JP4810399B2 - Sample table for electron beam equipment - Google Patents

Description

The present invention relates to an electron beam apparatus that observes a sample with an electron beam, and more particularly to a sample stage used in an electron beam apparatus that scans a sample with an electron beam to observe a secondary electron image and a transmission image.

  As an electron beam apparatus that observes a sample with an electron beam, a scanning electron microscope (SEM) that scans the sample to observe a secondary electron image, and a scanning transmission electron that scans the sample to observe a transmission image There are electron microscopes such as a microscope (Scanning Transmission Electron Microscope: STEM). In such electron microscopes, aberration correction is important for clear image observation with high resolution.

For example, in a length measurement SEM or the like, correction can be performed by providing a standard sample for correcting the focal point and aberration in the apparatus. As a standard sample, as described in Patent Document 1, a sample having an island structure of crystal grains on an amorphous film is suitable for correcting astigmatism. This is because the direction and amount of astigmatism are expressed as an extension of the image in a specific direction, and can be easily corrected using the difference in the appearance of the transmitted image. In other words, the crystal grains themselves are corrected at low magnification, and the transmission images of randomly arranged atoms of the amorphous film are corrected so as not to have directionality at high magnification.
Non-Patent Document 1 describes spherical aberration correction in STEM.

JP 2002-367551 A Kuniyasu Nakamura et al. “Spherical Aberration Correction of Scanning Transmission Electron Microscope and Its Application” Microscope Vol. 41, no. 1, 16-20 pages, 2006 M. Haider, et al., "Ultramicroscopy", 81, p163-175, 2000

  Recently, an aberration correction STEM incorporating an aberration corrector has been developed, and the resolution of an image has been further increased, and accordingly, more precise correction of focus and aberration has become important. In order to appropriately perform focus and aberration correction, the distance between the standard sample and the observation sample is an important factor.

  In the aberration correction STEM, when the distance between the standard sample and the observation sample is increased, the astigmatism and coma aberration change due to the minute change in magnetism of each sample, and correction cannot be performed well. The high-resolution observation conditions may not be transferred to the observation sample.

  In the length measurement SEM, the sample height alignment accuracy is not higher than that of the STEM. For this reason, when the distance between the standard sample and the observation sample is increased, there is a possibility that the optimum electron optical conditions corrected for aberrations at the standard sample position cannot be reproduced at the observation sample position.

In order to be able to observe the observation sample while maintaining the correction conditions obtained by the standard sample, it is important that the standard sample is in the vicinity of 100 μm or less from the observation sample.
However, in the conventional electron beam apparatus, no consideration has been given to the installation location of the standard sample.

  For example, STEM uses a high-resolution pole piece, so the inside of the sample chamber is narrow and the sample holder for the observation sample may come into contact with the standard sample. Therefore, it is difficult to provide the standard sample inside the apparatus. It was.

  In general, an observation sample is obtained by extracting a small sample piece from a sample using a focused ion beam (FIB). In the conventional sample stage for fixing the observation sample thus obtained, it is difficult to place a separate standard sample in the vicinity of the observation sample. The micro sample piece extracted by the FIB as the observation sample is so thick that the electron beam cannot be transmitted, and the correction operation cannot be performed because the observation sample itself has no thin film for correction.

  In addition, since an SEM that can only observe a secondary electron image cannot observe a transmission image, aberration correction using an amorphous film structure cannot be performed.

  Thus, there is a need for means that enables focus and aberration correction in SEM, STEM, and aberration correction STEM using a sample stage for fixing a micro sample piece extracted as an observation sample from a sample using FIB. ing.

  In view of the above, an object of the present invention is to provide a sample stage for an electron beam apparatus that enables focus and aberration correction.

  In the present invention, the above-mentioned problems are solved by providing a plurality of aberration correction holes on the surface on which the electron beam is incident on the electron beam apparatus sample stage for fixing the observation sample.

Preferably, the aberration correction holes have diameters of various sizes of about 10 nm to about 100 nm and are distributed within a range of about 100 μm from the observation sample.
The aberration correction hole may or may not penetrate through the electron beam apparatus sample stage.
The aberration correction hole may have a shape other than a circle .

