Method of imaging a sample using a charged particle beam device, method of calibrating a charged particle beam device and charged particle beam device

Abstract

A method for imaging a sample using a charged particle beam apparatus includes: determining a first focusing intensity of an objective lens of the charged particle beam apparatus, the first focusing intensity being adapted to focus a charged particle beam onto a first surface region of the sample; determining a first focal sub-range of a plurality of focal sub-ranges such that the first focusing intensity is within the first focal sub-range, wherein the plurality of focal sub-ranges are associated with a set of values ​​of a calibration parameter; determining a first value of the calibration parameter, the first value being associated with the first focal sub-range; and imaging the first surface region using the first value.

Description

Technical Field

[0001] This disclosure relates to a method for imaging a sample using a charged particle beam apparatus. Specifically, a large-area substrate for display manufacturing, having a non-planar surface, can be imaged. More specifically, the embodiments described herein relate to a method and apparatus for imaging a sample using a focused charged particle beam, specifically for at least one of metrology, inspection, and defect detection. Specifically, the embodiments described herein can be used to image a sample for performing measurements, such as critical dimension measurements. Additionally, a method for calibrating a charged particle beam apparatus and a charged particle beam apparatus for imaging a sample are described. Background Technology

[0002] In many applications, thin layers are deposited on substrates, such as glass substrates. The substrates are typically coated in a vacuum chamber of a coating apparatus. For some applications, vapor deposition is used in the vacuum chamber for substrate coating. Over the past few years, the price of electronic devices, specifically optoelectronic devices, has decreased significantly. Additionally, pixel density in displays has increased. For TFT displays, high-density TFT integration is advantageous. Despite the increasing number of thin-film transistors (TFTs) within the device, yield rates need to be improved and manufacturing costs need to be further reduced.

[0003] One or more structures or layers may be deposited on a substrate (such as a glass substrate) to form an array of electronic or optoelectronic devices (such as TFTs) on the substrate. The substrate on which the electronic or optoelectronic structures are formed is also referred to herein as a "sample". During the manufacture of TFT displays and other samples, it may be advantageous to image one or more structures deposited on the sample to monitor the quality of the sample.

[0004] For example, sample imaging can be performed using optical systems. However, features of the sample (e.g., the edges of fine lithographically defined lines) may appear blurred or widened in an optical system, or may not be distinguishable as independent features. Therefore, optical systems may be unsuitable for imaging some features of the sample. Charged particles (such as electrons) can be used to image the surface of the sample. Compared to optical systems, charged particles can provide better resolution and / or more accurate identification of features (such as the edges of lithographically defined structures).

[0005] However, imaging samples with uneven surfaces or those held on uneven substrates using charged particle beams can be challenging because the sample surface may not be located at the calibration distance from the objective lens, and the depth of field of the charged particle beam setup is limited. Refocusing the charged particle beam onto the sample surface can introduce measurement errors, while moving the sample surface to the focal point of the charged particle beam via platform movement can slow down imaging of the sample's surface area.

[0006] Therefore, considering the increasing demand for improved display quality on large-area substrates, there is a need for improved methods to investigate samples with high measurement accuracy and in a fast and reliable manner. Specifically, for example, when performing critical dimension measurements, there is a need for processing control of large-area samples with high or predetermined measurement accuracy. Summary of the Invention

[0007] According to various aspects of this disclosure, methods for imaging samples using a charged particle beam apparatus, methods for calibrating a charged particle beam apparatus, and charged particle beam apparatus for imaging samples are provided. Further aspects, benefits, and features of this disclosure will be apparent from the claims, description, and drawings.

[0008] According to one aspect, a method for imaging a sample using a charged particle beam apparatus is provided. The method includes: determining a first focusing intensity of an objective lens of the charged particle beam apparatus, the first focusing intensity being adapted to focus a charged particle beam onto a first surface region of the sample; determining a first focal sub-range of a plurality of focal sub-ranges such that the first focusing intensity is within the first focal sub-range, wherein the plurality of focal sub-ranges are associated with a set of values ​​of a calibration parameter; determining a first value of the calibration parameter, the first value being associated with the first focal sub-range; and imaging the first surface region using the first value.

[0009] According to another aspect, a method for calibrating a charged particle beam device is provided. The method includes: performing a first measurement by performing a first measurement of a calibration object for each of the first plurality of focused intensities; determining a measurement error by determining a measurement error based on the first measurement for each of the first plurality of focused intensities; determining a plurality of focal sub-ranges based on the measurement error and measurement accuracy; performing a second measurement by performing a second measurement of the calibration object for each of the plurality of focal sub-ranges; and determining a set of values ​​for calibration parameters based on the second measurement for the plurality of focal sub-ranges.

[0010] According to a further aspect, a charged particle beam apparatus for imaging a sample is provided. The charged particle beam apparatus includes: a platform for arranging the sample to be imaged; an objective lens configured to focus a charged particle beam propagating along an optical axis; and a computer-readable medium containing a program for imaging the sample, which, when executed by a processor, performs the method according to the embodiments described herein.

[0011] Further aspects, advantages and features of this disclosure will be apparent from the description and drawings. Attached Figure Description

[0012] The remainder of the specification, including the accompanying drawings, sets forth a full and practicable disclosure for those skilled in the art, wherein:

[0013] Figure 1 The illustration shows a charged particle beam device configured to operate according to the method described herein;

[0014] Figure 2 The diagram illustrates a schematic of an objective lens used to demonstrate the dependence of focusing distance on focusing intensity.

[0015] Figure 3A and Figure 3B The dependence of the field of view on the distance between the sample surface and the objective lens of the charged particle beam device is shown;

[0016] Figure 3C Imaging of a sample according to an embodiment described herein is shown.

[0017] Figure 4 This is a flowchart illustrating a method for calibrating a charged particle beam apparatus according to an embodiment described herein;

[0018] Figure 5A It is a schematic diagram that correlates measurement error with the first or more focusing intensities of the objective lens;

[0019] Figure 5B It is a schematic diagram used to define multiple focal sub-ranges of a chart;

[0020] Figure 6 It is a schematic diagram that correlates the orientation mismatch of the scan rotation with a second or more focus intensities;

[0021] Figure 7 This is a flowchart illustrating a method for imaging a sample according to an embodiment described herein. Detailed Implementation

[0022] Reference will now be made in detail to exemplary embodiments, one or more examples of which are illustrated in the figures. Each example is provided by way of illustration and is not intended to be limiting. For example, features shown or described as part of one embodiment may be used in other embodiments or in combination with other embodiments to produce yet another set of embodiments. This disclosure is intended to include such modifications and variations.

