TWI864777B - Method for calibrating deflectors of a charged particle beam device, and charged particle beam device - Google Patents

Abstract

A method for calibrating deflectors of a charged particle beam device, the deflectors deflecting a charged particle beam of the charged particle beam device based on device coordinates of the charged particle beam device, the method comprising: placing a specimen on a stage in a vacuum chamber, the specimen providing a periodic pattern, the periodic pattern comprising unit cell vectors in specimen coordinates of the specimen; acquiring a first image of a first region of the periodic pattern using the charged particle beam device; determining at least one first local distortion parameter based on the first image; acquiring a second image of a second region of the periodic pattern, the second region being remote from the first region; determining at least one second local distortion parameter based on the second image; determining a first vector in specimen coordinates between the first region and the second region based on the at least one first local distortion parameter and based on the at least one second local distortion parameter; and calibrating the deflectors based on the first vector.

Description

Method for calibrating a deflector of a charged particle beam device, and charged particle beam device

The present disclosure relates to a method for calibrating a deflector of a charged particle beam apparatus. More particularly, embodiments described herein relate to distortion calibration of a charged particle beam apparatus, such as a charged particle beam apparatus of an electron beam system. Further, a charged particle beam apparatus for imaging a sample is described.

In many applications, it is beneficial to inspect samples, such as substrates having structures formed thereon, in particular substrates having electronic or optoelectronic structures formed thereon. For example, samples can be inspected to monitor the quality of the sample, in particular to detect defects that may have occurred during processing of the substrate, for example during structuring or coating of the substrate.

In some applications, thin layers are deposited on substrates, for example on glass substrates or circuit board substrates. The substrate is usually coated in a vacuum chamber of a coating device, in particular using vapor deposition techniques. In the past few years, electronic devices, in particular optoelectronic devices, have been manufactured with an increasing density of structures. For example, for thin film transistor (TFT) displays, a high density of TFT integration is beneficial. Despite the increase in the number and density of structures within the device, the yield has to be increased and the manufacturing costs have to be further reduced.

During the manufacture of electronic or optoelectronic devices, such as displays, the deposited structure of a sample may be imaged to monitor the quality of the sample. For example, imaging of the sample may be accomplished using a charged particle beam device. The deflector of a charged particle beam device is traditionally calibrated using a calibration target having an array of marks arranged at known distances of a few millimeters. However, conventional calibration targets often require expensive, special masks to produce, and may further require special production processes. Furthermore, conventional calibration targets may not be readily available, may not be readily insertable into the system, may require storage space, and/or may not be very accurate. Furthermore, calibration of a deflector based on such a conventional calibration target may be slow and/or inaccurate.

Therefore, in view of the need to improve the quality, inspection and testing of displays or other samples, there is a need for an improved method for calibrating deflectors of charged particle beam equipment with high calibration accuracy and/or high calibration speed.

According to aspects of the present disclosure, a method for calibrating a deflector of a charged particle beam apparatus and a charged particle beam apparatus for imaging a sample are provided. Further aspects, advantages and beneficial features can be seen from the dependent claims, the specification and the accompanying drawings.

According to one aspect, a method for calibrating a deflector of a charged particle beam device is provided, wherein the deflectors deflect the charged particle beam of the charged particle beam device based on the device coordinates of the charged particle beam device. The method includes the following steps: placing a sample on a platform in a vacuum chamber, the sample providing a periodic pattern, the periodic pattern including a unit cell vector in the sample coordinates of the sample. The method includes the following steps: using the charged particle beam device to obtain a first image of a first area of the periodic pattern. The method includes the following steps: determining at least one first local distortion parameter based on the first image. The method further includes the following steps: obtaining a second image of a second area of the periodic pattern, the second area being far away from the first area. The method comprises the steps of determining at least one second local distortion parameter based on the second image. The method further comprises the steps of determining a first vector between the first region and the second region in sample coordinates based on the at least one first local distortion parameter and based on the at least one second local distortion parameter. The method comprises the steps of calibrating the deflectors based on the first vector.

According to another aspect, a charged particle beam device for imaging a sample is provided. The charged particle beam device includes: a platform for arranging the sample to be imaged; and a deflector for deflecting the charged particle beam of the charged particle beam device. The charged particle beam device further includes: a computer-readable medium containing a program for calibrating the deflectors, and when the program is executed by a processor, the method according to the embodiments described herein is executed.

According to another aspect, a method for calibrating a deflector (particularly a sub-deflector and/or a main deflector) of a charged particle beam device is provided, wherein the deflectors deflect the charged particle beam of the charged particle beam device based on the device coordinates of the charged particle beam device. The method comprises the following steps: placing a sample on a platform in a vacuum chamber, the sample providing a periodic pattern, the periodic pattern comprising a unit cell vector in the sample coordinates of the sample. The method comprises the following steps: using the charged particle beam device to obtain a first image of a first region of the periodic pattern. The method further comprises the following steps: determining at least one first local distortion parameter based on the first image, wherein the at least one first local distortion parameter is determined based on a Fourier transform of the first image. The step of determining the at least one first local distortion parameter may comprise the step of performing distribution fitting on at least one portion of the first image in frequency space, in particular distribution fitting based on a Gaussian distribution. The deflectors may be calibrated based on the at least one first local distortion parameter.

Embodiments are also directed to devices for implementing the disclosed methods and include device parts for performing each described method aspect. These method aspects can be performed by hardware components, computers programmed by appropriate software, any combination of the two, or in any other manner. In addition, embodiments according to the present disclosure are also directed to methods for operating the described devices and methods for making the devices and apparatus described herein. The methods for operating the described devices include method aspects for implementing each function of the device.

Reference will now be made in detail to exemplary embodiments, one or more of which are illustrated in the drawings. Each example is provided by way of explanation and is not meant to be limiting. For example, features illustrated or described as part of one embodiment may be used on or with other embodiments to yield further embodiments. The present disclosure is intended to include such modifications and variations.

In the following description of the drawings, the same figure numbers refer to the same parts. Only the differences related to each embodiment are described. The structures shown in the drawings are not necessarily drawn according to the true scale, but are used to better understand the embodiments.

