JP2009079728A - Dynamic vibration absorber using viscoelastic material and charged particle beam device using dynamic vibration absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dynamic vibration absorber using a viscoelastic material and a charged particle wire device using the dynamic vibration absorber which can appropriately adjust the natural frequency of vibration of the dynamic vibration absorber. <P>SOLUTION: The dynamic vibration absorber provided to a base plate 51 for vibration isolation is provided with the viscoelastic material 52 and a heavy weight 53 supported by the viscoelastic material 52. The viscoelastic material 52 is arranged in a predetermined position on the base plate 51, and the viscoelastic material 52 is a cluster of viscoelastic materials divided by a predetermined size. The dynamic vibration absorber is constituted so that the heavy weight 53 is placed on the viscoelastic material 52. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a dynamic vibration absorber using a viscoelastic material and a charged particle beam apparatus using the dynamic vibration absorber.

  For example, in an apparatus that performs precision work such as analysis, observation, and measurement of a sample such as an electron microscope, the sample is moved and rotated in the horizontal plane and in the vertical axis direction (optical axis direction) with high accuracy. Observation and analysis from the direction.

  When external vibrations (ie, disturbances) are transmitted to the base plate used to support the electron microscope and sample, the vibrations are transmitted to the analysis / observation / measurement device, sample, etc. for observation. As a result, the analysis results are adversely affected.

  The apparatus for performing precision work such as analysis, observation and measurement is manufactured with high accuracy in order to analyze very fine portions. For this reason, transmission of vibrations from the outside causes an error in a precisely adjusted device.

  In order to protect the charged particle beam apparatus from such disturbances, various anti-vibration measures are taken. As a conventional device of this type, an anti-vibration mount connecting portion is provided on the lower surface of four corner portions of a substantially rectangular flat plate having four sides or a portion adjacent to a cut portion obtained by cutting the corner portion. A flat base body, a damping material having a high loss factor supported on the upper surface of a portion adjacent to the four corner portions of the flat plate, and a portion adjacent to the four corner portions of the flat plate. A device is known in which four vibration-proof weights supported on the damping material are provided corresponding to the upper surface (see, for example, Patent Document 1).

This dynamic vibration absorber is usually designed so that its natural frequency matches or is close to the frequency to be controlled. The natural frequency f of this dynamic vibration absorber is as follows when the mass of a heavy object is m [kg] and the spring constant is k [N / m]:
f = (1 / 2π) × √ (k / m) (1)
It is represented by

In order to adjust the natural frequency f to be lower, for example, a method is adopted in which the spring constant k is lowered by increasing the mass m of the heavy object, reducing the area of the viscoelastic material, or increasing the thickness. .
Japanese Patent No. 3741558 (paragraphs 0008 to 0009, FIGS. 1 and 2)

  However, in order to reduce the natural frequency f, even if the mass m of the heavy object is to be increased, there is actually a limit to increasing the volume of the heavy object for design reasons. There are restrictions. Further, if the use area of the viscoelastic material is reduced in order to reduce the spring constant k, the damping capacity is lowered.

  Further, when the thickness of the viscoelastic material is increased, since the vibration amplitude of the vibration suppression target is constant, the strain amplitude with respect to the viscoelastic material is reduced. In general, a viscoelastic material tends to have a loss factor that increases as strain vibration increases. Therefore, a decrease in strain amplitude decreases the damping capacity of the dynamic vibration absorber.

  The present invention has been made in view of such problems. First, the natural frequency of the dynamic vibration absorber is not changed without changing the area and thickness of the viscoelastic material and without changing the mass of the heavy object. It is an object of the present invention to provide a dynamic vibration absorber and a charged particle beam device capable of appropriately adjusting the second characteristic, and capable of having a damping capability in a second wider frequency range.

(1) The invention described in claim 1 is a dynamic vibration absorber installed on a base plate, comprising a viscoelastic material arranged at a predetermined position on the base plate, and a heavy object supported by the viscoelastic material. The viscoelastic material is an aggregate of viscoelastic material units divided by a predetermined size, and the heavy object is placed on the viscoelastic material.
(2) The invention according to claim 2 is characterized in that an apparent spring constant is changed by changing a width with respect to a thickness of the viscoelastic material.
(3) The invention described in claim 3 is characterized in that the ratio of the width and thickness of the viscoelastic material is set to a certain value or less.
(4) According to a fourth aspect of the present invention, in a charged particle beam apparatus including a base plate and a charged particle beam apparatus main body supported on the base plate, the first to third positions of the base plate may be provided. The dynamic vibration absorber according to any one of the above is installed.

