Calibration method and device

Abstract

A method for calibrating a height measurement optical sensor of a substrate in a lithographic apparatus. The method includes determining a first height of a surface of the substrate within a region of interest using the height measurement optical sensor. The method also includes determining a second height of the surface of the substrate within the region of interest using a scanning probe microscope. The method further includes determining a calibration map of the height measurement optical sensor for the region of interest by comparing the first height and the second height.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to European application 22179381.3 filed on June 16, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a method for calibrating a height measuring optical sensor, which is configured to measure the height of a substrate, and an associated device for performing said method. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern to a substrate. For example, a lithographic apparatus may be used in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as a "design layout" or "design") of a patterning device (e.g., a mask, also referred to as a reticle) onto a layer of radiation-sensitive material (resist) disposed on a substrate (e.g., a wafer).

[0005] As semiconductor manufacturing processes continue to advance, the number of functional elements (such as transistors) per device has been steadily increasing for decades while the size of circuit elements has continued to decrease, following a trend commonly referred to as "Moore's law". In order to keep up with Moore's law, the semiconductor industry is seeking technologies that can produce smaller and smaller features. In order to project a pattern onto a substrate, a lithography device can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned on the substrate. Typical wavelengths currently used are 365nm (i-line), 248nm, 193nm, and 13.5nm. Lithography equipment using extreme ultraviolet (EUV) radiation (having a wavelength in the range of 4nm to 20nm, such as 6.7nm or 13.5nm) can be used to form smaller features on a substrate than lithography equipment using, for example, radiation with a wavelength of 193nm.

[0006] Typically, a substrate may include multiple layers (each layer has been patterned by a mask), and each layer may include multiple repetitions of the same pattern, the patterns being arranged in a two-dimensional array. As a result, the substrate includes a two-dimensional array of multiple copies of the same pattern (which itself is a three-dimensional pattern). Different points across the surface of the substrate may be at different heights, and therefore lithographic radiation that is focused on the surface of the substrate at a first point (at a first height) may not be focused at a second point (at a second height). In order to maintain focus on the substrate surface, the height of the surface of the substrate is measured and a corresponding correction is made.

[0007] A height measuring optical sensor may be used to measure the height of the surface of the substrate. However, it is known that light (used by a height measuring optical sensor to measure the height of the surface of the substrate) may partially penetrate into the substrate surface, rather than being reflected solely by the substrate surface, leading to measurement errors. It is also known that an air pressure gauge (i.e., a sensor that uses air flow to measure the distance to an object) may be used as an auxiliary measurement of the height of the surface of the substrate, for example, to provide calibration for a height measuring optical sensor. Summary of the invention

[0008] In a first example described herein, there is a method for calibrating a height measuring optical sensor for a substrate in a lithography device, comprising: determining a first height of a surface of the substrate within a region of interest using the height measuring optical sensor; determining a second height of the surface of the substrate within the region of interest using a scanning probe microscope; and determining a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

[0009] The calibration map may include a plurality of calibration values, each corresponding to a point or area within the region of interest. The substrate may include a plurality of layers, each layer having been patterned by photolithographic radiation patterned by a reticle (which may also be referred to as a mask). Each patterned layer includes multiple repetitions of the same pattern, the pattern being arranged in a two-dimensional array. Thus, the substrate includes a two-dimensional array of copies of the same pattern (the pattern itself being a three-dimensional pattern). The region of interest may be one such pattern. A pattern may be referred to as a field (or exposure field), indicating an area to be exposed by the photolithographic apparatus to form the next layer of the pattern. Each field may include one or more dies. In other words, the region of interest may correspond to a single die, or alternatively, a plurality of dies. Advantageously, the calibration method provides a method for calibrating the height measuring optical sensor, thereby allowing the height measuring optical sensor to measure the height of the surface of the substrate with high accuracy. The region of interest may be one of a plurality of regions of interest.

[0010] The method may further comprise applying the calibration map to other regions of the substrate corresponding to the region of interest. Regions corresponding to the region of interest are expected to interact with the radiation of the height measuring optical sensor in the same manner, and thus a calibration map determined for the region of interest may also be beneficially applied to any other regions corresponding to the region of interest. For example, if the region of interest corresponds to a field, the calibration map may be applied to other corresponding fields across the entire substrate. Applying the calibration map may comprise applying an offset to the height of the substrate as measured by the height measuring optical sensor. The offset may be different at different locations on the region of interest. During lithographic exposure, the obtained measurement results may be used when determining how to change the height (i.e., the z coordinate) of the substrate, for example, by adjusting the height of the substrate support on which the substrate is mounted. Additionally or alternatively, the obtained measurement results may be used to adjust the focus of the lithographic radiation, for example, by adjusting one or more optical elements of the lithographic apparatus.

[0011] The height measuring optical sensor may use UV radiation in use.The height measuring optical sensor may be referred to as a level sensor.

[0012] The scanning probe microscope may be an atomic force microscope (AFM) or a near-field scanning optical microscope (NSOM). Advantageously, the use of an AFM or NSOM provides a high-resolution second sensor that allows accurate calibration of the first sensor. As an alternative to a scanning probe microscope, an air pressure gauge may be used to determine the second height.

[0013] The scanning probe microscope may be one of a plurality of scanning probe microscopes. The plurality of scanning probe microscopes may be arranged into an array of scanning probe microscopes. Advantageously, the use of an array of scanning probe microscopes may allow the second height to be determined at a plurality of points (within the region of interest) at a single time, thereby reducing the time spent calibrating the first sensor.

[0014] Determining the second height may include measuring a height of a surface of the substrate within the region of interest using the scanning probe microscope.

[0015] Determining the second height may also include: measuring a plurality of heights of the surface of the substrate for at least one region of interest using the scanning probe microscope; and calculating an average of the plurality of heights. Advantageously, the method may ensure that the measured second height (determined by the scanning probe microscope) is comparable or equivalent to the second first height.

