JPH0697466A - Resonant tunneling diode and fabrication thereof - Google Patents

Abstract

PURPOSE:To provide a method of fabricating a resonant tunneling diode having a structure where opposite sides of a semiconductor layer are held between insulating levers, in which method a resonant tunneling diode using as a device material a semiconductor such as silicon not a compound semiconductor is fabricated using a conventionally established fine processing technique. CONSTITUTION:A silicon oxide film 22 is formed on a silicon substrate 20 the entire surface of the silicon oxide film 22 or a device formation region is irradiated with X rays having energy beyond a work function to release oxygen from the surface of the silicon oxide film 22 for reduction of the surface of the silicon oxide film 22. Hereby, there are formed silicon clusters 24 being silicon fine crystal grain on the surface of the silicon oxide film 22. A silicon oxide film 25 is formed as an upper layer oxide film to confine the silicon clusters 24 in the oxide film A polycrystalline silicon layer 26 is formed on the silicon oxide film 25, and electrodes are attached to the polycrystalline silicon layer 26 and to the back surface of the silicon substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonant tunnel diode having a structure in which both sides of a semiconductor layer are sandwiched by insulating layers and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with higher integration of LSIs, miniaturization of conventional elements such as MOS transistors and bipolar transistors is approaching the limit both in terms of manufacturing process and physically. For this reason, semiconductor elements have been formed in which the element is miniaturized by utilizing the quantum effect.
Resonant tunnel diodes are currently one of the semiconductor devices that utilize the quantum effect. The structure of this resonant tunnel diode will be described with reference to FIG.

Insulating layers 4 and 6 are formed on both sides of the semiconductor layer 2 so as to sandwich the semiconductor layer 2. Generally, the semiconductor layer 2 is formed of a compound semiconductor such as GaAs. The insulating layers 4 and 6 are also usually formed of a compound semiconductor such as AlGaAs, and are formed sufficiently thin so that a resonance tunnel effect due to electrons can be generated. These layers are MB
It is formed by the E method or the MOCVD method. Insulation layers 4, 6
Electrodes 8 and 10 are formed on the surface opposite to the semiconductor layer 2 so that a bias voltage can be applied to the semiconductor layer 2 (FIG. 6A). The resonant tunnel diode having such a structure has an energy band structure as shown in FIG. That is, a quantum well is formed between two potential barriers, and a conduction band level (resonance level) discretized by the quantum size effect is formed in the quantum well.

The electrodes 8, 1 of this resonant tunnel diode
The change in energy band when a bias voltage is applied to 0 will be described with reference to FIG. FIG. 7A shows an energy band structure when no voltage is applied. In this state,
No current flows because the potentials of the electrodes 8 and 10 are lower than the conduction band level (resonance level) in the quantum well.

When the voltage V applied to the electrode 8 is increased,
Due to the tunnel effect, electrons pass through the insulating layer 4 having a sufficiently thin thickness and the resonant tunnel current J _RT flows. When the potential V _{0 of the} electrode 8 formed on the insulating layer 4 on the left side of the figure matches the resonance level of the discretized semiconductor layer 2, a resonance tunnel current J _RT due to the resonance tunnel effect flows (FIG. 7).
(B)).

When the voltage V applied to the electrode 8 is further increased, the resonance tunnel current J _RT decreases, and the negative resistance characteristic is exhibited. When the lower end of the conductor becomes higher than the resonance level, it deviates from the resonance state, and the resonance tunnel current J _RT stops flowing, and the thermal excitation current J _RT that flows over the potential barrier.
Only _EX (Fig. 7 (c)). The negative resistance characteristic of the resonant tunnel diode is shown in FIG. The horizontal axis represents the applied bias voltage (V), and the vertical axis represents the current density (J). Figure 8
7A to 7C correspond to the states of FIGS. 7A to 7C. From (b) to (c) in FIG. 8, there is a negative resistance characteristic in which the current density conversely decreases even if the bias voltage is increased.

