JP2017076559A - Scanning type charged particle microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct, in a short time, an irradiation position of a charged particle beam in a scanning type charged particle microscope which scans a sample surface in a range to be measured with the charged particle beam to measure a predetermined physical quantity.SOLUTION: Provided is a scanning type charged particle microscope 1 which comprises: a charged particle beam control part 10 operable to scan a range to be measured with a charged particle beam; a first detector 9 operable to measure a reference image and a partial image; a second detector 11 operable to measure a predetermined physical quantity; a reference image acquisition part 22 operable to scan the range to be measured to acquire the reference image; a physical quantity measurement part 23 operable to scan the range to be measured and measure the predetermined physical quantity; a partial image acquisition part 24 operable to acquire the partial image in parallel with the measurement of the physical quantity; a drift calculating part 25 operable to compare the partial image with the reference image and to determine a drift quantity at an irradiation position; and a charged particle beam correcting part 26 operable to correct the irradiation position of the charged particle beam.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a scanning charged particle microscope, and more particularly to an electron beam microanalyzer that scans a measurement target region on a sample surface with an electron beam and detects characteristic X-rays emitted from the sample.

  In a scanning charged particle microscope, the measurement target range of the surface of the sample placed on the sample stage is scanned with a charged particle beam such as an electron beam to detect secondary electrons and characteristic X-rays emitted from the sample surface. Measure the sample surface shape and element distribution.

  One scanning charged particle microscope is an electron beam microanalyzer (EPMA) that detects a characteristic X-ray emitted from a sample by scanning a measurement target region on the surface of the sample with an electron beam. FIG. 1 shows a main configuration of the electron beam microanalyzer 101. The electron beam emitted from the electron beam source 102 sequentially passes through the focusing lens 103, the scanning coil 104, and the objective lens 105, and is irradiated on the surface of the sample 107 placed on the sample placing table 106. The irradiation position of the electron beam is moved by operating the scanning coil 104 by the driving unit 108 that operates based on a control signal from the control unit 110.

  In the measurement using the electron beam microanalyzer, the measurement target range on the sample surface is scanned with an electron beam, and secondary electrons are detected by the electron detector 109 at predetermined time intervals. Thereby, the intensity | strength of the secondary electron discharge | released from many measurement points spaced apart by the distance according to the said predetermined time interval and the scanning speed of an electron beam is obtained. An output signal from the electron detector 109 is sent to the control unit 110, and a secondary electron image of the measurement target range is created based on the output signal.

  Simultaneous with the detection of the secondary electrons, characteristic X-rays can be detected by the X-ray detector 111. In general, since the intensity of characteristic X-rays emitted from the sample surface is low, this scan is performed at a low speed in order to detect characteristic X-rays with sufficient intensity. Measurement that detects a predetermined physical quantity while scanning an electron beam or a sample stage and creates an image is called mapping.

  When the electron beam microanalyzer 101 continues to irradiate the sample with an electron beam for a long time, there may be a difference between the scanning of the electron beam and the measurement target range of the sample depending on the stability of the sample and the electron beam source. . Therefore, in the electron beam microanalyzer 101, there is a method of correcting the irradiation position of the electron beam during measurement in long-time mapping measurement.

  When correcting the irradiation position of the electron beam, first, a secondary electron image serving as a reference image for correction is acquired before measurement. The scanning for acquiring the reference image is performed at high speed, and when the size of the measurement target range is several μm × several μm, the creation of the reference image is completed in a few seconds. After the measurement is started, every time correction is performed, scanning of the electron beam is temporarily stopped, and a secondary electron image is acquired in the same area as the reference image in terms of control. Then, the obtained secondary electron image is compared with the reference image to determine the drift of the irradiation position of the electron beam, and the drive unit 108 is adjusted so as to cancel the drift. Thereby, the irradiation position of the electron beam on the surface of the sample 107 is corrected. When the correction of the electron beam irradiation position is completed, scanning and measurement are restarted from the position where scanning was stopped in the previous measurement (for example, Patent Documents 1 and 2).

JP 9-43173 A JP 2000-106121 A

  In the conventional method, scanning and measurement are stopped, the electron beam irradiation position is returned to the initial position, the same region as the reference image is scanned to obtain a secondary electron image, and the electron beam irradiation position is corrected. Repeatedly, there is a problem that the measurement time becomes long. On the other hand, if the correction interval is lengthened in order to shorten the measurement time, the uncorrected area becomes large, and there is a problem that a step is generated in the measurement image during correction.

