JP4628076B2 - Aberration correction method and aberration correction apparatus - Google Patents

Description

  The present invention relates to an automatic aberration correction method and apparatus, and an aberration corrector control method.

  A scanning electron microscope (SEM) will be described as an example of a sample surface observation apparatus using charged particles. FIG. 7 is a diagram showing a configuration example of a conventional apparatus. This figure shows a scanning electron microscope equipped with an aberration corrector. An electron beam 2 is emitted from the emitter 1, and the electron beam 2 incident on the aberration corrector 6 is controlled by the lens 3 acting on the electron beam 2, and the electron beam 2 emitted from the aberration corrector 6 is used as the objective lens 4. To focus on the surface of the sample 5.

  The electron beam 2 is scanned on the sample surface, and secondary electrons 7 emitted from the sample surface are detected by the secondary electron detector 8 in synchronization with the scanning, whereby an image is displayed on the CRT 12 in synchronization with the scanning signal. Display as. Since the detection efficiency of the secondary electrons 7 is usually low, noise is removed by the normal image integrator 9. The image from which the noise has been removed is displayed on the CRT 12. As an example of such an aberration corrector, a technique using a multipole is known (for example, see Non-Patent Document 1).

  Hereinafter, the technique shown in Non-Patent Document 1 will be described as an example. FIG. 8 is a diagram showing the configuration of the aberration corrector and the trajectory of the electron beam passing through it. In the figure, 6 is an aberration corrector. The multipoles are composed of four stages of multipoles, and are shown as a first multipole element 6a, a second multipole element 6b, a third multipole element 6c, and a fourth multipole element 6d, respectively. Usually, the multipole of each stage is a multipole of 8 or more. The electron beam 2 is simultaneously focused and diverged by the first multipole element 6a. As shown in the figure, the electron beam 2 subjected to the diverging action is referred to as an X orbit 6e, and the electron beam 2 subjected to the focusing action is referred to as a Y orbit 6f.

  The intensity of the first multipole element 6a is adjusted so that the Y orbit 6f passes through the center of the second multipole element 6b. Further, the intensity of the second multipole element 6b is adjusted so that the X orbit 6e passes through the center of the third multipole element 6c. At this time, in the second multipole element 6b, since the Y orbit 6f passes through the center of the second multipole element 6b, only the X orbit 6e receives a lens action. Similarly, in the third multipole element 6c, since the X orbit 6e passes through the center of the third multipole element 6c, only the Y orbit 6f receives a lens action. Thus, the Y orbit 6f of the electron beam 2 must pass through the center of the second multipole element 6b, and the X orbit 6e must pass through the center of the third multipole element 6c and be focused in each direction.

  Conventionally, this alignment is performed by wobbling the multipoles at each stage to see the amount of image movement and adjusting the intensity of the multipoles at each stage. For example, since each stage always has a mechanical center axis deviation, each stage is usually configured with a dipole, and by wobbling the multipoles at each stage, these are prevented from moving. Used to align the center of each step. In addition, as described above, the images of the multipole elements at each stage move so as to pass through the second multipole center and the third multipole center and converge in the Y direction and the X direction, respectively, due to the lens action of the multipole. It has been adjusted not to. Since these procedures are linked, the operator is adjusted by taking a great deal of time while confirming the movement and image quality of the image based on experience and intuition.

Aberration correction in a low voltage SEM by multipole corrector (Nuclear Instrument and Methods in Physics Research A 363 (1995) 316-325)

  As described above, in the aberration corrector composed of multipoles, there is always a mechanical center axis deviation in construction, and the operator experienced by wobbling the multipoles at each stage using multiple dipoles. It fits together. Further, inside the aberration corrector, a certain direction component of the electron beam must pass through the center of a certain stage and be converged, and this is adjusted by adjusting the intensity of the multipole element at each stage. . These procedures are linked in a complicated manner, and there is a problem that the operator takes a great deal of time to adjust from experience and intuition based on image movement and image quality.

The present invention has been made in view of such a problem, and an object thereof is to provide an aberration correction method and an aberration correction apparatus in which an ordinary operator can align the aberration corrector without being aware of the aberration corrector. It is said.

