JP6438780B2 - Charged particle beam apparatus and aberration correction method - Google Patents

Description

  The present invention relates to a charged particle beam apparatus equipped with an aberration corrector and an aberration correction method.

  In charged particle beam apparatuses typified by a scanning electron microscope (hereinafter referred to as SEM) and a scanning transmission electron microscope (hereinafter referred to as STEM), introduction of aberration correctors has been promoted in order to improve resolution. The aberration corrector is composed of multipole lenses installed in multiple stages, and generates an electric field or a magnetic field to remove aberrations contained in a charged particle beam passing through the interior as a multipole lens. As an aberration corrector, for example, as disclosed in Non-Patent Document 1, there is one using four stages of multipole lenses. In the charged particle beam apparatus, in general, in order to prevent a reduction in resolution due to unnecessary aberrations or the like, axis adjustment is performed to align the optical axis of the charged particle beam with the axis of the lens. For example, in Patent Document 1, the acceleration voltage or the lens intensity is finely moved (hereinafter referred to as a wobbler), and the lens itself is moved or the charged particle beam is deflected so as to eliminate the movement (shift) of the image at that time. Also disclosed is a method of adjusting the axis by changing the position of the charged particle beam incident on the lens by shifting the aperture position. Similarly, in an aberration corrector using a lens of a multipole field, it is also possible to adjust the axis by deflecting a charged particle beam so as to eliminate image movement by adding a wobbler to a quadrupole field acting as a lens. 2 is disclosed.

  The multistage multipole type aberration corrector has a configuration in which lenses are stacked in two or more stages, and basically, axis adjustment is required at all stages. For normal axis adjustment of multi-stage lenses, all lenses are temporarily stopped, and only one lens is turned on to adjust the axis, and then the next lens is turned on and adjusted in order. Can be executed. On the other hand, in the aberration corrector, since it is necessary to operate a plurality of multipole field lenses as a set, the multipole field lens other than the lens that performs the axial adjustment must be driven while the axis is adjusted. For this reason, it is necessary to perform a repetitive operation of adjusting the axis of a specific stage and then returning to the stage where the axis was adjusted before that and performing the axis adjustment again.

JP 58-106746 A JP 2006-140119 A

  In Patent Document 1, the axis adjustment of one lens is targeted, and no adjustment method is specifically mentioned regarding the adjustment of multistage lenses. The method of mechanically moving the lens in Patent Document 1 is effective because it is sufficient to adjust the lens axis once if it does not change dynamically. However, in the case of a multipole lens that superimposes a plurality of fields, it depends on the strength of the multipole. Since the shaft changes dynamically, there is a problem that if the operator mechanically adjusts the shaft each time it changes, the burden on the operator increases and adjustment time is required.

  Patent Document 2 discloses a basic axis adjustment method of a multi-stage multipole, but because adjustment is performed repeatedly, the adjustment man-hours increase in series according to the number of lens stages, and the adjustment time is greatly increased. It is feared that it will increase. In addition, if a large axis adjustment is necessary, the effect of the axis deviation on the lens below the adjustment stage becomes large, resulting in image blurring, or the charged particle beam is bent too much and hits a pole or an outer wall. There is a risk that adjustment itself cannot be performed, for example, an image of the sample cannot be obtained.

  An object of the present invention is to provide a charged particle beam apparatus and an aberration correction method for the charged particle beam apparatus that can reduce the number of adjustment steps and adjustment time even when a multistage multipole aberration corrector is provided.

As one embodiment for achieving the above object, an aberration corrector including two or more stages of multipoles for controlling the aberration of a charged particle beam,
A first deflector for deflecting the charged particle beam to adjust an incident position on the aberration corrector;
A power supply including a quadrupole wobbler circuit that performs fine movement of quadrupole intensity independently at each stage of the multipole;
A control unit for controlling the aberration corrector, the first deflector, and the power source;
An axis shift calculation unit for calculating an image shift amount due to the fine movement of the quadrupole intensity;
A deflection amount calculation unit that calculates a deflection amount fed back to the multipole element and the first deflector according to the image shift amount due to the fine movement of the quadrupole intensity at each stage;
The charged particle beam apparatus is characterized in that the deflection amount calculated according to the image shift amount by the deflection amount calculation unit is obtained by interlocking a plurality of stages of deflection in the aberration corrector. .

An aberration corrector including two or more stages of multipoles for controlling the aberration of the charged particle beam;
A deflector that deflects the charged particle beam to adjust the incident position on the aberration corrector;
A power supply including a quadrupole wobbler circuit that performs fine movement of quadrupole intensity independently at each stage of the multipole;
A controller for controlling the aberration corrector, the deflector, and the power source;
An axis shift calculation unit for calculating an image shift amount due to the fine movement of the quadrupole intensity;
A deflection amount calculation unit that calculates a deflection amount to be fed back to the multipole element and the deflector in accordance with a positional deviation amount due to fine movement of the quadrupole intensity of each stage;
The deflection amount calculation unit is positioned below the axis adjustment target stage when the deflection amount for performing the axis deviation adjustment in the axis adjustment target stage and the deflection amount is added to the stage above the axis target stage. The charged particle beam apparatus is characterized in that it calculates an image shift amount generated by a multipole element.