[0016] In a second example described herein, there is a lithographic apparatus comprising a height measuring optical sensor configured to determine a first height of a surface of a substrate within a region of interest; a scanning probe microscope configured to determine a second height of the surface of the substrate within the region of interest; and a processor configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height. In the lithographic apparatus, the substrate may be disposed on a substrate support, and in use, the substrate support may be moved in the substrate in a scanning direction. An array of scanning probe microscopes may be provided, such that the scanning probe microscopes are provided in a series extending in a direction perpendicular to the scanning direction. Advantageously, providing a lithographic apparatus having hardware used to perform the calibration method simplifies the calibration process and allows in-situ measurements.

[0017] In a third example described herein, there is a system comprising: a photolithography device comprising a height measuring optical sensor, the height measuring optical sensor being configured to determine a first height of a surface of a substrate within a region of interest; a scanning probe microscope, the scanning probe microscope being configured to determine a second height of the surface of the substrate within the region of interest; and a processor, the processor being configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

[0018] In a fourth example described herein, there is a lithography tool comprising: a height measuring optical sensor configured to determine a first height of a surface of a substrate within a region of interest; a scanning probe microscope configured to determine a second height of the surface of the substrate within the region of interest; and a processor configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

[0019] In a fifth example described herein, there is a metrology tool comprising: a height measuring optical sensor configured to determine a first height of a surface of a substrate within a region of interest; a scanning probe microscope configured to determine a second height of the surface of the substrate within the region of interest; and a processor configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

[0020] In a sixth example described herein, there is a computer-readable storage medium comprising instructions that, when executed by a computer, cause the computer to perform the method of the first example.

[0021] In a seventh example described herein, there is a calibration map comprising data corresponding to a region of interest of a substrate, wherein the substrate comprises a plurality of regions, each of the plurality of regions having been patterned with the same pattern. The calibration map may consist of data corresponding to only a single region of interest, and the calibration map may be sufficient to allow calibration of other regions (patterned with the same pattern). Beneficially, the calibration map may be smaller in size and reduce computational overhead.

[0022] In an eighth example described herein, there is a method of determining a height of a surface of a substrate, comprising: determining a height of a reference point; and determining the height of the surface of the substrate at one or more points using a plurality of scanning probe microscopes.

[0023] The one or more points may each be located within a single region of the substrate. The single region may be a die or a field. The reference point may be, for example, a mark or a label.

[0024] The plurality of scanning probe microscopes may be arranged in an array or a grid. For example, when arranged in a grid, the plurality of scanning probes may be arranged in a first row and a second row, and the second row may be offset relative to the first row. The plurality of scanning probe microscopes may be distributed such that the plurality of scanning probe microscopes extend at least across the combined width of the field and the associated scribe lanes. Alternatively, the plurality of scanning probe microscopes may be distributed such that the plurality of scanning probe microscopes extend at least across the width of the substrate and the reference track.

[0025] The substrate and the plurality of scanning probe microscopes may be movable relative to each other.

[0026] The determined heights of the surface of the substrate at the one or more points may be relative heights with respect to a height of a reference point.

[0027] In a ninth example described herein, there is a lithographic apparatus comprising a plurality of scanning probe microscopes configured to: determine a height of a reference point; and determine a height of a surface of the substrate at one or more points.

[0028] In a tenth example described herein, there is a metrology tool comprising a plurality of scanning probe microscopes configured to: determine a height of a reference point; and determine a height of a surface of the substrate at one or more points. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0030] Figure 1 A schematic overview of a lithographic apparatus is depicted;

[0031] Figure 2 An exemplary height measuring optical sensor is depicted;

[0032] Figure 3 depicts an example substrate exposed;

[0033] Figure 4 A flow chart depicting a method for calibrating a height measuring optical sensor;

[0034] Figure 5 An example scanning probe microscope is depicted;

[0035] Figure 6 depicts an example substrate having a first height measurement point and a second height measurement point;

[0036] Figure 7 depicts an example array of scanning probe microscopes configured to measure the height of a substrate; and

[0037] Figure 8 An example array of scanning probe microscopes configured to measure height of field is depicted. DETAILED DESCRIPTION

[0038] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365nm, 248nm, 193nm, 157nm or 126nm) and EUV radiation (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5nm to 100nm).

[0039] The terms "reticle", "mask" or "patterning device" as used in the present invention may be broadly interpreted to refer to a general patterning device that can be used to impart a patterned cross-section to an incident radiation beam that corresponds to the pattern to be produced in a target portion of the substrate. In this context, the term "light valve" may also be used. In addition to classical masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0040] Figure 1A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation), a mask support (e.g., a mask stage) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W, connected to a second positioner PW configured to accurately position the substrate support according to certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., a portion comprising one or more dies) of the substrate W.

[0041] In operation, the illumination system IL receives a radiation beam from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components for directing, shaping and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof. The illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0042] The term "projection system" PS as used in the present invention should be interpreted broadly to cover various types of projection systems suitable for the exposure radiation used and / or for other factors such as the use of immersion liquid or the use of vacuum, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems or any combination thereof. Any term "projection lens" used herein may be considered synonymous with the more general term "projection system" PS.

[0043] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by an immersion liquid having a relatively high refractive index, such as water, so as to fill the space between the projection system PS and the substrate W - this is also known as immersion lithography. More information on immersion techniques is given in US 6952253, which is incorporated herein by reference.

[0044] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as a "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel and / or a substrate W on one of the substrate supports WT may be used for exposing a pattern on another substrate W while a step of preparing the substrate W for subsequent exposure is being performed on the substrate W on another substrate support WT.

[0045] In addition to the substrate support WT, the lithographic apparatus LA may also comprise a measurement platform. The measurement platform is arranged to hold sensors and / or cleaning means. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measurement platform may hold a plurality of sensors. The cleaning means may be arranged to clean a part of the lithographic apparatus, for example a part of the projection system PS or a part of the system providing immersion liquid. The measurement platform may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0046] In operation, the radiation beam B is incident on a patterning device (e.g. a mask) MA held on the mask support MT and is patterned by a pattern (design layout) present on the patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and the position measurement system IF, the substrate support WT can be accurately moved, for example in order to position different target portions C in the path of the radiation beam B in a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor (in Figure 1 The patterning device MA (not explicitly depicted in the figure) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. The patterning device MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 occupy dedicated target portions as shown, the marks can be located in the space between target portions. When the substrate alignment marks P1, P2 are located between the target portions C, these substrate alignment marks are called scribe line alignment marks.

