JP2004319378A - Magnetic lens, and electron/ion beam optical instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the magnetic intensity by hysteresis characteristic of a magnetic lens cannot be determined uniquely. <P>SOLUTION: The magnetic lens 5 is a magnetic lens for focusing an electron beam or ion beam, which comprises a magnetic sensor 11 at the sample-side tip of a magnetic yoke 5b constituting the magnetic lens at least outside the axis 6 of an electronic optical system relative to the magnetic yoke 5b on the axis 6 side of the electronic optical system. The magnitude of the current supplied to a magnetic coil 5a is controlled by use of the output of the magnetic sensor, whereby the magnetic intensity is controlled to a predetermined value. According to this, the magnetism generated by the magnetic lens is controlled to a predetermined intensity to control the magnetic intensity to the predetermined value, whereby the focal distance is uniquely determined, and the distance on an observation sample is uniquely determined. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus that performs analysis, measurement, observation, and manufacturing using charged particles, and particularly relates to an electron beam or an ion included in an electron / ion beam optical device such as an electron microscope or a focused ion beam (FIB). The present invention relates to a magnetic lens such as a magnetic focusing lens for focusing a beam and a magnetic objective lens.
[0002]
[Prior art]
There are an electrostatic lens and a magnetic lens as a lens for focusing charged particles such as an electron beam and an ion beam, and a magnetic lens is generally used in a scanning electron microscope and the like. A magnetic lens is composed of a coil made of a copper wire or the like and a magnetic yoke made of pure iron or the like.A predetermined current is applied to the coil to generate magnetism, thereby forming a magnetic lens. Ion charged particles are focused.
[0003]
The strength of the magnetic lens can be controlled by the current supplied to the coil. The magnetic yoke has the effect of concentrating the magnetism generated from the coil on the magnetic pole, increasing the focusing power of the lens, and shortening the focal length.
[0004]
In addition to transmission electron microscopes (TEM) and scanning electron microscopes (SEM), magnetic lenses used in Auger analyzers, electron beam welding devices, electron beam lithography devices, and various semiconductor inspection devices are, for example, non-magnetic. It is described in Patent Document 1.
[0005]
[Non-patent document 1]
"Electron / Ion Beam Handbook" 3rd Edition Publisher Nikkan Kogyo Shimbun Publisher year October 28, 1998 (3rd edition)
Edit 132nd Committee of the Japan Society for the Promotion of Science [0006]
[Problems to be solved by the invention]
In a conventional magnetic lens (hereinafter referred to as a magnetic lens), a magnetic material such as pure iron is used for a magnetic yoke. These magnetic materials have hysteresis, and the intensity of the magnetism generated from the magnetic lens with respect to the current flowing through the coil has a different value depending on the history of excitation.
[0007]
In the autofocus function, the current flowing through the objective lens is changed stepwise, a numerical value representing the degree of focus of the image in each case is obtained, and the current value at the best focus is stored, and then, The strength of the lens is set by setting the stored current value at which the focus is best.
[0008]
At this time, the intensity of the magnetism generated from the magnetic lens differs depending on the history of excitation due to the magnetic hysteresis, and a current for obtaining a good focus cannot be uniquely determined. FIG. 7 is a diagram for explaining current control of the magnetic lens. In FIG. 7, when the current IF set by the focus function is applied to the coil to be excited, the magnetic intensity (indicated by the magnetic flux density B in the figure) generated from the magnetic lens changes from B1 to B2 due to the hysteresis characteristic. The value differs depending on the excitation history.
[0009]
Therefore, even if the current value obtained by the autofocus is passed through the objective lens, the focused magnet is not always generated due to the history of the excitation, and the electron beam on the sample is defocused.
[0010]
In an electron / ion beam optical device equipped with a magnetic lens, it is necessary to know the distance between two points in order to know the size of the observation target on the observation sample. The distance on the observation sample can be obtained by using the focal length obtained by the autofocus function. However, as described above, the magnetic intensity with respect to the coil current differs depending on the history of excitation due to the hysteresis characteristic. Cannot be uniquely determined, and the distance on the observation sample cannot be uniquely determined.
[0011]
Therefore, the present invention solves the problem that the magnetic intensity due to the hysteresis characteristic of the conventional magnetic lens is not uniquely determined, and aims to control the magnetism generated by the magnetic lens to a predetermined intensity. It is an object of the present invention to uniquely determine the focal length by controlling to a predetermined value and uniquely determine the distance on the observation sample.
[0012]
[Means for Solving the Problems]
The present invention measures the magnetic intensity generated by a magnetic lens and controls the exciting current based on the magnetic intensity.By using the magnetic intensity generated by the magnetic lens, the influence of the hysteresis characteristic of the magnetic lens can be reduced. The intensity of the exciting current supplied to the magnetic lens can be determined without receiving it.