[0007]

As described above, the resonance tunnel diode utilizing the quantum effect uses the compound semiconductor such as GaAs for the semiconductor layer 2 and AlGaAs for the insulating layers 4 and 6 as the element material. Therefore, L using a semiconductor such as silicon, for which an advanced fine processing technology has been established in element processing technology, processing equipment, or processing materials.
The SI process cannot be used as it is. In principle, even if the quantum effect can be used to form devices that exceed the limits of conventional devices, conventional LSIs using silicon
If the process is not available, there will be no industrial advantage.

If such a resonant tunnel diode is to be formed by using, for example, silicon instead of a compound semiconductor, the insulating layers 4 and 6 are formed of, for example, a silicon oxide film,
The semiconductor layer 2 sandwiched between the insulating layers 4 and 6 of the silicon oxide film is used as a silicon layer, and the silicon layer of the semiconductor layer 2 has a sufficient thickness so as to form a quantized conduction band level. It needs to be thin.

In order to realize this structure using a silicon material, the thickness of the silicon oxide film of the insulating layers 4 and 6 is 5 nm.
Must be: The thickness of the semiconductor layer 2 is 10
It is necessary to set the thickness to nm or less. Using the conventional fine processing technology as it is, 5-10 nm on the silicon oxide film
It is difficult to form a silicon thin film. further,
It is extremely difficult to form silicon fine crystal grains (fine clusters) that become three-dimensional quantum wells (quantum boxes) having a large quantum effect by the conventional fine processing technology.

An object of the present invention is to provide a resonant tunneling diode using not a compound semiconductor but a semiconductor such as silicon as a device material, and manufacturing this resonant tunneling diode by utilizing a conventionally established fine processing technique. To provide a method.

[0011]

The above object is to provide a semiconductor substrate, a semiconductor oxide film formed on the semiconductor substrate, a quantum well in the semiconductor oxide film, the quantum well being surrounded by the semiconductor oxide film. The present invention is achieved by a resonant tunnel diode characterized in that it has semiconductor fine crystal grains to be formed, an upper electrode formed on the semiconductor oxide film, and a lower electrode formed on the back surface of the semiconductor substrate.

[0012] Further, the above object is to provide a semiconductor substrate, a semiconductor oxide film formed on the semiconductor substrate, and a semiconductor micro-structure which forms a quantum well in the semiconductor oxide film and is surrounded by the semiconductor oxide film. The present invention is achieved by a resonant tunnel diode characterized by having a crystal grain and a pair of electrodes formed on the semiconductor oxide film so as to face each other so as to sandwich the formation region of the semiconductor fine crystal grain.

Another object of the present invention is to form a semiconductor oxide film on a semiconductor substrate and irradiate the surface of the semiconductor oxide film with an energy ray having an energy equal to or higher than a work function to release oxygen from the surface of the semiconductor oxide film. , Reducing the surface of the semiconductor oxide film to form semiconductor fine crystal grains on the surface of the semiconductor oxide film, forming an upper oxide film on the semiconductor fine crystal grains and on the semiconductor oxide film, and forming the semiconductor fine crystal grains Forming a quantum well structure sandwiched between the upper oxide film and the semiconductor oxide film, forming an upper electrode on the upper oxide film, and forming a lower electrode on the back surface of the semiconductor substrate. This is achieved by a method of manufacturing a diode.

Further, the above object is to form a semiconductor oxide film on a semiconductor substrate, and irradiate the surface of the semiconductor oxide film with an energy ray having energy higher than a work function to release oxygen from the surface of the semiconductor oxide film. Forming a semiconductor layer on the surface of the semiconductor oxide film by reducing the surface of the semiconductor oxide film,
Forming an upper oxide film on the semiconductor layer, forming a quantum well structure in which the semiconductor layer is sandwiched by the upper oxide film and the semiconductor oxide film, forming an upper electrode on the upper oxide film, This is achieved by a method of manufacturing a resonant tunnel diode, which comprises forming a lower electrode on the back surface of a semiconductor substrate.

