Setup and control method for lithography processes and related equipment - Patents.com

Abstract

A method is disclosed for performing a lithographic apparatus setup calibration and / or drift correction for a particular lithographic apparatus of a population of lithographic apparatus used in a manufacturing process for producing integrated circuits extending across multiple layers on a substrate, the method comprising: determining a spatial error distribution of an apparatus parameter across spatial coordinates on the substrate for each lithographic apparatus of the population of lithographic apparatuses and / or each layer of the multiple layers, determining a reference distribution by aggregating each of the spatial error distributions and optimizing the reference distribution such that a spatial distribution of a parameter of interest of the manufacturing process is jointly optimized across the population of lithographic apparatuses and / or the multiple layers, and using the reference distribution as a target distribution for the apparatus parameter for each lithographic apparatus and / or layer.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Application No. 22163435.5, filed March 22, 2022, which is incorporated by reference in its entirety into this specification.

[0002] The present invention relates to methods and apparatus that can be used, for example, in the manufacture of devices by lithography techniques, and to methods of manufacturing devices using lithography techniques. [Background technology]

[0003]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A patterning device, also known as a mask or reticle, can be used to generate the circuit pattern formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on the substrate (e.g. a silicon wafer). Typically, the transfer of the pattern is by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are successively patterned. These target portions are commonly referred to as "fields".

[0004]

[0004] In the manufacture of complex devices, many lithographic patterning steps are typically performed, which form functional features in successive layers on a substrate. Therefore, an important aspect of the performance of a lithographic apparatus is the ability to accurately and precisely place an applied pattern with respect to features defined in a previous layer (by the same apparatus or a different lithographic apparatus). For this purpose, the substrate is provided with a set of one or more alignment marks. Each mark is a structure whose position can be subsequently measured using a position sensor, typically an optical position sensor. The lithographic apparatus includes one or more alignment sensors, by which the position of the marks on the substrate can be precisely measured. Various types of marks and various types of alignment sensors are known from different manufacturers and different products of the same manufacturer.

[0005]

[0005] The lithographic apparatus comprises a projection system. The projection system includes optical elements such as, for example, lenses. Optical aberrations may result from imperfections of the optical elements. Optical aberrations may also result from projection effects such as, for example, heating of the optical elements that occurs during a lithographic exposure. The projection system model is used to determine one or more adjustments that can be made to the optical elements of the projection system. The determined adjustments may have the effect of reducing the optical aberrations in the projection system.

[0006]

[0006] For example, it may be desirable to provide improvements in the calibration, setup and control (e.g., drift control) aspects of a lithography process, for example for projection system setup or grid setup, which avoids or mitigates one or more of the problems of the prior art, whether identified herein or elsewhere. Summary of the Invention

[0007]

[0007] The invention in a first aspect provides a method for performing a lithographic apparatus setup calibration and / or drift correction for a particular lithographic apparatus of a population of lithographic apparatus used in a manufacturing process for producing integrated circuits extending across multiple layers on a substrate, the method comprising: determining a spatial error distribution of an apparatus parameter across spatial coordinates on the substrate for each lithographic apparatus of the population of lithographic apparatuses and / or each layer of the multiple layers, determining a reference distribution by aggregating each of the spatial error distributions and optimizing the reference distribution such that a spatial distribution of a parameter of interest of the manufacturing process is jointly optimized across the population of lithographic apparatuses and / or the multiple layers, and using the reference distribution as a target distribution for the apparatus parameter for each lithographic apparatus and / or layer.

[0008] In a second aspect of the present invention there is provided a computer program comprising program instructions operable to perform a method as claimed in any of the above claims when run on a suitable device.

[0009] The invention further provides a processing arrangement and a lithographic apparatus comprising the computer program of the second aspect.

[0010]

[0010] These and other aspects and advantages of the apparatus and methods disclosed herein will become apparent from a consideration of the following description of exemplary embodiments and drawings. [Brief description of the drawings]

[0011]

[0011] Some embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0012] [Figure 1] FIG. 1 depicts a lithographic apparatus. [Diagram 2] FIG. 2 shows a schematic of the measurement and exposure process in the apparatus of FIG. [Diagram 3]FIG. 3 is a flow chart of a method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Before describing embodiments of the present invention in detail, it is beneficial to present an example environment in which embodiments of the present invention may be implemented.

