JPH06208838A - Magnetic field type electron lens and electron beam device using same - Google Patents

Abstract

PURPOSE:To eliminate variation in the outer form of a magnetic path caused by thermal expansion, and to stabilize the intensity of an electron lens by changing the intensity of the electron lens while the current to be forced to flow in an excitation coil which is in the same magnetic path, is maintained at a fixed level. CONSTITUTION:Excitation coils 1, 2 wound around an electron beam route 10 as a center, into solenoid shape, are provided in a magnetic path 3, and an excitation current in reverse to that in the excitation coil 1 is fed to the excitation coil 2. Otherwise, the excitation coil 2 is wound in reverse direction to that of the excitation coil 1, and the intensity of an electron lens is controlled by controlling the feeding ratio I1/I2 while the total sum (I1+I2) of the excitation currents I1 and I2 is maintained at a fixed level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field type electron lens for converging or expanding a charged particle beam (hereinafter represented by an electron beam) such as an electron beam or an ion beam by utilizing a lens magnetic field generated by an exciting coil. The present invention also relates to an electron beam apparatus using the same and, more particularly, to a magnetic field type electron lens capable of changing the lens strength while keeping the current flowing through the exciting coil constant, and an electron beam apparatus using the same.

[0002]

2. Description of the Related Art Electron lenses are widely used for converging or expanding electron beams in various electron beam apparatuses such as electron microscopes, electron beam drawing (EB) apparatuses, and ion beam apparatuses. Generally, in a magnetic field type electron lens, an electron beam is converged or expanded by a magnetic field generated by passing a current through an exciting coil provided in a magnetic path.

When a strong electron lens action is required, it is necessary to increase the current flowing through the exciting coil or increase the number of turns of the exciting coil. However, in order to increase the exciting current, a large power source having the ability to pass a large current is required. In addition, when the number of turns of the exciting coil is increased, the resistance of the exciting coil increases, so that a high voltage must be generated.

In order to solve such a problem, for example, in Japanese Unexamined Patent Publication No. 3-20950, a plurality of exciting coils are provided in the same magnetic path, and the exciting coils are connected in parallel to each other to flow a current. As a result, a technique is disclosed in which the resistance of the exciting coil is reduced while increasing the number of turns of the exciting coil to suppress an increase in power supply voltage and an increase in current capacity.

[0005]

In the above-mentioned prior art, when the current flowing through the exciting coil is changed in order to change the strength of the electron lens, the power consumed by the coil is changed even if the resistance of the exciting coil does not change. Is proportional to the square of the exciting current. Therefore, when the exciting current is increased to increase the strength of the electron lens, the heat generated according to the electric power deforms the magnetic path, that is, the casing of the coil.
The deformation of the casing adversely affects the magnetic field strength of the electron lens and its distribution, and causes problems such as irregular drift of the electron beam spot. Note that, as a known example related to such a technique, there is, for example, US Pat. No. 4,306,149.

An object of the present invention is to solve the above-mentioned problems of the prior art and to change the magnetic field strength of the magnetic path without changing the temperature of the magnetic path, that is, without deforming the magnetic path. An object of the present invention is to provide a possible magnetic field type electron lens and an electron beam apparatus using the same.

[0007]

In order to achieve the above-mentioned object, according to the present invention, a plurality of exciting coils are arranged in a hollow donut-shaped casing, that is, a magnetic path, in the casing vertically and vertically. The exciting coils are arranged so as to substantially coincide with each other, and each exciting coil is independently controlled.

[0008]

When a part of a plurality of exciting coils arranged in the same magnetic path is excited so as to generate a magnetic field in the opposite direction to the other exciting coils, the electron lens strength is equal to that of the magnetic field generated by each exciting coil. There is a difference, and the current flowing inside the magnetic path is the sum of the currents flowing through the exciting coils. Therefore, if the current supply ratio to each coil is controlled while keeping the sum of the currents flowing in each exciting coil constant, the strength of the electron lens can be changed while keeping the heat generated inside the magnetic path constant. You can

If the heat generated inside the magnetic path is constant, the amount of thermal expansion that changes the outer shape of the magnetic path is also constant. Therefore, even if the electron lens strength is changed, the electron lens strength changes due to heat. There is no such thing.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 7 is a block diagram showing a schematic configuration of a transmission electron microscope to which the present invention is applied.

