WO2011052333A1 - 走査荷電粒子線装置、及び色球面収差補正方法 - Google Patents
走査荷電粒子線装置、及び色球面収差補正方法 Download PDFInfo
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- WO2011052333A1 WO2011052333A1 PCT/JP2010/066979 JP2010066979W WO2011052333A1 WO 2011052333 A1 WO2011052333 A1 WO 2011052333A1 JP 2010066979 W JP2010066979 W JP 2010066979W WO 2011052333 A1 WO2011052333 A1 WO 2011052333A1
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- chromatic
- aberration
- particle beam
- charged particle
- spherical aberration
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
- H01J37/153—Electron-optical or ion-optical arrangements for the correction of image defects, e.g. stigmators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
- H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
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- the present invention relates to a scanning charged particle beam apparatus that scans and irradiates a sample with a charged particle beam to acquire secondary electrons, reflected electrons, or transmitted electrons from the sample, and in particular, correction technology for chromatic spherical aberration in tilt observation thereof.
- a scanning charged particle beam apparatus that scans and irradiates a sample with a charged particle beam to acquire secondary electrons, reflected electrons, or transmitted electrons from the sample, and in particular, correction technology for chromatic spherical aberration in tilt observation thereof.
- Charged particle beam devices such as scanning electron microscopes (Scanning Electron Microscope: SEM) and transmission electron microscopes (Transmission Electron Microscope: TEM) use an electric or magnetic field to focus the charged particle beam.
- a lens is always used. In an electric or magnetic lens, various aberrations inevitably occur. Therefore, even if an attempt is made to narrow the charged particle beam by increasing the reduction ratio, if the aberration is large, the spot diameter cannot be reduced, and the fine structure cannot be observed and the dimensional measurement accuracy cannot be improved.
- This aberration corrector is usually composed of multipole lenses installed in multiple stages, and generates an electric field or magnetic field in the multipole lens, thereby removing aberrations contained in a charged particle beam passing through the interior.
- Non-Patent Document 1 a technique for correcting chromatic aberration is disclosed.
- Non-Patent Document 1 does not disclose chromatic spherical aberration (chromatic third-order aperture aberration or chromatic spherical aberration combination) measurement and chromatic spherical aberration correction technology at the time of tilt observation technology.
- Non-patent document 2 discloses chromatic spherical aberration during aberration correction.
- Non-Patent Document 2 discloses a condition in which the chromatic spherical aberration and the fifth-order spherical aberration increase due to aberration correction and the resolution is limited by using simulation, and the effective distance between the aberration corrector and the objective lens is reduced as a countermeasure. Is disclosed.
- Non-Patent Document 2 does not disclose a method for actually measuring chromatic spherical aberration, and does not disclose a method for canceling chromatic spherical aberration and other aberrations during tilt observation.
- Patent Document 1 discloses a technique in which the resolution is improved by performing aberration correction in tilt observation.
- a chromatic spherical aberration correction technique at the time of chromatic spherical aberration measurement and tilt observation is not disclosed.
- Patent Document 2 As a technique for detecting chromatic dispersion aberration of a charged particle beam apparatus and correcting it, there is a technique disclosed in Patent Document 2, for example. According to this technique, the movement due to the axis deviation when the acceleration voltage is changed from the current value is corrected. However, an aberration corrector and a tilt observation technique using the same are not disclosed.
- An object of the present invention is to provide a scanning charged particle beam apparatus capable of improving resolution in tilt observation using an aberration corrector, and a chromatic spherical aberration correction method thereof, paying attention to such conventional problems. It is in.
- a scanning charged particle beam apparatus using a charged particle beam which comprises a sample stage on which a sample is placed, and an aberration for correcting the aberration of the incident primary charged particle beam
- An irradiating optical system having a corrector and a deflector for deflecting the primary charged particle beam installed on the aberration corrector, and scanning the primary charged particle beam with respect to the sample placed on the sample stage;
- a detector for detecting secondary charged particles generated by scanning of the charged particle beam, a display unit for displaying an image of an output signal of the detector, and an irradiation angle of the primary charged particle beam to the sample using the deflector
- a scanning charged particle beam apparatus and a chromatic spherical aberration correction method are provided which control to change the accelerating voltage to the primary charged particle beam and to measure the amount of chromatic spherical aberration.
- the control unit determines the image per unit voltage with respect to the changed acceleration voltage with respect to the movement of the image caused by changing the acceleration voltage in the measurement of the amount of chromatic spherical aberration.
