JPH07130282A - Electron emission element and electronic equipment using it - Google Patents

Abstract

PURPOSE:To improve the density of emitted currents and enable the low-voltage operation by using a metal where the occupied electron state density in the vicinity of the Fermi level, as the electrode below an MIN type electron emission element. CONSTITUTION:A lower electrode 13 is vapor-deposited on a substrate 14, and thereon an insulating film 12 and an upper electrode 11 are formed in order to constitute an electron emission element. For this lower electrode 13, a matter is used, in which occupied electron state density in the range of coupling energy from right below Fermi level to 2eV such as the group 8 transition metal or the like is partially high. Hereby, the number of electrons contributing to tunnel phenomena increases, and the density of emitted currents improves.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron emitting device for emitting an electron beam in a plane and an electron beam application device using the same.

[0002]

2. Description of the Related Art One of electron-emitting devices which is expected to be able to extract a planar electron beam having a good monochromaticity is one which utilizes a tunnel phenomenon of a multilayer film in which a thin insulating film is sandwiched between electrodes. A typical example is metal-insulator-
A metal structure (MIM structure) is mentioned.

FIG. 2 shows a principle diagram when the MIM structure is operated as an electron-emitting device. When a voltage 17 (several V to 10 V) is applied between the upper electrode 11 and the lower electrode 13, an electric field in the insulating film 12 causes electrons near the Fermi level in the lower electrode 13 to pass through the barrier due to the tunnel phenomenon. , Appearing in the conduction band of the insulating film 12 and the upper electrode 11. Among these electrons, the electrons having energy equal to or higher than the work function φ of the upper electrode 11 are emitted into the vacuum 10.
Up to the present, electron emission based on this principle has been observed in Au-Al ₂ O ₃ -Al structures and the like (applied physics, Vol 3
2, No. 8, (1963) p568).

The electron emission device having the MIM structure has various advantages. First, since the device has a thin film-like simple structure, it is easy to increase the area, and it is easy to produce a planar electron-emitting device. In addition, since the upper electrode 11 is flat and has a large area, a vacuum 1 is used as compared with a field emission cathode array having a needle-shaped electron emission end.
The interface state with 0 is stable, is not easily affected by environmental gas, and can operate in a wide vacuum range. 1 more
It is a great advantage that electrons can be emitted by applying a low voltage of about 0 V and a high-voltage power source or the like is not required.

On the other hand, since the conventional electron beam drawing apparatus uses the point electron source, the exposure area is small, it takes time to draw the entire surface of the wafer, and the throughput is small. In order to improve the throughput, it is necessary to enable large-area batch exposure using an electron beam emitted from a planar electron source having a high emission current density and good monochromaticity.

As electronic devices, semiconductor devices have become the mainstream, replacing vacuum tube devices used in the past. This is because the semiconductor device is superior to the conventional vacuum tube device in terms of reliability and ease of integration. However, the saturation speed of electrons, which determines the operation speed of the device, is approximately 3 × 10 ⁵ m / s in a semiconductor, which is almost the speed of light in a vacuum, and thus the device may be accelerated. To achieve this, integration is possible,
It is necessary to realize a thin film electron source.

[0007]

When electrons are emitted according to the principle of FIG. 2, it is theoretically expected that an electron beam having a high emission current density and an energy width sufficiently narrower than that of a hot cathode can be obtained. . However, in the conventional electron-emitting device having the MIM structure, the ratio of the electron current emitted in the vacuum 10 (emission ratio) is lower than the diode current flowing into the upper electrode 11.
(1/10 ⁴ to 1/10 ⁶ ), the emission current density is small. Furthermore, it has been reported that the energy width of the emitted electrons is greatly expanded. In the conventional MIM structure electron-emitting device, when the tunneled electrons travel in the conduction band of the insulating film 12 and the upper electrode 11, the scattering of the electrons is large, and most of the electrons lose their energy and lose their energy. It is considered that electrons fall into various energy levels due to the fact that the radiation ratio falls to an energy level equal to or lower than the work function φ and the same scattering effect causes the energy width to widen.

It is an object of the present invention to supply a planar thin film electron source with improved emission current density and low energy dispersion, and an electron beam drawing apparatus and a micro vacuum tube device using the same for high throughput. It is to realize electronic application equipment.