The electron beam 17 emitted from the electron gun 12 is
The sample 16 is irradiated with the light after being converged by the irradiation lens systems 14 and 15. The electron beam that has passed through the sample 16 is magnified by the imaging lens system 34 and forms an image on the fluorescent plate 35 for image observation. The fluorescent plate 35 is lifted and stored at the time of taking a picture or observing an image with an image pickup device (TV camera) 36. When taking a picture, the film 49 is placed on the optical axis and exposed.

The exciting currents supplied to the irradiation lens systems 14 and 15 and the imaging lens system 34 are respectively supplied to the D / A converter 4.
0a-40f, power supplies 7a-7f, and data bus 43
It is controlled by a microprocessor 44 connected via. A control program is stored in the memory 45, and the arithmetic unit 46 performs arithmetic operations necessary for controlling the electron microscope main body. The display device (CRT or the like) 47 displays the image captured by the imaging device 36.

The transmission image detected by the image pickup device 36 is output as an image signal from the control device 37 and is stored in the storage device 38 (frame memory or the like). Frame memory 38
The image data stored in can be observed by the display device 47. The input device (I / O) 48 is for inputting parameters (coordinate position, shape, etc.) for designating an arbitrary region while observing a transmission image displayed on the display device 47, and for example, a keyboard or a mouse. Etc.

FIG. 1 is a diagram showing the structure of a magnetic field type electron lens which is a first embodiment of the present invention applied to the imaging lens system 34.

In the yoke (magnetic path) 3 for the electron lens, the first exciting coil 1 and the second exciting coil 2 are wound in the same winding direction like a solenoid around the charged particle beam passage 10 as a central axis. There is. The first excitation coil 1 is connected to the first excitation coil drive power supply 4, and the second excitation coil 2 is connected to the second excitation coil drive power supply 5.

Here, the current polarity of the first excitation coil drive power source 4 is constant, but the second excitation coil drive power source 5 is a bipolar type whose current polarity can be switched. Excitation currents I1 and I2 supplied from the first excitation coil drive power supply 4 and the second excitation coil drive power supply 5 to the respective excitation coils 1 and 2 are controlled by the excitation coil drive power supply control device 6. This control device 6, as shown in FIG.
The exciting currents I1 and I2 supplied to the exciting coils 1 and 2 are
Control is performed so that the total sum of those absolute values is always constant.

FIG. 3 is a diagram showing the relationship between the second exciting current I2 (horizontal axis) and the effective intensity (vertical axis) of the electron lens. It is the lens strength obtained by supplying the exciting current I1, and is the two-dot chain line M2.
Is the lens strength obtained by supplying the exciting current I2 to the second exciting coil 2. The solid line M is the sum (M1) of the lens intensities M1 and M2 obtained from the law of magnetic field superposition.
+ M2), that is, the effective intensity of the electron lens.

In the magnetic field type electron lens having such a structure, the exciting currents I1 and I2 supplied to the exciting coils 1 and 2 are used.
If the polarities are the same, the electron lens strength becomes constant as shown by the solid line AB. On the other hand, when only the direction of the current I2 flowing through the second exciting coil 2 is reversed and the polarities of I1 and I2 are reversed, the electron lens strength depends on the ratio of the currents I1 and I2 as shown by the solid line BCD in FIG. Change. In addition,
The negative lens strength in FIG. 3 means a state in which the direction of image rotation is opposite, which occurs at the same time as the refractive power in the case of a field lens.

By thus providing two sets of coils in the same magnetic path and making the directions of the currents flowing through the coils different, the total sum of the absolute values of the currents flowing in the same magnetic path can be kept constant. , It becomes possible to continuously change the intensity of the electron lens from zero to the maximum value.

The point E in FIG. 3 is composed of two exciting coils 1,
2 is the lens strength when the same currents of the same polarity are supplied, and point C is the lens strength when the same currents of opposite polarity are supplied to the two exciting coils 1 and 2. At point C, the magnetic fields generated by the two exciting coils 1 and 2 cancel each other out, so the lens strength is zero when viewed from the entire lens, but at point E, the magnetic fields generated by the exciting coils are added, and 2 times the lens action is obtained.