[0014]

[0013] Fig. 1 shows a schematic representation of a lithographic apparatus LA. The apparatus comprises an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV or DUV radiation), a patterning device support or support structure (e.g. mask table) MT constructed to support a patterning device (e.g. mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters, two substrate tables (e.g. wafer tables) WTa and WTb each constructed to hold a substrate (e.g. resist-coated wafer) W and each connected to a second positioner PW configured to accurately position the substrate according to certain parameters, and a projection system (e.g. refractive projection lens system) PS configured to project a pattern imparted by the patterning device MA in the radiation beam B onto a target portion C of the substrate W (e.g. comprising one or more dies). A reference frame RF connects the various components and serves as a reference for setting and measuring the positions of the patterning device and the substrate and features thereon.

[0015]

[0014] The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, to guide, shape, or control radiation.

[0016]

[0015] The patterning device support MT holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as whether or not the patterning device is held in a vacuum environment. The patterning device support may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The patterning device support MT may be for example a frame or a table, which may be fixed or movable as required. The patterning device support may ensure that the patterning device is at a desired position, for example with respect to the projection system.

[0017]

[0016] The term "patterning device" as used herein should be broadly interpreted as referring to any device that can be used to impart a pattern to a cross-section of a radiation beam so as to create a pattern in a target portion of a substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so-called assist features. Typically, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device to be created in the target portion, such as an integrated circuit.

[0018]

[0017] As depicted herein, the apparatus is of a transmissive type (e.g. employing a transmissive patterning device). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array of the type referred to above, or employing a reflective mask). Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Any use of the terms "reticle" or "mask" herein may be considered synonymous with the more general term "patterning device". The term "patterning device" may also be interpreted as referring to a device that digitally stores pattern information for use in controlling such a programmable patterning device.

[0019]

[0018] The term "projection system" as used herein should be broadly interpreted to encompass any type of projection system including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, appropriate for the exposure radiation being used, or other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered as synonymous with the more general term "projection system".

[0020]

[0019] The lithographic apparatus may also be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems.

[0021]

[0020] In operation, the illuminator IL receives a radiation beam from the radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the radiation source is an excimer laser. In such cases, the radiation source is not considered to form part of the lithographic apparatus, and the radiation beam is delivered from the source SO to the illuminator IL using a beam delivery system BD, which may include, for example, suitable directing mirrors and / or beam expanders. In other cases, the radiation source may be an integral part of the lithographic apparatus, for example when the radiation source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0022]

[0021] The illuminator IL may comprise, for example, an adjuster AD for adjusting the angular intensity distribution of the radiation beam, an integrator IN, and a condenser CO. The illuminator may be used to condition the radiation beam so that it has a desired uniformity and intensity distribution in its cross-section.

[0023]

[0022] The radiation beam B is incident on the patterning device MA, which is held on the patterning device support MT, and is patterned by the patterning device. After passing through the patterning device (e.g. mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam on a target portion C of the substrate W. Using the second positioner PW and a position sensor IF (e.g. an interferometer device, a linear encoder, a 2-D encoder or a capacitive sensor), the substrate table WTa or WTb can be accurately moved, for example, to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (not explicitly shown in Figure 1a) can also be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B, for example after mechanical retrieval from a mask library or during a scan.

[0024]

[0023] The patterning device (e.g. mask) MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although in the examples shown the substrate alignment marks occupy dedicated target portions, the substrate alignment marks may also be located in spaces between the target portions (these are known as scribe-line alignment marks). Similarly, in cases where more than one die is provided on the patterning device (e.g. mask) MA, the mask alignment marks may be located between the dies. Small alignment marks may also be included within the dies, between the device features, in which case it is desirable for the markers to be as small as possible and not require any different imaging or process conditions than adjacent features. Alignment systems for detecting alignment markers are further described below.

[0025]

[0024] The illustrated apparatus can be used in various modes. In scan mode, the patterning device support (e.g. mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the patterning device support (e.g. mask table) MT can be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width of the target portion (in non-scan direction) during a single dynamic exposure, while the length of the scanning motion determines the height of the target portion (in scan direction). Other types of lithographic apparatus and operation modes are possible, as are well known in the art. For example, a step mode is known. In so-called "maskless" lithography, a programmable patterning device is held stationary but with a changing pattern, and the substrate table WT is moved or scanned.

[0026]

[0025] Combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0027]

[0026] The lithographic apparatus LA is of the so-called dual stage type having two substrate tables WTa, WTb and two stations - an exposure station EXP and a measurement station MEA - between which the substrate tables can be exchanged. While one substrate on one substrate table is being exposed at the exposure station, another substrate can be loaded on the other substrate table at the measurement station and various preparation steps can be performed. This allows a substantial increase in the throughput of the apparatus. The preparation steps may include mapping the surface height profile of the substrate using the level sensor LS and measuring the position of an alignment marker on the substrate using the alignment sensor AS. In case the position sensor IF cannot measure the position of the substrate table while it is in the measurement station as well as the exposure station, a second position sensor may be provided to be able to track the position of the substrate table at both stations relative to the reference frame RF. Instead of the illustrated dual stage configuration, other configurations are known and can be used. For example, other lithographic apparatuses are known in which a substrate table and a measurement table are provided. These are coupled together when performing the preliminary measurements and then uncoupled while the substrate table undergoes exposure.

