(19)
(11)EP 2 912 442 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
13.05.2020 Bulletin 2020/20

(21)Application number: 13786542.4

(22)Date of filing:  24.10.2013
(51)Int. Cl.: 
G01N 23/2251  (2018.01)
H01J 37/317  (2006.01)
H01J 37/244  (2006.01)
(86)International application number:
PCT/NL2013/050746
(87)International publication number:
WO 2014/065663 (01.05.2014 Gazette  2014/18)

(54)

APPARATUS AND METHOD FOR INSPECTING A SURFACE OF A SAMPLE

VORRICHTUNG UND VERFAHREN ZUR INSPEKTION EINER PROBENOBERFLÄCHE

APPAREIL ET PROCÉDÉ POUR INSPECTER UNE SURFACE D'UN ÉCHANTILLON


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 25.10.2012 NL 2009696

(43)Date of publication of application:
02.09.2015 Bulletin 2015/36

(73)Proprietor: Technische Universiteit Delft
2628 CN Delft (NL)

(72)Inventor:
  • KRUIT, Pieter
    2628 CN Delft (NL)

(74)Representative: Peters, Sebastian Martinus 
Octrooibureau Vriesendorp & Gaade B.V. Koninginnegracht 19
2514 AB Den Haag
2514 AB Den Haag (NL)


(56)References cited: : 
WO-A1-2007/028596
US-A1- 2005 214 958
US-B2- 7 732 762
US-A- 4 823 006
US-A1- 2010 133 433
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    BACKGROUND



    [0001] The invention relates to an apparatus and a method for inspecting a surface of a sample. In particular the invention relates to an apparatus for inspecting a sample surface using a plurality of charged particle beams, such as a multi-beam scanning electron microscope. The invention may be applied to charged particles of any type, such as electrons, positrons, ions and others.

    [0002] The invention relates to an apparatus for detecting backscattered charged particles, such as electrons. These backscattered charged particles have almost the same energy as the primary charged particles. It is usually assumed that the charged particles lose up to a few hundred electron volts in the sample before coming out again. The angular distribution of the backscattered charged particles is much larger than the angular distribution of the primary charged particle beams. The backscattered charged particles that travel close to the axis of corresponding primary charged particle beam will travel back through the charged particle optical system along paths that closely resemble the primary charged particles and they will focus in about the same planes as the primary charged particle beams.

    [0003] Such an apparatus is for example disclosed in US patent 7,732,762. This US patent discloses an electron microscope comprising an electron emitter which, in use, emits a plurality of primary electron beams which are directed towards a surface of a specimen. The apparatus comprises a first lens system for focusing the electron beams into a first array of separated spots in an intermediate plane between the electron emitter and the specimen surface. The apparatus further comprises a second lens system for directing the primary electron beams from the intermediate plane towards the specimen surface and for focusing all primary electron beams into a second array of individual spots on the specimen surface. In particular the second lens system comprises a cascade of lenses, more in particular a microlens array which comprises an individual microlens for each individual electron beam.

    [0004] At the intermediate plane, a thin sheet-like plate comprising fluorescent material is disposed. The thin sheet comprises apertures, so that the primary electron beams are allowed to pass. The plate collects the back-scattered electrons and converts the collected electrons into photons. The photons are at least partially directed to an array of photo detectors by means of an optical lens system.

    [0005] A disadvantage of this system is that the distance between the individual spots on the specimen surface is relatively large due to the use of one objective microlens per electron beam. Consequently the known system is less suitable for inspecting small samples. It is noted that US 2010/0133433 A1 discloses a multi electron beam exposure apparatus. The apparatus comprises a first lens system for focusing the electron beams into a first array of separated spots in an intermediate plane between the electron emitter and the specimen surface, and a second lens system for directing the primary electron beams from the intermediate plane towards the specimen surface and for focusing all primary electron beams into a second array of individual spots on the specimen surface. A rotation coil is a ring form coil which is arranged in the intermediate plane so that it is coaxial with the central axis of the electron optical system and can generate a magnetic field which has a direction parallel to the central axis within the ring. The positions of the primary beams on the sample can be rotated around the central axis by the magnetic field induced by the rotation coil. Using this, the primary beams can be aligned parallel to the moving direction of the stage carrying the sample.

    [0006] It is an object of the present invention to provide a multi charged particle beam apparatus for inspecting a sample surface which provides a new detection arrangement for detecting the back-scattered electrons.

    SUMMARY OF THE INVENTION



    [0007] According to a first aspect, the invention provides an apparatus for inspecting a surface of a sample, as described in claim 1. The apparatus comprises a multi beam charged particle generator for generating an array of primary charged particle beams, and a charged particle optical system with an optical axis comprising:

    a first lens system for focusing the primary charged particle beams into a first array of separated spots in an intermediate plane, and

    a second lens system for directing the primary charged particle beams from the intermediate plane towards the sample surface and which comprises an electromagnetic or electrostatic objective lens which is common for at least the primary charged particle beams for focusing all primary charged particle beams into a second array of individual spots on the sample surface,

    wherein the apparatus comprises a position sensitive backscatter charged particle detector positioned in or near the intermediate plane, wherein said detector comprises one or more through openings for passing said primary charged particle beams there through, and wherein said second lens system is arranged for projecting backscattered charged particles from the second array of individual spots on the sample surface into an array of backscattered charged particle spots on the detector

    Using a single objective lens which is common for at least the primary charged particle beams, the individual spots on the sample surface can be arranged much closer to each other due to the use of the common lens for focusing all primary charged particle beams into the second array of individual spots on the sample surface. This makes the multi-beam apparatus of the invention more suitable for inspecting smaller samples, for example having a surface area of 1 mm2 or even smaller.

    [0008] It is noted that in the context of this application, a surface of a sample encompasses the top layer of the sample including material just below the boundary plane of the sample.

    [0009] It is further noted that in the context of this application, the one or more through openings for passing said primary charged particle beams there through, may comprise one or more holes in the detector, and may also comprise an opening adjacent to the detector.

    [0010] Preferably the intermediate plane where the primary beams are smallest is close to the plane in which the backscattered charged particles are also focused, at which plane the detector is preferably situated.

    [0011] In an embodiment the one or more through openings comprises an array of holes wherein each hole of the array of holes is arranged for passing one of said array of primary charged particle beams there through. In an embodiment, the diameter of the holes of the array of holes is substantially smaller than the pitch between the holes. Since the detector is arranged at least substantially in or near the intermediate plane where the primary charged particle beams are focused, the primary charged particle beams pass through sufficiently small holes in the detector so that there is enough surface area in the detector to allow efficient detection.

    [0012] However, arranging the individual spots much closer to each other on the sample surface according to the invention makes it more difficult to separate and distinguish backscattered charged particles from different spots on the sample surface. For example as shown in the apparatus as disclosed in US 7,732,762, the backscattered electrons are imaged at or around the position of the focused primary beams at the plate of fluorescent material. In this apparatus, a part of the backscattered electrons passes through the apertures in the plate of fluorescent material and are not detected. In the apparatus of the prior art, only the backscattered electrons which are not focused in the same spots as the primary beams and which form blurred spots at the plate of fluorescent material can be detected.

    [0013] On the one hand this further problem can be solved by an embodiment, wherein the second lens system is arranged for imaging the first array of separated spots from said intermediate plane onto the sample surface with a magnification in a range from 0.01 to 0.2. Thus the distance between adjacent spots at the detector is up to a 100 times larger then adjacent spots on the sample surface.

    [0014] According to the invention, the second lens system comprises one or more magnetic lenses which are arranged for rotating the array of primary charged particle beams around the optical axis on their way from said intermediate plane towards the sample, to position the second array with respect to the first array at an angle larger than 0 degrees and preferably smaller than 180 degrees around the optical axis, and wherein the one or more magnetic lenses are arranged for rotating the array of backscattered charged particle spots with respect to the first array at an angle larger than 0 degrees and preferably smaller than 360 degrees around the optical axis.