In the aberration correction method for a charged particle beam apparatus including a multistage multipole type aberration corrector including at least a first stage multipole and a second stage multipole,
A first step of acquiring a first image as a reference image;
A second step of exciting the first stage multipole by a fine movement of the quadrupole intensity to change the intensity of the quadrupole field;
A third step of acquiring a second image with the first stage multipole excited;
A fourth step for returning the excitation of the first stage multipole;
A fifth step of performing the steps from the second step to the fourth step on the second stage multipole;
A sixth step of obtaining an image shift amount of each stage using the first image and at least the second image obtained for the first stage multipole and the second stage multipole;
A seventh step of obtaining a deflection amount of each stage to be applied in order to perform axis adjustment from the image shift amount of each stage when the image shift amount exceeds a threshold;
An aberration correction method characterized by comprising:

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where a multistage multipole type | mold aberration corrector is provided, the charged particle beam apparatus which can reduce an axis adjustment man-hour and adjustment time, and its aberration correction method can be provided.

It is a schematic block diagram which shows an example of the electron beam apparatus (charged particle beam apparatus) which concerns on 1st Example of this invention. FIG. 2 is an electron optical schematic diagram of the electron beam apparatus shown in FIG. 1, where (a) is a trajectory (x trajectory) viewed from the y direction (direction orthogonal to the paper surface in FIG. 1), and (b) is an x direction (in FIG. 1). A trajectory (y trajectory) viewed from the left and right direction of the drawing is shown. FIG. 2 is an electron optical schematic diagram of an x-orbit in the electron beam apparatus shown in FIG. 1, where (a) shows an axial misalignment in the multipole 113, and (b) shows the strength of the multipole 113 with respect to (a). When weakened, (c) shows the case where the strength of the multipole element 113 is strengthened with respect to (a). It is an axis | shaft adjustment flowchart of the multistage multipole field in the aberration correction method which concerns on 1st Example of this invention. It is a schematic block diagram of the computer in the electron beam apparatus shown in FIG. It is a display example of the display part (GUI) in the electron beam apparatus shown in FIG. It is an electro-optic schematic diagram for demonstrating the axis adjustment in the aberration correction method which concerns on 1st Example of this invention, (a) is a state which has an axial shift | offset | difference in the multipole of each stage, (b) is each stage. (C) A state in which the shaft misalignment of each stage is separated into one in which the multi-pole element 112 has an axial misalignment, d) A state in which the shaft misalignment of each stage is separated into one in which the multi-pole element 113 has a shaft misalignment, and (e) a shaft misalignment in each stage is separated into one in which the multi-pole element 114 has a shaft misalignment. Shows the state. FIG. 6 is an electron optical schematic diagram when the axis of the multipole element 112 is adjusted from the state of FIG. It is an electro-optic schematic diagram for demonstrating the axis adjustment in the aberration correction method which concerns on 2nd Example of this invention, (a) is the state which has an axial shift | offset | difference in the multipole of each stage, (b) is a multipole. (C) is a state where there is an axis shift in the multipole elements after the multipole element 112, (d) is a state where there is an axis shift in the multipole elements after the multipole 113, (e) ) Indicates a state in which there is an axial deviation in the multipole elements after the multipole element 114.

  The outline of the present invention is as follows. That is, in the axis adjustment of each stage of a multipole aberration corrector composed of a plurality of stages of multipoles, a single wobbler is performed at each stage, and each stage axis shift is determined from each image shift obtained by a series of wobblers. The adjustment amount is obtained, and the axis adjustment dipole field and the accompanying dipole field are excited at the stage where the axis adjustment is performed and the upper and lower stages thereof. At this time, each axis deviation is treated as an independent axis deviation, and for each axis deviation adjustment, a value that does not change the incident axis below the axis adjustment stage is calculated, and the final output is the sum of the results. Exciting the dipole field (deflection field) of the axis adjustment, and adjust the multi-stage axis deviation at once. Further, when calculating the axis deviation, the influence of the upper stage deviation due to the lower stage deviation is calculated, and the apparent axis deviation due to the lower stage is eliminated from the upper stage deviation to calculate the axis adjustment amount. Thereby, in the axis adjustment of the multistage multipole lens, the adjustment can be performed in a short time because the adjustment can be performed at a plurality of stages all at once and with less man-hours.

  Examples will be described in detail below. In the embodiment, an example using an SEM equipped with an aberration corrector using a multistage multipole will be described. However, the present invention is not limited thereto, and an SEM provided with a multistage multipole aberration corrector, The present invention can be applied to all charged particle beam apparatuses including electron beam apparatuses such as STEM and TEM and ion beam apparatuses using ion beams. For simplification, only the parts necessary for the description are shown, and detailed configurations such as a detector and a lens power supply are omitted. Further, the x direction and the y direction in this embodiment are referred to for convenience in order to indicate specific directions. Moreover, the same code | symbol has shown the same component and may abbreviate | omit description.

  An electron beam apparatus and an aberration correction method according to a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic configuration diagram of an electron beam apparatus according to the present embodiment. A primary electron beam (not shown) emitted from the electron gun 101 is shaped into a parallel beam by the condenser lens 102, passes through the aberration corrector 103, is converged by the condenser lens 104, and is then collected by the objective lens 106. Focused on the sample 107. The spot converged at this time is scanned on the sample 107 by being deflected by the scanning coil 105 in the middle. In addition, the inside of the vacuum container 140 is evacuated, and the electron beam travels while the vacuum state is maintained from the electron gun 101 to the sample 107. The aberration corrector 103 corrects axial chromatic aberration and spherical aberration. The aberration corrector 103 is connected to a power source 131, and an electric field or a magnetic multipole field is excited in the aberration corrector 103 by the voltage and current output from the power source 131. The power supply 131 is further connected to a computer 300 that controls the entire system, and an output value to the aberration corrector 103 is changed in response to a command from the computer 300. Reference numerals 108 and 109 denote deflectors.

