WO2011016182A1 - 荷電粒子顕微鏡 - Google Patents
荷電粒子顕微鏡 Download PDFInfo
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- WO2011016182A1 WO2011016182A1 PCT/JP2010/004532 JP2010004532W WO2011016182A1 WO 2011016182 A1 WO2011016182 A1 WO 2011016182A1 JP 2010004532 W JP2010004532 W JP 2010004532W WO 2011016182 A1 WO2011016182 A1 WO 2011016182A1
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- charged particle
- sample
- deflector
- objective lens
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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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- 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
- H01J37/10—Lenses
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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
- H01J37/10—Lenses
- H01J37/145—Combinations of electrostatic and magnetic lenses
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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
- H01J37/21—Means for adjusting the focus
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/26—Electron or ion microscopes
- H01J2237/28—Scanning microscopes
- H01J2237/2813—Scanning microscopes characterised by the application
- H01J2237/2817—Pattern inspection
Definitions
- the present invention relates to a charged particle microscope, and more particularly to a technique for measuring or inspecting the dimension and shape of a circuit pattern formed on a sample.
- a charged particle microscope represented by a scanning electron microscope is an apparatus capable of observing a sample with high resolution on the order of nanometers.
- the process monitoring device is a device used in the manufacturing process, and automatic observation with high throughput is required.
- a method for speeding up the throughput there is a method of deflecting the trajectory of the primary charged particle beam using a deflection lens to move the observation location (hereinafter referred to as image shift).
- Image shift is not suitable for millimeter-order visual field movement because the primary charged particle beam trajectory is shifted from the lens axis, and resolution is degraded by increasing off-axis aberrations.
- the influence of resolution degradation is small, it is frequently used in process monitoring apparatuses that frequently perform visual field movement on the order of micrometers.
- the deflector used for image shift is composed of two stages, upper and lower.
- the upper deflector deflects the trajectory off-axis, and the lower deflector deflects the trajectory back so that the beam passes through the center axis of the objective lens. By doing so, off-axis aberrations are reduced.
- the ratio of the deflection amount of the upper deflector and the lower deflector (hereinafter referred to as the upper and lower stage ratio) is optimized by the deflection amount of the image shift by receiving the rotational action of the primary charged particle beam by the objective lens.
- the upper / lower ratio is reset according to the change of the image shift deflection condition, or the primary charged particles at the optimal upper / lower ratio using a different deflector from the image shift deflector. It is necessary to deflect so as to be a line trajectory. Furthermore, since the process monitoring apparatus used in the manufacturing process requires automatic observation, it is necessary to automatically set the above-described conditions in accordance with the image shift deflection amount.
- adjustment data as shown in Fig. 2 is acquired.
- the correction value when the optical trajectory shift that changes due to the change of the image shift is corrected using the optical trajectory corrector is associated with the image shift amount. Storing. Since dynamic focus control is controlled by a single focus system, the upper / lower ratio of the image shift may be associated with only the image shift.
- Patent Document 1 Japanese Patent Laid-Open No. 10-247465.
- an electromagnetic lens is used in the electromagnetic field superimposing objective lens by using an electromagnetic field superimposing lens in which an electrostatic lens is superimposed on the electromagnetic lens.
- a method of dynamically controlling the focus with an electrostatic lens while controlling is effective.
- the following problems occur.
- the excitation condition of the coil that corrects the deviation of the trajectory is different between when the electromagnetic lens is focused and when the electrostatic lens is used.
- the rotational component of the correction amount is an electromagnetic lens, the magnetic field strength changes with respect to the change in the height direction, so that the rotation is cancelled.
- a charged particle microscope having the following means.
- the output of the aligner coil is determined by the coil current of the objective lens, the electrode application voltage, the acceleration voltage, and the input value of the image shift coil.
- the feedback condition for stopping the visual field shift by dynamically changing the image shift condition is set. It is determined by the coil current, electrode applied voltage, acceleration voltage, and input value of the image shift coil.
- a table and calculation means for calculating by interpolation using multivariate data based on adjustment data under typical conditions of the apparatus are provided for (1) and (2). It has the function of preparing and checking the validity of the data in the table.
