JP2001202872A - Electric field emission type electron source and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the maximum current value being applied to a cathode from lowering in all cases that a tower type of cathode is finely thinned. SOLUTION: A drawer electrode 19A is formed on a silicon substrate 11 through a lower dioxide silicon film 16A and an upper dioxide silicon film 18A, which have a circular opening at a cathode forming area, respectively. A tower type of cathode 17 is formed inside of the lower dioxide silicon film 16A, the upper dioxide silicon film 18A, and the drawer electrode 19A, and a leading end of the cathode 17 has a steep portion of 2 nm radius formed by a crystal anisotropy etching process and thermal oxide of silicon process. An area surface, which is exposed through the openings of the lower dioxide silicon film 16A and the upper dioxide silicon film 18A in the silicon substrate 11, and a surface of the cathode 17 are coated with a thin surface coating film 20 formed from materials of lower work function.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field emission type electron source such as a cold cathode electron source which is expected to be applied to an electron beam pumped laser, a flat solid-state display device, an ultra-high speed micro vacuum device, and the like. In particular, the present invention relates to a field emission type electron source for semiconductor application capable of realizing integration and low voltage, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Advances in microfabrication technology for semiconductors have made it possible to manufacture minute field-emission electron sources, and vacuum microelectronics technology has been actively developed. In order to realize a high-performance field-emission electron source that can operate at a lower driving voltage, approaches such as creation of a miniaturized extraction electrode and a cathode having a sharp tip by applying LSI technology have been performed. I have.

[0003] As a first conventional example, a minute field emission type electron source formed using a silicon substrate and a method of manufacturing the same, which are disclosed in European Patent Publication No. 637050A2, are shown in FIGS. I will explain while.

First, as shown in FIG. 11A, a silicon oxide film 102 is formed on a (100) surface of a silicon substrate 101 made of silicon crystal by a thermal oxidation method. A resist film 103 is formed.

Next, as shown in FIG. 11B, a photoresist film 103 is formed by photolithography to a thickness of about 1 μm.
It is processed into a disk-shaped etching mask 103A having a diameter of m. Thereafter, the etching mask 103A is transferred to the silicon oxide film 102 by a dry etching method to form a disc-shaped body 102A, and then the etching mask 103A is formed.
Is removed.

Next, the silicon substrate 101 is subjected to anisotropic dry etching using the disk-shaped body 102A as a mask, so that the silicon substrate 101 is placed below the disk-shaped body 102A as shown in FIG. Cylindrical body 1
After the formation of the substrate 04A, the columnar body 104A is subjected to crystal anisotropic etching to form a side surface including a (331) plane and a top portion continuous with each other as shown in FIG. Drum 10 consisting of a pair of cones
4B is formed.

Next, as shown in FIG. 12A, after a thin first thermal oxide film 105 is formed on the surface of the drum-shaped body 104B and the silicon substrate 101, the silicon substrate 101A is formed by using the disk-shaped body 102A as a mask. By performing anisotropic dry etching on the substrate, as shown in FIG.
The drum-shaped body 104B is transformed into a drum-shaped columnar body 104C.

Next, as shown in FIG. 12C, a drum-shaped columnar body 104C and a silicon substrate 101 are formed by a thermal oxidation method.
By forming the second thermal oxide film 106 on the surface of
A tower-shaped cathode 107 having a small diameter and a steep tip is formed inside the drum-shaped columnar body 104C.

Next, as shown in FIG. 12 (d), the upper surface of the disk 102A and the upper surface of the disk 102A are formed by vapor deposition.
An insulating film 108 and a metal film 109 are sequentially deposited on the silicon substrate 101 in the vicinity of the above.

Next, as shown in FIG. 13, the second thermal oxide film 106 is subjected to wet etching to form the disc-shaped body 102A and the insulating film 108 deposited on the disc-shaped body 102A. Then, when the metal film 109 is removed, the tower-shaped cathode 107 is exposed, and an extraction electrode 109A made of the metal film 109 having the same inner diameter as the diameter of the disc-shaped body 102A is formed.

Hereinafter, as a second conventional example, Japanese Patent Application Laid-Open No.
A method for manufacturing a field-effect electron source using a low work function material disclosed in Japanese Patent No. 231675 will be described.

Japanese Patent Application Laid-Open No. 6-231675 describes the first
In addition to the approach described in the conventional example of reducing the size of the cathode and improving the cathode structure, an attempt to improve the cathode performance by selectively forming a low work function material at the tip of the cathode has been proposed. ing. This method of manufacturing a field emission type electron source comprises forming a cathode, selectively forming a low work function material on the surface of the tip of the cathode by oblique deposition, and then performing heat treatment to silicide. Then, the electron emission efficiency is greatly improved by reducing the work function of the tip portion of the cathode as a result.

[0013]

By the way, the field emission type electron source according to the first conventional example has a tower-shaped cathode having a minute diameter and a steep tip, so that a low voltage is required. Is possible, but has the following problems.

One of the important performances required for putting a field emission electron source into practical use is the stability and uniformity of electron emission.

