JP2006210035A - Electron lens and charged particle beam device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron lens capable of obtaining any lens strength without giving influence of a temperature change to the magnetic path of the electron lens, that is, without deforming the outer shape of the magnetic path and to provide a charged particle beam device using the lens. <P>SOLUTION: This electron lens has a plurality of exciting coils wound in the form of a solenoid in the magnetic path with a charged particle beam passage as a center, an exciting coil driving power supply to supply an exciting current to a plurality of the exciting coils, a switching means to switch the direction of the exciting current passed in a plurality of the exciting coils, and the exciting current has the same current value even if the direction of the current flow is switched. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electron lens and a charged particle beam device using the electron lens, and in particular, an electron lens capable of controlling the lens strength without changing the temperature of the magnetic path of the electron lens, that is, without deforming the magnetic path, and The present invention relates to a charged particle beam apparatus using this electron lens.

  The electron lens has a function of focusing or diverging a charged particle beam (hereinafter represented by an electron beam) such as an electron beam or an ion beam. Among them, the magnetic field type electron lens uses the interaction between the electron beam and magnetism to focus or diverge the electron beam, and is widely used in electron microscopes, ion beam devices, electron beam drawing devices, and the like. Yes.

  Generally, a magnetic field type electron lens has an exciting coil in a magnetic path, and realizes its function by using a magnetic field generated by passing an exciting current through the exciting coil.

  Here, in order to change the lens strength of the magnetic type electron lens, it is necessary to change the magnitude of the excitation current flowing through the excitation coil or to change the number of turns of the excitation coil. However, if the magnitude of the exciting current flowing through the exciting coil is changed, even if the resistance value of the exciting coil is constant, the power consumed by the exciting coil changes in proportion to the square of the exciting current.

  Further, since the resistance value of the exciting coil changes when the number of turns of the exciting coil is changed, the power consumed by the exciting coil changes even if the exciting current is constant. Therefore, the generated heat changes according to the power consumed by the exciting coil, and the temperature of the magnetic path of the electron lens changes, so that the magnetic path is deformed, that is, the casing is deformed.

  The deformation of the casing adversely affects the magnetic field strength of the electron lens and its distribution, and causes problems such as an irregular drift of the electron beam spot.

  As a method for improving this problem, as shown in Patent Document 1 (Japanese Patent Laid-Open No. 6-2088838), two excitation coils are provided in a magnetic path, and excitation flows through the respective excitation coils. There is known a method for keeping the sum of absolute values of current constant and eliminating a temperature change of the magnetic path of the electron lens.

Japanese Patent Laid-Open No. 6-208838

  However, in this method, since the ratio of the excitation current flowing through each excitation coil is changed, even if the total sum of the absolute values of the excitation current is kept constant, the total amount of heat generated in each excitation coil is not constant. This is because, as described above, the amount of heat generated in the exciting coil is related to the square of the exciting current, which eventually changes the temperature of the magnetic path of the electron lens and may adversely affect the electron lens. was there.

  An object of the present invention is to provide an electron lens capable of controlling an arbitrary lens intensity without changing the temperature of the magnetic path of the electron lens, that is, without changing the magnetic path, and a charged particle beam apparatus using the electron lens. It is to provide.

  The present invention includes a plurality of excitation coils wound in a solenoid shape around a charged particle beam path in a magnetic path, an excitation coil drive power source for supplying an excitation current to the plurality of excitation coils, and the plurality of the plurality of excitation coils. It has switching means for switching the direction of the exciting current flowing through the exciting coil, and the exciting current has the same current value even when the direction of the flow is switched.

  According to the present invention, since the current value of the exciting current is kept the same even when the flow direction is switched, it is possible to provide an electron lens and a charged particle beam apparatus that are extremely stable against the heat generation of the exciting coil. .

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings of the examples.

  FIG. 3 is a block diagram showing a schematic configuration of a transmission electron microscope provided with the electron lens of the present invention. The transmission electron microscope is one of charged particle beam apparatuses, and the charged particle beam apparatus includes an ion beam apparatus, an electron beam drawing apparatus, an electron beam inspection apparatus, an ion beam inspection apparatus, and the like.

