JPH05266853A - Beam position decision method and device for microbeam apparatus - Google Patents

Abstract

PURPOSE:To make direct decision of the positional relation for each beam on a specimen, by forming, with the use of an electronic lens, an image obtained by projection of secondary electrons emitted from the specimen through irradiation of at least two beams thereupon. CONSTITUTION:An electron beam 2 passes through an electron beam deflection plate 4, and an ion beam 3 passes through an ion beam deflection plate 5, to be radiated onto a specimen 1, so that secondary electrons 6 are emitted from the specimen 1. Next, a secondary electron optics unit 10 composed of a drawout lens 11, a focusing lens 12, and drift tubes 13a, 13b causes an emission pattern of the secondary electrons 6 emitted from the specimen 1 to be formed, as a projected image, on a required portion of an electron image detection unit 20. In the unit 20, the secondary electron image projected on the underside of an MCP 21 is amplified with an image distribution thereof being kept as it stands, and thereafter this electron image is converted into a light image by a phosphor plate 22. As a result, luminescent spots 7 in correct correspondence to the secondary electron emission spots on the specimen 1 appear on a plate 22, to enable visual recognition. The positional relation between respective beams on the specimen can be directly decided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for determining the irradiation position of a beam in a microbeam apparatus.

[0002]

2. Description of the Related Art As is well known, a microbeam is roughly 1
It is a narrow beam narrowed down to mmφ or less. As an apparatus using this micro beam, an Auger electron analyzer (AES) for analyzing a sample, an exposure apparatus for processing a sample, an apparatus for correcting various patterns such as a circuit pattern, etc. There is.

First, a conventional technique will be described by taking a conventional Auger electronic analyzer as an example. In the Auger electron analyzer, an electron beam is applied to a portion to be analyzed on the sample, and at the same time, an electron beam is emitted for cleaning the sample surface or measuring the elemental composition profile in the depth direction of the sample. The ion beam is applied to the same place where the beam is applied. In this case, the tip of the electron beam and the tip of the ion beam must match the point to be analyzed on the sample. If the positions of the two beams are displaced, the analysis accuracy will be significantly reduced.

However, conventionally, there is no good method for determining the positional relationship between these two beams on the sample, so that it is impossible to determine whether or not the irradiation positions of the two beams match.

The irradiation positions of the two beams are made to coincide with each other, that is, the irradiation positions of both beams (hereinafter, referred to as axis positions) are aligned at one point on the sample (hereinafter referred to as beam axis alignment, and one point thereof will be referred to as beam alignment). There are several conventional methods as the method for adjusting the axis.) However, there are problems in each method, and improvement thereof is strongly desired.

As conventional methods for aligning the axes of beams, there are the following methods, for example:

A method in which a fluorescent plate is placed at an axial alignment position instead of the sample in advance and the respective bright spots of the electron beam and the ion beam are made to coincide with each other.

A method in which a Faraday cup having a small hole is placed in advance at an axial alignment position so that the amount of current by each beam is maximized.

A standard sample having a thin film is placed at an axial alignment position in advance, the surface thereof is etched by an ion beam, and the position of the etching trace is observed by an electron beam scanning image, that is, an SEM image. How to do it together.

[0010]

[Problems to be Solved by the Invention]
In the method of and, since the alignment is not performed on the sample to be actually analyzed, even if the alignment can be performed on the fluorescent plate, Faraday cup, or standard sample without hindering analytical measurement, There is no guarantee that the axes of both beams will be aligned on the sample being analyzed.

The reason is that the beams themselves drift with time, and the positions of the axes of both beams are also displaced.
Also, if the height of the sample (vertical direction in each figure below) does not match the height of the fluorescent plate, Faraday cup, or standard sample when the axes of the beams are aligned, the positions of the axes of both beams will shift. Will be lost. Because,
Normally, the electron beam and ion beam are each 30 °
Since it has an opening angle of about 80 ° (for example, θ in FIG. 1A described later), if the height of the sample changes by ΔZ, the beam will have ΔZ · tan θ (θ = 30 °). ~ 80
A deviation of only (°) will occur. Recently, since the beam may be finely bundled down to the order of μm, it is necessary to match the heights of the beam and the sample in the order of μm. However, in general, since the sample has an irregular shape and has irregularities on the surface, it is extremely difficult to adjust the irradiation position of the beam on the sample to a specific point in space on the order of μm.

