Micro stage for particle beam column using piezo elements as actuator
09837245 ยท 2017-12-05
Assignee
Inventors
Cpc classification
H02N2/026
ELECTRICITY
H01J37/20
ELECTRICITY
International classification
G21K5/10
PHYSICS
H01J37/20
ELECTRICITY
H02N2/00
ELECTRICITY
H02N2/02
ELECTRICITY
Abstract
Disclosed herein is a micro stage using a piezoelectric element that can be reliably operated even in a vacuum environment. In a particle column requiring a high precision, for example, a microelectronic column, the micro stage can be used as a stage with micro or nano degree precision for alignment of parts of the column, or for moving a sample, and so on.
Claims
1. A micro stage comprising a movable body provided to move a target, and a main-body piezoelectric base to which the movable body is movably coupled, wherein the main-body piezoelectric base comprises side-surface pressurizing units for pressurizing the movable body, the movable body has inclined surfaces on portions thereof coming into contact with the respective side-surface pressurizing unit of the main-body piezoelectric base, the one or more side-surface pressurizing units comprise a side-surface pressurizing body pressurizing the movable body, a side-surface piezoelectric element coming into contact with the side-surface pressurizing body in order to move the movable body, and an inward pressurizing piezoelectric element provided on the side-surface piezoelectric element in order to press the side-surface pressurizing body toward the movable body, the inward pressurizing piezoelectric element that makes contact with the side-surface piezoelectric element is operated in a longitudinal mode and pressurizes and releases the movable body by depending on supply of voltage to the inward pressurizing piezoelectric element, and the side-surface piezoelectric element is operated in a shear mode and transversely moves the movable body, and pressurizing force is applied from the opposite side-surface pressurizing units of the main-body piezoelectric base to opposite sides of the movable body and thus pressurizes the movable body in an inclined direction so that the movable body is pressurized onto the main-body piezoelectric base while the movable body is moved.
2. The micro stage as set forth in claim 1, further comprising any one of or both: an inclined-surface guide bonded to one side or each of both sides of the movable body, the inclined-surface guide forming a downward and outward inclined surface and coming into contact with the corresponding side-surface pressurizing unit of the main-body piezoelectric base; and a bottom support part provided on a contact surface of the main-body piezoelectric base that makes contact with the movable body, the bottom support part supporting a bottom of the movable body.
3. The micro stage as set forth in claim 2, wherein the bottom support part comprises: a bottom pressurizing body coming into contact with the bottom of the movable body; and a bottom piezoelectric element disposed between the bottom pressurizing body and a seating surface of the main-body piezoelectric base.
4. The micro stage as set forth in claim 1, wherein the side-surface pressurizing unit further comprises an elastic part pressurizing the side-surface pressurizing body toward the movable body.
5. The micro stage as set forth in claim 2, wherein the side-surface pressurizing unit further comprises an elastic part pressurizing the side-surface pressurizing body toward the movable body.
6. The micro stage as set forth in claim 3, wherein the side-surface pressurizing unit further comprises an elastic part pressurizing the side-surface pressurizing body toward the movable body.
7. The micro stage as set forth in claim 1, wherein the bottom support part comprises: a bottom pressurizing body coming into contact with the bottom of the movable body; and a bottom piezoelectric element disposed between the bottom pressurizing body and a seating surface of the main-body piezoelectric base.
8. The micro stage as set forth in claim 7, wherein the side-surface pressurizing unit further comprises an elastic part pressurizing the side-surface pressurizing body toward the movable body.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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DESCRIPTION OF THE PREFERRED EMBODIMENT
(12) Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.
(13) A micro stage 100 using a piezoelectric element according to the embodiment of the present invention is a linear stage basically conducting linear movement and includes a main-body piezoelectric base 21 and a movable body 46 for use in transfer of a target.
(14) The purpose of the present invention is to provide a stage capable of using a piezoelectric element as an actuator even in an ultra-high vacuum environment. Minimizing contact points between parts of the piezoelectric element when operated and preventing the base and the linear piezoelectric element from moving away from each other when the stage is operated are the principle concepts of the present invention. That is, the micro stage according to the present invention is a stage that maintains the distance between the main-body piezoelectric base and the movable body constant, and minimizes a contact area therebetween.