  Here, the case where characteristic X-rays are measured with an electron beam microanalyzer has been described as an example. However, the same problem as described above also occurs when measuring reflected electrons, fluorescence, current, and the like. In addition, there is a problem similar to the above when the measurement target range is scanned with a charged particle beam (for example, an ion beam) other than an electron beam.

  The problem to be solved by the present invention is a scanning charged particle microscope that measures a predetermined physical quantity in a measurement target range by scanning the measurement target range of the surface of the measurement target sample with a charged particle beam such as an electron beam. The measurement is performed while correcting the irradiation position of the charged particle beam without extending the measurement time.

The present invention made to solve the above problems is a scanning charged particle microscope that measures a predetermined physical quantity in a measurement target range by scanning the measurement target range on the surface of the measurement target sample with a charged particle beam. And
a) Charging having a charged particle beam source for generating the charged particle beam and a scanning optical system for controlling the irradiation position of the charged particle beam emitted from the charged particle beam source to scan the measurement object range A particle beam control unit;
b) a first detector for measuring a physical quantity used for a reference image at an irradiation position of the charged particle beam of the measurement target sample;
c) a second detector for measuring the predetermined physical quantity at the irradiation position of the charged particle beam of the measurement target sample;
d) a reference image acquisition unit that scans the measurement target range with a charged particle beam and acquires a reference image of the measurement target range by the first detector;
e) after obtaining the reference image, scanning the measurement object range with a charged particle beam, and measuring the predetermined physical quantity by the second detector;
f) In parallel with the measurement of the predetermined physical quantity by the physical quantity measurement unit, a partial image acquisition unit that acquires a partial image corresponding to a part of the measurement target range by the first detector;
g) Collating the partial image with the reference image to identify the position of the partial image, and the position of the partial image and the charged particle beam control unit set when the partial image is acquired A drift calculation unit that compares the irradiation position and obtains the drift of the irradiation position of the charged particle beam;
h) a charged particle beam correction unit that corrects an irradiation position of the charged particle beam by the charged particle beam control unit based on the drift; and
It is characterized by providing.

The charged particle beam is, for example, an electron beam or an ion beam.
The physical quantity used for the reference image may itself be a measurement target. In that case, since the predetermined physical quantity and the physical quantity used for the reference image are the same physical quantity, one detector can be used as the first detector and the second detector.
The predetermined physical quantity is, for example, characteristic X-rays, fluorescence, reflected electrons, current, or voltage. Further, a plurality of physical quantities may be measured in parallel.

  In the scanning charged particle microscope according to the present invention, first, a measurement target range is scanned with a charged particle beam, and a reference image is acquired based on the detected intensity. Thereafter, the measurement target range is again scanned with the charged particle beam, and one physical quantity is measured simultaneously by the first detector, and a predetermined physical quantity is simultaneously measured by the second detector. Then, a partial image corresponding to a part of the measurement target range is acquired from the detection result by the first detector, and the position of the partial image is obtained by collating the partial image with the reference image. The position of the partial image obtained in this way is compared with the position where the charged particle beam should be irradiated (the control position of the charged particle beam) to determine the drift of the charged particle beam irradiation position, and charging is performed so as to cancel the drift. Correct the irradiation position of the particle beam. In this scanning electron microscope, in parallel with the measurement to acquire a predetermined physical quantity, the drift of the irradiation position of the charged particle beam is obtained and the irradiation position of the charged particle beam is corrected. Time can be shortened.

In the scanning charged particle microscope according to the present invention,
It is desirable that the charged particle beam correction unit corrects the irradiation position of the charged particle beam when the irradiation position of the charged particle beam reaches the end of the measurement target range.

  The conventional scanning charged particle microscope has a problem that when the charged particle beam irradiation position is corrected at a position other than the end of the measurement target range, the two-dimensional image becomes discontinuous and unnatural. On the other hand, in the charged particle microscope of the above aspect, since the irradiation position of the charged particle beam is corrected when the irradiation position of the charged particle beam is located at the end of the measurement target range, a continuous and natural two-dimensional image is acquired. be able to.

The partial image acquisition unit divides the partial image into a plurality of images,
It is preferable that the drift calculation unit obtains a division drift by comparing each of the plurality of images with a reference image, and obtains the drift based on the division drift.