  FIG. 4B shows a schematic configuration diagram of the computer 300. The computer 300 includes a power supply control unit 310 that controls the power supply of an electron gun, a condenser lens, an objective lens, and the like, an axis shift calculation unit 320 that calculates an image shift amount by a wobbler to each stage in a multistage multipole aberration corrector, The deflection amount calculation unit 330 that calculates the deflection amount according to the image shift amount by the wobbler, calculates the influence on the upper wobbler image shift amount by the lower axis deviation from each image shift obtained by the series of wobblers. A correction value calculation unit 340 that calculates a correction amount to be added to or subtracted from the upper shift amount, a control unit 350 that controls the whole, a display unit (GUI), and a storage unit 500 are provided. Reference numeral 510 indicates a memory, reference numeral 520 indicates storage, reference numeral 530 indicates table data, and reference numerals 531 and 532 indicate individual table data.

  FIG. 2 is an electron optical schematic diagram showing the trajectory of the electron beam 151 passing through the aberration corrector. Since the trajectory of the electron beam 151 passing through the aberration corrector 103 changes depending on the direction, the trajectory (x trajectory) seen from the y direction (the direction orthogonal to the paper surface in FIG. 1) is shown in FIG. ) Shows a trajectory (y trajectory) viewed from the x direction (left and right direction in FIG. 1). The aberration corrector 103 includes four stages of multipoles 111 to 114, and the orbit of the electron beam 151 is separated into an x orbit and a y orbit by a quadrupole field excited by the multipole 111, and then the multipole. The x-direction at the position 112 and the y-direction at the position of the multipole 113 are converged, and after passing through the multipole 114, the multipole element 111 is such that the x-orbit and y-orbit become symmetrical again (parallel orbit). A quadrupole field is excited in each of the multipole elements 114. The axis adjustment in the aberration corrector 103 is to make the optical axis 150 of the electron beam 151 coincide with the central axis of each of the four-stage quadrupole fields used for forming these trajectories. The multipole elements 111 to 114 are excited in such a manner that a dipole field, a hexapole field, an octupole field, etc. are superimposed on the quadrupole field, but the axis adjustment is performed only on the axis of the quadrupole field. This is because the central axis of the lens exists only in a two-fold symmetric field (4n pole as a multipole, n is a natural number), and the lower the order, the greater the effect of deviation near the axis. is there. For example, a quadrupole field is about 10 to the third power greater than an octupole field, and the influence of deviation is larger. Therefore, the effect of applying the present invention to a quadrupole field is high. Hereinafter, for the sake of simplicity in the present embodiment, it is assumed that the multipole element 111 to the multipole element 114 have a quadrupole field axis at the center of each figure.

  As an example of the occurrence of the axial misalignment, FIG. 3 shows an electron optical schematic diagram. Here, an axis deviation occurs in the x-orbit of the multipole element 113, and the axes of the other stages coincide with the optical axis 150. When the strength of the quadrupole field of the multipole element 113 is reduced from the state of FIG. 3A, the state of FIG. 3B is obtained, and when it is increased, the state of FIG. 3C is obtained. At this time, the optical axis 150 moves in accordance with the amount of excitation of the multipole element 113, and the observed SEM image is formed with an image centered on the position where the optical axis 150 intersects the sample 107. The quadrupole wobbler shifts the SEM image. In the state shown in FIG. 3A, in the stage other than the multipole 113, even when the quadrupole wobbler is performed, the respective quadrupole axes and the optical axes coincide with each other, so that no image shift occurs. In this way, the axis adjustment is performed by performing a quadrupole wobbler at each stage so that the image shift caused by the wobbler is eliminated.

  The flow of the quadrupole wobbler, image shift measurement, and axis adjustment in the aberration correction method according to the present embodiment will be described with reference to the flowchart shown in FIG. 4A, and details of the individual processing will be described with reference to FIGS. In FIG. 4A, a trajectory is formed and adjusted to a state where an SEM image can be acquired. The state of aberration correction may be any state before correction, during correction, or completion. Moreover, the axis adjustment with respect to the objective lens 106 and the condenser lenses 102 and 104 is appropriately performed. Various conditions can be set or changed on the GUI of the display unit 400.

  (Step S101): Axis adjustment is started. As an initial state, the counter n = 1 of the memory 510 of the computer 300 is set. If necessary, change the shooting magnification, scan direction, etc. to the specified values.

  (Step S <b> 102): The SEM image A is acquired as a reference image before the quadrupole wobbler by the quadrupole wobbler circuit arranged inside the power supply 131 and stored in the storage 520 in the computer 300. During the execution of steps S102 to S107, setting is made so as not to change the location such as stage movement or beam shift.

