JP2005005220A - Field emission type electron source element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably provide a field emission type electron source capable of obtaining a large current density at a low voltage with good reproducibility. <P>SOLUTION: The field emission type electron source comprises a plurality of conductive emitters 1b formed on a substrate so as to have a steep tip; and a leadout electrodes 5a formed so as to surround each emitter 1b in order to apply voltages to each emitter 1b for emitting electrons from the tips of each emitter 1b respectively. Segregated materials 7 having a composition different from that of a mother material composing the emitters 1b are dispersed locally on the surfaces of the emitters 1b. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cold cathode electron source expected to be applied to a flat-type solid display element or an ultrafast micro vacuum element, and more particularly to a field emission electron source capable of realizing a large current operation.
[0002]
[Prior art]
Advances in semiconductor microfabrication technology have enabled the formation of minute field emission cathodes. Since a cone-type field emission cathode proposed by Spindt et al. (Patent Document 1: CA Spindt, J. Appl. Phys. Vol. 39, p. 3504 (1986)), a minute field emission electron source has attracted attention. Has been done.
[0003]
Thereafter, a method of forming a cold cathode having a sharper tip shape by using crystal anisotropic etching, dry etching and thermal oxidation of silicon with a similar vertical structure was proposed (Patent Document 2: HF. Gray et al., IEDM Tech.Dig.p.776 (1986)), Patent Document 3: Besui, 1990 Fall Shingaku Zengakushu, 5, SC-8-2 (1990)).
[0004]
The electron emission characteristics of these field emission electron sources are affected by various factors such as the shape and material of the emitter tip and the structure of the electron source element including the extraction electrode. As one means for improving the electron emission characteristics of the field emission electron source, there is a concept of facilitating electron emission from the tip of the emitter by lowering the work function on the surface of the emitter.
[0005]
FIG. 6 is an enlarged view of a main part of a conventional field emission type electron source element. As shown in FIG. 6, many attempts have been made to cover the surface of the emitter 1b with a substance 91 having a work function lower than that of the base material of the emitter 1b at the tip of the emitter 1b.
[0006]
[Patent Document 1]
C. A. Spindt, J.M. Appl. Phys. Vol. 39, p. 3504 (1986),
[0007]
[Patent Document 2]
H. F. Gray et al. , IEDM Tech. Dig. p. 776 (1986)),
[0008]
[Patent Document 3]
Besui, 1990 Fall Shingaku Zengakushu 5, SC-8-2 (1990)
[0009]
[Problems to be solved by the invention]
The electron source shown in the conventional example is effective in reducing the work function on the surface of the emitter. However, depending on the film forming method, when the tip of the emitter is covered with a different material, in most cases, the radius of curvature of the tip becomes large or the tip is not covered at all.
[0010]
In general, the smaller the radius of curvature at the tip of the emitter, that is, the sharper the tip, the stronger the electric field concentration on the emitter tip due to the external electric field, and the easier it is to emit electrons. Therefore, a method for lowering the work function of the emitter surface without increasing the radius of curvature of the tip is desired.
[0011]
Also, in the method of covering the emitter tip with a material having a low work function, particularly when this treatment is performed in the final step, the side wall of the insulating film that electrically isolates the extraction electrode and the emitter is slightly conductive. A film is formed. For this reason, there is also a problem that a leak current is generated between the extraction electrode and the emitter.
[0012]
An object of the present invention is to locally form a portion having a relatively low work function on the emitter surface without impairing the shape of the sharpened emitter surface and without impairing electrical characteristics. An object of the present invention is to provide a field emission electron source capable of high current density stably and with good reproducibility.
[0013]
[Means for Solving the Problems]
The field emission electron source according to the present invention includes a plurality of conductive emitters formed on a substrate so as to have a steep tip, and a voltage applied to each emitter so that electrons are emitted from the tip of each emitter. And an extraction electrode formed so as to surround each emitter for application, and a segregated material having a composition different from the composition of the base material constituting the emitter is locally formed on the surface of the emitter. The material constituting the segregated material and the material constituting the emitter are non-totally solid solution type metals.