(1) According to the first aspect of the present invention, the weight of the dynamic vibration absorber is reduced by placing a heavy object on a viscoelastic material unit having a predetermined shape arranged at a predetermined interval. The coefficient can be increased, and a damping effect in a wider frequency range can be obtained.
(2) According to the invention described in claim 2, by changing the width with respect to the thickness of the viscoelastic material, the natural frequency of the dynamic vibration absorber is reduced, and thereby using this property, the area of the viscoelastic material is reduced. The natural frequency of the dynamic vibration absorber can be adjusted in accordance with the frequency to be damped without reducing the mass or increasing the mass of the heavy object.
(3) According to the invention described in claim 3, the natural frequency of the dynamic vibration absorber can be adjusted by changing the ratio of the width and thickness of the viscoelastic material, and the loss factor can be stabilized at a high value.
(4) According to the invention described in claim 4, by applying the dynamic vibration absorber using the viscoelastic material of the present invention to the charged particle beam device, the influence on the observation image due to the disturbance of the charged particle beam device is reduced. can do.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, the vertical direction is drawn in the horizontal direction. In the figure, 51 is a base plate as a vibration control object, and 52 is a viscoelastic material arranged at a predetermined position on the base plate 51. The viscoelastic material 52 is composed of an aggregate of units divided by a predetermined size. Reference numeral 53 denotes a heavy object (weight) supported by the viscoelastic material 52. As the heavy object 53, for example, an iron rectangular parallelepiped is used.

  What is shown on the right side of FIG. 1 shows the shape of the viscoelastic material, and is composed of an aggregate of strip-like viscoelastic material units. 52a is a single viscoelastic material, 52b is a viscoelastic material divided into two, 52c is a viscoelastic material divided into four, 52d is a viscoelastic material divided into eight, and 52e is 16 It is a divided viscoelastic material. For example, the case of the viscoelastic material 52c is taken as an example. In this case, it is shown that the viscoelastic material 52 c is formed from the four viscoelastic material units 54. The apparatus configured as described above will be described below.

  The viscoelastic material 52 is disposed on almost the entire surface in accordance with the shape of the heavy object 53. This is to maximize the use area of the viscoelastic material 52 and increase the damping capacity. And as shown on the right side of FIG. 1, the viscoelastic material 52 was divided | segmented into strip shape, and it provided with the clearance gap between each, and compared. The used viscoelastic material has a thickness of 2 [mm] and a total width of 64 [mm]. When the number of divisions is 1, 2, 4, 8, 16 (each width is 64, 32, 16, 8, 4 [mm]), the vibration control object to the heavy object 53 is respectively associated The vertical frequency transfer function was measured. The comparison results are shown in FIG. 2 as a transmission rate and in FIG. 3 as a phase difference.

  FIG. 2 is a diagram showing frequency transfer function comparison. In the figure, the horizontal axis represents frequency [Hz] and the vertical axis represents transmission rate. The transmission rate is expressed as the ratio of output to input. Here, the frequency is taken on the horizontal axis because it is necessary to know the characteristics of the dynamic vibration absorber of the viscoelastic material against noise. The viscoelastic material 52 has a common thickness of 2 mm. f1 is a characteristic in the case of no division, f2 is a characteristic in the case of 1/2 division, f3 is a characteristic in the case of 1/4 division, f4 is a characteristic in the case of 1/8 division, and f5 is a characteristic in the case of 1/8 division. The characteristics in the case of 16 divisions are shown. It can be seen that the transmission rate decreases from around 500 Hz for the characteristics f3 to f5. Regarding f1 and f2, the transmissibility shows 1 or more from a frequency of 500 Hz to 1000 Hz, and then attenuates.

  FIG. 3 is a diagram showing phase comparison characteristics. The horizontal axis represents frequency [Hz] and the vertical axis represents phase. In FIG. 3, the frequency at which the phase difference is −90 ° is the natural frequency of the dynamic vibration absorber. The used viscoelastic material has a thickness of 2 [mm] and a total width of 64 [mm]. In the figure, f11 is a characteristic in the case of no division, f12 is a characteristic in the case of 1/2 division, f13 is a characteristic in the case of 1/4 division, f14 is a characteristic in the case of 1/8 division, and f15 Indicates characteristics in the case of 1/16 division.

Looking at this characteristic, it was confirmed that the natural frequency decreased as the number of divisions increased, that is, the width of the strip narrowed. The effect of reducing the overall spring constant is due to the use of a characteristic known as a shape effect in the design of vibration-proof rubber. FIG. 4 is a view showing the outer shape of the square anti-vibration rubber. The length of the side is infinite, the width is a, and the thickness is h. If the length is sufficiently long relative to the width a, the length can be equivalently considered as an infinite length. If the initial Young's modulus at this time is E and the transverse elastic modulus is G, the shape factor S is S = a / 2h (2)
It is represented by In this case, the ratio between the Young's modulus and the transverse elastic modulus of the vibration-proof rubber shown in FIG.

