Dual beam system and method for separating the operating distance of a charged particle beam device due to constraints resulting from a clustered ion beam shape

Abstract

A method for acquiring a series of cross-sectional images parallel to each other of a measurement site on a wafer, comprising: 1a) providing a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column in a coincident arrangement, in which coincident arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface and form an angular arrangement GFE between the FIB optical axis and the CPB optical axis; 1b) in the coincident arrangement, by using the FIB column, removing a cross-sectional surface layer of the measurement site on the wafer to make a new cross-section for imaging accessible; 1c) shortening the working distance between the CPB imaging column and the wafer surface in a direction along the axis of the CPB imaging column; 1d) imaging a new cross-section at the measurement site on the wafer by the CPB imaging column at the shortened working distance regardless of the coincident arrangement; and 1e) lengthening the working distance between the CPB imaging column and the wafer surface in a direction along the axis of the CPB imaging column until the coincident arrangement is reached.

Description

Technical Field

[0001] The present invention relates to a dual beam apparatus and three-dimensional circuit pattern inspection by cross-sectioning an inspection volume.

Background Art

[0002] Semiconductor structures are one of the most sophisticated artificial structures, but they have various imperfections. Systems for quantitative 3D measurement, defect detection, or defect review explore these imperfections. Processed semiconductor structures are based on prior knowledge. Semiconductor structures are fabricated from a series of layers parallel to the substrate. For example, in a logic-type sample, metal lines extend parallel in a metal layer or a HAR (high aspect ratio) structure, and metal vias extend perpendicular to the metal layer. The angle between metal lines in different layers is 0° or 90°. On the other hand, in the case of a VNAND-type structure, each cross-section is known to be circular on average.

[0003] Semiconductor wafers have a diameter of, for example, 300 mm and consist of several sites, so-called dice, each containing at least one integrated circuit pattern, such as memory chips or processor chips. During processing, the semiconductor wafer goes through about 1000 process steps, and in the semiconductor wafer, about 100 or more parallel layers are formed, including transistor layers, wiring intermediate layers, and interconnect layers, and a plurality of 3D memory cell arrays in memory devices. The dimensions, shapes, and arrangements of semiconductor structures and patterns are affected by several factors. In the manufacture of 3D memory devices, important processes are currently etching and deposition. Other related process steps, such as lithographic exposure or implantation, also affect the characteristics of IC elements.

[0004] The aspect ratio and the number of layers of integrated circuits are constantly increasing, and the structure is growing three-dimensionally (vertically). The current height of the memory stack exceeds a dozen micrometers. In contrast, the feature size is getting smaller. The minimum feature size, i.e., the critical dimension, is less than 10 nm, for example, 7 nm or 5 nm, and will approach a feature size below 3 nm in the near future. While the complexity and dimensions of the semiconductor structure are growing three-dimensionally, the lateral dimensions of the integrated semiconductor structure are getting smaller. Therefore, it becomes difficult to measure the shape, dimensions, and orientation of 3D features and patterns, as well as their overlay, with high precision.

[0005] As the requirements for the resolution of charged particle imaging systems in three dimensions increase, the inspection and 3D analysis of integrated semiconductor circuits in wafers become increasingly difficult. The lateral measurement resolution of charged particle systems is usually limited by the sampling raster or dwell time per pixel of individual image points on the sample and the charged particle beam diameter. In an imaging system, the sampling raster resolution can be set and adapted to the charged particle beam diameter on the sample. The normal raster resolution is 2 nm or less, but in principle, the raster resolution limit can be reduced without physical constraints. The charged particle beam diameter has a limiting dimension determined by the operating conditions and lenses of the charged particle beam. The beam resolution is limited to about half of the beam diameter. A resolution of less than 2 nm is possible, for example, even less than 1 nm is possible.

[0006] A common method for generating 3D tomography data from semiconductor samples on the nanometer scale is the so-called slice and image approach, which is constituted by, for example, a dual beam system. A dual beam system equipped with a charged particle beam column for imaging and an FIB column for milling operates at a so-called coincidence point. That is, the charged particle beam optical axis, the FIB optical axis, and the sample surface meet (coincide) at a single point. By doing so, actual imaging is guaranteed at the sample point affected by milling, which is convenient.

[0007] The slice imaging method is described, for example, in WO2020 / 244795. According to the method of WO2020 / 244795, 3D volume inspection is performed on an inspection sample extracted from a semiconductor wafer. This method has the disadvantage that it is necessary to break the wafer to obtain a block-shaped inspection sample. On the other hand, this method is advantageous in that it can relatively shorten the working distance between a charged particle imaging device such as a scanning electron microscope (SEM), more precisely, between its column and the sample or wafer to be imaged. This is especially the case when two columns are arranged perpendicular to each other with the optical axis of the SEM arranged perpendicular to the sample surface. Generally, the resolution of the particle imaging device becomes higher as the working distance becomes shorter.

[0008] An alternative method for generating 3D tomography data from a semiconductor sample at the nanometer scale is described in WO2021 / 180600. According to the said document, the disadvantage of requiring wafer breakage is overcome by, on the one hand, milling or an FIB column and, on the other hand, a different geometric arrangement of the charged particle imaging column. With this arrangement, it is possible to move the coincidence point over the entire wafer without requiring wafer damage. In the so-called wedge-cut approach, the slice imaging method is used at an oblique angle on the surface of the semiconductor wafer. However, since the mutual arrangement of the two columns is subject to geometric constraints, the working distance from the charged particle imaging column to the sample or wafer to be imaged is longer than that of the method described in WO2020 / 244795. As a result, the imaging resolution, although good, is reduced.

[0009] DE102013102776 discloses a cross-section processing and observation method for determining a cut width by applying a dual beam system. In this system, a geometry different from the wedge-cut method is used. The FIB column is arranged perpendicular to the sample surface, and the SEM column is arranged at an oblique angle to the sample surface.

[0010] WO2021 / 180600 discloses a method for cross-sectional imaging of an inspection volume in a wafer. More specifically, it discloses a dual-beam apparatus and a three-dimensional circuit pattern inspection technique by cross-sectioning an inspection volume that extends longitudinally in the depth direction by more than 1 μm under the surface of a semiconductor wafer. In particular, WO2021 / 180600 discloses a method, a computer program product, and an apparatus for generating 3D volume image data of a deep inspection volume inside a wafer without taking out a sample from the wafer. The wedge cut method is applied. Further, WO2021 / 180600 relates to a method for 3D volume image generation and cross-sectional image alignment using a dual-beam apparatus for three-dimensional circuit pattern inspection.

[0011] DE102013102535 discloses a dual-beam apparatus in which an FIB column and an SEM column are arranged orthogonally to each other. The sample on which slicing and imaging are performed is placed on a special holder that enables edge cutting of the sample. SUMMARY OF THE INVENTION

[0012] Therefore, the general problem to be solved by the present invention is to overcome the disadvantages of the above-mentioned prior art.

[0013] A further problem of the present invention is to provide an improved slice imaging method that enables higher imaging resolution and a dual-beam system adapted thereto, especially in the presence of geometric constraints regarding the arrangement of the columns of the dual-beam apparatus, for example when the geometry of the wedge cut method is applied.

[0014] Furthermore, it aims to enable improvement in the flexibility of the workflow.

[0015] Furthermore, it aims to provide a high-speed workflow.

[0016] The above problems are solved by the subject matter of the independent claims. The dependent claims relate to advantageous embodiments.

[0017] This patent application claims the priority of U.S. Provisional Patent Application No. 63 / 365,548, filed on May 31, 2022, and incorporates the entire disclosure thereof by reference into this patent application. Further, this patent application claims the priority of German Patent Application No. 10 2022 117 601.0, filed on Jul. 14, 2022, and incorporates the entire disclosure thereof by reference into this patent application.

[0018] According to a first aspect of the present invention, the present invention is directed to a method for acquiring a series of cross-sectional images parallel to each other of a measurement site of a wafer. Further, this method can also be used for imaging other types of samples. However, its value becomes particularly apparent when applied to wafers that can improve the imaging resolution compared to a "normal" wedge cut FIB / SEM arrangement without the need to destroy or damage the entire wafer. This method 1a) providing a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column in a coincident arrangement, in which arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface and form an angular displacement GFE between the FIB optical axis and the CPB optical axis; 1b) in the coincident arrangement, by using the FIB column, removing a cross-sectional surface layer of the measurement site of the wafer to make a new cross-section for imaging accessible; 1c) shortening the working distance between the CPB imaging column and the wafer surface in a direction along the axis of the CPB imaging column; 1d) imaging a new cross-section at the measurement site of the wafer by the CPB imaging column at the shortened working distance regardless of the coincident arrangement; 1e) lengthening the working distance between the CPB imaging device and the wafer surface in a direction along the axis of the CPB imaging device until (again) reaching the coincident arrangement and includes.

[0019] In principle, any type of CPB imaging device is possible. For example, a scanning electron microscope (SEM) or a helium ion microscope (HIM) is possible.

[0020] In principle, this method applies an arrangement as known by the wedge cutting method. However, the present invention implements some advantageous differences in the workflow compared to the workflow known in the wedge cutting arrangement. The general considerations of the present inventors are as follows. That is, the arrangement angle GFE between the FIB column and the CPB imaging column cannot be completely freely selected. Usually, the smaller the working distance can be, the larger the angle GFE is, but the size of the angle GFE is limited by the available space in the system. When the working distance is short, the FIB column begins to interfere with the CPB imaging column.

[0021] Instead of operating in a coincidence arrangement throughout the workflow as known in the prior art, the present inventors have found it advantageous to temporarily abandon the entire coincidence arrangement. According to the present invention, the milling process is still performed in a coincidence arrangement, but the angle GFE is very small, and the imaging resolution decreases during the management of milling (however, of course, the CPB imaging beam is focused on the wafer surface). However, even if the imaging resolution decreases, it is still sufficient for the management of milling. And for the imaging process itself, (while maintaining the angle GFE as it is), the coincidence arrangement can be abandoned, and the working distance of the CPB imaging column can be shortened. As a result, the imaging itself is performed at a relatively short working distance, so that a higher imaging resolution can be achieved (of course, the CPB imaging column is set with a different focusing). When the imaging resolution increases, the slight disadvantage of the low imaging resolution in the milling process is also overcompensated.

[0022] The actuation distance is shortened by the relative movement between the CIP imaging column and the wafer surface along the axis of the CPB imaging column. For example, due to the movement of the vertical stage, the actuation distance is shortened along the axis of the CPB imaging column, so the coincidence point of the arrangement is only temporarily abandoned and can be relatively easily found again later. Furthermore, when a high-precision stage is applied, any displacement of the vertical stage due to the movement of the stage in the z direction is small compared to the change in the normal dimension in the z direction inside the wafer to be analyzed. Optionally, this method may include additional alignment steps. Alternatively, the relative movement between the CPB imaging column and the wafer surface can be achieved by moving the CPB imaging column. However, afterwards, it is necessary to move the FIB column in the same way prior to the movement of the CPB imaging column so as not to "interfere" with the CPB imaging column.

[0023] According to one example, a series of method steps 1b), 1c), 1d), and 1e) are repeatedly executed. This can be executed, for example, 2 times, 3 times, 10 times, 100 times, or 500 times.

[0024] According to one example, this method further includes the step of imaging the removal of the cross-sectional surface layer by the CPB imaging device in the coincidence arrangement. In this imaging, the milling process can be managed and the milling can be started / stopped at the correct position.

[0025] According to one embodiment, the step of shortening the working distance between the CPB imaging device and the wafer surface includes moving the stage that supports the semiconductor sample, particularly moving the stage vertically. The movement of the stage in the z-direction (vertical direction) can be performed with relatively high accuracy. Furthermore, such movement of the stage is relatively fast compared to the entire imaging time (for example, the movement of the stage is 1 s compared to an imaging time of 20 s to 30 s). Therefore, it does not significantly delay the entire process. Since the size of the movement of the stage in the z-direction can be, for example, about 2 to 3 mm, when the working distance is about 5 to 6 mm, for example, the movement of the stage can shorten the working distance to about half of the original working distance in the aligned arrangement. As a result, the imaging resolution can be increased by, for example, two digits or more.

[0026] According to one example, the CPB optical axis is aligned with the normal of the wafer surface. This facilitates the operation.