[0023] In the following description of the figures, the same reference numerals represent the same parts. Differences regarding individual embodiments are described only. The structures shown in the figures are not necessarily depicted to scale, but are used to better understand the embodiments.

[0024] Figure 1 The illustration shows a charged particle beam apparatus 100 configured to operate according to the methods described herein. The charged particle beam apparatus 100 may include a scanning electron microscope 102 having a beam source 110 configured to generate a charged particle beam 101, specifically an electron beam. The charged particle beam 101 may be guided along optical axis A through a column 103 of the scanning electron microscope 102. The internal volume of the column 103 may be evacuated. The scanning electron microscope 102 may include beam influencing elements, such as one or more beam deflectors, a scanning deflector 140, an accelerator 115, a decelerator, a lens element 120 or other focusing or defocusing elements, a beam corrector, a beam splitter, a detector, and / or additional elements for influencing the charged particle beam 101 propagating along optical axis A.

[0025] The charged particle beam device 100 includes a platform 20 for arranging a sample 10 to be imaged thereon, and an objective lens 150 configured to focus a charged particle beam onto the sample 10 arranged on the platform 20.

[0026] Platform 20 may be arranged within sample imaging chamber 105, and in some embodiments, sample imaging chamber 105 may be evacuated. In some embodiments, platform 20 may be a movable platform. Specifically, platform 20 may be movable in a plane (also referred to herein as the XY plane) perpendicular to the optical axis A of charged particle beam apparatus 100. By moving platform 20 in the XY plane or along the XY axis of charged particle beam apparatus 100, a designated surface region of sample 10 is moved to a region below scanning electron microscope 102, such that the designated surface region can be imaged by focusing charged particle beam 101 thereon. For example, in Figure 1 In the process, the first surface region 11 of the sample 10 intersects the optical axis A of the scanning electron microscope 102, allowing the first surface region 11 to be imaged. The platform 20 is also movable in the Z direction (i.e., in the direction of the optical axis A). In an embodiment, the platform 20 is movable in the XY plane and in the Z direction via a platform motion controller 181.

[0027] According to the embodiments described herein, one or more surface regions of sample 10 can be imaged using charged particle beam device 100. As used herein, the term "sample" can refer to a substrate on which one or more layers or features are formed. The sample can be imaged for one or more of the following purposes: (i) to perform metrology, specifically to measure the dimensions of one or more features of the sample, for example, in the lateral direction, i.e., in the XY plane, more specifically to perform critical dimension measurements; (ii) to detect defects; and / or (iii) to investigate or inspect the quality of the sample.

[0028] In some implementations, the surface of the sample to be imaged can be a non-planar surface. For example, the sample surface can be rough, non-uniform, or may include three-dimensional features or structures with varying heights formed thereon. Different surface regions of the sample can be positioned at different levels relative to the objective lens plane.

[0029] In some embodiments, a sample (which may have a planar or non-planar sample surface) may be arranged on platform 20, wherein platform 20 has a non-planar platform surface 13. For example, the non-planar platform surface 13 may have platform surface regions at different levels relative to the plane of objective lens 150. For example, the difference between the levels of the platform surface regions may be several hundred micrometers. Thus, when sample 10 is arranged on the non-planar platform surface 13, sample 10 may have a first surface region 11 and a second surface region 12 arranged at different levels. The “level” of the surface region of the sample arranged on the platform may refer to the distance of the surface region along the optical axis A or in the Z direction relative to the plane of objective lens 150. Figure 1 The diagram schematically depicts a sample 10 that may be arranged on a non-planar platform surface 13 of platform 20. The sample 10 may include a first surface region 11 provided at a first horizontal level and a second surface region 12 provided at a second horizontal level, laterally spaced from the first surface region 11. In other words, the distance of the first surface region 11 relative to the plane of objective lens 150 (specifically, the distance in the Z direction) is different from the distance of the second surface region 12 relative to the plane of objective lens 150.

[0030] For imaging a sample using a charged particle beam 101, the charged particle beam is typically focused onto the sample surface using an objective lens 150. When the charged particle beam 101 strikes the sample surface, it generates secondary electrons or backscattered electrons (also known as “signal electrons”). The signal electrons provide information about the spatial characteristics and dimensions of the sample surface and are detected using a detector 130. By scanning the charged particle beam 101 above the sample surface (e.g., using a scanning deflector 140) and detecting the signal electrons as a function of their generation location, the sample surface or a portion thereof can be imaged.

[0031] In some embodiments, one or more scanning deflectors 140 may be provided for scanning the charged particle beam 101 over the surface of the sample (e.g., in the X direction and / or the Y direction).

[0032] A charged particle beam can be focused into a small point on the sample surface. Focusing the charged particle beam into a small point increases the resolution of the obtainable image. Therefore, the sample surface should be positioned in the focal plane of the objective lens during imaging. The distance between the downstream end of the objective lens 150 and the focal plane of the charged particle beam positioned on the sample surface is generally referred to as the working distance WD of the charged particle beam device 100.

[0033] Imaging non-planar sample surfaces using charged particle beams can be challenging because not all surface areas lie within a common focal plane. For example, Figure 1 The first surface region 11 and the second surface region 12 are located in different focal planes. By locally adjusting the focusing intensity of the objective lens or by moving the platform along the optical axis A to focus the sample surface, a clear image of the surface region located at a varying distance from the objective lens can be achieved. The focusing intensity of the objective lens can be adjusted according to the local height of the surface region to be imaged. For example, the objective lens may include a magnetic lens component 151 with one or more coils. The focusing intensity of the objective lens can be increased by increasing the focusing current applied to one or more coils of the magnetic lens component 151 (decreasing the focusing distance), and the focusing intensity of the objective lens can be decreased by decreasing the focusing current applied to one or more coils (increasing the focusing distance). The focusing distance can be understood as the distance between the downstream end of the objective lens and the focal plane when the objective lens 150 is excited using the associated focusing current.

