JP2002062358A - Method for polishing sintered body crystal and particle detector using polished fluorescent substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mirror polish a cadmium oxysulfide fluorescent substance of a sintered body ceramics with a reduced number of dents/bumps and pores. SOLUTION: In polishing the cadmium oxysulfide fluorescent substance of the sintered body ceramics, diamond fine particles are used as an abrasive powder, and a tin face plate is used as an abrasive plate. Thereafter, the fluorescent substance is combined with a photodetector. Particles are brought into the fluorescent substance, and a light generated by the fluorescent substance is detected by the photodetector. A mirror face, without dents/bumps and pores on a surface, is obtained in this manner. Since the fluorescence generates no irregular reflection inside, when the mirror face is provided to the particle detector, fluorescence can be collected efficiently, and moreover, a resolution can be improved for the fluorescene having image information in comparison with, when the fluorescent substance is not ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing a crystal of a sintered body and a detector which enables highly sensitive particle beam detection.

[0002]

2. Description of the Related Art Polishing of a solid material is performed extremely frequently for various materials, and various studies have been made on a polishing mechanism and the like. For example, “Science of CMP” edited by Science Forum (published in 1997) and “Optical Technology Contact vol. 29, No. 12 (1991), p. Many descriptions have been made. Usually, polishing is performed by using an abrasive (abrasive grains), a polishing plate (a surface plate, a polisher), and a polishing liquid (including water) and rubbing an object against them.
In the above literature, as an abrasive, silica (aluminum oxide), alumina (aluminum oxide), cerium oxide,
Powder materials such as diamond particles are introduced. Silicas have been widely used for mirror polishing of silicon semiconductors, aluminas for metal materials, and cerium oxides for glass materials such as lenses. Next, as a polishing plate, quartz glass, bakelite, porous Teflon (registered trademark), polyurethane, hard glass, iron plate, copper plate, tin plate, lead plate, cedar plate and the like are introduced. Further, as the polishing liquid, potassium hydroxide solution and the like are introduced in addition to water and lubricating oil. As a method of combining these and polishing, other than a method of applying a so-called mechanical micro-cutting action, in which a polishing powder is simply dissolved in water and placed on a polishing plate, and the object is rubbed therewith. There are introduced mechanical chemical polishing in which the chemical dissolution action of the polishing liquid is superimposed on the action, and mechanochemical polishing using a chemical reaction induced by the mechanical action. In such a method, for example, a colloidal silica-based polishing powder is polished by using a potassium hydroxide solution polishing solution having a pH of about 10 to polish a silicon wafer or the like with a mirror surface and without distortion. It can be said that there are countless polishing methods in combination of the above conditions.

On the other hand, a material considered to be polished in the present application is cadmium oxide (Gd ₂ O ₂ S; gado) containing a small amount of praseodymium, cerium, and fluorine.
linium oxysulfide (hereinafter referred to as GOS). When measuring the intensity and energy of particle beams such as electron beams and ion beams with a measuring device, the particle beams are once converted into light beams by a phosphor, etc., and detected by a photodetector such as a semiconductor detector or a photomultiplier tube. However, in order to perform high-sensitivity measurement, it is advisable to use a phosphor having good energy conversion efficiency, that is, a phosphor having a large light emission amount. The aforementioned GOS has been recently developed as such a phosphor.
This phosphor is available from The Japan Society of Applied Physics, No. 30, 371-37
As disclosed on page 3, a sintered phosphor in which a small single crystal with a size of about 50 × 50 × 200 μm is baked and hardened
(Ceramic scintillator). It should be noted that there is no example showing a mirror polishing method with good flatness for this material.

[0004]

However, the present inventor has found that the above-mentioned polishing technique has the following problems.

That is, there are countless polishing methods in combination with the above-mentioned conditions, but the optimum method differs depending on the material and structure of the object and the purpose of use. Therefore, GO
Experimental determination is important for relatively complicated materials such as S that have been developed in recent years. A particular problem to be solved is the flatness of the surface after polishing. For example, when fluorescence generated inside is detected by a photodetector, it is necessary to take out the fluorescence without irregular reflection, and in many cases, the flatness of the phosphor surface is important. We will present a highly polished method. Here, regarding the flatness, in the case of a sintered ceramic (polycrystalline) material such as GOS, the presence or absence of crystal grain boundary defects (pores) is an important factor as well as the difference in surface height. .

An object of the present invention is to provide a technique capable of improving the flatness of a polished surface of a sintered body.