- the present invention is applied to a process monitoring apparatus, it is possible to provide a charged particle microscope that achieves both improvement in throughput and suppression of resolution degradation of acquired images. In addition, even when applied to a microscope for a purpose other than the process monitoring apparatus, it is possible to provide a charged particle microscope that easily obtains a microscope image without degradation in resolution.
- FIG. 3 is a control flow diagram of the scanning electron microscope shown in the first embodiment. The figure which shows the adjustment data used for the deflection amount of an image shift for determination.
- FIG. 3 is a diagram showing a schematic configuration diagram of a scanning electron microscope shown in Example 1; A table for determining control values of the electromagnetic objective lens and the electrostatic objective lens.
- FIGS. 9A and 9B are diagrams showing the behavior of optical trajectory correctors X and Y control current values when image shift deflection conditions are used as parameters.
- FIGS. FIG. 5 is a diagram showing a schematic configuration diagram of a scanning electron microscope shown in Example 2.
- FIG. 6 is a diagram showing a schematic configuration diagram of a scanning electron microscope shown in Example 3.
- FIG. 6 is a control flow diagram of a scanning electron microscope shown in Example 3. A table of correction values used for calculating the field-of-view deviation correction amount.
- Example 1 an example of correcting an optical trajectory by changing both an electromagnetic lens and an electrostatic lens of an electromagnetic field superposition type objective lens will be described.
- FIG. 3 shows a schematic configuration diagram of the scanning electron microscope of the present embodiment.
- a scanning electron microscope shown in FIG. 3 includes an electron optical system barrel 1, a power supply unit 2 for supplying various operating voltages and drive currents in the electron optical system barrel 1, and a digital circuit unit 3 for controlling the power supply unit 2. It is comprised by the host computer 4 which instruct
- the electron optical system barrel 1 includes an electron source 21 that generates a primary electron beam 11, an electromagnetic objective lens 30 that focuses the primary electron beam 11 on a sample 33, and a part of the magnetic pole of the electromagnetic objective lens 30 as an insulating plate 32.
- the magnetic pole 31 that is electrically insulated from the electromagnetic objective lens 30 by the first condenser lens 22 that controls the ratio of the primary electron beam 11 that passes through the diaphragm 23, and the primary electron beam 11 is appropriately incident on the objective lens 30.
- a second condenser lens 24 that converges in a certain range, an electrode 31 that can apply a voltage having the same potential as the voltage applied to the sample 33, and a first electron beam 11 that is two-dimensionally scanned on the plane of the sample 33.
- a voltage can be applied to the magnetic pole 31 independently of a magnetic path (not shown) constituting the electromagnetic objective lens 30, and an electric field lens is formed by the voltage applied to the magnetic pole 31, and the electromagnetic objective lens 30. And the magnetic pole 31 can be combined to act as an electromagnetic field superimposing lens.
- the objective lens composed of the electromagnetic objective lens 30, the magnetic path, and the magnetic pole 31 is an immersion lens.
- the first scanning deflector 25, the second scanning deflector 26, the first image shift deflector 27, the second image shift deflector 28, and the optical trajectory adjuster 29 are orthogonal to the scanning plane.
- deflectors and adjusters in the X direction and the Y direction are arranged so as to overlap each other, and the X direction and the Y direction can be controlled independently.
- the height measurement sensor 38 measures the sample height near the sample irradiation point of the primary electron beam 11 as needed. The measured value is converted into a distance from the reference position of the apparatus and transferred to the host computer 4 via the digital circuit unit 3.
- the reference position may take any position.
- the center position of the sample height that guarantees the operation of the apparatus may be used as the reference position.
- the sample stage 34 can independently move in two directions of an orthogonal coordinate system in a plane perpendicular to the incident direction of the primary electron beam 11 incident on the sample 33.
- the sample stage 34 can move the sample 33 to the coordinates of the observation position designated by the host computer 4.
- the same potential can be applied to the sample 33 and the shield electrode 36.
- the power supply unit 2 is a set of control power supplies for each component of the electron optical column 1, and includes a voltage control power supply 51 for the electron source 21, a control power supply 52 for the first focusing lens 22, and a second focusing lens 24.
- the digital circuit unit 3 is a set of circuits that control the operation of the power supply unit 2, and a control circuit is assigned to each control power supply in the power supply unit 2.