    [0015] By using a magnetic lens, the position of the second array is rotated with respect to the first array with an angle between 0 and 180 degrees. The backscattered charged particles, which preferably also pass through the same magnetic lens, are also rotated with respect to the second array with substantially the same angle between 0 and 180 degrees. It is noted that the rotation of the backscattered charged particles is in the same rotation direction as the rotation of the primary charged particle beams. The array of spots of the backscattered charged particles on the position sensitive detector at the intermediate plane is thus rotated with respect to the first array at an angle larger than 0 degrees and smaller than 360 degrees around the optical axis. This rotation provides a spatial separation between the array of spots of the backscattered charged particles with respect to the first array of separated spots of the primary beams at or near the intermediate plane, which allows to arrange the array of spots of the backscattered charged particles at a position in which they at least substantially deviate from the position of the first array. Thus by carefully selecting the rotation, the detection of the backscattered charged particles at or near the intermediate plane, at least substantially does not interfere with the passing of the primary charged particle beams. In the apparatus according to the invention, also the backscattered charged particles which are at least substantially focused in the intermediate plane can be detected.

    [0016] Contrarily to the apparatus according to US 7,732,762, the second lens system and/or the position of the detector in the apparatus of the invention can now be arranged in order to at least substantially reduce the blur of the spots of backscattered charged particles, or to focus the backscattered charged particles on small spots, which enhances the resolution of the detection arrangement of the invention.

    [0017] In an embodiment, the second lens system is arranged for projecting the backscatter charged particles from the individual spots on the sample surface through a common cross-over of the backscattered charged particles to substantially individual spots on the position sensitive backscatter charged particle detector. In an embodiment, an aperture is arranged in or near the plane comprising the common cross-over of the backscattered charged particles. Such a backscatter beam limiting aperture between the sample and the detector limits the acceptance angle of the backscattered charged particles, and is used to influence the contrast in the image of backscattered particles on the detector. The aperture can also be used to control and limit the size of the spots of backscattered particles on the detector. In an embodiment, said aperture comprises open areas to allow passage of certain angular directions of the backscattered charged particles, while blocking other angular directions.

    [0018] In an embodiment, the one or more magnetic lenses are arranged for rotating the array of backscattered charged particle spots with respect to the first array at an angle of substantially 180 degrees around the optical axis. In an embodiment, the detector comprises one through opening for passing said primary charged particle beams there through. Preferably this through opening is arranged adjacent to the detector or to the sensitive surface of the detector.

    [0019] In an embodiment, the position sensitive backscatter charged particle detector contains more than one pixel per backscatter charged particle beam. When using a position sensitive backscatter charged particle detector having many more pixels than backscatter spots, the backscatter signal is obtained by reading out the pixels of the detector. There is no need to determine in advance the location in the detector plane where the backscatter spots are going to end up.

    [0020] In an embodiment, the position sensitive backscatter charged particle detector is a CCD camera, a CMOS camera, an array of avalanche photo diodes, photo multipliers or PN junction semiconductor detector which gets signal from backscatter charged particles directly.

    [0021] In an embodiment, the position sensitive backscatter charged particle detector comprises a fluorescent screen arranged at least substantially in or near said intermediate plane and an optical arrangement for conveying photons from the fluorescent screen to a CCD camera, a CMOS camera, an array of avalanche photo diodes or photo multipliers.

    [0022] In an embodiment, the CCD camera, CMOS camera, array of avalanche photo diodes or photo multipliers is positioned such that the array of detector pixels coincides with the array of images of the individual backscatter beams.

    [0023] In an embodiment, the pitch between the spots in the second array of separated spots on the sample surface is between 0.3 and 30 micrometers.

    [0024] In an embodiment, the second lens system comprises magnetic and/or electrostatic charged particle deflectors for scanning the primary charged particle over the sample. In an embodiment, the magnetic and/or electrostatic charged particle deflectors are arranged and/or controllable for obtaining a substantially stationary positioning of the array of backscattered charged particle spots on the detector during scanning. A magnetic deflector deflects charged particles on their way towards the sample in the opposite direction as the charged particles moving from the sample to the detector. The latter causes a movement of the backscattered electron spots on the detector while scanning the primary beam. An electrostatic deflector, on the contrary, deflects beams of charged particle into a direction which is independent on the direction of the particles. Thus, employing an electrostatic deflector would seem to ensure no movement of the spots on the detector. However, the rotation of the image by the magnetic lens may still leave a movement. A double system of both magnetic and electrostatic deflectors gives sufficient adjustable parameters that the setting can be chosen during operation in order to ensure stable spot position on the detector during scanning.

    [0025] In an embodiment, the second lens system is arranged for projecting the primary charged particle beams through a common cross-over, and wherein the apparatus comprises a position sensitive secondary electron detector positioned at least substantially in or near a plane comprising said common cross-over. As discussed in more detail in the Dutch Patent Application 2009053, this embodiment provides a detection system in which the secondary electrons are detectable. This embodiment utilizes the energy difference between the secondary electrons and the primary charged particles, for example in a SEM the energy of the primary electrons is usually from 1 keV to 30 keV and the energy of secondary electrons is usually from 0 eV to 50 eV. The result of this energy difference is that the second lens system performs differently for primary charged particles than for secondary electrons. On the one hand, the second lens system is arranged for focusing all primary charged particle beams into an array of individual spots on the sample surface. On the other hand, the same lens system is used for directing the secondary electron beams towards the plane of the common cross-over. Since the secondary electrons have an energy which is much less than the energy of the primary charged particles, the lens system is arranged to spread the secondary electrons over an area which essentially surrounds the common cross-over. Thus, in or near a plane comprising said common cross-over, most of the secondary electron beams are spatially separated from the primary charged particle beams which are all concentrated in the common cross-over. It is noted that also the backscattered charged particles are at least substantially concentrated in the common cross-over, and thus are spatially separated from the secondary electron beams.

    [0026] By positioning a position sensitive secondary electron detector at least substantially in or near a plane comprising said common cross-over, preferably adjacent to and/or surrounding the common cross-over, most of the secondary electron beams can be detected without any interference to the primary charged particle beams or the backscattered charged particles.

    [0027] Accordingly, in an apparatus according to the invention, and in particular according to this embodiment, the backscattered charged particles are detectable using detectors arranged in the charged optical column of the apparatus. In addition, both the backscattered charged particles and the secondary electrons can be detected separately and substantially simultaneous.

    [0028] According to a second aspect, the invention provides a method for inspecting a surface of a sample as described in claim 13. The method comprising the steps of:

    generating an array of primary charged particle beams using a multi beam charged particle generator;

    focusing the primary charged particle beams into a first array of separated spots in an intermediate plane, using a first lens system;

    directing the primary charged particle beams from the intermediate plane towards the sample surface using a second lens system and focusing all primary charged particle beams into a second array of individual spots on the sample surface using an electromagnetic or electrostatic objective lens which is common for at least the primary charged particle beams;

    projecting backscattered charged particles from the second array of individual spots on the sample surface into an array of backscattered charged particle spots on the intermediate plane using said second lens system; and

    detecting said backscattered charged particles using a position sensitive backscatter charged particle detector positioned in or near the intermediate plane, wherein said detector comprises one or more through openings for passing said primary charged particle beams there through,
    wherein the second lens system comprises one or more magnetic lenses which are arranged to rotate the array of primary charged particle beams around the optical axis on their way from said intermediate plane towards the sample, and to position the second array with respect to the first array at an angle larger than 0 degrees and preferably smaller than 180 degrees around the optical axis, wherein the one or more magnetic lenses are arranged to rotate the array of backscattered charged particle spots with respect to the first array at an angle larger than 0 degrees and preferably smaller than 360 degrees around the optical axis.



    [0029] In an embodiment, the one or more magnetic lenses are arranged to rotate the array of backscattered charged particle spots with respect to the first array at an angle of substantially 180 degrees around the optical axis. In an embodiment, the detector comprises one through opening for passing said primary charged particle beams there through.

    [0030] In an embodiment, the second lens system comprises magnetic and/or electrostatic charged particle deflectors to scan the primary charged particle over the sample. In an embodiment, the magnetic and/or electrostatic charged particle deflectors are arranged and/or controllable to obtain a substantially stationary positioning of the array of backscattered charged particle spots on the detector during scanning.