[0028]

[0027] The lithographic apparatus LA further comprises a wavefront sensor WS, for example on each substrate table WTa, WTb. Such a sensor can measure the quality of the wavefront image as well as any aberrations, and thus allows for (for example parallel) measurement of the optical aberrations across the projection slit, and thus may allow for, for example, more accurate alignment, improved reticle heating correction, and fly lens heating correction. Such aberrations may be described as coefficients in a set of 2D mathematical functions called Zernike polynomials. These can be regrouped to represent several well-known optical aberrations, such as spherical, coma, astigmatism, etc. The wavefront sensor may comprise an interferometric wavefront measurement system, and may perform static measurements for lens aberrations up to higher orders. This may be implemented as an integrated measurement system used for system initialization and calibration. Alternatively, it may be used for monitoring and recalibration "on demand". Thus, depending on its design, the wavefront sensor may be capable of measuring lens aberrations per lot or per wafer.

[0029]

[0028] Figure 2 illustrates the steps of exposing a target portion (e.g. a die) on a substrate W in the dual stage apparatus of Figure 1. In the dashed box on the left are steps performed in the measurement station MEA, while on the right are steps performed in the exposure station EXP. As explained above, depending on the case, one of the substrate tables WTa, WTb is in the exposure station and the other is in the measurement station. For the purposes of this description, it is assumed that a substrate W is already loaded in the exposure station. In step 200, a new substrate W' is loaded into the apparatus by a mechanism not shown. These two substrates are processed in parallel to increase the throughput of the lithographic apparatus.

[0030]

[0029] First, referring to the newly loaded substrate W', this may be an unprocessed substrate prepared with new photoresist for the first exposure in the apparatus. However, in general, the lithography process described is only one step in a series of exposure and processing steps, so the substrate W' may have already passed through this and / or other lithography apparatuses several times and may also have subsequent processes to undergo. Particularly for the problem of improving overlay performance, the challenge is to ensure that the new pattern is applied accurately at the correct location on a substrate that has already undergone one or more cycles of patterning and processing. These processing steps progressively introduce distortions into the substrate that must be measured and corrected to achieve satisfactory overlay performance.

[0031]

[0030] As mentioned above, previous and / or subsequent patterning steps may be performed in other lithography apparatus, or even in different types of lithography apparatus. For example, some layers in a device manufacturing process that are very demanding in parameters such as resolution and overlay may be performed in a more advanced lithography tool than other layers that are less demanding. Thus, some layers may be exposed in an immersion type lithography tool, while others are exposed in a "dry" tool. Some layers may be exposed in a tool operating at DUV wavelengths, while others are exposed using EUV wavelength radiation.

[0032] In 202, alignment measurements using substrate marks P1 etc. and an image sensor (not shown) are used to measure and record the alignment of the substrate relative to the substrate tables WTa / WTb. In addition, several alignment marks across the substrate W' are measured using an alignment sensor AS. These measurements are used in one embodiment to establish a "wafer grid", which very accurately maps the distribution of marks across the substrate, including any distortions to a nominal rectangular grid.

[0033] In step 204, a map of the wafer height (Z) versus XY position is also measured using a level sensor LS. Conventionally, the height map is only used to achieve accurate focusing of the exposed pattern. In addition, the height map may be used for other purposes.

[0034] When the substrate W' is loaded, recipe data 206 are received that define the exposures to be made and also the wafer properties, the patterns previously created on the substrate W' and the patterns to be created on the substrate W'. To these recipe data, measurements of the wafer position, the wafer grid and the height map created in 202, 204 are added, so that a complete set of recipe and measurement data 208 can be passed to the exposure station EXP. For example, the alignment data measurements include the X and Y positions of the alignment targets formed in a fixed or nominally fixed relationship to the product pattern that is the product of the lithography process. These alignment data obtained just before exposure are used to generate an alignment model with parameters that fit the model to the data. These parameters and the alignment model are used during the exposure operation to correct the position of the pattern applied in the current lithography step. The model in use interpolates the position deviation between the measured positions. Conventional alignment models can include four, five or six parameters that together define the translation, rotation and scaling of an "ideal" grid of different dimensions. Advanced models that use more parameters are known.