( 1 ) The invention according to claim 1 is a method of controlling an aberration corrector comprising a plurality of stages of multipoles, wherein the controller fixes the multipole lens intensity ratio of each stage and simultaneously forms one lens. It is characterized by controlling. According to a fourth aspect of the present invention, there is provided an aberration correction apparatus including an aberration corrector including a plurality of stages of multipoles and a controller that controls the aberration corrector. The pole lens intensity ratio is fixed and controlled as one lens simultaneously.

( 2 ) The invention according to claim 2 is a method for controlling an aberration corrector comprising a plurality of stages of multipoles, wherein the controller fixes a lens intensity ratio between each stage of the multipole elements and the objective lens. It is characterized by controlling as two lenses simultaneously. According to a fifth aspect of the present invention, there is provided an aberration correction apparatus including an aberration corrector including a plurality of stages of multipoles and a controller for controlling the aberration corrector. The lens intensity ratio between the pole and the objective lens is fixed and controlled as one lens simultaneously.

( 3 ) In the invention according to claim 3 or 6 , the controller can fix the lens intensity ratio of the lenses combined with the multipole lens intensity ratio of each stage or the multipole element of each stage and the objective lens. It is characterized in that feedback is applied to the combined lens.

( 1 ) According to the invention described in claim 1 or 4, by fixing the multipole lens intensity ratio of each stage, it is possible to control one lens with one control signal, and simplify the control system. By doing so, it is possible to satisfactorily correct the axis deviation.

( 2 ) According to the invention of claim 2 or 5 , by fixing the lens intensity ratio between the multipole lens and the objective lens in each stage, it is possible to control one lens with one control signal, By simplifying the control system, it is possible to satisfactorily correct the axis deviation.

( 3 ) According to the invention of the third or sixth aspect , it is possible to control with one feedback amount with respect to one axial displacement amount, and to perform excellent axial displacement correction.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of the present invention. The same components as those in FIG. 7 are denoted by the same reference numerals. In the figure, 1 is an emitter emitting a charged particle beam, 2 is an electron beam emitted from the emitter 1, 3 is a lens acting on the electron beam 2, and 6 is various corrections of the electron beam 2 subjected to the lens action. An aberration corrector 4 is used to focus the electron beam 2 on the sample 5, 5 is a sample, 7 is a secondary electron emitted from the sample 5, and 8 is a secondary electron that detects the secondary electron 7. It is a detector.

  9 is an image accumulator for accumulating images to make the secondary electron image resistant to noise, 10 is an aberration correction controller for giving a control signal for aberration correction to the aberration corrector 6, and 11 is an aberration correction controller 10 or This is an automatic alignment device that gives an automatic alignment control signal to the objective lens 4. For example, a computer is used as the automatic alignment apparatus 11. A CRT 12 is connected to the image accumulator 9 and displays various information.

  In the present invention, a good sample surface image can be obtained by using circular particles, gold particles, or latex as the sample 5. The operation of the apparatus configured as described above will be described as follows.

  An electron beam 2 is emitted from the emitter 1, and the electron beam 2 incident on the aberration corrector 6 is controlled by the lens 3 acting on the electron beam 2. The electron beam 2 emitted from the aberration corrector 6 is controlled by the objective lens 4. Focusing on the surface of the sample 5. The electron beam 2 is scanned on the surface of the sample, and secondary electrons 7 emitted from the surface of the sample 5 are detected by the secondary electron detector 8 in synchronization with the scanning, whereby an image is displayed on the CRT 12 in synchronization with the scanning signal. Display as. Since the detection efficiency of the secondary electron detector 8 is usually low, noise is removed by the image integrator 9.

  The aberration correction controller 10 controls the lens strength of the aberration corrector 6. The automatic alignment apparatus 11 acquires an SEM image from the image accumulator 9, and determines the lens intensity for correcting the mechanical axis deviation of the aberration corrector 6 and the trajectory of the electron beam 2 inside the aberration corrector 6. The lens intensity to be controlled to the trajectory is calculated and the aberration correction controller 10 is instructed. The configuration and operation of the aberration corrector 6 are described in detail in Non-Patent Document 1. Hereinafter, the configuration and operation of the automatic alignment apparatus 11 according to the present invention will be described in detail with reference to FIG.

