JPH0574333A - Quantized electron beam generator - Google Patents

Abstract

PURPOSE:To take out electrons small in energy width and are great in density by containing the potential barrier layer of a specified semiconductor, the potential well layer of a semiconductor or metal, and the potential barrier on vacuum level. CONSTITUTION:An n-type InPGgAs layer 2, which includes silicon, an AlAsSb layer 3, and an InGaAs layer 4 are epitaxially grown on an n-type InP substrate 1. A gallium converging ion beam is injected, around the region rectangular in plane, from a layer 4 into the upper layer part of a layer 2 so as to form an insulating isolation 5. The layer 3 in the region surrounded by the isolation 5 becomes a potential barrier layer 6, and the upper layer 4 becomes a potential well layer 7. If the vacuum level of the layer 7 is inclined by applying voltage between the upper and lower electrodes 8 and 10, the electrons of the energy equal to the resonance level, which have tunneled the layers 6 and 7, permeate the vacuum barrier, and are taken out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantized electron beam generator.

[0002]

2. Description of the Related Art An electron beam (electron beam) of a measuring instrument such as a reflection electron microscope (SEM) using an electron beam in a vacuum.
) Sources include thermionic beam sources and field emission (Feeled Emi
ssion) radiation source and the like, and in particular in the case of field emission, the energy width of the electron beam can be narrowed down to a range of about 0.1 to 0.5 eV, so that it is used for relatively high resolution measurement.

In this field emission type electron beam source, as shown in FIG. 5 (a), a metal film is placed in a vacuum electric field.
The energy level of the vacuum around 1 is tilted.
The energy structure is as shown in (b).

According to this, the probability that the electrons in the metal film 51 tunnel through the inclined and thinned vacuum barrier becomes high, and the energy widths 0.1 to 0.1 as shown in FIG. 5 (c). 5
It becomes possible to take out eV electrons.

[0005]

However, the energy width is as wide as 0.1 to 0.5 eV, and electrons with uniform energy are required in actual use, and so-called blurring occurs in the energy width. It will be in the state of being.

For this reason, the tunneled electrons are spectrally analyzed to take out energetic electrons in an extremely narrow range δE. However, since the energy density in this range is small, it should be applied to a higher resolution electron microscope. There is a problem that you can not do it.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an electron beam generator capable of extracting electrons having a narrow energy width and a large energy density.

[0008]

[Means for Solving the Problems]
4, the quantized electron beam is characterized by having semiconductor potential barrier layers 6 and 26 for causing a resonance tunnel phenomenon, semiconductor or metal potential well layers 7 and 27, and a vacuum level potential barrier. Achieved by generator.

Alternatively, as illustrated in FIG. 3, the quantized electron beam generator is characterized in that an auxiliary barrier layer 12 is provided on the surface of the potential well layer 7. Alternatively, the semiconductor potential barrier layers 6, 2
6. The potential well layers 7 and 27 are formed to have a size capable of quantizing a wave vector in the lateral direction, which is achieved by the quantized electron beam generator.

Alternatively, the quantized electron beam generator is characterized in that Si, AlAs, AlSb, and AlAsSb are used as the potential barrier layers 6 and 26 of the semiconductor. Alternatively, as the potential well layers 7 and 27, Co
This is achieved by the above-mentioned quantized electron beam generator characterized by using Si ₂ , NiSi ₂ , AlNi, GaAs, InAs, InGaAs.

[0011]

[Operation] According to the present invention, as shown in FIG. 2 (a), one of the potential barriers causing the resonant tunneling phenomenon is formed by the vacuum level. In this case, the potential barrier is tilted by an electric field to be tunneled, but the tunneling probability is high, and since the electron extraction energy width is narrowed down to about 1 meV, the field intensity is the same as that of a normal field radiation source. Two orders of magnitude higher energy density is obtained.

Further, according to the present invention, the auxiliary barrier layer 12 is provided on the surface of the potential well layer 7. For this reason,
The trapping of electrons due to the surface states of the potential well layer 7 disappears, and the current density increases.

Further, according to the present invention, the wave vector of the electrons in the x and y directions along the surface of the potential well layer 7 is quantized. For this reason, a radiation source with extremely strong directivity can be obtained.

The materials mentioned above can be used for the potential barrier layer and the potential well layer of the semiconductor.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (A) Description of First Embodiment of the Present Invention FIG. 1 is a sectional view and a plan view of an apparatus showing an embodiment of the present invention.

In the figure, on the n ⁺ type InP substrate 1,
An n ⁺ type InGaAs layer 2, an AlAs _0.56 Sb _0.44 layer 3 and an In _0.53 Ga _0.47 As layer 4 each containing silicon at a concentration of 1 × 10 ¹⁹ / cm ³ were epitaxially grown to a thickness of 1 μm, 17.6 Å and 29.3 Å, respectively. There is.

Further, from the In _0.53 Ga _0.47 As layer 4 to the n ⁺ type InGa
In the upper layer portion of the As layer 2, a gallium-focused ion beam is injected and inactivated around a planar rectangular region having one side of 1000 Å, and an insulating isolation 5 is formed.