- the movement amount and direction are calculated, and when calculating the image movement amount and direction per unit voltage, the inclination of the primary charged particle beam is measured at at least three different angles in the same direction with respect to the inclination axis to obtain the inclination angle.
- the control unit in the measurement of the amount of chromatic spherical aberration, the control unit generates a focus shift by changing the acceleration voltage, and the unit of the acceleration voltage changed with respect to the focus shift
- the focus shift amount and direction per voltage are calculated, and when calculating the focus shift amount and direction per unit voltage, the tilt of the primary charged particle beam is measured in the same direction with respect to the tilt axis at at least two different tilt angles.
- a scanning charged particle beam apparatus and a method for controlling to calculate the amount of chromatic spherical aberration from a second-order coefficient of the polynomial by approximating the amount of focus shift per unit voltage with the inclination angle as a variable as a polynomial. provide.
- control unit has a chromatic aberration control function in the tilt observation of the sample, and the direction parallel to the sample surface due to the chromatic spherical aberration and the chromatic aberration at the tilt angle to be observed and the tilt angle that is axially symmetric with the tilt angle.
- a scanning charged particle beam apparatus and method for controlling the chromatic aberration to be more positive or negative than the state where the chromatic aberration is zero by this chromatic aberration control function are provided.
- the acceleration voltage is changed stepwise at a plurality of different tilt angles, and the beam movement or focus shift generated at that time is changed. From this, the amount of chromatic spherical aberration is measured.
- the chromatic aberration correction amount, the chromatic dispersion aberration correction amount, or the spherical aberration correction amount is controlled at a specific angle (tilt angle) at which the observation is performed, thereby canceling the chromatic spherical aberration, thereby reducing the resolution.
- the present invention provides a method for measuring chromatic spherical aberration and a method for canceling out other aberrations in tilted observation, it can be adjusted with high accuracy without the need for fixing optical conditions and without any effort, and high resolution in tilted observation. Can be realized. For this reason, the aberration corrector can be adjusted in a short time according to switching between the non-tilt state and the tilt observation state, and the resolution of the three-dimensional structure side wall observation can be improved.
- chromatic spherical aberration means a combination aberration caused by chromatic aberration and spherical aberration, and is proportional to the first order of energy and the third order of the opening angle.
- the amount of chromatic spherical aberration is controlled by changing and controlling the irradiation angle and direction of the electron beam to the sample and the acceleration voltage to the electron beam source using a deflector of a scanning electron microscope (SEM). taking measurement.
- SEM scanning electron microscope
- the image movement amount per unit voltage with respect to the changed acceleration voltage with respect to the image movement caused by changing the acceleration voltage by the acceleration voltage control function of the electron beam source is controlled.
- the inclination of the electron beam is measured in at least three different angles (tilt angles) in the same direction with respect to the tilt axis.
- the amount of image movement per unit voltage with the tilt angle as a variable is approximated as a polynomial, and the amount of chromatic spherical aberration is calculated from the third-order coefficient of this polynomial.
- FIG. 1 shows a schematic configuration of a scanning electron microscope (SEM) according to the present embodiment.
- SEM scanning electron microscope
- This scanning electron microscope roughly controls the SEM column 101 that irradiates or scans a sample with an electron beam, the sample chamber 102 in which the sample stage is stored, the SEM column 101 and the control for controlling each component of the sample chamber 102.
- the control unit 103 is configured as a unit.
- the control unit 103 as a control unit includes a control computer 30 and various power sources 21, 22, 23, 24, 25, 26, 27, 28, 29, 32, 33, 74, 75, such as an electron gun power source 20.
- a sample stage control mechanism 81 is included.
- control unit 103 includes a data storage 76 for storing and storing predetermined information and a program for operating the control computer 103, a monitor 77 that is a display unit for displaying an acquired image, a device and a device user.
- the console 78 is configured by an information input unit such as a keyboard and a mouse, for example.
- the aberration calculator 79 is a calculator that calculates various aberrations described later, and the calculation result is stored in the data storage 76.
- This aberration calculation function can also be executed by a program processing of a central processing unit (CPU) which is a processing unit (not shown) in the control computer 30. In this case, the control computer calculates the calculated color sphere. It goes without saying that aberrations and the like are stored in the data storage 76. Therefore, in the present specification, the function of the aberration calculating device 79 is included in the control unit.