  FIG. 2 is a diagram illustrating a configuration example of the automatic alignment apparatus. In the figure, reference numeral 11a denotes an alignment control device which outputs a control signal ΔVn for alignment control. 11b receives the output of the alignment control device and receives the SEM image 20, and extracts a beam shape. Reference numeral 13 denotes a beam shape output from the beam shape extraction device 11b. 11c is an axis misalignment quantification device that receives the beam shape 13 and quantifies the axis misalignment, 11e is a judgment device that receives the value quantified by the axis misalignment quantification device and determines whether to perform feedback control, 11d is a feedback device that receives the output of the determination device 11e and outputs a feedback control signal Vn. The operation of the present invention will be described using the apparatus configured as described above.

  The automatic alignment device 11 instructs the aberration correction controller 10 to change the intensity of a plurality of dipoles constituting the aberration corrector 6 in order to confirm the amount of axial deviation of the aberration corrector 6. In order to confirm whether the electron beam 2 passes through a predetermined trajectory inside the aberration corrector 6, the intensity of a plurality of multipoles constituting the aberration corrector 6 is set to the aberration correction controller 10. Instruct to change. In the beam shape extraction device 11b, in synchronization with the lens intensity change instruction ΔVn from the alignment control device 11a, the SEM image without the lens intensity change at that time and the SEM image at the time of the lens intensity change are acquired, and the beam shape is changed. calculate. A method of extracting a beam shape from these two SEM images is described in detail in a patent (WO 01/56057 AL). The outline is shown here.

  The SEM image when the lens intensity is changed is g1, and the SEM image when the lens intensity is not changed is g0. Further, the sample surface shape is s, the beam shape when the lens intensity is changed is p1, and the beam shape when the lens intensity is not changed is p0. At this time, the SEM images g1 and g0 are expressed as follows.

g1 = s * p1 (1)
g0 = s * p0 (2)
Here, “*” represents a convolution. When the equations (1) and (2) are Fourier transformed, the following equations are obtained. The capital letters indicate the Fourier-transformed ones.

G1 = S · P1 (3)
G0 = S · P0 (4)
Here, “·” indicates a product in Fourier space. When S is eliminated by the equations (3) and (4), the following equation is obtained.

G1 = (P1 · G0 / P0) = P10 · G0 (5)
Here, P1 / P0 = P10. Next, when the equation (5) is inverse Fourier transformed to a real space, the following equation is obtained.

g1 = F ⁻¹ [P10 · G0] (6)
Here, F ⁻¹ [] indicates an inverse Fourier transform. Since P10 is a known function, if G0 is known, the beam shape g1 can be calculated by equation (6).

  For example, assuming that the beam shape g0 when there is no change in lens intensity is a Gaussian distribution function, the beam shape 13 (g1) can be calculated because G0 is also a Gaussian distribution function. As shown in FIG. 2, the axis deviation quantification apparatus 11c quantifies the current axis deviation from the obtained beam shape 13 (g1). As a quantification method, for example, as shown in FIG. 3, the center of the beam shape FOV (Field Of View) is O, the center of gravity of the beam shape 13 is G, and the projection of the vector OG onto the X axis and the Y axis is performed. Is defined as Gx [mode] for the deviation in the X direction and Gy [mode] for the deviation in the Y direction. Note that the center can be used instead of the center of gravity.

  Here, Gx [mode] and Gy [mode] are functions of mode, and the mode means identification of the lens intensity change instructed by the alignment control device 11a. For example, mode = 1 means that the quadrupole of the first pole of the aberration corrector 6 is changed. The feedback device 11d calculates a feedback amount Vn [mode] instructed to the aberration correction controller 10 or the objective lens 4 from the quantified axis deviation amounts Gx [mode] and Gy [mode] by the following equation. Similarly, the feedback amount Vn is a function of mode. Usually, the feedback amount Vn is directional, and the feedback amount in the X direction is Vnx and the feedback amount in the Y direction is Vny.

Vnx [mode] = α [mode] × Gx [mode] (7-1)
Vny [mode] = β [mode] × Gy [mode] (7-2)
Here, α [mode] and β [mode] are similarly functions of mode.

  Thus, according to the present invention, automatic alignment by the aberration corrector can be performed by using the center of gravity or the center as the position of the charged particle beam shape.