[0035]

[0034] In 210, the wafers W' and W are swapped so that the measured substrate W' becomes the substrate W entering the exposure station EXP. In the exemplary apparatus of FIG. 1, this swapping is performed by exchanging the supports WTa and WTb in the apparatus so that the substrates W, W' remain precisely clamped and positioned on those supports to maintain the relative alignment of the substrate table and the substrate itself. Thus, once the tables are swapped, all that is required is to determine the relative position of the projection system PS and the substrate table WTb (previously WTa) in order to use the measurement information 202, 204 about the substrate W (previously W') in controlling the exposure step. In step 212, reticle alignment is performed using the mask alignment marks M1, M2. In steps 214, 216, 218, scanning movements and radiation pulses are applied to successive target positions across the substrate W to complete the exposure of multiple patterns.

[0036]

[0035] By using the alignment data and height maps obtained at the measurement station during the exposure steps, these patterns are precisely aligned to the desired locations, particularly to previously placed features on the same substrate. The exposed substrate, here labeled W", is unloaded from the apparatus in step 220 to undergo etching or other processes according to the exposed pattern.

[0037]

[0036] Those skilled in the art will appreciate that the above description is a simplified overview of some very detailed steps involved in one example of a real manufacturing situation. For example, rather than measuring alignment in a single pass, there will often be separate phases of coarse and fine measurements using the same or different marks. The coarse alignment measurement step and / or the fine alignment measurement step may be performed before or after the height measurement, or may be performed alternately.

[0038]

[0037] Before using a lithography apparatus or scanner, a number of setup or calibration operations need to be performed. One such setup operation includes lens setup. The goal of lens setup is to optimize the lens aberrations in the lithography system to a target, which may be, for example, zero. The lens quality and optimization of the lens setup determine how well the target is achieved for a particular system. Every lens has a different spatial distribution of lens aberration values ​​across the exposure field, usually called the lens fingerprint (LFP). Thus, lens performance is not the same for all scanners in a particular facility (fab), but has a population distribution. Lens setup may include minimizing the inherent lens fingerprint through the actuation of lens elements (typically called lens manipulators) to minimize the aberrations or lens fingerprint. Lens actuators can correct some of the lens fingerprint, but their actuation potential is limited, e.g., even after setup, there is a minimized baseline fingerprint or lens setup residual fingerprint.

[0039]

[0038] The lens setup may be performed using a lens model that relates the (setpoints of) the lens actuators to the aberrations and to the lens fingerprint LFP. The aberrations can be described, for example, in terms of coefficients multiplied by Zernike polynomials, such that a linear combination describes the aberrations of the lens (typically defined as the wavefront aberrations across the pupil plane). The lens manipulator characteristics and the aberration data are combined in the lens model, for example, based on measurements (for example, wavefront measurements using a wavefront sensor). The lens model is used to adjust the lens using the manipulators to achieve the desired optical performance. More specifically, a calibration lens model (CLM) may be used during the lens setup, which provides access to all possible lens actuators / manipulators. One or more other lens models may be used in a production setting that may provide access to only a subset of these actuators. The lens setup is currently performed for each individual scanner to minimize the root mean square of the lens aberrations over the exposure field of the individual scanner. Different aberrations (Zernikes) are typically given equal or nominal weighting in the optimization, with the exception of very high orders which can be weighted much lower.

[0040]

[0039] Another setup operation includes grid setup. This can be done, for example, as a calibration of the substrate table to determine a measurement grid and / or an exposure grid. The description herein is in the context of a twin stage scanner as illustrated in Fig. 1, where there is a measurement grid on the measurement size and an exposure grid on the exposure side. However, the grid setup concept is equally applicable to a single stage scanner, where only a single exposure grid is determined. Alternatively, the measurement grid may be associated with a separate and independent measurement station.

[0041]

[0040] On the measurement side, scanner internal metrology (e.g. using alignment and / or level sensors) is used to read out a wafer with existing marks to identify distortions of the measurement grid. This is usually done for measurement grid calibration. On the exposure side, the method starts with a projection procedure where a pattern is exposed onto the substrate at various positions. Since the projection procedure is performed every time the substrate is positioned relative to the exposure grid of the measurement system, deviations in this exposure grid are automatically copied onto the substrate together with the pattern. The calibration method then includes the act of performing a measurement where the projected pattern is read out. Thereby, the position of the pattern on the substrate is measured relative to the scanner grid or measurement grid. Deviations of this measurement grid are therefore automatically included in the measurement result. These deviations can be described by a scanner position deviation fingerprint or a position deviation map. The grid setup may be performed using a dedicated calibration substrate. Optimization may be performed similarly to lens setup, by manipulating appropriate scanner actuators (mainly stage actuators, although lens actuators could also be used) to minimize the position deviation fingerprint, e.g., by modifying the reticle and / or wafer stage trajectories accordingly. Typically, as with lens setup, this calibration is performed for each scanner individually, attempting to reduce the deviation to zero, but once again, the extent to which this is achievable is limited by actuation capabilities.

