JP5022981B2 - Charged particle beam equipment - Google Patents

Description

  The present invention relates to a charged particle beam apparatus, and in particular, may affect the stability of the irradiation position of an electron beam based on a secondary electron detection signal after the sample is irradiated with an electron beam (charged particle beam). The present invention relates to a charged particle beam apparatus that displays information related to low-frequency environmental disturbances.

  In recent years, in a charged particle beam apparatus such as a scanning electron microscope (SEM), the stability of the irradiation position of an electron beam has been increasingly required as the resolution is improved. For example, in a semiconductor inspection apparatus using SEM, a stage on which a sample is placed is moved, the sample is scanned with an electron beam, secondary electrons emitted from the sample are captured, and an SEM image (detected image of a charged particle beam apparatus) To evaluate the pattern line width and defects. And with the miniaturization of inspection objects such as semiconductor parts, high stability of the irradiation position of the electron beam is becoming more necessary.

  In the case of an SEM image, the image quality is often judged from the resolution, the number of pixels, contrast, edge sharpness, and the like. As a factor that affects the resolution and edge sharpness, there is a change in the irradiation position of the electron beam on the sample. In other words, when environmental disturbances such as vibration (vibration caused by trains, vehicles, people, etc.), magnetic field, noise, etc. act on the device, the optical axis of the electron beam shifts and the stage vibrates slightly. It cannot be deflected, and therefore, the edge of the SEM image becomes unclear or noise occurs locally.

  For example, in Patent Document 1, a technique related to an electron beam drawing apparatus that performs drawing with high accuracy by detecting vibration transmitted to the electron beam drawing apparatus from an external environment such as floor vibration and correcting the deflection of the irradiation position of the electron beam. Is disclosed.

  However, the technique disclosed in Patent Document 1 relates to an electron beam drawing apparatus, and not to an SEM or the like. Further, the disclosed technique of Patent Document 1 uses reflected electrons, and is different from the technique using secondary electrons, and is not easy to apply to SEM or the like. It is difficult to achieve accuracy.

Therefore, the inventors of the present invention have applied for a position of an electron beam irradiation position synchronized with a secondary electron detection signal when acquiring an SEM image in a patent application (Japanese Patent Application No. 2008-054223: hereinafter referred to as “prior application patent”). A measurement method was proposed. In this method, a pattern edge is scanned with an electron beam, and a high-frequency component due to scanning of the charged particle beam is removed from the secondary electron detection signal at that time by a low-pass filter, thereby extracting a low-frequency vibration component or noise component. Can do. That is, it is possible to detect a shift in the irradiation position of the electron beam due to an environmental disturbance from the secondary electron detection signal when acquiring one SEM image, and handle it as a stability evaluation parameter.
Japanese Patent No. 3075468

  However, there is a waiting time (time lag) between acquiring one SEM image and acquiring the next SEM image. Therefore, in the technology of the prior application patent, the secondary electron detection signal has a continuous waveform if it is within the acquisition time of one SEM image, but it includes a discontinuous waveform when the SEM image is switched. Further, when acquiring a plurality of SEM images or performing frequency analysis such as FFT (Fast Fourier Transform) at 1 Hz or less, a continuous waveform of 1 second or more is required.

  Therefore, the present invention has been made to solve the above-described problems, and in the charged particle beam apparatus, even when the detection is performed based on the secondary electron detection signal including the discontinuous waveform at the time of switching of the detection image, It is an object to display highly accurate analysis information for evaluating the stability of the irradiation position of a line.

  In order to solve the above-described problems, the present invention has a function of generating a detection image by irradiating a charged particle beam to a sample, detecting secondary electrons generated from the sample with a detector, and further, This is a charged particle beam apparatus having a function of displaying information on low-frequency environmental disturbance that may affect the stability of the irradiation position of the particle beam. The charged particle beam apparatus receives an AC coupling for removing an offset of a secondary electron detection signal output from the detector and an input of the secondary electron detection signal from which the offset is removed, and scans the charged particle beam. Accepts the input of the secondary electron detection signal from which the high frequency component has been removed, and cancels the discontinuous waveform component at the time of switching of the detected image, and complements based on the continuous waveform component Complementing means, analysis means for analyzing the frequency of the waveform of the supplemented secondary electron detection signal, and display means for displaying the result of the frequency analysis as information relating to the low-frequency environmental disturbance. And Other means will be described later.

  According to the present invention, in a charged particle beam apparatus, even when based on a secondary electron detection signal including a discontinuous waveform when a detection image is switched, high accuracy for evaluating the stability of the irradiation position of an electron beam. Analysis information can be displayed.