[0034] Figure 2 Objective lenses 150 and charged particle beams 101 for three different focusing intensities are shown. For each of the three different focusing intensities, the charged particle beam 101 is focused at a different focusing distance from objective lens 150, specifically at working distance WD, a first distance D1, or a second distance D2. By adjusting the focusing intensity of objective lens 150 (specifically, the focusing current), the focusing plane can be shifted toward or away from objective lens 150. Samples with varying surface levels can be clearly imaged by locally adjusting the focusing intensity of objective lens 150. In other words, when imaging a non-uniform sample surface or a sample arranged on a non-planar platform, the focusing intensity of objective lens 150 can be changed according to the level of the surface area to be imaged.

[0035] A change in the focusing intensity of the objective lens 150, used to focus the charged particle beam 101 on a surface region of sample 10, can result in, for example, a change in the pixel size (nm / pixel) in the acquired image. For example, as... Figure 3AAs shown, feature 310 on sample surface 308 of the sample can be located at a working distance WD from objective lens 150. Scan deflector 140 can deflect the electron beam with a first deflection 342, such that feature 310 is observed in a first field of view 312 of the image scan of charged particle beam 101. For example, charged particle beam 101 can be calibrated for measurement at working distance WD. Specifically, pixels in the acquired image can be correlated with dimensions (e.g., lengths on sample surface 308) on sample surface 308. Thus, the correlation between the scanning current of scan deflector 140 and the first field of view 312 is known, and the actual size of feature 310 can be determined from the acquired image of sample surface 308.

[0036] exist Figure 3B In the process, the sample is positioned for imaging different surface regions of sample surface 308. Another feature 311, the same size as feature 310, is positioned at an unknown distance D from the objective lens at a distance of 150. X The charged particle beam 101 can be focused onto the sample surface 308. Scanning the sample surface 308 with a first deflection 342 can result in observing a second field of view 314 on the sample surface 308, which may differ from the first field of view 312. For example, in Figure 3B In the middle, the second field of view is 314 greater than Figure 3A The first field of view shown is 312, specifically because Figure 3B The unknown distance D X Greater than Figure 3A The working distance WD in the middle. Therefore, with the first field of view 312 ( Figure 3A Compared to feature 310 in the second field of view 314, another feature 311 of sample 10 is... Figure 3B In this context, the feature may appear smaller. Specifically, the size or critical size of another feature 311 may appear smaller compared to its actual size. Similarly, when the distance between the surface area of ​​the sample and the objective lens is less than a predetermined working distance (e.g., working distance WD), the feature of the sample may appear larger than its actual size. Measuring the size of a feature located at a distance different from the predetermined working distance using conventional techniques can negatively impact the accuracy of the measurement.

[0037] In this context, it should be noted that for charged particle beams with high landing energy on the sample, measurement errors can be quite low. However, when using charged particle beams with low landing energy, such as electron beams with a landing energy of 5 keV or less (specifically 1 keV or less), measurement errors can become significant. Thus, measurement errors can become noticeable when the charged particle beam apparatus includes a low-voltage SEM (LV-SEM).

[0038] Low-energy electron beams are advantageous for imaging glass samples or other non-conductive samples. However, low-energy electron beams are more sensitive to changes in the distance between the sample surface and the objective lens. Conventional methods for imaging non-planar samples or samples on non-planar platforms do not provide the level of accuracy or throughput suitable for performing metrology, review, or inspection of large-area substrates, such as glass substrates used to manufacture flat panel and / or TFT-based displays.

[0039] According to the methods and apparatus described herein, a charged particle beam apparatus can be calibrated for imaging a sample, specifically for imaging the sample surface with a predetermined measurement accuracy.

[0040] According to an embodiment, a method for calibrating a charged particle beam apparatus is provided. The method may include arranging a calibration sample on a platform of the charged particle apparatus. The calibration sample may have a calibration object on its surface. The calibration object may have known dimensions. For example, the calibration object may include lines positioned at a known distance or at a known spacing. The lines may be formed by photolithography. The calibration sample may specifically be a calibration standard. For example, the calibration standard may be provided by a standards association.

[0041] In some implementations, the method may include defining a measurement accuracy for the charged particle beam device. For example, the measurement accuracy may depend on processing limitations and / or on an acceptable level of inaccuracy. Measurement accuracy can be provided as dimensional accuracy, such as the accuracy of length measurements in an image of a surface region. For example, measurement accuracy can be provided as length measurement accuracy, for example, in nanometers. In implementations, the measurement accuracy may be less than 20 nm, specifically less than 10 nm, more specifically less than 5 nm, less than 2 nm, or less than 0.5 nm. In this document, the measurement accuracy determined for calibrating the charged particle beam device may also be referred to as a predetermined measurement accuracy.

[0042] In an implementation, the method may include defining an operating point for the post 103 of the charged particle beam apparatus 100. The operating point may include at least one operating point setting, specifically at least one of acceleration energy, landing energy, current of the magnetic lens element, scanning deflector current, astigmatism correction current, and reduction of the electron beam from the beam source 110 (electron gun) to the calibration sample. Specifically, the operating point may include an operating point setting for the landing energy such that a landing energy of 5 keV or less (specifically 1 keV or less) is provided to the charged particle beam. Defining the operating point may include positioning the calibration sample at a working distance WD from the objective lens 150 (specifically at the nominal value of the working distance). The charged particle beam may be focused onto a surface area of ​​the calibration sample containing the calibration object. The charged particle beam may be focused onto the surface area of ​​the calibration sample using the operating point focusing intensity.

[0043] In some implementations, defining the operating point may include determining an operating point calibration value for calibration parameters (specifically, deflector parameters). In some implementations, defining the operating point may include determining a scan rotation such that the XY axes of the calibration sample or calibration object are aligned with the XY axes of the image scan of the charged particle beam apparatus used for the operating point. For example, a scan rotation may be determined such that the scan direction of the charged particle beam is at least substantially perpendicular to the longitudinal axis of the calibration object (e.g., a line on the calibration sample).

[0044] Figure 4 The illustration shows a flowchart of a method for calibrating a charged particle beam apparatus according to an embodiment of the present disclosure. In the embodiment, the method includes performing a first measurement (block 410) by performing a first measurement of the calibrated object for each of a first plurality of focus intensities. The first plurality of focus intensities may be selected within a range of focus intensities having corresponding focus distance ranges, for example, such that the focus distance range spans hundreds of micrometers, for example, at least 100 μm, specifically at least 200 μm or at least 300 μm.

