WO2025237883A1

WO2025237883A1 - Architecture of charged particle beam system for inline-semiconductor applications

Info

Publication number: WO2025237883A1
Application number: PCT/EP2025/062869
Authority: WO
Inventors: Dirk Zeidler; Erik Loopstra
Original assignee: Carl Zeiss SMT GmbH; Carl Zeiss Multisem GmbH
Current assignee: Carl Zeiss SMT GmbH; Carl Zeiss Multisem GmbH
Priority date: 2024-05-13
Filing date: 2025-05-12
Publication date: 2025-11-20
Anticipated expiration: 2026-11-13

Abstract

An improved architecture of wafer inspection system with high stability comprises a charged particle beam column and a wafer stage, both mounted to a baseplate in a vacuum enclosure. The charged particle beam column is attached to a baseplate via at least one damping system. Thereby, disturbances such as vibrations are reduced to a minimum and high precision measurements can be obtained even for long measurement times.

Description

Title

Architecture of charged particle beam system for inlinesemiconductor applications

Field

The present invention relates to an inspection apparatus for semiconductor wafers in a fabrication environment utilizing a charged particle beam system. With the architecture of the inspection apparatus, a nanometer precision is provided. The inspection apparatus can be utilized for various inspection tasks, such as quantitative metrology, defect detection, process monitoring, or defect review of integrated circuits within a semiconductor wafer fabrication environment.

Background

Semiconductor structures are amongst the finest man-made structures. Semiconductor manufacturing involves precise manipulation, e.g., lithography or etching, of materials such as silicon or silicon oxide at very fine scales in the range of nm. A wafer made of a thin slice of silicon serves as the substrate for microelectronic devices containing semiconductor structures built in and upon the wafer. The semiconductor structures are constructed layer by layer using repeated processing steps that involve repeated chemical, mechanical, thermal and optical processes. Dimensions, shapes and placements of the semiconductor structures and patters are subject to several influences. For example, during the manufacturing of 3D- memory devices, the critical processes are currently etching and deposition. Other involved process steps such as the lithography exposure or implantation also can have an impact on the properties of the elements of the integrated circuits. Fabricated semiconductor structures suffer from rare and different imperfections. Devices for quantitative metrology, defect- detection or defect review are looking for these imperfections. Semiconductor structures are fabricated by determined processes and are based on prior knowledge. The semiconductor structures are manufactured in a sequence of layers being parallel to a surface of a substrate. For example, in a logic type sample, metal lines are running parallel in metal layers or, in a memory device, HAR (high aspect ratio) structures and metal vias run perpendicular to the metal layers. The angle between metal lines in different layers is either 0° or 90°. On the other hand, for VNAND type structures it is known that their cross-sections are circular on average. Furthermore, a semiconductor wafer has a diameter of 300 mm and consist of a plurality of several sites, so called dies, each comprising at least one integrated circuit pattern such as for example of a memory chip or of a processor chip. During fabrication, semiconductor wafers run through 1000 or more process steps, and within the semiconductor wafer, about 100 and more parallel layers are formed, comprising the transistor layers, the layers of the middle of the line, and the interconnect layers and, in memory devices, a plurality of 3D arrays of memory cells.

The aspect ratio and the number of layers of integrated circuits constantly increases and the structures are growing into 3^rd (vertical) dimension. The current height of the memory stacks is exceeding a dozen of micrometers. In contrast, the minimum features size is becoming smaller. The minimum feature size or critical dimension is below 10nm, for example 7nm or 5nm, and is approaching feature sizes about and below 3nm in near future. The overlay requirements can even be more demanding and be below 1nm. Therefore, precision requirements for wafer inspection are already very demanding and will even be increasing in near future.

The high resolution can only be reached by charged particle beam imaging systems.

However, charged particle beam systems are susceptible to vibrations and noise of various kind. For example, in some wafer inspection systems, a wafer is moved such that different preselected inspection sites are subsequentially arranged at the line of sight of a charged particle imaging tool. During a precision measurement with requirements of 1 nm or even less, for example, the wafer is not moved, and a charged particle beam is scanned over a small segment of the surface of the wafer to generate an inspection image for the measurement task. During a measurement task, a scanning image is acquired with a measurement time which can easily reach about one second. During this long measurement time, relative positions between wafer surface and line of sight of the charged particle beam system must be known and controlled within a large frequency range. Any dynamic change of the relative positions between wafer surface and line of sight of the charged particle beam system cause a deterioration of the inspection result.

It is a task of the invention to improve a wafer inspection apparatus and to enable a high- resolution measurement during long measurement times. It is a task of the invention to provide a wafer inspection apparatus which is capable to minimize any dynamic changes of the relative positions between wafer surface and line of sight of the charged particle beam system. It is a further task of the invention to provide a wafer inspection apparatus which is capable to precisely measure any dynamic changes of the relative positions between wafer surface and line of sight of the charged particle beam system. It is a further task of the invention to provide a system architecture of a wafer inspection apparatus which is capable to precisely control dynamic changes of a wafer inspection apparatus within a semiconductor fabrication environment.

Summary

The objects of the invention are solved by the embodiments and examples below.