However, in the first conventional example, the emission current of the cathode is strongly affected by the vacuum atmosphere during operation and the surface condition of the tip of the cathode. For example, the work function or the like changes, and as a result, the operating current greatly changes. For this reason, the above-mentioned required performance of stability and uniformity of electron emission was not satisfied. This is thought to be because the emitted electrons collide with the residual gas near the cathode during operation to generate ions, and the ions collide with the cathode tip, thereby changing the surface state of the cathode tip. .

Therefore, in order to suppress these current fluctuations, a method of stabilizing the emission current by integrating the cathodes on a large scale and averaging the individual electron emission fluctuations, and a method for suppressing the current fluctuation in the cathode electrodes. There has been proposed a method of forcibly suppressing a current fluctuation by adding an element such as an FET having the following.

However, these methods cause a great increase in manufacturing cost due to a decrease in the degree of freedom in element design and a necessity of adding a new element structure. Has become.

Further, in a tower-shaped cathode shown in the second conventional example in which a surface coating film made of a material having a low work function is selectively formed on the tip of the cathode, as described below. There's a problem. That is, in the tower-shaped cathode, the emission current emitted from the cathode is concentrated at the root portion of the tower. Therefore, when a large current operation is performed, large Joule heat is generated at the root portion of the tower where the current is concentrated. If the current exceeds the allowable value determined by the substrate resistance and the cross-sectional area of the tower, the temperature of the cathode rises due to the generated Joule heat, and if the temperature exceeds the melting point of the material constituting the cathode, the cathode May be dissolved and the element may be destroyed.

As described above, as the size of the cathode is reduced in order to reduce the operating current, the maximum current value that can be passed through the cathode is also reduced, which is a major obstacle in performing a large current operation. It is.

Further, as in the second conventional example, a low work function material is selectively formed at the tip of the cathode by oblique vapor deposition, and then heat treatment is performed to form a silicide film at the tip of the cathode. Although this method has the potential to solve the above-mentioned problem, it has the following problems since the silicide film uses a deposition process of a metal film and a reaction process by a subsequent heat treatment.

In general, when a film is formed by a vapor deposition method, a film thickness variation in a wafer is likely to occur because the vapor deposition source is a point source. In addition, since the silicide film formation process by the subsequent heat treatment utilizes the crystal reaction at the interface between the deposited metal and the underlying silicon substrate, the progress of the silicide reaction and the silicide The film quality tends to vary, and there is a problem in forming the tip of the cathode, which requires a minute shape.

The microstructure at the tip of the cathode, particularly the radius of curvature at the tip, is a parameter that has a large effect on the operating voltage characteristics during electron emission. When calculations are performed to compare the electric field concentration coefficients assuming that the cathode structure other than the radius of curvature of the tip is the same, the radius of curvature of the tip is 10 nm to 2n.
By changing to m, the electric field concentration coefficient is doubled. According to the second conventional example, a variation in the radius of curvature of the tip of the cathode of about 10 nm easily occurs due to the influence of the variation in the silicide process,
As a result, variations in element characteristics occur, which is a major problem in practical use.

In view of the above, it is a first object of the present invention to prevent the maximum current value that can be supplied to the cathode from being reduced even when the tower-shaped cathode is miniaturized. A second object is to make it possible to emit electrons well and to reduce variations in operating voltage characteristics at the time of electron emission, even if there is a slight variation.

[0024]

According to a first aspect of the present invention, a low work function material is formed on a surface of a cathode and a surface of a portion of a substrate exposed to an opening of an extraction electrode. It forms a surface coating layer.

The first field emission type electron source according to the present invention comprises:
A substrate, an extraction electrode formed on the substrate via an insulating film and having an opening in a cathode formation region, a tower-shaped cathode formed in the opening of the extraction electrode on the substrate, a surface of the cathode, and a substrate And a surface coating layer made of a low work function material continuously formed on the surface of the portion exposed to the opening of the extraction electrode.

According to the first field emission type electron source, a surface coating layer made of a low work function material is continuously formed on the surface of the cathode and the surface of the substrate exposed at the opening of the extraction electrode. Therefore, the allowable current value determined by the substrate resistance and the cross-sectional area of the tower-shaped cathode increases, so that even when the tower-shaped cathode is miniaturized, it is possible to avoid a situation where current is concentrated at the base of the cathode.

In the first field emission type electron source, the low work function material is a high melting point metal material made of Cr, Mo, Nb, Ta, Ti, W or Zr, or a carbide or nitride of the high melting point metal material. Alternatively, it is preferable to contain a silicide.

In order to achieve the second object, the second invention is to form a high-concentration impurity layer containing a high concentration of impurities on the surface of the cathode.

The second field emission type electron source according to the present invention comprises:
A substrate, an extraction electrode formed on the substrate via an insulating film and having an opening in a cathode formation region, a cathode formed in the opening of the extraction electrode on the substrate, and a substrate formed on a surface portion of the cathode. And a high-concentration impurity layer having an impurity concentration higher than that of

According to the second field emission type electron source, since the high concentration impurity layer is formed on the surface of the cathode, electrons can be satisfactorily emitted from the surface of the cathode.