The determination device 11e corrects the shaft misalignment when Gx and Gy are smaller than the threshold values compared to the predetermined threshold values from the shaft misalignment amounts Gx [mode] and Gy [mode] identified by the mode, respectively. If it is determined that the correction has been performed, the correction is terminated. If it is determined that the correction of the axial deviation is insufficient, the alignment control device 11a is instructed and repeatedly controlled. For example, the control method is determined to be complete when the following expression is satisfied by the threshold value γ [mode] set for each mode.
| Gx [mode] | <γ [mode] and | Gy [mode] | <γ [mode] (8)
According to the present invention, it is possible to satisfactorily perform the axial deviation correction by performing the axial deviation correction independently for the Gx and Gy. In addition, according to the present invention, the amount of misalignment can be sufficiently reduced by repeating the automatic alignment process until the quantified amount of misalignment falls within a certain threshold. In this case, it is possible to automatically determine whether or not the axis deviation (alignment) of the apparatus has been corrected by comparing the quantified axis deviation amount with a certain threshold value.

  FIG. 8 shows the configuration of the aberration corrector 6 using a multipole element and the trajectory of the electron beam 2 passing through the aberration corrector 6. The multipole is composed of four stages of multipoles, which are shown as a first multipole 6a, a second multipole 6b, a third multipole 6c, and a fourth multipole 6d, respectively. Usually, the multipole of each stage is a multipole of 8 or more. According to Non-Patent Document 1, the electron beam 2 is simultaneously subjected to focusing and diverging action by the first multipole element.

  Now, as shown in FIG. 8, the electron beam 2 subjected to the diverging action is referred to as an X orbit 6e, and the electron beam subjected to the focusing action is referred to as a Y orbit 6f. The intensity of the first multipole element 6a is adjusted so that the Y orbit 6f passes through the center of the second multipole element 6b and is focused. Further, the intensity of the multipole element 6b is adjusted so that the X orbit 6e passes through the center of the third multipole element 6c and converges. At this time, in the second multipole element, the Y orbit 6f passes through the center of the second multipole element 6b and is not affected, and only the X orbit 6e receives the lens action.

  Similarly, in the third multipole element, the X orbit 6e is not affected because it passes through the center of the multipole element 6c, and only the Y orbit 6f is subjected to the lens action. Thus, the Y orbit 6f of the electron beam 2 must pass through the center of the multipole 6b and be focused, and the X orbit 6e must pass through the center of the multipole 6c and be focused. FIG. 4 is an explanatory diagram when the electron beam is deviated from the trajectory when the first-stage lens intensity of the multipole element is changed. The electron beam 2 passes through the centers of the second multipole element 6b and the third multipole element 6c, but the X orbit 6e is not focused on the center of the third multipole element, and the Y orbit 6f is at the center of the second multipole element. The case where it is not focused is shown.

  In this case, the tilt and position of the electron beam 2 coming out of the aberration corrector 6 change and blur as an image. Further, if the electron beam 2 does not pass through the center of each stage multipole, the image moves when the lens intensity of each stage multipole is changed. In the non-patent document 1, the electron beam 2 is controlled by a quadrupole among the multipoles at each stage. When the electron beam does not pass through the center of the multipole, the center of the first-stage quadrupole wobbles the first-stage quadrupole field, and the electron beam is deflected on the electron light source side of the aberration corrector 6 (not shown). It can be found by controlling 2 and searching for a point where the image does not move.

  The second stage quadrupole center is found by wobbling the second stage quadrupole field and controlling the electron beam 2 with the first stage dipole (equivalent to a deflector) to find the point where the image does not move. It is done. Similarly, the third-stage quadrupole center and the fourth-stage quadrupole center can be searched. Further, in order to pass the electron beam 2 emitted from the aberration corrector 6 through the center of the objective lens 4, the objective lens intensity can be wobbled, and the center of the objective lens can be found by the fourth dipole. In the present invention, this operation is performed by the automatic alignment device 11. For example, when passing through the center of the second stage quadrupole, in the automatic alignment apparatus 11 shown in FIG. 2, the aberration correction controller 10 so that the alignment controller 11a changes the quadrupole field intensity of the second stage by ΔVn. To instruct.

  The aberration correction controller 10 controls the aberration corrector 6 so as to be instructed. As a result of the aberration corrector 6 changing the second-stage multipole field by ΔVn, the SEM image moves, and the beam shape extraction device 11b inputs the SEM image and the SEM when there is no lens intensity change. The beam shape 13 is calculated, the axis deviation quantification device 11c quantifies the axis deviation amount, and the feedback device 11d calculates the feedback amount for the first stage dipole and instructs the aberration corrector 6 or the objective lens 4 To do. The determination device 11e instructs the alignment control device 11a to repeat the correction from the quantified axis deviation amount until the expression (8) is satisfied.

