JP6014801B2 - Micro-site imaging device - Google Patents

Description

  The present invention relates to a microscopic region imaging apparatus, and more particularly to a microscopic region imaging apparatus that images a sample.

  In general, an ion beam having a minute spot such as a focused ion beam is used in a time-of-flight secondary ion mass spectrometer (TOF-SIMS), a scanning electron microscope (SEM), or the like. For example, if TOF-SIMS is used, scanning ion microscope (SIM) image observation can be performed with high resolution, and a secondary ion image can be obtained by combining this with a mass spectrometer. By obtaining a secondary ion image, it is possible to image a fine portion of the sample and perform various analyses. When acquiring a secondary ion image, the surface image may be observed with a SIM image in order to set the field of view, but the sample is irradiated with an ion beam prior to analysis, and the surface of the sample is worn or altered. Is inevitable.

  Further, for example, in TOF-SIMS, an ion beam is irradiated toward the sample surface, and a DC high voltage is applied between the sample surface and the analyzer to generate a so-called extraction electric field to generate a secondary to the mass spectrometer. Ions are being drawn. However, the irradiated ion beam is bent due to the influence of the applied extraction electric field, and the ion beam is irradiated to a position different from the desired irradiation position. As a result, the secondary ion image is shifted. It is known. In acquiring a secondary ion image, the direction of the extraction electric field applied to each of the positive secondary ion and the negative secondary ion is reversed, and therefore, between the positive secondary ion image and the negative secondary ion image. The problem of misalignment arises. Furthermore, the positional deviation also becomes a problem in a scanning electron microscope that observes the surface of a sample using an electron beam.

  For example, Patent Document 1 discloses a focused ion beam apparatus that corrects such positional deviation. In Patent Document 1, the amount of movement of the secondary ion image is measured in advance, and the XY stage on which the sample is placed is moved according to the amount of movement, or the scanning electrode of the focused ion beam is controlled. Thus, the deviation of the secondary ion image is corrected. Even in this case, since it is necessary to measure the amount of movement by irradiating the focused ion beam in advance, wear and alteration of the sample surface cannot be avoided. Furthermore, in the case of an uneven sample, it is difficult to accurately predict the amount of movement. Further, since the beam is bent when the extraction electric field is applied and measurement is performed in this state, there is a problem that the incident angle of the beam with respect to the sample changes strictly.

  Further, for example, in Patent Document 2, a detection ion is registered in advance in a sample, and a focused ion beam apparatus that corrects an irradiation position of an ion beam by calculating a shift amount of position information based on the registered mark. Is disclosed. Even in this case, since the imaged secondary ion image is generated with the focused focused ion beam being bent, the secondary ion image may be distorted, and only the position correction is performed. In some cases, it could not be corrected sufficiently. Furthermore, in the case of an uneven sample, it is difficult to accurately predict the amount of movement.

  In addition, Non-Patent Document 1 discloses TOF-SIMS that achieves high resolution by a delay extraction method. In this method, ions generated by ion beam irradiation are free-flighted without acceleration, and are extracted after being delayed by several hundred ns after ion beam irradiation. As a result, the generated ions can be simultaneously extracted and the mass resolution can be improved.

JP-A-8-227145 JP 2010-9987 A

Koichi Tanaka, Takaya Sato, Kenichi Yoshino “Basics of Delayed Extraction” Japan Society for Mass Spectrometry, 2009, Vol. 57, no. 1, p. 31-36

  In order to prevent the displacement of the irradiation position of the focused ion beam during SIM image observation, SEM image observation, and acquisition of positive secondary ion images and negative secondary ion images, in any case, analysis with the sample surface Considering the straightness of the focused ion beam or electron beam, it is best to apply no drawing electric field to the apparatus and to have no electric field. However, unless an electric field is applied, secondary ions generated on the surface cannot be taken into the mass spectrometer. This point cannot be solved by the above-mentioned Patent Document 1 and Patent Document 2.

  Furthermore, in the technique of Non-Patent Document 1, if the delay time is too long, the generated ions are dissipated and cannot be extracted to the mass spectrometer, resulting in a decrease in sensitivity. Further, it was difficult to determine how much delay time should be set.

