Sub - field control of a lithography process and associated equipment

Abstract

Disclosed is a method for determining a correction for control of a lithography process for exposing a pattern in an exposure field using a lithography apparatus. The method comprises: obtaining a spatial distribution describing a spatial variation of a performance parameter over at least a portion of the exposure field; and jointly determining a control profile for the spatial distribution to ensure a minimum contrast quality while minimizing an error in the performance parameter. The jointly determined control profile includes at least a stage control profile for controlling a stage arrangement of the lithography apparatus and a lens manipulator control profile for controlling a lens manipulator of the lithography apparatus, the lens manipulator of the lithography apparatus being operable to perform a correction of at least a magnification in a direction perpendicular to the substrate plane.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to European Application No. 19196357.8, filed on September 10, 2019, and European Application No. 19197575.4, filed on September 16, 2019, the entire contents of which are incorporated herein by reference. Field of the invention

[0003] The present invention relates to methods and apparatus for applying a pattern to a substrate and / or measuring the pattern during a lithography process. Background art

[0004] A lithographic apparatus is a machine that applies a desired pattern onto a substrate (usually onto a target portion of the substrate). A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such an example, a patterning device (alternatively referred to as a mask or reticle) can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including a part of a die, a single die, or several dice) on the substrate (e.g., a silicon wafer). Usually, the transfer of the pattern is effected via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Usually, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion at once; and so-called scanners, in which the pattern is scanned by a radiation beam in a given direction ("scan" direction) while the substrate is scanned synchronously parallel or anti-parallel to this direction, so as to irradiate each target portion. The pattern can also be transferred from the patterning device onto the substrate by imprinting the pattern onto the substrate.

[0005] To monitor the lithography process, parameters of the patterned substrate are measured. For example, the parameters can include overlay errors between successive layers formed in or on the patterned substrate, and critical dimension (CD) of the developed photosensitive resist. Such measurements can be performed on product substrates and / or on dedicated metrology targets. There are various techniques for measuring microstructures, i.e., microstructures, formed during the lithography process, including the use of scanning electron microscopes and various dedicated tools. A fast and non-invasive form of dedicated inspection tool is a scatterometer, in which a radiation beam is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured. Two main types of scatterometers are known. A spectroscopic scatterometer directs a broadband radiation beam onto the substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered into a specific narrow angular range. An angularly resolved scatterometer uses a monochromatic radiation beam and measures the intensity of the scattered radiation as a function of angle.

[0006] Examples of known scatterometers include angular resolution scatterometers of the type described in US2006033921A1 and US2010201963A1. The targets used by such scatterometers are relatively large gratings, e.g., 40 μm by 40 μm, and the measurement beam produces a spot smaller than the grating (i.e., the grating is underfilled). In addition to measuring feature shape by reconstruction, such devices can also be used to measure diffraction-based overlay, as described in the published patent application US2006066855A1. Diffraction-based overlay metrology using dark field imaging of diffraction orders enables overlay metrology of smaller targets. Examples of dark field imaging metrology can be found in international patent applications WO 2009 / 078708 and WO 2009 / 106279, the entire contents of which are hereby incorporated by reference. Further developments of the technology have been described in the 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 one image. The contents of all these applications are also incorporated herein by reference.

[0007] Currently, the overlay error is controlled and corrected by a correction model, such as that described in US2013230797A1. Advanced process control techniques have been introduced in recent years and measurements are made on the metrology targets applied to the substrate and the device patterns applied. These targets allow the use of high throughput inspection equipment, such as scatterometers, to measure overlay, and the results of the measurements can be used to generate corrections that are fed back into the lithography equipment when subsequent substrates are patterned. An example of advanced process control (APC) is described, for example, in US2012008127A1. The inspection equipment can be separate from the lithography equipment. Within the lithography equipment, a wafer correction model is conventionally applied based on measurements of overlay targets set on the substrate as a preparatory step for each patterning operation. The correction model now includes higher order terms to correct for non-linear deformation of the wafer. The correction model can also be extended to take into account other measurement results and / or calculated effects, such as thermal deformation during the patterning operation.

[0008] Although using a higher-order model may be able to account for more effects, the use of such a model may be limited if the patterning device itself does not provide control over the corresponding parameters during the patterning operation. In addition, even advanced correction models may be insufficient to correct certain overlay errors or may not be optimized to correct certain overlay errors.

[0009] It would be desirable to improve such process control methods. SUMMARY OF THE INVENTION

[0010] In a first aspect of the invention, there is provided a method for determining a correction for the control of a lithography process for exposing a pattern on an exposure field using a lithography apparatus, the method comprising: obtaining a spatial distribution describing a spatial variation of a performance parameter over at least a portion of the exposure field; and jointly determining a control profile for the spatial distribution to ensure a minimum contrast quality while minimizing an error in the performance parameter, the jointly determined control profile comprising at least a stage control profile for controlling a stage arrangement of the lithography apparatus and a lens manipulator control profile for controlling a lens manipulator of the lithography apparatus, the lens manipulator of the lithography apparatus being operable to perform a correction on at least a magnification in a direction perpendicular to the substrate plane.

[0011] In a second aspect of the invention, there is provided a computer program comprising program instructions operable to perform the method of the first aspect when run on a suitable device.

[0012] In a third aspect of the invention, there is provided a lithography apparatus comprising: an illumination system configured to provide a radiation beam; a stage arrangement comprising a first stage for supporting a patterning device and a second stage for holding a substrate, the patterning device being configured to impart a pattern to the radiation beam in a cross-section of the radiation beam; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; a lens manipulator configured to apply a correction to the patterned radiation beam in accordance with a lens manipulator control profile, the lens manipulator being located near a field plane; and a controller configured to perform the method according to the first aspect.

[0013] In a fourth aspect of the invention, there is provided a method of performing co - determined stage control and dynamic lens control for controlling a lithography process of exposing a pattern in an exposure field using a lithographic apparatus, the method comprising: co - determining a stage control profile and a dynamic lens control profile, the stage control profile being configured to correct one or more spatially varying performance parameters, the dynamic lens control profile being configured to stabilize the effect of the stage control on contrast with a minimal impact on the one or more performance parameters.

[0014] In a fifth aspect of the invention, there is provided a method of determining a stage control profile for a stage used within a lithographic apparatus when projecting an image of a pattern onto a substrate, the method comprising: obtaining a spatial variation across at least a portion of the substrate of position parameters associated with the positioning of the projected image; and determining the control profile for the stage based on the spatial variation of the position parameters and the correction potential of a lens manipulator for stabilizing or mitigating image contrast degradation, the image contrast degradation being caused by an expected effect of a dynamic stage position error associated with the stage control profile configured to correct the spatial variation of the position parameters.

[0015] In a sixth aspect of the invention, there is provided a method of determining a dynamic control profile for a manipulator of a lens used within a lithographic apparatus when projecting an image of a pattern onto a substrate, the method comprising: obtaining a spatial variation across at least a portion of the substrate of position parameters associated with the positioning of the projected image; and determining the dynamic control profile for the manipulator based on a desired stabilization or mitigation of image contrast degradation, the image contrast degradation being caused by the expected effect of a dynamic stage position error associated with a stage control profile configured to correct the spatial variation of the position parameters.

[0016] Additional aspects, 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. Based on the teachings contained herein, additional embodiments will be apparent to those skilled in the art. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

[0018] Figure 1 A lithographic apparatus and other equipment forming a production facility for semiconductor devices are depicted;

[0019] Figure 2 Schematic representation depicting overall lithography, showing the collaboration between three key technologies for optimizing semiconductor manufacturing;

[0020] Figure 3 Exemplary source of process parameters is shown;

[0021] Figure 4 Is a graph of overlay versus field position along the scan direction, showing the measured overlay; and a fitting correction modeled and / or implemented using a control grid determined by a method according to an embodiment of the present invention;

[0022] Figure 5 Schematically depicts a deformable reflector that can be used in a method according to an embodiment of the present invention;

[0023] Figure 6 Schematically depicts a part of a lithographic apparatus including a deformable reflector that can be used in a method according to an embodiment of the present invention;

[0024] Figure 7 Is a graph of overlay residual OV versus moving standard deviation MSD for a conventional method and a method according to an embodiment of the present invention; and

[0025] Figure 8 Is a flowchart describing a method according to an embodiment of the present invention. Detailed Description

[0026] Before describing embodiments of the present invention in detail, it is instructive to present an example environment in which embodiments of the present invention can be implemented.