E / G = 4 + 3.290S ² (3)
Therefore, the equation (3) is applied to most squares.
By the way, the apparent spring constant decreases as the ratio of width to thickness (for example, a / h in the case of FIG. 4) decreases. Thereby, it was shown that the natural frequency of the dynamic vibration absorber can be adjusted without changing the total area of the viscoelastic material.

  In FIG. 3, when the number of divisions is 4 or more, that is, in the characteristics f13 to f15, the phase change becomes slow and falls within a certain characteristic. In the case of f11 and f12 where the number of divisions is smaller, the phase change is steep, and the maximum value of the transmission rate increases with this as shown in FIG. This indicates that the apparent loss coefficient can be stabilized at a large value by setting the ratio of the width to the thickness of the viscoelastic material to a certain level or less. According to this embodiment, by changing the width with respect to the thickness of the viscoelastic material, the natural frequency of the dynamic vibration absorber is reduced, thereby reducing the area of the viscoelastic material using this property, The natural frequency of the dynamic vibration absorber can be adjusted in accordance with the frequency to be controlled without increasing the mass of the vibration absorber.

  When the loss factor is increased, the effective frequency bandwidth of the dynamic vibration absorber is increased. FIG. 5 shows the force applied by an ideal tuned vibration absorber. The horizontal axis represents frequency [Hz], and the vertical axis represents the vibration absorber force. The figure shows the cases of loss factor η = 0.1, 0.2, 0.5. The change of the real part and imaginary part of reaction force FD is shown about the same frequency parameter. This reaction force is limited to a relatively narrow frequency band when the loss coefficient η is small, but it can be seen that the frequency band increases as the loss coefficient increases. This characteristic is important when targeting a fairly wide frequency range.

  In the anti-vibration base plate described in Patent Document 1 described above, it is required to simultaneously suppress a plurality of natural vibration modes of the base plate. Therefore, vibration of a wider frequency band can be achieved by dividing the viscoelastic material, and it is not necessary to use a plurality of dynamic vibration absorbers provided for each frequency in parallel.

  As described above, the ratio of the width and the thickness of the viscoelastic material required to stabilize the maximum value of the transfer function is low when the thickness of the viscoelastic material is 2 [mm] and 3 [mm]. Was about 8 or less. However, when the thickness is 1 [mm], the characteristic of phase change is not stable unless this ratio is smaller. As mentioned above, the thinner the viscoelastic material, the greater the distortion amplitude and the loss factor can be expected to increase, but the spring constant in the expansion / contraction direction increases when the thickness is reduced, so the number of divisions is increased. Therefore, the width of the strip must be narrowed and the apparent spring constant must be lowered.

  If the width is smaller than the thickness, the stability as a structure is lacking, and actual application becomes difficult. According to this embodiment, the natural frequency of the dynamic vibration absorber can be adjusted by changing the ratio of the width and thickness of the viscoelastic material, and the loss factor can be stabilized at a high value.

  In the above description, the case of using a strip-shaped viscoelastic material unit is taken as an example. However, the present invention is not limited to this, and the same applies when a circular or square viscoelastic material is used. There is an effect.

  Based on the above-described experiment, a dynamic vibration absorber using a viscoelastic material having a thickness of 2 [mm] and a width of 16 [mm] × 4 is mounted on the vibration-proof base plate disclosed in Patent Document 1, and acoustic processing is performed. The acceleration at the edge of the base plate under shaking was measured. FIG. 6 shows a comparison of acceleration spectra with and without a dynamic vibration absorber. The horizontal axis is frequency, and the vertical axis is frequency. f21 shows the characteristics when there is no dynamic vibration absorber, and f22 shows the characteristics when there is a dynamic vibration absorber. As is apparent from the figure, the effect of the dynamic vibration absorber was recognized in a wide frequency band ranging from 300 Hz to 1.3 kHz. The apparatus on which this base plate is mounted is an SEM, but the effect of the dynamic vibration absorber was remarkably recognized in the comparison of the amount of image noise generated by acoustic excitation.

  FIG. 7 is a diagram showing a configuration example of a charged particle beam apparatus using the dynamic vibration absorber according to the present invention. Here, the case where SEM (scanning electron microscope) is used as a charged particle beam apparatus is taken as an example. The SEM 1 includes four anti-vibration mounts 3 having a low spring constant supported on a gantry 2, an anti-vibration base plate P supported on the anti-vibration mount 3, and a microscope supported on the base plate P. It has a main body 4. An exhaust pipe 6 is connected to the microscope body 4.