[0014]
In the method of manufacturing a field emission electron source according to the present invention, after forming an emitter composed of a plurality of conductive convex microstructures having a sharp tip on the surface, a material different from the emitter is formed on the surface of the emitter. A step of uniformly forming the conductive thin film, a step of alloying the emitter surface and a part of the conductive thin film by heat treatment at a predetermined temperature, a step of etching away the conductive thin film, and the alloy And a step of locally forming a segregated material having a composition different from that of the base material of the emitter on the surface of the emitter by performing a heat treatment again at a temperature higher than the temperature in the forming step. The conductive thin film made of a material different from the emitter formed on the surface is made of a non-total solid solution type metal.
[0015]
In the method of manufacturing a field emission electron source according to the present invention, after forming an emitter composed of a plurality of conductive convex microstructures having a sharp tip on the surface, a material different from the emitter is formed on the surface of the emitter. A step of forming a micro conductive material locally scattered and a heat treatment at a predetermined temperature to alloy the emitter surface and a part of the micro conductive material, or to form a micro conductive material on the emitter surface. Including a step of partially diffusing and locally forming a segregated material having a composition different from that of the base material of the emitter on the emitter surface, and a step of etching and removing the minute conductive material. The conductive thin film made of a material different from the emitter formed on the surface of the formed emitter is made of a non-total solid solution type metal.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
In the field emission electron source according to the present embodiment, segregated substances having a composition different from the composition of the base material constituting the emitter are locally scattered on the surface of the emitter. The material constituting the emitter and the material constituting the emitter are non-totally solid solution type metals. For this reason, there is a part where the work function is locally lowered at the tip of the emitter, and this part becomes a trigger, and it becomes easy to emit electrons to the electric field from the extraction electrode. As a result, electrons can be emitted at a lower voltage than before.
[0017]
Embodiments of the present invention will be described below with reference to the drawings.
[0018]
(Embodiment 1)
1A to 1E are cross-sectional views showing a method for manufacturing the field emission electron source device according to the first embodiment, and FIG. 2 shows the field emission electron source device according to the first embodiment. It is a principal part enlarged view.
[0019]
First, as shown in FIG. 1A, a disk-shaped dot pattern 2 made of a silicon dioxide film is formed on the surface of a silicon substrate 1 having a resistance lowered by introducing impurities. Then, using the dot pattern 2 as a mask, the surface of the silicon substrate 1 is etched isotropically and anisotropically to form a columnar silicon 1a having a convex upper portion.
[0020]
Next, as shown in FIG. 1B, the silicon substrate 1 is heat-treated at a predetermined temperature for a certain period of time to form a thermal oxide film 3 on the surface of the silicon substrate 1 containing the columnar silicon 1a, and the inside thereof is sharpened A columnar emitter 1b having a tip is formed.
[0021]
Thereafter, as shown in FIG. 1C, after the thermal oxide film 3 is removed, an insulating film 4 made of a silicon dioxide film is formed on the entire surface of the substrate 1 including the emitter 1b by using a thermal CVD method or a plasma CVD method, and A conductive film 5 made of a polycrystalline silicon film containing phosphorus as an impurity is formed. Thereafter, a planarization film (not shown) made of a photoresist or a coating type insulating film is applied to the entire surface (not shown), and the entire surface of the planarization film is uniformly etched to reflect the shape of the emitter 1b. The conductive film is etched in a state in which a part of the convex portion of the film is exposed, and an opening is provided in the conductive film above the emitter 1b to form the extraction electrode 5a. Thereafter, a part of the insulating film 4 is removed by etching through the opening of the extraction electrode 5a to expose the emitter 1b.
[0022]
Subsequently, aluminum or a metal film 6a containing aluminum as a main component is formed on the entire surface of the substrate 1 by sputtering or vacuum evaporation, and heat treatment is performed at a predetermined temperature (see FIG. 1D). In the first embodiment, a rapid thermal annealing method (Rapid Thermal Anneal, RTA method) is used, and heat treatment is performed at about 500 ° C. for 1 minute in a vacuum or in an inert gas atmosphere.