[0027] According to one example, the FIB optical axis is arranged at an oblique angle with respect to the wafer surface (the upper surface of the wafer).

[0028] According to one example, the arrangement angle GFE is 45° or less, preferably 40° or less, and most preferably 35° or less. Since imaging by CPB imaging of a largely inclined surface may cause problems, the angle GFE is preferably 30° or more.

[0029] According to one example, the step of shortening the working distance between the CPB imaging columns includes moving the CPB imaging column along the PCB optical axis. Here, the stage can be locally fixed.

[0030] Furthermore, the present invention is directed to a computer program product including program code configured to execute the methods as described above in various examples. The program code can be segmented or divided into a plurality of parts or modules. In principle, any computer language can be applied as a programming language.

[0031] Furthermore, the present invention is a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column configured to be provided in a coincident arrangement, in which coincident arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface, form an arrangement angle GFE between the FIB optical axis and the CPB optical axis, and the CPB optical axis is arranged in a direction perpendicular to the wafer surface, the FIB column and the CPB imaging column; a stage configured to support the wafer and configured to be movable in a direction perpendicular to the wafer surface; and a controller and is directed to a single-chamber system including a controller configured to control the FIB column, the CPB imaging column, and the stage so that the controller executes the methods as described above in various examples.

[0032] The stage can directly or indirectly support the wafer or sample. In one example, a chuck is disposed on the stage itself, and the wafer is disposed on the chuck. By using the chuck, the wafer can be disposed flat, for example, by electrostatic adsorption. The stage is movable not only in a direction perpendicular to the wafer surface (usually defined as the z direction), but also in other directions and / or rotatable.

[0033] Other systems can be used as well to execute the methods as described above in various examples.

[0034] According to a second main aspect of the present invention, the present invention is a method for acquiring a series of cross-sectional images parallel to each other of a measurement site of a wafer, wherein the wafer is supported by a stage, and the method includes 2a) Providing a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column in an offset arrangement, in which offset arrangement, the FIB column optical axis and the CPB optical axis intersect the wafer surface at two different positions, and the difference between the two different positions defines an offset on the wafer surface, and this offset enables an independent setting of the working distances of the FIB column and the CPB imaging column without geometric constraints due to the shape and / or position of the FIB column and the CPB imaging column; 2b) Removing the cross-sectional surface layer of the first measurement site of the wafer by using the FIB column to provide access to a new cross-section for imaging; 2c) Moving the wafer surface by moving the stage relative to the FIB column and the CPB imaging column according to the offset; 2d) Imaging a new cross-section of the first measurement site of the wafer with the CPB imaging column A method comprising the above steps is targeted.

[0035] According to this second main aspect of the present invention, instead of abandoning the concept of the coincidence point, an offset arrangement is used. Since the working distances of the FIB column and the CPB imaging column can be set independently of each other, it is convenient for optimization. In particular, the short working distance of the CPB imaging column is not hindered by the FIB column. Therefore, the imaging resolution can be improved compared to the "normal" wedge cut arrangement with a coincidence point. The additional stage movement can also be performed relatively quickly. The use of a high-precision stage is advantageous. Optionally, one or more positioning or alignment steps can be performed. Also, according to this second main aspect of the present invention, it is not necessary to destroy or damage the entire wafer. In one example, this method can be performed in an arrangement where the FIB optical axis is arranged at an oblique angle with respect to the upper surface of the wafer, similar to the "normal" wedge cut method.

[0036] According to one example, this method further includes step 2e) of moving the wafer surface by moving the stage with respect to the FIB column and the CPB imaging column according to the offset.

[0037] In principle, this step 2e) can be realized in two different ways. According to one example, step 2e) is the reverse of step 2c), where the measurement site is milled at the first position, transferred to the second position for imaging, returned to the first position for further milling. In this case, overall, only two different columns are applied. However, according to an alternative approach, three or more columns can be applied and arranged alternately in a row, for example, each can be offset from each other by the same value. And the processing can be executed in the processing line. With each offset, the measurement site advances from one column to the next.

[0038] According to one example, a series of method steps 2b), 2c), 2d), and 2e) are repeatedly executed.

[0039] According to one example, the relative movement includes the lateral movement of the stage or the rotation of the stage. According to the rotation of the stage, a relatively well-defined and high-speed switching between the two positions, one where milling is performed and the other where imaging is performed, becomes possible. Lateral movement is preferred, for example, in the execution of the processing line.

[0040] According to one example, the operating distance of the FIB column is optimized and / or the operating distance of the CPB imaging column is optimized.

[0041] According to one example, the offset corresponds to the distance between a first measurement site on the wafer surface and a second measurement site on the wafer surface.

[0042] According to one example, this method further includes the step of obtaining a series of cross-sectional images parallel to each other of the second measurement site of the wafer by repeatedly executing a series of method steps 2b), 2c), and 2d) at the second measurement site, The step of removing the cross-sectional surface layer of the second measurement site of the wafer is executed simultaneously with the step of imaging a new cross-section of the first measurement site of the wafer by the CPB imaging column. The step of removing the cross-sectional surface layer of the first measurement site of the wafer is executed simultaneously with the step of imaging a new cross-section of the second measurement site of the wafer by the CPB imaging column.

[0043] According to this example, the overall speed can be increased by parallelizing the entire process. At least some of the milling (removal of the cross-sectional image layer) and imaging method steps are executed simultaneously. The processing steps at least partially overlap in time. For example, it is possible to start the milling and imaging processing steps at the same time, but it is also possible to finish one process earlier (faster) than the other. Having a common starting point is convenient for process synchronization. Other implementations are also possible.

[0044] According to another aspect of the present invention, the present invention is directed to a computer program product including program code configured to execute the method as described above in various examples.

[0045] According to another aspect of the present invention, the present invention is a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column configured to be arranged in an offset arrangement, in which offset arrangement, the FIB optical axis and the CPB optical axis intersect the wafer surface at two different positions, and the difference between the two different positions defines an offset on the wafer surface, and this offset has a size large enough to enable independent setting of the working distances of the FIB column and the CPB imaging column without geometric constraints due to the shape and / or position of the FIB column and the CPB imaging column, the FIB column and the CPB imaging column, a stage configured to support the wafer and configured to be movable in a plane parallel to the wafer surface, a controller and A single-chamber system is targeted, where the controller is configured to control a FIB apparatus, a CPB imaging apparatus, and a stage so that the controller executes the method as described above in various examples of the second main aspect of the present invention.

[0046] The stage is movable in a plane parallel to the wafer surface. Thus, the stage can be rotated, for example, about an axis perpendicular to the wafer surface. Additionally or alternatively, the stage can be configured to move laterally, for example, in the x-direction and / or the y-direction. Further additionally, the stage can be made movable in the vertical direction (z-direction).

[0047] In various examples of the second main aspect of the present invention, other systems can be similarly used to execute the method as described above.

[0048] According to a third main aspect of the present invention, the present invention is a method for acquiring a series of cross-sectional images parallel to each other of a measurement site of a wafer, 3a) providing a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column in a coincident arrangement, in which the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface and form an arrangement angle GFE between the FIB optical axis and the CPB optical axis; 3b) determining the optimization operating distance of the FIB column and the trade-off operating distance of the CPB imaging column, or determining the trade-off operating distance of the FIB column and the optimization operating distance of the CPB imaging column; 3c) moving the FIB column along its optical axis and arranging the FIB column at the determined (optimization or trade-off) operating distance, and / or moving the CPB imaging column along its optical axis and arranging the CPB imaging column at the determined (trade-off or optimization) operating distance; 3d) By using an FIB column arranged at the operating distance, removing the cross-sectional surface layer of the measurement site of the wafer to enable access to a new cross-section for imaging; 3e) Imaging a new cross-section of the measurement site of the wafer with a CPB imaging column arranged at the operating distance; A method is targeted.

[0049] According to this embodiment, in specific steps, it is determined which of the aspects "milling" or "imaging" is more important. Then, by optimizing the operating distance assigned to each of the columns, a greater weight or priority is given to the more important aspect. The other operating distance, referred to as the "trade-off" operating distance, is selected according to what is not optimal but still good and / or the next-best possibility. For example, in the case of a use case where imaging resolution is more important than milling quality, the operating distance of the CPB imaging column can be shortened at the expense of shortening the operating distance of the FIB column. An algorithm for determining the trade-off operating distance can be applied. Also, according to this third main aspect of the present invention, it is not necessary to destroy or damage the entire wafer. In one example, this method can be performed in an arrangement where the FIB optical axis is arranged at an oblique angle with respect to the upper surface of the wafer, similar to the "normal" wedge cut method.

[0050] According to one example, a series of method steps 3d) and 3e) are repeatedly executed.

[0051] According to one example, step 3c) Shortening the operating distance of the FIB column and lengthening the operating distance of the CPB imaging column, or Lengthening the operating distance of the FIB column and shortening the operating distance of the CPB imaging column is included.

[0052] According to one aspect of the present invention, the present invention is directed to a computer program product including program code configured to execute the methods as described above in various embodiments according to the third main aspect of the present invention.

[0053] According to one aspect of the present invention, the present invention A focused ion beam (FIB) column and a charged particle beam (CPB) imaging column configured to be arranged in a coincident arrangement, in which coincident arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface, and an arrangement angle GFE is formed between the FIB optical axis and the CPB optical axis. The FIB column is configured to be movable along its FIB optical axis, and the CPB imaging column is configured to be movable along its CPB optical axis, the FIB column and the CPB imaging column, A stage configured to support the wafer, A controller Comprising A single-chamber system in which the controller is configured to control the FIB column, the CPB imaging column, and the stage so as to execute the methods as described above in various examples regarding the third main aspect of the present invention.

[0054] Other systems can be similarly used to execute the methods as described above in various examples of the third main aspect of the present invention.

[0055] According to a fourth main aspect of the present invention, the present invention is a method for acquiring a series of first cross-sectional images of a first measurement site on a first wafer and a series of second cross-sectional images of a second measurement site on a second wafer, comprising: 4a) Providing the first wafer on a first stage and positioning the first wafer on the first stage; 4b) Providing the second wafer on a second stage and positioning the second wafer on the second stage; 4c) By using a FIB column operating at a set FIB operating distance, removing the first cross-sectional surface layer of the first measurement site of the first wafer to provide access to a first new cross-section for imaging; 4d) Exchanging the positions of the first stage and the second stage; 4e) Imaging the first new cross-section of the first measurement site of the first wafer with a CPB imaging column at a set operating distance, and simultaneously, by using a FIB column at a set FIB operating distance, removing the second cross-sectional surface layer of the second measurement site of the second wafer to provide access to a second new cross-section for imaging; 4f) Exchanging the positions of the first stage and the second stage; 4g) Imaging the second new cross-section of the second measurement site of the second wafer with a CPB imaging column at a set operating distance, and simultaneously, by using a FIB column at a set FIB operating distance, removing another first cross-sectional surface layer of the first measurement site of the first wafer to provide access to another first new cross-section for imaging A method is provided that includes the above steps.

[0056] According to one example, the set operating distance of the CPB imaging column can be the optimal operating distance for a particular use case. Similarly, the set operating distance of the FIB imaging column can be the optimal operating distance for a particular use case. The operating distances can be set independently of each other because the columns do not interfere with each other but are used in combination with different stages.

[0057] The exchange or switching of the positions of the first and second stages is known in the art and can be implemented by a similar method as described, for example, in U.S. Patent No. 7,161,659. Exchanging the positions of the stages parallelizes the process and makes it faster.

[0058] According to one example, the series of method steps 4d), 4e), 4f), and 4g) are repeatedly executed. These method steps are preferably repeated until the measurement sites in both wafers are milled and imaged at the desired slice thickness.

[0059] According to one embodiment, a plurality of first measurement sites on a first wafer are sequentially milled and sequentially imaged, and a plurality of second measurement sites on a second wafer are sequentially milled and sequentially imaged. Therefore, before the exchange of the stage positions, it is preferable that all the measurement sites existing on one wafer are milled (one slice) or imaged respectively. Milling and imaging are again parallel, that is, at least partially executed simultaneously.