[0027] Figure 1 The lithographic apparatus LA is shown at 200 as part of an industrial production facility implementing a high-volume lithography manufacturing process. In this example, the manufacturing process is adapted for the manufacture of semiconductor products (integrated circuits) on a substrate (such as a semiconductor wafer). Those skilled in the art will understand that a variety of products can be manufactured by processing different types of substrates in variations of such processes. The production of semiconductor products is used only as an example of great current commercial significance.

[0028] Within the lithographic apparatus (or simply "litho tool" 200), the measurement station MEA is shown at 202 and the exposure station EXP is shown at 204. The control unit LACU is shown at 206. In this example, each substrate visits the measurement station and the exposure station to have a pattern applied. For example, in an optical lithographic apparatus, a projection system is used to transfer a product pattern from a patterning device MA to the substrate using conditioned radiation and the projection system. This transfer is accomplished by forming an image of the pattern in a layer of radiation-sensitive resist material.

[0029] As used herein, the term "projection system" should be interpreted broadly to cover any type of projection system suitable for the exposure radiation used or for other factors such as the use of an immersion liquid or the use of a vacuum, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof. The patterning device MA may be a mask or a reticle that imparts a pattern to a radiation beam transmitted or reflected by the patterning device. Well-known operating modes include step mode and scan mode. It is well known that the projection system can work in a variety of ways with the support and positioning systems for the substrate and the patterning device to apply the desired pattern to a number of target portions across the entire substrate. A programmable patterning device may be used instead of a reticle with a fixed pattern. For example, the radiation may include electromagnetic radiation in the deep ultraviolet (DUV) or extreme ultraviolet (EUV) band. The present disclosure is also applicable to other types of lithography processes that utilize, for example, electron beams, such as imprint lithography and direct write lithography.

[0030] The lithography apparatus control unit LACU controls all movements and measurements of various actuators and sensors to accommodate the substrate W and the reticle MA and to perform the patterning operation. The LACU also includes signal processing and data processing capabilities for performing the desired calculations related to the operation of the apparatus. In practice, the control unit LACU will be implemented as a system with many subunits, each subunit handling the real-time data acquisition, processing, and control of subsystems or components within the apparatus.

[0031] Before applying the pattern to the substrate at the exposure station EXP, the substrate is processed at the measurement station MEA such that various preparatory steps can be performed. The preparatory steps may include using a level sensor to map the surface height of the substrate and using an alignment sensor to measure the positions of alignment marks on the substrate. The alignment marks are nominally arranged in a regular grid pattern. However, due to inaccuracies in the production of the marks and also due to distortions occurring throughout the processing of the substrate, the marks deviate from the ideal grid. Therefore, in cases where the device is to print product features at the correct locations with very high accuracy, in addition to measuring the position and orientation of the substrate, the alignment sensor must actually also measure in detail the positions of a large number of marks across the substrate area. The device may be of the so-called dual-platform type having two substrate tables, each substrate table having a positioning system controlled by the control unit LACU. While one substrate on one substrate table is being exposed at the exposure station EXP, another substrate can be loaded onto the other substrate table at the measurement station MEA such that various preparatory steps can be performed. Therefore, the measurement of the alignment marks is very time-consuming and the provision of two substrate tables enables a significant increase in the throughput of the device. If the position sensor IF cannot measure the position of the substrate table when the substrate table is at the measurement station and at the exposure station, a second position sensor may be provided to enable tracking of the position of the substrate table at both stations. The lithographic apparatus LA may for example be of the so-called dual-platform type, having two substrate tables and two stations (an exposure station and a measurement station) between which the substrate tables can be exchanged.

[0032] Within a production facility, the apparatus 200 forms part of a "lithography cell" or "lithography cluster" which also includes a coating apparatus 208 for coating a photosensitive resist and other coatings onto a substrate W for patterning by the apparatus 200. At the output side of the apparatus 200, a baking apparatus 210 and a developing apparatus 212 are provided for developing the exposed pattern into a solid resist pattern. Between all these apparatuses, a substrate transport system is responsible for supporting the substrate and transferring the substrate from one apparatus to the next. These apparatuses, often collectively referred to as a coating and developing system or a track, are under the control of a coating and developing system control unit or a track control unit which is itself controlled by a management control system SCS which also controls the lithographic apparatus via the lithographic apparatus control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency. The management control system SCS receives configuration recipe information R which provides in great detail the definition of the steps to be performed to produce each patterned substrate.

[0033] Once the pattern has been applied and developed in the lithography unit, the patterned substrate 220 is transferred to other processing equipment such as that illustrated at 222, 224, 226. A wide range of processing steps are implemented by the various equipment in a typical manufacturing facility. By way of example, in this embodiment, equipment 222 is an etch station and equipment 224 performs an etch anneal step. Additional physical and / or chemical processing steps are applied in additional equipment 226 and so on. Many types of operations may be required to fabricate a real device, such as deposition of materials, modification of surface material properties (oxidation, doping, ion implantation, etc.), chemical mechanical polishing (CMP), etc. In fact, equipment 226 may represent a series of different processing steps performed in one or more pieces of equipment. As another example, equipment and processing steps for implementing self-aligned multi-patterning may be provided to generate multiple smaller features based on a precursor pattern placed by the lithography equipment.

[0034] As is well known, the fabrication of semiconductor devices involves many repetitions of such processing to build up layer by layer on the substrate a device structure having the appropriate materials and patterns. Thus, the substrate 230 arriving at the lithography cluster may be a newly prepared substrate, or it may be a substrate that has previously been processed in this cluster or entirely in another piece of equipment. Similarly, depending on the processing required, the substrate 232 leaving equipment 226 may be returned for subsequent patterning operations in the same lithography cluster, the substrate 232 may be designated for patterning operations in a different cluster, or they may be finished products to be sent for dicing and packaging.

[0035] Each layer of the product structure requires a different set of process steps and the equipment 226 used at each layer may be completely different in type. In addition, even in cases where the processing steps to be applied by equipment 226 are nominally the same, in a large facility there may be several ostensibly identical machines working in parallel to perform step 226 on different substrates. Small setup differences or defects between these machines may mean that the small setup differences or defects affect different substrates in different ways. Even steps that are relatively common for each layer (such as etching (equipment 222)) may be implemented by several etching devices that are nominally identical but work in parallel to maximize throughput. In addition, in practice, different layers require different etching processes (such as chemical etching, plasma etching) and special requirements (such as anisotropic etching for example) depending on the details of the material to be etched.

[0036] The previous and / or subsequent processes (such as those just mentioned) may be carried out in other lithography apparatuses, and may even be carried out in lithography apparatuses of a different type. For example, some layers in a device manufacturing process that require very high specifications in terms of parameters such as resolution and overlay may be carried out in more advanced lithography tools compared to other layers with less stringent requirements. Thus, some layers may be exposed in an immersion lithography tool, while other layers are exposed in a "dry" tool. Some layers may be exposed in a tool operating at a DUV wavelength, while other layers are exposed using EUV wavelength radiation.

[0037] In order to expose the substrate correctly and consistently by the lithography apparatus, it is desirable to inspect the exposed substrate to measure properties such as overlay errors between subsequent layers, line thickness, critical dimension (CD), etc. Thus, the manufacturing facility in which the lithography cell LC is located also includes a metrology system that receives some or all of the substrates W that have been processed in the lithography cell. The metrology results are provided directly or indirectly to the management control system SCS. If an error is detected, the exposure of subsequent substrates can be adjusted, especially if the metrology can be completed quickly enough such that other substrates in the same batch are still to be exposed. Moreover, the exposed substrates can be stripped and reworked to improve yield, or discarded, thereby avoiding further processing of substrates known to be defective. In the case where only some target portions of the substrate are defective, additional exposure can be carried out only on the good target portions.