- CPU central processing unit
- the Schottky electron source 1 is an electron source that uses the Schottky effect by diffusing oxygen and zirconium into a single crystal of tungsten, and a suppressor electrode 2 and an extraction electrode 3 are provided in the vicinity thereof.
- the Schottky electron source 1 is heated and a voltage of about +2 kV is applied between the extraction electrode 3 and Schottky electrons are emitted.
- a negative voltage is applied to the suppressor electrode 2 to suppress emission of electrons from other than the tip of the Schottky electron source 1.
- the electrons exiting the hole of the extraction electrode 3 are accelerated and converged by the electrostatic lens formed by the first anode 4 and the second anode 5, and the converged electrons enter the subsequent component along the optical axis 60.
- the electron beam is converged by the first condenser lens 6, the beam current is limited by the movable diaphragm 9, passes through the second condenser lens 7 and the deflector 8, and enters the aberration corrector 10.
- the condenser lens 7 is adjusted so that the beam incident on the aberration corrector becomes parallel. When there is no inclination, the trajectory of the electron beam is adjusted by the deflector 8 so as to pass through the axis of the aberration corrector 10.
- a description will be given taking a quadrupole-octupole aberration corrector 10 as an example.
- a quadrupole and an octupole are formed.
- a 12-pole electrode which may also serve as a magnetic pole
- a dipole, a hexapole Twelve poles can also be formed and used to electrically correct field distortions caused by electrode, pole assembly errors, and pole material inhomogeneities.
- the electron beam given chromatic aberration and spherical aberration that cancels the objective lens 17 by the aberration corrector 10 is deflected by the objective aligner 12 so as to pass through the objective lens axis, and is converged on the sample 18 by the objective lens 17.
- the spot is scanned on the sample by the scanning deflector 15.
- a sample stage 80 having a sample placement surface on which the sample 17 is placed is stored.
- the secondary electrons generated by the electron beam irradiation pass through the objective lens 17 and hit the reflector 72 to generate electrons.
- the generated electrons are detected by the secondary electron detector 73, but the position where the secondary electrons strike the reflecting plate 72 can also be adjusted by the ExB deflector 71.
- the detected secondary electron signal is taken into the control computer 30 as a luminance signal synchronized with scanning.
- the control computer 30 performs appropriate processing on the captured luminance signal information and displays it on the monitor 77 as an SEM image.
- the reflector 72 is necessarily required. is not.
- control unit 103 which is a control unit includes the electron gun power source 20, the control voltage source 21, the acceleration voltage source 22, the first condenser lens power source 23, the second condenser lens power source 24, the deflection coil power source 25, and the aberration corrector.
- the flow of measurement is shown in the flowchart shown in FIG.
- This flowchart mainly shows an operation flow by the control unit described above. Steps after the start of measurement (S10 to S19) will be described in detail later.
- the inclination can change the inclination angle in various directions in 360 degrees, but in this embodiment, only the inclination angle is continuously changed for a specific direction, and the inclination angle is 2N + 1 times at ⁇ t intervals, Assume that the acceleration voltage is changed 2M + 1 times at ⁇ E intervals.
- N and M are natural numbers of 1 or more.
- the tilt angle t is an angle from the vertical direction where the electron beam is incident on the sample 18.
- the tilt angle t is set by deflecting an electron beam incident on the aberration corrector 10 using the deflector 8. At this time, the optical system is adjusted so as to change only the tilt angle t of the electron beam to the sample 18 without changing the object point of the objective lens. This adjustment is performed by parallel movement of the electron beam when the electron beam at the deflector 8 is parallel.
- the acquired image is stored in the data storage 76 or the like.
- FIG. 3 shows an example of a graph in which the movement amount and the variation of the acceleration voltage are plotted in one direction.
- the slope of this graph is the movement amount Iv (t) per change in acceleration voltage.
- Iv (t) is stored in the data storage 76 or the like in a state in which the obtained two directions are distinguished for each direction.
- the moving amount Iv (t) applied with the acceleration voltage E0 is proportional to the cube of the inclination angle t
- the coefficient is proportional to the deviation of CsC (chromatic spherical aberration coefficient), the inclination angle t, and the coefficient Is proportional to the deviation of Cc (chromatic aberration coefficient) and energy
- the coefficient is the sum of deviations of C0 (chromatic dispersion aberration amount), which is expressed by the following equation (1).
