Method for voltage contrast imaging using a microparticle multi-beam microscope, microparticle multi-beam microscope for voltage contrast imaging, and semiconductor structure using voltage contrast imaging using a microparticle multi-beam microscope

Abstract

The present invention comprises a method, a particle multi-beam microscope and a semiconductor structure to charge a semiconductor sample by a plurality of particle beams of the particle multi-beam microscope and perform high-resolution voltage contrast imaging without switching the particle multi-beam microscope or moving the semiconductor sample. In this case, the summed total current formed by the sum of the selected particle beams each having a low particle current generates a charge and thus a voltage difference in the semiconductor structure.

Description

Technical Field

[0001] The invention relates to a method for detecting defects, in particular in semiconductor structures, by voltage contrast imaging using a particle multibeam microscope. Furthermore, the invention relates to a particle multibeam microscope, in particular suitable for voltage contrast imaging on semiconductor structures. Furthermore, the invention relates to a semiconductor structure for voltage contrast imaging using a particle multibeam microscope. Background Art

[0002] Particle beam microscopes with multiple particle beams are known from the prior art. US 9673024 B2 discloses a device of this type using electrons as particle particles, wherein an aperture mask is arranged downstream of an electron beam source and multiple particle beams are generated in a particle beam grid configuration. The multiple particle beams pass through a particle beam optical unit comprising a beam splitter, and each particle beam is focused in parallel onto the sample. The secondary electrons reflected back or emitted there are captured in parallel by the particle beam optical unit and guided via a beam splitter to a detector unit, which can distinguish each individual beam of the particle beam grid configuration. A regular particle beam grid configuration of about 10x10 beams arranged in a conventional Cartesian or hexagonal grid is a customary configuration, wherein the distance between individual particle beams is about 10 μm. In order to detect the complete image field, the particle beams in the particle beam grid configuration are synchronously guided on the sample in a sawtooth motion, for example by a scanning unit, and the time series of the detector signals is converted into a spatial configuration for determining an image segment. Alternatively, a particle multi-beam microscope with a parallel configuration of multiple particle beam microscopes comprising individual beams is known. The microparticles used in microparticle beam microscopy can be electrons or charged particles such as metal ions (eg, gallium ions) or gas ions (eg, helium).

[0003] Voltage contrast images are usually produced by a structure that absorbs the electrical charge and then observed using a microparticle beam microscope. In this case, a microparticle beam is scanned or passed in a scanning manner over the sample to be examined and the reflected microparticles or secondary emissions (such as secondary electrons or photons) are detected.

[0004] So-called passive voltage contrast imaging involves detecting the stored charge states in the structure. K. Crosby et al., “Towards Fast and Direct Memory Read-out by Multi-beam Scanning Electron Microscopy and Deep Learning Image Classification” (Microscopy and Microanalysis 25.S2 (2019), pp 192–193) describes a method for passive voltage contrast imaging using a microbeam microscope (MSEM) with multiple microbeams. In this case, imaging is performed on the memory cells of an EEPROM, where the data is stored in the form of charge. The stored data can therefore be inferred from the voltage contrast of the imaging of the memory cells. In this case, imaging is performed with a very low dose of the microbeam so as not to affect the charge of the memory cells.

[0005] Voltage contrast imaging is a known method for detecting defects in semiconductor structures. Such defects may be caused by process fluctuations during integrated semiconductor production or by incomplete process maturity during process development. Therefore, voltage contrast imaging is used for process development and process monitoring in the production of integrated semiconductor circuits.

[0006] In this case, the particle beam always contributes to the charging of the sample to be examined. However, since changes in the imaging properties of the sample due to charging are generally undesirable, low particle currents are used during imaging. However, high resolution requires low particle currents, and the charging effect is small at high resolution. Voltage contrast imaging with high particle currents is possible, but greatly limits the imaging, especially the resolution of imaging with a particle beam microscope.

[0007] In general, the resolution of a microparticle beam microscope is mainly determined by the lens aberrations. For example, the diameter d of the electron beam focus is E By electron beam source source Image diameter, diffraction error d diffraction and the lens aberration d of the electron beam optical unit aberrations Composition:

[0008]

[0009] Diffraction error d diffraction As the aperture angle α increases, it decreases. Lens aberration d aberrationIt consists of many individual aberrations, such as astigmatism, spherical aberration, coma and chromatic aberration, or aberrations due to the dispersion in the energy band ΔE of the micro-beam. Lens aberrations increase greatly with increasing aperture angle α and are minimized by corresponding design and correction of the micro-beam optical unit up to the maximum aperture angle α. max The aperture angle α of the imaging of microparticles is usually max Set so that the diffraction error d diffraction and lens aberration d aberration Together we become the smallest.

[0010] For the required high resolution in the range of a few nanometers, a small diameter d of the focus of the particle beam is required. E For this purpose, the particle beam source is imaged in a reduced manner by an imaging ratio M < 1, so that the reduced source image size d is negligible. source The smaller imaging ratio M leads to an aperture angle α max The increase of the aperture of the individual particle beams and thus the increase of lens aberrations leads to an increase of the angular aperture of the individual particle beams. Therefore, high-resolution imaging is only possible with very small aperture angles at the particle beam source and low radiation intensities enable high-resolution imaging.

[0011] Therefore, in the prior art, in order to charge a sample for voltage contrast imaging, for example, a large magnification is selected, with the result that the source image is magnified and the resolution is reduced. This leads to a larger aperture angle at the electron beam source and more charges are absorbed and introduced into the sample. On the other hand, voltage contrast imaging using a microparticle beam microscope with high resolution and simultaneous charging has been possible only in limited cases so far.

[0012] US 7528614 B2 proposes an alternative method for charging the sample. For this purpose, US 7528614 B2 proposes a separate pre-charged electron beam gun (so-called "flood gun") for charging the sample. It is mentioned that multiple such pre-charged electron beam guns can also be used. In a second step, voltage contrast imaging is performed with a high-resolution microparticle beam microscope. It is mentioned that the microparticle beam microscope can be a multi-beam microscope. A separate pre-charged electron beam gun only allows for an overall, spatially unresolved charging of the sample, and a large working distance is required between the sample and the high-resolution microparticle beam microscope. In principle, it is necessary to enable the flood gun to reach the area of ​​the sample to be charged. This is difficult for high-resolution electron microscopes with a small working distance, because the flood gun must then introduce radiation from the side at a very shallow angle. This configuration is particularly problematic for microparticle multi-beam microscopes with a large diameter last lens module for the microparticle beam.

[0013] Furthermore, high-resolution microparticle beam microscopes are usually operated in a so-called immersion mode, with an electric or magnetic field between the sample and the microparticle beam microscope. This immersion field further hinders the charging of the sample by a separate pre-charged electron beam gun. US 9165742 B1 discloses other examples of separate pre-charged electron beam guns, which additionally require time-consuming switching and realignment of the optical unit of the microparticle beam electron microscope.

[0014] Currently, the minimum lateral structure dimension (CD) of semiconductor structures is about 5 nm, and it should be expected that the minimum structure dimension will continue to shrink and will be less than 3 nm, less than 2 nm or even lower within a few years. A resolution of this order of magnitude is only possible with low particle currents. In order to introduce a sufficient amount of charge into the semiconductor structure to be measured and to ensure sufficient resolution, the prior art uses a time-consuming two-stage process for voltage contrast imaging. In the first stage, the sample to be inspected is charged in the so-called pre-charge mode and the particle beam microscope is operated with a high particle current. In a second step, the particle beam microscope is then switched to a high-resolution imaging mode with a low particle current and a voltage contrast image is captured.

[0015] US 5959459 A proposes a method for voltage contrast imaging with a two-stage process of different magnifications. The sample is charged at a first, lower magnification, while the suspected defect is located at a second, higher magnification. This process requires spatial movement of the sample; in particular, in order to switch to a particularly high resolution, the distance between the sample and the microbeam optical unit needs to be changed. Therefore, this method is very time-consuming. Therefore, this method cannot be used for current requirements in terms of resolution and throughput.

[0016] US 2017 / 0287675 A1 proposes such a two-stage process for voltage contrast imaging, wherein for a first step in a pre-charging mode, a control unit modifies one or more components of the microparticle beam microscope.

[0017] US 7217579 B2 proposes a two-stage process for voltage contrast imaging to monitor a manufacturing process, in which specific test structures or PCMs are applied or introduced on a wafer. A small area of ​​these extensive PCMs, a so-called pad or platelet, is brought into the small field of view of the SEM. In a first step, the SEM is operated in a pre-charge mode until the test structure is sufficiently charged. In a second step, the SEM is switched to an imaging mode and a voltage contrast image is captured. In addition to the disadvantages already mentioned, the small field of view of the SEM further limits the configuration and design of the extensive test structures or PCMs.

[0018] The two-stage process for voltage contrast imaging has various disadvantages and limitations. Firstly, the possibility of switching needs to be specifically taken into account in the design of the microparticle beam microscope. Secondly, the two-stage process for voltage contrast imaging is time-consuming. For example, when the microparticle beam microscope switches from high current mode to low current mode, it may be necessary to recalibrate and determine the image position of the microparticle beam microscope. Hysteresis effects in the magnetic components may lead to poorly reproducible alignment settings. In addition, as a result of the switching, a change of the charge state may be induced in the device, which in turn leads to drift in the case of switching.

[0019] Furthermore, during the two-stage process, in particular when switching a microparticle beam microscope, a time interval occurs between charging and voltage contrast imaging, with the result that the two-stage process with switching can only be used to a limited extent. Due to the natural loss of charge in the semiconductor sample, for example due to leakage currents or tunneling currents, the charge and thus also the voltage decrease over time, so that large voltages, for example from small capacitances of small semiconductor structures, decrease rapidly and can no longer be measured reliably.

[0020] WO 2019 / 115391 A1 proposes a method for voltage contrast imaging for determining alignment errors. The document proposes to provide conductive test structures in each case in a manner stacked on top of each other in different adjacent layers of an integrated semiconductor. Due to process errors during the production of a layer, the test structure in this layer may have an incorrect lateral configuration, so that the test structure may no longer overlap with the test structure in an adjacent layer. The interrupted connection affects the capacitance of the structure and thus the voltage contrast imaging of the electron microscope.

[0021] If the corresponding test structures in adjacent layers no longer overlap, an interruption occurs between two test structures. Here, WO 2019 / 115391 A1 proposes the use of large alignment marks for optical alignment. Therefore, the proposed method is only suitable for very rough alignment. Furthermore, the application does not explain the solution for charging the large capacitance of the alignment marks with a low current of a high-resolution micro-beam microscope.

[0022] Voltage contrast imaging on semiconductor structures of different sizes or with different capacitances is another problem in the prior art. In case of charging by means of a "readout gun" or by means of a particle beam microscope in pre-charge mode, it is possible to ensure that even very large structures with large capacitances are adequately charged, given a sufficient charge amount and / or irradiation time. Using a particle beam microscope with high resolution and low particle currents, only very small amounts of charge can be introduced into the sample, and therefore only very small semiconductor structures with small capacitances can be adequately charged in a limited time. Conversely, very long irradiation times are required in high resolution mode to charge larger branched structures. Summary of the invention

[0023] Against the above background, it is an object of the present invention to provide a method for charging structures and performing voltage contrast imaging by high-resolution particle multibeam microscopy, in particular in semiconductor samples.