[0013]
The magnetic lens of the present invention is a magnetic lens that focuses an electron beam or an ion beam, and is a sample-side tip of a magnetic yoke constituting the magnetic lens, at least with respect to a magnetic yoke on an axial side of the electron optical system. The magnetic sensor is provided outside the axis of the electron optical system.
[0014]
When an exciting current is applied to the coil of the magnetic lens, magnetism is generated between the magnetic poles of the magnetic yoke and around the magnetic yoke. The magnetic lens focuses an electron beam or an ion beam on a sample by magnetism generated on the axis side of the electron optical system. There is a certain relationship between the magnetic intensity on the axis side of the electron optical system and the magnetic intensity outside the magnetic yoke with respect to the axis of the electron optical system. In the magnetic lens of the present invention, the magnetic intensity on the axis side of the electron optical system is obtained by measuring the magnetic intensity using a magnetic sensor provided outside the magnetic yoke.
[0015]
The arrangement position of the magnetic sensor can be determined according to the shape of the magnetic yoke, but by setting the magnetic yoke at least on the axial side of the electron optical system on the opposite side (outside) to the axis of the electronic optical system. The magnetic intensity of the magnetic lens can be measured without affecting charged particles such as an electron beam and an ion beam passing through the axis of the electron optical system.
[0016]
The control of the exciting current supplied to the magnetic lens of the present invention is performed so that the magnetic intensity generated by the magnetic lens based on the output of the magnetic sensor becomes a predetermined value. According to this control, by determining the exciting current from the target magnetic strength, the exciting current is automatically determined according to the hysteresis characteristic of the magnetic lens, and the exciting current can be determined with respect to the magnetic strength.
[0017]
FIG. 4 is a diagram for explaining current control of the magnetic lens of the present invention. In FIG. 4, the exciting current I supplied to the magnetic lens differs from the magnetic intensity (indicated by the magnetic flux density B in the figure) BF preset by the focus function due to the hysteresis characteristic (for example, I1 or I2). ), The excitation current I, which becomes the magnetic intensity B, which is the control target, is one according to the excitation history of the excitation lens. Therefore, it is necessary to adjust the excitation current by changing the excitation current stepwise so as to obtain the predetermined magnetic intensity. Can determine the exciting current.
[0018]
Further, the present invention can be an electron / ion beam optical device provided with the above-described magnetic lens, and can determine the distance between any two points on the observation sample based on the output of the magnetic sensor. The focal length is determined based on the output of the magnetic sensor, and the distance between any two points on the observation sample is determined from the magnification corresponding to the focal length.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
1 and 2 are schematic diagrams for explaining a magnetic lens and an electron / ion beam optical device according to the present invention.
[0021]
1 and 2, an electron / ion beam optical apparatus 1 includes a charged particle beam source 2, a focusing lens 3 for focusing a charged particle beam from the charged particle beam source 2, and an objective for focusing the charged particle beam on a sample 7. A lens 5, disposed between the focusing lens 3 and the objective lens 5, provided with an objective aperture 4 for narrowing the charged particle beam to the objective lens 5, and a scanning coil 10 for scanning the charged particle beam on the sample 7; These are arranged along the axis 6 of the electron optical system.
[0022]
The charged particle beam source 2 emits a charged particle beam such as an electron beam or an ion beam. The emitted charged particle beam travels along the axis 6 of the electron optical system, and is focused on the sample 7 by the focusing lens 3 and the objective lens 5. When the charged particle beam is irradiated onto the sample 7, the sample 7 emits, for example, a secondary electron beam or a characteristic X-ray. Secondary electrons emitted from the sample 7 are detected by a secondary electron detector 9.
[0023]
The magnetic lens 5 includes an objective lens coil 5a and an objective lens yoke 5b. An exciting current is supplied from an objective lens driving power supply 13 to the objective lens coil 5a to generate magnetism. The objective lens yoke 5b concentrates the generated magnetism at the tip of the yoke to increase the magnetic strength. The tip of the objective lens yoke 5b is arranged near the axis 6 of the electron optical system on the sample 7 side, and efficiently focuses the charged particle beam passing through the axis 6 of the electron optical system on the sample 7.
[0024]
The magnetic lens 5 of the present invention includes a magnetic sensor 11 at least outside the axis 6 with respect to the magnetic yoke portion on the axis 6 side of the electron optical system. The output of the magnetic sensor 11 determines the magnitude of the current supplied to the coil of the objective lens by the control means 12 and controls the objective lens drive power supply 13.