    [0031] In an embodiment, the sample surface is moved at constant speed in a first direction while the primary charged particle beams are scanned repeatedly in a second direction at least substantially perpendicular to the first direction. This provides a new way of studying samples with a scanning charged particle beam microscope: off-line microscopy wherein a full sample surface, for example over an area of one square millimeter, is scanned and imaged at nanometer resolution after which the full sample surface is available to the specialist, for example a biologist, for studying and/or inspecting the image on a computer, instead of behind the microscope.

    [0032] According to a third aspect, the invention provides an apparatus for inspecting a surface of a sample, wherein the apparatus comprises a multi beam charged particle generator for generating an array of primary charged particle beams, and a charged particle optical system with an optical axis comprising:

    a first lens system for focusing the primary charged particle beams into a first array of separated spots in an intermediate plane, and

    a second lens system for directing the primary charged particle beams from the intermediate plane towards the sample surface and for focusing all primary charged particle beams into a second array of individual spots on the sample surface,

    wherein the apparatus comprises a position sensitive backscatter charged particle detector positioned at least substantially in or near the intermediate plane, and in that the second lens system comprises an electromagnetic lens which is common for at least the primary charged particle beams and which is arranged for rotating the array of primary charged particle beams around the optical axis to position the second array with respect to the first array at an angle larger than 0 degrees and smaller than 180 degrees around the optical axis.



    [0033] In an embodiment, the second lens system comprises a single objective lens. In an embodiment, this single objective lens is the electromagnetic lens which is arranged for rotating the array of primary charged particles beams around the optical axis. In an alternative embodiment, the single objective lens is an additional lens between the electromagnetic lens and the sample. In this alternative embodiment, the single objective lens comprises a electromagnetic lens or an electrostatic lens.

    [0034] The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0035] The invention will be elucidated on the basis of an exemplary embodiment shown in the attached drawings, in which:

    Figure 1 shows an example of a Multi-Beam Scanning Electron Microscope (MBSEM) according to the invention,

    Figure 2 shows part of the beam path of a second example of a MBSEM according to the invention,

    Figure 3 shows part of the beam path of a third example of a MBSEM according to the invention,

    Figure 4 shows a schematic cross section of the beam path of an example of a MBSEM according to the invention at the intermediate plane thereof,

    Figure 5 shows a schematic cross section of the beam path of a further example of a MBSEM according to the invention at the intermediate plane thereof, and

    Figure 6 shows an further example of a Multi-Beam Scanning Electron Microscope (MBSEM) according to the invention.


    DETAILED DESCRIPTION OF THE INVENTION



    [0036] Figure 1 shows an example of a Multi-Beam Scanning Electron Microscope (MBSEM) of the invention.

    [0037] The MBSEM 1 comprises a multi beam charged particle generator 2 for generating an array of primary charged particle beams 3, in this case an array of primary electron beams 3. The multi beam electron generator 2 comprises at least one electron source 4 for generating a diverging electron beam 5. The diverging electron beam 5 is split into an array of focused primary electron beams 3 by an aperture lens array 6. The primary electron beams 3 are subsequently directed towards a sample 15, as schematically indicated by the arrow P.

    [0038] The multiple images of the source 4 are positioned on the object principle plane of an accelerator lens 7. The accelerator lens 7 directs the primary electron beams 3 towards the optical axis 8 and creates a first common cross-over 9 of all the primary electron beams 3.

    [0039] The first common cross-over 9 is imaged by the magnetic condenser lens 10 onto a variable aperture 16 that acts as a current limiting aperture. At the variable aperture 16 a second common cross-over of all the primary electron beams 3 is created.

    [0040] The MBSEM comprises a lens system 13, 14 for directing the primary charged particle beams from the common cross-over at the variable aperture 16 towards the sample surface 15 and for focusing all primary charged particle beams 3 into an array of individual spots on the sample surface 15. The lens system comprises an intermediate magnetic lens 13 for imaging the variable aperture 16 onto a coma free plane of the objective lens 14, which objective lens 14 creates an array of focused primary electron beams on the sample surface 15.

    [0041] In addition the MBSEM is provided with scan coils 18 for scanning the array of focused primary electron beams over the sample surface 15.

    [0042] In the MBSEM as shown in figure 1, there are at least two alternative positions which are suitable for detecting the backscattered charged particles:
    A first position can be found between the intermediate magnetic lens 13 and the objective lens 14. In this case the intermediate magnetic lens 13 is at least part of the first lens system which focuses the primary electron beams 3 into a first array of separated spots in an intermediate plane where a position sensitive backscatter charged particle detector 11 is arranged, as shown in figure 1. The objective lens 14 is at least part of the second lens system for directing the primary electron beams 3 from the detector 11 plane towards the surface of the sample 15, and for focusing all primary charged particle beams 3 into a second array of individual spots. The objective lens 14 comprises an electromagnetic lens which is common for the primary electron beams 3 and is arranged for rotating the array of primary electron beams 3 around the optical axis 8 to position the second array on the target 15 with respect to the first array at the detector 11 plane at an angle larger than 0 degrees and smaller than 180 degrees around the optical axis 8, as will be explained in more detail in the discussion of figures 4 and 5 below.

    [0043] A second position can be found between the aperture lens array 6 and the magnetic condenser lens 10. In this case the aperture lens array 6 is at least part of the first lens system which focuses the primary electron beams 3 into a first array of separated spots in an intermediate plane where a position sensitive backscatter charged particle detector 12 is arranged, as shown in figure 1. The magnetic condenser lens 10 is at least part of the second lens system for directing the primary electron beams 3 from the detector 12 plane towards the surface of the sample 15, and for focusing all primary charged particle beams 3 into a second array of individual spots. The second lens system comprises an electromagnetic lens which is common for the primary electron beams 3. One or more of the magnetic condenser lens 10, the intermediate magnetic lens 13 and the objective lens 14 comprises the electromagnetic lens, which is arranged for rotating the array of primary electron beams 3 around the optical axis 8 to position the second array on the target 15 with respect to the first array at the detector 12 plane at an angle larger than 0 degrees and smaller than 180 degrees around the optical axis 8, as will be explained in more detail in the discussion of figures 4 and 5 below.

    [0044] It is noted that in order to detect the backscattered electrons, a detector is either arranged at the position of the first detector 11, or at the position of the second detector 12. The backscattered electron detector 11, 12 is arranged to acquire the individual backscatter electron image of each single primary electron beam spot on the sample surface 15. This means, that when the sample surface 15 is scanned in this MBSEM 1, multiple images can be acquired at the same time in one single scan period.

    [0045] Figure 2 shown a schematic and simplified representation of the same set-up of figure 1, in particular the example as shown in figure 2 only comprises one common cross-over at the position of the variable aperture 216, in stead of the two common cross-over in figure 1. When using only one common cross-over, the magnetic condenser lens 10 as shown in figure 1 can be omitted.

    [0046] Again, in the setup as shown in figure 2, there are two positions which are suitable for detecting the backscattered charged particles:
    A first position can be found between the intermediate magnetic lens 213 and the objective lens 214. In this case the intermediate magnetic lens 213 is at least part of the first lens system which focuses the primary electron beams 23 into a first array of separated spots in an intermediate plane where a position sensitive backscatter electron detector 211 is arranged, as shown in figure 2. The objective lens 214 is at least part of the second lens system for directing the primary electron beams 23 from the detector 211 plane towards the surface of the sample 215, and for focusing all primary charged particle beams 23 into a second array of individual spots. The objective lens 214 comprises an electromagnetic lens which is common for the primary electron beams 23 and is arranged for rotating the array of primary electron beams 23 around the optical axis 28 to position the second array on the target 215 with respect to the first array at the detector 211 plane at an angle larger than 0 degrees and smaller than 180 degrees around the optical axis 28, as will be explained in more detail in the discussion of figures 4 and 5 below.

    [0047] It is noted that in the objective lens 214, a variable aperture 217 is arranged as a backscatter beam limiting aperture between the sample 215 and the detector 211. The backscatter beam limiting aperture 217 limits the acceptance angle of the backscattered electrons, and is used to influence the contrast in the image of backscattered particles on the detector 211. The aperture 217 can also be used to control and limit the size of the spots of backscattered particles on the detector 211.