  (Step S103): The output of the power supply 131 is changed as a quadrupole wobbler by the quadrupole wobbling circuit arranged in the power supply 131 according to the instruction of the control unit 350 of the computer 300, and the strength of the n-th quadrupole field is changed. To do. Here, ΔQn is added as a predetermined amount of excitation of a quadrupole field. Note that the value of ΔQn may be set differently for each stage, and may be changed according to the optical reduction ratio, acceleration voltage, and opening angle. Further, when it is predicted that the image shift amount will not overlap as compared with the SEM image A acquired in step S102 due to the large axis deviation amount, ΔQn is decreased, and the proper use is performed according to the situation even under the same conditions.

  (Step S <b> 104): The SEM image B (n) after adding ΔQn is acquired and stored in the storage 520 in the computer 300.

  (Step S105): ΔQn added in Step S103 is subtracted by an instruction of the control unit 350 of the computer 300, and the excitation amount of the n-stage quadrupole field is returned to the state of Step S102.

  (Step S106): The computer 300 determines whether the counter n = 4. If n = 4, the quadrupole wobbler has been executed for all stages, and the process proceeds to step S108. If n ≠ 4, the process proceeds to step S107.

  (Step S107): 1 is added to the counter n, the process returns to Step S103 again, and the quadrupole wobbler and SEM images of Steps S103 to S105 are taken at a stage different from that before the loop.

(Step S108): The SEM image B (i) (i = 1 to 4) of 1-4 stages obtained in Step S104 is compared with the SEM image A, and the i-th stage image shift amount by the quadrupole wobbler (W _ix , W _iy ) is calculated. The image shift amount can be calculated from the pattern matching of two images by image processing such as two-dimensional normalized cross-correlation by the axis shift calculation unit 320 of the computer 300. The obtained image shift amount (W _ix , W _iy ) and ΔQi set as the wobbler are stored in the storage 520 of the computer 300.

(Step S109): With respect to the image shift amount (W _ix , W _iy ) of the i (= 1 to 4) stage obtained in Step S107, the computer 300 determines whether each shift amount is equal to or less than a predetermined threshold value. To do. If the image shift amounts of all four stages are less than or equal to the threshold value, it is determined that the axis deviation is small, and the process proceeds to step S112. If the image shift amount exceeds the threshold value, the process proceeds to step S110. The threshold value is determined independently for each stage based on a value necessary for satisfying the required resolution or a value that does not hinder adjustment as an image shift amount with respect to the excitation amount applied by the quadrupole wobbler. The threshold value determined here can be visualized by the display unit (GUI) 400 of the computer 300, and can be changed in consideration of the trade-off relationship between required accuracy and adjustment speed. An example of the GUI screen when setting or changing the threshold is shown in FIG. 4C.

(Step S110): Excitation of a dipole field (deflection field) to be applied to perform axis adjustment from the image shift amount (W _ix , W _iy ) at the i (= 1 to 4) stage obtained in Step S109. The amount (ΔI _ix , ΔI _iy ) is calculated by the deflection amount calculation unit 330 of the computer 300. Details of the excitation amount (ΔI _ix , ΔI _iy ) of the dipole field will be described later. The dipole field may be an electric field or a magnetic field. In this embodiment, the dipole field is unified by the magnetic field, and the excitation amount of the dipole field (ΔI _ix , ΔI _iy ) = dipole current amount. In the case of using an electric field, it is read as a voltage, and a unit of a coefficient described later may be read as a voltage instead of a current.

(Step S111): The output of the power supply 131 is changed by an instruction from the control unit 350 of the computer 300, and the dipole current amounts (ΔI _ix , ΔI _iy ) are added to the multipole elements 111 to 114 and the deflector 108. In addition, the counter n is initialized to 1. In this step, it is possible to change the observation location, such as moving the stage to prevent image contamination. Further, when an SEM image focus shift occurs due to the addition of (ΔI _ix , ΔI _iy ), focus adjustment may be performed.

  (Step S112): The axis adjustment is finished. The image shift amount and the adjustment amount measured by this axis adjustment may be stored in the storage 520 of the computer 300, and a dipole current amount appropriate for the adjustment in step S110 may be recalculated and used for the next axis adjustment.

  In this measurement example, n = 1 is incremented by 1 and all stages are measured in order. However, any order may be used, and it is not always necessary to measure at all stages. For example, when the axis adjustment is repeated, if the axis deviation of the 1st and 2nd stage is sufficiently smaller than the threshold value and only the 4th stage of the axis adjustment is required in a certain measurement, the next time, only the 3rd and 4th stage are measured. However, there is no problem in practical use. Further, although the image shift amount from the reference image is calculated by setting the excitation amount applied to the quadrupole wobbler as ΔQn, it is also possible to calculate the image shift from each image added with ± ΔQn wobbler. The flow of image shift measurement and axis adjustment by the quadrupole wobbler has been described above.

  Details of step S110, which is an individual process, will be described from the flow shown in FIG. 4A. First, the basic concept of axis adjustment of a multistage multipole will be described with reference to FIGS. 5 and 6. The central axis 152 in FIG. 5A passes through the central axes of the multipole element 111 to the multipole element 114, the condenser lens 104, and the objective lens 106, and coincides with the axis of the quadrupole lens. The optical axis 150 of the electron beam in FIG. 5 (a) does not coincide with the central axis 152 in the multipole elements 111 to 114, and there is an axial misalignment in each stage of the multipole element. Except for special cases, the shaft misalignment in a multi-stage lens causes a shaft misalignment in the lower stage along with the axis misalignment in the upper stage when it occurs in the upper stage. However, the multi-stage shaft misalignment as shown in FIG. 5 (a) is also considered once separated into those in which one stage of shaft misalignment occurs as shown in FIGS. 5 (b) to 5 (e). In addition, it is possible to perform multi-stage axis adjustment. This multi-stage axis adjustment can be realized by performing the following control by the control unit 350 of the computer 300, for example.