  In view of such circumstances, the present invention is intended to provide a microscopic region imaging apparatus capable of obtaining a secondary ion image under an optimized condition without causing a shift in irradiation position of a focused ion beam. .

  In order to achieve the above-described object of the present invention, a micro-site imaging apparatus according to the present invention includes a focused ion beam irradiation unit that irradiates a target sample with a focused ion beam in pulses, and a focused ion of the focused ion beam irradiation unit. An ion beam pulse control unit capable of controlling the pulse timing of the beam, an imaging unit for generating a secondary ion image from secondary ions excited by the focused ion beam irradiated from the focused ion beam irradiation unit, and focused ions An extraction electric field generation unit that applies an extraction electric field in a pulsed manner to a secondary ion excited by the focused ion beam irradiated from the beam irradiation unit at a timing when the focused ion beam is not irradiated; An extraction electric field pulse controller that can control the pulse timing of the extraction electric field and an ion beam pulse control A secondary ion image comparison unit for comparing and analyzing a secondary ion image generated by the imaging unit by image recognition when the delay time of the pulse timing by the extraction electric field pulse control unit is different from the pulse timing by the unit, and a secondary ion A delay time determining unit that determines a delay time of the pulse timing by the extraction electric field pulse control unit with respect to the pulse timing by the ion beam pulse control unit based on a comparison result by the image comparison unit.

  Here, the delay time determination unit may determine the optimum delay time by feedback control.

  Furthermore, an electron beam irradiation unit that irradiates the target sample with an electron beam in a pulsed manner, and an electron beam pulse control unit that can control the pulse timing of the electron beam of the electron beam irradiation unit, and the imaging unit, A secondary electron image is also generated from the secondary electrons excited by the electron beam irradiated from the electron beam irradiation unit, and the secondary ion image comparison unit performs a pulse by the extraction electric field pulse control unit with respect to the pulse timing by the electron beam pulse control unit. The secondary electron image generated by the imaging unit when the timing delay time is varied is also compared and analyzed by image recognition, and the delay time determining unit is an electron beam pulse control unit based on the comparison result of the secondary ion image comparing unit. Also determine the delay time of the pulse timing by the extraction electric field pulse controller with respect to the pulse timing by It may be of.

  Further, the focused ion beam irradiation unit and the electron microscope may be arranged so as to be 45 degrees with respect to the surface normal of the table on which the sample is placed.

  The fine site imaging apparatus of the present invention has an advantage that a secondary ion image can be obtained under optimized conditions without causing a shift in the irradiation position of the focused ion beam.

FIG. 1 is a schematic block diagram for explaining a microscopic region imaging apparatus of the present invention. FIG. 2 is a graph showing changes in secondary ion intensity with respect to delay time. FIG. 3 is an example in which the secondary ion image is blurred. FIG. 4 is a schematic block diagram for explaining another embodiment of the microscopic region imaging apparatus of the present invention. FIG. 5 is a specific example of each image obtained by the fine region imaging apparatus of the present invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described together with illustrated examples. FIG. 1 is a schematic block diagram for explaining a microscopic region imaging apparatus of the present invention. As shown in the figure, the fine region imaging apparatus of the present invention for imaging a sample includes a focused ion beam irradiation unit 10, an ion beam pulse control unit 20, an imaging unit 30, an extraction electric field generation unit 40, and an extraction electric field pulse control. The unit 50, the secondary ion image comparison unit 60, and the delay time determination unit 70 are mainly configured. A sample 1 as a target is placed on a table 2. The table 2 may be an XY stage made of, for example, a conductor.

  The focused ion beam irradiation unit 10 is a device that can irradiate a sample 1 as a target with a focused ion beam (FIB) in a pulse shape. The focused ion beam irradiation unit 10 focuses a beam obtained by accelerating ions with an electric field and irradiates the target. By using the focused ion beam irradiation unit 10 and switching to the direct current mode instead of the pulse mode, it is possible to observe the SIM image. The SIM image is obtained by observing the state of the sample surface by measuring secondary electrons popping out from the sample 1 when the sample 1 is irradiated with the ion beam. The focused ion beam irradiation unit 10 is configured to be able to irradiate the ion beam in a pulse shape, and the target is irradiated with the ion beam at a predetermined pulse timing (pulse width, pulse period). This pulse timing is configured to be controllable by an ion beam pulse controller 20 described later.