  When the contrast of the reference image in the measurement target range is small, it may be difficult to accurately check the partial image and the reference image. If the position of the partial image is specified incorrectly, the irradiation position of the charged particle beam cannot be corrected correctly. As described above, by dividing the partial image into a plurality of images, obtaining a division drift for each of the plurality of images, and obtaining a drift based on the plurality of division drifts, the position of the partial image is incorrect. Therefore, the irradiation position of the charged particle beam can be accurately corrected. In this aspect, for example, it is possible to perform a statistical process in which an outlier is excluded from a plurality of division drifts and a drift is obtained from the remaining average value.

  By using the scanning charged particle microscope according to the present invention, it is possible to perform measurement for acquiring a two-dimensional image while correcting the irradiation position of the charged particle beam in a shorter time than before.

The principal part block diagram of the conventional electron beam microanalyzer. BRIEF DESCRIPTION OF THE DRAWINGS The principal part block diagram of the electron beam microanalyzer which is one Example of the scanning charged particle microscope which concerns on this invention. The figure explaining the scanning of the measurement object range in the electron beam microanalyzer of a present Example. An example of the reference | standard image in a present Example. The figure explaining collation of a divided image in this example, and calculation of drift.

  An electron beam microanalyzer that is one embodiment of a scanning charged particle microscope according to the present invention will be described below with reference to the drawings.

  The electron beam microanalyzer 1 according to this embodiment is an apparatus that irradiates a sample 7 placed on a sample placing table 6 with an electron beam and detects electrons and characteristic X-rays emitted therefrom. An electron beam microanalyzer 1 includes an electron beam source 2, a focusing lens 3 that focuses an electron beam emitted from the electron beam source 2, a scanning coil 4 that moves an irradiation position of the electron beam, an objective lens 5, and the scanning coil 4. An electron beam control unit 10 having a driving unit 8 for operating the electron beam, an electron detector 9 (PMT) for detecting electrons emitted from the sample 7, an X-ray detector 11 for detecting characteristic X-rays, and operations of the respective units The control part 20 which controls is provided.

  In addition to the storage unit 21, the control unit 20 includes a reference image acquisition unit 22, a physical quantity measurement unit 23, a partial image acquisition unit 24, a drift calculation unit 25, and a charged particle beam correction unit 26 as functional blocks. The entity of the control unit 20 is a personal computer in which a required OS and software are installed, and the input unit 30 and the display unit 40 are connected. The storage unit 21 stores the size of the measurement target range on the surface of the sample 7, the arrangement of measurement points in the measurement target range, the scanning speed (first speed, high speed) at the time of acquiring a reference image, Measurement condition information including a second speed, a low speed), and a partial image acquisition time interval is determined and stored in advance by the user. Details of these will be described later.

  In this embodiment, each measurement point arranged in a grid of 640 × 480 is sequentially irradiated onto a rectangular measurement target range on the surface of the sample 7, and the intensity of characteristic X-rays emitted from each point is measured. taking measurement. Each measurement point is represented as P (1,1), P (2,1),..., P (640,480), and is positioned as shown in FIG. P (1,1) is the initial position (scanning start position) of electron beam irradiation, and P (640,480) is the scanning end position. When scanning the measurement target range with the electron beam, the electron beam control unit 10 moves the electron beam irradiation position from the measurement point P (1, 1) in the X-axis direction, and the measurement point P (640, 1) located at the end. ) Is moved in the Y-axis direction (Y direction), and then the electron beam irradiation position is moved from the measurement point P (1, 2) to the measurement point P (640, 2). That is, the movement in the X direction (line scanning) and the movement in the Y direction are repeated, and when the measurement point P (640, 480) that is the end position is reached, the irradiation position of the electron beam is set to the measurement point P (1, 1, the initial position). Move to 1).

Next, the sample measurement operation using the electron beam microanalyzer 1 of the present embodiment will be described.
When the user instructs the start of measurement, the electron beam control unit 10 moves the electron beam at a high speed as described above at the first speed stored in the storage unit 21. Then, secondary electrons emitted from the sample 7 are detected by the electron detector 9 at each measurement point at a time interval corresponding to the separation interval between the first speed and the measurement point. The output from the electron detector 9 is sequentially accumulated in the storage unit 21, and based on the detection result of the secondary electrons, the reference image acquisition unit 22 performs a reference image (640 pixels × 640 pixels) that is a secondary electron image of the entire measurement target range. 480 pixel image). FIG. 4 shows an example of the reference image.