  That is, in this control, when a dipole field is applied to adjust the axis of a specific stage, an incidental dipole is installed so as not to change the incident position of the optical axis 150 of the stage arranged below the specific stage. Apply the field. As a specific example, FIG. 6 shows an example in which the axis of the multipole element 112 is adjusted from the state of FIG. Here, a dipole field is applied to the multipole element 111 from the state of FIG. 5A to change the orbit on the multipole element 112 of the optical axis 150 from the orbit 153 to the orbit 154, and the optical axis 150 is the center of the multipole element 112. It is adjusted to pass through the shaft. At the same time, an additional dipole field is applied to the multipole 112 so that the trajectory 154 passes the coordinates 155 on the same multipole 113 as the orbit 153, and an additional dipole field is applied to the multipole 113. Control is performed so that the trajectory after the multipole element 113 does not change. For the accompanying dipole field, a value proportional to the intensity of the dipole field used for axis adjustment is used. By this control, it is possible to influence the lower stage by the axis adjustment for one stage, and the axis adjustment of the multistage multipole can be processed as the sum of the axis adjustment of the single stage multipole. Note that a second deflector (not shown) for deflecting the charged particle beam and adjusting the incident position on the multipole more accurately can be arranged between each stage of the multipole.

The specific processing content in step S110 for the above control will be described. For simplicity, it is assumed that the x-direction and y-direction of the dipole field and the x-direction and y-direction of the image shift amount coincide. Even if the directions do not match, if the transformation is performed using the rotation matrix, the calculation result when the directions match can be used. The relationship between the image shift amount (W _ix , W _iy ) at the i-th stage and the axis adjustment dipole current (ΔI _ix , ΔI _iy ) in step S110 can be expressed as in equations (1) and (2). .

(W _i : i-stage single-stage quadrupole wobbler image shift amount [m], δI _ix : i-stage single-stage axis adjustment dipole current [A], k _ix : i-stage adjustment coefficient [m / A], where i = 0 is the coefficient of the deflector 108)

(ΔIi: final applied dipole current [A], aix to dix: i-stage dependent (reverse) coefficient to device coefficient determined by orbit)
Equation (1) corresponds to the independent control of FIG. 5, and Equation (2) corresponds to the accompanying dipole field of FIG. 6 and their addition. The left side of equation (1) is a matrix representation of the image shift amounts (Wix, Wiy) by the i-th quadrupole wobbler for four stages (the first column is the x direction, the second column is the y direction, the row Is multipole 11 to 14 stages). On the other hand, the right side of the equation (1) represents the amount of dipole current necessary to cancel each image shift and its coefficient. Specifically, (δIix, δIiy) means the x direction and y direction of the i-th dipole current. Note that i = 0 is a dipole current of the deflector 108.
kix is a coefficient related to the current of the i-th stage, and is determined as table data in advance and stored in the table data 530. The relationship between the image shift Wi and δIi is adjusted by changing the intensity of the i−1 stage (upper) dipole field with respect to the image shift by the i stage quadrupole wobbler. However, the zero portion on the right side corresponds to the portions of the multipole 112 in FIG. 2A and the multipole 113 in FIG. 2B that converge in the x and y directions, respectively. This is because the image shift due to the pole wobble does not occur. Because there is no image shift,
Adjustment is also unnecessary. In addition, the second and second variables are included in the third stage x and fourth stage y direction of the matrix. This is because the image shift in the convergent direction does not occur for the same reason as the zero term on the right side. ,
It means that the axial deviation can be adjusted in the same manner in both the dipole of the converged stage and the dipole field of the upper stage (even if mixed). However, since there are practically no solutions when there are two variables, a constraint condition is imposed such that only one of them is used. Alternatively, when a multipole field used for correction is applied, the applied dipole field may be selected. This is because when an unintended dipole field is generated by excitation of a multipole field, it is desirable to correct at that stage.
The left side of Equation (2) represents the dipole current (ΔIix, ΔIiiy) to be finally applied,
A value obtained by adding the dipole currents necessary for individual axis adjustment on the right side is calculated. Further, the coefficient on the right side of Expression (2) represents, for example, a coefficient applied incidentally to the dipole current δI0 applied to the deflector 108 for the first stage axis adjustment. Specifically, a0x is applied as the coefficient of the dipole field applied in the x direction of the first stage, and b0x is applied as the coefficient of the dipole field applied in the x direction of the second stage in the x direction of the third stage. C0x is represented as a coefficient of a dipole field, and d0x is represented as a coefficient of a dipole field applied in the x direction of the fourth stage. These coefficients are also determined as table data in advance and are stored in the table data 530. Since the coefficients are generalized here, they are described in all stages. However, in actuality, since only the lower two stages of the axis adjustment target stage need be attached to the applied current, c0x and d0x are zero. Good. Also, the multipole 112 in FIG.
In the case where a portion that converges in the x-direction and y-direction of the multipole element 113 in FIG. 2B is sandwiched, a plurality of combinations can be made for the dependent coefficients, but the solution can be obtained by setting b1x and c2y to zero. Set the constraint condition so that it is determined as one.

