EP4214519A1

EP4214519A1 - Method, system and parts for enabling navigation in a scanning probe microscopy system

Info

Publication number: EP4214519A1
Application number: EP21794211.9A
Authority: EP
Inventors: Hamed Sadeghian Marnani; Godefridus Cornelis Antonius COUWELEERS
Original assignee: Nearfield Instruments BV
Current assignee: Nearfield Instruments BV
Priority date: 2020-09-17
Filing date: 2021-09-16
Publication date: 2023-07-26
Also published as: WO2022060224A1; NL2026497B1

Abstract

The present document relates to a method of calibrating a scanning probe microscopy system for enabling navigation. The system comprises one of more scan heads, a coordinate reference grid and a substrate carrier. The substrate carrier includes a carrier surface arranged opposite the coordinate reference grid and remotely therefrom such as to define a working space for the one or more scan heads. For enabling navigation between the scan heads and the substrate carrier, a relation is determined, using a sensor encoder cooperating with the coordinate reference grid, between a relative position of an optical sensor and the coordinate reference grid. This provides coordinate system data indicative of a coordinate system for the optical sensor relative to the grid, the optical sensor being fixed relative to the sensor encoder. Furthermore, a relative offset location of the probe tip and the head encoder of the scan head is determined, in order to allow positioning of the probe tip using the coordinate system obtained. The document also relates to a method of wafer alignment, an optical sensor, a support therefore, an assembly, a scanning probe microscopy system and a computer program product.

Description

Title: Method, system and parts for enabling navigation in a scanning probe microscopy system.

Field of the invention

The present invention is directed at a method of calibrating a scanning probe microscopy system for enabling navigation, wherein the scanning probe microscopy system comprises one of more scan heads, a coordinate reference grid and a substrate carrier, wherein each of the one or more scan heads comprises a probe including a probe tip for scanning of a substrate surface for performing measurements, and a head encoder cooperating with the coordinate reference grid; wherein, for supporting a substrate, the substrate carrier includes a carrier surface, the carrier surface being arranged opposite the coordinate reference grid and remotely therefrom such as to define a working space for the one or more scan heads between the coordinate reference grid and the carrier surface. The invention is further directed at a method of performing substrate alignment that is based on such a calibration, an optical sensor, a support therefore, an assembly, a scanning probe microscopy system and a computer program product.

Background

Conventional calibration methods and method of performing wafer alignment to allow navigation of a scan head of a scanning probe microscopy (SPM) system relative to a substrate surface, for example rely on cooperation between an optical microscope or imaging device and a scan head in an SPM system. The optical system is used to obtain a rough overall image of an area on a substrate or substrate carrier, such as to provide a rough determination of a location and an orientation of the substrate. The scan head and probe tip are then used to scan a smaller area that can be recognized and that can be used to determine a fine positioning. Typically, these methods use the imaging and scanning of a marker on a substrate, and in many cases a number of such markers to obtain an accurate alignment and positioning. The calibration, as accurate as it needs to be, is not a speedy process. However, once it has been done for a substrate it can be relied upon for the duration of the measurements, as long as ambient and system temperatures remain stable.

The calibration method, however, is not very suitable to be used in SPM systems wherein multiple scan heads are available to scan several sites or areas on a surface of a substrate simultaneously. A disadvantage, in this respect, is that calibration needs to be performed for each scan head which therefore considerably slows down the process of scanning the substrate. This in itself is already problematic because it significantly diminishes the advantage of scanning several sites simultaneously. However, in an industrial setting where throughput is important, this disadvantage even more problematic.

Summary of the invention

It is an object of the present invention to overcome the abovementioned drawbacks of the prior art and to provide a calibration method that can be performed quickly for an arbitrary number scan heads of an SPM system.

To this end, there is provided herewith a method as described earlier, wherein for enabling navigation between at least one of the scan heads and a substrate carrier, the method comprises the steps of: a) determining, using a sensor encoder cooperating with the coordinate reference grid, a relation between a relative position of an optical sensor and the coordinate reference grid, such as to provide coordinate system data indicative of a coordinate system for the optical sensor, wherein the optical sensor is fixed relative to the sensor encoder; and b) determining, for the at least one scan head, a relative offset location of the probe tip and the head encoder of the scan head.

The present invention, in accordance with a first aspect, applies an optical sensor with a sensor encoder. The sensor encoder cooperates with the coordinate reference grid to form a grid encoder. Furthermore, each of the scan heads includes a head encoder in order to cooperate with the coordinate reference grid for enabling navigation. In the first step, using the sensor encoder, a relation between a relative position of the optical sensor and the coordinate reference grid is determined. This, for example, can be done by sensing or imaging references (e.g. structures or marks) of which the location is known, while obtaining location data using the position signal from the sensor encoder. Relating the obtained location data to the known locations of these references allows to provide coordinate system data that is indicative of a coordinate system wherein the optical sensor is moving in relation to the coordinate reference grid. Prerequisite for this is that the optical sensor is fixed relative to the sensor encoder, such that there is a direct and stable relation between the read-out position signal from the encoder and the actual position of the optical sensor.

The grid encoder is a positioning sensor consisting of the coordinate reference grid and the one or more encoders applied in the present system. In a two dimensional grid encoder, the movable encoders read a geometric pattern (grid) encoded in the grid plate to determine their location on the grid. Location data can be acquired from the position signal provided by the encoder. The coordinate system obtained in the first step above maps the real locations within the SPM system to XY coordinates in the plane of the grid plate. In a next step in accordance with the invention, a relative offset location of the probe tip and the head encoder of each scan head (or at least the scan heads to be used later) is established. This enables to use the encoder readings from each of the head encoders to exactly determine the locations of the probe tips in the plane of the grid. Hence, the determined coordinate system can be applied directly to the position data obtained from each head encoder to determine exactly the current location of the probe tip in the system. A controller of the system, e.g. a central controller of the SPM system or a local controller on each scan head, may then be applied to navigate the probe tip to e.g. a desired location in the system.

