Alignment system for aligning metrology devices and an associated method

Abstract

The present disclosure relates to alignment or calibrating techniques for aligning at least one downlook metrology device and at least one uplook metrology device with respect to each other. In particular, the present disclosure pertains to an apparatus and a computer implemented method for aligning at least one downlook metrology device and at least one uplook metrology device with respect to each other, for example but not exclusively for the purpose of mounting components on a substrate.

Description

[0001] Alignment system for aligning metrology devices and an associated method

[0002] CROSS REFERENCE TO RELATED APPLICATION

[0003] The International application claims the priority of DE 10 2023 133 898.6 filed on 2023- 12-04; this application is incorporated by reference herein in its entirety.

[0004] TECHNICAL FIELD

[0005] The present disclosure relates to alignment or calibrating techniques for aligning at least one downlook metrology device and at least one uplook metrology device with respect to each other. In particular, the present disclosure pertains to an apparatus and a computer implemented method for aligning at least one downlook metrology device and at least one uplook metrology device with respect to each other, for example for the purpose of mounting components on a substrate.

[0006] BACKGROUND AND STATE-OF-THE ART

[0007] In the semiconductor industry components, typically electronic or optical components, in particular semiconductor chips and flip chips, are mounted in an automated process on a substrate. In the known field, this automated mounting is also referred to as bonding process or assembly process, and is performed using high tech apparatuses, called die bonders or pick and place machines. With e.g., a die bonding apparatus, components in the form of semiconductor chips, flip chips, micromechanical, micro- optical and electro-optical components, and similar are deposited on substrates such as lead frames, printed circuit boards, ceramics, wafers, etc. and mechanically and electrically bonded.

[0008] The components are picked up by a bond head at a removal location, in particular held by vacuum or electrostatic force, moved to a substrate location, and deposited at a precisely defined position on the substrate. The bond head is part of a pick and place apparatus or system, which enables accurate movement of the bond head in at least three space directions. In order to enable the component to be positioned accurately on the substrate, both the exact position of the component gripped by the bond head with respect to the positioning axis of the bond head and the exact position of the substrate place must be determined.

[0009] Known die bonding apparatuses available on the market achieve in the best case a positioning accuracy of 2 to 3 micrometres at a 3-sigma standard deviation, while processing 4000 to 8000 dies per hour. They implement various metrology devices, such as an uplook vision device (or component vision device) to locate the die component on the bond head and a downlook vision device (or substrate vision device) to locate the bond position on the substrate, where the die component needs to be positioned and bonded. To accurately place a die component on the bond position, sophisticated methods are required to calibrate the field of view of the downlook metrology device and the field of view of the uplook metrology device. For certain system configurations and to achieve even higher die component placements, it is beneficial for the machine software to be able to relate the field of view of the downlook metrology device and the field of view of the uplook metrology device to each other. This relationship between the measurement systems of the two metrology devices is determined during an alignment or calibration procedure.

[0010] In the prior art various known procedures are implemented to establish this relationship between the measurement systems of the various metrology devices. When implementing metrology devices, the most common way is to use a reference element or calibration target which contains reference markers. The metrology devices can locate the reference markers and calculate a common coordinate system or “register” the mutual position of the metrology devices relative to one another.

[0011] These known alignment techniques are prone to various optical errors, such as locating the reference markers under different optical conditions. Such different optical conditions can occur when the relative position of the reference element to one of the metrology device changes in-between the location of the reference markers by the metrology devices.

[0012] Localization errors can also occur when operating distances of the metrology devices to the calibration target during calibration and to the component or substrate during processing are different. Such different operating distances can lead to errors due to mechanical tolerances or tilt of the calibration target with respect to the optical axes of the metrology devices.

[0013] Moreover, refocussing of a metrology device during an alignment or calibration step can lead to similar errors.

[0014] For example, a tilt of the reference element with respect to the optical axes of the metrology devices can lead to optical errors due to the refractive index of the reference element. These drawbacks adversely affect a correct alignment of both metrology device measurement systems relative to each other. And although these drawbacks are acceptable and tolerable within the error budget of current pick and place apparatuses, they are not acceptable for systems with far more stringent accuracy requirements such as 200 nm at a 3-sigma standard deviation and below. Such more accurate requirements are needed for high-end packages of the near future in order to significantly increase the density of the electrical connectors in-between the die and the substrate.

[0015] In addition, due to changes over time within the apparatuses such as thermal drifts, the calibrated relationship between the two metrology devices is prone to change. This effect is called calibration ageing. State-of-the-art apparatuses counter this effect by a re-calibration procedure that includes either cyclically running at least part of the basic calibration routine and / or at certain trigger points (e.g., after a certain time has passed, after a warm-up cycle or after an operator interaction). This approach typically has a negative impact on the system throughput and / or on the placement accuracy when the re-calibration is performed too often or to seldom. There are no direct methods to detect calibration ageing to ensure that the calibrated relationship remains within a given tolerance while maintaining a high throughput.

[0016] Accordingly, it is a goal of the present disclosure to provide an improved alignment system and alignment method, which allow achieve a higher placement accuracy compared to the state of the art while maintaining a high throughput.

[0017] SUMMARY OF THE DISCLOSURE

[0018] According to a first example of the disclosure, an alignment system is provided Alignment system for aligning at least one downlook metrology device and at least one uplook metrology device with respect to each other, the alignment system at least comprising: at least one uplook metrology device having at least one uplook focal plane and an uplook field of view directed towards at least one second downlook metrology device; wherein the at least one downlook metrology device has at least one downlook focal plane and a downlook field of view directed towards the at least one uplook metrology device, and a reference element comprising at least one first marker; wherein, in a first alignment condition, the alignment system is structured to position the reference element within the uplook focal plane and in the downlook focal plane such that the at least one first marker is oriented in the at least one uplook focal plane, and the at least one downlook metrology device is structured to focus in a first focus condition on the at least one first marker; and wherein the alignment system is structured to align the at least one downlook focal plane of the at least one downlook metrology device with the uplook focal plane of the at least one uplook metrology device based on at least the first focus condition.

[0019] Accordingly, optical aberrations such as errors in the correct location of the various reference markers at different optical conditions may be cancelled out to a high degree. Thus, a more precise alignment or calibration of both metrology device systems is achieved allowing implementation in systems with more stringent accuracy requirements.

[0020] In a further advantageous example, the alignment system is structured to align the at least one downlook focal plane of the at least one downlook metrology device with the uplook focal plane of the at least one uplook metrology device based on the first focus condition and one or more parameters selected from optical properties of the reference element, a thickness of the reference element, and a depth of focus of the at least one downlook metrology device.

[0021] In a more accurate example, the alignment system further comprises at least one second marker oriented in the at least one uplook focal plane, and wherein, in the first alignment condition, the at least one downlook metrology device is structured to focus on the at least one second marker, and wherein, in a second alignment condition, the alignment system is structured to position the reference element outside the downlook field of view, and the at least one downlook metrology device is structured to focus in a second focus condition on the at least one second marker, and wherein the alignment system is structured to align the at least one downlook focal plane of the at least one downlook metrology device with the uplook focal plane of the at least one uplook metrology device based on both the first focus condition and the second focus condition.

[0022] Herewith the downlook metrology device is aligned and will know the position to a high degree of accuracy, for example of a tool holder with a semiconductor die, thus ensuring a higher placement accuracy compared to the state of the art.

[0023] In a further advantageous example, the alignment system further comprises a support frame that is structured to be in a fixed position relative to the at least one uplook metrology device and structured to support the reference element in the first alignment condition.

[0024] Preferably, the second marker is mounted to the supporting frame, further ensuring a precise and repetitive alignment.

[0025] For alignment purposes, the alignment system is structured to transform a first focused position of the at least one second marker acquired by the at least one downlook metrology device in the first alignment condition to a second focused position of the at least one second marker acquired by the at least one downlook metrology device in the second alignment condition. In particular, the transformation can involve transforming to transform the first focused position of the at least one first marker to the second focused position of the at least one first marker. In an example the transformation can be performed computationally through translation, preferably in a plane perpendicular to the first longitudinal axis and / or through rotation around the first longitudinal axis. Other transformation techniques may include rotation, shearing, tilting or the use of high order Zernike polynomials.

[0026] In an advantageous example, the alignment system comprises at least one third marker being positioned at a distance from and at a first side of the uplook focal plane seen in a direction parallel to a mutual longitudinal axis of the at least one second downlook metrology device and the at least one second uplook metrology device. Optionally, the alignment system may further comprise at least one frame component and / or further support frame component containing at least one third marker.

[0027] In an advantageous example, the alignment system comprises at least one fourth marker positioned at a distance from and at a second, opposite side of the uplook focal plane seen in a direction parallel to a mutual longitudinal axis of the at least one second downlook metrology device and the at least one second uplook metrology device. Optionally, the alignment system may further comprise at least one frame component and / or further support frame component containing at least one third marker and / or at least one fourth marker

[0028] The presence of additional third and fourth markers, optionally mounted on a supporting frame, in particular present on a separate frame component not containing the first and second markers, allow for correcting changes in the calibrated relationship (X, Y, rotZ) between the two metrology device systems due to thermal drifts (calibration ageing). A benefit of the third and fourth markers over the second and third markers when used to detect calibration ageing, is due to a large degree to a refraction of the separate frame component whereby a degree of tilt does not have a highly negative influence on the alignment accuracy.