In the second field emission type electron source, the cathode has a tower shape, and the high-concentration impurity layer is continuous with the surface of the cathode and the surface of the substrate exposed at the opening of the extraction electrode. It is preferable that it is formed.

In the second field emission electron source, the high concentration impurity layer preferably has a sheet resistance of 10 kΩ or less.

In the first method of manufacturing a field emission type electron source according to the present invention, a substrate is etched using an etching mask formed on the substrate to form a tower-shaped cathode on the substrate. A cathode forming step, and after sequentially depositing an insulating film and a conductive film over the entire surface of the substrate, by lifting off the insulating film and the conductive film on the etching mask,
Forming an extraction electrode having an opening around the cathode; and forming a surface coating layer made of a low work function material on the surface of the cathode and the surface of the substrate exposed to the opening of the extraction electrode. And a process.

According to the first method for manufacturing a field emission type electron source, a tower-shaped cathode and an extraction electrode having an opening around the cathode are formed, and then a surface coating layer made of a low work function material is formed. In addition, a surface coating layer made of a low work function material can be reliably formed continuously on the surface of the cathode and the surface of the portion of the substrate exposed to the opening of the extraction electrode.

In the first method for manufacturing a field emission type electron source, the step of forming a surface coating layer preferably includes a step of forming a surface coating layer by a collimated sputtering method having deposition directionality.

A second method for manufacturing a field emission type electron source according to the present invention includes a cathode forming step of forming a cathode on a substrate by etching the substrate using an etching mask formed on the substrate. Forming an extraction electrode having an opening around the cathode by lifting off the insulating film and the conductive film on the etching mask after sequentially depositing the insulating film and the conductive film on the entire surface of the substrate; A high-concentration impurity layer forming step of forming a high-concentration impurity layer having an impurity concentration higher than the impurity concentration of the substrate on the surface of the substrate.

According to the second method for manufacturing a field emission electron source, a high-concentration impurity layer is formed after a cathode and a lead electrode having an opening around the cathode are formed. A high-concentration impurity layer can be formed.

In the second method for manufacturing a field emission type electron source, the step of forming a high concentration impurity layer includes the step of forming a deposited film containing an impurity element on the surface of the cathode, and the step of forming the deposited film by the instantaneous heat treatment. It is preferable to include a step of forming a high-concentration impurity layer on the surface of the cathode by solid-phase diffusion of the impurity element on the surface of the cathode, and a step of removing the deposited film.

In the second method for manufacturing a field emission type electron source, the high concentration impurity layer forming step forms a high concentration impurity layer on the surface of the cathode by ion-implanting an impurity element into the surface of the cathode. Preferably, a step is included.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, the structure of a field emission type electron source according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1A shows FIG.
FIG. 1B shows a cross-sectional structure taken along the line II in FIG.
Indicates a planar structure.

As shown in FIGS. 1A and 1B, on a silicon substrate 11 made of silicon crystal, a lower silicon oxide film 16A having a circular opening in an array-shaped cathode formation region. In addition, a lead electrode 19A is formed via an insulating film made of the upper silicon oxide film 18A. In this case, the diameter of the opening of the extraction electrode 19A is equal to the lower silicon oxide film 16A and the upper silicon oxide film 18A.
The lower silicon oxide film 16A is smaller than the diameter of the opening of
The peripheral surface of the opening of the upper silicon oxide film 18A is recessed from the peripheral surface of the opening of the extraction electrode 19A.

A tower-shaped cathode 17 having a circular cross section is formed inside the openings of the lower silicon oxide film 16A, the upper silicon oxide film 18A, and the extraction electrode 19A. Radius 2n formed by anisotropic etching and thermal oxidation process of silicon
It has a steep shape of not more than m.

The regions of the silicon substrate 11 exposed to the openings of the lower silicon oxide film 16A and the upper silicon oxide film 18A and the surface of the cathode 17 have a thin surface made of a refractory metal material or a low work function material made of a compound material thereof. It is covered with the coating film 20. Examples of low work function materials include Cr, No, Nb, Ta, Ti, W and Zr.
And the like, or a material containing one or two or more compound materials such as carbide, nitride or silicide of these high melting point metal materials can be appropriately used. The physical and chemical properties of the surface can be improved. For example, a TiN film is formed on the surface of the cathode 17 by sputtering as a surface coating film 20 by sputtering.
When formed to a thickness of about m, the steep shape at the tip of the underlying cathode 17 is almost left, and the cathode 17 covered with the steeply shaped TiN film can be realized. While the work function of silicon is about 4.8 eV,
The work function of TiN is estimated to be about 2.9 eV, and the work function of the tip surface of the cathode 17 can be greatly reduced. As a result, it is possible to greatly reduce the extraction voltage required for electron emission. In addition, since the coating material constituting the surface coating film 20 is considered to be more stable in chemical properties than silicon, it is also considered to be effective in improving the stability of current during electron emission operation. .

