JP4071473B2 - Scanning electron microscope with monochromator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a scanning electron microscope, and more particularly to a scanning electron microscope equipped with a monochromator that monotonizes the energy of an irradiation electron beam.
[0002]
[Prior art]
In recent scanning electron microscopes (SEMs), there is an increasing number of cases in which the acceleration energy of irradiated electron beams is lowered for the purpose of preventing charging of electron beams such as semiconductor samples. In such a low-acceleration SEM, since the energy width of the irradiated electrons is larger than the acceleration energy, a sufficiently small spot diameter cannot be obtained due to so-called chromatic aberration, and the image resolution is limited. Even if the field emission type is used instead of the conventional filament type for the electron source and the energy width is reduced to 25%, if the acceleration voltage is lowered by 25%, the chromatic aberration becomes the same and the image resolution is not improved.
[0003]
Therefore, a technique called monochromatic (monochrome) has been proposed as a method for further reducing the energy width of irradiated electrons. As the first method, for example, as described in JP-A-4-233145, a method using a monochromatic energy filter composed of four hemispherical electrostatic field is known. This filter has a capacitor electrode structure on four hemispheres which have a symmetrical plane in the filter and are arranged symmetrically on both sides thereof, and different voltages are applied to the outer and inner hemispherical electrodes of each capacitor to apply an electron beam. The energy width is limited by an energy selection slit provided on the plane of symmetry, and finally the point is converged by canceling the dispersion.
[0004]
As a second method, for example, a method using a two-stage Wien filter is known as described in Japanese Patent Application Laid-Open No. 2000-100361. This is because the energy emitted from the particle beam source is dispersed by the first Wien filter, the energy width is limited by the aperture (aperture), the dispersion is canceled by the second Wien filter, and guided to the objective lens. To converge the point.
[0005]
[Problems to be solved by the invention]
However, in the method using the static electrodes on the four hemispheres described in Japanese Patent Laid-Open No. 4-233145, the overall length is shortened, but a large vacuum space is required in the lateral direction, and the true container is enlarged. There was a problem to do. In general, an electron microscope is designed so that gravity is applied to the mirror evenly in a symmetric shape, but this method cannot be symmetric and the gravity applied to the mirror is unbalanced. There was also a problem of becoming. In addition, the precision machining of the toroidal capacitor electrode surface has a problem that the manufacturing cost increases.
[0006]
In the two-stage Wien filter method described in Japanese Patent Laid-Open No. 2000-100361, there is a big problem with the Wien filter itself. That is, since the Wien filter inserts a static electrode between narrow magnetic poles, a uniform electric field sufficient for the spread of the beam in a plane (x, y) perpendicular to the traveling direction (z) of the beam, A magnetic field cannot be obtained. For this reason, the convergence of the peripheral part of the beam is disturbed with respect to the central part, and the resolution and the transmittance tend to be lowered, and there is a problem that it is difficult to process the edge electric field to correct this.
[0007]
In other words, the methods described in JP-A-4-233145 and JP-A-2000-10031 have a problem that they are not always practical.
[0008]
An object of the present invention is to provide a scanning electron microscope equipped with a practical monochromator capable of increasing the image resolution by making the energy of the irradiation electron beam monochromatic, reducing the chromatic aberration, and reducing the spot system. It is in.
[0009]
[Means for Solving the Problems]
(1) To achieve the above object, the present invention provides an electron gun for generating and accelerating an electron beam, a first focusing lens for focusing the electron beam, and a second focusing lens for reducing the formed crossover. And a scanning electron microscope for irradiating the sample with the electron beam generated from the electron gun, and between the first focusing lens and the second focusing lens. Arranged, fan-shaped magnetic field with two front stages and two rear stages Two fan-shaped magnetic poles each forming When , It is composed of a slit, and the slit is Two Fan-shaped magnetic field Two fan-shaped magnetic poles forming And the latter part Two Fan-shaped magnetic field Two fan-shaped magnetic poles forming Are arranged on the mirror symmetry plane in the middle of the first stage, and the above-mentioned fan-shaped magnetic field restricts the different energy of the electron beam emitted from the crossover of the first focusing lens, and the two fan-shaped magnetic fields Two fan-shaped magnetic poles forming And two fan-shaped magnetic fields at the back Two fan-shaped magnetic poles forming Is arranged along the irradiation direction of the electron beam, and the latter stage Two The fan-shaped magnetic field spatially converges the divergent electron beam again and makes the energy dispersion non-dispersed to be an object point of the second focusing lens. Two pieces formed by fan-shaped magnetic poles The sector magnetic field deflects the electron beam converged by the first focusing lens out of the optical axis from the electron gun to the objective lens, and then returns the energy dispersed electron beam to the optical axis of the electron beam. Pass the slit, and the two Two pieces formed by fan-shaped magnetic poles The fan-shaped magnetic field deflects the electron beam that has passed through the slit by the two fan-shaped magnetic fields in the previous stage again to the outside of the optical axis, and then returns the energy-dispersed electron beam to the optical axis of the electron beam for point convergence. An electronic energy monochromator is provided.