According to an embodiment, a wafer inspection system is comprising a baseplate configured for being disposed on a floor in a fabrication environment. A wafer inspection system is comprising a stage with a wafer chuck for holding during use a wafer and for positioning an inspection site on a surface of the wafer at a line of sight of a charged particle beam column. The stage is directly connected to the baseplate, for example via a support base of the stage. A wafer inspection system according to the embodiment is further comprising a rigid frame for supporting the charged particle beam column. The rigid frame is connected to the baseplate via at least one damping system. In an example, the stage, the rigid frame and the charged particle beam column are arranged within a vacuum enclosure. Thereby, any transfer of noise to the stage or rigid frame or charged particle beam column is reduced. In an example, the baseplate is formed as an integral part of the vacuum enclosure. In an example, the rigid frame forms a part of the vacuum enclosure.

In an example, a wafer inspection system is comprising an active control system configured for active controlling the at least one damping system. In an example, a wafer inspection system is comprising a first position measurement system configured for performing a position measurement between the rigid frame and the stage or wafer chuck. The position measurement signal of the first position measurement system between the rigid frame and the stage or wafer chuck is received and analyzed by the active control system. Active control system is then configured to generate and provide a drive signal to the at least one damping system. Thereby, an active control of the relative position between rigid frame and stage or wafer chuck is achieved. The active control can be performed with a control frequency of up to e.g. 50% of the lowest Eigenfrequency of the rigid frame, for example up to 20 Hz, or up to 50Hz.

A wafer inspection system of an example is further comprising a control unit for controlling the charged particle beam column. The control unit is in communication with the active control system. The control unit is configured to compensate a residual change of a position of the inspection site relative to a position of the stage by providing a compensation signal to a deflection scanner of the charged particle beam column. Thereby, a drift in the relative position is compensated. Thereby, any change in the relative position between rigid frame and stage or wafer chuck is compensated with higher frequencies above the control frequency of 20Hz or 50Hz of the at least one damping system.

A wafer inspection system of an example is further comprising a focused ion beam column arranged at an angle GFE to the charged particle beam column. The focused ion beam column is supported by the rigid frame. The angle GFE can be between 35° and 90°. In another example, the charged particle beam column is a multi-beam charged particle beam system operating with a plurality of for example 100, 300, 1000 or more primary charged particle beamlets.

A wafer inspection system of an example is further comprising a support cabinet. The support cabinet is separately mounted to the floor. The support cabinet is comprising at least one vacuum pump connected to the vacuum enclosure via flexible bellows. The support cabinet can further by comprising the control unit for controlling the charged particle beam column, the active control system, a stage control unit, and an operation control unit for operating the wafer inspection system. By separately mounting components in a support cabinet onto the floor of the fabrication environment, any electronic noise or heat transfer to the separately mounted charged particle beam column is reduced.

In an example, the baseplate of the wafer inspection system is disposed on the floor via at least three mounting pedestals.

In an example, the wafer inspection system is further comprising a rigid mounting pedestal attached to the baseplate. The rigid mounting pedestal is configured for supporting the rigid frame via the damping systems such that the damping systems are arranged at a system level corresponding to a center of gravity of the charged particle beam column, or center of gravity of the rigid frame together with the charged particle beam column, respectively. In an example, the rigid frame comprises a frame protrusion for holding the first position measurement system at a system level of the stage or wafer chuck.

In an example, the wafer inspection system is comprising a metrology frame for holding a second position measurement system configured for performing a position measurement between the metrology frame and the stage. The metrology frame is further configured for holding a third position measurement system configured for performing a position measurement between the metrology frame and the charged particle beam column. Preferably, the metrology frame extends between a system level of the wafer stage and a level of at least the lower part of the charged particle beam column. Even more preferably, the metrology frame extends between a system level of the wafer stage and a level of center of gravity of the charged particle beam column, or center of gravity of the rigid frame together with the charged particle beam column, respectively. In an example, the metrology frame is mounted via a second damping or active mounting system to the baseplate.

While the examples and embodiments are described at the examples of semiconductor wafers, it is understood that the invention is not limited to semiconductor wafers but can for example also be applied to reticles or masks for semiconductor fabrication.

The invention described by examples and embodiments is not limited to the embodiments and examples but can be implemented by those skilled in the art by various combinations or modifications thereof. The present invention will be even more fully understood with reference to the following drawings:

Figure 1 shows an illustration of a wafer inspection or metrology system for 3D volume inspection with a dual beam device.

Figure 2 is an illustration of the slice-and image method of a volume inspection in a wafer. Figure 3 illustrates an example of a cross-section image, obtained by the slice-and image method

Figure 4 shows an illustration of a wafer inspection or metrology system using a multibeam charged particle beam system

Figure 5 shows examples of an improved architecture of a wafer inspection system Figure 6 illustrates a drift corrected pixel raster of a digital image

Throughout the figures and the description, same reference numbers are used to describe same features or components. The scanning frequency of the charged particle imaging beam is for example 80MHz, corresponding to typical dwell time at each individual pixel location of few ns, for example 12.5ns, 20ns, 30ns or 50ns. In the disclosure, the term drift is used as describing any temporal position displacement on time scales between few nanoseconds and several hours, thus drift is used to cover a range of frequencies below one Hertz up to the several MHz, corresponding to the frequencies below the scanning frequency, the measurement time for acquisition of one inspection image of for example 0.8s to 1s, or even more. High-frequent drifts are also called dynamic vibrations and are for example introduced due to noise. For example, a 3D inspection of an inspection volume within a wafer or a wafer sample may require several hours of slicing and imaging. For example, an acquisition of a representative high-resolution image segment of a wafer with a multi-beam charged particle beam system may still require one hour or more. During such long-time scales, noise levels may change, and for example thermal drift may deteriorate a measurement.