[0042] After setup, scanners are typically not stable as components may drift, leading to changes in the lens fingerprint and / or position deviations. Scanner drift control aims to measure and correct these drifts for the initial scanner setup at start-up (T=0).

[0043]

[0042] Therefore, these setup methods only take into account the individual scanner. However, it is becoming more and more common that different layers are exposed on different physical scanners, sometimes including different scanner models or scanner types. For these machine-to-machine (M2M) matching applications (e.g., matched machine overlay (MMO) applications), the lens fingerprint (LFP) and / or misregistration fingerprint (or other fingerprints) that are individually and usually minimized may not provide the best results (e.g., lowest MMO) for the final product after exposure of multiple layers. Although there are ways to address some of these issues during production, it is desirable to provide a solution in the scanner setup (and control of drift). This is because it reduces the logistical burden of managing sub-recipes for each layer for each machine combination and is not dependent on more limited capabilities such as the lens model used during production.

[0044]

[0043] Furthermore, certain types of machines are only used in certain application areas (e.g., front-end-of-line FEOL). This is not taken into account in the current setup routines, and therefore (e.g., lens) setup residuals may not reflect the actual optimum within that application area. This may be exacerbated by the fact that certain layers in an application area (with certain sensitivities) are often more important than other layers (with certain sensitivities) in terms of overlay. Typically, different features have different characteristics and therefore may have different sensitivities. By setting up each machine in isolation, it is not taken into account the population of scanners, the scanners for the population, or what each scanner is used for.

[0045]

[0044] To address these issues, it is proposed to perform a scanner (lithographic apparatus) setup correction and / or drift correction for a particular scanner of a population of scanners used in a manufacturing process for manufacturing an integrated circuit and / or a layer extending across a plurality of layers contained in the integrated circuit. The method includes determining, for each lithographic apparatus of the population of lithographic apparatuses and / or for each layer of the plurality of layers, a spatial distribution or fingerprint (e.g., spatial error distribution or error fingerprint) of an apparatus parameter (e.g., an aberration parameter or a stage performance parameter) across spatial coordinates on a substrate, determining a reference distribution by aggregating each of the spatial error distributions such that the spatial distribution of a parameter of interest of the manufacturing process is jointly optimized across the population of lithographic apparatuses and / or the plurality of layers, optimizing the reference distribution, and determining a setup correction and / or drift correction to correct the manufacturing process using the reference distribution as a target distribution for each scanner and / or layer.

[0046] The reference distribution may be common for all scanners and / or layers. The reference distribution may be optimized to minimize the error range (e.g., aberration range or position deviation range) of a parameter of interest for a scanner population and / or multiple layers.

[0047] The spatial distribution or fingerprint for each scanner or layer used to determine the reference distribution may include a spatial error distribution or error fingerprint, such as a residual fingerprint following a conventional set-up procedure (e.g., conventional lens set-up or grid set-up). Alternatively, the spatial distribution (in the context of lens set-up) may be determined from population data of lenses from a lens supplier.

[0048]

[0047] The step of determining a reference distribution from each of the spatial distributions may include a step of determining a weighted average of the spatial distributions. The optimization step may include determining a weight per scanner / layer for which the weighted average is determined, the weight being determined to optimize a parameter of interest of the manufacturing process (e.g., to optimize a cost function related to or in terms of the parameter of interest). The parameter of interest may be, for example, any parameter indicative of overlay, edge placement error, or yield (function of integrated circuits). The weights of the individual scanner fingerprints may be determined iteratively until one or more criteria are reached, for example, until the error range for the parameter of interest is minimized (e.g., maximum absolute minimization, RMS minimization, or any other suitable minimization) over the scanner population and / or all layers.

[0049]

[0048] The joint optimization may also take into account any specific sensitivities or weights specific to a particular application associated with (e.g., performed by) one or more scanners / layers. Such area-specific sensitivities may describe the relationship between aberrations and resulting pattern shifts and may depend on the features being imaged and the corresponding illumination settings. Typically, in a particular application area (e.g., FEOL), similar types of features are exposed across different layers with similar / complementary illumination settings. Thus, the Zernike sensitivities are expected to be similar. Thus, aberrations with low sensitivity ("Zernikes") contribute less to the "end result" (e.g., pattern shift) than Zernikes with overall high sensitivity. Therefore, it is less important to optimize / minimize low sensitivity Zernikes compared to high sensitivity Zernikes.