[0024] Another object of the present invention is to enable high-resolution voltage contrast imaging with pre-charging without switching the microparticle multibeam microscope.

[0025] Another object of the present invention is to provide a method for simultaneously and locally charging structures in a targeted manner, in particular in semiconductor samples, and for high-resolution voltage contrast imaging by means of high-resolution particle multibeam microscopy.

[0026] Another object of the present invention is to provide a method for simultaneously and locally charging structures with different capacitances in a targeted manner, particularly in a semiconductor sample, and for performing high-resolution voltage contrast imaging of semiconductor structures with different capacitances by means of a high-resolution particle multi-beam microscope.

[0027] Another object of the present invention is to provide a high-resolution microparticle multi-beam microscope for voltage contrast imaging on specific structures, particularly semiconductor structures.

[0028] It is another object of the present invention to provide a semiconductor structure for defect detection by voltage contrast imaging with a particle multi-beam microscope.

[0029] Another object of the invention is to provide test structures for which small lateral errors (e.g. about 1 nm) in the layer construction of a semiconductor structure can lead to voltage contrast changes and can be charged by a particle beam grid configuration and can be used for high-resolution voltage contrast imaging.

[0030] Another object of the present invention is to provide a method, a particle multi-beam microscope, and a semiconductor structure for determining deviations or defects in the semiconductor structure for process development of a manufacturing process of the semiconductor structure.

[0031] Another object of the present invention is to provide a method, a particle multi-beam microscope, and a semiconductor structure for determining deviations or defects in the semiconductor structure.

[0032] Description of the Specific Embodiments of the Invention

[0033] The present invention provides a method for charging a chargeable structure (e.g., a semiconductor structure) in a sample (particularly a semiconductor sample) and performing voltage contrast imaging by means of a high-resolution particle multibeam microscope having a low particle current of selected individual particle beams in a particle beam grid configuration. In this case, the added total current formed by the sum of the selected particle beams each having a low particle current generates a charge and thus a voltage difference in the chargeable structure or semiconductor structure. According to the present invention, the particle beam microscope used for charging and determining the voltage contrast remains unchanged, and the individual particle currents of the first and second particle beams remain substantially the same.

[0034] One embodiment of the present invention relates to a method for performing voltage contrast imaging on a sample using a particle multi-beam microscope having a plurality of individual particle beams in a grid configuration, comprising scanning a sample having at least one chargeable structure with a plurality of individual particle beams, charging the sample with a first number of first particle beams in the particle multi-beam microscope, and determining a voltage contrast at the at least one chargeable structure of the sample with a second number of second particle beams in the particle multi-beam microscope. In one embodiment, at least one first particle beam in the first number of first particle beams is not included in the second number of second particle beams. In one embodiment, at least one second particle beam in the second number of second particle beams is not included in the first number of first particle beams. In one embodiment, the first number of first particle beams includes at least one first particle beam. In one embodiment, the second number of second particle beams includes at least one second particle beam. In one embodiment, the first number of first particle beams includes at least two first particle beams, wherein each of the at least two first particle beams has a first particle current, and the added total current formed by the sum of the at least two first particle currents generates an accumulated charge, thereby generating a voltage difference in the structure. The particle current of the second particle beam used for determining the voltage contrast at the sample is less than the sum total current of the first number of first particle beams, so that the accumulated charge of the chargeable structure due to the particle current of the second particle beam remains substantially unchanged. In a specific embodiment of the present invention, a particle beam of the first number of first particle beams is identical to at least one particle beam of the second number of second particle beams.

[0035] A specific embodiment of the present invention provides a method for precharging a chargeable structure in a sample, followed by voltage contrast imaging by a microparticle multibeam microscope. In this case, the precharging is performed in a high-resolution microparticle multibeam microscope. The summed total current formed by the sum of multiple microparticle beams each having a low microparticle current generates a charge and thus a voltage difference in the chargeable structure, which can be detected in the second step of voltage contrast imaging by a high-resolution microparticle multibeam microscope according to the present invention, without switching the microparticle multibeam microscope or moving the sample by a moving device.

[0036] Another specific embodiment of the present invention provides a method for simultaneously charging chargeable structures in a sample and performing voltage contrast imaging by a microparticle multibeam microscope without a pre-charging mode. The charging and voltage contrast determination is therefore performed in a temporally overlapping manner or simultaneously during the process of scanning the sample using the microparticle multibeam microscope. In this case, during the charging of the sample with at least one first microparticle beam of a first number of first microparticle beams, at least one structure is charged in a spatially resolved manner. In this case, a plurality of selected microparticle beams, each with a low microparticle current, generates an added total current, a charge and therefore a voltage difference in the chargeable structure. In this method, charging is performed by a plurality of microparticle beams selected from a microparticle beam grid configuration simultaneously with voltage contrast imaging. In a specific embodiment, the present invention is implemented on an electrically connected structure, such as a semiconductor structure, which extends over a plurality of microparticle beams from a microparticle beam grid configuration.

[0037] Another embodiment of the present invention provides a method for charging chargeable structures in a sample and performing high resolution voltage contrast imaging by microparticle multi-beam microscopy, wherein the selected structures are charged in a targeted manner at at least one first scanning position of at least one first microparticle beam, and voltage contrast imaging is performed in a targeted manner at at least one second scanning position of at least one second microparticle beam, wherein the second scanning position is different from the first scanning position. In one embodiment of the present invention, the at least one first charging microparticle beam can be the same as the at least one second voltage contrast imaging microparticle beam.

[0038] A specific embodiment of the present invention, regarding the above method, further includes using a third number of third particle beams of the particle multi-beam microscope to switch the capacitance of a chargeable structure (especially a semiconductor structure) in the sample and generate dynamic changes in the voltage contrast in the process of determining the voltage contrast.

[0039] Another specific embodiment of the present invention provides a method, wherein a first structure is charged with a first amount of charge by a first configuration of the particle beam, and a second structure is charged with a second amount of charge by a second configuration of the particle beam, so that the two structures have approximately the same voltage, wherein the first and second structures have different capacitances. In this case, the first and second structures can be adapted to a grid configuration, or a specific predefined grid configuration can be provided for voltage contrast imaging of the first and second structures.

[0040] Another specific embodiment of the present invention provides a high-resolution microparticle multi-beam microscope for voltage contrast imaging of a specific chargeable structure, in particular a semiconductor structure, wherein the microparticle beam grid configuration is adapted to the chargeable structure, in particular a semiconductor structure. To this end, for example, a predefined aperture plate is implemented to produce a spatially adapted microparticle beam grid configuration, wherein the microparticle beam grid configuration is adapted to the chargeable structure for targeted, simultaneous charging and voltage contrast imaging. To this end, the predefined aperture plate has at least one first aperture opening for charging the structure, and at least one second aperture opening for high-resolution voltage contrast imaging of the sample.

[0041] A specific embodiment relates to a microparticle multibeam microscope for voltage contrast imaging on a sample, in particular a semiconductor sample, comprising at least one first predefined aperture plate for generating a plurality of microparticle beams arranged in a grid, wherein the predefined aperture plate is configured to generate at least one first microparticle beam for cumulative charging of a chargeable structure and at least one second microparticle beam for voltage contrast imaging on the chargeable structure, and at least one first microparticle beam is different from at least one second microparticle beam in at least one characteristic in an image plane of the microparticle multibeam microscope (in which the sample is arranged), wherein the at least one characteristic comprises beam current, beam spacing, beam focus or beam shape. To this end, the microparticle multibeam microscope comprises at least one predefined aperture plate having different openings or different focuses and / or a predefined focus array by a fine focusing optical unit. In particular, the at least one predefined aperture plate can be suitable for charging and voltage contrast imaging on the sample.

[0042] In a specific embodiment, the aperture plate has holes with different opening diameters or opening areas to generate different beam currents for different beams. At least one first hole with a larger first diameter generates a large beam current on the sample to charge a structure at a location of the sample conjugated to the at least one first hole, and at least one second hole with a smaller second opening area or diameter generates a small beam current to perform high-resolution voltage contrast imaging on the sample at a location conjugated to the at least one second hole.

[0043] Another specific embodiment of the invention provides a high-resolution particle multi-beam microscope for voltage contrast imaging, in particular for semiconductor structures, wherein the high-resolution particle multi-beam microscope is implemented so that the field areas of the individual particle beams in the particle beam grid configuration overlap in the object plane, so that the sample is irradiated multiple times by the particle beams in the overlapping area. Thus, in particular, the semiconductor structure can be charged at at least one position by at least one first particle beam of the particle beam grid configuration, and the semiconductor structure can be imaged with voltage contrast at least at the same position by at least one second particle beam of the particle beam grid configuration. In one configuration of the specific embodiment, the first and second particle beams can be formed in different ways, for example by allocating holes with different opening areas or diameters in an aperture plate to produce the particle beam grid configuration.

[0044] In a specific embodiment, predefined aperture plates of a high-resolution microparticle multibeam microscope can be implemented to be interchangeable.

[0045] A specific embodiment of the present invention relates to the above method, wherein a specific semiconductor structure is configured for voltage contrast imaging using a grid configuration of a microparticle beam microscope. The specific semiconductor structure is designed so that charging and voltage contrast imaging can be achieved in a targeted manner and simultaneously by multiple microparticle beams from the microparticle beam grid configuration.

[0046] Another embodiment of the present invention provides a semiconductor structure for detecting small lateral errors in the layer construction of the semiconductor structure, which result in voltage contrast changes and can be charged and imaged with high resolution voltage contrast in parallel by a microbeam grid configuration. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention will be explained in more detail below with reference to the accompanying drawings, in which:

[0048] Figure 1a MSEM-based example showing microparticle multibeam microscopy;

[0049] Figure 1b MSEM-based example, schematically showing the beam path of primary electrons in microparticle multibeam microscopy;

[0050] Figure 1c MSEM-based example, schematically showing the beam path of secondary electrons in microparticle multibeam microscopy;

[0051] Figure 2a A simplified cross-section through a semiconductor in the xz direction is schematically shown;

[0052] Figure 2b schematically shows a simplified cross-section through the layers of a semiconductor in the xy direction;

[0053] Figure 3 A first exemplary embodiment of charging and voltage contrast imaging is shown based on an example of a typical semiconductor structure;

[0054] Figure 4 Based on an example of a typical semiconductor structure, a second exemplary embodiment with dynamic voltage contrast imaging is shown;

[0055] Figure 5a An aperture plate is shown in which the arrangement of apertures is spatially adapted to the semiconductor structure;

[0056] Figure 5b An aperture plate with holes of different sizes is shown in cross-section;

[0057] Figure 5c An aperture plate having a plurality of aperture openings for charging a semiconductor sample is shown;

[0058] Figure 6 An aperture plate with different holes and different spaces for individual particle beams is shown;

[0059] Figure 7 An aperture plate is shown with different holes and different focal positions of individual particle beams; and

[0060] Figure 8 Shown is a test structure designed for determining the overlay accuracy of the layer structure of a semiconductor structure using MSEM. DETAILED DESCRIPTION

[0061] Voltage contrast images are produced by structures that absorb electrical charges and are then observed using particle beam microscopy (which uses charged particles). In this case, a primary particle beam is scanned or passed in a scanning manner over the sample to be examined, and reflected particle particles or secondary emissions, such as secondary electrons or photons, are detected.

