JP3234373B2 - Magnetic field type electron lens and electron beam device using the same - Google Patents

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 which uses a lens magnetic field generated by an exciting coil to converge or expand a charged particle beam (hereinafter, represented by an electron beam) such as an electron beam or an ion beam. More particularly, the present invention relates to a magnetic field type electron lens capable of changing a lens strength while keeping a current flowing through an exciting coil constant, and an electron beam apparatus using the same.

[0002]

2. Description of the Related Art Electron lenses are widely used in various electron beam apparatuses such as an electron microscope, an electron beam lithography (EB) apparatus, and an ion beam apparatus to focus or expand an electron beam. Generally, in a magnetic field type electron lens, an electron beam is converged or expanded by a magnetic field generated by flowing a current through an excitation coil provided in a magnetic path.

Here, 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 supply having the ability to flow a large current is required. Further, when the number of turns of the exciting coil is increased, the resistance of the exciting coil increases, so that there is a problem that a high voltage must be generated.

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

[0005]

According to the above-mentioned prior art, when the current flowing through the exciting coil is changed to change the strength of the electron lens, the power consumed by the coil does not change 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 magnetic path, that is, the casing of the coil is deformed by the heat generated in accordance with the electric power.
Deformation of the casing adversely affects the magnetic field strength of the electron lens and its distribution, causing problems such as, for example, irregular drift of the electron beam spot. A known example related to such a technique 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 without changing the temperature of the magnetic path, that is, without deforming the magnetic path at all. It is an object of the present invention to provide a possible magnetic field type electron lens and an electron beam device using the same.

[0007]

In order to achieve the above-mentioned object, according to the present invention, a plurality of exciting coils are vertically arranged in a hollow donut-shaped casing, that is, a magnetic path. The excitation coils were arranged so as to substantially coincide with each other, and each excitation coil was 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 a direction opposite to that of the other exciting coils, the electron lens strength is reduced by the magnetic field generated by each exciting coil. The current flowing inside the magnetic path is the sum of the currents flowing through the respective exciting coils. Therefore, by controlling the current supply ratio to each coil while keeping the sum of the currents flowing through each excitation coil constant, it is possible to change the strength of the electron lens while keeping the heat generated inside the magnetic path constant. Can be.

Further, 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 the heat. Never.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail 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 light is converged by the irradiation lens systems 14 and 15 and is irradiated on the sample 16. The electron beam transmitted through the sample 16 is enlarged by the imaging lens system 34 and forms an image on the image observation fluorescent plate 35. The fluorescent plate 35 is lifted up and stored at the time of taking a picture or observing an image with an imaging device (TV camera) 36. At the time of photographing, the film 49 is set on the optical axis and is exposed.

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

The transmitted image detected by the image pickup device 36 is output as an image signal from the control device 37 and is taken into a storage device 38 (frame memory or the like). Frame memory 38
Can be observed by the display device 47. The input device (I / O) 48 inputs parameters (coordinate position, shape, etc.) for specifying an arbitrary area while observing the transmission image displayed on the display device 47, and includes, for example, a keyboard and a mouse. And so on.

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

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

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

FIG. 3 is a diagram showing the relationship between the second excitation current I2 (horizontal axis) and the effective intensity (vertical axis) of the electron lens. The lens strength obtained by supplying the exciting current I1, which is indicated by a 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 represents 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 configuration, the exciting currents I1 and I2 supplied to the exciting coils 1 and 2 are provided.
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 to make I1 and I2 reverse polarities, as shown by the solid line BCD in FIG. 3, the electron lens strength depends on the ratio of the currents I1 and I2. Change. In addition,
The negative lens strength in FIG. 3 means a state in which the rotating direction of the image is opposite to that of the field lens, which is generated simultaneously with the refractive power.

If two sets of coils are provided in the same magnetic path and the directions of the currents flowing in the coils are made different from each other, the total sum of the absolute values of the currents flowing in the same magnetic path is kept constant. In addition, the intensity of the electron lens can be continuously changed from zero to the maximum value.

The point E in FIG.
2 is the lens strength when the same current of the same phase flows through the two coils, and point C is the lens strength when the same current of the opposite phase flows through 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 that the lens intensity becomes zero when viewed as a whole lens, but at point E the magnetic fields generated by the exciting coils are added, and A double lens action is obtained.

According to this embodiment, it is possible to change the strength of the electron lens while keeping the sum of the absolute values of the currents flowing in the same magnetic path constant. When applied to the imaging lens system of various electron beam apparatuses, drift and the like of the electron beam spot are prevented, and observation and analysis with high resolution can be performed.

The present invention can be applied not only to the above-described imaging lens system but also to an 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 aperture 13, and thereafter, the electron beam 17 is irradiated onto the sample 16 via the first converging lens 14 and the second converging lens 15.

