A new multi-beam apparatus with a total FOV variable in size, orientation and incident angle, is proposed. The new apparatus provides more flexibility to speed the sample observation and enable more samples observable. More specifically, as a yield management tool to inspect and/or review defects on wafers/masks in semiconductor manufacturing industry, the new apparatus provide more possibilities to achieve a high throughput and detect more kinds of defects.
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0. 99. A method to configure a multi-beam apparatus for observing a surface of a sample, the method comprising:
forming a plurality of virtual images of an electron source using an image-forming device with electron optics elements, wherein the virtual images are used to form a plurality of probe spots on the surface; and
moving the image forming device along a primary axis to vary pitches of the plurality of probe spots.
0. 80. A source-conversion unit comprising:
a beamlet-limit device with a plurality of beam-limit openings configured to allow a plurality of beamlets to pass through: and
an image-forming device movable along a primary optical axis and comprising a plurality of electron optics elements, wherein at least some of the plurality of electron optics are configured to deflect at least some of the plurality of beamlets towards the primary optical axis.
79. A method for observing a sample surface, said method comprising steps of:
providing a plurality of charged particle beams with a plurality of crossovers respectively using a source-conversion unit;
projecting the plurality of crossovers onto the sample surface to form a plurality of probe spots thereon using an objective lens;
scanning the plurality of probe spots on the sample surface; and
changing a distance from a deflection angles of the plurality of charged particle beams plane of the source-conversion unit to the objective lens such that pitches of the plurality of probe spots can be adjusted.
78. An apparatus, comprising:
a source for providing a primary charged particle beam;
a beamlet-limit means with beam-limit openings for using allowing a plurality of beamlets of the primary charged particle beam to pass through, the plurality of beamlets being used to form a plurality of images of the source;
an objective lens for projecting the plurality of images onto a sample surface to form a plurality of probe spots; and
an image-forming means with electron optics elements for adjusting pitches of the plurality of probe spots on the sample surface by moving along a primary optical axis.
55. A method to configure a multi-beam apparatus for observing a surface of a sample, comprising steps of:
configuring an image-forming means of a source-conversion unit movable along a primary optical axis thereof, the image-forming means having a plurality of electron optics elements;
using said image-forming means to form a plurality of virtual images of an electron source respectively;
using an objective lens to image said plurality of virtual images onto said surface and form a plurality of probe spots thereon; and
moving said image-forming means to vary pitches of said plurality of probe spots.
77. An apparatus, comprising:
a source for providing a primary charged particle beam;
a source-conversion unit for dividing the primary charged particle beam into a plurality of charged particle beamlets and using which to form a plurality of images of the source respectively, the source-conversion unit comprising a beamlet-limit means with beam-limit openings and an image-forming means with electron optics elements;
an objective lens below said source-conversion unit for projecting the plurality of images onto a sample surface;
wherein pitches of the plurality of charged particle beamlets on the sample surface are adjustable by changing deflection angles of the plurality of charged particle beamlets prior entering a distance from a deflection plane of the source-conversion unit to the objective lens.
0. 87. A multi-beam apparatus comprising:
an electron source configured to generate a charged-particle beam along a primary optical axis:
a source-conversion unit comprising:
a beamlet-limit device with a plurality of beam-limit openings configured to allow a plurality of beamlets of the charged-particle beam to pass through, and
an image-forming device movable along the primary optical axis and comprising a plurality of electron optics elements, wherein at least some of the plurality of electron optics are configured to deflect at least some of the plurality of beamlets towards the primary optical axis: and
an objective lens configured to focus the plurality of beamlets on a surface of a sample to form a plurality of probe spots.
1. A multi-beam apparatus for observing a surface of a sample, comprising:
an electron source;
a condenser lens below said electron source;
a source-conversion unit below said condenser lens;
an objective lens below said source-conversion unit;
a deflection scanning unit below said source-conversion unit;
a sample stage below said objective lens;
a beam separator below said source-conversion unit;
a secondary projection imaging system; and
an electron detection device with a plurality of detection elements,
wherein said electron source, said condenser lens and said objective lens are aligned with a primary optical axis of said apparatus, and said sample stage sustains said sample so that said surface faces to said objective lens,
wherein said source-conversion unit comprises a beamlet-limit means with a plurality of beam-limit openings, and an image-forming means with a plurality of electron optics elements and movable along said primary optical axis,
wherein said electron source generates a primary-electron beam along said primary optical axis and said condenser lens focuses said primary-electron beam,
wherein a plurality of beamlets of said primary-electron beam pass through said plurality of beam-limit openings respectively, and is deflected by said plurality of electron optics elements towards said primary optical axis to form a plurality of virtual images of said electron source respectively,
wherein said plurality of beamlets is focused by said objective lens onto said surface and therefore forms a plurality of probe spots thereon respectively, and said deflection scanning unit deflects said plurality of beamlets to scan said plurality of probe spots respectively over a plurality of scanned regions within an observed area on said surface,
wherein a plurality of secondary electron beams is generated by said plurality of probe spots respectively from said plurality of scanned regions and directed into said secondary projection imaging system by said beam separator, said secondary projection imaging system focuses and keeps said plurality of secondary electron beams to be detected by said plurality of detection elements respectively, and each detection element therefore provides an image signal of one corresponding scanned region.