- the third-order coefficient CsC in Equation 1 is the chromatic spherical aberration coefficient
- the first-order coefficient Cc is the chromatic aberration coefficient
- the constant term C0 is the amount of chromatic dispersion aberration. Therefore, from the third-order coefficient of the above polynomial, Chromatic spherical aberration can be calculated.
- the calculation of the amount of chromatic spherical aberration can be executed by the CPU in the control computer 30 of the control unit or the aberration calculator 79. It goes without saying that other aberration calculations are similar. All the calculation results are stored in the data storage 76 by the control computer 30 as described above.
- the chromatic spherical aberration can be measured by performing the steps (S10) to (S19).
- the direction of inclination is performed in one specific direction (plus side, minus side), but chromatic spherical aberration measurement considering asymmetry can be performed by measuring in at least two directions such as orthogonal inclination directions. You can do it.
- the change of the tilt angle and the acceleration voltage may be other than the one shown in the present embodiment, such as the one in which the order is changed alternately between the plus side and the minus side, and the change intervals may not be equal. However, it is desirable to change the acceleration voltage within a range of several volts and the inclination angle within a range of several to 10 degrees.
- the resolution reduction suppressing method is cancellation of chromatic aberration and chromatic spherical aberration. That is, the control unit of the present embodiment has a chromatic aberration control function in the observation of the tilt of the sample. At the tilt angle to be observed and the tilt angle that is axially symmetric with respect to the tilt angle, the chromatic aberration control function controls the chromatic aberration to be more positive or negative than a state where the chromatic aberration is zero.
- chromatic spherical aberration is a main factor for a decrease in resolution in tilt observation after aberration correction.
- Equation 1 The cancellation of chromatic aberration and chromatic spherical aberration will be described using Equation 1 and FIG.
- the dispersion with respect to energy increases as the inclination is increased as shown in FIG.
- the aberration corrector 10 corrects chromatic aberration, but functions as an apparatus that increases or decreases the amount of chromatic aberration. Therefore, if the chromatic aberration coefficient Cc is controlled so as to satisfy the following expression 2 at a specific inclination angle t1, the effect of energy dispersion due to the chromatic spherical aberration CsC can be canceled at the inclination angle t1.
- the method for suppressing the reduction in resolution due to chromatic spherical aberration during tilt observation after aberration correction in the present embodiment has been described above.
- an example was given at specific angles t1 and -t1, but even different inclination angles can be offset by adjusting the amount of chromatic aberration.
- the chromatic aberration may be controlled based on a table prepared in advance only during tilting so as to be compatible with high-resolution observation on the axis. In this case, the deviation from the chromatic spherical aberration canceling condition can be adjusted relatively easily by finely adjusting the tilt angle.
- the control unit 103 which is a control unit of the scanning electron microscope (SEM), has a chromatic dispersion aberration control function, and an image generated in a direction parallel to the sample surface due to chromatic spherical aberration and chromatic aberration at an inclination angle to be observed.
- the chromatic dispersion aberration control function controls so that the chromatic dispersion aberration when not tilting is more positive or negative than the zero state.
- the method of this example is the offset between the chromatic dispersion aberration and the chromatic spherical aberration.
- the chromatic dispersion aberration is controlled by the aberration corrector so as to satisfy the following expression 4 at the specific inclination angle t1 in the expression 1, the effect of energy dispersion due to the chromatic spherical aberration can be canceled at the inclination angle t1.
- FIG. 6 shows the state.
- the difference from the first embodiment is that the condition for canceling out chromatic spherical aberration is not satisfied at the inclination angle -t1.
- the condition for canceling out chromatic spherical aberration is not satisfied at the inclination angle -t1.
- the resolution is lowered in the absence of inclination. Since CsC does not change even if the chromatic dispersion aberration is changed, the prediction of the solution becomes simple.
- the greatest advantage is that the chromatic spherical aberration can be canceled while the chromatic aberration is also corrected.
- an example at a specific angle has been described, but even at different inclination angles, it can be canceled out with chromatic spherical aberration by adjusting the amount of chromatic dispersion aberration.
- the chromatic dispersion aberration since the amount of chromatic dispersion aberration must be changed in proportion to the cube of the tilt angle, the adjustment voltage and the like need to be changed to the third power, and the adjustable range for the tilt angle is that of the first embodiment due to the limit of the power source. Is too narrow. Further, in order to be compatible with high-resolution observation on the axis, the chromatic dispersion aberration may be controlled based on a table prepared in advance only during tilting. In this case, the chromatic spherical aberration cancellation deviation can be adjusted relatively easily by finely adjusting the tilt angle.