As a method different from the above-mentioned conventional method,
There is a conventional method of aligning the beam axis using the sample itself to be actually analyzed. In this method, the sample is scanned with each of an electron beam and an ion beam, the dose of secondary electrons generated by this scanning is detected, and each scan image is displayed on a CRT synchronized with the scan. The method itself for displaying a scanning image is the same as the technique generally used in SEM (scanning electron microscope). Since the images obtained by the electron beam and the ion beam are obtained from the same sample, basically the images should have the same shape. Therefore, the irradiation position of the beam is adjusted so that the images match. However, the electron beam and the ion beam are actually different in appearance of the image due to the difference in the type of the beam, and the two images having the difference in the beam diameter, the beam current, the irradiation direction, and / or the scanning direction are matched. The work is not easy. Further, when the surface of the sample is smooth, the secondary electron amount does not change depending on the location, so that the whole has the same brightness and nothing can be seen as an image, so this method cannot be applied. become.

Further, in addition to the above-mentioned problems, it is impossible in principle to monitor the alignment state of the beam during the actual measurement by any of the conventional methods. This is because the beam cannot be scanned because the beam has to be fixed during the measurement.
(Of course, this is not possible with a method that requires replacing the sample with a special one.) In the Auger analysis method, especially in the depth direction analysis, the measurement time often takes several hours or longer. During this long time, the positional deviation of the beam axis due to the drift of the beam itself and the axial positional deviation due to the charge-up of the sample surface occur, but these positional deviations are suppressed with an accuracy of the order of μm. Since it is extremely difficult, accurate analysis could not be expected by the conventional method.

The above is a description of conventional problems in the Auger analysis method. However, instead of the X-ray beam and the ion beam in the ESCA (XPS) analysis method, instead of X-rays, synchrotron radiation, laser, and neutral particles are used. Even with the analysis method using
Aligning the axes of the two beams was as difficult as the conventional method described above. This is also a problem common to various apparatuses that use two or more microbeams in exposure apparatuses and pattern correction apparatuses.

The present invention has been made to solve the above problems. Therefore, an object of the present invention is to determine the positional relationship of the beam on the sample for various operations (for example,
The position of the axes of the two beams can be accurately and easily determined by making a determination when performing (analysis work).
Accordingly, it is to provide a beam position determination method that enables highly accurate work.

[0016]

In order to achieve this object, in determining the positions of these beams in a micro-beam device that irradiates a sample with at least two beams, two beams generated from the sample by each beam irradiation are measured.
A method of determining the positional relationship of the respective beams on the sample by forming a projected image of the next electron by an electron lens and detecting the position of the projected image is adopted.

Then, in the microbeam device for irradiating the sample with at least two beams, an electron lens for forming a projected image of secondary electrons generated from the sample by each beam irradiation, and a projected image formed by this electron lens This beam position determination device is configured by including a detection device that detects the position of 1) and a determination unit that determines the positional relationship of each beam on the sample from the position of the projected image detected by this detection device.

When the microbeam device is an Auger electron analysis device, the beam position determination device has a remarkable effect.

A detection device for detecting the position of the projected image of the beam position determination device is composed of an MCP (multi-channel plate), a fluorescent plate and a camera, and an image is displayed on the CRT by utilizing the scanning of secondary electrons. Some are configured to display, and some are configured with an electron energy spectroscope, an inlet lens unit, and a deflection unit.

