JP5970394B2 - Inspection device - Google Patents

Description

  The present invention relates to an inspection apparatus that inspects a sample by deflecting an electron beam.

As background art in this technical field, there is JP 2011-108650 A (Patent Document 1). This publication states that “by adding a weak hexapole to the crossover between hexapoles, it is possible to make a Rose-like or Clew-like corrector without A5 or D6. By adding both a hexapole and a dodecapole, a correction device without both A5 and D6 is produced. "
Moreover, there exists Unexamined-Japanese-Patent No. 2008-97902 (patent document 2). In this publication, “the electron beam apparatus is provided with astigmatism adjusting means for adjusting the astigmatism of the electron beam, and the correction voltage for maximizing the focus evaluation value obtained from the image of the pattern formed on the sample W is provided. The astigmatism adjusting means is a multipole having a plurality of pairs of electrodes or coils facing each other about the optical axis of the electron beam.

JP 2011-108650 A JP 2008-97902 A

In an inspection apparatus that performs semiconductor inspection or the like, the electron beam is deflected by using a magnetic field or an electric field, and irradiated to a target position. An electron beam deflector is configured with a coil as a counter electrode when deflected by a magnetic field and a counter electrode as a basic unit when deflected by an electric field. When the deflector is a coil, positive and negative currents are passed through the counter electrode, and when the electrode is an electrode, the positive and negative voltages are applied to the counter electrode. At this time, if the current and voltage are not reversed, the position of the focal point formed by the electron beam in the depth (z-axis) direction differs in the x-axis direction and the y-axis direction. Astigmatism error occurs.
Also, if the waveform timing of the current applied to the opposite coil or the voltage applied to the electrode is not perfect, the polarity of the current or voltage will not be reversed, and even in this case, an astigmatism error will occur.
When astigmatism occurs due to astigmatism error, the focus shape of the electron beam becomes elliptical, and the image obtained from the semiconductor measurement and inspection equipment becomes blurry in a certain direction and becomes unclear. There is a problem that inspection accuracy is lowered.
With respect to this problem, Patent Document 1 describes a method for reducing astigmatism by adding a lens for astigmatism adjustment. However, as the lens is added, the semiconductor measurement / inspection apparatus becomes enormous, There is a possibility that the astigmatism adjusting lens itself becomes a new disturbance to the electron beam.
Patent Document 2 describes that the inspection accuracy is improved by providing an astigmatism adjuster composed of a coil, but it does not improve the generation of astigmatism itself, and astigmatism adjustment is not performed. In order to carry out with high accuracy, it is necessary to use a multi-pole coil, which is expensive.
In addition, in an inspection using an electron beam, it is necessary to increase the scanning speed in order to suppress the amount of charge on the specimen. However, in order to increase the scanning speed, it is necessary to control the deflector at a high speed. When there is a timing difference between positive and negative signals to the coils and electrodes to be performed, there is a problem that this timing difference becomes relatively larger as scanning is accelerated. For example, consider a case where the timing difference between positive and negative signals input to the deflector is 100 ns. For example, if the time taken to scan one scanning line at a normal speed is 50 μs, the timing difference per scanning line is 0.2%. When a sawtooth wave is used to control the deflector, the rate of time deviation is directly proportional to the current and voltage, so the deviation of the current flowing in the opposite coil and the voltage applied to the electrode is 0.2%. Next, when the scanning speed is doubled, the time taken to scan one scanning line is 25 μs. On the other hand, since the timing difference between the positive and negative signals remains 100 ns regardless of the scanning time, the timing difference per scanning line is doubled to 0.4%, and the current flowing through the opposite coil and the voltage applied to the electrode The deviation is doubled to 0.4%. Further, when the scanning speed is increased by 5 times, the current flowing in the opposite coil and the voltage applied to the electrode are also increased by 5 times to 1.0%, and the increase in the scanning speed remains as it is, and the current and voltage of the deflector remain unchanged. Appears as a difference. Although these values are small as absolute percentages, since the beam diameter of the electron beam is very small, it is greatly affected in practice.
Since the astigmatism error itself occurs in the techniques of Patent Document 1 and Patent Document 2, there is the above-mentioned problem, and if it is attempted to suppress this, the apparatus configuration may be increased in size and cost, and control may be complicated. There is.
Therefore, an object of the present invention is to provide an inspection apparatus capable of measuring with high accuracy by an inexpensive configuration.