Fig. 1 shows a charged particle beam device 100 configured to operate according to the methods described herein. The charged particle beam device 100 may include a scanning microscope 102, in particular a scanning electron microscope, whose beam source 110 is configured to generate a charged particle beam 101, in particular an electron beam. The charged particle beam 101 may be directed along an optical axis A through a column 103 of the scanning microscope 102. The inner volume of the column 103 may be evacuated. The scanning microscope 102 may include beam influencing elements (such as an accelerator 115, a decelerator, a lens element 120, a deflector 140 or other focusing or defocusing elements), a beam corrector, a beam splitter, a detector and/or other elements provided for influencing the charged particle beam 101 propagating along the optical axis A.

The charged particle beam device 100 includes a platform 20 for placing a sample 10 thereon. The term "sample" used herein may relate to a substrate on which one or more layers, features or electrical devices (such as TFTs) are formed. For example, the sample may be a display, or may include one or more displays. The sample 10 may be placed on the platform 20 for calibrating the charged particle beam device 100, in particular the deflector 140, and/or for imaging the sample 10, for example for testing or examining the sample 10. The platform 20 may be arranged in an imaging chamber 105, which may be evacuated in some embodiments. The platform 20 may be a movable platform. In particular, the platform 20 may be movable in a plane perpendicular to the optical axis A of the charged particle beam device 100 (also referred to herein as the X-Y plane). The platform 20 can move in a direction Z parallel to the optical axis A.

The scanning microscope 102 may include one or more focusing lenses, such as one or more focusing lenses of the lens element 120. The one or more focusing lenses may be configured to focus the charged particle beam 101 onto a sample 10 disposed on the platform 20. When the charged particle beam 101 hits the surface of the sample 10, secondary electrons or backscattered electrons (also referred to as "signal electrons") are generated. The signal electrons provide information about the size, spatial properties and/or other properties of the surface features of the sample 10. The signal electrons can be detected with a detector. By scanning the charged particle beam 101 on the surface of the sample 10 (for example, with a deflector 140) and detecting the signal electrons as a function of the location where the signal electrons are generated, the surface of the sample 10 or a region thereof can be imaged.

In an embodiment, a deflector 140 may be provided for positioning the charged particle beam 101 on the surface of the sample 10 and/or for scanning the charged particle beam 101 on the surface of the sample 10, for example, in the X direction and/or in the Y direction. In some embodiments, the deflector 140 includes a main deflector 142 and an auxiliary deflector 144. For example, the main deflector 142 may be a magnetic deflector. The auxiliary deflector 144 may be an electrostatic deflector. In an embodiment, the main deflector and/or the auxiliary deflector may each include two or more deflectors, particularly for deflecting the charged particle beam 101 to two or more different directions. According to some embodiments, the main deflector 142 may be configured to position the charged particle beam 101 at a specified position in a specified area on the sample 10. The auxiliary deflector 144 or the main deflector 142 can scan the charged particle beam 101 on a specified area, for example, for imaging the specified area or for testing electrical equipment arranged in the specified area. For example, in FIG1 , the charged particle beam 101 is deflected by the main deflector 142 to a first position 16 in a first area 14 of the sample 10, and the first area 14 spans a first scanning range 18. The auxiliary deflector 144 or the main deflector 142 can scan the charged particle beam 101 on the first area 14 by scanning the charged particle beam 101 in the first scanning range 18.

According to some embodiments, the charged particle beam device 100 is configured to review and/or test samples. For example, the sample to be reviewed and/or tested can be a panel level packaging (PLP) substrate or an advanced packaging (AP) substrate, which can be non-contact tested using a charged particle beam to identify and characterize defects, such as short circuits, open circuits and/or leakage. In another example, the sample can be a display, which includes a substrate and a plurality of display pixels arranged thereon. The display pixels can be tested by applying a voltage pattern to the display pixels and then positioning the charged particle beam 101 (particularly an electron beam) to each display pixel. The voltage contrast of the secondary electrons generated by the charged particle beam 101 striking the display pixels can be measured and evaluated. The more negative a display pixel is, the more secondary electrons are emitted. The more positive a display pixel is, the fewer secondary electrons are emitted. Defective display pixels are revealed by showing an incorrect voltage in a voltage contrast image.

However, the review or testing of PLP substrates, AP substrates, displays or other electronic or optoelectronic devices relies on the accurate positioning of the charged particle beam 101 on the deflection area, which can be scanned using the main deflector 142 and the auxiliary deflector 144. In some embodiments, the deflection area can be, for example, larger than 25 square centimeters, in particular larger than 100 square centimeters or larger than 400 square centimeters. In order to achieve accurate positioning of the charged particle beam 101 on the entire deflection area covered by the column 103, a so-called distortion calibration can be performed on the deflector 140. The distortion calibration can provide a two-dimensional (2D) calibration function that converts the deflector digital/analog converter values (D/A converter values) into sample coordinates on the entire deflection area - and vice versa.

As used herein, sample coordinates may refer to the coordinates of the sample 10. Specifically, the sample coordinates may be expressed in terms of a measure of length. The sample coordinates may be particularly specified in units of length, such as micrometers or millimeters. The distance and direction in the sample coordinates may indicate a true distance and a true direction on the sample 10. In an embodiment, the charged particle beam device 100 may locate the charged particle beam 101 based on internal coordinates of the charged particle beam device 100, which are referred to herein as "device coordinates." In an embodiment, the device coordinates may be or may correspond to values of a D/A converter. The device coordinates may be expressed, for example, in pixels of the charged particle beam device. For example, in an image acquired by the charged particle beam device 100, an object having a first shape in the sample coordinates may appear as a distorted second shape in the device coordinates. The distortion of the first shape may include, for example, stretching, rotation and/or tilting of the first shape. Further, the distortion may be different in different regions of the deflection region. The calibration function may take this distortion into account and may provide accurate positioning of the charged particle beam 101 on the deflection region, in particular on the deflection region of the main deflector and/or the auxiliary deflector.