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(16) The main-body piezoelectric base 21 includes side-surface pressurizing units 22 that are used to move the movable body 46. Each side-surface pressurizing unit 22 includes a side-surface pressurizing body 221 and a side-surface piezoelectric element 222. The movable body 46 is moved relative to the-body main-body piezoelectric base 21 by the operation of the side-surface piezoelectric element 222. Given this, it is desirable that the side-surface piezoelectric element 222 be a shear mode piezoelectric element. The shear mode piezoelectric element is operated such that the movable body 46 can be moved in a transverse direction of the main-body piezoelectric base 21. The operation method of the piezoelectric element is similar or equal to that of the conventional piezoelectric stage. Therefore, a detailed description thereof will be omitted.
(17) As shown in the drawings, a surface of the movable body 46 that faces the side-surface pressurizing body 221 of the side-surface pressurizing unit 22 is inclined downward such that a horizontal cross-sectional area of the movable body 46 is increased from the top to the bottom, that is, toward the surface of the main-body piezoelectric base 21 that faces the movable body 46. Due to the downward and outward inclined surface of the movable body 46, the movable body 46 is biased toward the main-body piezoelectric base 21 so that the movable body can be maintained in close contact with contact parts of the main-body piezoelectric base 21. Thereby, because the close contact state of the movable body 46 can be maintained even when moving, the movable body 46 can be prevented from wobbling or moving away from the main-body piezoelectric base 21. The downward and outward inclined surface may be formed on either side of the movable body 46 or each of the opposite sides thereof. That is, although only any one side of the movable body 46 may have a downward and outward inclined surface while the other side thereof has a vertical surface, it is desirable that the opposite side surfaces of the movable body 46 that face the respective side-surface pressurizing units 22 each comprise a downward and outward inclined surface, as shown in the drawing.
(18) As shown in
(19) Each side-surface pressurizing unit 22 includes the side-surface piezoelectric element 222 for movement operation, and the side-surface pressurizing body 221 that is moved by the side-surface piezoelectric element 222. In detail, a first side of the side-surface pressurizing body 221 comes into contact with the side-surface piezoelectric element 222, and a second side thereof comes into contact with the movable body 46. The side-surface pressurizing body 221 may be embodied in various other shapes, for example, a semicircular shape, a triangular pyramidal shape, a protrusion shape, etc.
(20) In this embodiment, downward and outward inclined surfaces 461 are formed on the respective opposite sides of the movable body 46. The pressurizing bodies 221 of the side-surface pressurizing units 22 come into contact with the respective inclined surfaces 461 of the movable body 46. Thus, the pressurizing bodies 221 act such that the movement of the movable body 46 toward the pressurizing bodies 221 is restricted.
(21) The bottom of the movable body 46 comes into contact with the upper surface of the central portion of the main-body piezoelectric base 21, wherein they may make surface contact with each other, or the bottom of the movable body may come into contact with protruding bottom support parts 24 provided on a seating surface 241 of the main-body piezoelectric base 21, as shown in the drawings. Each bottom support part 24 making contact with the movable body 46 may have a simple hemispheric shape or protrusion shape. Furthermore, the bottom support part having a hemispheric shape, a protrusion shape, etc. comes into contact with the bottom of the movable body 46 may be made of ruby, alumina, sapphire, steel, etc. in the same manner as that of the side-surface pressurizing body functioning to compress or support a part. Desirably, the bottom support part is made of material capable of ensuring normal operation without changing in conditions or characteristics even in a vacuum environment. Furthermore, the bottom support parts are used as a means for maintaining the movable body 46 horizontal.
(22)
(23) The general construction of the micro stage 100 of
(24) Other than the above-mentioned characteristics of the micro stage 100 of
(25)
(26) In detail, as shown in
(27) In this embodiment, the movable body 46 that linearly moves relative to the main-body piezoelectric base 21 is operated both by the side-surface pressurizing units 22 that are disposed on the opposite sides of the movable body 46 and linearly move and pressurize the movable body 46 and by the side-surface piezoelectric elements 222 and the bottom piezoelectric elements 243 of the bottom support parts 24 that support the bottom of the movable body 46. Therefore, the linear movement of the movable body 46 relative to the main-body piezoelectric base 21 can be conducted more reliably and precisely.