In order to solve the above problems, for example, the configuration described in the claims is adopted.
The present application includes a plurality of means for solving the above-described problems. For example, an inspection apparatus that inspects a sample by deflecting an electron beam includes an electron gun that irradiates an electron beam, and an electron beam. A deflector for deflecting; a deflection control unit for generating a deflection signal for controlling the deflector; a digital-analog converter for converting the deflection signal of the deflection control unit into an analog signal; and an input from the digital-analog converter An inverting amplifier that outputs the first output signal without changing the polarity of the signal, and a non-inverting amplifier that inverts the polarity of the input signal from the digital-analog converter and outputs the second output signal. A first variable delay section that outputs a variable delay amount of the first output signal; a second variable delay section that outputs a variable delay amount of the input second output signal; 1st and 2nd A delay control unit that controls a delay amount of the variable delay unit, wherein at least one of the first and second output signals is set to a set delay amount by the delay control unit. Controlling at least one of the two variable delay units.

  ADVANTAGE OF THE INVENTION According to this invention, the test | inspection apparatus which can be measured accurately can be provided with an inexpensive structure.

It is an example of the block diagram of a semiconductor measuring device. It is an example of the block diagram of the deflection | deviation part concerning a 1st Example. It is an example of RC filter characteristic. It is an example of a structure of the variable delay part using RC filter. It is a structural example of a Bessel filter. It is an example of a structure of the variable delay part concerning a 2nd Example. It is a structural example of the variable delay part concerning a 3rd Example. It is a structural example of an interface. It is an example of the block diagram of the deflection | deviation part as described in a 4th Example. It is an example of the flow of the automatic control concerning a 1st Example.

  Hereinafter, examples will be described with reference to the drawings.

  In this embodiment, a configuration of a semiconductor measuring device will be described as an example of an inspection device that inspects a sample by deflecting an electron beam.

  First, FIG. 1 shows a configuration of a semiconductor measuring device. The semiconductor measuring device includes an electron gun 1 that outputs an electron beam 3, a focusing lens 2 that focuses the electron beam 3, a deflecting unit 10 that changes the direction of the electron beam 3 and controls the position at which the electron beam is applied to the material 5, and an electron beam. 3 An objective lens 4 for refocusing, a sample 5 as an object to be measured, an electron beam 3 hits the sample 5, and is composed of secondary electrons 6 emitted and a detector 7 for detecting the emitted secondary electrons.

  FIG. 2 shows the configuration of the deflection unit 10. The deflection unit 10 outputs a deflection control unit 101 that controls the magnitude of deflection using a digital signal, a DAC (digital-analog converter) 102 that converts a digital signal into an analog signal, and a signal obtained by inverting the sign of an input signal. An inverting amplifier 103, a non-inverting amplifier 106 that outputs the signal without changing the sign of the input signal, and a variable delay that can output the input signal by giving a group delay (function of time delay with respect to frequency) and adjusting the group delay amount. Sections 104 and 107, amplification amplifiers 105 and 108 for amplifying analog signals, a deflector 109 for deflecting an electron beam, and a delay control section 110 for controlling a delay amount. Further, a user interface 111 is provided for the user to input a delay amount of the delay control unit, and the delay control unit 110 of the deflection unit 10 is controlled by an input from the user interface. The user interface 111 may be provided so as to be fixed to the deflection unit, or may be provided detachably on the deflection unit. Further, only the user interface may be provided alone. Further, either wired connection or wireless connection may be used.

  Since the deflection is performed in each of the x-axis direction and the y-axis direction, the deflection unit 10 is provided for each axis. Further, when there are a plurality of deflection electrodes on the upper and lower sides depending on the configuration of the semiconductor measuring device, the deflection unit 10 is provided for the number of stages.