[0038] Figure 1 Also shown is metrology equipment 240, which is arranged to perform parameter measurements on a product at a desired platform during the manufacturing process. A common example of a metrology station in a modern lithography production facility is a scatterometer, for example, a dark field scatterometer, an angular resolved scatterometer or a spectroscopic scatterometer, and the scatterometer can be applied to measure the properties of the developed substrate at 220 before etching in the apparatus 222. In the case of using the metrology equipment 240, it can be determined, for example, that important performance parameters such as overlay or critical dimension (CD) do not meet the specified accuracy requirements in the developed resist. Before the etching step, there is an opportunity to strip the developed resist and reprocess the substrate 220 through the lithography cluster. Small adjustments can be made over time by the management control system SCS and / or the control unit LACU 206, and the metrology results 242 from the equipment 240 can be used to maintain the accurate performance of the patterning operation in the lithography cluster, thereby minimizing the risk of manufacturing out-of-specification products that require rework.

[0039] In addition, metrology equipment 240 and / or other metrology equipment (not shown) can be applied to measure properties of the processed substrates 232, 234 and the incoming substrate 230. The metrology equipment can be used on the processed substrates to determine important parameters such as overlay or CD.

[0040] Generally, the patterning process in the lithography apparatus LA is one of the most critical steps in the processing, which requires high accuracy in the sizing and placement of the structures on the substrate W. To ensure such high accuracy, three systems can be combined in a so-called "integrated" control environment, as Figure 2 depicted. One of these systems is the lithography apparatus LA, which is (virtually) connected to a metrology tool MET (second system) and to a computer system CL (third system). The key to such an "integrated" environment is to optimize the cooperation between these three systems to enhance the overall process window and to provide a tight control loop to ensure that the patterning process performed by the lithography apparatus LA remains within a process window. The process window defines a range of process parameters (e.g., dose, focus, overlay) within which a particular manufacturing process produces defined results (e.g., a functional semiconductor device) – typically allowing the process parameters in the lithography process or patterning process to vary within these parameter ranges.

[0041] The computer system CL can use the (portion of the) design layout to be patterned to predict which resolution enhancement techniques will be used, and to perform computational lithography simulations and calculations to determine which mask layout and lithography apparatus settings achieve the maximum overall process window for the patterning process (as Figure 2 depicted by the double arrows in the first scale SC1). Typically, the resolution enhancement techniques are arranged to match the patterning capabilities of the lithography apparatus LA. The computer system CL can also be used to detect where within the process window the lithography apparatus LA is currently operating (e.g., using inputs from the metrology tool MET) to predict whether there may be defects due to, for example, sub-optimal processing (depicted by the arrow pointing to "0" in the second scale SC2 in Figure 2 ).

[0042] The metrology tool MET can provide inputs to the computer system CL to enable accurate simulations and predictions, and can provide feedback to the lithography apparatus LA to identify possible drifts, for example in the calibration state of the lithography apparatus LA (depicted by the multiple arrows in the third scale SC3 in Figure 2 ).

[0043] Various techniques can be used to improve the accuracy of pattern reproduction onto a substrate. The accurate reproduction of a pattern onto a substrate is not the only concern in the production of an IC. Another concern is yield, which is typically measured by how many functional devices a device manufacturer or a device manufacturing process can produce per substrate. Various methods can be employed to improve yield. One such method attempts to make the production of a device (e.g., imaging a portion of a design layout onto a substrate using a lithography apparatus such as a scanner) more tolerant to perturbations in at least one of the processing parameters during the processing of the substrate (e.g., during imaging a portion of a design layout onto a substrate using a lithography apparatus). The concept of an Overlapped Process Window (OPW) is a useful tool for such a method. The production of a device (e.g., an IC) can include other steps such as substrate measurement before, after, or during imaging; loading or unloading the substrate; loading or unloading the patterning device; positioning a die under the projection optics before exposure; stepping from one die to another die, etc. Additionally, various patterns on the patterning device can have different process windows (i.e., the space of the processing parameters upon which a pattern within specification will be produced). Examples of pattern specifications related to potential systematic defects include inspection necking, line pullback, line thinning, CD, edge placement, overlay, resist top loss, resist undercut, and / or bridging. The process window of all or some of the patterns (usually the patterns within a specific area) on the patterning device can be obtained by combining (e.g., overlaying) the process windows of each individual pattern. The process window of these patterns is thus referred to as an overlapped process window. The boundaries of the OPW can include the boundaries of the process windows of some of the individual patterns. In other words, these individual patterns limit the OPW. These individual patterns can be referred to as "hot spots", "critical features", or "Process Window Limiting Patterns (PWLP)", and "hot spots", "critical features", or "Process Window Limiting Patterns" are used interchangeably herein. When controlling the lithography process, it is possible and usually low-cost to focus on the hot spots. When the hot spots are defect-free, it is likely that all patterns are defect-free. Imaging becomes more tolerant to perturbations when the value of the processing parameter is closer to the OPW if the value of the processing parameter is outside the OPW, or when the value of the processing parameter is farther from the boundary of the OPW if the value of the processing parameter is inside the OPW.

[0044] Figure 3Exemplary sources of process parameter 350 are shown. One source can be data 310 of a processing apparatus, such as parameters of a lithography apparatus, projection optics, a substrate stage, etc., parameters of a track or a coat develop system, etc. Another source can be data 320 from various substrate metrology tools, such as a substrate height map, a focus map, a critical dimension uniformity (CDU) map, etc. Data 320 can be obtained before a step (e.g., development) that the substrate to be applied experiences and prevents rework of the substrate. Another source can be data 330 from one or more patterning device metrology tools, a patterning device CDU map, changes in a patterning device (e.g., mask) film stack parameters, etc. Yet another source can be data 340 from an operator of the processing apparatus.

[0045] Control of the lithography process is generally based on measurements that are fed back or fed forward, and then modeled using, for example, inter-field (feature identification across the entire substrate) or intra-field (feature identification across the entire field) models. U.S. Patent Application 20180292761, which is incorporated herein by reference, describes a control method for controlling performance parameters such as overlay at the sub-field level using an advanced correction model. Another control method using sub-field control is described in European Patent Application EP3343294A1, which is also incorporated herein by reference. Each sub-field can be associated with, for example, a single die or its functional area.

[0046] However, although an advanced correction model can include, for example, 20 to 30 parameters, currently used lithography apparatuses (for simplicity, the term "scanner" will be used throughout the description) may not have actuators corresponding to one or more of the parameters. Therefore, only a subset of the entire parameter set of the model can be used at any given time. Additionally, because advanced models require many measurements, it is not desirable to use these models in all cases because the time required to perform the necessary measurements reduces throughput.

[0047] Some of the main contributing factors to overlay errors include, but are not limited to, the following:

[0048] Scanner-specific errors: These errors can be caused by various subsystems of the scanner used during exposure of the substrate, thereby actually generating scanner-specific feature identifications;

[0049] Process-induced wafer deformation: Various processes performed on the substrate can deform the substrate or wafer;

[0050] Irradiation setting differences: These differences are caused by settings of the irradiation system, such as the shape of the aperture, lens actuator positioning, etc.;

[0051] Heating effects - The effects induced by heating will vary between individual sub - fields of the substrate (especially for a substrate where each sub - field includes different types of components or structures);

[0052] Mask writing errors: Due to limitations in the manufacture of the patterning device, errors may already exist in the patterning device; and

[0053] Topography variations: The substrate may have topography (height) variations (especially around the edges of the wafer).

[0054] It is possible to model the overlay error for multiple individual sub - fields in a field (e.g., at the die level or at the level of other functional regions) instead of for the entire field; or in addition to modeling the entire field, it is also possible to model the overlay error for multiple individual sub - fields in a field. Although the latter requires more processing time, since both the field and the sub - fields within the field are modeled, it allows for the correction of error sources that pertain only to specific sub - fields as well as error sources that pertain to the entire field. Of course, other combinations such as modeling the entire field and only certain sub - fields are possible.

[0055] Even when the errors are modeled adequately, there are difficulties in actuating or initiating the resulting corrections. Some corrections cannot be effectively actuated or initiated using only the available control parameters (control knobs). Additionally, while other corrections may be actuatable, actually doing so may lead to undesirable side effects. Basically, due to dynamic and control limitations and sensitivities, there are limitations in terms of what the scanner can actually do to implement the corrections.