[0025]
FIG. 1 shows an example of a configuration in which the magnetic sensor 11 is arranged between two forked yokes of the objective lens yoke 5b. According to this configuration example, the magnetic sensor 11 measures the magnetic intensity on the sample side generated between the forked yokes of the objective lens yoke 5b. FIG. 2 shows a configuration example in which the magnetic sensor 11 is arranged outside the forked outer yoke of the objective lens yoke 5b. According to this configuration example, the magnetic sensor 11 measures the sample-side magnetic intensity generated outside the objective lens yoke 5b.
[0026]
The magnetic intensity at these positions has a fixed relationship with the magnetic intensity generated on the axis 6 of the electron optical system near the tip of the objective lens yoke 5b, and the output of the magnetic sensor 11 causes the objective lens to detect charged particles. The focusing magnetic intensity can be determined.
[0027]
FIG. 3 is a diagram for explaining an example of the arrangement of the magnetic sensors. Various types of objective lenses have been proposed. For example, the objective lens 5A shown in FIG. 3A has a lens structure called a pinhole lens, the objective lens 5B shown in FIG. 3B has a lens structure called a snorkel lens, and is shown in FIG. The objective lens 5C has a lens structure called a single pole lens. Each figure shows a cross section.
[0028]
In any of the above-described objective lenses 5A to 5C, the tip of the objective lens yoke 5b on the sample 7 side is arranged close to the axis 6 of the electron optical system, and the magnetism generated by the objective lens coil 5a is placed on the sample. They are being aggregated.
[0029]
In the objective lens 5A shown in FIG. 3A, an objective lens yoke 5b is provided with an inner yoke part and an outer yoke part connected to the axis 6 of the electron optical system, and faces the sample 7 side. The portion is open and generates magnetism between the tips of the opposing yokes. The magnetic sensor 11 is disposed near the tip of the opposed yoke and outside the shaft 6 of the electron optical system with respect to the inner yoke. The magnetic strength at this position shows almost the same magnetic strength characteristics as the magnetism between the tips of the opposing yokes and the magnetism on the shaft 6.
[0030]
In the objective lens 5B shown in FIG. 3B, the objective lens yoke 5b is provided with a bifurcated shape of an inner yoke portion and an outer yoke portion connected to the axis 6 of the electron optical system. The portion facing the sample 7 side is opened, and magnetism is generated between the tips of the opposing yokes. The magnetic sensor 11 is disposed between the forked yokes near the tip of the opposed yoke. The magnetic strength at this position shows almost the same magnetic strength characteristics as the magnetism between the tips of the opposing yokes and the magnetism on the shaft 6.
[0031]
In the objective lens 5C shown in FIG. 3 (c), the objective lens yoke 5b has only a yoke part inside the axis 6 of the electron optical system, and the tip thereof is connected to the axis 6 of the electron optical system on the sample 7 side. They are arranged close to each other to generate magnetism at the tip of the yoke. The magnetic sensor 11 is arranged near the tip of the yoke and on the opposite side of the yoke from the axis 6 of the electron optical system. The magnetic strength at this position shows almost the same magnetic strength characteristics as the magnetism on the shaft 6 at the tip of the yoke.
[0032]
Although the output measured by the magnetic sensor 11 does not match the magnetic intensity on the axis 6 of the electron optical system, there is a predetermined relationship between this output and the magnetic intensity. The magnetic intensity on the axis 6 can be determined.
[0033]
In FIG. 4 described above, when the magnetic intensity on the vertical axis (indicated by the magnetic flux density B in the figure) is the magnetic intensity measured by the magnetic sensor 11, this magnetic intensity is It shows the magnetic intensity generated by the exciting current supplied to the lens coil 5a. Therefore, by controlling the excitation current I while referring to the output of the magnetic sensor 11 so that the target magnetic intensity is attained in advance, the target magnetic intensity can be set regardless of the hysteresis characteristics.
[0034]
In the autofocus process, the supply current flowing through the magnetic lens is changed stepwise, a numerical value representing the degree of focus of the image is obtained in each case, and the output of the magnetic sensor when the best focus is obtained is stored. Then, by setting the current value while referring to the output of the magnetic sensor so that the stored magnetic intensity is the best in focus, the intensity of the magnetic lens can be set to a value in focus. .
[0035]
In the control of the magnetic lens, a current value is obtained based on the output of the magnetic sensor 11 in the control means 12 and the output of the magnetic sensor when the best focus is stored in advance stored in advance. This is performed by controlling the lens driving means 13.
[0036]
Next, a description will be given of a point of obtaining a distance between any two points on an observation sample in an electron / ion beam optical apparatus having a magnetic lens.