  Next, a configuration example of the variable delay units 104 and 107 is shown in FIG. The variable delay units 104 and 107 are RC low-pass filters composed of resistors and capacitors. The resistance value is variable, the capacitor value is variable, or both are composed of variable elements. In FIG. 4, both elements are variable as an example.

  Examples of the characteristics of this low-pass filter are shown in FIGS. First, as shown in FIG. 3A, the resistance and capacitor values are set so that the cut-off frequency of the low-pass filter is equal to or higher than the signal frequency of the analog signal for performing deflection control. When the cut-off frequency is set in this way, the analog signal is not affected by the cut-off characteristic of the filter, so that the variable delay unit can perform signal output only by delaying without changing the waveform of the input signal.

  Next, the group delay characteristic is shown in FIG. The resistor and capacitor values are set together with the cutoff frequency so that the frequency component of the signal enters the frequency at which the group delay characteristic of the low-pass filter is flat. When the signal frequency component reaches a portion where the group delay amount is not flat, distortion occurs in the output signal of the variable delay section. On the other hand, the group delay amount of the portion where the frequency characteristic is flat corresponds to the delay amount given to the entire signal. That is, as the group delay amount increases, the delay amount increases.

  In the RC low-pass filter, the group delay decreases as the cut-off frequency increases. Therefore, the group delay amount can be reduced by changing the resistance value and the capacitor value small. The cut-off characteristic and the change characteristic of the delay amount are shown for each line type in (a) and (b) of FIG. 3, respectively.

  When solid lines 1001 and 1011 set a large resistance value or capacitor value and a large delay amount, the cutoff frequency is low and the group delay amount is large. The characteristics of the broken lines 1002 and 1012 are set when the resistance value or the capacitor value is set smaller than the case of the solid line, and the delay amount is set small, and the characteristics of the dotted lines 1003 and 1013 are set further smaller than the resistance value or the capacitor value This is a characteristic when the delay amount is further reduced.

The time waveform of the above three conditions is shown in FIG. By increasing the resistance value and the capacitor value, only the delay is given to the thin solid input waveform 1020 without distorting the waveform, and the delay amount is increased in the order of the dotted line 1023, the broken line 1022, and the solid line 1021. And output.
According to the above principle, according to the present invention, it is possible to control so as to eliminate the delay generated between the inverting amplifier and the non-inverting amplifier.

  FIG. 8 shows an example of the user interface 111. The user interface 111 includes a measurement image display unit 1061, a delay setting scroll bar 1062, and a delay amount display unit. The delay setting scroll bar and the delay amount display section are provided for each of the + and − electrodes for each of the x axis and the y axis. For example, the + X scroll bar and delay amount display in the figure correspond to the delay amount of the variable delay unit 107 that controls the positive signal delay of the deflector 109 in FIG. 2, and the −X scroll bar is the negative signal. This corresponds to the delay amount of the variable delay unit 104 that controls the delay. The delay control unit 110 controls the delay amounts of the variable delay units 104 and 107 by moving the respective scroll bars. While viewing the measurement result of the measurement image display unit 1061, the user moves the delay amount of each electrode of the deflector by using, for example, a mouse to move the delay setting scroll bar, and adjusts the delay amount so that the flow of the image due to astigmatism error is not visible. I do. Note that the above-described user adjustment may be automated and controlled.

  In this embodiment, the delay control unit is controlled by user input. However, the delay control unit may be automatically controlled by a computer or the like. FIG. 10 shows an example of the flow of automatic control. First, the delay amount of the deflection circuit is set to a predetermined initial value (S11). In that state, astigmatism detection is performed, and then the delay amount is increased by one unit, and further astigmatism detection is performed (S12, S13, S14). Thereafter, the astigmatism error amount before and after the delay amount increase is compared. If the error decreases, the delay amount is further increased (S15-Yes, S13), and if the error does not decrease, the process proceeds to the next flow ( S15-No). This time, the amount of delay of the deflection circuit is reduced, and astigmatism detection is performed (S16, S17). Thereafter, the astigmatism error amount before and after the delay amount decrease is compared, and if the error decreases, the delay amount is further decreased (S18-Yes, S16), and if the error does not decrease, the next previous delay The amount is returned to and the control is terminated (S-No, S19). It is desirable to perform these controls for both the + and − electrodes for the x-axis and y-axis. Also, the numerical change of the delay amount of automatic control and the process of the measurement image are displayed during the control so that the user can easily make final adjustment manually after the automatic control. Furthermore, the control range of the delay amount may be set in advance on the GUI before the automatic control is performed so that the delay amount does not greatly deviate.

