TW202417845A - Method of calibrating in a scanning probe microscopy system an optical microscope,calibration structure and scanning probe microscopy device - Google Patents

Abstract

The present document relates to a method of calibrating, in a scanning probe microscopy system, an optical microscope. The optical microscope is configured for providing a reference data for positioning a probe tip on a surface of a substrate. The calibration is performed using a calibration structure being a spatial structure including features at different Z-levels relative to a Z-axis, the Z-axis being perpendicular to the surface of the substrate. The method comprises a step of obtaining, with the optical microscope, at least two images of at least a part of the calibration structure. The at least two images are focused in at least two different levels of the Z-levels. The method further comprises a step of determining a lateral shift, in a direction perpendicular to the Z-axis, of the calibration structure as depicted in the at least two images focused in the at least two different levels. The invention is further directed at a calibration structure, a substrate carrier and scanning probe microscopy device.

Description

Method for calibrating an optical microscope in a scanning probe microscope system, calibration structure and scanning probe microscope device

The present invention relates to a method for calibrating an optical microscope in a scanning probe microscope system. The present invention further relates to a calibration structure, a substrate carrier and a scanning probe microscope device.

Scanning probe microscopy (SPM) can obtain a highly accurate image of a very small portion of a surface. The image can be a surface topography image or a substrate topography image, or even a combination thereof imaging multiple layers, which can be surface layers or layers at different depths below a surface. The technique can image surface areas with typical cross-sections of about 0.001 to 100 micrometers (μm). Because of this scale and accuracy, the technique is suitable for performing wafer inspection, for example for monitoring the process of semiconductor devices during their manufacture.

If there is a scale of the image relative to the size of a typical wafer, it is important to have a high accuracy positioning system that can accurately position the probe tip of the SPM at the desired location on the wafer surface in order to perform the scan. In an industrial application, such as in semiconductor manufacturing, in addition to the need for high accuracy, maximum throughput of the process is another requirement. Therefore, it is ideal that the probe tip is accurately placed at the desired location as quickly as possible in order to start scanning and reduce the delay caused by the positioning process.

Various techniques are currently available for positioning a probe tip on the surface of a substrate. Many of these techniques therefore utilize optical microscopes to assist in the positioning process. In addition to positioning, optical microscopes or sensors that require optics are also used for various reasons when scanning. Typically, an SPM system includes an internal positioning reference, such as a grid plate so that the position of the probe tip in the system, i.e. relative to the substrate carrier, is known very accurately. In order to locate a position on a wafer, an optical microscope can be used to correlate the position of the probe tip in the system to a precise position on the surface of the wafer. Obviously, any information obtained from the microscope image must be accurate enough to be placed accurately at the desired position using typical scales including maximum magnification. Therefore, accurate calibration of the equipment is extremely important. This is a difficult procedure in terms of the desired accuracy.

An object of the present invention is to provide an accurate calibration method for an optical microscope for a scanning probe microscope system, which can in particular reduce the deviation in determining an XY position on a wafer surface.

To achieve this object, a method for calibrating an optical microscope in a scanning probe microscope system is provided, wherein the optical microscope is configured to provide a reference data for positioning a probe tip on a surface of a substrate, wherein the calibration is performed using a calibration structure, wherein the calibration structure is a spatial structure of a topography volume at different Z layers relative to a Z axis, wherein the Z axis is perpendicular to the surface of the substrate, wherein the method comprises the following steps: obtaining at least two images of at least a portion of the calibration structure with the optical microscope, wherein the at least two images are focused on at least two different layers among the Z layers; and determining a lateral displacement of the calibration structure in a direction perpendicular to the Z axis, wherein the lateral displacement is displayed in the at least two images focused on the at least two different layers.

At the geometric scale of interest of the optical microscope (tens of micrometers), a substrate, such as a wafer, cannot be described as a flat surface. Therefore, an optical microscope, which is used in particular for correctly positioning a probe tip on a substrate surface in an SPM system, must be frequently refocused depending on the local height of the substrate surface. In order to focus, a focusing objective in the microscope must be moved accurately along the optical axis of the microscope. Usually, a precision actuator element is used to move the focusing objective along the optical axis. However, regardless of its accuracy, the precision actuator usually produces a certain lateral movement relative to the optical axis along the path of the focusing objective along the optical axis. This lateral movement produces an error in the determined XY position on the wafer due to image displacements, for example on an imaging screen. The method of the invention uses a multi-layer calibration structure in order to measure this lateral displacement at different Z levels used for focusing. In lens systems, focusing is performed by moving a lens in the direction of the optical axis relative to an imaging screen (e.g. a CCD unit of a camera). Usually, in order to obtain the desired accuracy, the movement of the lens for this purpose is accomplished by an actuator. Because the amount of accuracy that can be achieved is limited, this movement cannot be achieved without some lateral movement. Therefore, a lateral displacement of the image of some degree depends on the focusing is produced.