    [0048] Alternatively, a position sensitive electron detector 212 is arranged at a second position above the intermediate magnetic lens 213. Above the detector 212, the first lens system (not shown) is arranged, which is for example the same as the multi electron beam generator 2 as shown in figure 1, which focuses the primary electron beams 23 into a first array of separated spots in an intermediate plane where a position sensitive backscatter charged particle detector 212 is arranged, as shown in figure 2. The intermediate magnetic lens 213 is at least part of the second lens system for directing the primary electron beams 23 from the detector 212 plane towards the surface of the sample 215, and for focusing all primary charged particle beams 23 into a second array of individual spots. The second lens system comprises an electromagnetic lens which is common for the primary electron beams 23. One or more of the intermediate magnetic lens 213 and the objective lens 214 comprises the electromagnetic lens, which is arranged for rotating the array of primary electron beams 23 around the optical axis 28 to position the second array on the target 215 with respect to the first array at the detector 212 plane at an angle larger than 0 degrees and smaller than 180 degrees around the optical axis 8, as will be explained in more detail in the discussion of figures 4 and 5 below.

    [0049] Figure 3 shows a further example of an optical setup in a MBSEM for detecting backscattered electrons. In this setup, the position sensitive backscatter electron detector 311 is arranged between a collimating lens 310 and a focusing lens 313. The accelerator lens 37 and the collimating lens 310 are at least part of the first lens system which focuses the primary electron beams 33 into a first array of separated spots in an intermediate plane where a position sensitive backscatter electron detector 311 is arranged, as shown in figure 3. The focusing lens 313 and the objective lens 314 are at least part of the second lens system for directing the primary electron beams 33 from the detector 311 plane towards the surface of the sample 315, and for focusing all primary charged particle beams 33 into a second array of individual spots. One or more of the focusing lens 313 and the objective lens 314 comprises an electromagnetic lens which is common for the primary electron beams 33 and is arranged for rotating the array of primary electron beams 33 around the optical axis 38 to position the second array on the target 315 with respect to the first array at the detector 311 plane at an angle larger than 0 degrees and smaller than 180 degrees around the optical axis 38, as will be explained in more detail in the discussion of figures 4 and 5 below. In the objective lens 314, a variable aperture 317 is arranged as a backscatter beam limiting aperture between the sample 315 and the detector 311.

    [0050] When the focusing lens 313 is used as the electromagnetic lens for rotating the array of primary electron beams 33 around the optical axis 38, than the objective lens 314 can also be an electrostatic lens. It is noted that an electrostatic lens does not provide a rotation of the electron beams around the optical axis 38.

    [0051] The effect of the rotation of electron beams 3, 13, 33 around the optical axis 8, 28, 38 is demonstrated in figures 4 and 5.

    [0052] Figure 4 shows a schematic view of the surface of an example of a position sensitive backscatter electron detector 411, which surface faces the sample. The detector 411 is provided with an array of holes 42 for letting the primary charged particle beams 42 pass through on their way from the charged particle source 2 toward the sample surface 15. Since the detector 411 is arranged at least substantially in or near the intermediate plane where the charged particle beams 43 are focused, the detector 411 is arranged at a plane where the primary charged particle beams 43 are smallest. Thus the holes 42 in the detector 411 are sufficiently small to have enough surface area left for detecting the backscattered charged particles. The holes 42 are located at the position where the charged particle beams 43 are focused into the first array of separated spots.

    [0053] Between the detector 411 and the sample an electromagnetic lens which is common for all charged particle beams and which is arranged for rotating the array of primary beams around the optical axis 48, the position of the second array of individual spots on the sample surface is rotated with respect to the holes 42 with an angle between 0 and 180 degrees. The backscattered charged particles, which also traverse the same electromagnetic lens, are also rotated with respect to the second array with substantially the same angle between 0 and 180 degrees. The array of spots 44 of the backscattered charged particles on the position sensitive detector 411 at the intermediate plane is thus rotated with respect to the primary charged particle beams 43 at an angle α larger than 0 degrees and smaller than 360 degrees around the optical axis 48. This rotation provides a spatial separation between the array of spots 44 of the backscattered charged particles with respect to the holes 42, which allows to arrange the array of spots 44 of the backscattered charged particles at a position in which they at least substantially deviate from the position of the primary beams 43. When the backscattered charged particles 44 impinge on the surface of the detector, they are converted into a signal which read out and this data is transferred to a computer for storage and/or further evaluation.

    [0054] As shown in the example in figure 4, the plane where the primary beams 43 are smallest and where they traverse through the holes 42 is close to or arranged in the plane in which the backscattered charged particles are also focused into small spots 44.

    [0055] The surface of the position sensitive detector 411 is covered by a large number of pixels and the spots 44 of backscattered charged particles on the detector 411 are detectable as long as one or more of the spots 44 do not overlie one or more of the holes 42. When using a position sensitive detector 411 with a large number of pixels, many more pixels than backscatter spots 44, it is not necessary to determine in advance where the backscatter spots 44 are going to end up exactly on the detector 411.

    [0056] Figure 5 shows a schematic view of the surface of a further example of a position sensitive backscatter electron detector 511, which surface faces the sample. This detector 511 is not provided with an array of holes. In stead, the detector 511 is arranged adjacent to the optical axis 58 and substantially covers half of the optical beam path of the charged particle optical system. The other half is without the obstruction of the detector 511 for letting the primary charged particle beams 53 pass through on their way from the charged particle source 2 toward the sample surface 15.

    [0057] Again, an electromagnetic lens is arranged between the detector 511 and the sample, which lens is common for all charged particle beams and which is arranged for rotating the array of primary beams 53 around the optical axis 58. In this example the position of the second array of individual spots on the sample surface is rotated with respect to the primary beams 53 with an angle of approximately 90 degrees around the optical axis 58. The backscattered charged particles, which also traverse the same electromagnetic lens, are also rotated with respect to the second array in the same direction and with substantially the same angle of approximately 90 degrees. The array of spots 54 of the backscattered charged particles on the position sensitive detector 511 at the intermediate plane is thus rotated with respect to the primary charged particle beams 53 at an angle of approximately 180 degrees around the optical axis 58. Due to this rotation the array of spots 54 of the backscattered charged particles are moved to the side of the optical beam path where the detector 511 is positioned. When the backscattered charged particles 54 impinge on the surface of the detector 511, they are converted into a signal which read out and this data is transferred to a computer for storage and/or further evaluation.

    [0058] In an embodiment, the position sensitive backscatter charged particle detector 411, 511 is a CCD camera, a CMOS camera, an array of avalanche photo diodes, photo multipliers or PN junction semiconductor detector which gets signal from backscatter charged particles directly. In an alternative embodiment the detector 411, 511 comprises a fluorescence screen at the intermediate plane, and an optical arrangement for conveying photons from the fluorescence screen onto a photon detector, such as a CCD camera, as described in more detail in the Dutch Patent Application 2009053, which is incorporated herein by reference.

    [0059] Figure 6 shows essentially the same MBSEM as shown in figure 1 and as described in detail above, wherein the backscatter electron detector 12 in the position between the aperture lens array 6 and the magnetic condenser lens 10. The MBSEM as shown in figure 6 is furthermore provided with a position sensitive secondary electron detector 17 positioned at least substantially in or near a plane comprising a common cross-over, in this case directly below the variable aperture 16. This secondary electron detector 17 is arranged to acquire the individual secondary electron image of each single primary electron beam spot on the sample surface 15, and the backscatter electron detector 12 is arranged to acquire the individual backscatter electron image of each single primary electron beam spot on the sample surface 15. This means, that when the sample surface 15 is scanned in this MBSEM 1, multiple images of the backscattered electrons and the secondary electrons can be acquired at the same time in one single scan period.