  When the reference image is obtained, the electron beam control unit 10 reduces the irradiation position of the electron beam from the measurement point P (1, 1), which is the initial position, at the second speed stored in the storage unit 21 as described above. Move with. Then, the physical quantity measuring unit 23 detects the characteristic X-rays emitted from the sample 7 at each measurement point at the time interval corresponding to the separation interval between the second speed and the measurement point, and in parallel with this. Then, the partial image acquisition unit 24 detects secondary electrons by the electron detector 9. Outputs from the X-ray detector 11 and the electron detector 9 are sequentially stored in the storage unit 21.

  When the time corresponding to the acquisition time interval of the partial images stored in the storage unit 21 has elapsed since the start of the movement of the electron beam at the second speed, the partial image acquisition unit 24 stores the secondary electrons accumulated in the storage unit. A partial image is created using the detection result. In this embodiment, a partial image is created every time the irradiation position of the electron beam is moved four times in the X-axis direction (every four lines are scanned). FIG. 5A shows an example of the partial image. The example shown in FIG. 5A is a secondary electron image acquired near the center (in the Y-axis direction) in the measurement target range.

  When the partial image as shown in FIG. 5A is acquired, the partial image acquisition unit 24 further divides it into a plurality of divided images having a predetermined size. In this embodiment, the image is divided into eight divided images each having a size of 4 pixels × 80 pixels as shown in FIG.

When the divided images are created, the drift calculator 25 collates each divided image with the reference image (pattern matching), and determines the position on each reference image (FIG. 5C). In FIG. 5C, a position indicated by a broken line is an ideal irradiation position of the electron beam by the electron beam control unit 10, and a position indicated by a solid line is a collation position of each divided image. When the position of each divided image is determined, the ideal irradiation position and the collation position are compared for each, and the drift amount and the drift direction of the electron beam are obtained. The length of the arrow in FIG. 5C is the drift amount, and the direction of the arrow is the drift direction. That is, this arrow is a vector representing the drift of each divided image (drift vector, corresponding to the divided drift in the present invention). When the drift vectors of all the divided images are determined, the correction direction and correction amount (distance) of the electron beam irradiation position are determined based on these drift vectors. For example, the correction direction and the correction amount can be obtained by averaging the drift amounts and directions of a plurality of divided images (eight in this embodiment).
The above processing by the partial image acquisition unit 24 and the drift calculation unit 25 is performed in parallel with the movement of the electron beam by the electron beam control unit 10 and the detection of characteristic X-rays and secondary electrons.

When the correction direction and correction amount of the electron beam irradiation position are determined, the charged particle beam correction unit 26 confirms the electron beam irradiation position at that time, and the irradiation position is at the end of the measurement target range in the X-axis direction. Wait until the measurement point is located. Then, when the detection of X-rays and secondary electrons at the measurement point is completed and the irradiation position of the electron beam is moved in the Y-axis direction, electrons are corrected using the correction direction and correction amount determined by the drift calculation unit 25. Correct the irradiation position.
The acquisition of the partial image, creation of the divided image, calculation of the drift vector, and correction of the electron beam irradiation position are repeatedly performed from the start to the end of scanning of the measurement target range. In the second and subsequent drift calculations, partial images acquired after the previous drift calculation are used.

  In the electron beam microanalyzer 1 of the present embodiment, the drift of the electron beam irradiation position from the partial image is performed without stopping the operation of moving the electron beam at the second speed at a low speed and measuring characteristic X-rays emitted from the irradiation position. And correct the electron beam irradiation position. Therefore, the measurement time is shortened compared to the conventional apparatus that stops the above operation every time the electron beam irradiation position is corrected.

  Further, in the electron beam microanalyzer 1 of the present embodiment, the charged particle beam correction unit 26 waits until the irradiation position of the electron beam reaches the end of the measurement target range, and the electron beam from the measurement point of the end is measured. When changing the irradiation position, the electron beam irradiation position is corrected. Therefore, a continuous and natural two-dimensional image (in this embodiment, a two-dimensional distribution image of a specific element) is obtained.

  Furthermore, in the electron beam microanalyzer 1 of the present embodiment, the partial image acquisition unit 24 divides the acquired partial image into a plurality of (eight) divided images, and obtains the drift amount and direction for each of them.

When the contrast of the reference image in the measurement target range is small, it may be difficult to accurately match (pattern matching) the partial image and the reference image. Even in such a case, as in the present embodiment, the partial image is divided into a plurality of divided images, and each of the plurality of divided images is subjected to pattern matching to obtain a plurality of drift amounts and drift directions (divided drifts). Since the electron beam irradiation position correction direction and amount are determined, the electron beam irradiation position can be corrected more accurately.
In the above embodiment, as the simplest example, the example in which the drift vectors of a plurality of divided images are averaged to correct the electron beam irradiation position has been described. Various methods can be used, such as determining the correction amount and direction of the electron beam by averaging after removing the outlier of the amount.

