JPH1116483A - Cold cathode and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold cathode and its manufacturing method wherein an emitter is formed with a high density and a field emission current is large. SOLUTION: An auxiliary film 2 composed of silicon dioxide is formed on a substrate 1 composed of silicon. An opening 2a is provided in the auxiliary film 2 and an emitter 3 is formed in this opening 2a. The emitter 3 consist of silicon thin line parts 3a and metallic parts 3b on their ends. A gate electrode 4 is formed around the opening 2a. The emitter 3 is formed such that the auxiliary film 2 is formed on the substrate 1, thereafter that gold is evaporated thereon, and that the silicon thin line parts 3a are caused to grow by heating them to 440 deg.C in a silane gas atmosphere. By lowering heating temperature, formation density of molten alloy drops of gold with silicon can be made larger and their diameters can be made smaller and therefore formation density of the silicon thin line parts 3a can be made larger and their diameters can be made smaller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cold cathode which emits electrons toward an anode when a voltage is applied, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as such a cold cathode, molybdenum (Mo) is vapor-deposited on the surface of a substrate having an opening formed thereon.
It is known that a conical emitter is formed in an opening. In the cold cathode, when a high voltage is applied between the cold cathode and the anode arranged at an interval, electrons are emitted from the tip (the top of the cone) of the emitter toward the anode by a tunnel effect. A gate electrode is formed on the surface of the substrate so as to surround the tip of the emitter, so that the spread of the electron beam emitted from the emitter can be controlled.

[0003]

However, the conventional cold cathode has a problem that it cannot be integrated at a high density and the field emission current is small. For example, for use in a field emission display, an output of about 10 mA / cm ² is required at an electric field of 1 × 10 ⁷ V / m, whereas a conventional cold cathode uses 10 mA / c.
1 × 10 to obtain m ² field emission current
Electric field of ^{8 ~10 9} V / m was required.

On the other hand, VLS (Vapor-Li)
It has been proposed to use various silicon (Si) thin wires grown by the liquid-liquid (Quid-Solid) method (EI Givargizov, J. Vac. Sci. Techno. B11 (2), p. 44).
9). The VLS method is a method in which gold (Au) is deposited on a silicon substrate to form a molten alloy droplet of silicon and gold, and then heated while supplying a raw material gas of silicon to grow a silicon fine wire. In the past, it has been reported that silicon tetrachloride (SiCl ₄ ) is used as a silicon source gas (Wagner et al., Appl. Phys.
Lett. 4, no.5, 89 (1964), Givargizov, J. Cryst. G
rowth, 31, 20 (1975)).

However, in the conventional method using silicon tetrachloride, a thin wire cannot be grown unless the temperature is high, and there has been a problem that materials usable for the substrate are limited. Further, the thin wires cannot be formed densely, so that the integration density cannot be increased.
There was also a problem that it was not possible to grow a material having a thickness of 0 nm or less, and it was difficult to put it to practical use.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a cold cathode in which an emitter is formed at a high density by using a thin wire and a field emission current is large, and a manufacturing method thereof. It is in.

[0007]

A cold cathode according to the present invention emits electrons from an emitter toward an anode arranged at an interval when a voltage is applied, and the emitter has a fine line shape. Things.

According to the method of manufacturing a cold cathode of the present invention, a cold cathode which emits electrons from an emitter toward an anode arranged at a distance is manufactured, and a catalyst for growing the emitter is placed on a substrate. And a growth step of, after depositing a catalyst, heating in an atmosphere containing a raw material gas of a substance constituting the emitter to selectively grow a fine-line emitter on the surface of the substrate.

In the cold cathode of the present invention, when a voltage is applied between the cold cathode and the anode arranged at an interval, electrons are emitted from the thin wire-shaped emitter toward the anode.

In the method of manufacturing a cold cathode according to the present invention, after a catalyst is deposited on a substrate, the cold cathode is heated in an atmosphere containing a source gas of a substance constituting the emitter. At this time, a fine line-shaped emitter is selectively grown on the surface of the substrate by the action of the catalyst.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
1 shows a configuration of a cold cathode according to the embodiment. This cold cathode emits electrons toward an anode (not shown) arranged at an interval when a voltage is applied. For example, an n-type impurity such as phosphorus (P) or arsenic (As) or boron ( B) Conductive substrate 1 made of silicon single crystal doped with p-type impurities such as gallium (Ga)
It has. On the substrate 1, for example, a thickness of 2 nm
An insulating auxiliary film 2 made of 100 nm of silicon dioxide (SiO ₂ ) is formed. The auxiliary film 2 is provided with a plurality of openings 2a having a diameter of, for example, 1 nm to 10 μm in a matrix. In FIG. 1, a plurality of openings 2a are provided.
One of them is shown in an enlarged manner.