    [0060] In summary, the invention relates to an apparatus and method for inspecting a sample. The apparatus comprises a generator for generating an array of primary charged particle beams, and a charged particle optical system with an optical axis. The optical system comprises a first lens system for focusing all primary beams into a first array of spots in an intermediate plane, and a second lens system for focusing all primary beams into a second array of spots on the sample surface. The apparatus comprises a position sensitive backscattered charged particle detector positioned at or near the intermediate plane. The second lens system comprises an electromagnetic or electrostatic lens which is common for all charged particle beams. Preferably the second lens system comprises a magnetic lens for rotating the array of primary beams around the optical axis to position the second array with respect to the first array at an angle.

    [0061] It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention.


    Claims

    1. An apparatus for inspecting a surface of a sample, wherein the apparatus comprises a multi beam charged particle generator (2) for generating an array of primary charged particle beams (3,23,33,43,53), and a charged particle optical system with an optical axis (8, 28, 38,48,58) comprising:

    a first lens system (13, 213, 37, 310) for focusing the primary charged particle beams (3, 23, 33, 43, 53) into a first array of separated spots in an intermediate plane, and

    a second lens system (14, 214, 313, 314) for directing the primary charged particle beams (3, 23, 33, 43, 53) from the intermediate plane towards the sample surface (15, 215, 315) and which comprises an electromagnetic or electrostatic objective lens which is common for at least the primary charged particle beams (3, 23, 33, 43, 53) for focusing all primary charged particle beams into a second array of individual spots on the sample surface (15, 215, 315),

    wherein the apparatus comprises a position sensitive backscatter charged particle detector (11, 211, 311, 411, 511) positioned in or near the intermediate plane, wherein said detector comprises one or more through openings (42) for passing said primary charged particle beams (3, 23, 33, 43, 53) therethrough and wherein said second lens system (14, 214, 313, 314) is arranged to project backscattered charged particles from the second array of individual spots on the sample surface into an array of backscattered charged particle spots (44, 54) on the detector,

    characterized in that the second lens system (14, 214, 313, 314) comprises one or more magnetic lenses which are adapted to rotate the array of primary charged particle beams (3, 23, 33, 43, 53) around the optical axis (8, 28, 38, 48, 58) on their way from said intermediate plane towards the sample (15, 215, 315), to position the second array with respect to the first array at an angle larger than 0 degrees and preferably smaller than 180 degrees around the optical axis (8, 28, 38, 48, 58), and

    wherein the one or more magnetic lenses are adapted to rotate the array of backscattered charged particle spots (44, 54) with respect to the first array at an angle larger than 0 degrees and preferably smaller than 360 degrees around the optical axis (8, 28, 38, 48, 58).


     
    2. Apparatus according to claim 1, wherein said one or more through openings comprise an array of holes (42) wherein each hole of the array of holes (42) is adapted to pass one of said array of primary charged particle beams (43) there through, preferably wherein the diameter of the holes of the array of holes (42) is substantially smaller than the pitch between the holes.
     
    3. Apparatus according to claim 1 or 2, wherein the one or more magnetic lenses are adapted to rotate the array of backscattered charged particle spots (54) with respect to the first array at an angle of substantially 180 degrees around the optical axis (58).
     
    4. Apparatus according to claim 3, wherein the detector (511) comprises one through opening for passing said primary charged particle beams (53) there through.
     
    5. Apparatus according to any one of the preceding claims, wherein the second lens system (14, 214, 313, 314) is adapted to project the backscatter charged particles from the individual spots on the sample surface through a common cross-over of the backscattered charged particles to substantially individual spots (44, 54) on the position sensitive backscatter charged particle detector (11, 211, 311, 411, 511).
     
    6. Apparatus according to claim 5, wherein an aperture (217, 317) is arranged in or near the plane comprising the common cross-over of the backscattered charged particles, preferably wherein said aperture (217, 317) comprises open areas to allow passage of certain angular directions of the backscattered charged particles, while blocking other angular directions.
     
    7. Apparatus according to any one of the preceding claims, wherein the position sensitive backscatter charged particle detector (11, 211, 311, 411, 511) contains more than one pixel per backscatter charged particle beam, and/or wherein the position sensitive backscatter charged particle detector (11, 211, 311, 411, 511) is a CCD camera, a CMOS camera, an array of avalanche photo diodes, photo multipliers or PN junction semiconductor detector which gets signal from backscatter charged particles directly.
     
    8. Apparatus according to any one of the claims 1 to 6, wherein the position sensitive backscatter charged particle detector (11, 211, 311, 411, 511) comprises a fluorescent screen arranged at least substantially in or near said intermediate plane and an optical arrangement for conveying photons from the fluorescent screen to a CCD camera, a CMOS camera, an array of avalanche photo diodes or photo multipliers, preferably wherein the CCD camera, CMOS camera, array of avalanche photo diodes or photo multipliers is positioned such that the array of detector pixels coincides with the array of images of the individual backscatter beams.
     
    9. Apparatus according to any one of the preceding claims, wherein the second lens system (14, 214, 313, 314) is adapted to image the first array of separated spots (43, 53) from said intermediate plane onto the sample surface with a magnification in a range from 0.01 to 0.2.
     
    10. Apparatus according to any one of the preceding claims, wherein the pitch between the spots in the second array of separated spots on the sample surface (15, 215, 315) is between 0.3 and 30 micrometers.
     
    11. Apparatus according to any one of the preceding claims, wherein the second lens system (14, 214) is adapted to project the primary charged particle beams through a common cross-over, and wherein the apparatus comprises a position sensitive secondary electron detector (16, 216) positioned at least substantially in or near a plane comprising said common cross-over.
     
    12. Apparatus according to any one of the preceding claims, wherein the second lens system (14) comprises magnetic and/or electrostatic charged particle deflectors (18) for scanning the primary charged particle beams over the sample (15), preferably wherein the magnetic and/or electrostatic charged particle deflectors (18) are arranged and/or controllable to obtain a substantially stationary positioning of the array of backscattered charged particle spots on the detector (11) during scanning.
     
    13. Method for inspecting a surface of a sample comprising the steps of:

    generating an array of primary charged particle beams (3, 23, 33, 43, 53) using a multi beam charged particle generator (2);

    focusing the primary charged particle beams (3, 23, 33, 43, 53) into a first array of separated spots in an intermediate plane, using a first lens system (13, 213, 37, 310) ;

    directing the primary charged particle beams from the intermediate plane towards the sample surface (15, 215, 315) using a second lens system (14, 214, 313, 314) and focusing all primary charged particle beams into a second array of individual spots on the sample surface (15, 215, 315) using an electromagnetic or electrostatic objective lens which is common for at least the primary charged particle beams (3, 23, 33, 43, 53);

    projecting backscattered charged particles from the second array of individual spots on the sample surface into an array of backscattered charged particle spots (44, 54) on the intermediate plane using said second lens system 14, 214, 313, 314); and

    detecting said backscattered charged particles using a position sensitive backscatter charged particle detector (11, 211, 311, 411, 511) positioned in or near the intermediate plane, wherein said detector comprises one or more through openings (42) for passing said primary charged particle beams (3, 23, 33, 43, 53) there through, characterized in that the second lens system (14, 214, 313, 314) comprises one or more magnetic lenses which are arranged to rotate the array of primary charged particle beams (3, 23, 33, 43, 53) around the optical axis (8, 28, 38, 48, 58) on their way from said intermediate plane towards the sample (15, 215, 315), and to position the second array with respect to the first array at an angle larger than 0 degrees and preferably smaller than 180 degrees around the optical axis (8, 28, 38, 48, 58), wherein the one or more magnetic lenses are arranged to rotate the array of backscattered charged particle spots (44, 54) with respect to the first array at an angle larger than 0 degrees and preferably smaller than 360 degrees around the optical axis (8, 28, 38, 48, 58).


     
    14. Method according to claim 13, wherein the one or more magnetic lenses are arranged to rotate the array of backscattered charged particle spots (44, 54) with respect to the first array at an angle of substantially 180 degrees around the optical axis (8, 28, 38, 48, 58), preferably wherein the detector (511) comprises one through opening for passing said primary charged particle beams (53) there through.
     