[0029] In an advantageous example, the alignment system comprises at least one fifth marker oriented in the at least one uplook focal plane. Optionally, the alignment system may further comprise at least one frame component and / or further support frame component containing at least one third marker and / or at least one fourth marker and / or at least one fifth marker. Optionally, alignment or calibration of the at least one downlook metrology device can therefore be further enhanced using at least one fifth marker oriented in the at least one uplook metrology plane.

[0030] In a preferred example, the at least one frame component and / or further support frame component is made of a material having a refraction index of n in the range of 1.9 to 2.1 , in particular 1.95 to 2.05, more in particular 1.975 to 2.025, even more in particular 1.99 to 2.01 and even more in particular 1.995 to 2.005.

[0031] The above calibration ageing effect can be corrected to a high degree if the at least one uplook metrology device is structured to additionally determine, in the first alignment condition, an initial position of the at least one fourth marker and / or of the at least one fifth marker and, in the second alignment condition, to determine a subsequent position of the at least one fourth marker and / or the at least one fifth marker; and wherein the alignment system is structured to re-align the at least one downlook focal plane of the at least one downlook metrology device with the at least one uplook focal plane of the at least one uplook metrology device based on one or more initial positions and / or one or more subsequent positions thus determined.

[0032] Advantageously, the reference element is coplanar. Optionally, the reference element may be transmissive to a high degree for the at least one downlook metrology device.

[0033] It is noted that in an improved example, in either the first alignment condition and / or the second alignment condition, the at least one downlook metrology device is structured to focus in the first focus condition and / or second focus condition through refocusing of its at least one downlook focal plane.

[0034] Alternatively, the at least one downlook metrology device can further comprise a displacement module structured to displace the at least one downlook metrology device from the first focus condition towards the second focus condition at least in the direction essentially parallel to a mutual longitudinal axis of the at least one second downlook metrology device and the at least one second uplook metrology device.

[0035] The mutual longitudinal axis may be a Z-axis of an XYZ-system of coordinates.

[0036] The disclosure also pertains to a computer-implemented method for aligning at least one downlook metrology device and at least one uplook metrology device with respect to each other, the alignment method at least comprising the steps of: i) orienting at least one uplook metrology device having an uplook focal plane and an uplook field of view towards at least one second downlook metrology device; ii) directing at least one downlook metrology device having at least one downlook focal plane and a downlook field of view towards the at least one uplook metrology device; iii) mounting, in a first alignment condition, a reference element comprising at least one first marker within the uplook field of view and within the downlook field of view; and iv-1) orienting the at least one first marker in the uplook focal plane; v) focusing the at least one downlook metrology device in a first focusing condition on the at least one first marker; vi) aligning the downlook focal plane of the at least one downlook metrology device with the uplook focal plane of the at least one uplook metrology device based on the first focusing condition.

[0037] With the method, an optical aberration such as a tilting of the reference element and shifts of the focal plane due to the thickness thereof are cancelled out to a high degree. Thus, a more precise alignment or calibration of on or more metrology devices relative to each other is achieved allowing implementation in systems with far more stringent accuracy requirements.

[0038] A further improvement as to a more precise alignment is achieved by the aligning step vi) being based on the first focus condition and one or more parameters selected from optical properties of the reference element, a thickness of the reference element, and a depth of focus of the at least one downlook metrology device. Optical properties may be influenced by a material, a refractive index, or similar.

[0039] It may be advantageous if the computer-implemented method further comprises the steps of iv-2) orienting at least one second marker in the at least one uplook focal plane; iv-3) focusing the at least one downlook metrology device on the at least one second marker; vii) removing, in a second alignment condition, the reference element outside the uplook field of view and the downlook field of view, and viii) focusing the at least one downlook metrology device in a second focusing condition on the at least one second marker, and vi-2) aligning the second focal plane of the at least one downlook metrology device with the uplook focal plane of the at least one uplook metrology device based on the first focusing condition and the second focusing condition.

[0040] It may be advantageous if the alignment step vi-2) comprising the step of ix) transforming a first focused position of the at least one first marker acquired by the at least one downlook metrology device in the first focusing condition to a second focused position of the at least one first marker acquired by the at least one downlook metrology device in the second focusing condition.

[0041] It may be advantageous if the transform step ix) comprises transforming the first focused position to the second focused position through translation in a plane perpendicular to a mutual longitudinal axis of the at least one second downlook metrology device and the at least one second uplook metrology device and / or through rotation around the mutual longitudinal axis.

[0042] It may be advantageous if the alignment system comprises at least a third marker being positioned at a distance from and at a first side of the uplook focal plane as viewed in a direction parallel to a mutual longitudinal axis of the at least one second downlook metrology device and the at least one second uplook metrology device, and the method comprises the further steps of: determining, with the at least one downlook metrology device, in the first focusing condition an initial position of the at least one third marker and in the second focusing condition a subsequent position of the at least one third marker; and re-aligning the downlook focal plane of the at least one downlook metrology device with the uplook focal plane of the at least one uplook metrology device based on one or more initial positions and / or one or more subsequent positions thus determined.

[0043] It may be advantageous if the alignment system further comprises at least one fourth marker positioned at a distance from and at a second, opposite side of the uplook focal plane seen in a direction parallel to a mutual longitudinal axis of the at least one second downlook metrology device and the at least one second uplook metrology device, and the method comprises the further steps of: determining, with the at least one uplook metrology device, in the first focusing condition an initial position of the at least one fourth marker and in the second focusing condition a subsequent position of the at least one fourth marker; and re-aligning the downlook focal plane of the at least one downlook metrology device with the uplook focal plane of the at least one uplook metrology device based on one or more initial positions and / or one or more subsequent positions of the at least one third marker and / or the at least one fourth marker thus determined.

[0044] It may be advantageous if the alignment system comprises at least one fifth marker oriented in the at least one uplook focal plane, and the method comprises the further steps of: determining, with the at least one uplook metrology device, in the first focusing condition an initial position of the at least one fifth marker and in the second focusing condition a subsequent position of the at least one fifth marker; and realigning the downlook focal plane of the at least one downlook metrology device with the uplook focal plane of the at least one uplook metrology device based on one or more initial positions and one or more subsequent positions of the at least one second marker and / or the at least one fifth marker thus determined. The present disclosure also pertains to a computer program or product comprising instructions which, when the program is executed by a computer, in particular a computer associated with the alignment system according to the disclosure, cause the computer to carry out steps of the computer-implemented method according to the disclosure.

[0045] Similarly, the disclosure pertains also to a computer-readable storage medium comprising instructions which, when executed by a computer, in particular a computer associated with the alignment system according to the disclosure, cause the computer to carry out steps of the computer-implemented method according to the disclosure.

[0046] BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The disclosure will now be discussed with reference to the drawings, wherein:

[0048] Figure 1 depicts first pick and place apparatus using an alignment technique;

[0049] Figure 2 depicts an optical error associated with the alignment techniques depicted in Figure 1 ;

[0050] Figures 3 to 12 depict various aspects of an example of an alignment system according to the disclosure;

[0051] Figures 13 to 18 depict further aspects of the alignment system as depicted in Figures 3 to 12, in a first and second alignment position;

[0052] Figures 19 to 22 depict alternative aspects of the alignment system as depicted in Figures 3 to 12, in a first and second alignment position;

[0053] Figures 23 to 24 depict a second pick and place apparatus using an alignment technique according to the disclosure;

[0054] Figure 24 depicts a third pick and place apparatus using an alignment technique according to the disclosure.

[0055] DETAILED DESCRIPTION OF THE DISCLOSURE

[0056] For a proper understanding of the disclosure, in the detailed description below corresponding elements or parts of the disclosure will be denoted with identical reference numerals in the drawings.

[0057] Figure 1 depicts in a schematic and exemplary manner a first embodiment of a pick and place apparatus 10 (a first pick and place apparatus). The first pick and place apparatus 10 interacts with a substrate 20 on which multiple semiconductor dies 211 , 212, 213 are to be mounted as specific locations on the substrate 20 and achieves in the best case a positioning accuracy of 2 to 3 micrometers at a 3-sigma standard deviation.

[0058] The first pick and place apparatus 10 implements at least one first downlook metrology device 12 and at least one first uplook metrology device 11 , which are to be aligned precisely with respect to each other and the substrate 20. A precise alignment ascertains a precise positioning of the semiconductor die 211 , 212, 213 on the desired location on the substrate 20. For placement and bonding at the desired location on the substrate 20, the respective semiconductor die 213 is depicted as being held by a first embodiment of a bond head 13 (a first bond head).

