JP2754175B2 - Manufacturing method of cold electron-emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a flat panel display (FPD) type image display device, an optical printer,
Electron microscopes, electron beam exposure devices, etc., a cold electron emitting element that can be used as an electron source or electron gun for various electron beam utilizing devices, or in a simple case, also as an electron emission source for micro illumination such as a simple illumination lamp. The present invention relates to a manufacturing method, particularly to a manufacturing method suitable for sharpening the tip of an emitter (also referred to as a cold cathode or a cathode).

[0002]

2. Description of the Related Art At present, a cathode ray tube (cathode ray tube: CR) which may be said to be the only vacuum tube that is widely used.
As noted in T), rather than applying a large amount of thermal energy to the cathode to cause thermionic emission, an intense electric field of generally 10 ⁶ to 10 ⁷ V / cm or more is applied to the metal surface, thereby Field emission type electron-emitting devices that emit cold electrons (also called field emission electrons or strong field emission electrons), that is, research on cold electron emission devices,
Nowadays, it is becoming rich. If such a type of element is put to practical use in various places, heat energy accompanied by extremely large power consumption required for a cathode heater in a CRT or the like becomes unnecessary, and the element itself can be extremely small. Power is also greatly reduced, and the housing is dramatically reduced in size (thinner) and lighter.

However, since the electric field is governed by Poisson's equation, the tip of the emitter serving as the cold electron emission end is made as sharp as possible (the apex angle of the emitter is made as small as possible).
The more the electric field concentration is localized, the more efficiently the field emission can be caused even at a relatively low extraction voltage, and the practical application is more realistic. Therefore, various techniques have been devised in the related art as to how to sharpen the tip of the emitter. Among them, there is a conventional method called a molding method as shown in FIG. 2 as a method for producing an emitter with good reproducibility and with few material restrictions.

First, as shown in FIG. 2A, a thermal oxide film (silicon oxide film) having a thickness of about 0.3 μm is formed on the main surface of the silicon substrate 11 in the plane orientation (100), as shown in FIG.
After forming 12 and forming a photoresist 13 thereon,
As shown in FIG. 2B, the photoresist 13 is patterned by a general lithography technique so that a plurality of square openings are arranged at an appropriate pitch in an in-plane one-dimensional direction or an in-plane two-dimensional direction. . Each square opening substantially corresponds to the bottom surface of each pyramid-shaped (quadrangular pyramid-shaped) emitter finally formed, although a slight dimensional difference is caused by reducing the number of subsequent etching steps.

Using the photoresist 13 patterned as described above as an etching mask, the silicon oxide film 12 is also etched by applying a well-known lithography technique using, for example, buffered hydrofluoric acid, as shown in FIG. Next, an opening 14 exposing the surface of the silicon substrate 11 is opened. In this state, when anisotropic etching is performed in a potassium hydroxide (KOH) solution, as shown in FIG. 2D, the silicon substrate 11 exposed through each opening 14 An inverted pyramid-shaped (inverted quadrangular pyramid-shaped) concave portion 15 having (111) planes as side surfaces is formed.

Thereafter, the thermal oxide film 12 and the photoresist 13 remaining on the surface of the silicon substrate 11 are removed by, for example, immersion in a hydrofluoric acid solution to obtain an emitter for the emitter as shown in FIG. A mold is completed. Then, as shown in FIG. 2 (F), each inverted pyramid-shaped recess 15 is successively filled with an emitter material 16 for forming an emitter, for example, a refractory metal or diamond. However, diamonds are preferred over refractory metals. This is because its side is a (111) plane with negative electron affinity, which is extremely stable chemically and physically. Further, a preferable method for filling is, for example, hot filament CVD (chemical vapor deposition).

Thereafter, the silicon substrate 11 is dissolved and removed by, for example, dipping in a potassium hydroxide solution.
If 11 is removed, as shown in Fig. 2 (G),
The emitter 18 can be formed to have a sharp and sharp 18.

[0008]

[0005] In such a conventional method,
(a) In principle, there are few restrictions on the emitter material 16 and various materials can be used. (b) Therefore, as described above, in addition to the refractory metal, it is desirable in terms of electrical characteristics as an emitter material, but it is chemically and physically. Although it is extremely stable, it is possible to manufacture diamond emitters, which are rather difficult to process with other processing methods. (C) Since the mold shape depends on the plane orientation of the silicon substrate, the accuracy is high, and the emitter shape to be manufactured is high. Has excellent reproducibility and uniformity.