[0023]
Thereafter, after all the metal film 6a is removed by wet etching, a heat treatment is performed in vacuum at 800 ° C. for 1 hour. As a result, local segregation portions 7 where aluminum is segregated locally are scattered on the surface of the emitter 1a. Emitter 1b was formed (see FIG. 1 (e) and FIG. 2). In the first embodiment, the same local segregated material 7 is also formed on the surface of the extraction electrode 5a, but this is not an essential problem.
[0024]
In the field emission electron source shown in the first embodiment, a segregated material different from the base material locally exists in the local segregation portion 7 on the surface of the emitter 1b. Further, the shape of the tip of the emitter 1b was not different from that before the metal film 6a was formed.
[0025]
In the field emission electron source according to the first embodiment, when a positive electric field was applied to the extraction electrode 5a with respect to the emitter 1b, electron emission was started at a voltage lower by about 10V than a normal silicon-only emitter. The local segregated material in Embodiment 1 is aluminum, which is a material having a work function lower than that of silicon. From this, it is considered that this local segregated material played the role of lowering the effective work function of the surface of the emitter 1b.
[0026]
As described above, according to the first embodiment, the segregated material having a composition different from the composition of the base material constituting the emitter 1b is locally scattered in the local segregation portion 7 on the surface of the emitter 1b. . For this reason, since there is a part where the work function is locally lowered at the tip of the emitter 1b, the part becomes a trigger, and the electron emission from the extraction electrode 5a becomes easy. As a result, electrons can be emitted at a lower voltage than before.
[0027]
(Embodiment 2)
3 (a) to 3 (e) are cross-sectional views illustrating a method for manufacturing a field emission type electron source device according to the second embodiment. Components described above with reference to FIGS. 1A to 1E are denoted by the same reference numerals. Therefore, detailed description of these components is omitted.
[0028]
A disk-shaped dot pattern 2 made of a silicon dioxide film is formed on the surface of the silicon substrate 1 whose resistance has been reduced by introducing impurities (see FIGS. 3A to 3C). Then, the surface of the silicon substrate 1 is isotropically and anisotropically etched using the dot pattern 2 as a mask to form a columnar silicon 1a having a convex upper portion, and then an emitter 1b, an insulating film 4 and an extraction electrode 5a are formed. The process of etching away a part of the insulating film 4 through the opening of the extraction electrode 5a to expose the emitter 1b is the same as that in the first embodiment. For this reason, detailed description is omitted.
[0029]
After the emitter 1b is exposed, metal particles 6b such as gallium, indium and hafnium are formed in an island shape on the substrate surface by plasma CVD using an organic metal, and heat treatment is performed at a predetermined temperature (FIG. 3D). reference). In Embodiment 2, heat treatment is performed at about 400 ° C. for 30 minutes using a vacuum heat treatment furnace.
[0030]
Thereafter, all the remaining portions of the metal particles 6b are removed by wet etching, and then heat treatment is performed in vacuum at 600 ° C. for 1 hour. As a result, an alloy of the metal particles 6b and silicon is locally formed on the surface of the emitter 1a. As a result, the emitter 1b in which the local segregation portions 7 segregated in the region are scattered is formed (see FIG. 3E).
[0031]
In the second embodiment, since the CVD method is used as the method for forming the metal particles 6b, the metal particles 6b are also formed in the shape of islands on the sidewalls of the insulating film 4, but the metal particles 6b and the insulating film 4 are made of a compound. Since it is not formed, all the metal particles 6b are removed during the wet etching process. For this reason, defects such as leakage do not occur.
[0032]
Even in the field emission electron source shown in the second embodiment, the electron emission start voltage is low because it is considered that a segregated material different from the base material is locally present in the local segregation portion 7 on the surface of the emitter 1b. The voltage could be realized.
[0033]
(Embodiment 3)
4 (a) to 4 (e) are cross-sectional views illustrating a method for manufacturing a field emission type electron source device according to the third embodiment. Components described above with reference to FIGS. 1A to 1E are denoted by the same reference numerals. Therefore, detailed description of these components is omitted.