With such a configuration, a monochromator capable of increasing the image resolution by making the energy of the irradiation electron beam monochromatic, reducing the chromatic aberration, and reducing the spot system can be put into practical use.
[0010]
(2) In the above (1), preferably, the electron energy monochromator deflects the electron beam to about 90 degrees with the first sector magnetic field and deflects to about 180 degrees with the second sector magnetic field, and again After entering the first sector magnetic field and deflecting approximately 90 degrees, exiting at the same angle as the first incident direction, converging in the mirror symmetry plane, and limiting the energy by the slit, the third sector shape Incident into the magnetic field and deflected by approximately 90 degrees, deflected by approximately 180 degrees by the fourth sector magnetic field, again incident on the third sector magnetic field and deflected by approximately 90 degrees, and emitted in the same direction as the initial incident direction. Thus, a non-dispersive crossover is formed and used as an object point of the second focusing lens.
[0011]
(3) In the above (2), preferably, in the monochromator, the object point of the first focusing lens is converged in the x direction (energy dispersion direction) at the entrance of the second sector magnetic field by the first sector magnetic field. The second sector magnetic field converges at the exit in the x direction, and the first sector magnetic field again converges in the x direction to a position symmetrical to the first object point, and almost in the y direction (line of magnetic force). parallel Become a beam , Su In the third and fourth sector magnetic fields in the subsequent stage, the electron beam trajectory with the same path as the preceding sector magnetic field is drawn, and the first object with respect to the intermediate mirror symmetry plane (slit position) is reduced. It has non-dispersive and point convergence convergence at a position symmetrical to the point.
[0012]
(4) In the above (1), preferably, the monochromator is configured such that the entrance magnetic pole end surface of the first sector magnetic field in the previous sector magnetic field has an incident angle in a deflection direction with respect to a vertical plane of the beam incident direction. Mochi, The beam is After emission, in the y direction (direction of magnetic field) with respect to the central axis (traveling direction) of the beam parallel The output magnetic pole end face of the third sector magnetic field in the subsequent sector magnetic field has an incident angle that is mirror-symmetrical with the incident angle of the first sector magnetic field, and at the same time at the convergence point in the x direction with respect to the y direction after emission. It converges to form a crossover.
[0013]
(5) In the above (1), preferably, the monochromator has a mirror symmetry plane z1 with respect to the first sector magnetic field, the second sector magnetic field, the object point, and the slit constituting the preceding sector magnetic field, The third sector magnetic field, the fourth sector magnetic field, and the slit and the point convergence crossover constituting the latter sector magnetic field have a mirror symmetry plane z3, and the first sector magnetic field, the second sector magnetic field, the object point, and the slit are: The third sector magnetic field, the fourth sector magnetic field, and the intermediate mirror symmetry plane z2 including the slit, the point convergence crossover, and the slit constitute a mirror symmetrical shape, and the cross after the third sector magnetic field. At the over-point, the energy dispersion coefficient becomes zero (non-dispersion), and a convergence characteristic for removing secondary aberration coefficients related to the opening angles α and β in the x and y directions of the beam is provided.
[0014]
(6) In the above (1), preferably, the monochromator forms the first and second sector magnetic fields constituting the preceding sector magnetic field by an integral magnetic path (yoke), and the latter sector magnetic field. The third and fourth fan-shaped magnetic fields constituting the are formed by separate integral magnetic paths (yokes).
[0015]
(7) In the above (1), preferably, the monochromator is configured such that the first and second sector magnetic fields constituting the preceding sector magnetic field and the third and fourth sector constituting the subsequent sector magnetic field. The magnetic field is formed by an integral magnetic path (yoke).