[0059] In the context of this disclosure, it should be understood that with a metrology device is meant a specialized piece of equipment for performing various precise measurements, inspection, and quality control of objects or components. In this application a nonlimiting example of a metrology device used for implementing examples of the disclosure can be a vision device. A vision device may also be implemented as one or more components of a camera.

[0060] The terms uplook and downlook are used to describe the common orientations of the metrology devices depicted in the figures. However, these metrology devices may be used in any other orientations and may be interchangeable with each other in some configurations.

[0061] The first uplook metrology device 11 exhibits a field of view 0 directed towards the substrate 20 and towards the first downlook metrology device 12. Similarly, the first downlook metrology device 12 has a field of view 1220 directed towards the substrate 20 and towards the first uplook metrology device 11.

[0062] The sensing and / or imaging as performed by the first uplook metrology device 11 is denoted by first uplook imaging rays 1111 and second uplook imaging rays 1112. The sensing and / or imaging as performed by the first downlook metrology device 12 is denoted by first downlook imaging rays 1211 and second downlook imaging rays 1212.

[0063] To position the first bond head 13 with the semiconductor die 213 at the correct location above the placement position on the substrate 20, the bond position on the substrate 20 needs to be determined. To accurately place a semiconductor die 211 , 212, 213 on the bond position it is required that the machine software can relate the field of view 1220 of the first downlook metrology device 12 and the field of view 1120 of the first uplook metrology device 11 to each other. This relationship between the two metrology device systems is usually measured during an alignment or calibration procedure. Various methods may be implemented to establish this relationship between metrology devices such as between the first uplook metrology device 11 and the first downlook metrology device 12. A common way is to use a reference element or calibration target which contains reference markers. Both first metrology devices 11 , 12 are arranged to locate the reference markers and to calculate a common coordinate system and / or to “register” one or more mutual positions of the metrology devices 11 , 12 relative to one another.

[0064] A first embodiment of a reference element 14 (a first reference element) is shown in Figure 2. The first reference element 14 comprises one or more markers 1411. As depicted, the markers 1411 are either on the top side of the first reference element 14, facing the first downlook metrology device 12, or on the bottom side of the first reference element 14, facing the first uplook metrology device 11. Both first metrology devices 11 , 12 are arranged to locate those markers 1411 and establish one or more mutual relationships in, for example, X, Y, and / or rotZ within an XYZ-system of coordinates of the first pick and place apparatus 10.

[0065] After an alignment relationship between the two first metrology devices 11 , 12 is established, both first metrology devices 11 , 12 arrange a suitably precise alignment of the first bond head 13 relative to the intended bond position on the substrate 20, with the assistance of a bond head marker 1311 mounted to the first bond head 13, a die marker 2132 present on the semiconductor die 213, and a substrate marker mounted on the substrate 20.

[0066] Such alignment techniques are prone to various optical errors, such as locating the various reference markers under different optical conditions. Such different optical conditions can occur, for example, when the relative position of the first reference element 14 to one or more of the first metrology devices 11 ,12 changes between location measurements of the reference markers 1411 by the first metrology devices 11 , 12.

[0067] Localization errors can also occur, for example, when operating distances of the metrology systems to a calibration target during calibration, and to the component or substrate during processing, are different. Such different operating distances can lead to errors due to, for example, mechanical tolerances and / or tilt of a calibration target with respect to an optical axis of one or more first metrology devices 11 , 12.

[0068] These drawbacks may adversely affect a degree of correct alignment of the first metrology devices 11 , 12 relative to each other. And although these drawbacks may be acceptable and tolerable within the error budget of the first pick and place apparatus 10, they may not be acceptable for systems with far more stringent accuracy requirements, such as 200 nm at a 3-sigma standard deviation and below. Such more accurate requirements are needed in, for example, hybrid bonding.

[0069] In addition, factors such as thermal drifts within an apparatus may change a calibrated relationship (for example, in X, Y, and / or rotZ) between the two first metrology devices

[0070] 11 , 12. This effect is called calibration ageing. The first pick and place apparatus 10 may counter this effect by cyclically running one or more calibration routines, either automatically and / or at certain trigger points (e.g., after a warm-up cycle or after an operator interaction). However, there is no direct method to detect calibration ageing.

[0071] As a solution to the above drawback, the present disclosure presents improved alignment systems and methods for aligning at least one downlook metrology device and at least one uplook metrology device with respect to each other. The improved alignment systems and methods described below can be implemented in many and various applications wherein a higher degree of alignment accuracy between metrology devices is desired. For example, the improved alignment systems and methods described below may be implemented by suitable modifying a pick and place apparatuses, such as suitable modifying the first pick and place apparatus as depicted in Figures 1 and 2.

[0072] For a proper understanding of the improved alignment systems and methods, the detailed description below refers to corresponding elements or parts of the disclosure with identical reference numerals as used in Figures 3 to 25. After a general introduction to the key elements and parts shown in more than one Figure, the Figures will be described in more detail.

[0073] Figures 23 to 24 depict a second embodiment of a pick and place apparatus (a second pick and place apparatus), which together with the improved alignment system 100 also implements a second embodiment of a bond head 130 (a second bond head) provided with bond head marker(s) 13013 and a view passage 13075 of the second bond head 130. Similarly, Figure 25 depicts a third embodiment of a pick and place apparatus (a third pick and place apparatus), which together with the improved alignment system 100 implement the second bond head 130 provided with bond head marker(s) 13013 and a view passage 13075 of the second bond head 130. A view passage 13075 is as depicted in Figures 23 and 24 a passage, structured to provide an optical path for a downlook metrology device 120 to focus on a bond head marker 13013. For example, a view passage 13075 may be a hollow space or it may be structured of a material which is at least in some areas transmissive to a high degree for imaging rays of a downlook metrology device 120.

[0074] Figures 3, 5, 7, 9, 11 , 13, 15, 17, 19, 21 , 23 and 25 show schematic side views of various examples of the improved alignment system 100 according to the disclosure. Figures 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24 show schematic top views of the corresponding fields of view of both at least one second uplook metrology device 110 and of at least one second downlook metrology device 120.

[0075] The improved alignment system 100 is suitable for aligning at least one second downlook metrology device 120 and at least one second uplook metrology device 110 with respect to each other. The alignment system 100 comprises at least one second uplook metrology device 110 that is provided with at least one uplook focal plane 11099 and an uplook field of view 11020. The uplook field of view 11020 of the at least one second uplook metrology device 110 is directed towards the at least one second downlook metrology device 120. Similarly, the at least one second downlook metrology device 120 is provided with at least one downlook focal plane 12099 and a downlook field of view 12020. The downlook field of view 12020 of the at least one second downlook metrology device 120 is directed towards the at least one second uplook metrology device 110.

[0076] Although the Figures schematically show at least one second uplook metrology device 110 and at least one second downlook metrology device 120 facing each other perpendicularly in a direct line, it should be noted that this orientation of metrology devices facing each other is an example and that the mutual position of the second metrology devices does not necessarily imply a perpendicular facing relationship. However, it may be advantageous if the at least one second uplook metrology device 110 and the at least one second downlook metrology device 120 are both located on a Z-axis of an XYZ-system of coordinates in which the improved alignment system 100 is operating.

[0077] The sensing and / or imaging as performed by the at least one second uplook metrology device 110 is denoted by first uplook imaging rays 11011. The sensing and / or imaging as performed by the at least one second downlook metrology device 120 is denoted by first downlook imaging rays 12011 .

[0078] During selected steps of the improved alignment method depicted in Figures 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 19 and 20, the improved alignment system 100 includes a second embodiment of a reference element 310 (a second reference element) arranged between the at least one second downlook metrology device 120 and at least one second uplook metrology device 110. The second reference element 310 comprises at least one first marker 315 on, at or proximate a first surface 3101 of the second reference element 310. Suitable markers may be provided by modifying a chrome layer on the first surface of a glass plate. The improved alignment system 100 is arranged to position the at least one first marker 315 within the uplook field of view 11020 such that the first surface 3101 faces the at least one second uplook metrology device 110 and such that the at least one second uplook metrology device 110 may sense and / or image the at least one first marker 315. The second reference element 310 further comprises a second surface 3102, opposite to the first surface 3101. The improved alignment system 100 is arranged to position the at least one first marker 315 within the downlook field of view 12020 such that the second surface 3102 faces the at least one second downlook metrology device 120. For achieving a high degree of optical calibration, the second reference element 310 is preferably coplanar to a high degree. The second reference element 310 is sufficiently transmissive for such that the at least one second downlook metrology device 120 may sense and / or image the at least one first marker 315. In a preferred example, the second reference element 310 is transmissive to a high degree for the at least one second downlook metrology device 120. The alignment system 100 is structured to position the reference element 310 within the uplook focal plane 11099 and in the downlook focal plane 12099 such that the at least one first marker 315 is oriented in the at least one uplook focal plane 11099, and the at least one downlook metrology device 120 is structured to focus in a first focus condition on the at least one first marker 315; and wherein the alignment system 100 is structured to align the at least one downlook focal plane 12099 of the at least one downlook metrology device 120 with the uplook focal plane 11099) of the at least one uplook metrology device 110 based on at least the first focus condition.