  According to the present invention, a sample stage for an electron beam apparatus that enables focus and aberration correction is realized.

  The present invention will be described below with reference to the drawings. In these figures, the dimensions of each element are not drawn to scale for clarity.

  FIG. 1 is a plan view showing an example of a basic configuration of a sample stage for an electron beam apparatus according to the present invention. The electron beam apparatus sample stage 1 has a cylindrical shape with a diameter of about 3 mm, and a portion for fixing the observation sample is cut into a rectangle. One or more circular aberration correction holes 2 having a diameter of about 10 nm to about 100 nm are regularly or irregularly distributed on the upper surface of the electron beam apparatus sample table 1 on which the electron beam is incident. Are provided to constitute an aberration correction pattern. In order to improve the correction accuracy, the aberration correction hole 2 is desirably arranged in the vicinity of the observation sample 4, for example, within a range of about 100 μm from the observation sample 4.

  The size of the aberration correction hole is determined for the following reason. FIG. 10 is a diagram for explaining the relationship between defocus and aberration. As shown in FIG. 10, when measuring the shape of the probe image, aberrations are emphasized when the focus is greatly defocused, but there is a measurement limit. Therefore, the defocus amount that is normally used is about ± 100 nm. As described in Non-Patent Documents 1 and 2, generally, a convergence angle for obtaining a resolution of about 0.1 nm in a 200 kV aberration correction STEM is about 20 to 30 mrad. FIG. 11 is a diagram for explaining the relationship between the resolution and the convergence angle. As shown in FIG. 11, when the convergence angle is set to 25 mrad, the shape of the hole with a diameter of 10 nm is changed by 50%, so that the probe image cannot be measured correctly. In addition, if such a hole is observed at a high magnification, there is a problem because sample contamination and sample drift are easily affected.

  On the other hand, since the shape of a 100 nm diameter hole only changes by 5%, the amount of change is too small to be measured correctly. In addition, when the defocus is ± 100 nm or more in a hole having a diameter of 100 nm, the measurement result is not stable due to the hysteresis of the objective lens. FIG. 12 is a graph in which the horizontal axis indicates the shape correction rate and the vertical axis indicates the correction accuracy. For the above reason, the correction accuracy with respect to the shape change rate is as shown in FIG. 12, and therefore the appropriate hole diameter of the aberration correction hole is about 10 nm to about 100 nm.

  2 is a diagram showing the shape of the aberration correction hole 2 shown in FIG. 1, FIG. 2 (a) is a plan view similar to FIG. 1, and FIG. 2 (b) is a straight line AA ′ of FIG. 2 (a). FIG. As shown in FIG. 2B, it is desirable that the cross-sectional shape of the aberration correcting hole 2 is a taper that expands in the direction in which the electron beam 3 is incident so that an edge effect is produced.

  FIG. 13 is a graph showing the relationship between resolution and edge effect and acceleration voltage. The vertical axis represents the resolution and the edge effect, and the horizontal axis represents the acceleration voltage. As shown in FIG. 13, incident electrons are diffused inside the sample as the acceleration voltage is higher. Therefore, information around the electron beam irradiation region is mixed, and the resolution and contrast of the SE (Secondary Electron) image are lowered. Resulting in. However, since the edge effect increases as the accelerating voltage increases, the aberration correction hole can be observed with high contrast by forming a taper shape that widens in the direction in which the electron beam 3 enters. Therefore, since the edge detection rate is improved even at an acceleration voltage of 200 kV, the accuracy of aberration correction is improved.

  FIG. 3 is a plan view showing a position at which the sample 4 is arranged in the electron beam apparatus sample stage 1 shown in FIG. The observation sample 4 is extracted as a small sample piece from the sample by the FIB microsampling method using, for example, an FIB processing apparatus, and fixed at a position as shown in FIG.

  The aberration correction hole may have a shape other than a circle. FIG. 4 is a plan view showing examples of various shapes of the aberration correction holes. The aberration correction hole 2 has a shape other than a circle and is composed of a plurality of curves or straight lines.