Another object of the present invention is to provide a technique capable of reducing defects at crystal grain boundaries of a sintered body.

Another object of the present invention is to provide a technique capable of detecting and imaging particles with high sensitivity and high resolution.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0010]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, the present invention focuses on the GOS of a sintered body crystal of a sintered ceramic as a phosphor material having a high light emission, and uses diamond fine particles as a polishing powder and a tin plate as a polishing plate. As a result, mirror polishing is performed, and the difference in surface height and the amount of crystal grain boundary defects (pores) can be suppressed.

Further, the present invention combines the phosphor polished as described above with a photodetector, and allows a particle beam to be incident on the phosphor.
The generated fluorescence is detected by a photodetector.

[0013]

FIG. 1 shows an embodiment of the present invention.
The tool configuration used in the polishing operation is shown. The upper part of FIG. 1 is a view of the various components shown in the lower part of FIG. 1 as viewed from above. Fixing jig 10
GOS (Gd ₂ O ₂ S; gadolinium o)
(xysulfide) 101 is fixed using an adhesive 102.
Here, as the adhesive 102, paraffin or the like which can be detached by heating and cooling is suitable. Thus GOS1
After fixing 01, the fixing jig is further inserted into the jig guide 103. A polishing powder 105 is applied on the polishing plate 104, and the GOS 101 is applied to the polishing plate 1 using a jig guide 103.
Polishing is carried out by rubbing the polishing pad 104 or the polishing powder 105. Here, the inner diameter of the jig guide 103 is slightly larger than the outer diameter of the fixed jig 100 so that the fixed jig 100 does not play inside during the polishing operation. The radius of the contact portion of the jig guide 103 with the polishing plate 104 is set to be as large as possible for the GOS 101 by making the radius larger than that of the handle portion.
And the polishing plate 104 can always maintain the parallel relationship with high precision.

As described above, since GOS is a polycrystalline material, the surface thereof becomes significantly uneven by a polishing method similar to that of a silicon wafer or a glass lens. This will be described with reference to FIG. FIG. 2A is a diagram in which the GOS after polishing is observed from the polished surface side, and FIG. 2B is a diagram in a cross-sectional direction at an arbitrary position in FIG. 2A. The GOS sample 50 is composed of many particles 51 each of which is a single crystal. Particles 51
As described in the English journal of the Japan Society of Applied Physics,
It is a cube of about 50 × 200 × 200 μm on average and GOS
Is a polycrystalline body in which these particles are sintered in various directions. Since the polishing rate of each particle differs depending on the crystal orientation, after polishing using a combination of a polishing plate and polishing powder in which this is remarkably exhibited, remarkable irregularities appear on the surface as shown in FIG. Since it is a polycrystalline body, there is a grain boundary 52 between the grains, which is a discontinuous contact surface of the crystal. Since the polishing powder and the polishing solution easily penetrate into the grain boundary 52, the polishing rate is generally increased. In particular, the point where the grain boundaries gather three or four times is a markedly deep hole
(Pore), that is, a defect 53 occurs. For example, when irradiating with radiation such as an electron beam and detecting fluorescence generated inside with a photodetector, it is necessary to take out the fluorescence without diffuse reflection, and the flatness of the phosphor surface is important. In many cases, surface irregularities or defects generated during polishing greatly hinder such applications. Therefore, in the present invention, the possibility of flat polishing was experimentally searched for using various combinations of polishing plates and polishing powder. Table 1 summarizes the studied polishing methods.

[0015]

[Table 1] The above-mentioned colloidal silica-based, alumina-based, cerium oxide, diamond particles and the like were combined with a polishing plate considered suitable. In the experiment using the colloidal silica as the polishing powder, mechanochemical polishing was performed using a pH10-KOH aqueous solution as a polishing liquid. In polishing with diamond particles, a neutral lubricating oil was used as a polishing liquid.
All other polishing used water as a polishing liquid. Hereinafter, the polishing results will be evaluated using an optical microscope photograph (magnification: 50) of the GOS surface after polishing. Combinations of the polishing powder and the polishing plate are as shown in Table 1, and the polishing time is 12 minutes in each case.

