JP4931359B2 - Electron beam equipment - Google Patents

Description

  The present invention relates to an electron beam apparatus, and more particularly to an electron beam apparatus that can evaluate a sample having a pattern with a minimum line width of 0.1 μm or less with high throughput and high reliability.

Conventionally, an electron that has been made to obtain an ultra-high resolution image by correcting axial chromatic aberration by an axially symmetric lens using an axial chromatic aberration correction lens composed of a four-stage quadrupole lens and a two-stage quadrupole magnetic lens. Wire systems have been proposed.
In addition, electrons emitted from the electron gun are converted into a multi-beam through a plurality of apertures, the multi-beam is reduced and imaged on the sample, a multi-beam of secondary electrons emitted from the sample is expanded, and a plurality of detections are performed. There is also known an electron beam apparatus which detects with a detector.

The above-described axial chromatic aberration correction lens has good off-axis aberration characteristics in the vicinity of the optical axis, but off-axis aberration characteristics in a region away from the optical axis is not good, and off-axis aberrations in a region away from the optical axis. There is a problem of producing.
Further, there has been no use of obtaining a large current by using a large NA aperture by correcting axial chromatic aberration, not for obtaining an ultra-high resolution image.
In the multi-beam type electron beam apparatus, it is necessary to accurately adjust the beam interval and the angle (rotation angle) between the beam arrangement direction and the reference coordinate axis of the electron beam apparatus. However, there is a problem that these adjustments cannot be performed accurately.
The present invention has been made in view of such problems of the conventional example, and a first object thereof is an axis generated by an axial chromatic aberration correction lens in an electron beam apparatus using the axial chromatic aberration correction lens. It is to be able to correct external aberrations satisfactorily.
The second object of the present invention is to accurately and easily evaluate the beam interval and the angle formed by the beam arrangement direction and the reference coordinate axis in a multi-beam type electron beam apparatus using inexpensive means. Is to be able to.

In order to achieve the above object, in an electron beam apparatus according to the present invention, information on a sample is obtained by irradiating the sample with an electron beam and detecting electrons emitted from the sample. Is
An axial chromatic aberration correction lens composed of a multipole lens;
And an auxiliary lens whose main surface coincides with the image surface on the incident side of the axial chromatic aberration correction lens.

In the above-described electron beam apparatus according to the present invention, the apparatus is configured to divide the field of view into a plurality of sub-fields and repeatedly execute irradiation of the primary electron beam and detection of the secondary electron beam for each sub-field of view. The axial chromatic aberration correction lens is preferably included in the magnifying optical system included in the secondary optical system. Further, it is preferable that the apparatus further includes means for shaping the primary electron beam into a rectangle included in the primary optical system.
Further, in the electron beam apparatus according to the present invention, the apparatus is further included in the primary optical system, and means for irradiating the sample with a primary electron beam as a multi-beam, and a plurality of 2 comprising electrons emitted from the sample. Detection means comprising a plurality of detectors for detecting secondary electron beams respectively;
It is preferable to include a multi-beam evaluation unit that evaluates the rotation angle between the arrangement direction of the multi-beams and the reference coordinate system of the electron beam apparatus and the beam interval of the multi-beams. In this case, it is preferable that the axial chromatic aberration correction lens and the auxiliary lens are included in the primary optical system, and the multi-beam evaluation means uses the y-axis of the reference coordinate system (where the y-axis is the stage continuous movement direction). It is preferable that the evaluation is performed based on the interval between signals respectively obtained from a plurality of detectors when a marker parallel to is scanned in the x-axis direction.

Since the present invention is configured as described above and the auxiliary lens is provided on the image surface on the incident side of the axial chromatic aberration correction lens, off-axis aberrations generated by the axial chromatic aberration correction lens can be reduced. Therefore, highly accurate image data with reduced aberration can be obtained.
Further, in the multi-beam type electron beam apparatus, using the obtained signal interval, it is evaluated whether the angle formed by the beam arrangement direction and the reference coordinate axis is appropriate and whether the beam interval is equal to the design value. These can be adjusted accurately.

  FIG. 1 shows a main part of an electron beam apparatus according to a first embodiment of the present invention. In this electron beam apparatus, the size of the irradiation region and the current density are adjusted by the two-stage condenser lenses 2 and 3 and the electron beam emitted from the electron gun 1 is formed by a rectangular opening 4 such as a square. The shaped rectangular electron beam is irradiated onto the sample 10 through the two-stage shaping lenses 5 and 6 and further through the beam separator 7 and the objective lens 9. In order to prevent the primary electron beam from affecting the secondary electron beam, the path of the primary electron beam should be different from the path of the secondary electron beam even after the primary electron beam passes through the beam separator 7. ing. Therefore, an opening 23 for the primary electron beam is provided.