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0. 12. A multi-beam apparatus for observing a surface of a sample, comprising:
an electron source;
a condenser lens below said electron source;
a source-conversion unit below said condenser lens;
an objective lens below said source-conversion unit;
a deflection scanning unit below said source-conversion unit;
a sample stage below said objective lens;
a beam separator below said source-conversion unit;
a secondary projection imaging system; and
an electron detection device with a plurality of detection elements,
wherein said electron source, said condenser lens and said objective lens are aligned with a primary optical axis of said apparatus, and said sample stage sustains said sample so that said surface faces to said objective lens,
wherein said source-conversion unit comprises a beamlet-limit means with a plurality of beam-limit openings, a first image-forming means with a plurality of first electron optics elements and a second image-forming means with a plurality of second electron optics elements, said second image-forming means is below said first image-forming means and movable in a radial direction, and one of said first image-forming means and said second image-forming means is used as an active image-forming means,
wherein said electron source generates a primary-electron beam along said primary optical axis and said condenser lens focuses said primary-electron beam,
wherein a plurality of beamlets of said primary-electron beam pass through said plurality of beam-limit openings respectively, and is deflected by said active image-forming means towards said primary optical axis to form a plurality of virtual images of said electron source respectively,
wherein said plurality of beamlets is focused by said objective lens onto said surface and therefore forms a plurality of probe spots thereon respectively, and said deflection scanning unit deflect said plurality of beamlets to scan said plurality of probe spots respectively over a plurality of scanned regions within an observed area on said surface,
wherein a plurality of secondary electron beams is generated by said plurality of probe spots respectively from said plurality of scanned regions and directed into said secondary projection imaging system by said beam separator, said secondary projection imaging system focuses and keeps said plurality of secondary electron beams to be detected by said plurality of detection elements respectively, and each detection element therefore provides an image signal of one corresponding scanned region.
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0. 23. An multi-beam apparatus for observing a surface of a sample, comprising:
an electron source;
a condenser lens below said electron source;
a source-conversion unit below said condenser lens;
an objective lens below said source-conversion unit;
a deflection scanning unit below said source-conversion unit;
a sample stage below said objective lens;
a beam separator below said source-conversion unit;
a secondary projection imaging system; and
an electron detection device with a plurality of detection elements,
wherein said electron source, said condenser lens and said objective lens are aligned with a primary optical axis of said apparatus, a first principal plane of said objective lens is movable along said primary optical axis, and said sample stage sustains said sample so that said surface faces to said objective lens,
wherein said source-conversion unit comprises a beamlet-limit means with a plurality of beam-limit openings, and an image-forming means with a plurality of electron optics elements,
wherein said electron source generates a primary-electron beam along said primary optical axis and said condenser lens focuses said primary-electron beam,
wherein a plurality of beamlets of said primary-electron beam pass through said plurality of beam-limit openings respectively, and is deflected by said plurality of electron optics elements towards said primary optical axis to form a plurality of virtual images of said electron source respectively,
wherein said plurality of beamlets is focused by said objective lens onto said surface and therefore forms a plurality of probe spots thereon respectively, and said deflection scanning unit deflects said plurality of beamlets to scan said plurality of probe spots respectively over a plurality of scanned regions within an observed area on said surface,
wherein a plurality of secondary electron beams is generated by said plurality of probe spots respectively from said plurality of scanned regions and directed into said secondary projection imaging system by said beam separator, said secondary projection imaging system focuses and keeps said plurality of secondary electron beams to be detected by said plurality of detection elements respectively, and each detection element therefore provides an image signal of one corresponding scanned region.
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0. 40. A multi-beam apparatus for observing a surface of a sample, comprising:
an electron source;
a condenser lens below said electron source;
a source-conversion unit below said condenser lens;
a transfer lens below said source-conversion unit;
a field lens below said transfer lens;
an objective lens below said field lens;
a deflection scanning unit below said source-conversion unit;
a sample stage below said objective lens;
a beam separator below said source-conversion unit;
a secondary projection imaging system; and
an electron detection device with a plurality of detection elements,
wherein said electron source, said condenser lens, said transfer lens, said field lens and said objective lens are aligned with a primary optical axis of said apparatus, and said sample stage sustains said sample so that said surface faces to said objective lens,
wherein said source-conversion unit comprises a beamlet-limit means with a plurality of beam-limit openings, and an image-forming means with a plurality of electron optics elements,
wherein said electron source generates a primary-electron beam along said primary optical axis and said condenser lens focuses said primary-electron beam,
wherein a plurality of beamlets of said primary-electron beam pass through said plurality of beam-limit openings respectively, and is deflected by said plurality of electron optics elements towards said primary optical axis to form a plurality of first virtual images of said electron source respectively,
wherein said transfer lens images said plurality of first virtual images onto an intermediate image plane and therefore forms a plurality of second real images respectively thereon, said field lens is placed on said intermediate image plane and bends said plurality of beamlets, said objective lens images said plurality of second real images onto said surface and therefore forms a plurality of probe spots thereon respectively, and said deflection scanning unit deflects said plurality of beamlets to scan said plurality of probe spots respectively over a plurality of scanned regions within an observed area on said surface,
wherein a plurality of secondary electron beams is generated by said plurality of probe spots respectively from said plurality of scanned regions and directed into said secondary projection imaging system by said beam separator, said secondary projection imaging system focuses and keeps said plurality of secondary electron beams to be detected by said plurality of detection elements respectively, and each detection element therefore provides an image signal of one corresponding scanned region.
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0. 56. A method to configure a multi-beam apparatus for observing a surface of a sample, comprising steps of:
configuring a source-conversion unit with a first image-forming means and a second image-forming means, wherein said second image-forming means is farther away from an electron source than said first image-forming means and movable in a radial direction of said apparatus;
using one of said first image-forming means and said second image-forming means as an active image-forming means, wherein when said first image-forming means is used, said second image-forming means is moved away;
using said active image-forming means to form a plurality of virtual images of said electron source respectively;
using an objective lens to image said plurality of virtual images onto said surface and form a plurality of probe spots thereon; and
changing said active image-forming means between said first image-forming means and said second image-forming means to vary pitches of said plurality of probe spots.
0. 57. A method to configure a multi-beam apparatus for observing a surface of a sample, comprising steps of:
configuring an objective lens with a first principal plane movable along a primary optical axis of said apparatus;
using an image-forming means of a source-conversion unit to form a plurality of virtual images of an electron source respectively;
using said objective lens to image said plurality of virtual images onto said surface and form a plurality of probe spots thereon; and
moving said first principal plane to vary pitches of said plurality of probe spots.