[0079] As depicted in Figure 3, the alignment system 100 may be provided with a control unit 711 , suitable for the proper control of the various components of the improved alignment system 100. For example, the control unit 711 is capable of controlling the at least one second uplook metrology device 110 via a first control line 7111 and capable of controlling the at least one second downlook metrology device 120 via a second control line 7112. The control unit 711 may, for example, receive sensory data (e.g., image data) from one or more metrology devices 110, 120, perform one or more alignment process steps, perform one or more re-alignment process steps as described below, generate proper control signals for controlling one or more metrology devices 110, 120, generate proper control signals for other components as described herein, or any combination thereof. For clarity, the control unit 711 and the control lines 7111 , 7112 are not shown in the other figures.

[0080] As depicted in Figure 21 , the alignment system 100 may comprise at least one displacement module 740, arranged to displace the at least one second downlook metrology device 120 from and / or to the second reference element 310 in a positive and / or negative direction approximate along the Z-axis. A degree of displacement may be predetermined and / or controlled such that the at least one first marker 315 is oriented in a downlook focal plane 12089, 12099. A degree of displacement may be controlled by the control unit 711 based on control signals via a displacement control line 7401. Additionally, or alternatively, focusing of the at least one second downlook metrology device 120 can be established in other ways, for example through focusing of an imaging lens of the at least one second downlook metrology device 120. For clarity, the at least one displacement module 740 and the displacement control line 7401 are not shown in the other figures.

[0081] More specifically, Figure 3 depicts a schematic sideview, lying in an approximate XZ plane, of a first operational state of the improved alignment system 100 according to the disclosure, wherein this first operational state is also defined a first alignment condition. The at least one second uplook metrology device 110 and the at least one second downlook metrology device 120 are located along an approximate YZ plane, facing each other and separated by the second reference element 310. The second reference element 310 extends in an approximate XY plane between the at least one second uplook metrology device 110 and the at least one second downlook metrology device 120. The second reference element 310 is viewed from a side in Figure 3, with a side face extending along an approximate XZ plane having a thickness 3199 extending approximately along the Z axis. The second reference element 310 has a first surface 3101 extending in an approximate XY plane, whereby the first surface 3101 faces the at least one second uplook metrology device 110. The second reference element 310 further has a second surface 3102 extending in an approximate XY plane, whereby the second surface 3102 faces the at least one second downlook metrology device 120. The average separation between the first surface 3101 and the second surface 3102 is the thickness 3199 of the second reference element 310. At least one first marker 315 is provided at the first surface side 3101 of the second reference element 310. In the example depicted, multiple markers 315 are provided at the first surface side 3101 of the second reference element 310.

[0082] Figure 4 show a schematic top view of the corresponding fields of view of both the at least one second uplook metrology device 110 and of at least one second downlook metrology device 120 during the first alignment condition depicted in Figure 3. The schematic top view is depicted lying in an approximate XY plane. At least one first marker 315 is depicted at the first surface side 3101 of the second reference element 310. In the example depicted, multiple markers 315 are provided at the first surface side 3101 of the second reference element 310. Preferably, the multiple markers 315 are arranged in a matrix array as shown in in the example of Figure 4.

[0083] The uplook field of view 11020 of the at least one second uplook metrology device 110 extends in an approximate XY plane, and is directed towards the first surface 3101 of the second reference element 310. The downlook field of view 12020 of the at least one second downlook metrology device 120 extends in an approximate XY plane, and is directed towards the second surface 3102 of the second reference element 310.

[0084] In the first alignment condition depicted in Figure 3, the second reference element 310 is positioned within the uplook field of view 11020 of the at least one second uplook metrology device 110 such that the at least one first marker 315 is oriented in the at least one uplook focal plane 11099 of the at least one second uplook metrology device 110. This ensures that the at least one second uplook metrology device 110 has a focused view on the at least one first marker 315 of the second reference element 310. The second reference element 310 is also positioned in the downlook field of view 12020 of the at least one second downlook metrology device 120. For the purpose of positioning the second reference element 310 within the uplook field of view 11020 and in the downlook field of view 12020, the improved alignment system 100 may be provided with a suitable positioning module. The positioning module may be controlled by the control unit 711. The positioning module is structured to position the second reference element 310 in and out of the uplook field of view 11020. The positioning module is also structured to position the second reference element 310 in the downlook field of view 12020. Alternatively, in either the first alignment condition and / or in the second alignment condition (described below), the at least one second downlook metrology device 120 may focus in the first condition through refocusing of its at least one downlook focal plane 1289, 12099. As described below, the at least one second downlook metrology device 120 may also focus a second focus condition through refocusing of its at least one downlook focal plane 12089, 12099.

[0085] In general, the at least one downlook metrology device 120 is arranged to focus on at least two focal planes. A first focal plane 12089 of the at least one downlook metrology device 120 representing an initial focusing position, or a focusing position when no second reference element 310 is present to influence the imaging by the at least one second metrology device 120. A second focal plane 12099 of the at least one downlook metrology device 120 representing a modified focusing position, or a focusing position when a second reference element 310 is present, and the focusing is modified to correct for the imaging influence of the second reference element 310.

[0086] Whilst in the first alignment condition depicted in Figure 3 and 4, the at least one first marker 315 of the second reference element 310 is in a more or less focused orientation in the at least one uplook focal plane 11099 of the at least one second uplook metrology device 110. However, the at least one first marker 315 of the second reference element 310 is not necessarily in a focused orientation of the at least one downlook metrology device 120. For example, as depicted in FIG. 3 and FIG. 4, the at least one downlook metrology device 120 may be focused on a first focal plane 12089 which is not the same as the at least one uplook focal plane 11099. Thus, in the first alignment condition, the at least one second downlook metrology device 120 is operated such that it focusses on the at least one first marker 315 of the second reference element 310, thereby arranging the at least one first marker 315 of the second reference element 310 to be oriented in a second focal plane 12099 of the at least one downlook metrology device 120. The second focal plane 12099 is approximately co-planar with the uplook focal plane 11099 of the second uplook metrology device 110. Once the at least one second downlook metrology device 120 has focused on the at least one first marker 315 of the second reference element 310, this focusing determines or sets a first focus condition of the at least one second downlook metrology device 120. The at least one first marker 315 of the second reference element 310 is oriented in the second focal plane 12099 of the at least one downlook metrology device 120 in the first focus condition. The focusing principle of the at least one second downlook metrology device 120 can be established in various ways, for example through focusing of an imaging lens of the at least one second downlook metrology device 120, and / or by means of the displacement module, thus ensuring that the at least one first marker 315 is oriented in the second downlook focal plane 12099.

[0087] Next, based on the fact that the at least one uplook metrology device 110 is also focused on the at least one first marker 315 because the at least one first marker 315 is positioned in the uplook focal plane 11099, and the second downlook focal plane 12099 and the uplook focal plane 11099 are approximately co-planar, the improved alignment system 100 is capable to align the second downlook focal plane 12099 of the at least one second downlook metrology device 120 with the uplook focal plane 11099 of the at least one second uplook metrology device 110 based on at least the first focus condition of the at least one second downlook metrology device 120. In particular, the improved alignment system 100 is structured to align the second downlook focal plane 12099 of the at least one second downlook metrology device 120 with the uplook focal plane 11099 of the at least one second uplook metrology device 110 based on the first focus condition and with the assistance one or more parameters selected from optical properties of the second reference element 310. These optical properties can be based on the material and / or a refractive index of the second reference element 310, a thickness 3199 of the second reference element, and a depth of focus of the at least one second downlook metrology device 120.

[0088] Although the above alignment principle provides an improvement of the known alignment techniques, a further improvement can be achieved when taking the thickness 3199 of the second reference element 310 into account. Although the at least one first marker 315 is at the same Z height, they may optically not be in the same focal plane of both second metrology devices 110, 120 due to a focus shift effect of the second reference element 310. This is shown in Figure 3 where the first focal plane 12089 of the at least one second downlook metrology device 120 is initially not in the same XY plane as the focal plane 11099 of the at least one second uplook metrology device 110.

[0089] More specifically, Figure 7 depicts a schematic sideview, lying in an approximate XZ plane, of a further improvement of the alignment principle according to the disclosure. The improved alignment system 100 further optionally comprises at least one second marker 3005 which is oriented in the at least one uplook focal plane 11099 of the at least one second uplook metrology device 100. The improved and more accurate alignment is achieved, as, in the first alignment condition thus with the second reference element 310 being positioned within both the uplook field of view 11020 and in the downlook field of view 12020, the at least one second downlook metrology device 120 is structured to focus also on the at least one second marker 3005. Figure 8 show a schematic top view of the corresponding fields of view of both the at least one second uplook metrology device 110 and of at least one second downlook metrology device 120 during the alignment step depicted in Figure 7. The schematic top view is depicted lying in an approximate XY plane.