A first example of a charged particle beam device 1 of a wafer inspection system is illustrated in Figure 1. The wafer inspection system 1000 of this example is configured for a slice and imaging method under a wedge cut geometry with a charged particle beam device 1.

For the investigation of 3D inspection volumes in semiconductor wafers, the slice and imaging method has been introduced. A 3D volume image is generated from an inspection volume inside a wafer in a wedge-cut geometry, without the need of a removal of a sample piece from the wafer. The slice and image method is applied to an inspection volume with dimensions of few pm, for example with a lateral extension of 5pm to 10pm in wafers with diameters of 200mm or 300mm. The lateral extension can also be larger and reach up to 30 or 50 micrometers. A V-shaped groove or edge is milled in the top surface of an integrated semiconductor wafer 8 to make accessible a cross-section surface at an angle to the top surface 55. 3D volume images of inspection volumes are acquired at a limited number of inspection sites, for example representative sites of dies, for example at process control monitors (PCM), or at sites identified by other inspection tools. The slice and image method will destroy the wafer only locally, and other dies may still be used, or the wafer may still be used for further processing. The methods and inspection systems according to the 3D Volume image generation are described in WO 2021 1 180600 A1 , which is fully incorporated herein by reference. For a wafer 8, several inspection sites, comprising inspection sites 6.1 and 6.2, are defined in a location map or inspection list generated from an inspection tool or from design information. The wafer 8 is placed on a wafer support surface 15 of a wafer chuck 151. Wafer chucks 151 can for example hold a wafer 8 by electrostatic forces. The wafer chuck 151 is mounted on a stage 155 with actuators and position control. Actuators and means for precision control for a wafer stage such as Laser interferometers are known in the art. A control unit 16 is configured to control the wafer stage 155 and to adjust an inspection site 6.1 of the wafer 8 at the intersection point 43 of the charged particle beam device 1. The charged particle beam device 1 of this example is configured as a dual beam device and is comprising a FIB column 50 with a FIB optical axis 48 and a charged particle beam (CPB) imaging system 40 with optical axis 42. The focused ion beam column 50 is arranged at an angle GF to the surface of the wafer support surface 15 of the wafer stage 155. Therefore, during use, the wafer surface 55 is arranged at a slant angle GF to the FIB axis 48. During use, the wafer surface 55 is arranged at or close to the intersection point 43 of both optical axes of FIB and CPB imaging system. FIB axis 48 and CPB imaging system axis 42 include an angle GFE, and the CPB imaging system axis 42 forms an angle GE with the normal to the wafer support surface 15. In the coordinate system of figure 1 , the normal to the wafer support surface 15 is given by the z-axis. The focused ion beam (FIB) 51 is generated by the FIB-column 50 and is impinging under angle GF on the surface 55 of the wafer 8. Slanted cross-section surfaces are milled into the wafer by ion beam milling at the inspection site 6.1 under approximately the slant angle GF. In the example of figure 1 , the slant angle GF is approximately 30°. The actual slant angle of the slanted cross-section surface can deviate from the slant angle GF by up to 1° to 4° due to the beam divergency of the focused ion beam, for example a Gallium-lon beam. The FIB column 50 can for example be a Gallium FIB, or a FIB with a gas field ion source (GFIS) with other kinds of ion species, such as Xenon, Neon or Argon ions. With the charged particle beam imaging system 40, inclined under angle GE to the normal to the wafer support surface 15, images of the milled cross-section surfaces are acquired. In the example of Figure 1, the angle GE is about 15°. However, other arrangements are possible as well, for example with GE = GF, such that the CPB imaging system axis 42 is perpendicular to the FIB axis 48, or with GE = 0°, such that the CPB imaging system axis 42 is perpendicular to the wafer support surface 15.

During imaging, a beam of charged particles 44 is scanned by a scanning unit of the charged particle beam imaging system 40 along a scan path over a cross-section surface of the wafer 8 at inspection site 6.1 , and secondary particles as well as scattered particles are generated. For example, secondary electron particle detector 17.1 collects at least some of the secondary particles and scattered particles and communicates the particle count with a control unit 19. Other detectors for other of interaction products may be present as well, for example in-lens detector 17.2 for collection of backscattered charged particles. Control unit 19 is in control of the charged particle beam imaging column 40 and of the FIB column 50 and connected to a stage control unit 16 to control the position of the wafer 8 mounted on the wafer support surface15 via the wafer stage 155. Control unit 19 communicates with operation control unit 2, which triggers placement and alignment for example of inspection site 6.1 of the wafer 8 at the intersection point 43 via wafer stage movement and triggers repeatedly operations of FIB milling, image acquisition and stage movements. Each new intersection surface is milled by the FIB beam 51 , and imaged by the charged particle imaging beam 44, which is for example a scanning electron beam or a Helium-lon- beam of a Helium ion microscope (HIM). In an example, the dual beam system comprises a first focused ion beam system 50 arranged at a first angle GF1 and a second focused ion column arranged at the second angle GF2, and the wafer is rotated between milling at the first angle GF1 and the second angle GF2, while imaging is performed by the imaging charged particle beam column 40, which is for example arranged perpendicular to the wafer surface 55.