- the host computer 5 can control the operation of each control power supply in the power supply unit 2 based on the digital value assigned to each control circuit in the digital circuit unit 3.
- the acquired image is obtained by detecting the secondary signal 12 such as secondary electrons generated from the sample 19 by the irradiation of the primary electron beam 11 with the secondary signal detector 35, and detecting the detection intensity with the digital value by the analog-digital converter 37. Then, the digital value is transferred to the host computer 5 and information on the digital value is arranged in the scanning order.
- the secondary signal 12 such as secondary electrons generated from the sample 19 by the irradiation of the primary electron beam 11 with the secondary signal detector 35
- the detection intensity with the digital value by the analog-digital converter 37.
- FIG. 1 shows a control flow diagram of the scanning electron microscope executed in the internal program of the host computer 5.
- the electron beam acceleration voltage at the time of observation is set by “setting of electron beam acceleration voltage” 101.
- the sample is placed on the stage by “introducing the sample to the stage” 102, and the average sample height is obtained by “measuring the average sample height” 103.
- the average sample height is an average value of the height distribution of the observation sample, and is an average value obtained by measuring the representative position in the sample surface by the height measurement sensor 38.
- the setting value of the electromagnetic objective lens is calculated from the electron beam acceleration voltage and the average sample height, and the control value is assigned to the control circuit 80 by “Setting of electromagnetic objective lens” 104 to control the electromagnetic objective lens 30.
- stage movement 105 is executed, and when the target observation position is reached, the stage is stopped by “stop stage” 106. At this time, since an error occurs between the stage stop position and the target observation position, control is performed by “setting image shift value” 108 based on the error calculated by “calculate error between target observation position and stop position” 107.
- control values By assigning control values to the circuit 77 and the control circuit 78 and controlling the first image shift deflector 27 and the second image shift deflector 28, the error is corrected by deflecting the electron beam.
- the sample height at the stage stop position is measured by “Measurement of sample height” 109, and the electron beam acceleration voltage is set by “Setting of electrostatic objective lens” 110.
- the set value of the electrostatic objective lens calculated from the median value of the sample height and the sample height after the stage is stopped is assigned to the control circuit 79, and the applied voltage of the electrode 31 is controlled. Thereby, the electron beam 11 is focused on the sample.
- “optical trajectory adjustment value setting” 111 is used to set the electron beam acceleration voltage, the median sample height, and the stage stop.
- an observation image is acquired in “image acquisition” 112.
- the determination sequence of “Is image acquisition completed at all observation points?” 113 if “No”, the sequence returns to “Start stage movement” 105 and repeats the sequence, and if “Yes”, “End of observation, The “sample removal” 114 is executed, and the observation is completed.
- FIG. 4 the focus condition determined by the control value of the electromagnetic objective lens and the electrostatic objective lens with respect to the measurement value of the height measurement sensor 38 and the deflection condition of the image shift deflector, and the control condition of the optical trajectory corrector are determined.
- An example of a table used for this is shown.
- an electromagnetic objective lens control value which is a condition for obtaining just focus, obtained by device adjustment, and static
- This table exists for each acceleration voltage, and exists for each condition of the object surface position to be set when the apparatus is operated by changing the object surface position.
- the average sample height is a value for deriving an objective lens control value that provides a just focus when the control value of the electrostatic objective lens is fixed to a reference value.
- Vobj g (Ha, Hm) (Equation 2)
- ALX s (Ha, Hm, ISX, ISY) (Expression 3)
- ALY t (Ha, Hm, ISX, ISY) (Expression 4)
- Ha is an average height of the sample
- Hm is a measured value of the sample height
- ISX is an image shift deflector X control value
- ISY is an image shift deflector Y control value
- Iobj is an electromagnetic objective lens control value
- Vobj is an electrostatic objective.
- ALX is an optical trajectory corrector X control value
- ALY is an optical trajectory corrector Y control value.
- Adjustment of this table determines the coefficients of the aforementioned function.
- the electromagnetic and electrostatic objective lens control values that determine the focus are dependent variables, and are adjusted as follows, for example. Since the right expressions of (Expression 1) to (Expression 4) are all determined by Ha, they can be acquired simultaneously as follows.