As shown in FIG. 1A, when the insulating film composed of the lower silicon oxide film 16A and the upper silicon oxide film 18A is recessed from the extraction electrode 19A, the surface coating film 20 becomes , The insulation between the cathode 17 and the extraction electrode 19A is kept good, and short-circuiting does not occur. In particular, in an emitter array structure in which large-scale elements are integrated,
This is an extremely effective structure for improving the yield of devices and the reliability of device operation.

Hereinafter, a method of manufacturing the field emission type electron source according to the first embodiment will be described with reference to FIGS.

First, as shown in FIG. 5A, a first silicon oxide film 12 is formed on a (100) plane of a silicon substrate 11 made of silicon crystal by a thermal oxidation method. A photoresist film 13 is deposited on the film 12.

Next, as shown in FIG. 5B, the photoresist film 13 is subjected to photolithography to form a disk-shaped resist mask 13A having a diameter of about 0.5 μm. The resist mask 13A is transferred to the first silicon oxide film 12 by performing anisotropic dry etching on the first silicon oxide film 12 using the
Form 2A.

Next, as shown in FIG. 5C, after removing the resist mask 13A, the silicon oxide mask 12A is removed.
Anisotropic dry etching is performed on the silicon substrate 11 by using
Form A.

Next, as shown in FIG. 5D, the columnar body 14A is wet-etched by using an etching solution having a crystalline anisotropy property, for example, ethylenediamine and an aqueous solution of pyrocatechol. The side is (33
1) A drum-shaped body 14B having a surface including a surface and having a constricted central portion is formed. In this case, the diameter of the constricted portion is set to 0.1 by designing the diameter of the silicon oxide mask 12A and the depth of the constricted portion in advance from the azimuthal angle of the crystal.
The drum-shaped body 14B having a microstructure of about μm can be formed uniformly and with good reproducibility.

Next, as shown in FIG.
To protect the constriction of 4B, the drum-shaped body 1 is thermally oxidized.
After a thin second silicon oxide film 15 having a thickness of, for example, about 10 nm is formed on the side wall of 4B, the silicon substrate 11 is again subjected to anisotropic dry etching using the silicon oxide mask 12A to remove the silicon substrate 11 By performing vertical etching, a drum-shaped columnar body 14C is formed on the surface of the silicon substrate 11, as shown in FIG.

Next, as shown in FIG. 6C, the third silicon oxide film 1 having a thickness of, for example, about 100 nm is formed on the surfaces of the drum-shaped pillars 14C and the silicon substrate 11 by a thermal oxidation method.
By forming 6, the cathode 17 is formed inside the drum-shaped columnar body 14C. Thus, the drum-shaped columnar body 14C
The reason for forming the third silicon oxide film 16 on the surface of
This is because the tip of the cathode 17 is sharpened and the insulating property of the insulating film below the extraction electrode described later is strengthened. In this case, a temperature lower than the melting point of silicon oxide, for example, 9
When thermal oxidation is performed under a temperature condition of about 50 ° C., a cathode 17 made of silicon and a third silicon oxide film 16
Since stress is generated in the vicinity of the interface between the cathode 17 and the cathode 17, it is possible to form the cathode 17 having a very steep tip.
In addition, a silicon oxide film formed by a thermal oxidation method has a higher insulation resistance because it has better film quality than a silicon oxide film formed by another method, for example, a vapor deposition method.
As a result, it is possible to form a highly reliable element having excellent insulation when a voltage is applied to the extraction electrode described later.

Next, as shown in FIG. 6D, a fourth silicon oxide film 18 used as an insulating film and a conductive film 19 used as a lead electrode are sequentially deposited by a vacuum evaporation method via a silicon oxide mask 12A. I do. By introducing an ozone gas when the fourth silicon oxide film 18 is vacuum-deposited, a high-quality silicon oxide film having excellent insulating properties can be formed. In addition, as the conductive film 19, N
By using the b-metal film, it is possible to form a lead electrode having excellent uniformity during a lift-off process described later.

Next, as shown in FIG. 7A, wet etching is performed in an ultrasonic atmosphere using a buffered hydrofluoric acid solution to selectively remove the side wall of the cathode 17 and the silicon oxide mask 12A. By doing so, the conductive film 19 deposited on the silicon oxide mask 12A is lifted off, and the extraction electrode 19A and the cathode 17 having minute openings are exposed. In this case, by adjusting the wet etching time to such an extent that the third and fourth silicon oxide films 16 and 18 are over-etched,
Lower silicon oxide film 16A and upper silicon oxide film 18
The peripheral surface of the opening A can be retracted from the peripheral surface of the opening of the extraction electrode 19A.

Next, as shown in FIG. 7 (b), the surface coating film 2 is made of a metal material having a low work function or a coating material made of a compound material of the metal material by sputtering over the entire surface.
When 0 is formed, the field emission type electron source according to the first embodiment is obtained.

As described above, by using the sputtering method, even if a coating material made of a high melting point metal material or a compound material of a high melting point metal material is used, a surface coating film having excellent coating characteristics can be formed on the cathode 17. 20 can be formed.