[0047] In order to illustrate the present invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes, namely the x-axis, the y-axis and the z-axis. Each of the three axes is orthogonal to the other two axes. The rotation around the x-axis is called the Rx rotation. The rotation around the y-axis is called the Ry rotation. The rotation around the z-axis is called the Rz rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is in the vertical direction. The Cartesian coordinate system is not limited to the present invention and is only used for illustration. As an alternative, another coordinate system (such as a cylindrical coordinate system) can be used to illustrate the present invention. The direction of the Cartesian coordinate system can be different, for example, so that the z-axis has a component along the horizontal plane.

[0048] A topography measurement system, a level sensor or a height sensor, which can be integrated in a lithographic device, is arranged to measure the topography of the top surface of a substrate (or wafer). The level sensor may also be referred to as a height measurement optical sensor. A topography map (also referred to as a height map) of the substrate can be generated from these measurements indicating the height of the substrate as a function of the position on the substrate. This height map can then be used to correct the position of the substrate during the transfer of the pattern on the substrate so as to provide an aerial image of the pattern forming device at a properly focused position on the substrate. It should be understood that the "height" in this context refers to a dimension that is significantly out of the plane (also referred to as the Z axis) relative to the substrate. Typically, the level sensor or height sensor performs measurements at a fixed position (relative to its own optical system), and the relative movement between the substrate and the optical system of the level sensor or height sensor produces height measurements at multiple positions across the entire substrate.

[0049] Figure 2 An example of a level sensor or height sensor LS known in the art is schematically shown, which only illustrates the principle of operation. In this example, the level sensor comprises an optical system, which comprises a projection unit LSP and a detection unit LSD. The projection unit LSP comprises a radiation source LSO, which provides a radiation beam LSB applied by a projection grating PGR of the projection unit LSP. The radiation source LSO can be, for example, a narrowband radiation source or a broadband radiation source (such as a supercontinuum light source), polarized or non-polarized, pulsed or continuous (such as a polarized or non-polarized laser beam). The radiation source LSO may include a plurality of radiation sources with different multiple colors, or multiple wavelength ranges, such as a plurality of LEDs. The radiation source LSO of the level sensor LS is not limited to visible radiation, but may additionally or alternatively cover UV and / or IR radiation and any wavelength range suitable for reflection from the surface of the substrate.

[0050] The projection grating PGR is a periodic grating including a periodic structure, which generates a radiation beam BE1 with a periodically varying intensity. The radiation beam BE1 with a periodically varying intensity is directed toward a measurement location MLO on a substrate W at an incident angle ANG between 0 and 90 degrees (typically between 70 and 80 degrees) relative to an axis (Z axis) perpendicular to the incident substrate surface. At the measurement location MLO, the patterned radiation beam BE1 is reflected by the substrate W (indicated by arrow BE2) and directed toward the detection unit LSD.

[0051] In order to determine the height level at the measurement location MLO, the level sensor further comprises a detection system comprising a detection grating DGR, a detector DET and a processing unit (not shown) for processing an output signal of the detector DET. The detection grating DGR may be identical to the projection grating PGR. The detector DET generates a detector output signal indicative of the received light, such as a photodetector generating a detector output signal indicative of the intensity of the received light, or such as a camera generating a detector output signal indicative of the spatial distribution of the received intensity. The detector DET may comprise any combination of one or more detector types.

[0052] By means of triangulation techniques the height level at the measurement location MLO can be determined.The detected height level is typically related to the signal intensity as measured by the detector DET, which has a periodicity that depends inter alia on the projection grating PGR design and the (oblique) angle of incidence ANG.

[0053] The projection unit LSP and / or the detection unit LSD may comprise further optical elements such as lenses and / or mirrors along the path of the patterned radiation beam between the projection grating PGR and the detection grating DGR (not shown).

[0054] In an embodiment, the detection grating DGR may be omitted and the detector DET may be placed where the detection grating DGR is located. This configuration provides a more direct detection of the image of the projection grating PGR.

[0055] In order to effectively cover the surface of the substrate W, the level sensor LS may be configured to project an array of measurement beams BE1 onto the surface of the substrate W, thereby generating an array of spots or measurement areas MLO covering a larger measurement range.

[0056] For example, various height sensors of a general type are disclosed in US7265364 and US7646471, both of which are incorporated herein by reference. A height sensor using UV radiation instead of visible light or infrared radiation is disclosed in US2010233600A1, incorporated herein by reference. In WO2016102127A1, incorporated herein by reference, a compact height sensor is described that uses a multi-element detector to detect and identify the position of a grating image without the need for a detection grating.

[0057] During use, the radiation beam BE1 emitted by the projection unit LSP may interact with the surface of the substrate W in an unpredictable way. For example, the surface may be provided with a plurality of layers (each layer except the first layer is provided on top of another layer), and each layer may partially reflect the radiation beam BE1. The method used by the level sensor LS to determine the height level at the measurement location MLO may not be able to predict such measurement errors (such as those caused by multiple partial reflections of the radiation beam BE1), and therefore the determined height level may be inaccurate without calibration. Although such measurement errors are difficult to predict, the effect on the height level determined by the level sensor LS may be consistent. In other words, if the level sensor LS determines the height level of a single point multiple times, the level sensor LS should determine the same or approximately the same height level each time. Similarly, if there are multiple points on the surface of the substrate W, which have similar heights and are provided with similar multiple layers, the level sensor LS should determine the same or approximately the same height level for each point.

[0058] It is known that the above-mentioned measurement errors are caused by optical effects (e.g. multiple partial reflections of the radiation beam BE1) and should not occur when using mechanical measurement methods (e.g. using a barometric proximity sensor, such as the air pressure gauge described below) to measure the height of the surface of the substrate W. Therefore, mechanical measurement methods may be used in addition (to calibrate and reduce measurement errors) or as an alternative to the level sensor LS.

[0059] An air pressure gauge can determine the height of the surface of a substrate W by directing an outward air flow onto the surface and determining the height by means of a differential flow measurement relative to a reference. The height measurement determined by the air pressure gauge is typically measured with nanometer accuracy, i.e. precision, without suffering from unwanted optical interactions. Disadvantages of the air pressure gauge include a very slow measurement process and sensitivity to temperature and drift.