[0062] Semiconductor structures that can absorb charge are usually metals, such as metal compounds in integrated circuits, but can also be doped regions in silicon, such as doped regions in photosensitive semiconductor cells or memory cells. In this case, the capacitance of the semiconductor structure can be between a few electrons and hundreds of thousands of electrons. Depending on the amount of the introduced charge Q and the capacitance C, a potential or a voltage difference dV=Q / C is formed between the chargeable semiconductor structure and the surroundings and firstly affects the charged particles of the microparticle beam microscope attractively or repulsively. Secondly, the charge Q or the voltage difference dV also affects the number and energy of the secondary electrons. In general, therefore, the voltage difference or charging of the semiconductor structure affects the imaging of the microparticle beam microscope. Therefore, depending on the charging or the voltage difference dV of the semiconductor structure, a change in the image contrast in the form of bright and dark areas is obtained, which is why this is also called voltage contrast imaging. Since the material composition is known for the semiconductor structure, the charge state of the observed semiconductor structure can be derived from the image contrast or brightness difference of such a voltage contrast image. According to the invention, an advantageous method for voltage contrast imaging is realized by a microparticle multibeam microscope or a microparticle beam microscope with a plurality of microparticle beams.

[0063] Currently, the minimum lateral structure dimension (CD) of semiconductor structures is about 5 nm, and it should be expected that the minimum structure dimension will continue to shrink and will be less than 3 nm, less than 2 nm or even lower within a few years. Resolution of this order of magnitude is only possible with low particle currents.

[0064] An example of a microparticle beam microscope having multiple microparticle beams with electrons as microparticles is also called a "multi-beam scanning electron microscope", abbreviated as MSEM. Figures 1a to 1c Describe the functions of MSEM. Figure 1a The arrangement and the function of an MSEM are schematically shown. The MSEM 1 consists of a first object unit 10 with an objective lens 12 and a deflection unit (not shown in the figure), by means of which the electron beams of the MSEM 1 in an object plane 11 can be deflected perpendicularly to the propagation direction of the electron beams in order to scan a field region in the object plane 11 with each electron beam. The sample surface of the sample S can be arranged in the object plane 11 by means of a positioning unit (not shown). In this case, a plurality of primary electron beams 3 are focused by the objective lens 12 and a plurality of electron beam focal points 5 are generated in an electron multibeam grid configuration (referred to as grid configuration 4 for short) in the object plane 11. Subsequently, a plurality of secondary electron beams 9, which are absorbed and collimated by the objective lens 12, are directed by means of a beam splitter 40 onto a beam path 43 in the direction of a detection unit 20. The detection unit 20 comprises a projection lens or a projection lens system 25, which generates a plurality of focal points in an image plane 23 from the plurality of secondary electron beams 9. In the image plane, a spatially resolved detector 27 is arranged in the volume 29 and can detect secondary electrons coming from each electron beam 9 respectively.

[0065] The plurality of primary electron beams 3 are generated by an electron multi-beam generating device 30, wherein the electron multi-beam generating device 30 has an electron beam source 31, a collimating lens 33, a downstream aperture plate arrangement APA, and an objective lens or field lens 37. Optionally, a multi-beam aperture ("blind plate") BP is additionally arranged behind the aperture plate arrangement APA. The field lens 37 and the objective lens 12 together form an image of the plurality of primary electron beams 3 passing through the openings in the optional multi-beam aperture BP and thus together form an electron beam focus or scanning spot 5 in the image plane 11, wherein the grid arrangement 4 of the electron beam focus 5 is determined by the design of the aperture plate APA and the optional multi-beam aperture ("blind plate") BP.

[0066] In a specific embodiment, a predefined aperture plate APA of a high-resolution particle multibeam microscope is replaceable together with an optional, assigned multibeam aperture BP. For example, a mechanical receptacle 45 can be provided in the MSEM, which can receive at least one further replaceable aperture plate APA2 and an optional second BP2. The first aperture plate can, for example, be one of the particularly suitable aperture plates explained below, and the other aperture plate can, for example, be implemented for a particle beam spacing of less than 10 μm or 12 μm at the image plane 11, and can, for example, be designed for a smaller particle beam spacing of about 5 μm at the image plane 11, for example, voltage contrast imaging on a CMOS sensor with a pixel size of about 5 μm. Typical particle beam spacings at the image plane 11 are in the range of 5 μm to 15 μm, and specific embodiments with particle beam spacings of 100 μm or up to 200 μm are possible.

[0067] Between the field lens 37 and the objective lens 12 , the plurality of primary electron beams 3 pass through a beam splitter 40 on a beam path 42 .

[0068] For illustration purposes, Figure 1a An electron multibeam grid configuration 4 is shown having 25 individual beam focal points 5 in a square regular grid with a pitch P1 = 10 μm. In practice, a larger number, e.g. 10 x 10, 20 x 20, 100 x 100 or more individual beam focal points 5 are possible, and other grid configurations 4 are known (e.g. a hexagonal grid), in which the pitch P1 of the individual beam focal points 5 in the image plane 23 may be in the range of 1 μm to 200 μm.

[0069] Figure 1bThe beam path of the primary electrons in the MSEM (particularly the multi-beam generating device) is schematically illustrated. The total beam direction 250 of the primary electrons is indicated by an arrow. The electron beam source 231 generates a divergent electron beam 239, which is focused by a collimating lens 233 to form an electron beam 238. The parallel electron beam 238 illuminates an aperture plate configuration APA. The aperture plate configuration APA includes at least one aperture plate 291 having a plurality of aperture openings 292 configured in a grid configuration, wherein a plurality of electron beams 203 pass through the aperture openings 292. In this specification, for simplicity, each electron beam 203 passing through the aperture opening 292 is referred to as an electron beam or a microparticle beam. The aperture plate APA further includes the function of focusing individual electron beams in the plurality of electron beams 3. Focusing can be achieved, for example, by electrodes (not shown), which form an electron optical microlens behind each aperture opening of the aperture plate configuration APA. In addition, a focusing array including a plurality of electron optical lenses or a fine focusing optical unit can be provided downstream of the aperture plate configuration APA. To this end, a further pair of electrodes is arranged behind the aperture plate APA. For the sake of simplicity, the microlenses of the focusing and focusing array are represented as lens array 294. As a result, a plurality of electron beam focal points 276 are generated in an aperture plane 295 arranged downstream of the aperture plate APA, in which a multi-beam aperture BP ("blanking plate") is selectively arranged. The selective multi-beam aperture BP comprises a plurality of openings arranged in a grid configuration, corresponding to the focal points 276 of the plurality of electron beams 203 and allowing the plurality of electron beams 203 to pass through. Only three aperture openings 292 and three lenses of the lens array 294 as well as three electron beams 203 are schematically shown. The field lens 237 finally gathers the electron beam beam 203 diverging downstream of the aperture plane 295. By means of the field lens 237 and the objective lens 212, the plurality of electron beam focal points are imaged into the image plane 211, for example in a reduced manner, and form the focal point 205 of the primary electron beam 203 of the MSEM in the grid configuration 4. The stop plane 295 is imaged by the field lens 237 and the objective 212 into the image plane 211, and the focus 276 is therefore conjugate to the focus 205 in the image plane 211. For simplicity, the aperture opening 292 and the lenses of the lens array 294 are also indicated as being conjugate or assigned to the focus of the individual beams.

[0070] The sample (e.g. semiconductor sample 200) held on the sample holder 280 is arranged in the image plane 211. The sample holder 280 (e.g. wafer chuck) is connected to the positioning unit 281, which may have five, six or more degrees of freedom for example, to align, position and move the sample.

[0071] For the required high resolution in the range of a few nanometers, a small diameter d of the individual beam focus is required. E The diameter d of the individual beam focus 205 is E Can be less than 5nm to 200nm. Diameter dE The diameter d of the image of the electron beam source source , diffraction error d diffraction The lens aberration d of the field lens 237 and the objective lens 212 aberrations Composition:

[0072]

[0073] Among them, the diffraction error

[0074]

[0075] The electron beam source 231 is imaged in a reduced manner by an imaging ratio M < 1, so that the reduced source image size d source . Lens aberration d aberration It consists of many individual aberrations such as astigmatism, spherical aberration, coma and chromatic aberration, or aberrations due to dispersion over the energy bandwidth ΔE of the electron beam. Lens aberrations increase with increasing aperture angle α and are minimized by corresponding design and correction of the electron beam optical unit. For example, spherical aberration increases approximately cubically with increasing aperture angle α. The aperture angle α is predefined by the aperture opening 292 of the aperture plate APA and increases with the electron imaging performed by the field lens 237 and the objective lens 212. In order to keep the aberrations small and ensure high resolution, the aperture opening 292 of the aperture plate APA has a correspondingly small design for this purpose. The aperture opening 292 of the electron beam 203 for the high-resolution mode has a small aperture diameter, for example, between 10-50 μm and a spacing between 30-250 μm, for example an aperture diameter of 20 μm and a spacing of 70 μm. A transmittance of 4-10% is thus achieved, which corresponds to a low beam current. Further optimization may achieve transmissions up to 15% or even up to 20% in high resolution mode.Thus, only relatively small apertures with relatively low transmissions of less than 20% and thus relatively low beam currents are suitable for high resolution mode.

[0076] This therefore results in a relatively low radiation intensity of the individual high-resolution electron beams of the MSEM.However, according to the invention, a very large number of electron beams, for example 25 or 100 or more electron beams, are provided and a high summed total current is obtained.

[0077] The primary electrons of each electron beam (3, 203) interact with the sample and are backscattered or generate secondary electrons. For simplicity, the backscattered electrons and secondary electrons are collectively referred to as the term "secondary electrons" below. Given other constant beam parameters, the proportion of secondary electrons generated or backscattered depends on the local composition of the sample, such as the surface morphology, material composition or local voltage difference dV of the sample. Figure 1cThe beam path of the secondary electron beam (9, 209) is schematically shown. The total beam direction 251 of the secondary electrons emitted from the sample 200 is indicated by the arrow 251. A portion of the secondary electrons is absorbed and focused by the objective lens (12, 212). Therefore, from a plurality of individual beam focal points (5, 205) in the grid configuration 4, a plurality of secondary electron beams (9, 209) in the same grid configuration 4 are generated, wherein the respective radiation intensities of the plurality of secondary electron beams (9, 209) allow conclusions to be drawn about the respective local composition of the sample, the material composition and the local voltage difference dV.

[0078] Starting from the focal point (5, 205), the secondary electron beam (9, 209) is emitted divergently and imaged by the electron-optical objective (12, 212) and the projection lens (25, 225) to the detector plane (23, 223). In this case, the secondary electrons are deflected by the beam splitter (40, 240) in the direction of the electron-optical projection lens (25, 225). Figure 1b and Figure 1c The illustration in the figure is greatly simplified here; for example, the beam splitter 240 may include multiple magnetic fields, which, for example, deflect both the primary electron beam and the secondary electron beam to the right without being dispersed along the beam direction, such as Figure 1a As shown. A detection unit ( Figure 1c not shown).

