JP2006066212A - Charged particle beam device, control method for charged particle beam device, and method for forming scanning digital signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce useless time not contributing to formation of a sample image by suppressing ringing in a scanning driving signal, and to reduce damage generated in the sample. <P>SOLUTION: This charged particle beam device is provided with a deflector 4 making a charged-particle beam 21 emitted from a charged-particle beam source 1 scan on the sample 5 and a signal former forming the scanning digital signal converted into a scanning driving signal supplied to the deflector 4. The fall time of the scanning digital signal is prolonged as the amplitude of the scanning digital signal becomes larger. The ringing occurring in the scanning driving signal becomes easier to occur as the steepness of a change of the scanning driving signal becomes larger, however, in this invention, the fall time of the scanning driving signal is set longer as the amplitude becomes larger by the control. Thus, the ringing in the scanning driving signal can be suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a charged particle beam apparatus such as a scanning electron microscope, a method for controlling the charged particle beam apparatus, and a method for forming a scanning digital signal.

  In a charged particle beam apparatus such as a scanning electron microscope, a sample is irradiated with a charged particle beam emitted from a charged particle beam source, and information on the sample obtained thereby can be detected. Hereinafter, a scanning electron microscope will be described as an example of the charged particle beam apparatus.

  In a scanning electron microscope, an electron beam which is a charged particle beam is emitted from an electron gun which is a charged particle beam source. The electron beam emitted from the electron gun is irradiated onto the sample by an electron optical system including a focusing lens, an objective lens, and a deflector. At this time, the electron beam is deflected by the deflector to scan the sample.

  Detected electrons such as secondary electrons are generated from the sample irradiated with the electron beam. The generated electrons to be detected are detected by a detector, thereby forming a sample image.

  A scanning drive signal (scanning drive current) is supplied to the deflector for scanning the electron beam applied to the sample. The deflector is driven based on the scanning drive signal to deflect the electron beam, and thereby the electron beam scans on the sample.

  An example of the scanning drive signal supplied to the deflector is shown in FIG. In the figure, S1 is a scanning drive signal in the prior art.

  The scanning drive signal S1 repeats the amplitude between two current values (set minimum value I1, set maximum value I2) set corresponding to the region where the electron beam scans on the sample by the deflector. It is formed. At this time, after the scanning drive signal S1 rises to the set maximum value I2, the scan drive signal S1 is set so that when the scan drive signal S1 falls from the set maximum value I2 to the set minimum value I1, it instantaneously falls to the set minimum value I1. Sometimes. Here, when the scanning drive signal S1 falls from the set maximum value I2 to the set minimum value I1, the electron beam deflected by the deflector is turned back on the sample accordingly.

  When the scanning drive signal S1 is set so as to instantaneously fall from the set maximum value I2 to the set minimum value I1, a back electromotive force is generated in the deflector due to a sudden current fluctuation at the fall. As a result, the scanning drive signal S1 falls below the set minimum value I1. Therefore, when the scan drive signal S1 falls, the scan drive signal S1 falls to an unset current value I3 that is lower than the set minimum value I1.

  As a result, immediately after the scan drive signal S1 reaches the set minimum value I1 from the set maximum value I2, the signal waveform of the scan drive signal S1 includes ringing (distortion) including a decrease from the set minimum value I1 to the non-set current value I3. ) S11 occurs. This ringing S11 passes through the non-setting current value I3 from the time t1 when the scanning drive signal S1 reaches the set minimum value I1, and then repeats up and down fluctuations, and then rises stably and returns to the set minimum value I1. It occurs in the period T1 up to the time point t2.

  After the return time t2, the current value of the scanning drive signal S1 rises stably during a period T2 from the set minimum current value I1 to the set maximum current value I2 until the time t3. Thereafter, as described above, the current value of the scanning drive signal S1 passes through the set minimum current value I1 and drops to the non-set current value I3. Note that T in the figure indicates the period (scanning period) of the scanning drive signal S1.

  As described above, when ringing S11 occurs in the scanning drive signal S1, the period T1 during which the ringing S11 occurs is a period that does not contribute to the formation of the sample image. Therefore, normally, even if detected electrons from the sample are detected by the detector during the period T1, detection data by the detector in the period T1 is not selected as data for forming a sample image.

  That is, the detection data of the detected electrons detected during the period T1 in the period T of the scanning drive signal S1 is not selected. Then, detection data of the detected electrons detected during the period T2 during which the scanning drive signal S1 rises stably from the set minimum value I1 to the set maximum value I2 is selected, and a sample image is formed based on the detected data. Like to do.