  Further, the aberration correction hole does not have to penetrate the sample table for the electron beam apparatus as shown in FIG. FIG. 5 is a cross-sectional view showing the shape of such an aberration correction hole that does not penetrate the electron beam apparatus sample stage. FIG. 5A is a plan view, and FIG. 5B is a straight line in FIG. It is sectional drawing in AA '. As shown in FIG. 5B, the aberration correction holes 6 and 7 are depressions or grooves that do not penetrate the electron beam apparatus sample stage.

  Instead of the aberration correction pattern in the aberration correction hole, an aberration correction thin film may be provided on the electron beam apparatus sample stage. FIG. 6 is a plan view showing a sample stage for an electron beam apparatus having such an aberration correction thin film. An aberration correction thin film 8 is fitted in the electron beam apparatus sample stage 1. The aberration correcting thin film 8 has island-like crystal particles distributed on an amorphous film. The aberration correction thin film 8 is desirably arranged as close to the observation sample 4 as possible, for example, within 100 μm from the observation sample 4.

  Furthermore, instead of the aberration correction pattern in the aberration correction hole, a plurality of deposited metal fine particles having a diameter of about 10 nm to about 100 nm may be provided. FIG. 7 is a plan view showing a sample stage for an electron beam apparatus having aberration correcting metal particles. A plurality of aberration correcting metal fine particles 9 having a diameter of about 10 nm to about 100 nm are deposited on the upper surface of the electron beam apparatus sample stage 1. In order to improve the correction accuracy, the aberration correcting metal fine particles 9 are desirably arranged in the vicinity of the observation sample 4, for example, within a range of about 100 μm from the observation sample 4.

  FIG. 8 is a diagram showing another example of the configuration of the sample stage for the electron beam apparatus of the present invention. In the example shown in this figure, the electron beam apparatus sample stage 10 has a needle-like shape in which a truncated cone-shaped part is placed on a cylindrical part, and is a mechanism capable of rotating 360 ° about the cylindrical and conical axes. Have The observation sample 4 is fixed to the upper surface of the truncated cone portion of the needle-shaped electron beam apparatus sample table 10. One or more circular aberration correction holes 2 having a diameter of about 10 nm to about 100 nm, which are similar to the example shown in FIG. Aberration correction patterns are regularly distributed. It is desirable that the aberration correction hole in FIG. 8 also has a tapered shape that widens in the direction in which the electron beam enters. These aberration correction holes 2 are desirably arranged in the vicinity of the observation sample 4 in order to improve the correction accuracy. For example, the aberration correction holes 2 are arranged within a range of about 100 μm from the observation sample 4. The aberration correction hole 2 in FIG. 8 may also have a shape other than a circle. Furthermore, instead of the aberration correction pattern by the aberration correction hole, the aberration correction thin film 8 shown in FIG. 6 or the aberration correction metal particles 9 shown in FIG. 7 may be provided.

  As an example, a method for using the electron beam apparatus sample stage of the present invention in the aberration correction STEM will be described. The electron beam apparatus sample stage to be used is the same regardless of which one shown in FIGS. 1 to 8 is used. Here, an example will be described using the electron beam apparatus sample stage shown in FIGS.

  First, using a FIB processing observation apparatus or the like, a minute sample piece is extracted from the sample as the observation sample 4 by the FIB microsampling method.

  Next, the sample holder to which the electron beam apparatus sample stage 1 is attached is inserted into the FIB processing observation apparatus, and the extracted observation sample 4 is fixed to the electron beam apparatus sample stage 1 at the position shown in FIG. The thin film is processed to a thickness of about 100 nm.

  After the observation sample 4 is processed into a thin film, a sample holder is inserted into the aberration correction STEM to search for a thin film processed portion of the observation sample 4, and then an aberration correction operation is performed using the hole 2 in the vicinity of the observation sample 4.

  The procedure of such aberration correction operation will be described below with reference to a flowchart. FIG. 9 is a flowchart for explaining an aberration correction procedure by the electron beam apparatus sample stage of the present invention.

