherein at least a portion of the measurement pattern has been printed by the photolithography apparatus using an angularly asymmetrical illumination pupil.

[0156] 15. A computer program comprising processor-readable instructions that, when executed on a suitable processor-controlled device, cause the processor-controlled device to perform the method according to any one of aspects 1 to 14.

[0157] 16. A pattern forming apparatus having a structure, wherein the structure causes a measurement pattern to be generated when printed onto a substrate, wherein the measurement pattern is adapted for focal length measurement or monitoring of a photolithography process according to any one of aspects 1 to 14.

[0158] 17. A photolithography unit capable of operating to perform the method according to any one of aspects 1 to 14.

[0159] 18. A substrate having a structure, wherein the structure is a measurement pattern for determining or monitoring the focal length of a photolithography process based on a signal measured by a measurement tool according to radiation scattered by the measurement pattern;

[0160] The position of at least a portion of the measurement pattern depends on the focal length;

[0161] At least a portion of the measurement pattern has been printed by a photolithography device using an angularly asymmetrical illumination pupil.

[0162] 19. A measurement pattern for determining or monitoring the focal length of a photolithography process based on signals measured by a measurement tool;

[0163] The position of at least a portion of the measurement pattern depends on the focal length;

[0164] At least a portion of the measurement pattern has been printed by a photolithography device using an angularly asymmetrical illumination pupil.

[0165] The substrate on which these measurement patterns are formed can be a production wafer or an experimental wafer in product development. The substrate on which these measurement patterns are formed can also be a dedicated measurement wafer, such as a monitoring wafer that is processed intermittently as part of an advanced process control (APC) mechanism.

[0166] Associated with the physical grating structure of the measurement pattern realized on the substrate and patterning apparatus, embodiments may include a computer program containing one or more sequences of machine-readable instructions describing methods for designing the measurement pattern, measurement fitting schemes, and / or controlling inspection equipment to implement illumination modes and other aspects of those measurement fitting schemes. Such a computer program may be executed, for example, in a separate computer system for the design / control process. As mentioned, the calculation and control steps may be performed in the unit PU and / or [other components] of the apparatus in FIG3. Figure 2 The computer program is executed, either entirely or partially, within the LACU (Large Control Unit). A data storage medium (e.g., semiconductor memory, magnetic disk, or optical disk) containing such a computer program may also be provided.

[0167] The terms “radiation” and “beam” as used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having wavelengths of 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.

[0168] The term "lens" can refer to any one or a combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components, as the context allows.

[0169] Although the terms "measuring equipment / tools / systems" or "inspection equipment / tools / systems" are specifically mentioned, these terms can refer to tools, equipment, or systems of the same or similar type. For example, inspection or measuring equipment including embodiments of the present invention can be used to determine the characteristics of a structure on a substrate or on a wafer. For example, inspection or measuring equipment including embodiments of the present invention can be used to detect defects in a substrate or defects in a structure on a substrate or on a wafer. In such embodiments, the characteristics of interest concerning the structure on the substrate may relate to defects in the structure, the absence of a specific portion of the structure, or the presence of unwanted structures on the substrate or on the wafer.

[0170] It is desirable to provide methods and apparatus for measuring targets that can improve productivity, flexibility, and / or accuracy. Furthermore, while not limited thereto, methods and apparatus will have significant advantages if they can be applied to target structures that can be read using techniques based on dark-field images, bright-field images, or bright-field pupils.

[0171] The scope and extent 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 method for measuring focal length in a photolithography process, the method comprising: The receiving substrate has had a measurement pattern printed on it using a photolithography apparatus and an illumination pupil. The measurement pattern is illuminated using a measurement tool to measure the signal based on the radiation scattered by the measurement pattern. The focal length of the photolithography process is determined or monitored based on the measured signals; The position of at least a portion of the measurement pattern depends on the focal length; In this process, at least a portion of the measurement pattern has been printed by the photolithography equipment using an angularly asymmetrical illumination pupil; The measurement pattern includes a first sub-target and a second sub-target, and the first sub-target and the second sub-target are printed by the photolithography equipment using different angularly asymmetrical illumination pupils.

2. The method according to claim 1, wherein, The measuring tool is a scattering instrument, and optionally, the measuring tool is an angle-resolved scattering instrument.