By controlling the thickness of the surface coating film 20 to about 10 nm or less, a surface shape that accurately reflects the structure of the underlying cathode 17 can be obtained. As a result, even after the surface coating film 20 is formed, it is possible to obtain the cathode 17 having a microstructure with a tip portion on the order of nm.

When the surface coating film 20 is formed by using a collimated sputtering method having good directivity in the deposition direction, even if the opening of the extraction electrode 19A is minute, the surface coating film 20 can be formed. Can be uniformly formed not only on the surface of the cathode 17 but also on the bottom portion of the silicon substrate 11 exposed to the opening of the extraction electrode 19A.
Therefore, it is possible to apply the surface coating process even to a minute element structure in which a lower operating voltage can be expected, which is advantageous in improving the performance of the element.

Further, the above-described manufacturing method is excellent in process uniformity and reproducibility, and makes it possible to form a field emission type electron source array having minute dimensions with high precision and high density.

Further, since a coating material made of a high melting point metal material having a low work function or a compound material of a high melting point metal material can be formed on the surface of the cathode 17 made of silicon with higher precision, the electron emission is smaller than in the conventional case. Operating voltage can be greatly reduced.

(Second Embodiment) Hereinafter, a structure of a field emission type electron source according to a second embodiment of the present invention will be described with reference to FIG. FIG. 2A shows a cross-sectional structure taken along the line II-II in FIG. 2B, and FIG. 2B shows a planar structure.

As shown in FIGS. 2A and 2B, on a silicon substrate 11 made of silicon crystal, a lower silicon oxide film 16A having a circular opening in an array-shaped cathode formation region. In addition, a lead electrode 19A is formed via an insulating film made of the upper silicon oxide film 18A. In this case, the diameter of the opening of the extraction electrode 19A is equal to the lower silicon oxide film 16A and the upper silicon oxide film 18A.
The lower silicon oxide film 16A is smaller than the diameter of the opening of
The peripheral surface of the opening of the upper silicon oxide film 18A is recessed from the peripheral surface of the opening of the extraction electrode 19A.

A tower-shaped cathode 17 having a circular cross section is formed inside the openings of the lower silicon oxide film 16A, the upper silicon oxide film 18A, and the lead electrode 19A. Radius 2n formed by anisotropic etching and thermal oxidation process of silicon
It has a steep shape of not more than m.

The surface of the region of the silicon substrate 11 exposed to the openings of the lower silicon oxide film 16A and the upper silicon oxide film 18A and the surface of the cathode 17 are of the same conductivity type as the silicon substrate 11 and Also, the high-concentration impurity layer 22 having a high impurity concentration is formed thin.

By using n-type as the conductivity type of the silicon substrate 11 and phosphorus as an impurity of the high-concentration impurity layer 22 and setting the sheet resistance of the high-concentration impurity layer 22 to 10 kΩ or less, the electron emission efficiency at the tip of the cathode 17 is improved. It can be greatly improved. As a result, it is possible to significantly reduce the extraction voltage required for a predetermined electron emission amount, or to significantly increase the electron emission amount at a predetermined extraction voltage.

Hereinafter, a method for manufacturing the field emission type electron source according to the second embodiment will be described with reference to FIGS.

First, as shown in FIG. 8A, a first silicon oxide film 12 is formed on the (100) plane of a silicon substrate 11 made of silicon crystal by a thermal oxidation method, and then the first silicon oxide film 12 is formed. A photoresist film 13 is deposited on the film 12.

Next, as shown in FIG. 8B, a photolithography method is performed on the photoresist film 13 to form a disk-shaped resist mask 13A having a diameter of about 0.5 μm. The resist mask 13A is transferred to the first silicon oxide film 12 by performing anisotropic dry etching on the first silicon oxide film 12 using the
Form 2A.

Next, as shown in FIG. 8C, after removing the resist mask 13A, the silicon oxide mask 12A is removed.
Anisotropic dry etching is performed on the silicon substrate 11 by using
Form A.

Next, as shown in FIG. 8D, the columnar body 14A is wet-etched using an etching solution having a crystalline anisotropy property, for example, ethylenediamine and an aqueous solution of pyrocatechol. The side is (33
1) A drum-shaped body 14B having a surface including a surface and having a constricted central portion is formed. In this case, the diameter of the constricted portion is set to 0.1 by designing the diameter of the silicon oxide mask 12A and the depth of the constricted portion in advance from the azimuthal angle of the crystal.
The drum-shaped body 14B having a microstructure of about μm can be formed uniformly and with good reproducibility.

Next, as shown in FIG.
To protect the constriction of 4B, the drum-shaped body 1 is thermally oxidized.
After a thin second silicon oxide film 15 having a thickness of, for example, about 10 nm is formed on the side wall of 4B, the silicon substrate 11 is again subjected to anisotropic dry etching using the silicon oxide mask 12A to remove the silicon substrate 11 By performing vertical etching, a drum-shaped columnar body 14C is formed on the surface of the silicon substrate 11, as shown in FIG. 9B.