  The X orbit must be focused on the center of the third multipole, and the Y orbit must be focused on the center of the second multipole. FIG. 9 shows electron beam trajectories in the XZ plane and the YZ plane. The one shown in FIG. 9A is the X orbit, and the one shown in FIG. 9B is the Y orbit. In order for the Y orbit 6f to focus on the center of the second multipole element (in this case, the quadrupole element), it is determined whether or not the electron beam 2 is focused on the dipole center in the Y direction of the multipole element. That is, when the intensity of the dipole field in the Y direction of the second stage is changed by ΔVn, as shown in FIG. 5, the Y orbit 6f is focused on the center of the second multipole element (in this case, the dipole element). In this case, even if the magnitude of the dipole field changes, the electron beam 2 emitted from one point is focused on one point on the surface of the sample 5 by the objective lens 4, so that the SEM image does not move.

  However, if the Y orbit 6f is not focused on the center of the second multipole element (in this case, the dipole element), the object point 18 shown in FIG. 5 changes the intensity of the second-stage pole field by ΔVn. Sometimes it moves and as a result the SEM image moves. That is, if the quadrupole field intensity or the objective lens of each stage is adjusted so that the SEM image does not move even if the intensity of the dipole field of the second stage is changed by ΔVn, the Y orbit 6f becomes the second multipole element. (In this case, it is focused on the center of the quadrupole).

  For example, the SEM image can be prevented from moving by adjusting the first-stage quadrupole field. However, the same can be achieved by using other quadrupoles. However, as shown in FIG. 4, since the multipole applies the focusing action and the divergence action to the electron beam 2 at the same time, it affects the other axis. Must be adjusted. Similarly, the X orbit 6e is focused on the center of the third multipole element (in this case, the quadrupole element). That is, the quadrupole field intensity or objective lens of each stage is adjusted so that the SEM image does not move by changing the third stage dipole field.

  In the present invention, this operation is performed by the automatic alignment apparatus 11. That is, for example, when the Y orbit 6f is focused on the center of the second multipole element (in this case, the quadrupole element), in the automatic alignment apparatus 11 shown in FIG. The aberration correction controller 10 is instructed to change the intensity of the dipole field by ΔVn. The aberration correction controller 10 controls the aberration corrector 6 so as to be instructed. As a result of the aberration corrector 6 changing the dipole field strength in the Y direction of the second stage by Δn, the SEM image moves, and the SEM image and the SEM image when there is no change in the lens strength are extracted in the beam shape. The apparatus 11b inputs, extracts the beam shape 13, the axis deviation quantification apparatus 11c quantifies the axis deviation amount, and the feedback apparatus 11d calculates the feedback amount for the quadrupole or objective lens at each stage, thereby controlling aberration correction. The instrument 11 or the objective lens. The determination device 11e instructs the alignment control device 11a to repeat the correction operation until the expression (8) is satisfied from the quantified axis deviation amount.

  According to the present invention, it is possible to obtain a sample surface image when the lens intensity is shifted. Further, as the amount of axial deviation of the apparatus, the amount of axial deviation of the apparatus can be obtained by multiplying a constant that is the difference between the position of the center of gravity and the origin using one or two extracted charged particle beam shapes. Also, as the amount of axial deviation of the apparatus, the amount of axial deviation of the apparatus can be obtained by multiplying a constant that is the difference between the center position and the origin using one or two extracted charged particle beam shapes. Further, according to the present invention, automatic alignment by the aberration corrector can be performed by applying feedback to the aberration corrector or the objective lens in accordance with a value obtained by multiplying the obtained amount of axial deviation by a constant. Further, as the lens intensity of the aberration corrector to be fed back, automatic alignment by the aberration corrector can be performed using a dipole or a quadrupole as the multipole of each stage of the 4-stage multipole.