According to this embodiment, the strength of the electron lens can be changed while keeping the total sum of the absolute values of the currents flowing in the same magnetic path constant. When applied to an image forming lens system of various electron beam devices, drift and the like of electron beam spots are prevented, and observation / analysis with high resolution becomes possible.

By the way, the present invention can be applied not only to the above-mentioned image forming lens system, but also to the irradiation lens system as in the second and third embodiments described below.

FIG. 5 is a diagram schematically showing the operation of the irradiation lens systems 14 and 15 to which the present invention is applied. The aperture angle of the electron beam 17 emitted from the electron source 12 is limited by the diaphragm 13, and then the sample 16 is irradiated through the first converging lens 14 and the second converging lens 15.

When a sample is analyzed with a transmission electron microscope, first, as shown in FIG. 3A, the sample 16 is irradiated with the electron beam 17 in a spread state to obtain a transmission image of the sample. In the image thus obtained, a portion to be analyzed (a minute portion) is determined, and as shown in FIG. 6B, the portion is irradiated with a finely focused electron beam. Then, secondary information such as secondary electrons and X-rays generated from this portion is detected by a well-known detector to obtain data relating to composition and makeup structure.

FIG. 4 is a diagram showing the configuration of the second converging lens 15a which is the second embodiment of the present invention, and the same reference numerals as those used above denote the same or equivalent portions. In the present embodiment, the first and second exciting coils use a common exciting coil driving power source 7, and only the direction of the current I2 flowing through the second exciting coil 2 is switched by a polarity switching device 8 such as a switch, so that the electronic lens The operation can be easily turned on / off. That is, this electronic lens 15a
The on state of is shown in Fig. 5 (a) and the off state is shown in Fig. 5 (a).
It is shown in (b).

As a modified example of this embodiment, when the switch 8 is switched, the microprocessor 44 controls the power supply 7 to temporarily (approximately 1 second) the current applied to the coils 1 and 2.
By making it zero, it is possible to prevent wear of the contacts of the switch 8.

The exciting coils 1 and 2 used in this embodiment
The number of turns is 560 and it is 2.3A.
Was applied.

FIG. 6 is a diagram showing the configuration of the second converging lens 15b which is the third embodiment of the present invention, and the same reference numerals as those used above denote the same or equivalent portions.

In the embodiment described with reference to FIG. 4, the first exciting coil 1 and the second exciting coil 2 are connected in series, but in the present embodiment, the first exciting coil 21 is connected to the first exciting coil 21. The feature is that both the second and third exciting coils 22 and 23 are connected in parallel.

In the present embodiment, the coils 21 to 23 have the same number of turns. The winding directions are the same for the first and second exciting coils and the opposite directions for the first and third exciting coils. The switch 28 selectively connects one of the second and third exciting coils and the power supply 7. A current is constantly supplied to the first exciting coil 21 from the power supply 7.

As is apparent from the figure, when the second exciting coil 22 is selected by the switch 28, the electron lens 15 is turned on, and the electron lens strength is the magnetic field generated by the first and second exciting coils. It is represented by the sum of. On the other hand, when the third exciting coil 23 is selected by the switch 28, the magnetic field generated by the first exciting coil 21 and the magnetic field generated by the third exciting coil 23 cancel each other, and as a result, the electron lens 15 becomes Virtually off.

When an ordinary electron lens is used, the current for exciting the second converging lens 15 greatly changes, so that the temperature of the second converging lens 15 changes drastically and the electron lens 15
Stability is lost, causing defocusing and electron beam temperature drift. On the other hand, if the configuration of the present invention is applied to the second converging lens 15, only the lens strength can be changed (on / off) while the exciting current of the second converging lens 15 is kept constant. The temperature drift of the two-converging lens 15 is eliminated, and stable performance can be obtained.

In the above-mentioned embodiment, the exciting currents I1 and I2 supplied to the exciting coils 1 and 2 are reversed in order to generate opposite magnetic fields in the exciting coils 1 and 2. The present invention is not limited to this, and the exciting coils 1 and 2 may be wound in opposite directions.

Further, in the above-mentioned embodiments, the case where the electron lens of the present invention is applied to a transmission electron microscope has been described as an example, but the present invention is not limited to this, and a scanning electron microscope or an electron beam drawing is used. The present invention can also be applied to other electron beam devices such as a device.