[0045] In some implementations, the first plurality of focus intensities may be equally spaced within a focus intensity range. The focus intensity range may include the operating point focus intensity. Specifically, the focus intensity range may include at least one focus intensity less than the operating point focus intensity and / or at least one focus intensity greater than the operating point focus intensity.

[0046] For example, such as Figure 5A As shown, the first multiple focus intensities F -N ..., F -1 F0, F1, ..., F N This may include the operating point focus intensity F0. Figure 5A In the middle, the first multiple focus intensities F -N ..., F -1 F0, F1, ..., FN It is determined by adding a multiple (specifically an integer (-N, ..., N) times) of the focus intensity difference R to the focus intensity F0 at the operating point. For example, the first multiple focus intensity F -N ..., F -1 F0, F1, ..., F N It can be calculated using F0-NR, ..., F0-R, F0, F0+R, ..., F0+NR.

[0047] In this implementation, the calibrated object is focused for each of a plurality of focusing intensities of the objective lens. For example, for the minimum focusing intensity F among the first plurality of focusing intensities. -N The platform can move downwards along the optical axis until the surface is in focus. This is for the minimum focusing intensity F. -N After performing the first measurement, for the next focusing intensity F -N+1 The platform can be moved upwards to focus the calibration object. The method can then continue targeting the first plurality of focus intensities F. -N ..., F -1 F0, F1, ..., F N Each of them performs the first measurement.

[0048] In some implementations, the calibration object can be manually focused by an operator of the charged particle beam device. The operator can move the platform along the optical axis to find a platform position that provides a clear image of the calibration object. In some implementations, the calibration object can be focused using variable-distance autofocus processing. Variable-distance autofocus processing may include imaging the calibration object at varying distances from the objective lens and analyzing the image sharpness of the acquired images. Optionally, image contrast may be analyzed. The distance between the objective lens and the calibration object can be varied between acquired images by moving the platform along the optical axis. Specifically, by optimizing image sharpness, images can be acquired at distances between the calibration object and the objective lens during iterative convergence. The convergence iterative process may include selecting the distance between the calibration object and the objective lens based on a golden ratio search method or a Fibonacci search method.

[0049] As used herein, a focused surface region or a charged particle beam focused on a surface region can be understood as such that the surface region is located at the focal point of the charged particle beam. Image scanning of the surface region can provide a clear image of the surface region. The surface region can be in optimal focus. For example, the charged particle beam can be focused into a small dot on the surface region. Specifically, the surface region can be focused manually or by an autofocus process (e.g., by a variable distance autofocus process or a variable focus autofocus process according to the embodiments described herein).

[0050] Once the calibration object is focused for one of the first plurality of focus intensities, performing a first measurement may include acquiring an image of the calibration object. Performing the first measurement may include measuring the dimensions of the calibration object in the acquired image. Specifically, the dimensions may be the lateral dimensions of the calibration object. The dimensions of the calibration object may have known values. For example, the dimensions may be the spacing between the lines of the calibration object. The first measurement of the calibration object may be performed for each of the first plurality of focus intensities.

[0051] In one implementation, the method includes determining a measurement error (block 420) by determining a measurement error for each of a first plurality of focus intensities based on a first measurement. The measurement error can be determined based on the first measurement and on a known value of the size of the calibrated object. For example, the measurement error can be determined for each of the first plurality of focus intensities as the difference between the corresponding first measurement of the size and a known value of the size. For example, as... Figure 5A As shown, the measurement error 520 can be plotted in the graph of error E versus focus intensity F.

[0052] In one implementation, the method includes determining a plurality of focal sub-ranges (block 430) based on measurement error and measurement accuracy (specifically, a predetermined measurement accuracy). Measurement accuracy may be defined or provided according to the implementation described herein. Determining the plurality of focal sub-ranges may include fitting a measurement error function to the measurement error. For example, the measurement error function may be a linear fit. Linear fitting may be used under certain conditions. In another implementation, a curve different from a linear fit may be used to fit the measurement error. Figure 5A In this process, the measurement error 520 is fitted by the measurement error function 522, specifically by linear fitting.

[0053] According to the implementation method, multiple focal sub-ranges can be determined based on a measurement error function and measurement accuracy. In some implementations, multiple sub-ranges can be determined such that within each of the multiple focal sub-ranges, the error range spanned by the measurement error function is less than or equal to the measurement accuracy. Specifically, the error function and the multiple of the measurement accuracy can be used to determine additional multiple focus intensities F. a F b ...F i F j ..., F x F y The multiple of measurement accuracy can specifically include the multiple of measurement accuracy contained within the range spanned by the measurement error. For example, additional focus intensities can be calculated using the inverse function of the measurement error function. Specifically, additional focus intensities can be calculated by applying the inverse function to the multiple of measurement accuracy. Multiple focus subranges can each be defined as the range between two adjacent focus intensities of the additional focus intensities.

[0054] Figure 5B The determination of several focal sub-ranges according to the embodiments described herein is illustrated. Figure 5B Including measurement error 520 ( Figure 5A The measurement error function 522 is defined. A horizontal line 524 can be provided along the axis of error E at multiples of the measurement accuracy U. A vertical line 526 can be provided at the intersection of the horizontal line 524 and the measurement error function 522. The intersection of the vertical line 526 and the axis of focus intensity F can provide multiple additional focus intensities F. a F b ..., F i F j ..., F x F y Multiple focal subranges can be defined along the axis of the focal intensity F at multiple additional focal intensities F. a F b ..., F i F j ...F x F y The range between adjacent focus intensities. For example, multiple focus subranges may include subranges [F a ,F b ]、...、[F i ,F j ]、...、[F x ,F y Within each subrange, the measurement error can be less than the measurement accuracy U. Multiple focal subranges can each span a subrange width ΔF. Specifically, if the measurement error function 522 is a linear fit, the multiple focal subranges can have the same subrange width ΔF. In another embodiment, specifically, if the measurement error function is determined to be a curve different from the linear fit, the subrange widths of the different focal subranges of the multiple focal subranges can be different.