    15. Method according to claim 13 or 14, wherein the second lens system comprises magnetic and/or electrostatic charged particle deflectors (18) to scan the primary charged particle beams (3) over the sample (15), preferably wherein the magnetic and/or electrostatic charged particle deflectors (18) are arranged and/or controllable to obtain a substantially stationary positioning of the array of backscattered charged particle spots on the detector (11) during scanning, preferably in which the sample surface (15) is moved at constant speed in a first-direction while the primary charged particle beams (3) are scanned repeatedly in a second direction at least substantially perpendicular to the first direction.
     


    Ansprüche

    1. Vorrichtung zur Inspektion einer Oberfläche einer Probe, wobei die Vorrichtung einen Multibeam-Generator (2) für geladenen Teilchen zum Erzeugen einer Anordnung von Primärstrahlen geladener Teilchen (3, 23, 33, 43, 53) und ein optisches System für geladenen Teilchen mit einer optischen Achse (8, 28, 38, 48, 58) umfasst, umfassend:

    ein erstes Linsensystem (13, 213, 37, 310) zum Fokussieren der Primärstrahlen geladener Teilchen (3, 23, 33, 43, 53) in eine erste Anordnung von getrennten Punkten in einer Zwischenebene, und

    ein zweites Linsensystem (14, 214, 313, 314) zum Lenken der Primärstrahlen geladener Teilchen (3, 23, 33, 43, 53) von der Zwischenebene zur Probenoberfläche (15, 215, 315), und das eine elektromagnetische oder elektrostatische Objektivlinse umfasst, die mindestens für die Primärstrahlen geladener Teilchen (3, 23, 33, 43, 53) gemeinsam ausgebildet ist zum Fokussieren aller Primärstrahlen geladener Teilchen in eine zweite Anordnung von einzelnen Punkten auf der Probenoberfläche (15, 215, 315),

    wobei die Vorrichtung einen positionsempfindlichen Rückstreudetektor (11, 211, 311, 411, 511) für geladenen Teilchen umfasst, der in oder nahe der Zwischenebene positioniert ist, wobei der Detektor eine oder mehrere Durchgangsöffnungen (42) umfasst, die die Primärstrahlen geladener Teilchen (3, 23, 33, 43, 53) hindurchpassieren lassen, und

    wobei das zweite Linsensystem (14, 214, 313, 314) dazu angeordnet ist, dass es rückgestreute geladene Teilchen von der zweiten Anordnung von Einzelpunkten auf der Probenoberfläche in eine Anordnung von Rückstreupunkten (44, 54) von geladenen Teilchen auf dem Detektor projiziert,

    dadurch gekennzeichnet, dass

    das zweite Linsensystem (14, 214, 313, 314) eine oder mehrere magnetische Linsen umfasst, die dazu ausgebildet sind, dass sie die Anordnung von Primärstrahlen geladener Teilchen (3, 23, 33, 43, 53) auf ihrem Weg von der Zwischenebene zur Probe (15, 215, 315) um die optische Achse (8, 28, 38, 48, 58) drehen, so dass die zweite Anordnung in Bezug auf die erste Anordnung in einem Winkel von mehr als 0 Grad und bevorzugt weniger als 180 Grad um die optische Achse (8, 28, 38, 48, 58) positioniert wird, und

    wobei die eine oder die mehreren magnetischen Linsen dazu ausgebildet sind, dass sie die Anordnung von Rückstreupunkten (44, 54) von geladenen Teilchen in Bezug auf die erste Anordnung in einem Winkel von mehr als 0 Grad und bevorzugt weniger als 360 Grad um die optische Achse (8, 28, 38, 48, 58) drehen.


     
    2. Vorrichtung nach Anspruch 1, wobei die eine oder die mehreren Durchgangsöffnungen eine Anordnung von Löchern (42) umfassen, wobei jedes Loch der Anordnung von Löchern (42) dazu ausgebildet ist, dass es einen Strahl der Anordnung von Primärstrahlen (43) geladener Teilchen hindurchpassieren lässt, wobei bevorzugt der Durchmesser der Löcher der Anordnung von Löchern (42) wesentlich kleiner ist als der Abstand zwischen den Löchern.
     
    3. Vorrichtung nach Anspruch 1 oder 2, wobei die eine oder die mehreren magnetischen Linsen dazu ausgebildet sind, dass sie die Anordnung von Rückstreupunkten (54) von geladenen Teilchen in Bezug auf die erste Anordnung in einem Winkel von im Wesentlichen 180 Grad um die optische Achse (58) drehen.
     
    4. Vorrichtung nach Anspruch 3, wobei der Detektor (511) eine Durchgangsöffnung umfasst, durch die die Primärstrahlen geladener Teilchen (53) hindurchpassieren.
     
    5. Vorrichtung nach einem der vorhergehenden Ansprüche, wobei das zweite Linsensystem (14, 214, 313, 314) dazu ausgebildet ist, dass es die geladenen Rückstreuteilchen von den Einzelpunkten auf der Probenoberfläche durch ein gemeinsames Crossover der rückgestreuten geladenen Teilchen im Wesentlichen zu Einzelpunkten (44, 54) auf dem positionsempfindlichen Rückstreudetektor (11, 211, 311, 411, 511) von geladenen Teilchen projiziert.
     
    6. Vorrichtung nach Anspruch 5, wobei eine Blende (217, 317) in oder nahe der Ebene angeordnet ist, die das gemeinsame Crossover der rückgestreuten geladenen Teilchen umfasst, wobei die Blende (217, 317) bevorzugt offene Bereiche umfasst, so dass ein Passieren von gewissen Winkelrichtungen der rückgestreuten geladenen Teilchen möglich ist, während andere Winkelrichtungen gesperrt sind.
     
    7. Vorrichtung nach einem der vorhergehenden Ansprüche, wobei der positionsempfindliche Rückstreudetektor (11, 211, 311, 411, 511) für geladenen Teilchen mehr als ein Pixel pro Rückstreustrahl geladener Teilchen enthält, und/oder wobei der positionsempfindliche Rückstreudetektor (11, 211, 311, 411, 511) für geladenen Teilchen als CCD-Kamera, CMOS-Kamera, Lawinenphotodiodenarray, Photomultiplier oder PN-Halbleiterübergangsdetektor ausgebildet ist und direkt ein Signal von den geladenen Rückstreuteilchen erhält.
     
    8. Vorrichtung nach einem der Ansprüche 1 bis 6, wobei der positionsempfindliche Rückstreudetektor (11, 211, 311, 411, 511) für geladenen Teilchen einen Fluoreszenzschirm, der mindestens im Wesentlichen in oder nahe der Zwischenebene angeordnet ist, und eine optische Anordnung zum Befördern von Photonen vom Fluoreszenzschirm zu einer CCD-Kamera, einer CMOS-Kamera, einem Lawinenphotodiodenarray oder Photomultipliern umfasst, wobei bevorzugt die CCD-Kamera, die CMOS-Kamera, das Lawinenphotodiodenarray oder die Photomultiplier derart angeordnet ist/sind, dass die Anordnung von Detektorpixeln mit der Anordnung von Abbildungen der einzelnen Rückstreustrahlen übereinstimmt.
     
    9. Vorrichtung nach einem der vorhergehenden Ansprüche, wobei das zweite Linsensystem (14, 214, 313, 314) dazu ausgebildet ist, dass es die erste Anordnung von getrennten Punkten (43, 53) von der Zwischenebene auf die Probenoberfläche mit einer Vergrößerung in einem Bereich von 0,01 bis 0,2 abbildet.
     
    10. Vorrichtung nach einem der vorhergehenden Ansprüche, wobei der Abstand zwischen den Punkten in der zweiten Anordnung von getrennten Punkten auf der Probenoberfläche (15, 215; 315) zwischen 0,3 und 30 Mikrometern beträgt.
     
    11. Vorrichtung nach einem der vorhergehenden Ansprüche, wobei das zweite Linsensystem (14, 214) dazu ausgebildet ist, dass es die Primärstrahlen geladener Teilchen durch ein gemeinsames Crossover projiziert, und wobei die Vorrichtung einen positionsempfindlichen Sekundärelektronendetektor (16, 216) umfasst, der mindestens im Wesentlichen in oder nahe einer Ebene positioniert ist, die das gemeinsame Crossover umfasst.
     