In step S110 , a correction term expressed by the following equation (3) is further added.

(W _i : i-stage single-stage quadrupole wobbler image shift amount [m], w _i : i-stage quadrupole wobbler image shift amount measured value [m], p _{iy to} r _ix : i-stage influence coefficient to orbit determined apparatus coefficient)
In FIG. 5 or the quadrupole wobbler of Equation (1), the image shift at each stage is treated as independent. However, in reality, it is not completely independent, and when there is an axis shift at the lower stage, the upper stage is larger than the axis shift amount. Since the image shift is measured, a process for canceling this amount is performed here. In Equation (3), W _i is the true image shift by the quadrupole wobbler, the image shift measured at the i-th stage is w _i , and the upper image shift is multiplied by the coefficients p _{iy to} r _ix to the lower-stage image shift amount. A correction term for the quantity. The coefficients p _{iy to} r _ix are determined as table data in advance and are stored in the table data 530. The image shift of the correction term has a unidirectional relationship that has an influence from the lower stage to the upper stage but does not have an influence from the upper stage to the lower stage, and the matrix on the right side of the equation (3) is the multipole 111 to the multipole in order. It affects the image shift of 114 quadrupole wobbler. Since the difference between W _i and w _i is not so large, this processing is not necessarily required for the axis adjustment, but the number of repetitions of the axis adjustment can be reduced by adding the difference. This completes the detailed description of step S110. Various coefficients such as p _{iy to} r _ix used in this embodiment can be changed on the GUI of the computer 300. In this embodiment, the multi-stage axis adjustment is performed once, but it can be performed one by one in order.

  As a result of performing aberration correction using the electron beam apparatus shown in FIG. 1 and the flow shown in FIG. 4A, the man-hour for adjusting the axis can be reduced, and the adjustment time can be reduced to tens of the conventional one.

In some cases, an axial shift is intentionally generated for the purpose of suppressing chromatic dispersion and improving the resolution of beam tilt. In this case, it is possible to generate any axial deviation amount at any stage of W _i by setting a specific value of the formula (1). Further, the dipole field applied by the deflector 108 assumes the parallel movement (shift) of a two-stage deflection electron beam. In addition to this, when the beam tilt (tilt) is used as a degree of freedom, it is compatible with the dipole field applied to the multipole 111, so that the beam tilt by the deflector 108 is used instead of the dipole field of the multipole 111. You may adjust.

  The contents controlled by the control unit 350 are summarized as follows. That is, the control unit 350 refers to the table data 530 and based on a plurality of deflection amounts calculated by the deflection amount calculation unit 330 for correcting the axis deviation, the upper multipole element of the multipole that is the target of the axis deviation correction. Alternatively, deflection is performed by the deflector (first deflector) 108 to correct the axis misalignment of the target multipole element, and at the same time, according to the deflection amount for correcting the axis misalignment, the axis misalignment is deflected to correct the axis misalignment. Control is performed so as not to change the incident position on the multipole or lens located in the lower stage of the modified multipole. Further, in accordance with the deflection amount for correcting the shaft misalignment calculated by the deflection amount calculating unit 330 with reference to the table data 530, the deflection is applied at the lower multipole of the misalignment correcting multipole, and the lower position. To control the incident position on the multipole or lens. In addition, using all the deflection amounts calculated by the deflection amount calculation unit 330, a deflection signal is input simultaneously in a plurality of stages, and control is performed so as to simultaneously adjust the axial deviation of the multi-poles in the plurality of stages. When the second deflector (not shown) that deflects the charged particle beam between the stages of the multipole element and adjusts the incident position on the multipole element is provided, the control unit uses the deflection amount calculation unit 330 to shift the axis. Based on a plurality of deflection amounts calculated for correction, the first deflector 108 at the upper stage of the multipole that is the target of correction of the axial deviation is deflected to correct the axial deviation of the target multipole and simultaneously correct the axial deviation. The second deflector disposed between the corrected multi-pole of the axial deviation and the lower multi-pole according to the deflection amount for the incident position on the multi-pole or lens positioned at the lower stage of the corrected multi-pole of the axial deviation And control so as not to change the angle.

  The correction value calculation unit calculates the effect of the lower axis shift on the upper wobbler image shift amount from each image shift obtained by a series of wobblers in the axis shift measurement of each stage of the aberration corrector. The amount of addition or subtraction is calculated for the shift amount. The table data 530 includes a coefficient for calculating a correction value. The display unit (GUI) displays and sets a coefficient for calculating a correction value included in the table data 530, or displays and sets a threshold parameter indicating a threshold of an image shift amount allowed in each stage of the multipole. It can be performed.

  As described above, according to the present embodiment, it is possible to provide a charged particle beam apparatus and an aberration correction method thereof that can reduce the man-hours and the adjustment time even when the multistage multipole aberration corrector is provided.

  A second embodiment of the present invention will be described. Note that the matters described in the first embodiment but not described in the present embodiment can be applied to the present embodiment as long as there is no particular circumstance.

  The present embodiment shows an example in which different processing is performed for the calculation of the intensity of the axis adjustment dipole field in step S110 of the first embodiment. Adjustments other than this processing are the same as those in the first embodiment. In the first embodiment, the image shifts obtained at each stage are separated into those in which only one stage has an axial shift. However, in this embodiment, as shown in FIG. And process.