Next, as shown in FIG. 9C, the third silicon oxide film 1 having a thickness of, for example, about 100 nm is formed on the surface of the drum-shaped columnar body 14C and the silicon substrate 11 by a thermal oxidation method.
By forming 6, the cathode 17 is formed inside the drum-shaped columnar body 14C. Thus, the drum-shaped columnar body 14C
The reason for forming the third silicon oxide film 16 on the surface of
This is because the tip of the cathode 17 is sharpened and the insulating property of the insulating film below the extraction electrode described later is strengthened. In this case, a temperature lower than the melting point of silicon oxide, for example, 9
When thermal oxidation is performed under a temperature condition of about 50 ° C., a cathode 17 made of silicon and a third silicon oxide film 16
Since stress is generated in the vicinity of the interface between the cathode 17 and the cathode 17, it is possible to form the cathode 17 having a very steep tip.
In addition, a silicon oxide film formed by a thermal oxidation method has a higher insulation resistance because it has better film quality than a silicon oxide film formed by another method, for example, a vapor deposition method.
As a result, it is possible to form a highly reliable element having excellent insulation when a voltage is applied to the extraction electrode described later.

Next, as shown in FIG. 9D, a fourth silicon oxide film 18 used as an insulating film and a conductive film 19 used as a lead electrode are sequentially deposited by a vacuum evaporation method via a silicon oxide mask 12A. I do. By introducing an ozone gas when the fourth silicon oxide film 18 is vacuum-deposited, a high-quality silicon oxide film having excellent insulating properties can be formed. In addition, as the conductive film 19, N
By using the b-metal film, it is possible to form a lead electrode having excellent uniformity during a lift-off process described later.

Next, as shown in FIG. 10A, wet etching is performed in an ultrasonic atmosphere using a buffered hydrofluoric acid solution to selectively remove the side wall of the cathode 17 and the silicon oxide mask 12A. As a result, the conductive film 19 deposited on the silicon oxide mask 12A is lifted off, and the extraction electrode 19A having a minute opening is lifted off.
And the cathode 17 is exposed. In this case, the wet etching time is set to the third and fourth silicon oxide films 16 and 18.
Is adjusted to the extent that is overetched, the peripheral surfaces of the openings of the lower silicon oxide film 16A and the upper silicon oxide film 18A can be retracted from the peripheral surfaces of the openings of the extraction electrode 19A.

Next, as shown in FIG.
After a glass layer containing a high-concentration impurity element, for example, a phosphorus glass layer 21 is deposited over the entire surface of the silicon substrate 11 including the silicon substrate 7, the instantaneous thermal heating method (RTA method) is used to appropriately adjust the phosphorus glass layer 21. By performing a heat treatment, the impurity element contained in the phosphorus glass layer 21 is diffused into the surface of the cathode 17 in a solid layer, and the high concentration impurity layer 22 is formed on the surface of the cathode 17 as shown in FIG. Form. Thus, the high-concentration impurity layer 22 having a sheet resistance with a resistivity of 10 kΩ or less can be uniformly formed on the surface of the cathode 17 to a depth of about several tens nm. Thereafter, when the phosphorus glass layer 21 is removed, a field emission type electron source according to the second embodiment is obtained.

In the manufacturing method of the second embodiment, the high-concentration impurity layer 22 is formed by the solid diffusion method using the phosphor glass layer 21.
The impurity element may be introduced into the surface of the substrate 7 using a low-energy ion implantation method, and then heat-treated to activate the impurity element, thereby forming the high-concentration impurity layer 22. In this case, for example, a high-concentration impurity layer having a depth of about several tens nm is implanted into the surface of the cathode 17 by ion-implanting phosphorus as an impurity element under the condition of about 5 keV as acceleration energy at the time of ion implantation. 22 can be formed uniformly.

As described above, according to the method of manufacturing the field emission electron source according to the second embodiment, the high-concentration impurity layer 22 can be uniformly formed on the surface of the cathode 17 with high productivity. Further, since the impurity concentration at the tip of the cathode 17 can be set high, the electron emission efficiency is significantly improved,
As a result, it is possible to significantly reduce the extraction voltage required for a predetermined electron emission amount, or to significantly increase the electron emission amount at a predetermined extraction voltage.

In the method of manufacturing the field emission type electron source according to the first and second embodiments, a crystal anisotropic etching and a thermal oxidation process are used to realize a steep tip of the cathode 17. Thus, the cathode 17 and the lead electrode 19A were formed on the (100) plane of the silicon substrate 11 made of silicon crystal. Alternatively, for example, after forming a polysilicon film on a glass substrate at a low temperature, It is also possible to adopt a method of crystallizing the polysilicon film in a predetermined region by performing a heat treatment such as laser annealing on a predetermined region of the polysilicon film where the field emission electron source is to be formed. This makes it possible to form a large-area array of field emission electron sources on an inexpensive glass substrate.

In place of the silicon substrate 11 in the first or second embodiment, another semiconductor material, for example, Ga
It is also possible to use a substrate made of a compound semiconductor such as As.