According to the method, at least two images of the calibration structure or a part thereof are obtained using the optical microscope. These images are focused on at least two different layers in the Z layer of the multi-layer calibration structure. For example, different images are obtained by focusing on different morphologies with different edges or other optically visible elements arranged in different Z layers, wherein the focusing objective lens is focused differently using the precision actuator element. From these images, a lateral displacement of the calibration structure in a direction perpendicular to the Z axis is determined, and the lateral displacement is displayed in the images focused on at least two different layers. This lateral displacement can be used by the SPM system as a calibration data relative to different focusing layers. Therefore, the present invention can correct images obtained with an optical microscope that can correct the lateral movement caused by refocusing the optical elements. There are various sources that can cause this lateral movement or displacement in the acquired image. One of these sources is the precision actuator used to move the objective between different focusing distances. Although the objective used for this refocusing can be moved accurately in the direction along the light path, tiny imperfections in the actuator produce small off-axis displacements of the objective that cause the image formed on the screen of a camera or optical sensor to shift. However, for the scanning probe microscope (SPM), these movements increase the deviation in determining a position on a sample surface. It will be appreciated that any source of deviation should be eliminated as much as possible to obtain the desired accuracy of an SPM system of the order of tens of nanometers. The optical microscope in an SPM system plays a particular role in coarse positioning and calibration of the system, for example determining the exact position of fiducial marks or certain features. The most accurate possible determination can particularly prevent errors in positioning the probe tip.

In certain embodiments, the step of acquiring at least two images is performed by acquiring a series of images of the calibration structure while refocusing the optical microscope through a range of Z layers, and wherein the step of determining a lateral displacement is performed by detecting movement of the calibration structure through the series of images. If a series of images is acquired, a change in the lateral displacement indicates a lateral, i.e., yaw, movement of the objective lens relative to the optical path due to the precision actuator. It should be noted that yaw movement relative to the optical path is not the only possible cause of the lateral displacement. Lens defects, defects in other components of the optical element, or temperature changes can similarly cause the lateral displacements. The present invention can quantify these lateral displacements caused by a substantially static or semi-static source that does not change while the measurement is being made. Systematic errors are an example of this, but similarly in a controlled environment the room temperature may similarly remain substantially constant throughout the measurement period.

In some embodiments, the step of acquiring at least two images includes the steps of: focusing the optical microscope on a first layer in the Z layers to acquire a first image of one or more first topography in the first layer, and acquiring a first reference position from the first image based on a position of at least one first topography in the first topography; focusing the optical microscope on a second layer in the Z layers to acquire a second image of one or more second topography in the second layer, and acquiring a second reference position from the second image based on a position of at least one second topography in the second topography, and wherein the step of determining the lateral displacement includes comparing the first reference position and the second reference position to determine a deviation representing the lateral displacement. For example, a representation of the lateral displacement can be obtained by comparing how much the second reference position is displaced relative to the first reference position. For example, if the topography is provided by concentric shapes to form the calibration structure, the midpoints of these shapes must coincide. If a deviation is found therein in which one of the midpoints is displaced laterally relative to one another, this indicates a mutual lateral displacement between the two Z layers associated with the imaged first and second topography. In a different example, if the positions of the two topography are known, a lateral displacement can be determined immediately from the images. Furthermore, if the two topography in the two layers coincide (or have at least one coincident part), the displacement can also be determined more directly from the comparison (for example, in the case where the calibration structure is formed by a stationary post or rod extending in the Z direction).

In some of these embodiments, determining the deviation includes determining deviation data representing a distance and direction of the lateral displacement from the first and second reference positions, wherein the method further includes storing the deviation data as calibration data associated with the second layer. The data may be stored in a database or memory (accessible locally or remotely via a network) in a table, an algorithm, or a set of data points that may be used by the SPM system during measurement.

In some of the above embodiments, the calibration structure comprises a plurality of concentric structures at different layers, such as concentric rings, squares, triangles or polygons, and wherein determining the first and second reference positions comprises determining a centroid of the structure at each first or second layer. As described above, the centroids of the concentric shapes must coincide, so if there are differences therebetween, these differences represent a lateral displacement between the layers under consideration.

In some embodiments, the step of determining the lateral displacement further comprises: determining corresponding actual positions of the first and second reference positions obtained from the first and second images from a calibration structure data in a data repository; determining an actual difference vector data between the actual position of the first reference position and the actual position of the second reference position from the corresponding actual positions; determining an image difference vector data between the first reference position and the second reference position from the first and second reference positions obtained from the first and second images; and comparing the actual difference vector data and the image difference vector data to determine the deviation representing the lateral displacement. In these embodiments, the acquired images are compared using data of the actual positions of the topographic volumes of the calibration structure. This information may be pre-stored in a database or memory. For example, the calibration structure may be arranged on the measurement frame or on a substrate holder or other component of the SPM system so that the exact position of the calibration structure and its features is fixed and known. This can be accessed as a calibration data, thereby implementing the above method. The lateral displacement of multiple features can thus be determined quickly and accurately.

In some embodiments, the step of obtaining at least two images includes focusing the optical microscope on a plurality of different layers and obtaining a reference position at each layer based on a position of at least one morphology at each layer, and wherein the step of determining the lateral displacement includes: calculating deviation data representing a relevant lateral displacement at each layer from the reference positions; and storing the deviation data associated with each layer as calibration data in a data repository accessible by the scanning probe microscope system.