Still further, the above object is to form a semiconductor oxide film on a semiconductor substrate and irradiate the surface of the semiconductor oxide film with an energy ray having an energy higher than a work function to desorb oxygen from the surface of the semiconductor oxide film. Then, the semiconductor oxide film surface is reduced to form semiconductor fine crystal grains on the semiconductor oxide film surface, and a quantum well structure is formed by the semiconductor fine crystal grains and the semiconductor oxide film around the semiconductor fine crystal grains, This is achieved by a method of manufacturing a resonant tunnel diode, characterized in that a pair of electrodes facing each other are formed on the semiconductor oxide film so as to sandwich the formation region of the semiconductor fine crystal grains.

[0016]

According to the present invention, the surface of the semiconductor oxide film is irradiated with an energy ray having energy higher than the work function to desorb oxygen from the surface of the semiconductor oxide film, and the surface of the semiconductor oxide film is reduced to reduce the surface of the semiconductor oxide film. Since the semiconductor fine crystal grains are formed in the above, it is possible to realize a resonant tunnel diode using a semiconductor such as silicon as a device material by utilizing the conventional fine processing technology.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A resonance tunnel diode and a method of manufacturing the same according to a first embodiment of the present invention will be described with reference to FIGS. The resonant tunnel diode according to the present embodiment is a silicon microcrystal produced by desorption of oxygen when a light beam, an electron beam, or a charged particle beam is irradiated as an energy beam having an energy equal to or higher than a work function on the surface of a silicon oxide film. The feature is that grains (silicon clusters) are used as quantum wells.

The structure of the resonant tunnel diode according to this embodiment will be described with reference to FIG. Low resistance silicon substrate 2
0, a silicon oxide film 22 having a thickness of 2 to 10 nm is formed. The size of 1 nmφ in the silicon oxide film 22
A large number of silicon clusters (silicon fine crystal grains) 24, which are lumps of silicon having a diameter of ˜5 nm, are formed. On the silicon oxide film 22, a polycrystalline silicon layer 2 serving as an upper electrode is formed.
6 is formed. Electrodes are attached to the polycrystalline silicon layer 26 and the back surface of the silicon substrate 20, respectively.

As described above, the resonant tunnel diode according to the present embodiment has a plurality of quantum well structures, in which silicon clusters 24 are sandwiched between silicon oxide films 22 in the electrode direction, formed in parallel in the substrate surface direction. Next, a method of manufacturing the resonance tunnel diode according to the present embodiment will be described with reference to FIG.

First, a silicon oxide film 22 having a thickness of 2 to 5 nm is formed on a silicon substrate 20 having a low resistance layer for extracting electrodes by, for example, a thermal oxidation method (FIG. 2).
(A)). Next, the entire surface of the silicon oxide film 22 or a predetermined region for element formation is irradiated with X-rays as energy rays having an energy equal to or higher than the work function. That is, X-rays having the energy of the intensity necessary to release the electrons that combine silicon (Si) and oxygen (O) are emitted from the silicon oxide film 22 (SiO ₂ ) 22.
Irradiate the surface. This X-ray irradiation is carried out under the ultrahigh vacuum or hydrogen atmosphere so that the oxygen (O) in the silicon oxide film 22 is
Perform about 2 minutes at 1 W / cm ² to excite the S orbit.
The substrate temperature of the silicon substrate 20 during X-ray irradiation is 600 ° C. or lower (FIG. 2B).

An electron beam may be irradiated instead of the high energy light such as X-ray. In the case of an electron beam, an electron beam of 50 mA / cm ² is irradiated for about 2 minutes at an acceleration voltage of several kV or higher. Thus, by irradiating the surface of the silicon oxide film 22 with an energy ray having an energy equal to or higher than the work function to desorb oxygen from the surface of the silicon oxide film 22 and reduce the surface of the silicon oxide film 22, the surface of the silicon oxide film 22 is reduced. A large number of silicon clusters having a thickness of 1 to 5 μm are deposited on the surface. Clusters grow when the irradiation time of high energy rays is increased,
It becomes a thin film of μm.