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration of a scanning electron microscope including a monochromator according to an embodiment of the present invention will be described with reference to FIGS.
First, the optical system of the scanning electron microscope provided with the monochromator according to the present embodiment will be described with reference to FIG.
FIG. 1 is a configuration diagram of an optical system of a scanning electron microscope including a monochromator according to an embodiment of the present invention.
Similar to the normally known scanning electron microscope, the scanning electron microscope according to the present embodiment includes the field emission electron source 1, the first focusing lens 4, the second focusing lens 13, and the scanning coils 15 and 16. An objective lens 17 and a secondary electron detector 19. Further, in the present embodiment, the first sector magnetic field 6, the second sector magnetic field 7, the energy selection slit 8, the third sector magnetic field 9, the fourth sector magnetic field 10, and the aperture 12 constituting the monochromator are provided. I have. In the figure, reference numeral 2 is the central axis of the electron beam, 3 is the beam spread, 5 is the crossover, 11 is the crossover, 14 is the crossover, 18 is the sample, and 22 is the secondary electron beam. ing.
[0017]
Next, the operation principle of the scanning electron microscope with a monochromator of this embodiment will be described. The electron beam 3 accelerated and emitted from the electron source 1 is connected to the crossover 5 by the first focusing lens 4. Thereafter, the first sector magnetic field 6 deflects 90 degrees, the second sector magnetic field 7 deflects 180 degrees, the first sector magnetic field 6 deflects 90 degrees again, converges in the x direction at the position of the slit 8, and energy is selected. The Thereafter, the third sector magnetic field 9 and the fourth sector magnetic field 10 again draw a similar trajectory to converge at the position of the crossover 11, and the energy dispersion generated in the previous stage (first and second sector magnetic fields 6 and 7) is dispersed. Offset to form a non-dispersed crossover 14. The monochromatic crossover 14 is reduced by the second focusing lens 13 and further reduced by the objective lens 17 to form a minute crossover on the sample surface 18. This beam is scanned by the scanning coils 15 and 16, and the generated secondary electrons 22 are detected by the detector 19 and displayed on the CRT as a microscopic image.
[0018]
Next, details of the trajectory of the electron beam by the electron optical system of the monochromator of the scanning electron microscope with a monochromator according to the present embodiment will be described with reference to FIG. FIG. 2 is an explanatory diagram showing details of the trajectory of the electron beam by the electron optical system of the monochromator of the scanning electron microscope with a monochromator according to an embodiment of the present invention. 2A is a front view showing the beam in the x direction (direction perpendicular to the magnetic field lines), and FIG. 2B is a side view of FIG. It shows the spread of the beam in the direction of the magnetic field lines.
[0019]
In the figure, when the energy of the electron beam spreads 3a and 3b indicated by dotted lines is E, the energy of the electron beams 3A and 3B indicated by broken lines is E−ΔE, and the electron beams 3a and 3b and the electron beam 3A , 3B are electron beams having an energy difference ΔE.
[0020]
The first sector magnetic field 6 and the second sector magnetic field 7 are arranged symmetrically with respect to the line AA, and electrons emitted from the crossover 5 of the first focusing lens 4 as shown in FIG. The beam 3 a converges at the position 20 of the slit 8 after converging at the entrance and exit of the second sector magnetic field 7 in the x direction. On the other hand, the electron beam 3A having different energy draws a trajectory indicated by a broken line in the figure and is dispersed on the slit 8 by the first and second sector magnetic fields 6 and 7. Therefore, by reducing the slit width of the slit 8, only an electron beam having a predetermined energy is selected and monochrome is achieved.
[0021]
The third sector magnetic field 9 and the fourth sector magnetic field 10 are also arranged symmetrically with respect to the line A′-A ′. Further, with respect to the line BB, the set of the first sector magnetic field 6 and the second sector magnetic field 7 is arranged in mirror symmetry with the set of the third sector magnetic field 9 and the fourth sector magnetic field 10. Here, the line BB is referred to as a mirror symmetry plane. Lines AA and A′-A ′ are also referred to as mirror symmetry planes. Further, the mirror symmetry plane of line BB is also referred to as an intermediate mirror symmetry plane in distinction from the mirror symmetry planes of line AA and line A′-A ′. A line AA, a line A′-A ′, and a line BB are lines in the y direction (direction of magnetic lines of force), respectively.