[0090] Subsequently, in a second alignment condition (described below), the improved alignment system positions the second reference element 310 outside the downlook field of view 12020 of the at least one second downlook metrology device 120. Then, the at least one second downlook metrology device 120 subsequently re-focusses on the at least one second marker 3005, which re-focusing ascertains a second focus condition. The further improved alignment of the improved alignment system 100 according to the disclosure improves the alignment of the at least one downlook focal plane 12099 of the at least one second downlook metrology device 120 with the uplook focal plane 11099 of the at least one second uplook metrology device 110 based on both the first focus condition and the second focus condition. With this improved alignment optical distortion caused by the thickness 3199 of the second reference element 310 may be corrected to a high degree, and the downlook focal plane 12099 actually coincides with the uplook focal plane 11099. The second alignment condition is for example depicted in Figure 15, 16, Figure 17, 18, and Figure 21 , 22 where the second reference element 310 is removed from the field of views 11020 and 12020 and the downlook focal plane is no longer at the first focal plane 12089 but coincides, to a high degree, at the second focal plane 11099 with the uplook focal plane 11099.

[0091] In Figures 5, 6, Figures 7, 8, Figures 9, 10 and Figures 11 , 12, an alternative example is shown, wherein the improved alignment system 100 comprises a support frame 300 that is structured to be mounted in a fixed position relative to the at least one second uplook metrology device 110. The support frame 300 supports the second reference element 310 in the first alignment condition.

[0092] Contrary to the example of Figures 7, 8 wherein the at least one second marker 3005 is mounted at a different location within the uplook focal plane 11099 in the improved alignment system 100, Figures 9, 10 show an example of the disclosure, wherein the at least one second marker 3005 is mounted to the support frame 300. The support frame 300 can be made as one single component for supporting the second reference element 310, and / or in another example as depicted in the Figures as mentioned, the support frame 300 may be composed of various support frame component(s) 301 which are similarly mounted in a fixed position relative to the at least one second uplook metrology device 110 with the improved alignment system 100.

[0093] As to the alignment principle, it should be noted that the improved alignment system 100 is structured to transform a first focused position of the at least one second marker 3005 acquired by the at least one second downlook metrology device 120 in the first alignment condition to a second focused position of the at least one second marker 3005 acquired by the at least one second downlook metrology device 120 in the second alignment condition. This transformation T maps the position of the at least one second marker 3005 defined in the first alignment condition to the position of the at least one second marker 3005 defined in the second alignment condition.

[0094] Preferably the transformation T may encompass a rigid body transformation with the degrees of freedom translation in X and Y and rotZ orientations of the XYZ coordinate system. Other transformations can be implemented such as shearing, rotation, tilting, etc. With the use of high quality telecentric optics, minor tilt changes (rotX, rotY) of the at least one second downlook metrology device 120 due to imperfections of the Z axis can be at least partially compensated, however it is also possible to compute a more sophisticated mapping T that takes account of higher order distortions with more degrees of freedom (e.g. additional degrees of freedom such as scaling in X, scaleX, and / or Y, scaleY, or the use of high order Zernike polynomials).

[0095] The improved alignment system 100 according to the disclosure may implement various examples of transformation techniques such as transformation of the first focused position of the at least one first marker 315 to the second focused position of the at least one first marker 315 (and vice versa) through translation, preferably in a plane perpendicular to a mutual longitudinal axis of the at least one second downlook metrology device 120 and the at least one second uplook metrology device 110 and / or through rotation around the mutual longitudinal axis.

[0096] The same transformation T (associated with the mapping of the position of the at least one second marker 3005 defined in the first alignment condition to the position of the at least one second marker 3005 defined in the second alignment condition) is now applied to the positions of the at least one first marker 315 as defined in the first alignment condition in the first downlook focal plane 12089 by the at least one second downlook metrology device 120 and this provides the improved alignment system 100 with the field of view calibration data for the at least one second downlook metrology device 120 now at the intended Z position (or in the intended second focal plane) 12099.

[0097] At this stage, both focal planes 11099 and 12099 are aligned and the field of views 11020 and 12020 of both second metrology devices 110 and 120 essentially overlap. By computing a transformation S between those field of views 11020 and 12020, the control unit 711 of the improved alignment system 100 may be structured to computationally map an image (or a position I orientation in an image) of the at least one second uplook metrology device 110 to the field of view 12020 of the at least one second downlook metrology device 120 and vice versa using S.

[0098] This means, that both second metrology devices 110, 120 are now aligned to a high degree within their coinciding focal planes 11099 and 12099.

[0099] Furthermore, if the positions of at least one first marker 315 on the second reference element 310 are known very precisely (either by means of an external measurement or by an extremely precise manufacturing process) the at least one first marker 315 can be used to calibrate the field-of-views 11020 and 12020 of both the at least one second uplook metrology device 110 and the at least one second downlook metrology device 120 to a shared Cartesian XYZ coordinate system, thereby correcting optical aberrations of the optical systems to a high degree. For some applications, such as in the apparatus 10 depicted in Figure 1 , the semiconductor die marker 2132 and the substrate marker 2012 may coincide to a high degree at the bond position, and therefore this additional calibration might not be necessary.

[0100] In order to correct for changes in the calibrated relationship (X, Y, rotZ) between the measurement systems of the two second metrology devices 110, 120 due to thermal drifts also known as calibration ageing the improved alignment system 100 comprises at least one third marker 3025 (see Figures 13, 14 and Figures 15, 16), wherein the at least one third marker 3025 is positioned at a distance from and at a first side of the uplook focal plane 11099 of the second uplook metrology device 110 as viewed in a direction parallel to a mutual longitudinal axis of the at least one second downlook metrology device 120 and the at least one second uplook metrology device 110. Note that in Figures 13, 14 and Figures 15, 16, the at least one third marker 3025 is positioned at the side of the uplook focal plane 11099 (indicated as the first side) which is closest to the at least one second uplook metrology device 110 and thus farthest from the at least one second downlook metrology device 120.

[0101] In addition to the at least one third marker 3025, the improved alignment system 100 may implement an improved correction to calibration ageing, as it may comprise at least one fourth marker 3026. This at least one fourth marker 3026 is also positioned at a distance from, and also at a second, opposite side of the uplook focal plane 11099 of the second uplook metrology device 110 as viewed in a direction parallel to a mutual longitudinal axis of the at least one second downlook metrology device 120 and the at least one second uplook metrology device 110. Note that in Figures 13, 14 and Figures 15, 164B the at least one fourth marker 3026 is positioned at the side of the uplook focal plane 11099 (indicated as the second side) which is closest to the at least one second downlook metrology device 120 and thus farthest from the at least one second uplook metrology device 110.

[0102] The additional at least one third marker 3025 and at least one fourth markers 3026 may optionally be comprised in one or more frame components. For example, the at least one third marker 3025 and at least one fourth marker 3026 can mounted to separate or the same frame components 3021 , 3022, 3023 of the support frame 300, wherein the one or more frame components 3021 , 3022, 3023 do not contain or incorporate any of the at least one first marker 315 and the at least one second marker 3005. It may be advantageous to comprise the at least one third marker 3025 and the at least one fourth marker 3026 in the same frame component 3021 , 3022, 3023, as depicted in FIG. 13, 14, 15, 16, 19, 20, 21 and 22. The at least one third marker 3025 and the at least one fourth marker 3026 are arranged to determine at least one orientation and / or position of one or more first uplook metrology devices 110, relative to one or more downlook metrology devices 120. The frame components 3021 , 3022, 3023 comprise an optical mark carrier with a first carrier surface and a second carrier surface, wherein the second carrier surface is opposite to the first carrier surface. The at least one third marker 3025 is arranged on or proximate the first carrier surface, and the at least one fourth marker 3026 is arranged on or proximate the second carrier surface. The at least one third marker 3025 is arranged to allow one or more first images to be made by the one or more downlook cameras 120 through the optical mark carrier if the one or more downlook cameras 120 are facing the second carrier surface. The at least one fourth marker 3026 is arranged to allow one or more second images to be made through the optical mark carrier by the one or more uplook cameras 110 if the one or more uplook cameras 110 are facing the first carrier surface. The one or more first images are arranged to provide a first orientation and / or position of the one or more downlook cameras 120 relative to the at least one third marker 3025. The one or more second images are arranged to provide a second orientation and / or position of the one or more uplook cameras relative to the at least one fourth marker 3026. Optionally, at least one alignment imaging or calibration parameter of the one or more downlook cameras 120 and the one or more uplook cameras 110 may be determined using a first orientation, a first position, a second orientation, a second position, or any combination thereof.

[0103] The optical mark carrier may be further advantageous if it has an average refractive index (n) of approximately 2, or in the range of 1 .0 to 3.0; or 1 .5 to 2.5; or 1.7 to 2.3; or 1.75 to 2.25; or 1.8 to 2.2; or 1.85 to 2.15; or 1.9 to 2.1 ; or 1.95 to 2.05.