[0079] Furthermore, by means of a scanning mechanism (not shown), a plurality of primary electron beams (3, 203) are moved together and in parallel on the sample (S, 200). In this case, the focus (5, 205) is offset at a distance corresponding to P1 or slightly greater than P1 so that the field areas scanned by the different electron beams overlap slightly. Thus, the sample surface is scanned regionally by a plurality of electron beams (3, 203) without any gaps. Scanning mechanisms for this purpose are well known. Together with the deflection of the primary electron beam (3, 203), the secondary electron beam (9, 209) is also directed back. The time sequence of the signals detected by the detector 27 is converted into a lateral spatial position in the object plane (11, 211). Thus, in the simplified example shown, a regional image of a portion of the sample surface with an area of ​​50x 50μm is generated, which is composed of 5x 5 individual images, each of which has an area of ​​approximately P1=10μm.

[0080] High-resolution imaging is generally understood to mean that the diameter d of the individual beam focal points (5, 205) is E Imaging of less than 30 nm, less than 15 nm, especially less than 5 nm (eg, down to 3 nm or 2 nm). The range of the source point of the secondary electron beam (9, 209) can also include a range of several nanometers, such as less than 30 nm.

[0081] Figure 1aAs an example, an MSEM 1 with 25 individual electron beams 3 in a grid configuration 4 is shown. However, the number of electron beams can be much higher, for example 10×10 electron beams, 10,000 electron beams or more. Using a large number of individual beams arranged in a grid configuration and swept together over the semiconductor sample in a joint scanning process, a very high throughput is achieved, i.e. a large area is captured per unit time. For 100 electron beams, the throughput achieved by the MSEM 1 is about 3.5 mm 2 / min. Using a larger number of beams, a higher output can be achieved, such as 100mm 2 / min or greater than 350mm 2 / min.

[0082] In the following of this application, MSEM 1 is used as a representative of a microparticle multi-beam microscope, and is not intended to be limited to an electron beam microscope in a specific embodiment of MSEM. For example, microparticle particles can generally be charged particles, such as electrons, metal ions (such as gallium ions), or ions of rare gases (such as helium or neon). An exemplary specific embodiment of a semiconductor sample will be described below. However, the present invention is not limited to semiconductor samples.

[0083] Figure 2 shows two typical cross sections through a semiconductor structure. Figure 2a A cross section perpendicular to the surface 50 of the semiconductor is shown, wherein the image is produced by a particle beam microscope. In the image, the metal structures appear brighter than the non-conductive structures. The surface 50 of the substrate or wafer defines a segment towards the top. A plurality of individual layers 54.1 ... 54.22 are arranged parallel to the surface 50, each of which can be structured. In this case, layers with many conductive structures 54.1, 54.3, ... alternate with insulating layers 54.2, 54.4 having only a small number of conductive connections or through-holes. In a representative manner, one such conductive connection 55 between a conductive structure 56 in layer 54.1 and layer 54.3 is shown. In contrast, another conductive structure 57 in layer 54.1 has no connection to layer 54.3.

[0084] The lateral dimensions of the semiconductor structures and the layer thicknesses of the layers decrease with increasing depth z. The penultimate layer 54.21 directly adjoins a layer 54.22, wherein the layer 54.22 comprises, for example, doped structures of the underlying semiconductor material silicon 51. One such doped structure 58 is indicated by way of example. A plurality of conductive structures are located between them, one of which 59 is highlighted by way of example.

[0085] The number and selection of layers are to be understood only as examples; the integrated semiconductor may contain a different number of layers as well as other layers.

[0086] The range of conductive structures or structures that can absorb charge and can therefore be used for voltage contrast imaging varies greatly. Structure 56 is connected to layer 54.3, wherein layer 54.3 in this cross-sectional plane is completely implemented as a conductive layer and further has a connection to the underlying conductive layer 54.5. Therefore, this semiconductor structure is very extensive and has a large capacitance C1, which must be charged with a large amount of charge Q1 to generate a voltage difference dV. The charge amount Q1 can be, for example, a majority greater than tens of thousands of electrons (for example, greater than one hundred thousand electrons). In contrast, doped structure 58 has only a very small range and a very small capacitance C2, so that a very small amount of charge Q2 of some individual electrons is sufficient to generate a local voltage difference dV. For example, if too many electrons are fed to doped structure 58 and they exceed the capacitance C2 of doped structure 58, the excess electrons flow away and charge adjacent structures (for example structure 59). Therefore, it is no longer possible to decide whether structure 59 is incorrectly connected to structure 58 or whether it is just structure 58 that is overcharged by charge carriers.

[0087] Figure 2b By way of example an XY cross section through layer 54.17 is shown. Layer 54.17 comprises a plurality of electrically conductive connections which vary in extent and which produce connections between structures in layers 54.15 and 54.19.

[0088] In particular, the conductive structures in the lower layers 54.19 to 54.21 can also be implemented as electrodes of transistors, for example as gates. Charging of such gates can, for example, connect two other semiconductor structures with capacitances C4 and C5 to each other in an electrically conductive manner via the space charge region and produce a switchably connected semiconductor structure with capacitance C6.

[0089] Figure 3 By way of example, charging and voltage contrast imaging on a schematically illustrated semiconductor sample 60 is shown, wherein the charging and imaging is performed on the surface 50 of the semiconductor sample 60, i.e. the surface 50 of the semiconductor sample 60 is arranged in the object plane 11 of the MSEM 1. Near the surface 50 of a substrate 51 made of silicon, the semiconductor sample 60 comprises a plurality of layers, of which the layer 54.5 is highlighted by way of example. These layers comprise conductive structures, such as the structure 57 in the layer 54.5 or the gate electrode 66 in the bottommost layer, and connections or vias 55.

[0090] A semiconductor structure is irradiated at a surface 50 by a plurality of spaced apart electron beams 3 in a grid structure 4 of an MSEM 1, three of which are indicated by way of example as (n-1), n ​​and (n+1). Instead of a scanning point or focus 5 of a primary electron beam 3, a secondary electron beam 9 is emitted from the sample surface 50. The scanning position of the emitted electron beam 9 largely coincides with the focus of the primary electron beam 3, but the secondary electron beam 9 has, for example, a higher divergence, which is shown in a simplified manner by a wider beam cone. At each scanning position, for example the first scanning position 62.0, the (n-1)th electron beam 3 generates an interaction zone 61.0 with the substrate. The nth electron beam correspondingly generates an interaction zone 61.1 and, in the case of a deflection during a subsequent scan, an interaction zone 61.2. In this case, depending on the material and the landing energy of the particle beam, the interaction zone 61.0, 61.1 or 61.2 may have an extent of several tens of nanometers perpendicular to the beam direction and in the beam direction. Depending on the extent of the interaction zone, the irradiation may result in charging of the conductive structures overlapping the interaction zone. Thus, for example, the conductive structure 56 is charged by the (n-1)th electron beam and the nth electron beam at the scanning positions 62.0, 62.1 and 63.1 with the interaction zones 61.0, 61.1 and 61.2, and at other scanning positions (not shown). In the example, a non-conductive material (e.g. silicon) is located on the substrate surface 50 at the scanning position 62.1. Only a small amount of the nth secondary electrons 9 are excited by the nth primary electron beam 3, and the non-conductive structure appears dim in the image. On the other hand, at the scanning position 62.2 of the n+1th electron beam, there is a conductive structure which emits a plurality of n+1th secondary electrons 9 when irradiated by the n+1th electron beam, and appears as a bright area in the image as shown in FIG. 2 .

[0091] The n-th electron beam is guided by a scanning unit of the MSEM 1 along a scanning direction 65 across the substrate surface 50 together with the other electron beams n-1, n+1 and in the process passes through a plurality of scanning positions or focal points (5), such as a second scanning position 63.1 and a third scanning position 64.1 of the respective n-th electron beam. In addition to the electron beams n-1, n and n+1 shown as examples, in a grid configuration of the MSEM, a plurality of other electron beams (not shown) are guided across the substrate surface 50. Overall, a large portion of the semiconductor sample is regionally scanned in the process. The primary and secondary electron beam waveguides of the n-th electron beam and, for example, individual secondary electron beam waveguides are shown here as dashed lines and are labeled with reference symbols n' and n".

[0092] In a specific embodiment, in a semiconductor sample 60, the semiconductor structure is precharged in a first step, and then voltage contrast imaging is performed in a second step. In this case, precharging is performed in a high-resolution microparticle multi-beam microscope during a first scanning process. The summed total current formed by the sum of a plurality of microparticle beams (e.g., 5×5 or 10×10 electron beams, each with a low microparticle current) generates a charge in the semiconductor structure and thus a voltage difference. The total charging current corresponds to the cumulative sum of the small individual currents of the high-resolution individual beams 3, so its amount is, for example, 25 times or 100 times or more relative to the individual electron beams. Compared to the individual high-resolution electron beams of the SEM, the cumulative irradiation of the semiconductor sample 60 by a plurality of individual high-resolution electron beams 3 will result in: compared with charging by a single beam at a certain position on the sample with the same beam current and the same dwell time, the semiconductor sample 60 is charged at least 25 times, 100 times or more overall. In the second step, voltage contrast imaging is performed by a high-resolution microparticle multi-beam microscope through a second scanning process without switching the microparticle multi-beam microscope or moving the sample by a moving device.

[0093] The low individual currents using the multi-beam configuration 4 thus ensure in each case high-resolution voltage contrast imaging with a resolution in the nanometer range, for example below 30 nm, 10 nm or 5 nm, and possibly with a resolution of 3 nm or 2 nm.

[0094] Thus, by means of a high-resolution particle multi-beam microscope with low particle current of individual particle beams 3 of a particle beam grid configuration 4, it is possible to charge semiconductor structures in a first step and to perform high-resolution voltage contrast imaging with a lateral resolution in the range of several nanometers in a second step in a semiconductor sample 60. In this method for performing voltage contrast imaging on a semiconductor sample, a particle multi-beam microscope with a plurality of individual particle beams in a grid configuration is used to scan a semiconductor sample having at least one semiconductor structure by means of the plurality of individual particle beams. In this process, the semiconductor sample is charged with a first number of first particle beams of the particle multi-beam microscope, and a voltage contrast is determined at at least one semiconductor structure of the semiconductor sample with a second number of second particle beams of the particle multi-beam microscope. In this case, at least one first particle beam of the first number of first particle beams for charging the sample may not be included in the second number of second particle beams for imaging the sample, or at least one second particle beam of the second number of second particle beams may not be included in the first number of first particle beams.

[0095] In another exemplary embodiment, charging is performed by a plurality of selected individual electron beams with high spatial resolution. Figure 3Two other examples of the invention are schematically illustrated. In particular, in this example, the first step of charging and the second step of voltage contrast imaging can be implemented in a time overlapping manner, or even in complete parallelism during the process of scanning the semiconductor sample in a scan manner.

[0096] In this illustrative example, the semiconductor structure 53 below the third scanning position 64.1 of the nth electron beam extends to below the first scanning position 62.2 of another adjacent n+1th electron beam of the grid configuration 4 of the multiple electron beams 3 of the MSEM 1. Before the nth electron beam reaches the scanning position 64.1, the semiconductor structure 53 below the irradiation point 64.1 is charged by the n+1th electron beam. During the entire scanning process of the n+1th electron beam, the semiconductor structure 53 undergoes a targeted, spatially resolved charging, for example at the scanning position 62.2 or 64.2, wherein even other electron beams (not shown) may also contribute to the charging of the semiconductor structure 53. As a result, a relatively large amount of charge is obtained, and the semiconductor structure 53 may have a voltage difference dV, which can cause a contrast change during imaging at the scanning position 64.1. Due to the accumulated charge, the secondary electrons emitted at the scanning position 64.1 may, for example, be lower than the secondary electrons emitted at the scanning position 62.2 due to the first excitation of the n+1th electron beam. Thus, charging can be performed with the microparticle beam at at least one first scanning position, and voltage contrast can be determined with the microparticle beam at at least one second scanning position different from the first scanning position.