The secondary electrons emitted from the sample 10 pass through the NA aperture 24 provided in the NA aperture plate 8 and are deflected by the beam separator 7 and deflected in the vertical direction by the aberration correcting electrostatic deflector 11. An enlarged image is formed on the main surface. The secondary electron beam diverging from the auxiliary lens 12 passes through the axial chromatic aberration correction lenses 14 to 17 and forms an image on the main surface of the auxiliary lens 18 for the magnifying lens 19.
Since the enlarged image formed on the main surface of the auxiliary lens 12 is also formed at a position away from the optical axis, the secondary electron beam diverged from the auxiliary lens 12 is directly used as the axial chromatic aberration correction lenses 14 to 17. When incident on the lens, a large off-axis aberration occurs. In order to solve this problem, the image of the opening 24 is formed by the auxiliary lens 12 at substantially the center 18 in the optical axis direction of the axial chromatic aberration correction lenses 14 to 17.
The secondary electron image whose axial chromatic aberration is corrected is magnified by the magnifying lens 19, forms a magnified image on the main surface of the auxiliary lens 20, and the final magnified image is formed on the light receiving surface of the EBCCD detection unit 22 by the final magnifying lens 21. And the final magnified image is detected by the EBCCD 22. A normal CCD detects light and outputs an electrical signal, while an EBCCD is a detector that detects an electron beam instead of light and outputs an electrical signal. Reference numeral 13 denotes an axis alignment deflector for the axial chromatic aberration correction lenses 14 to 17.

The field of view on the sample 10 is divided into, for example, a plurality of square subfields of five, and image data is acquired by irradiation of the primary electron beam and detection of the secondary electron beam in units of subfields. The subfield is selected based on the deflection control signal from the subfield controller 34 so that the primary electron beam is deflected by the two-stage deflectors 26 and 27 so as to take the trajectory 32. The orbit 32 is an orbit when irradiating the sub-field on the left side of the optical axis, and secondary electrons emitted by the irradiation travel on the orbit 33. The sub visual field control unit 34 is controlled by the CPU 28.
When the subfield is far from the optical axis, only the secondary electron beam passes through the NA aperture 24 and passes through the orbit 33 enters the secondary optical system. A deflection control signal is supplied to the aberration correction deflector 11, and the trajectory is corrected so that the secondary electron beam after passing through the aberration correction deflector 11 coincides with the optical axis of the secondary optical system.

  As shown in FIG. 2, the EBCCD detection unit 22 includes four EBCCD detectors, and is deflected by the deflector 35 so that secondary electron images are formed in the order of the arrows. Extraction of image data from each EBCCD is executed by switching the electronic switch 40 by the CPU 28. Since the exposure can be performed four times while the image data is extracted from one EBCCD and stored in the memory 41, the exposure can be performed without loss until the data extraction time is about four times the exposure time.

  That is, when the exposure of one EBCCD detector 221 of the EBCCD detector 22 is completed, extraction of image data from the detector to the memory 41 is started, and at the same time, the next sub-field image is formed on the EBCCD detector 222. To be deflected. Next, exposure to the EBCCD detector 222 is started after the settling time, and when the exposure of the EBCCD detector 222 is completed after a predetermined time, the extraction of the image from the detector to the memory 44 is started, and the EBCCD detector 223 is started. Is deflected so that exposure to is started. Similarly, deflection, settling, and exposure are performed for each EBCCD detector 221 to 224 in the order shown by the arrows in FIG. 2 and data is extracted. Accordingly, in each EBCCD detector, the time from the end of the exposure to the start of the next exposure is the sum of the exposure time × 3 and the settling time × 4 (≈exposure time × 4). It is necessary to retrieve data. Therefore, if the data extraction time is about 4 times or less of the time required for exposure, the processing can be performed without time loss.

  FIG. 3 shows the main part of the electron beam apparatus according to the second embodiment of the present invention. In the electron beam apparatus of this embodiment, the electron beam emitted from the electron gun 51 is focused by the condenser lens 52 and irradiates the multi-aperture 53, thereby forming a multi-beam. The multi-beam is irradiated onto the sample 48 via the reduction lenses 54 and 55 and the objective lens 47. At this time, the multi-beam is deflected so as to scan the sample 48 by the electrostatic deflectors 45 and 53.