[0056] Figure 4Illustrated is a specific example of an in-field overlap signature that is difficult to correct during actuation. It shows a graph of the overlap OV (y-axis) versus the scan direction Y in an exposure field. Each cross represents a measured overlap value, and each dot is the corresponding compensation correction necessary. The fitted line is the (approximate ideal) correction distribution that is fitted to the corrections (dots). The sawtooth pattern exhibited in the overlap signature is evident; each of the roughly linear segments corresponds to a single die (the graph represents overlap measurements across 4 dies). The correction distribution follows (and thus compensates for) the overlap signature. This signature is considered the result of larger stresses induced by larger stacks, such as those used in, for example, 3D-NAND or DRAM processes. Such stresses manifest themselves at both the wafer level (resulting in significant wafer warping) and the die level. At the die level, the overlap signature includes magnification within each die. Since there are multiple dies within the exposure field, the resulting in-field overlap signature exhibits the sawtooth pattern shown (typically on the order of tens of nm). Depending on the orientation of the device, the pattern can be either through-slit or through-scan. Regardless of the orientation, this overlap pattern is challenging to correct using available models and actuators. It should also be noted that this overlap or edge placement error (EPE), manifested as a sawtooth pattern (e.g., caused by stresses within the die in 3D-NAND or DRAM processes, as Figure 4 illustrated therein) presents a purely exemplary specific challenge that the methods described herein are designed to address; it should be understood that such methods can be used to correct any other higher-order overlap, EPE, or focus signature (such as, for example, in-field signatures at high frequencies).

[0057] To optimally correct the overlap signature as Figure 4 depicted herein, it is possible to be smaller than the pitch of the periodic distribution (e.g., less than Figure 4It is important to adjust the scanner at the spatial scale of one "tooth" of the repetitive sawtooth distribution. Such individual tooth regions are typically associated with cell structures within individual dies. Accordingly, the interface of the scanner should allow individually controllable regions to be defined within the exposure field. This concept is known as the subfield control interface; an example of this concept is disclosed in the aforementioned European patent application EP3343294A1. For example, the control profile of the wafer stage of the scanner configured for the first cell die / cell structure can be defined largely independently of the control profile of the second cell / die structure positioned further along the scan direction. The subfield control infrastructure allows for a more optimized correction of repetitive overlay (or focus) variations at subfield resolution. Additionally, the ability to independently control different subfield regions allows for mitigation of die-to-die or cell-to-cell variations in overlay / focus feature signatures within the die and / or cell.

[0058] Typically, scanner overlay control uses dynamic stage position control to adjust the placement of structures (features) to minimize overlay errors. In principle, this can be implemented by pre-correcting for expected overlay error signatures (e.g., as induced by the accumulation of stress due to the application of subsequent layers) and / or by adjusting the placement of features within subsequent layers to align sufficiently with features in the previous layer. Dynamic control in the context of this document refers to a control strategy where the stage actuators and / or lens manipulators of interest are continuously adjusted during the actual exposure operation; e.g., during the exposure of a pattern on the substrate.

[0059] Scanner overlay correction is typically applied by the stage controller and / or lens manipulator of the projection lens (odd aberration control can be used to control the placement of features). However, as already mentioned, the scanner cannot fully track any desired overlay correction distribution. One reason for this is due to the constraints on the speed and acceleration achievable by the wafer (and reticle) stage. Another reason is the fact that the scanner exposes the substrate using a relatively large illumination spot (the so-called slit length represents the size of the bright spot in the scan direction, reference European patent application EP19150960.3, which is hereby incorporated by reference in its entirety). The extent of the bright spot means that during scan exposure, in cases where the desired overlay correction is not just a simple offset across the entire die / cell, some portions of the features within the die / cell will always be sub-optimally positioned. This variation in the effective position (overlay) correction during the scan operation effectively results in blurring of the spatial image of the features, which in turn leads to a loss of contrast. This dynamic effect is commonly referred to as the moving standard deviation (MSD). The limitations on stage positioning are typically associated with the average position (overlay) error and are commonly referred to as the moving average (MA) error.

[0060] More specifically, the moving average (MA) error and moving standard deviation (MSD) of the errors of a lithography platform relate to a critical time window that includes the time interval during which each point on the die is exposed (in other words: receives photons). If the average position error of the points on the die is high during this time interval (in other words: high MA error), the effect is an offset of the exposed image, resulting in an overlay error. If the standard deviation of the position error is high during this time interval (in other words: high MSD error), the image may be smeared, resulting in a degradation error. When accurately following the high-frequency sub-field distribution to achieve a small MA error, this will typically come at the cost of the MSD error, which will disrupt the contrast; this defines the limit of the overlay correction potential that can be achieved because at some points, the MSD loss becomes too large.

[0061] Both the contrast loss due to MSD and the average overlay error (MA) are contributing factors to the overall edge placement error (EPE) budget and therefore need to be carefully balanced when determining a certain control profile for the wafer and / or mask platform; typically, a more MA-targeted control method will result in a higher MSD impact, while an MSD-targeted control strategy may lead to an unacceptably large MA error. EPE is a combined error resulting from global critical dimension uniformity (CDU), local CDU (e.g., line edge roughness LER / line width roughness LWR), and overlay error. These parameters have the greatest impact on yield because errors in these parameters affect the relative positioning of features, and any two features either inadvertently touch or inadvertently fail to touch.

[0062] Thus, the correction and / or control profile should be balanced such that a) the MSD characteristics associated with the control profile do not unduly degrade the imaging quality of the features, and b) the MA characteristics associated with the control profile do not unduly degrade the overlay. One way to address the requirement of balancing MA and MSD is to determine the maximum allowable MSD degradation and use this maximum allowable MSD degradation as a limit or constraint when optimizing the overlay / MA control.

[0063] Relatively new optical elements have become available in some scanners. Such optical elements include a deformable reflector (or a pair of such deformable reflectors), sometimes referred to as a semi-dome or semi-vault mirror. The deformable reflector is disclosed in WO2018 / 134010, which is incorporated herein by reference. By actuating the deformable reflector to give it a particular configuration, a correction distribution can be applied to a patterned radiation beam (i.e., patterned by the mask) by reflecting it in that particular configuration. The deformable reflector can be positioned adjacent to the field plane of the scanner (e.g., in the projection optics). The shape of the wavefront of the radiation reflected from the deformable reflector can be adjusted via deformation of the deformable reflector. The wavefront can be adjusted such that lithography errors such as overlay errors are reduced. The deformable reflector advantageously is able to reduce lithography errors from a variety of different sources. The deformable reflector advantageously is able to reduce lithography errors across the entire field plane of the lithography apparatus. In particular, the deformable reflector provides greater flexibility when applying slitwise correction (correction along the length of the slit), and thus provides a very fast manipulation of the geometric deformation of the patterned radiation beam (such as magnification error (when traveling along the scan direction)), even on a time scale smaller than the time taken to move the slit across a point on the wafer. Such magnification error can manifest itself as a sawtooth pattern or otherwise. Other geometric deformations than magnification, such as barrel distortion, pincushion distortion, moustache distortion, chromatic aberration, etc., can also be induced by the deformable reflector (or any other lens manipulator element with the same functionality).

[0064] Figure 5 Schematically depicts a deformable reflector 1 according to an embodiment of the present invention. In Figure 5 the example, the deformable reflector 1 includes an array 2 of actuating elements that is generally rectangular. The array 2 of actuating elements can take any desired form, e.g., the array 2 of actuating elements can be generally circular. The deformable reflector 1 can include more or fewer actuating elements than Figure 5 shown. The deformable reflector 1 can, for example, include from about 50 actuating elements to about 200 actuating elements. Each actuating element can be configured to actuate a different part 3 of the deformable reflector 1. In Figure 5 the example, the actuating elements, and their corresponding parts 3 are generally square-shaped. The actuating elements and parts 3 of the deformable reflector 1 can take any desired shape, e.g., generally circular, generally rectangular, etc. In Figure 5In the example, the deformable reflector is substantially rectangular. The deformable reflector 1 can take any desired shape, for example, the deformable reflector 1 can be substantially circular. The deformable reflector 1 can be curved or planar. The surface area of the deformable reflector 1 and / or the surface area of the actuator element array 2 can be selected as required. For example, the surface area of the deformable reflector 1 and / or the actuator element array 2 can depend at least in part on the projection system of the lithographic apparatus in which the deformable reflector 1 is positioned.