  The ion beam pulse control unit 20 can control the pulse timing of the focused ion beam of the focused ion beam irradiation unit 10. For example, the ion beam pulse control unit 20 may intermittently shift control the electrodes of the sweep mechanism of the focused ion beam irradiation unit 10. Thereby, the focused ion beam is controlled to intermittently pass through the opening of the aperture plate, and the ion beam that has intermittently passed becomes a pulse shape. The pulse timing of the pulsed ion beam is controlled by the ion beam pulse controller 20. For example, the ion beam pulse control unit 20 is a pulse power source for driving the electrodes of the sweep mechanism of the focused ion beam irradiation unit 10, as long as the pulse timing can be controlled using the pulse period of the pulse power source. good.

  The imaging unit 30 generates a secondary ion image from secondary ions excited by the focused ion beam irradiated from the focused ion beam irradiation unit 10. Specifically, the imaging unit 30 may be, for example, a time-of-flight mass spectrometer (TOF-MS) or a time-of-flight secondary ion mass spectrometer (TOF-SIMS). Secondary ions excited by the focused ion beam are drawn into the imaging unit 30 by an extraction electric field generated by an extraction electric field generation unit 40 described later.

  The extraction electric field generating unit 40 applies an extraction electric field in a pulsed manner to the secondary ions excited by the focused ion beam irradiated from the focused ion beam irradiation unit 10 at a timing when the focused ion beam is not irradiated. It is. Secondary ions excited by the focused ion beam are extracted toward the imaging unit 30 by the extraction electric field generated by the extraction electric field generation unit 40. The extraction electric field of the extraction electric field generating unit 40 is applied in the opposite direction during positive secondary ion analysis and negative secondary ion analysis. The extraction electric field generation unit 40 is composed of a high voltage pulse circuit using, for example, a power transistor, and applies an extraction electric field between the table 2 and the imaging unit 30 at a predetermined pulse timing (pulse width, pulse period). Anything is possible. This pulse timing is configured to be controllable by an extraction electric field pulse control unit 50 described later. Since the extraction electric field is applied at a timing when the focused ion beam is not irradiated, the irradiation timing of the ion beam pulse is set to a non-electric field condition where the extraction electric field is not applied. Therefore, there is no possibility that the ion beam is bent, and the image at the intended position is generated in the imaging unit 30.

  The extraction electric field pulse control unit 50 can control the pulse timing of the extraction electric field of the extraction electric field generation unit 40. The extraction electric field pulse control unit 50 only needs to be able to turn on / off the power transistor, for example, so as to output the pulse voltage of the extraction electric field generation unit 40 at a predetermined pulse timing.

  The secondary ion image comparison unit 60 performs comparative analysis of the secondary ion image generated by the imaging unit 30 by image recognition. The secondary ion image to be comparatively analyzed is an image when the delay time of the pulse timing by the extraction electric field pulse control unit 50 with respect to the pulse timing by the ion beam pulse control unit 20 is varied.