  8 is an explanatory view of the base plate P of FIG. 7, FIG. 8A is a top view, and 8B is a sectional view taken along the line IIB-IIB of FIG. In FIG. 8, the anti-vibration base plate P has a flat base body 11. The flat base body 11 has a shape in which four corner portions of a rectangular flat plate formed by four sides are cut out. The shape of the cut portion is a right isosceles triangle.

  Anti-vibration mount coupling portions 26 to 29 are provided on the lower surface of the base body 11 adjacent to the oblique sides 16 to 19. The anti-vibration mount 3 is connected to the anti-vibration mount connecting portions 26 to 29. A frame-shaped rib 31 is provided inside the four anti-vibration mount connecting portions 26 to 29 on the lower surface of the base body 11. The frame-shaped rib 31 includes side ribs 32 to 35 parallel to the respective sides 12 to 15, side ribs 32 to 35 provided in parallel to the respective oblique sides 12 to 15, and the respective oblique sides 16 to 19 and the hypotenuse-facing ribs 36 to 39 arranged in parallel to and opposite to 19.

  A pair of hypotenuse facing ribs 36, 39 and 37, 38 facing each other among the hypotenuse opposing ribs 36 to 39 constitute a first hypotenuse rib 36, 39 and a second hypotenuse rib 37, 38, respectively. The first oblique side opposing ribs 36 and 39 and the second oblique side opposing ribs 37 and 38 are arranged perpendicular to each other.

  The frame-like rib 31 formed by the side ribs 32 to 35 and the oblique side opposing ribs 36 to 39 is provided on the bottom surface of the base body 11 so that the four anti-vibration mount connecting portions 26 to 29 do not have the same shape. It is asymmetrical with respect to the center.

  The hypotenuse-facing ribs 36 to 39 are formed at positions away from the hypotenuses 16 to 19 in order to form the anti-vibration mount connecting portions 26 to 29 between the hypotenuses 16 to 19. . Accordingly, the total length of the oblique side opposing ribs 36 to 39 is formed longer than the total length of the side ribs 32 to 35.

  In the SEM configured as described above, the corners of the four sides of the base plate P are cut off, and the viscoelastic material 16 according to the present invention is placed thereon, and the heavy object 47 is placed on the viscoelastic material 16. Is placed. That is, four dynamic vibration absorbers according to the present invention are attached to the four hypotenuses 16 to 19 on the base plate P of the SEM 1. In the apparatus configured in this way, it is possible to obtain a sufficient damping effect against disturbance noise and the like.

  In the above-described embodiment, the case where the present invention is applied to the SEM has been described. However, the present invention is not limited to this, and is similarly applied to other charged particle beam apparatuses (for example, charged particle beam drawing apparatuses). be able to.

  As described above, according to the present invention, first, the natural frequency of the dynamic vibration absorber is appropriately adjusted without changing the area and thickness of the viscoelastic material and without changing the mass of the heavy object. In addition, it is possible to provide a dynamic vibration absorber and a charged particle beam device capable of providing damping performance in a second, wider frequency range.

It is a block diagram which shows one embodiment of this invention. It is a figure which shows frequency transfer function comparison. It is a figure which shows a phase comparison characteristic. It is a figure which shows the external shape of a square vibration-proof rubber. It is a figure which shows the force applied by an ideal synchronous vibration absorber It is a figure which shows the acceleration spectrum comparison by dynamic vibration absorber presence or absence. It is a figure which shows the structural example of the charged particle beam apparatus using the dynamic vibration absorber which concerns on this invention. It is a block diagram of the anti-vibration base plate.

Explanation of symbols

51 Base plate (for vibration control)
52 Viscoelastic material 53 Heavy object (sleep)

Claims (4)

A dynamic vibration absorber installed on a base plate,
A viscoelastic material arranged at a predetermined position on the base plate;
A heavy object supported by the viscoelastic material,
The viscoelastic material is an aggregate of viscoelastic material units divided by a predetermined size,
The heavy object is placed on the viscoelastic material,
A dynamic vibration absorber using a viscoelastic material.   2. The dynamic vibration absorber using a viscoelastic material according to claim 1, wherein an apparent spring constant is changed by changing a width with respect to a thickness of the viscoelastic material.   2. The dynamic vibration absorber using a viscoelastic material according to claim 1, wherein a ratio of a width and a thickness of the viscoelastic material is set to a predetermined value or less. A base plate;
A charged particle beam apparatus main body supported on the base plate;
In the charged particle beam device constituted by
A charged particle beam apparatus comprising the dynamic vibration absorber according to claim 1 installed at a predetermined position of the base plate.

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