In each of the openings 2a, a plurality of thin-line emitters 3 are formed substantially perpendicular to the substrate 1. Each of the emitters 3 emits electrons injected through the substrate 1 toward an anode (not shown), and includes a silicon thin wire portion 3a made of silicon and a metal portion 3b formed at an end thereof and made of an appropriate metal. It is configured. Appropriate n-type impurities or p-type impurities may be added to the crystal of silicon constituting the silicon thin wire portion 3a, but the impurities may not be added.

The metal constituting the metal portion 3b is preferably gold, silver (Ag), indium (In), tin (Sn), or an alloy containing these. In particular, tin, indium (In), or an alloy containing them is preferable because of its small work function and easy emission of electrons. Incidentally, the work function of gold is about 5.3 eV, the work function of n-type silicon is about 4.0 eV, and the work function of tin is about 4.4 eV.
Further, since the metal portion 3b functions as a catalyst when growing the silicon thin wire portion 3a, gold, silver, indium, or an alloy containing these, which has excellent properties as a catalyst, may be used as the metal constituting the metal portion 3b. Is preferred.

The thickness of each emitter 3 is 1000 nm or less,
Preferably it is 100 nm or less. The length of each emitter 3 is shorter than the thickness of the auxiliary film 2 so that the tip of each emitter 3 does not project from the opening 2a. Note that each emitter 3 (specifically, the silicon thin wire portion 3a) may be bent (or curved) as shown in FIG. The density (the number per unit area) in the opening 2a of the emitter 3 is high, for example, 1 × 10 ⁶ to 1 ×.
It is about 10 ¹¹ / cm ² .

A gate electrode 4 made of an appropriate metal such as aluminum or gold is formed on the auxiliary film 2 around the opening 2a (that is, so as to surround the vicinity of the tip of the emitter 3). The spread of the electrons emitted from can be controlled.

The cold cathode having such a structure emits electrons as follows when a voltage is applied between the cold cathode and an anode (not shown) arranged at an interval.

FIG. 2 and FIG. 3 show the structure of the band gap in the cold cathode. FIG. 2 shows a state when no voltage is applied, and FIG. 3 shows a state when a voltage is applied. FIGS. 2 and 3 show a case where the silicon fine wire portion 3a is made of silicon to which no impurity is added.

In this cold cathode, almost no free electrons exist in the silicon thin wire portion 3a, and when no voltage is applied, as shown in FIG. 2, the interface between the substrate 1 and the silicon thin wire portion 3a and the silicon thin wire portion 3a A potential barrier exists at the interface between the thin wire portion 3a and the metal portion 3b. Here, when a voltage is applied in the forward direction (assuming a forward bias state),
As shown in FIG. 3, the silicon thin wire portion 3a is
The potential barrier in the case where electrons flow in b becomes smaller, and the electrons flow more easily. Thereby, the electrons are emitted from the metal part 3b through the substrate 1 and the silicon thin wire part 3a. At this time, the spread of the emitted electrons is controlled by the voltage applied to the gate electrode 4.

Here, the case where the silicon thin wire portion 3a is made of silicon to which no impurity is added has been described. However, when the silicon thin wire portion 3a is made of n-type or p-type silicon, electrons are similarly emitted. I do.

Such a cold cathode can be manufactured as follows.

FIG. 4 shows each manufacturing process of the cold cathode according to the present embodiment. First, as shown in FIG. 4A, for example, an n-type or p-type single-crystal silicon substrate 1 is inserted into a reaction furnace (not shown) and oxidized, and an oxide film is formed on the surface of the substrate 1 as an auxiliary film 2. Form.

Next, a photoresist film (not shown) is applied and formed on the substrate 1 on which the auxiliary film 2 is formed, and the photoresist film is selectively exposed and patterned. Subsequently, using the patterned photoresist film as a mask, the auxiliary film 2 is etched for an appropriate time using an etchant containing hydrofluoric acid (HF). Thereby, as shown in FIG. 4B, a plurality of openings 2a are formed in the auxiliary film 2 in a matrix corresponding to the formation positions of the respective emitters 3 (the above, the auxiliary film forming step).