    12. Vorrichtung nach einem der vorhergehenden Ansprüche, wobei das zweite Linsensystem (14) magnetische und/oder elektrostatische Deflektoren (18) für geladenen Teilchen zum Abtasten der Primärstrahlen geladener Teilchen über der Probe (15) umfasst, wobei die magnetischen und/oder elektrostatischen Deflektoren (18) für geladenen Teilchen bevorzugt so angeordnet und/oder ansteuerbar sind, dass eine im Wesentlichen stationäre Positionierung der Anordnung von Rückstreupunkten von geladenen Teilchen auf dem Detektor (11) beim Abtasten erhalten wird.
     
    13. Verfahren zur Inspektion einer Oberfläche einer Probe, umfassend die Schritte:

    Erzeugen einer Anordnung von Primärstrahlen geladener Teilchen (3, 23, 33, 43, 53) mit einem Multibeam-Generator (2) für geladenen Teilchen;

    Fokussieren der Primärstrahlen geladener Teilchen (3, 23, 33, 43, 53) in eine erste Anordnung von getrennten Punkten in einer Zwischenebene mit einem ersten Linsensystem (13, 213, 37, 310);

    Lenken der Primärstrahlen geladener Teilchen von der Zwischenebene zur Probenoberfläche (15, 215, 315) mit einem zweiten Linsensystem (14, 214, 313, 314) und

    Fokussieren aller Primärstrahlen geladener Teilchen in eine zweite Anordnung von einzelnen Punkten auf der Probenoberfläche (15, 215, 315) mit einer elektromagnetischen oder elektrostatischen Objektivlinse, die mindestens für die Primärstrahlen geladener Teilchen (3, 23, 33, 43, 53) gemeinsam ausgebildet ist;

    Projizieren von rückgestreuten geladenen Teilchen von der zweiten Anordnung von Einzelpunkten auf der Probenoberfläche in eine Anordnung von Rückstreupunkten (44, 54) von geladenen Teilchen auf der Zwischenebene mit dem zweiten Linsensystem (14, 214, 313, 314); und

    Detektieren der rückgestreuten geladenen Teilchen mit einem positionsempfindlichen Rückstreudetektor (11, 211, 311, 411, 511) für geladenen Teilchen, der in oder nahe der Zwischenebene positioniert ist, wobei der Detektor eine oder mehrere Durchgangsöffnungen (42) umfasst, die die Primärstrahlen geladener Teilchen (3, 23, 33, 43, 53) hindurchpassieren lassen,

    dadurch gekennzeichnet, dass

    das zweite Linsensystem (14, 214, 313, 314) eine oder mehrere magnetische Linsen umfasst, die dazu angeordnet sind, dass sie die Anordnung von Primärstrahlen geladener Teilchen (3, 23, 33, 43, 53) auf ihrem Weg von der Zwischenebene zur Probe (15, 215, 315) um die optische Achse (8, 28, 38, 48, 58) drehen, und die zweite Anordnung in Bezug auf die erste Anordnung in einem Winkel von mehr als 0 Grad und bevorzugt weniger als 180 Grad um die optische Achse (8, 28, 38, 48, 58) positionieren, wobei die eine oder die mehreren magnetischen Linsen dazu angeordnet sind, dass sie die Anordnung von Rückstreupunkten (44, 54) von geladenen Teilchen in Bezug auf die erste Anordnung in einem Winkel von mehr als 0 Grad und bevorzugt weniger als 360 Grad um die optische Achse (8, 28, 38, 48, 58) drehen.


     
    14. Verfahren nach Anspruch 13, wobei die eine oder die mehreren magnetischen Linsen dazu angeordnet sind, dass sie die Anordnung von Rückstreupunkten (44, 54) von geladenen Teilchen in Bezug auf die erste Anordnung in einem Winkel von im Wesentlichen 180 Grad um die optische Achse (8, 28, 38, 48, 58) drehen, wobei der Detektor (511) bevorzugt eine Durchgangsöffnung umfasst, durch die die Primärstrahlen geladener Teilchen (53) hindurchpassieren.
     
    15. Verfahren nach Anspruch 13 oder 14, wobei das zweite Linsensystem magnetische und/oder elektrostatische Deflektoren (18) für geladenen Teilchen zum Abtasten der Primärstrahlen (3) geladener Teilchen über der Probe (15) umfasst, wobei die magnetischen und/oder elektrostatischen Deflektoren (18) für geladenen Teilchen bevorzugt so angeordnet und/oder ansteuerbar sind, dass eine im Wesentlichen stationäre Positionierung der Anordnung von Rückstreupunkten von geladenen Teilchen auf dem Detektor (11) beim Abtasten erhalten wird, bei dem bevorzugt die Probenoberfläche (15) mit einer konstanten Geschwindigkeit in eine erste Richtung bewegt wird, während die Primärstrahlen (3) geladener Teilchen wiederholt in einer zweiten Richtung abgetastet werden, die mindestens im Wesentlichen senkrecht zur ersten Richtung liegt.
     


    Revendications

    1. Appareil pour l'inspection d'une surface d'un échantillon, dans lequel l'appareil comprend un générateur de particules chargées à faisceaux multiples (2) pour générer un réseau de faisceaux de particules chargées primaires (3, 23, 33, 43, 53) et un système optique à particules chargées avec un axe optique (8, 28, 38, 48, 58) comprenant :

    un premier système de lentille (13, 213, 37, 310) pour focaliser les faisceaux de particules chargées primaires (3, 23, 33, 43, 53) en un premier réseau de faisceaux ponctuels séparés dans un plan intermédiaire, et

    un second système de lentille (14, 214, 313, 314) pour diriger les faisceaux de particules chargées primaires (3, 23, 33, 43, 53) du plan intermédiaire vers la surface d'échantillon (15, 215, 315) et qui comprend une lentille d'objectif électromagnétique ou électrostatique qui est commune pour au moins les faisceaux de particules chargées primaires (3, 23, 33, 43, 53) pour focaliser tous les faisceaux de particules chargées primaires en un second réseau de faisceaux ponctuels séparés sur la surface d'échantillon (15, 215, 315) ,

    dans lequel l'appareil comprend un détecteur de particules chargées à rétrodiffusion sensible à la position (11, 211, 311, 411, 511) positionné dans ou près du plan intermédiaire, dans lequel ledit détecteur comprend une ou plusieurs ouvertures passantes (42) pour faire passer au travers lesdits faisceaux de particules chargées primaires (3, 23, 33, 43, 53) et dans lequel ledit second système de lentille (14, 214, 313, 314) est agencé pour projeter des particules chargées rétrodiffusées provenant du second réseau de faisceaux ponctuels individuels sur la surface d'échantillon en un réseau de faisceaux ponctuels de particules chargées rétrodiffusées (44, 54) sur le détecteur,

    caractérisé en ce que le second système de lentille (14, 214, 313, 314) comprend une ou plusieurs lentilles magnétiques qui sont adaptées pour faire tourner le réseau de faisceaux de particules chargées primaires (3, 23, 33, 43, 53) autour de l'axe optique (8, 28, 38, 48, 58) sur leur chemin dudit plan intermédiaire vers l'échantillon (15, 215, 315), pour positionner le second réseau par rapport au premier réseau à un angle supérieur à 0 degré et de préférence inférieur à 180 degrés autour de l'axe optique (8, 28, 38, 48, 58), et

    dans lequel les une ou plusieurs lentilles magnétiques sont adaptées pour faire tourner le réseau de faisceaux ponctuels de particules chargées rétrodiffusées (44, 54) par rapport au premier réseau à un angle supérieur à 0 degré et de préférence inférieur à 360 degrés autour de l'axe optique (8, 28, 38, 48, 58).


     
    2. Appareil selon la revendication 1, dans lequel lesdites une ou plusieurs ouvertures passantes comprennent un réseau de trous (42) dans lequel chaque trou du réseau de trous (42) est adapté pour faire passer au travers un dudit réseau de faisceaux de particules chargées primaires (43), de préférence dans lequel le diamètre des trous du réseau de trous (42) est sensiblement inférieur au pas entre les trous.
     