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(29) In this embodiment, a side-surface pressurizing unit 22 is coupled to the main-body piezoelectric base 21 by an elastic part 25. The elastic part 25 may be provided only on either side of the main-body piezoelectric base 21 or on each of the opposite sides thereof. The elastic part 25 elastically pushes the corresponding side-surface pressurizing unit 22 toward the movable body 46 that is disposed between the side-surface pressurizing units 22. The elastic part 25 may be separately manufactured having a thin plate spring structure and then coupled to the main-body piezoelectric base 21. Alternatively, the elastic part 25 may be integrally formed with the main-body piezoelectric base 21. The force with which the opposite side-surface pressurizing bodies 221 pressurize the movable body 46 by means of the elastic part 25 also acts as force compressing the movable body 46 toward the main-body piezoelectric base from the contact parts of the inclined surfaces 461 of the movable body 46. Thus, downward force is applied to the movable body 46, whereby the movable body 46 can be more reliably maintained in contact with the main-body piezoelectric base 21.
(30)
(31) The inward pressurizing piezoelectric element 223 desirably comprises a piezoelectric element that is operated in a longitudinal mode. That is, in this embodiment, the side-surface pressurizing unit 22 that transversely pressurizes and moves the movable body 46 further includes the inward pressurizing piezoelectric element 223 that is provided on the side-surface piezoelectric element 222 and is operated in the longitudinal mode. Therefore, depending on supply of voltage to the inward pressurizing piezoelectric element 223, the side-surface pressurizing body 221 and the side-surface piezoelectric element 222 that makes contact with the inward pressurizing piezoelectric element 223 pressurize the movable body 46 or release it. During the pressurizing operation by the inward pressurizing piezoelectric element 223, contact force is applied between the movable body and the main-body piezoelectric base in the same principle as that of the embodiment with the above-mentioned elastic part. On the other hand, when the pressurizing force of the inward pressurizing piezoelectric element 223 is removed, the contact force that has been applied between the movable body and the main-body piezoelectric base is also removed.
(32) It is desirable that the elastic force of the elastic part be determined depending on external force applied to the micro stage. As the elastic force of the elastic part is increased, the contact force between the movable body and the main-body piezoelectric base is increased, but the force of the piezoelectric element to move the movable body must also be increased. Given this, the elastic force of the elastic part is determined considering the mobility of the movable body. As the elastic force of the elastic part is reduced, the mobility of the movable body is increased, but the movable body may be undesirably moved by external force. Therefore, the elastic force of the elastic part must be adjusted depending on the purpose of use of the micro stage. Thus, when the elastic part having a comparatively high elastic force is used to increase the precision of the micro stage, it is desirable that a separate stopper (not shown) be provided to limit a range within which the elastic force of the elastic part can be applied to the movable body, and the inward pressurizing piezoelectric element be used to ensure the mobility of the movable body. Of course, this embodiment may further include the inclined-surface guide 462 of
(33) In this embodiment, although using both the elastic part and the inward pressurizing piezoelectric element has been illustrated as being desirable, only one of them may be used depending on the purpose of use of the micro stage.
(34) Furthermore, although each of the embodiments of
(35) In the description of the above-mentioned embodiments or following embodiments of the micro stage 100 according to the present invention, the construction of the micro stage 100 has been or will be mainly illustrated with regard to a rectangular one- or two-dimensional movement method. Using the following description and examples shown in the attached drawings, the micro stage can also be applied to a three-dimensional movement method as well as to the one- or two-dimensional movement method. For example, if two one-dimensional-movement stages are used, the two-dimensional movement method can be embodied. Likewise, if three one-dimensional-movement stages are used, a micro stage that can implement three-dimensional movement can be embodied.
(36)
(37) In each of the embodiments of
(38) Hereinafter, the micro stage according to the preset invention will be explained in more detail with reference to
(39) First, the embodiment of
(40) The intermediate side-surface pressurizing body 321 may be embodied in other various shapes, for example, a semicircular shape, a triangular pyramidal shape, a protrusion shape, etc. In this embodiment, downward and outward inclined surfaces 461 are formed on the respective opposite sides of the movable body 46. The intermediate side-surface pressurizing bodies 321 of the intermediate side-surface pressurizing units 32 come into contact with the respective inclined surfaces 461 of the movable body 46. Thus, the intermediate side-surface pressurizing bodies 321 apply force to the movable body 46 inward.