However, conversely, when a mold formed depending on the plane orientation of the silicon substrate is used, the vertex angle of the produced emitter is inevitably about 70 °, and it is desired to make the vertex angle smaller. However, a pyramid shape having steeper sides cannot be obtained. The radius of curvature at the tip of the emitter (generally directly related to the sharpness, the smaller the better), is difficult to measure exactly, but remains at about 1000 °.

Further, this kind of cold electron-emitting device can operate in principle with a single emitter, but from a practical point of view, in order to obtain a high electron flow density per unit area, It is required to integrate a plurality of or a large number of emitters at a high density. In order to satisfy this, naturally, the smaller the area of the bottom square of each emitter, in other words, the shorter the length of one side of the bottom square, the smaller the interval between adjacent emitters, which is good. However, in the above-described conventional method, the apex angle is almost uniquely determined only according to the plane orientation of the silicon substrate as described above. Therefore, the height of the pyramid-type emitter 17 (the depth of the inverted pyramid-type recess 15) If you try to take enough, the size of one side of the bottom square can not be made too small, and in order to take the necessary height as a practical element, the side of the bottom square should be no more than 20 μm, no matter how small Also
The limit was about 10 μm.

The present invention has been made in view of the foregoing points, and has the advantages of the above-described conventional method, but has a sharper tip and occupies a smaller area. Is to be produced.

[0012]

However, according to the present invention, which has been made to achieve the above object, as shown in FIG. 2E, one principal surface of the silicon substrate has a (111) plane orientation. Up to the point where the inverted pyramid-shaped concave portion composed of the four side surfaces is formed, the same procedure as in the conventional method described above may be followed. In other words, the characteristic manufacturing process of the present invention is:
A silicon substrate on which an inverted pyramid-shaped concave portion composed of four side surfaces having a (111) plane orientation is formed in advance is used as a starting member, and is applied to the silicon substrate.

First, the silicon substrate as the starting member is immersed in a surface oxide film removing solution, preferably in a hydrofluoric acid volume for an appropriate time, preferably, for example, about 10 minutes, and is naturally formed on the side surface of the inverted pyramid-shaped concave portion. Remove any surface oxides that may be present, exposing the crystal surface. As described above, the starting member is a silicon substrate manufactured in accordance with the process described with reference to FIG. 2, and the starting member remains in the previous process of FIG. 2 (D) to obtain the structure of FIG. 2 (E). If a hydrofluoric acid solution is used to remove the silicon oxide film 12 and the photoresist 13 on the silicon oxide film 12 and has not been exposed to a polluted environment such as an air environment, the first of the present invention. As far as the surface oxide film removing step, which is the step, can be used as the immersion step in a hydrofluoric acid solution in the preceding step. However, the immersion time is optional, and it may be preferable to take a longer time than the above-mentioned time.

Next, a fine powder of high hardness, preferably diamond fine powder having a suitable average particle size, preferably from 0.1 μm to 0.5 μm, is contained, and the silicon substrate is at least physically and chemically damaged. Difficult solution, preferably in acetone solution for a suitable time, preferably
Washing is performed by a physical or mechanical vibration method such as ultrasonic cleaning for about 60 minutes. Since this cleaning process is performed by mixing high-hardness fine powder into the solution, it can be said that this is a polishing process for each side surface of the inverted pyramid-shaped concave portion, or more positively a scratching process. In addition, a solution that is hard to damage the silicon substrate at least physically and chemically is, of course,
Includes solutions that do not damage at all. Further, it is desirable to use an ultrasonic vibration method since a simple and uniform scratching treatment can be performed, but a mechanical solution stirring method or the like can also be employed.

After the above-mentioned scratching step, anisotropic etching is performed using a tetramethylammonium hydroxide solution (hereinafter abbreviated as TMAH solution). The etching conditions are preferably a solution concentration of 15% and a solution temperature of 90 ° C. for an appropriate time, preferably about one minute.

By reducing such steps, the inverted pyramid-shaped concave portion in the starting member is defined by a side surface that is more steeply inclined from the middle in the depth direction, and the angle formed by the opposite side surface at the bottom of the concave portion is 40 °. It can be sharpened below about 30 °. The reason for this, although there is no evidence at this time, is probably near the bottom of the inverted pyramidal recess.
This is probably due to the higher (301) plane instead of the (111) plane.