In some embodiments, in order to obtain the at least two images, the optical microscope comprises a camera cooperating with a focusing objective, wherein the camera and the focusing objective are arranged so that a field of view can be obtained by the camera, wherein the field of view includes at least a portion of an outermost periphery of the calibration structure. This provides an optimal width Z height range. The more Z-layer elements of the calibration structure are within the field of view, the more different Z layers can be calibrated. If a complete periphery is within the field of view, a reference XY position can be most accurately determined by analyzing the image (for example in order to determine the centroid of a circle). If at least a portion of the periphery is within the field of view, at least the corresponding Z layer of the periphery structure can be obtained in the calibration.

In certain embodiments, the calibration structure comprises one or more structural topography bodies provided at different Z layers of the topography bodies, wherein the structural topography bodies include one or more side walls for supporting the elevated surface of the structural topography body at each Z layer, wherein at least one of the side walls includes a lateral contraction relative to each elevated surface so as to be invisible to the optical microscope. The lateral contraction parts are not visible in the image and therefore do not blur the image at the edge of the elevated surface. Therefore, a sharp image of this edge can be obtained, and the sharp image can accurately determine the lateral displacement.

In certain embodiments, the calibration structure comprises one or more structural features of the features provided at different Z layers, wherein the structural features include one or more elevated surfaces at each Z layer, and wherein the elevated surfaces include edges defining a perimeter of the elevated surfaces, wherein at least one of the edges includes a contrasting color. Similar to the above, by using a different contrasting color, the sharpness of the edge in focus can be improved and the lateral displacement can be accurately determined.

According to a second aspect, a calibration structure is provided for use according to a method according to the first aspect and for cooperating with an optical microscope of a scanning probe microscope system, the calibration structure comprising a spatial structure of a structural morphology body at different Z layers relative to a Z axis, for performing the following steps: obtaining at least two images of at least a portion of the calibration structure using the optical microscope, wherein the at least two images are focused on at least two different layers among the Z layers; and determining a lateral displacement of the calibration structure in a direction perpendicular to the Z axis, the lateral displacement being displayed in the at least two images focused on the at least two different layers.

According to a second aspect, a substrate carrier for use with a scanning probe microscope is provided, the substrate carrier comprising a carrier surface for supporting a substrate to be inspected with the scanning probe microscope, wherein the substrate carrier comprises a calibration structure according to the second aspect.

In addition, according to a second aspect, a scanning probe microscope device is provided, which includes a substrate carrier for supporting a substrate to be inspected, the scanning probe microscope device includes a probe head, the probe head includes a probe including a cantilever and a probe tip, the probe head further includes a beam detector configuration for monitoring a deflection of the probe tip during scanning, wherein the scanning probe microscope device further includes an assembly for providing a reference The invention relates to an optical microscope having reference data, the reference data being used to position the probe tip in a desired measurement position on the surface of the substrate, wherein the optical microscope comprises a focusing objective lens for focusing an image acquired by the microscope at a desired Z layer relative to a Z axis, the Z axis being perpendicular to the surface of the substrate, and wherein the substrate carrier comprises a calibration structure according to the second aspect for calibrating the optical microscope.

In FIG. 1 , the scanning probe microscopy (SPM) system 1 comprises a base 5 and a substrate carrier 3. The substrate carrier 3 comprises a supporting surface 7 on which a substrate 4 can be placed. The substrate 4 can be placed so that a surface 8 of the substrate to be inspected using the SPM system faces the base 5. The base 5 comprises a coordinate reference grid plate 6. The coordinate reference grid plate is part of a grid encoder consisting of the plate 6 and at least one encoder 15. Typically, in the system 1 according to the invention, a plurality of encoders cooperate with the grid plate 6. For example, each element moving in the working space 2 between the sample carrier 3 and the grid plate 6 may comprise an encoder 15 cooperating with the grid plate 6 to determine its position on the grid plate 6. The encoder 15 and the encoders cooperating with the coordinate reference grid plate 6 read the reference grid to obtain the coordinate data of its current position on the grid 6. In Fig. 1, the encoder 15 is mounted on a support 13 providing the probe head 10, which is connected to an arm 12 of a positioning unit module. The support 13 includes an optical sensor 14, the encoder 15 and a probe 26, which includes a cantilever 27 and a probe tip 28 for scanning the surface 8 of a substrate 4.

To inspect the substrate 4, the probe tip 28 is brought into contact with the substrate surface 8 at a desired location and an area of the substrate surface 8 is scanned using the probe tip 28. The probe tip 28 thus contacts various nanometer or tens of nanometer sized features on the surface 8 which change the deflection of the cantilever 27. This can be measured using a sensing arrangement which typically includes an optical beam deflection (OBD) arrangement (not shown), wherein the position of the probe tip 28 is monitored by a laser beam which strikes the back side of the probe tip 28 and reflects back towards an optical sensor (quadrant photodetector). It will be appreciated that other suitable deflection detection methods may be used as an alternative or in addition to the above methods, such as piezoelectric, piezoresistive or capacitive sensing methods. The probe 26 can scan with the probe tip 28 in contact mode, non-contact mode, tapping mode or any other mode. In addition, the SPM system 1 can implement an acoustic or ultrasonic measurement technique to probe the structure below the surface 8.