  FIG. 2 shows a graph of change in secondary ion intensity with respect to the delay time. FIG. 2A shows a case where various parameters of the mass spectrometer are optimized when delay extraction is not performed, that is, in a condition where an extraction electric field is already applied at the time of focused ion beam irradiation. This is the secondary ion intensity when it is increased. FIG. 2B shows the case where delay extraction is performed, that is, for example, when the delay time is 0.25 μs, various parameters of the mass spectrometer as the imaging unit 30 are optimized, and the delay time is gradually increased. The secondary ionic strength of the case. In FIG. 2A, the delay time of 0 μs means that the extraction electric field is applied simultaneously with the focused ion beam irradiation, and means that the region where the delay time is positive performs the delay extraction. As can be seen from FIG. 2A, the secondary ion intensity becomes maximum at a delay time of about 0.1 μs, and thereafter decreases rapidly. This is because, if the delay time is excessive, the secondary ions emitted from the sample surface are spatially dissipated and the rate of secondary ion incorporation into the imaging unit 30 is reduced. On the other hand, as can be seen from FIG. 2 (b), the secondary ion intensity becomes maximum at the optimized delay time, and thereafter, as in FIG. 2 (a), the delay time becomes excessive, and the secondary ions released from the sample surface. Ions are spatially dissipated, the secondary ion uptake rate into the imaging unit 30 is reduced, and the secondary ion intensity is rapidly reduced. Thus, when the delay time is excessive, the problem of a decrease in secondary ion intensity, that is, a decrease in sensitivity appears, and therefore the delay time should be shortened. However, the high voltage pulse for creating the extraction electric field generated by the extraction electric field generation unit 40 has a certain transition time until it reaches a predetermined high voltage from the zero electric field state. If the delay time is shortened so as to contact within this period, an extraction electric field is applied during irradiation of the focused ion beam. As a result, the focused ion beam is bent, and the secondary ion image appears as a superposition of an image without an electric field and an image with an electric field applied, that is, the obtained image is blurred. FIG. 3 shows an example in which the secondary ion image is blurred. Thus, if a change in the electric field occurs during beam irradiation, it causes blurring of the secondary ion image. Therefore, in the fine region imaging apparatus of the present invention, the generated secondary ion image is comparatively analyzed by image recognition using the secondary ion image comparison unit 60. Here, it is determined whether or not an image in which the secondary ion image is superimposed or an image in which the delay time is different between the images is a misaligned image. Here, as image recognition, for example, a difference between images may be detected, or a feature point in the image may be extracted to extract a movement amount of the feature point, thereby detecting a positional deviation of the image. Such an image recognition technique may be a conventional technique or a technique that will appear in the future.

  Then, the delay time determination unit 70 determines the delay time of the pulse timing by the extraction electric field pulse control unit with respect to the pulse timing by the ion beam pulse control unit 20 based on the comparison result by the secondary ion image comparison unit 60. That is, the delay time of the pulse timing is determined based on the comparison result by the secondary ion image comparison unit 60 so that the secondary ion image is not superimposed and the image is not misaligned. In other words, the delay time is started from approximately zero and is delayed until the secondary ion image is not displaced, and the delay time at which the displacement is not displaced may be used as the pulse timing.

  With this configuration, the fine region imaging apparatus of the present invention can obtain a secondary ion image under optimized conditions without causing a shift in the irradiation position of the focused ion beam.

  Further, the delay time determination unit 70 may determine the optimum delay time by feedback control in order to prevent the optimum delay time from deviating due to, for example, a temperature condition that changes from moment to moment. That is, the delay time determination unit 70 may determine the delay time only once when observing a new sample, or performs feedback control during observation, for example, while trying to shorten the delay time, misalignment occurs. In such a case, feedback control can be performed so as to increase the delay time.

  FIG. 4 is a schematic block diagram for explaining another embodiment of the microscopic region imaging apparatus of the present invention. In the figure, the portions denoted by the same reference numerals as those in FIG. In the illustrated example, an electron beam irradiation unit 80 for irradiating the target sample 1 with an electron beam in a pulsed manner is further provided in the example of FIG. The positional relationship between the electron beam irradiation unit 80 and the focused ion beam irradiation unit 10 is not particularly limited, but may be arranged so as to be 45 degrees with respect to the surface normal of the table 2 on which the sample 1 is placed. . The electron beam irradiation unit 80 may be an electron microscope, for example. The sample can be irradiated with an electron beam by the electron beam irradiation unit 80, and an image obtained from secondary electrons generated therefrom can be observed. Since this electron beam is also affected by the extraction electric field, if the electron beam is applied while the extraction electric field is applied, the electron beam bends and image displacement becomes a problem. Therefore, in this example as well, an electron beam pulse control unit 90 that can control the pulse timing of the electron beam of the electron beam irradiation unit 80 may be provided. If the pulse timing of the focused ion beam and the pulse of the electron beam are synchronized, the same portion can be observed with a scanning electron microscope even during irradiation of the focused ion beam. However, for example, if the irradiation area of the focused ion beam is determined in advance, the electron beam need not be pulsed.

  The imaging unit 30 also generates a secondary electron image from secondary electrons excited by the electron beam irradiated from the electron beam irradiation unit 80. The secondary ion image comparison unit 60 also generates a secondary electron image generated by the imaging unit when the delay time of the pulse timing by the extraction electric field pulse control unit 50 is different from the pulse timing by the electron beam pulse control unit 90. Perform comparative analysis by image recognition. Further, the delay time determination unit 70 may determine the delay time of the pulse timing by the extraction electric field pulse control unit 50 with respect to the pulse timing by the electron beam pulse control unit 90 based on the comparison result by the secondary ion image comparison unit 60.