[0037]
The objective lens adjusts the focal length WD of the charged particle beam by the focusing power of the lens. For example, if the exciting current supplied to the objective lens coil is increased to increase the focusing power of the lens, the focal length WD is shortened. Conversely, if the exciting current supplied to the objective lens coil is reduced to reduce the focusing power of the lens, The focal length WD becomes longer. The scanning angle θ of the electron beam is determined from the focal length WD and the magnification of the observation image. Further, the length of the region of the observation image is L1 (= 2WD tan θ) on the sample from the scanning angle.
[0038]
From the above relationship, a predetermined relationship is established between the magnetic intensity of the objective lens and the distance on the observation sample via the magnification and the focal length of the observation image. FIG. 5 is a diagram for explaining the relationship between the magnetic intensity B of the objective lens and the focal length WD, the scanning angle, and the distance L between two points on the observation sample.
[0039]
FIG. 5A shows a case where the magnetic intensity B1 of the objective lens is weak. In this case, the focal length WD1 increases, and the distance L1 between two points on the observation sample increases. On the other hand, FIG. 5B shows a case where the magnetic intensity B2 of the objective lens is high. In this case, the focal length WD2 becomes shorter, and the distance L2 between two points on the observation sample becomes longer.
[0040]
Therefore, the focal length is determined from the magnetic intensity measured by the magnetic sensor by previously determining the relationship between the magnetic intensity of the objective lens and the focal length, and the relationship between the focal length and the distance between two points on the observation sample. Further, the relationship with the distance between two points on the observation sample can be obtained. FIG. 6 is a diagram schematically illustrating the relationship between the magnetic intensity of the magnetic lens and the distance between two points on the observation sample. For example, when the magnetic intensity measured by the magnetic sensor is B1, this relationship is shown. The distance L1 between two points on the observation sample at this magnetic intensity can be obtained using the above.
[0041]
The distance L between two points arbitrarily selected on the observation image is, for example, a ratio of the length M1 of one side of the region of the observation image to the distance L between the two points at the magnetic intensity set at that time, It can be obtained from the length L1 obtained by the calculation of 2WD tan θ.
[0042]
The above-described calculation for obtaining the focal length and the distance between any two points can be performed by any calculation unit that inputs the output of the magnetic sensor, and can be performed by the control unit 12, for example.
[0043]
According to the present invention, it is possible to control the intensity of the objective lens so as to obtain a desired magnetic intensity regardless of the past excitation history.
[0044]
Further, according to the present invention, the distance between any two points on the observation sample can be obtained.
[0045]
【The invention's effect】
As described above, according to the magnetic lens of the present invention, the problem that the magnetic intensity due to the hysteresis characteristic of the magnetic lens is not uniquely determined with respect to the exciting current is solved, and the magnetic intensity generated by the magnetic lens is reduced to a predetermined intensity. The focal length can be uniquely determined by controlling the magnetic intensity to a predetermined value, and the distance on the observation sample can be uniquely determined.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining a magnetic lens and an electron / ion beam optical device according to the present invention.
FIG. 2 is a schematic diagram for explaining a magnetic lens and an electron / ion beam optical device according to the present invention.
FIG. 3 is a diagram for explaining an example of arrangement of a magnetic sensor according to the present invention.
FIG. 4 is a diagram for explaining current control of the magnetic lens of the present invention.
FIG. 5 is a diagram for explaining a relationship between a magnetic intensity B of an objective lens, a focal length WD, and a distance L between two points on an observation sample.
FIG. 6 is a diagram schematically illustrating a relationship between the magnetic intensity of a magnetic lens and a distance between two points on an observation sample.
FIG. 7 is a diagram for explaining current control of a magnetic lens.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electron and ion beam optical equipment, 2 ... Charged particle beam source, 3 ... Focusing lens, 4 ... Objective aperture, 5 ... Objective lens, 5a ... Objective lens coil, 5b ... Objective lens yoke, 6 ... Electron optical system axis, 7: sample, 8: secondary electron beam, 9: secondary electron detector, 10: scanning coil, 11: magnetic sensor, 12: control means, 13: power supply for driving the objective lens.

Claims (3)

A magnetic lens that focuses an electron beam or an ion beam, and a magnetic sensor outside the axis of the magnetic yoke constituting the magnetic lens, which is at the sample-side tip and at least the magnetic yoke on the axis side of the electron optical system. A magnetic lens, comprising: 2. The magnetic lens according to claim 1, wherein the intensity of the exciting current of the magnetic lens is controlled based on the output of the magnetic sensor so that the magnetic intensity generated by the magnetic lens becomes a predetermined value. An electron / ion beam optical apparatus comprising the magnetic lens according to claim 1,
An electron / ion beam optical apparatus, wherein a distance between any two points on an observation sample is obtained based on an output of the magnetic sensor.

Images