In step S901, the field of view moves to a field of view with an aberration correction hole.
In step S902, an SE image / STEM image in under focus (UF) and over focus (OF) is acquired, and each is compared to obtain a primary aberration (astigmatism) and focus. Adjust to the value of.
In step S903, while tilting the electron beam, a plurality of SE images / STEM images having different tilts are acquired in UF and OF, and each is compared to obtain secondary aberration (third-order astigmatism) and coma aberration, Adjust to a predetermined value.
In step S904, in order to adjust in more detail, the number of tilt directions of the electron beam is increased, SE / STEM images are acquired in UF and OF, and the spherical aberration is obtained by comparing each to obtain a predetermined value. Adjust to.
In step S905, the observation sample position is returned to and observation is started.

  Thus, aberration correction is performed by changing the focus and measuring the deconvolution probe images of UF and OF. Therefore, in order to perform correction with high accuracy, it is better that the number of edges of the aberration correction hole is larger and the contrast is higher.

  For aberration correction, SE images are more suitable than STEM images for the following reasons. As described above, since the change in the edge of the aberration correction hole pattern is used for the aberration correction, either the SE image or the STEM image may be used as long as the structure can be clearly observed. However, in order to correct with the STEM image, it is necessary to observe the penetrating pattern, and since the information is integrated in the thickness direction, the edge change does not occur accurately, and the correction accuracy may be reduced.

  On the other hand, the SE image is information on the sample surface, and the change in the edge of the pattern is accurately reflected in the image, so that the correction accuracy improves. Therefore, it is preferable to use an SE image of the aberration correction hole for aberration correction.

  The present invention can be used for a sample stage used in an electron beam apparatus for observing a sample with an electron beam.

It is a top view which shows an example of the fundamental structure of the sample stand for electron beam apparatuses of this invention. It is a figure which shows the shape of the hole for aberration correction, (a) is a top view, (b) is sectional drawing in the straight line AA 'of (a). It is a top view which shows the position which arrange | positions a sample in the sample stand for electron beam apparatuses. It is a top view which shows the example of various shapes of the hole for aberration correction. It is sectional drawing which shows the shape of the hole for aberration correction, (a) is a top view, (b) is sectional drawing in the straight line AA 'of (a). It is a top view which shows the sample stand for electron beam apparatuses which has a thin film for aberration correction. It is a top view which shows the sample stand for electron beam apparatuses which has a metal particle for aberration correction. It is a figure which shows the other example of a structure of the sample stand for electron beam apparatuses of this invention. It is a flowchart explaining the aberration correction procedure by the sample stand for electron beam apparatuses of this invention. It is a figure explaining the relationship between a defocus and an aberration. It is a figure explaining the relationship between resolution and a convergence angle. It is a graph which shows the relationship between a shape change rate and correction accuracy. It is a graph which shows the relationship between resolution, an edge effect, and an acceleration voltage.

Explanation of symbols

1, 10 Sample stage 2, 6, 7 for electron beam apparatus 3 Aberration correction hole 3 Electron beam 4 Observation sample 8 Aberration correction thin film 9 Aberration correction metal particle

Claims (8)

A sample stage for an electron beam apparatus for fixing an observation sample,
A sample stage for an electron beam apparatus, wherein a plurality of aberration correction holes having various dimensions are provided on a surface on which an electron beam is incident.   2. The sample stage for an electron beam apparatus according to claim 1, wherein the diameter of the aberration correcting hole is about 10 nm to about 100 nm.   2. The sample stage for an electron beam apparatus according to claim 1, wherein the aberration correcting hole has a tapered shape that expands in a direction in which the electron beam enters.   2. The sample stage for an electron beam apparatus according to claim 1, wherein the aberration correcting hole is disposed within about 100 [mu] m from the observation sample.   2. The sample stage for an electron beam apparatus according to claim 1, wherein the aberration correcting hole penetrates the sample stage for the electron beam apparatus.   2. The sample table for an electron beam apparatus according to claim 1, wherein the aberration correcting hole does not penetrate the sample table for the electron beam apparatus.   2. The sample stage for an electron beam apparatus according to claim 1, wherein the aberration correcting hole is not circular. The sample table for an electron beam apparatus has a shape in which a truncated cone part is placed on a cylindrical part, and has a mechanism that can rotate 360 ° around the axis of the cylindrical part and the truncated cone part,
The sample is fixed to the upper surface of the truncated cone part,
The sample table for an electron beam apparatus according to claim 1, wherein the aberration correction hole is provided on a side surface of the truncated cone part.

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