The optical sensor 14 can be used to support the correct positioning of the probe tip on the surface in a fast and reliable manner. The optical sensor 14 can assist in navigating through the surface 8, assist in the approach method to place the probe tip 28 on the surface and assist in calibrating the system, for example by observing reference marks 9 (e.g. FIG. 4A ) or determining the exact position of the probe tip 28 relative to the system (e.g. after each replacement thereof). Preferably, the optical sensor 14 must be as accurate as possible in these respects and also needs to know its position within the system 1 (e.g. relative to a fixed point on the arm 12 or relative to the base 5 or substrate carrier 3). In the embodiment described here, the optical sensor 14 is a microsensor, but the invention is not limited to a specific design.

An optical sensor 14 example that can be used in the system of Fig. 1, 4a and 4b is shown in Fig. 3 that provides a see-through effect of the optical sensor 14. The optical sensor 14 is composed of a camera 20 such as a CMOS camera to obtain the image of the substrate surface. Alternatively, a CCD camera or a different type of optical sensor unit can be used. The sensor is further composed of a hole 21 and a barrel lens 22. The barrel lens 22 is connected to an actuator, and the actuator can adjust the distance between the camera 20 and the barrel lens 22 so as to focus the image of the substrate surface 8 or the image of the surface to be imaged on the camera 20 to obtain a sharp image.

The lens system is an infinity-corrected lens system. On the front side, the optical sensor 14 is further formed by a sensor aperture 17 and comprises a redirection mirror 25 which forms an angle of π/4 radians with the longitudinal axis through the sensor 14 to redirect the imaging plane view of the surface 8 of the substrate to the lens system. Furthermore, the optical sensor 14 comprises an infinity-corrected microscope objective 29 with a long working distance, which is used to obtain a correct focus on the Z layer perpendicular to the sample surface 8. The light port of this objective 29 is, for example, 0.28. The objective lens 29 can be similarly moved along the optical axis 23 through the lens system using a precision actuator 24 suspended from a structure of the optical sensor 14 by flexures 33 to achieve focus at a precise Z level. The actuator 24 can be a piezoelectric actuator and the flexures 23 can be provided by bending elements or leaf springs or a leaf spring system to allow very accurate focus adjustment and stability. The magnification of the resulting optical microscope (due to the combination of the barrel lens 22 and the objective lens 29) can be, for example, three times to twenty times, and in this example provides a five-fold magnification.

The optical sensor 14 further comprises a printed circuit board 30 on which, for example, a plurality of light emitting diodes 31 (LEDs) provide illumination of the substrate surface for imaging. In addition, a capacitive sensor 32 can determine the distance to the substrate surface in order to quickly achieve correct focusing of the image. The capacitive sensor 32 can also be used to perform other measurements, thereby determining, for example, a tilt of the substrate relative to the grid plate 6.

An optical sensor 14 is schematically shown in FIGS. 2A and 2B and is constituted by the optical microscope system described above with respect to FIG. 3. In FIG. 2A, the objective lens 29 can be precisely moved in a direction along the optical axis 23 to adjust the focus of the system on the surface 8. In the illustrated case, the surface 8 in the region 35 imaged at the position includes a recognizable feature volume 9. This image is acquired by focusing the lens 29 on the correct Z layer on the surface 8, which is then focused by the barrel lens 22 on the camera 20. The image 36 is acquired with the camera 20, and from the image the position (X, Y) on the surface 8 and the size of the feature volume 9 can be determined.

FIG. 2B shows what can typically be touched by refocusing the lens 29 at a different Z layer. On the left side of the figure, it can be seen that the surface 8 is not completely flat and that the topography can be focused at different Z layers. It is assumed that the lens 29 is first focused on the topography 9-2 and then refocused on the topography 9-1 at one of the different Z layers. To do this, on the right side of the figure, the lens 29 is moved along the optical axis 23 to a different position ending at the position shown by 29′. However, due to this movement, despite the high precision of the actuator 24, a slight lateral movement is still produced. This movement can be seen as a lateral displacement in the image: the surface 8 appears to have been displaced to position 8′. Therefore, the position of the topographic body 9-1 is also displaced in the image obtained by the camera 20 due to the refocusing of the lens 29.

FIG4A shows a portion of a scanning probe microscope system 1 according to an embodiment and includes a probe head 10 having an optical sensor 14 in use, and FIG4B shows a method of calibrating the optical sensor 14 according to an embodiment. The optical sensor 14 provides an important feature of the present invention and in the embodiment shown includes a mini camera unit 20 having a field of view 19 through its sensor aperture 17. The optical sensor 14 further includes an aperture 21, a focusing lens 22 and actuators 24. The actuators 24 can adjust the distance between the camera 20 and the focusing optics 22 to focus the image on the surface of the substrate 8. Furthermore, in order to utilize the available space in the workspace 2 parallel to the surface of the grid plate 6, a mirror 25 redirects the field of view of the camera 20 from a horizontal direction to a vertical direction, as shown in FIG4a. As described later, the optical sensor 14 is mechanically fixed to the support 13 and the arm 12. In addition, the electrical connection for data transmission to the system 1 is provided by the electrical connection interface 18.