0. 58. A method to configure a multi-beam apparatus for observing a surface of a sample, comprising steps of:
configuring an objective lens with a lower magnetic lens and an electrostatic lens in said apparatus;
using an image-forming means of a source-conversion unit to form a plurality of virtual images of an electron source respectively;
using said objective lens to image said plurality of virtual images onto said surface and form a plurality of probe spots thereon; and
changing a ratio of focusing powers of said magnetic lens and said electrostatic lens to select an orientation of said plurality of probe spots.
0. 59. The method according to
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0. 61. A method to configure a multi-beam apparatus for observing a surface of a sample, comprising steps of:
using an image-forming means of a source-conversion unit to deflect a plurality of beamlets from an electron source to form a plurality of first virtual images thereof respectively;
using an objective lens to image said plurality of virtual images onto said surface and form a plurality of probe spots thereon; and
setting deflection angles of said plurality of beamlets due to said image-forming means so that said plurality of beamlets lands on said surface with same or substantially same landing angles.
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0. 65. A method to configure a multi-beam apparatus for observing a surface of a sample, comprising steps of:
using an image-forming means of a source-conversion unit to deflect a plurality of beamlets from an electron source to form a plurality of first virtual images thereof respectively;
using a transfer lens to image said plurality of first virtual images onto an intermediate image plane and forms a plurality of second real images respectively;
placing a field lens on said intermediate image plane to bend said plurality of beamlets; and
using an objective lens to image said plurality of second real images onto said surface and form a plurality of probe spots thereon.
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0. 81. The source-conversion unit of claim 80, wherein the deflection of the at least some of the plurality of beamlets towards the primary optical axis form a plurality of virtual images of an electron source.
0. 82. The source-conversion unit of claim 80, wherein the at least some of the plurality of electron optics elements are configured to deflect at least some of the plurality of beamlets at deflection angles to reduce off-axis aberrations of a plurality of probe spots.
0. 83. The source-conversion unit of claim 82, wherein the plurality of probe spots have pitches that are varied together by moving the image-forming device along the primary optical axis.
0. 84. The source-conversion unit of claim 82, wherein the plurality of probe spots have an orientation that is selectable by varying a ratio of focusing powers of a magnetic lens and an electrostatic lens.
0. 85. The source-conversion unit of claim 82, wherein the deflection angles enable the at least some of the plurality of beamlets to land on a surface of a sample perpendicularly or substantially perpendicularly.
0. 86. The source-conversion unit of claim 82, wherein the deflection angles enable the at least some of the plurality of beamlets to obliquely land on a surface of a sample with a same or substantially same landing angles.
0. 88. The multi-beam apparatus of claim 87, wherein the deflection of the at least some of the plurality of beamlets towards the primary optical axis form a plurality of virtual images of the electron source.
0. 89. The multi-beam apparatus of claim 87, wherein the objective lens comprises a magnetic lens and an electrostatic lens.
0. 90. The multi-beam apparatus of claim 89, wherein the magnetic lens and the electrostatic lens are configured to enable a selection of an orientation of the plurality of probe by varying a ratio of focusing powers of the magnetic lens and the electrostatic lens.
0. 91. The multi-beam apparatus of claim 87, wherein the plurality of probe spots have pitches that are varied together by moving the image-forming device along the primary optical axis.
0. 92. The multi-beam apparatus of claim 87, wherein the at least some of the plurality of electron optics elements are configured to deflect at least some of the plurality of beamlets at deflection angles to reduce off-axis aberrations of the plurality of probe spots.
0. 93. The multi-beam apparatus of claim 92, wherein the deflection angles enable the at least some of the plurality of beamlets to land on a surface of a sample perpendicularly or substantially perpendicularly.
0. 94. The multi-beam apparatus of claim 92, wherein the deflection angles enable the at least some of the plurality of beamlets to obliquely land on a surface of a sample with same or substantially same landing angles.
0. 95. The multi-beam apparatus of claim 87, further comprising a deflection scanning unit positioned above a front focal plan of the objective lens.
0. 96. The multi-beam apparatus of claim 95, wherein the deflection scanning unit is configured to tilt the plurality of beamlets to obliquely land on the surface with a same or substantially the same landing angles.
0. 97. The multi-beam apparatus of claim 87, further comprising a beamlet-tilting deflector positioned between the source-conversion unit and a front focal plan of the objective lens.
0. 98. The multi-beam apparatus of claim 97, wherein the beamlet-tilting deflector is configured to tilt the plurality of beamlets to obliquely land on the surface with a same or substantially the same landing angles.
0. 100. The method of claim 99, further comprising forming the plurality of probe spots on the sample using an objective lens to image the plurality of virtual images on the surface.
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This application is a reissue of U.S. Pat. No. 10,062,541 B2, issued on Aug. 28, 2018, from U.S. patent application Ser. No. 15/417,360, filed Jan. 27, 2017, which claims the benefit of priority of U.S. provisional application No. 62/287,626 entitled to Ren et al. filed on Jan. 27, 2016 and entitled “Apparatus of Plural Charged-Particle Beams”, the entire disclosures of which are incorporated herein by reference. The contents of the above-identified applications are incorporated herein by reference in their entireties.
This application is related to U.S. application Ser. No. 15/065,342 entitled to Ren et al. filed on Mar. 9, 2016 and entitled “Apparatus of Plural Charged-Particle Beams”, the entire disclosures of which are incorporated herein by reference
This application is related to U.S. application Ser. No. 15/078,369 entitled to Ren et al. filed on Mar. 23, 2016 and entitled “Apparatus of Plural Charged-Particle Beams”, the entire disclosures of which are incorporated herein by reference.
This application is related to U.S. application Ser. No. 15/150,858 entitled to Liu et al. filed on May 10, 2016 and entitled “Apparatus of Plural Charged-Particle Beams”, the entire disclosures of which are incorporated herein by reference.
This application is related to U.S. application Ser. No. 15/213,781 entitled to Li et al. filed on Jul. 19, 2016 and entitled “Apparatus of Plural Charged-Particle Beams”, the entire disclosures of which are incorporated herein by reference.