The dual beam system 1 further comprises a gas injection system (GIS) 79, with a gas nozzle connected via a valve (not shown) to at least one gas reservoir (not shown). Thereby, controlled amounts of precursor gases can be provided during milling or imaging, and for example metal coatings can be generated. For example, alignment marks or fiducials can be generated. For example, a Tungsten metal coating is generated by providing Tungsten Hexacarbonyl. The metal coating can be shaped by ion beam milling and alignment markers or fiducials are formed in proximity to an inspection site. Thereby, a precise registration and image alignment of the plurality of cross section images is enabled. With dedicated precursor gases, a milling operation by FIB 51 can be enhanced. For example, a homogeneity of a milling operation in compositions of different material can be improved and curtaining can be reduced. Compositions of materials in a semiconductor wafer can comprise Silicon, Silicon Dioxide, Silicon Nitride, Copper, Aluminum, Tungsten or other materials. Preferred precursor gases are comprising at least one of Ammonia, Ammonium Hydroxide, Ammonium Carbamate, Bromine, Chlorine, Hydrazine, Hydrogen Peroxide, Hadacidin, Iodine, di-iodo- ethane, Isopropanol, Methy Difluoroacetate, Nitroethane, Nitroethanol, Nitrogen, Nitrogen Tetroxide, Nitrogen Trifluoride, Nitromethane, Nitropropane, Nitrobutane, Oxygen, Ozone, PMCPS, Tungsten Hexacarbonyl, Water, or Xenon Difluoride. Other gases are, however, are possible as well, for example methoxy acetylchloride, methyl acetate, methyl nitroacetate, ethyl acetate, ethyl nitroacetate, propyl acetate, propyl nitroacetate, nitro ethyl acetate, methyl methoxyacetate, and methoxy acetylchloride, Acetic acid or thiolacetic acid, Hexafluoroacetylacetone, silazane, trifluoroacetamide, dicobalt octacarbonyl, molybdenum hexacarbonyl, and combinations thereof.

Furthermore, dual beam system 1 further comprises a contact pin 81. Contact pin 81 is connected to a manipulator (not shown) for precise movement of the contact pin 81, for example under control of the charged particle beam 44 during an image acquisition. Thereby, structures present on the wafer surface can be contacted and electrically connected to control device 19.

Figure 2 illustrates the wedge cut geometry at the example of a 3D-memory stack. Figure 2 illustrates the situation, when the surface 52 is the most recently milled cross-section surface which was milled by FIB 51. The cross-section surface 52 is scanned for example by scanning electron (SEM) beam 44, which is in the example of Figure 2 arranged at normal incidence to the wafer surface 55, and a high-resolution cross-section image slice is generated. The cross-section surfaces 53.1...53.N are subsequently milled with a FIB beam 51 at an angle GF of approximately 30° to the wafer surface 55, but other angles GF, for example between GF = 20° and GF = 60° are possible as well. The cross-section image slice comprises first cross-section image features, formed by intersections with high aspect ratio (HAR) structures or vias (for example first cross-section image features of HAR-structures 4.1 , 4.2, and 4.3) and second cross-section image features formed by intersections with layers L.1 ... L.M, which comprise for example SiO2, SiN- or Tungsten lines. Some of the lines are also called “word-lines”. The maximum number M of layers is typically more than fifty, for example more than one hundred or even more than two-hundred. The HAR- structures and layers extend throughout the inspection volume 160 in the wafer 8 but may comprise gaps. The HAR structures typically have diameters below 100nm, for example about 80nm, or for example 40nm. The cross-section image slices contain therefore first cross-section image features as intersections or cross-sections of the HAR structures at different depth (Z) at the respective XY-location. In case of vertical memory HAR structures of a cylindrical shape, the obtained first cross-sections image features are circular or elliptical structures at various depths determined by the locations of the structures on the sloped cross-section surface 52. The memory stack extends in the Z-direction perpendicular to the wafer surface 55. The thickness d or minimum distances d between two adjacent crosssection image slices is adjusted to values typically in the order of few nm, for example 30nm, 20nm, 10nm, 5nm, 4nm or even less. Once a layer of material of predetermined thickness d is removed with FIB, a next cross-section surface 53. i... 53. N is exposed and accessible for imaging with the charged particle imaging beam 44. During repeated milling and imaging, a plurality of cross sections is formed, and a plurality of cross section images are obtained, such that an inspection volume 160 of size LX x LY x LZ is properly sampled and for example a 3D volume image can be generated. Thereby, the damage to the wafer is limited to the inspection volume 160 plus a damaged volume in y-direction of length LYO. With an inspection depth LZ about 10pm, the additional damage volume in y-direction is typically limited to below 20pm.

Figure 3 shows an example of a cross-section image slice 311 generated by the imaging charged particle beam 44, corresponding to the cross-section surface 52. The cross-section image slice 311 comprises an edge line 315 between the slanted cross-section and the surface 55 of the wafer at the edge coordinate y1 . Right to the edge, the image slice 311 shows several cross-sections 307.1...307. S through the HAR structures which are intersected by the cross-section surface 52. In addition, the image slice 311 comprises crosssections of several word lines 313.1 to 313.3 at different depths or z-positions.