  In the electron beam apparatus according to the second embodiment, an auxiliary lens 56 is provided at an image formation position by the reduction lens 55, and axial chromatic aberration correction lenses 58 to 61 each including a four-stage quadrupole lens are disposed downstream thereof. At the image position of the reduction lens 55, the multi-beam spreads in a range of about 20 μm from the optical axis, so that the axial chromatic aberration correction lenses 58 to 61 generate off-axis aberrations. This off-axis aberration can be reduced by forming the image of the NA aperture 42 on the center 43 of the axial chromatic aberration correction lenses 14 to 17 by the auxiliary lens 56. As a result, an 8 × 8 multi-beam can be obtained using each beam having a beam intensity of 6.25 nA and a beam diameter of 25 nm. This is obtained by the simulation of the electron optical system having the above-described configuration, and details thereof are described in the literature, and thus description thereof is omitted here.

The secondary electrons emitted from the sample 48 are accelerated by the objective lens 47, separated from the primary electron beam by the beam separator 46, and headed to the secondary optical system. In the secondary optical system, the secondary electron beam is magnified by the two-stage magnifying lenses 49 and 50, projected onto the detection unit 62, and detected. The detector 62 is composed of a plurality of detectors having the same number of primary electron beams as multi-beams, and the arrangement pitch of these detectors and the pitch of the secondary electron image of the main surface of the detector 62 are matched. The lenses 49 and 50 are zoomed.
In FIG. 3, reference numeral 63 denotes a CPU that controls the operation of the entire electron beam apparatus, and signals obtained by the detectors of the detector 62 are stored in a memory (not shown) under the control of the CPU 63.

The CPU 63 has a function of evaluating the beam interval of the primary electron beam, which is a multi-beam, and the angle (rotation angle) θ between the beam arrangement and the xy coordinate axes. Hereinafter, this function will be described by taking a case where the multi-beam has 4 rows and 4 columns as an example.
In order to execute this function, a signal synthesizer 64 for synthesizing signals from a plurality of detectors is provided, and the signal from the signal synthesizer 64 is supplied to the CP 63. And as shown to (A) of FIG. 4, the pattern 65 parallel to the y-axis (continuous movement direction of a stage) of the xy coordinate system which is a reference | standard coordinate of an electron beam apparatus is provided on the test sample, The sample is irradiated with the multi-beam, and the multi-beam is scanned so as to be orthogonal to the x-axis direction, that is, the pattern 65.

  As a result, a signal that becomes a high level every time the electron beam irradiates the pattern 52 as shown in FIG. 4B is obtained from the plurality of detectors constituting the detection unit 62, and the signal synthesis unit A signal obtained by combining these from 64 (the lowermost end of FIG. 4B) is supplied to the CPU 63. Among the combined signals, the first to fourth signals are signals obtained when the four electron beams in the first row of the multi-beams irradiate the pattern 65. The second is a signal obtained when the electron beams in the second, third, and fourth rows of the multi-beams irradiate the pattern 65, respectively.

The CPU 63 first determines whether or not the rotation angle θ is appropriate by detecting the time interval between these signals. That is, in the case of a 4-by-4 multi-beam, if the rotation angle θ is inappropriate, the interval between the two signals obtained in the fourth and fifth is the first and second (or second and third). , Or the third and fourth) is different from the interval between the two signals obtained. If the fourth and fifth signal intervals are large compared to the other signal intervals, this indicates that the rotation angle θ is too small. Conversely, if the signal interval is small, the rotation angle is too large. Represents.
The CPU 63 detects the interval between the signals output from the respective detectors, compares the signal intervals, and determines whether the interval between the fourth and fifth signals is larger or smaller than the interval between the other signals. Then, based on the result, the CPU 63 generates an output indicating whether the rotation angle should be reduced or increased. Note that the rotation angle θ can be adjusted and the signal intervals can be matched by slightly rotating the multi-opening 53 or by slightly rotating the lenses 54 and 55 as the rotating lenses.

After adjusting the rotation angle θ and matching the signal interval, the CPU 63 evaluates whether the beam interval is as designed, that is, whether the raster interval is equal to the pixel size or an integral multiple thereof. To do. This evaluation can be performed by detecting the interval between the 1st and 4th signals, dividing it by 3, and comparing it with the design value. There is a possibility that an error may be included when the evaluation is performed based on the interval between adjacent signals. However, the evaluation can be performed with high accuracy by performing the evaluation as described above. An interval between the 1st and 16th signals may be detected, and a value obtained by dividing the interval by 15 may be compared with a design value. Thereby, more accurate evaluation can be performed.
Alternatively, the interval between the 2nd and 15th signals may be detected, and a value obtained by dividing the interval by 13 may be compared with the design value. When evaluated in this way, distortion due to the primary optical system appears greatly in the four corner beams of the multi-beam arranged in a matrix, so that even when distortion occurs due to the primary optical system, the evaluation of the beam spacing is improved. Can be done with precision.
When the beam interval is different from the design value, it can be made to coincide with the design value by adjusting the reduction ratio of the primary optical system.