- the image shift deflector X control value is C2
- the image shift deflector X control value is D2 (no deflection state in which no current is applied to each of the image shift deflectors X and Y) )
- An electrostatic objective lens control value A1 that sets the electrostatic objective lens control value to the reference value G and adjusts the focus with the electromagnetic objective lens to obtain a just focus, and an optical trajectory corrector.
- the optical trajectory is adjusted in order to obtain the optical trajectory corrector X control value E14 and the optical trajectory corrector Y control value F14 when the primary electron beam passes through the center of the lens.
- the sample height is changed with the sample average height fixed to Z1, and the sample height is measured.
- the value is changed to Z2 and Z3, and focus adjustment is performed by the electrostatic objective lens, and electrostatic objective lens control values G + G1 and G + G2 at that time are obtained.
- the adjustment value of the optical trajectory corrector at the time of image shift under each focus condition is obtained by changing the image shift in the same manner as described above.
- each input condition is performed with each input condition as three conditions.
- the sample height to be adjusted is not limited to three conditions, and the number of conditions depends on the required accuracy of the focus setting and the correction function. It is changed as appropriate.
- the adjustment of the optical trajectory correctors X and Y when the input values described in this table are a combination of the minimum value, median value, and maximum value that can be controlled, each input value that can be set as a device is stored in this table. A value that is not less than the minimum value and not more than the maximum value of the input values to be described is taken, and the calculation of the output value when the input value is other than the value described in the table is obtained by interpolation.
- the dimensional tolerance and assembly tolerance of the objective lens and deflector are factors that cause asymmetry in the control of the above-described formula, particularly the optical trajectory corrector. Since the correction function differs depending on the cause of this asymmetry, if it is corrected strictly, it becomes a high-order function, and the number of adjustment points for determining the coefficient of the function increases.
- a spline function may be introduced into the aforementioned function. The spline function may be introduced to the entire function, or when a strictly determined function is required for the symmetric component, the spline function may be introduced to the asymmetric component to obtain the sum of the symmetric component and the asymmetric component.
- the sample height is fixed and a just focus is obtained.
- the optical trajectory corrector X and the Y control current value when the electromagnetic objective lens current value and the electrostatic objective lens voltage value are changed are set to different image shift conditions (only one of the image shift deflectors X and Y). For example, as shown in FIG. 5, the optical trajectory corrector X and Y control current values with respect to the current value of the electromagnetic objective lens may behave differently with respect to the image shift condition. I can confirm.
- the input values described in this table may not include the minimum and maximum values that can be controlled, and the calculation of output values in cases other than the input values described in the table in that case is interpolated.
- the output value obtained by extrapolation is small in deviation from the ideal control value to be set and does not significantly affect the resolution degradation.
- the allowable range may be defined as a resolution degradation within 10%.
- the optical trajectory adjuster 29 can be appropriately controlled, and a clear image without resolution deterioration can be obtained.
- the scanning deflection and the image shift deflection may be performed by the same deflector.
- the configuration of this embodiment is shown in FIG.
- scanning deflection and image shift deflection are performed by the same deflector. That is, in this configuration, the first scanning deflector 25, the second scanning deflector 26, the first image shift deflector 27, and the second image shift deflector 28 described in the first embodiment are replaced with the first deflector. 39 and the second deflector 40.
- the first deflector 39 is the sum of the scan control power supply 62 of the first deflector and the image shift control power supply 64 of the first deflector, and the scan control power supply 63 of the second deflector and the second deflector. It is controlled by the added value of the image shift control power supply 65.
- the scanning control power sources 62 and 63 have different periods, and output an alternating current component whose amplitude changes with respect to the observation range of the display image.
- the image shift control power sources 64 and 65 change depending on the observation center of the display image.
- the direct current component to be output is output and added to change the median value of the scanning deflection current, thereby realizing an image shift. Since the other apparatus configuration and adjustment data acquisition method are the same as those in the first embodiment, description thereof will be omitted. In this configuration, all deflection positions are implemented by deflectors, so not only the optical trajectory at the time of image shift deflection but also the optical trajectory at the time of scanning deflection should be optimized with the correction function at the time of image shift deflection. Is possible.
- the AC component current and the DC component current for controlling the deflector are controlled independently and added.
- a control current for the same deflector if it is possible to form a control current for the same deflector.