[0104] Optionally, calibration of the at least one second downlook metrology device 120 can be further enhanced using at least one fifth marker 3035, wherein the at least one fifth marker 3035 is oriented in the at least one uplook focal plane 11099 and optionally mounted to further frame components 3031 , 3032, 3033 of the support frame 300 as shown in Figures 11 , 12.

[0105] In a preferred example, the frame component and in particular the frame component 3021 , 3022, 3023 is made of a material having a refraction index of n in the range of 1.9 to 2.1 , in particular 1.95 to 2.05, more in particular 1.975 to 2.025, even more in particular 1.99 to 2.01 and even more in particular 1.995 to 2.005. The above calibration ageing effect can be corrected to a high degree, if the at least one second uplook metrology device 110 is structured to additionally determine, in the first alignment condition, an initial position of the at least one fourth marker 3026 and / or of the at least one fifth marker 3035 and, in the second alignment condition, to determine a subsequent position of the at least one fourth 3026 and / or at least one fifth marker 3035. Next, the re-alignment step of the improved alignment system 100 encompassing re-alignment of the at least one downlook focal plane 12099 of the at least one second downlook metrology device 120 with the at least one uplook focal plane 11099 of the at least one second uplook metrology device 110 based on one or more initial positions and one or more subsequent positions thus determined.

[0106] The positions of the at least one third marker 3025, at least one fourth marker 3026 and / or at least one fifth marker 3035 can be checked by either the at least one second uplook metrology device 110 and the at least one second downlook metrology device 120 and compared with their pre-determined positions during an initial alignment or calibration. As long as these measured positions do not change beyond a specification for the at least one second uplook metrology device 110 and / or the at least one second downlook metrology device 120 compared to the positions as determined during the initial alignment or calibration step, the calibration is considered still correct and unaffected.

[0107] This approach does not require additional stage movements or image acquisitions since the measurement on the various third, fourth and / or fifth markers can be done at the very same time as the uplook adjust measurement on the semiconductor die 211 , 212, 213 prior to its positioning and bonding on the substrate 21 (see, for example, Figure 1).

[0108] In the event that the pre-determined calibration positions of the at least one third marker 3025, at least one fourth marker 3026 and at least one fifth marker 3035 start to change due to thermal drift, vibrations, etc. , calibration ageing will be observed by the control unit 711 of the improved alignment system 100. In such case the control unit 711 has multiple options, such as a re-run and refreshment of the calibration of the positions of the at least one third marker 3025, at least one fourth marker 3026 and at least one fifth marker 3035. This option however takes time. Alternatively, adjustment of the XY and rotZ drifts of the various markers can be performed, and the calibration can be easily corrected computationally by the control unit. Additionally, higher order effects can be detected by comparing the distances of the markers in the edges of the field of view, which are the most sensitive areas of the improved alignment system 100. This can be either used to computationally map the results back with a multi-DoF (scaling, etc.) or higher order transformation or to trigger a new calibration aging process.

[0109] To ensure an accurate alignment procedure, it is evident that in between steps of the alignment procedure the mutual orientation of the various components in the optical system remain undisturbed. Accordingly, the improved alignment system 100 may comprise attachment features to attach, in the first alignment condition, the second reference element 310 in a position relative to the at least one second uplook metrology device 110. These attachment features may attach the second reference element 310 in a position relative to the at least one second uplook metrology device 110 using magnetic force. Accordingly, the second reference element 310 may be provided with magnetic contacts which interact through magnetism with corresponding magnetic contacts provided on at least the at least one second uplook metrology device 110 or on the support structure 300 and / or support frame components 301.

[0110] In an alternative example, which similarly ensures a high degree of undisturbed mutual orientation of the various components in the optical system, attachment features are provided to attach, in the first alignment condition, the second reference element 310 in a position relative to the at least one second uplook metrology device 110 using vacuum. For example, a vacuum pump device may be provided, which creates an under pressure or vacuum at locations (e.g. via an air duct or air inlet opening) where the second reference element 310 rests on the support structure 300 and / or support frame components 301.

[0111] In another example, the attachment features are structured to attach, in the first alignment condition, the second reference element 310 relative to the at least one second uplook metrology device 110 on the support frame 300 in a mechanical formfitting manner. For example, the attachment features may consist of at least one pair of cooperating first and second interlocking elements, the first interlocking element forming a monolithic part with the support frame 300 and / or support frame components 301 , and the second interlocking element forming a monolithic part with the second reference element 310.

[0112] In particular, the pair of cooperating first and second interlocking elements can be configured as at least one dent and at least one bulge, wherein the at least one dent and the at least one bulge exhibit a circular, elliptical or torus configuration. For example, at least part of the outer dimensions of the at least one bulge are oversized compared to the corresponding part of the inner dimensions of the cooperating dent. The various first, second, third, fourth and fifth markers can be provided in the form of flat line-shaped or spot-shaped fiducials as depicted in the Figures. Alternatively, these fiducials can be formed as small balls.

[0113] The disclosure also pertains to a computer implemented method for aligning at least one second downlook metrology device 120 and at least one second uplook metrology device 110 with respect to each other. The computer implement alignment method can be performed by the control unit 711 and may at least comprise the steps of: i) orienting at least one second uplook metrology device 110 having an uplook focal plane 11099 and an uplook field of view 11020 directed towards at least one second downlook metrology device 120; ii) directing the at least one second downlook metrology device 120 having at least one downlook focal plane 12099, 12089 and a downlook field of view 12020 towards the at least one second uplook metrology device 110; iii) mounting, in a first alignment condition, a second reference element 310 comprising at least one first marker 315 within the uplook field of view 11020 of the at least one second uplook metrology device 110, and within the downlook field of view 12020 of at least one second downlook metrology device 120; and iv-1) orienting the at least one first marker 315 in the uplook focal plane 11099; v) focusing the at least one second downlook metrology device 120 in a first focusing condition on the at least one first marker 315; vi) aligning the downlook focal plane 12099 of the at least one second downlook metrology device 120 with the uplook focal plane 11099 of the at least one second uplook metrology device 110 based on the first focusing condition.

[0114] Additionally, the method may further comprise the improvement in that the aligning step vi) is based on the first focus condition and one or more parameters selected from optical properties of the second reference element 310 such as material, refractive index, a thickness of the second reference element 310, and a depth of focus of the at least one second downlook metrology device 120.

[0115] A further improved alignment procedure of the method according to the disclosure has the steps of iv-2) orienting at least one second marker 3005 in the at least one uplook focal plane 11099; iv-3) focusing the at least one second downlook metrology device 120 on the at least one second marker 3005; vii) removing, in a second alignment condition, the second reference element 310 outside the uplook field of view 11020 and outside the downlook field of view 12020, and viii) focusing the at least one second downlook metrology device 120 in a second focusing condition on the at least one second marker 3005, and vi-2) aligning the second focal plane 12099 of the at least one second downlook metrology device 120 with the uplook focal plane 11099 of the at least one second uplook metrology device 110 based on the first focusing condition and the second focusing condition.

[0116] Preferably, the alignment step vi-2) may comprise the step of ix) transforming a first focused position of the at least one first marker 315 acquired by the at least one second downlook metrology device 120 in the first focusing condition to a second focused position of the at least one first marker 315 acquired by the at least one second downlook metrology device 120 in the second focusing condition.

[0117] The computer implemented method according to the disclosure is designed to perform the transformation step ix) by transforming the first focused position to the second focused position through translation in a plane perpendicular to a mutual longitudinal axis of the at least one second downlook metrology device 120 and the at least one second uplook metrology device 110 and / or through rotation around the mutual longitudinal axis.

[0118] The disclosure also pertains to a computer program or product comprising instructions which, when the program is executed by a computer, for example by the control unit 711 , causes the computer and / or control unit 711 to carry out one or more steps of the computer implemented method according to the disclosure.

[0119] The disclosure also pertains to computer-readable storage medium comprising instructions which instructions, when executed by a computer and / or control unit 711 , cause the computer and / or control unit 711 to carry out one or more steps of the computer implemented method according to the disclosure.

[0120] A preferred implementation of the improved alignment system 100 and / or the improved alignment method has two main objectives: Step 1): At least one calibration and / or alignment of the at least one second downlook metrology device 120 and at least one second uplook metrology device 110 that are facing each other;

[0121] Step 2): At least one measurement to determine whether this calibration and / or alignment is still valid.

[0122] Step 1) is depicted in, for example Figure 3 and Figure 5. A reference element 130 is provided with at least one first marker 315 on the bottom side as depicted, for example using a chrome layer on a glass. At least one uplook device 110 is arranged to view the bottom side of the reference element 130, with a focal plane 11099 where the at least one first marker 315 is. This focal plane 11099 is the plane where the key imaging takes place, providing a high degree of accuracy reasons. At least one downlook device 120 is arranged to look at a top side as depicted of reference element 130. The at least one downlook device 120 is arranged to also focus on the at least one first marker 315, but must image and / or sense through a thickness 3199 of the transmissive reference element 130. This causes a shift of focus due to a refraction through the transmissive material which must be taken into account - this is the first focus condition.