  In addition, in order to cancel the first undulation of the ringing, there is also a method of adding a pulse-like signal in a direction opposite to the first undulation (see, for example, Patent Document 1).

JP-A-8-335547

  As described above, when ringing occurs at the fall of the scanning drive signal S1, the ringing generation period T1 is a period that does not contribute to the formation of the sample image. Therefore, when the ringing occurrence period T1 is lengthened, a useless time that does not contribute to the formation of the sample image increases.

  In particular, when the scanning cycle T of the scanning drive signal S1 is shortened in order to perform a fast scanning of the electron beam on the sample, the proportion of the ringing generation period T1 in the scanning cycle T increases, and the sample image is formed. The proportion of wasted time that does not contribute increases.

  In addition, since the electron beam is irradiated on the sample even during the ringing generation period T1, if the ringing generation period T1 becomes longer, the irradiated electron beam may cause damage to the sample.

  The present invention has been made in view of the above points, and by suppressing the occurrence of ringing in the scanning drive signal, the useless time that does not contribute to the formation of the sample image is reduced, and damage to the sample is reduced. It is an object of the present invention to provide a charged particle beam apparatus, a charged particle beam apparatus control method, and a scanning digital signal forming method that can be reduced.

  A charged particle beam apparatus according to the present invention converts a charged particle beam source, a deflector for scanning the charged particle beam emitted from the charged particle beam source onto the sample, and a scanning drive signal supplied to the deflector. A charged particle beam device including a signal generator for forming a digital signal for scanning, wherein the fall time of the digital signal for scanning formed by the signal generator increases the amplitude of the digital signal for scanning It is characterized in that it is lengthened according to the condition.

  Another charged particle beam apparatus according to the present invention includes a charged particle beam source, a deflector for scanning a charged particle beam emitted from the charged particle beam source on a sample, and a scan supplied to the deflector. A charged particle beam device including a signal former that forms a scanning digital signal that is converted into a drive signal, wherein the falling time of the scanning digital signal formed by the signal former is determined by the scanning digital signal The frequency is increased as the frequency increases.

  Furthermore, the charged particle beam apparatus control method according to the present invention is supplied to a charged particle beam source, a deflector for scanning a charged particle beam emitted from the charged particle beam source on a sample, and the deflector. A method for controlling a charged particle beam apparatus, comprising: a signal former that forms a scanning digital signal converted into a scanning drive signal; and a controller for controlling the charged particle beam source, the deflector, and the signal former. The falling time of the scanning digital signal formed by the signal generator is lengthened as the amplitude of the scanning digital signal is increased under the control of the control unit.

  Another charged particle beam apparatus control method according to the present invention includes a charged particle beam source, a deflector for scanning a charged particle beam emitted from the charged particle beam source, and a deflector. Of a charged particle beam apparatus comprising: a signal former that forms a scanning digital signal that is converted into a scanning drive signal that is generated; and a control unit that controls the charged particle beam source, the deflector, and the signal former The method is characterized in that the falling time of the scanning digital signal formed by the signal generator is lengthened as the frequency of the scanning digital signal is increased under the control of the control unit.

  A method for forming a scanning digital signal according to the present invention is a method for forming a scanning digital signal to be converted into a scanning drive signal supplied to a deflector for scanning a charged particle beam on a sample, The falling time of the scanning digital signal is made longer as the amplitude of the scanning digital signal increases.

  A method for forming a scanning digital signal according to the present invention is a method for forming a scanning digital signal to be converted into a scanning drive signal supplied to a deflector for scanning a charged particle beam on a sample, The falling time of the scanning digital signal is made longer as the frequency of the scanning digital signal becomes higher.

  In general, the ringing generated in the scanning drive signal is likely to occur as the change in the scanning drive signal becomes steep.

  Therefore, in the present invention, the falling time of the scanning digital signal converted into the scanning drive signal is lengthened as the amplitude of the scanning digital signal increases.

  In the present invention, the falling time of the scanning digital signal converted into the scanning drive signal is lengthened as the frequency of the scanning digital signal increases.

  As a result, the steep change of the scanning drive signal formed by converting the scanning digital signal is reduced and reduced, and the occurrence of ringing can be suppressed.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2 is a schematic configuration diagram showing a charged particle beam apparatus according to the present invention. This charged particle beam apparatus has a configuration of a scanning electron microscope.