Each digital image of each cross-section surface comprises first cross-section features of HAR channels and second cross-section features of word lines at different depths. The depth of the word lines 313.1 to 313.3 is constant over large areas of a wafer. In an example, the word lines 313.1 to 313.3 are used as reference for a determination of the depth coordinate of a cross-section image slice 311. With the word lines 313.1 to 313.3, a depth map Z(x,y) of the slanted cross-section surface 52 can be generated. In another example, the distance to the edge line 315 is used for computation of the depth map Z(x,y). Thereby, for each pixel with transversal coordinates [x,y] according to the scanning operation of the charged particle imaging system 40, a depth coordinate according to the depth map Z(x,y) can be computed and high precision volume measurements are possible with the slice-and image-method in wedge-cut geometry. Examples and further details of image registration and depth map computation are provided in WO 2021 1 180600 A1 , cited above and incorporated herein by reference.

Further, after performing a segmentation and annotation of a cross-section image of a semiconductor object of interest, HAR channel cross sections are identified and properties of HAR channel cross sections are determined by machine learning methods. Examples are described in WO 2022/223229A1 and PCT/EP2022/082590, which are hereby incorporated by reference. During a wafer inspection task, for example diameters of HAR channels or relative positions of HAR channels with respect to each other are determined with sub-nm precision. Vibrations or noise, however, typically causes distortion during a scanning image acquisition, leading to incorrect measurement results.

Figure 4 illustrates a second example of a charged particle beam device 1. Here, the charged particle beam device 1 is given by a multi-beam charged particle beam system. A primary electron beam 309 is generated by an electron source 31 and condenser lenses 303. Within a multi-beam generating unit 305, multiple primary electron beamlets 3.1 to 3.3 are generated. Here, only three primary beamlets 3.1 to 3.3 are shown, but there can be many more primary beamlets, for example J = 91 , J = 331 beamlets or even more, for example J = 1000 beamlets arranged in hexagonal or cartesian raster. The multi-beam generating unit 305 for example comprises at least one multi-aperture plate. Other examples of multiple- beam formation comprise a photocathode and corresponding Laser illumination system to generate an array of primary electron beamlets. The plurality of primary electron beamlets is guided and focused by a sequence of electron optical elements, comprising electrode or electrostatic lens 331 , field lenses 333a and 333b and objective lens 33 to form a plurality of focus points 5.1 to 5.3 in the image plane 101 , where the surface of wafer 8 is arranged. A wafer voltage may be provided by wafer voltage supply 503 via wafer support surface 151 to the wafer 8. At the focus points 5.1 to 5.3, secondary or backscattered electrons (in the following jointly called “secondary electrons”) are emitted or extracted from the wafer surface. Secondary electron beamlets 9.1 to 9.3 are thus formed be objective lens 33 and guided via beam divider 400 to a detection unit 200. The detection unit 200 is comprising a sequence of electron-optical lenses 206, configured to form the focus points 215.1 to 215.3 on a spatially resolving electron detector 17. During image acquisition of an image patch with a diameter of 100pm or more by the plurality of primary beamlets 3, scanning deflector 29 jointly deflects each beamlet over a small segment of the image patch. A plurality of secondary electron signals is individually collected by electron detector 17 and a digital image of image patch is stitched together. Despite the larger image patches which can be acquired with a multibeam charged particle beam system, a high-resolution image acquisition of a larger part of a wafer surface may still require long time intervals of up to one hour or even more. Vibrations or noise typically causes distortion during the scanning image acquisition and are leading to incorrect measurement results.

According to the disclosure, an improved wafer inspection system is provided with a reduced sensitivity to vibrations or noise and therefore reduced distortions and improved imaging contrast. Figure 5a illustrates a first embodiment of an architecture of an improved wafer inspection system 1000. Same reference numbers are used as in the figures 1 and 4, and reference is also made to the description of the figures above. The wafer inspection system 1000 is installed in a fabrication environment for semiconductor wafer fabrication and installed on a fab floor 801. Fab floor 801 is very stuff and has a high mass. Vacuum enclosure 803 is installed at the fab floor 801 with a rigid mounting base or baseplate 807. Rigid mounting base or baseplate 807 is levelled and connected to floor 801 with a plurality of at least three mounting pedestals 831. The support base 809 of stage 155 is directly connected to the fab floor 801 via the rigid mounting baseplate 807. The stage 155 is movable in for example three, five or even six degrees of freedom and includes stage bearings 811. At least one charged particle beam device 1 is mounted and rigidly connected to a frame 25, which is arranged within the vacuum enclosure 803. The rigid frame 25 is connected to the baseplate 807 with damping system 813, for example active mounting pedestals 813. The charged particle beam device 1 and frame 25 are entirely enclosed by vacuum enclosure 803. Vacuum pumps 805 are in this example mounted within a separated support cabinet which is separately mounted to the fab floor 801. Thereby any vibrations from vacuum pumps 805 are separately transferred to fab floor 801. Vacuum pumps 805 can be connected to vacuum enclosure 803 by soft mounting, for example including flexible or soft bellows 63. Thereby, a transfer of noise from vacuum pumps 805 to vacuum enclosure 803 is minimized.