As probe tips need to be replaced frequently in operation due to wear thereof during scanning, the offset distance of the probe tip relative to the encoder is not fixed. Therefore, step b) will be repeated for each scan head after each probe tip replacement. There are various ways to implement the step of determining the relative offset location of the probe tip and the head encoder. In some embodiments, step b) is performed by the steps of: bl) determining, using the optical sensor and the sensor encoder cooperating with the coordinate reference grid, location data of a location of a fiducial marker in the coordinate system, wherein the fiducial marker is included on the substrate carrier; and b2) determining, for the at least one scan head, the relative offset location of the probe tip and the head encoder of the scan head by scanning, using the probe tip of the respective scanner, the fiducial marker while obtaining head location data via the head encoder. A fiducial marker located on the substrate carrier may consist of both a rough pattern to be recognized by the optical sensor and a fine pattern to be recognizer from a scan by a probe tip. Step bl) will provide the exact location of the fiducial marker in the coordinate system, whereas step b2) enables to determine therefrom the offset of the probe. The latter may for example be done by recognizing the pattern obtained using the probe tip, and relate it to the image obtained using the optical sensor. From this and from the location data provided by the head encoder at each pixel measured by the probe tip, the exact relative offset between the probe tip and the head encoder can be determined. In conventional methods, the recalibration of each scan head after probe replacement further slows down the process considerably. The present invention enables this to be done very quickly. In the above embodiments, by relating the location of the fiducial marker to the coordinate system, and then sensing the fiducial marker with the probe tip, each scan head can be quickly recalibrated after probe replacement by determining the relative offset of the probe tip in relation to the head encoder using the images of the fiducial marker, for example in the above manner. This manner of quickly determining the probe tip offset is however not the only manner in which this offset may be obtained by the present invention, as will be made clear further down below with respect to some further embodiments.

First, in accordance with some embodiments of the method of the invention, the optical sensor and the sensor encoder are included on a sensing element, wherein the sensing element is operating separate and individually from the one or more scan heads. In these embodiments, the sensor element is an individual element operating independently from the scan heads within the system. Such an independent sensing element may be moved around the system and placed in certain locations using a positioning unit module, e.g. a placement arm that is controlled from outside the working space between the grid plate and the carrier surface. However, in other embodiments, such an individual sensor element comprises other driving means or may even be e.g. self-propelled using for example a gas bearing and precision motion actuators.

In some further embodiments, the optical sensor is included on at least one of the scan heads, and the sensor encoder is provided by the head encoder of the scan head. Here, one or more of the available scan heads may be equipped with an additional optical sensor, which uses the head encoder of the scan head as sensor encoder. One of the advantages is that a separate sensor element in this case is not needed, thereby saving working space and allowing for the use of an additional scan head. Another advantage is that steps bl) and b2) described with respect to the embodiments above, can be carried out at once for the scan head supporting the optical sensor. In some particular of these embodiments, the system comprises a plurality of scan heads, and at least two of the scan heads include an optical sensor, wherein for each of the at least two scan heads the sensor encoder is provided by the head encoder of the respective scan head. The application of an optical sensor on multiple or even each scan head has various advantages. As will be understood, this enables the use of multiple optical sensors during the calibration process, which shortens the time to carry out the calibration.

A particular advantage that may be achieved with using an optical sensor fixed to a scan head, is that the optical sensor can be used as a distance sensor to obtain information about the distance to the substrate surface in relation to a reference point (e.g. the probe tip) on the scan head. This information can be used to roughly control the height positioning. Furthermore, in an optical sensor suitable to carry out the invention, in a particular embodiment thereof, the sensor includes an additional capacitive sensor to aid in the focusing of the imaging sensor on the surface. The information of the capacitive sensor likewise enables to determine the distance to the substrate surface.

In accordance with some particular embodiments, the optical sensor is included on at least one of the scan heads, and the optical sensor is placed such that the probe tip is within a field of view of the optical sensor, wherein step b) is performed by determining the relative offset of the probe tip and the head encoder from image data obtained with the optical sensor. In this particular class of embodiments, wherein any of one of the scan heads, multiple scan heads or all scan heads may include an optical sensor, the probe tip(s) are within sight - i.e. within the field of view - of the optical sensor such that from the images taken with the optical sensor, the relative offset of the probe tip in relation to the encoder can directly be obtained. In some embodiments of the invention, step a) is performed by sensing, using the optical sensor, the or each location of one or more calibration markers that are distributed across the carrier surface. The scanning of calibration markers distributed across the work space at several locations, enables to obtain accurate coordinate system data. In some embodiments, the one or more calibration markers may be provided on a calibration substrate surface to be loaded onto the carrier surface for carrying out step a). Here, a calibration substrate (e.g. a calibration wafer) may be loaded onto the substrate carrier on which a plurality of calibration marker is provided. This calibration substrate may be removed again after step a). In other or further embodiments, the one or more calibration markers are included on the carrier surface of the substrate carrier, wherein step a) is performed by scanning the carrier surface in absence of a substrate. Here the calibration markers are already present on the substrate carrier, fixing their positions to the metrology frame. In this case, no calibration substrate is needed and the system is enabled to perform a self-calibration after replacing a mark sensor or grid plate.

In accordance with a second aspect, there is provided a method of performing substrate alignment for establishing a relation between a relative positions on a substrate and a coordinate system provided by coordinate system data in a scanning probe microscopy system, wherein the coordinate system data is obtained using a method according to the first aspect, wherein the scanning probe microscopy system comprises one of more scan heads, a coordinate reference grid and a substrate carrier, wherein each of the one or more scan heads comprises a probe including a probe tip for scanning of a substrate surface for performing measurements, and a head encoder cooperating with the coordinate reference grid; wherein, for supporting a substrate, the substrate carrier includes a carrier surface, the carrier surface being arranged opposite the coordinate reference grid and remotely therefrom such as to define a working space for the one or more scan heads between the coordinate reference grid and the carrier surface; wherein the method comprises: providing a substrate on the carrier surface, the substrate comprising a plurality of alignment marks; determining, using an optical sensor fixed to a sensor encoder, first location data of a location of a first alignment mark on the substrate and orientation data of the first alignment mark with respect to the coordinate system; predicting, using the first location data, the orientation data and substrate layout data, one or more second location data of locations of one or more second alignment marks with respect to the coordinate system; and mapping, by sensing with the optical sensor, the one or more second alignment marks to the coordinate system by moving the optical sensor to the locations provided by the predicted second location data, and providing alignment data of an alignment of the substrate to the coordinate system.