[0055] According to an implementation, the method includes performing a second measurement (block 440) by performing a second measurement of the calibrated object for each of a plurality of focal sub-ranges. Performing the second measurement may include determining a calibrated focus intensity for each of the plurality of focal sub-ranges. For example, the calibrated focus intensity may be the center focus intensity or the average focus intensity of each of the plurality of focal sub-ranges. See also Figure 5B For each of the multiple focal sub-ranges, the calibrated focus intensity can be determined, for example, (F... a +F b ) / 2、...、(F i +F j ) / 2、...、(F x +F y) / 2.

[0056] In some implementations, each of the plurality of focal sub-ranges has a calibrated focus intensity for performing the second measurement. The objective lens can focus a charged particle beam using the calibrated focus intensity of one of the plurality of focal sub-ranges. The calibration object can be focused by moving a platform along the optical axis. The calibration object can be focused manually or by using a variable-distance autofocusing process according to the embodiments described herein.

[0057] Once the calibration object is in focus, performing a second measurement may include acquiring an image of the calibration object. Performing the second measurement may include measuring the dimensions of the calibration object in the acquired image, specifically its lateral dimensions. Dimensions (e.g., the spacing between the lines of the calibration object) may have known values. The second measurement of the calibration object may be performed for each of a plurality of focal subranges.

[0058] According to one embodiment, the method includes determining a set of values ​​(block 450) of calibration parameters for a plurality of focal sub-ranges based on a second measurement. This set of values ​​may be determined based on a second measurement of the size of the calibrated object and known values ​​of the size of the calibrated object. The set of values ​​may include at least one value associated with each of the plurality of focal sub-ranges. The calibration parameters can be used to image a sample, specifically for critical size measurements.

[0059] In some implementations, the calibration parameters are deflector parameters. Deflector parameters can be parameters used to control the deflection provided by the scanning deflector of the charged particle beam apparatus. Specifically, this set of values ​​can include a set of deflector current values ​​and / or a set of deflector voltage values. This set of values ​​can be determined such that, for each calibrated focus intensity, the field of view scanned by the charged particle beam using the calibration parameters has the same size. Specifically, this set of values ​​can be determined such that, for each calibrated focus intensity, the field of view has the same size as the reference field of view at the operating point focus intensity. Calibrating the charged particle beam apparatus according to the implementations described herein enables imaging of a sample with measurement accuracy (specifically, a predetermined measurement accuracy), specifically performing a measurement or critical size measurement. Specifically, measurements with predetermined measurement accuracy can be provided for any focus intensity within a plurality of focal sub-ranges.

[0060] In some implementations, multiple focal sub-ranges (specifically, multiple focal sub-ranges as a whole) may correspond to a focal distance range. The focal distance range can span hundreds of micrometers, for example, at least 100 μm, specifically at least 200 μm or at least 300 μm. According to implementations, a set of calibration parameters is provided that enables accurate measurements over a wide range of focal distances, specifically for samples such as large-area substrates, samples arranged on non-planar platforms, or samples having surface regions positioned at several distances (these distances differing by hundreds of micrometers) from the objective plane.

[0061] According to some implementations, the method may include determining orientation mismatch by determining an orientation mismatch of the scan rotation of the charged particle beam apparatus relative to the calibration object for each of a second plurality of focus intensities. Orientation mismatch at different focus intensities may arise from different magnetic fields provided at different focus intensities (specifically, at different focus currents). Specifically, the magnetic field may bend the trajectory of the charged particles in the charged particle beam, causing the scan rotation or scan direction of the charged particle beam to have orientation mismatch at different focus intensities.

[0062] In an implementation, for each of the second plurality of focus intensities, orientation mismatch can be an image scan showing an orientation difference relative to a reference image scan performed at a reference focus intensity (specifically, at the operating point focus intensity). An orientation mismatch of an image scan can be determined as, for example, a difference in the XY-axis orientation (e.g., angular orientation) of the image scan relative to the XY-axis orientation of the calibrated object. Orientation mismatch can be determined manually or automatically, for example, using an edge-finding algorithm such as a Sobel edge detector.

[0063] In some implementations, the second plurality of focus intensities may be the same as the first plurality of focus intensities. Specifically, the orientation mismatch can be determined by performing a first measurement of the calibrated object for each of the first plurality of focus intensities, for example, Figure 4 Block 410. For example, the calibration object can be focused for each of the first plurality of focus intensities. Orientation mismatch can be determined in a first image of the calibration object. Orientation mismatch can be corrected. A first measurement can be performed in a second image of the calibration object, specifically in the second image acquired after correction of orientation mismatch. The first measurement can be performed according to the embodiments described herein.

[0064] In some implementations, the second plurality of focus intensities may differ from the first plurality of focus intensities. The calibration object can be focused for each of the second plurality of focus intensities, for example, by manually moving the platform or by using variable-distance autofocus processing. Once the calibration object is in focus for one of the second plurality of focus intensities, an orientation mismatch can be determined. An orientation mismatch can be determined for each of the second plurality of focus intensities.

[0065] According to an implementation, the method may include determining the correlation between focus intensity and scan rotation based on directional mismatch and a second plurality of focus intensities. The correlation may be, for example, a function, such as an analytical expression, or a table relating focus intensity and scan rotation. The correlation may be determined by fitting a fitted curve to the directional mismatch as a function of focus intensity. The fitted curve may be, for example, a linear fitted curve.

[0066] Figure 6 The diagram illustrates a graph of scan rotation ΔSC and focus intensity F. The graph includes a directional mismatch of 630° determined for each of the second plurality of focus intensities. Figure 6 In the middle, the second plurality of focus intensities correspond to the first plurality of focus intensities F -N ..., F -1 F0, F1, ..., F N By fitting curve 632 (in Figure 6 Specifically, the correlation between focus intensity F and scan rotation ΔSC is determined by fitting an orientation mismatch 630 using a linear fitting curve. This correlation between focus intensity and scan rotation can be used to correct the scan rotation of an image scan. The correlation between focus intensity and scan rotation can be used as a predetermined correlation, specifically for imaging a sample according to the embodiments described herein. Based on the correlation between focus intensity and scan rotation, the scan rotation can be corrected before performing a second measurement according to the method of this disclosure. The correlation can be used to image a sample according to the embodiments described herein, specifically for adjusting the scan rotation parameters.