[0020]

The projection image of secondary electrons generated from the sample by irradiation of at least two beams is formed by using an electron lens, and the position of the projection image is detected. Therefore, the positional relationship of each beam on the sample can be directly measured. Can be determined.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. In addition, the figure is to the extent that this invention can be understood,
The shape, size, and positional relationship of each component are only schematically shown.

FIG. 1A is a diagram for explaining the beam position determining method according to the first embodiment of the present invention, and is an explanatory diagram when it is applied to an Auger electron analyzer as a microbeam device. ..

In the present invention, the sample is irradiated with at least two beams. In this embodiment, the electron beam 2 passes through the electron beam deflecting plate 4 and the ion beam 3 passes through the ion beam deflecting plate 5 to irradiate the sample 1. Secondary electrons 6 are emitted from the sample 1 to be analyzed by the irradiation of both beams. The secondary electron optical unit 10 includes the extraction lens 1
1, focusing lens 12 and drift tube 13a, 1
3b. The extraction lens, focusing lens and drift tube are all axisymmetric with respect to the optical axis of the cone and / or cylinder. The secondary electron optical unit 10 has a function of forming the above-described secondary electron emission pattern emitted from the sample 1 as a projection on a required portion of the electronic image detection unit 20.

The electronic image detection unit 20 includes an MCP (multi-channel plate) 21 and a glass substrate fluorescent plate 22.
And a camera 23. 7 of FIG. 1 (A)
Is the bright spot of the fluorescent screen. The Auger electron analyzer requires an electron gun and an electron energy analyzer, but since these are not the gist of the present invention, their description and illustration are omitted.

Next, an example of the operating method of the Auger electron analyzer for performing beam display will be described. Sample 1
Is 0V, the extraction lens 11 has about + 100V, the focusing lens 12 has about −100V, and the drift tubes 13a and 13b have the same +10 as the extraction lens.
A voltage of about 0 V is applied.

When the secondary electrons 6 are emitted from the sample 1, the secondary electrons 6 are attracted upward in the figure by the axially symmetric electric field created by the extraction lens 11. The secondary electrons that have passed through the extraction lens 11 move in the drift tube 13b by being accelerated and moved upward in the figure, and then are focused by the axially symmetric electric field of the focusing lens 12, pass through the drift tube 13a, and enter the electrons. It is projected on the lower surface (light receiving surface) of the MCP (multi-channel plate) 21 of the image detection unit 20.

Since all the electric fields in the secondary electron optical unit 10 are axially symmetric, they act as electron lenses for the secondary electrons 6 and have a mapping characteristic as a whole. Therefore, if the voltage applied to the two lenses of the extraction lens 11 and the focusing lens 12 is adjusted, the emission distribution of the secondary electrons on the sample 1 is reproduced as a projection image on the lower surface of the MCP 21 as a similar distribution of arbitrary magnification. It will be. That is, the emission pattern is projected here.

In the electronic image detection unit 20, the MCP 21
The secondary electron image projected on the lower surface of the is amplified while maintaining the image distribution, and then the secondary electron image is converted into light by the fluorescent plate 22. By doing so, the image of the fluorescent plate 22 correctly represents the emission distribution of the secondary electrons on the sample 1. That is, a bright spot 7 that correctly corresponds to the secondary electron generation place on the sample 1 appears on the fluorescent plate 22 and can be visually recognized. Further, the converted projection image is photographed by the camera 23 so that the image can be observed at any place.

When the sample 1 is irradiated with the electron beam 2 or the ion beam 3, secondary electrons 6 are always emitted from the irradiation region on the sample. The energy of the secondary electrons is almost the same regardless of the excitation source (electrons, ions, etc.). Therefore, the adjustment of the voltage applied to the lens of the electronic image detection unit 20 may be the same regardless of the excitation source. Therefore, the fluorescent plate 22 has two bright spots 7 formed by the electron beam 2 and the ion beam 3.
a and 7b appear. These bright points represent the irradiation positions of the respective beams on the sample 1.