[0022]
The electron beam that has passed through the slit 8 draws a similar electron trajectory by the third and fourth fan-shaped magnetic fields 9 and 10 placed in mirror symmetry with respect to the mirror symmetry plane indicated by the line BB. In over 11, the variance is canceled and x converges.
[0023]
On the other hand, as shown in FIG. 2B, the orbit of the electron beam 3b in the y direction is parallel to the z axis after the incidence due to the so-called oblique incidence effect on the edge magnetic field of the first sector magnetic field 6. An appropriate incident angle is selected so that Therefore, in the slit 8, the electron beam 3b is on a thin line. After passing through the slit 8, the parallel beam is converged at the crossover 11 by the third and fourth sector magnetic fields 9 and 10 which are arranged in mirror symmetry with respect to the intermediate mirror symmetry plane (line BB). Therefore, in the crossover 11, the sector magnetic field parameters are selected so that convergence in the x and y directions and triple convergence of non-dispersion (dispersion is zero) are achieved.
[0024]
TRIO (T. Matsuo, H. Matsuda et al .; Computer Program '' TRIO '' for Third Order Calculation of Ion Trajectory; Mass Spectrometry 24 (1976), pp19-62) is used.
[0025]
Here, the parameters used for the trajectory calculation of the monochromator of the scanning electron microscope with a monochromator according to the present embodiment will be described with reference to FIG.
FIG. 3 is an explanatory diagram of parameters used for the monochromator trajectory calculation of the scanning electron microscope with a monochromator according to an embodiment of the present invention.
[0026]
With respect to the first sector magnetic field 6 and the second sector magnetic field 7, the third sector magnetic field 9 and the fourth sector magnetic field 10 are arranged in mirror symmetry with respect to the plane z2. The surface z2 is a mirror-symmetric surface of line BB shown in FIG. The surface z0 is a position of an object point with respect to the first sector magnetic field 6, and is a surface on which the crossover 5 of FIG. 2 is formed. The surface z4 is positioned mirror-symmetrically with the surface z0 with respect to the surface z2, is a position where an object point is formed by the third sector magnetic field 8, and is a position where the crossover 11 of FIG. 2 is formed. . The plane z1 is a mirror-symmetric plane (line AA in FIG. 2) of the first sector magnetic field 6 and the second sector magnetic field 7, and the plane z0 and the plane z2 are in symmetrical positions with respect to the plane z1. The surface z3 is a mirror symmetric surface (line A′-A ′ in FIG. 2) of the third sector magnetic field 9 and the fourth sector magnetic field 10, and the surface z2 and the surface z4 are in a mirror symmetric position with respect to the surface z3. .
[0027]
When the free space distance from the object point 5 with respect to the first sector magnetic field 6 to the incident position of the electron beam with respect to the first sector magnetic field 6 is DL1, the third sector magnetic field 9 is emitted from the object point formed by the third sector magnetic field 9. The free space distance to the position is also DL1. The free space distance from the exit position of the first sector magnetic field 6 to the incident position of the second sector magnetic field 7 and the free space distance from the exit position of the second sector magnetic field 7 to the entrance position of the first sector magnetic field 6 are DL2 respectively. And Similarly, the free space distance from the emission position of the third sector magnetic field 9 to the incidence position of the fourth sector magnetic field 10 and the free space distance from the emission position of the fourth sector magnetic field 10 to the incidence position of the third sector magnetic field 9 are also calculated. , DL2 respectively. When the free space distance from the exit position of the first sector magnetic field 6 to the slit 8 is DL3 with respect to the surface z2, the free space distance from the slit 8 to the incident position of the third sector magnetic field 9 is also DL3. .
[0028]
In addition, the incident angle with respect to the first sector magnetic field 6 and the exit angle from the third sector magnetic field 9 are equal to each other and are EP1. Moreover, the incident angle with respect to the 3rd sector magnetic field 9 and the exit angle from the 1st sector magnetic field 6 are equal, respectively, and are set to EP2.
[0029]
Further, the deflection orbit radius in the first sector magnetic field 6 and the third sector magnetic field 9 is AM1, and the deflection orbit radius in the second sector magnetic field 7 and the fourth sector magnetic field 10 is AM2.