[0009]

The above object can be achieved by each of the following.

1) As a lower electrode in the MIM structure,
The occupied electron state is localized near the Fermi level due to electron correlation, and the occupied electron state density is locally increased to improve the tunnel current density.

2) In the MIM structure, as the lower electrode having a high occupied electronic state density near the Fermi level, a substance whose electronic state density is mainly formed by d band and f band is used.

3) In the MIM structure, a Group 8 transition metal having a very high occupied electronic state density mainly due to the d band is used as a lower electrode metal immediately below the Fermi level.

4) Pd, Pt, N as the Group 8 transition metal
i, Co, Fe are used.

5) An alloy composed of a plurality of Group 8 transition metals is used as the lower electrode metal.

6) The driving voltage of the electron-emitting device having the MIM structure is set to the electron-emitting threshold voltage of the upper electrode metal +0.5 V or less.

[0016]

In the MIM structure electron-emitting device, as shown in FIG. 2, a higher electric field is applied to the insulating film 12 than the upper electrode 11 and the lower electrode 13 to emit electrons tunneled through the effectively thinned barrier. . In this case, the tunnel current density j is T (E), the Fermi distribution function is f (E), the electron state density is D (E), the tunnel barrier is the tunneling barrier, and the transmission probability is T (E) for electrons of the energy E in the occupied electronic state of the lower electrode 13. When the velocity of the electrons incident on is denoted by v and the elementary charge is denoted by e, it is expressed by Equation 1.

[0017]

[Equation 1]

Here, ∫dk means integration in the momentum space.

Since the transmission probability T (E) is sensitively affected by the thickness and height of the barrier, in practice, most of the tunneling electrons are electrons near the Fermi level. Therefore, in order to increase the emission current density, as the lower electrode 13, the occupied electronic state density D (E) near the Fermi level (directly below the Fermi level to the binding energy of 2 eV) in the region where the transmission probability T (E) is particularly high. ) May be used.

Since the total number of occupied electronic states making up the valence band does not differ greatly depending on the element, in order to increase the occupied electronic state density near the Fermi level, the electronic state density near the Fermi level caused by electron correlation can be increased. Take advantage of localization at. As an example for realizing this, a substance whose occupied electronic states in the upper part of the valence band mainly originate in the d band and the f band may be used. These are based on the following grounds.

Generally, d-electrons and f-electrons have large repulsive force due to electron correlation (Coulomb interaction between electrons) and have small band dispersion, so that they are localized in terms of energy. That is, since the number of bands per unit energy increases, the electronic density of states becomes extremely high locally near a certain energy. On the other hand, Al, which has been used in the conventional MIM electron source from the viewpoint of easiness of oxide film formation, has s-band and p-band in the vicinity of the Fermi level, which is due to Coulomb interaction between electrons. Since the repulsive force is small, the band dispersion is large and the energy spreads, and the electronic density of states per unit energy is locally low. It is clear from the study of the electronic structure by photoelectron spectroscopy that the ratio becomes several tens to 100 times.

FIG. 3 shows a schematic diagram of photoelectron spectra of Ni (18) having an electronic state caused by the d band and Al (19) which has been conventionally used (for details, see the topics.
In Applied Physics Vol. 27 (1979
Year) p204 and p369: Topics in Applied Phy
sics Vol. 27 (1979) p204 and p369). Ni (18) has a localized high electron density in the range of 2 eV from just below the Fermi level, while Al (1
It is clear that 9) has a broad electron density of states in the range of 8 eV. Therefore, if the lower electrode 13 of the electron-emitting device having the MIM structure is formed so that the d-band and the f-band form occupied electronic states in the vicinity of the Fermi level, the emission current density of the electron-emitting device can be significantly increased (tens to 100 times). Can be achieved.

Specifically, the Group 8 transition metal is effective because it has a very large occupied electronic state mainly due to the d band just below the Fermi level. Among Group 8 transition metals, Pd, Pt,
Since Ni, Co, and Fe have relatively low melting points, they can be easily formed into a film by a vapor deposition method or the like and are suitable for device fabrication. Also, the lower electrode 1
3 includes CoPt, which is an alloy of Group 8 transition metals,
NiS which is a compound containing FeNi or the like and a Group 8 transition metal
i ₂ or the like can also be used.