After each opening 2a is formed in the auxiliary film 2, the photoresist film is removed with, for example, acetone. After that, the substrate 1 is washed and dried, and then inserted into a reaction furnace (not shown).
A metal that serves as a catalyst when growing the emitter 3 (that is, the thin silicon wire portion 3a) is deposited on the surface of the substrate (deposition step). Since the metal deposited here finally constitutes the metal part 3b of the emitter 3, it can act as a catalyst (that is, form a molten alloy droplet with silicon).
In addition, those suitable for forming the metal portion 3b (that is, gold, silver, indium, tin, and the like described above) are preferable. Thereby, as shown in FIG. 4C, the catalyst layers 11 are respectively formed on the auxiliary film 2 and on the substrate 1 exposed by the respective openings 2a of the auxiliary film 2. The thickness of the catalyst layer 11 to be formed is preferably thin, for example, preferably 6 nm or less. This is because the molten alloy droplet 11a formed in the growth step described later (FIG. 4D)
This is because the thickness of the emitter 3 is reduced by reducing the size of the emitter 3).

After forming the catalyst layer 11, the substrate 1 is placed in a reaction furnace (not shown) at 200 to 600 ° C.,
While heating to a temperature of 00 to 350 ° C., the silicon thin wire portion 3
a constituting silicon (for example, silane (Si
H ₄ ) gas) (growth step). As a result, as shown in FIG. 4D, the catalyst layer 11 on the substrate 1 exposed by each opening 2a of the auxiliary film 2 is
Part of the silicon on the surface of the substrate is dissolved and aggregated to form one opening 2
a, a plurality of molten alloy droplets 11a are respectively formed.
On the other hand, since silicon dioxide constituting the auxiliary film 2 is stable on the auxiliary film 11, no molten alloy droplet 11a is formed.

At this time, the substrate 1 is not heated to
The reason for setting the temperature to not more than 0 ° C. is that if the temperature is increased,
Since the agglomeration of a proceeds rapidly, the density of the molten alloy droplet 11a (that is, the density of the emitter 3) decreases, and the diameter of the molten alloy droplet 11a increases (that is, the thickness of the emitter 3 increases). Because.

The molten alloy droplet 11a formed here serves as a catalyst in the decomposition reaction of the silicon raw material gas, and the silicon raw material gas is selectively decomposed in these molten alloy droplets 11a to produce silicon. For example, silane gas is decomposed by the decomposition reaction shown in Formula 1 to produce silicon.

[0028]

[Formula 1] SiH ₄ → Si + 2H ₂ (1)

The silicon generated by the decomposition is diffused into each molten alloy droplet 11a, and is epitaxially bonded to the interface between each molten alloy droplet 11a and the substrate 1. Here, when the diameter of the molten alloy droplet 11a reaches or exceeds the critical value due to the Gibbs-Thomson effect due to agglomeration, as shown in FIG. A thin line having a thickness corresponding to the diameter of 11a grows to form a silicon thin line portion 3a. The supply of the silicon source gas is stopped when the silicon thin wire portion 3a has grown to the vicinity of the upper portion of the opening 2a, and the growth process is completed. Incidentally, the silicon source gas is also decomposed by the catalytic action in the catalyst layer 11 on the auxiliary film 2, but the molten alloy with silicon has good wettability to the surface of silicon dioxide (that is, the surface of the auxiliary film 2). As it has, it is hard to aggregate,
Epitaxial growth of silicon is unlikely to occur.

The silicon source gas used here is:
Gibbs free energy of decomposition reaction
) A change (ΔG) having a small value is preferable. This is because a small value of the Gibbs free energy change of the decomposition reaction has a relatively high chemical potential,
This is because a fine wire (silicon fine wire portion 3a) having a high chemical potential and a small diameter can be grown. In particular, it is preferable that the value of the Gibbs free energy change of the decomposition reaction can be negative even at a low temperature of 600 ° C. or less at which the molten alloy droplet 11a does not rapidly agglomerate. That is, in addition to the silane gas exemplified above, a silane (Si ₂ H ₆ ) gas, a trisilane (Si ₃ H ₈ ) gas, or a mixed gas thereof is preferable. On the other hand, the conventionally used silicon chloride gas has a positive value in the Gibbs free energy change of the decomposition reaction even at a high temperature of about 1000 ° C., and is not preferable unless the temperature is high.