  As described above, the automatic alignment apparatus 11 according to the present invention performs a plurality of alignments. For example, the automatic alignment apparatus 11 can be distinguished as follows by identifying the number of modes.

mode = 1 The electron beam is passed through the first stage multipole center. mode = 2 The electron beam is passed through the second stage multipole center. mode = 3 The electron beam is passed through the third stage multipole center. mode = 4 The electron beam is passed through the fourth stage. Pass through the center of the stage multipole mode = 5 pass the electron beam through the center of the objective lens mode = 6 focus the Y orbit to the center of the second stage multipole mode = 7 mode = 1 focus the X orbit to the center of the third stage multipole The alignment controller 11a monitors the alignments ˜7, and the correction is repeated until all the conditions are satisfied. The order of alignment may be from the numerical order of mode, but there is no need to be particular about it.

  In the case of mode = 1 to 4 where the electron beam is passed through the center of each pole, for example, when mode = 1, feedback amounts Vnx [mode = 1] and Vny calculated by equations (7-1) and (7-2) [Mode1] is applied to each of the X and Y deflectors disposed on the emitter side of the aberration corrector.

  When mode = 2, the feedback amounts Vnx [mode = 2] and Vny [mode = 2] calculated by the equations (7-1) and (7-2) are 2 in the X and Y directions of the first stage of the aberration corrector. Applied to each pole.

  When mode = 3, the feedback amounts Vnx [mode = 3] and Vny [mode = 3] calculated by equations (7-1) and (7-2) are 2 in the X and Y directions of the second stage of the aberration corrector. Applied to each pole.

  When mode = 4, the feedback amounts Vnx [mode = 4] and Vny [mode = 4] calculated by the equations (7-1) and (7-2) are 2 in the X and Y directions of the third stage of the aberration corrector. Applied to each pole.

  When mode = 5, the feedback amounts Vnx [mode = 5] and Vny [mode = 5] calculated by the equations (7-1) and (7-2) are 2 in the X and Y directions of the fourth stage of the aberration corrector. Applied to each pole.

  When the Y trajectory is focused on the center of the second stage multipole, the X orbit is changed by fixing the lens intensity ratio of the first, second, and third stage quadrupoles to Ay: By: Cy. The focal point of the Y orbit can be moved near the center of the second stage multipole while focusing on the center of the third stage multipole, and the feedback amount Vny [mode = 6] calculated by the equation (7-2) is used as the lens. Apply to the quadrupoles of the first, second, and third stages according to the intensity ratio Ay: By: Cy.

  That is, Ay · Vny is applied to the first stage quadrupole, By · Vny is applied to the second stage quadrupole, and Cy · Vny is applied to the third stage quadrupole.

  The lens intensity ratio is, for example, 4: -1: -1, but is not limited, and when the first-stage quadrupole field intensity is experimentally shifted by Ay, the image is focused again. The second stage quadrupole field strength may be set to By and the third stage quadrupole field strength may be set to Cy.

  Similarly, when the X orbit is focused on the center of the third stage multipole, by fixing the lens intensity ratio of the second, third, and fourth stage quadrupoles to Bx: Cx: Dx, The focusing point of the X orbit can be moved near the center of the third stage multipole while the Y orbit is focused on the center of the second stage multipole, and the feedback amount Vnx [mode = 7] is applied to the quadrupoles of the second, third, and fourth stages according to the lens intensity ratio Bx: Cx: Dx.

  That is, Bx · Vnx is applied to the second stage quadrupole, Cx · Vnx is applied to the third stage quadrupole, and Dx · Vnx is applied to the fourth stage quadrupole.

  The lens intensity ratio is, for example, −1: −1: 4, but is not limited. When the fourth stage quadrupole field intensity is experimentally shifted by Dx, the image is focused again. The second stage quadrupole field strength may be set to Bx, and the third stage quadrupole field strength may be set to Cx.

  Further, as another method of focusing the X orbit on the center of the third stage multipole, the Y orbit becomes the second stage multiple by fixing the lens intensity ratio of the second and third stage quadrupoles to Bx: Cx. The focal point of the X orbit can be moved near the center of the third stage multipole while focusing on the pole center, and the feedback amount Vnx [mode = 7] calculated by the equation (7-1) is used as the lens intensity ratio Bx. : Applied to the quadrupoles of the second and third stages according to Cx. At this time, the focus at the sample position is shifted, but it can be corrected by adjusting the objective lens intensity. Therefore, as a whole, the second stage quadrupole, the third stage quadrupole, and the objective lens intensity may be fixed to Bx: Cx: Ox, respectively, and feedback may be applied.