The method in accordance with the first aspect calibrated the SPM system in order to provide a coordinate system and a direct relation between position readings from an encoder cooperating with the coordinate reference grid and the exact XY position of a probe tip in the SPM system for each scan head. As a next step, upon loading of each substrate onto the substrate carrier, the substrate needs to be aligned relative to the coordinate system (or vice versa). As may be appreciated, in order to accurately perform surface measurements, the orientation and position of the substrate on the carrier surface needs to be mapped to the coordinate system. To this end, in accordance with the second aspect, the optical sensor determines first location data of a location of a first alignment mark on the substrate and orientation data of the first alignment mark with respect to the coordinate system. For example, the optical sensor may start by sensing a center alignment mark if the substrate is a wafer. From this the position may be determined and as well as an estimate of the orientation of the substrate. Then, based on the first location data, the orientation data and substrate layout data, one or more second location data of locations of one or more second alignment marks are predicted with respect to the coordinate system. The optical sensor will then be moved to the predicted locations to perform a sensing of the second alignment marks. The one or more second alignment marks may then be mapped to the coordinate system by obtaining their positions with the encoder (i.e. the sensor encoder, or the head encoder in case the optical sensor is fixed to a scan head). From this alignment data of an alignment of the substrate to the coordinate system can be determined, e.g. by a controller of the SPM system. The substrate is thereby mapped onto the coordinate system, such that a probe tip of one of the scan heads may be placed at any desired location on the substrate surface, using the grid encoder.

In some embodiments, the substrate layout data may be obtained by loading the substrate layout data into a memory of the scanning probe microscopy system, wherein the memory is communicatively connected to a controller of the system. Alternatively, or additionally, the substrate layout data may be obtained from a data communication network, such as from a remote data storage location or a remote server. Furthermore, the substrate layout data may also be obtained from input by an operator of the scanning probe microscopy system. For example, in that event, relative location data of alignment markers may be received via manual input, or in addition to substrate layout data already present in the memory (e.g. as a correction or to provide details of an additional marker). Furthermore, in some embodiments, the substrate layout data may be obtained from a further optical instrument, such as a camera. In that case, a camera imaging a large area of the substrate may be providing an image form which alignment markers can be recognized and their rough locations can be determined. Any of these embodiments are possible alone or in combinations with others.

In accordance with a third aspect, there is provided a method of navigating at least one scan head of a plurality of scan heads of a scanning probe microscopy system to a location of interest on a substrate, wherein the method includes a method of performing substrate alignment according to the second aspect, wherein each of the one or more scan heads includes a head encoder, and wherein the method comprises: obtaining, for the at least one scan head, a point of interest location indication of a point of interest on the substrate; determining, using the alignment data, location data of the point of interest indicative of a coordinate in the coordinate system; and moving the at least one scan head to the coordinate indicated by the location data of the point of interest.

The invention further provides an optical sensor for use in any of the methods described above. Therefore, in accordance with a fourth aspect, there is provided an optical sensor for use in a scanning probe microscopy system, comprising a structural element supporting an imaging sensor, one or more focusing objectives, and at least one actuator for adapting a distance between the imaging sensor and the focusing objectives, for enabling focusing of the imaging sensor onto a surface to be imaged, such as a substrate surface, a carrier surface of a substrate carrier, or a fiducial marker on the substrate carrier; wherein the structural element comprises fixation structures for enabling fixation of the optical sensor to a support including an encoder configured for cooperating with a coordinate reference grid of the scanning probe microscopy system, for enabling fixing of the optical sensor relative to the encoder for enabling the encoder to serve as a sensor encoder in a method according to the first, second or third aspect.

In some embodiments, the imaging sensor is a complementary metal oxide semiconductor (CMOS) camera. An advantage of a CMOS is the low energy consumption thereof, which makes it suitable for use in mobile entities such as e.g. a sensing element as mentioned herein. Alternatively, a CCD chip may likewise be applied dependent on preferences in the design. In some embodiments, the actuator includes one or more piezo elements cooperating with flexures. This provides a miniature but precise actuator structure for adjusting the focusing of the imaging sensor. Furthermore, in some embodiments, the one or more focusing objectives include a tube lens. Together a compact design of the optical sensor may be obtained. To this end, in some embodiments, the optical sensor further includes a redirection mirror for enabling placement of the imaging sensor and the one or more focusing objectives along an optical axis parallel to the coordinate reference grid in use, while obtaining images with the imaging sensor in an off axis direction relative to the optical axis. The requirements in terms of size of the sensor between the grid and the carrier surface are far more strict than in a direction parallel to the grid plate. Hence, using a mirror or other redirection optical element to perform off axis imaging with respect to an optical axis (or longitudinal axis) of the optical sensor enables to make use of the less strict size requirements in this parallel direction.

In accordance with a fifth aspect, there is provided a support, wherein the support is configured to be used in a scanning probe microscopy system, the support further comprising an encoder configured for cooperating with a coordinate reference grid of the scanning probe microscopy system, wherein the encoder is fixed relative to the optical sensor upon fixing of the optical sensor to the support for enabling the encoder to serve as a sensor encoder in a method according to the first, second or third aspect, wherein the support is further configured for moving in a working space of the scanning probe microscopy system defined between the coordinate reference grid and a carrier surface of a substrate carrier, such as to enable imaging of substrate surface supported by the substrate carrier while simultaneously obtaining location data of a current location of the support relative to the coordinate reference grid. The support enables fixing of the optical sensor relative to the encoder as required in the method in accordance with the first aspect.

In some embodiments, the support is comprised by at least one of a groups comprising: a positioning arm of the scanning probe microscopy system; a scan head including a probe and a probe tip, wherein the encoder is provided by a head encoder of the scan head; a support structure suitable for being placed by a placement arm of the scanning probe microscopy system; and a support structure comprising a motion driver or actuator for enabling independent movement of the support relative to a coordinate reference grid, such as by using or providing a gas bearing. The support enables to integrate the optical sensor in different ways into the SPM system, as is clear from the above embodiments.