FIG. 3 shows a photoelectron spectrum of silicon deposited on the surface of the silicon oxide film 22 when the thermally oxidized silicon is irradiated with X-rays capable of exciting the 1S orbit of oxygen. The horizontal axis represents the binding energy (eV), and the vertical axis represents the photoelectron spectrum intensity. In the figure, the solid line A shows the case where the detection angle is 90 °, the chain line B shows the case where the detection angle is 45 °, and the broken line C shows the case where the detection angle is 30 °.

In the figure, Si2p element is
It is a signal from Si in the Si cluster and depends on the detection angle.
Shows that the property is localized on the outermost surface 2 nm. Si2p d
ioxide is SiO₂Signal from Si inside,
Shows that there are more deeper regions than clusters
You Si2p suboxide is a cluster and SiO.
₂Is a signal from Si existing between
Deeply SiO₂Indicates that it exists in a region much shallower than
You

From another measurement, it was found that the ratio of Si to SiO _{2 on} the outermost surface was 1: 1.
It can be seen that a large number of silicon clusters 24 each having a size of 1 nmφ to 5 nmφ are formed, surrounded by the silicon oxide film 22 in the region (1). Next, a silicon oxide film 25 is formed as an upper oxide film on the silicon cluster 24 and the silicon oxide film 22 to confine the silicon cluster 24 in the oxide film. Next, a polycrystalline silicon layer 26 is formed on the silicon oxide film 25, and electrodes are attached to the polycrystalline silicon layer 26 and the back surface of the silicon substrate (FIG. 2C).

In this way, a quantum well structure in which the silicon cluster 24 is sandwiched between the silicon oxide films 22 and 25 is formed in the electrode direction, and the quantum well structure is formed in parallel with the substrate surface direction. The resonant tunnel diode of the embodiment is completed. In this way, by irradiating the silicon oxide film with a light beam or an electron beam having energy equal to or higher than the work function, silicon clusters can be easily formed. The formed silicon cluster is about 1 nmφ
Since it has a size of about 5 nmφ and is surrounded by an oxide film, it is possible to form a quantum well structure in which the conduction band levels in the silicon cluster are discretized. By using this silicon cluster, a resonant tunnel diode using silicon as a material can be easily formed. Since clusters can be formed using silicon oxide, which is a typical silicon material, many existing LSI techniques can be used, including established fine processing techniques such as X-ray and electron beam lithography.

A resonance tunnel diode and a method of manufacturing the same according to a second embodiment of the present invention will be described with reference to FIGS. The resonant tunneling diode according to the present embodiment also has a silicon minute amount generated by desorption of oxygen when a light beam, an electron beam, or a charged particle beam is applied to the surface of the silicon oxide film as an energy ray having an energy higher than a work function. It is characterized by using crystal grains (silicon clusters) as quantum wells.

The structure of the resonant tunnel diode according to this embodiment will be described with reference to FIG. A silicon oxide film 22 having a thickness of 10 nm or more is formed on the silicon substrate 20. The size is 1 nmφ to 2 nmφ in the cluster formation region in the silicon oxide film 22 in the vicinity of the surface of the silicon oxide film 22 and having a width D = 0.1 μm to 0.3 μm.
About 100 silicon clusters (silicon fine crystal grains) 24, which are lumps of silicon, are formed. On the silicon oxide film 22 above the silicon cluster 24, a silicon oxide film 30 as a protective film is almost formed on the silicon cluster 24.
The width D is formed so as to cover the upper part. A polycrystalline silicon layer 32 is formed on both sides of a silicon oxide film 30 as a protective film on the silicon oxide film 22 so as to sandwich the silicon cluster 24. An electrode is attached to each of the polycrystalline silicon layers 32.

As described above, in the resonant tunneling diode according to the present embodiment, the silicon cluster 24 forms a quantum well structure with the silicon oxide film 22 between the adjacent silicon clusters 24 as a potential barrier layer, and two quantum well structures are formed. Are formed in series in the substrate surface direction in series with the electrode direction formed on the polycrystalline silicon layer 32. Next, a method of manufacturing the resonant tunnel diode according to this embodiment will be described with reference to FIG.