This application is related to U.S. application Ser. No. 15/216,258 entitled to Ren et al. filed on Jul. 21, 2016 and entitled “Apparatus of Plural Charged-Particle Beams”, the entire disclosures of which are incorporated herein by reference.
This application is related to U.S. application Ser. No. 15/365,145 entitled to Ren et al. filed on Nov. 30, 2016 and entitled “Apparatus of Plural Charged-Particle Beams”, the entire disclosures of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus with a plurality of charged-particle beams. More particularly, it relates to an apparatus which employs plural charged-particle beams to simultaneously acquire images of plural scanned regions within an observed area on a sample surface. Hence, the apparatus can be used to inspect and/or review defects on wafers/masks with high resolution and high throughput in semiconductor manufacturing industry.
2. Description of the Prior Art
The following description and examples are not admitted to be prior art by their mention in this Background section. For manufacturing semiconductor IC chips, pattern defects and/or uninvited particles (residuals) inevitably appear on surfaces of wafers/mask during fabrication processes, which reduce the yield to a great degree. Accordingly, the yield management tools are used to inspect and/or review the defects and the particles. To meet the more and more advanced requirements on performance of IC chips, the patterns with smaller and smaller critical feature dimensions have been adopted. Consequently, the conventional yield management tools with optical beam gradually become incompetent due to diffraction effect, and the yield management tools with electron beam are more and more employed. Compared to a photon beam, an electron beam has a shorter wavelength and thereby possibly offering superior spatial resolution. Currently, the yield management tools with electron beams employ the principle of scanning electron microscope (SEM) with a single electron beam, and as well known their throughputs are not competent for mass production. Although increasing the beam currents can improve the throughputs, the superior spatial resolutions will be fundamentally deteriorated by Coulomb Effect which increases with the beam currents.
For mitigating the limitation on throughput, instead of using a single electron beam with a large current, a promising solution is to use a plurality of electron beams each with a small current. The plurality of electron beams forms a plurality of probe spots or simply called as a probe spot array on one being-inspected or observed surface of a sample. The plurality of probe spots can respectively and simultaneously scan a plurality of small scanned regions within a large observed area on the sample surface. The electrons of each probe spot generate secondary electrons from the sample surface where they land on. The secondary electrons comprise slow secondary electrons (energies ≤50 eV) and backscattered electrons (energies close to landing energies of the electrons). The secondary electrons from the plurality of small scanned regions can be respectively and simultaneously collected by a plurality of electron detectors. Consequently, the image of the large observed area including all of the small scanned regions can be obtained much faster than scanning the large observed area with a single beam.
The plurality of electron beams can be either from a plurality of electron sources respectively, or from a single electron source. For the former, the plurality of electron beams is usually focused onto and scans the plurality of small scanned regions by a plurality of columns respectively, and the secondary electrons from each scanned region are detected by one electron detector inside the corresponding column. The apparatus therefore is generally called as a multi-column apparatus. On the sample surface, the beam interval or pitch is on the order of several to tens millimeters.
For the latter, a source-conversion unit virtually changes the single electron source into a plurality of sub-sources. The source-conversion unit comprises one beamlet-limit (or beamlet-forming) means with a plurality of beam-limit openings and one image-forming means with a plurality of electron optics elements. The plurality of beam-limit openings divides the primary-electron beam generated by the single electron source into a plurality of sub-beams or beamlets respectively, and the plurality of electron optics elements influence the plurality of beamlets to form a plurality of first parallel (virtual or real) images of the single electron source respectively. Each first image is the cross-over of one beamlet and can be taken as one sub-source which emits the corresponding beamlet. To make more beamlets available, the beamlet intervals are at micro meter level. Naturally, one primary projection imaging system and one deflection scanning unit within one single column are used to project the plurality of first parallel images onto and scan the plurality of small scanned regions respectively. The plurality of secondary electron beams therefrom is directed by one beam separator into one secondary projection imaging system, and then focused by the secondary projection imaging system to be respectively detected by a plurality of detection elements of one electron detection device inside the single column. The plurality of detection elements can be a plurality of electron detectors placed side by side or a plurality of pixels of one electron detector. The apparatus therefore is generally called as a multi-beam apparatus
The beamlet-limit means is usually an electric-conduction plate with through-holes, and a plurality of through-holes therein functions the plurality of beam-limit openings respectively. For the image-forming means, each electron optics element either focuses one beamlet to form one real image (such as U.S. Pat. No. 7,244,949 and the fourth related application in the CROSS REFERENCE), or deflects one beamlet to form one virtual image (such as U.S. Pat. No. 6,943,349 and the other related applications in the CROSS REFERENCE).
In
In a multi-beam apparatus, each beamlet scans one sub-FOV (field of view) on the sample surface, and the total FOV is the sum of the sub-FOVs of the plural beamlets. Each sub-FOV is equal or smaller than the beamlet pitch on the sample surface (Ps in
The continuous scanning mode (a sample continuously moving in the direction perpendicular to a scanning direction of a primary electron beam) is a conventional method to get high throughput in a conventional single-beam apparatus. If using this method in a multi-beam apparatus, it is better to match the orientation of the total FOV or the probe spot array with the stage moving direction. As well known, if there is one magnetic lens in the primary projection imaging system, the magnetic field thereof will rotate the plural beamlets and the total FOV as a result. Due to the magnetic field is varied with respect to the observing conditions (such as landing energies and currents of plural beamlets), the rotation angle of the total FOV will accordingly vary.
For some sample, a specific match between the orientations of patterns thereon and the probe spot array may be required. Making the orientation of the probe spot array selectable can compensate the mismatch due to the limited loading accuracy, and therefore can increase the throughput by avoiding the time-consuming of re-loading. In addition, to effectively observe some patterns of a sample, the plural beamlets may be required to land onto the sample surface with specific incident angles. Making the incident angles selectable can enable more samples or patterns observable, and will be one more preferred function.