- the same effect can be obtained in a configuration in which an addition value of an AC component control value and a DC component control value used as a control value in the digital control unit is directly input to the control power source.
- two deflectors capable of superimposing the scanning deflection control current and the image shift deflection control current are arranged, and each is independently used as a scanning deflector and an image shift deflector as in the configuration described in the first embodiment. It can also be used to optimize the optical trajectory for each deflector.
- Example 3 an example will be described in which a change in beam landing position on a sample at the time of a focus change is reduced when a plurality of electrostatic lenses are used as an objective lens.
- FIG. 7 shows a schematic configuration diagram of the scanning electron microscope of the present embodiment.
- a control circuit 82 is newly added for beam landing position control to the apparatus configuration described in the first embodiment.
- the control values of the control circuit 82 are added to the control values of the control circuit 77 and the control circuit 78, respectively, and used as new control values for controlling the control power supply 57 and the control power supply 58.
- the electrostatic lens used for focus control as a role of the objective lens is a focus condition corresponding to the height measured by the height measurement sensor 36 using a lens that operates by applying a voltage to the magnetic pole 31.
- FIG. 8 shows a control flow diagram of the scanning electron microscope executed in the internal program of the host computer 5.
- the flow from “electron beam acceleration voltage setting” 101 to “electrostatic objective lens setting” 110 is the same as the control flow described in FIG.
- image shift value setting” 108 and “electrostatic objective lens setting” 110 are executed, a focus determination sequence is executed. In the focus determination sequence, an image is acquired while changing the focus condition, a focus condition expected to be just focus is calculated from the sharpness of the acquired image, and an operation for setting the focus condition is executed.
- the generated visual field shift amount is returned in the sequence of “add the visual field shift amount at the sample applied voltage Vjust to the image shift value” 121. Add the correct image shift value.
- “Acquire Image” 112 is executed. Since the method for setting the optical trajectory adjustment value in the present embodiment is the same as the method described in the first embodiment, the description thereof is omitted.
- FIG. 9 shows an example of a correction value table used for calculating the field-of-view deviation correction amounts 116 and 121.
- the three conditions of the image shift deflector Y control values D1, D2, and D3, the field deviation correction X control value and the field deviation correction Y control value obtained by the apparatus adjustment are described.
- the input / output relationship is as follows: average sample height, sample height measurement value, image shift deflector X control value, image shift deflector Y control value are input values, field shift correction X control value, field shift correction Y control.
- the value is the output value. Similar to the table in FIG. 4 of the first embodiment, this table exists for each acceleration voltage. When the apparatus is operated by changing the object surface position, the table exists for each object surface position condition to be set. Since the calculation method of the output value using the table is the same as the calculation method using the table described in FIG.
- Example 4 describes an operation that provides a criterion for determining whether or not the optical trajectory correction table needs to be corrected. Since the apparatus configuration and the optical trajectory correction method are the same as those described in the first or second embodiment, the description thereof will be omitted.
- FIG. 10 shows an example of the correction data reliability check screen.
- the correction data check screen 141 includes an OK command button 142, a Cancel command button 143, and a reliability determination display screen 144.
- OK command button 142 When the correction data check screen 141 is displayed, a sequence for checking the reliability of the correction data from the relative deviation between the calculated value obtained from the correction data and the actual measurement value operates.
- FIG. 11 shows an example of an operation sequence at the time of checking the reliability of the correction data according to this embodiment.
- “Move to first image shift confirmation position” 151 “Calculate optical trajectory adjustment values Ea and Fa from correction table” 152 is calculated from the correction table at the first image shift confirmation position. To obtain the corrected value. Since “Please select OK when the optical trajectory adjustment is completed” is displayed on the correction data check screen 141, “obtain optical trajectory adjustment values Eb and Fb from adjustment” 153 is executed by manual adjustment.
- the OK command button 142 is clicked, “move to the second image shift confirmation position” 154 is executed, and “calculate the optical trajectory adjustment values Ec and Fc from the correction table” 155 to execute the second image shift confirmation position.