First, a silicon oxide film 22 having a thickness of 10 nm or more is formed on the silicon substrate 20 by using, for example, a thermal oxidation method (FIG. 5A). Next, in the element formation region on the surface of the silicon oxide film 22, a silicon oxide film (SiO _{2 )} 22
Therefore, X-rays are irradiated as energy rays having energy equal to or higher than the work function in order to emit electrons that combine silicon (Si) and oxygen (O). The X-ray irradiation is performed under an ultrahigh vacuum or a hydrogen atmosphere in an amount of 1 W / in order to excite the 1S orbit of oxygen (O) in the silicon oxide film 22.
Irradiation in cm ² for about 2 minutes. The substrate temperature of the silicon substrate 20 during X-ray irradiation is 600 ° C. or lower. The irradiation region is a cluster formation region having a width D = about 0.1 μm to 0.3 μm (FIG. 5B). An electron beam may be irradiated instead of high energy light such as X-ray. Several k for electron beam
An accelerating voltage of V or higher is irradiated with an electron beam of 50 mA / cm ² for about 2 minutes.

In this way, the surface of the silicon oxide film 22 is irradiated with an energy ray having an energy higher than the work function to desorb oxygen from the surface of the silicon oxide film 22 and reduce the surface of the silicon oxide film 22. Membrane 22
Silicon clusters 24 that are silicon micro-crystal grains on the surface
About 100 are deposited. Next, a silicon oxide film 25 is formed as an upper oxide film on the silicon cluster 24 and the silicon oxide film 22, and the silicon cluster 24 is enclosed in the oxide film. Next, a silicon oxide film 30 having a width D is formed on the silicon oxide film 25 on which the silicon clusters 24 are formed.

Next, a polycrystalline silicon layer 32 is formed on the silicon oxide film 25 on both sides of the silicon oxide film 30, and an electrode is attached on each polycrystalline silicon layer 32 (FIG. 5).
(C)). In this way, the two polycrystalline silicon layers 3
The resonant tunnel diode according to the present embodiment is completed, in which the quantum wells formed by a large number of silicon clusters 24 are formed in the substrate surface direction in series with the electrode formed in 2.

As described above, according to this embodiment, it is possible to form a resonance tunnel diode in which multiple potential wells are provided and resonance tunneling is performed in series. Also in this embodiment, the silicon clusters can be easily formed by irradiating the silicon oxide film with a light beam or an electron beam having energy higher than the work function.
Since the formed silicon cluster has a size of about 1 nmφ to 5 nmφ and is surrounded by an oxide film, a quantum well structure in which the conduction band levels in the silicon cluster are discretized should be formed. You can By using this silicon cluster, a resonant tunnel diode using silicon as a material can be easily formed. Since clusters can be formed using silicon oxide, which is a typical silicon material, many existing LSI techniques can be used, including established fine processing techniques such as X-ray and electron beam lithography.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, in the method of manufacturing the resonant tunnel diode of the above embodiment, the silicon oxide film 22 formed on the silicon substrate 20 is formed by the thermal oxidation method, but it may be formed by using another method such as the CVD method.
Further, although the resonant tunnel diode in which the quantum box using the silicon cluster is formed is shown in the first embodiment, a silicon layer may be formed instead of the silicon cluster. In this case, by irradiating the surface of the silicon oxide film 22 with energy rays with a high dose amount, the deposited silicon clusters are grown to form a silicon layer.

[0034]

As described above, according to the present invention, the surface of the semiconductor oxide film is irradiated with an energy ray having an energy higher than the work function to desorb oxygen from the surface of the semiconductor oxide film and reduce the surface of the semiconductor oxide film. Since the semiconductor fine crystal grains are formed on the surface of the semiconductor oxide film, a resonant tunnel diode using a semiconductor such as silicon as an element material can be realized by utilizing the conventional fine processing technology.