According to an embodiment of the present disclosure, a method for calibrating a deflector 140 of a charged particle beam apparatus 100 (particularly for calibrating a secondary deflector and/or a main deflector of the charged particle beam apparatus 100) is provided. FIG. 2 shows a flow chart of a method 200 according to an embodiment described herein. The charged particle beam apparatus 100 may be configured to deflect a charged particle beam 101 of the charged particle beam apparatus 100 based on the apparatus coordinates of the charged particle beam apparatus 100.

In an embodiment, the method 200 includes the following steps: placing a sample 10 on a platform 20 in a vacuum chamber (box 210). The sample 10 provides a periodic pattern 12. In some embodiments, the sample 10 includes a substrate 11 and an array of electrical devices formed on the substrate 11. For example, the sample 10 can be a display, which includes a glass substrate and display pixels formed thereon, and the display pixels particularly include TFTs. The periodic pattern 12 can be provided by applying a voltage pattern to the array of electrical devices. In particular, the periodic pattern 12 can be provided by applying a first voltage to a first group of electrical devices and applying a second voltage to a second group of electrical devices, the second voltage being different from the first voltage. Additionally or alternatively, the periodic pattern may be provided by periodically arranged structures on the substrate. In images acquired using the charged particle beam apparatus 100, the structures may show different material contrasts or different topographic contrasts. For example, these structures may include lithographically generated, high-resolution patterns on the substrate, particularly permanent patterns. More specifically, the structures of the pattern may not be electrically addressable.

FIG3 shows a periodic pattern 12 of a sample 10, wherein the sample 10 includes a display. The display may include display pixels 410, such as shown in FIG4. The display pixels 410 shown in FIGS. 3 and 4 may be similar or identical in structure. The periodic pattern 12 may be provided by applying a voltage pattern to the display pixels 410 of the sample 10. More specifically, a positive voltage may be applied to the display pixels of the first group 310, and a negative voltage may be applied to the display pixels of the second group 320. In FIG3, the voltage pattern is applied according to a checkerboard pattern. In further embodiments, the voltage pattern may be applied according to different periodic patterns.

In an embodiment of the present disclosure, the periodic pattern 12 has unit cell vectors e, f in the sample coordinates x, y of the sample 10, in particular, the unit cell vectors e, f of the original unit cell of the periodic pattern 12. For example, FIG. 3 shows the unit cell vectors e, f of the periodic pattern 12, including a first unit cell vector e=(e _x , e _y ) and a second unit cell vector f=(f _x , f _y ) in the sample coordinates x, y. In an embodiment, the length of each unit cell vector e, f of the periodic pattern 12 is at most 2 mm, in particular at most 1.5 mm or at most 1 mm. In some embodiments, the length of each unit cell vector e, f of the periodic pattern 12 can be at least 500 nanometers, in particular at least 1 micrometer or at least 5 micrometers.

According to an embodiment, the method 200 comprises the following steps: obtaining a first image 500 of a first region 14 of a periodic pattern 12 using a charged particle beam device 100 (box 220). In particular, the charged particle beam 101 may be deflected to a first position 16 of the first region 14 using a main deflector 142. The first image 500 may be obtained by scanning the charged particle beam 101 over the first region 14. In some embodiments, the charged particle beam 101 may be scanned over the first region 14 using the main deflector 142, in particular for calibrating the main deflector 142. In further embodiments, which may be combined with other embodiments described herein, the charged particle beam 101 may be scanned over the first region 14 using the auxiliary deflector 144, in particular for calibrating the auxiliary deflector 144. In an embodiment, the first image includes at least two unit cells of the periodic pattern 12, in particular at least four unit cells or at least eight unit cells.

In some embodiments, particularly if the periodic pattern 12 is provided by applying a voltage pattern, the first image can be obtained by voltage contrast imaging. In voltage contrast imaging, the voltage contrast of secondary electrons generated by the charged particle beam 101 that strikes the periodic pattern 12 is measured and evaluated to obtain an image such as the first image 500. For example, FIG5 illustrates a first image 500 of the first region 14 of the periodic pattern 12 shown in FIG3. The periodic pattern 12 provided by the voltage pattern can be observed by voltage contrast imaging of the display pixel 410. The more negative the voltage of the display pixel 410, the more secondary electrons are emitted. The more positive the voltage of the display pixel 410, the fewer secondary electrons are emitted. The first image 500 shows the periodic pattern 12 in the device coordinates s, t, wherein the periodic pattern 12 is distorted. In further embodiments, other imaging techniques (such as conventional SEM imaging, in particular without applying different voltages to the sample) may be used to obtain the first image of the periodic pattern. For example, if the periodic pattern is provided by structures on the substrate, where these structures are not electrically addressable or cannot be electrically addressable, then conventional imaging methods may be used.

In an embodiment, the method 200 includes the following steps: determining at least one first local distortion parameter based on the first image 500 (box 230). The at least one first local distortion parameter can indicate the distortion of the periodic pattern 12 in the first image 500. According to some embodiments, the at least one first local distortion parameter includes a first local distortion matrix U. The first local distortion matrix U can provide a local transformation between sample coordinates x, y and device coordinates s, t, especially for the first image 500. In the first image 500, the imaged periodic pattern can have image cell vectors u=( _us , _ut ) and v=( _vs , _vt ), for example as shown in Figure 5. In an embodiment, the first local distortion matrix U may in particular provide a conversion between cell vectors e, f in sample coordinates x, y and image cell vectors u, v in device coordinates s, t, for example according to equation 1. The cell vectors e, f of the periodic pattern 12 may be known, for example from the manufacture of the sample 10. The image cell vectors u, v may be determined based on the first image 500, in particular according to the embodiments described herein. (Equation 1)

In some embodiments, the at least one first local distortion parameter is determined based on a Fourier transform of the first image 500. The Fourier transform may be a fast Fourier transform. The Fourier transform may be a discrete Fourier transform. The Fourier transform may be a two-dimensional (2D) Fourier transform of the first image 500. For example, the Fourier transform may be a 2D fast Fourier transform. For example, the Fourier transform may be determined according to Equation 2 using an image resolution N, using k, l = 0, 1 ... N-1, and using an image gray level g. (Equation 2)