[0050]

[0049] The reference distributions can be used as target distributions for each scanner and / or layer during set-up before production begins, and / or as targets for drift control during production.

[0051]

[0050] Figure 3 is a flow chart showing the above concept in the context of lens setup. Each of a population of scanners SC1...SCn has a lens fingerprint LFP1...LFPn, respectively. The population of scanners may include two or more scanners used in a particular manufacturing process. Each fingerprint may be a residual fingerprint from a (for example, conventional) lens setup operation. In step 300, a reference fingerprint RFP is determined from these fingerprints LFP1...LFPn. The reference fingerprint RFP may include an aggregate, more specifically, a weighted average of the lens fingerprints (WALP) of the individual scanners. The weighting is arbitrary for the first iteration and may be optimized over further iterations of the method until convergence. In step 310, the reference fingerprint RFP is subtracted from each of the individual scanner lens fingerprints LFP1...LFPn to obtain a difference fingerprint dLFP1...dLFPn. In step 320, using the difference fingerprints dLFP1...dLFPn as input, further lens setups can be performed for each scanner to obtain further residual lens fingerprints LFP1'...LFPn'. Optionally, this step may include optimizing the Zernike weights in the lens model (step 330) to account for the fact that within an application domain it may be more important to optimize certain more important Zernikes compared to others. If the Zernike weights ZW are optimized (this step and / or the next step), they become additional parameters in the global optimization in addition to the weights for WALP.

[0052]

[0051] In optional step 340, for each scanner, the resulting residual lens fingerprints LFP1'...LFPn' can be combined (e.g., multiplied) with region-specific sensitivities or any other applicable weights (e.g., all 1's). Region-specific sensitivities can be chosen, for example, to emphasize the most overlapping critical aberrations for a given application area. This step, and the optional Zernike optimization in the previous step, can attribute a larger weight to certain aberrations ("Zernikes") in the lens model if they are deemed more important or critical. This is because it allows the actuator more working space to minimize these more critical Zernikes. Of course, the aberration sensitivities are not necessarily known, or the application area for a particular scanner may be so broad that all Zernikes are deemed to be of similar importance. In this case, each Zernike can be given a fixed equal weight in both the lens model (step 330) and in the calculation of the cost function (step 340), in a similar manner as is currently done in CLM.

[0053] In step 350, the residual lens fingerprints LFP1'...LFPn' (optionally combined with the sensitivities in the previous step) are summed and a suitable evaluation (e.g., by a cost function CF) is performed. This may include, for example, a maxabs (or other suitable) minimization across all scanners (or other applicable metric) that minimizes the error bounds of the residual lens fingerprints LFP1'...LFPn'. Steps 300-350 may be repeated iteratively to optimize the individual scanner fingerprints until convergence on a set of weights for WALP that minimizes the maxabs (or other suitable evaluation) of the cost function across the population of scanners.

[0054]

[0053] In a specific example where sensitivity is considered, an individual scanner LFP may contain a 13x64 matrix, i.e. 13 positions in the exposure slit, 64 Zernikes. This LFP can be multiplied by the 64 Zernike sensitivities to produce a pattern shift for the 13 positions in the slit. This can be done for all scanners. The WALP is a weighted average of this pattern shift across all scanners. Alternatively, a weighted average of the 13x64 lens fingerprints may be calculated first, and then the matrix may be multiplied by the 64 row sensitivity vector.

[0055] To implement such a method, the cost function may take the following form, as a specific example:

number

[0056]

[0055] Optimization may utilize a standard (e.g., gradient descent based) optimizer, or if there are a large number of parameters to be optimized in parallel (e.g., weights per slit position and Zernike weights in the lens setup), optimization based on an evolutionary algorithm (e.g., a genetic algorithm) may be used.

[0057]

[0056] The philosophy behind this approach is that it may be better to minimize the setup operations towards a non-zero criterion (i.e., aiming to eliminate all errors / aberrations / deviations) rather than towards zero. If this criterion fingerprint is common to all scanners and is configured to minimize the population aberration range, the overall performance (e.g., in terms of MMO) across all applicable scanner combinations can be improved (e.g., minimizing MMO) for a given application area (e.g., also taking into account the application area specific importance of certain aberrations, errors and / or layers).