  In the figure, reference numeral 1 denotes an electron gun serving as a charged particle beam source. From the electron gun 1, an electron beam 21 which is a charged particle beam is accelerated toward the sample 5 and emitted. The electron beam 21 emitted from the electron gun 1 is irradiated in a state of being finely focused on the sample 5 by the focusing lens 2 and the objective lens 3. At this time, the electron beam 21 is appropriately deflected by the deflector 2, whereby the electron beam 21 is scanned on the sample 5.

  From the sample 5 irradiated with the electron beam 21, detected electrons 22 such as secondary electrons are generated. The detected electrons 22 are detected by the electron detector 6.

  The electron detector 6 outputs a detection signal based on the detected detection result of the detected electrons 22. The detection signal output from the electron detector 6 is amplified, converted to a digital signal by the A / D conversion unit 8, and sent to the frame memory 11.

  The frame memory 11 creates image data for displaying a scanning image (sample image) of the sample based on the detection signal and a scanning digital signal described later.

  The image data created by the frame memory 11 is sent to the display unit 12 via the bus line 9. The display unit 12 displays an image to be a sample image based on the sent image data.

  A control unit 10 is connected to the bus line 9. The control unit 10 sends predetermined drive control signals to the drive units 1 a to 3 a for driving the electron gun 1, the focusing lens 2, and the objective lens 3, and controls them. Further, the control unit 10 sends a scan control signal to the scan drive signal creation unit 7 connected to the deflector 4 to control the scan drive signal creation unit 7. The scanning drive signal forming unit 7 is for supplying a scanning drive signal to the deflector 4. Note that the scanning drive signal creation unit 7, the A / D converter 8, and the frame memory 11 are incorporated on the same substrate (board) to constitute an image processor 13.

  The control unit 10 also controls the display unit 12. An operator who operates the charged particle beam apparatus can observe the sample 5 by visually confirming the sample image displayed on the display unit 12.

  Here, a detailed configuration of the scanning drive signal generation unit 7 is shown in FIG. In the figure, the scanning drive signal generator 7 includes a signal generator 30. A scanning control signal from the control unit 10 (see FIG. 2) is sent to the signal generator 30 via the bus line 9.

  The signal generator 30 receives the scanning control signal sent from the control unit 10 and forms a scanning digital signal. Thereby, the signal forming unit 30 is controlled by the control unit 10.

  Here, the signal generator 30 is provided with a memory 30a, and scan drive data is stored in the memory 30a. The signal generator 30 forms a scanning digital signal based on the scanning drive data stored in the memory 30a.

  The scanning digital signal formed by the signal generator 30 is converted into a scanning driving signal (scanning driving current) which is an analog signal by the D / A converter 31 and sent to the amplifier 32 via the resistor R1. The scanning digital signal is also sent to the frame memory 11 (see FIG. 2).

  The amplifier 32 amplifies the received scanning drive signal and supplies it to the deflector 4. Here, in the example of FIG. 3, the deflector 4 is composed of a deflection coil. Hereinafter, in the description with reference to FIG. 3, the deflector 4 is described as the deflection coil 4.

  The scanning drive signal supplied to the deflection coil 4 returns to the amplifier 32 via the deflection coil 4 and the feedback resistor R2.

  A magnification selection circuit 33 for selecting a specific magnification in the scanning electron microscope which is the charged particle beam device is disposed between the deflection coil 4 and the feedback resistor R2. The magnification selection circuit 33 includes a switch unit S including a plurality of (four in this embodiment) switches that are selectively opened and closed. One end side of each switch constituting the switch unit S is connected to a wiring connecting the deflection coil 4 and the feedback resistor R2. The other end of each switch is grounded via a plurality (four) of reference resistors R3 to R6 having different resistance values for selecting a specific magnification.

  The resistance values of the reference resistors R3 to R6 connected to the other end of each switch have different resistance values depending on the selected magnification.

  Then, by selecting only one of these switches constituting the switch unit S and closing it, any one of the reference resistors R3 to R6 connected to the switch is selected. Become. Thereby, a specific magnification in the scanning electron microscope is selected.

  The resistance values of the reference resistors R3 to R6 are set to 10Ω, 100Ω, 1kΩ, and 10kΩ as an example. In this case, when a reference resistor having a low resistance value is selected, the magnification becomes low, and when a reference resistor having a high resistance value is selected, the magnification becomes high.

  Selection of each switch constituting the switch unit S is performed by a manual operation by an operator. Note that the selection may be performed under the control of the control unit 10.

  The above is the configuration of the scanning electron microscope which is the charged particle beam apparatus according to the present invention. Next, in the scanning electron microscope, the scanning drive signal that is formed by the scanning drive signal creation unit 7 and supplied to the deflector 4 will be described.