  Now, the electron beam 47 emitted from the electron gun 42 which is a means for generating charged particles is converged by the irradiation lens systems 44 and 45 and irradiated onto the sample 46. The electron beam transmitted through the sample 46 is magnified by the imaging lens system 64 and forms an image on the fluorescent plate 65 for image observation. The fluorescent plate 65 is lifted and stored when taking a picture or observing an image with the imaging device (TV camera) 66. At the time of taking a picture, the film 79 is placed on the optical axis and exposed.

  Excitation currents supplied to the irradiation lens systems 44 and 45 and the imaging lens system 64 are respectively supplied by D / A converters 70a to 70f, power supplies 37a to 37f, and a microprocessor 74 connected via a data bus 73. Be controlled. A control program is stored in the memory 75, and the arithmetic unit 76 performs calculations necessary for controlling the electron microscope main body. A display device (CRT or the like) 77 displays an image captured by the imaging device 66.

  The transmission image detected by the imaging device 66 is output as an image signal from the control device 37 and taken into the storage device 68 (frame memory or the like). The image data stored in the frame memory 68 can be observed by the display device 77. An input device (I / O) 78 inputs parameters (coordinate position, shape, etc.) for designating an arbitrary region while observing a transmission image displayed on the display device 78. For example, a keyboard or a mouse is used. Etc.

  FIG. 1 and FIG. 2 are detailed views showing the structure of a magnetic field type electron lens which is an embodiment of the main part of the present invention applied to the imaging lens system 34.

  In the yoke (magnetic path) 9 for the electronic lens, the excitation coil 1a having 4 turns, the 4 excitation coil 1b, the 8 excitation coil 2, the 16 excitation coil 3, and the 32 excitation coil are provided. Coil 4, 64 winding excitation coil 5, 128 winding excitation coil 6, 256 winding excitation coil 7, 512 winding excitation coil 8 are provided.

  Each exciting coil is wound in the same direction like a solenoid with the charged particle beam passage 10 as a central axis. The excitation coil 1a is directly connected to the excitation coil drive power supply 21a as shown in FIG. 2, and the excitation coil 1b is connected to the excitation coil 1b drive power supply 21b via the polarity switch 11b (switching means) of the excitation coil 1b. Has been.

  Hereinafter, similarly, the excitation coils 2, 3, 4, 5, 6, 7, and 8 are respectively excited through the excitation coil polarity switches 12, 13, 14, 15, 16, 17, and 18 (switching means). The coil drive power supplies 22, 23, 24, 25, 26, 27 and 28 are connected.

  The excitation coil polarity switchers 11b, 12, 13, 14, 15, 16, 17, and 18 are controlled by the control device 19 and can change the direction of the excitation current flowing through each excitation coil.

  The control device 19 is mainly composed of a microprocessor 74. The switching means is built in the exciting coil driving power source.

  Here, as shown in FIG. 5, the following exciting currents are passed from the respective exciting coil driving power sources to the respective exciting coils.

(1) Excitation current whose magnitude is substantially equal and in a constant direction: I
(2) With the polarity switch of each excitation coil, the excitation current only in the direction opposite to that of (1): -I At this time, the lens strengths M _{1a to} M ₈ obtained by each excitation coil are as shown in Table 1. .

  However, the case where the exciting current I was passed through the exciting coil 1a (the number of turns: 4 turns) was defined as a positive direction, and the magnitude at that time was defined as m.

The effective intensity of the electron lens provided in the electron microscope is the sum of the lens intensity of each exciting coil (M _1a + M _1b + M ₂ + M ₃ + M ₄ + M ₅ + M ₆ + M ₇ + M ₈ ) based on the law of magnetic field superposition. Therefore, FIG. 4 shows the effective lens strength obtained by arbitrarily and independently switching only the direction of each excitation current by the polarity switch of each excitation coil.

  In FIG. 4, the horizontal axis represents a control signal (digital signal) input value to the control device 19, and the vertical axis represents the effective lens strength of the electronic lens.