The present invention will provide methods to realize the foregoing functions in a multi-beam apparatus, especially for those proposed in the CROSS REFERENCE and used as yield management tools in semiconductor manufacturing industry.
The object of this invention is to provide a new multi-beam apparatus for observing a sample with high resolution and high throughput and in flexibly varying observing conditions. Based on the conventional multi-beam apparatuses in the CROSS REFERENCE, this invention proposes several methods to configure the new multi-beam apparatus with a variable total FOV. In the new apparatus, the total FOV can be variable in size, orientation and incident angle. Hence the new apparatus provides more flexibility to speed the sample observation and enable more kinds of samples observable. More specifically, if being used as a yield management tool in semiconductor manufacturing industry to inspect and/or review defects on wafers/masks, the new apparatus can provide more possibilities to achieve a high throughput and detect more kinds of defects.
Accordingly, the invention therefore provides a multi-beam apparatus for observing a surface of a sample, which comprises an electron source, a condenser lens below the electron source, a source-conversion unit below the condenser lens, an objective lens below the source-conversion unit, a deflection scanning unit below the source-conversion unit, a sample stage below the objective lens, a beam separator below the source-conversion unit, a secondary projection imaging system, and an electron detection device with a plurality of detection elements. The electron source, the condenser lens and the objective lens are aligned with a primary optical axis of the apparatus, and the sample stage sustains the sample so that the surface faces to the objective lens. The source-conversion unit comprises a beamlet-limit means with a plurality of beam-limit openings, and an image-forming means with a plurality of electron optics elements and movable along the primary optical axis. The electron source generates a primary-electron beam along the primary optical axis and the condenser lens focuses the primary-electron beam. A plurality of beamlets of the primary-electron beam pass through the plurality of beam-limit openings respectively, and is deflected by the plurality of electron optics elements towards the primary optical axis to form a plurality of virtual images of the electron source respectively. The plurality of beamlets is focused by the objective lens onto the surface and therefore forms a plurality of probe spots thereon respectively, and the deflection scanning unit deflects the plurality of beamlets to scan the plurality of probe spots respectively over a plurality of scanned regions within an observed area on the surface. A plurality of secondary electron beams is generated by the plurality of probe spots respectively from the plurality of scanned regions and directed into the secondary projection imaging system by the beam separator, the secondary projection imaging system focuses and keeps the plurality of secondary electron beams to be detected by the plurality of detection elements respectively, and each detection element therefore provides an image signal of one corresponding scanned region.
Deflection angles of the plurality of beamlets due to the plurality of electron optics elements are respectively set to reduce off-axis aberrations of the plurality of probe spots. Pitches of the plurality of probe spots are varied together by moving the image-forming means along the primary optical axis. The objective lens comprises a magnetic lens and an electrostatic lens. An orientation of the plurality of probe spots is selectable by varying a ratio of focusing powers of the magnetic lens and the electrostatic lens.
The deflection angles may ensure the plurality of beamlets to land on the surface perpendicularly or substantially perpendicularly. The deflection angles may ensure the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles. The deflection scanning unit is above a front focal plane of the objective lens. The deflection scanning unit tilts the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles. The apparatus may further comprise a beamlet-tilting deflector between the source-conversion unit and a front focal plane of the objective lens. The beamlet-tilting deflector tilts the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles.
The invention also provides a multi-beam apparatus for observing a surface of a sample, which comprises an electron source, a condenser lens below the electron source, a source-conversion unit below the condenser lens, an objective lens below the source-conversion unit, a deflection scanning unit below the source-conversion unit, a sample stage below the objective lens, a beam separator below the source-conversion unit, a secondary projection imaging system, and an electron detection device with a plurality of detection elements. The electron source, the condenser lens and the objective lens are aligned with a primary optical axis of the apparatus, and the sample stage sustains the sample so that the surface faces to the objective lens. The source-conversion unit comprises a beamlet-limit means with a plurality of beam-limit openings, a first image-forming means with a plurality of first electron optics elements and a second image-forming means with a plurality of second electron optics elements, the second image-forming means is below the first image-forming means and movable in a radial direction, and one of the first image-forming means and the second image-forming means is used as an active image-forming means. The electron source generates a primary-electron beam along the primary optical axis and the condenser lens focuses the primary-electron beam. A plurality of beamlets of the primary-electron beam pass through the plurality of beam-limit openings respectively, and is deflected by the active image-forming means towards the primary optical axis to form a plurality of virtual images of the electron source respectively. The plurality of beamlets is focused by the objective lens onto the surface and therefore forms a plurality of probe spots thereon respectively, and the deflection scanning unit deflects the plurality of beamlets to scan the plurality of probe spots respectively over a plurality of scanned regions within an observed area on the surface. A plurality of secondary electron beams is generated by the plurality of probe spots respectively from the plurality of scanned regions and directed into the secondary projection imaging system by the beam separator, the secondary projection imaging system focuses and keeps the plurality of secondary electron beams to be detected by the plurality of detection elements respectively, and each detection element therefore provides an image signal of one corresponding scanned region.
Deflection angles of the plurality of beamlets due to the active image-forming means are respectively set to reduce off-axis aberrations of the plurality of probe spots. Pitches of the plurality of probe spots are varied together by changing the active image-forming means between the first image-forming means and the second image-forming means, and when the first image-forming means is selected, the second image-forming means is moved outside so as not to block the plurality of beamlets. The objective lens comprises a magnetic lens and an electrostatic lens. An orientation of the plurality of probe spots is selectable by varying a ratio of focusing powers of the magnetic lens and the electrostatic lens.
The deflection angles may ensure the plurality of beamlets to land on the surface perpendicularly or substantially perpendicularly. The deflection angles may ensure the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles. The deflection scanning unit is above a front focal plane of the objective lens. The deflection scanning unit tilts the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles. The apparatus may further comprise a beamlet-tilting deflector between the source-conversion unit and a front focal plane of the objective lens. The beamlet-tilting deflector tilts the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles.