[0097] Simultaneous voltage contrast imaging and charging will be explained based on another example. At the scanning positions 62.1 and 63.1, the n-th primary electron beam excites only a small amount of secondary electrons in the insulating material silicon, and due to possible charging of adjacent conductive structures, the insulating structure does not change or at most a small change. However, the n-th electron beam with the interaction area 61.1 or 61.2 below the scanning positions 62.1 and 63.1, respectively, contributes to the spatially resolved local charging of the semiconductor structure 56 in each case. Likewise, in this exemplary example, the adjacent (n-1)-th electron beam contributes to the charging of the structure 56. Therefore, before the (n-1)-th electron beam reaches the scanning point 64.0, the connected semiconductor structure 56 experiences cumulative charging and therefore a voltage difference dV. At the scanning point 64.0, due to the charging and the voltage difference dV at the semiconductor structure 56, the (n-1)-th electron beam can only excite a smaller amount of secondary electrons 9, and a darker image point appears.

[0098] Since simultaneous irradiation with a plurality of selected at least one first particle beams 3 from the particle multi-beam grid arrangement 4 results in cumulative charging of, for example, a semiconductor structure 53 or 56 in a semiconductor sample 60, the voltage contrast of individual semiconductor structures can be changed in a targeted manner during imaging. The number of at least one first particle beam 3 of the particle multi-beam microscope 1 can in particular be greater than or equal to two, so that the added total current formed by the sum of at least two first particle beams, each of which has a low particle current, generates charging and thus different voltages in the semiconductor structure 53 or 56. Therefore, the particle current of the second particle beam used to determine the voltage contrast of the semiconductor sample 60 is lower than the total particle current (introduced into the semiconductor sample) of the at least one first particle beam used to charge the semiconductor sample 60. As shown in the example of the (n-1)th particle beam, the second particle beam used for voltage contrast imaging at a later scanning position 64.0 can be the same as the first particle beam at a first earlier scanning position 62.0. In this case, the particle current of the second particle beam for determining the voltage contrast at the semiconductor sample 60 is in particular lower than the added total current of the first number of first particle beams, so that the accumulated charge of the semiconductor structure 60 due to the particle current of the second particle beam remains essentially unchanged. The particle beam microscope can remain unchanged, in particular for charging and determining the voltage contrast, and the individual particle currents of the first particle beam and the second particle beam can remain unchanged, and they can be identical.

[0099] In this case, according to Figure 3The schematic embodiment of shows a small extract from a microparticle beam grid arrangement 4 and a semiconductor sample 60, and it is understood that the semiconductor structures 53 and 56 can generally be charged locally in a spatially resolved manner by a further microparticle beam (not shown). For example, address lines or readout lines can extend over a large area, for example more than several millimeters in the semiconductor sample 60, and can be charged by a plurality of individual electron beams 3 (e.g. 5 or 10 or more), each with a low individual radiation current. Thus, it is possible to charge semiconductor structures and perform voltage contrast imaging in the semiconductor sample 60 simultaneously without a pre-charge mode by microparticle multi-beam microscopy. In this case, at least one first particle beam of the grid arrangement 4 at at least one first scanning position 62.0, 62.2 and (optionally) at least one second particle beam of the grid arrangement 4 at at least one second scanning position 63.1 spaced apart generate charging and thus voltage differences in the semiconductor structure, wherein at at least one third scanning position 64.0, 64.1 spaced apart from the first scanning positions the voltage difference dV in the semiconductor structure is detected as a voltage contrast change at the third scanning point 64.0, 64.1. In this case, this voltage contrast imaging is performed at at least one electrically connected semiconductor structure 53, 56, which extends over at least two adjacent particle beams 3 from the particle beam grid arrangement 4. In a particular embodiment, the scanning areas or field areas of the individual particle beams can overlap, so that a first scanning point of a first particle beam overlaps a second scanning point of a second particle beam.

[0100] A plurality of microbeams makes it possible to charge semiconductor structures with different ranges and different capacitances with different charges, so that a large and extensive semiconductor structure with a large capacitance and a small and limited semiconductor structure with a low capacitance both present approximately the same voltage dV. A large and extensive semiconductor structure with a larger capacitance Ck is charged by a larger number K of individual microbeams 3 with a larger amount of charge, while a smaller, more limited semiconductor structure with a capacitance Cl (which extends only over several or one field area of ​​a microbeam 3) is charged only by a smaller number L of individual microbeams or by a single microbeam with a smaller amount of charge. In this case, a similar voltage difference dV is obtained in both semiconductor structures if L / K corresponds approximately to the ratio Cl / Ck.

[0101] In this way, the basic structure of the semiconductor sample 60 can be inferred by the targeted accumulated charge of the individual semiconductor structures, and defects in the semiconductor structure of the semiconductor sample 60 can be inferred, for example, from the deviation of the obtained image from the expected image.

[0102] In this regard, for example, it is possible to check whether two spaced-apart line segments in an integrated semiconductor are conductively connected or perforated, or are electrically insulated relative to each other. For this purpose, for example, a charge is introduced at a first line segment of the two line segments, and a voltage contrast is measured at another second line segment of the semiconductor structure. Therefore, on the one hand, it is possible to check whether the semiconductor structure that should be conductively connected is actually conductively connected and, for example, not interrupted, so as to have a capacitance lower than the target capacitance of this structure. For example, the voltage contrast at such an interrupted structure therefore deviates from the desired voltage contrast and is higher. On the other hand, it is possible to check whether two semiconductor structures that should not be electrically connected, for example, are mistakenly connected due to a short circuit, so as to have a capacitance greater than the target capacitance of this structure. For example, the voltage contrast at such a connection structure therefore deviates from the expected voltage contrast and is lower.

[0103] Due to simultaneous charging and voltage contrast imaging, the time period between charging and voltage contrast imaging is reduced. Therefore, natural loss of charge in a semiconductor sample due to leakage or tunneling current is reduced, and the charge is not reduced, and therefore the voltage is not reduced, resulting in a large voltage from a small capacitance of a small semiconductor structure, for example, can be reliably measured.

[0104] In another specific embodiment, for example, voltage contrast imaging is performed on a semiconductor structure connected to a large capacitor (e.g. ground). Next, charging and imaging are performed on the same semiconductor structure, wherein the fact that the semiconductor structure is connected to the large capacitor can be determined based on the voltage contrast. In this case, the voltage is low due to the conductive connection to the large capacitor. In the case of an interruption, the introduced charge cannot flow away, and the voltage is higher, and the image contrast of the semiconductor structure changes. For example, the image contrast is reduced.

[0105] In another specific embodiment, quantitative voltage contrast imaging is performed. This involves determining the capacitance of a so-called "floating" semiconductor structure that is not connected to a reference potential. Depending on the capacitance of the "floating" semiconductor structure, a specific voltage difference is established during targeted charging with a specific charge. This voltage difference is generated simultaneously with the multiple microparticle beams and is determined from the image contrast by high-resolution voltage contrast imaging, wherein the charging and thus the image contrast can be varied continuously over the irradiation time. In this way, deviations from the expected capacitance of the "floating" semiconductor structure can be detected.

[0106] Reference Figure 4A specific embodiment of dynamic voltage contrast imaging is described. During the scanning of multiple electron beams 3 on the substrate surface 50, the branched semiconductor structure 67 with a large capacitance C can be charged by multiple electron beams 3 with low beam current. In this example, in the simplified diagram, these are the (n-1)th and nth electron beams. The sum of the individual low beam currents of the multiple individual electron beams 3 produces sufficient charging to produce a voltage difference of dV, which produces a sufficient contrast change in the voltage contrast imaging of the semiconductor structure 67. In this case, the low beam current can also achieve high resolution imaging. Figure 4 In the example of , another semiconductor structure 68 conductively connected to the gate 66 is charged at least at the scanning position 63.1 of the n-th electron beam. Due to the charging of the gate, a space charge region is generated in the doped structure (the so-called fin) in the layer 54.22. This creates a connection between the semiconductor structure 67 and the semiconductor structure 69 in an adjacent area outside the field area scanned by the electron beam (which scans over the semiconductor structure 67). By this switching operation, the charges introduced in the semiconductor structures 67 and 69 can compensate each other, and by further switching operations, it is possible to compensate with other semiconductor structures (for example, with a more distant semiconductor structure 70). In voltage contrast imaging, for example, during the imaging of the structure 67 under the n-1-th electron beam, if the n-th electron beam passes through the scanning position 63.1 above the semiconductor structure 68, the voltage contrast changes suddenly, so that the charge from the semiconductor structure 67 can flow to the semiconductor structure 69. In this way, dynamic voltage contrast imaging with sudden changes in the image contrast of individual semiconductor structures is achieved. During dynamic voltage contrast imaging, sudden, dynamic contrast changes occur at individual semiconductor structures by targeted local charging and targeted local excitation of switching processes, which lead to a sudden change in capacitance in time and thus to charging of the semiconductor structure. For example, a first electron beam can scan the semiconductor structure several times in an imaging manner while scanning over the field region, while a further third electron beam triggers the switching process and changes (e.g. doubles) the capacitance of the semiconductor structure and in the process reduces (e.g. halves) the voltage. During the scanning of the field region of the semiconductor structure with the first electron beam, the image contrast of this semiconductor structure then changes suddenly by a relatively large absolute value; for example, the image contrast doubles due to the halving of the voltage. In contrast, during conventional voltage contrast imaging, the voltage contrast changes slowly and continuously due to the continuously increasing charging.

[0107] In an exemplary embodiment of dynamic voltage contrast imaging, for example, voltage contrast imaging or dynamic voltage contrast imaging using MSEM 1 is also repeated a number of times. In this way, it is possible to record a series of images over time. Further information about the temporal distribution or temporal variation of the voltage contrast is determined from this. For example, in a subsequent scan of a subsequent image, the connection achieved during the first scan using the MSEM can be interrupted again by a switching process, so that the voltage contrast is varied in a targeted manner over the individual image recordings of the image sequence.

[0108] By means of dynamic voltage contrast imaging, the basic structure of the semiconductor sample 60 can be inferred, and defects in the semiconductor structure of the semiconductor sample 60 can be inferred, for example, from the dynamic voltage contrast imaging using the MSEM 1. This is done, for example, by comparing voltage contrast imaging using the MSEM on a reference sample with the sample to be tested and deciding on possible defects based on the differences with respect to the reference images, or by comparing voltage contrast imaging using the MSEM with measurement simulations of CAD data of the semiconductor sample, or by comparing dynamic voltage contrast imaging with conventional quasi-static voltage contrast imaging.

[0109] In this way, it is therefore also possible to carry out functional tests of integrated semiconductor components in semiconductor samples. In one specific embodiment, the capacitance of the semiconductor structure is determined from a voltage comparison curve that varies over time by continuous, cumulative charging of the semiconductor structure. Smaller capacitances can be charged faster and larger voltage differences can be obtained faster than relatively larger capacitances. In another specific embodiment, the semiconductor structure can be switchable and the switching process can be achieved, for example, by targeted charging of the gate electrodes of the transistors and at the same time a change in the voltage difference at the subsequently connected or interrupted semiconductor structure can be observed. Targeted charging of the gate electrode of the source follower transistor and the simultaneous voltage comparison measurement further allow the characteristic curve of the source follower transistor to be approximately determined.

