Patent Application
20150041676
The present invention relates to a noise-proof cover used in a charged particle beam apparatus and, more particularly, to a noise-proof cover that can suppress the influence of sound having a specific frequency and a charged particle beam apparatus.
In a charged particle beam apparatus such as an electron microscope for performing observation of a microstructure at high resolution using an electron beam, occurrence of an image failure is revealed by very small vibration or sound from the outside according to improvement of resolution. Therefore, for the purpose of preventing occurrence of an image failure caused by emission of setting environment sound, a noise-proof cover for covering an apparatus from the outer side is set as means for blocking transmission of a sound wave emitted to the apparatus.
The noise-proof cover usually forms a hexahedral structure having upper and lower, left and right, and upper and lower surfaces taking into account a wraparound characteristic of a sound wave and in view of workability and a reduction in costs.
To improve noise-proof performance of the cover, it is effective to absorb sound on the inside of the cover and stretch an organic porous material around the inner surface of the cover. However, in general, the charged particle beam apparatus is used in a clean room. In some case, dusting characteristics due to a spray of the organic material hinder dust resistance of the clean room to cause a problem. As means for preventing this problem, a technique for covering a sound absorbing material with dust-proof fiber and attaching the sound absorbing material to the inner surface of the noise-proof cover is disclosed in PTL 1.
In general, in the field of acoustical engineering, it is known that a resonance frequency depending on the shape of a container because of air vibration in a mouth portion of the shape of a flask-shaped container is present. This is called Helmholtz resonator. There is a technique for absorbing sound making use of this sound absorption principle. For example, as a sound absorption structure that makes use of this technique, a sound absorption structure made of a box member including a large number of small holes is disclosed in PTL 2. A structure in which the Helmholtz resonator is set in a sash portion of a double window is disclosed in PTL 3 and PTL 4. A structure in which the Helmholtz resonator is set in a lower part of a skirt portion of a railway car is disclosed in PTL 5.
PTL 1: JP-A-2006-79870
PTL 2: JP-A-2008-138505
PTL 3: Japanese Patent No. 4232153
PTL 4: JP-A-2010-216104
PTL 5: Japanese Patent No. 3911208
In a charged particle beam apparatus having high resolution, a noise-proof cover is set as means for blocking transmission of a sound wave emitted to an apparatus. Consequently, noise resistant performance for a relatively high frequency is improved. However, on the other hand, noise resistant performance is sometimes deteriorated in a low-frequency region. This is caused because, whereas, in general design, a part sensitive to vibration in an apparatus is arranged near a cover center, since an anti-node of a sound pressure of an acoustic standing wave generated in the cover is present exactly in the cover center at a certain frequency, the part sensitive to vibration is excited.
When the vibration caused by the sound at the specific frequency is treated by the noise-proof cover of PTL 1, the thickness of the sound absorbing material to be set increases because a target frequency is low. In the conventional technique disclosed in PTL 2, it is necessary to open innumerable holes having an opening diameter equal to or smaller than a plate thickness. Since it is difficult to open the holes with general punching, laser machining needs to be separately performed. As a result, it is likely that manufacturing costs increase. Further, in PTL 3 or PTL 5, a structure such as a shape and a setting place for enabling efficient sound absorption is not provided by a sound absorption structure specialized for a frequency that causes a problem in the charged particle beam apparatus.
A noise-proof cover and a charged particle beam apparatus having an object of realizing both of suppression of an image failure caused by a specific frequency and a reduction in size are explained below.
As an aspect for attaining the object, there is proposed below a noise-proof cover that surrounds a charged particle beam apparatus, the noise-proof cover including a hollow section forming member that forms a cylindrical body having a wall surface extending along an inner wall of the noise-proof cover, one end of the cylindrical body formed by the hollow section forming member being opened and the other end of the cylindrical section being closed, and a charged particle beam apparatus surrounded by the noise-proof cover.
With the configuration explained above, it is possible to provide the noise-proof cover and the charged particle beam apparatus that do not need a thick sound absorbing material or the like, have small sizes, and suppress an image failure caused by a specific frequency.