- the method described in the present embodiment makes it possible to achieve high resolution in tilt observation during aberration correction without having to fix optical conditions.
- the control unit of the scanning electron microscope (SEM) in this example has a spherical aberration control function in tilt observation of the sample using the irradiation angle control function, and is parallel to the sample surface by chromatic spherical aberration and chromatic aberration at the tilt angle to be observed.
- the spherical aberration control function controls the spherical aberration to be more positive or negative than the zero state so as to suppress blurring of the image generated in any direction.
- this chromatic spherical aberration is a function of the spherical aberration correction amount, it can be reduced by changing the correction amount. Further, higher order chromatic spherical aberration and chromatic spherical aberration that are proportional to the first order with respect to energy and fifth order with respect to the opening angle can be canceled out.
- FIG. 7 shows the state.
- the quadrupole, four-stage aberration corrector if the direction of the octupole that performs spherical aberration correction and the tilt direction match, only the octupole in charge is changed, and only the spherical aberration in the tilt direction is controlled. To do. By doing so, it is possible to correct only the aberrations caused by the tilt while suppressing the generation of extra aberrations.
- the method of the present embodiment creates a condition such that the effect of the chromatic spherical aberration is zero at a specific tilt angle within the feasible range of the voltage or current applied to the aberration corrector. I can't. Therefore, in addition to the above spherical aberration control, the chromatic spherical surface is offset at a specific inclination angle in combination with the chromatic aberration shown in the first embodiment, the chromatic dispersion aberration shown in the second embodiment, or both methods. The effect of aberration may be zero. When this method is used, the voltage and current required for correction can be reduced as compared with other methods, but the spherical aberration increases. However, the influence of the remaining spherical aberration component and the fifth-order spherical aberration can be reduced by adding a coma aberration correction hexapole and astigmatism correction.
- Embodiment 1 an embodiment of another measurement method different from the chromatic spherical aberration measurement method of Embodiment 1 will be shown.
- the apparatus configuration of the present embodiment is the same as that of the first embodiment.
- the control unit of the scanning electron microscope (SEM) generates a focus shift by changing the acceleration voltage, and the focus shift amount and direction per unit voltage of the acceleration voltage changed with respect to the focus shift
- the inclination of the primary charged particle beam is measured at at least two different angles in the same direction with respect to the inclination axis.
- the amount of focus shift per unit voltage with ⁇ as a variable is approximated as a polynomial that is a second or higher order function, and the amount of chromatic spherical aberration is calculated from the second order coefficient of the polynomial.
- the flow of the chromatic spherical aberration measurement method in this embodiment will be described with reference to the flowchart shown in FIG. 360 degrees can be measured by changing the tilt angle in various directions, but the measurement is performed by fixing the tilt angle in one specific direction. That is, it is assumed that the measurement is performed by changing the tilt angle 2N + 1 times at ⁇ t intervals, changing the acceleration voltage 2M + 1 times at ⁇ E intervals, and changing the focus value 2L + 1 times at ⁇ f intervals.
- the focus value the current value of the objective lens 17 focused on the sample, the retarding voltage value of the retarding power source 29, and the like can be used, the convergence position of the electron beam is changed, and the difference between the focus values and the actual sample surface is changed.
- the inclination angle t is an angle from the vertical direction where the electron beam is incident on the sample 18 as in the first embodiment.
- the inclination angle is determined by deflecting the electron beam incident on the aberration corrector 10 using the deflector 8. At this time, the optical system is adjusted to change only the tilt angle of the electron beam to the sample 18 without changing the object point.
- the SEM image can be acquired. Note that aberration correction is not essential for the measurement conditions.
- the focus position at the acceleration voltage E is calculated.
- the focus position is calculated by distinguishing two directions such as a tilt direction on the sample surface and a direction orthogonal to the tilt.
- the focus position is calculated using the sharpest focus value in the direction obtained from the image acquired in step (S23).
- the sharpest calculation in a specific direction can be obtained by a conventional method used in astigmatism measurement such as, for example, differentiation of an image.
- the focus position is stored in the data storage 76 or the like in a state in which the two directions are distinguished for each direction.
- the acceleration voltage and the tilt angle at that time are also stored in a corresponding manner.
- S28 The acceleration voltage is increased by ⁇ E, and the process proceeds again to step (S22).