The best mode for carrying out the present invention (hereinafter referred to as “embodiment”) will be described below with reference to the drawings (refer to drawings other than the referenced drawings as appropriate).
FIG. 1 is a configuration diagram of a charged particle beam apparatus. In the charged particle beam apparatus 100, the electron beam 2 emitted from the electron source 1 is converged by the objective lens 4 and deflected by the deflection lens 5 inside the electron optical column 3. Further, the electron beam 2 is scanned within the deflection region on the sample 6, and the detection signal of the secondary electrons captured by the detector 7 is amplified by the amplifier 11 and sent to the computer device 30 of the console 8. Information such as the surface shape of the sample 6 can be obtained by the computer device 30.

  The console 8 includes a computer device 30 and a display 9 (display means). The computer device 30 includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), a hard disk drive (HDD), an input / output interface, and the like. Functions of the device 31 and the like are realized. The image processing device 12 creates a detection image based on information from the amplifier 11. The arithmetic processing unit 31 (analyzing means) performs an FFT operation, an averaging process (a process that calculates and uses an addition average of a plurality of data), and the like.

  In order to obtain an image (detection image) with good resolution, the electron beam 2 must converge finely and the optical axis of the electron beam 2 must be stable with respect to the sample 6. Therefore, the purpose of the charged particle beam apparatus 100 according to the present embodiment is to display on the display 9 highly accurate analysis information regarding low-frequency environmental disturbance that may affect the stability of the irradiation position of the electron beam. It becomes.

  Here, in order to help understanding, the technology of the prior application patent will be described. FIG. 9 is an explanatory diagram of the stability evaluation method of the irradiation position of the electron beam in the prior patent. In addition, the same code | symbol is attached | subjected to the same structure as FIG. 1, and description is abbreviate | omitted. As shown in FIG. 9, the pattern edge 10, which is the edge of the pattern formed on the sample 6, is applied to the deflection region of the electron beam 2. In this way, by observing the pattern edge 10 at a high magnification, it is possible to measure fluctuations in a lower range (lower frequency) than the deflection scanning frequency of the electron beam, and to evaluate the stability of the irradiation position of the electron beam.

  The detector 7 detects secondary electrons emitted from the sample 6, and the amplifier 11 amplifies the detected information. Information 91 amplified by the amplifier 11 (the vertical axis is voltage and the horizontal axis is time) is sent to the image processing device 12, and the image processing device 12 processes and displays the SEM image 14 on the display 9. In the SEM image 14 when the region including the pattern edge 10 is scanned with the electron beam 2, the edge portion is displayed brightly (the narrow region on the right side), and other regions are displayed darkly (the wide region on the left side).

  Since the unstable behavior of the irradiation position of the electron beam appears as a change in the light / dark ratio for each line, only the fluctuation component of the irradiation position of the electron beam is obtained by passing the light / dark signal of the deflection cycle through the low-pass filter 13. (Information 92) is obtained. Thereafter, an FFT calculation 15 (frequency analysis) or the like is performed on the information 92 to obtain a power spectrum related to environmental disturbance (vibration or the like) that causes an unstable behavior of the irradiation position of the electron beam.

  Thus, according to the technique of the prior application patent, a continuous waveform can be obtained within the time to acquire one SEM image 14. However, when several SEM images are acquired and averaged, or when the lower limit frequency of FFT analysis is set to 1 Hz or less, a continuous waveform is required even during image switching. Therefore, in the following first to sixth embodiments of the present invention, a method for obtaining the continuous waveform, and analysis processing and display based on the continuous waveform will be described.

(First embodiment)
FIG. 2 is a diagram illustrating a configuration of the charged particle beam apparatus according to the first embodiment. In addition, the same code | symbol is attached | subjected to the same structure as FIG. 9, and description is abbreviate | omitted suitably. In the first embodiment, a method of obtaining information for evaluating the stability of the irradiation position of the electron beam by reducing the influence of the discontinuous secondary electron detection signal when the SEM image 14 is switched will be described.

  After scanning the region including the pattern edge 10 with the electron beam 2, the secondary electrons emitted from the region are captured by the detector 7, the output is amplified by the amplifier 11, and processed into an image by the image processing device 12. The SEM image 14 is assumed. Here, FIG. 3 is a schematic diagram showing each waveform when the secondary electron detection signal is sequentially processed. In addition, (a) TP1- (e) TP5 of FIG. 3 is a signal at the time of TP1-TP5 shown in FIG.