[0034]
A disk-like dot pattern 2 made of a silicon dioxide film is formed on the surface of the silicon substrate 1 whose resistance has been lowered by introducing impurities. Then, the surface of the silicon substrate 1 is etched isotropically and anisotropically using the dot pattern 2 as a mask to form columnar silicon having a convex upper portion, and then the silicon substrate 1 is heat-treated at a predetermined temperature for a certain time. A thermal oxide film 3 is formed on the surface of a silicon substrate 1 containing columnar silicon, and a columnar emitter 1b having a sharp tip portion is formed therein (see FIG. 4A).
[0035]
After removing the entire surface of the thermal oxide film 3, a metal paste 6c mainly composed of silver having a viscosity with an organic solvent is applied to the entire surface, and heat treatment is performed at a predetermined temperature (see FIG. 4B). In Embodiment 3, heat treatment was performed at about 250 ° C. for 30 minutes in a clean oven into which an inert gas was introduced.
[0036]
Thereafter, all of the remaining metal paste 6c was removed with a mixed solution of phosphoric acid, nitric acid, acetic acid and water, and then heat treatment was performed at 850 ° C. for 1 minute in vacuum using the RTA method. Emitters 1b interspersed with local segregation portions 7 where silver was segregated locally were formed (see FIG. 4C).
[0037]
Thereafter, an insulating film 4 made of a silicon dioxide film and a conductive film 5 made of a polycrystalline silicon film containing phosphorus as impurities are formed on the entire surface of the substrate including the emitter 1b by using a thermal CVD method or a plasma CVD method (FIG. 4 (d)).
[0038]
Subsequently, a photoresist or a planarizing film (not shown) made of a coating-type insulating film is applied to the entire surface, and etching is uniformly performed on the entire surface of the planarizing film to reflect the shape of the emitter 1b. The conductive film 5 is etched in a state where a part of the convex portion of the conductive film 5 is exposed, and an opening is provided in the conductive film 5 above the emitter 1b to form a lead electrode 5a. Finally, a portion of the insulating film 4 is removed by etching through the opening of the extraction electrode 5a to expose the emitter 1b, thereby completing the field emission electron source (see FIG. 4E).
[0039]
The manufacturing method of the field emission electron source shown in the third embodiment is different from the first and second embodiments described above, and immediately after the emitter 1b is formed, the emitter 1b is used by using the metal paste 6c. A segregated material different from the base material is locally formed on the surface of the substrate. Also in the field emission electron source according to the third embodiment, when a positive electric field was applied to the extraction electrode 5a with respect to the emitter 1b, electron emission at a lower voltage than that of a normal silicon-only emitter was confirmed.
[0040]
(Embodiment 4)
5 (a) to 5 (d) are cross-sectional views showing a method for manufacturing a field emission type electron source device according to Embodiment 4. FIG. Components described above with reference to FIGS. 1A to 1E are denoted by the same reference numerals. Therefore, detailed description of these components is omitted.
[0041]
A disk-shaped dot pattern 2 made of a silicon dioxide film is formed on the surface of the silicon substrate 1 whose resistance has been reduced by introducing impurities (see FIG. 5A). The surface of the silicon substrate 1 is etched isotropically and anisotropically using the dot pattern 2 as a mask to form a columnar silicon 1a having a convex top, and then an emitter 1b is formed by thermal oxidation, and the thermal oxide film 3 is removed. Since the process until the emitter 1b is exposed is the same as that in the third embodiment, detailed description thereof is omitted.
[0042]
After the emitter 1b is exposed, metal fluoride 6d containing magnesium fluoride as a main component is formed in an island shape on the substrate surface by vacuum evaporation using magnesium fluoride as an evaporation source, and heat treatment is performed at a predetermined temperature (FIG. 5). (See (b)). In Embodiment Mode 4, heat treatment is performed at about 500 ° C. for 30 minutes using a vacuum heat treatment furnace.
[0043]
Thereafter, all remaining portions of the metal particles 6d were removed by wet etching, and then heat treatment was performed at 700 ° C. for 1 minute in vacuum using the RTA method. As a result, the metal particles 6d and silicon were formed on the surface of the emitter 1a. As a result, an emitter 1b was formed in which local segregation portions 7 in which the alloy was locally segregated were scattered (see FIG. 5C).