After a mold having such a sharpened inverted pyramid-shaped concave portion is completed according to the present invention, a washing step or a drying step using a washing solution such as pure water or acetone is applied as necessary. Thereafter, the process may return to the same step as the conventional method, and the concave portion is filled with the emitter material. In this connection, it is preferable to grow a refractory metal, preferably diamond, on the side surface of the recess by chemical vapor deposition. After filling the emitter material, if the silicon substrate is removed by an appropriate method such as dissolution and removal by immersion in a potassium hydroxide solution, an emitter for a cold electron emission device manufactured according to the present invention can be obtained.

The present inventor has also described a step of removing the surface oxide film, a step of treating the side surface of the inverted pyramid-shaped recess, and an etching step using a TMAH solution for anisotropic etching. Then, a method of repeating this unit continuous process group two or more times as needed is also proposed. Thus, the depth of the inverted pyramid-shaped concave portion can be increased while the vertex angle of the finally formed emitter is kept sharp.

Of course, the number and pitch of the inverted pyramid-shaped concave portions formed on the silicon substrate are arbitrary design items.
In principle, even a single emitter can be operated as a cold electron-emitting device. However, more generally, a large number of emitters are integrated as described above. In this case, according to the present invention, as described above, the vertex angle of the pyramid-type emitter can be sufficiently reduced to a minimum of about 30 °, so that even if the height of the pyramid is sufficiently taken, the size of one side of the bottom square of the base is taken. Can be kept small. Therefore, adjacent pyramids can be brought closer to each other, and higher density can be achieved as compared with the case of following the conventional method.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below with reference to FIG. However, FIG. 1 shows only characteristic steps added or changed to the conventional method according to the present invention,
As shown in FIG. 1 (A), a silicon substrate 11 as a starting member to which the present invention is applied is a silicon substrate on which an inverted pyramid-shaped concave portion 15 having four side surfaces having a (111) plane orientation is formed in advance. is there. That is, the silicon substrate 11 shown in FIG.
Inverted pyramid-shaped recess produced according to the steps up to (E)
It may be a silicon substrate 11 having 15.

In this embodiment of the present invention, the silicon substrate 11 on which the inverted pyramid-shaped concave portion 15 is formed in advance
Is first immersed in a hydrofluoric acid solution for about 10 minutes to remove a silicon oxide film which may be naturally formed on the substrate surface or the side surface of the inverted pyramid-shaped concave portion 15. However, the silicon substrate 11 as a starting member is formed by the conventional method described with reference to FIG. 2 and remains in the step of FIG. 2 (D) one step before the step of FIG. 2 (E). If a hydrofluoric acid solution is used to remove the silicon oxide film 12 and the photoresist 13 thereon, and the substrate is not exposed to a contaminated environment such as the atmosphere thereafter, the first step of this embodiment The step of removing the surface oxide film may be also used as the step of dipping in a hydrofluoric acid solution in the preceding step. The immersion time is also arbitrary in principle, and it may be preferable to take a longer time than the above-mentioned time.

Next, ultrasonic cleaning is performed in an acetone solution containing a fine diamond powder having an appropriate average particle diameter, preferably from 0.1 μm to 0.5 μm. However, since this cleaning process is performed by mixing diamond fine powder into the solution, it becomes a polishing process for each side surface of the inverted pyramid-shaped concave portion 15, or a more aggressive scratching process.

After the scratching process, anisotropic etching is performed using a TMAH solution. The etching conditions are preferably a solution concentration of 15% and a solution temperature of 90 ° C. for about one minute.

By reducing such steps, as shown in FIG. 1B, the inverted pyramid-shaped concave portion in the starting member is formed.
15 is a sharpened inverted pyramid that is defined by a side surface that is more steeply inclined from the middle of the depth direction, and the angle formed by the opposite side surface at the bottom of the concave portion is at least 40 ° or less, and at least about 30 ° at the minimum. It was confirmed that the mold concave portion 21 was formed, and the radius of curvature at the tip was also reduced to 500 ° or less. The reason for this has not been quantitatively verified so far, but it is probably that the immediate vicinity of the deepest bottom of the inverted pyramid-shaped recess is (11
It is presumed that the (301) plane was not a 1) plane but a higher order (301) plane.Moreover, due to the synergistic effect of the above-described scratching step and this anisotropic etching step, it was deeper than the conventional method, and ,
It is considered that a good sharpened inverted pyramid-shaped concave shape with a small tip radius of curvature was obtained.