The signal waveform output from the amplifier 11 is a waveform synchronized with the deflection scanning period of the electron beam as shown in FIG. 3A, and the waiting time (time T) after the scanning of one SEM image is repeated. between ₁ through T _2, between time _T 3 through T ₄₎ is. The processing after the signal of FIG. 3A is obtained is different from the case of the comparative technique (the prior application patent).

  By passing the output waveform of TP1 through the AC coupling 16, the DC (direct current) offset is removed (the waveform is as shown in FIG. 3B). That is, the output waveform of TP2 in FIG. 3B is a parallel translation of the output waveform of TP1 in FIG. 3A so that the average (or center) value is 0 (zero) V. . The AC coupling 16 has a circuit configuration that removes a DC component (DC component) of the electrical signal.

Next, by passing the output waveform of TP2 through the first low-pass filter 17, fluctuations in the irradiation position of the electron beam (deviation from the actual irradiation position with respect to the target position) are obtained (in FIG. 3C). Waveform). That is, the first low-pass filter 17 serves to remove a high-frequency component (for example, about several kiloHz) by scanning with an electron beam. However, the waveform of the TP3 is (between times _T 1 through T _2, the waveform between the time _T 3 through T ₄₎ square wave of noise when switching images to the amplitude of fluctuation is large, even if the FFT operation Sufficient detection accuracy cannot be obtained.

  Therefore, as shown in FIG. 2, the output of the first low-pass filter 17 is used as the input signal of the analog switch 18 (complementing means), and at the same time, this signal is inverted by the inverting amplifier 19 and used as the control input of the analog switch 18. . The analog switch 18 is turned on when the control input signal is at a low level (L), and is turned off when the control input signal is at a high level (H). The output of the analog switch 18 and GND are connected by a high resistance 20. With this configuration, while the information on the fluctuation of the electron beam irradiation position in the SEM image 14 is obtained, the analog switch 18 is turned on, and the fluctuation signal is output to the subsequent circuit. On the other hand, when the SEM image 14 is switched, the GND (zero) potential is output to the subsequent stage of the analog switch 18. The output waveform by the analog switch 18 is as shown by TP4 in FIG. Note that the level of the control input signal of the analog switch 18 may be appropriately adjusted by an amplifier.

  Thereafter, by passing the waveform of TP4 including the section of output zero (V) through the second low-pass filter 21 (complementing means), the influence of the discontinuous waveform at the time of switching of the SEM images can be reduced. (This is the waveform of TP5 in FIG. 3 (e)). Since the discontinuous waveform is composed of a high-frequency periodic function, the second low-pass filter 21 serves to reduce this high-frequency component and pass the low-frequency component to be evaluated. As a result, the second low-pass filter 21 can supplement the discontinuous waveform component (the portion set to zero potential) at the time of switching of the SEM images with the continuous waveform component. The second low-pass filter 21 can reduce the influence of noise when the analog switch 18 is switched. Further, the signal waveform band is limited (high-frequency cut) as a previous stage of frequency analysis thereafter. Can do.

  Thus, according to the charged particle beam apparatus 100 of 1st Embodiment, beam displacement (electron beam irradiation position) can be directly monitored as a voltage signal by signal processing with a simple analog circuit. After that, this voltage signal is subjected to A / D (analog to digital) conversion and frequency analysis, and the result of the frequency analysis is displayed as information on low-frequency environmental disturbance, so that the user can change the detected image. The stability of the irradiation position of the electron beam can be evaluated without being significantly affected by the discontinuous waveform of the secondary electron detection signal at the time (details will be described later in the second to sixth embodiments).

(Second Embodiment)
FIG. 4 is a diagram illustrating a configuration of the charged particle beam apparatus according to the second embodiment. In the second embodiment, since the configuration from the detector 7 to the second low-pass filter 21 is the same as that in the first embodiment, description of the configuration of that portion is omitted. The signal output from the second low-pass filter 21 is then converted into a digital signal by the A / D converter 22, and the computer device 30 stores it in the memory 23. The window processing 24, the FFT operation 15, and the averaging processing 25 are performed. And the calculation processing result is displayed on the display 9 (the display content will be described later in the sixth embodiment). Note that the window process 24 is to gradually reduce both the start and end points of data cut (window) in order to reduce leakage error (leakage error), and to make the boundary of the next cycle close to zero. This is a weighting process.