[0110] For example, with a single beam microscope from the prior art, the scanning direction is set so that the beam scans over two contact pads in a line, which are conductively connected in the semiconductor structure. As a result, the two contact pads are charged to a greater extent than if the semiconductor structure were positioned in different directions. In the prior art, this leads to differences in voltage contrast imaging due to the orientation of the semiconductor sample or the scanning direction. Using an MSEM with multiple electron beams arranged adjacent to each other in a grid configuration, this dependence on the scanning direction or sample orientation is largely eliminated, making the voltage contrast imaging largely isotropic, i.e., independent of direction.

[0111] For example, using a single beam microscope from the prior art, a semiconductor sample is scanned in a first image field of about 10 μm-20 μm in a first scan and in a further image field in a second scan, wherein the semiconductor sample is moved between the first scan and the second scan by a stage. The sample can discharge again in the time between the first scan and the second scan, resulting in a decay and thus in a corruption of the voltage contrast imaging. For example, the switching connection for dynamic voltage contrast imaging can be interrupted again. Using an MSEM with multiple electron beams arranged adjacent to each other in a grid configuration, larger image fields of 100 μm ... 200 μm or 500 μm can be obtained, so that unwanted longer discharge processes do not have an influence on the voltage contrast imaging. Discharge processes always occur, for example due to thermal effects, leakage or surface currents.

[0112] In the case of a large conductive semiconductor structure with many contact pads connected through the contact, a stronger charging effect is achieved with MSEM with many electron beams. Using larger image fields of MSEM up to hundreds of microns (eg up to 500 microns), fracture contacts in the semiconductor structure can be quickly identified before the charged semiconductor structure can be discharged again.

[0113] Another specific embodiment of the present invention provides a high-resolution microparticle multi-beam microscope for voltage contrast imaging of chargeable structures, wherein at least one characteristic of at least one first microparticle beam and at least one second microparticle beam of a microparticle beam grid configuration is realized differently, wherein the at least one characteristic can be, for example, beam current, beam spacing, beam diameter, focus position or beam shape. In this case, the at least one characteristic of the microparticle beam is considered to represent a characteristic of the microparticle beam in an image plane or object plane 11, in which a sample with a chargeable structure can be arranged.

[0114] The predefined aperture plate produces a spatially suitable particle beam grille configuration in the image plane or object plane 11 , which is suitable for simultaneous charging and voltage contrast imaging. In a specific embodiment, the predefined aperture plate has holes of different diameters or opening areas for generating different particle beam currents. Figure 5a An example of this specific embodiment is described. In this specific embodiment, the grid configuration 4 of the particle multi-beam microscope (eg, MSEM 1) is suitable for voltage contrast imaging. In this case, a predefined aperture plate APA and a selective multi-beam aperture ("shade plate") are designed for different individual beam currents and spacings, wherein Figure 5a A plan view of a predefined aperture plate APA is shown.

[0115] The aperture plate APA has twelve first large holes in the outer region for a first microparticle beam having a large beam current for charging (a large aperture opening 73 is indicated by way of example). The aperture plate APA has sixteen second small holes in the inner region for a second microparticle beam having a small beam current for high-resolution imaging (a small aperture opening 72 is indicated by way of example). In this case, in the microparticle beam grid configuration, the distance between the first aperture opening having a larger opening area and the second aperture opening having a smaller opening area than the first aperture opening is variable. In this specific embodiment of the aperture plate APA for a microparticle multi-beam microscope, a semiconductor sample is charged by a first plurality of first microparticle beams having a large beam current, and a high-resolution voltage contrast image is generated by a second plurality of second microparticle beams. Therefore, a microscope for performing voltage contrast imaging on a semiconductor sample is provided, which uses a microparticle multi-beam microscope having a plurality of individual microparticle beams in a grid configuration, wherein the microscope is designed to scan a semiconductor sample having at least one semiconductor structure by a plurality of individual microparticle beams in a scanning manner. In this case, a voltage contrast is determined at at least one semiconductor structure of the semiconductor sample using a second number of second microbeams of the microbeam microscope, and the semiconductor sample is charged using a first number of first microbeams of the microbeam microscope. In a specific embodiment, at least one first microbeam of the first number of first microbeams is not included in the second number of second microbeams, or at least one second microbeam of the second number of second microbeams is not included in the first number of first microbeams. The microbeam microscope can remain unchanged for charging and determining the voltage contrast, and the individual microbeam currents of the first and second microbeams can remain unchanged and different.

[0116] Figure 5a The lower half shows the cross-section of the APA through the aperture plate configuration along line AB. The aperture plate is arranged next to the aperture opening (by examples 73 and 72) with a microlens array 320 which in an exemplary embodiment may be implemented only in the direction of the light beam downstream of the small aperture opening 72 . Regarding microlens arrays, refer to Figure 1b The BP (shadow plate) is selectively provided downstream in the beam direction and allows the focal point of the electron or particle beam focused by the microlens array 320 to pass through.

[0117] The apertures of the second plurality of second particle beams for high-resolution mode have, for example, a small aperture diameter between 10-50 μm and a spacing of 30-250 μm. Thus, a transmittance of 4-10% is achieved, which corresponds to a low beam current. Further optimization makes it possible to achieve a transmittance of up to 19% in high-resolution mode. Using a large aperture diameter (e.g., 55 μm to 75 μm) of the first plurality of first particle beams or high-current beams, a transmittance greater than 25% (e.g., 30% or 50%) is achieved. Through different apertures, it is possible to set different beam currents between different beams, wherein it is possible to achieve different ratios of beam currents relative to each other in the range of 2-10 times. However, spherical aberration increases with increasing aperture diameter, about the third power relative to the aperture diameter. A second aperture having only a lower transmittance of less than 20% and therefore a smaller beam current is suitable for a high-resolution mode with a resolution in the range of several nanometers or less.

[0118] Figure 5b The cross-section through the predefined aperture plate APA is shown. From the incident direction 74 , the focused particle beam 75 (eg, electron beam 38 in FIG. 1 ) is incident on the aperture plate APA with the second small opening 76 and the first large opening 77 . A microlens for focusing the passing first and second micrometal beams 79 and 78 (see About Figure 1b The multi-beam aperture BP is selectively configured on the focal plane 81. Figure 5a The plurality of particle beams in the grid configuration further propagate in direction 80 . Next, the focus in the focal plane is imaged into the object plane 11 of the particle beam microscope by the downstream particulate beam optical unit according to FIG. 1 .

[0119] When large openings and small openings are alternately arranged in the aperture plate APA, such as Figure 5b As shown, microlens or other fine focusing optical units of the focusing array may be implemented identically for the first particle beam 79 and the second particle beam 78 , such as having the same diameter. However, it is also possible to design collimating optical units differently for the first particle beam 79 and the second particle beam 78 .

[0120] like Figure 5c As shown, for example, the aperture plate configuration APA of MSEM may also have a large number of first (large) aperture openings 73.1, especially greater than the number of second (small) aperture openings 72.1 for high resolution imaging. This ensures an especially large additional particle current for charging the sample for voltage contrast imaging.

[0121] The different aperture openings of the aperture plate configuration APA according to the invention, in addition to having different opening areas for producing a spatially adapted particle beam grid configuration in the image plane or object plane 11, may also have a further adaptation of the aperture opening of the aperture plate configuration APA, which takes into account, for example, lens aberrations of a downstream imaging system of the particle beam. Such a further adaptation of the aperture opening of the aperture plate configuration APA is described, for example, in WO 2005 / 024881 (in particular FIGS. 14 , 15 and 18 ), which is hereby fully incorporated herein. What can be achieved by this adaptation of the aperture opening of the aperture plate configuration APA is that the formation of the second particle beams with a beamlet current for high-resolution imaging in the image plane or object plane 11 of the MSEM is substantially identical, and that each first particle beam for voltage contrast imaging obtains approximately the same high resolution of, for example, 2 nm during voltage contrast imaging, which is achieved by the fact that the appropriate aperture opening of the aperture plate configuration APA takes into account field-related lens aberrations, for example, astigmatism or field curvature of the downstream imaging system for each particle beam. The adaptation of the aperture openings of the aperture plate configuration APA may further include a small displacement of the aperture openings to compensate for distortion aberrations of the downstream imaging system for each particle beam and to ensure a uniform, equidistant configuration of the individual particle beams in the image plane 11 for voltage comparison imaging.

[0122] Figure 6 A further grid configuration 4 is shown based on a predefined aperture plate APA with small and large holes, wherein the assigned image field segments are in each case swept by the electron beam generated by each hole during the scan in the object plane and are covered by the common scanning of a plurality of particle beams. A small aperture opening 72 shapes a second particle beam, wherein a second image segment 82 is assigned to the second particle beam. Another larger aperture opening 73 shapes a first particle beam, wherein a first image segment 83 is assigned to the first particle beam. Image segments 82 and 83 and all other image segments assigned to other particle beams of the particle beam grid configuration are at least partially scanned in mid-air by a scanning unit of the particle beam microscope.

[0123] Thus, by means of the predefined aperture plate APA, it is possible to image individual second image field segments in the object plane with high resolution using the second microparticle beam and to charge the semiconductor sample with the first microparticle beam having a higher microparticle current in other first image field segments. For this purpose, the predefined aperture plate has at least one first larger hole for charging the semiconductor structure at a first image field segment conjugate to the at least one first larger hole, and has at least one second smaller hole for high resolution voltage contrast imaging of the semiconductor sample at a second image field segment conjugate to the at least one second smaller hole.

[0124] In a specific embodiment, the particle beam grid configuration is designed in such a way that the image field segments of the different individual particle beams overlap during scanning. Due to the overlap of the image field segments, the semiconductor sample is irradiated with a beam of particles at the overlapping position. An example of overlapping areas is Figure 6 87. The second image segment 85 is assigned to the smaller second aperture 84 and the first image segment 88 is assigned to the larger first aperture 87, wherein the two apertures 84 and 87 have a smaller spacing, which is in particular smaller than the scanning area of ​​the two electron beams passing through the apertures 84, 87 in the object plane. The assigned image field segments 85 and 88 thus form a large overlapping area 86. In this case, the overlapping area is in particular greater than 20% of the image field segment, for example greater than 50% of the image field segment. Before the second microparticle beam formed by the second aperture 84 reaches the overlapping area 86, the overlapping area 86 has already been precharged by the first microparticle beam formed by the first aperture 87. Thus, the semiconductor structure can be charged at at least one position by at least one first microparticle beam configured by the microparticle beam grid, and the semiconductor structure can be imaged at at least the same position by at least one second microparticle beam configured by the microparticle beam grid at a subsequent scanning position using voltage contrast.

[0125] As shown, in one example, the first and second apertures 72, 84 and 73, 87, in addition to having different extents and opening areas, may also have different shapes; in this regard, in particular, the second, larger aperture may also be hexagonal (not shown) or rectangular and thus produce different beam cross-sections or intensity distributions of particles or microparticles in the object plane. It may thus further be achieved that the focus of the first microparticle beam in the image plane of a microparticle multibeam microscope for charging a chargeable structure has a larger extent than the focus of the second microparticle beam in the image plane of a microparticle multibeam microscope for high-resolution voltage contrast imaging, for example.