[0065] The actuator element can be configured to deform a portion 3 of the deformable reflector 1 such that the portion 3 of the deformable reflector 1 moves in a direction perpendicular to the surface of the deformable reflector 1 (i.e., along the z-axis). The actuator element is configured to move the portion 3 of the deformable reflector 1 from a rest position where the actuator element does not apply a force to the portion 3 to an actuation position where the actuator element applies a force to the portion 3. The actuator element can be configured to move the portion along the z-axis over a range of about 50 nm in the positive z-direction and about 50 nm in the negative z-direction, thus allowing a movement range of about 100 nm along the z-axis. The actuator element can be configured to move the portion along the z-axis in increments of about 0.1 nm, for example. The actuator element can be configured to move the portion 3 of the deformable reflector 1 over a larger or smaller range and in larger or smaller increments. As will be appreciated, the distance by which the actuator element can deform the deformable reflector 1 can be determined in part by the thickness of the deformable reflector 1 and / or the material forming the deformable reflector 1. A deformable reflector suitable for use in an EUV lithographic apparatus can be thicker than a deformable reflector suitable for use in a UV lithographic apparatus.

[0066] The actuator element can include, for example, a piezoelectric actuator. A voltage can be applied to the piezoelectric actuator to cause deformation of the piezoelectric actuator. The deformation of the piezoelectric actuator can cause deformation of the portion 3 of the deformable reflector 1 in which the piezoelectric actuator is positioned. Applying a larger voltage to the piezoelectric actuator can cause a larger deformation of the piezoelectric actuator and thus a larger deformation of the portion 3 of the deformable reflector 1 in which the piezoelectric actuator is positioned.

[0067] By actuating the actuating element and deforming a portion of the deformable reflector 1, the wavefront of the radiation reflected from the deformable reflector 1 can be adjusted. The scale of the wavefront adjustment that the deformable reflector 1 can perform can be partly determined by the area of the portion 3 of the deformable reflector 1 that can be deformed by the actuating element. That is, compared to using a larger actuating element to deform a larger portion of the deformable reflector 1, using a smaller actuating element to deform a smaller portion of the deformable reflector 1 enables a finer adjustment of the wavefront reflected from the deformable reflector 1. An actuating element can be configured, for example, to actuate a portion 3 of the deformable reflector 1 having an area in the range of about 25 mm 2 to about 500 mm 2 The portion 3. Generally, the actuating element can be configured to actuate a portion 3 of the deformable reflector 1 having any desired area.

[0068] The wavefront can be adjusted such that lithography errors such as overlay errors and / or focus errors are reduced. To reduce lithography errors, the lithography errors are first determined. The lithography errors can be determined via direct measurement (e.g., using a detector system), indirect measurement (e.g., performing a lithography exposure in a resist and analyzing the resist), and / or prediction (e.g., by inputting data into a computer model and running the computer model). For example, data related to the lithography errors can be measured and input into a computer model. The computer model can be configured to receive the data and perform calculations using the data to predict the lithography errors.

[0069] Once the lithography errors have been determined, a correction distribution for the patterned radiation beam can be determined. The correction distribution is configured to reduce the lithography errors when the correction distribution is applied to the patterned radiation beam. The correction distribution can include a modification of the wavefront required to reduce the lithography errors. The correction distribution is applied to the patterned radiation beam by actuating the actuating element to deform a portion 3 of the deformable reflector 1. Some portions 3 may not undergo deformation. Different portions can be deformed by different amounts and / or in different directions. The portions to be deformed and the amount of deformation to be applied to those portions can be determined by a processor configured to receive the correction distribution and calculate the deformation of the portion of the deformable reflector 1 required to apply the correction distribution to the patterned radiation beam.

[0070] Figure 6 A portion of a lithographic apparatus including a deformable reflector 1 is schematically depicted. In Figure 6 In an example, the deformable reflector 1 is located in the projection system of the lithographic apparatus (such as Figure 1within the projection system PL). The projection system PL may include a plurality of other optical elements such as mirrors, lenses, etc. ( Figure 6 not shown in

[0071] The sub-apertures of the deformable reflector 1 may be defined as a region of the deformable reflector 1 across which incident radiation is focused onto the same field position (i.e., the same position on the substrate W). The distance between the deformable reflector 1 and the field plane 4 may partially determine the overlap of the sub-apertures of the deformable reflector 1. The deformable reflector 1 is positioned adjacent to the field plane 4. That is, the deformable reflector 1 is positioned at a distance from the field plane 4 such that the sub-apertures at the center of the actuator element array do not overlap with the sub-apertures at the edge of the actuator element array. The deformable reflector 1 may be configured such that, for example, the sub-apertures of the deformable reflector 1 have a diameter of approximately 50 mm. The deformable reflector 1 may be adjacent to a plurality of field planes.

[0072] The patterned radiation beam PB entering the projection system PL may interact with other optical elements ( Figure 6 not shown in

[0073] before being incident on the deformable reflector 1. The radiation PB is reflected from the deformable reflector 1 and is incident on the reflector 5. The radiation PB is reflected from the reflector 5 (which may optionally include a second deformable mirror) and may then interact with other optical elements in the projection system PL before exiting the projection system PL and being incident on the substrate W held by the substrate table WT. Other arrangements of the deformable reflector 1 are possible. Actuation of the deformable reflector 1 may occur during the projection of the patterned radiation beam PB. Alternatively, actuation of the deformable reflector 1 may occur before the projection of the patterned radiation beam PB, and portions of the deformable reflector 1 may be held in their new positions during the projection of the patterned radiation beam PB. The deformable reflector 1 may be used in combination with other optical element manipulators present in the projection system PL to correct lithography errors.

[0074] It is proposed herein to use the deformable reflector in a control strategy for actively reducing dynamic components such as MSD; for example, in cases where high-frequency overlap control is required. By reducing MSD, the range of overlap correction will be greater, resulting in better overlap control (e.g., smaller overlap errors).

[0075] In addition to typical (high-frequency) control based on overlapping data, platform and / or lens manipulator control based on alignment data is also within the scope of the present invention. Generally, overlapping data includes densely measured position data (the positional difference or increment between at least two layers applied to the substrate), which allows for platform control with a relatively high spatial resolution. However, alignment data based on measurements of alignment marks distributed across the entire substrate can also be densely measured and thus also allows for platform control with a relatively high spatial resolution, which also gives rise to the use of platform control profiles that will likely introduce a large number of dynamic platform position errors (or error variations). Accordingly, embodiments disclosed herein are equally applicable to the generation of control profiles based on position data associated with overlapping, alignment, and (when related to focus performance) leveling sensor data.

[0076] The proposed method includes jointly determining (e.g., jointly optimizing) lithography control parameters (e.g., in particular platform control parameters related to wafer platform / mask platform control, as well as other parameters such as lens control parameters), and one or more deformable reflector control parameters related to controlling such a deformable reflector or semi-dome mirror element. In this way, the MA correction ability of the platform can be improved without additional MSDy effects. The output of the method can include improved trajectories / distributions to be sent to the platform and the deformable reflector.

[0077] The deformable reflector can achieve MSD reduction by optimizing the dynamic adjustment of geometric deformation (such as magnification in the y direction) in order to reduce the average (e.g., RMS) deviation of the Y position of the imaged feature relative to the nominal position over the entire scan integration time, while still maintaining a fixed average position. There is still a need for platform Y control to provide actual overlay or alignment correction based on actual MA control (which actively shifts the center of the feature image).

[0078] Alternatively, the platform control parameters (platform control profile) can be determined based on the required correction for the obtained position parameters (based on overlay, alignment, or leveling correction data), and knowledge of the correction potential of the lens manipulator in stabilizing or mitigating contrast degradation caused by applying the control profile to correct the position.

[0079] Alternatively, the lens manipulator control profile can be determined based on knowledge of the platform control profile, e.g., when position parameter data is available and it is expected that the platform control profile can be calculated, and subsequently the lens manipulator control profile can be determined in order to mitigate or stabilize image contrast degradation caused by dynamic platform position errors introduced when using the platform control profile to control the platform.

[0080] The new proposal may optionally include a Wiener-based method (the Wiener-based attenuation control method is described in the published Dutch application NL2021296A, which is incorporated herein by reference). This Wiener-based method includes taking into account the known finite slit width (the slit size in the scanning direction) when determining the correction distribution. This may include using an appropriate scheme to deconvolve the effect of the slit width (e.g., the intensity distribution within the slit) according to the correction distribution to determine the deconvolved correction distribution that provides improved performance during exposure. This may include using a Wiener filter-based algorithm to solve the attenuation problem when determining the correction distribution and defining the scanner actuator trajectory. This optimizes the MA performance, overlap performance, focus performance, and MSD performance, and thus optimizes the imaging performance. For specific applications, the proposed technique can also be made flexible in terms of the MA versus MSD balance.