In the MIM type electron-emitting device which achieves a high emission current density by such a method, it is not necessary to apply an excessive voltage to obtain a target emission current density.
Therefore, if the driving voltage applied to both electrodes is limited to the electron emission threshold voltage of the upper electrode +0.5 V or less, the electrons tunneled from the energy level lower than the Fermi level by 0.5 eV or more and the insulating film 12 Or the upper electrode 11
Since the electrons scattered inside and losing energy can be cut, the energy width of the emitted electrons can be suppressed to 0.5 eV or less. That is, an electron beam having good monochromaticity can be obtained. Further, since the operation is performed at a low voltage, it is possible to prevent the insulating film 12 from being broken, and it is possible to extend the life of the electron-emitting device.

Since the exposure time in the electron beam drawing apparatus is shortened in inverse proportion to the emission current density, if a planar electron source having a high emission current density as described above is used, large-area batch exposure in a short time is performed. It is possible to significantly improve the throughput. Further, when a signal amplifying element using a micro vacuum tube is created, the emission current density is improved and the mutual conductance is improved, so that noise reduction, high gain and high speed of the element are realized.

[0026]

EXAMPLE An example using the present invention will be described with reference to FIG. Pd of 10 nm is vapor-deposited as the lower electrode 13 on the substrate 14 whose surface is cleaned. Pt, N as the lower electrode 13
When using i, Co, Fe, etc., a desired metal or alloy is vapor-deposited. As the substrate 14, for example, a silicon substrate having a silicon oxide film formed on its surface by thermal oxidation may be used. Then, Al is vapor-deposited to a thickness of 4 nm in the same vacuum.
Only the Al on the upper surface of the two-layer film is oxidized by the anodic oxidation method. Anodization is performed with a 3% ammonium tartrate aqueous solution at a formation voltage of 4V. Since the film thickness of Al that can be oxidized by anodic oxidation depends on the formation voltage with high accuracy, only 4 nm of Al can be selectively oxidized at the formation voltage of 4V. In this way, Al ₂ is formed on the lower electrode 13 composed of Pd.
The insulating film 12 composed of O ₃ can be formed. Needless to say, when the film thickness of Al is set to a value other than 4 nm, the formation voltage is set to a voltage corresponding thereto. Next, the insulating film 12
The upper electrode 11 is formed on top. As the upper electrode 11,
For example, Au may be formed to a thickness of 10 nm by vapor deposition in an ultrahigh vacuum.

In the present embodiment, it is also effective to use the vapor phase oxidation method instead of the anodic oxidation method for the Al oxidation process. A two-layer film of Al and Pd was placed in a vacuum chamber and 0.001 ~
By introducing oxygen of about 10 Torr and heating the substrate, Al is oxidized and the insulating film 12 made of Al ₂ O ₃ can be formed. Silicon oxide SiO as the insulating film 12
_{When 2} is used, this gas phase oxidation method is more effective. Further, in the present embodiment, the upper electrode 11 may be made of a semiconductor which is doped with impurities at a high concentration to have a low resistance. For example, Si doped with phosphorus P is effective.

Another embodiment using the present invention is shown in FIG.
The lower electrode 13 and the insulating film 12 are formed in the same manner as in the previous embodiment. Next, an insulator such as SiO ₂ or Al ₂ O ₃ is vapor-deposited with a film thickness of about 50 nm by a chemical vapor deposition method (CVD method) or the like to form the protective layer 15. On top of this, the upper electrode 1
1 is formed in the same manner as in the previous embodiment. Furthermore, Au
Electrode terminal 1 by depositing a low resistance material such as 100 nm
6 is formed. In the MIM electron-emitting device thus formed, the peripheral portions of the upper electrode 11 and the lower electrode 13 are covered with the thick protective layer 15, so that the electric field concentration on the peripheral portions of the electrodes is prevented. Therefore, stable electron emission and long life of the electron-emitting device can be realized. Further, since the electrode terminal 16 has a larger film thickness than the upper electrode 11, it has a low resistance and prevents a voltage drop due to an operating current flowing from the upper electrode 11 to the lower electrode 13 when operating the MIM electron-emitting device.