3. The method according to any of the preceding claims, wherein, The measurement tool measures dark-field imaging.

4. The method according to claim 3, wherein, The measuring tool measures the dark-field imaging of the diffraction order diffracted by the measuring pattern.

5. The method according to any one of claims 1, 2, and 4, wherein, The step of receiving the substrate includes receiving the substrate on which the measurement pattern has been printed using extreme ultraviolet radiation.

6. The method according to any one of claims 1, 2, and 4, wherein, The measurement pattern includes a periodic structure and a periodic intermediate structure, wherein the periodic structure and the periodic intermediate structure are different and form an interlaced pattern.

7. The method according to any one of claims 1, 2, and 4, wherein, The signal includes information about at least one of the intensity and phase difference of a relatively higher diffraction order, which may optionally be a -1 diffraction order and a +1 diffraction order.

8. The method according to any one of claims 1, 2, and 4, wherein, The measurement pattern includes a first sub-target and a second sub-target, wherein the first sub-target and the second sub-target are printed by the photolithography equipment using different angularly asymmetrical illumination pupils.

9. The method according to any one of claims 1, 2, and 4, wherein, The measurement pattern includes a first part and a second part, wherein the positions of the first part and the second part have different defocus offsets.

10. The method according to any one of claims 1, 2, and 4, wherein, The measurement pattern includes a first sub-target and a second sub-target, wherein the first sub-target and the second sub-target have different designs, and wherein the first sub-target and the second sub-target are printed by the photolithography equipment using the same angularly asymmetrical illumination pupil.

11. The method according to any one of claims 1, 2, and 4, wherein, The measurement pattern at least partially overlaps with the periodic structure, wherein the periodic structure is located on the substrate at a layer different from the layer of the measurement pattern.

12. The method according to any one of claims 1, 2, and 4, wherein, The measurement pattern includes an angularly symmetrical structure.

13. A method for measuring focal length in a photolithography process, the method comprising: The receiving substrate has had a measurement pattern printed on it using a photolithography apparatus and an illumination pupil. The measurement pattern is illuminated using a measurement tool to measure the signal based on the radiation scattered by the measurement pattern. The focal length of the photolithography process is determined or monitored based on the measured signals; The measurement pattern includes a first part and a second part; Wherein, the first part has a first position offset from focus and the second part has a second position offset from focus; Wherein, the first position offset and the second position offset are different; The measurement pattern includes a first sub-target and a second sub-target, and the first sub-target and the second sub-target are printed by the photolithography equipment using different angularly asymmetrical illumination pupils.

14. The method according to claim 13, wherein, At least a portion of the measurement pattern has been printed by the photolithography equipment using an angularly asymmetrical illumination pupil.

15. A computer program comprising processor-readable instructions that, when executed on a suitable processor-controlled device, cause the processor-controlled device to perform the method of any one of claims 1 to 14.

16. A pattern forming apparatus having a structure, wherein, The structure enables the generation of a measurement pattern when printed onto a substrate, wherein the measurement pattern is adapted to the method of any one of claims 1 to 14.

17. A photolithography unit capable of operating to perform the method according to any one of claims 1 to 14.

18. A substrate having a structure, wherein, The structure is a measurement pattern used to determine or monitor the focal length of the photolithography process based on a signal measured by a measurement tool, which is derived from radiation scattered by the measurement pattern. The position of at least a portion of the measurement pattern depends on the focal length; In this process, at least a portion of the measurement pattern has been printed by a photolithography device using an angularly asymmetrical illumination pupil; The measurement pattern includes a first sub-target and a second sub-target, and the first sub-target and the second sub-target are printed by the photolithography equipment using different angularly asymmetrical illumination pupils.

19. A measurement pattern for determining or monitoring the focal length of a photolithography process based on signals measured by a measurement tool; in, The position of at least a portion of the measurement pattern depends on the focal length; In this process, at least a portion of the measurement pattern has been printed by a photolithography device using an angularly asymmetrical illumination pupil; The measurement pattern includes a first sub-target and a second sub-target, and the first sub-target and the second sub-target are printed by the photolithography equipment using different angularly asymmetrical illumination pupils.

Images