(41) The bottom of the intermediate piezoelectric base 31 comes into contact with the seating surface 241 formed on the upper surface of the central portion of the main-body piezoelectric base 21. The bottom of the movable body 46 comes into contact with an intermediate seating surface 341 formed on an upper surface of a central portion of the intermediate piezoelectric base 31.
(42) Here, these parts may make surface contact with each other, or the bottom of the intermediate piezoelectric base 31 or the movable body 46 may come into contact with protruding bottom support parts provided on the corresponding seating surface, as shown in the drawings. Each bottom support part 24 of the seating surface 241 making contact with the intermediate piezoelectric base 31 or each intermediate bottom support part 34 of the intermediate seating surface 341 making contact with the movable body 46 may have a simple hemispheric shape or protrusion shape.
(43) The embodiment of
(44) Other than the above-mentioned characteristics of the micro stage 100 of
(45)
(46) In this embodiment, the movable body 46 that linearly moves relative to the intermediate piezoelectric base 31 is operated both by the intermediate side-surface pressurizing units 32 that are disposed on the opposite sides of the movable body 46 and linearly move and pressurize the movable body 46, and by the intermediate side-surface piezoelectric elements 322 and the intermediate bottom piezoelectric elements 343 of the intermediate bottom support parts 34 that support the bottom of the movable body 46. Therefore, the linear movement of the movable body 46 relative to the intermediate piezoelectric base 31 can be conducted more reliably and precisely.
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(48) In this embodiment, the intermediate side-surface pressurizing unit 32 is coupled to the intermediate piezoelectric base 31 by the elastic part 35. The elastic part 35 may be provided only on either side of the intermediate piezoelectric base 31 or on each of the opposite sides thereof. The elastic part 35 elastically pushes the corresponding intermediate side-surface pressurizing unit 32 toward the movable body 46 that is disposed between the intermediate side-surface pressurizing units 32. The elastic part 35 may be separately manufactured having a thin plate spring structure and then coupled to the intermediate piezoelectric base 31. Alternatively, the elastic part 35 may be integrally formed with the intermediate piezoelectric base 31.
(49) Corresponding to the embodiment of
(50) In this embodiment, the intermediate side-surface pressurizing unit 32 that transversely pressurizes and moves the movable body 46 further includes an intermediate-inward-pressurizing piezoelectric element 323 that is provided on the intermediate side-surface piezoelectric element 322 and is operated in the longitudinal mode. The intermediate-inward-pressurizing piezoelectric element 323 may also be disposed on either side of the movable body or on each of the opposite sides thereof.
(51) Meanwhile, a particle emission source, an electronic lens or an electronic lens layer(s) of a particle beam column such as a microelectronic column (micro column) may be provided in the movable body of the micro stage according to each of the embodiments of the present invention. In this case, the particle beam column in which the particle emission source, the electronic lens, or the like are installed in the micro stage of the present invention can be manufactured. If such a particle beam column is manufactured, high-precise movement of the particle emission source, the electronic lens, etc. is embodied by means of the micro stage of the present invention, whereby optical axis adjustment of the lens and the particle emission source of the particle beam column can be markedly facilitated.
(52) The particle emission source, the electronic lens, or the electronic lens may be installed in the movable body of the micro stage of every embodiment of the present invention or may be mounted to the surface of the movable body. In the case of being installed in the movable body, a wire reception hole for wiring from the particle emission source is desirably formed an internal or side-surface through hole in at least one of the main-body piezoelectric base and the intermediate piezoelectric base of the micro stage. More desirably, a through hole is formed along the central axes of the parts.
(53) That is, the through hole for wiring without impeding the movement of the micro stage is formed in the central portions of the movable body, the main-body piezoelectric base, and the intermediate piezoelectric base. Via a feedthrough for a vacuum chamber, wires are desirably connected to a control system, which is disposed outside the vacuum chamber.
(54) If the particle emission source is mounted to the surface of the movable body, it must be reliably fixed, and wires must also reliably fixed in place by means of the wire reception hole or a separate fastener to prevent the wires from impeding the movement of the micro stage.
(55) In the case where the electronic lens or the electronic lens layer is installed, through holes must be formed in the movable body, the main-body piezoelectric base and the intermediate piezoelectric base so as to form a path for passing a particle beam as well as a path for wiring.