The periodic pattern 12 (particularly the image cell vectors u, v) is reflected by the peaks in the amplitude R := |F| of the Fourier transform F, more particularly by the peaks at the peak positions a, b, where a = ( _ak , a _l ) and b = (b _k , b _l ). In an embodiment, the image cell vectors u, v can be determined based on the Fourier transform of the first image 500. Determining the image cell vectors u, v can include determining the peak positions a, b in the frequency space of the Fourier transform of the first image 500. The peak positions a, b can be defined as vectors pointing to the peaks 620 in the Fourier transform, particularly the vectors from the central peak 610 to the two peaks 620 closest to the central peak 610. For example, FIG. 6 illustrates the amplitude R of the Fourier transform in the frequency space coordinates k, l. The Fourier transform includes the central peak 610. Each vector corresponding to the peak position a, b points to a peak 620 that is closest to the central peak 610. Due to symmetry reasons, it may be sufficient to determine two peak positions a, b.

According to some embodiments, determining the at least one first local distortion parameter includes performing distribution fitting on at least a portion of the first image 500 in frequency space. In particular, peaks 620 closest to a central peak 610 of the Fourier transform of the first image 500 may be fitted using a distribution. In some embodiments, each peak 620 may be fitted by fitting a peak value 705 of the peak 620 and neighboring values of the peak 620 (e.g., peak value 705 and eight neighboring values 710). The maximum value determined by distribution fitting and Can be used as peak positions a, b. Distribution fitting can especially provide a more accurate determination of peak positions a, b.

In some embodiments, the distribution fitting is based on a Gaussian distribution, in particular a two-dimensional Gaussian distribution. In particular, the peak 620 can be fitted using a Gaussian distribution to determine the maximum value a ⁰ , b ⁰ of the peak 620. For example, FIG. 7 illustrates a peak 705 and eight neighboring values 710 of the peak 705 corresponding to the peak position a of FIG. 6 fitted in frequency space using a Gaussian distribution. In particular, the two-dimensional Gaussian distribution R(k, l) can be fitted to the data values using parameters c ₁ , c ₂ , c ₃ , k ₀ and l ₀ to determine the location of the peak maximum value a=(k ₀ , l ₀ ). For example, Equation 3 provides a two-dimensional Gaussian distribution. If the peaks in the Fourier transform do not have a minimum height, then the parameter _c1 can be used to identify images without periodic patterns. (Equation 3)

According to an embodiment, the image cell vectors u and v of the first image 500 may be determined based on the peak positions a and b, for example, according to Equation 4. For example, the cell vectors u and v shown in FIG5 may be determined based on the peak positions a and b determined in the frequency space. (Equation 4)

Based on the cell vectors e, f and on the image cell vectors u, v, a first local distortion matrix U can be determined, in particular according to equation 5. (Equation 5)

The at least one first local distortion parameter (in particular the first local distortion matrix U) can be used for local distortion calibration. The local distortion calibration can be used to calibrate the secondary deflector 144 , in particular for the first region 14 .

In order to calibrate the deflector 140 (particularly the main deflector 142) for other regions of the deflection area (particularly the entire deflection area) of the main deflector 142 and the auxiliary deflector 144, a global distortion calibration can be performed. Performing the global distortion calibration can include performing additional local distortion calibration on other regions of the periodic pattern in the deflection area. The global distortion calibration can further include determining vectors between regions that have been subjected to local distortion calibration.

In some embodiments, the method 200 includes the following steps: obtaining a second image 810 of a second region 910 of the periodic pattern 12 (box 240). The first region 14 and the second region 910 are regions of the periodic pattern 12 displayed in the first image 500 and the second image 810, respectively. The second region 910 can be far away from the first region 14. In particular, the first region 14 and the second region can be non-intersecting regions of the periodic pattern 12. The first region 14 and the second region can be non-overlapping regions, and can also be non-adjacent regions of the periodic pattern 12. The charged particle beam 101 can be deflected to a second position of the second region 910 using the main deflector 142, and the second position is different from the first position 16. The second image 810 can be obtained by scanning the charged particle beam 101 over the second area 910 (particularly scanning using the main deflector 142). In an embodiment, the second image 810 includes at least two cells of the periodic pattern 12, particularly at least four cells or at least eight cells.

According to an embodiment of the present disclosure, the method 200 comprises the step of determining at least one second local distortion parameter based on the second image 810 (block 250). The at least one second local distortion parameter may be determined based on the second image 810 similarly to the determination of the at least one first local distortion parameter based on the first image 500. In particular, the at least one second local distortion parameter may be determined based on a Fourier transform of the second image 810. The step of determining the at least one second local distortion parameter may comprise the step of performing a distribution fit on at least one portion of the second image in frequency space, in particular using a Gaussian distribution.

In some embodiments, the at least one second local distortion parameter includes a second local distortion matrix U′. The second local distortion matrix U′ may provide a local transformation between sample coordinates and device coordinates, particularly for the second image 810 and the second region 910.

According to some embodiments, the method 200 includes the step of determining a first vector d _g ′ between the first region 14 and the second region 910 in the sample coordinates based on the at least one first local distortion parameter and based on the at least one second local distortion parameter (block 260). The first vector d _g ′ may connect the first location 16 where the first image 500 was acquired to the second location where the second image 810 was acquired. In an embodiment, the first vector d _g ′ in the sample coordinates x, y may correspond to an image connection vector d _g in the device coordinates s, t, the image connection vector d _g connecting the first image 500 and the second image 810. For example, the image connection vector d _g may connect the center of the first image 500 to the center of the second image 810.

Figures 8 and 9 schematically illustrate the determination of the first vector _dg ' according to an embodiment. Figure 8 illustrates a first image 500 of a first region 14 of a periodic pattern 12 and a second image 810 of a second region 910 of the periodic pattern 12. The image connection vector _dg connects the center of the first image 500 and the center of the second image 810 in device coordinates s, t. In an embodiment, the image connection vector _dg is predetermined or can be calculated based on the first position and the second position in the device coordinates s, t. Figure 9 schematically shows a periodic pattern 12 in sample coordinates x, y, the periodic pattern including the first region 14 and the second region 910. Figure 9 shows the first vector _dg ' in the sample coordinates x, y, which corresponds to the image connection vector _dg in the device coordinates s, t.