  FIG. 4 is a diagram showing a scanning drive signal supplied to the deflector 4 in the present invention. In the figure, S2 is a scanning drive signal in the present invention.

  This scanning drive signal S2 repeats the amplitude between two current values (set minimum value I1, set maximum value I2) set corresponding to the region where the electron beam 21 scans the sample 5 by the deflector 4. In this way, it is formed by the scanning drive signal creation unit 7. The scan drive signal S2 formed by the scan drive signal generator 7 is supplied to the deflector 4 as described above, whereby the deflector 4 is driven and the electron beam 21 is deflected.

  Here, in the present invention, when the current value of the scanning drive signal S2 rises to the set maximum current value I2, and then falls from the set maximum current value I2 to the set minimum current value I1, a predetermined fall time T3 is set. I am trying to provide it. That is, the fall time T3 is provided as a period from time t5 when the current value of the scanning drive signal S2 reaches the set maximum current value I2 to time t6 when it reaches the set minimum current value I1.

  Thus, by providing the predetermined fall time T3, a sudden current fluctuation does not occur in the deflector 4 when the scan drive signal S2 falls, and the generation of the back electromotive force can be suppressed. As a result, the occurrence of ringing that has occurred in the prior art can be suppressed. When the current value of the scanning drive signal S2 falls from the set maximum value I2 to the set minimum value I1, the electron beam 21 deflected by the deflector 4 is turned back accordingly.

  After reaching the time point t6 after the falling time T3 has elapsed from the time point t5, the current value of the scanning drive signal S2 is during a period T4 from the set minimum current value I1 to the time point t7 when reaching the set maximum current value I2. It rises stably at. Then, the current value of the scanning drive signal S2 falls to the set minimum current value I1 after the fall time T3 has elapsed after reaching the set maximum current value I2. Note that T5 in the figure indicates the period (scanning period) of the scanning drive signal S2.

  Here, the fall time T3 in the scan drive signal S2 is controlled to be set longer as the amplitude of the scan drive signal S2 increases. This amplitude refers to the difference (I2−I1) between the set maximum current value I2 and the set minimum current value I1 in the current value of the scanning drive signal S2.

  As described above, the scan drive signal S2 is a digital signal for scanning formed based on the scan drive data stored in the memory 30a of the signal generator 30 in the scan drive signal generating unit 7 as described above. After being converted into an analog signal by the converter 31, it is created by amplifying by the amplifier 32.

  Since the scanning digital signal is converted into the scanning drive signal S2 by the D / A converter 31, it has a falling time equal to the falling time T3 (hereinafter, the falling is also referred to as T3). The falling time T3 in the scanning digital signal is formed so as to increase as the amplitude increases. At this time, the scan drive data for forming such a scanning digital signal is stored in the memory 30a of the signal generator 30. The scan drive signal S2 created by converting the scanning digital signal has a falling time T3 that is set longer as the amplitude increases, as described above.

  In general, ringing that occurs in a scanning drive signal is likely to occur as the scan drive signal changes more rapidly. Therefore, an increase in the amplitude of the scanning drive signal corresponding to the amplitude of the scanning digital signal is a factor that increases the steepness of the change in the scanning drive signal.

  Therefore, in the present invention, the falling time T3 is set in the scanning drive signal S2 by providing the falling time T3 in the scanning digital signal. Then, the fall time T3 is set so as to increase as the amplitude of the scanning digital signal increases.

  As a result, the fall time T3 of the scanning drive signal S2 becomes longer as its amplitude increases. As a result, the steep change of the scan drive signal S2 at the fall of the scan drive signal S2 is alleviated and reduced, and the occurrence of ringing in the scan drive signal S2 can be suppressed.

  Here, the scanning drive signal S1 (see FIG. 1) in the prior art will be compared with the scanning drive signal S2 (see FIG. 4) in the present invention. On the other hand, the fall time T3 in the present invention is short.

  Therefore, according to the present invention, it is possible to reduce useless time that does not contribute to the formation of the sample image, and to reduce damage generated on the sample.

  As a result, the cycle T5 of the scan drive signal S2 in the present invention is shorter than the cycle T of the scan drive signal S1 in the prior art, and the electron beam 21 can be scanned efficiently.

  In the above-described example, the falling time T3 of the scanning digital signal is set to be longer as the amplitude of the scanning digital signal increases. However, a modified example is also conceivable.

  In the modification of the present embodiment, the falling time T3 of the scanning digital signal is set longer as the frequency of the scanning digital signal becomes lower.

  Also in this case, the steep change of the scanning drive signal S2 created by converting the scanning digital signal is alleviated and reduced, and the occurrence of ringing in the scanning drive signal S2 can be suppressed.