During use, any vibrations or dynamic forces generated by moving stage 155 is absorbed by the rigid fab floor 801 of very high mass. Due to energy conservation, vibrations transferred from stage 155 or any other sources of noise of the wafer inspection system 1000 to the fab floor 801 may only cause floor vibrations of very much reduced amplitude. The charged particle beam devices 1 and frame 25 are isolated from floor vibrations by damping system 813, such that a transfer of floor noise to frame 25 is highly reduced. Frame 25 serves as mechanical platform to support charged particle beam devices 1 and serves as metrology reference frame for measurement systems 21 for control of the position of the stage 155 with respect to for example the line of sight of imaging electron beam column 40. Such measurement systems 21 can for example comprise Laser interferometers with Laser beams 27 for measuring and controlling a distance between frame 25 and wafer chuck 151 , but other measurement systems 21 are possible as well, such as grating encoders, confocal operating lenses, or lens arrays ore the like. Only one measurement system 21 with Laser beam 27 is shown in figure 5a, but it is understood that there is more than one measurement system 21 , including at least one measurement system 21 for each degree of freedom of the stage 155. Frame 25 is construed with high mass and a lowest Eigenfrequencies of about 100Hz or more.

In an example, damping systems 813 comprise damping structures such as springs, high density elastic material or other passive noise absorbers capable of damping high frequent vibrations of the fab floor 801. In an example, damping systems 813 further comprises active damping systems. In an example, the wafer inspection system 1000 comprise an active position control system controlled by active control system 23. Active control system 23 receives position command by stage control unit 16 and position information by measurement systems 21. Active control system 23 is connected to drives within the damping system 813 to actively control position of an inspection site 6 on a wafer 8 mounted via wafer chuck 151 to stage 155 relative to the line of sight 36 of a charged particle beam device 1. Thereby, the relative position of the charged particle beam devices 1 supported by frame 25 is controlled with respect to the position of the wafer stage 155 or wafer chuck 151. Active position control can comprise a) active position control of the frame 25 by actuators within the active mounting pedestals 813; such position control can be performed up to a large fraction of the Eigenfrequency of the frame 25, for example up to 20Hz or 50Hz. b) position control by stage movements via actuators of the stage 155; such position control can be performed up to a large fraction of the Eigenfrequency of the stage 155, for example up to 50Hz or 100Hz. c) position control of the charged particle beam by e.g. beam deflection scanner 29 (see for example figure 4). Such position control can be performed up to the scanning frequency, for example up to 100kHz or more.

Operation control unit 2 and control unit 19 of the at least one charged particle beam devices 1 are mounted separately within support cabinet 61. Thereby, any noise from for example water cooling or cooling fans is isolated from the wafer stage 155 and the at least one charged particle beam device 1. Since wafer stage 155 and the at least one charged particle beam device 1 supported by frame 25 are fully enclosed by vacuum enclosure 803, any acoustic noise or fluctuating room pressure of the fab environment, and any thermal drift is isolated via the vacuum gap between vacuum enclosure 803 and for example the frame 25 or the at least one charged particle beam devices 1. Thereby, environmental influences are reduced to a minimum. The vacuum enclosure 803 can further be provided with coils for reducing influences of fluctuations of external magnetic fields (not shown) on the at least one charged particle beam device 1. The support cabinet 61 can further be provided with coils for reducing leakage of magnetic fields (not shown). The vacuum enclosure 803 typically is made from conductive material and can be connected to ground for reducing influences of external electric fields (not shown) on the at least one charged particle beam device 1. Thereby, influences of for example elevators or transport systems within a fabrication environment are minimized.

Figure 5b illustrates a second embodiment of an architecture of an improved wafer inspection system 1000. Same reference numbers are used as in the figures 1 , 4 and 5, and reference is also made to the description of the figures above. According to the second embodiment, the at least one charged particle beam devices 1 is only partly integrated in the vacuum enclosure 803. The at least one charged particle beam device 1 of this example is a multi-beam charged particle beam system of figure 4 and is supported by frame 25 and connected to vacuum enclosure 803 via flexible vacuum sealing bellows 821. Thereby, only the frame 25 is fully encapsulated by vacuum enclosure 803. Thereby, a volume of a vacuum enclosure 803 is reduced and charged particle beam device 1 has a better accessibility for service and exchange of for example the electron source 31.

Figure 5c illustrates a third embodiment of an architecture of an improved wafer inspection system 1000. Same reference numbers are used as in the figures 1 , 4 and 5, and reference is also made to the description of the figures above. Here, frame 25 is rigidly mounted inside the vacuum enclosure 803 to the fab floor 801. The support base 809 of stage 155, however, is mounted via soft damping system 813 to the fab floor 801. Here, a precision control of the position of the inspection site with respect to for example electron beam 44 can be directly controlled by stage controller 16 or by active control system 23 or a combination of both. For example, short stroke but fast actuators can be provided within the soft damping system 813 for fast control of a position of the support base 809 of long stroke wafer stage 155 for positioning an inspections site 6 at the surface of a 300mm-wafer 8 at the position of the line of sight 36 or electron beam 44. Short stroke actuators are driven by active control system 23 to compensate for high frequent movements of stage 155 during a measurement task, when the wafer 8 is supposed to stand still during the measurement time.