The above-described embodiment is an example, and can be appropriately changed in accordance with the gist of the present invention.
Although the electron beam microanalyzer has been described as an example in the above embodiment, an ion beam can be used as an excitation source instead of the electron beam. In the above embodiment, secondary electrons (physical quantities used in the reference image in the present invention) are detected to create a reference image, and characteristic X-rays (predetermined physical quantities in the present invention) are detected to detect the secondary element of a specific element. Although it is configured to obtain a dimensional distribution image, other physical quantities (such as reflected electrons and fluorescence) can be detected as the physical quantity used for the reference image and the predetermined physical quantity, and the present invention is used in various scanning charged particle microscopes. Can be used. Furthermore, the physical quantity itself used for the reference image may be a measurement target.

Moreover, although the example which calculates | requires drift amount using the some divided image was demonstrated in the said Example, you may make it obtain | require drift amount by pattern-matching a partial image as it is.
Furthermore, in the above embodiment, when one two-dimensional image is acquired, an example in which the electron beam irradiation position is corrected by waiting until the electron beam irradiation position is located at the end of the measurement target range has been described. In a configuration in which a plurality of two-dimensional images are acquired by repeatedly scanning the measurement target range, the electron beam irradiation position is corrected each time one two-dimensional image is acquired (that is, every time the measurement target range is scanned). You can also

DESCRIPTION OF SYMBOLS 1 ... Electron beam microanalyzer 2 ... Electron beam source 3 ... Condensing lens 4 ... Scanning coil 5 ... Objective lens 6 ... Sample mounting base 7 ... Sample 8 ... Drive part 9 ... Electron detector 11 ... X-ray detector 20 ... Control part DESCRIPTION OF SYMBOLS 21 ... Memory | storage part 22 ... Reference | standard image acquisition part 23 ... Physical quantity measurement part 24 ... Partial image acquisition part 25 ... Drift calculation part 26 ... Charged particle beam correction | amendment part 30 ... Input part 40 ... Display part

Claims (5)

A scanning charged particle microscope that measures a predetermined physical quantity in a measurement target range by scanning the measurement target range on the surface of a measurement target sample with a charged particle beam,
a) Charging having a charged particle beam source for generating the charged particle beam and a scanning optical system for controlling the irradiation position of the charged particle beam emitted from the charged particle beam source to scan the measurement object range A particle beam control unit;
b) a first detector for measuring a physical quantity used for a reference image at an irradiation position of the charged particle beam of the measurement target sample;
c) a second detector for measuring the predetermined physical quantity at the irradiation position of the charged particle beam of the measurement target sample;
d) a reference image acquisition unit that scans the measurement target range with a charged particle beam and acquires a reference image of the measurement target range by the first detector;
e) after obtaining the reference image, scanning the measurement object range with a charged particle beam, and measuring the predetermined physical quantity by the second detector;
f) In parallel with the measurement of the predetermined physical quantity by the physical quantity measurement unit, a partial image acquisition unit that acquires a partial image corresponding to a part of the measurement target range by the first detector;
g) Collating the partial image with the reference image to identify the position of the partial image, and the position of the partial image and the charged particle beam control unit set when the partial image is acquired A drift calculation unit that compares the irradiation position and obtains the drift of the irradiation position of the charged particle beam;
h) a charged particle beam correction unit that corrects an irradiation position of the charged particle beam by the charged particle beam control unit based on the drift; and
A scanning charged particle microscope comprising:   2. The scanning according to claim 1, wherein the charged particle beam correction unit corrects the irradiation position of the charged particle beam when the irradiation position of the charged particle beam reaches an end of the measurement target range. Type charged particle microscope.   2. The scanning charged particle microscope according to claim 1, wherein the charged particle beam correction unit corrects an irradiation position of the charged particle beam when the scanning of the measurement target range by the charged particle beam is completed. . The partial image acquisition unit divides the partial image into a plurality of images,
The charged particle according to claim 1, wherein the drift calculation unit obtains a divided drift amount by comparing each of the plurality of images with a reference image, and obtains the drift amount based on the divided drift amount. microscope.   The scanning according to claim 1, wherein the charged particle beam is an electron beam, a physical quantity used for the reference image is a secondary electron, and the second detector is an X-ray detector. Type charged particle microscope.