- a correction value calculated from the correction table is obtained. Since “Please select OK when the optical trajectory adjustment is completed” is displayed on the correction data check screen 141, execute “obtain optical trajectory adjustment values Ed and Fd from adjustment” 156 by manual adjustment, When the OK command button 142 is clicked, a “(Eb ⁇ Ea) ⁇ (Ed ⁇ Ec) ⁇ Eth and (Fb ⁇ Fa) ⁇ (Ed ⁇ Ec) ⁇ Eth” 157 determination sequence is executed. Here, it is determined whether the following Expression 5 and Expression 6 are satisfied.
- Eth and Fth are preset values that are allowable values of deviation of the adjustment value. If Expression 5 and Expression 6 are satisfied, it is determined that correction is not necessary, and “output“ normal ”to determination” 158 is operated. On the other hand, when Expression 5 and Expression 6 are not satisfied, “output“ re-adjustment required ”for determination” 159 is operated to notify the user that adjustment data needs to be readjusted. Through the above implementation, the reliability of the adjustment data can be easily confirmed.
- SYMBOLS 1 Electro-optical system barrel, 2 ... Power supply unit, 3 ... Digital circuit unit, 4 ... Host computer, 11 ... Primary electron beam, 21 ... Electron source, 22 ... First condenser lens, 23 ... Aperture, 24 ... First Two condenser lenses, 30 ... electromagnetic objective lens, 31 ... magnetic pole, 32 ... insulating plate, 33 ... sample, 25 ... first scanning deflector, 26 ... second scanning deflector, 27 ... first image shift Deflector, 28 ... second image shift deflector, 29 ... optical trajectory adjuster, 35 ... secondary signal detector, 34 ... sample stage, 36 ... shield electrode, 38 ... height measuring sensor, 51, 59, 61 ... Voltage control power supply, 52, 53, 54, 55, 56, 57, 58 ... Control power supply, 60 ... Coil current control power supply.
Abstract
Description
(1)イメージシフト時に、磁界レンズの回転作用により、レンズ中心から軌道がずれる。この軌道のずれを補正するコイルの励磁条件が電磁レンズでフォーカスした場合と静電レンズの場合とで異なる。補正量の回転成分が電磁レンズの場合には、高さ方向の変化に対して磁界の強度が変化するために回転がキャンセルされる方向に作用するが、静電レンズの場合には、磁界の強度が変化しないため、高さ方向の変化に対して回転成分がキャンセルされる作用が発生しない。また、補正精度は分解能に影響を与えるため、高分解能化を目的とした荷電粒子顕微鏡においては高精度補正が要求される。