[Brief description of drawings]

FIG. 1 is a diagram showing a resonant tunneling diode according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a method of manufacturing the resonant tunneling diode according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a photoelectron spectrum by X-ray irradiation.

FIG. 4 is a diagram showing a resonant tunneling diode according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a method of manufacturing a resonance tunnel diode according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a structure of a resonant tunnel diode.

FIG. 7 is a diagram showing changes in the energy band of a resonant tunnel diode due to voltage application.

FIG. 8 is a diagram showing voltage-current characteristics of a resonant tunnel diode.

[Explanation of Codes] 2 ... Semiconductor layer 4, 6 ... Insulating layer 8, 10 ... Electrode 20 ... Silicon substrate 22 ... Silicon oxide film 24 ... Silicon cluster 25 ... Silicon oxide film 26 ... Polycrystalline silicon layer 30 ... Silicon oxide film 32 ... Polycrystalline silicon layer

Claims (7)

[Claims] 1. A semiconductor substrate, a semiconductor oxide film formed on the semiconductor substrate, and semiconductor fine crystal grains in the semiconductor oxide film, which are surrounded by the semiconductor oxide film to form quantum wells. A resonance tunnel diode comprising an upper electrode formed on the semiconductor oxide film and a lower electrode formed on the back surface of the semiconductor substrate. 2. A semiconductor substrate, a semiconductor oxide film formed on the semiconductor substrate, and semiconductor fine crystal grains in the semiconductor oxide film, which are surrounded by the semiconductor oxide film to form quantum wells. A resonance tunnel diode, comprising: a pair of electrodes formed on the semiconductor oxide film so as to face each other so as to sandwich the formation region of the semiconductor fine crystal grains. 3. The resonant tunnel diode according to claim 1, wherein the semiconductor is silicon. 4. A semiconductor oxide film is formed on a semiconductor substrate, and the surface of the semiconductor oxide film is irradiated with an energy ray having an energy equal to or higher than a work function to desorb oxygen from the surface of the semiconductor oxide film, whereby the semiconductor oxide film is oxidized. The surface of the film is reduced to form semiconductor fine crystal grains on the surface of the semiconductor oxide film, an upper layer oxide film is formed on the semiconductor fine crystal grains and the semiconductor oxide film, and the semiconductor fine crystal grains are converted to the upper layer oxidation. Forming a quantum well structure sandwiched between a film and the semiconductor oxide film, forming an upper electrode on the upper oxide film, and forming a lower electrode on the back surface of the semiconductor substrate. . 5. A semiconductor oxide film is formed on a semiconductor substrate, and the surface of the semiconductor oxide film is irradiated with an energy ray having an energy equal to or higher than a work function to desorb oxygen from the surface of the semiconductor oxide film, whereby the semiconductor oxide film is oxidized. A quantum well in which a film surface is reduced to form a semiconductor layer on the surface of the semiconductor oxide film, an upper oxide film is formed on the semiconductor layer, and the semiconductor layer is sandwiched between the upper oxide film and the semiconductor oxide film. A method of manufacturing a resonant tunnel diode, comprising forming a structure, forming an upper electrode on the upper oxide film, and forming a lower electrode on the back surface of the semiconductor substrate. 6. A semiconductor oxide film is formed on a semiconductor substrate, and the surface of the semiconductor oxide film is irradiated with an energy ray having an energy equal to or higher than a work function to desorb oxygen from the surface of the semiconductor oxide film, thereby oxidizing the semiconductor oxide. The film surface is reduced to form semiconductor fine crystal grains on the surface of the semiconductor oxide film, and a quantum well structure is formed by the semiconductor fine crystal grains and the semiconductor oxide film around the semiconductor fine crystal grains. A method of manufacturing a resonance tunnel diode, characterized in that a pair of electrodes facing each other are formed so as to sandwich the formation region of the semiconductor fine crystal grains. 7. The method of manufacturing a resonant tunnel diode according to claim 3, wherein the semiconductor is silicon.