[0123] The uplook device 110 and downlook device 120 image and / or sense the at least one first marker 315 at approximately the same time and at approximately the same environmental conditions such as temperature, humidity etc. One or more fields of view of the metrology device 110, 120 are then calibrated, usually internally within the device, with one or more positions of at least one first marker 315. Further, from the at least two images of the at least one first marker 315 from both metrology devices 110, 120, a mapping and / or transformation is computed that allows a translation and / or transformation of one or more positions in one field of view to another field of view, thereby aligning and / or calibrating the measurement system of the at least one uplook device 110 with the measurement system of the at least one downlook device 120.

[0124] Step 2) is depicted in, for example, Figures 15, 16, 17, 18, 21 , 22 and 23. After calibration and / or alignment in step 1), the reference element 130 with the at least one first marker 315 is removed from a field of view of the at least one uplook metrology device 110. During use of the apparatus, such as production, the validity of the calibration and / or alignment can be determined without having to mount the reference element 130 frequently. To detect if the calibration and / or alignment is still valid, at least one other marker is required. These other markers are the at least one second marker 3005, the at least one third marker 3025, the at least one fourth marker 3026, and / or the at least one fifth marker 3035. At least two of these other markers face upwards and can be sensed and / or image by at least one downlook metrology device 120. At least two of these other markers face downwards and can be sensed and / or image by at least one uplook metrology device 110. After removal of the reference element 130, the focus distance of the at least one downlook device 120 shifts compared to the first focus position. Therefore, a metrology device is used with a sufficiently high depth of field is used as the at least one downlook metrology device 120 to sense and / or image the other markers on the focal plane 11099. Additionally or alternatively, the at least one downlook metrology device 120 may be arranged to refocus on the one or more other marks - this is the “second focus condition”. Refocusing can be a movement of the downlook metrology device 120a and / or a change in focus and / or a change in the metrology device 120 between at least two focal planes.

[0125] During the calibration and / or alignment in step 1), at least one position of at least one first marker 315 was sensed and / or imaged - this is considered an “initial position”. In step 2), without the reference element 130, at least one position of one or more of the other markers is imaged without requiring a loss of production throughput - this is a “subsequent position”. By comparing at least one “initial position” with at least one “subsequent position”, a degree of validity of the alignment and / or calibrations in step 1) may be determined in step 2).

[0126] The improved alignment system and methods described herein may be advantageously further improved by using the “optical reference device for determining an orientation and / or position of a camera”, disclosed in the co-pending application DE 10 2023 133 895.1 , filed 4thof December 2023 by the same applicant, which is incorporated herein by reference. The optical reference device is for determining at least one orientation and / or position of one or more first cameras, arranged as one or more uplook or downlook cameras, relative to one or more second cameras, arranged respectively as one or more downlook or uplook cameras, the optical tool reference comprising: a mark carrier with a first carrier surface and a second carrier surface, wherein the second carrier surface is opposite to the first carrier surface; at least one first reference of one or more first markers on or proximate the first carrier surface, and at least one second reference of one or more first markers on or proximate the second carrier surface; wherein the mark carrier comprises one or more imaging portions; wherein the at least one first reference is arranged to allow one or more first images to be made by the one or more first cameras through the one or more imaging portions if the one or more first cameras are facing the second carrier surface; wherein the at least one second reference is arranged to allow one or more second images to be made through the one or more imaging portions by the one or more second cameras if the one or more second cameras facing the first carrier surface; wherein the one or more first images are arranged to provide a first orientation and / or position of the one or more first cameras relative to the at least one first reference; and wherein the one or more second images are arranged to provide a second orientation and / or position of the one or more second cameras relative to the at least one second reference.

[0127] The optical tool reference may be further advantageous if an average refractive index (n) of the imaging portions is approximately 2, or in the range of 1.0 to 3.0; or 1.5 to 2.5; or 1.7 to 2.3; or 1.75 to 2.25; or 1.8 to 2.2; or 1.85 to 2.15; or 1.9 to 2.1 ; or 1.95 to 2.05.

[0128] During an alignment or calibration procedure described herein, and for obviating at least one error when determining the first position, the alignment system may comprise fixating features structured to fixate, in the first alignment condition, the reference element in a position relative to the at least one uplook metrology device.

[0129] In one example, the fixating features are structured to fixate, in the first alignment condition, the reference element in a position relative to the at least one uplook metrology device using magnetic force, whereas in another example, the fixating features are structured to fixate, in the first alignment condition, the reference element in a position relative to the at least one uplook metrology device using vacuum.

[0130] Alternatively, in another example, the fixating features are structured to fixate, in the first alignment condition, the reference element relative to the at least one uplook metrology device on the supporting frame and wherein the fixating features consist of at least one pair of cooperating first and second interlocking elements.

[0131] In the latter example, the pair of cooperating first and second interlocking elements may be configured as at least one dent and at least one bulge, with the at least one dent and the at least one bulge exhibiting a circular, elliptical or torus configuration. Also, at least part of the outer dimensions of the at least one bulge may be oversized compared to the corresponding part of the inner dimensions of the cooperating dent, thereby ensuring an auto-centering effect of the reference element on the on the supporting frame.

[0132] LIST OF REFERENCES

[0133] 10 first pick and place apparatus

[0134] 11 first uplook metrology device

[0135] 12 first downlook metrology device 13 first bond head

[0136] 14 first reference element

[0137] 20 substrate

[0138] 100 improved alignment system

[0139] 110 second uplook metrology device

[0140] 120 second downlook metrology device

[0141] 130 second bond head

[0142] 211 semiconductor die

[0143] 212 semiconductor die

[0144] 213 semiconductor die

[0145] 300 support frame

[0146] 301 support frame component

[0147] 310 second reference element

[0148] 315 first marker

[0149] 711 control unit of improved alignment system

[0150] 740 displacement module for second downlook metrology device

[0151] 1111 first uplook imaging rays of first uplook metrology device

[0152] 1112 second uplook imaging rays of first uplook metrology device

[0153] 1120 field of view of first uplook metrology device

[0154] 1211 first downlook imaging rays of first downlook metrology device

[0155] 1212 second downlook imaging rays of first downlook metrology device

[0156] 1220 field of view of first downlook metrology device

[0157] 1311 marker of first bond head

[0158] 1411 marker of first reference element

[0159] 2012 substrate marker

[0160] 2132 die marker

[0161] 3005 second marker

[0162] 3021 frame component

[0163] 3022 frame component

[0164] 3023 frame component

[0165] 3025 third marker

[0166] 3026 fourth marker

[0167] 3031 further support frame component

[0168] 3032 further support frame component

[0169] 3033 further support frame component

[0170] 3035 fifth marker

[0171] 3101 first surface side of second reference element

[0172] 3102 second surface side of second reference element

[0173] 3199 thickness of second reference element

[0174] 7111 first control line for second uplook metrology device

[0175] 7112 second control line for second downlook metrology device

[0176] 7401 control line for displacement module

[0177] 11011 first uplook imaging rays of second uplook metrology device

[0178] 11012 second uplook imaging rays of second uplook metrology device

[0179] 11020 uplook field of view of second uplook metrology device

[0180] 11099 uplook focal plane of second uplook metrology device

[0181] 12011 first downlook imaging rays of second downlook metrology device

[0182] 12020 field of view of second downlook metrology device

[0183] 12089 first focal plane of second downlook metrology device

[0184] 12099 second focal plane of second downlook metrology device

[0185] 13013 marker of second bond head

[0186] 13075 view passage of bond head

Claims

CLAIMS1. Alignment system (100) for aligning at least one downlook metrology device (120) and at least one uplook metrology device (110) with respect to each other, the alignment system (100) at least comprising: at least one uplook metrology device (110) having at least one uplook focal plane (11099) and an uplook field of view (11020) directed towards at least one second downlook metrology device (120); wherein the at least one downlook metrology device (120) has at least one downlook focal plane (12099) and a downlook field of view (12020) directed towards the at least one uplook metrology device (110), and a reference element (310) comprising at least one first marker (315); wherein, in a first alignment condition, the alignment system (100) is structured to position the reference element (310) within the uplook focal plane (11099) and in the downlook focal plane (12099) such that the at least one first marker (315) is oriented in the at least one uplook focal plane (11099), and the at least one downlook metrology device (120) is structured to focus in a first focus condition on the at least one first marker (315); and wherein the alignment system (100) is structured to align the at least one downlook focal plane (12099) of the at least one downlook metrology device (120) with the uplook focal plane (11099) of the at least one uplook metrology device (110) based on at least the first focus condition.

2. Alignment system (100) according to claim 1 , wherein the alignment system (100) is structured to align the at least one downlook focal plane (12099) of the at least one downlook metrology device (120) with the uplook focal plane (11099) of the at least one uplook metrology device (110) based on the first focus condition and one or more parameters selected from optical properties of the reference element (310), a thickness (3199) of the reference element (310), and a depth of focus of the at least one downlook metrology device (120).