[0060] Figure 3An example substrate 300 is depicted after exposure to patterned lithographic radiation, ie, radiation beam B. The substrate 300 may be identical to substrate W. The substrate may be circular or any other shape, but is depicted as a rectangle for ease of illustration.

[0061] The substrate 300 comprises a plurality of layers, each layer comprising a processed structure, the processed structure having been patterned by photolithographic radiation patterned by a mask, and subsequently processed. Subsequent processing typically comprises developing the substrate to reveal the pattern (on a photoresist), etching to reveal the pattern in the resist, depositing material onto the exposed resist, and removing the remaining resist. A new resist layer is then applied before subsequent exposure of the pattern, and the processing steps are repeated. Those skilled in the art will recognize that the exact processing steps may differ depending on the requirements of each layer. Each patterned layer comprises multiple repetitions of the same pattern 311, 321, 331, 341, 351, 361, and the patterns are arranged in a two-dimensional array. Therefore, the substrate 300 comprises a two-dimensional array of copies of the same pattern 311, 321, 331, 341, 351, 361. The patterns 311, 321, 331, 341, 351, 361, when processed, produce a three-dimensional stack of multiple processed layers. In other words, by repeatedly exposing and processing the substrate as discussed above, a stack of multiple layers is built up (in the z-direction), wherein each layer has a pattern (in the x and y directions) wherein material is present in some regions of the pattern and not in other regions of the pattern.

[0062] Each of the processed layers may include different materials and / or each processed layer may have different reflectivities. Additionally or alternatively, the structure (or density of the structure) in the layer may affect the reflectivity. For example, the line (or density of the line) in the layer in one area may result in different reflectivities for a second area having different lines or different line densities. The structure disposed at a portion of the pattern may not be disposed at another portion of the pattern. For example, pattern 311 includes circular structures 313, square structures 315, and rectangular structures 317 (such structures are only for exemplary purposes, and other structures, such as lines, columns, and / or holes, may be provided). The first layer includes a circular structure 313, a second layer including a rectangular structure 317 is provided below the first layer, and a third layer including a square structure 315 is provided below the second layer. Due to the different reflectivities of the multiple layers including each of the structures 313, 315, and 317, the height measurement optical sensor may detect different measurement errors when measuring the height of each of the structures 313, 315, and 317. In other words, even if the height of the surface of the substrate 300 is uniform, the height measuring optical sensor can measure different heights of the surface of the substrate 300 .

[0063] A pattern (eg, pattern 311) may be referred to as a field (or exposure field), indicating an area to be exposed by the lithography apparatus LA to form a next layer of the pattern 311. Each field may include one or more dies.

[0064] Since each field 311, 321, 331, 341, 351, 361 is patterned using lithography light patterned by the same mask, each corresponding field is the same (or approximately the same). Therefore, a point in a first region (e.g., the field 311) may have a first reflectivity that is the same as a second reflectivity of a corresponding point in a second region (e.g., the field 321). Similarly, in the case where the substrate 300 includes one or more layers, the layer provided at a point (i.e., at an xy coordinate) in a first volume (e.g., field 311) may be the same layer as the layer provided at a corresponding point in a second volume (e.g., field 321).

[0065] By determining a property of one point of the substrate W in a first field (i.e., the region of interest), properties of corresponding points in other fields can be inferred. The property may be a calibration correction required for the level sensor LS to accurately measure the height of the surface of the substrate W. Alternatively, the property 6 may be the height of the surface of the substrate W (as discussed further below).

[0066] Figure 4A flow chart of a method 400 for calibrating a height measuring optical sensor is depicted. In step 401, a first height is determined using a height measuring optical sensor. In step 402, a second height is determined using a scanning probe microscope. In step 403, a calibration map is determined for the height measuring optical sensor.

[0067] The method 400 may include determining an area of ​​interest. For example, referring to the example substrate 300 (including six fields 311, 321, 331, 341, 351), the field 311 may be determined as an area of ​​interest. The area of ​​the substrate W corresponding to each field may be determined by the final pattern required on the substrate W. In a first example, the substrate 300 (of a specific size) may be exposed by 200 fields, and in a second example, the substrate 300 (of the same specific size) may be exposed by 300 fields. The area of ​​interest determined for the first example substrate may correspond to a different area than the area corresponding to the area of ​​interest determined for the second example substrate. Alternatively, the area of ​​interest may correspond to multiple fields and / or the entire substrate. The area of ​​interest may correspond to a single die, or alternatively, multiple dies. For example, each field may correspond to multiple dies, and the area of ​​interest may correspond to the same multiple dies. In the case where a field contains multiple dies, the area of ​​interest may be one die. The area of ​​interest may be one area of ​​interest among multiple areas of interest.

[0068] In step 401, a first height is determined using a height measuring optical sensor. The first height may be determined for a point in the region of interest. The height measuring optical sensor may be a level sensor LS (as described above). The height measuring optical sensor may utilize UV ​​and / or visible radiation. Determining the first height using the height measuring optical sensor 401 may include measuring the first height.

[0069] Method 400 may also include determining the location (ie, x and y coordinates) of the point. The coordinates of the point may be stored as local coordinates (ie, in a local coordinate system of the region of interest) or global coordinates (and optionally converted to a local coordinate system of the region of interest).

[0070] In step 402, a second height is determined using a scanning probe microscope. The second height may be determined for the same point in the region of interest as the point at which the first height was determined. The scanning probe microscope may be an atomic force microscope (AFM), a near-field scanning optical microscope (NSOM), a scanning tunneling microscope (STM), a scanning electrochemical microscope (SECM), or any other device with a lower sensitivity to sub-layer structures (relative to super-layer structures), such as, for example, a white light interferometry system, a digital holographic microscope, a barometer arrangement, or a confocal sensor, capable of extracting the height at the top and bottom surfaces of the resist layer.