FIG. 7A shows the same axial misalignment as that in FIG. 5A, but is separated from this into the optical systems in FIGS. 7B, 7C, 7D, and 7E. In FIG. 7B, the dipole field is excited in the deflector 108 from the state where there is no axis deviation, causing the axis deviation in the multipole element 111, and the axis deviation is also generated in the lower multipole elements 112 to 114. It is a thing. Similarly, in FIGS. 7C, 7D, and 7E, the multipole element 112, the multipole element 113, and the multipole element 114 are shifted from each other in a state where there is no axis shift, and the respective axis shift stages are moved. Axis misalignment occurred in subsequent stages. When the axis adjustment is performed on the condenser lens 104, FIG. 7 (e) and FIG. 5 (e) are at the lowest stage, and the same processing is performed as a single axis adjustment. However, in FIG. 7 (e), the misalignment adjustment of the multipole element 114 according to FIGS. 7 (b) to 7 (c) is performed, and FIG. 5 (e) is a dipole field generated accompanying the upper stage adjustment. The idea and calculation method are different in that the amount of excitation is added. The relationship between (W _ix , W _iy ) in the formula (1) of the first embodiment and the axis adjustment dipole current (ΔI _ix , ΔI _iy ) can be expressed as in the formula (4) in this embodiment.

(W _i : i-stage single-stage quadrupole wobbler image shift amount [m], ΔI _ix : i-stage axis adjustment dipole current [A], s _{ix to} v _iy : i-stage influence coefficient [m / A], i = 0 is a coefficient of the deflector 108)
When this equation is solved as a simultaneous equation, a dipole current at each stage necessary for adjusting the axis of the multipole can be obtained. However, in equation (4), the number of equations is three for the number of variables ΔI _i , and therefore the only solution cannot be obtained as it is. This is because the multipole elements 112 in FIG. 2A and the multipole elements 113 in FIG. 2B converge in the x and y directions as in the first embodiment. Therefore, in order to obtain a unique solution, it is necessary to set in advance constraints such as ΔI _2x = 0 and ΔI _3y = 0. Note that ΔI ₄ cannot be obtained in Equation (4), but a value can be calculated by expanding the matrix and including the axis of the condenser lens 104.

  The example of the processing different from that of the first embodiment has been described for the calculation of the intensity of the dipole field for the axis adjustment in step S110. Note that the difference from the effect of the first embodiment is that, in the lower stage, the image shift measurement error due to the upper quadrupole wobbler is accumulated on the adjustment amount, so even if the lower axis is aligned, the lower stage is pulled. As a result, the accuracy of the lower axis adjustment amount may deteriorate, the convergence of the axis adjustment may decrease, and the adjustment time may become longer. However, even in that case, since adjustment can be performed collectively, adjustment can be performed in a shorter time than adjustment by itself.

  The deflection amount calculation unit in the present embodiment includes a dependent deflection amount calculation unit that calculates a deflection amount to be applied to the axis adjustment target stage in order to cancel the image shift amount generated by the multipole element positioned below the axis adjustment target stage. The deflection amount calculated by the deflection amount calculation unit and the deflection amount for adjusting the misalignment of all axes can be output simultaneously.

  As a result of performing aberration correction using the electron beam apparatus shown in FIG. 1 and the flow shown in FIG. 4A, man-hours for adjusting the axis can be reduced, and adjustment time can be reduced.

  As described above, according to the present embodiment, it is possible to provide a charged particle beam apparatus and an aberration correction method thereof that can reduce the man-hours and the adjustment time even when the multistage multipole aberration corrector is provided.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 101 ... Electron gun, 102 ... Condenser lens, 103 ... Aberration corrector, 104 ... Condenser lens, 105 ... Scanning coil, 106 ... Objective lens, 107 ... Sample, 108 ... Deflector, 109 ... Deflector, 111 ... First stage Multipole, 112 ... 2nd stage multipole, 113 ... 3rd stage multipole, 114 ... 4th stage multipole, 131 ... Power supply, 140 ... Vacuum vessel, 150 ... Optical axis, 151 ... Electron beam, 152 ... Center axis 153 ... Optical axis trajectory, 154 ... Optical axis trajectory, 155 ... Coordinate, 300 ... Computer, 310 ... Power supply control unit, 320 ... Axis deviation calculation unit, 330 ... Deflection amount calculation unit, 340 ... Correction value calculation unit, 350 ... Control unit, 400 ... Display unit (GUI), 500 ... Storage unit, 510 ... Memory, 520 ... Storage, 530 ... Table data, 531 ... Individual table data, 532 ... Individual table Data.

Claims (13)