The AlAs _0.56 Sb _0.44 layer 3 in the rectangular region surrounded by the isolation 5 becomes the potential barrier layer 6, and the In _0.53 Ga _0.47 As layer 4 _thereabove becomes the potential well layer 7.

Reference numeral 8 represents the potential well layer 7 exposed from the hole 9.
In the donut-shaped electrode to be emitted, In _0.53Ga_0.47As layer 4
They are arranged at an interval of 1 to 2 μm on the top.
-A voltage is applied between the nut-shaped electrode 8 and the electrode 10 on the lower surface of the substrate 1.
The electric field on the potential well 7 by applying
Is configured to cause.

Reference numeral 11 in the drawing denotes an insulating film for supporting the donut-shaped electrode 8 on the In _0.53 Ga _0.47 As layer 4. In the above-described embodiment, a voltage is applied between the upper and lower electrodes 8 and 10 so that the surface of the potential well layer 7 is evacuated to 1
An electric field of about 10 ⁷ V / cm is generated and the vacuum level is shown in FIG.
When tilted as shown in (a), the resonance level E tunneled through the potential barrier layer 6 and the potential well layer 7
Electrons with energy equal to ₀ are extracted through the vacuum barrier.

The current density and energy density of this embodiment are
A comparative study will be made with the conventional device shown in FIG. Usually, in a semiconductor heterojunction, the potential of a tunnel barrier that can be formed is low, and the effective mass of electrons is small. For this reason, when a resonance tunneling barrier (Resonance Tunneling Baria) is formed by a semiconductor barrier and a vacuum barrier, most of the electrons are reflected by the vacuum barrier, and it has been considered ineffective to extract them into a vacuum.

In fact, the resonance level E resulting from this₀Electronic in
Transmission probability T (E₀) Is T (E₀) = T_s/ T_vAnd from 1
Is much smaller (T_s； Transmission accuracy of tunnel barrier layer
Rate, T _vThe transmission probability of the vacuum barrier).

However, according to the theoretical consideration described below, even in such a case, the energy half width Δ of the resonance level is narrow.
It was found that the energy density of the electrons taken out at E ₀ is much higher than that of the field emission electron beam source.

[0024] Here, the electron wave vector in _{vacuum, k x ~k x + δk x} ( horizontal (x) _{direction) k y ~k y + δk y} ( horizontal (y) direction) k _z ^v ~k _z The current density and energy density of electrons included in the range of ^V + δk _z ^V (longitudinal (z) direction) will be obtained.

In the case of the electron source of field emission type that transmits vacuum level metal current density ^{J = (q / 2π 2 h} ) δk x δk y T v δE ∴ energy density _{= J / δE = qδk x δk} y T _v / _2π ² h _{^{(although, δE = (h 2 k z}} v / 4π 2 m 0) · δk z v, q is a charge amount, h is Planck's constant.) field emission by a resonant tunneling barrier by the semiconductor and vacuum here the case of the electron source type, if the half width Delta] E ₀ = &Dgr; E of resonant _{level, (2πh / qδk x δk y} ) · J = (π / 2) · ΔE 0 · t p = (π / 2 ) · ΔE ₀ · T _v / T _s = E ₀ T _v / 2 (where peak transmission probability t _p = T _v / T _s and ΔE ₀ = E ₀ (T _v + T _s ) / π). Since there is a relationship, the current density J is obtained by the following equation.

[0026] ^{J = (q / 2π 2 h} ) · δk x δk y T v · (E 0/2) ∴ energy density _{= J / ΔE 0 = (E} 0 / 2ΔE 0) qδk x δk y T v / 2π ² h Therefore, when using a resonant tunnel barrier, T _s / T
Despite the reflection of _v , the energy density in δE (= ΔE ₀ ) is increased by E ₀ / 2ΔE ₀ compared to the conventional device, and the relationship between the energy density I and the electric field E is shown as follows: It becomes like the solid line in Fig. 2 (b). In this case, the InGaAs
All electrons tunnel from layer 2 would be condensed into the Delta] E _0, if the Delta] E ₀ and 1meV, E ₀ / 2Δ
E ₀ is a two-digit number.

It should be noted that the curve indicated by the alternate long and short dash line represents the case of the conventional device, and it is understood that not only the energy width of the tunneling electrons is wide and blur occurs, but also the current energy density thereof is low.

(B) Description of the Second Embodiment of the Present Invention In the above-mentioned first embodiment, the potential well layer 7 is exposed in a vacuum. However, as shown in FIG. 3 (a), A sub-barrier layer 12 made of In _0.52 Al _0.48 As may be interposed on the potential well layer 7. The energy band is as shown in Fig. 3 (b).

According to this, the surface level of the potential well layer 7 is removed, the trapping of electrons by this is eliminated, and the electron density is increased. In FIG. 3A, the same symbols as those in FIG. 1 indicate the same elements.

(C) Description of Third Embodiment of the Present Invention Further, as the electron beam source by the resonance tunnel barrier, an MSM (metal / semiconductor / metal) structure can be used in addition to the above structure.