According to an embodiment, determining the first vector d _g ′ comprises determining an approximate first vector d _g0 ′ based on the first local distortion matrix U, based on the second local distortion matrix U′ and based on the image connection vector d _g . In particular, the approximate first vector d _g0 ′ may be determined based on an average value of the first local distortion matrix U and the second local distortion matrix U′, in particular according to Equation 6. (Equation 6)

In an embodiment, the first vector d _g ' may be further determined more accurately than the approximate first vector d _g0 '. In particular, the distortion may vary along the image connection vector d _g . The first vector d _g ' may be more accurately determined based on the periodicity of the periodic pattern 12. In an embodiment, the first vector d _g ' is further determined based on the unit cell vectors e, f of the periodic pattern 12. Determining the first vector d _g ' based on the periodic pattern 12 may particularly include determining a shift vector indicating a shift or offset between the periodic pattern 12 and each of the first image 500 and the second image 810.

According to an embodiment, the at least one first local distortion parameter includes a first shift vector _s1 . The first shift vector _s1 may indicate a first offset between the periodic pattern 12 and the first image 500. For example, the first shift vector _s1 may indicate an offset between a pattern reference point of the periodic pattern 12 and an image reference point of the first image 500. The pattern reference point may be a reference point of a unit cell of the periodic pattern 12, in particular a feature point of the unit cell. For example, in FIG. 8 , the pattern reference point is a corner of a rectangle in a chessboard pattern. The image reference point of the first image 500 may be, for example, the center of the first image 500. In an embodiment, the first shift vector _s1 may be determined based on a Fourier transform of the first image 500. The displacement of the image s = (s _s , s _t ) (in device coordinates s, t) changes the phase φ of the Fourier transform F =: R·e ^{‑i φ} by Δφ, in particular according to Equation 7. (Equation 7)

By defining the phase φ of the Fourier transform F as caused by the shift s, the shift s can be calculated from the phase φ of the peaks a, b in the Fourier transform. In particular, the shift s can be calculated from the phase φ of the peaks a, b (see equations 8 and 9), where the maximum value of the peak 620 determined by the distribution fit in frequency space is and is used as the peak position a, b. The shift s can be calculated according to Equation 10. (Equation 8) (Equation 9) (Equation 10)

For example, the first shift vector s ₁ may be calculated as the shift s of the first image 500 .

According to an embodiment, the at least one second local distortion parameter includes a second shift vector _s2 . The second shift vector _s2 may indicate a second shift or offset between the periodic pattern 12 and the second image 810. The second shift vector _s2 may be calculated based on the second image 810, similar to the calculation of the first shift vector _s1 based on the first image 500. In particular, the second shift vector _s2 may be calculated as a shift s of the second image 810.

A first shift vector s ₁ in device coordinates s, t can be converted into a transformed first shift vector s ₁ ' in sample coordinates x, y, in particular based on the first local distortion matrix U by s ₁ '=U ^-1 ·s ₁ . Similarly, a second shift vector s ₂ in device coordinates s, t can be converted into a transformed second shift vector s ₂ ' in sample coordinates x, y, in particular based on the second local distortion matrix U' by s ₂ '=U' ^-1 ·s ₂ .

The vector addition of the first shift vector s ₁ , the image connection vector d _g and the second shift vector s ₂ may provide a vector _du in device coordinates s, t, where the vector _du points from a pattern reference point of the first image 500 to another pattern reference point of the second image 810, as shown, for example, in FIG8 . Similar to the vector _du in device coordinates s, t, the reference vector _du ' in sample coordinates x, y connects two reference points of the periodic pattern 12, as shown, for example, in FIG9 . The reference vector du _' =(d _ux ', d _uy ') must be an integer i, j times the unit cell vector e, f (see Equation 11) because each of the transformed first shift vector s ₁ ' and the transformed second shift vector s ₂ ' points to a pattern reference point of the unit cell. (Equation 11)

The approximate reference vector d _u0 ′ = d _g0 ′ + s ₂ ′ − s ₁ ′ can be determined based on the approximate first vector d _g0 ′ and the shift vectors s ₂ ′ and s ₁ ′. As an approximation to integers, non-integer numbers i _r and j _r can be determined based on the approximate reference vector d _u0 ′, for example according to Equation 12. (Equation 12)

Next, the integers i, j can be determined by rounding the non-integers i _r and j _r , respectively. Based on the integers i, j corresponding to the reference vector _du ', the first vector d _g ' can be determined by vector addition, in particular according to equation 13. (Equation 13)

According to an embodiment, the method includes the following steps: calibrating the deflector based on the first vector _dg ' (box 270). In an embodiment, the first vector _dg ' provides the accurate relative position of the second image 810 relative to the first image 500 in the sample coordinates x, y. The first vector _dg ' and the corresponding image connection vector _dg can be used to determine the relationship between the sample coordinates x, y and the device coordinates s, t. The determined relationship can be used, for example, to determine a calibration function or a calibration lookup table. Further, one or more local distortion parameters can be interpolated for the area between the first area 14 and the second area 910. In some embodiments, the local distortion matrix can be interpolated for any area between the first area 14 and the second area 910 based on the first local distortion matrix U and the second local distortion matrix U'.

In an embodiment, the method 200 further comprises the step of determining a plurality of other vectors in the sample coordinates x, y based on other images of non-intersecting regions of the periodic pattern 12. According to an embodiment, the first image 500, the second image 810 and the other images are acquired at the grid position 1010, in particular at the grid position 1010 in the device coordinates s, t.

In embodiments, the distance between a first position of the first image and a second position of the second image and/or the distance between the grid positions may be selected such that the absolute deviation of the non-integer numbers i _r and j _r from the corresponding integer numbers i, j remains small, for example less than 0.3 or less than 0.2. In the event of larger absolute deviations, a smaller distance between the positions in the device coordinates s, t may be selected for calibration. In some embodiments, the distance between the positions in the sample coordinates x, y may be greater than 1 mm, in particular greater than 2 mm or greater than 3 mm. For example, the distance may be about 5 mm.