[0060] According to one example, the step of removing the first cross-sectional layer surface and / or the second cross-sectional layer surface is controlled by low-resolution imaging, and / or the step of imaging a new first cross-section and / or a new second cross-section includes high-resolution imaging. The terms "high-resolution" and "low-resolution" imaging are relative terms and should not be interpreted in an absolute sense. However, these terms indicate that one of the resolutions is either higher or lower than the other. This can affect the applicable column / each working distance. Regarding the arrangement of the FIB column used for milling, since a relatively low imaging resolution is sufficient for the management or monitoring of milling, for example, another CPB imaging column that can be arranged according to the normal wedge cut symmetry can be applied. In this beam intersection arrangement, since the milling process is a more important process, the working distance of the FIB column can be optimized, and the working distance of the CPB imaging column can be adapted to the set working distance of this preferred FIB column. In contrast, in the case of the imaging process as an actual image generation process, an optimal working distance can be set for the imaging of the measurement sites arranged on the wafer of the stage actually existing at the position of the CPB imaging column.

[0061] According to one example, the low-resolution imaging is performed by a low-resolution scanning electron microscope (SEM) arranged in a beam intersection arrangement with an FIB column used for removing the first cross-sectional surface layer and the second cross-sectional surface layer, and / or the high-resolution imaging is performed by a high-resolution scanning electron microscope (SEM), a helium ion microscope (HIM), or a multi-beam scanning electron microscope (MultiSEM). As the high-resolution scanning electron microscope, for example, a corrected scanning electron microscope equipped with an additional electrostatic lens for correcting imaging aberration is possible.

[0062] According to one example, the step of exchanging the positions of the first stage and the second stage includes transferring positioning information. Therefore, it is not necessary to separately position the wafers on each stage for each column, and in principle, one positioning is sufficient. Optionally, an additional alignment step can be incorporated to correct small position deviations.

[0063] According to one example, the FIB column is arranged in the first chamber, and the CPB imaging column is arranged in the second chamber. This is convenient because the imaging quality of the (high-resolution) CPB imaging column is not degraded by the redeposition of milling.

[0064] According to one example, the step of exchanging the positions of the first stage and the second stage includes transferring one of the stages from the first chamber to the second chamber and vice versa. This transfer can be realized via one or two vacuum locks.

[0065] According to one aspect of the present invention, the present invention is directed to a computer program product including program code configured to execute a method as described above with respect to various examples according to the main fourth aspect of the present invention.

[0066] According to one aspect of the present invention, the present invention is A first chamber comprising a focused ion beam (FIB) column and a low-resolution charged particle beam (CPB) imaging column configured to be arranged in a wedge-cut matching arrangement, in which arrangement the FIB optical axis of the FIB column and the CPB optical axis of the low-resolution CPB imaging column coincide on the wafer surface and form an arrangement angle GFE between the FIB optical axis and the CPB optical axis, the first chamber; A second chamber comprising a high-resolution CPB imaging column, the optical axis of which is arranged perpendicular to the wafer surface, the second chamber; A first stage for supporting a first wafer; A second stage for supporting a second wafer; A stage exchange mechanism configured to exchange the positions of the first stage and the second stage; A controller Comprising The controller is configured to control a first chamber comprising an FIB column and a low-resolution CPB imaging column, a second chamber comprising a high-resolution CPB imaging column, a first stage, a second stage, and a stage exchange mechanism so as to execute the methods as described above in various examples of the fourth principal aspect of the present invention. The dual-chamber system is targeted.

[0067] In various examples of the fourth principal aspect of the present invention, other systems can be similarly used to execute the methods as described above.

[0068] According to a fifth principal aspect of the present invention, the present invention is a method for acquiring at least one series of parallel cross-sectional images of at least one measurement site of a wafer, comprising: 5a) In a first chamber, providing a first focused ion beam (FIB) column and a first charged particle beam (CPB) imaging column in a wedge-cut matching arrangement, in which arrangement the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface and form an arrangement angle GFE between the FIB optical axis and the CPB optical axis; 5b) A step of providing a second FIB column and a second CPB imaging column in the second chamber in an edge cut matching arrangement, in which arrangement, the FIB optical axis of the second FIB column and the CPB optical axis of the second CPB imaging column coincide and are perpendicular to each other on the wafer surface or the sample surface, the optical axis of the second CPB column is arranged perpendicular to the wafer surface or the sample surface, and the CPB column is arranged with a short working distance enabling high-resolution imaging; 5c) A step of positioning a first wafer including at least one measurement site on a first stage; 5d) In the first chamber, generating at least one chunk by milling around at least one measurement site with a first FIB column, and a step of controlling the milling with a first CPB imaging column in the first chamber; 5e) Lifting at least one chunk from the wafer and placing at least one chunk on a sample holder such that the measurement site of each chunk is arranged at the edge of the sample holder; 5f) A step of transferring a sample holder including at least one chunk into the second chamber; 5g) A step of positioning at least one measurement site included in at least one chunk on a second stage; 5h) In the second chamber, repeatedly milling at least one chunk with a second FIB column and repeatedly imaging at least one chunk with a second CPB column to obtain at least one series of parallel cross-sectional images of at least one measurement site A method as claimed is intended.

[0069] By this lifting procedure and proper placement of the chunks (at the edges) on the sample holder, it can be ensured that the region of interest or the measurement site is close to the edge of the sample holder. This enables the placement of the PCB imaging column perpendicular to the surface of the wafer or the surface of the chunk, resulting in a shorter possible working distance and higher imaging resolution.

[0070] According to one example, this method includes the step of moving the second stage to make the second measurement site for milling and imaging accessible. The second measurement site is usually included in the second chunk. Also, this second chunk is arranged at the edge of the sample holder. Moving the second stage can be realized in different ways, and this movement can be determined by the geometric characteristics of the second stage. If the second stage is round (its surface is a circle), this movement is preferably a rotation. If the second stage is in a bank shape (for example, realized by a belt), this movement is preferably a lateral movement. Thus, overall, a linear arrangement of the chunks is realized on the bank, and all chunks can be arranged at the edge.

[0071] According to one example, this method further includes providing a plurality of sample holders and sequentially handling the plurality of sample holders in the first chamber and the second chamber according to steps 5d) to 5h). Therefore, more chunks can be extracted from one wafer than when they can be arranged on one sample holder. Naturally, the entire process can be repeated for subsequent wafers.

[0072] According to a further aspect, the present invention is directed to a computer program product including program code configured to execute a method as described above in various embodiments of the fifth main aspect.

[0073] According to a further aspect of the present invention, the present invention is a first chamber, wherein A first focused ion beam (FIB) column and a first charged particle beam (CPB) imaging column configured to be arranged in a wedge cut matching arrangement, in which wedge cut matching arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the low-resolution CPB imaging column coincide on the wafer surface, and an arrangement angle GFE is formed between the FIB optical axis and the CPB optical axis, the first FIB column and the first CPB imaging column, A first stage for supporting the wafer, A sample holder configured to support at least one chunk, and A manipulator configured to lift a chunk milled from the wafer and configured to place the chunk on the sample holder Comprising a first chamber, A second chamber, A second FIB column and a second CPB imaging column in an edge cut matching arrangement, in which edge cut matching arrangement, the FIB optical axis of the second FIB column and the CPB optical axis of the second CPB imaging column coincide and are perpendicular to each other on the wafer surface or the sample surface, the optical axis of the second CPB column is arranged perpendicular to the wafer surface or the sample surface, and the second CPB column is arranged with a short working distance enabling high-resolution imaging, the second FIB column and the second CPB imaging column, and A second stage configured to support the sample holder Comprising a second chamber, A sample holder transfer mechanism configured to transfer the sample holder from the first chamber to the second chamber and to place the sample holder on the second stage, and A controller Comprising, A dual-chamber system is targeted, which includes a first chamber comprising a first FIB column, a first CPB imaging column, a first stage, a sample holder, and a manipulator, a second chamber comprising a second FIB column, a second CPB imaging column, and a second stage, and a sample holder transfer mechanism, such that the controller executes a method as described above with respect to the fifth main aspect of the present invention.

[0074] This example enables efficient batch processing.

[0075] Other systems can be similarly used to execute a method as described above in various examples of the fifth main aspect of the present invention.

[0076] The above-described embodiments or examples can be combined in whole or in part with each other as long as no technical contradiction occurs. This also holds true for examples or embodiments representing different aspects or main aspects of the present invention.

[0077] The present invention will be further understood more deeply by referring to the following drawings.

Brief Description of the Drawings

[0078]

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Figure 14

DETAILED DESCRIPTION OF THE INVENTION

[0079] In the figures, the same reference numerals indicate the same features even if not separately described in the text.

[0080] FIG. 1 is a schematic diagram of a general cross-sectional imaging method for obtaining a 3D volume image of an integrated semiconductor sample. In the cross-sectional method, also referred to as the slice imaging method, the acquisition of a three-dimensional (3D) volume image is realized in a “step and repeat” manner. First, an integrated semiconductor sample is prepared for a general cross-sectional imaging method by a method known in the art. After a small block or chunk is extracted from the wafer, it is analyzed separately. Throughout the present disclosure, “cross-sectional image” and “slice” are used as synonyms. In one step, a thin surface layer of the material, i.e., a “slice,” is removed. This material slice can be removed by a plurality of methods known in the art, including the use of focused ion beam milling or polishing at an incident angle by a focused ion beam (FIB) column 50. For example, the focused ion beam 51 propagates substantially parallel to the z-axis and is scanned in the y direction to mill the upper surface 55 of the sample 10 (for example, a part of the wafer is possible), exposing a new cross-sectional surface 52 in the yz plane. As a result, the newly exposed cross-sectional surface 52 is accessible for imaging. In a subsequent step, a cross-sectional image slice 100.1 is obtained by raster scanning the cross-sectional surface layer 52 by a charged particle beam (CPB) imaging system 40 such as a scanning electron microscope (SEM) or a second FIB. The optical axis 42 of the charged particle imaging system 40 can be arranged parallel to the x direction or inclined at an angle with respect to the x direction. To reveal the material contrast inside the integrated semiconductor sample, secondary electrons and backscattered electrons are collected by a detector (not shown) and visualized as different gray levels in the cross-sectional image slice 100.1. A brighter measurement result is generated by the metal structure. Through the cross-sectional surfaces 53 and 54 and further cross-sectional surfaces at an equal distance d, the removal of the surface layer by milling and the cross-sectional imaging process are repeated, and a three-dimensional (3D) data set is constructed by obtaining a series of 2D cross-sectional image slices 1000 including cross-sectional image slices 100.2, 100.3, ··· 100.N at different depths. A representative cross-sectional image slice 100.1 is obtained by measuring a commercially available Intel processor integrated semiconductor chip with a 14 nm technology.

[0081] By this method, the cross-sectional surface in the integrated semiconductor sample is then milled by a focused ion beam to expose or make accessible a series of cross-sectional surfaces for imaging, and at least first and second cross-sectional image slices are generated by imaging each cross-sectional surface of the integrated semiconductor sample with the charged particle beam imaging system 40. A 3D image of the integrated semiconductor structure is reconstructed from a series of N 2D cross-sectional image slices 1000. The distance d between the cross-sectional image slices 100.1, 100.2, 100.3 can be controlled by the FIB milling or polishing process, and a range of 1 nm to 30 nm is possible.

[0082] As shown in FIG. 1, in the above example, the cross-sectional image plane is oriented perpendicular to the upper surface 55 of the integrated semiconductor wafer, and the normal line of the wafer upper surface 55 is oriented parallel to the z direction. Thereby, the 2D cross-sectional image slices are oriented parallel to the yz plane. In other words, the cross-sectional image plane includes the z-axis or the wafer normal axis, and the imaging direction x is parallel to the wafer surface. Therefore, the conventional slice imaging method in this conventional geometry can only be applied to samples extracted from the wafer.

[0083] Also, of course, it is possible to exchange the positions of the FIB column 50 and the CPB imaging column 40. And the CPB optical axis can be oriented perpendicular to the upper surface 55 of the sample 10. This arrangement is preferable when imaging the HAR structure extending in the depth direction of the sample 10.

[0084] In both of the above arrangements, the working distances of the FIB column and the CPB imaging column can be set individually. Therefore, both working distances can be optimized. Generally, the shorter the working distance, the higher the imaging resolution. Therefore, since a short working distance can be set without geometric constraints, high-resolution imaging by the CPB imaging column 40 becomes possible.