In accordance with a sixth aspect, there is provided an assembly comprising an optical sensor according to the fourth aspect and a support according to the fifth aspect.

Yet in accordance with a seventh aspect, there is provided a scanning probe microscopy system comprising one of more scan heads, a coordinate reference grid and a substrate carrier, wherein each of the one or more scan heads comprises a probe including a probe tip for scanning of a substrate surface for performing measurements, and a head encoder cooperating with the coordinate reference grid; wherein, for supporting a substrate, the substrate carrier includes a carrier surface, the carrier surface being arranged opposite the coordinate reference grid and remotely therefrom such as to define a working space for the one or more scan heads between the coordinate reference grid and the carrier surface; wherein the system further comprises an optical sensor fixed relative to a sensor encoder, the sensor encoder being configured for cooperating with the coordinate reference grid; and wherein the system further comprises a memory and a controller, wherein the controller is configured for performing the steps of: a) determining, using a location signal from the sensor encoder cooperating with the coordinate reference grid, a relation between a relative location of the optical sensor and the coordinate reference grid, such as to provide coordinate system data indicative of a coordinate system for the optical sensor; b) determining, for the at least one scan head, a relative offset location of the probe tip and the head encoder of the scan head. The SPM system of this type may be applied in any of the above methods.

In particular, in some embodiments, the controller is further configured for performing the step b) by the steps of: bl) determining, using the optical sensor and the sensor encoder cooperating with the coordinate reference grid, location data of a location of a fiducial marker in the coordinate system, wherein the fiducial marker is included on the substrate carrier; and b2) determining, for the at least one scan head, the relative offset location of the probe tip and the head encoder of the scan head by scanning, using the probe tip of the respective scanner, the fiducial marker while obtaining head location data via the head encoder.

In accordance with an eighth aspect, there is provided a computer program product comprising instructions which, when loaded into a memory of a scanning probe microscopy system according to the seventh aspect, enable the controller of the system to perform a method according to the first, second or third aspect.

Brief description of the drawings

The invention will further be elucidated by description of some specific embodiments thereof, making reference to the attached drawings. The detailed description provides examples of possible implementations of the invention, but is not to be regarded as describing the only embodiments falling under the scope. The scope of the invention is defined in the claims, and the description is to be regarded as illustrative without being restrictive on the invention. In the drawings:

Figures la through 1c schematically illustrate a method in accordance with the present invention performed on a system in accordance with an embodiment of the present invention; Figure 2a through 2c schematically illustrate a method of aligning a substrate, in accordance with a further embodiment of the present invention;

Figure 3 schematically illustrates an optical sensor in accordance with an embodiment of the present invention;

Figure 4 schematically illustrates a support in accordance with an embodiment of the present invention, bearing an optical element in accordance with an embodiment and a scan head, in a system in accordance with an embodiment of the invention.

Detailed description

In figures la through 1c, a method in accordance with an embodiment of the first aspect of the present invention is schematically illustrated by showing a system in accordance with an embodiment of the invention wherein the method is applied step by step. In figure la, a scanning probe microscopy system 1 comprises a base 5 and a substrate carrier 3. The base 5 comprises a coordinate reference grid plate 6. The coordinate reference grid plate is part of a grid encoder, which consists of the plate 6 and at least one encoder 15. Typically, in the system 1 in accordance with the present invention, a plurality of encoders cooperate with the grid plate 6. For example, each element that is moving within the working space 2 between the sample carrier 3 and the grid plate 6 may comprise an encoder 15 that cooperates with the grid plate 6 in order to determine its position on the grid plate 6. The encoder 15, and each other encoder cooperating with the coordinate reference grid plate 6, (reads) the reference grid in order to obtain the coordinate data of its current location on the grid 6.

In figure la, the encoder 15 is mounted on a support 13 which is part of an arm 12 of a positioning unit module. The support 13 comprises an optical sensor 14 and the encoder 15. The optical sensor 14 provides an important aspect of the invention and, in the illustrated embodiment, includes a miniature camera unit 20 having a field of view 19 through its sensor opening 17. The optical sensor 14 further comprises an aperture 21, a focusing lens 22 and actuators 24. The actuators 24 enable to adjust the distance between the camera 20 and the focusing optics 22 for enabling focusing of the image on the surface of the substrate 8. Furthermore, in order to make use of the available space parallel to the surface of the grid plate 6 in the working space 2, a mirror 25 redirects the field of view of the camera 20 from a horizontal into a vertical direction as illustrated in figure la. The optical sensor 14 is mechanically fixed to the support 13 and the arm 12, as will be described later. Furthermore, electrical connections for data transfer to the system 1 are provided via the electrical connection interface 18.

The camera 20 must be accurate enough to be able to recognize alignment marks on the wafer. The sizes of such marks are typically within a range of 20*20 micrometer up to 50*50 micrometer, but of course the size these marks may vary and may become smaller over time. The resolution of the image features of alignment marks may typically be down to 1 micrometer, which may likewise be subject to change (i.e. decrease) over time. The camera 20 may be adapted accordingly dependent on the size and/or resolution of the alignment marks, and should be able to distinguish the necessary image features in order to carry out its task. For example, pixel resolution of camera 20 in the object plane (e.g. surface to be read, bearing the marks) may be smaller than or equal to 2 micrometer, preferably smaller than or equal to 1.0 micrometer, more preferable smaller than or equal to 0.5 micrometer. Furthermore, magnification of the camera may be 5 to 100 times, preferably 10 to 50 times, and the camera may be able to operate with at least two magnification factors for low and high magnification. The camera must be able to detect alignment features on a wafer surface, which may be placed as close as 1 millimeter from the edge of the wafer. Power consumption of the camera is preferably as low as possible to reduce thermal dissipation and unwanted effects on the accuracy. The field of view 19 of camera 20 may be at least 0.5 millimeter, preferably at least 0.9 millimeter.