(2)静電レンズと電磁レンズのレンズ中心を完全に一致させることができず、荷電粒子線を複数のレンズ中心に同時に通過させることは困難であるため、ひとつのレンズ中心を通すことになる。このとき、荷電粒子線をレンズ中心に合わせた系にてフォーカスを変化させた場合はフォーカス変化時に同一の箇所で発生しないが、これとは別の系でフォーカスを変化させた場合、視野の移動が発生することになる。また、視野ずれはイメージシフトによって方向が変化する。この視野ずれは、画像を取得しながら、その先鋭度判定によって合焦点位置を判定するオートフォーカスの精度を劣化させる要因となる。
(3)前述の(1)(2)の現象は、装置ごとに振る舞いが異なる。これは、たとえば装置の組み立て精度にも起因するため、全く同一の振る舞いの装置を作成することは困難である。また、レンズ中心を通すための補正条件が外乱などの環境変化によって長期的には安定しないことが知られている。
(1)アライナコイルの出力を、対物レンズのコイル電流と電極印加電圧、加速電圧およびイメージシフトコイルの入力値によって決定する。
(2)レンズ中心を通したフォーカス系以外にてフォーカスを振る場合に発生する視野ずれを抑制するために、イメージシフト条件を動的に変化させて視野ずれを止めるためのフィードバック条件を対物レンズのコイル電流と電極印加電圧、加速電圧およびイメージシフトコイルの入力値によって決定する。
(3)アライナコイル出力値の決定に用いる演算手法に、装置の代表条件での調整データを元に多変量データによる補間によって算出するためのテーブルと演算手段を(1)(2)に対して準備し、テーブルのデータの有効性をチェックする機能を有する。
それぞれの関係を以下の式に示す。
Iobj=f(Ha,Vobj=G)・・・(式1)
Vobj=g(Ha,Hm)・・・・・・・(式2)
ALX=s(Ha,Hm,ISX,ISY)・・・(式3)
ALY=t(Ha,Hm,ISX,ISY)・・・(式4)
Haは試料平均高さ、Hmは試料高さ計測値、ISXはイメージシフト偏向器X制御値、ISYはイメージシフト偏向器Y制御値、Iobjは電磁型対物レンズ制御値、Vobjは静電型対物レンズ制御値、ALXは光学軌道補正器X制御値、ALYは光学軌道補正器Y制御値である。本テーブルの調整によって前述の関数の係数が決定される。特に、フォーカスを決定する電磁型および静電型対物レンズ制御値は、それぞれ従属する変数であるため、たとえば次のように調整する。(式1)から(式4)の右式はすべてHaによって決定されることから、次のように同時に取得することが可能である。
この構成では、偏向位置がすべて偏向器にて実施されるため、イメージシフト偏向時の光
学軌道だけでなく、走査偏向時の光学軌道に対してもイメージシフト偏向時の補正関数で
最適化することが可能となる。
実行後、「試料印加電圧の変化分の視野ずれ量をイメージシフト値に加算」116のシーケンスを実行することにより、試料印加電圧の変化時に発生する視野ずれ量をあらかじめホストコンピュータ4に格納されている補正テーブルのデータをもとに算出した値を制御回路82に割り当てて制御電源57および58が制御される。なお、上記の「試料印加電圧を変化」115は、実施例1で述べたように、電圧制御電源61から試料33およびシールド電極36に印加する電圧を変化させて行うものとする。「光学軌道調整値の設定」111では116にて再設定されたイメージシフト値に対応する光学軌道調整値が設定される。その後、「フォーカス判定画像の取得」117にて画像を取得後、「フォーカス判定画像取得終了か?」118にて未終了の場合は115のシーケンスに戻って116、111、117を繰り返す。118のシーケンスにて終了の場合は「ジャストフォーカス条件Vjustの算出」119のシーケンスを実行し、得られたフォーカス判定画像の評価値から合焦点位置と判定する試料印加電圧Vjustを算出する。得られたフォーカス条件の算出値は、「試料印加電圧Vjustの設定」120のシーケンスでの試料印加電圧の設定値Vjustに反映される。試料印加電圧を初期値に対して変更すると、視野ずれが発生するため、「試料印加電圧Vjust時の視野ずれ量をイメージシフト値に加算」121のシーケンスにて、発生する視野ずれ分を戻すようなイメージシフト値を加算する。このとき、最適な光学軌道を通る条件が変化するので、「光学軌道調整値の設定」122のシーケンスでは、121にて設定されたイメージシフト値に対応する光学軌道調整値が設定された後、「画像の取得」112が実行される。本実施例における光学軌道調整値の設定方法は実施例1に記載の方法と同一なので説明を割愛する。「全観察点での画像取得終了か?」113の判定にてまだ観察すべき箇所が残っている場合は、「試料印加電圧の初期化」123を実行した後105以下の動作を繰り返し、113の判定にて観察すべき箇所がない場合は「観察の終了、試料の取り出し」114を実行し、観察を終了する。
(Eb-Ea)-(Ed-Ec)<Eth・・・・(式5)