[0030]
The deflection angle WM1 of the first and third sector magnetic fields 6 and 9 is set to 90 degrees, and the deflection angle WM2 of the second and fourth sector magnetic fields 7 and 10 is set to 180 degrees. It is not necessary. For example, the deflection angle WM1 of the first and third sector magnetic fields 6 and 9 can be set to 80 degrees, and the deflection angle WM2 of the second and fourth sector magnetic fields 7 and 10 can be set to 200 degrees. In this case, when the first sector magnetic field 6 and the second sector magnetic field 7 are parallel, the entrance / exit is oblique entrance / exit, and the entrance / exit between the third sector magnetic field 9 and the fourth sector magnetic field 10 is also oblique entrance / exit. Due to the edge magnetic field effect, it has a lens action in the y direction. On the other hand, when the deflection angle WM1 of the first and third sector magnetic fields 6 and 9 is 90 degrees and the deflection angle WM2 of the second and fourth sector magnetic fields 7 and 10 is set to 180 degrees, the first sector magnetic field 6 Since the entrance / exit between the third sector magnetic field 7 and the fourth sector magnetic field 10 is also a right-angle entrance / exit, there is no convergence in the y direction, and design, manufacture, and adjustment are easy. become.
[0031]
As described above, in the monochromator of the present embodiment, the trajectory parameters based on the first and second sector magnetic fields and the trajectory parameters based on the third and fourth sector magnetic fields are set mirror-symmetrically with respect to the xy plane at the plane z2. .
[0032]
Cross-over electron beam size (x ₁ , Y ₁ ) Is negligibly small, when the beam divergence angles are 2α and 2β and the energy width is δ (= ΔE / E) with respect to the orthogonal xy axis where the energy dispersion direction is x, the monochromator lens system Beam width x in the x direction after passing through ₂ Is a quadratic approximation and is represented by the following equation (1).
x ₂ = A × α + D × δ + AD × αδ + DD × δ ² + AA × α ² + BB × β ² ... (1)
Here, A is an x-direction aberration coefficient, D is an energy dispersion coefficient, and AD, DD, AA, and BB are secondary aberration coefficients related to the energy spread and space spread angle of each beam.
[0033]
The beam width y in the y direction ₂ Is the following equation (2),
y ₂ = B × β + BA × βα (2)
Given in
Here, the convergence condition of the monochromator according to the present embodiment will be described with reference to FIGS. 4 and 5.
FIG. 4 is a diagram showing changes in the primary aberration coefficients A, B, and D of the monochromator according to the embodiment of the present invention. FIG. 5 is a diagram illustrating changes in the secondary aberration coefficients AA, BB, and BA of the monochromator according to the embodiment of the present invention.
[0034]
4 and 5 show the monochromator by determining the deflection orbit radii AM1 and AM2, the incident and exit angles EP1 and EP2, and the free space distances DL1, DL2 and DL3 as shown in FIG. Seeking convergence.
[0035]
Deflection radius AM1: 0.015
Deflection radius AM2: 0.005
Incident angle EP1 to the first sector magnetic field: 16.5
Incident angle EP2 to the first sector magnetic field: 16.5
Free space distance DL1: 0.03
Free space distance DL2: 0.012
Free space distance DL3: 0.03
The unit of the parameter is MKS unit.
First, changes in the primary aberration coefficients A, B, and D of the beam in the monochromator will be described with reference to FIG. In FIG. 4, the horizontal axis represents the z-axis of the beam traveling direction. The leftmost zero represents the crossover 5, M1, M2, M3, and M4 represent the first, second, third, and fourth sector magnetic fields 6, 7, 9, and 10, respectively, the middle is the slit 8, and the right end is the monochrome convergence. Point 11 is represented. The vertical axis in FIG. 4 represents the primary aberration coefficients A, B, and D at the respective positions.
[0036]
As is apparent from FIG. 4, the x direction converges (A = 0) at the slit position, and the energy dispersion coefficient D is 0.04. The beam in the y direction is parallel to the z axis after exiting M1 until the slit and M3 incidence (B = 0.18), but after exiting M3 in the subsequent stage, the x and y directions are at the right end position 11. At the same time, it converges and the variance is offset.
[0037]
As described above, in the first-order approximation orbit calculation, triple convergence (A = B = D = 0) is achieved in terms of both space and energy at the monochrome convergence point of the monochromator of the present embodiment.