When a sample is analyzed by a transmission electron microscope, first, as shown in FIG. 1A, the sample 16 is irradiated with the electron beam 17 expanded so as to obtain a transmission image of the sample. In the image thus obtained, a portion to be analyzed (small portion) is determined, and as shown in FIG. 4B, the portion is irradiated with a narrowed electron beam. Then, secondary information such as secondary electrons and X-rays generated from this portion is detected by a well-known detector, and data that is linked to the composition and the makeup structure is obtained.

FIG. 4 is a view showing the structure of a second converging lens 15a according to a second embodiment of the present invention, and the same reference numerals as those described above denote the same or equivalent parts. In the present embodiment, the first and second excitation coils use a common excitation coil drive power source 7 and only the direction of the current I2 flowing through the second excitation coil 2 is switched by a polarity switching device 8 such as a switch, so that the electronic lens The function can be easily turned on / off. That is, this electronic lens 15a
FIG. 5 (a) shows the ON state of FIG. 5, and FIG.
(b).

As a modification 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.
In this case, the contact of the switch 8 can be prevented from being worn.

The excitation coils 1 and 2 used in this embodiment
Has 560 turns and 2.3A
Was applied.

FIG. 6 is a view showing the structure of a second converging lens 15b according to a third embodiment of the present invention, and the same reference numerals as those described above denote the same or equivalent parts.

In the embodiment described with reference to FIG. 4, the first excitation coil 1 and the second excitation coil 2 are connected in series. In the present embodiment, however, the first excitation coil 21 is connected to the first excitation coil 21. It is characterized in that both the second and third excitation coils 22 and 23 are connected in parallel.

In this embodiment, the number of turns of each of the coils 21 to 23 is the same. The winding direction is the same for the first and second excitation coils, and is opposite for the first and third excitation coils. The switch 28 selectively connects one of the second and third excitation coils and the power supply 7. A current is always supplied from the power supply 7 to the first excitation coil 21.

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

When a normal electron lens is used, the current for exciting the second converging lens 15 fluctuates greatly.
Loss of stability, blurring of the focus and temperature drift of the electron beam. 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-described embodiment, the excitation currents I1 and I2 supplied to the respective excitation coils are reversed in order to generate the opposite magnetic fields in the respective excitation 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.

In the above-described embodiment, the case where the electron lens of the present invention is applied to a transmission electron microscope has been described as an example. However, the present invention is not limited to this, and the present invention is not limited thereto. It can be applied to other electron beam devices such as a device.

[0035]

As described above, according to the present invention, the strength of the electron lens can be changed while the amount of current flowing in the same excitation of the electron lens is kept constant. Temperature drift can be eliminated. Therefore, a very thermally stable electron lens can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a magnetic field type electron lens according to a first embodiment of the present invention.

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

FIG. 3 is a diagram illustrating a method of controlling the strength of an electronic lens according to the present invention.

FIG. 4 is a configuration diagram of a magnetic field type electron lens according to 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 according to 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]

DESCRIPTION OF SYMBOLS 1 ... 1st excitation coil, 2 ... 2nd excitation coil, 3 ... Yoke,
4 First excitation coil drive power supply 5 Second 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 Electronic Source, 13: stop, 14: first converging lens, 15: second converging lens, 16: sample, 17: electron beam

Continuation of the front page (72) Inventor Yuji Sato 882 Ma, Katsuta-shi, Ibaraki Pref. Hitachi, Ltd. Instrumentation Division (56) References JP-A-48-47265 (JP, A) JP-A-48-94358 ( JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01J 37/141

Claims (3)

(57) [Claims] 1. A solenoid wound around an electron beam path
In the magnetic field type electron lens for energizing the excited excitation coil to generate a lens magnetic field , the first and second excitation coils are overlapped in the electron beam irradiation direction.
A magnetic path yoke to be accommodated, a means for fixedly connecting one end of the first excitation coil to one pole of a power supply, and a first end of the second excitation coil connected to the other end of the first excitation coil. A first mode in which the other end of the second excitation coil 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 connected to the other end of the first excitation coil. Switching means having a second mode connected to the end , wherein when the first mode is selected by the switching means, the first mode is selected.
The exciting coil and the second exciting coil are excited so that their respective magnetic fields are strengthened, and when the second mode is selected,
A magnetic field type electron lens characterized in that the magnetic fields are excited so as to substantially cancel each other. 2. A solenoid wound around an electron beam path.
In the magnetic field type electron lens for energizing the excited excitation coil to generate a lens magnetic field , the first and second excitation coils are overlapped in the electron beam irradiation direction.
A magnetic path yoke which accommodates the excitation state of the second excitation coil, wherein the magnetic field type electron lens, characterized in that the first excitation coil; and a excitation control means for independently controlling. 3. An electron beam apparatus, wherein an irradiation lens system is constituted by the magnetic field type electron lens according to claim 1 or 2.