In figure la, a calibration wafer 8, which is provided by a special wafer with alignment marks 9 (i.e. 9-1...9-5...9-n) is provided on the sample carrier, thereby providing the substrate surface that can be used for calibration of the system 1. Furthermore, the sample carrier 3 comprises, e.g. on an edge thereof, a fiducial marker 4.

In a method in accordance with an embodiment of the present invention, as illustrated in figure la, as a first step the system must be calibrated in order to obtain a coordinate system which enables any element in the working space 2 to be properly navigated in use. The coordinate system to be determined is associated with the SPM system, reference grid plate 6 and the optical sensor 14. If any of these latter elements: the optical sensor 14 or the grid plate 6, is to be replaced, a new calibration of the system is needed in order to obtain a correct coordinate system associated with the elements. However, because typically neither the grid plate 6, nor the optical sensor 14 requires frequent replacement, the calibration step is typically performed on first use of the system 1, and occasionally after replacement of any of these elements. As may be appreciated, a skilled person is free to perform the calibration step as often as deemed necessary or desired, and the invention is not limited to performing the calibration step only at the times indicated hereinabove.

The first step illustrated in figure la is the sensing, or imaging, of a sufficient number of calibration markers 9-n by the optical sensor 14. This is done by moving the optical sensor 14 across the surface of the grid 6 while obtaining location data of the current location of encoder 15 of the support 13. For example at each of the locations 9-1, 9-2, 9-3, 9-4 and 9-5 illustrated in figure la, the optical sensor 14 obtained an image of the calibration marker, e.g. calibration marker 9-4, while registering, associated therewith, the current location data obtained from the encoder 15. The layout of the calibration wafer 8 is exactly known in the system 1, and therefore by taking the images from the calibration markers 9-n and registering these associated with the location data obtained from the encoder 15, a relation between the positions of the calibration markers 9-n and the location data from the coordinate reference grid 6 can be established. This provides the coordinate system data which is indicative of the coordinate system for the optical sensor. As may be appreciated, it is important herein that the optical sensor 14 is fixed relative to the encoder 15 such that the location data obtained from the encoder 15 can be reliably related to the images obtained with the optical sensor 14.

Although in figure la, the step of obtaining a relation between the relative positioning of the optical sensor 14 and a coordinate reference grid 6 is performed using a calibration wafer 8, the skilled person may appreciate that it is not an essential step to the invention to use a calibration wafer such as wafer 8. Alternatively, known fixed references in the system 1 may likewise be used for determining such a relation. For example, in an alternative embodiment the substrate carrier 3 may for example include scannable calibration references directly on its bearer surface 7, such that the loading of a calibration wafer 8 is not required. Also the calibration wafer 8 not necessarily needs to be a special wafer comprising special marks, but may also be a wafer of which the layout is exactly known in the system 1, and which comprises distinguishable marks on its surface. The skilled person may recognize the various alternatives for implementing this step.

After performing the first calibration step illustrated in figure la, the method of the present invention may continue by performing a determination of a relative offset location of the probe tip and the head encoder of the scan head 30. Figures lb and 1c illustrate this step in an embodiment of the present invention. However, the steps illustrated in figures lb and 1c are merely examples in accordance with one embodiment of the invention, and in an alternative embodiment this relative offset location of the probe tip may be determined in a different manner. Briefly referring to figure 1c, the relative offset location of the probe tip 37 with respect to the head encoder 31 defines a relation between the location data obtained with the head encoder 31 and the exact location of the probe tip 37 at that moment. This information is needed in order to be able to properly navigate the probe tip to a desired location for scanning a substrate surface, as will be explained later. A scan head 30 may comprise a variety of different elements, but at least includes the encoder 31 and the miniature atomic force microscope unit 32. The miniature ATM unit 32 includes a probe 35 including a cantilever 36 and a probe tip 37. The probe tip 37 is used to scan across the surface of e.g. a substrate, in order to determine the geometry of the surface topography of the substrate or the exact locations of embedded structures underneath the surface of the substrate using e.g. an acoustic signal applied to the substrate or the probe 35 or both. In the example illustrated in figure 1c a regular topography measurement is illustrated schematically. The miniature ATM 32 thus comprises a probe 35, a laser 41 (e.g. a semiconductor laser) and an optical sensor 38. The laser 41 and the optical sensor 38 together form an optical beam deflection unit (OBD unit) which enables to exactly determine the deflection of the probe tip 37 due to surface structures sensed with the AFM. The laser 41 and the optical sensor 38 are controlled by controller 40 which also obtains the sensor signal from optical sensor 38 and e.g. location data from the encoder 31. This is transmitted to the system electronics 1. In the embodiment illustrated in figure 1c, the scan head 30 comprises an onboard processor 40 that is used as a controller of a scan head. The skilled person may appreciate that a decentral controller may be located somewhere in the SPM system to perform the same and/or additional tasks as described herein. Back to figure lb, the step of determining irrelative offset location for the probe tip 37 is performed by a first performing... step of determining, using the optical sensor 14 described above, location data of a fiducial marker 4 which is located on the substrate carrier 3. This is done by imaging the fiducial marker 4 with the optical sensor 14, while taking a current location of the support 13 by the encoder 15. The step of scanning the fiducial marker 4 with the optical sensor 14 is needed each time when the system 1 is used because the location of the fiducial marker 4 in the SPM system 1 is not fixed. The reason for this is that temperature differences in and around the SPM system 1 result in miniature differences in the exact location of the fiducial marker 4. Therefore, at least each time when the system 1 is used, but more preferably as often as necessary, this calibration step may be performed. Thereafter, the step illustrated in figure 1c is performed. Here, the fiducial marker 4 is again imaged, by scanning the surface of the fiducial marker with the probe tip 37 in order to obtain an AFM image thereof. The scanning of the fiducial marker 4 is performed in an area including the location for the fiducial marker 4 obtained with encoder 15 of the optical sensor 14 in the preceding step. This will provide a detailed AFM image of the fiducial marker 4, or a fraction thereof, which may be related to the image obtained with the optical sensor 14 in the preceding step by image recognition. From the data obtained with the encoder 31 and the image recognition step, the exact relation between the location data obtained from the encoder 31 and the position of the probe tip 37 can be obtained. From this, using the coordinate system already obtained during the calibration step illustrated in figure la, the scan head 30 including the encoder 31 and miniature AFM 32, can be navigated through the working space 2 to any location relative to the grid plate 6 in order to obtain images of the substrate.