- the slope of this graph is the focus change amount Cv (t) per change in acceleration voltage.
- Cv (t) is stored in the data storage 76 or the like in a state in which the obtained two directions are distinguished for each direction.
- the chromatic spherical aberration in the tilt direction can be calculated from the second-order coefficient.
- Cv (t) is also calculated for the direction orthogonal to the inclination direction. However, since the inclination angle in the orthogonal direction is 0, Cc in the orthogonal direction can be calculated.
- the chromatic spherical aberration can also be measured by performing (S20) to (S33). Since the method of this embodiment is based on the focus shift, it is affected by the aperture diameter. Therefore, when the aperture diameter cannot be ignored with respect to the tilt angle, calculation is performed in consideration of the aperture diameter. For example, if the inclination angle of the electron beam passing through the inside of the diaphragm with respect to the inclination is ⁇ 1, and the inclination angle passing through the outside is ⁇ 2, it can be obtained by solving the simultaneous equations of Equation 7 below.
- chromatic spherical aberration measurement in consideration of asymmetry can be performed by measuring in at least two directions such as orthogonal inclination directions.
- Example 1 The method described above makes it possible to measure chromatic spherical aberration.
- the difference in effect between Example 1 and this example will be described.
- both chromatic spherical aberration and chromatic aberration can be measured, but chromatic dispersion aberration cannot be measured by the method of this embodiment alone.
- Example 1 since it is necessary to detect the movement of the image, there are cases where the measurement cannot be performed well when there is a movement more than expected or when the image blur is larger than the movement.
- the measurable range is relatively wide.
- Example 1 is suitable for measurement when the chromatic spherical aberration is relatively small, and this example is suitable for measurement when the chromatic spherical aberration is relatively large. Is suitable.
- the control unit includes at least any two functions of a chromatic aberration control function, a chromatic dispersion aberration control function, and a spherical aberration control function, Using at least two functions, it suppresses chromatic spherical aberration and image blur caused by chromatic aberration in a direction parallel to the sample surface at the tilt angle to be observed, and causes image blur caused by chromatic aberration and spherical aberration generated during the suppression. It is also possible to configure a charged particle beam apparatus that controls to select and observe the smallest combination.