(56) Furthermore, contact portions of the side-surface pressurizing unit, the bottom pressurization body, the inclined surface guide, the intermediate bottom pressurization body, the inclined-surface guide, etc. may be made of ruby, alumina, sapphire, steel or the like and desirably made of material capable of ensuring normal operation without changing in conditions or characteristics even in a vacuum environment.
(57) Hereinafter, an operation embodiment of the micro stage 100 using a piezoelectric element according to the present invention having the above-mentioned construction will be described. Although the operation embodiment of the micro stage 100 will be explained based on the embodiment of
(58) First, a process of moving the intermediate piezoelectric base 31 relative to the main-body piezoelectric base 21 will be described.
(59) With regard to the installation state of the micro stage, a first side portion of the main-body piezoelectric base 21 protrudes upwards. The inward pressurizing piezoelectric element 223, the side-surface piezoelectric element 222 and the hemispheric side-surface pressurizing body 221 protrude inward from the first side portion of the main-body piezoelectric base 21, thus forming the side-surface pressurizing unit 22 on the first side portion of the main-body piezoelectric base 21.
(60) The hemispheric bottom support parts 24 are provided on the seating surface 241 formed on the upper surface of the central portion of the main-body piezoelectric base 21.
(61) The intermediate piezoelectric base 31 is disposed such that: a left portion of the intermediate piezoelectric base 31 comes into contact with the side-surface pressurizing unit 22 that is provided on the left portion of the main-body piezoelectric base 21; and the bottom of the intermediate piezoelectric base 31 makes contact with the bottom support parts 24.
(62) Subsequently, the other side-surface pressurizing unit 22 is coupled to a second side portion of the main-body piezoelectric base 21.
(63) The side-surface pressurizing unit 22 that comes into contact with a right portion of the intermediate piezoelectric base 31 includes the inward pressurizing piezoelectric element 223, the side-surface piezoelectric element 222, and the hemispheric side-surface pressurizing body 221 that makes contact with the right portion of the intermediate piezoelectric base 31.
(64) In this assembly state, the opposite side surfaces and the bottom of the intermediate piezoelectric base 31 are covered with the parts coupled to the main-body piezoelectric base 21. In addition, each of the opposite side surfaces of the intermediate piezoelectric base 31 comprises a downward and outward inclined surface. Consequently, with regard to four directions including upward, downward, leftward and rightward, among the six degrees of freedom, the movement of the intermediate piezoelectric base 31 is restricted.
(65) As the voltage applied to the shear mode piezoelectric element 222 gradually increases from 0 V to several tens or hundreds of V, a free surface of the shear mode piezoelectric element that is opposite to a fixed surface thereof is moved by shear force along with the movable body 46 that is brought into close contact with the free surface of the shear mode piezoelectric element. In this state, when the applied voltage is momentarily dropped to 0 V, only the shear mode piezoelectric element 222 and the side-surface pressurizing body 221 return to their initial positions, and the movable body 46 remains at the last position because of the law of inertia. When such voltage applying operations are successively conducted, the movable body 46 is linearly moved forward. To move the movable body 46 in the reverse direction, operations of applying voltage from 0 V to minus several tens or hundreds of V have only to be successively conducted. As such, the stage using the shear mode piezoelectric element according to the present invention can continuously move the movable body without restriction. Therefore, as the length of the movable body is increased, the distance of movement of the stage is also increased. When voltage is applied to the inward pressurizing piezoelectric element 223, the intermediate piezoelectric base 31 is pushed in the transverse direction by the characteristics of the inward pressurizing piezoelectric element 223 that is operated in the longitudinal mode. Thereby, the contact force between the main-body piezoelectric base 21 and the intermediate piezoelectric base 31 is increased.
(66) Thereafter, when voltage is applied to each of the shear mode side-surface piezoelectric elements 222 that are provided on the opposite sides of the main-body piezoelectric base 21, the side-surface pressurizing body 221 and the intermediate piezoelectric base 31 are moved in the transverse direction (forward or rearward in
(67) Subsequently, when the voltage that has been applied to the inward pressurizing piezoelectric element 223 is interrupted, the force that has been applied to the intermediate piezoelectric base 31 is reduced. At this time, when the voltage that has been applied to the side-surface piezoelectric element 222 is also interrupted, only the side-surface pressurizing body 221 returns to its original position while the intermediate piezoelectric base 31 remains at the last position. Therefore, the intermediate piezoelectric base 31 is moved by a predetermined distance relative to the main-body piezoelectric base 21 in a piezoelectric operation manner.