Figures lb and 1c illustrate the calibration wafer 8 in the sample carrier 3. This calibration wafer 8 is not needed during the steps illustrated in figures lb and 1c, and may be completely absent while performing these steps. The determination of the relative offset of the probe tip in the example illustrated in figures lb and 1c is completely based on the location of the fiducial marker 4 which is located on the substrate carrier 3, and thus not on the substrate therein.

The data obtained with the steps illustrated in figures la, lb and 1c forms the basis for enabling navigation through the working space 2. As indicated hereinabove, the step of determining relative offset position of the probe tip 37 with respect to the encoder 31 may be performed in a different manner than is illustrated in figures lb and 1c. For example, in accordance with an embodiment of the present invention, the optical sensor 14 may be jointly mounted to a support arm 12 including an atomic force microscope 32. The both systems may be integrated in such a way that the field of view 19 of the optical sensor 14 includes at least the probe tip 37. In this way, each image that is taken with the optical sensor 14 includes the location of the probe tip, and therefore the exact offset between the encoder 31 (which due to this integration also provides the encoder 15) and the location of the probe tip can be obtained directly from this image.

Once the coordinate system is available, and the location of each probe tip of each scan head 30 in the system 1 relative to the associated encoder 31 is known, the elements can be navigated throughout a working space 2 to each location relative to the substrate carrier 3 and the grid plate 6 using the coordinate system. However, in order to properly enable navigation to a desired location on an arbitrary wafer loaded into the substrate carrier 3, one more step is needed in order to align such a production wafer 48 with the coordinate system: i.e. a relation needs to be defined between the exact position and orientation of the production wafer 48 in a substrate carrier 3 relative to the coordinate system obtained. This step may also easily be performed using the optical sensor 14 in accordance with the present invention. Reference is made to figures 2a through 2c. figure 2a schematically illustrates a production wafer 48 onto which schematically a reference grid is illustrated intended to provide a reference to the coordinate reference grid plate 6 illustrated in the system 1 of figures la through 1c. In order to properly ahgn the production wafer 48 to the coordinate system obtained through calibration, we first perform a sensing or imaging of the center alignment mark 49 in the center of the wafer 48. Figure 2b provides an example image of an alignment marker 49. The alignment marker 49 provides a pattern of measurable structures 53, including a cross hair type structure 54 in the middle thereof. The illustration in figure 2b is just an example of an alignment marker on a wafer, such as wafer 48. In reality many different types of alignment markers are used in the industry, and the alignment marker of an arbitrary wafer 48 may have a completely different design than the design illustrated in figure 2b. Figure 2b merely illustrates an example that enables to explain the present invention. Schematically, a copy of the center 53 of alignment marker 49 is illustrated in figure 2c. On the left side of figure 2c, the alignment marker 49 is exactly aligned with a coordinate system reference axis 55 of the coordinate system obtained during the calibration steps. However, on the right side of figure 2c, the same alignment marker 49’ is illustrated with a slightly different orientation angle. The axis 55’ is the notional axis through the cross hairs 54 in the middle of the alignment mark 49’ and the angular difference between the axis 55 and axis 55’ is the angle R_z 58, the rotation around the height axis in the system 1.

Once a new production wafer 58 is loaded into the substrate carrier 3, in order to determine the alignment of the production wafer 48, the center alignment marker 49 is imaged using the optical sensor 14. For example an image is illustrated on the right side of figure 2 may be obtained with the optical sensor. From this image, and based on the coordinate system data in the system 1, the orientation angle R_z 58 may be determined, as well as the exact x and y position data of the coordinates of alignment marker 49 with respect to the reference grid 6. In the memory of the system 1, blue print data or data of the design of the wafer 48, and in particular the location of alternative alignment markers 50-1, 50-2, 50-3 and 50-4 may be available. Because the exact position xo, yo and r_zo of alignment marker 49 are known from the determination step with the optical sensor 14, the exact locations of the alignment markers 50-1 through 50-4 can be determined. The optical sensor 14 can then be moved to the determined locations in order to scan the other alignment markers 50-1 through 50-4. From this, an exact orientation of the wafer 48 with respect to the coordinate system can be determined, which can be used in order to navigate each of the scan heads to a desired location of the wafer.

Figure 3 illustrates a see-through impression of an optical sensor 14, for example the optical sensor 14 illustrated in figures la and lb. The optical sensor 14 consists of a camera 20, for example a CMOS camera to obtain images of the substrate surface. Alternatively, a CCD camera may be applied or a different type of optical sensor unit. The sensor further consists of an aperture 21, and a focusing lens 22 which in the present example is a tube lens. The focusing lens 22 connects to an actuator 24 suspending with flexures 23 from a structure of the optical sensor. The actuator 24 and flexures 23 enable to adjust the distance between the camera 20 and the focusing lens 22 in order to focus the image of camera 20 on the substrate surface or the surface to be imaged (e.g. the surface of the substrate carrier carrying the fiducial marker 4). The optical sensor 14 further consists of a sensor opening 17 and includes a redirection mirror 25 which makes an angle of n/4 with the longitudinal axis through the sensor 14 in order to redirect the imaging plain onto the surface of the substrate. The optical sensor 14 further comprises a printed circuit board 26 onto which for example a plurality of light emitting diodes (LED’s) provide illumination of the substrate surface for imaging. Also, capacitive sensor 28 enables to determine the distance to the substrate surface in order to perform correct focusing of the image quickly. The capacitive sensor 28 may further be applied to perform additional measurements from which e.g. a tilting of the substrate relative to the grid plate 6 may be determined. Furthermore, the optical sensor 14 comprises an infinity corrected microscopy objective 29 with a long working distance. The numeric aperture of this objective 29 for example may be 0,28. The magnification of the tube lens 22 for example may be three times to eight times, and in the present example provides a five time magnification. The actuator 24 may be a piezo actuator and the flexures 23 may be provided by bending elements or leaf springs or a system of leaf springs to allow very accurate focusing adjustment and stability.