Determining each of the plurality of other vectors may include determining at least one other local distortion parameter based on one of the other images. The at least one other local distortion parameter for the other images may be determined similarly to determining the at least one first local distortion parameter for the first image 500. Based on the at least one other local distortion parameter and based on the at least one previously determined local distortion parameter, the other vectors of the plurality of other vectors may be determined. Each of the plurality of other vectors may be determined similarly to determining the first vector d _g '.

For example, a second vector of the plurality of other vectors may be determined in accordance with the operations outlined with respect to blocks 240, 250, 260 of method 200. In particular, after determining the first vector _dg ', a third image may be acquired at a grid location 1010 remote from the second location. At least one third local distortion parameter may be determined based on the third image. The second vector may be determined based on the at least one second local distortion parameter associated with the second image 810, and further determined based on the at least one third local distortion parameter.

According to some embodiments, the first position for acquiring the first image may be the center position of the grid position 1010. Subsequent images may be acquired at grid positions adjacent to the grid position 1010. For example, the first image, the second image, and the other images may be acquired along the grid positions, particularly starting from the center position, following a square spiral path 1020, such as shown in FIG.

In an embodiment, the method 200 includes the step of calibrating the deflector 140 based on the plurality of other vectors, in particular based on the first vector _dg ' and the plurality of other vectors. For example, FIG11 illustrates positions in sample coordinates x, y corresponding to the grid positions 1010 shown in FIG10. Graphs based on FIGS10 and 11 allow for determining a calibration function or calibration lookup table that relates the grid positions 1010 in device coordinates s, t (FIG10) to the corresponding positions 1110 in sample coordinates x, y (FIG11), and vice versa.

In particular, based on the relationship between the device coordinates s, t and the specimen coordinates x, y, the inverse of the distortion correction function can be determined, which provides the deflector D/A converter values in the device coordinates s, t as a function of the specimen coordinates x, y. For example, FIG. 12 illustrates a plurality of D/A converter values in the device coordinates s, t corresponding to a plurality of equally spaced grid positions in the specimen coordinates x, y.

Further, the local distortion matrix determined for grid position 1010 may be interpolated between grid positions 1010. For example, FIG13 illustrates an example of a distortion calibration result based on calibration using a display to provide a periodic pattern. In particular, FIG13 shows a matrix element _U1 of a local distortion matrix determined at grid position 1010 and interpolated between grid positions 1010. In contrast, FIG14 illustrates an example of a matrix element _U1 determined based on a previous calibration technique based on calibration using L-shaped markers spaced approximately 5 mm apart. In particular, deflector calibration based on a local distortion matrix determined according to the embodiments described herein ( FIG. 13 ) can be more accurate and show less noise than deflector calibration according to previous calibration techniques ( FIG. 14 ). Main deflector calibration according to the embodiments described herein can provide, in particular, more reliable calibration. In particular, manual corrections can be reduced or avoided. Furthermore, calibration of the auxiliary deflector can be performed approximately 10 times faster than previous calibration techniques.

According to a further embodiment, a method for calibrating a deflector 140, in particular a sub-deflector 144, of a charged particle beam device 100 is provided. The method may include any of the operations of the method 200 described herein, in particular the operations described with respect to blocks 210, 220, and 230 of the method 200. The method may further include the step of calibrating the deflector 140, in particular the sub-deflector 144, based on the at least one first local distortion parameter. For example, the sub-deflector 144 may be calibrated based on a first local distortion matrix determined for the acquired first image 500.

In some embodiments, which may be combined with other embodiments, a method for calibrating one or more deflectors of a charged particle beam device can be partially or fully automated. In particular, automated calibration and/or imaging can provide high throughput and/or reduce costs.

According to some embodiments, a charged particle beam device can be used or configured to image, test and/or review a packaging substrate (such as a PLP substrate or an AP substrate). Over the years, the complexity of packaging substrates has been increasing in order to reduce the space requirements of semiconductor packages. In order to reduce manufacturing costs, some packaging technologies have been proposed, such as 2.5D IC, 3D-IC and wafer-level packaging (WLP), such as fan-out WLP. In WLP technology, integrated circuits are packaged before being cut. The "packaging substrate" used in this article relates to a packaging substrate configured for use with advanced packaging technology, particularly WLP technology or panel-level packaging (PLP) technology.

"2.5D integrated circuits" (2.5D ICs) and "3D integrated circuits" (3D ICs) combine multiple dies in a single integrated package. Here, two or more dies are placed on a package substrate, such as a silicon interposer or a panel-level package substrate. In 2.5D ICs, the dies are placed side by side on the package substrate, while in 3D ICs, at least some of the dies are placed on top of other dies. The assembly can be packaged as a single part, which can reduce cost and size compared to traditional 2D circuit board assemblies.

The package substrate typically includes a plurality of device-to-device electrical interconnect paths for providing electrical connections between chips or dies to be placed on the package substrate. The device-to-device electrical interconnect paths may extend vertically (perpendicular to the surface of the package substrate) and/or horizontally (parallel to the surface of the package substrate) through the body of the package substrate and through terminals exposed at the surface of the package substrate (referred to herein as surface contacts) in a complex network of connections.

An advanced packaging (AP) substrate provides electrical interconnect paths between devices on or within a wafer such as a silicon wafer. For example, an AP substrate may include through silicon vias (TSVs) (which are provided in a silicon interposer, for example), other conductive lines extending through the AP substrate. A panel-level packaging substrate is provided by a composite material, such as a printed circuit board (PCB) material or another composite material, including, for example, ceramic and glass materials.

A manufactured panel-level package substrate is configured to integrate multiple devices (e.g., chips/dies that may be heterogeneous (e.g., may have different sizes and configurations)) in a single integrated package. Further, an AP substrate can be combined on a PLP substrate. A panel-level substrate typically provides sites for multiple chips, dies, or AP substrates placed on its surface (e.g., on one or both sides thereof), as well as electrical interconnect paths between multiple devices extending through the body of the PLP substrate.