  By comprising in this way, it becomes possible to obtain a secondary electron image (SEM image), a scanning ion microscope image (SIM image), a positive secondary ion image, and a negative secondary ion image all without a position shift. FIG. 5 shows a specific example of each image obtained by the fine region imaging apparatus of the present invention. The upper row is an image obtained by the fine region imaging apparatus of the present invention, and the lower row is an image obtained as a comparative example while applying an extraction electric field without performing delay control. The irradiation position of the focused ion beam and the irradiation position of the electron beam were made to coincide with the same position on the sample in the absence of an extraction electric field. In the comparative example, it can be seen that when the extraction electric field is applied, the focused ion beam and the electron beam are changed by the electric field and are displaced from each other vertically. In addition, when acquiring a positive secondary ion image or a negative secondary ion image, the direction of the electric field is reversed. On the other hand, in the fine region imaging apparatus of the present invention, since no electric field is maintained at the moment when the focused ion beam or electron beam is irradiated, no displacement occurs in any image, and It can be seen that there is no image blur because there is no fluctuation of the electric field during beam irradiation. In addition, since the image is generated in a state where the delay time is always optimized, all of the obtained images are clear.

  It should be noted that the fine region imaging apparatus of the present invention is not limited to the illustrated examples described above, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Sample 2 Table 10 Focused ion beam irradiation part 20 Ion beam pulse control part 30 Imaging part 40 Extraction electric field generation part 50 Extraction electric field pulse control part 60 Secondary ion image comparison part 70 Delay time determination part 80 Electron beam irradiation part 90 Electron beam Pulse control unit

Claims (4)

A micro site imaging apparatus for imaging a sample, the micro site imaging apparatus comprising:
A focused ion beam irradiation unit that irradiates the target sample with a focused ion beam in a pulsed manner; and
An ion beam pulse control unit capable of controlling the pulse timing of the focused ion beam of the focused ion beam irradiation unit;
An imaging unit for generating a secondary ion image from secondary ions excited by the focused ion beam irradiated from the focused ion beam irradiation unit;
An extraction electric field generating unit that applies an extraction electric field in a pulsed manner to a secondary ion excited by the focused ion beam irradiated from the focused ion beam irradiation unit at a timing when the focused ion beam is not irradiated;
An extraction electric field pulse control unit capable of controlling the pulse timing of the extraction electric field of the extraction electric field generation unit;
A secondary ion image comparison unit for comparing and analyzing secondary ion images generated by the imaging unit by image recognition when the delay time of the pulse timing by the extraction electric field pulse control unit is different from the pulse timing by the ion beam pulse control unit When,
A delay time determination unit that determines a delay time of the pulse timing by the extraction electric field pulse control unit with respect to the pulse timing by the ion beam pulse control unit according to the comparison result by the secondary ion image comparison unit;
A microscopic region imaging apparatus comprising:   2. The microscopic region imaging apparatus according to claim 1, wherein the delay time determining unit determines an optimal delay time by feedback control. The fine region imaging apparatus according to claim 1 or 2, further comprising: an electron beam irradiation unit configured to irradiate the target sample with an electron beam in a pulsed manner;
An electron beam pulse control unit capable of controlling the pulse timing of the electron beam of the electron beam irradiation unit,
The imaging unit also generates a secondary electron image from secondary electrons excited by the electron beam irradiated from the electron beam irradiation unit,
The secondary ion image comparison unit compares the secondary electron image generated by the imaging unit by image recognition when the delay time of the pulse timing by the extraction electric field pulse control unit is different from the pulse timing by the electron beam pulse control unit. Parse and
The delay time determination unit also determines the delay time of the pulse timing by the extraction electric field pulse control unit with respect to the pulse timing by the electron beam pulse control unit, based on the comparison result by the secondary ion image comparison unit.
A fine region imaging apparatus characterized by the above.   4. The fine region imaging apparatus according to claim 3, wherein the focused ion beam irradiation unit and the electron microscope are respectively arranged so as to be 45 degrees with respect to a surface normal of a table on which a sample is placed. Micro site imaging device.