Figure 4 shows an example of a placement arm 12 with integrated supporter 13 onto which an optical sensor 14 is mounted. The optical sensor 14 is mounted with dow pins 64 and screws 62 to the arm 12 and support 13. The screws 62 are connected to the reference point 60 on the opposite side, extending through holes in the optical sensor 14. This allows a very stable and precisely adjustable fixation that allows to accurately position and fix the optical sensor 14 in six degrees of freedom. The screws 62 and references 60 enable to fix the optical sensor 14 in a stable way in the direction A and the rotation dimensions R_x and R_z. The dow pins 64 enable fixing and positioning in the positions X and Z, and in the rotation dimension R_y. Therewith, the optical sensor 14 is firmly fixed relative to the encoder 15 underneath the support 13 (not visible in figure 4). In the figure, also the locations of the sensor opening 17 and the electrical interface 18 is illustrated. Also fixed to the positioning arm 12 and support 13 is a scan head 30 including a probe 35. In the illustrated embodiment, the probe tip 37 (not shown) is not visible in the field of view of the camera 20. However, in different embodiments, as explained hereinabove, the scan head 30 and the optical sensor 14 may be integrated in such a way that the probe tip 37 of the probe 25 will be visible in the field of view of the camera, somewhere in the region 17 in figure 4. The present invention has been described in terms of some specific embodiments thereof. It will be appreciated that the embodiments shown in the drawings and described herein are intended for illustrated purposes only and are not by any manner or means intended to be restrictive on the invention. It is believed that the operation and construction of the present invention will be apparent from the foregoing description and drawings appended thereto. It will be clear to the skilled person that the invention is not limited to any embodiment herein described and that modifications are possible which should be considered within the scope of the appended claims. Also kinematic inversions are considered inherently disclosed and to be within the scope of the invention. Moreover, any of the components and elements of the various embodiments disclosed may be combined or may be incorporated in other embodiments where considered necessary, desired or preferred, without departing from the scope of the invention as defined in the claims.

In the claims, any reference signs shall not be construed as limiting the claim. The term 'comprising' and ‘including’ when used in this description or the appended claims should not be construed in an exclusive or exhaustive sense but rather in an inclusive sense. Thus the expression ‘comprising’ as used herein does not exclude the presence of other elements or steps in addition to those listed in any claim. Furthermore, the words ‘a’ and ‘an’ shall not be construed as limited to ‘only one’, but instead are used to mean ‘at least one’, and do not exclude a plurality. Features that are not specifically or explicitly described or claimed may be additionally included in the structure of the invention within its scope. Expressions such as: "means for ...” should be read as: "component configured for ..." or "member constructed to ..." and should be construed to include equivalents for the structures disclosed. The use of expressions like: "critical", "preferred", "especially preferred" etc. is not intended to limit the invention. Additions, deletions, and modifications within the purview of the skilled person may generally be made without departing from the spirit and scope of the invention, as is determined by the claims. The invention may be practiced otherwise then as specifically described herein, and is only limited by the appended claims.

Claims

26 Claims

1. Method of calibrating a scanning probe microscopy system for enabling navigation, wherein the scanning probe microscopy system comprises one of more scan heads, a coordinate reference grid and a substrate carrier, wherein each of the one or more scan heads comprises a probe including a probe tip for scanning of a substrate surface for performing measurements, and a head encoder cooperating with the coordinate reference grid; wherein, for supporting a substrate, the substrate carrier includes a carrier surface, the carrier surface being arranged opposite the coordinate reference grid and remotely therefrom such as to define a working space for the one or more scan heads between the coordinate reference grid and the carrier surface, wherein for enabling navigation between at least one of the scan heads and a substrate carrier, the method comprises the steps of: a) determining, using a sensor encoder cooperating with the coordinate reference grid, a relation between a relative position of an optical sensor and the coordinate reference grid, such as to provide coordinate system data indicative of a coordinate system for the optical sensor, wherein the optical sensor is fixed relative to the sensor encoder; b) determining, for the at least one scan head, a relative offset location of the probe tip and the head encoder of the scan head.

2. Method according to claim 1, wherein step b) is performed by the steps of: b 1) determining, using the optical sensor and the sensor encoder cooperating with the coordinate reference grid, location data of a location of a fiducial marker in the coordinate system, wherein the fiducial marker is included on the substrate carrier; and b2) determining, for the at least one scan head, the relative offset location of the probe tip and the head encoder of the scan head by scanning, using the probe tip of the respective scanner, the fiducial marker while obtaining head location data via the head encoder.

3. Method according to any one or more of the preceding claims, wherein at least one of: the optical sensor and the sensor encoder are included on a sensing element, wherein the sensing element is operating separate and individually from the one or more scan heads; wherein the optical sensor is included on at least one of the scan heads, and wherein the sensor encoder is provided by the head encoder of the scan head; wherein the system comprises a plurality of scan heads, wherein at least two of the scan heads include an optical sensor, and wherein for each of the at least two scan heads the sensor encoder is provided by the head encoder of the respective scan head.

4. Method according to any one or more of the preceding claims, wherein the optical sensor is included on at least one of the scan heads, and wherein the optical sensor is placed such that the probe tip is within a field of view of the optical sensor, wherein step b) is performed by determining the relative offset of the probe tip and the head encoder from image data obtained with the optical sensor.

5. Method according to any one or more of the preceding claims, wherein step a) is performed by sensing, using the optical sensor, the or each location of one or more calibration markers that are distributed across the carrier surface.

6. Method according to claim 5, wherein at least one of: the one or more calibration markers are provided on a calibration substrate surface to be loaded onto the carrier surface for carrying out step a); or the one or more calibration markers are included on the carrier surface of the substrate carrier, wherein step a) is performed by scanning the carrier surface in absence of a substrate.