- the present invention is useful as a scanning charged particle beam apparatus such as a scanning electron microscope, a semiconductor inspection apparatus, a scanning transmission electron microscope, and a focused ion beam apparatus.
- Aberration corrector power source 27 ... Scanning coil power source, 28 ... Objective lens power source , 29 ... retarding power supply, 30 ... control computer, 32 ... astigmatism correction coil power supply, 33 ... objective aligner power supply, 60 ... optical axis, 71 ... ExB deflector, 72 ... reflector, 73 ... secondary electron detector, 74 ... Secondary electron detector power supply, 75 ... ExB deflector power supply, 76 ... Data storage, 77 ... Nita, 78 ... console, 79 ... aberration calculating unit, 80 ... sample stage 81 ... sample stage control mechanism, 100 ... vacuum vessel, 101 ... column, 102 ... Sample chamber, 103 ... Control unit.
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Abstract
Description
コンデンサーレンズ7では収差補正器に入射するビームが平行となるよう調整される。傾斜なしのとき偏向器8によって電子ビームの軌道は収差補正器10の軸を通るように調節される。本実施例では4極-8極子系の収差補正器10を例に説明する。
(S11):加速電圧EをE0-MΔEに設定する。本実施例では簡単のため、始めにE0-MΔEを設定したが、どの電圧から開始しても良い。
(S14):加速電圧をΔE増やし、ステップ(S12)へ再度進む。このステップでは軸の再調整や、フォーカス合わせ、非点補正など一切行わない。
(S17):傾斜角をΔt増やし、ステップ(S11)へ再度進む。このステップでは軸の再調整は行わない。
以上(S10)から(S19)を行うことで色球面収差を測定できる。また上述のフローで傾斜の方向は特定の一方向(プラス側、マイナス側)について行ったが、直交する傾斜方向など、少なくとも2方向について測定することで、非対称性を考慮した色球面収差測定が行えることになる。
の効果を相殺することができる。
本実施例では特定の角度での例を挙げたが、異なる傾斜角においても、色分散収差量を調整することで色球面収差と相殺することができる。しかしながら、傾斜角の3乗に比例して色分散収差量を変更しなければならないため、調整電圧等も3乗の変更が必要となり、傾斜角に対する調整可能範囲は電源の限界により実施例1よりも狭い。また、軸上での高分解能観察と両立できるよう、傾斜時にのみあらかじめ用意しておいたテーブルに基づいた色分散収差に制御するよう動作してもよい。その際に色球面収差相殺ズレは、傾斜角の方を微調整すれば、比較的簡単にあわせられる。
(S21):加速電圧EをE0-MΔEに設定する。本実施例では簡単のため、始めにE0-MΔEを設定したが、順番には特に意味はない。
(S22):フォーカス値FをF0-LΔfに設定する。本実施例では簡単のため、始めにF0-LΔfを設定したが、順番には特に意味はない。
(S25):フォーカス値をΔf増やし、再度ステップ(S23)へ進む。このステップでは軸の再調整は行わないが、イメージシフトは行っても良い。
(S28):加速電圧をΔE増やし、再度ステップ(S22)へ進む。
(S31):傾斜角をΔt増やし、ステップ(S21)へ再度進む。このステップでは軸の再調整は行わない。
以上(S20)から(S33)を行うことでも色球面収差を測定できる。なお、本実施例の方法はフォーカスズレをもとにするため、絞り径の影響を受ける。したがって、傾斜角に対して絞り径が無視できない場合は、絞り径を考慮した計算をする。例えば、傾斜に対して絞りの内側を通る電子線の傾斜角をα1、外側を通る傾斜角をα2とすると下式7の連立方程式を解くことで求まる。
102…試料室、103…制御ユニット。
Claims (12)
- 荷電粒子線を利用する走査荷電粒子線装置であって、
試料を載置する試料ステージと、入射した1次荷電粒子線の収差を補正する収差補正器と前記収差補正器の上部に設置された前記1次荷電粒子線を偏向する偏向器を有し、前記試料ステージ上に載置された試料に対して前記1次荷電粒子線を走査する照射光学系と、前記荷電粒子線の走査により発生する2次荷電粒子を検出する検出器と、前記検出器の出力信号を画像表示する表示部と、前記偏向器を用いて前記1次荷電粒子線の前記試料への照射角度と方向、及び前記1次荷電粒子線への加速電圧を変更して、色球面収差量を測定するよう制御する制御部を備えた、
ことを特徴とする走査荷電粒子線装置。 - 請求項1に記載の走査荷電粒子線装置であって、
前記制御部は、