[0071] Determining the second height using the scanning probe microscope 402 may include measuring the height of the surface at a single point (e.g., the same point in the region of interest as the point used to determine the first height). Alternatively, determining the second height using the scanning probe microscope 402 may include measuring multiple measurements and calculating an average. For example, the height of the surface at a single point may be measured multiple times by a scanning probe microscope. Additionally or alternatively, the height of the surface at multiple points (i.e., points near the same point in the region of interest as the point used to determine the first height, and optionally including the same point in the region of interest as the point used to determine the first height) may be measured by a scanning probe microscope. Additionally or alternatively, the scanning probe microscope may be one of a plurality of scanning probe microscopes, and each of the plurality of scanning probe microscopes may provide one or more measurements. Calculating an average may include determining a mean of a plurality of measurements. Beneficially, measuring a plurality of measurements and calculating an average may help ensure that the second height corresponds to the first height, regardless of the difference between the spatial resolution of the height measurement optical sensor and the scanning probe microscope (i.e., the resolution across the x and y dimensions when measuring the z dimension).

[0072] The point in the region of interest (i.e., the point at which the first height and the second height are determined) may be one of a plurality of points (each of the plurality of points being located in the same region of interest, or alternatively, in different regions of interest). In other words, the first height may be determined for a plurality of points, and the second height may be determined for the same plurality of points.

[0073] Steps 401 and 402 may be performed in any order. In other words, the first height may be determined by a height measuring optical sensor before or after the second height is determined by the scanning probe microscope.

[0074] In step 403, a calibration map is determined for the height measuring optical sensor. In other words, for each point having a first height (determined using the height measuring optical sensor) and a second height (determined using the scanning probe microscope), a calibration value may be determined (by assuming that the second height is a "true" value, without measurement errors caused by optical effects, or with reduced measurement errors caused by optical effects). The calibration value may also be referred to as an offset. The calibration map may include a plurality of calibration values ​​and corresponding coordinates for each calibration value. Determining the calibration map may include populating the calibration map with calibration values ​​and corresponding coordinates. The corresponding calibration value (for each point) may be determined by subtracting the first height from the second height. For example, for a point, the first height may be determined to be 50 nm, the second height may be determined to be 60 nm, and the corresponding calibration value may be determined to be +10 nm. In other words, the height at the point has been determined by the height measuring optical sensor to be 10 nm less than the "true" value, and the height determined by the height measuring optical sensor at the same (or similar point) should be corrected by increasing this value by 10 nm. The coordinates (for each calibration value) may be local coordinates (e.g., local to the region of interest). By determining the calibration value for each point (of the plurality of points) in the region of interest, a calibration map may be determined. The points may be distributed across the region of interest. Thus, the calibration map may include a plurality of calibration values ​​corresponding to points distributed across the region of interest.

[0075] Determining the calibration graph 403 may include using interpolation. For example, if a first point and a second point have calibration values ​​of +10 nm and +20 nm, respectively, a third point between the first point and the second point may be determined to have a calibration value of +15 nm. Additionally or alternatively, when applying the calibration graph, interpolation may be used.

[0076] The area on the substrate corresponding to the calibrated area of ​​interest is expected to interact with the radiation of the height measuring optical sensor in the same way. Therefore, the calibration map determined for the area of ​​interest can also be beneficially applied to any other area corresponding to the area of ​​interest. For example, if the area of ​​interest corresponds to a field, the calibration map can be applied to other corresponding fields on the substrate. The calibration map may include data corresponding to the area of ​​interest of the substrate W. For points in the field corresponding to the area of ​​interest, corresponding calibration values ​​can be determined. In other words, the calibration map may include data corresponding to a single field, and calibration values ​​for other fields can be inferred for other fields.

[0077] The method 400 may further comprise applying the calibration map. Applying the calibration map may comprise determining calibration values ​​for points (in the field). As discussed below, applying the calibration map may comprise calibrating the height of the substrate W as measured by the height measuring optical sensor, and optionally adjusting the height of the substrate W by moving the substrate support WT accordingly. In examples comprising a plurality of regions of interest, a region of interest corresponding to the field may be determined. The region of interest corresponding to the field may be determined by identifying matching features, using stored data (such as an identifier), determining coordinates, or otherwise.

[0078] The position of the point (i.e., the point to which the calibration map is to be applied) may be determined. For example, the position of the point may be determined by measuring the coordinates (e.g., x, y coordinates) of a point on the surface of the substrate W measured (or to be measured) by the height measuring optical sensor. The point on the surface of the substrate W may be a point on the top surface of one or more processed layers and / or features of the substrate W.

[0079] A calibration value from the calibration map corresponding to the point may be identified. For example, the position of the point may be converted into local coordinates (local to the field). The local coordinates of the field may correspond to local coordinates of the region of interest. The local coordinates may allow a calibration value to be determined from the calibration map. For example, if the point has local (to the field) coordinates of (4, 5), a calibration value of local (to the region of interest) coordinates (4, 5) in the region of interest may be used for the point and determined from the calibration map. As discussed above, interpolation may be used when identifying a calibration value corresponding to the point. The calibration value corresponding to the point may be identified in different ways. For example, a calibration value from the calibration map having coordinates closest to the point may be identified.

[0080] Applying the calibration map may include calibrating the measurement results provided by the height measuring optical sensor. For example, if the height measuring optical sensor measures a point of the surface of the substrate W as 5 nm and the corresponding calibration value is +2 nm, the calibrated measurement result may be 7 nm. In other words, the calibration provides a correction for the measurement result, and the calibrated measurement result may also be referred to as a corrected measurement result. Since the calibration values ​​are provided by the calibration map, the calibration values ​​may have different values ​​at different points on the substrate W.

[0081] The calibrated height measurements (provided by the height measuring optical sensor and by applying the calibration map) may be used in any conventional manner. For example, the calibrated height measurements may be used to determine how to change the height (i.e. the z-coordinate) of the substrate W. For example, the height of the substrate may be changed by adjusting the height of the substrate support WT on which the substrate W is mounted. Additionally or alternatively, the obtained measurements may be used to adjust the focus of the radiation beam B, for example by adjusting one or more optical elements of the lithographic apparatus LA.

[0082] The determination of how to change the height of the substrate W may not be entirely dependent on a single (calibrated or uncalibrated) height measurement. As is known in the art, due to the arrangement of the lithographic apparatus LA, multiple regions within a field (e.g., multiple regions aligned with a common y-coordinate) may be exposed to the radiation at a single time. Typically, multiple height measurements corresponding to points across multiple regions (i.e., uncalibrated measurements provided by the height measuring optical sensor) may be used to provide an average height measurement for determining a change in the height of the substrate W. Calibrated height measurements may also be used in such a way that a single change in the height of the substrate W is determined for use when multiple regions are exposed to the radiation beam B.