Further, in these embodiments, the lower electrode 1
When Al formed on 3 is used as an epitaxial film, the insulating film 12 obtained by oxidizing it can have good crystallinity. By doing so, the probability of scattering of electrons tunneling from the lower electrode 13 to the upper electrode 11 in the insulating film 12 decreases, so that the tunnel current increases and the amount of current emitted into the vacuum also increases. Also, the kinetic energy distribution of the emitted electrons becomes smaller, and a high-quality electron beam with small energy dispersion can be obtained. Further, when the lower electrode 13 is an epitaxial growth film or a single crystal film, Al formed on the lower electrode 13 is likely to become an epitaxial film or an orientation film, so that it is also effective to form the lower electrode 13 as an epitaxial film.

FIG. 5 shows another embodiment according to the present invention. A single crystal substrate such as Pd or Pt is used as the lower electrode 13
And an insulating film 12, a protective layer 15, and an upper electrode 1 on top of it.
1, the electrode terminal 16 is formed. The method of forming these is similar to that of the previous embodiment. As described above, by using the single crystal for the lower electrode 13, the crystallinity of the insulating film 12 and the upper electrode 11 is improved, so that the amount of current of emitted electrons is increased and the beam characteristics are also improved. On the street.

FIG. 6 shows an example in which the MIM planar electron-emitting device of the present invention is mounted on an electron beam drawing apparatus. The planar electron beam generated from the MIM electron-emitting device 21 is a mask 22 made of Si.
Is shaped into an integrated circuit pattern. After passing through the blanker 23, this electron beam is reduced by the electron lens 24, passes through the deflector 25, and is transferred onto the wafer 26. The wafer 26 is placed on the movable stage 27 to move the exposure range. When the planar electron source of the present invention is used, the emission current density is high and the exposure time for one exposure is short, and since large-area batch exposure is possible, the number of stage movements is reduced, and throughput can be greatly improved. Becomes

FIG. 7 shows an example of another electron beam drawing apparatus. The MIM electron-emitting device of the present invention is formed into a large number of small grids. The MIM electron-emitting device matrixes 28 operate independently and are controlled by the circuit pattern generators 29, respectively, and are shaped into integrated circuit patterns as a whole. After that, it is transferred onto the wafer 26 by the same system as described above. The effect of improving the throughput using the planar electron source of the present invention is as described above. In the case of this device, since the circuit pattern can be electrically shaped arbitrarily, it is more flexible than the case of using a mask, and the throughput can be further improved.

FIG. 8 shows an example in which the MIM planar electron-emitting device of the present invention is applied as a micro vacuum tube. 100n on the surface
Highly-concentrated P-doped Si substrate 3 having m thermal oxide film 30 formed thereon
1) A 1 × 1 mm ² MIM formation region is patterned by a photolithography process, and the oxide film is etched by 100 nm. Using a metal mask there, Pd is vapor-deposited 8
The lower electrode 13 is formed to a thickness of 5 nm. Al is similarly formed thereon to a thickness of 5 nm. All of this is oxidized by thermal oxidation to form the insulating film 12. Next, Au for 10n
Then, the upper electrode 11 is formed by vapor deposition to complete the MIM structure.

Next, an insulating thick film 32 of SiO ₂ is deposited to a thickness of 1000 nm on both sides of the electron emission surface by the RF sputtering method, and an anode plate 33 for taking out an emission current is bonded thereon. This completes the micro vacuum tube. The applied voltage 17 is applied between the high-concentration P-doped Si substrate 31 and the upper electrode 11. 50 V is applied as an electron pull-in voltage 34 between the upper electrode 11 and the anode plate 33. When the applied voltage 17 is increased from 0V, the emission current sharply increases at a certain threshold value or more. This is the lower electrode 1
3, the upper electrode 11, the anode plate 33 as the source,
Considering the gate and drain, the characteristics are the same as those of the enhancement type field effect transistor. MI of the present invention
When the M electron source is used, the emission current, that is, the drain current is high, and the transconductance of the element is increased, so that the device has low noise, high gain, and high speed.

[0035]

According to the present invention, the emission current density can be significantly improved by using a metal having a large occupied electronic state density near the Fermi level as the lower electrode metal of the MIM type electron-emitting device. Furthermore, the effect enables low-voltage operation, so that the electron beam can be monochromatic and dielectric breakdown can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view of an electron-emitting device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an operating principle of an MIM type electron-emitting device.