The invention also provides a multi-beam apparatus for observing a surface of a sample, which comprises an electron source, a condenser lens below the electron source, a source-conversion unit below the condenser lens, an objective lens below the source-conversion unit, a deflection scanning unit below the source-conversion unit, a sample stage below the objective lens, a beam separator below the source-conversion unit, a secondary projection imaging system, and an electron detection device with a plurality of detection elements. The electron source, the condenser lens and the objective lens are aligned with a primary optical axis of the apparatus, a first principal plane of the objective lens is movable along the primary optical axis, and the sample stage sustains the sample so that the surface faces to the objective lens. The source-conversion unit comprises a beamlet-limit means with a plurality of beam-limit openings, and an image-forming means with a plurality of electron optics elements. The electron source generates a primary-electron beam along the primary optical axis and the condenser lens focuses the primary-electron beam. A plurality of beamlets of the primary-electron beam pass through the plurality of beam-limit openings respectively, and is deflected by the plurality of electron optics elements towards the primary optical axis to form a plurality of virtual images of the electron source respectively. The plurality of beamlets is focused by the objective lens onto the surface and therefore forms a plurality of probe spots thereon respectively, and the deflection scanning unit deflects the plurality of beamlets to scan the plurality of probe spots respectively over a plurality of scanned regions within an observed area on the surface. A plurality of secondary electron beams is generated by the plurality of probe spots respectively from the plurality of scanned regions and directed into the secondary projection imaging system by the beam separator, the secondary projection imaging system focuses and keeps the plurality of secondary electron beams to be detected by the plurality of detection elements respectively, and each detection element therefore provides an image signal of one corresponding scanned region.
Deflection angles of the plurality of beamlets due to the plurality of electron optics elements are respectively set to reduce off-axis aberrations of the plurality of probe spots. Pitches of the plurality of probe spots are varied together by moving the first principal plane along the primary optical axis.
The deflection angles may ensure the plurality of beamlets to land on the surface perpendicularly or substantially perpendicularly. The deflection angles may ensure the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles. The deflection scanning unit is above a front focal plane of the objective lens. The deflection scanning unit tilts the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles. The apparatus may further comprise a beamlet-tilting deflector between the source-conversion unit and a front focal plane of the objective lens. The beamlet-tilting deflector tilts the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles. The objective lens comprises a lower magnetic lens and an electrostatic lens. The electrostatic lens comprises a field-control electrode and a field-moving electrode, and generates an electrostatic field. A potential of the field-control electrode is set to control the electrostatic field on the surface for the sample free of electrical breakdown. A potential of the field-moving electrode is set to move the electrostatic field for moving the first principal plane. An orientation of the plurality of probe spots is selectable by varying either or both of potentials of the field-control electrode and the field-moving electrode. The apparatus may further comprise an upper magnetic lens above the lower magnetic lens. The first principal plane is moved by varying a ratio of focusing powers of the lower magnetic lens and the upper magnetic lens. An orientation of the plurality of probe spots is selectable by setting polarities of magnetic fields of the upper and lower magnetic lenses same or opposite.
The invention also provides a multi-beam apparatus for observing a surface of a sample, which comprises an electron source, a condenser lens below the electron source, a source-conversion unit below the condenser lens, a transfer lens below the source-conversion unit, a field lens below the transfer lens, an objective lens below the field lens, a deflection scanning unit below the source-conversion unit, a sample stage below the objective lens, a beam separator below the source-conversion unit, a secondary projection imaging system, and an electron detection device with a plurality of detection elements. The electron source, the condenser lens, the transfer lens, the field lens and the objective lens are aligned with a primary optical axis of the apparatus, and the sample stage sustains the sample so that the surface faces to the objective lens. The source-conversion unit comprises a beamlet-limit means with a plurality of beam-limit openings, and an image-forming means with a plurality of electron optics elements. The electron source generates a primary-electron beam along the primary optical axis and the condenser lens focuses the primary-electron beam. A plurality of beamlets of the primary-electron beam pass through the plurality of beam-limit openings respectively, and is deflected by the plurality of electron optics elements towards the primary optical axis to form a plurality of first virtual images of the electron source respectively. The transfer lens images the plurality of first virtual images onto an intermediate image plane and therefore forms a plurality of second real images respectively thereon, the field lens is placed on the intermediate image plane and bends the plurality of beamlets, the objective lens images the plurality of second real images onto the surface and therefore forms a plurality of probe spots thereon respectively, and the deflection scanning unit deflects the plurality of beamlets to scan the plurality of probe spots respectively over a plurality of scanned regions within an observed area on the surface. A plurality of secondary electron beams is generated by the plurality of probe spots respectively from the plurality of scanned regions and directed into the secondary projection imaging system by the beam separator, the secondary projection imaging system focuses and keeps the plurality of secondary electron beams to be detected by the plurality of detection elements respectively, and each detection element therefore provides an image signal of one corresponding scanned region.
Bending angles of the plurality of beamlets due to the field lens are set to reduce off-axis aberrations of the plurality of probe spots. Deflection angles of the plurality of beamlets due to the plurality of electron optics elements are adjusted to change pitches of the plurality of probe spots respectively. The objective lens comprises a first magnetic lens and a first electrostatic lens. An orientation of the plurality of probe spots is selectable by varying a ratio of focusing powers of the first magnetic lens and the first electrostatic lens. The transfer lens comprises a second magnetic lens and a second electrostatic lens. An orientation of the plurality of probe spots is selectable by varying a ratio of focusing powers of the second magnetic lens and the second electrostatic lens. The field lens comprises a third magnetic lens and a third electrostatic lens. An orientation of the plurality of probe spots is selectable by varying a ratio of focusing powers of the third magnetic lens and the third electrostatic lens. The bending angles and deflection angles of the plurality of beamlets due to the plurality of electron optics elements may ensure the plurality of beamlets to land on the surface perpendicularly or substantially perpendicularly. The bending angles and deflection angles of the plurality of beamlets due to the plurality of electron optics elements may ensure the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles. The deflection scanning unit is above a front focal plane of the objective lens. The deflection scanning unit tilts the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles. The apparatus may further comprise a beamlet-tilting deflector between the source-conversion unit and a front focal plane of the objective lens. The beamlet-tilting deflector tilts the plurality of beamlets to obliquely land on the surface with same or substantially same landing angles.