FIG. 1B is an enlarged view of the main part of the portion shown in FIG. 1A, and FIG. 1C and FIG.
The image on the fluorescent plate 22 and the irradiation position on the sample 1 are shown in FIG. 6a is a secondary electron by an electron beam, and 6b is a secondary electron by an ion beam. In addition, 7a is due to the electron beam,
Further, 7b is a bright spot of the fluorescent plate by the ion beam. If the electron beam 2 or the ion beam 3 is moved by the respective deflecting plates 4 or 5 so that the bright spots 7a and 7b on the fluorescent plate 22 are coincident with or concentric with each other, the deflecting plates 4 and 5 respectively move the sample 1 on the sample 1. The irradiation positions of the beams also coincide with each other, and the alignment of the beams is completed. Since the axial position of the beam can be moved by the deflecting plates 4 or 5 by the conventional ordinary electron beam deflecting technique, detailed description thereof will be omitted. In this example, the MCP 21 is used to amplify the secondary electrons in the electronic image detection unit 20, but the MCP is not always necessary, and if the amount of the secondary electrons is sufficient, the secondary electrons are directly projected onto the fluorescent screen 22. You can also do it.

In this beam alignment method, the material of the sample 1 may be any material. This is because, even if there is a difference in the amount of any object, secondary electrons are always emitted by beam irradiation. Therefore, the beam position can be displayed even for the sample itself to be actually analyzed.
In addition, the beam alignment can be continuously monitored during the actual analysis. Because there is no need to scan the beam, and the energy of secondary electrons is very low, 10 to 20 eV, while the energy of Auger analysis is 100 to 2000 eV.
This is because V is high and does not affect each other.

That is, according to this beam position determination method, there is no need to prepare a special sample for axis alignment, and the beam axis alignment can be performed very easily and more accurately than in the prior art. Even if a beam drift occurs in the analysis for a long time, it can be easily corrected without interrupting the analysis.

FIG. 2 is a diagram for explaining a second embodiment of the beam position determining method of the present invention. Also in this embodiment, an example using an Auger electron analyzer as a microbeam device will be described. The components corresponding to those shown in FIG. 1 will be described with the same reference numerals. 14 is a deflector for secondary electrons, 15 is an imaging aperture plate having a hole (aperture) 15a, 30 is an electron detector, and 40 is a CRT.
Is.

In the second embodiment of FIG. 2, the image is directly displayed on the electronic image detection unit 20 in the first embodiment of FIG. 1, whereas the secondary electron deflector 14 is used. An image is displayed on the CRT 40 using scanning.

That is, the image formed at the position of the hole of the image forming aperture plate 15 is scanned by the secondary electron deflector 14. As a result, the small hole 15 in the imaging aperture plate 15
a through the electron detector 30 (eg channel type 2
The electrons detected by the secondary electron multiplier are signals that change in time series. This signal is transmitted to the secondary electron deflector 1
When placed in a CRT that scans in synchronism with the scanning signal applied to 4, a bright spot indicating the position of the beam on the sample is displayed on the CRT.

FIG. 3 is a diagram for explaining a third embodiment of the beam position determining method of the present invention, which is an example in which the present invention is applied to an Auger electron analyzer. 40a is an electron energy spectrometer, 41 is an inlet lens unit, 42
Is a deflector. The constituents corresponding to the constituents shown in FIG. 1A are designated by the same reference numerals.

Reference numeral 21a is an MCP installed at the end of the inlet lens portion, where there is usually the aperture 42a.
A hole 2 is formed in the center of the MCP 21a and the fluorescent plate 22a.
1b and 22b are provided. 23 is a camera.
The inlet lens unit 41 is for projecting (mapping) Auger electrons originally generated from the sample 1 onto the aperture 42a. That is, it has a function of projecting electrons of 100 to 200 eV. Therefore, the same function as the secondary electron optical unit 10 of projecting electrons of 10 to 20 eV shown in FIG. 1A can be provided by changing the lens applied voltage or the like. Therefore, the position of the beam irradiated on the sample 1 is set to the MCP21.
It can be displayed on a. Since this MCP 21a is provided with the hole 21b, when the bright spot comes to the center part, it is partly chipped, but this does not cause a great problem in axis alignment.