[0083] As discussed above, the lithographic apparatus LA may include a level sensor LS (i.e., a height measuring optical sensor). The lithographic apparatus LA may also include one or more scanning probe microscopes to allow the method 400 to be performed. For example, a plurality of scanning probe microscopes may be provided and arranged in an array so that the second height of a plurality of points (within a region of interest) may be determined at a single time, thereby reducing the time spent calibrating the first sensor. Additionally or alternatively, in examples where the second height (for a single point) comprises measuring a plurality of measurements across a region and calculating an average, the plurality of scanning probe microscopes may allow a plurality of measurements to be measured at a single time.

[0084] Figure 5 An example scanning probe microscope 520 is depicted. Figure 5 The exemplary scanning probe microscope 520 depicted in the method 400 is an atomic force microscope (AFM) 520, but as will be clear to those skilled in the art, other scanning probe microscopes may be suitable for use in the method 400. The AFM 520 includes a tip 524 disposed on the end of a cantilever 522. A light source (e.g., a laser) 526 provides a radiation beam 528 that is reflected from the back side of the tip 524 toward a photodiode 529. Alternatively, the radiation beam 528 may be reflected off a side of the cantilever 522 that is proximate to the back side of the tip 524.

[0085] In use, the height of the tip 524 is changed (e.g., by adjusting the bend in the cantilever 522) so that the tip 524 contacts the surface 511 of the sample 510. As the height of the tip 524 changes, the intensity of the radiation beam 528 received by the photodiode 529 changes, and the height of the surface 511 of the sample 510 can be inferred. The sample 510 and AFM 520 are moved relative to each other (e.g., in Figure 5 The tip 524 may be moved horizontally in the sample 510 so that the AFM can measure the height of the sample 510 at different points. For example, the tip 524 may contact the first surface 511 of the sample 510, and the first intensity of the radiation beam 528 may be detected by the photodiode 529 to measure the first height of the first surface 511. The AFM 520 may then be moved. The tip 524 may then contact the second surface 512 of the sample 510, and the second intensity of the radiation beam 528 may be detected by the photodiode 529 to measure the second height of the second surface 512. In this manner, the AFM 520 may measure the height of the surface of the sample 510 at different points. Although the AFM 520 has been described as operating in a contact mode, as is known in the art, the AFM may operate in different modes. For example, the AFM 520 can be operated in a tapping mode, in which the tip 524 is repeatedly raised and lowered, a contact mode (in which the tip 524 continuously contacts the surface of the sample 510), or a non-contact mode (in which the tip 524 continuously comes into close proximity with (but does not contact) the surface of the sample 510). Any mode, including those described herein, can be applied to any embodiment of the present invention.

[0086] Figure 6An example substrate 600 is depicted. Although measurements have been described so far with respect to points, as discussed above, the scanning probe microscope and in particular the height measurement optical sensor may each have a different non-zero spatial resolution. In other words, the radiation beam BE1 (provided by the height measurement optical sensor) may have a relatively wide cross-sectional area (i.e., an area transverse to the direction of the radiation beam BE1), and thus the height (measured by the height measurement optical sensor) may correspond to a relatively wide cross-sectional area of ​​the surface of the substrate W. The scanning probe microscope may make each measurement across a relatively small area (e.g., determined by the sharpness of the tip 524). Thus, the scanning probe microscope may make multiple measurements within the area to which the measurements made by the height measurement optical sensor correspond. A plurality of first measurement regions 611, 612, 613, 614 are indicated on the substrate 600, each of the first measurement regions 611, 612, 613, 614 corresponding to a first height measurement (i.e., measured by the height measurement optical sensor) and indicating the spatial resolution of the height measurement optical sensor. Figure 6 A magnified view of a first measurement region 614 with a plurality of second measurement points 621, 622, 623, 624, 625, 626 (i.e., possible points that can be measured by the scanning probe microscope) is depicted. The scanning probe microscope may make a single measurement corresponding to the first measurement region 614, for example at the second measurement point 621 (at the center of the first measurement region 614). Alternatively, as discussed above, the scanning probe microscope (or scanning probe microscopes) may measure a plurality of second measurements, and an average may be calculated.

[0087] Figure 7 An example array of scanning probe microscopes 730 configured to measure the height of a substrate 701 is depicted.

[0088] A plurality of scanning probe microscopes 731, 732, 734 are provided to measure the height of the surface of the substrate 701 at a plurality of points. The plurality of scanning probe microscopes 731, 732, 734 may be arranged as follows: Figure 7 Alternatively, the plurality of scanning probe microscopes 731, 732, 734 may be arranged in a grid or a lattice. For example, a first row of scanning probe microscopes may extend in a first direction, a second row of scanning probe microscopes may extend in the first direction, and the second row may be offset relative to the first row in the first direction and in a second direction perpendicular to the first direction.

[0089] Reference tracks 711, 712, 713, 714 may be provided on each side of the substrate 701. The reference tracks 711, 712 extend substantially in a first direction and the reference tracks 713, 714 extend substantially in a second direction. The reference tracks 711, 712, 713, 714 may allow a reference height to be determined. Other markings may be provided to determine the reference height to be determined, such as markings or labels. Examples of such markings are substrate alignment marks P1, P2 (on Figure 1 depicted in ).

[0090] Each of the scanning probe microscopes 731 , 732 , 734 may be secured to a rigid member 730 that extends across the substrate 701 from a first reference rail 711 to a second reference rail 712 .

[0091] A plurality of scanning probe microscopes 734 are provided to determine the height of the surface of the substrate. The rigid member 730 can be moved relative to the substrate 701 to allow the plurality of scanning probe microscopes 734 to determine the height of the surface of the substrate at a plurality of points. For example, when the scanning probe microscopes 731, 732, 734 are arranged in a single line extending in a first direction, the rigid member 730 can be moved relative to the substrate 701 in a second direction perpendicular to the first direction. Alternatively, the substrate 701 can be moved relative to the rigid member 730.