The amount of the silicon source gas to be supplied is
For example, if the partial pressure of the silicon source gas in the reactor is 0.
Adjust so as to be 5 Torr or more. This is because the higher the partial pressure, the more the fine wire with a smaller diameter can be grown.

In the case where the silicon thin wire portion 3a is made of silicon to which impurities are added, an impurity source gas is supplied into the reaction furnace together with the silicon source gas. For example, when phosphorus is added as an n-type impurity, a phosphine (PH ₃ ) gas is introduced, and when boron is added as a p-type impurity, a diborane (B ₂ H ₆ ) gas is introduced.

When the silicon thin wire portion 3a is formed and cooled as described above, the molten alloy droplet 11a precipitates and solidifies the dissolved silicon to form the metal portion 3b. after that,
A gate electrode 4 is formed by depositing a suitable metal on the auxiliary film 2 from obliquely above. Thereby, the cold cathode according to the present embodiment is formed.

The fact that a high field emission current can be obtained with the cold cathode according to the present embodiment will be described based on specific examples.

First, in the same manner as described above, n-type silicon single crystal substrate 1 (111 plane, specific resistance ρ = 0.01 Ωcm)
And an auxiliary film 2 made of an oxide film was formed. In the auxiliary film 2, a plurality of openings 2a having a diameter of 0.5 to 2.0 μm were formed. Then, in the same manner as described above,
After forming the catalyst layer 11 by vapor deposition with a thickness of
10mTorr to 1.0T while heating to ℃
orr is supplied for 140 seconds with a partial pressure of
Grew. Subsequently, the gate electrode 4 was formed in the same manner as described above to obtain a cold cathode.

The thickness of the silicon thin wire portion 3a in the cold cathode thus obtained is very thin, about 10 to 100 nm, and the density in the opening 2a is 10 ⁸ to 10 ¹¹ / cm.
^{It was 2} and very big.

An anode was arranged at an appropriate interval from the cold cathode, and a voltage was applied between the anode and the anode to measure a field emission current. Measurement area (range) at that time
Was about 3 mm ² . The result is shown in FIG. From this result, it can be estimated that an output of 10 mA / cm ² can be obtained with the cold cathode by an electric field of 6 to 7 × 10 ⁷ V / m. In the field emission display, 1
An output of about 10 mA / cm ² is required by an electric field of × 10 ⁷ V / m. That is, according to this cold cathode,
It is possible to obtain a field emission current large enough to be practically used.

Before and after the field emission current was measured, the emitter 3 was scanned with a scanning electron microscope (SE).
M; Scanning Electron Microscope).
As a result, no damage to the emitter 3 was observed by the measurement of the field emission current.

As described above, according to the cold cathode according to the present embodiment, since the thin-film emitter composed of the silicon thin-wire portion 3a and the metal portion 3b is provided, the emitter can be formed at a high density. And a large field emission current can be obtained.

Further, according to the method of manufacturing a cold cathode according to the present embodiment, since the silicon source gas is supplied while heating after the catalyst is deposited on the substrate 1, it is easy to form a thin wire. An emitter 3 can be formed.

Further, as the silicon source gas, a gas whose Gibbs free energy change in the decomposition reaction can be negative even at a low temperature of 600 ° C. or less is used, and the silicon fine wire portion 3a is grown at a low temperature of 300 to 600 ° C. or less. Therefore, the silicon thin line portions 3a having a sufficiently small thickness can be formed at a high density.

In addition, since the catalyst is deposited via the auxiliary film 2 having the opening 2a on the substrate 1, the formation position of the emitter 3 can be controlled, and the cold cathode according to the design can be formed. It can be easily manufactured.

(Second Embodiment) FIG. 6 shows a second embodiment of the present invention.
1 shows a configuration of a cold cathode according to the embodiment. This cold cathode is the same as the cold cathode of the first embodiment except that the substrate 1 is made of an appropriate material (for example, glass) and the emitter 3 is formed on the substrate 1 via the seed crystal layer 25. It has the same configuration. Therefore, here, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

The seed crystal layer 25 serves as a conductive layer for injecting electrons into the emitter 3 and serves as a seed crystal when the emitter 3 (that is, the silicon thin line portion 3a) is grown by the VLS method. is there. This seed crystal layer 25 is made of, for example, silicon single crystal or silicon polycrystal doped with an appropriate n-type impurity or p-type impurity.