[0085] However, common problems still exist. That is, the measurement sites on the wafer need to be near the edge of the wafer in order to enable measurement according to the illustrated geometric arrangement of columns 40 and 50. Otherwise, it is necessary to break the wafer, and it is also necessary to extract the sample 10 or the chunk from the wafer and artificially generate an edge and thus a situation suitable for separate analysis.

[0086] Figure 2 discloses a method of generating a 3D volume image using a slice image method applied to an inspection volume inside a wafer in a so-called "wedge cut" method, i.e., wedge cut geometry, without the need to remove the sample 10 from the wafer 8. The slice image method is applied to the inspection volume for a lateral extension of several μm, for example, 5 μm to 10 μm in a 200 mm to 300 mm wafer, without removing a sample from the wafer 8. By milling a groove or an edge on the upper surface 55 of the integrated semiconductor wafer 8, access to a cross-sectional surface at an angle with respect to the upper surface 55 becomes possible. The 3D volume image of the inspection volume is acquired at a limited number of measurement sites, such as representative sites of the die, for example, sites identified by a process control monitor (PCM) or other inspection tools. In the slice image method, since the wafer is only locally damaged, other dies can still be used, or the wafer can still be used for separate processing.

[0087] FIG. 2 discloses a wafer inspection system 500 comprising a dual beam apparatus 1 and configured for slice imaging method under wedge cut geometry. For a wafer 8, a plurality of measurement sites including measurement sites 6.1 and 6.2 are defined in an arrangement map or inspection list generated from inspection tools or design information. The wafer 8 is placed on a wafer support table 15. The wafer support table 15 is mounted on a stage 155 including actuators and position control. In the art, actuators and means for accurate control of a wafer stage, such as a laser interferometer, are known. The control unit 16 is configured to control the wafer stage 155 and adjust the measurement site 6.1 of the wafer 8 at the intersection 43 of the dual beam apparatus 1. The dual beam apparatus 1 comprises an FIB column 50 with an FIB optical axis 48 and a charged particle beam (CPB) imaging system 40 with an optical axis 42. At the intersection 43 of both optical axes of the FIB and CPB imaging systems, the wafer surface 55 is arranged at an oblique angle GF with respect to the FIB axis 48. The FIB axis 48 and the CPB imaging system axis 42 include an angle GFE, and the CPB imaging optical axis 42 forms an angle GE with the normal of the wafer surface 55. In the coordinate system of FIG. 1, the normal of the wafer surface 55 is given by the z-axis. A focused ion beam (FIB) 51 is generated by the FIB column 50 and impinges on the surface 55 of the wafer 8 at an angle GF. By ion beam milling at an approximate tilt angle GF at the inspection site 6.1, an oblique cross-sectional surface is milled into the wafer. In the example of FIG. 2, the tilt angle GF is about 30°. The actual tilt angle of the oblique cross-sectional surface may deviate from the tilt angle GF by up to 1° to 4° due to beam divergence of a focused ion beam such as a gallium ion beam. An image of the milled surface is acquired by the charged particle beam imaging system 40 tilted at an angle GE with respect to the normal of the wafer. In the example of FIG. 2, the angle GE is about 15°. However, other arrangements are possible as well. For example, when GE = GF, the CPB imaging system axis 42 is perpendicular to the FIB axis 48, and when GE = 0°, the CPB imaging system axis 42 is perpendicular to the wafer surface 55.

[0088] During imaging, the beam 44 of charged particles is scanned along a scanning path on the cross-sectional surface of the wafer 8 at the measurement site 6.1 by the scanning unit of the charged particle beam imaging system 40, generating secondary particles and scattered particles. The particle detector 17 collects at least a part of the secondary particles and scattered particles and transmits the number of particles to the control unit 19. Other detectors for other types of interaction products may also exist similarly. The control unit 19 is connected to the control unit 16 that controls the charged particle beam imaging column 40 and the FIB column 50 and controls the position of the wafer 8 mounted on the wafer support table 15 via the wafer stage 155. The control unit 19 communicates with the operation control unit 2 that triggers, for example, the arrangement and alignment of the measurement site 6.1 of the wafer 8 at the intersection 43 by the movement of the wafer stage, and repeatedly triggers the operations of FIB milling, image acquisition, and stage movement.

[0089] Each new intersection surface is milled by the FIB beam 51 and imaged by a charged particle imaging beam 44 such as a scanning electron beam or a helium ion beam of a helium ion microscope (HIM).

[0090] However, since both the FIB column 50 and the CPB imaging column 40 are arranged above the upper surface 55 of the wafer, there are geometric constraints in their respective arrangements. When the working distance is short, the columns 40 and 50 begin to interfere with each other, so it is no longer possible to optimize both working distances individually. As a general practical principle, the position of the FIB column 50 limits, and thus "defines", the working distance of the CPB imaging column 40. The working distance of the CPB imaging column 40 usually cannot be made shorter than 4 - 5 mm. In contrast, as shown in FIG. 1, the working distance of the CPB imaging column 40 can be made as short as about 2 mm. Therefore, in the wedge cut arrangement shown in FIG. 2, the imaging resolution is usually one order of magnitude lower compared to the edge arrangement shown in FIG. 1.

[0091] Figure 3 shows additional details of the slice imaging method in wedge cut geometry. By repeating the slice imaging method in wedge cut geometry, a plurality of J cross-sectional image slices including image slices of cross-sectional surfaces 52, 53.i ··· 53.J are generated, and a 3D volume image of the inspection volume 160 at the inspection site 6.1 of the wafer 8 at the measurement site 6.1 is generated. Figure 3 shows the wedge cut geometry in an example of a 3D memory stack. The cross-sectional surfaces 53.1 ··· 53.N are milled by the FIB beam 51 at an angle GF of about 30° with respect to the wafer surface 9, but other angles GF such as between GF = 20° and GF = 60° are also possible. Figure 3 shows a situation where the surface 52 is a new cross-sectional surface that was last milled by the FIB 51. The cross-sectional surface 52 is arranged to be perpendicularly incident with respect to the wafer surface 55 in the example of Figure 3, for example, scanned by the SEM beam 44, and a high-resolution cross-sectional image slice is generated. The cross-sectional image slice includes a first cross-sectional image feature formed by crossing a high aspect ratio (HAR) structure or a via (for example, the first cross-sectional image features of the HAR structures 4.1, 4.2, and 4.3), and a second cross-sectional image feature formed by crossing a layer L.1 ··· L.M including, for example, SiO2, SiN, or tungsten wire, or a word line layer. The maximum number of layers M is usually more than 50, for example, more than 100 or more than 200. The HAR structure and the layer extend through almost the entire volume of the wafer, but may include gaps. The HAR structure usually has a diameter of less than 100 nm, for example, about 80 nm or 40 nm. Therefore, the cross-sectional image slice includes the first cross-sectional image feature as the intersection or cross-section of the HAR structure footprint at different depths (Z) at each XY position. In the case of a cylindrical vertical memory HAR structure, the first cross-sectional image feature obtained is a circular or elliptical structure at various depths determined by the position of the structure on the inclined cross-sectional surface 52. The memory stack extends in the Z direction perpendicular to the wafer surface 55. The thickness d or the minimum distance d between two adjacent cross-sectional image slices is usually adjusted to a value on the order of several nanometers, for example, 30 nm, 20 nm, 10 nm, 5 nm, 4 nm or less.When a material layer of a predetermined thickness d is removed by FIB, the next cross-sectional surfaces 53.i ··· 53.J for imaging are exposed and accessible by the charged particle imaging beam 44.

[0092] FIG. 4 shows an oblique cross-sectional image slice through a plurality of HAR structures. More specifically, FIG. 4 shows a cross-sectional image slice 311.1 generated by the imaging charged particle beam 41 and corresponding to the cross-sectional surface 301.1. The cross-sectional image slice 311.1 includes an edge line 315 between the oblique cross-section at the edge coordinate y1 and the surface 55 of the wafer. On the right side of the edge, the image slice 311.1 shows a plurality of cross-sections 307.1 ··· 307.S through the HAR structure where the cross-sectional surface 301.1 intersects. Also, the image slice 311.1 includes cross-sections of a plurality of word lines 313.1 to 313.3 at different depths, i.e., z positions. With these word lines 313.1 to 313.3, a depth map Z1(x, y) of the oblique cross-sectional surface 301.1 can be generated.

[0093] In one example, the features and 3D positions of the semiconductor structure of interest, e.g., the positions of the HAR channels, are detected by an image processing method, for example, from the HAR centroid. 3D volume image generation including the image processing method and feature-based alignment is further described in U.S. Provisional Patent Application No. 62 / 858,470 and German Patent Application Publication No. 102019006645.6, the entire scope of which is incorporated herein by reference. It should be noted that these layers and HAR structures do not need to extend over the entire measurement volume.

[0094] For the improvement of measurement problems in 3D tomography data and 3D measurement, an improvement in imaging resolution is desirable. At the same time, it is assumed that the wafer including the measurement site of interest can still be used without being damaged after the generation of the 3D image of the measurement site.

[0095] As described in the summary of this specification, the present invention solves these problems by separating the operating distance of the CPB imaging column from the constraints due to the FIB shape. Hereinafter, a plurality of examples for further explaining the present invention will be described. However, these examples shall not be regarded as limiting the present invention.

[0096] FIG. 5 shows a first workflow according to the present invention, and FIG. 6 schematically shows a dual-beam apparatus 1 suitable for executing the first workflow. FIG. 6a discloses a slightly improved wedge cut arrangement in principle as compared with the wedge cut arrangement shown in FIG. 2. Similar to FIG. 2, a wafer 8 including a plurality of measurement sites 6 (here, two measurement sites) is disposed on a wafer support table 15 held by a stage 155. The stage in the illustrated example is movable in three full spatial dimensions (x, y, z) indicated by arrows. Further, rotation of the stage 155 or at least rotation of the wafer support table 15 is also possible. These movements can be controlled by a stage control unit 16 (not shown in FIG. 6).

[0097] In the illustrated example, the CPB imaging optical axis 42 is disposed perpendicular to the upper surface 55 of the wafer. This enables top-down imaging of the HAR structure in the sample or wafer 8 in principle. The FIB column 50.1 is disposed at an oblique angle with respect to the upper surface 55 of the wafer. The FIB optical axis 48 and the CPB optical axis 42 intersect each other at a coincidence point 43 on the upper surface 55 of the wafer. However, as compared with the arrangement shown in FIG. 2, in FIG. 6a, the arrangement angle GFE between the FIB optical axis 48 and the CPB optical axis 42 is smaller. Thereby, when imaging is executed at this position, the operating distance of the CPB imaging column becomes longer. However, according to the present invention, only the milling process by the FIB column 50.1 is executed in the illustrated coincidence arrangement. In the illustrated example, the operating distance of the FIB column 50.1 can be optimally selected.

[0098] After the cross-sectional surface layer is removed by FIB50.1, the FIB stops or pauses. Thereafter, the arrangement of columns 50.1 and 40 changes to the arrangement shown in Fig. 6b. That is, along the direction of the CPB optical axis, the working distance of the CPB imaging column 42 becomes shorter. In the illustrated case, this shortening is realized by the movement of the stage 155 in the z-direction of the stage indicated by the large arrow. However, in principle, it is also possible to move the CPB imaging column 40 itself additionally or alternatively. After the shortening of the working distance, imaging is performed with this shortened working distance. When the working distance becomes shorter in this way, the imaging resolution can be increased. Furthermore, the movement of the stage in the z-direction can be performed quite rapidly and with quite high precision. After imaging one accessible cross-section, the stage 155 (or the CPB imaging column 40) can move downward again until the coincidence arrangement is reached again. Thereafter, milling of the next slice by FIB50.1 is possible, and the process can be repeated for the measurement site 6 and other measurement sites.

[0099] Fig. 14 further shows the geometric characteristics and constraints in the dual-beam system 1. Fig. 14a) shows the geometric arrangement in the case of a wedge cut according to the prior art, and Fig. 14b) shows the geometric characteristics and advantages according to the first aspect of the present invention. In practice, the available space between the columns 50, 40 and the sample or wafer 8 is limited by the final lens among a series of lenses of the focused ion beam column 50 and the charged particle beam column 40. The outer shapes of the columns 50, 40 near the wafer 8 can be approximated by frustums of cones each having an opening angle α FIB and α CPB . It is clear that the FIB column 50 and the CPB imaging column 40 must not interfere with each other, and in particular, the FIB column 50 must not be arranged within the available space below the CPB imaging column 40.