[0067] A method for imaging a sample using a charged particle beam apparatus is provided, according to embodiments that can be combined with other embodiments described herein. The method can be combined with methods for calibrating a charged particle beam apparatus according to embodiments described herein.

[0068] See Figure 1 The method may include arranging a sample on platform 20 of charged particle beam apparatus 100. The sample 10 includes a first surface region 11 to be imaged using charged particle beam apparatus 100. The first surface region 11 is arranged at an unknown distance D from objective lens 150. XThe first surface region 11 may not be positioned within the focusing plane of the objective lens 150. Additionally, the first surface region 11 may not be positioned at a predetermined working distance WD from the objective lens 150. In some embodiments, the method may include configuring the charged particle beam device to operate at an operating point. The operating point may be defined according to the embodiments described herein.

[0069] Figure 7 The illustration shows a flowchart of a method for imaging a sample according to an embodiment described herein. According to the embodiment, the method includes determining a first focusing intensity (block 710) of an objective lens of a charged particle beam apparatus, the first focusing intensity being adapted to focus a charged particle beam 101 onto a first surface region 11 of the sample 10. In the embodiment, the first focusing intensity may be determined manually.

[0070] In some implementations, a variable focus autofocus process is used to determine the first focus intensity. The variable focus autofocus process may include imaging the first surface region 11 with varying focus intensities of the objective lens 150 and analyzing the image sharpness of the acquired images. Optionally, image contrast may be analyzed. For example, the focus intensity of the objective lens 150 can vary between acquired images by changing the focusing current of the objective lens. By optimizing image sharpness, images for each focus intensity can be obtained during an iterative convergence process. The iterative convergence process may include selecting the varying focus intensity based on a golden ratio search method or a Fibonacci search method.

[0071] According to one embodiment, the method includes determining a first focal sub-range of a plurality of focal sub-ranges such that a first focused intensity is achieved within the first focal sub-range (block 720), wherein the plurality of focal sub-ranges are associated with a set of values ​​of calibration parameters. The plurality of focal sub-ranges (specifically, predetermined plurality of focal sub-ranges) can be determined prior to imaging of a sample. Specifically, the plurality of focal sub-ranges can be determined by calibrating a charged particle beam apparatus according to the embodiments described herein.

[0072] In some implementations, each of the plurality of focal sub-ranges may have a calibrated focus intensity. This set of values ​​provides deflection of the charged particle beam such that the field of view at each calibrated focus intensity has the same size. In some implementations, the calibration parameters are deflector parameters. Specifically, the set of values ​​may include a set of deflector current values ​​and / or a set of deflector voltage values.

[0073] According to one embodiment, the method includes determining a first value for a calibration parameter, the first value being associated with a first focal subrange (block 730). For example, the first value could be a first deflector current value or a first deflector voltage value. The first value provides deflection of the charged particle beam, enabling imaging of the sample with predetermined measurement accuracy for any focused intensity within the first focal subrange.

[0074] In one implementation, the method includes imaging a first surface region with a first value (block 740). For example, the first surface region may be imaged by performing one or more of the following: metrology, defect inspection and examination of the characteristics of the sample, and / or measurement (such as critical size measurement).

[0075] See Figure 3C This illustrates an implementation of a method for imaging a sample. Figure 3C In the sample surface 308, a first surface region 11 is positioned along the optical axis of the charged particle beam device. The sample surface 308 may have additional features 311 positioned within the first surface region 11. The first surface region 11 is positioned at an unknown distance D from the objective lens 150. X The charged particle beam 101 is focused onto the first surface region 11 using a first focusing intensity. The first focusing intensity can be determined using a variable focus autofocusing process according to an embodiment described herein. A first focus subrange containing the first focusing intensity is determined from a plurality of focus subranges. A first value is determined from a set of values ​​of calibration parameters, wherein the first value is associated with the first focus subrange. For example, in Figure 3C In this context, the calibration parameters can be deflector parameters, and the first value can be a first deflector current value used to scan deflector 140. The first value can provide a second deflection 344 of the charged particle beam 101, allowing the calibrated field of view 316 to be scanned by the charged particle beam 101. The first surface region 11 can be imaged, for example, by acquiring an image of the calibrated field of view 316. This image can be used, for example, to perform a critical size measurement of another feature 311. The calibrated field of view 316 can have at least substantially the same first field of view 312 as the sample surface 308 positioned at the working distance WD (e.g., as shown in the image). Figure 3A (As shown) the same size. "At least substantially the same size" can be understood as such that the pixel size (nm / pixel) of the acquired image is such that the performed measurement will have inaccuracy within the predetermined measurement accuracy in the calibrated field of view 316 of the image.

[0076] In some implementations, imaging the first surface region may include acquiring a first image of the first surface region using a first value from a set of values. The first value can be used to control the deflection of a charged particle beam during image scanning to acquire the first image. The method may include measuring the size of a first object in the first image. Specifically, the size may be the lateral dimension of the first object. For example, the size may be a critical dimension of the first object. The size may be measured with a predetermined measurement accuracy.

[0077] The embodiments of this disclosure enable accurate measurements in a fast and reliable manner. Specifically, the embodiments offer the advantage that measurements (e.g., critical size measurements) can be performed with predetermined measurement accuracy in surface regions of the sample, wherein the surface regions are located at different distances from the objective plane. More specifically, the focus intensity can be maintained at nm / pixel specifications for multiple focal subranges, specifically without measurement errors exceeding the predetermined measurement accuracy. Imaging the sample using variable focus autofocus processing (specifically for performing accurate measurements) can increase the throughput of metrology, sample inspection, or sample examination.

[0078] According to some embodiments, the method may include adjusting the scanning rotation parameters of the charged particle beam apparatus based on a first focus intensity and a predetermined correlation between the focus intensity and the scanning rotation. The predetermined correlation between the focus intensity and the scanning rotation (also referred to herein as the correlation between focus intensity and scanning rotation) can be determined by calibrating the charged particle beam apparatus according to embodiments described herein. Adjustment of the scanning rotation parameters can be performed before imaging a first surface region using the first value. Adjustment of the scanning rotation parameters can increase the consistency and / or accuracy of the measurement. For example, the measurement can be performed in images of different surface regions of the sample, such that in each image, the scanning direction is perpendicular to the longitudinal direction of a feature on the sample surface.