Next, changes in the secondary aberration coefficients AA, BB, and BA of the beam in the monochromator will be described with reference to FIG. Also in FIG. 5, as in FIG. 4, the horizontal axis represents the beam traveling direction z-axis. The leftmost zero represents the crossover 5, M1, M2, M3, and M4 represent the first, second, third, and fourth sector magnetic fields 6, 7, 9, and 10, respectively, the middle is the slit 8, and the right end is the monochrome convergence. Point 11 is represented. The vertical axis in FIG. 5 represents the secondary aberration coefficients AA, BB, and BA at the respective positions.
[0038]
As shown in FIG. 5, even in the second-order approximation aberration coefficients, all of the second-order aberration coefficients AA, BB, BA relating to the spatial expansion of the equations (1) and (2) are removed at the final monochrome convergence point. (AA = BB = BA = 0). This is an effect due to mirror symmetry at the slit position of the monochromator.
[0039]
As described above, if the monochromator of the present embodiment is disposed under the first focusing lens of the scanning electron microscope, the first and second aberration coefficients A and B are made monochromatic by the energy limiting slit. , D, AA, BB, and BA are all converged to obtain a monochrome convergence point. If this is used as an object point of the second focusing lens and reduced by the objective lens, a spot free from chromatic aberration can be obtained and the resolution can be improved.
[0040]
Next, a specific first configuration of the monochromator used in the scanning electron microscope according to the embodiment of the present invention will be described with reference to FIG. FIG. 6 shows a first configuration of a monochromator used in a scanning electron microscope according to an embodiment of the present invention, and FIG. 6 (A) is a front sectional view including a central orbit axis z. 6 (B) is a side sectional view. In addition,
The same reference numerals as those in FIG. 2 denote the same parts.
[0041]
In the present embodiment, the monochromator is composed of two parts, so to speak. Exciting coils 42 and 53, a first magnetic pole 43, and a second magnetic pole 54 are attached to the yoke 40, and form the magnetic paths of the first and second sector magnetic fields 6 and 7 shown in FIG. . A passage 49 is provided between the first magnetic field and the second magnetic field. In addition, an entrance 45 is provided at the entrance of the first magnetic field, and an exit 46 is provided at the exit of the first magnetic field. With the above configuration, the first part of the monochromator is configured.
[0042]
The yoke 41 is provided with exciting coils 56 and 57, a third magnetic pole 44, and a fourth magnetic pole 55, and forms a magnetic path for the third and fourth sector magnetic fields 9 and 10 shown in FIG. ing. A passage 50 is provided between the third magnetic field and the fourth magnetic field. Further, an entrance 47 is provided at the entrance of the third magnetic field, and an exit 48 is provided at the exit of the third magnetic field. With the above configuration, the second part of the monochromator is configured.
[0043]
Desirably, the first and second parts of the monochromator are essentially identical and mirror-symmetric.
[0044]
In this example, each can be easily finely adjusted to the beam axis of the SEM.
[0045]
Next, a specific second configuration of the monochromator used in the scanning electron microscope according to the embodiment of the present invention will be described with reference to FIG. FIG. 7 shows a second configuration of the monochromator used in the scanning electron microscope according to one embodiment of the present invention, and FIG. 7A is a front sectional view including the central orbit axis z. 7 (B) is a side sectional view. In addition,
The same reference numerals as those in FIG. 2 denote the same parts.
[0046]
In this embodiment, the monochromator is composed of one part, that is, a single unit. Exciting coils 42 and 53, a first magnetic pole 43 and a second magnetic pole 54 are attached to the yoke 51, and the magnetic paths of the first and second sector magnetic fields 6 and 7 shown in FIG. Yes. A passage 49 is provided between the first magnetic field and the second magnetic field. Similarly, the exciting coil 56, 57 and the third magnetic pole 45 and the fourth magnetic pole 55 are attached to the yoke 51, and the magnetic paths of the third and fourth sector magnetic fields 9, 10 shown in FIG. Forming. A passage 50 is provided between the third magnetic field and the fourth magnetic field.
[0047]
An entrance port 45 is provided at the entrance of the first magnetic field, and an exit port 46 is provided at the exit of the first magnetic field. Further, an entrance 47 is provided at the entrance of the third magnetic field, and an exit 48 is provided at the exit of the third magnetic field.
[0048]
Further, a hole 52 for accommodating a slit is provided, and the slit 8 is accommodated in the hole 52.
[0049]
In this example, since the four magnetic poles are housed in one magnetic path, the relative position is guaranteed with machining accuracy, so a monochromator with excellent symmetry can be created and the number of parts is reduced. be able to.