It is worth noting that the size of the panel-level substrate is not limited to the size of the wafer. For example, the panel-level substrate can be rectangular or have another shape. Specifically, the panel-level substrate can provide a larger surface area than the surface area of a typical wafer, for example, 1000 cm² or more. For example, the size of the panel-level substrate can be 30 cm x 30 cm or more, 60 cm x 30 cm or more, 60 cm x 60 cm or more.

In some embodiments, the charged particle beam apparatus is configured to image and/or calibrate with a sample, including a large area substrate for display manufacturing, having a surface area of 1 m² or greater. The surface area can be from about 1.375 ^m2 (1100 mm×1250 mm—GEN 5) to about 10 ^m2 , more specifically, from about 2 ^m2 to about 10 ^m2 , or even up to 12 ^m2 . For example, the substrate may be GEN 7.5 (corresponding to a surface area of approximately 4.39 m² (1.95 m x 2.25 m)), GEN 8.5 (corresponding to a surface area of approximately 5.7 m² (2.2 m x 2.5 m)) or even GEN 10.5 (corresponding to a surface area of approximately 10 m² (2.95 m x 3.37 m)). Even larger generations (such as GEN 11 and GEN 12) may be implemented.

The sample may comprise a non-flexible substrate such as a glass substrate or a glass plate or a flexible substrate such as a web or foil or a thin sheet of glass. The sample may be a coated substrate on which one or more thin layers of material or other features are deposited, for example by a physical vapor deposition (PVD) process or a chemical vapor deposition process (CVD) or a lithographic process or an etching process. In particular, the sample may comprise a substrate for display manufacturing and a plurality of electronic or optoelectronic devices formed thereon. The electronic or optoelectronic devices formed on the substrate are typically thin film devices comprising a stack of thin layers. For example, the sample may be a substrate on which an array of thin film transistors (TFTs) are formed, for example, a substrate based on thin film transistors.

According to an embodiment of the present disclosure, a charged particle beam apparatus 100 for imaging a sample 10 includes a platform 20 for arranging the sample 10 to be imaged. The charged particle beam apparatus 100 may further include one or more deflectors 140 for deflecting a charged particle beam 101 of the charged particle beam apparatus 100. In an embodiment, the charged particle beam apparatus 100 includes a computer-readable medium, which contains a program for calibrating the one or more deflectors 140, and when the program is executed by a processor, the method according to the embodiment described herein is executed, in particular, the method for calibrating the one or more deflectors of the charged particle beam apparatus 100. Charged particle beam apparatus 100 may be configured to image sample 10 based on calibration performed according to the methods described herein.

In some embodiments, the charged particle beam apparatus 100 includes a controller 160, which is connected to the charged particle beam apparatus 100 (see, for example, FIG. 1). The controller 160 of the charged particle beam apparatus 100 may include a central processing unit (CPU), a computer-readable medium according to the embodiments described herein, and, for example, support circuits. To facilitate control of the charged particle beam apparatus 100, the CPU may be one of any form of general-purpose computer processors that can be used in an industrial environment 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 accessible memory devices, such as random access memory, read-only memory, a hard disk, or any other form of local or remote digital storage. Support circuits may be coupled to the CPU for supporting the processor in a conventional manner. Support circuits include caches, power supplies, clock circuits, input/output circuitry and associated subsystems, and the like. Instructions for calibrating the one or more deflectors 140 of the charged particle beam apparatus 100 are typically stored in a computer-readable medium as software routines, commonly referred to as recipes. Software routines may also be stored and/or executed by a second CPU that is remote from the hardware controlled by the CPU. The software routine, when executed by the CPU, transforms the general purpose computer into a special purpose computer (controller) that controls the charged particle beam apparatus 100 and is capable of calibrating the one or more deflectors 140 of the charged particle beam apparatus 100 according to any embodiment of the present disclosure. Although the methods of the present disclosure are discussed as being implemented as software routines, some of the method operations disclosed therein may also be implemented in hardware and by a software controller. Thus, the embodiments may be implemented in software when executed on a computer system, in hardware as a special application integrated circuit or other type of hardware implementation, or in a combination of software and hardware. The controller 160 may execute (or perform) a method for calibrating one or more deflectors of a charged particle beam apparatus according to embodiments described herein.

According to the embodiments described herein, the methods of the present disclosure may be performed using computer programs, software, computer software products, and interrelated 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.

Methods according to embodiments described herein may be used to calibrate charged particle beam equipment for process control (e.g., for producing packaging substrates, such as PLP substrates or AP substrates, flat panels, displays, OLED devices (such as OLED screens), TFT-based substrates, and/or other samples on which a plurality of electronic or optoelectronic devices are formed). Process control may include, for example, periodic monitoring, imaging, and/or defect review.

Embodiments of the present disclosure can advantageously provide faster and/or more accurate calibration of one or more deflectors of a charged particle device, such as a scanning electron microscope. Further, calibration according to embodiments can be performed without conventional calibration plates, which can be expensive, can require storage space, and/or can require the production of special masks. For example, calibration according to embodiments can be performed using a sample comprising a substrate having an accurate, high-resolution periodic pattern. Such a sample can be readily available or can be produced using an existing mask, such as a mask used to manufacture electronic or optoelectronic devices. In some embodiments, the sample used for calibration can be a sample to be tested or reviewed, such as a display.

While the foregoing is directed to certain embodiments, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims which follow.

10: sample 11: substrate 12: periodic pattern 14: region 16: position 18: scanning range 20: platform 100: charged particle beam device 101: charged particle beam 102: scanning microscope 103: column 105: imaging chamber 110: beam source 115: accelerator 120: lens element 140: deflector 142: main deflector 144: auxiliary deflector 160: controller 200: Method 210: Box 220: Box 230: Box 240: Box 250: Box 260: Box 270: Box 310: Group 320: Group 410: Display pixel 500: Image 610: Center peak 620: Peak 705: Peak value 710: Value 810: Image 910: Region 1010: Grid position 1020: Path 1110: Position A: Axis a: Peak position b: Peak position d _g : Vector d _g ': Vector d _u : Vector d _u ': Vector e: Cell vector f: Cell vector s ₁ ': Shift vector s ₂ : Shift vector s ₂ ': Shift vector u: Image cell vector v: Image cell vector

The disclosure that fully and enablingly enables one of ordinary skill in the art is set forth in the remainder of the specification including references to the accompanying drawings.