When this device is viewed as an electron energy spectroscope, the MCP 21a with a hole serves as an aperture plate as it is. Therefore,
In this embodiment, the device can have a beam axis alignment function without impairing the function of the electron energy spectrometer 40a.

All of the above are examples in which the present invention is applied to an Auger electron spectroscopic device. However, in addition to this, an X-ray beam and an ion beam in an esca (XPS) device, and a sims (SIMS) device can be used. It goes without saying that the method of the present invention can be effectively used for ion beams and neutralizing electron beams.

The present invention can also be applied to an apparatus using synchrotron radiation, a laser, or a neutron beam. That is, the method of the present invention can be conveniently used for any beam generated by secondary electrons.

In the above embodiment, the case of two beams has been described, but the present invention can be applied to the case of three beams or more.

In addition, although all of the above examples are displayed visually, the position is not necessarily limited to a human recognizable form. For example, the position of the projected image may be read by a computer having a position recognition function, the correction amount may be calculated, the beam may be adjusted, and the axes may be automatically aligned.

[0043]

According to the apparatus and method of the present invention, the positional relationship of microbeam irradiation on a sample is clearly displayed,
Since the axis alignment of the beam becomes easy and accurate, the accuracy and reliability of the Auger electron analyzer can be improved.

[Brief description of drawings]

FIG. 1A shows a first beam position determining method according to the present invention.
2B is a diagram for explaining the embodiment of FIG. (C) is a diagram of an image on the fluorescent plate, and (D) is a diagram of an irradiation position on the sample.

FIG. 2 is a diagram for explaining a second embodiment of the beam position determination method of the present invention.

FIG. 3 is a diagram for explaining a third embodiment of the beam position determination method of the present invention.

[Explanation of symbols]

1: Sample 2: Electron beam 3: Ion beam
4, 5: Deflection plate 6, 6a, 6b: Secondary electron 7, 7a, 7b: Bright spot 10: Secondary electron optical unit 11: Extraction lens 12: Focusing lens 13a, 13b: Drift tube 14: Secondary electron Deflector 15: Imaging aperture plate 15a, 21b, 22b, 42a: Hole (aperture) 20: Electronic image detection unit 21: MCP 21
a: MCP with a hole 22: Fluorescent plate 22a: Fluorescent plate with a hole 2
3: Camera 30: Electron detector 40: CRT 40a: Electron energy spectroscope 41: Inlet lens unit 42: Deflection unit

Claims (6)

[Claims] 1. When performing beam position determination in a microbeam device for irradiating a sample with at least two beams, a projected image of secondary electrons generated from the sample by each beam irradiation is formed using an electron lens, and A beam position determination method in a microbeam device, characterized in that the positional relationship of each beam on the sample is determined by detecting the position of a projected image. 2. A microbeam device for irradiating a sample with at least two beams, and an electron lens for forming a projected image of secondary electrons generated from the sample by each irradiation of the beam, and a projected image formed by this electron lens. Beam position in the microbeam device, comprising a detection device for detecting the position of the beam and a determination unit for determining the positional relationship of the respective beams on the sample from the position of the projected image detected by the detection device. Judgment device. 3. The beam position determination device according to claim 2, wherein the microbeam device is an Auger electron analysis device. 4. A detection device for detecting the position of a projected image is M
The beam position determination device according to claim 2 or 3, comprising a CP (multi-channel plate), a fluorescent plate, and a camera. 5. A detection device for detecting the position of a projected image is 2
The beam position determination device according to claim 2, wherein the beam position determination device is configured to display an image on a CRT by utilizing the scanning of the next electron. 6. The beam position determination device according to claim 2, wherein the detection device for detecting the position of the projected image is composed of an electron energy spectroscope, an inlet lens section, and a deflection section.