  As described above, according to the charged particle beam apparatus 100 of the second embodiment, the frequency analysis such as the window process 24, the FFT calculation 15, and the averaging process 25 is performed on the signal output from the second low-pass filter 21. By displaying the result of the frequency analysis as information on low-frequency environmental disturbance, the user can influence the discontinuous waveform of the secondary electron detection signal when the detection image of the charged particle beam device is switched. The stability of the irradiation position of the electron beam can be evaluated without receiving much.

(Third embodiment)
FIG. 5 is a diagram illustrating a configuration of the charged particle beam apparatus according to the third embodiment. The feature of the third embodiment is that the output of the amplifier 11 is A / D converted, and the subsequent processing is performed by a program (software). Specifically, first, the A / D converter 22 converts the signal output from the amplifier 11 into a digital signal. Thereafter, the computer device 30 writes the A / D converted data (FIG. 3A) to the memory 23 and performs the offset adjustment 26 (FIG. 3B). Next, the computer apparatus 30 processes the output by the first low-pass filter 17a (low-pass filter by software) (FIG. 3C), and falls below the threshold value V _L (negative value) by the zero complement 27. In this case, the output is supplemented with zero potential (FIG. 3 (d)). Then, the computer apparatus 30 processes the output by the second low-pass filter 21a (software low-pass filter), and thereafter, as in the case of the first embodiment, the window process 24, the FFT operation 15, and the averaging process 25, and the calculation result is displayed on the display 9.

  As described above, according to the charged particle beam apparatus 100 of the third embodiment, the analog circuit is not required by processing the part processed by the analog circuit in the first embodiment and the second embodiment in software. Cost reduction can be realized.

(Fourth embodiment)
FIG. 6 is a diagram illustrating a configuration of the charged particle beam apparatus according to the fourth embodiment. In the fourth embodiment, the processing content is the same as in the third embodiment, but the amplifier 11 and the A / D converter 22 are also integrated as a console 8.

  Thus, according to the charged particle beam apparatus 100 of 4th Embodiment, management of an apparatus becomes easy by integrating the whole processing structure of the signal output from the detector 7 in the console 8. FIG.

(Fifth embodiment)
FIG. 7 is a diagram illustrating a configuration of the charged particle beam device according to the fifth embodiment. In the fifth embodiment, the processing contents are the same as in the third embodiment, but the functions from the memory 23 that receives the digital output of the A / D converter 22 to the averaging process 25 are the FPGA (Field Programmable Gate Array). 40 (or CPLD (Complex Programmable Logic Device)). That is, in this case, the computer apparatus 30 in the configuration of FIG. 1 is replaced with the FPGA 40 (or CPLD).

  As described above, according to the charged particle beam apparatus of the fifth embodiment, calculation is performed with the FPGA 40 (or CPLD) that operates according to the hardware description language, thereby speeding up the calculation and reducing the cost by eliminating the need for a computer device. And easy implementation.

(Sixth embodiment)
FIG. 8 is a screen example of a display that displays the result of frequency analysis. On the display 9, an SEM image 14, a condition 50, a graph 28, and a power spectrum 29 are displayed.

The condition 50 indicates each condition when acquiring the SEM image 14.
A graph 28 shows a time history waveform (waveform showing a temporal change) of fluctuation of the irradiation position of the electron beam when three SEM images 14 are acquired, the vertical axis is displacement, and the horizontal axis is time.
The power spectrum 29 is the result of FFT calculation of the above-described time history waveform, the vertical axis is amplitude, and the horizontal axis is frequency.

  As described above, the secondary electron detection signal becomes discontinuous when the SEM image is switched, but the influence of the discontinuous waveform is reduced by the method described in the first to fifth embodiments. In the power spectrum 29, a resolution sufficient to identify a spectrum caused by power supply synchronization noise and mechanical vibration can be obtained. Furthermore, although the frequency analysis result can be smoothed by the averaging process, this is not necessarily an essential process.

  As described above, according to the screen example of the sixth embodiment, the result of the frequency analysis can be displayed as information related to the low-frequency environmental disturbance. Thereby, the user can evaluate the stability of the irradiation position of the electron beam without being greatly affected by the discontinuous waveform of the secondary electron detection signal when the detection image of the charged particle beam apparatus is switched.

  Thus, according to the charged particle beam apparatus 100 of each embodiment, the discontinuous waveform component at the time of switching of the detection image is canceled and complemented by the continuous waveform component, and the waveform of the complemented secondary electron detection signal is obtained. The frequency analysis is performed, and the result of the frequency analysis is displayed as information related to the low-frequency environmental disturbance, so that the user can obtain a discontinuous waveform of the secondary electron detection signal when the detection image of the charged particle beam device is switched. It is possible to evaluate the stability of the irradiation position of the electron beam without being greatly affected by the above.