  The control signal has 224 switching steps. That is, 224 different combinations of excitation coils can be selected.

  Here, from the conditions such as the number of excitation coils and the number of turns, the effective strength of the electron lens is from 2 m to 2 m from 256 m to 0, that is, the effective number of turns of the electron lens is from 1024 to 0. It can be arbitrarily obtained in increments of 8 up to -1016.

  This is as if the D / A converter connected to the conventional electronic lens power supply is operated, and does not impair the operability of the conventional control system. In the present embodiment, the configuration is made in consideration of ease of control, fineness of control, and the like. For these reasons, the number of exciting coils whose polarity can be switched is set to 8, and the number of turns is set to 4, 8, 16, 32, 64, 128, 256, and 512, respectively. In addition to this, by providing an exciting coil having four turns without polarity switching means, the lens strength can be made zero.

  Note that the negative lens strength in FIG. 4 means a state in which the rotational direction of the image is generated in the opposite direction, which occurs simultaneously with the refractive power in the case of the field lens. Moreover, the negative number of turns corresponds to the winding direction of the exciting coil being reversed.

  According to the present embodiment, since it is possible to change the intensity of the electron lens while keeping the absolute value of the current flowing through each exciting coil in the same magnetic path constant, this electron lens is used as an imaging lens. Various electron beam apparatuses such as an electron microscope provided in the system can observe and analyze with high resolution by preventing thermal expansion, temperature drift, and the like due to heat generation of the coil.

  In this embodiment, the transmission electron microscope provided with the imaging lens system according to the present invention has been described. However, the present invention can be applied to an irradiation system lens as well.

  Furthermore, the present invention can be applied not only to a transmission electron microscope but also to other electron beam apparatuses such as a scanning electron microscope, an ion beam apparatus, and an electron beam drawing apparatus.

It is sectional drawing of the magnetic field type electronic coil concerning the Example of this invention. It is a block diagram of the magnetic field type electronic coil concerning the Example of this invention. It is a schematic block diagram of the transmission electron microscope concerning the Example of this invention. It is the figure which showed the control method of the electron lens intensity | strength concerning the Example of this invention. The figure which concerns on the Example of this invention and showed the relationship between each exciting coil and exciting current.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1a-8 ... Excitation coil, 9 ... Relay, 10 ... Charged particle beam path, 11b-18 ... Polarity switch of excitation coil 1b-8, 19 ... Control apparatus, 21a-28 ... Excitation coil 1a-8 drive power supply, 42 ... electron source, 44 ... second focusing lens, 45 ... first focusing lens, 46 ... sample, 47 ... electron beam.

Claims (8)

  A plurality of excitation coils wound in a solenoid shape around a charged particle beam path in a magnetic path, an excitation coil drive power supply for supplying an excitation current to the plurality of excitation coils, and a flow through the plurality of excitation coils An electronic lens comprising switching means for switching the direction of excitation current, wherein the excitation current has the same current value even when the direction of flow is switched. The electron lens according to claim 1,
The number of said exciting coils is 3 or 8 or more, The electron lens characterized by the above-mentioned. The electron lens according to claim 1,
2. An electron lens characterized in that the turns ratio of the exciting coil is t, t, 2t,..., 2 ⁽ⁿ⁻²⁾ · t turns. The electron lens according to claim 1,
The excitation lens driving power source is provided for each of the excitation coils. The electron lens according to claim 1,
The electronic lens according to claim 1, wherein the switching means is provided individually for the exciting coil. The electron lens according to claim 1,
An electronic lens comprising an excitation coil that is not switched by the switching means in the plurality of excitation coils. The electron lens according to claim 1,
An electronic lens comprising a control device for controlling switching by the switching means.   A plurality of excitation coils wound in a solenoid shape around a charged particle beam path in a magnetic path, an excitation coil drive power supply for supplying an excitation current to the plurality of excitation coils, and a flow through the plurality of excitation coils A charged particle beam comprising switching means for switching the direction of the excitation current and charged particle generation means for generating charged particles, wherein the excitation current has the same current value even when the flow direction is switched apparatus.

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