[0079] According to embodiments that may be combined with other embodiments described herein, the method may include sequentially imaging multiple surface regions of the sample 10. For example, firstly... Figure 1 A first surface region 11 of the sample 10 is imaged, and subsequently, a second surface region 12 of the sample 10, positioned at different levels or heights, is imaged. The surface profile of the sample or non-planar platform surface 13 may not be previously known, such that after imaging the first surface region 11, a second focusing intensity can be determined for focusing the charged particle beam 101 onto the second surface region 12 of the sample 10. According to the embodiments described herein, the method can be performed for each of the second surface region 12 and / or multiple surface regions as for the first surface region 11.

[0080] In some embodiments of this disclosure, which can be combined with other embodiments, the charged particle beam has a landing energy of 5 keV or less (specifically 1 keV or less). Specifically, the charged particle beam 101 impacts the sample with this landing energy. See also Figure 1Objective lens 150 may include a decelerating electric field component 152 configured to slow down the charged particle beam 101 to a landing energy of 5 keV or less. The decelerating electric field component 152 may include decelerating electrodes. Specifically, charged particle beam device 100 may include low-voltage SEM (LV-SEM). Low-energy charged particle beams (specifically low-energy electron beams) do not penetrate deeply into the sample and thus provide excellent, high-quality information about features on the sample surface. Specifically, compared to high-energy electron beams, the advantage of having a landing energy of 5 keV or less (specifically 1 keV or less) is that beam-induced damage and charging from the electron beam impacting the sample are negligible.

[0081] In some embodiments that can be combined with other implementations, the methods for imaging the sample and / or calibrating the charged particle device can be partially or fully automated. Specifically, automated calibration and / or imaging can provide high throughput and / or reduced costs. According to this disclosure, imaging for metrology, inspection, and / or sample examination can be performed on a portion of the sample surface, for example, based on sampling above the sample surface.

[0082] In some embodiments, the charged particle beam device is configured for imaging a sample, the sample comprising a 1m... 2 Large-area substrates for display manufacturing, or even larger ones, with surface areas ranging from approximately 1.375 m². 2 (1100mm x 1250mm - GEN 5) to approximately 9m 2 More specifically from about 2m 2 Approximately 9m 2 Or even as high as 12m 2 For example, the substrate can be GEN 7.5 (corresponding to approximately 4.39 μm). 2 (Surface area of ​​1.95m x 2.25m), GEN 8.5 (corresponding to approximately 5.7m) 2 (surface area of ​​2.2m x 2.5m), or even GEN 10 (corresponding to approximately 9m) 2 (Surface area of ​​2.88m × 3130m). Even larger generations, such as GEN 11 and GEN 12, can be implemented.

[0083] The sample may include a non-flexible substrate (e.g., a glass substrate or glass plate) or a flexible substrate (such as a mesh, foil, or thin glass sheet). The sample may be a coated substrate on which one or more thin material layers or other features are deposited, for example, by physical vapor deposition (PVD), chemical vapor deposition (CVD), photolithography, or etching. Specifically, the sample may be a substrate for display manufacturing on which multiple electronic or optoelectronic devices are formed. The electronic or optoelectronic devices formed on the substrate typically include thin-film devices with stacked thin layers. For example, the sample may be a substrate on which a thin-film transistor (TFT) array is formed, such as a thin-film transistor-based substrate.

[0084] The embodiments described herein specifically relate to imaging a sample, wherein the sample includes a structure formed on a substrate. In some embodiments, the structure may be formed by photolithography and / or etching. The structure may include electronic or optoelectronic devices, such as transistors, specifically thin-film transistors. The sample may include a large-area substrate, specifically a large-area substrate used in display manufacturing, for example, having a 1m² area. 2 Or a larger surface area.

[0085] According to embodiments of this disclosure, a charged particle beam apparatus 100 for imaging a sample 10 includes a platform 20 for arranging the sample 10 to be imaged or for calibrating a sample. The charged particle beam apparatus 100 includes an objective lens 150 configured to focus a charged particle beam 101 propagating along optical axis A. The charged particle beam apparatus 100 includes a computer-readable medium containing a program for imaging the sample, which, when executed by a processor, performs a method according to embodiments described herein, specifically a method for imaging the sample. In some embodiments, the computer-readable medium contains additional program for calibrating the charged particle beam apparatus, which, when executed by a processor, performs a method for calibrating the charged particle beam apparatus 100 according to embodiments described herein.

[0086] In some embodiments, the charged particle beam apparatus includes a controller 160 connected to the charged particle beam apparatus 100. The controller 160 of the charged particle beam apparatus 100 may include a central processing unit (CPU), a computer-readable medium according to embodiments described herein, and, for example, support circuitry. To facilitate control of the charged particle beam apparatus, the CPU may be one of any type of general-purpose computer processor that can be used in industrial settings to control various components and subprocessors. The computer-readable medium is coupled to the CPU. The computer-readable medium or memory may be one or more readily available memory devices, such as random access memory, read-only memory, floppy disk, hard disk, or any other form of digital storage (local or remote). Support circuitry may be coupled to the CPU for conventionally supporting the processor. This circuitry includes cache memory, power supplies, clock circuitry, input / output circuitry and related subsystems, and the like. Instructions for imaging samples and / or for calibrating the charged particle beam apparatus are stored substantially in the computer-readable medium as software routines commonly referred to as recipes. The software routines may also be stored and / or executed by a second CPU located at a remote hardware endpoint controlled by the CPU. When executed by the CPU, the software routines convert a general-purpose computer into a dedicated computer (controller) that controls the charged particle beam apparatus and can provide imaging and / or calibration of the charged particle beam apparatus for any of the embodiments of this disclosure. Although the methods of this disclosure are described as implemented as software routines, some of the method operations disclosed herein can be performed in hardware and by a software controller. Thus, embodiments can be implemented in software when executed on a computer system, in hardware as an application-specific integrated circuit or other type of hardware implementation, or in a combination of software and hardware. The controller can execute or perform methods for imaging samples according to embodiments of this disclosure and / or methods for calibrating the charged particle beam apparatus according to the embodiments described herein.

[0087] According to the embodiments described herein, the methods of this disclosure can be performed using computer programs, software, computer software products, and related controllers, which may have a CPU, a computer-readable medium or memory, a user interface, and input and output devices that communicate with corresponding components of the device.