The invention also provides a method to configure a multi-beam apparatus for observing a surface of a sample, which comprises steps of configuring an image-forming means of a source-conversion unit movable along a primary optical axis thereof; using the image-forming means to form a plurality of virtual images of an electron source respectively; using an objective lens to image the plurality of virtual images onto the surface and form a plurality of probe spots thereon; and moving the image-forming means to vary pitches of the plurality of probe spots.
The invention also provides a method to configure a multi-beam apparatus for observing a surface of a sample, which comprises steps of configuring a source-conversion unit with a first image-forming means and a second image-forming means, wherein the second image-forming means is farther away from an electron source than the first image-forming means and movable in a radial direction of the apparatus; using one of the first image-forming means and the second image-forming means as an active image-forming means, wherein when the first image-forming means is used, the second image-forming means is moved away; using the active image-forming means to form a plurality of virtual images of the electron source respectively; using an objective lens to image the plurality of virtual images onto the surface and form a plurality of probe spots thereon; and changing the active image-forming means between the first image-forming means and the second image-forming means to vary pitches of the plurality of probe spots.
The invention also provides a method to configure a multi-beam apparatus for observing a surface of a sample, which comprises steps of configuring an objective lens with a first principal plane movable along a primary optical axis of the apparatus; using an image-forming means of a source- conversion unit to form a plurality of virtual images of an electron source respectively; using the objective lens to image the plurality of virtual images onto the surface and form a plurality of probe spots thereon; and moving the first principal plane to vary pitches of the plurality of probe spots.
The invention also provides a method to configure a multi-beam apparatus for observing a surface of a sample, which comprises steps of configuring an objective lens with a lower magnetic lens and an electrostatic lens in the apparatus; using an image-forming means of a source-conversion unit to form a plurality of virtual images of an electron source respectively; using the objective lens to image the plurality of virtual images onto the surface and form a plurality of probe spots thereon; and changing a ratio of focusing powers of the magnetic lens and the electrostatic lens to select an orientation of the plurality of probe spots.
The method may further comprise a step of configuring the objective lens with an upper magnetic lens farther away from the surface than the lower magnetic lens. The method may further comprise a step of changing polarities of magnetic fields of the upper and lower magnetic lenses to select the orientation.
The invention also provides a method to configure a multi-beam apparatus for observing a surface of a sample, which comprises steps of using an image-forming means of a source-conversion unit to deflect a plurality of beamlets from an electron source to form a plurality of first virtual images thereof respectively; using an objective lens to image the plurality of virtual images onto the surface and form a plurality of probe spots thereon; and setting deflection angles of the plurality of beamlets due to the image-forming means so that the plurality of beamlets lands on the surface with same or substantially same landing angles.
The method may further comprise a step of changing the deflection angles to equally vary the landing angles. The method may further comprise a step of using a deflection scanning unit to tilt the plurality of beamlets so as to equally vary the landing angles. The method may further comprise a step of using a beamlet-tilting deflector to tilt the plurality of beamlets so as to equally vary the landing angles.
The invention also provides a method to configure a multi-beam apparatus for observing a surface of a sample, which comprises steps of using an image-forming means of a source-conversion unit to deflect a plurality of beamlets from an electron source to form a plurality of first virtual images thereof respectively; using a transfer lens to image the plurality of first virtual images onto an intermediate image plane and forms a plurality of second real images respectively; placing a field lens on the intermediate image plane to bend the plurality of beamlets; and using an objective lens to image the plurality of second real images onto the surface and form a plurality of probe spots thereon.
The method may further comprise a step of changing deflection angles of the plurality of beamlets due to the image-forming means to vary pitches of the plurality of probe spots. The method may further comprise a step of setting deflection angles of the plurality of beamlets due to the image-forming means and bending angles of the plurality of beamlets due to the field lens so that the plurality of beamlets lands on the surface with same or substantially same landing angles. The method may further comprise a step of varying the deflection angles to equally change the landing angles. The method may further comprise a step of using a deflection scanning unit to tilt the plurality of beamlets to equally change the landing angles. The method may further comprise a step of using a beamlet-tilting deflector to tilt the plurality of beamlets to equally change the landing angles. The method may further comprise a step of configuring the objective lens with a first magnetic lens and a first electrostatic lens. The method may further comprise a step of changing a ratio of focusing powers of the first magnetic lens and the first electrostatic lens to select an orientation of the plurality of probe spots. The method may further comprise a step of configuring the transfer lens with a second magnetic lens and a second electrostatic lens. The method may further comprise a step of changing a ratio of focusing powers of the second magnetic lens and the second electrostatic lens to select an orientation of the plurality of probe spots. The method may further comprise a step of configuring the field lens with a third magnetic lens and a third electrostatic lens. The method may further comprise a step of changing a ratio of focusing powers of the third magnetic lens and the third electrostatic lens to select an orientation of the plurality of probe spots.
The invention also provides an apparatus, which comprises a source for providing a primary charged particle beam, a source-conversion unit for dividing the primary charged particle beam into a plurality of charged particle beamlets and using which to form a plurality of images of the source respectively, and an objective lens below the source-conversion unit for projecting the plurality of images onto a sample surface. Pitches of the plurality of charged particle beamlets on the sample surface are adjustable by changing deflection angles of the plurality of charged particle beamlets prior entering the objective lens.
The invention also provides an apparatus, which comprises a source for providing a primary charged particle beam, means for using a plurality of beamlets of the primary charged particle beam to form a plurality of images of the source, an objective lens for projecting the plurality of images onto a sample surface to form a plurality of probe spots, and means for adjusting pitches of the plurality of probe spots on the sample surface.