[0100] Furthermore, according to the arrangement of the dual-beam apparatus 1 according to the prior art as shown in FIG. 14a, the bottom edge 49 of the FIB column 50 is arranged parallel to the wafer 8 and the wafer upper surface 55. When the distance h between the bottom edge 49 and the wafer upper surface 55 is selected to be short, the operating distance WD1 between the CPB imaging columns 40 also becomes similarly short, and in principle, high-resolution imaging may be possible (in principle, the shorter the operating distance, the higher the resolution). In practice, there is a minimum distance h and thus a minimum possible operating distance WD1. Otherwise, the FIB column 50 would come into contact with the wafer 8. Furthermore, it should be noted that the wafer 8 usually needs to move within a plane perpendicular to the optical axis (here, the z-axis) of the CPB imaging column 40, and it is necessary to ensure that it does not come into contact with the FIB column 50 during movement.

[0101] According to the first aspect of the present invention, the geometric arrangement of the dual-beam apparatus 1 is different. That is, as shown in FIG. 14b), the FIB column 50 is retracted from the wafer 8, the bottom edge 49 is not arranged parallel to the wafer upper surface 55, and the arrangement angle GFE2 is smaller than the arrangement angle GFE1. For this reason, in the milling process, the operating distance WD2 of the CPB imaging column 40 is larger than the operating distance WD1 shown in FIG. 14a). Therefore, during milling in the coincidence arrangement (corresponding to the first position Pos1 of the wafer 8 and the wafer upper surface 55), the resolution of the CPB imaging column 40 is reduced. However, even with this resolution, it is still sufficient for milling management.

[0102] On the other hand, after milling, in the new arrangement according to the first aspect of the present invention, for example, by moving the stage in the z direction by dz, the relative distance between the wafer upper surface 55 and the CPB imaging column 40 can be shortened. In FIG. 14b), the shortened second position Pos2 is also shown. At the second position Pos2, high-resolution imaging becomes possible by using the operating distance WD3, which is shorter than the operating distance WD1.

[0103] FIG. 5 summarizes an exemplary workflow. In step S1, a focused ion beam (FIB) column 50.1 and a charged particle beam (CPB) imaging column 40 are provided in a coincident arrangement. In step S2, at the coincident arrangement, by using the FIB column 50.1, the cross-sectional surface layer of the measurement site 6 of the wafer 8 is removed, making it possible to access a new cross-section for imaging. In step S3, for example, by moving the z-direction stage, the working distance between the CPB imaging column 40 and the wafer top surface 55 is shortened in the direction along the optical axis 42 of the CPB imaging column 40. In step S4, with the shortened working distance and regardless of the coincident arrangement, a new cross-section at the measurement site 6 of the wafer 8 is imaged by the CPB imaging column 40. In step S5, until (again) the coincident arrangement is reached, the working distance between the CPB imaging column 40 and the wafer top surface 55 is lengthened in the direction along the axis 42 of the CPB imaging column 40. Steps S2 to S5 can be repeatedly executed until the measurement site is completely milled and imaged. Thereafter, in step S6, the process ends. Naturally, the workflow can be repeated for the next measurement site 6.

[0104] FIG. 7 shows a second workflow according to the present invention, and FIG. 8 schematically shows a dual beam apparatus 1 suitable for executing the second workflow. In contrast to the first workflow in which the coincidence point is still used during milling, in the second workflow, the coincidence point is completely abandoned. Instead of the coincidence arrangement, an offset arrangement of two columns 50.1 and 40 is applied. According to the illustrated offset arrangement, the FIB column optical axis 48 and the CPB optical axis 42 intersect the wafer surface 55 at two different points or positions, and the difference between the two different positions defines the offset level with respect to the wafer upper surface 55 indicated by the double-headed arrow. According to this offset, the working distances of the FIB column 50.1 and the CPB imaging column 40 can be set independently without geometric constraints due to the shapes and / or positions of the FIB column 50.1 and the CPB imaging column 40. Therefore, an optimal working distance can be set for both the FIB column 50.1 and the CPB imaging column 40. However, before performing imaging or milling, it is necessary to relatively move the wafer with respect to the two columns 50.1 and 40 according to the offset. What enables this relative movement is, for example, the movement of the stage, such as the movement of the stage in the lateral direction (in the illustrated example, the y direction).

[0105] Note that the offset can be flexibly set within a specific range. In practice, the offset has a minimum size such that the columns 50.1 and 40 can no longer interfere with each other. However, the offset can be made larger than this minimum size. Therefore, it is preferable to adjust the offset to the distance between the two measurement sites 6 on the wafer 8. In this way, it becomes possible to mill the first measurement site and image the second measurement site. By applying additional columns, milling and imaging can be further parallelized. It is also possible to rotate the stage 155 (or at least the wafer support table 15) to switch between the two measurement sites 6. This also enables parallelization of milling and imaging of the two measurement sites 6.

[0106] FIG. 7 summarizes an exemplary workflow. In step S10, a focused ion beam (FIB) column 50.1 and a charged particle beam (CPB) imaging column 40 are provided in an offset arrangement. Both working distances can be optimally selected. In step S11, by using the FIB column 50.1, the cross-sectional surface layer of the first measurement site 6 of the wafer 8 is removed, thereby enabling access to a new cross-section for imaging. In step S12, according to the offset, the wafer surface moves relatively, for example, by moving the lateral stage or rotating the stage. In step S13, a new cross-section of the first measurement site 6 of the wafer 8 is imaged by the CPB imaging column 40. In step S14, again according to the offset, the wafer 8 moves relatively (returns). Thereafter, in step S11, the next cross-sectional surface layer can be removed, and steps S12 to S14 are repeated. In step S15, for example, when site 6 is completely milled and imaged, the process ends. Thereafter, another site 6 can be milled and imaged. As already described above, when the offset is adjusted to the distance between different measurement sites 6, parallelization of the process is also possible.

[0107] FIG. 9 shows a third workflow according to the present invention. In step S20, a focused ion beam (FIB) column 50.1 and a charged particle beam (CPB) imaging column 40 are provided in a coincident arrangement. In step S21, the optimized operating distance of the FIB column and the trade-off operating distance of the CPB imaging column are determined, or the trade-off operating distance of the FIB column and the optimized operating distance of the CPB imaging column are determined. In step S22, the FIB column is moved along its optical axis so that the FIB column is arranged at the determined (optimized or trade-off) operating distance, and / or the CPB imaging column is moved along its optical axis so that the CPB imaging column is arranged at the determined (trade-off or optimized) operating distance. In step S23, by using the FIB column 50.1 arranged at the operating distance, the cross-sectional surface layer of the measurement site of the wafer 8 is removed, so that a new cross-section for imaging becomes accessible. In step S24, a new cross-section of the measurement site 6 of the wafer 8 is imaged by the CPB imaging column 40 arranged at the operating distance. Milling and imaging (steps S23 and S24) are repeatable. In step S25, the process ends. The operating distances of the FIB column and the CPB imaging column do not both become optimal at the same time. However, one of these is optimally selected (meaning the best under a given situation or constraint), and the other is still selected as well as possible under the given situation and constraints including the optimized given operating distance of the other column. For example, in a use case where the imaging resolution is more important than the milling quality, the operating distance of the CPB imaging column 40 can be shortened at the expense of shortening the operating distance of the FIB column 50.1. An algorithm for determining the trade-off operating distance can be applied.

[0108] Figure 10 shows the fourth workflow according to the present invention, and Figure 11 schematically shows a dual-chamber system suitable for executing the fourth workflow. The dual-chamber system includes a first chamber 70.1 and a second chamber 70.2. According to this dual-chamber solution, milling and high-resolution imaging are spatially separated. In the first chamber 70.1, milling is performed. In the second chamber 70.2, high-resolution imaging is performed. The wafer 8 is transferred between the two chambers 70.1 and 70.2 so that milling and high-resolution imaging can be alternately performed.

[0109] More specifically, the first chamber 70.1 includes a dual-beam system 1.1 including an FIB column 50.1 and a CPB imaging column 40.1 arranged according to a coincidence arrangement. However, the CPB imaging column 40.1 is not used for the imaging of the cross-section itself, but is only applied to the management / monitoring of the milling process by the FIB 50.1. For this management or monitoring, usually, a low imaging resolution is sufficient. Therefore, the operating distance of the FIB column 50.1 can be optimized at the expense of the imaging resolution (longer operating distance) of the CPB imaging column 40.

[0110] When the cross-sectional surface layer is easily milled, the wafer 8 is transferred into the second chamber 70.2 for high-resolution imaging. According to the illustrated example, the second chamber 70.2 includes a high-resolution CPB imaging device 40.2. In principle, this device 40.2 can be the same as the device 40.1 in the first chamber, but since the operating distance can be optimized, the imaging resolution is increased. In the second chamber 70.2, it is preferable to apply a more functional CPB imaging device 40.2 different from the first chamber 70.1. Examples include a high-resolution scanning electron microscope (SEM), a corrected SEM with additional electrostatic lenses for suppressing imaging aberration, or a multi-beam scanning electron microscope (MultiSEM or mSEM).

[0111] The transfer of the wafer 8 between the two chambers 70.1 and 70.2 can be realized by different methods. One possibility is the transfer of the wafer support table 15 on which the wafer 8 is already positioned. Alternatively, it is possible to transfer the entire stage 155.1 from one chamber to the other chamber. This method can be further improved when the second stage 155.2 is applied. In this case, the operations for the two wafers 8.1 and 8.2 can be parallelized. For example, while one wafer 8.1 is being milled in the first chamber 70.1, the second wafer 8.2 can be imaged in the second chamber 70.2, and vice versa. The exchange of the stages can be carried out via the stage transfer interface 80. Optionally, this transfer interface 80 h can be provided with one or two vacuum locks (not shown) for removing, for example, the milling deposition material from the imaging chamber, i.e., the second chamber 70.2.

[0112] FIG. 10 exemplarily summarizes a possible workflow of a method for acquiring a series of first cross-sectional images of a first measurement site 6.1 on a first wafer 8.1 and for acquiring a series of second cross-sectional images of a second measurement site 6.2 on a second wafer 8.2. In step S30, the first wafer 8.1 is provided on the first stage 155.1 and the first wafer 8.1 is positioned on the first stage 155.1. In step S31, the second wafer 8.2 is provided on the second stage 155.2 and the second wafer 8.2 is positioned on the second stage 155.2. In step S32, by using the FIB column 50.1 operating at the set FIB working distance, the first cross-sectional surface layer of the first measurement site 6.1 of the first wafer 8.1 is removed, whereby a first new cross-section for imaging becomes accessible. In step S33, the positions of the first stage 155.1 and the second stage 155.2 are exchanged. In step S34, by the CPB imaging column 40.2 at the set operating distance, the first new cross-section of the first measurement site 6.1 of the first wafer 8.1 is imaged, and at the same time, by using the FIB column 50.1 at the set FIB working distance, the second cross-sectional surface layer of the second measurement site 6.2 of the second wafer 8.2 is milled, whereby a second new cross-section for imaging becomes accessible. In step S35, the positions of the first stage 155.1 and the second stage 155.2 are changed again, and the wafers 8.1 and 8.2 are transferred between the chambers respectively. In step S36, by the CPB imaging column 40.2 at the set operating distance, the second new cross-section of the second measurement site 6.2 of the second wafer 8.2 is imaged, and at the same time, by using the FIB column 40.1 at the set FIB working distance, another first cross-sectional surface layer of the first measurement site 6.1 of the first wafer 8.1 is removed, whereby another first new cross-section for imaging becomes accessible. Steps S33 to S36 can be repeated until the two measurement sites 6.1 and 6.2 are completely milled and imaged. In step S37, an exemplary process ends. It is also possible to mill and image sequentially for a plurality of measurement sites 6 on each of the wafers 8.1, 8.2.In this scenario, since the transfer time from chamber 70.1 to chamber 70.2 can be kept even shorter, the overall process is speeded up further.