[0126] Figure 7Another configuration of a predefined aperture plate APA is shown. The aperture plate 91 is followed by a grid arrangement of different fine focusing optical units 92 and a main focusing optical unit 93 (which consists of a number of electron optical lenses), which in each case jointly focus the electron beams 78, 95 and 96 passing through the aperture plate 91. In this example, no multi-beam diaphragm BP is arranged downstream of the aperture plate APA, but a multi-beam diaphragm BP with different diaphragm openings can be provided. The fine focusing optical unit 92 has a different focusing effect for each microparticle beam, so that, for example, the microparticle beam 78 for high-resolution imaging is focused in the focal plane 81 by the joint effect of the main focusing optical unit 93 and the fine focusing optical unit 92 with a medium focusing effect. In contrast, the fine focusing optical unit 92 has a stronger focusing effect for the microparticle beam 96, so that the microparticle beam 96 for regional charging with a large current and a large aperture is focused to a focal point upstream of the focal plane 81 and thus leads to regional charging of the semiconductor sample in the object plane of the MSEM 1, which is conjugate to the focal plane 81. Another microparticle beam 95 for local charging using high current is focused by the focusing effect of the main focusing optical unit 93 and the fine focusing optical unit 92 (which is weaker than the effect for the microparticle beam 78) to a focus which is only a certain distance downstream of the focal plane 81, and thus likewise results in regional charging of the semiconductor sample in the object plane of the MSEM 1, which is conjugate to the focal plane 81, wherein, however, the charging by the microparticle beam 95 is carried out over a smaller lateral range than the charging by the microparticle beam 96.

[0127] As described above, according to the present invention, different aperture openings of the aperture plate configuration APA and different focusing effects of the fine focusing optical unit for generating a spatially adapted microparticle beam grid configuration in the image plane or object plane 11 may have further adaptation of the aperture openings of the aperture plate configuration APA or the focusing effect of the fine focusing optical unit, which allows, for example, lens aberrations of a downstream imaging system of the microparticle beam. For example, different focusing effects of the fine focusing optical unit may be additionally included to allow for field curvature of a downstream imaging system of the microparticle beam.

[0128] With the particle multibeam microscope, it is possible to perform voltage contrast imaging without providing an additional electron beam gun for precharging the semiconductor sample or without switching the particle beam microscope from a precharging mode to a high-resolution mode. Voltage contrast imaging with the particle multibeam microscope is possible by means of a predefined aperture plate, which is adapted to a specific semiconductor sample. By exchanging the aperture plate APA, it is possible to adapt the particle multibeam microscope 1 to different semiconductor samples 60, without having to replace the particle multibeam microscope 1. For this purpose, a replacement unit can be provided for replacing the aperture plate APA in the particle multibeam microscope (see Figure 1a ).

[0129] In an alternative specific embodiment of the present invention, a semiconductor sample is disclosed, which includes a specific semiconductor structure for voltage contrast imaging, which is suitable for a microparticle multi-beam microscope with a predefined aperture plate APA. The specific semiconductor structure that produces the voltage contrast image can be a functional semiconductor structure or a semiconductor structure introduced into an integrated semiconductor only for the purpose of process monitoring and representative functional monitoring of the semiconductor. These semiconductor structures (also called test structures) are also called process control monitors (PCM) in English. The specific semiconductor structure design enables charging and voltage contrast imaging to be achieved in a targeted manner and simultaneously through multiple microparticle beams from a microparticle beam grid configuration.

[0130] For this purpose, a particular semiconductor structure is configured to have a spacing and range suitable for a predefined particle beam spacing, or a semiconductor structure is designed such that it extends in a bifurcated manner in at least one direction, thereby charging by a plurality of at least two individual particle beams. Furthermore, the test structure may be constructed from a plurality of semiconductor structures forming a switching element (eg, transistor).

[0131] exist Figure 8 A specific exemplary embodiment of a semiconductor structure constructed for voltage contrast imaging using a microparticle multibeam microscope is set forth in the accompanying drawings. The semiconductor structure in a semiconductor sample for simultaneous charge and voltage contrast imaging using a microparticle multibeam microscope comprises near-surface elements that are suitable for beam spacing of at least two microparticle beams of the microparticle multibeam microscope. Typical beam spacings are in the range of 5 μm–12 μm; embodiments with beam spacings of 100 μm or up to 200 μm are possible.

[0132] Figure 8 A semiconductor structure is shown for detecting small lateral errors in the layer construction of a semiconductor structure. Such lateral errors are also called overlay errors. The overlay accuracy or overlay requirements for semiconductor layers are in the range of a fraction of the minimum structure dimension or CD ("critical dimension"). For the lowest layers of integrated semiconductors, the minimum structure dimension is currently about 5 nm, and the minimum structure dimension foreseeable in the near future is 3 nm or less. Therefore, the overlay accuracy between such a layer and the adjacent layer is less than 2 nm, and in the near future less than 1 nm.

[0133] Therefore, in order to measure small overlay accuracies of less than 2 nm, the specific test structure is configured such that small lateral errors of less than 2 nm result in interruption of the conductive contact.

[0134] Figure 8A specific semiconductor structure 100 is shown, which can be used for non-destructive testing of an overlay error of less than 2 nm using voltage contrast imaging with a microparticle multibeam microscope 1. To this end, the semiconductor structure 100 is configured so that it is charged with a first microparticle beam via a first near-surface structure 106. The first microparticle beam is shown in a simplified manner at a first scanning position 110 and a second scanning position 112. The first near-surface structure 106 is conductively connected to a structure 105 located deeper in the semiconductor sample. In this example, the deeper structure 105 is located in the (l+1)th layer 103. To this end, the first near-surface structure 106 is implemented in a larger manner so that a large part of the first scanning path 114 or an image field segment of the first microparticle beam overlaps the structure 106. The semiconductor structure 100 further has a smaller second near-surface structure 107. The second microparticle beam is shown in a simplified manner at a first scanning position 111 and a second scanning position 113. The second microparticle beam only scans the smaller second near-surface structure 107 with a second scanning path 115 at the end of the common scanning of the two microparticle beams, i.e. at the second scanning position 113. The small second near-surface structure 107 is conductively connected to a deeper structure 104 in a layer adjacent to the (l+1)th layer 103 (hereinafter, the first layer 102). In this case, the structures 104 and 105 are arranged so that they form a contact area 108 in the overlapping area in the interface 109 between the first layer 102 and the (l+1)th layer 103, whose extent Dx in at least one direction is less than the allowable overlap error in this direction. This is based on Figure 8 The cross-sectional view in the plane 109 of the lower half is illustrated. For example, the range Dx can be less than 2 nm or less than 1 nm. A semiconductor structure 100 with an electrically conductive connection is formed by the contact region. By means of a parallel scanning process, the structure 100 is charged by the first particle beam 110, 112 during a first scanning path 114, so that the second particle beam records a voltage contrast change at a second scanning point 113, and thus the connected structure 100 can be deduced. If there is an overlay error greater than Dx in the x-direction between the first layer 102 and the (l+1)th layer 103, so that, for example, the first layer 102 is displaced in the negative x-direction and / or the (l+1)th layer 103 is displaced in the positive x-direction, the contact region is interrupted and the second particle beam cannot record a voltage contrast change at the second scanning point 113. A second mirrored semiconductor structure can be provided for the overlay error in the opposite displacement directions of the two layers 102, 103. The semiconductor structure for the overlay error in the y-direction can be similarly implemented in a manner rotated by 90° or by a specific embodiment of the contact region 108 having an overlap region Dy in the y-direction, such as Figure 8As shown. With this particular semiconductor structure 100, the overlap region between two layers in an integrated semiconductor can therefore be determined non-destructively by voltage contrast imaging with a microparticle multibeam microscope. These test structures have an overlap region between two semiconductor layers and can form a contact region whose extent Dx and / or Dy is on the order of a fraction of CD, for example less than 2 nm or less than 1 nm.

[0135] In the present application, the MSEM 1 or the electron beam of the electron beam grid configuration is used as a representative of the microparticle multi-beam microscope, and in the specific embodiment of the MSEM, it is not intended to limit electrons as microparticle particles or electron beam microscopes. Microparticle particles can generally be charged particles, such as electrons, metal ions (such as gallium ions), or ions of noble gases (such as helium or neon).

[0136] In the examples, voltage contrast imaging is explained in a simplified manner for the case where the image contrast at the semiconductor structure decreases with increasing voltage. However, depending on the choice of the position in the so-called "yield curve" of the secondary microparticle particles, it is possible that the image contrast at the semiconductor structure increases with increasing voltage. However, the increase in image contrast with increasing voltage allows voltage contrast imaging according to the invention to be performed in a completely analogous manner and is covered by the exemplary embodiments.

[0137] In the example shown in particular in Figure 1, a MSEM 1 is schematically shown with individual beam splitters or lenses associated with beam optics, such as collimating lenses, objective lenses, field lenses. For a person skilled in the art, it is of course a simplification of this diagram and that the beam splitters or lenses associated with the beam optics may be formed by a plurality of electromagnetic elements.

[0138] Another aspect of voltage contrast imaging in combination with simultaneous charging with a microparticle multibeam microscope is the increased throughput of the microparticle multibeam microscope compared to a single beam microscope. The number of microparticle beams is many times higher than in a single beam microscope (such as a SEM), for example 100 times, 1000 times or 10000 times higher. Using a large number of individual microparticle beams that are configured in a grid configuration and swept together over the semiconductor sample in a joint scanning process, a very high throughput can be achieved, i.e., voltage contrast images of a semiconductor sample of a large area are captured per unit time. In the case of cumulative charging by multiple microparticle beams, it is not necessary to switch the microparticle multibeam microscope, and there is high-resolution voltage contrast imaging with a resolution better than 30 nm or even better than 5 nm and an output of more than 3.5 square millimeters / minute. In particular, using replaceable or predefined aperture plates or on predefined semiconductor structures, this allows fast process monitoring, for example determining overlay errors in semiconductor samples.

[0139] The drawings of semiconductor structures are schematic and more simplified. However, based on the drawings and descriptions of the above examples, a person skilled in the art can grasp the underlying concepts and explanations and apply them to a real semiconductor and a real particle beam microscope, respectively, through routine actions.

[0140] In an exemplary embodiment, voltage contrast imaging using a microparticle multibeam microscope is explained based on the example of a semiconductor sample. In general, voltage contrast imaging using a microparticle multibeam microscope according to the present invention can be performed on any desired sample containing a chargeable structure. The example implemented on a semiconductor sample can be applied to any other sample. Such a sample can be a mineralogical sample, a biological sample, or a microscopic sample produced, for example, by 3D printing.

[0141] Furthermore, the exemplary embodiments should not be understood as isolated exemplary embodiments, but can also be combined in a convenient manner by a person skilled in the art; in this regard, for example, the exemplary embodiments according to Figure 8 The exemplary specific embodiment is similar to that according to FIG. 1 or FIG. 5 to Figure 7 Combination of exemplary embodiments.