[0092] One or more of the scanning probe microscopes 731, 732 may be provided to determine the height of a reference marker, i.e., a reference mark, i.e., a reference track 711, 712. By determining the height of the reference mark and determining the height of the surface of the substrate at a plurality of points, the relative height of the surface of the substrate may be determined. In other words, the relative height may be the height relative to the reference mark.

[0093] Figure 8 An example array of scanning probe microscopes 830 configured to measure the height of a field 801 is depicted. The field 801 is shown with associated lines 841, 842 and adjacent fields 802, 803. The array of scanning probe microscopes 830 is arranged similarly to the array of scanning probe microscopes 830. Reference marks may be provided in the scribe lanes 841, 842. One or more scanning probe microscopes 831, 832 are provided for determining the reference marks to determine the height of the reference marks in the scribe lanes 841, 842.

[0094] Similar to method 400, the determined heights (and corresponding coordinates) may be used to determine a height map. The height map may correspond to the entire substrate, or alternatively, to a field.

[0095] Once a height map has been determined for a single field, the height of the surface of the substrate in the corresponding field can be inferred. In other words, if a first field is patterned with a pattern and a second field is patterned with the same pattern, the height measurement of the first field may also correspond to the second field.

[0096] Although Figure 8 An array of scanning probe microscopes 830 configured to measure the height of field 801 is depicted, but field 801 (and adjacent fields 802, 803) may alternatively consist of a die and adjacent dies, respectively. Thus, where the height map has been determined for a single die, the height of the surface of the substrate in the corresponding die may be inferred.

[0097] The lithographic apparatus may be provided with a plurality of scanning probe microscopes to allow the height of the surface of the substrate to be determined.

[0098] A lithography tool (i.e., a tool configured to pattern a substrate using radiation) may be provided with a plurality of scanning probe microscopes and a processor to allow the height of the surface of the substrate to be determined. Such a lithography tool may allow the method disclosed herein to be performed. For example, the lithography tool may be used to determine a second height of the substrate using a scanning probe microscope (i.e., step 402). The substrate may be provided in a lithography apparatus comprising a height measuring optical sensor, which allows the first height to be performed (i.e., step 401). The first height and the second height may then be used to determine a calibration map for the height measuring optical sensor (i.e., step 403).

[0099] The lithography tool may also be provided with a height measurement optical sensor to allow the method 400 to be performed entirely by the lithography tool. The lithography tool may be an online tool, i.e. the tool may be used as part of a production process and for each substrate produced. Alternatively, the lithography tool may be an offline tool, i.e. the tool may be used for some but not all substrates produced in a production process.

[0100] A metrology tool is a tool configured to measure properties of a lithographic apparatus or a substrate patterned by a lithographic apparatus. For example, a metrology tool may monitor the overlay and / or focus performance of a lithographic apparatus by measuring a substrate patterned by the lithographic apparatus. A metrology tool may be provided with a plurality of scanning probe microscopes and a processor to allow the height of the surface of a substrate to be determined. The metrology tool (or apparatus) may also be provided with a height measurement optical sensor to allow the method 400 to be performed.

[0101] The system may be provided with a lithographic apparatus and a plurality of scanning probe microscopes and a processor to allow the height of the surface of the substrate to be determined. The system may also be provided with a height measuring optical sensor to allow the method 400 to be performed.

[0102] As discussed, the lithographic apparatus LA may be provided with two or more substrate supports WT (i.e. a "dual stage"). In such a dual stage lithographic apparatus LA, a plurality of scanning probe microscopes may be provided so that the method described herein may be performed before or after the substrate W has been exposed to the radiation beam B. In other words, when a first substrate W (on a first substrate support WT) is exposed to the radiation beam B, a second substrate W (on a second substrate support WT) may be measured by the plurality of scanning probe microscopes before or after the second substrate W is exposed to the radiation beam B.

[0103] Although the method described herein has been described with respect to a substrate W that has been or is to be exposed to lithographic radiation (ie radiation beam B), as will be clear to the skilled person, the method (and corresponding apparatus) may advantageously be adapted for use with substrates that have not been exposed to lithographic radiation.

[0104] Likewise, although the methods described herein have been described with respect to DUV lithographic radiation, as will be clear to the skilled person, the methods (and corresponding apparatus) may advantageously be adapted for use with EUV lithographic radiation (and corresponding apparatus).

[0105] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0106] Those skilled in the art will appreciate that in the context of these alternative applications, any use of the term "wafer" or "die" in the present disclosure may be considered synonymous with the more general term "substrate" or "target portion," respectively. The substrates referred to herein may be processed before or after exposure in, for example, a coating and developing system or track (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where applicable, the disclosure herein may be applied to such substrate processing tools and other substrate processing tools. In addition, a substrate may be processed more than once, for example to produce a multi-layer IC, such that the term substrate used herein may also refer to a substrate that already includes multiple processed layers.

[0107] Although specific reference is made herein to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus for measuring or processing an object such as a wafer (or other substrate) or a mask (or other pattern forming device). These apparatuses may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0108] 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 is not limited to optical lithography and may be used in other applications, such as imprint lithography, where the context permits.

[0109] Where context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium that can be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form that can be read by a machine (e.g., a computing device). For example, a machine-readable magnetic storage medium may include a read-only memory (ROM); a random access memory (RAM); a magnetic storage medium; an optical storage medium; a flash memory device; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.), etc. In addition, herein, firmware, software, routines, instructions may be described as performing certain actions. However, it should be understood that such descriptions are for convenience only, and that these actions are actually generated by a computing device, a processor, a controller, or other device that executes firmware, software, routines, instructions, etc., and in doing so may cause an actuator or other device to interact with the physical world.

[0110] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in a manner different from that described. The above description is intended to be exemplary and not restrictive. Therefore, it will be appreciated by those skilled in the art that modifications may be made to the present invention as described without departing from the scope of the claims set forth below. Other aspects of the present invention are set forth in the following numbered aspects.

[0111] 1. A method for calibrating a height measurement optical sensor of a substrate in a lithographic apparatus, comprising:

[0112] determining a first height of a surface of the substrate within a region of interest using the height measuring optical sensor;

[0113] determining a second height of the surface of the substrate within the region of interest using a scanning probe microscope; and

[0114] A calibration map of the height measuring optical sensor for the region of interest is determined by comparing the first height and the second height.