[0081] The attenuation may be related to the convolution of the intensity distribution within the slit. The problem can also be generalized / summarized for the noise injected into the desired correction. The convolved noisy correction distribution y includes the input correction distribution or the setpoint s convolved with the slit intensity distribution h to obtain the noise-free convolved correction distribution r subjected to the injection of noise n. Only the (noisy) convolved correction distribution y and the slit intensity distribution h are known. The aim is to deconvolve the slit distribution by determining the "deslitted" or deconvolved distribution g such that the difference between the corrected (or "deslitted") correction distribution or setpoint and the input correction distribution s is minimized (e.g., such that the mean square error or RMS error is minimized). In the case where the convolved noisy correction distribution y is the available correction (as in this case), the problem becomes estimating the deslitted correction distribution which, when actuated, will minimize the slit convolution error. In the presence of noise, the variables are randomly variable, and thus the expected value of the deconvolved distribution g can be regarded as:

[0082]

[0083] The Wiener filter can be used to solve this problem. The Wiener filter is a technique used in signal processing to extract a desired signal from an observed noisy process. The Wiener filter can be used, for example, to restore an image blurred by a known low-pass filter. Wiener filtering performs an optimal compromise between inverse filtering and noise smoothing. This solves the problem in the frequency domain by performing a Fourier transform or FFT on each of the variables. This simplifies the solution because the convolution now becomes multiplication. The problem then becomes:

[0084]

[0085] which can be solved by the following equation:

[0086]

[0087] where S PSD (f) is the average power spectral density of the original calibration distribution s, N PSD (f) is the average power spectral density of the noise n, and the superscript * indicates the complex conjugate. Thus, the Wiener filter can be used to provide a deconvolved, calibrated (deslitted) setpoint for the actuator in the scanner

[0088] The noise N PSD (f) term can be used to tune the optimization between MA and MSD. In an embodiment, it can be assumed that the noise term N PSD takes a single value (white noise) over all frequencies f. The lower limit value of the noise term N PSD will enhance MA while reducing MSD, and the upper limit value will do the opposite.

[0089] Therefore, in this method, the scanner currently tracks the overlap (e.g., dy) distribution during the scan performed via platform control. Attenuation limits the correction ability, and the Wiener filter method attempts to rebalance MA and MSD. This situation is illustrated by the first curve CV1 of Figure 7 which shows the expected overlap or alignment residual OV varying with the induced MSD MSDy. The maximum acceptable MSD MSDy max is shown (which can be user-selected or otherwise calculated), which effectively limits the minimum achievable overlap residual OV (optimal overlap), and thus limits the full potential of the platform actuation, even if the scanner is physically capable of performing the platform actuation. In other words, although it may be possible to further reduce MA and the overlap residual through platform correction, this may not be allowed due to its impact on MSD and thus on contrast and EPE.

[0090] By jointly optimizing the platform and the deformable reflector (e.g., using the same Wiener filter method), the portion of the induced MSD will be compensated by the deformable reflector within the slit, thereby for a given maximum acceptable MSD MSDy max , a greater correction potential can be achieved via platform actuation. As shown by Figure 7 the second curve CV2, which depicts the same relationship as the curve CV1 for the joint optimization method disclosed herein. The result of the joint optimization method and the in-slit correction using the deformable reflector is that for the same maximum acceptable MSD MSDy max , the overlapping residue will be significantly improved, thereby causing a significant overlapping improvement ΔOV.

[0091] In an embodiment, the joint optimization may include minimizing a set of objective functions:

[0092]

[0093] where dy is the overlapping dy distribution, is the platform actuation matrix, is the lens actuation matrix, t is the platform trajectory, l is the lens trajectory, and Ω is the slit distribution.

[0094] The lens actuation matrix includes the deformable reflector actuation matrix (and other lens elements), and the lens trajectory l includes the deformable reflector trajectory among other lens trajectories. The slit distribution Ω is constant.

[0095] The first objective function among these objective functions describes the optimization of the MA using platform control. This optionally includes the slit distribution as a reminder of the Wiener filter mechanism. The second objective function among these objective functions describes the control of the lens elements, and in particular the control of the deformable reflector, to maintain the quadratic form of the MSD induced by the platform under control, i.e., the quadratic form. The third objective function among these objective functions is included to clarify that the control of the deformable reflector does not contribute to the final overlap of the MA in the slit. In this way, the Wiener-based platform actuation is fully utilized via the first objective function to compensate the overlapping (dy) distribution.

[0096] At the same time, the set of equations must be minimized, such that the set of equations can be combined within a single larger matrix system or matrix group; for example, the optimization in the form:

[0097]

[0098] The degree of contrast (MSD) improvement depends on the degree of in-slit control achievable using the deformable reflector. The simplest implementation may only include y-translation (translation parameter Ty) control. A significant improvement in this regard can be achieved by including tilt (magnification parameter MagY) control. In addition, continuous improvement can be achieved by utilizing curvature parameters and / or higher-order (e.g., third-order) in-slit control.

[0099] Figure 8 FIG. is a flowchart of the proposed method for each layer. At step 800, stress performance parameters (e.g., overlay) characteristics within the die are measured. At step 810, the maximum allowable MSD is determined based on layer characteristics (e.g., this operation can typically be performed for each layer, and each layer has different sensitivities to MSD). Based on the results of steps 800 and 810, a jointly optimized control strategy is determined 820 for exposing multiple layers, and the joint optimization is performed for at least stage control and control of the deformable reflector (semi-dome mirror). Optionally, the joint optimization may also include optimizing lens control parameters. The result of step 820 will be a control profile 830, including a stage control profile, a deformable reflector control profile, and (optionally) a lens control profile. These profiles 830 can be fed back to the SIM in a simulation-based loop. Finally, at step 840, the performance on the actual product can be verified (e.g., via metrology) and fed back to the EXP in an experiment-based loop.

[0100] In this way, the correction range of sub-field correction for overlay (or other parameters of interest) can be extended for a given MSD limit. This optimization can be performed for each layer.

[0101] The jointly optimized correction distribution can undergo further optimization within the scanner, e.g., based on scanner metrology (alignment / leveling, etc.) or other metrology, to determine the actual correction distribution implemented during exposure.

[0102] In other embodiments, the joint optimization step can consider (e.g., jointly optimize) control parameters rather than stage / projection lens and deformable reflector control profiles that affect the performance parameters. For example, the jointly optimized scanner control profile can be further optimized according to focus, dose, etc. (all of which also affect EPE).

[0103] In all of the above examples, the optimization can be performed based on any of the disclosed performance parameters (overlay, EPE, etc.). In an embodiment, the performance parameter error is associated with the stress induced by the application of subsequent layers, where the joint optimization is based on the expected performance parameter residuals.

[0104] It can be shown that this method will result in improved overlay and, consequently, improved yield.

[0105] While the foregoing description has described using at least one deformable reflector to apply wavefront correction to correct magnification, it should be understood that the deformable reflector is only one type of lens manipulator that can be used to implement the methods disclosed herein. It should be understood that the teachings herein can be extended to any other type of lens manipulator (such as a zoom lens) capable of adequately achieving rapid y-fold magnification correction, and all references to the deformable reflector should be understood to encompass other lens manipulators.

[0106] While the patterning device has been described in the form of a physical mask, the term "patterning device" in this application also includes a data product that conveys a pattern in digital form (e.g., for use in conjunction with a programmable patterning device).

[0107] Other embodiments of the invention are disclosed in the list of numbered aspects below:

[0108] 1. A method for determining a correction for controlling a lithography process for exposing a pattern on an exposure field using a lithography apparatus, the method comprising:

[0109] obtaining a spatial distribution that describes a spatial variation of a performance parameter across at least a portion of the exposure field; and

[0110] co-determining a control profile for the spatial distribution to ensure a minimum contrast quality while minimizing an error in the performance parameter, the co-determined control profile including at least a stage control profile for controlling a stage arrangement of the lithography apparatus and a lens manipulator control profile for controlling a lens manipulator of the lithography apparatus, the lens manipulator of the lithography apparatus being operable to perform a correction of at least magnification in a direction perpendicular to the substrate plane.