The camera 20 is accurate enough to identify the alignment marks on the wafer. The size of the marks is typically in the range of 20*20 microns to 50*50 microns, but of course the size of these marks can vary and can become smaller as technology develops. The present invention is not limited in this regard. The resolution of the image topography of the alignment marks can typically be reduced to 1 micron and can similarly change (decrease) over time. The camera 20 can therefore be modified based on the size and/or resolution of the alignment marks, and should be able to distinguish the necessary image topography in order to perform its work. For example, the pixel resolution of the camera 20 in the object plane (e.g., the surface to be read having the marks) can be less than or equal to 2 microns, preferably less than or equal to 1.0 micron and more preferably less than or equal to 0.5 micron. Furthermore, the camera can be operated with a magnification factor of at least two for low and high magnification. The camera must be able to detect alignment features on a wafer surface and can be placed as close as 1 mm relative to the edge of the wafer. The power consumption of the camera should be as low as possible to reduce heat dissipation and unnecessary effects on accuracy. The field of view 19 of the camera 20 can be at least 0.5 mm and preferably at least 0.9 mm.

In FIG. 4B , according to a method of the invention, the arm 12 is retracted to a position such that the optical sensor 14 can be focused on the calibration structure 11. The calibration structure 11 can be disposed on the substrate carrier 3 on a surface of the substrate carrier close to the substrate 4. To perform calibration, a plurality of different layers of the calibration structure 11 can be imaged by refocusing the lens 29 on the correct layer. This can result in a plurality of images, from which the mutual lateral displacements representing the errors caused by refocusing on each imaged Z layer can be determined.

Figures 5A, 5B, 6A and 6B show two different embodiments of a calibration structure according to the present invention. The present invention is not limited to this particular structure, nor is it limited to the use of concentric shapes, but in principle any desired design of the calibration structure 11 can be used, as long as there are morphologies at at least two different Z layers. In the embodiment of Figures 5A and 5B, the calibration structure 11 is formed by a plurality of stacked disk-shaped structure morphologies 40-1, 40-2, ..., 40-8, 40-9. Each of the structures 40-1 to 40-9 includes a contrasting edge 42 that can be seen in the field of view of the microscope when focusing on it. It is not important that the edge 42 has a contrasting color, but according to some embodiments these edges 42 can be made to have a color that is different from the surrounding environment. This allows the optical sensor 14 to focus sharply on the edge. As shown in FIG5B, the edges 42 of the structures 40-1 to 40-9 together form a plurality of concentric circles when viewed from above in the field of view of the optical sensor 14.

Alternatively or additionally, the calibration structure 11 may comprise a feature having a different shape. In FIG6A , another calibration structure 11 ′ is formed by concentric squares stacked on top of each other in different layers. The squares 40 similarly include edges 42, and when viewed from above in FIG6B , these edges form a plurality of concentric squares in the field of view of the optical sensor 14.

FIG. 7A shows a calibration structure 11 similar to the calibration structure 11 of FIG. 5A . In FIG. 7B , an enlarged view of the concentric circles in the field of view of the optical sensor 14 is shown. The edges 42 of the concentric circles are numbered 42-1 to 42-9. In the case of FIG. 7B , the optical sensor 14 is focused on a layer that coincides with edge 42-7. As shown in FIG. 7B , the edge 42-7 is sharply defined, while the other edges 42-1 to 42-6 and 42-8 and 42-9 are blurred. In this respect, the figure is schematic: in fact, the farther the circle is from the focal point, the more blurred it is generally. Therefore, 42-5 and 42-9 should be more blurred than 42-6 and 42-8, etc. (42-1 is the most blurred). The centroid of all edges 42-1 to 42-9 is specified by point 45 at the center of the figure. However, due to the refocusing on the layer that coincides with edge 42-7, the lens 29 is slightly moved away from axis 23. Therefore, the entire image shown in Figure 7B is similarly displaced laterally. The circle 42-7' shows the actual position of edge 42-7 that would be found if no lateral displacement occurred. In order to determine the amount of lateral displacement at each Z layer, images can be made at each of the layers 42-1 to 42-9 by continuously refocusing each image at each Z layer to be imaged. At each Z layer, the centroid can be calculated. The centroid of all concentric circles in the figure should coincide with the center of the figure at any Z layer. However, the centroids are slightly shifted in the X and Y directions depending on the Z layer being focused on, this shift being caused by the yaw motion of the lens 29. For example, the centroid of the circle 42-7' is represented by the midpoint 46 and can be found, for example, when focusing on layer 42-1. By calculating these deviations, a calibration value can be obtained at each Z layer, which can calibrate the system and correct for the lateral shift caused by focusing on different Z layers when used.

Returning to Figure 8, another embodiment of a calibration structure 11 is shown. The calibration structure 11 of Figure 8 includes a handle 50 that elevates the pyramidal base formed by the calibration structure 11. The handle 50 may correspond to a typical thickness of a wafer so that if the handle is placed close to a substrate, the Z layer of the calibration structure 11 generally corresponds to the range of Z layers to be covered by the SPM system 1 when in use.