An embodiment explained below relates to a charged particle beam apparatus in which an image failure occurs because of acoustic excitation. As an example, the embodiment relates to a noise-proof cover for reducing noise and vibration from an outside environment. In particular, it is assumed that the noise-proof cover is used in a clean room or the like.
In particular, in this embodiment, concerning a noise-proof cover for a high-resolution charged particle beam apparatus set for the purpose of preventing occurrence of an image failure caused by setting environment sound, a structure for evenly improving noise resistance performance over all frequency bands and realized inexpensively without spoiling dust resistance enough for use in a clean room, which is a setting environment of the charged particle beam apparatus, and easiness of cover opening and closing that takes into account maintenance.
More specifically, in this embodiment, concerning a charged particle beam apparatus configured by an electron gun, a sample chamber, and a detector and a noise-proof cover that covers the outer side of the charged particle beam apparatus, an example is explained in which the charged particle beam apparatus can discriminate an object equal to or smaller than 100 nm and can perform observation at extremely high resolution, the electron gun or the detector or both of the electron gun and the detector are arranged at an end of the apparatus, the sample chamber is arranged in the center of the apparatus, the noise-proof cover has cylindrical hollow sections, one sides of which are opened and the other sides of which are closed with respect to an inner surface, and opening portions of the cylindrical hollow sections are arranged to be present at up, down, left, and right direction ends or up, down, left, and right direction centers in a cover inside or both of the ends and the centers.
The noise-proof cover including a hollow section forming member that forms cylindrical bodies having the wall surfaces extending along the inner wall of the noise-proof cover, one ends of the cylindrical bodies formed by the hollow section forming member being opened and the other ends of the cylindrical bodies being closed, as explained above can efficiently eliminate the influence of sound caused in the cover. Specifically, it is possible to set, in the position of an anti-node of a sound pressure of an acoustic standing wave generated in the cover, a sound absorbing mechanism having a large sound absorption characteristic at a generated frequency of the acoustic standing wave. The noise-proof cover explained in detail below is effectively applied to, in particular, a charged particle beam apparatus having high resolution and can prevent occurrence of an image failure caused by setting environment sound.
The noise-proof cover explained below can improve noise resistant performance evenly over all frequency bands. It is possible to inexpensively provide the noise-proof cover without spoiling dust resistance enough for use in a clean room, which is a setting environment of the charged particle beam apparatus, and easiness of cover opening and closing that takes into account maintenance.
The charged particle beam apparatus explained below indicates apparatuses that perform high-accuracy inspection, observation, and machining such as a general purpose scanning electron microscope, a transmission electron microscope, a measuring apparatus (CD-SEM), a review apparatus, a defect inspection apparatus, and a sample machining apparatus using a charged particle beam and refers to an apparatus in general in which an image failure is caused by very small vibration of the apparatus.
Since the charged particle beam apparatus is an imaging apparatus as explained above, main performance of the charged particle beam apparatus is resolution. However, since a very small structure is enlarged and displayed, an image failure is caused by an extremely trivial disturbance. The vibration damping base 109 is set to prevent an image failure caused by vibration from a floor. As an effect of the vibration damping base 109, the image failure due to the floor vibration is reduced. On the other hand, according to improvement of resolution to be higher in definition, in particular, in a recent high-resolution model, that realizes resolution equal to or smaller than 100 nm, an image failure caused by setting environment sound of the charged particle beam apparatus is also revealed.
A correspondence relation between the setting environment sound and an amount of the image failure is explained below. An emitted sound pressure and an amount of an image failure at the time when a sound wave is emitted to the charged particle beam apparatus are measured and grasped. A sound pressure obtained by calculating, on the basis of a correspondence relation between the emitted sound pressure and the amount of the image failure, a setting environment sound of which dB or less is required to reduce a degree of the image failure to a predetermined value or less is referred to as “allowable sound pressure”. A larger value of the “allowable sound pressure” means that predetermined resolution can be secured even in a poor environment and indicates that noise resistance performance is high.