FIG. 5A shows the main part of the electron beam apparatus according to the third embodiment of the present invention. In the electron beam apparatus according to the third embodiment, the Wien filter 70 is used instead of the auxiliary lens 58, the axis alignment lens 57, and the quadrupole lenses 58 to 61 in the second embodiment shown in FIG. It is. Also in the electron beam apparatus of the third embodiment, it is possible to prevent an increase in aberration caused by a wide field of view. The Wien filter 70 can be made non-dispersive by focusing twice, as shown by the trajectory 82.
Also in the electron beam apparatus of the third embodiment, the angle θ and the beam interval between the multi-beam arrangement and the xy coordinate system can be adjusted by the method described with reference to FIG.

  FIG. 5B shows ¼ of the cross-sectional shape centered on the optical axis 81 of the Wien filter 70. The Wien filter 70 includes a cylindrical yoke 71 made of permalloy, twelve-pole electrodes (cum poles) 72 to 74 made of permalloy, coils 75 to 77 for generating a magnetic field for correction, and spacers that insulate the electrodes. 78-80. By applying a voltage to the twelve-pole electrodes 72 to 74 to generate an electric field, a magnetic field, a quadrupole electromagnetic field for correcting chromatic aberration, and a hexapole electromagnetic field for correcting spherical aberration, an axial chromatic aberration is generated. And spherical aberration can be corrected.

It is explanatory drawing which shows the electron optical system of the electron beam apparatus of 1st Embodiment which concerns on this invention. FIG. 2 is an explanatory diagram showing a means for extracting image data from EBCCD in the electron beam apparatus shown in FIG. 1. It is explanatory drawing which shows the electron optical system of the electron beam apparatus of 2nd Embodiment which concerns on this invention. FIG. 4 is an explanatory diagram for explaining the evaluation of the rotation angle between the multi-beam arrangement and the xy coordinate axes and the evaluation of the beam interval of the multi-beam in the electron beam apparatus shown in FIG. 3. It is explanatory drawing which shows the electron optical system of the electron beam apparatus of the 3rd Embodiment concerning this invention.

Claims (5)

In an electron beam apparatus that obtains information on a sample by irradiating the sample with an electron beam and detecting electrons emitted from the sample,
A primary optical system for irradiating a sample with a primary electron beam;
A secondary optical system for guiding secondary electrons emitted from a sample to a detector,
An objective lens;
A beam separator for separating a primary electron beam and a secondary electron;
An NA aperture disposed between the objective lens and the beam separator;
An axial chromatic aberration correction lens composed of a multipole lens;
An auxiliary lens disposed between the axial chromatic aberration correction lens and the beam separator, and an auxiliary lens for forming an image of the NA aperture at the center of the axial chromatic aberration correction lens in the optical axis direction ;
An electron beam apparatus comprising : a secondary optical system including: The electron beam apparatus according to claim 1,
The apparatus is configured to divide a field of view into a plurality of sub-fields and repeatedly execute irradiation of a primary electron beam and detection of a secondary electron beam for each sub-field of view.
An electron beam apparatus, wherein the longitudinal chromatic aberration correction lens is included in an enlarging optical system included in a secondary optical system. 3. The electron beam apparatus according to claim 1, wherein the apparatus further comprises:
An electron beam apparatus comprising a means for forming a primary electron beam into a rectangular shape, which is included in a primary optical system. The electron beam apparatus according to claim 1, further comprising:
Means for irradiating the specimen with a primary electron beam as a multi-beam included in the primary optical system;
Detection means comprising a plurality of detectors for respectively detecting a plurality of secondary electron beams comprising electrons emitted from the sample;
An electron beam apparatus comprising: multi-beam evaluation means for evaluating a rotation angle between a multi-beam arrangement direction and a reference coordinate system of the electron beam apparatus, and evaluating a beam interval of the multi-beam. 5. The electron beam apparatus according to claim 4, wherein the multi-beam evaluation means includes a plurality of detectors when a marker parallel to the y-axis (where the y-axis is the stage continuous movement direction) of the reference coordinate system is scanned in the x-axis direction. An electron beam apparatus configured to perform evaluation based on an interval of signals obtained from each.

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