[0113] FIG. 12 shows a fifth workflow according to the present invention, and FIG. 13 schematically shows a dual-chamber system suitable for executing the fifth workflow.

[0114] The first chamber 70.1 includes a first focused ion beam (FIB) column 50.1 and a first charged particle beam (CPB) imaging column 40.1 arranged in a wedge cut matching arrangement. The chamber 70.1 further includes a first stage 155.1 on which a wafer 8 including a plurality of measurement sites 6 is arranged. The first chamber 70.1 is only used for sample preparation. This sample preparation includes the extraction of a 3D block or chunk 61 from the wafer. The first FIB column 50.1 is used for milling around the measurement site 6 and not for removing slices. The first CPB imaging column 40.1 is only used for managing the surrounding milling. Therefore, a relatively low imaging resolution is sufficient for the first CPB imaging column 40.1. According to this example, the first chamber 70.1 further includes a manipulator 21 for lifting the chunk 61 milled from the wafer 8. The manipulator 21 can place one or more chunks 61 on the sample holder 60, and the chunk 61 is arranged at the edge of the sample holder 60. Milling, lifting, and chunk placement can be controlled directly or indirectly by the operation control unit 2.

[0115] Subsequently, one or more chunks 61 placed on the sample holder 60 can be transferred from the first chamber 70.1 to the second chamber 70.2 for milling and imaging. This transfer can be performed, for example, via a sample transfer interface 80 including two vacuum locks. In this way, after transferring the sample holder 60 including the chunk 61, it can be placed on the second stage 155.2 of the second chamber 70.2. However, the holder 60 can also be transferred together with the stages (not shown in FIG. 13) placed thereon respectively. It is also possible to provide two or more sample holders 60. Providing two or more sample holders 60 can contribute to the parallelization of the process. For example, when placing the chunk 61 on the first holder 60 in the first chamber 70.1, it is already possible to image the chunk 61 placed on the second holder 60 in the second chamber 70.2.

[0116] In this example, the second chamber 70.2 includes a second FIB column 50.2 and a second CPB imaging column 40.2 in a matching arrangement. Since the measurement site 6 is extracted and placed at the edge of the sample holder 60, it is possible to use the high-resolution arrangement of the FIB column 50.2 and the CPB column 40.2 that enables edge cutting. Milling by the FIB column 50.2 can be performed alternately with high-resolution imaging by the CPB imaging column 40.2 in a method based on principles known in the art. Other details have been described, for example, with respect to FIG. 1.

[0117] As another possibility, there may be provided an additional chamber (not shown) including an additional FIB / CPB arrangement applied to milling and high-resolution imaging. This enables further acceleration of the workflow.

[0118] An exemplary workflow for acquiring at least one series of parallel cross-sectional images of at least one measurement site 6 of the wafer 8 is shown in FIG. 12.

[0119] In step S40, in the first chamber 70.1, the first focused ion beam (FIB) column 50.1 and the first charged particle beam (CPB) imaging column 40.1 are provided in a wedge cut alignment arrangement. In this alignment arrangement, the FIB optical axis 48 of the FIB column 50.1 and the CPB optical axis 42 of the CPB imaging column 40.1 coincide on the surface of the wafer 8, and an arrangement angle GFE is formed between the FIB optical axis and the CPB optical axis.

[0120] In step S41, in the second chamber 70.2, the second FIB column 50.2 and the second CPB imaging column 40.2 are provided in an edge cut alignment arrangement. In this edge cut alignment arrangement, the FIB optical axis of the second FIB column and the CPB optical axis of the second CPB imaging column coincide on the surface 55 of the wafer 8 or the sample and are perpendicular to each other. The optical axis of the second CPB column 40.2 is arranged perpendicular to the surface 55 of the wafer or the sample, and the second CPB column 40.2 is arranged with a short working distance that enables high-resolution imaging.

[0121] In step S42, the first wafer 8 including at least one measurement site 6 is positioned on the first stage 155.

[0122] In step S43, in the first chamber 70.1, at least one chunk 61 is generated by milling around at least one measurement site 6 with the first FIB column 50.1, and the milling is controlled by the first CPB imaging column 40.1 in the first chamber 70.1.

[0123] In step S44, at least one chunk 61 is lifted from the wafer 8, and at least one chunk 61 is placed on the sample holder 60 such that the measurement site 6 of each chunk 61 is arranged at the edge of the sample holder 60.

[0124] In step S45, the sample holder 60 including at least one chunk 61 is transferred into the second chamber 70.2.

[0125] In step S46, at least one measurement site 6 included in at least one chunk 61 is positioned on the second stage 155.2.

[0126] In step S47, in the second chamber 70.2, at least one chunk 61 is repeatedly milled by the second FIB column 50.2, and at least one series of parallel cross-sectional images of at least one measurement site 6 is obtained by repeatedly imaging at least one chunk 61 by the second CPB column 40.2. Here, due to the geometric arrangement of the chunk 61, high-resolution imaging is possible.

[0127] In any step S48, by rotation of the second stage 155.2, a second measurement site 6.2 for milling and imaging is arranged on the second chunk 61.

[0128] Optionally, a plurality of sample holders 60, and in accordance with steps S43 to S47, sequential handling of the plurality of sample holders 60 in the first chamber 70.1 and the second chamber 70.2 can be performed.

[0129] Those skilled in the art will recognize other workflows and systems without departing from the scope of the invention as defined by the claims.

[0130] Hereinafter, examples of the present invention will be described.

[0131] Example 1. A method for obtaining a series of cross-sectional images parallel to each other of measurement sites on a wafer, comprising: 1a) providing a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column in a coincident arrangement, in which the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface and form an arrangement angle GFE between the FIB optical axis and the CPB optical axis; 1b) In a consistent configuration, a step of making a new cross-section for imaging accessible by removing the cross-sectional surface layer of the measurement site of the wafer using the FIB column; 1c) A step of shortening the operating distance between the CPB imaging column and the wafer surface in a direction along the axis of the CPB imaging column; 1d) A step of imaging a new cross-section at the measurement site of the wafer using the CPB imaging column regardless of the consistent configuration at the shortened operating distance; 1e) A step of lengthening the operating distance between the CPB imaging column and the wafer surface in a direction along the axis of the CPB imaging column until the consistent configuration is reached A method comprising.

[0132] Example 2. The method according to Example 1, wherein a series of method steps 1b), 1c), 1d), and 1e) are repeatedly executed.

[0133] Example 3. The method according to Example 1, further comprising a step of imaging the removal of the cross-sectional surface layer by the CPB imaging column in a consistent configuration.

[0134] Example 4. The method according to Example 1, wherein the step of shortening the operating distance between the CPB imaging column and the wafer surface includes moving the stage supporting the semiconductor sample, in particular, moving the stage vertically.

[0135] Example 5. The method according to Example 4, wherein the CPB optical axis is aligned with the normal of the wafer surface.

[0136] Example 6. The method according to Example 1, wherein for the arrangement angle GFE, the relationship 30° ≤ GFE ≤ 45°, in particular 30° ≤ GFE ≤ 40° or 30° ≤ GFE ≤ 35° holds.

[0137] Example 7. The method according to Example 1, wherein the step of shortening the operating distance between the PCB imaging columns includes moving the PCB imaging column along the PCB optical axis.

[0138] A computer program product comprising program code configured to execute the method described in Example 8.

[0139] Example 9. A focused ion beam (FIB) column and a charged particle beam (CPB) imaging column configured to be arranged in a coincident arrangement, in which coincident arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface, form an arrangement angle GFE between the FIB optical axis and the CPB optical axis, and the CPB optical axis is arranged in a direction perpendicular to the wafer surface, and the FIB column and the CPB imaging column, A stage configured to support the wafer and configured to be movable in a direction perpendicular to the wafer surface, And a controller Comprising, A single-chamber system in which the controller is configured to control the FIB column, the CPB imaging column, and the stage so as to execute the method described in Example 1.

[0140] Example 10. A method for obtaining a series of cross-sectional images parallel to each other of a measurement site of a wafer, wherein the wafer is supported by a stage, and the method comprises: 2a) Providing a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column in an offset arrangement, in which offset arrangement, the FIB column optical axis and the CPB optical axis intersect the wafer surface at two different positions, and the difference between the two different positions defines an offset on the wafer surface, and this offset enables independent setting of the working distances of the FIB column and the CPB imaging column without geometric constraints due to the shape and / or position of the FIB column and the CPB imaging column; 2b) By using the FIB column, removing the cross-sectional surface layer of the first measurement site of the wafer to make a new cross-section for imaging accessible; 2c) Moving the wafer surface by moving the stage with respect to the FIB column and the CPB imaging column according to the offset; 2d) Imaging a new cross-section of the first measurement site of the wafer by a CPB imaging column, and A method comprising:

[0141] Example 11. The method according to Example 10, further comprising: 2e) moving the wafer surface by moving the stage with respect to the FIB column and the CPB imaging column according to the offset.

[0142] Example 12. The method according to Example 11, wherein a series of method steps 2b), 2c), 2d), and 2e) are repeatedly executed.

[0143] Example 13. The method according to Example 10, wherein the relative movement includes lateral movement of the stage or rotation of the stage.

[0144] Example 14. The method according to Example 10, wherein the operating distance of the FIB column is optimized and / or the operating distance of the CPB imaging column is optimized.

[0145] Example 15. The method according to Example 10, wherein the offset matches the distance between the first measurement site on the wafer surface and the second measurement site on the wafer surface.

[0146] Example 16. Further comprising: at the second measurement site, obtaining a series of cross-sectional images parallel to each other of the second measurement site of the wafer by repeatedly executing a series of method steps 2b), 2c), and 2d), The step of removing the cross-sectional surface layer of the second measurement site of the wafer is executed simultaneously with the step of imaging a new cross-section of the first measurement site of the wafer by the CPB imaging column, The step of removing the cross-sectional surface layer of the first measurement site of the wafer is executed simultaneously with the step of imaging a new cross-section of the second measurement site of the wafer by the CPB imaging column. The method according to Example 15.

[0147] Example 17. A computer program product comprising program code configured to execute the method according to Example 10.

[0148] Example 18. A focused ion beam (FIB) column and a charged particle beam (CPB) imaging column configured to be arranged in an offset arrangement, in which offset arrangement, the FIB optical axis and the CPB optical axis intersect the wafer surface at two different positions, and the difference between the two different positions defines an offset on the wafer surface, and this offset has a size large enough to enable independent setting of the working distances of the FIB column and the CPB imaging column without geometric constraints due to the shape and / or position of the FIB column and the CPB imaging column, an FIB column and a CPB imaging column, a stage configured to support the wafer and configured to be movable in a plane parallel to the wafer surface, a controller and A single-chamber system comprising a controller configured to control the FIB apparatus, the CPB imaging apparatus, and the stage so that the controller executes the method described in Example 10.

[0149] Example 19. A method for obtaining a series of cross-sectional images parallel to each other of a measurement site of a wafer, 3a) providing a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column in a coincident arrangement, in which coincident arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface, and an arrangement angle GFE is formed between the FIB optical axis and the CPB optical axis; 3b) determining the optimal working distance of the FIB column and the trade-off working distance of the CPB imaging column, or determining the trade-off working distance of the FIB column and the optimal working distance of the CPB imaging column; 3c) moving the FIB column along its optical axis and arranging the FIB column at the determined working distance, and / or moving the CPB imaging column along its optical axis and arranging the CPB imaging column at the determined working distance; 3d) By using the FIB column arranged at the operating distance, removing the cross-sectional surface layer of the measurement site of the wafer to enable access to a new cross-section for imaging; 3e) Imaging a new cross-section of the measurement site of the wafer with a CPB imaging column arranged at the operating distance; A method comprising:

[0150] Example 20. The method according to Example 19, wherein a series of method steps 3d) and 3e) are repeatedly executed.

[0151] Example 21. Step 3c) comprises: Shortening the operating distance of the FIB column and lengthening the operating distance of the CPB imaging column, or Lengthening the operating distance of the FIB column and shortening the operating distance of the CPB imaging column. A method according to Example 19.

[0152] Example 22. A computer program product comprising program code configured to execute the method according to Example 19.