[0058] In the context of a lens setup, the weights to be optimized may include weights for each position in the exposure slit and, optionally, Zernike weights for the lens setup (e.g., CLM). The cost function may further receive Zernike sensitivities to make it more application domain specific.

[0059]

[0058] The algorithm is run offline (e.g., on a server) for calibration or training, and the reference distribution (e.g., WALP) is used by the individual scanners for control. This calibration can be repeated / updated at regular intervals to account for drift (e.g., lens drift or position drift). The algorithm can be extended to include weights per slit position, constraints on the reference distribution (e.g., to minimize collateral effects on MMO), and / or to co-optimize individual (dynamic) Zernike weights in the lens model for further optimization towards the application domain (which can further reduce the associated aberration range).

[0060]

[0059] Although the specific embodiments described have been provided in the context of lens setup and / or lens drift control, the concepts can be used for other setup or drift control operations, such as grid setup or drift control. Thus, any reference in the text above to a lens fingerprint can be equally applied to a position deviation fingerprint (a map describing the spatial variation of position deviations) in a grid setup background to determine a reference position deviation fingerprint. This reference position deviation fingerprint can be a weighted average (or other mapping function) of the individual position deviation fingerprints, which allows for determining corrections to the exposure trajectory (wafer stage and / or reticle stage control / actuation), but the corrections can also use lens actuation.

[0061]

[0060] Further embodiments of the present invention are disclosed in the following list of numbered clauses: 1. A method for performing lithographic apparatus setup calibration and / or drift correction for a particular lithographic apparatus of a population of lithographic apparatus used in a manufacturing process for producing integrated circuits extending across multiple layers on a substrate, the method comprising: determining a spatial error distribution of an apparatus parameter across spatial coordinates on the substrate for each lithographic apparatus of the population of lithographic apparatus and / or for each layer of the plurality of layers; determining a reference distribution by aggregating each of the spatial error distributions and optimizing the reference distribution such that the spatial distribution of the parameter of interest of the manufacturing process is jointly optimized across a population and / or multiple layers of the lithographic apparatus; using the reference distributions as target distributions for the equipment parameters for each lithographic tool and / or layer; A method comprising: 2. The method according to clause 1, wherein the reference distribution is common to all lithographic devices and / or layers. 3. The method of claim 1 or 2, wherein the reference distribution is optimized to minimize the error range of an apparatus parameter across a population and / or multiple layers of a lithographic apparatus. 4. The method of any of clauses 1-3, wherein the spatial error distribution for each lithographic apparatus or layer used to determine the reference distribution comprises a residual error fingerprint following an initial or simulated set-up procedure. 5. The method of any of clauses 1-4, wherein aggregating includes performing a weighted average of the spatial error distribution. 6. The method of claim 5, wherein optimizing the reference distribution includes determining weights per lithographic apparatus and / or layer for the weighted average, the weights being determined to optimize a parameter of interest of the manufacturing process. 7. The method of claim 6, wherein determining the reference distribution includes performing an iterative optimization of the weights until at least one convergence criterion is satisfied. 8. The method of claim 6 or 7, wherein the aggregating step comprises determining a mapping function that maps the spatial error distributions weighted by the respective weights to a weighted average of the spatial error distributions. 9. The method of any of clauses 1-8, wherein the parameter of interest is any parameter indicative of overlay, edge placement error, or yield. 10. The method of any of clauses 1 to 9, wherein the step of determining the reference distribution constitutes at least one sensitivity or weight specific to a particular application associated with one or more of the lithographic apparatus and / or the layer and / or the integrated circuit. 11. The method according to any of clauses 1 to 10, wherein the reference distributions are used as target distributions for each lithographic apparatus and / or layer during a set-up or calibration operation before production begins. 12. The method according to any of clauses 1 to 11, wherein the reference distribution is used as a target distribution for drift control during production, such that any drift is corrected towards the target distribution. 13. The method according to any of clauses 1 to 12, wherein the apparatus parameters are aberrations of a projection system of a lithographic apparatus and the set-up includes a lens set-up for calibrating the projection system. 14. The method of claim 13, wherein the step of determining the reference distribution further comprises optimizing aberrations or Zernike weights in a lens model used in the lens setup. 15. The method of claim 14, wherein optimizing the aberration or Zernike weights includes attributing weights to one or more aberrations or Zernikes based on a particular application relating to one or more of the lithographic apparatus and / or the layer and / or the integrated circuit. 16. The method of claim 13, 14 or 15, wherein each spatial error distribution comprises a lens fingerprint describing the lens aberration per position of the exposure slit. 17. A method according to any of clauses 1 to 12, wherein the apparatus parameter is a position deviation in one or both of a reticle stage and a substrate stage of a lithographic apparatus and the set-up includes a grid set-up for calibrating a measurement and / or exposure grid. 18. The method of claim 17, wherein each spatial error distribution comprises a position deviation fingerprint. 19. A method according to any of clauses 1 to 18, comprising performing the method for each lithographic apparatus in the population. 20. A computer program comprising program instructions operable, when executed on a suitable device, to carry out the method according to any of clauses 1 to 19. 21. A non-transitory computer program carrier containing a computer program as defined in clause 20. 22. A computer program carrier containing a computer program according to clause 20; a processor operable to execute a computer program; A processing configuration comprising: 23. A lithographic apparatus comprising a processing arrangement according to clause 22.