FIG. 3 is a photoelectron spectrum diagram of Ni and Al.

FIG. 4 is a sectional view of an electron-emitting device according to an embodiment of the present invention.

FIG. 5 is a sectional view of an electron-emitting device according to an embodiment of the present invention.

FIG. 6 is a configuration diagram of an embodiment of an electron beam drawing apparatus using the electron-emitting device of the present invention.

FIG. 7 is a configuration diagram of an embodiment of an electron beam drawing apparatus using the electron-emitting device of the present invention.

FIG. 8 is a cross-sectional view of an embodiment of a signal amplifying device of a micro vacuum tube using the electron emitting device of the present invention.

[Explanation of symbols]

11 ... Upper electrode, 12 ... Insulating film, 13 ... Lower electrode, 14
... substrate, 15 ... protective layer, 16 ... electrode terminal.

Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location H01L 21/027 49/00 (72) Inventor Toshiyuki Aida 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central (72) Inventor Tomio Yaguchi, 1-280, Higashi Koikeku, Kokubunji, Tokyo, Central Research Laboratory, Hitachi, Ltd. (72) Inventor, Tadashi Seisei, 1-280, Higashi Koikeku, Kokubunji, Tokyo, Hitachi, Central Research Center ( 72) Inventor Emiko Yamada 1-280, Higashi Koigokubo, Kokubunji City, Tokyo Metropolitan Research Center, Hitachi, Ltd.

Claims (12)

[Claims] 1. An electron-emitting device having a structure in which an insulating film is sandwiched between an upper electrode and a lower electrode made of a metal or a semiconductor, the lower electrode being used as a lower electrode in an occupied electronic state of the entire valence band, An electron-emitting device characterized by using a substance having a locally high occupied state density of electrons in the vicinity of the Fermi level (range of binding energy of 2 eV from immediately below the Fermi level). 2. The electron-emitting device according to claim 1, wherein a substance having a localized high occupied electronic state density due to electron correlation is used as a lower electrode in the vicinity of the Fermi level. . 3. The electron-emitting device according to claim 1, wherein the occupied electronic states in the vicinity of the Fermi level of the lower electrode are mainly formed locally by the d band and f band having a high occupied electronic state density. An electron-emitting device characterized by using one. 4. The electron-emitting device according to claim 1, wherein
An electron-emitting device characterized by using, as a lower electrode, a Group 8 transition metal of the periodic table having a high occupied electronic state density mainly due to the d band just below the Fermi level. 5. The group 8 transition metal according to claim 3 is Pd,
An electron-emitting device characterized by using Pt, Ni, Co, Fe. 6. The electron-emitting device according to claim 1, wherein
An electron-emitting device characterized in that an alloy composed of a plurality of Group 8 transition metal elements or a compound containing a Group 8 transition metal element is used as the lower electrode. 7. The electron-emitting device according to claim 1, wherein
An electron-emitting device characterized in that a single crystal, a single crystal film, or an alignment film of a metal or alloy of a Group 8 transition element or a compound containing a Group 8 transition element is used as the lower electrode. 8. The electron-emitting device according to claim 1, wherein
An electron-emitting device characterized in that another metal is formed on a metal forming a lower electrode and is oxidized to form an insulating film. 9. The electron-emitting device according to claim 1, wherein
An electron-emitting device characterized in that a driving voltage applied to the upper electrode and the lower electrode is suppressed within a range of an electron-emission threshold voltage of the upper electrode metal +0.5 V or less for emission. 10. An electron-emitting device according to any one of claims 1 to 9, a mask portion for transmitting and patterning an electron beam only at a desired position, and an electron optics for projecting the patterned electron beam onto a surface to be exposed. An electron beam drawing device composed of a system. 11. An electron emission device according to claim 1, wherein the electron emission devices are arranged in a matrix and each of them can operate independently, and a pattern signal is generated from pattern data to generate the electron emission. An electron beam drawing apparatus comprising a pattern generator for outputting to an electron source and an electron optical system for projecting an electron beam of a desired pattern emitted from the electron emitting source onto a surface to be exposed. 12. A signal amplifying device comprising the electron-emitting device according to claim 1 and a third electrode for collecting electrons emitted from the electron-emitting device.