[0035]

As described above, according to the present invention, since the strength of the electron lens can be changed while keeping the amount of current flowing in the same excitation of the electron lens constant, thermal expansion due to heat generation of the coil, Temperature drift can be eliminated. Therefore, it is possible to realize a thermally stable electron lens.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a magnetic field type electron lens that is a first embodiment of the present invention.

FIG. 2 is a diagram showing a method for controlling an exciting coil according to the present invention.

FIG. 3 is a diagram showing a method for controlling the electron lens strength according to the present invention.

FIG. 4 is a configuration diagram of a magnetic field type electron lens that is a second embodiment of the present invention.

FIG. 5 is an operation principle diagram of an irradiation lens system to which the present invention is applied.

FIG. 6 is a configuration diagram of a magnetic field type electron lens that is a third embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a transmission electron microscope to which the present invention is applied.

[Explanation of symbols]

1 ... 1st exciting coil, 2 ... 2nd exciting coil, 3 ... yoke,
4 ... 1st excitation coil drive power supply, 5 ... 2nd excitation coil drive power supply, 6 ... Excitation coil drive power supply control device, 7 ... Excitation coil drive power supply, 8 ... Polarity switching device, 10 ... Charged particle beam path, 12 ... Electron Source, 13 ... Aperture, 14 ... First converging lens, 15 ... Second converging lens, 16 ... Sample, 17 ... Electron beam

Front Page Continuation (72) Inventor Yuji Sato, 882, Ige, Katsuta-shi, Ibaraki Hitachi, Ltd. Measuring Instruments Division

Claims (9)

[Claims] 1. A magnetic field type electron comprising at least first and second exciting coils wound like a solenoid around an electron beam passage in a magnetic path, and energizing each exciting coil to generate a lens magnetic field. In the lens, a magnetic field type electron lens comprising an excitation control means for controlling an excitation state of the second excitation coil independently of the first excitation coil. 2. The excitation control means independently controls the supply ratio of the excitation current to each excitation coil while keeping the total sum of the absolute values of the excitation current supplied to each excitation coil substantially constant. The magnetic field type electron lens according to claim 1. 3. The first exciting coil and the second exciting coil have the same number of turns and the same winding direction, respectively, and the excitation control means has an absolute value of a current supplied to the first exciting coil and the second exciting coil. 3. The magnetic field type electron lens according to claim 1, wherein the polarity and the polarity are independently controlled. 4. The first exciting coil and the second exciting coil have the same number of turns and opposite winding directions, and the excitation control means includes the first exciting coil and the second exciting coil.
The magnetic field type electron lens according to claim 1, wherein the absolute value and the polarity of the current supplied to the exciting coil are independently controlled. 5. A means for fixedly connecting one end of the first exciting coil to one pole of a power source, and one end of the second exciting coil connected to the other end of the first exciting coil and a second exciting coil. A first mode in which the other end is connected to the other pole of the power supply, and one end of the second excitation coil is connected to the other pole of the power supply and the other end of the second excitation coil is the first
Switching means having a second mode connected to the other end of the exciting coil, the first mode being selected by the switching means.
The exciting coil and the second exciting coil are excited so that their respective magnetic fields are mutually strengthened, and when the second mode is selected,
5. The magnetic field type electron lens according to claim 1, wherein the respective magnetic fields are excited so as to be substantially canceled. 6. When switching the mode of the switching means,
6. The magnetic field type electron lens according to claim 5, further comprising means for temporarily turning off the power source. 7. A third exciting coil wound in the magnetic path together with the first and second exciting coils, means for exciting the first exciting coil, and any one of the second exciting coil and the third exciting coil. Selective excitation means for selectively exciting one of the two is provided. When the second excitation coil is selectively excited by the selective excitation means, the magnetic fields of the first excitation coil and the second excitation coil reinforce each other. 5. When excited and selectively excited by the third exciting coil, the first exciting coil and the third exciting coil are excited so that their respective magnetic fields are substantially canceled. The magnetic field type electron lens according to any one of 1. 8. An electron beam apparatus, wherein an imaging lens system is constituted by the magnetic field type electron lens according to any one of claims 1 to 4. 9. An electron beam apparatus, wherein an irradiation lens system is constituted by the magnetic field type electron lens according to any one of claims 5 to 7.