[0115] 2. The method of clause 1, further comprising applying the calibration map to other regions of the substrate corresponding to the region of interest.

[0116] 3. The method according to any preceding aspect, wherein the scanning probe microscope is an atomic force microscope (AFM) or a near-field scanning optical microscope (NSOM).

[0117] 4. The method according to any preceding aspect, wherein the scanning probe microscope is one scanning probe microscope among a plurality of scanning probe microscopes.

[0118] 5. The method according to any preceding aspect, wherein determining the second height comprises:

[0119] The height of the surface of the substrate within the region of interest is measured using the scanning probe microscope.

[0120] 6. The method according to any preceding aspect, wherein determining the second height comprises:

[0121] determining a plurality of heights of the surface of the substrate for the at least one region of interest using the scanning probe microscope; and

[0122] An average of the plurality of heights is calculated.

[0123] 7. A lithographic apparatus comprising:

[0124] a height measuring optical sensor configured to determine a first height of a surface of the substrate within a region of interest;

[0125] a scanning probe microscope configured to determine a second height of the surface of the substrate within the region of interest; and

[0126] A processor is configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

[0127] 8. A system comprising:

[0128] a lithographic apparatus comprising a height measuring optical sensor configured to determine a first height of a surface of a substrate within a region of interest;

[0129] a scanning probe microscope configured to determine a second height of the surface of the substrate within the region of interest; and

[0130] A processor is configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

[0131] 9. A lithography tool comprising:

[0132] a height measuring optical sensor configured to determine a first height of a surface of the substrate within a region of interest;

[0133] a scanning probe microscope configured to determine a second height of the surface of the substrate within the region of interest; and

[0134] A processor is configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

[0135] 10. A measuring tool comprising:

[0136] a height measuring optical sensor configured to determine a first height of a surface of the substrate within a region of interest;

[0137] a scanning probe microscope configured to determine a second height of the surface of the substrate within the region of interest; and

[0138] A processor is configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

[0139] 11. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to perform the method according to aspects 1 to 6.

[0140] 12. A calibration map comprising data corresponding to a region of interest of a substrate, wherein the substrate comprises a plurality of regions, each of the plurality of regions having been patterned with the same pattern.

[0141] 13. A method for determining the height of a surface of a substrate, comprising:

[0142] Determine the height of the reference point; and

[0143] A plurality of scanning probe microscopes is used to determine the height of the surface of the substrate at one or more points.

[0144] 14. The method of clause 13, wherein the determined height of the surface of the substrate at the one or more points is a relative height relative to a height of a reference point.

[0145] 15. A lithographic apparatus comprising a plurality of scanning probe microscopes, the scanning probe microscopes being configured to:

[0146] Determine the height of the reference point; and

[0147] The height of the surface of the substrate at one or more points is determined.

[0148] 16. A metrology tool comprising a plurality of scanning probe microscopes, the plurality of scanning probe microscopes being configured to:

[0149] Determine the height of the reference point; and

[0150] The height of the surface of the substrate at one or more points is determined.

Claims

1. A method for calibrating a height measurement optical sensor of a substrate in a lithographic apparatus, comprising: determining a first height of a surface of the substrate within a region of interest using the height measuring optical sensor; determining a second height of the surface of the substrate within the region of interest using a scanning probe microscope; as well as A calibration map of the height measuring optical sensor for the region of interest is determined by comparing the first height and the second height. 2 . The method of claim 1 , further comprising applying the calibration map to other regions of the substrate corresponding to the region of interest.

3. A method according to any preceding claim, wherein: The scanning probe microscope is an atomic force microscope (AFM) or a near-field scanning optical microscope (NSOM).

4. A method according to any preceding claim, wherein: The scanning probe microscope is one scanning probe microscope among a plurality of scanning probe microscopes.

5. A method according to any preceding claim, wherein: Determining the second height includes: The height of the surface of the substrate within the region of interest is measured using the scanning probe microscope.

6. A method according to any preceding claim, wherein: Determining the second height includes: determining a plurality of heights of the surface of the substrate for the at least one region of interest using the scanning probe microscope; and An average of the plurality of heights is calculated.

7. A lithographic apparatus comprising: a height measuring optical sensor configured to determine a first height of a surface of the substrate within a region of interest; a scanning probe microscope configured to determine a second height of the surface of the substrate within the region of interest; as well as A processor is configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

8. A system comprising: a lithographic apparatus comprising a height measuring optical sensor configured to determine a first height of a surface of a substrate within a region of interest; a scanning probe microscope configured to determine a second height of the surface of the substrate within the region of interest; as well as A processor is configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

9. A lithography tool comprising: a height measuring optical sensor configured to determine a first height of a surface of the substrate within a region of interest; a scanning probe microscope configured to determine a second height of the surface of the substrate within the region of interest; as well as A processor is configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

10. A measuring tool comprising: a height measuring optical sensor configured to determine a first height of a surface of the substrate within a region of interest; a scanning probe microscope configured to determine a second height of the surface of the substrate within the region of interest; as well as A processor is configured to determine a calibration map of the height measuring optical sensor for the region of interest by comparing the first height and the second height.

11. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to perform the method according to claims 1 to 6.

12. A calibration map comprising data corresponding to a region of interest of a substrate, wherein the substrate comprises a plurality of regions, each of the plurality of regions having been patterned with the same pattern.

13. A method of determining the height of a surface of a substrate, comprising: Determine the height of the reference point; and A plurality of scanning probe microscopes is used to determine the height of the surface of the substrate at one or more points.

14. The method according to claim 13, wherein: The determined heights of the surface of the substrate at the one or more points are relative heights with respect to a height of a reference point.

15. A lithographic apparatus comprising a plurality of scanning probe microscopes, the scanning probe microscopes being configured to: Determine the height of the reference point; and The height of the surface of the substrate at one or more points is determined.

16. A metrology tool comprising a plurality of scanning probe microscopes, the plurality of scanning probe microscopes being configured to: Determine the height of the reference point; and The height of the surface of the substrate at one or more points is determined.

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