  Further, in each of the above embodiments, for the purpose of further reducing damage generated on the sample 5, blanking of the electron beam is performed so that the electron beam 21 is not irradiated on the sample 5 during the fall time T3. It is also possible. This blanking is an operation of removing the electron beam 21 emitted from the electron gun 1 from the sample 5, and a blanking electrostatic deflector (not shown) provided between the electron gun 1 and the focusing lens 2. Can be performed by controlling the driving by the control unit 10.

  By doing so, the sample 5 is not irradiated with the electron beam 21 at the fall time T3 of the scanning drive signal S2, and therefore the time during which the sample 5 is irradiated with the electron beam 21 during the period T5 in the scanning drive signal S2. Can be reduced. Thereby, the damage of the sample 5 resulting from irradiation of the electron beam 21 can be further reduced.

It is a figure which shows an example of the scanning drive signal supplied to a deflector in a prior art. It is a schematic block diagram which shows the charged particle beam apparatus in this invention. It is a figure which shows the detailed structure of a scanning drive signal preparation part. In the present invention, it is a diagram showing a scanning drive signal supplied to a deflector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electron gun (charged particle beam source), 2 ... Condensing lens, 3 ... Objective lens, 4 ... Deflector, 5 ... Sample, 6 ... Electron detector, 7 ... Scanning drive signal formation part, 10 ... Control part, 11 ... Frame memory, 12 ... Display unit, 21 ... Electron beam (charged particle beam)

Claims (11)

A charged particle beam source, a deflector for scanning the charged particle beam emitted from the charged particle beam source on the sample, and a signal forming a scanning digital signal converted into a scanning drive signal supplied to the deflector In a charged particle beam apparatus comprising a former, a charge is characterized in that the falling time of the scanning digital signal formed by the signal former is lengthened as the amplitude of the scanning digital signal increases. Particle beam device. A charged particle beam source, a deflector for scanning the charged particle beam emitted from the charged particle beam source on the sample, and a signal forming a scanning digital signal converted into a scanning drive signal supplied to the deflector In a charged particle beam apparatus comprising a former, a charge is characterized in that the falling time of the scanning digital signal formed by the signal former is lengthened as the frequency of the scanning digital signal increases. Particle beam device. 3. The charged particle beam apparatus according to claim 1, wherein blanking of the charged particle beam is performed during a fall time of the scanning digital signal. The charged particle beam apparatus according to claim 1, wherein the charged particle beam is an electron beam. A charged particle beam source, a deflector for scanning the charged particle beam emitted from the charged particle beam source on the sample, and a signal forming a scanning digital signal converted into a scanning drive signal supplied to the deflector In a control method of a charged particle beam apparatus comprising a former and a charged particle beam source, a deflector, and a control unit for controlling the signal former, a scanning unit formed by the signal former is controlled by the control unit A method for controlling a charged particle beam apparatus, characterized in that a falling time of a digital signal is lengthened in accordance with an increase in amplitude of the scanning digital signal. A charged particle beam source, a deflector for scanning the charged particle beam emitted from the charged particle beam source on the sample, and a signal forming a scanning digital signal converted into a scanning drive signal supplied to the deflector In a control method of a charged particle beam apparatus including a former and a charged particle beam source, a deflector, and a control unit for controlling the signal former, a scanning unit formed by the signal former is controlled by the control unit. A method for controlling a charged particle beam apparatus, characterized in that a falling time of a digital signal is lengthened in accordance with an increase in frequency of the scanning digital signal. 7. The charged particle beam apparatus control method according to claim 5, wherein blanking of the charged particle beam is performed during a fall time of the scanning digital signal under the control of the control unit. The method for controlling a charged particle beam apparatus according to claim 5, wherein the charged particle beam is an electron beam. In a method for forming a scanning digital signal that is converted into a scanning drive signal supplied to a deflector for scanning a charged particle beam on a sample, the fall time of the scanning digital signal is determined by the amplitude of the scanning digital signal. A method for forming a digital signal for scanning, characterized in that the length of the digital signal is increased as the value of the scanning signal increases. In a method for forming a scanning digital signal to be converted into a scanning drive signal supplied to a deflector for scanning a charged particle beam on a sample, the fall time of the scanning digital signal is determined by the frequency of the scanning digital signal. A method for forming a digital signal for scanning, characterized in that the length of the digital signal is increased in accordance with an increase in height. 11. The method of forming a scanning digital signal according to claim 9, wherein the charged particle beam is an electron beam.

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