[0044]
Also in the field emission electron source device according to the fourth embodiment, when a positive electric field was applied to the extraction electrode 5a with respect to the emitter 1b, electron emission at a lower voltage was confirmed as compared with a normal silicon-only emitter. .
[0045]
In the first to fourth embodiments described above, the field emission electron source using the tower type silicon as the emitter has been described. However, the present invention is not limited to this. The requirement of the present invention is that a metal film is formed on the surface of the formed emitter or a metal paste is applied, and then a part of the metal film or metal-paste is left or alloyed on the surface of the base emitter. It is to make a part with a low work function locally by forming a segregated material of a material different from the emitter base on the surface of the emitter by subsequent heat treatment, and at the same time, both of them are formed at the initial stage of the emitter surface. The feature is that the shape does not change at all.
[0046]
Therefore, according to the requirements of the present invention, not only a field emission electron source using tower type silicon but also a so-called Spindt type field emission electron source in which protrusions are formed by vapor deposition of a metal film through an opening. It is also possible to apply to.
[0047]
【The invention's effect】
As described above, according to the present invention, a portion having a relatively low work function is locally formed on the emitter surface without impairing the shape of the sharpened emitter surface and without impairing electrical characteristics. Thus, it is possible to provide a field emission electron source capable of a large current density at a low voltage stably and with good reproducibility.
[Brief description of the drawings]
FIGS. 1A to 1E are cross-sectional views illustrating a method for manufacturing a field emission type electron source device according to Embodiment 1. FIGS.
FIG. 2 is an enlarged view of a main part of the field emission type electron source device according to the first embodiment.
FIGS. 3A to 3E are cross-sectional views showing a method for manufacturing a field emission electron source device according to Embodiment 2. FIGS.
FIGS. 4A to 4E are cross-sectional views illustrating a method for manufacturing a field emission electron source device according to Embodiment 3. FIGS.
FIGS. 5A to 5D are cross-sectional views illustrating a method for manufacturing a field emission type electron source device according to Embodiment 4. FIGS.
FIG. 6 is an enlarged view of a main part of a conventional field emission type electron source element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Silicon substrate 1a Columnar silicon 1b Emitter 2 Dot pattern 3 Thermal oxide film 4 Insulating layer 5 Conductive film formation 5a Lead electrode 6a Metal film 6b Metal film 6c Metal film 6d Metal paste 7 Local segregation material

Claims (3)

A plurality of conductive emitters formed on the substrate to have a sharp tip;
An extraction electrode formed to surround each emitter in order to apply a voltage to each emitter so that electrons are emitted from the tip of each emitter;
On the surface of the emitter, segregated substances having a composition different from the composition of the base material constituting the emitter are locally scattered,
2. The field emission electron source according to claim 1, wherein the material constituting the segregated material and the material constituting the emitter are non-totally solid solution type metals. A step of uniformly forming a conductive thin film of a material different from the emitter on the surface of the emitter after forming an emitter composed of a plurality of conductive convex microstructures having a sharp tip on the surface;
Performing a heat treatment at a predetermined temperature to alloy the emitter surface with a portion of the conductive thin film; and
Etching away the conductive thin film;
Including a step of locally performing a heat treatment again at a temperature higher than the temperature in the alloying step to locally form a segregated material having a composition different from that of the base material of the emitter on the emitter surface.
A method of manufacturing a field emission electron source, wherein the conductive thin film made of a material different from the emitter formed on the surface of the formed emitter is made of a non-total solid solution type metal. After forming an emitter made of a plurality of conductive convex microstructures having a sharp tip on the surface, the surface of the emitter is formed by locally interspersing microconductive materials of a material different from the emitter. Process,
A heat treatment is performed at a predetermined temperature to alloy the emitter surface and a part of the minute conductive material, or a part of the minute conductive material is diffused to the emitter surface, so that the base material of the emitter on the emitter surface. A step of locally forming a segregated material having a composition different from that of
And removing the fine conductive material by etching,
A method of manufacturing a field emission electron source, wherein the conductive thin film made of a material different from the emitter formed on the surface of the formed emitter is made of a non-total solid solution type metal.

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