Figure 5d illustrates a fourth embodiment of an architecture of an improved wafer inspection system 1000. Same reference numbers are used as in the figures 1 , 4 and 5, and reference is also made to the description of the figures above. Here, the frame 25 is mounted via soft or active damping system 813 to rigid mounting pedestals 815, which are mounted via baseplate 807 and passive pedestals 831 to the fab floor 801. The arrangement of the soft or active damping system 813 is thus not directly above the fab floor 801 , but at a higher system level 827 above fab floor 801 . Thereby, a weight of a frame 25 is reduced. By arranging active damping system 813 closer to the at least one charged particle beam devices 1 , a length of the lever arms between active damping system 813 and line of sight 36 is reduced. For example, by arranging the active damping system 813 in a system level 827 comprising a center of gravity of the at least one charged particle beam devices 1 , parasitic movement of the at least one charged particle beam devices 1 and the actuator range of actuators within the active damping system 813 can be reduced. The frame 25 of this example comprises a frame protrusion 825 below the system level 827 to support measurement system 21 and to serve as a rigid reference for measurement of the position of the wafer chuck 151 with respect to the line of sight 36 of the at least one charged particle beam devices 1. In this embodiment, the rigid mounting pedestals 815 can be integral part of the vacuum enclosure 803.

Figure 5e illustrates a fifth embodiment of an architecture of an improved wafer inspection system 1000. Same reference numbers are used as in the figures 1 , 4 and 5, and reference is also made to the description of the figures above. The frame 25, further also called the column frame 25, is mounted via first active damping system 813 to rigid mounting pedestal 815, which are mounted to the fab floor 801 . The baseplate 807 is here formed as an integral part of the rigid mounting pedestals 815. By first arranging active mounting pedestals 813a and 813b even closer to the at least one charged particle beam devices 1 , a length of the lever arms between active mounting pedestals 813a and 813b and line of sight 36 is even further reduced. The first measurement system 21a for position control of the wafer chuck 151 via for example first Laser beam 27a is mounted to a separate metrology frame 851. The metrology frame 851 is connected to fab floor 801 via the second active mounting system 871 . A relative position of the metrology frame 851 with respect to the line of sight 36 of the at least one charged particle beam devices 1 is established via a second measurement system 21b, for example using second Laser beam 27b. The second measurement system 21b comprises three or more different measurement systems capable of measuring the relative distance between column frame 25 or at least one charged particle beam device 1 in at least three degrees of freedom.

In an example, the metrology frame 851 is considered as the stable reference of the wafer inspection system 1000. Stage controller 16 control stage position via stage actuators of stage 155. First active mounting pedestals 813a and 813b actively controlled by active control system 23 to maintain the relative position between line of sight 36 and inspection site 6 on the wafer 8. The second measurement system 21b between metrology frame 851 and column frame 25 or a charged particle beam device 1 provides the control signal for the position control of the column frame 25 via first active mounting pedestals 813a and 813b.

In an example, the second active mounting system 871 is used for initial alignment only, and the metrology frame 851 is during use rigidly connected to the fab floor 801. In an example, such a system is controlled by accelerometers connected to the metrology frame 851 for active compensation of movements of the metrology frame 851 by the actuators of the second active mounting system 871.

In another example, the column frame 25 is considered as the stable reference of the wafer inspection system 1000. Active control system 23 controls the position of the metrology frame 851 via second active mounting system 871. The second measurement system 21b provides the control signal for the position control of the metrology frame 851.

In the fifth embodiment, the rigid mounting pedestals 815 can be formed as a rigidly connected lower support body and form a part of a vacuum enclosure 803. It is, however, also possible to enclose the rigid mounting pedestals 815, the frame 25 and the charged particle beam column 1 within the vacuum enclosure 803.

It is understood that some solutions of the embodiments can also be combined. For example, the fifth embodiment can be combined with the soft or active mounting system for supporting the support frame of stage 155 according to the third embodiment.

According to the embodiments, sources of drift, noise or vibrations are separated and isolated. At least some of the embodiments take advantage from conditions within a fabrication environment with the high stiffness, high mass, and low vibrations of a fab floor 801. In some embodiments, the fab floor 801 is utilized as stable reference. In other embodiments, a stable reference is established within the wafer inspection system 1000.

Figure 6 shows a scanning raster of a scanning electron beam device 40, comprising a plurality of N scanning lines with dwell points. According to an embodiments, deviations or position displacement vector components dx, dy can be monitored with high precision with the first and second measurement systems 21a and 21b. At least a low frequencycontribution of deviations can be compensated during use, wherein the frequency cut-off is limited by the control circuit. Control circuits with bandwidths up to more than 100 kHz are possible, for example even bandwidths of several MHz. Residual position displacement vector components dx, dy of the final 2D pixel coordinate map correspond to the real coordinates of the dwell points on a cross section surface can be compensated during postprocessing.

A wafer inspection system 1000 according to the embodiments comprises at least one closed metrology and control loop. Thereby, deviations of the position of an inspection site with respect to a line of sight of a scanning electron beam system are monitored and at least partially compensated. The measurement or monitoring can be performed with high bandwidth, thus allowing for control loops with high bandwidth. Control loops include active compensation via at least one of a movement of a wafer stage, a first or second active mounting system, or a deflection scanner. Knowledge of the residual displacements further enable correction in post-processing (e.g., image pixel correction).