FIG. 4 is a sectional view showing the embodiment.
A first cobalt silicide (CoSi ₂ ) layer 22, a silicon (Si) layer 23, and a second CoSi ₂ layer are formed on the n ⁺ type Si substrate 21.
The layers 24 are formed by about 27.2Å, 27.2Å and 27.2Å, respectively. Then, from the second CoSi ₂ layer 24 first CoSi ₂
The layer overlying the layer 22 is etched in a mesa shape so that a planar rectangular region remains, and the etched portion is filled with an insulating layer 25. As the etching method, focused ion beam etching,
Sputter etching or the like is used.

Then, a second CoSi ₂ film having a rectangular shape is formed.
The layer 24 becomes the potential well layer 27, and the Si layer 23 thereunder becomes the potential barrier layer 26. Further, a donut-shaped electrode 29 is formed around the potential well layer 27 via an insulating film 28.
A plate-shaped electrode 30 is attached to the lower surface of the.

Also in this embodiment, when a voltage is applied between the electrodes 29 and 30 to incline the vacuum level on the potential well layer 27 as in the first and second embodiments, the potential barrier layer 26 and The electrons that have passed through the potential well layer 27 tunnel through the vacuum level, and the tunneled energy density becomes high.

As described above, when the electron beam source is formed on the silicon substrate 21, it becomes easy to form other elements on the same substrate, which facilitates integration. A sub-barrier layer made of a semiconductor such as Si or an insulator may be formed on the potential well layer of this embodiment.

(D) Description of Other Embodiments of the Present Invention In the above-mentioned embodiments, the potential barrier layer and the potential well layer are formed in a rectangular shape, and one side thereof is about 1000 Å. Is about 100Å, the electron density increases and the transverse (plane direction) wave vector is quantized to k _x = ± π / L _x , k _y = ± π / L _y A strong electron beam source can be obtained. In this case, the emission direction of the electrons does not spread over the whole, but jumps out from the corner portion of the rectangular potential well layer.

Although AlAsSb and Si are used as the potential barrier layer in the above-mentioned embodiments, AlAs and Al
A material such as Sb may be used. In addition to InGaAs and CoSi ₂ , the potential well layers include NiSi ₂ , AlNi, and Ga.
As or InAs may be used.

In the above embodiments, the case where one potential well layer and one potential barrier layer are formed has been described, but a large number of them may be arranged in a mesh shape or a striking shape.

[0038]

As described above, according to the present invention, since one of the potential barriers that causes the resonance tunnel phenomenon is formed by the vacuum level, the potential barrier that is tilted by the electric field is tunneled. The tunnel probability is high, and the electron extraction energy width can be narrowed down to about 1 meV, and an energy density higher by about two orders of magnitude can be obtained with the same electric field strength as compared with a normal electric field radiation source.

Further, according to the present invention, since the auxiliary barrier layer is provided on the surface of the potential well layer, the trapping of electrons due to the surface level of the potential well layer is eliminated,
The current density can be increased.

Further, according to the present invention, since the wave vector of the electrons in the x and y directions along the surface of the potential well layer is quantized, it is possible to obtain a radiation source having extremely strong directivity. Become.

[Brief description of drawings]

FIG. 1 is a sectional view and a plan view of an apparatus showing a first embodiment of the present invention.

FIG. 2 is an energy band diagram of a device showing a first embodiment of the present invention and a characteristic diagram showing current energy density.

FIG. 3 is a sectional view of an apparatus showing a second embodiment of the present invention and its energy band diagram.

FIG. 4 is a sectional view of an apparatus showing a third embodiment of the present invention.

FIG. 5 is a cross-sectional view showing an example of a conventional device, an energy band diagram, and a characteristic diagram showing energy density.

[Explanation of symbols]

1 InP substrate 2 InGaAs layer 3 AlAsSb layer 4 InGaAs layer 5 Isolation 6 Potential barrier layer 7 Potential well layer 8, 10 Electrode 9 Hole 11 Insulation film 12 Sub barrier layer 21 Si substrate 22, 24 CoSi ₂ layer 23 Si layer 25 Insulation layer 26 potential barrier layer 27 potential well layer 28 insulating film 29, 30 electrode

Claims (5)

[Claims] 1. Quantization characterized by having a semiconductor potential barrier layer (6, 26) for causing a resonance tunnel phenomenon, a semiconductor or metal potential well layer (7, 27) and a vacuum level potential barrier. Electron beam generator. 2. The quantized electron beam generator according to claim 1, wherein an auxiliary barrier layer (12) is provided on the surface of the potential well layer (7, 27). 3. A potential barrier layer (6,
27), The quantized electron beam generator according to claim 1 or 2, wherein the potential well layer (7, 27) is formed to have a size capable of quantizing a lateral wave number vector. 4. A potential barrier layer (6,
The quantized electron beam generator according to claim 1, wherein Si, AlAs, AlSb, or AlAsSb is used as 26). 5. The quantized electron beam generator according to claim 1, wherein CoSi ₂ , NiSi ₂ , AlNi, GaAs, InAs and InGaAs are used as the potential well layers (7, 27).