Figure 9 shows the sidewalls 55 of the structures that together form the calibration structure 11 being retracted. At each Z level there is an edge 42 and a sidewall 55 extending below the edge 42 to the calibration structure 11 of the next lower level. By shaping the sidewall 55 so that it is retracted relative to the edge 42, a better focus of the edge 42 is obtained because material from the calibration structure below the edge 42 is not seen in the field of view.

In Figure 10, another calibration structure 11' is shown. Here, the calibration structure 11' is provided by a hole in the material of the substrate carrier 3. In the surface 54 of the substrate carrier 3, the hole 11" is formed to provide steps 40 at a plurality of different levels. It will be appreciated that in the field of view of the optical sensor 14, this provides an image similar to the images shown in Figures 5B and 7B.

FIG. 11 schematically shows a method according to an embodiment of the present invention. In the method of the present invention, in a first step, a first image of the calibration structure 11 is obtained, and the first image is focused on one of the Z layers that coincides with the edge 42 of the calibration structure 11. Then, in step 120, the image obtained in step 110 is calculated, and the image can be used to determine a first position of the lateral displacement. For example, in the example of FIG. 7B , the centroid of the concentric circles is calculated. Alternatively or additionally, a fixed known point of the structures can be used as a reference point. For example, the exact position of one or more corner points of the focused edge 42 of the calibration structure 11' in FIGS. 6A and 6B can also be determined. It will be appreciated by a person of ordinary skill that other appropriate reference positions can be similarly calculated. In step 130, it is determined whether the calibration structure of the next layer needs to be imaged. If the calibration structure 11 of another Z layer needs to be imaged, then after step 130 the method continues in step 100. Otherwise the method continues in step 140. In step 140, the lateral displacement is determined at each Z layer from the reference position obtained in step 120 for each Z layer to be used as calibration data. Then, in step 150, the calibration data is stored in a memory 90 of the SPM system. Alternatively, an external memory or database can be used to store the calibration data and an external memory or database can be accessed via a data network.

In FIG. 12 , another embodiment of a method according to the invention is shown. Here, steps 100, 120 and 130 are similar to the method of step 11 and include acquiring images at a plurality of Z layers of the calibration structure 11 and calculating reference positions from these images. At the same time, in step 200, the SPM system 1 may access a data store, such as a database or memory, in order to obtain information about the calibration structure 11 under consideration. For example, the calibration structure 11 may be a fixed calibration structure integrated in the SPM system 1 and calibration data representing the calibration structure 11 and its precise position of each of the structures 40 at various Z layers may be stored in the memory. For example, in the case of concentric circles, the exact centroid position of the circle formed by edge 42 may be stored in the memory of the SPM system 1. Thus, in step 200, for each reference position, the actual position is retrieved from the memory. In step 210, it is determined whether an actual position below a reference position can be retrieved from the memory.

Then, in step 220, a vector difference factor data between the actual position of the first reference position and the actual position of the second reference position is determined from the corresponding actual position obtained in step 200 and the reference position in step 120. For example, consider using the corner points of edge 42 of Figure 6B. Assume that for each of the structures 40 in Figure 6B, one of the corner points of the edges 42 is used as a reference position. Then in step 200, the actual position corresponding to each of these reference positions can be obtained from the memory. This is possible because the precise position of the calibration structure 11' in the SPM system 1 is known and these positions can therefore be stored as system calibration data during manufacturing. In step 220, these actual positions are made to correspond to the reference positions from step 120, and vector data between each two reference positions can be determined. For example, the vector between the first corner point of the outermost square and the next corner point of the next square can be determined as a real vector between these points. Then, in step 235, the system 1 determines the imaging difference vector data between each two reference positions from the image obtained in step 100 from the reference position obtained in step 120. Then, in step 140, the system calculates the difference between the actual difference vector data obtained in step 220 and the imaging difference vector data obtained in step 235 to determine the deviation representing the lateral displacement at each Z layer. In step 150, this information is stored in the memory or external database 90 as calibration data.

The present invention has been described by certain specific embodiments thereof. It is understood that the embodiments shown in the drawings and described herein are intended for illustration only and are not intended to limit the present invention by any manner or means. It is believed that the operation and construction of the present invention can be understood from the foregoing description and the accompanying drawings. It is understood by those of ordinary skill that the present invention is not limited to any embodiment described herein and may have modifications that should be considered within the scope of the additional claims. Dynamic backpropagation may be considered to have been originally disclosed and should be within the scope of the present invention. In addition, without departing from the scope of the present invention as defined in the claims, any components and elements of the various embodiments disclosed herein may be combined or may be added to other embodiments when deemed necessary, required or preferred.

In the claims, any reference sign should not be interpreted as limiting the claim. When used in this description or the appended claims, the terms "comprising" and "including" should not be interpreted in an exclusive or exhaustive manner but in an inclusive manner. Therefore, the expression "comprising" used herein does not exclude the presence of other elements or steps in addition to the elements or steps listed in any claim. In addition, the word "a" should not be interpreted as limited to "only one", but is used to mean "at least one", and does not exclude the plurality. Features that are not specifically or explicitly described or claimed may be otherwise included in the structure of the present invention and are within its scope. For example, the expression "device for..." should be interpreted as: "assembly configured for..." or "structured as a component for..." and should be interpreted to include equivalents of the disclosed structure. The use of expressions such as "important", "preferable", "particularly preferred", etc. is not intended to limit the invention. Additions, deletions, and modifications within the scope of one of ordinary skill in the art may generally be made without departing from the spirit and scope of the invention as determined by the claims. The invention may be practiced differently than as specifically described herein and is limited only by the claims appended hereto.