Further, in the first and second embodiments, the cathode 17 has a tower shape and the extraction electrode 19A
Are also circular, but the shape of the cathode 17 and the shape of the opening of the extraction electrode 19 are not limited.
Hereinafter, an embodiment in which the shape of the cathode 17 is different from the first embodiment and the second embodiment will be described.

(Third Embodiment) Hereinafter, a structure of a field emission type electron source according to a third embodiment of the present invention will be described with reference to FIG. FIG. 3A shows a cross-sectional structure taken along line III-III in FIG. 3B, and FIG. 3B shows a planar structure.

As shown in FIGS. 3A and 3B, on a silicon substrate 11 made of silicon crystal, a lower oxide having openings in rectangular cathode forming regions arranged in an array is provided. A lead electrode 19A is formed via an insulating film composed of the silicon film 16A and the upper silicon oxide film 18A. In this case, the length of each side of the opening of the extraction electrode 19A is smaller than the length of each side of the opening of the lower silicon oxide film 16A and the upper silicon oxide film 18A, and the lower silicon oxide film 16A and the upper silicon oxide The peripheral surface of the opening of the film 18A is recessed from the peripheral surface of the opening of the extraction electrode 19A.

A cathode 17 having a wedge structure is formed inside the openings of the lower silicon oxide film 16A, the upper silicon oxide film 18A and the lead electrode 19A.

The surface of the region of the silicon substrate 11 exposed to the openings of the lower silicon oxide film 16A and the upper silicon oxide film 18A and the surface of the cathode 17 are of the same conductivity type as the silicon substrate 11, and Also, the high concentration impurity layer 22 having a high impurity concentration is formed shallowly.

(Fourth Embodiment) Hereinafter, a structure of a field emission type electron source according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 4A shows a cross-sectional structure taken along line III-III in FIG. 4B, and FIG. 4B shows a planar structure.

As shown in FIGS. 4A and 4B, on a silicon substrate 11 made of silicon crystal, a lower oxide having openings in circular cathode forming regions arranged in an array is provided. A lead electrode 19A is formed via an insulating film composed of the silicon film 16A and the upper silicon oxide film 18A. In this case, the diameter of the opening of the extraction electrode 19A is smaller than the diameter of the opening of the lower silicon oxide film 16A and the upper silicon oxide film 18A, and the peripheral surfaces of the openings of the lower silicon oxide film 16A and the upper silicon oxide film 18A are drawn. It is recessed from the peripheral surface of the opening of the electrode 19A.

A conical cathode 17 is formed inside the openings of the lower silicon oxide film 16A, the upper silicon oxide film 18A and the extraction electrode 19A.

The surface of the region of the silicon substrate 11 exposed to the openings of the lower silicon oxide film 16A and the upper silicon oxide film 18A and the surface of the cathode 17 are of the same conductivity type as the silicon substrate 11 and Also, the high concentration impurity layer 22 having a high impurity concentration is formed shallowly.

[0088]

According to the first field emission type electron source, the allowable current value determined by the substrate resistance and the cross-sectional area of the tower-shaped cathode becomes large. Therefore, even if the tower-shaped cathode is miniaturized, it remains at the base of the cathode. Since a situation in which current is concentrated can be avoided, a situation in which Joule heat is generated at the base of the cathode can be avoided, so that even when the cathode is driven with a large current, there is no danger of the cathode melting and element breakdown. .

In the first field emission type electron source, the low work function material is a high melting point metal material made of Cr, Mo, Nb, Ta, Ti, W or Zr or a carbide, nitride or When limited to those containing silicide, these low work function materials are generally used in the process of semiconductor devices made of silicon and have excellent reactivity with the silicon substrate, so that the surface coating film can be formed uniformly and Since the element can be formed with high productivity, the element can have high performance. In addition, the element can be easily accepted in a process of a semiconductor device made of ordinary silicon, and thus is industrially useful.

According to the second field emission type electron source, electrons can be emitted from the surface of the cathode satisfactorily, so that the power consumption of the device can be reduced.

In the second field-emission electron source, the cathode has a tower shape, and the high-concentration impurity layer is formed on the surface of the cathode and on the surface of the substrate exposed at the opening of the extraction electrode. As in the case of the first field emission electron source, the allowable current value determined by the substrate resistance and the cross-sectional area of the tower-shaped cathode increases, and even when the tower-shaped cathode is miniaturized, Joule heat is generated at the base of the cathode. Therefore, even if the cathode is driven with a large current, there is no danger that the cathode will melt and the element will be destroyed.

In the second field emission type electron source, if the high concentration impurity layer has a sheet resistance of 10 kΩ or less,
Since the electron emission can be significantly improved, the power consumption of the device can be greatly reduced.

According to the first method for manufacturing a field emission type electron source, a surface coating layer made of a low work function material is continuously provided on the surface of the cathode and the surface of the portion of the substrate exposed to the opening of the extraction electrode. One field emission electron source can be manufactured simply and with good reproducibility.

In the first method for manufacturing a field emission type electron source, if the step of forming a surface coating layer includes a step of forming a surface coating layer by a collimated sputtering method having deposition directionality, the collimated sputtering method has a deposition performance. Therefore, even if the element is miniaturized and the diameter of the opening of the extraction electrode is reduced, the surface coating layer can be reliably deposited, and the reliability of the element is improved.