An aberration corrector including two or more multipole elements for controlling the aberration of the charged particle beam;
A first deflector for deflecting the charged particle beam to adjust an incident position on the aberration corrector;
A power supply including a quadrupole wobbler circuit that performs fine movement of quadrupole intensity independently at each stage of the multipole;
A control unit for controlling the aberration corrector, the first deflector, and the power source;
An axis shift calculation unit for calculating an image shift amount due to the fine movement of the quadrupole intensity;
A deflection amount calculation unit that calculates a deflection amount fed back to the multipole element and the first deflector according to the image shift amount due to the fine movement of the quadrupole intensity at each stage;
The control unit refers to the table data, and based on the plurality of deflection amounts calculated by the deflection amount calculation unit for correcting the axis deviation, the upper multipole element of the multipole that is the target of the axis deviation correction or the A deflection is performed by the first deflector to correct the axial shift of the multipole that is the correction target of the axial shift,
At the same time, in accordance with the deflection amount for correcting the axial misalignment, the multipole element that is the correction target of the axial misalignment performs deflection, and the multipole element or the lens that is positioned in the lower stage of the multipolar element that is the correction target of the axial misalignment A charged particle beam apparatus that is controlled so as not to change an incident position. The charged particle beam apparatus according to claim 1,
The control unit refers to the table data, and in accordance with the deflection amount for correcting the axial deviation calculated by the deflection amount calculating unit, the multipole element in the lower stage of the multipole that is the target of the axial deviation correction The charged particle beam apparatus is characterized in that the control is performed so as not to change the incident position on the multipole element or the lens positioned further below. The charged particle beam apparatus according to claim 1,
In the measurement of the axial shift at each stage of the aberration corrector, the effect of the lower axis shift on the upper wobbler image shift amount is calculated from each image shift obtained by a series of wobblers and added to the upper shift amount. Alternatively, the charged particle beam apparatus includes a correction value calculation unit that calculates a subtraction amount, and the table data includes a coefficient for calculating a correction value. The charged particle beam device according to claim 3.
The charged particle beam apparatus further comprising a display unit for displaying and setting a coefficient for calculating the correction value included in the table data. The charged particle beam apparatus according to claim 1,
Table data for calculating a second deflection amount to be fed back to the plurality of multipoles based on the deflection amount;
The charged particle beam apparatus, wherein the control unit is configured to simultaneously input deflection signals in a plurality of stages using the second deflection amount and simultaneously adjust the axial deviation of the multipoles in a plurality of stages. . The charged particle beam device according to claim 1,
And a second deflector for deflecting the charged particle beam between each stage of the multipole and adjusting an incident position on the multipole,
The control unit deflects with the first deflector in the upper stage of the multipole that is the correction target of the axial deviation based on the plurality of deflection amounts calculated for correcting the axial deviation by the deflection amount calculating unit. To correct the axial deviation of the multipole that is the correction target of the axial deviation, and at the same time, according to the deflection amount for correcting the axial deviation, between the multipole that is the correction target of the axial deviation and the lower multipole. The second deflector arranged at the position is controlled so as not to change the angle and the incident position on the multipole element or the lens located in the lower stage of the multipole element whose axis deviation is to be corrected. A charged particle beam device. The charged particle beam device according to claim 1,
A charged particle beam apparatus, further comprising a display unit for displaying and setting a threshold parameter indicating a threshold value of the image shift amount allowed in each stage of the multipole element. An aberration corrector including two or more multipole elements for controlling the aberration of the charged particle beam;
A deflector that deflects the charged particle beam to adjust the incident position on the aberration corrector;
A power supply including a quadrupole wobbler circuit that performs fine movement of quadrupole intensity independently at each stage of the multipole;
A controller for controlling the aberration corrector, the deflector, and the power source;
An axis shift calculation unit for calculating an image shift amount due to the fine movement of the quadrupole intensity;
A deflection amount calculation unit that calculates a deflection amount to be fed back to the multipole element and the deflector according to a positional deviation amount due to the fine movement of the quadrupole intensity at each stage;
The deflection amount calculation unit is positioned below the axis adjustment target stage when the deflection amount for performing an axis deviation adjustment in the axis adjustment target stage and the deflection amount is added to the stage above the axis adjustment target stage. A charged particle beam apparatus that calculates an image shift amount generated by a multipole element. The charged particle beam device according to claim 8.
The deflection amount calculation unit includes a dependent deflection amount calculation unit that calculates a deflection amount to be applied to the axis adjustment target stage in order to cancel an image shift amount generated by a multipole element positioned below the axis adjustment target stage. A charged particle beam apparatus characterized by simultaneously outputting a deflection amount calculated by a quantity calculation unit and a deflection amount for adjusting the deviation of all axes. In an aberration correction method for a charged particle beam apparatus including a multistage multipole type aberration corrector including at least a first stage multipole and a second stage multipole,
A first step of acquiring a first image as a reference image;
A second step of exciting the first stage multipole by a fine movement of the quadrupole intensity to change the intensity of the quadrupole field;
A third step of acquiring a second image with the first stage multipole excited;
A fourth step of returning the excitation of the first stage multipole to the state of the first step ;
A fifth step of performing the steps from the second step to the fourth step on the second stage multipole;
A sixth step of obtaining an image shift amount of each stage using the first image and at least the second image obtained for the first stage multipole and the second stage multipole;
A seventh step of obtaining a deflection amount of each stage to be applied in order to perform axis adjustment from the image shift amount of each stage when the image shift amount exceeds a threshold;
An aberration correction method comprising: The aberration correction method according to claim 10.
An aberration correction method characterized by using, as a standard image, an image acquired by a quadrupole wobbler under a condition different from that of the second step, instead of the first image. The aberration correction method according to claim 10.
The seventh step includes an excitation amount such that a central axis of a specific stage multipole coincides with an optical axis, and a charged particle beam orbit after the lower stage of the specific stage does not change, and the image An aberration correction method comprising: obtaining a relationship with a shift amount, and obtaining the deflection amount using the excitation amount. The aberration correction method according to claim 12, wherein
3. The aberration correction method according to claim 1, wherein the excitation amount is an excitation amount for an axis-adjusted dipole field and an accompanying dipole field.

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