The method and wafer inspection system 1000 can be used for quantitative metrology, but can also be used for defect detection, process monitoring, defect review, and inspection of integrated circuits within semiconductor wafers. The invention described by examples and embodiments is however not limited to the clauses but can be implemented by those skilled in the art by various combinations or modifications.

A list of reference numbers is provided:

1 charged particle beam device

2 Operation Control Unit

4 cross sections of first structures

6 inspection site

8 wafer

9 secondary electron beamlet

15 wafer support surface

16 stage control unit

17 Electron detector

19 Control Unit

21 Line of sight

23 active control system

25 Metrology Frame

27 position measurement

29 scanning deflector

31 electron source

33 objective lens

40 charged particle beam (CPB) imaging system

42 Optical Axis of imaging system

43 Intersection point

44 Imaging charged particle beam

48 Fib Optical Axis

50 FIB column

51 focused ion beam 52 cross section surface

53 cross section surface

55 wafer top surface

61 support cabinet

79 Gas Injection system

81 contact pin

101 image plane

151 wafer chuck

155 wafer stage

160 inspection volume

200 detection unit

206 electron-optical lenses

215 focus points

303 condenser lens

305 Multi-beam generating unit

307 measured cross section image of HAR structure

311 cross section image slice

313 word line

315 edge of cross-section surface with wafer surface

331 electrostatic lens

333 field lens

400 beam divider

503 wafer voltage supply

801 Fab floor

803 vacuum enclosure

805 vacuum pumps

807 rigid mounting base ("Baseplate")

809 support base 811 stage bearings

813 soft or active mounting system

815 rigid mounting pedestal

821 vacuum bellows 825 frame protrusion

827 system level

831 floor mounting pedestal

851 metrology frame

871 second active mounting system

1000 Wafer inspection system

Claims

1. A wafer inspection system (1000), comprising

- a vacuum enclosure (803);

- a baseplate (807) configured for being disposed on a floor (801) in a fabrication environment;

- a stage (155) with a wafer chuck (151) for holding during use a wafer (8) and for positioning an inspection site (6) on a surface (15) of the wafer (8) at a line of sight (36) of a charged particle beam column (1), the stage (155) being connected to the baseplate (807);

- a rigid frame (25) for supporting the charged particle beam column (1), the rigid frame (25) being connected to the baseplate (807) via at least one damping system (813); wherein the stage (155), the rigid frame (25) and the charged particle beam column (1) are arranged within the vacuum enclosure (803).

2. The system (1000) of claim 1, further comprising a first position measurement system (21) configured for performing a position measurement (27) between the rigid frame (25) and the stage (155).

3. The system (1000) of claim 1 or 2, further comprising an active control system (23) configured for active controlling at least one damping system (813).

4. The system (1000) of claim 3, further comprising a control unit (19) for controlling the charged particle beam column (1), the control unit (19) being in communication with the active control system (23), the control unit (19) being configured to compensate a residual change of a position of the inspection site (6) relative to a position of the stage (155) by providing a compensation signal to a deflection scanner (29) of the charged particle beam column (1).

5. The system (1000) of any of the claims 1 to 4, further comprising a focused ion beam column (50) arranged at an angle GFE to the charged particle beam column (1), the focused ion beam column (50) being supported by the rigid frame (25).

6. The system (1000) of any of the claims 1 to 4, wherein the charged particle beam column (1) is a multi-beam charged particle beam system operating with a plurality of primary charged particle beamlets (3).

7. The system (1000) of any of the claims 1 to 6, further comprising a support cabinet (61) separately mounted to the floor (801), the support cabinet (61) being comprising at least one vacuum pump (805) connected to the vacuum enclosure (803) via flexible bellows (63).

8. The system (1000) of claim 7, wherein the support cabinet (61) is further comprising a control unit (19) for controlling the charged particle beam column (1), an active control system (23), a stage control unit (16), and an operation control unit (2) for operating the wafer inspection system (1000).

9. The system (1000) of any of the claims 1 to 8, wherein the baseplate (807) is integral part of the vacuum enclosure (803).

10. The system (1000) of any of the claims 1 to 9, wherein the baseplate (807) is disposed on the floor (801) via at least three mounting pedestals (831).

11. The system (1000) of any of the claims 1 to 10, further comprising a rigid mounting pedestal (815) attached to the baseplate (807), the rigid mounting pedestal (815) being configured for supporting the rigid frame (25) via the damping systems (813, 813a, 813b) such that the damping systems (813,813a, 813b) is arranged at a system level (827) corresponding to a center of gravity of the charged particle beam column (1).

12. The system (1000) of claim 11 , wherein the rigid frame (25) comprises a frame protrusion (825) for holding the first position measurement system (21) at a system level of the stage (155).

13. The system (1000) of claim 11, further comprising a metrology frame (851) for holding a second position measurement system (21a) configured for performing a position measurement (27a) between the metrology frame (851) and the stage (155), and a third position measurement system (21b) configured for performing a position measurement (27b) between the metrology frame (851) and the charged particle beam column (1).

14. The system (1000) of claim 13, wherein the metrology frame (851) is mounted via a second damping or active mounting system (871) to the baseplate (807).