According to the second method for manufacturing a field emission type electron source, a high-concentration impurity layer can be selectively formed on the surface of the cathode. A field emission electron source can be manufactured easily and with good reproducibility.

In the second method for manufacturing a field emission type electron source, the high concentration impurity forming step comprises forming a deposited film containing the impurity element on the surface of the cathode, and then removing the impurity element contained in the deposited film by an instantaneous heat treatment method. When the step of solid-phase diffusion on the surface of the cathode is included, the high-concentration impurity layer can be selectively formed on the surface of the cathode without fail.

In the second method of manufacturing a field emission type electron source, the high concentration impurity forming step is a step of forming a high concentration impurity layer on the surface of the cathode by ion-implanting an impurity element into the surface of the cathode. In this case, the high-concentration impurity layer can be reliably formed selectively on the surface of the cathode.

[Brief description of the drawings]

FIGS. 1A and 1B show a field emission type electron source according to a first embodiment of the present invention, wherein FIG. 1A is a cross-sectional view taken along the line II in FIG. 1B, and FIG.

FIGS. 2A and 2B show a field emission type electron source according to a second embodiment of the present invention, wherein FIG. 2A is a cross-sectional view taken along the line II-II in FIG.

3A and 3B show a field emission type electron source according to a third embodiment of the present invention, wherein FIG. 3A is a cross-sectional view taken along line III-III in FIG. 3B, and FIG. 3B is a plan view.

FIGS. 4A and 4B show a field emission electron source according to a fourth embodiment of the present invention, wherein FIG. 4A is a cross-sectional view taken along the line IV-IV in FIG.

FIGS. 5A to 5D are cross-sectional views showing each step of a method for manufacturing a field emission electron source according to the first embodiment of the present invention.

FIGS. 6A to 6D are cross-sectional views illustrating respective steps of a method for manufacturing a field emission electron source according to the first embodiment of the present invention.

FIGS. 7A and 7B are cross-sectional views showing steps of a method for manufacturing a field emission electron source according to the first embodiment of the present invention.

FIGS. 8A to 8D are cross-sectional views showing each step of a method for manufacturing a field emission electron source according to a second embodiment of the present invention.

FIGS. 9A to 9D are cross-sectional views showing steps of a method for manufacturing a field emission electron source according to a second embodiment of the present invention.

FIGS. 10A to 10C are cross-sectional views illustrating steps of a method for manufacturing a field emission electron source according to a second embodiment of the present invention.

FIGS. 11A to 11D are cross-sectional views showing steps of a conventional method for manufacturing a field emission electron source.

12 (a) to 12 (d) are cross-sectional views showing steps of a conventional method for manufacturing a field emission electron source.

FIG. 13 is a cross-sectional view showing each step of a conventional method for manufacturing a field emission electron source.

[Explanation of symbols]

 Reference Signs List 11 silicon substrate 12 first silicon oxide film 12A silicon oxide mask 13 photoresist film 13A resist mask 14A columnar body 14B drum-shaped body 14C drum-shaped columnar body 15 second silicon oxide film 16 third silicon oxide film 17 Cathode 18 Fourth silicon oxide film 19 Conductive film 19A Leader electrode 20 Surface coating film 21 Phosphorus glass layer 22 High concentration impurity layer

Claims (6)

[Claims] 1. A substrate, a lead electrode formed on the substrate via an insulating film and having an opening in a cathode forming region, a cathode formed in the opening of the lead electrode on the substrate, and the cathode And a high-concentration impurity layer having an impurity concentration higher than the impurity concentration of the substrate. 2. The cathode has a tower shape, and the high concentration impurity layer is formed continuously on a surface of the cathode and a surface of a portion of the substrate exposed to an opening of the extraction electrode. The field emission type electron source according to claim 1, wherein: 3. The high-concentration impurity layer has a sheet resistance of 10 kΩ or less.
3. A field emission type electron source according to claim 1. 4. A cathode forming step of performing etching on the substrate using an etching mask formed on the substrate to form a cathode on the substrate; and an insulating film and a conductive film over the entire surface of the substrate. Forming an extraction electrode having an opening around the cathode by lifting off the insulating film and the conductive film on the etching mask; and depositing impurities on the surface of the cathode on the etching mask. Forming a high-concentration impurity layer having an impurity concentration higher than the impurity concentration. 5. The step of forming a high-concentration impurity layer, comprising: forming a deposition film containing an impurity element on the surface of the cathode; and solid-phase diffusion of the impurity element contained in the deposition film onto the surface of the cathode. The method for manufacturing a field emission type electron source according to claim 4, further comprising: a step of forming the high concentration impurity layer on the surface of the cathode; and a step of removing the deposited film. 6. The step of forming a high-concentration impurity layer, wherein the impurity element is ion-implanted into a surface portion of the cathode,
5. The method according to claim 4, further comprising a step of forming the high concentration impurity layer on a surface of the cathode.