1: Scanning probe microscopy (SPM) system 2: Workspace 3: Substrate carrier; Sample carrier 4: Substrate 5: Base 6: (Coordinate reference) Grid plate 7: Support surface 8,54: Surface 8’,29’: Position 9: Benchmark; Topography 9-1,9-2: Topography 10: Probe tip 11,11’: Calibration structure 11”: Hole 12: Arm 13: Support 14: Optical sensor 15: Encoder 17: Sensor hole 18: Electrical connection interface 19: Field of view 20: Camera 21: Hole 22: Tube lens; Focusing lens; Focusing optics 23: Optical axis 24: actuator 25: redirector mirror; mirror 26: probe 27: cantilever 28: probe tip 29: objective lens; lens 30: printed circuit board 31: light-emitting diode 32: capacitive sensor 33: deflector 35: region 36: image 40: step 40-1,40-2,…,40-8,40-9: dish-shaped structure morphology; structure; square 42,42-1,42-2,42-3,42-4,42-5,42-6,42-7,42-8,42-9: edge 42-7’: circle 45: point 46: midpoint 50: handle 55: side wall 90: memory or external database 100,120,130,140,150,200,210,220,235: steps

The present invention is further described by describing certain specific embodiments of the present invention with reference to the accompanying drawings. The detailed description provides possible embodiments of the present invention, but should not be considered as describing the only embodiments falling within the scope. The scope of the present invention is defined in the scope of the application, and the description should be considered as illustrative rather than limiting of the present invention. In the drawings: FIG. 1 schematically shows a scanning probe microscope system according to an embodiment; FIG. 2A schematically shows an optical microscope for use with the system of FIG. 1 and which can be calibrated using an embodiment of the present invention; FIG. 2B shows the problem of lateral displacement when refocusing in an optical microscope shown in FIG. 2A; FIG. 3 schematically shows an optical microscope of a scanning probe microscope system according to the present invention; FIGS. 4A and 4B schematically show a method according to an embodiment of the present invention; FIGS. 5A and 5B schematically show a calibration structure according to an embodiment of the present invention; FIGS. 6A and 6B schematically show a calibration structure according to an embodiment of the present invention; FIGS. 7A and 7B schematically show a method example according to an embodiment of the present invention; FIG8 schematically shows a calibration structure according to an embodiment of the present invention; FIG9 schematically shows a side wall of a portion of a calibration structure according to an embodiment of the present invention; FIG10 schematically shows a calibration structure according to an embodiment of the present invention; FIG11 schematically shows a method according to an embodiment of the present invention; FIG12 schematically shows a method according to an embodiment of the present invention.

3: Substrate carrier; sample carrier

4: Base material

5: Base

6: (Coordinate reference) Grid plate

7: Loading surface

8: Surface

9: Benchmarks; morphological bodies

10: Probe head

11: Calibration structure

12: Arms

13: Support parts

14: Optical sensor

15: Encoder

19: Horizon

23: Light axis

26: Probe

27: hanging arms

28: Probe tip

29:Objective lens; lens

Claims (14)