[0111] 2. The method according to aspect 1, wherein the lens manipulator comprises one or more deformable reflectors.

[0112] 3. The method according to aspect 1 or 2, wherein the lens manipulator is configured to adjust a wavefront of patterned radiation adjacent to an image plane of the lithography apparatus.

[0113] 4. The method according to aspect 1, 2, or 3, wherein a co-optimized control profile is determined for sub-field control.

[0114] 5. The method according to aspect 4, wherein the method is performed to determine a corresponding set of the co-determined control profiles for each sub-field of the exposure field.

[0115] 6. The method according to any of the foregoing aspects, wherein the jointly determined control profile further comprises a projection lens control profile for controlling a projection lens within the lithographic apparatus.

[0116] 7. The method according to any of the foregoing aspects, wherein ensuring the minimum contrast quality comprises imposing a maximum allowable moving standard deviation of error in the control of the stage arrangement.

[0117] 8. The method according to any of the foregoing aspects, wherein the step of jointly determining the control profile comprises determining a jointly optimized control profile of the spatial distribution to ensure the minimum contrast quality while minimizing the error in the performance parameter, and each control profile in the jointly determined control profile comprises the jointly optimized control profile.

[0118] 9. The method according to aspect 8, wherein the joint optimization comprises moving average optimization of MA via the stage control profile and lens optimization via the lens manipulator control profile.

[0119] 10. The method according to aspect 9, wherein the lens optimization is aimed at minimizing the quadratic form of the stage-induced MSD.

[0120] 11. The method according to aspect 9 or 10, wherein the joint optimization comprises causing the lens manipulator control profile not to contribute to the function of MA in the exposure slit of the lithographic apparatus.

[0121] 12. The method according to any of the foregoing aspects, comprising applying a deconvolution scheme to at least the stage control profile, wherein the structure of the deconvolution scheme is based on the size of the illumination profile in the scan direction, at least the stage control profile comprises a convolved control profile, the convolved control profile is convolved with the illumination profile defined by the exposure slit, and the deconvolution scheme deconvolves the convolved control profile to minimize the error resulting from the convolution.

[0122] 13. The method according to aspect 12, wherein the deconvolution scheme comprises determining a Wiener deconvolution filter, and the Wiener deconvolution filter deconvolves the convolved control profile and the illumination profile in the presence of noise.

[0123] 14. The method according to any of the foregoing aspects, wherein the lens manipulator control profile comprises magnification parameter control.

[0124] 15. The method according to any of the foregoing aspects, wherein the lens manipulator control profile comprises a curvature parameter.

[0125] 16. The method according to any of the foregoing aspects, wherein the lens manipulator control profile includes higher order slit control.

[0126] 19. The method according to any of the foregoing aspects, wherein the performance parameter includes or relates to overlap.

[0127] 20. The method according to any of the foregoing aspects, wherein the performance parameter includes edge placement error.

[0128] 21. The method according to any of the foregoing aspects, wherein the platform arrangement includes a first platform for supporting and positioning a substrate and a second platform for supporting and positioning a patterning device, and the platform control profile includes one or more profiles for combined control of the first platform and the second platform.

[0129] 22. The method according to any of the foregoing aspects, wherein the spatial distribution is derived based on known stress signatures within a die.

[0130] 23. The method according to any of the foregoing aspects, wherein the co - determination step includes performing a co - determined platform control profile and a lens manipulator control profile, wherein the platform control profile is configured to correct the performance parameter and the lens manipulator control profile is configured to stabilize the impact of the platform control on contrast with a minimal impact on the performance parameter.

[0131] 24. A method of performing co - determined platform control and dynamic lens control for controlling a lithography process of exposing a pattern on an exposure field using a lithographic apparatus, the method comprising:

[0132] Co - determining a platform control profile and a dynamic lens control profile, the platform control profile being configured to correct one or more spatially varying performance parameters, the dynamic lens control profile being operative to stabilize the impact of the platform control on contrast with a minimal impact on the one or more performance parameters.

[0133] 25. The method according to aspect 24, wherein the dynamic lens control profile is operative to control at least one or more deformable reflectors.

[0134] 26. The method according to any of the foregoing aspects, including performing a lithography process based on the co - optimized control profile.

[0135] 27. A computer program comprising program instructions operative to perform the method according to any one of aspects 1 to 26 when run on a suitable device.

[0136] 28. A non - transitory computer program carrier, comprising a computer program according to aspect 27.

[0137] 29. A lithographic apparatus, comprising:

[0138] An illumination system configured to provide a radiation beam;

[0139] A platform arrangement comprising a first platform for supporting a patterning device and a second platform for holding a substrate, the patterning device being configured to impart a pattern to the radiation beam in a cross - section of the radiation beam;

[0140] A projection system configured to project the patterned radiation beam onto a target portion of the substrate;

[0141] A lens manipulator configured to apply a correction to the patterned radiation beam according to a lens manipulator control profile, the lens manipulator being located near the field plane; and

[0142] A controller configured to perform the method according to any one of aspects 1 to 26.

[0143] 30. The lithographic apparatus according to aspect 29, wherein the lens manipulator comprises one or more deformable reflectors configured to reflect the patterned radiation beam and to apply a wavefront adjustment thereto according to the lens manipulator control profile in order to apply the correction.

[0144] 31. A method of determining a dynamic control profile for a manipulator of a lens used in a lithographic apparatus when projecting an image of a pattern onto a substrate, the method comprising:

[0145] Obtaining a spatial variation across at least a portion of the substrate of position parameters associated with the positioning of the projected image; and

[0146] Determining the dynamic control profile for the manipulator based on a desired stabilization or mitigation of image contrast degradation caused by an expected effect of a dynamic platform position error associated with a platform control profile configured to correct the spatial variation of the position parameters.

[0147] 32. The method according to aspect 31, wherein the position parameters are associated with alignment data and / or overlay data obtained based on measurements performed on the substrate.

[0148] 33. The method according to aspect 31 or 32, wherein the dynamic platform position error is expressed as a moving standard deviation of the position errors generated during the control of the platform.

[0149] 34. The method according to any one of aspects 31 to 33, wherein the dynamic control profile for the manipulator is configured to provide dynamic control of the magnification in a direction parallel to the scan direction.

[0150] 35. A method of determining a platform control profile for a platform used in a lithographic apparatus for projecting an image of a pattern onto a substrate, the method comprising:

[0151] obtaining a spatial variation across at least a portion of the substrate of position parameters associated with the positioning of the projected image; and

[0152] determining the control profile for the platform based on the spatial variation of the position parameters and the correction potential of a lens manipulator for stabilizing or reducing image contrast degradation, the image contrast degradation being caused by an expected effect of a dynamic platform position error associated with the platform control profile configured to correct the spatial variation of the position parameters.

[0153] 36. The method according to aspect 35, wherein the position parameters are associated with alignment data and / or overlay data obtained based on measurements performed on the substrate.

[0154] 37. The method according to aspect 35 or 36, wherein the dynamic platform position error is expressed as a moving standard deviation of the position errors generated during the control of the platform.

[0155] 38. The method according to any one of aspects 35 to 37, wherein the correction potential of the lens manipulator is associated with a dynamically controllable magnification applied to the image in a direction parallel to the scan direction.

[0156] 39. A method of performing co-determined platform control and dynamic lens control for controlling a lithographic process for exposing a pattern in an exposure field using a lithographic apparatus, the method comprising: co-determining a platform control profile and a dynamic lens control profile, the platform control profile being configured to correct one or more spatially varying performance parameters, the dynamic lens control profile being configured to mitigate or stabilize the effect of the platform control on the contrast of the exposed pattern.

[0157] 40. The method according to aspect 39, wherein jointly determining comprises applying a constraint to the dynamic lens control profile so as to limit the effect of the dynamic lens control profile on the one or more performance parameters.

[0158] 41. The method according to aspect 39 or 40, wherein the dynamic lens control profile is operable to control at least one or more deformable reflectors.

[0159] 42. The method according to any one of aspects 39 to 41, wherein the jointly determined control profile is determined for sub - field control.