From Table 1, it can be considered that the irregularities often increase with time, so that the polishing rate differs due to the difference in the crystal plane orientation of the microcrystal, and as a result, irregularities occur on the surface. Colloidal silica has a small particle size and is a proven method for mirror polishing of silicon wafers.However, since an alkaline polishing liquid is used, the anisotropy of the polishing rate with respect to the crystal orientation is large, and sintered ceramics, That is, it was found that the polishing method was not suitable for the polycrystalline GOS. The method showing the best polishing characteristics in this experiment was a case where diamond powder having a particle size of about 1 μm or less was used as the polishing powder and a tin face plate was used as the polishing plate. Since this abrasive powder had high hardness, it was not compatible with leather resins, and an experiment was conducted using a tin face plate having higher hardness and flexibility. The used diamond powder was dissolved in a fat-like paste, and it is considered that this fat and oil plays a role of a polishing liquid. In this case, almost no irregularities were observed on the sample surface, and the pores were extremely small and small. The polishing accuracy can be observed with an optical microscope image, and it can be seen that the maximum pore size is 40 μm. Judging from the pixel size of the image sensor, the maximum size of the pore is
It is generally necessary to continue polishing until it is less than 50 μm. The observation of the polished surface state includes, in addition to the observation with an optical microscope as in the present embodiment, a method in which a metal thin film is vapor-deposited on the surface and observed with an electron microscope while maintaining conductivity.

Next, an example of a particle detector using a GOS phosphor having a mirror surface obtained by polishing as described above will be described. GOS
Phosphors are characterized by a large light emission, and by using this, incident particles can be electron beams, ion beams, atomic beams, molecular beams, photon beams (including X-rays and γ-rays), other elementary particles, In any case, a highly sensitive detector can be realized. FIG. 3 shows an example in which the phosphor of the present application is applied to a camera that captures a transmission electron microscope (TEM) image. In the electron microscope 1, an electron beam 3 emitted from an electron beam source 2 is applied to a sample 9 by an objective lens 10. The electron beam 3 receives an interaction such as diffraction reflecting a crystal structure, a composition, and the like in the sample 9 and transmits through the sample 9 which has been thinned in advance. The transmitted electron beam 3 is thinned on the glass window 5 by an electron lens 8 such as an intermediate lens or a projection lens.
An image is formed on the mirror-polished GOS phosphor 4. FIG.
3A illustrates an imaging method using the imaging tube 7 using the lens 6, and FIG. 3B illustrates imaging using a charge coupled device (CCD) 12 via an optical fiber plate 11. Here, the optical fiber plate 11 is a bundle of optical fibers. In any case, the electron beam image is converted into a light image by the GOS phosphor 4 which is thinned, mirror-polished, and placed in a vacuum, and this light image is captured. Normally, the intensity of the electron beam 3 is weak, and if a large amount of the electron beam 3 is extracted from the electron beam source 2 in order to obtain a signal intensity, the irradiation damage to the sample 9 increases, which is inconvenient. Therefore, in order to obtain an image having an excellent S / N ratio, a phosphor having a high efficiency of converting an electron beam into light, that is, a phosphor having a large amount of light emission is important, and in this regard, a GOS phosphor is advantageous. However, since the GOS phosphor is a sintered ceramic, its surface has large irregularities. As shown on the right side of FIG. 4, the incident electron beam 3 is scattered on the surface. Light rays are irregularly reflected by a light reflecting film 13 made of aluminum or the like which is thinly formed on the surface. As a result, efficient light collection cannot be performed by a photodetector provided below the glass window 5, and furthermore, light generated by a phosphor is generated. There is a problem that the resolution of the image is reduced. Therefore, the above problem was solved by performing mirror polishing with few irregularities and pores by the polishing method described in the present application, and as shown on the left side of FIG. 4, efficient light collection and high resolution were realized.

Although the electron microscope in which the incident particles are electrons has been described above as an example, the same applies to other particle beams. Next, as an example in which the incident particles are photons, FIG. 5 shows an example of X-ray imaging used for medical purposes. In normal X-ray photography, X-rays 36 generated from an X-ray generator 34 are irradiated on a subject 35, and transmitted X-rays are photographed with a film or a camera. This embodiment shows an example of camera shooting. Since the transmitted X-rays have too short a wavelength, the camera 4
It is difficult to detect with 3. Therefore, first, the light is converted into a light beam 42 having a wavelength near visible light by the GOS phosphor 38, and this is formed on the imaging surface of the camera 43 by the optical lens 41 directly or through the light reflection film 37. You. Therefore, since the image information held by the X-rays is converted into an optical image by the phosphor, the situation is the same as in the embodiment shown in FIGS.