[0088] The methods described herein allow for the calibration of charged particle beam devices (e.g., scanning electron microscopes) and / or the imaging of samples using charged particle beam devices. The methods described herein provide high or predetermined measurement fidelity. Specifically, the methods allow for imaging of surface regions and / or performing measurements with predetermined measurement accuracy, wherein the surface regions can be located at unknown distances from the objective. Specifically, embodiments can provide corrections for scan deflection or field of view to maintain nm / pixel specifications in image scanning at different focusing intensities. The methods of this disclosure can allow for accurate measurements over a large defocus range (specifically, over a focusing distance range spanning hundreds of micrometers). The embodiments described herein can increase the throughput of metrology, sample inspection, and / or sample examination. Embodiments can provide corrections for scan rotation, specifically for increasing the consistency of measurements in surface regions positioned at different levels relative to the objective. The methods described herein can provide enhanced accuracy for critical size measurements in LV-SEM, specifically for large-area and / or non-planar and / or electrically floating (cannot be brought to a certain potential) samples located on non-planar platforms.

[0089] The methods described herein can be used for process control, for example, for producing flat panels, displays, OLED devices (such as OLED screens), TFT-based substrates, or other samples, including multiple electronic or optoelectronic devices formed thereon. Process control may include periodic monitoring of certain critical dimensions, imaging and / or measurement, and defect inspection.

[0090] While the foregoing relates to some implementations, other and additional implementations may be devised without departing from its basic scope, and the scope of this disclosure is defined by the appended claims.

Claims

1. A method for imaging a sample using a charged particle beam device, comprising the following steps: Determine a first focusing intensity of the objective lens of the charged particle beam device, the first focusing intensity being adapted to focus a charged particle beam on a first surface region of the sample; A first focal subrange is defined among a plurality of focal subranges such that the first focus intensity is within the first focal subrange, wherein the plurality of focal subranges are associated with a set of values ​​of calibration parameters; Determine a first value for the calibration parameter, the first value being associated with the first focal subrange; as well as The first surface region is imaged using the first value. The plurality of focal sub-ranges are determined in the following manner: The first measurement is performed by performing a first measurement of the calibrated object for each of the first plurality of focus intensities; The measurement error is determined by determining the measurement error for each of the first plurality of focus intensities based on the first measurement. as well as The plurality of focal sub-ranges are determined based on the measurement error and the measurement accuracy, such that the error range spanned by the measurement error in each of the plurality of focal sub-ranges is less than or equal to the measurement accuracy.

2. The method according to claim 1, wherein the calibration parameter is a deflector parameter.

3. The method of claim 2, wherein the set of values ​​comprises at least one of a set of deflector current values ​​and a set of deflector voltage values.

4. The method of claim 1, further comprising the following steps: The scanning rotation parameters of the charged particle beam device are adjusted based on the first focusing intensity and based on a predetermined relationship between the focusing intensity and the scanning rotation.

5. The method of claim 1, wherein the first focus intensity is determined by variable focus autofocus processing.

6. The method of claim 5, wherein the variable focus autofocus processing comprises imaging the first surface region using different focusing intensities of the objective lens and analyzing the image sharpness of the obtained image.

7. The method according to any one of claims 1 to 6, wherein imaging the first surface region comprises the following steps: A first image of the first surface region is obtained using the first value; and The method further includes the following steps: Measure the size of the first object in the first image.

8. The method according to any one of claims 1 to 6, wherein the charged particle beam provides landing energy of 5 keV or less.

9. The method according to any one of claims 1 to 6, wherein the sample comprises having a 1m 2 Or larger surface area substrates used for display manufacturing.

10. A method for calibrating a charged particle beam device, comprising the following steps: The first measurement is performed by performing a first measurement of the calibrated object for each of the first plurality of focus intensities; The measurement error is determined by determining the measurement error for each of the first plurality of focus intensities based on the first measurement. Based on the measurement error and measurement accuracy, a plurality of focal sub-ranges are determined such that in each of the plurality of focal sub-ranges, the error range traversed by the measurement error is less than or equal to the measurement accuracy; The second measurement is performed by performing a second measurement of the calibrated object for each of the plurality of focal sub-ranges; as well as A set of values ​​for calibration parameters of the plurality of focal sub-ranges are determined based on the second measurement.

11. The method of claim 10, wherein the calibration parameter is a deflector parameter.

12. The method of claim 11, wherein the set of values ​​comprises at least one of a set of deflector current values ​​and a set of deflector voltage values.

13. The method of claim 10, wherein the calibration further comprises the following steps: Orientation mismatch is determined by determining the orientation mismatch of the scanning rotation of the charged particle beam device relative to the calibration object for each of the second plurality of calibration intensities; and The relationship between focus intensity and scanning rotation is determined based on the directional mismatch and the second plurality of focus intensities.

14. The method of any one of claims 10 to 13, wherein performing at least one of the first measurement and performing the second measurement comprises the step of: bringing the calibration object into the focus of the charged particle beam using a variable distance autofocusing process.

15. The method of claim 14, wherein the variable distance autofocus processing comprises the following steps: The calibration object is imaged at different distances from the objective lens, and the image sharpness of the obtained images is analyzed.

16. The method according to any one of claims 10 to 13, wherein each of the plurality of focal subranges has a calibrated focus intensity for performing the second measurement.

17. The method according to any one of claims 10 to 13, wherein the charged particle beam provides landing energy of 5 keV or less.

18. The method of claim 17, wherein the charged particle beam provides landing energy of 1 keV or less.

19. The method according to any one of claims 10 to 13, wherein the charged particle beam device is configured for imaging a sample, the sample comprising a 1m 2 Or larger surface area substrates used in display manufacturing.

20. A charged particle beam device for imaging a sample, comprising: Platform, the platform being used to arrange the sample to be imaged; An objective lens configured to focus a beam of charged particles propagating along the optical axis; as well as A computer-readable medium containing a program for imaging the sample, which, when executed by a processor, performs the method according to any one of claims 1 to 6.

21. The charged particle beam apparatus of claim 20, wherein the computer-readable medium contains an additional program for calibrating the charged particle beam apparatus, which, when executed by the processor, performs the method according to any one of claims 10 to 13.

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