前記色球面収差量の測定において、前記加速電圧を変更することで生じる画像の移動について、変更した前記加速電圧に対する単位電圧あたりの画像移動量と方向を算出し、
前記単位電圧あたりの画像移動量と方向の算出において、前記1次荷電粒子線の傾斜を傾斜軸に対して同一の向きで少なくとも3種異なる角度において測定して、前記傾斜角を変数とする前記単位電圧あたりの画像移動量を多項式として近似し、前記多項式の3次の係数から前記色球面収差量を算出する、
ことを特徴とする走査荷電粒子線装置。 - 請求項1に記載の走査荷電粒子線装置であって、
前記制御部は、
前記色球面収差量の測定において、前記加速電圧を変更することでフォーカスズレを発生させ、前記フォーカスズレに対して変更した前記加速電圧の単位電圧あたりのフォーカスズレ量と方向を算出し、前記単位電圧あたりのフォーカスズレ量と方向の算出に際し、前記1次荷電粒子線の傾斜を傾斜軸に対して同一の向きで少なくとも2種異なる傾斜角において測定し、前記傾斜角を変数とする前記単位電圧あたりのフォーカスズレ量を多項式として近似し、前記多項式の2次の係数から前記色球面収差量を算出する、
ことを特徴とする走査荷電粒子線装置。 - 請求項1に記載の走査荷電粒子線装置であって、
前記制御部は、前記試料の傾斜観察において色収差制御機能を有し、観察する傾斜角および当該傾斜角と軸対称の関係にある傾斜角において、色球面収差および色収差によって試料面と平行な方向に生じる画像のボケを抑制するため、前記色収差制御機能により色収差が0となる状態よりも正もしくは負になるよう制御する、
ことを特徴とする走査荷電粒子線装置。 - 請求項1に記載の走査荷電粒子線装置であって、
前記制御部は、前記試料の傾斜観察において色分散収差制御機能を有し、観察する傾斜角において色球面収差および色収差によって試料面と平行な方向に生じる画像のボケを抑制するよう、前記色分散収差制御機能により、傾斜しない場合の色分散収差が0の状態よりも正もしくは負になるように制御する、
ことを特徴とする走査荷電粒子線装置。 - 請求項1に記載の走査荷電粒子線装置であって、
前記制御部は、前記試料の傾斜観察において球面収差制御機能を有し、観察する傾斜角において色球面収差および色収差によって試料面と平行な方向に生じる画像のボケを抑制するように前記球面収差制御機能により球面収差が0の状態よりも正もしくは負に制御する、
ことを特徴とする走査荷電粒子線装置。 - 請求項1に記載の走査荷電粒子線装置であって、
前記制御部は、照射角度制御による前記試料の傾斜観察において、色収差制御機能、色分散収差制御機能、球面収差制御機能の少なくともいずれか二つの機能を含み、このうちの少なくとも二つの機能を用いて観察する傾斜角において、色球面収差および色収差によって試料面と平行な方向に生じる画像のボケを抑制し,且つ抑制の際の生じる色収差と球面収差によって生じる画像のボケが最小となる組み合わせを選択して観察するよう制御する、
ことを特徴とする走査荷電粒子線装置。 - 荷電粒子線を利用する走査荷電粒子線装置であって、
試料を載置する試料ステージと、
前記試料ステージ上に載置された試料に対して1次荷電粒子線を走査する照射光学系と、
前記1次荷電粒子線の走査により発生する2次荷電粒子を検出する検出器と、前記検出器の出力信号を画像表示する表示部と、
前記試料ステージ、前記照射光学系、前記検出器、前記表示部を制御する制御部と、
前記制御部に接続される記憶部とを備え、
前記照射光学系は、入射した前記1次荷電粒子線の収差を補正する収差補正器と前記1次荷電粒子線を偏向する偏向器とを有し、
前記制御部は、前記偏向器を用いて前記1次荷電粒子線の前記試料への照射角度と方向、及び前記1次荷電粒子線への加速電圧を変更制御して測定した色球面収差量を前記記憶部に保存する、
ことを特徴とする走査荷電粒子線装置。 - 試料を載置する試料ステージと、入射した1次荷電粒子線の収差を補正する収差補正器と前記1次荷電粒子線を偏向する偏向器を有し、前記試料ステージ上に載置された試料に対して前記1次荷電粒子線を走査する照射光学系と、前記荷電粒子線の走査により発生する2次荷電粒子を検出する検出器と、前記検出器の出力信号を画像表示する表示部とを備えた荷電粒子線装置の制御部による色球面収差補正方法であって、
前記偏向器を用いて前記1次荷電粒子線の前記試料への照射角度と方向、及び前記1次荷電粒子線への加速電圧を変更制御して、色球面収差量を測定する、
ことを特徴とする色球面収差補正方法。 - 請求項9に記載の色球面収差補正方法であって、
前記色球面収差量の測定において、前記加速電圧を変更することで生じる画像の移動について、変更した前記加速電圧に対する単位電圧あたりの画像移動量と方向を算出し、前記単位電圧あたりの画像移動量と方向の算出について前記1次荷電粒子線の傾斜を傾斜軸に対して同一の向きで少なくとも3つの異なる角度において測定して当該角度を変数とする前記単位電圧あたりの画像移動量を多項式として近似し、前記多項式の3次の係数から前記色球面収差量を算出する、
ことを特徴とする色球面収差補正方法。 - 請求項9に記載の色球面収差補正方法であって、
前記色球面収差量の測定において、前記加速電圧を変更することでフォーカスズレを発生させ、前記フォーカスズレに対して変更した前記加速電圧の単位電圧あたりのフォーカスズレ量と方向を算出し、前記単位電圧あたりのフォーカスズレ量と方向の算出の際、前記1次荷電粒子線の傾斜を傾斜軸に対して同一の向きで少なくとも2種異なる傾斜角において測定し、前記傾斜角を変数とする前記単位電圧あたりのフォーカスズレ量を多項式として近似し、前記多項式の2次の係数から前記色球面収差量を算出する、
ことを特徴とする色球面収差補正方法。 - 請求項9に記載の色球面収差補正方法であって、
前記試料の傾斜観察において色収差制御機能を有し、観察する傾斜角において色球面収差および色収差によって試料面と平行な方向に生じる画像のボケが前記傾斜角および前記傾斜角と軸対称の関係にある傾斜角において、前記色収差制御機能により色収差が0となる状態よりも正もしくは負になるよう制御する、
ことを特徴とする色球面収差補正方法。
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