In the cold cathode having such a configuration, after the seed crystal layer 25 is deposited on an appropriate substrate 1, the auxiliary film 2 made of silicon dioxide is formed by, for example, a plasma CVD (Chemical Vapor Deposition) method. Except for the first
It can be manufactured in the same manner as in the embodiment.

As described above, according to the cold cathode according to the present embodiment, the seed crystal layer 25 is provided between the substrate 1 and the emitter 3, so that the material constituting the substrate 1 can be arbitrarily selected. Can be. Therefore, it can be applied to various uses.

Further, according to the method for manufacturing a cold cathode according to the present embodiment, the temperature in the growth step is set to 300 to 600 ° C.
As described below, the substrate 1 can be made of a heat-sensitive material (eg, glass). Therefore, the cold cathode of the present embodiment can be realized.

As described above, the present invention has been described with reference to the first and second embodiments. However, the present invention is not limited to each of the above embodiments, and can be variously modified. For example,
In each of the above embodiments, the emitter 3 is provided with the silicon thin wire portion 3a, but may be provided with a thin wire portion made of a material other than silicon. In that case, the cold cathode of the present invention can be easily realized if it can be formed by the VLS method.

In each of the above embodiments, the auxiliary film 2 is formed of silicon dioxide. However, the auxiliary film 2 may be formed of, for example, silicon nitride (Si ₃ N ₄ ) or a suitable resin, which has an insulating property and is formed by evaporation. It may be formed of another substance as long as it does not react with the catalyst deposited in the process.

[0050]

As described above, according to the cold cathode of the present invention, since the thin-line emitter is provided, the emitter can be formed with a high density and a large field emission current can be obtained. This has the effect.

Further, according to the cold cathode manufacturing method of the present invention, the catalyst is deposited on the substrate and then heated in the raw material gas atmosphere, so that a fine wire emitter can be easily formed. it can. Therefore, there is an effect that the cold cathode of the present invention can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a cold cathode according to a first embodiment of the present invention.

FIG. 2 is a band configuration diagram for explaining the operation of the cold cathode shown in FIG.

FIG. 3 is a band configuration diagram for explaining the operation of the cold cathode shown in FIG. 1;

FIG. 4 is a cross-sectional view for explaining a manufacturing process of the cold cathode shown in FIG.

FIG. 5 is a characteristic diagram showing a relationship between an applied voltage and a field emission current in the cold cathode shown in FIG.

FIG. 6 is a cross-sectional view illustrating a configuration of a cold cathode according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Auxiliary film, 2a ... Opening, 3 ... Emitter, 3
a: silicon fine wire portion, 3b: metal portion, 4: gate electrode,
11: catalyst layer, 11a: molten alloy droplet, 25: seed crystal layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Setsuo Usui 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Satoshi Nakata 6-35-35 Kita Shinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (10)

[Claims] 1. A cold cathode which emits electrons from an emitter toward anodes spaced apart by application of a voltage, wherein the emitter has a thin line shape. 2. The cold cathode according to claim 1, wherein the emitter includes a silicon thin wire portion made of silicon. 3. The cold cathode according to claim 2, wherein the silicon thin wire portion is made of silicon to which an impurity is added. 4. The cold cathode according to claim 2, wherein the emitter has a metal portion made of a metal at a tip. 5. The cold cathode according to claim 4, wherein said metal portion contains at least one metal selected from the group consisting of gold, silver, indium and tin. 6. A semiconductor device comprising: a substrate on which the emitter is formed; and a seed crystal layer formed between the substrate and the emitter and serving as a seed crystal when forming the emitter. The cold cathode according to claim 1, wherein 7. A method for producing a cold cathode that emits electrons from an emitter toward an anode that is spaced apart, comprising: a deposition step of depositing a catalyst for growing an emitter on a substrate; And then heating in an atmosphere containing a source gas of a substance constituting the emitter to selectively grow a fine-line emitter on the surface of the substrate. 8. In the growth step, the substrate is heated in an atmosphere containing a silicon source gas in which silicon is generated by a decomposition reaction and the Gibbs free energy in the decomposition reaction at 1000 ° C. or less is a negative value, and the silicon 8. The method according to claim 7, wherein an emitter having a thin line portion is formed. 9. The method according to claim 8, wherein in the growing step, heating is performed at a temperature of 700 ° C. or less. 10. The method according to claim 7, further comprising an auxiliary film forming step of forming an auxiliary film having an opening corresponding to a position where an emitter is formed on the substrate, prior to the vapor deposition step. Manufacturing method of cathode.