(68) A process of moving the movable body 46 relative to the intermediate piezoelectric base 31 will be described in detail below.
(69) With regard to the installation state of the micro stage, a first side portion (that is, a left portion in
(70) The intermediate bottom support parts 34 are provided on the intermediate seating surface 341 formed on the upper surface of the central portion of the intermediate piezoelectric base 31.
(71) The movable body 46 is disposed such that: the left side surface of the movable body 46 comes into contact with the intermediate side-surface pressurizing unit 32 provided on the left portion of the intermediate piezoelectric base 31; and the bottom of the movable body 46 comes into contact with the intermediate bottom support part 34.
(72) Subsequently, the other intermediate side-surface pressurizing unit 32 (disposed at the right portion of
(73) The intermediate side-surface pressurizing unit 32 that comes into contact with the left side surface of the movable body 46 includes the intermediate-inward-pressurizing piezoelectric element 323, the intermediate side-surface piezoelectric element 322, and the hemispheric intermediate side-surface pressurizing body 321 that makes contact with the left side surface of the movable body 46.
(74) In this assembly state, the opposite side surfaces and the bottom of the movable body 46 are covered with the parts coupled to the intermediate piezoelectric base 31. In addition, each of the opposite side surfaces of the movable body 46 comprises a downward and outward inclined surface. Consequently, with regard to four directions including upward, downward, leftward and rightward among the six degrees of freedom, the movement of the movable body 46 is restricted.
(75) When voltage is applied to the intermediate-inward-pressurizing piezoelectric element 323 that makes contact with the intermediate elastic part 35, the movable body 46 is compressed in the transverse direction by the characteristics of the intermediate-inward-pressurizing piezoelectric element 323 that is operated in the longitudinal mode. Thereby, the contact force between the intermediate piezoelectric base 31 and the movable body 46 is increased.
(76) Thereafter, when voltage is applied to each of the shear mode intermediate side-surface piezoelectric elements 322 that are provided on the opposite sides of the intermediate piezoelectric base 31, the intermediate side-surface pressurizing body 321 and the movable body 46 are moved in the transverse direction.
(77) Subsequently, when the voltage that has been applied to the intermediate-inward-pressurizing piezoelectric element 323 is interrupted, the force that has been applied to the movable body 46 is reduced. At this time, when the voltage that has been applied to the intermediate side-surface piezoelectric element 322 is also interrupted, only the intermediate side-surface pressurizing body 321 returns to its original position while the movable body 46 remains at the last position. Therefore, the movable body 46 is moved by a predetermined distance relative to the intermediate piezoelectric base 31 in a piezoelectric operation manner.
(78) Therefore, a sample or the like that is placed on the movable body 46 can be moved relative to the main-body piezoelectric base 21 in biaxial directions including the X-axis and Y-axis. As a result, the micro stage 100 according to the present invention can rapidly, precisely, and reliably move the sample in a desired direction.
(79) As described above, the present invention provides a micro stage that uses a piezoelectric element as an actuator. The micro stage can be reliably operated with nanometer-level precision even in a vacuum environment.
(80) Furthermore, the micro stage of the present invention is configured such that the distance between the piezoelectric element and moving parts can be maximally reduced, whereby the micro stage can be precisely operated.
(81) The piezoelectric element according to the present invention can continuously move a movable body so that there is no limit in the distance of movement of the micro stage
(82) There is no need for applying voltage to the piezoelectric element in a stationary state because the micro stage can be physically stable.
(83) Furthermore, in the present invention, a downward and outward inclined surface is formed on each of the opposite sides of the movable body that moves a target. Therefore, force applied from both side-surface pressurizing units to the movable body also pushes the movable body downward, thus preventing a gap between the movable body and a base from occurring while the movable body moves.
(84) Moreover, in the present invention, the piezoelectric element is used to move a particle emission source, so that the movement and operation of the particle emission source can become more reliable.
(85) Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.