After the mold having such a sharpened inverted pyramid-shaped concave portion 21 is completed, a cleaning step using a cleaning solution such as pure water or acetone or a drying step is performed, if necessary. Then, the process may return to the same step as the conventional method, and the sharpened inverted pyramid-shaped concave portion 21 is filled with the emitter material 16 as shown in FIG. In this connection, it is preferable to grow the refractory metal, preferably diamond, on the side surface of the recess by chemical vapor deposition.

After the emitter material 16 is filled, the silicon substrate 11 is dissolved and removed by, for example, dipping in a potassium hydroxide solution, or the silicon substrate 11 is removed by an appropriate removing method such as an appropriate mechanical peeling method (not shown). By removing 11, as shown in FIG. 1D, an emitter 17 for a cold electron emission device manufactured according to the present invention can be obtained.

The emitter 17 molded in this manner is well matched to the mold shape, the apex angle is sharpened to a minimum of about 30 °, and the radius of curvature of the tip 22 is 5 °.
It was less than 00Å. This is, of course, a value far superior to that produced by the conventional method described above. The scratching process using a solution containing diamond fine powder not only contributes to the sharpening of the deepest portion of the inverted pyramid-shaped concave portion due to a synergistic effect with the anisotropic etching process, but also sharpens the emitter material 16. For example, when the growth is performed in the inverted pyramid-shaped concave portion 21 by chemical vapor deposition, the "nucleus" of the growth is easily formed, and the shape of the pyramid-type emitter 17 finally formed with respect to the mold shape is matched. It seems to have a function to improve the properties.

In any case, since the apex angle of the emitter 17 formed according to the present invention is small, not only the electric field concentration effect is enhanced, but also the height of the emitter 17 (the depth of the sharpened inverted pyramid-shaped concave portion 21). In the case where the required size is taken as an element, if the required height is the same, the size of one side of the bottom square of the foot can be considerably reduced as compared with the conventional method described with reference to FIG. For example, when using the conventional method, the bottom dimension is 20 μm
In order to obtain the same height as the emitter height when the height is set to about the same, according to the present invention, the bottom dimension is only about 6 μm.
This is, of course, desirable because, in principle, it is possible to reduce the size of an element that operates with a single emitter.
More practically, when constructing a cold electron-emitting device in which a plurality of (many) emitters 17 are integrated, it is extremely advantageous in increasing the integration density and miniaturizing the device.

It should be noted that the above-described surface oxide film removing step, the step of scratching the side surface of the inverted pyramid-shaped concave portion, and the TMAH
A method of repeating the anisotropic etching process using a solution as a set of unit continuous process groups and repeating this unit continuous process group two or more times as needed is also proposed. With this, the depth of the inverted pyramid-shaped concave portion, and finally the height of the finally formed emitter 17 are set to required dimensions while keeping the apex angle of the finally formed emitter sharp according to the number of repetitions. Can be adjusted.

The embodiment of the present invention has been described above. However, any modifications can be freely made by those skilled in the art as long as they conform to the gist of the present invention. For example, in the above-described embodiment, the diamond fine powder is used in the step of scratching the side surface of the sharpened inverted pyramid-shaped concave portion 21, but it can be replaced with another high-hardness fine powder. The dispersion medium of the fine powder is not limited to the acetone solution, and at least the silicon substrate 11 is physically and
Any solution that is hardly damaged chemically may be used. Emitter material 16
Also, although diamond is desirable, other refractory metals may be used.

[0031]

According to the present invention, a cold electron-emitting device having an extremely sharp emitter can be provided with good reproducibility.
The sharp emitter tip enhances the electric field concentration efficiency, and eventually increases the operation efficiency as a cold electron emitting device. It also leads to power saving. In addition, since an emitter shape having a high aspect ratio (a high ratio of the height dimension to the bottom dimension) can be obtained,
If the required height is the same, an emitter with a smaller bottom dimension can be manufactured as compared with the case where it is manufactured by the conventional method, and the element size can be reduced. If necessary, even when a large number of emitters are integrated, adjacent emitters can be much closer to each other, and a high integration density can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a group of steps in one embodiment of the manufacturing method of the present invention.

FIG. 2 is an explanatory view in the order of steps when manufacturing a cold electron-emitting device having a pyramid-shaped emitter according to a conventional manufacturing method.

[Explanation of symbols]

 11 silicon substrate, 12 silicon oxide film, 13 photoresist, 14 opening, 15 inverted pyramid recess, 16 emitter material, 17 emitter, 21 sharpened inverted pyramid recess, 22 emitter tip.