7. Method of performing substrate alignment for establishing a relation between a relative positions on a substrate and a coordinate system provided by coordinate system data in a scanning probe microscopy system, wherein the coordinate system data is obtained using a method according to any one or more of the preceding claims, wherein the scanning probe microscopy system comprises one of more scan heads, a coordinate reference grid and a substrate carrier, wherein each of the one or more scan heads comprises a probe including a probe tip for scanning of a substrate surface for performing measurements, and a head encoder cooperating with the coordinate reference grid; wherein, for supporting a substrate, the substrate carrier includes a carrier surface, the carrier surface being arranged opposite the coordinate reference grid and remotely therefrom such as to define a working space for the one or more scan heads between the coordinate reference grid and the carrier surface; wherein the method comprises: providing a substrate on the carrier surface, the substrate comprising a plurality of alignment marks; 29 determining, using an optical sensor fixed to a sensor encoder, first location data of a location of a first alignment mark on the substrate and orientation data of the first alignment mark with respect to the coordinate system; predicting, using the first location data, the orientation data and substrate layout data, one or more second location data of locations of one or more second alignment marks with respect to the coordinate system; and mapping, by sensing with the optical sensor, the one or more second alignment marks to the coordinate system by moving the optical sensor to the locations provided by the predicted second location data, and providing alignment data of an alignment of the substrate to the coordinate system.

8. Method according to claim 7, wherein the substrate layout data is obtained by at least one of: loading the substrate layout data into a memory of the scanning probe microscopy system, wherein the memory is communicatively connected to a controller of the system; obtaining the substrate layout data from a data communication network, such as from a remote data storage location or a remote server; obtaining the substrate layout data from input by an operator of the scanning probe microscopy system; obtaining the substrate layout data from a further optical instrument, such as a camera.

9. Method of navigating at least one scan head of a plurality of scan heads of a scanning probe microscopy system to a location of interest on a substrate, wherein the method includes a method of performing substrate alignment according to claim 7, wherein each of the one or more scan heads includes a head encoder, and wherein the method comprises: 30 obtaining, for the at least one scan head, a point of interest location indication of a point of interest on the substrate; determining, using the alignment data, location data of the point of interest indicative of a coordinate in the coordinate system; and moving the at least one scan head to the coordinate indicated by the location data of the point of interest.

10. Optical sensor for use in a scanning probe microscopy system, comprising a structural element supporting an imaging sensor, one or more focusing objectives, and at least one actuator for adapting a distance between the imaging sensor and the focusing objectives, for enabling focusing of the imaging sensor onto a surface to be imaged, such as a substrate surface, a carrier surface of a substrate carrier, or a fiducial marker on the substrate carrier; wherein the structural element comprises fixation structures for enabling fixation of the optical sensor to a support including an encoder configured for cooperating with a coordinate reference grid of the scanning probe microscopy system, for enabling fixing of the optical sensor relative to the encoder for enabling the encoder to serve as a sensor encoder in a method according to any one or more of the preceding claims.

11. Optical sensor according to claim 10, wherein at least one of: the imaging sensor is a CMOS camera; and the actuator includes one or more piezo elements cooperating with flexures; and the one or more focusing objectives include a tube lens.

12. Optical sensor according to any of the claims 10 or 11, further including a redirection mirror for enabling placement of the imaging sensor and the one or more focusing objectives along an optical axis parallel to the 31 coordinate reference grid in use, while obtaining images with the imaging sensor in an off axis direction relative to the optical axis.

13. Support for receiving an optical sensor according to any of the claims 10-12 to be fixed thereto, wherein the support is configured to be used in a scanning probe microscopy system, the support further comprising an encoder configured for cooperating with a coordinate reference grid of the scanning probe microscopy system, wherein the encoder is fixed relative to the optical sensor upon fixing of the optical sensor to the support for enabling the encoder to serve as a sensor encoder in a method according to any one or more of the claims 1-9, wherein the support is further configured for moving in a working space of the scanning probe microscopy system defined between the coordinate reference grid and a carrier surface of a substrate carrier, such as to enable imaging of substrate surface supported by the substrate carrier while simultaneously obtaining location data of a current location of the support relative to the coordinate reference grid.

14. Support according to claim 13, wherein the support is comprised by at least one of a groups comprising: a positioning arm of the scanning probe microscopy system; a scan head including a probe and a probe tip, wherein the encoder is provided by a head encoder of the scan head; a support structure suitable for being placed by a placement arm of the scanning probe microscopy system; and a support structure comprising a motion driver or actuator for enabling independent movement of the support relative to a coordinate reference grid, such as by using or providing a gas bearing.

15. Assembly comprising an optical sensor according to any one or more of claims 10-12 and a support according to any one or more of claims 13-14. 32

16. Scanning probe microscopy system comprising one of more scan heads, a coordinate reference grid and a substrate carrier, wherein each of the one or more scan heads comprises a probe including a probe tip for scanning of a substrate surface for performing measurements, and a head encoder cooperating with the coordinate reference grid; wherein, for supporting a substrate, the substrate carrier includes a carrier surface, the carrier surface being arranged opposite the coordinate reference grid and remotely therefrom such as to define a working space for the one or more scan heads between the coordinate reference grid and the carrier surface; wherein the system further comprises an optical sensor fixed relative to a sensor encoder, the sensor encoder being configured for cooperating with the coordinate reference grid; and wherein the system further comprises a memory and a controller, wherein the controller is configured for performing the steps of: a) determining, using a location signal from the sensor encoder cooperating with the coordinate reference grid, a relation between a relative location of the optical sensor and the coordinate reference grid, such as to provide coordinate system data indicative of a coordinate system for the optical sensor; b) determining, for the at least one scan head, a relative offset location of the probe tip and the head encoder of the scan head.

17. Scanning probe microscopy system according to claim 16, wherein the controller is further configured for performing the step b) by the steps of: b 1) determining, using the optical sensor and the sensor encoder cooperating with the coordinate reference grid, location data of a location of a fiducial marker in the coordinate system, wherein the fiducial marker is included on the substrate carrier; and b2) determining, for the at least one scan head, the relative offset location of the probe tip and the head encoder of the scan 33 head by scanning, using the probe tip of the respective scanner, the fiducial marker while obtaining head location data via the head encoder.

18. Computer program product comprising instructions which, when loaded into a memory of a scanning probe microscopy system according to claim 16 or 17, enable the controller of the system to perform a method according to any of the claim 1-9.