3. Alignment system (100) according to claim 1 or 2, wherein the alignment system (100) further comprises at least one second marker (3005) oriented in the at least one uplook focal plane (11099), and wherein, in the first alignment condition,the at least one downlook metrology device (120) is structured to focus on the at least one second marker (3005), and wherein, in a second alignment condition, the alignment system (100) is structured to position the reference element (310) outside the downlook field of view (12020), and the at least one downlook metrology device (120) is structured to focus in a second focus condition on the at least one second marker (3005), and wherein the alignment system (100) is structured to align the at least one downlook focal plane (12099) of the at least one downlook metrology device (120) with the uplook focal plane (11099) of the at least one uplook metrology device (110) based on both the first focus condition and the second focus condition.

4. Alignment system (100) according to any one of the claims 1 to 3, wherein the alignment system (100) further comprises a support frame (300) that is structured to be in a fixed position relative to the at least one uplook metrology device (110) and structured to support the reference element (310) in the first alignment condition.

5. Alignment system (100) according to claim 4, wherein the second marker (3005) is mounted to the support frame (300).

6. Alignment system (100) according to any one or more of the claims 3 to 5, wherein, for alignment purposes, the alignment system (100) is structured to transform a first focused position of the at least one second marker (3005) acquired by the at least one downlook metrology device (120) in the first alignment condition to a second focused position of the at least one second marker (3005) acquired by the at least one downlook metrology device (120) in the second alignment condition.

7. Alignment system (100) according to claim 6, wherein the alignment system (100) is structured to transform the first focused position of the at least one first marker (315) to the second focused position of the at least one first marker (315).

8. Alignment system (100) according to any one or more of the preceding claims, wherein the alignment system (100) comprises at least one third marker (3025) being positioned at a distance from and at a first side of the uplook focal plane (11099) seen in a direction parallel to a mutual longitudinal axis of the at least one second downlook metrology device (120) and the at least one second uplook metrology device (110).

9. Alignment system (100) according to any one or more of the preceding claims, wherein the alignment system (100) comprises at least one fourth marker (3026) positioned at a distance from and at a second, opposite side of the uplook focal plane (11099) seen in a direction parallel to a mutual longitudinal axis of the at least one second downlook metrology device (120) and the at least one second uplook metrology device (110).

10. Alignment system (100) according to any one or more of the preceding claims, wherein the alignment system (100) comprises at least one fifth marker (3035) oriented in the at least one uplook focal plane (11099).

11. Alignment system (100) according to claim 8 or 9 or 10, further comprising at least one frame component (302, 3021 , 3022, 3023) and / or further support frame component (3031 , 3032, 3033) containing at least one third marker (3025) and / or at least one fourth marker (3026) and / or at least one fifth marker (3035).

12. Alignment system (100) according to claim 11 , wherein the at least one frame component (302, 3021 , 3022, 3023) and / or further support frame component (3031 , 3032, 3033) is made of a material having a refraction index of n in the range of 1.9 to 2.1 , in particular 1.95 to 2.05, more in particular 1.975 to 2.025, even more in particular 1.99 to 2.01 and even more in particular 1.995 to 2.005.

13. Alignment system (100) according to any one or more of the claims 8 to 12, wherein the at least one uplook metrology device (110) is structured to additionally determine, in the first alignment condition, an initial position of the at least one fourth marker (3026) and / or of the at least one fifth marker (3035) and, in the second alignment condition, to determine a subsequent position of the at least one fourth marker (3026) and / or the at least one fifth marker (3035); and wherein the alignment system (100) is structured to re-align the at least one downlook focal plane (12099) of the at least one downlook metrology device (120) with the at least one uplook focal plane (11099) of the at least one uplook metrology device (110) based on one or more initial positions and / or one or more subsequent positions thus determined.

14. Alignment system (100) according to any one or more of the preceding claims, wherein the reference element (310) is coplanar.

15. Alignment system according to claim 14, wherein the reference element (310) is transmissive to a high degree for the at least one downlook metrology device (120).

16. Alignment system (100) according to any one or more of the claims 3 to 15, wherein, in either the first alignment condition and / or the second alignment condition, the at least one downlook metrology device (120) is structured to focus in the first focus condition and / or second focus condition through refocusing of its at least one downlook focal plane (12099).

17. Alignment system (100) according to any one or more of the claims 3 to 16, further comprising a displacement module structured to displace the at least one downlook metrology device (120) from the first focus condition towards the second focus condition at least in the direction essentially parallel to a mutual longitudinal axis of the at least one second downlook metrology device (120) and the at least one second uplook metrology device (110).

18. Computer-implemented method for aligning at least one downlook metrology device (120) and at least one uplook metrology device (110) with respect to each other, the alignment method at least comprising the steps of: i) orienting at least one uplook metrology device (110) having an uplook focal plane (11099) and an uplook field of view (11020) towards at least one second downlook metrology device (120); ii) directing at least one downlook metrology device (120) having at least one downlook focal plane (12099) and a downlook field of view (12020) towards the at least one uplook metrology device (110); iii) mounting, in a first alignment condition, a reference element (310) comprising at least one first marker (315) within the uplook field of view and within the downlook field of view; and iv-1) orienting the at least one first marker (315) in the uplook focal plane (11099); v) focusing the at least one downlook metrology device (120) in a first focusing condition on the at least one first marker (315); vi) aligning the downlook focal plane (12099) of the at least one downlook metrology device (120) with the uplook focal plane (11099) of the at least one uplook metrology device (110) based on the first focusing condition.

19. Computer-implemented method according to claim 18, wherein the aligning step vi) is based on the first focus condition and one or more parameters selected from optical properties of the reference element (310), a thickness (3199) of the reference element (310), and a depth of focus of the at least one downlook metrology device (120).

20. Computer-implemented method according to claim 18 or 19, further comprising the steps of iv-2) orienting at least one second marker (3005) in the at least one uplook focal plane (11099); iv-3) focusing the at least one downlook metrology device (120) on the at least one second marker (3005); vii) removing, in a second alignment condition, the reference element (310) outside the uplook field of view and the downlook field of view, and viii) focusing the at least one downlook metrology device (120) in a second focusing condition on the at least one second marker (3005), and vi-2) aligning the second focal plane of the at least one downlook metrology device (120) with the uplook focal plane (11099) of the at least one uplook metrology device based on the first focusing condition and the second focusing condition.

21. Computer-implemented method according to claim 20, wherein the alignment step vi-2) comprising the step of ix) transforming a first focused position of the at least one first marker (315) acquired by the at least one downlook metrology device (120) in the first focusing condition to a second focused position of the at least one first marker (315) acquired by the at least one downlook metrology device (120) in the second focusing condition.

22. Computer-implemented method according to claim 21 , wherein the transform step ix) comprises transforming the first focused position to the second focused position through translation in a plane perpendicular to a mutual longitudinal axis of the at least one second downlook metrology device (120) and the at least one second uplook metrology device (110) and / or through rotation around the mutual longitudinal axis.

23. Computer implemented method according to any one of the claims 19 to 22, wherein the alignment system comprises at least a third marker (3025) being positioned at a distance from and at a first side of the uplook focal plane (11099) as viewed in a direction parallel to a mutual longitudinal axis of the at least one second downlook metrology device (120) and the at least one second uplook metrology device (110), and the method comprises the further steps of: determining, with the at least one downlook metrology device (120), in the first focusing condition an initial position of the at least one third marker (3025) and inthe second focusing condition a subsequent position of the at least one third marker (3025); and re-aligning the downlook focal plane (12099) of the at least one downlook metrology device (120) with the uplook focal plane (11099) of the at least one uplook metrology device (110) based on one or more initial positions and / or one or more subsequent positions thus determined.

24. Computer-implemented method according to claim 23, wherein the alignment system (100) further comprises at least one fourth marker (3026) positioned at a distance from and at a second, opposite side of the uplook focal plane (11099) seen in a direction parallel to a mutual longitudinal axis of the at least one second downlook metrology device (120) and the at least one second uplook metrology device (110), and the method comprises the further steps of: determining, with the at least one uplook metrology device (110), in the first focusing condition an initial position of the at least one fourth marker (3026) and in the second focusing condition a subsequent position of the at least one fourth marker (3026); and re-aligning the downlook focal plane (12099) of the at least one downlook metrology device (120) with the uplook focal plane (11099) of the at least one uplook metrology device (110) based on one or more initial positions and / or one or more subsequent positions of the at least one third marker (3025) and / or the at least one fourth marker (3026) thus determined.

25. Computer-implemented method according to any one of the claims 20 to 24, wherein the alignment system (100) comprises at least one fifth marker (3035) oriented in the at least one uplook focal plane (11099), and the method comprises the further steps of: determining, with the at least one uplook metrology device (110), in the first focusing condition an initial position of the at least one fifth marker (3035) and in the second focusing condition a subsequent position of the at least one fifth marker (3035); and re-aligning the downlook focal plane (12099) of the at least one downlook metrology device (120) with the uplook focal plane (11099) of the at least one uplook metrology device (110) based on one or more initial positions and one or more subsequent positions of the at least one second marker (3005) and / or the at least one fifth marker (3035) thus determined.

Images