  That is, Bx / Vnx is applied to the second stage quadrupole, Cx / Vnx is applied to the third stage quadrupole, and Ox / Vnx is applied to the objective lens.

  The lens intensity ratio is, for example, −1: 1: Ox, but is not limited, and the second stage quadrupole is such that when the objective lens intensity is experimentally shifted by Ox, the image is focused again. The field intensity may be set to Bx, and the third stage quadrupole field intensity may be set to Cx.

  According to the present invention, automatic alignment by the aberration corrector can be performed by using any one of 2, 3, or 5 sample surface images to be used. Further, automatic alignment by the aberration corrector can be performed using an image obtained by shifting the lens intensity of the aberration corrector by a predetermined amount and an image at the current value. Further, automatic alignment by the aberration corrector can be performed using an image obtained by shifting the lens intensity of the aberration corrector by a predetermined amount in the X and Y directions and an image at the current value. In addition, automatic alignment can be performed using an aberration corrector composed of four stages of multipoles. In addition, automatic alignment by the aberration corrector can be performed by using at least four or more quadrupoles as four-stage multipoles. Furthermore, automatic alignment by an aberration corrector can be performed using the number of multipoles in each stage of the four stages of multipoles as dipoles, quadrupoles, hexapoles, and octupoles.

  As described above, according to the present invention, an ordinary operator can automatically correct the alignment of the aberration corrector without being aware of the aberration corrector.

  In addition, according to the present invention, since the current magnitude of the axis deviation is quantified, the operation state of the automatic alignment apparatus 11, for example, a GUI (Graphical User Interface) 15 on the CRT 12 as shown in FIG. The operator can be supported by displaying the beam shape 13 and the history of the amount of axial deviation of the apparatus. Reference numeral 14 denotes a beam shape FOV. From this figure, it can be seen that Gx shows a characteristic in which the amount of axial deviation gradually decreases as the number of trials increases, while Gy shows a characteristic in which the amount of axial deviation increases in the middle and then decreases.

It is a block diagram which shows one embodiment of this invention. It is a figure which shows the structural example of an automatic alignment apparatus. It is explanatory drawing of the method of quantification. It is explanatory drawing when an electron beam deviates from an orbit. It is a figure which shows the track | orbit of an electron beam. It is a figure which shows the mode of the display by this invention. It is a figure which shows the structural example of a conventional apparatus. It is a figure which shows the structure of an aberration corrector, and the trajectory of the electron beam which passes through the inside. It is a figure which shows an electron beam orbit by a XZ surface and a YZ surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Emitter 2 Electron beam 3 Lens 4 Objective lens 5 Sample 6 Aberration corrector 7 Secondary electron 8 Secondary electron detector 9 Image accumulator 10 Aberration correction controller 11 Automatic alignment apparatus 12 CRT

Claims (6)

In the control method of the aberration corrector composed of multistage multipoles,
A method for controlling an aberration corrector, wherein the controller controls the multipole lens intensity ratio at each stage in a fixed manner and simultaneously controls the lens as one lens. In the control method of the aberration corrector composed of multistage multipoles,
A method for controlling an aberration corrector, wherein a controller controls a lens intensity ratio between a multipole element and an objective lens at each stage and controls the lenses simultaneously as a single lens. The controller applies feedback to a lens combined with a fixed multi-pole lens intensity ratio at each stage or a lens combined with a fixed lens intensity ratio between each multi-pole element and an objective lens. 3. The method for controlling an aberration corrector according to claim 1 , wherein the aberration corrector is controllable.   In an aberration correction apparatus comprising an aberration corrector composed of a multistage multipole element and a controller for controlling the aberration corrector,
  An aberration correction apparatus characterized in that the controller multi-pole lens intensity ratio of each stage is fixed and controlled as one lens at the same time.   In an aberration correction apparatus comprising an aberration corrector composed of a multistage multipole element and a controller for controlling the aberration corrector,
  An aberration correction apparatus characterized in that the controller controls the lens intensity ratio between the multipole element and the objective lens at each stage and controls them simultaneously as one lens.   The controller applies feedback to a lens combined with a fixed multi-pole lens intensity ratio at each stage or a lens combined with a fixed lens intensity ratio between each multi-pole element and an objective lens. The aberration correction apparatus according to claim 4 or 5, characterized in that:

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