FIG1 shows a charged particle beam apparatus configured to operate according to the methods described herein;

FIG2 is a flow chart illustrating a method for calibrating a deflector of a charged particle beam apparatus according to an embodiment described herein;

FIG3 schematically illustrates the periodic pattern provided by the sample in sample coordinates;

FIG4 shows a schematic diagram of a display pixel array of a display used as a sample for calibrating a charged particle beam apparatus;

FIG5 shows a first image of the periodic pattern of FIG3 in device coordinates;

FIG6 illustrates a portion of the Fourier transform of an image of a periodic pattern;

FIG7 shows the distribution fitting of the peak value of the Fourier transform of FIG6;

FIG8 schematically illustrates a first image and a second image;

FIG. 9 is a schematic diagram showing a portion of a periodic pattern and vectors used to determine a first vector according to an embodiment described herein;

FIG10 illustrates the grid locations in device coordinates for acquiring images of periodic patterns;

Figure 11 shows the locations in the specimen coordinates, which correspond to the grid locations in Figure 10;

FIG12 illustrates the deflector digital/analog (D/A) converter values in device coordinates for a plurality of grid locations in specimen coordinates;

FIG. 13 shows calibration results based on calibration according to embodiments described herein; and

FIG. 14 illustrates the calibration results based on calibration according to previous calibration techniques.

Domestic storage information (please note the order of storage institution, date, and number) None

Overseas storage information (please note the order of storage country, institution, date, and number) None

10: Samples

11: Substrate

12: Periodic patterns

14: Region

16: Location

18: Scanning range

20: Platform

100: Charged particle beam equipment

101: Charged particle beam

102: Scanning microscope

103: Pillar

105: Imaging chamber

110: beam source

115: Accelerator

120: Lens element

140: Deflector

142: Main deflector

144: Auxiliary deflector

160: Controller

A: Optical axis

Claims (17)

A method for calibrating a deflector of a charged particle beam device, wherein the deflectors deflect a charged particle beam of the charged particle beam device based on the device coordinates of the charged particle beam device, the method comprising the following steps: placing a sample on a platform in a vacuum chamber, the sample providing a periodic pattern, the periodic pattern comprising unit cells in the sample coordinates of the sample cell) vector; using the charged particle beam device to obtain a first image of a first region of the periodic pattern; determining at least one first local distortion parameter based on the first image; obtaining a second image of a second region of the periodic pattern, the second region being away from the first region; determining at least one second local distortion parameter based on the second image; determining a first vector between the first region and the second region in the sample coordinates based on the at least one first local distortion parameter and based on the at least one second local distortion parameter; and calibrating the deflectors based on the first vector; wherein the at least one first local distortion parameter is determined based on a Fourier transform of the first image; and wherein the at least one second local distortion parameter is determined based on a Fourier transform of the second image. The method as claimed in claim 1, wherein the first vector is further determined based on the unit cell vectors of the periodic pattern. The method of claim 1, wherein the step of determining the at least one first local distortion parameter comprises the following steps: performing distribution fitting on at least one portion of the first image in frequency space; and wherein the step of determining the at least one second local distortion parameter comprises the following steps: performing distribution fitting on at least one portion of the second image in frequency space. A method as claimed in claim 3, wherein the distribution fitting is based on a Gaussian distribution. The method of claim 1, wherein the at least one first local distortion parameter comprises a first local distortion matrix, wherein the at least one second local distortion parameter comprises a second local distortion matrix, and wherein each of the first local distortion matrix and the second local distortion matrix provides a local transformation between the sample coordinates and the device coordinates. A method as claimed in any one of claims 1 to 5, wherein the at least one first local distortion parameter comprises a first shift vector indicating a first offset between the periodic pattern and the first image; and wherein the at least one second local distortion parameter comprises a second shift vector indicating a second offset between the periodic pattern and the second image. A method as claimed in any one of claims 1 to 5, wherein the deflectors include a main deflector and a secondary deflector. The method of claim 7, wherein each of the first image and the second image is obtained by scanning the charged particle beam using the main deflector. A method as described in claim 7, wherein the main deflector is used to deflect the charged particle beam to a first position to obtain the first image; and wherein the main deflector is used to deflect the charged particle beam to a second position to obtain the second image. A method as claimed in any one of claims 1 to 5, wherein each of the unit cell vectors of the periodic pattern has a length of at most 2 mm. A method as described in any one of claims 1 to 5, wherein each of the first image and the second image includes at least two cells of the periodic pattern. A method as claimed in any one of claims 1 to 5, wherein each of the first image and the second image includes at least four cells. A method as claimed in any one of claims 1 to 5, wherein the sample comprises a substrate and an array of electrical devices formed on the substrate, and wherein the periodic pattern is provided by applying a first voltage to a first group of the electrical devices and applying a second voltage to a second group of the electrical devices, the second voltage being different from the first voltage. The method as claimed in any one of claims 1 to 5 further comprises the following steps: determining a plurality of other vectors in the sample coordinates based on other images of non-intersecting regions of the periodic pattern, wherein the step of determining each of the plurality of other vectors comprises the following steps: determining at least one other local distortion parameter based on one of the other images; determining the other vector based on the at least one other local distortion parameter and based on at least one previously determined local distortion parameter; and calibrating the deflectors based on the plurality of other vectors. A method as claimed in claim 14, wherein the first image, the second image and the other images are acquired at grid locations. A method as claimed in claim 14, wherein the first image, the second image and the other images are acquired at grid locations in device coordinates. A charged particle beam device for imaging a sample, the charged particle beam device comprising: a platform for arranging the sample to be imaged; a deflector for deflecting a charged particle beam of the charged particle beam device; and a computer-readable medium containing a program for calibrating the deflectors, the program, when executed by a processor, performs the method described in any one of claims 1 to 5.