(Fb-Fa)-(Ed-Ec)<Eth・・・・(式6)
EthおよびFthは、あらかじめ設定された値で調整値のずれの許容値を意味する。
式5および式6を満たせば補正は必要なしと判断され、「判定に「正常」を出力」158を動作させる。一方、式5および式6を満たさない場合、「判定に「再調整要」を出力」159を動作させ、調整データの再調整が必要である旨をユーザに告知する。
以上の実施によって、調整データの信頼性を容易に確認することが可能となった。
Claims (10)
- 被計測試料を保持する試料ステージを格納する試料室と、前記被計測試料上に荷電粒子線を二次元に走査して発生する二次信号を検出して出力する荷電粒子光学鏡筒とを備えた荷電粒子顕微鏡であって、
前記荷電粒子光学鏡筒は、前記被計測試料上に前記荷電粒子線を集束させる対物レンズと、
前記荷電粒子線が走査される前記被計測試料上の走査領域において該走査の中心を所望の位置に設定する偏向器と、
前記荷電粒子線を前記走査領域の中心に設定した時に発生する前記対物レンズの軸外収差を低減させる光軸調整器を有すると共に、
前記対物レンズの軸外収差を所定値以下に制御する前記光軸調整器の制御値を格納する設定値記憶部と、前記対物レンズと前記偏向器と前記光軸調整器のそれぞれの制御値を制御する制御部とを具備してなる演算処理装置を有し、
前記対物レンズは、電磁レンズおよび静電レンズからなる複数のレンズによって構成されるイマージョンレンズであり、
前記設定値記憶部は、前記電磁レンズおよび静電レンズのそれぞれの制御値と前記偏向器の制御値によって決定される前記光軸調整器の制御値を格納することを特徴とする荷電粒子顕微鏡。 - 請求項1記載の荷電粒子顕微鏡であって、
前記偏向器は、イメージシフト偏向器で構成される
ことを特徴とする荷電粒子顕微鏡。 - 請求項1記載の荷電粒子顕微鏡であって、
前記偏向器は、イメージシフト偏向器および走査偏向器で構成される
ことを特徴とする荷電粒子顕微鏡。 - 請求項1記載の荷電粒子顕微鏡であって、
前記試料ステージが前記被計測試料の保持機構を有すると共に、前記被計測試料の高さを測定する高さ計測装置と、
同一被計測試料における試料高さの変化による前記対物レンズの焦点位置の変化分を静電レンズの調整によって追随させて所望の集束条件を求める手段を有することを特徴とする荷電粒子顕微鏡。 - 請求項4記載の荷電粒子顕微鏡であって、
前記被計測試料の保持機構が静電チャック方式による保持機構である
ことを特徴とする荷電粒子顕微鏡。 - 請求項4記載の荷電粒子顕微鏡であって、
前記被計測試料に電圧を印加し、かつ該電圧を変化させることによって前記荷電粒子線が前記被計測試料上で所望の焦点位置に集束させる手段を有する
ことを特徴とする荷電粒子顕微鏡。 - 被計測試料を保持する試料ステージを格納する試料室と、前記被計測試料上に荷電粒子線を二次元に走査して発生する二次信号を検出して出力する荷電粒子光学鏡筒とを備えた荷電粒子顕微鏡であって、
前記荷電粒子光学鏡筒は、前記被計測試料上に前記荷電粒子線を集束させる対物レンズと、
前記荷電粒子線が走査される前記被計測試料上の走査領域において該走査の中心を所望の位置に設定する偏向器と、
前記荷電粒子線を前記走査領域の中心に設定した時に発生する前記対物レンズの軸外収差を低減させる光軸調整器を有すると共に、
前記対物レンズの軸外収差を最小とする前記光軸調整器の制御値を格納する設定値記憶部と、前記対物レンズと前記偏向器と前記光軸調整器のそれぞれの制御値を制御する第1の制御部と、前記被計測試料に電圧を印加することにより生じる前記荷電粒子線の前記被計測試料への着床位置のずれ量を計測し該ずれ量に基づいて前記第1の制御部の制御値に補正を加える第2の制御部とを具備してなる演算処理装置を有し、
前記設定値記憶部は、前記対物レンズの制御値と前記偏向器の制御値によって決定される前記光軸調整器の制御値を格納することを特徴とする荷電粒子顕微鏡。 - 請求項7記載の荷電粒子顕微鏡であって、
前記対物レンズが電磁レンズおよび静電レンズからなる複数のレンズによって構成されるイマージョンレンズである
ことを特徴とする荷電粒子顕微鏡。 - 請求項7記載の荷電粒子顕微鏡であって、
前記試料ステージが前記被計測試料の保持機構を有すると共に、前記被計測試料の高さを測定する高さ計測装置と、
同一被計測試料における試料高さの変化による前記対物レンズの焦点位置の変化分を静電レンズの調整によって追随させ、所望の集束条件を求める手段を有することを特徴とする荷電粒子顕微鏡。 - 請求項7に記載の荷電粒子顕微鏡であって、
前記第2の制御部は、与えられたフォーカス条件に応じて前記偏向器を制御することにより焦点位置の変化時に取得する画像の観察位置の変化を低減させる制御条件を算出し、算出された前記制御条件を基に前記与えられたフォーカス条件を所望のフォーカス条件に補正することを特徴とする荷電粒子顕微鏡。
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