[0019]

Advantageous effects obtained by typical ones of the inventions disclosed by the present application will be briefly described as follows.
It is as follows. (1) According to the present invention, focusing on the GOS of a sintered body crystal of a sintered ceramic as a high emission phosphor material, diamond fine particles are used as polishing powder, and a tin face plate is used as a polishing plate. The flatness of the polished surface of the aggregate can be improved. (2) According to the present invention, focusing on GOS of a sintered body crystal of a sintered ceramic as a phosphor material having a high light emission, using diamond fine particles as a polishing powder and a tin face plate as a polishing plate, firing is performed. It is possible to reduce the loss of crystal grain boundaries of the compact. (3) According to the present invention, by using the above-described phosphor and combining it with a photodetector, it becomes possible to perform particle detection and imaging with high sensitivity and high resolution.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a method for polishing a cadmium oxide sulfide body by a polishing method according to an embodiment of the present invention.

FIGS. 2 (a) and (b) are explanatory views showing the surface and cross-sectional state of cadmium oxalfide after polishing studied by the present inventors.

3 (a) and 3 (b) are explanatory views showing an example in which a mirror-polished cadmium oxide phosphide phosphor according to an embodiment of the present invention is applied to an image capturing detector of a transmission electron microscope. is there.

FIG. 4 is an explanatory diagram showing generation and propagation of an incident electron beam and fluorescence in a mirror-polished cadmium oxide phosphide and an unpolished cadmium oxide phosphide according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an example in which a mirror-polished cadmium oxide phosphide, which is another embodiment of the present invention, is applied to an imaging detector of an X-ray diagnostic apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electron microscope 2 electron beam source 3 electron beam 4 cadmium oxide phosphide 5 glass window 6 lens 7 imaging tube 8 electron lens 9 sample 10 objective lens 11 optical fiber plate 12 charge-coupled device (CCD) 13 light reflection film 14 light emission Point 34 X-ray generator 35 Subject, 36 X-ray 37 Light reflecting film 38 Cadolinium oxalphide phosphor 39 Transparent electrode, 41 Optical lens 42 Light beam 43 Camera 50 Cadolinium oxalphide sample 51 Particle, 52 Grain boundary 53 Defect REFERENCE SIGNS LIST 100 Fixing jig 101 Cadolinium oxalide 102 Adhesive 103 Jig guide 104 Polishing plate 105 Polishing powder

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09K 11/00 C09K 11/00 E 5C036 11/84 CPD 11/84 CPD G01T 1/29 G01T 1/29 A H01J 29/18 H01J 29/18 M 37/244 37/244 (72) Inventor Hiroshi Kakibayashi 1-280 Higashi Koigabo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor Masaya Iwaki Wako-shi, Saitama 2-1, Hirosawa RIKEN (72) Inventor Toshiki Niino 2-1 Hirosawa, Wako-shi, Saitama F-term (reference) 2G088 EE29 EE30 FF12 GG10 GG16 GG20 JJ05 JJ37 LL15 3C058 AA07 AA09 CA05 CB01 DA02 4C093 AA01 CA02 CA31 EB01 EB04 EB20 EB30 4H001 CA08 XA08 XA16 XA64 YA09 YA58 YA59 5C033 NN03 NN04 NP08 5C036 AA01

Claims (10)

[Claims] In a surface polishing of a sintered body crystal using a polishing powder, a polishing plate and a polishing liquid, polishing is performed in order to suppress unevenness height of a polished surface and a size of a defect generated at a crystal grain boundary of a sintered body. A polishing method using diamond fine particles as powder and a tin plate as a polishing plate. 2. A polishing method according to claim 1, wherein the base material of the sintered body crystal is cadmium oxide. 3. The polishing method according to claim 2, wherein praseodymium, cerium, and fluorine are added to the cadmium oxide sulfide. 4. The polishing method according to claim 2, wherein the polishing is continued until the maximum size of a defect generated at a crystal grain boundary of the sintered body becomes 50 μm or less. 5. A polishing method using an optical microscope or an electron microscope as a means for observing the defect according to claim 4. 6. The polishing method according to claim 1, wherein the polishing liquid is water or another neutral liquid. 7. The polishing method according to claim 6, wherein the acid alkalinity of the neutral solution is between 6 and 8 in terms of pH. 8. A phosphor polished by the polishing method according to claim 1 as a phosphor for converting a particle beam into light, a photodetector for detecting the light, and transmitting the light to the photodetector. A particle detector comprising a member. 9. The particle detector according to claim 8, wherein the photodetector is an image sensor capable of detecting a two-dimensional light intensity distribution. 10. The particle detector according to claim 9, wherein the image pickup device is an image pickup tube or a charge-coupled device.