[0153] Example 23. A focused ion beam (FIB) column and a charged particle beam (CPB) imaging column configured to be arranged in a coincident arrangement, in which the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface, forming an arrangement angle GFE between the FIB optical axis and the CPB optical axis; The FIB column is configured to be movable along its FIB optical axis, and the CPB imaging column is configured to be movable along its CPB optical axis; an FIB column and a CPB imaging column; A stage configured to support the wafer; A controller; Comprising: A single-chamber system, wherein the controller is configured to control the FIB column, the CPB imaging column, and the stage to execute the method according to Example 19.

[0154] Example 24. A method for obtaining a series of first cross-sectional images of a first measurement site on a first wafer and for obtaining a series of second cross-sectional images of a second measurement site on a second wafer, comprising: 4a) providing the first wafer on a first stage and positioning the first wafer on the first stage; 4b) providing the second wafer on a second stage and positioning the second wafer on the second stage; 4c) making accessible a first new cross-section for imaging by removing a first cross-sectional surface layer of the first measurement site of the first wafer by using a FIB column operating at a set FIB working distance; 4d) exchanging the positions of the first stage and the second stage; 4e) imaging the first new cross-section of the first measurement site of the first wafer by a CPB imaging column at a set working distance, and simultaneously making accessible a second new cross-section for imaging by removing a second cross-sectional surface layer of the second measurement site of the second wafer by using a FIB column at a set FIB working distance; 4f) exchanging the positions of the first stage and the second stage; 4g) imaging the second new cross-section of the second measurement site of the second wafer by a CPB imaging column at a set working distance, and simultaneously making accessible another first new cross-section for imaging by removing another first cross-sectional surface layer of the first measurement site of the first wafer by using a FIB column at a set FIB working distance. A method comprising the above steps.

[0155] Example 25. The method according to Example 24, wherein the series of method steps 4d), 4e), 4f), and 4g) are repeatedly executed.

[0156] Example 26. The method according to Example 24, wherein a plurality of first measurement sites on the first wafer are sequentially milled and sequentially imaged, and a plurality of second measurement sites on the second wafer are sequentially milled and sequentially imaged. Example 27. The method according to Example 24, wherein a plurality of second measurement sites on the second wafer are sequentially milled and sequentially imaged.

[0157] Example 27. The step of removing the surface of the first cross-sectional layer and / or the surface of the second cross-sectional layer is controlled by low-resolution imaging, and / or The method according to Example 24, wherein the step of imaging a new first cross-section and / or a new second cross-section includes high-resolution imaging.

[0158] Example 28. The low-resolution imaging is performed by an FIB column used for removing the surface layer of the first cross-section and the surface layer of the second cross-section, or a low-resolution scanning electron microscope (SEM) arranged in a beam intersection arrangement with the FIB column used for removing the surface layer of the first cross-section and the surface layer of the second cross-section, and / or The method according to Example 27, wherein the high-resolution imaging is performed by a high-resolution scanning electron microscope (SEM), a helium ion microscope (HIM), or a multi-beam scanning electron microscope (MultiSEM).

[0159] Example 29. The method according to Example 24, wherein the step of exchanging the positions of the first stage and the second stage includes transferring positioning information.

[0160] Example 30. The method according to Example 24, wherein the FIB column is arranged in the first chamber and the CPB imaging column is arranged in the second chamber.

[0161] Example 31. The method according to Example 30, wherein the step of exchanging the positions of the first stage and the second stage includes transferring one of the stages from the first chamber to the second chamber and vice versa.

[0162] Example 32. A computer program product including program code configured to execute the method according to Example 24.

[0163] Example 33. A first chamber comprising a focused ion beam (FIB) column and a low-resolution charged particle beam (CPB) imaging column configured to be arranged in a wedge cut alignment arrangement, in which alignment arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the low-resolution CPB imaging column coincide on the wafer surface, forming an arrangement angle GFE between the FIB optical axis and the CPB optical axis, the first chamber, A second chamber comprising a high-resolution CPB imaging column, the optical axis of which is arranged perpendicular to the wafer surface, the second chamber, A first stage for supporting the first wafer, A second stage for supporting the second wafer, A stage exchange mechanism configured to exchange the positions of the first stage and the second stage, A controller Comprising, The controller is configured to control the first chamber comprising the FIB column and the low-resolution CPB imaging column, the second chamber comprising the high-resolution CPB imaging column, the first stage, the second stage, and the stage exchange mechanism so as to execute the method described in Example 28. A dual-chamber system.

[0164] Example 34. A method for obtaining at least one series of parallel cross-sectional images of at least one measurement site of a wafer, 5a) In a first chamber, providing a first focused ion beam (FIB) column and a first charged particle beam (CPB) imaging column in a wedge cut alignment arrangement, in which alignment arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface, forming an arrangement angle GFE between the FIB optical axis and the CPB optical axis, the step, 5b) A step of providing a second FIB column and a second CPB imaging column in the second chamber in an edge-cut matching arrangement, in which arrangement, the FIB optical axis of the second FIB column and the CPB optical axis of the second CPB imaging column coincide and are perpendicular to each other on the wafer surface or the sample surface, the optical axis of the second CPB column is arranged perpendicular to the wafer surface or the sample surface, and the CPB column is arranged with a short working distance enabling high-resolution imaging, 5c) A step of positioning a first wafer including at least one measurement site on a first stage, 5d) In the first chamber, generating at least one chunk by milling around at least one measurement site with a first FIB column, and a step of managing the milling with a first CPB imaging column in the first chamber, 5e) Lifting at least the chunk from the wafer and placing at least one chunk on a sample holder such that the measurement site of each chunk is arranged at the edge of the sample holder, 5f) A step of transferring a holder including at least one chunk into the second chamber, 5g) A step of positioning at least one measurement site included in at least one chunk on a second stage, 5h) In the second chamber, repeatedly milling at least one chunk with a second FIB column and repeatedly imaging at least one chunk with a second CPB column to obtain at least one series of parallel cross-sectional images of at least one measurement site A method comprising.

[0165] Example 35.5i) The method according to Example 34, further comprising a step of moving the second stage to enable access to a second measurement site for milling and imaging.

[0166] Example 36. The method according to Example 34, further comprising providing a plurality of sample holders and sequentially handling the plurality of sample holders in the first chamber and the second chamber according to steps 5d) to 5h).

[0167] Example 37. A computer program product comprising program code configured to execute the method according to Example 34.

[0168] Example 38. A first chamber, a first focused ion beam (FIB) column and a first charged particle beam (CPB) imaging column configured to be arranged in a wedge cut matching arrangement, in which wedge cut matching arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the low-resolution CPB imaging column coincide on the wafer surface, and a placement angle GFE is formed between the FIB optical axis and the CPB optical axis, the first FIB column and the first CPB imaging column; a first stage for supporting the wafer; a sample holder configured to support at least one chunk; and a manipulator configured to lift a chunk milled from the wafer and configured to place the chunk on the sample holder comprising a first chamber; a second chamber, a second FIB column and a second CPB imaging column in an edge cut matching arrangement, in which edge cut matching arrangement, the FIB optical axis of the second FIB column and the CPB optical axis of the second CPB imaging column coincide on the wafer surface or the sample surface and are perpendicular to each other, the optical axis of the second CPB column is arranged perpendicular to the wafer surface or the sample surface, and the second CPB column is arranged with a short working distance enabling high-resolution imaging, the second FIB column and the second CPB imaging column; and a second stage configured to support the sample holder comprising a second chamber; A sample holder transfer mechanism configured to transfer a sample holder from a first chamber to a second chamber and to place the sample holder on a second stage, a controller, and comprising, a dual chamber system configured for a controller to execute the method described in Example 34, the dual chamber system including a first chamber comprising a first FIB column, a first CPB imaging column, a first stage, a sample holder, and a manipulator, a second chamber comprising a second FIB column, a second CPB imaging column, and a second stage, and a sample holder transfer mechanism.

Explanation of Signs

[0169] 1 Dual beam device 2 Operation control unit 4 First cross-sectional image feature 6 Measurement site 8 Wafer 10 Sample (e.g., extracted from a wafer) 15 Wafer support table 16 Stage control unit 17 Secondary electron detector 19 Control unit 21 Manipulator 40 Charged particle beam (CPB) imaging column 42 Optical axis of the imaging system 43 Intersection point 44 Charged particle beam for imaging 46 Scanning path 48 FIB optical axis 49 Bottom edge 50 FIB column 51 Focused ion beam 52 Cross-sectional surface 53 Cross-sectional surface 54 Cross-sectional surface 55 Wafer upper surface 60 Sample holder 61 Chuck 70 Chamber 80 Transfer Interface 100 Cross-sectional Image Slice 155 Wafer Stage 160 Inspection Volume 307 Measurement Cross-sectional Image of HAR Structure 311 Cross-sectional Image Slice 313 Word Line 315 Edge with the Surface 500 Wafer Inspection System 1000 Series of 2D Image Slices Layers L.1···L.M d Distance between Adjacent Cross-sections or Adjacent Cross-sectional Image Slices GF Milling Angle (Angle between the Wafer Surface and the FIB Axis at the Intersection) GE Imaging Angle (Angle between the Axis of the CPB Imaging System and the Normal to the Wafer Surface at the Intersection) GFE Arrangement Angle (Angle between the FIB Axis and the Axis of the CPB Imaging System) GFE1 Arrangement Angle (Angle between the FIB Axis and the Axis of the CPB Imaging System) GFE2 Arrangement Angle (Angle between the FIB Axis and the Axis of the CPB Imaging System) WD1 Operating Distance WD2 Operating Distance WD3 Operating Distance dz Difference in Height, Movement of the Stage h Height h’ Height Pos1 Position 1 during Milling Pos2 Position 2 during High-resolution Imaging α FIB Opening Angle of the FIB Column α CPB Opening Angle of the CPB Imaging Column

Claims

1. A method for obtaining a series of cross-sectional images parallel to each other of a measurement site on a wafer, comprising: 1a) providing a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column in a coincident arrangement, in which the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface, and an arrangement angle GFE is formed between the FIB optical axis and the CPB optical axis; 1b) in the coincident arrangement, removing a cross-sectional surface layer of the measurement site on the wafer by using the FIB column to make a new cross-section for imaging accessible; 1c) shortening the working distance between the CPB imaging column and the wafer surface in a direction along the axis of the CPB imaging column; 1d) imaging the new cross-section at the measurement site on the wafer by the CPB imaging column at the shortened working distance, regardless of the coincident arrangement; 1e) lengthening the working distance between the CPB imaging column and the wafer surface in the direction along the axis of the CPB imaging column until the coincident arrangement is reached. A method comprising the above steps.

2. The method according to claim 1, wherein the series of method steps 1b), 1c), 1d), and 1e) are repeatedly executed.

3. The method according to claim 1 or 2, further comprising imaging the removal of the cross-sectional surface layer by the CPB imaging column in the coincident arrangement.

4. The method according to any one of claims 1 to 3, wherein the step of shortening the working distance between the CPB imaging column and the wafer surface includes moving a stage supporting a semiconductor sample, in particular moving the stage vertically.

5. The method according to any one of claims 1 to 4, wherein the CPB optical axis is aligned with the normal of the wafer surface.

6. The method according to any one of claims 1 to 5, wherein the FIB optical axis is arranged at an oblique angle with respect to the upper surface of the wafer.

7. The method according to any one of claims 1 to 6, wherein the relationship 30° ≤ GFE ≤ 45°, in particular 30° ≤ GFE ≤ 40° or 30° ≤ GFE ≤ 35°, holds for the arrangement angle GFE.

8. The method according to any one of claims 1 to 7, wherein the step of shortening the operating distance between the PCB imaging columns includes moving the PCB imaging columns along the PCB optical axis.

9. A computer program product comprising program code configured to execute the method according to any one of claims 1 to 8.

10. A focused ion beam (FIB) column and a charged particle beam (CPB) imaging column configured to be arranged in a coincident arrangement, wherein in the coincident arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface, an arrangement angle GFE is formed between the FIB optical axis and the CPB optical axis, and the CPB optical axis is arranged in a direction perpendicular to the wafer surface, a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column; A stage configured to support a wafer and configured to be movable in a direction perpendicular to the wafer surface; A controller and A single-chamber system, wherein the controller is configured to control the FIB column, the CPB imaging column, and the stage so as to execute the method according to any one of claims 1 to 8.