  As described above, by adjusting the delay by the variable delay unit and performing deflection, even if there is a delay difference between the outputs of the inverting amplifier and the non-inverting amplifier, the two electrodes of the deflector are symmetrical. Voltage can be applied. By applying positive and negative symmetric voltages to the deflector, astigmatism errors can be reduced, and a well-measured measurement image can be obtained.

  Therefore, according to the present invention, it is possible to provide an inspection apparatus capable of measuring with high accuracy by an inexpensive configuration. In this embodiment, the delay amount adjustment operation has been described focusing on the timing difference between the inverting amplifier and the non-inverting amplifier. However, the configuration of the present embodiment is the delay amount of the inverting amplifier, the non-inverting amplifier, and the amplification amplifier. It is also possible to reduce timing differences due to individual variations.

  The configuration of another variable delay unit that replaces the variable delay unit described in the first embodiment will be described. The configuration other than the variable delay unit is the same as that described in the first embodiment, and a description thereof is omitted.

  A Bessel filter is a filter having a flat group delay characteristic in the pass band. FIG. 5A shows a configuration example of a second-order Bessel filter, FIG. 5B shows a third-order Bessel filter, and FIG. 5C shows a configuration example of an n-order Bessel filter. In the Bessel filter, the group delay amount increases as the order increases. On the other hand, the Bessel filter cannot control the amount of delay while maintaining the filter characteristics by using a variable element by design.

  FIG. 6 shows an example of a variable delay unit using a Bessel filter. The pass-through 104, the second-order filter 1042, the third-order filter 1043, the fourth-order filter 1044,. Since the delay amount increases in the order of pass-through, second-order filter, third-order filter,..., The amount of delay is varied by switching to an order that provides the desired delay amount. Note that the number of n of the n-th order filter may be arbitrary, and the combination of the order of the filter group may be arbitrary. Further, a filter other than the Bessel filter may be used as the filter.

  As a result, according to the present invention according to the present embodiment, control is performed so as to eliminate the delay generated between the inverting amplifier and the non-inverting amplifier, so that no astigmatism error occurs, and the low-cost configuration provides high accuracy. A measurable inspection device can be provided.

  The configuration of another variable delay unit that replaces the variable delay unit described in the first embodiment will be described. The configuration other than the variable delay unit is the same as that described in the first embodiment, and description thereof is omitted.

  FIG. 7 shows a configuration example using a plurality of filters. A plurality of filters 1051, 1052, 1053, and 1054 and a changeover switch 1055 are included. The filters 1051 to 1054 are connected in series, and the delay amount of each filter is added to the later stage. Therefore, the delay amount increases as the output of the subsequent stage filter. By switching the switch 1055, the delay amount can be made variable. As the filter, the aforementioned Bessel filter or RC filter can be used.

  As a result, according to the present invention according to the present embodiment, control is performed so as to eliminate the delay generated between the inverting amplifier and the non-inverting amplifier, so that no astigmatism error occurs, and the low-cost configuration provides high accuracy. A measurable inspection device can be provided.

In the present embodiment, an example of the deflecting unit 20 capable of adjusting astigmatism errors having a configuration in which the magnitude of noise is further reduced will be described.
FIG. 9 is an example of a configuration diagram illustrating the deflecting unit 20 according to the second embodiment. In addition to the deflection control unit 101, the inverting amplifier 103, the non-inverting amplifier 106, the amplification amplifiers 105 and 108, the deflector 109, the delay control unit 110, and the user interface 111, which are the same as those in the first embodiment, the clock generation unit 205, the clock It comprises DACs 201 and 203 that perform digital-analog conversion according to timing, and variable delay units 202 and 204 that delay the clock with variable delay amount.