    3. Appareil selon la revendication 1 ou 2, dans lequel les une ou plusieurs lentilles magnétiques sont adaptées pour faire tourner le réseau de faisceaux ponctuels de particules chargées rétrodiffusées (54) par rapport au premier réseau à un angle de sensiblement 180 degrés autour de l'axe optique (58).
     
    4. Appareil selon la revendication 3, dans lequel le détecteur (511) comprend une ouverture passante pour faire passer au travers lesdits faisceaux de particules chargées primaires (53).
     
    5. Appareil selon l'une quelconque des revendications précédentes, dans lequel le second système de lentille (14, 214, 313, 314) est adapté pour projeter les particules chargées rétrodiffusées provenant des faisceaux ponctuels individuels sur la surface d'échantillon à travers une confluence commune des particules chargées rétrodiffusées à des faisceaux ponctuels sensiblement individuels (44, 54) sur le détecteur de particules chargées à rétrodiffusion sensible à la position (11, 211, 311, 411, 511).
     
    6. Appareil selon la revendication 5, dans lequel une ouverture (217, 317) est agencée dans ou près du plan comprenant la confluence commune des particules chargées rétrodiffusées, de préférence dans lequel ladite ouverture (217, 317) comprend des zones ouvertes pour permettre le passage de certaines directions angulaires des particules chargées rétrodiffusées, tout en bloquant d'autres directions angulaires.
     
    7. Appareil selon l'une quelconque des revendications précédentes, dans lequel le détecteur de particules chargées à rétrodiffusion sensible à la position (11, 211, 311, 411, 511) contient plus d'un pixel par faisceau de particules chargées rétrodiffusées, et/ou dans lequel le détecteur de particules chargées à rétrodiffusion sensible à la position (11, 211, 311, 411, 511) est une caméra CCD, une caméra CMOS, un réseau de photodiodes à avalanche, de photomultiplicateurs ou un détecteur à semi-conducteur à jonction PN qui obtient un signal directement à partir des particules chargées rétrodiffusées.
     
    8. Appareil selon l'une quelconque des revendications 1 à 6, dans lequel le détecteur de particules chargées à rétrodiffusion sensible à la position (11, 211, 311, 411, 511) comprend un écran fluorescent agencé au moins sensiblement dans ou près dudit plan intermédiaire et un agencement optique pour acheminer des photons de l'écran fluorescent à une caméra CCD, une caméra CMOS, un réseau de photodiodes à avalanche ou de photomultiplicateurs, de préférence dans lequel la caméra CCD, la caméra CMOS, le réseau de photodiodes à avalanche ou de photomultiplicateurs est positionné de manière que le réseau de pixels de détecteur coïncide avec le réseau d'images des faisceaux rétrodiffusés individuels.
     
    9. Appareil selon l'une quelconque des revendications précédentes, dans lequel le second système de lentille (14, 214, 313, 314) est adapté pour imager le premier réseau de faisceaux ponctuels séparés (43, 53) provenant dudit plan intermédiaire sur la surface d'échantillon avec un agrandissement dans une plage de 0,01 à 0,2.
     
    10. Appareil selon l'une quelconque des revendications précédentes, dans lequel le pas entre les faisceaux ponctuels dans le second réseau de faisceaux ponctuels séparés sur la surface d'échantillon (15, 215, 315) est entre 0,3 et 30 micromètres.
     
    11. Appareil selon l'une quelconque des revendications précédentes, dans lequel le second système de lentille (14, 214) est adapté pour projeter les faisceaux de particules chargées primaires à travers une convergence commune, et dans lequel l'appareil comprend un détecteur d'électrons secondaires sensible à la position (16, 216) positionné au moins sensiblement dans ou près d'un plan comprenant ladite convergence commune.
     
    12. Appareil selon l'une quelconque des revendications précédentes, dans lequel le second système de lentille (14) comprend des déflecteurs de particules chargées magnétiques et/ou électrostatiques (18) pour balayer les faisceaux de particules chargées primaires sur l'échantillon (15), de préférence dans lequel les déflecteurs de particules chargées magnétiques et/ou électrostatiques (18) sont agencés et/ou peuvent être commandés pour obtenir un positionnement sensiblement stationnaire du réseau de faisceaux ponctuels de particules chargées rétrodiffusées (11) durant le balayage.
     
    13. Méthode pour l'inspection d'une surface d'un échantillon, comprenant les étapes suivantes :

    la génération d'un réseau de faisceaux de particules chargées primaires (3, 23, 33, 43, 53) en utilisant un générateur de particules chargées à faisceaux multiples (2) ;

    la focalisation des faisceaux de particules chargées primaires (3, 23, 33, 43, 53) en un premier réseau de faisceaux ponctuels séparés dans un plan intermédiaire, en utilisant un premier système de lentille (13, 213, 37, 310) ;

    diriger les faisceaux de particules chargées primaires du plan intermédiaire vers la surface d'échantillon (15, 215, 315) en utilisant un second système de lentille (14, 214, 313, 314) et la focalisation de tous les faisceaux de particules chargées primaires en un second réseau de faisceaux ponctuels séparés sur la surface d'échantillon (15, 215, 315) en utilisant une lentille d'objectif électromagnétique ou électrostatique qui est commune pour au moins les faisceaux de particules chargées primaires (3, 23, 33, 43, 53) ;

    la projection de particules chargées rétrodiffusées provenant du second réseau de faisceaux ponctuels individuels sur la surface d'échantillon en un réseau de faisceaux ponctuels de particules chargées rétrodiffusées (44, 54) sur le plan intermédiaire en utilisant ledit second système de lentille (14, 214, 313, 314) ; et

    la détection desdites particules chargées rétrodiffusées en utilisant un détecteur de particules chargées à rétrodiffusion sensible à la position (11, 211, 311, 411, 511) positionné dans ou près du plan intermédiaire, dans laquelle ledit détecteur comprend une ou plusieurs ouvertures passantes (42) pour faire passer au travers lesdits faisceaux de particules chargées primaires (3, 23, 33, 43, 53), caractérisée en ce que ledit second système de lentille (14, 214, 313, 314) comprend une ou plusieurs lentilles magnétiques qui sont agencées pour faire tourner le réseau de faisceaux de particules chargées primaires (3, 23, 33, 43, 53) autour de l'axe optique (8, 28, 38, 48, 58) sur leur chemin dudit plan intermédiaire vers l'échantillon (15, 215, 315), et pour positionner le second réseau par rapport au premier réseau à un angle supérieur à 0 degré et de préférence inférieur à 180 degrés autour de l'axe optique (8, 28, 38, 48, 58), dans laquelle les une ou plusieurs lentilles magnétiques sont adaptées pour faire tourner le réseau de faisceaux ponctuels de particules chargées rétrodiffusées (44, 54) par rapport au premier réseau à un angle supérieur à 0 degré et de préférence inférieur à 360 degrés autour de l'axe optique (8, 28, 38, 48, 58).


     
    14. Méthode selon la revendication 13, dans laquelle les une ou plusieurs lentilles magnétiques sont adaptées pour faire tourner le réseau de faisceaux ponctuels de particules chargées rétrodiffusées (44. 54) par rapport au premier réseau à un angle de sensiblement 180 degrés autour de l'axe optique (8, 28, 38, 48, 58), de préférence dans laquelle le détecteur (511) comprend une ouverture passante pour faire passer au travers lesdits faisceaux de particules chargées primaires (53).
     
    15. Méthode selon la revendication 13 ou 14, dans laquelle le second système de lentille comprend des déflecteurs de particules chargées magnétiques et/ou électrostatiques (18) pour balayer les faisceaux de particules chargées primaires (3) sur l'échantillon (15), de préférence dans laquelle les déflecteurs de particules chargées magnétiques et/ou électrostatiques (18) sont agencés et/ou peuvent être commandés pour obtenir un positionnement sensiblement stationnaire du réseau de faisceaux ponctuels de particules chargées rétrodiffusées (11) durant le balayage, de préférence dans laquelle la surface d'échantillon (15) est déplacée à une vitesse constante dans une première direction alors que les faisceaux de particules chargées primaires (3) sont balayés de manière répétée dans une seconde direction au moins sensiblement perpendiculaire à la première direction.
     




    Drawing


















    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description