11. A method for acquiring a series of cross-sectional images parallel to each other of a measurement site of a wafer, wherein the wafer is supported by a stage, and the method includes: 2a) providing a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column in an offset arrangement, wherein in the offset arrangement, the FIB column optical axis and the CPB optical axis intersect the wafer surface at two different positions, and the difference between the two different positions defines an offset on the wafer surface, and the offset enables independent setting of the operating distances of the FIB column and the CPB imaging column without geometric constraints due to the shapes and / or positions of the FIB column and the CPB imaging column; 2b) using the FIB column to remove a cross-sectional surface layer of a first measurement site of the wafer to provide access to a new cross-section for imaging; 2c) moving the wafer surface by moving the stage relative to the FIB column and the CPB imaging column according to the offset. 2d) imaging, by means of the CPB imaging column, a new cross-section of the first measurement site of the wafer A method comprising: **Claim 12** 2e) further comprising moving the wafer surface by moving the stage relative to the FIB column and the CPB imaging column according to the offset, the method according to claim 11. **Claim 13** The method according to claim 12, wherein the series of method steps 2b), 2c), 2d), and 2e) are repeatedly executed. **Claim 14** The method according to claim 12 or 13, wherein the relative movement includes a lateral movement of the stage or a rotation of the stage. **Claim 15** The method according to any one of claims 12 to 14, wherein the operating distance of the FIB column is optimized and / or the operating distance of the CPB imaging column is optimized. **Claim 16** The method according to any one of claims 12 to 15, wherein the offset corresponds to the distance between the first measurement site on the wafer surface and a second measurement site on the wafer surface. **Claim 17** further comprising obtaining, at the second measurement site, a series of cross-sectional images parallel to each other of the second measurement site of the wafer by repeatedly executing the series of method steps 2b), 2c), and 2d), the step of removing the cross-sectional surface layer of the second measurement site of the wafer is executed simultaneously with the step of imaging, by means of the CPB imaging column, a new cross-section of the first measurement site of the wafer, the step of removing the cross-sectional surface layer of the first measurement site of the wafer is executed simultaneously with the step of imaging, by means of the CPB imaging column, a new cross-section of the second measurement site of the wafer, the method according to claim 16. **Claim 18** The method according to any one of claims 12 to 17, wherein the FIB optical axis is arranged at an oblique angle with respect to the upper surface of the wafer. **Claim 19** A computer program product comprising program code configured to execute the method according to any one of claims 12 to 18. **Claim 20** A focused ion beam (FIB) column and a charged particle beam (CPB) imaging column configured to be arranged in an offset arrangement, wherein in the offset arrangement, the FIB optical axis and the CPB optical axis intersect the wafer surface at two different positions, and the difference between the two different positions defines an offset on the wafer surface, and the offset is large enough to allow independent setting of the working distances of the FIB column and the CPB imaging column without geometric constraints due to the shape and / or position of the FIB column and the CPB imaging column. An FIB column and a CPB imaging column, A stage configured to support a wafer and movable in a plane parallel to the wafer surface A controller Comprising A single-chamber system, wherein the controller is configured to control the FIB device, the CPB imaging device, and the stage so as to execute the method according to any one of claims 12 to 18.

21. A method for acquiring a series of cross-sectional images parallel to each other of a measurement site of a wafer, comprising: 3a) providing a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column in a coincident arrangement, wherein in the coincident arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface, and an arrangement angle GFE is formed between the FIB optical axis and the CPB optical axis; 3b) determining an optimum working distance of the FIB column and a trade-off working distance of the CPB imaging column, or determining a trade-off working distance of the FIB column and an optimum working distance of the CPB imaging column; 3c) moving the FIB column along its optical axis and arranging the FIB column at the determined working distance, and / or moving the CPB imaging column along its optical axis and arranging the CPB imaging column at the determined working distance; 3d) making a new cross-section for imaging accessible by removing a cross-sectional surface layer of the measurement site of the wafer by using the FIB column arranged at the working distance; 3e) imaging the new cross-section of the measurement site of the wafer by the CPB imaging column arranged at the working distance A method comprising

22. The method according to claim 21, wherein the series of method steps 3d) and 3e) are repeatedly executed.

23. Step 3c) comprises shortening the operating distance of the FIB column and lengthening the operating distance of the CPB imaging column, or lengthening the operating distance of the FIB column and shortening the operating distance of the CPB imaging column The method according to claim 21 or 22, comprising

24. The method according to any one of claims 21 to 23, wherein the FIB optical axis is arranged at an oblique angle with respect to the upper surface of the wafer.

25. A computer program product comprising program code configured to execute the method according to any one of claims 21 to 24.

26. A focused ion beam (FIB) column and a charged particle beam (CPB) imaging column configured to be arranged in a coincident arrangement, in which coincident arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface, forming an arrangement angle GFE between the FIB optical axis and the CPB optical axis, The FIB column is configured to be movable along its FIB optical axis, and the CPB imaging column is configured to be movable along its CPB optical axis, an FIB column and a CPB imaging column, A stage configured to support the wafer, A controller Comprising A single-chamber system, wherein the controller is configured to control the FIB column, the CPB imaging column, and the stage so as to execute the method according to any one of claims 21 to 24.

27. A method for acquiring a series of first cross-sectional images of a first measurement site on a first wafer and a series of second cross-sectional images of a second measurement site on a second wafer, comprising 4a) providing the first wafer on a first stage and positioning the first wafer on the first stage; 4b) providing the second wafer on a second stage and positioning the second wafer on the second stage; 4c) making accessible a first new cross-section for imaging by removing a first cross-sectional surface layer of the first measurement site of the first wafer by using an FIB column operating at a set FIB operating distance; 4d) exchanging the positions of the first stage and the second stage; 4e) imaging a first new cross-section of the first measurement site of the first wafer with the CPB imaging column at the set operating distance, and at the same time, making accessible a second new cross-section for imaging by removing a second cross-section surface layer of the second measurement site of the second wafer by using the FIB column at the set FIB operating distance; 4f) exchanging the positions of the first stage and the second stage; 4g) imaging a second new cross-section of the second measurement site of the second wafer with the CPB imaging column at the set operating distance, and at the same time, making accessible another first new cross-section for imaging by removing another first cross-section surface layer of the first measurement site of the first wafer by using the FIB column at the set FIB operating distance A method comprising the above steps.

28. The method according to claim 27, wherein the series of method steps 4d), 4e), 4f), and 4g) are repeatedly executed.

29. A plurality of first measurement sites on the first wafer are sequentially milled and sequentially imaged, A plurality of second measurement sites on the second wafer are sequentially milled and sequentially imaged. The method according to claim 27 or 28.

30. The step of removing the first cross-section layer surface and / or the second cross-section layer surface is controlled by low-resolution imaging, and / or The step of imaging the new first cross-section and / or the new second cross-section includes high-resolution imaging. The method according to any one of claims 27 to 29.

31. The low-resolution imaging is performed by the FIB column used for removing the first cross-section surface layer and the second cross-section surface layer, or by a low-resolution scanning electron microscope (SEM) arranged in a beam intersection arrangement with the FIB column used for removing the first cross-section surface layer and the second cross-section surface layer, and / or The high-resolution imaging is performed by a high-resolution scanning electron microscope (SEM), a helium ion microscope (HIM), or a multi-beam scanning electron microscope (MultiSEM). The method according to claim 30.

32. The method according to any one of claims 27 to 31, wherein the step of exchanging the positions of the first stage and the second stage includes transferring positioning information.

33. The method according to any one of claims 27 to 31, wherein the FIB column is disposed in a first chamber and the CPB imaging column is disposed in a second chamber.

34. The method according to claim 33, wherein the step of exchanging the positions of the first stage and the second stage includes transferring one of the stages from the first chamber to the second chamber and vice versa.

35. A computer program product comprising program code configured to execute the method according to any one of claims 27 to 34.

36. A first chamber comprising a focused ion beam (FIB) column and a low-resolution charged particle beam (CPB) imaging column configured to be disposed in a wedge cut alignment arrangement, in which alignment arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the low-resolution CPB imaging column coincide on the wafer surface, and an arrangement angle GFE is formed between the FIB optical axis and the CPB optical axis; A second chamber comprising a high-resolution CPB imaging column, the optical axis of which is disposed perpendicular to the wafer surface; A first stage for supporting a first wafer; A second stage for supporting a second wafer; A stage exchange mechanism configured to exchange the positions of the first stage and the second stage; A controller and comprising A dual-chamber system, wherein the controller is configured to control the first chamber comprising the FIB column and the low-resolution CPB imaging column, the second chamber comprising the high-resolution CPB imaging column, the first stage, the second stage, and the stage exchange mechanism so as to execute the method according to any one of claims 27 to 34.

37. A method for acquiring at least one series of parallel cross-sectional images of at least one measurement site of a wafer, comprising 5a) In a first chamber, providing a first focused ion beam (FIB) column and a first charged particle beam (CPB) imaging column in a wedge cut alignment, wherein in the alignment, the FIB optical axis of the FIB column and the CPB optical axis of the CPB imaging column coincide on the wafer surface, and an angular displacement GFE is formed between the FIB optical axis and the CPB optical axis; 5b) In a second chamber, providing a second FIB column and a second CPB imaging column in an edge cut alignment, wherein in the edge cut alignment, the FIB optical axis of the second FIB column and the CPB optical axis of the second CPB imaging column coincide on the wafer surface or the sample surface and are perpendicular to each other, the optical axis of the second CPB column is arranged perpendicular to the wafer surface or the sample surface, and the CPB column is arranged with a short working distance enabling high-resolution imaging; 5c) Positioning the first wafer including at least one measurement site on a first stage; 5d) In the first chamber, generating at least one chunk by milling around the at least one measurement site with the first FIB column, and controlling the milling with the first CPB imaging column in the first chamber; 5e) Lifting the at least one chunk from the wafer and placing the at least one chunk on the sample holder such that the measurement site of each chunk is arranged at the edge of the sample holder; 5f) Transferring the holder including the at least one chunk into the second chamber; 5g) Positioning the at least one measurement site included in the at least one chunk on a second stage; 5h) In the second chamber, repeatedly milling the at least one chunk with the second FIB column and repeatedly imaging the at least one chunk with the second CPB column to obtain at least one series of parallel cross-sectional images of the at least one measurement site; A method comprising the above steps.

38. 5i) The method according to claim 37, further comprising the step of moving the second stage to provide access to a second measurement site for milling and imaging.

39. The method according to claim 37 or 38, further comprising providing a plurality of sample holders and sequentially handling the plurality of sample holders in the first chamber and the second chamber according to steps 5d) to 5h).

40. A computer program product comprising program code configured to execute the method according to any one of claims 37 to 39.

41. A first chamber, comprising: A first focused ion beam (FIB) column and a first charged particle beam (CPB) imaging column configured to be arranged in a wedge cut matching arrangement, in which wedge cut matching arrangement, the FIB optical axis of the FIB column and the CPB optical axis of the low-resolution CPB imaging column coincide on the wafer surface, and an arrangement angle GFE is formed between the FIB optical axis and the CPB optical axis, the first FIB column and the first CPB imaging column; A first stage for supporting a wafer; A sample holder configured to support at least one chuck; and A manipulator configured to lift a chuck milled from the wafer and to place the chuck on the sample holder Comprising a first chamber; A second chamber, comprising: A second FIB column and a second CPB imaging column in an edge cut matching arrangement, in which edge cut matching arrangement, the FIB optical axis of the second FIB column and the CPB optical axis of the second CPB imaging column coincide on the wafer surface or the sample surface and are perpendicular to each other, the optical axis of the second CPB column is arranged perpendicular to the wafer surface or the sample surface, and the second CPB column is arranged with a short working distance enabling high-resolution imaging, the second FIB column and the second CPB imaging column; and A second stage configured to support the sample holder Comprising a second chamber; A sample holder transfer mechanism configured to transfer the sample holder from the first chamber to the second chamber and to place the sample holder on the second stage; and A controller comprising a dual-chamber system configured for the first FIB column, the first CPB imaging column, the first stage, the sample holder, and the manipulator in the first chamber comprising the first chamber, the second FIB column, the second CPB imaging column, and the second stage, and the sample holder transfer mechanism, such that the controller executes the method according to any one of claims 37 to 39.

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