[0050]
As described above, according to the present embodiment, a monochromator capable of increasing the image resolution of a scanning electron microscope by making the energy of the irradiated electron beam monochromatic, reducing the chromatic aberration, and reducing the spot system is put into practical use. Can be
[0051]
【The invention's effect】
According to the present invention, it is possible to put to practical use a monochromator capable of increasing the image resolution by making the energy of the irradiation electron beam monochromatic, reducing the chromatic aberration, and reducing the spot system.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an optical system of a scanning electron microscope including a monochromator according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing details of an electron beam trajectory by an electron optical system of a monochromator according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram of parameters used for trajectory calculation of a monochromator according to an embodiment of the present invention.
FIG. 4 is a diagram showing changes in a monochromator of primary aberration coefficients A, B, and D according to an embodiment of the present invention.
FIG. 5 is a diagram showing a change in a monochromator of secondary aberration coefficients AA, BB, BA according to an embodiment of the present invention.
FIG. 6 is a first block diagram of a monochromator used in a scanning electron microscope according to an embodiment of the present invention.
FIG. 7 is a second block diagram of a monochromator used in a scanning electron microscope according to an embodiment of the present invention.
[Explanation of symbols]
1. Field emission electron source
2 ... Center axis of electron beam
3 ... Beam spread
4. First focusing lens
5,14 ... Crossover
6 ... 1st sector magnetic field (M1)
7 ... Second sector magnetic field (M2)
8 ... Energy selection slit
9 ... Third sector magnetic field (M3)
10 ... Fourth sector magnetic field (M4)
11. Crossover (monochrome convergence point)
12 ... Aperture
13. Second focusing lens
15, 16 ... Coil for scanning
17 ... Objective lens
18 ... Sample
19 ... Secondary electron detector
20: Intermediate convergence point
21 ... Intermediate mirror symmetry plane
22 ... Secondary electrons
40, 41, 51 ... York
42, 53 ... Excitation coil
43 ... 1st magnetic pole
44 ... Third magnetic pole
45, 47 ... Entrance
46, 48 ... Outlet
49, 50 ... passage
52. Hole for accommodating slit
54. Second magnetic pole
55 ... 4th magnetic pole
56, 57 ... excitation coil

Claims (7)

An electron beam irradiation system comprising an electron gun for generating and accelerating an electron beam, a first focusing lens for converging the electron beam, a second focusing lens for reducing the formed crossover, and an objective lens for further reduction In a scanning electron microscope for irradiating a sample with an electron beam generated from the electron gun,
Disposed between the first focusing lens and the second focusing lens;
It consists of two fan-shaped magnetic poles that form two fan-stage magnetic fields and two fan-stage magnetic fields , respectively , and slits.
The slit is arranged in two mirror-symmetrical surface of the intermediate portion of the fan-shaped magnetic pole forming the two magnetic sector of two fan-shaped magnetic poles and the subsequent forming two magnetic sector of the previous stage, the previous stage Limiting the different energies of the electron beam emanating from the crossover of the first focusing lens with
The two fan-shaped magnetic poles forming the two fan-shaped magnetic fields and the two fan-shaped magnetic poles forming the two subsequent fan-shaped magnetic fields are arranged along the irradiation direction of the electron beam,
The two fan-shaped magnetic fields at the latter stage spatially converge the divergent electron beam again, make the energy dispersion non-dispersive, and use it as an object point of the second focusing lens,
The two fan-shaped magnetic fields formed by the two fan-shaped magnetic poles in the preceding stage deflect the electron beam focused by the first focusing lens out of the optical axis from the electron gun to the objective lens, Return the dispersed electron beam to the optical axis of the electron beam, pass through the slit,
The two fan-shaped magnetic fields formed by the two fan-shaped magnetic poles in the rear stage are electrons that have been dispersed in energy after deflecting the electron beam that has passed through the slit by the two fan-shaped magnetic fields in the previous stage again to the outside of the optical axis. A scanning electron microscope with a monochromator provided with an electron energy monochromator for returning the beam to the optical axis of the electron beam and focusing the spot. The scanning electron microscope with a monochromator according to claim 1,
The above electronic energy monochromator is
The first sector magnetic field deflects the electron beam to approximately 90 degrees,
Again incident on the first magnetic sector are deflected approximately 180 degrees in the second magnetic sector deflected approximately 90 degrees, and is emitted at the same angle as the incident direction of the first, the Oite magnetic field lines in a mirror symmetry plane While converging in the orthogonal direction (x direction) ,
After the energy is limited by the slit, it is incident on the third sector magnetic field and deflected by approximately 90 degrees, is deflected by approximately 180 degrees by the fourth sector magnetic field, and is incident again on the third sector magnetic field and is approximately 90 degrees. A scanning electron microscope with a monochromator, which deflects and emits in the same direction as the first incident direction to form a non-dispersive cross-over and is used as an object point of the second focusing lens. The scanning electron microscope with a monochromator according to claim 2,
The monochromator
The object point of the first focusing lens is converged in the x direction (energy dispersion direction) at the entrance of the second sector magnetic field by the first sector magnetic field, and converged in the x direction at the exit by the second sector magnetic field, Again, the first sector magnetic field converges in the x direction to a mirror symmetrical position with the first object point,
In the y direction (magnetic field direction), the beam becomes almost parallel, and the energy width is reduced by the slit.