  The deflection control unit 101 outputs a deflection control signal to the DACs 201 and 203 as a digital signal. The DACs 201 and 203 perform digital-analog conversion based on the timing of the input clock signal. On the other hand, the clock generation unit generates a clock signal and outputs it to the variable delay units 202 and 204. The variable delay units 202 and 204 delay the set amounts of the clock signals, respectively, and output them to the DACs 201 and 203. The DACs 201 and 203 output analog signals in accordance with the timing of the input clock signal. The inverting amplifier 103 inverts and outputs the input signal, and the non-inverting amplifier outputs the input signal as it is. Thereafter, the amplification amplifiers 105 and 108 amplify the signal and output a deflection control signal to each electrode of the deflector. The user operates the user interface 111 to set the delay amount in the delay control unit 110, and the delay control unit 110 controls the delay amounts of the variable delay units 202 and 204 to the set values.

  By adopting such a configuration, the number of DACs is larger than that in the first embodiment. However, since the DACs are on the positive side and the negative side, there is no correlation between the noises included in the outputs of the two DACs. As a result, according to the present invention according to the present embodiment, by controlling to eliminate the delay generated between the inverting amplifier and the non-inverting amplifier, astigmatism error does not occur, An inspection apparatus capable of measuring with high accuracy can be provided with an inexpensive configuration.

DESCRIPTION OF SYMBOLS 1 Semiconductor measuring device 10 Deflection part 101 Deflection control part 102 DAC
103 Inverting amplifiers 104 and 107 Variable delay units 105 and 108 Amplifying amplifier 106 Non-inverting amplifier 109 Deflector 110 Delay control unit 111 User interface

Claims (5)

An inspection apparatus for inspecting a sample by deflecting an electron beam,
An electron gun that emits an electron beam;
A deflector for deflecting the electron beam;
A deflection controller for generating a deflection signal for controlling the deflector;
A digital-analog converter that converts the deflection signal of the deflection control unit into an analog signal; an inverting amplifier that inverts the polarity of the input signal from the digital-analog converter and outputs a first output signal;
A non-inverting amplifier that outputs a second output signal without changing the polarity of the input signal from the digital-analog converter;
A first variable delay unit that outputs a variable amount of delay of the input first output signal;
A second variable delay unit that outputs a variable amount of delay of the input second output signal;
A delay control unit that controls a delay amount of the first and second variable delay units, and the delay control unit sets at least one of the first and second output signals to a set delay amount. As described above, the inspection apparatus controls at least one of the first and second variable delay units. The inspection device according to claim 1,
The first and second variable delay units use RC filters configured by using variable resistors and / or variable capacitors, respectively. The inspection device according to claim 1,
The inspection apparatus according to claim 1, wherein the first and second variable delay units are configured to switch filters of different orders with a switch. The inspection device according to claim 1,
The inspection apparatus according to claim 1, wherein the first and second variable delay units are configured to switch a multi-stage connected filter with a switch. An inspection apparatus for inspecting a sample by deflecting an electron beam,
  An electron gun that emits an electron beam;
  A deflector for deflecting the electron beam;
  A deflection controller for generating a deflection signal for controlling the deflector;
A clock generator;
First and second digital-analog converters for converting a deflection signal of the deflection controller into an analog signal;
  An inverting amplifier that inverts the polarity of the input signal from the first digital-analog converter and outputs a first output signal;
  A non-inverting amplifier that outputs a second output signal without changing the polarity of the input signal from the second digital-analog converter;
  A first variable delay unit that delays the clock from the clock generation unit with a variable delay amount and inputs the delay to the first digital-analog converter;
  A second variable delay unit that delays the clock from the clock generation unit with a variable delay amount and inputs the delay to the second digital-analog converter;
  A delay control unit for controlling a delay amount of the first and second variable delay units,
  The delay control unit performs control so as to eliminate a delay generated between the inverting amplifier and the non-inverting amplifier.

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