  In addition, the analog switch 18 that accepts the input of the secondary electron detection signal from which the high-frequency component has been removed and sets the discontinuous waveform component to zero potential when the detected image is switched, and the secondary that has the discontinuous waveform component set to zero potential. The complementing means can be specifically realized by the second low-pass filter 21 for complementing the portion that has received the input of the electronic detection signal and made zero potential with the continuous waveform component.

  Furthermore, a time history waveform (a time history waveform including waveforms before and after switching of a plurality of detected images) of an irradiation position variation on the sample 6 of the electron beam 2 and a result of frequency analysis of the time history waveform. By displaying on the display 9, it is possible to display highly accurate analysis results regarding the plurality of SEM images 14.

  In addition, since the result of the frequency analysis includes the power spectrum of the time history waveform, the user can easily evaluate the stability of the irradiation position of the electron beam.

  This is the end of the description of the embodiments, but the aspects of the present invention are not limited to these. For example, the charged particle beam apparatus of each embodiment can be applied to a semiconductor inspection apparatus, a length measurement SEM, an analysis SEM, and the like. Further, the frequency analysis may not be based on the FFT calculation but may be based on a normal FT (Fourier Transform) calculation. In addition, the specific configuration can be changed as appropriate without departing from the spirit of the present invention.

It is a block diagram of a charged particle beam apparatus. It is a figure which shows the structure of the charged particle beam apparatus of 1st Embodiment. It is a schematic diagram which shows each waveform when a secondary electron detection signal is processed sequentially. It is a figure which shows the structure of the charged particle beam apparatus of 2nd Embodiment. It is a figure which shows the structure of the charged particle beam apparatus of 3rd Embodiment. It is a figure which shows the structure of the charged particle beam apparatus of 4th Embodiment. It is a figure which shows the structure of the charged particle beam apparatus of 5th Embodiment. It is an example of the screen of the display which displays the result of a frequency analysis. It is explanatory drawing of the stability evaluation method of the irradiation position of the electron beam in a prior application patent.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electron source 2 Electron beam 3 Electron optical column 4 Objective lens 5 Deflection lens 6 Sample 7 Detector 8 Console 9 Display 10 Pattern edge 11 Amplifier 12 Image processing apparatus 13 Low pass filter 14 SEM image 15 FFT calculation 16 AC coupling 17 17a First low-pass filter 18 Analog switch 19 Inverting amplifier 20 High resistance 21, 21a Second low-pass filter 22 A / D converter 23 Memory 24 Window processing 25 Averaging processing 26 Offset adjustment 27 Zero interpolation 28 Graph 29 Power spectrum 30 Computer device 40 FPGA (CPLD)
100 charged particle beam equipment

Claims (4)

A function to generate a detection image by irradiating a sample with a charged particle beam and detecting secondary electrons generated from the sample with a detector. Further, it may affect the stability of the irradiation position of the charged particle beam. A charged particle beam apparatus having a function of displaying information on environmental low-frequency environmental disturbances,
AC coupling for removing the offset of the secondary electron detection signal output from the detector;
A low-pass filter that receives an input of the secondary electron detection signal from which the offset is removed, and removes a high-frequency component due to scanning of the charged particle beam;
Complementing means for receiving an input of the secondary electron detection signal from which the high-frequency component has been removed, canceling the discontinuous waveform component at the time of switching of the detected image, and complementing based on the continuous waveform component;
Analyzing means for analyzing the frequency of the waveform of the complemented secondary electron detection signal;
Display means for displaying the result of the frequency analysis as information on the low-frequency environmental disturbance;
A charged particle beam apparatus comprising: The supplement means is
A switch that receives an input of the secondary electron detection signal from which the high-frequency component has been removed, and sets the discontinuous waveform component at the time of switching of the detected image to zero potential;
A second low-pass filter for accepting an input of a secondary electron detection signal in which the discontinuous waveform component is set to zero potential, and complementing the portion set to zero potential based on the continuous waveform component;
The charged particle beam apparatus according to claim 1, comprising: The display means includes
A time history waveform representing a temporal change in fluctuation of the irradiation position of the charged particle beam on the sample and a result of frequency analysis of the time history waveform are displayed, and the time history waveform includes a plurality of the detected images. The charged particle beam device according to claim 1, wherein the charged particle beam device includes waveforms before and after switching. The result of the frequency analysis includes a power spectrum related to a time history waveform representing a temporal change in the variation of the irradiation position of the charged particle beam on the sample. The charged particle beam apparatus according to claim 1.

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