The invention also provides a method for observing a sample surface, which comprises steps of providing a plurality of charged particle beams with a plurality of crossovers respectively, projecting the plurality of crossovers onto the sample surface to form a plurality of probe spots thereon, scanning the plurality of probe spots on the sample surface, and changing deflection angles of the plurality of charged particle beams such that pitches of the plurality of spots can be adjusted.
Other advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of the present invention.
The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:
Various example embodiments of the present invention will now be described more fully with reference to the accompanying drawings in which some example embodiments of the invention are shown. Without limiting the scope of the protection of the present invention, all the description and drawings of the embodiments will exemplarily be referred to an electron beam. However, the embodiments are not used to limit the present invention to specific charged particles.
In the drawings, relative dimensions of each component and among every component may be exaggerated for clarity. Within the following description of the drawings, the same or like reference numbers refer to the same or like components or entities, and only the differences with respect to the individual embodiments are described.
Accordingly, while example embodiments of the invention are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments of the invention to the particular forms disclosed, but on the contrary, example embodiments of the invention are to cover all modifications, equivalents, and alternatives falling within the scope of the invention.
In this invention, “axial” means “in the optical axis direction of an electron optics element (such as a round lens or a multipole lens), or an imaging system or an apparatus”, “radial” means “in a direction perpendicular to the optical axis”, “on-axial” means “on or aligned with the optical axis, and “off-axis” means “not on or aligned with the optical axis”.
In this invention, “an imaging system is aligned with an optical axis” means “all the electron optics elements (such round lens and multipole lens) are aligned with the optical axis”.
In this invention, X, Y and Z axe form Cartesian coordinate. The optical axis of the primary projection imaging system is on the Z-axis, and the primary electron beam travels along the Z-axis.
In this invention, “primary electrons” means “electrons emitted from an electron source and incident onto a being-observed or inspected surface of a sample, and “secondary electrons” means “electrons generated from the surface by the “primary electrons”.
In this invention, “pitch” means an interval between two adjacent beamlets or beams on a plane.
In this invention, “effective deflection plane of a deflector” means “the plane where the total deflection function of the deflector can be equivalent to happen”.
Based on some conventional multi-beam apparatuses proposed in the CROSS REFERENCE, this invention proposes several methods to configure a new multi-beam apparatus with a variable total FOV. In the new apparatus, the total FOV can be variable in size, orientation and illumination angle. To clearly express the methods, the multi-beam apparatus in
In each of those conventional multi-beam apparatuses, the plural beamlets are deflected towards the optical axis by the image-forming means. The deflection angles of the plural beamlets are set to minimize the off-axis aberrations of the plural probe spots due to the objective lens. Accordingly the plural deflected beamlets typically pass through or approach the front focal point of the objective lens, i.e. forming an on-axis crossover on or close to the front focal plane of the objective lens. The pitches of the plural probe spots therefore depend on the deflection angles of the plural beamlets and the first (or object) focal length of the objective lens. Hence the pitches can be varied by changing the deflection angles and/or the first focal length of the objective lens. For example, in
In the embodiment 400A in
The embodiment 500A in
In
In the embodiment 600A in
The objective lens in one conventional multi-beam apparatus is an electromagnetic compound lens, as one embodiment 131-1 shown in
Next three solutions for configuring the movable objective lens 631 are proposed in terms of the conventional objective lens 131-1 in
In
In
Next some methods of intentionally rotating the probe spot array will be proposed, which can be used to eliminate the orientation variation of the total FOV with respect to changes in the observing conditions and/or accurately match the orientations of sample patterns and the probe spot array. As mentioned above, the objective lens in one conventional multi-beam apparatus is typically an electromagnetic compound lens, such as the embodiment 131-1 shown in
For each of the foregoing embodiments 300A, 400A and 500A of the new apparatus in
For the embodiment 500A in
In each of the foregoing embodiments, the plural beamlets are normal or substantially normal incident onto the sample surface, i.e. the incident angles or landing angles (angles formed with the normal of the sample surface) of the plural beamlets are approximately equal to zero. To effectively observe some patterns of a sample, the incident angles are better a little larger than zero. In this case, to ensure plural beamlets perform alike, the plural beamlets are required to have same incident angles. To do so, the crossover CV of the plural beamles needs to be shifted away from the optical axis. The shift of the crossover CV can be done by the image-forming means or one additional beamlet-tilting deflector.
Although each of the foregoing embodiments of the new apparatus only employs one or two of the methods for varying the total FOV in size, orientation and incident angle, the methods can be combined in many ways. For example the new apparatus can use one movable image-forming means and one movable objective lens together, or use one movable objective lens, one transfer lens and one field lens together. Although the methods are shown and explained by taking the embodiment 200A in
In summary, based on the conventional multi-beam apparatuses proposed in the CROSS REFERENCE, this invention proposes several methods to configure a new multi-beam apparatus whose total FOV is variable in size, orientation and incident angle. Hence the new apparatus provides more flexibility to speed the sample observation and enable more kinds of samples observable. More specifically, the new apparatus can be used as a yield management to provide more possibilities to achieve a high throughput and detect more kinds of defects. Three methods are proposed to change the pitches of the plural beamlets on the sample surface for varying the size of the total FOV, i.e. using a movable image-forming means in the source-conversion unit, using a movable objective lens, and using a transfer lens and a field lens between the source-conversion unit and the objective lens. Three methods are employed to intentionally rotate the probe spot array for varying the orientation of the total FOV, i.e. using an electromagnetic compound objective lens and varying the electric field thereof, using one objective lens with two magnetic lenses and setting the magnetic fields thereof opposite in polarity, and using one magnetic lens in either or both of the transfer lens and the field lens. Three methods are proposed to shift the crossover of the plural beamlets away from the optical axis for equally varying the landing angles of the plural beamlets on the sample surface. The shift can be done by the image-forming means, or one additional beamlet-tilting deflector, or the deflection scanning unit.
Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that other modifications and variation can be made without departing the spirit and scope of the invention as hereafter claimed.
Liu, Xuedong, Ren, Weiming, Hu, Xuerang, Chen, Zhong-Wei
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