Claims (15)

(57) [Claims] 1. A method of manufacturing a cold electron-emitting device for emitting cold electrons from an emitter by concentrating an electric field on the tip of the emitter; A surface oxide film removing step of immersing the formed silicon substrate in a surface oxide film removing solution; and placing the silicon substrate in a solution containing high-hardness fine powder and at least hardly physically and chemically damaging the silicon substrate. Dipping and vibrating the solution relative to the silicon substrate,
A scratching step of damaging the side surface of the inverted pyramid-shaped recess with the high-hardness fine powder; immersing the silicon substrate in a tetramethylammonium hydroxide solution to further anisotropically etch and sharpen the inverted pyramid-shaped recess An etching step for forming an inverted pyramid-shaped recess; an emitter material filling step for filling an emitter material in the sharpened inverted pyramid-shaped recess; and a step of removing the silicon substrate after filling the emitter material; A method for manufacturing a cold electron-emitting device comprising: 2. The method according to claim 1, further comprising a step of washing and drying the silicon substrate on which the sharpened inverted pyramid-shaped recess is formed after the etching step and before the emitter material filling step. A method for manufacturing a cold electron-emitting device. 3. The method according to claim 1, wherein the surface oxide film removing step, the scratching step, and the etching step are a unit continuous step group, and the unit continuous step group is repeated a plurality of times. A method for manufacturing a cold electron-emitting device. 4. The method according to claim 1, wherein said surface oxide film removing solution is a hydrofluoric acid solution. 5. The method according to claim 1, wherein said high-hardness fine powder is diamond fine powder. 6. The method according to claim 1, wherein said fine powder of high hardness has an average particle diameter of 0.1 μm or less.
0.5 μm or less; 7. The method according to claim 1, wherein the solution containing the high-hardness fine powder and hardly damaging the silicon substrate at least physically or chemically is an acetone solution. A method for manufacturing a cold electron-emitting device. 8. The manufacturing method according to claim 1, wherein ultrasonic waves are used to vibrate the solution relative to the silicon substrate in the scratching step. Method for producing a cold electron emitting device. 9. The manufacturing method according to claim 1, wherein the solution is agitated instead of being vibrated relative to the silicon substrate in the scratching step. A method for manufacturing a cold electron emission element. 10. The cold electron-emitting device according to claim 1, wherein the emitter material filled in the sharpened inverted pyramid-shaped recess is a refractory metal. Method of manufacturing. 11. The method according to claim 1, wherein the emitter material filled in the sharpened inverted pyramid-shaped concave portion is diamond. Method. 12. The manufacturing method according to claim 1, wherein the step of filling the emitter material in the sharpened inverted pyramid-shaped concave portion includes filling the emitter material in the sharpened inverted pyramid-shaped concave portion. A method for producing a cold electron-emitting device, wherein the method comprises a step of subjecting a material to chemical vapor deposition. 13. The method according to claim 1, wherein after the filling of the emitter material, the step of removing the silicon substrate comprises immersing the silicon substrate in a potassium hydroxide solution. A method of dissolving and removing a silicon substrate; 14. A method of manufacturing a cold electron-emitting device for emitting cold electrons from an emitter by concentrating an electric field on the tip of the emitter; Dipping the formed silicon substrate in a hydrofluoric acid solution to remove the surface oxide film; dipping the silicon substrate in an acetone solution containing diamond fine powder having an average particle diameter of 0.1 μm to 0.5 μm;
A process in which the acetone solution is vibrated by ultrasonic vibration to damage the side surface of the inverted pyramid-shaped recess with the diamond fine powder; a solution concentration of 15% and a solution temperature of 90 ° C.
Dipping the silicon substrate in a tetramethylammonium hydroxide solution, and further anisotropically etching the inverted pyramid-shaped recess to form a sharpened inverted pyramid-shaped recess; Cleaning and drying the formed silicon substrate using pure water and acetone; and chemically vapor-depositing diamond as an emitter material in the sharpened inverted pyramid-shaped recess; and after filling the diamond, Dipping the silicon substrate in a potassium hydroxide solution to dissolve and remove the silicon substrate. 15. The method according to claim 14, wherein:
A method for producing a cold electron-emitting device, comprising: the step of removing a surface oxide film, the step of scratching, and the step of etching as a unit continuous step group, and repeating the unit continuous step group a plurality of times.