As a method of improving resistance against the image failure caused by the setting environment sound, that is, noise resistance performance, recently, a noise-proof cover 200 shown in
However, as shown in
This is because an acoustic standing wave shown in
In embodiments explained below, a structure for effectively reducing an intra-cover acoustic sanding wave taking advantage of the fact that the acoustic standing wave generated in the cover is generated at a frequency determined by a dimension of the cover. The embodiments are explained below with reference to the drawings.
In this embodiment, an embodiment of a noise-proof cover structure that can effectively reduce an intra-cover acoustic standing wave and a charged particle beam apparatus including the noise-proof cover structure is explained with reference to
As explained above, among the charged particle beam apparatuses, in particular, in the transmission electron microscope, the portion of the holder 105 is susceptible to vibration because of the structure of the transmission electron microscope. Therefore, the noise resistance performance is lower near the peculiar frequency of the holder 105 than at frequencies around the peculiar frequency. The deterioration in the noise resistance performance at this frequency is reduced by setting the noise-proof cover 200. However, at another frequency lower than the peculiar frequency of the holder 105, an acoustic standing wave having an anti-node of a sound pressure near the cover center where the holder is arranged is generated and the noise resistance performance is deteriorated. Incidentally, the generated frequency of the acoustic standing wave (an acoustic mode) having the anti-node of the sound pressure in the cover center where the holder is arranged depends on the shape and the dimension of the cover. For example, in a 2nd mode in vertical direction, when the height of the cover is represented as h [m], the generated frequency is 340/h [Hz]. If the height of the cover is set to 2 [m], the generated frequency in the 2nd mode in vertical direction is 170 [Hz].
On the other hand, it is known that, when sound having a wavelength four times as long as the length of a cylinder, one side of which is closed and the other side of which is opened, arrives, the cylinder emits sound having an opposite phase of a phase of the arriving sound wave again to thereby cancel the original arriving sound and reduce (absorb) the arriving sound. This is called an acoustic tube. When the length of the acoustic tube is represented as l [m], a frequency at which the acoustic tube displays a sound absorption effect most is 340/41 [Hz].
When the standing wave in the 2nd mode in vertical direction generated in the cover having the height h [m] is effectively absorbed using the acoustic tube, the length l [m] is 1=h/4 [m] and is exactly length for equally dividing the height direction. To display the sound absorption effect to the maximum, it is desirable to set the opening sections 211 in the positions of anti-nodes of a sound pressure. In the 2nd mode in vertical direction, the opening sections are arranged to be present on the cover upper inner surface, the cover lower inner surface, and the cover inner height direction center.
In this embodiment, two noise-proof panels illustrated in
When such components are arranged on the cover inner surfaces in the arrangement shown in
Effects of the structure explained in the first embodiment are explained with reference to
Concerning these models, when a point sound source is arranged in a position of 1 m on the cover side surface outer side and 1 m on the floor and a reflection surface simulating the floor is set in a position 10 mm below the cover lower end, a result obtained by calculating sound leaking from a gap between the floor and the cover and transmitting to the cover inside is shown in
In this embodiment, an example of a structure in which acoustic standing waves in a 2nd mode in vertical direction and a 1st mode in horizontal direction can be suppressed by setting an acoustic tube using not only a side surface but also an inner surface of a ceiling and a floor surface is explained with reference to
A pattern of combination with perforated panels is explained as another embodiment with reference to
A pattern in which cylindrical hollow sections are set in multiple stages on a noise-proof cover inner surface is explained as still another embodiment with reference to FIG. 13. In
By skillfully setting the multistage structure of the cylindrical hollow sections, it is possible to expect improvement of noise resistance performance in all frequency bands. For example, in the model 2 applied with the first embodiment in the lower figure of
A pattern in which cylindrical hollow sections arranged in multiple stages are arranged to be suspended from a noise-proof cover ceiling is explained as still another embodiment with reference to
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-055233 | Mar 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/053788 | 2/18/2013 | WO | 00 |