[0142] Reference numerals list

[0143] 1 Particle Multibeam Microscopy Based on MSEM Example

[0144] 3 Electron beam

[0145] 4 Electron multi-beam grid configuration, referred to as grid configuration

[0146] 5 Electron beam focus

[0147] 9 Secondary electron beam

[0148] 10 Object Units

[0149] 11 Image plane or object plane

[0150] 12 Objective lens

[0151] 20 Detection Units

[0152] 23 Image plane

[0153] 25 Projection lens

[0154] 27 Detector

[0155] 29 Volume

[0156] 30 Electron multi-beam generator

[0157] 31 Electron beam source

[0158] 33. Collimating lens or collimating lens system

[0159] 37 Field lens or field lens system

[0160] 38 Parallel electron beam

[0161] 39 Divergent Electron Beam

[0162] 40 Beam Splitter

[0163] 42 Beam path from the electron multi-beam generating device 30 to the object unit 10

[0164] 43 Beam path from object unit 10 to detection unit 20

[0165] 45 Mechanical unit for replacing APA and BP

[0166] 50 Surface of substrate or wafer

[0167] 51 Semiconductor material silicon

[0168] 53 First semiconductor structure

[0169] 54.1-22 Multiple individual layers

[0170] 54.17 Selected Layers

[0171] 54.22 Doped Layers

[0172] 55 Conductive connection or through hole

[0173] 56 Semiconductor structures with large capacitance

[0174] 57 Conductive structure

[0175] 58 Fins or doped structures with low capacitance

[0176] 59 Semiconductor structure with intermediate capacitance

[0177] 60 semiconductor samples

[0178] 61.1, 61.2 Interaction zone

[0179] 62.1, 62.2, 62.3 First scanning positions of the nth, n+1th and n+2th electron beams

[0180] 63.1 The second scanning position of the nth electron beam

[0181] 64.1, 64.2 The third scanning position of the nth and n+1th electron beams

[0182] 65 Scan direction

[0183] 66 Gate

[0184] 67 Branched semiconductor structure

[0185] 68 Other semiconductor structures

[0186] 69 Other semiconductor structures

[0187] 70 Other semiconductor structures

[0188] 72 Small aperture opening

[0189] 73 Large aperture opening

[0190] 74 The incident direction of the incident particle beam

[0191] 75 Incident focused microparticle beam

[0192] 76 Small opening

[0193] 77 Large aperture opening

[0194] 78 Particle beam with small beam current

[0195] 79 Particle beam with high beam current

[0196] 80 Direction of individual particle beams in the particle beam grid configuration 81 focal plane

[0197] 82 Image field segment about hole 72

[0198] 83 Image field segment about hole 73

[0199] 84 Additional small holes

[0200] 85 Image segment about hole 84

[0201] 86 Overlapping Area

[0202] 87 Another large hole

[0203] 88 Image segment about hole 87

[0204] 91 Aperture Plate

[0205] 92 Fine Focus Optical Unit

[0206] 93 Focusing Array

[0207] 94 Microparticle beams for high-resolution imaging

[0208] 95 Microparticle beams with local charging at high current

[0209] 96 Microparticle beams with localized charging at high currents 100 Semiconductor structures for measuring overlay error 101 Surface

[0210] 102nd floor 1103 Layer 1 I+1

[0211] 104 Structure in Layer 1

[0212] 105 Structure in layer l+1

[0213] 106 First Near-Surface Structure

[0214] 107 Second Near-Surface Structure

[0215] 108 contact area

[0216] 109 Interface between layer 1 and layer l+1

[0217] 110 First particle beam at first scanning position

[0218] 111 The second particle beam at the first scanning position

[0219] 112 First particle beam at second scanning position

[0220] 113 The second particle beam at the second scanning position

[0221] 114 First scanning path

[0222] 115 Second scanning path

[0223] 200 Substrate S or sample

[0224] 203 Primary electron beam

[0225] 205 Focus of individual beam 203 in image plane 211

[0226] 209 Secondary Electron Beam

[0227] 211 Image plane

[0228] 212 Electron Optical Imaging Lens

[0229] 223 Detector plane

[0230] 225 Electron Optical Imaging Lens

[0231] 231 Electron beam source

[0232] 233 Electron Optical Converging Lens

[0233] 237 Electron optical imaging lens or field lens

[0234] 238 Collimated electron beam

[0235] 239 Divergent Electron Beam

[0236] 240 Beam Splitter

[0237] 242 Primary electron beam

[0238] 276 Electron beam focus in the opening of the shielding plate BP

[0239] 280 Sample holder, e.g. wafer chuck

[0240] 281 Mobile Station

[0241] 291 Aperture Plate

[0242] 292 Aperture opening of aperture plate

[0243] 294 Microlens Array

[0244] 295 Focal plane of microlens array 294

[0245] 320 Microlens Array

Claims

1. A method of voltage contrast imaging using a microparticle multibeam microscope (1) having a plurality of individual microparticle beams (3) in a grid configuration (4), comprising: a. scanning the plurality of individual particle beams (3) over a sample (60) having at least one chargeable structure (53, 56, 59, 67, 68, 69, 70, 100) in a scanning manner, b. charging the sample (60) with a first number of first particle beams (3) of the particle multi-beam microscope (1), c. determining a voltage contrast at the at least one chargeable structure (53, 56, 59, 67, 68, 69, 70, 100) of the sample (60) using a second number of second particle beams (3) of the particle multibeam microscope (1), in, The charging in step b and the determining of the voltage contrast in step c are performed simultaneously, and Wherein, the microparticle multi-beam microscope comprises an aperture plate configured to generate a plurality of microparticle beams; The first number of first beams of first particles differs from the second number of second beams of second particles in at least one characteristic; and The aperture plate includes at least one member selected from the group consisting of: different aperture openings, different focusing by a fine focusing optical unit, and a focusing array.

2. The method of claim 1, wherein the method is performed on a semiconductor sample (60).

3. The method of claim 1, wherein at least one first microparticle beam (3) of the first number of first microparticle beams (3) is not contained in the second number of second microparticle beams, or at least one second microparticle beam (3) of the second number of second microparticle beams (3) is not contained in the first number of first microparticle beams (3).

4. The method according to any one of claims 1 to 3, wherein the first number of first micro-particle beams (3) comprises at least one first micro-particle beam (3).

5. The method according to any one of claims 1 to 3, wherein the second number of second micro-particle beams (3) comprises at least one second micro-particle beam (3).

6. A method as described in any one of claims 1-3, wherein in the process of charging the sample (60) with at least one first particle beam (3) of the first number of first particle beams (3), the at least one chargeable structure (53, 56, 59, 67, 68, 69, 70, 100) is charged in a targeted manner in a spatially resolved manner.

7. A method as described in any one of claims 1 to 3, wherein the first number of first particle beams (3) includes at least two first particle beams (3), wherein the at least two first particle beams (3) each have a first particle current, and the added total current formed by the sum of the at least two first particle currents generates a cumulative charge, thereby generating a voltage difference in the chargeable structure (53, 56, 59, 67, 68, 69, 70, 100).

8. A method as claimed in claim 7, wherein the particle current of the second particle beam used to determine the voltage contrast at the sample (60) is less than the added total current of the first number of first particle beams (3), so that the accumulated charge of the chargeable structure (53, 56, 59, 67, 68, 69, 70, 100) remains essentially unchanged due to the particle current of the second particle beam.

9. A method as described in any one of claims 1-3, wherein the charging in step b and the determination of the voltage contrast in step c are performed under the same settings of the particle multi-beam microscope (1), and the individual particle currents of the first and second particle beams (3) remain essentially unchanged in steps b and c.

10. The method of any one of claims 1-3, wherein the charging in step b and the determining of the voltage contrast in step c are performed simultaneously in step (1a) in a scanning manner while scanning across the sample.

11. A method as described in any one of claims 1 to 3, wherein the charging in step 1b is performed with a first microparticle beam (3) at at least one first scanning position (62.1, 62.2, 110, 111), and the determining of the voltage contrast in step 1c is performed with a second microparticle beam (3) at at least one second scanning position (63.1, 64.1, 111, 113) different from the first scanning position.

12. The method according to any one of claims 1 to 3, wherein at least one of the first number of first micro-particle beams (3) is identical to at least one of the second number of second micro-particle beams (3).

13. The method according to any one of claims 1 to 3, further comprising: d. Using a third particle beam (3) of a third number of the particle multi-beam microscope (1) to switch the capacitance of the structure (53, 56, 59, 67, 68, 69, 70, 100) of the sample (60), and generating a dynamic change in the voltage contrast during the process of determining the voltage contrast in step 1c.

14. The method of any one of claims 1-3, wherein the structure (53, 56, 59, 67, 68, 69, 70, 100) is configured to perform the voltage contrast imaging using the grid configuration (4) of the particle beam microscope (1).

15. The method of any one of claims 1-3, wherein the sample is a semiconductor sample and the chargeable structure is a semiconductor structure.

16. A particle multi-beam microscope (1) for performing voltage contrast imaging on a semiconductor sample, comprising at least one first predefined aperture plate (APA, APA1) for generating a plurality of particle beams (3) arranged in a grid configuration (4) in an image plane (11) of the particle multi-beam microscope (1), wherein the predefined aperture plate (APA, APA1) is configured to generate at least one first particle beam to image a semiconductor structure (53, 56, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 91, 99, 91, 99, 91, 99, 91, 99, 91, 99, 99, 90 ... 67, 68, 69, 70, 100) are cumulatively charged, and at least one second microparticle beam is generated to perform voltage contrast imaging on the semiconductor structure (53, 56, 59, 67, 68, 69, 70, 100) configured in the image plane (11) of the microparticle multi-beam microscope (1), and in the image plane (11) of the microparticle multi-beam microscope (1), the at least one first microparticle beam is different from the at least one second microparticle beam in at least one characteristic, wherein the charging and the voltage contrast imaging are performed simultaneously.

17. The particle multi-beam microscope (1) of claim 16, wherein the at least one characteristic comprises beam current, beam spacing, beam focus or beam shape.

18. A particle multi-beam microscope (1) as described in claim 16 or 17, wherein the at least one predefined aperture plate (APA, APA1) comprises: different aperture openings (72, 73, 84, 87) or different focusing and / or focusing arrays (93) through a fine focusing optical unit (92).

19. The particle multi-beam microscope (1) as claimed in claim 16 or 17, wherein the at least one predefined aperture plate (APA, APA1) is suitable for the voltage contrast imaging on a semiconductor sample (60).

20. The particle multi-beam microscope (1) according to claim 16 or 17, wherein the at least one predefined aperture plate (APA, APA1) is exchangeable.

21. A semiconductor structure in a semiconductor sample, for simultaneous charging and voltage contrast imaging using a particle multibeam microscope (1), wherein the semiconductor structure comprises a near-surface element adapted for the beam spacing of at least two particle beams of the particle multibeam microscope (1).

22. The semiconductor structure of claim 21, wherein at least two of the near-surface elements have a spacing between 5 μm and 12 μm.

23. A semiconductor structure as described in claim 21 or 22, wherein a first near-surface element and a second near-surface element are arranged at a distance from each other, the first near-surface element is conductively connected to a first conductive conductor track in a deeper first layer, and the second near-surface element is conductively connected to a second conductive conductor track in a deeper second layer, wherein the first layer and the second layer are continuous layers in the construction of the semiconductor structure, and wherein the first conductor track and the second conductor track have an overlap that is less than an overlap error that can be allowed by the semiconductor structure. The semiconductor structure of claim 23 , wherein the overlap is less than 2 nm.

Images