[0160] 43. The method according to any one of aspects 39 to 42, comprising applying a de - convolution scheme to at least the platform control profile, wherein the structure of the de - convolution scheme is based on the size of the illumination profile in the scan direction, at least the platform control profile comprising a convolved control profile that is convolved with the illumination profile as defined by the exposure slit, and the de - convolution scheme de - convolves the convolved control profile to minimize the error resulting from the convolution.

[0161] 44. A computer program comprising program instructions that are operable to perform the method according to any one of aspects 31 to 43 when run on a suitable device.

[0162] 45. A non - transitory computer program carrier comprising the computer program according to aspect 44.

[0163] 46. A method of determining a dynamic control profile for a manipulator of a lens used in a lithographic apparatus for projecting an image of a pattern onto a substrate, the method comprising:

[0164] obtaining a spatial variation across at least a portion of the substrate of position parameters associated with the positioning of the projected image; and

[0165] determining the dynamic control profile for the manipulator based on a desired stabilization or mitigation of image contrast degradation resulting from the expected effect of a dynamic platform position error associated with a platform control profile configured to correct for the spatial variation of the position parameters, wherein the dynamic control profile is configured to dynamically adjust a geometric distortion of the projected image during projection.

[0166] 47. The method according to aspect 46, wherein the geometric distortion is a magnification in a direction parallel to the scan direction.

[0167] 48. A method for determining a platform control profile for a platform used within a lithographic apparatus when projecting an image of a pattern onto a substrate, the method comprising:

[0168] obtaining a spatial variation over at least a portion of the substrate of position parameters associated with the positioning of the projected image; and

[0169] determining the control profile for the platform based on the spatial variation of the position parameters and the correction potential of a dynamically controllable lens manipulator for stabilizing or mitigating image contrast degradation, the image contrast degradation being due to an expected effect of a dynamic platform position error associated with the platform control profile configured to correct the spatial variation of the position parameters, wherein the dynamically controllable lens manipulator is configured to dynamically adjust geometric distortion of the projected image during projection.

[0170] 49. The method according to aspect 48, wherein the correction potential of the lens manipulator is associated with a dynamically controllable magnification applied to the image in a direction parallel to the scan direction.

[0171] 50. A method for performing co - determined platform control and dynamic lens control for controlling a lithographic process for exposing a pattern in an exposure field using a lithographic apparatus, the method comprising: co - determining a platform control profile and a dynamic lens control profile, the platform control profile being configured to correct one or more spatially varying performance parameters, the dynamic lens control profile being configured to mitigate or stabilize the effect of the platform control on the contrast of the exposed pattern, wherein the dynamic lens control profile is configured to dynamically adjust geometric distortion of the exposed pattern during exposure.

[0172] Although embodiments of the invention have been specifically mentioned above in the context of use in optical lithography, it should be understood that embodiments of the invention can be used in other applications, such as imprint lithography, and, where the context allows, are not limited to optical lithography. In imprint lithography, the topography in the patterning device defines the pattern created on the substrate. The topography of the patterning device can be pressed into a resist layer supplied to the substrate, whereby the resist is cured by application of electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist, leaving a pattern therein.

[0173] The terms “radiation” and “beam” as used in relation to the lithographic apparatus cover all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of or about 365 nm, 355 nm, 248 nm, 193 nm, 157 nm or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 nm to 20 nm), as well as particle beams such as ion beams or electron beams.

[0174] The term “lens” can refer, where the context allows, to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

[0175] The foregoing description of the specific embodiments will sufficiently disclose the general nature of the present invention, such that others can, without departing from the general concept of the present invention, readily modify and / or adapt these specific embodiments for various applications by applying knowledge within the scope of the art without undue experimentation. Therefore, based on the teachings and guidance presented herein, these adaptations and modifications are intended to fall within the meaning and scope of the equivalents of the disclosed embodiments. It should be understood that the language or terminology herein is for the purpose of description and not limitation, so that the terminology or language of this specification is to be interpreted by those skilled in the art in accordance with the said teachings and the said guidance.

[0176] Therefore, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents.

Claims

1. A method for determining a dynamic control profile of a manipulator of a lens used in a lithographic apparatus for projecting an image of a pattern onto a substrate, the method comprising: obtaining a spatial variation across at least a portion of the substrate of position parameters associated with the positioning of the projected image; and determining the dynamic control profile for the manipulator based on stabilization or mitigation of image contrast degradation resulting from an expected effect of a dynamic stage position error associated with a stage control profile configured to correct the spatial variation of the position parameters, wherein the dynamic control profile for the manipulator is configured to dynamically adjust geometric distortion of the projected image during projection.

2. The method according to claim 1, wherein the position parameters are associated with alignment data and / or overlay data obtained from measurements performed on the substrate.

3. The method according to claim 1, wherein the dynamic stage position error is expressed as a moving standard deviation of position errors generated during control of the stage.

4. The method according to claim 1, wherein the geometric distortion is magnification in a direction parallel to the scan direction.

5. A method for determining a stage control profile of a stage used in a lithographic apparatus for projecting an image of a pattern onto a substrate, the method comprising: obtaining a spatial variation across at least a portion of the substrate of position parameters associated with the positioning of the projected image; and determining the control profile for the stage based on the spatial variation of the position parameters and a correction potential of a dynamically controllable lens manipulator for stabilization or mitigation of image contrast degradation resulting from an expected effect of a dynamic stage position error associated with the stage control profile configured to correct the spatial variation of the position parameters, wherein the dynamically controllable lens manipulator is configured to dynamically adjust geometric distortion of the projected image during projection.

6. The method according to claim 5, wherein the position parameters are associated with alignment data and / or overlay data obtained from measurements performed on the substrate.

7. The method according to claim 5, wherein the dynamic stage position error is expressed as a moving standard deviation of position errors generated during control of the stage.

8. The method according to claim 5, wherein the correction potential of the lens manipulator is associated with a dynamically controllable magnification applied to the image in a direction parallel to the scan direction.

9. A method of performing jointly determined platform control and dynamic lens control for controlling a lithography process for exposing a pattern in an exposure field using a lithography apparatus, the method comprising: Co-determining a stage control profile and a dynamic lens control profile, the stage control profile being configured to correct one or more spatially varying performance parameters, the dynamic lens control profile being configured to mitigate or stabilize the effect of the stage control on the contrast of the exposed pattern, wherein the dynamic lens control profile is configured to dynamically adjust geometric distortion of the exposed pattern during exposure.

10. The method according to claim 9, wherein co-determining comprises applying a constraint to the dynamic lens control profile so as to limit the effect of the dynamic lens control profile on the one or more performance parameters.

11. The method according to claim 9, wherein the dynamic lens control profile is operable to control at least one or more deformable reflectors.

12. The method according to claim 9, wherein the co-determined control profile is determined for sub-field control.

13. The method according to claim 9, further comprising applying a deconvolution scheme to at least the platform control profile, wherein the structure of the deconvolution scheme is based on the dimension of the illumination profile in the scan direction, at least the platform control profile comprising a convolved control profile that is convolved with the illumination profile as defined by the exposure slit, the deconvolution scheme deconvolving the convolved control profile to minimize the error resulting from the convolution.

14. A computer program product comprising program instructions operable to determine a dynamic control profile for a manipulator of a lens used in a lithographic apparatus for projecting an image of a pattern onto a substrate, the program instructions being configured to: obtain a spatial variation across at least a portion of the substrate of a position parameter associated with the positioning of the projected image; and determine the dynamic control profile for the manipulator based on stabilization or mitigation of image contrast degradation resulting from an expected effect of a dynamic platform position error associated with a platform control profile configured to correct the spatial variation of the position parameter, wherein the dynamic control profile for the manipulator is configured to dynamically adjust geometric distortion of the projected image during projection.

15. A computer program product comprising program instructions operable to determine a platform control profile for a platform used in a lithographic apparatus for projecting an image of a pattern onto a substrate, the program instructions being configured to: obtain a spatial variation across at least a portion of the substrate of a position parameter associated with the positioning of the projected image; and determine the control profile for the platform based on the spatial variation of the position parameter and the correction potential of a dynamically controllable lens manipulator for stabilizing or mitigating image contrast degradation resulting from an expected effect of a dynamic platform position error associated with the platform control profile configured to correct the spatial variation of the position parameter, wherein the dynamically controllable lens manipulator is configured to dynamically adjust geometric distortion of the projected image during projection.

16. A non-transitory computer program carrier comprising the computer program product according to claim 14 or 15.

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