[0062]

[0061] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may also be used in other applications, for example imprint lithography, and is not limited to optical lithography, where circumstances permit. In imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device is pressed into a layer of resist applied to the substrate, where the resist is hardened by electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is moved out of the resist after the resist has hardened, leaving a pattern in the resist.

[0063]

[0062] As used herein, the terms "radiation" and "beam" encompass all types of electromagnetic radiation, including ultraviolet (UV) (e.g., having a wavelength of 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm, or wavelengths approximately these values), and extreme ultraviolet (EUV) (e.g., having a wavelength in the range of 1 to 100 nm), as well as particulate beams such as ion beams and electron beams.

[0064] The term "lens", depending on the context, can refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components. Reflective components are more likely to be used in devices operating in the UV and / or EUV range.

[0065]

[0064] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. 1. A method for performing lithographic apparatus setup calibration and / or drift correction for a particular lithographic apparatus of a population of lithographic apparatus used in a manufacturing process for producing an integrated circuit extending across multiple layers on a substrate, the method comprising: determining a spatial error distribution of an apparatus parameter across spatial coordinates on the substrate for each lithographic apparatus in the population of lithographic apparatuses and / or for each layer of the plurality of layers; determining a reference distribution by aggregating each of the spatial error distributions and optimizing the reference distribution such that a spatial distribution of a parameter of interest of the manufacturing process is jointly optimized across the population of lithographic apparatuses and / or the plurality of layers; using said reference distributions as target distributions for said device parameters for each lithographic device and / or layer; A method comprising:

2. The method of claim 1 , wherein the reference distribution is common to all lithographic devices and / or layers.

3. The method of claim 1 , wherein the reference distribution is optimized to minimize an error range of the apparatus parameter across a population of lithographic apparatus and / or across the plurality of layers.

4. The method of claim 1 , wherein the spatial error distribution for each lithographic apparatus or layer used to determine the reference distribution comprises a residual error fingerprint following an initial or simulated set-up procedure.

5. The method of claim 1 , wherein the aggregating comprises performing a weighted average of the spatial error distributions.

6. 6. The method of claim 5, wherein optimizing the reference distribution comprises determining weights per lithographic apparatus and / or layer for the weighted average, the weights being determined to optimize the parameter of interest of the manufacturing process.

7. The method of claim 6 , wherein determining the reference distribution comprises performing an iterative optimization of the weights until at least one convergence criterion is met.

8. The method of claim 6 , wherein the aggregating step comprises determining a mapping function that maps the spatial error distributions weighted by each of the weights to the weighted average of the spatial error distributions.

9. The method of claim 1 , wherein the parameter of interest is overlay, edge placement error, or any parameter indicative of yield.

10. 2. The method of claim 1, wherein determining the reference distribution comprises at least one sensitivity or weighting specific to a particular application associated with one or more of the lithographic apparatus and / or layers and / or integrated circuits.

11. The method of claim 1 , wherein the reference distributions are used as target distributions for each lithographic apparatus and / or layer during a pre-production set-up or calibration operation.

12. The method of claim 1 , wherein the reference distribution is used as the target distribution for drift control during production, such that any drift is corrected towards the target distribution.

13. The method of claim 1 , wherein the apparatus parameters are aberrations of a projection system of a lithographic apparatus and the set-up comprises a lens set-up for calibrating the projection system.

14. The method of claim 13 , wherein determining the reference distribution further comprises optimizing aberrations or Zernike weights in a lens model used in the lens setup.

15. The method of claim 1 , wherein the apparatus parameter is a position deviation of one or both of a reticle stage and a substrate stage of the lithographic apparatus, and the set-up comprises a grid set-up for calibrating a measurement and / or exposure grid.

16. A computer program comprising program instructions operable to perform the method according to any of claims 1 to 15, when the computer program is run on a suitable device.

17. 17. A non-transitory computer program carrier comprising a computer program according to claim 16.

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