A method for calibrating an optical microscope in a scanning probe microscope system, the optical microscope being configured to provide a reference for positioning a probe tip on a surface of a substrate, wherein the calibration is performed using a calibration structure, the calibration structure being a spatial structure including a morphology body at different Z layers relative to a Z axis, the Z axis being perpendicular to the surface of the substrate, wherein the method comprises the following steps: taking at least two images of at least a portion of the calibration structure using the optical microscope, wherein the at least two images are focused on at least two different layers in the Z layers; and determining a lateral displacement of the calibration structure in a direction perpendicular to the Z axis, the lateral displacement being displayed in the at least two images focused on the at least two different layers. The method of claim 1, wherein the step of acquiring at least two images is performed by acquiring a series of images of the calibration structure during refocusing of the optical microscope through a Z-layer range, and wherein the step of determining a lateral displacement is performed by detecting movement of the calibration structure through the series of images. The method of claim 1 or 2, wherein the step of obtaining at least two images comprises the following steps: Focusing the optical microscope on a first layer among the Z layers to obtain a first image of one or more first morphologies in the first layer, and obtaining a first reference position from the first image according to a position of at least one first morphology in the first morphologies; Focusing the optical microscope on a second layer among the Z layers to obtain a second image of one or more second morphologies in the second layer, and obtaining a second reference position from the second image according to a position of at least one second morphology in the second morphologies; and wherein the step of determining the lateral displacement comprises comparing the first reference position and the second reference position to determine a deviation representing the lateral displacement. A method as claimed in claim 3, wherein determining the deviation includes determining deviation data representing a distance and direction of the lateral displacement from the first reference position and the second reference position, wherein the method further includes storing the deviation data as calibration data associated with the second layer. A method as claimed in claim 3 or 4, wherein the calibration structure comprises a plurality of concentric structures in the different layers, such as concentric rings, squares, triangles or polygons, and wherein determining the first reference position and the second reference position comprises determining a centroid of the structure in each first layer or second layer. The method of any one of claims 3 to 5, wherein the step of determining the lateral displacement further comprises: Determining the corresponding actual positions of the first reference position and the second reference position obtained from the first image and the second image from a calibration structure data in a data storage library; Determining an actual difference vector data between the actual position of the first reference position and the actual position of the second reference position from the corresponding actual positions; Determining an image difference vector data between the first reference position and the second reference position from the first reference position and the second reference position obtained from the first image and the second image; and Comparing the actual difference vector data and the image difference vector data to determine the deviation representing the lateral displacement. A method as claimed in any one of claims 1 to 6, wherein the step of obtaining at least two images comprises focusing the optical microscope on a plurality of different layers and obtaining a reference position at each layer based on a position of at least one morphology at each layer, and wherein the step of determining the lateral displacement comprises: calculating deviation data representing a relevant lateral displacement at each layer from the reference positions; and storing the deviation data associated with each layer as calibration data in a data repository accessible by the scanning probe microscope system. A method as in any one of claims 1 to 7, wherein in order to obtain the at least two images, the optical microscope includes a camera cooperating with a focusing objective, wherein the camera and the focusing objective are configured to obtain a field of view by the camera, wherein the field of view includes at least a portion of an outermost periphery of the calibration structure. A method as in any one of claims 1 to 8, wherein the calibration structure includes one or more structural morphologies provided at different Z layers, wherein the structural morphologies include one or more side walls for supporting elevated surfaces of the structural morphologies at each Z layer, wherein at least one of the side walls includes a laterally contracted portion relative to each elevated surface so as to be invisible to the optical microscope. A method as in any one of claims 1 to 9, wherein the calibration structure comprises one or more structural topography bodies of the said topography bodies provided at different Z layers, wherein the said structural topography bodies include one or more elevated surfaces at each of the Z layers, and wherein the said elevated surfaces include edges defining a perimeter of the said elevated surfaces, wherein at least one of the said edges includes a contrasting color. A substrate carrier for use in a scanning probe microscope device, the substrate carrier comprising a carrier surface for supporting a substrate to be inspected by the scanning probe microscope device, wherein the substrate carrier comprises a calibration structure for use in a method as in any one of claims 1 to 10, for cooperating with a scanning probe microscope system, the calibration structure being a spatial structure including a structural morphology body at different Z layers relative to a Z axis, for performing the following steps: Acquiring at least two images of at least a portion of the calibration structure with the optical microscope, wherein the at least two images are focused on at least two different layers in the Z layers; and Determining a lateral displacement of the calibration structure in a direction perpendicular to the Z axis, the lateral displacement being displayed in the at least two images focused on the at least two different layers. A scanning probe microscope device, comprising a substrate carrier for supporting a substrate to be inspected, the scanning probe microscope device comprising a probe head, the probe head comprising a probe including a cantilever and a probe tip, the probe head further comprising a beam detector configuration for monitoring a deflection of the probe tip during scanning, wherein the scanning probe microscope device further comprises an optical microscope configured to provide a reference data, the reference data is used to position the probe tip in a desired measurement position on the surface of the substrate, wherein the optical microscope comprises a focusing objective lens, the focusing objective lens is used to focus an image obtained by the microscope on a desired Z layer relative to a Z axis, the Z axis is perpendicular to the surface of the substrate, and The substrate carrier includes a calibration structure for calibrating the optical microscope, for use in the method of any one of claims 1 to 10 and for cooperating with an optical microscope of a scanning probe microscope system, the calibration structure being a spatial structure including structural morphologies at different Z layers relative to a Z axis, for performing the following steps: Acquiring at least two images of at least a portion of the calibration structure using the optical microscope, wherein the at least two images are focused on at least two different layers in the Z layers; and Determining a lateral displacement of the calibration structure in a direction perpendicular to the Z axis, the lateral displacement being displayed in the at least two images focused on the at least two different layers. A scanning probe microscope device as claimed in claim 12, wherein the focusing lens cooperates with a precision actuator for moving the focusing lens along an optical axis in order to focus the optical microscope, and wherein the scanning probe microscope device further comprises a controller for controlling the precision actuator to implement the focusing, the controller cooperates with a camera for receiving images acquired using the optical microscope, and wherein the controller is configured to implement the following steps: Acquire at least two images of at least a portion of the calibration structure using the optical microscope, wherein the at least two images are focused on at least two different layers in the Z layers; and Determine a lateral displacement of the calibration structure in a direction perpendicular to the Z axis, the lateral displacement being displayed in the at least two images focused on the at least two different layers. A scanning probe microscope device as claimed in claim 13, wherein the controller is further configured to: focus the optical microscope on a plurality of different layers and obtain a reference position at each layer based on a position of at least one morphology at each layer, and wherein, in order to determine the lateral displacement, the controller is configured to: calculate deviation data representing a relevant lateral displacement at each layer from the reference positions; and store the deviation data associated with each layer as calibration data in a data repository accessible by the scanning probe microscope system.