In the third and fourth sector magnetic fields in the subsequent stage, the trajectory of the electron beam is drawn with the same mirror-symmetric path as the sector magnetic field in the previous stage, and is mirror-symmetric to the first object point with respect to the intermediate mirror symmetry plane (slit position). A scanning electron microscope with a monochromator, characterized by non-dispersion in position and convergence of point convergence. The scanning electron microscope with a monochromator according to claim 1,
The monochromator
Of the two sector magnetic poles forming the preceding sector magnetic field , the entrance magnetic pole end surface of the sector magnetic pole forming the first sector magnetic field has an incident angle in the deflection direction with respect to the vertical plane of the beam incident direction, and the beam Is parallel to the central axis (traveling direction) of the beam in the y direction (direction of magnetic field lines) after emission,
Of the two fan magnetic poles forming the latter sector magnetic field , the exit magnetic pole end surface of the sector magnetic pole forming the third sector magnetic field has the incident angle of the sector magnetic pole forming the first sector magnetic field and the mirror symmetrical exit angle. A scanning electron microscope with a monochromator, wherein the crossover is formed by simultaneously converging at the convergence point in the x direction with respect to the y direction after emission. The scanning electron microscope with a monochromator according to claim 1,
The monochromator
It has a mirror-symmetric plane z1 with respect to the fan- shaped magnetic pole that forms the first sector-shaped magnetic field and the sector-shaped magnetic pole that forms the second sector-shaped magnetic field , the object point, and the slit.
Further, it has a mirror-symmetric plane z3 with respect to the sector magnetic pole forming the third sector magnetic field , the sector magnetic pole forming the fourth sector magnetic field and the slit, and the point convergence crossover constituting the subsequent sector magnetic field,
The sector magnetic pole that forms the first sector magnetic field , the sector magnetic pole that forms the second sector magnetic field , the object point, and the slit form a third sector magnetic field that constitutes the two sector magnetic poles that form the subsequent sector magnetic field . The fan-shaped magnetic pole and the sector-shaped magnetic field that forms the fourth sector-shaped magnetic field are symmetrical with respect to the intermediate mirror symmetry plane z2 including the slit, the point convergence crossover, and the slit.
At the crossover point after the third sector magnetic field, the energy dispersion coefficient becomes zero (non-dispersion) and has a convergence characteristic that removes secondary aberration coefficients related to the opening angles α and β in the x and y directions of the beam. A scanning electron microscope with a monochromator. The scanning electron microscope with a monochromator according to claim 1,
Said monochromator forms a fan-shaped magnetic poles that form a first and second magnetic sector constituting the two fan-shaped magnetic poles that form two magnetic sector of the previous stage in integral yaw click, the subsequent two third and fourth scanning electron with monochrometer, characterized in that the fan-shaped magnetic pole for forming a magnetic sector is formed by a separate piece of yaw click constituting two sectorial pole forming the magnetic sector electronic microscope. The scanning electron microscope with a monochromator according to claim 1,
Said monochromator, a fan-shaped magnetic poles forming the first and second magnetic sector constituting the two fan-shaped magnetic poles that form two magnetic sector of the previous stage to form two magnetic sector of the subsequent two third and fourth with the monochromator, characterized in that formed integrally of yaw click the sector pole for forming a magnetic sector scanning electron electron microscope constituting a fan pole.

Images