JPH0936317A - Memory device and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Object] To provide a memory device utilizing the Coulomb blockade effect, the characteristics of which can be easily controlled by a conventional microfabrication method. A first resistor 4 in which metal or semiconductor fine particles are dispersed, which are formed between a pair of electrodes 2 and 3 on an insulating substrate 1, and formed on the resistor 4 with an electrical insulator substance 5 interposed therebetween. The second resistor 6 and the third electrode 7 formed on the resistor 6 are used to store electrons in the first resistor 4 and to generate electrodes 2 and 3 by the electrostatic field generated at the end. The memory state is confirmed by monitoring the change in the tunnel current flowing during the period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a memory device that uses a tunnel junction and can operate in units of one electron, and a method of manufacturing the same.

[0002]

2. Description of the Related Art LSIs, which support the information-oriented society, are highly integrated by miniaturizing semiconductor elements, that is, transistors. Further, by miniaturizing the element, the traveling distance and capacity of the carrier can be reduced, and high performance of the LSI such as high speed can be achieved. 16M DRA now in mass production
In M, the gate length is 0.5 μm, and in 64M DRAM, which has started to be sample-shipped, the gate length is 0.35 μm.
It is about μm, and operation has been confirmed at the research stage even with a gate length of 0.1 μm or less.

However, when such elements are further miniaturized, physical problems such as generation of tunnel leakage current between the gate electrode and the semiconductor substrate, and further, the number of electrons per operation are reduced. Therefore, there is a fundamental problem that the statistical fluctuation of the number of electrons is increased and a malfunction easily occurs. For this reason, there has been proposed a single-electron tunnel element that operates by controlling individual electrons, rather than using the statistical properties of electrons as the basis of operation, as in the current LSI. The feature of this device is that as the device becomes finer, the operation becomes complete and the ultimate characteristics can be obtained. For example, by applying this to a memory, it is 6 orders of magnitude faster than the human brain and 6 times faster than the current semiconductor memory.
Large-capacity memory can be obtained.

[0004]

The single electron tunnel device has its operating principle based on the Coulomb blockade effect. In order to bring out this effect, the capacitance of the island sandwiched by the tunnel junctions is made small. There is a need. Considering room temperature operation in particular, it is necessary to set the island capacitance to 1 aF or less, and in order to manufacture such a structure, a nm level structure forming technique is necessary.

At present, the technology for producing such a fine structure is scarce, and some devices utilizing a natural structure have been proposed. For example, "Appl. Phys. Lett., Vol.61, 1992,
atomic layer doping GaA as described in p3145 "
A single-electron tunneling device with side gates beside the s-thin wire and a single-electron tunneling device using ultra-thin polysilicon as a channel as described in "Proc. IEDM, 1993, p541" were manufactured. ing. However, the former is GaA
Since the tunnel junction is formed by utilizing the random arrangement of charged impurities existing in the s-thin wire, and the latter uses the grains in polysilicon as islands, and the part where electrons easily flow is used as the channel. It was difficult to manufacture the device with good controllability, and the characteristics of the manufactured devices also varied.

The present invention solves the above problems of the prior art,
An object of the present invention is to provide a memory device having a relatively simple structure and capable of controlling Coulomb blockade characteristics by a conventional fine processing method, and a manufacturing method thereof.

[0007]

In order to achieve the above object, in the memory element of the present invention, a first resistor including at least a plurality of fine particles of metal or semiconductor is formed between the first and second electrodes. Then, a second resistor containing at least a plurality of fine particles of metal or semiconductor is formed on the first resistor via an electrically insulating substance, and a third electrode is formed on the second resistor. It is characterized by a different configuration.

In the above structure, it is preferable that the current flowing through the resistor when a voltage is applied is a tunnel current flowing through at least one or more fine particles.

Further, it is preferable that the first resistor, the second resistor, and the electrically insulating substance between the first resistor and the second resistor are laminated in layers.

The fine particles are preferably separated by an electrically insulating substance. Further, it is preferable that the electrically insulating substance between the particles and the electrically insulating substance between the first resistor and the second resistor are the same material.

The diameter of the metal or semiconductor fine particles is preferably 50 nm or less.

Further, the electrically insulating substance is preferably an oxide or a nitride. Next, a method of manufacturing a memory device according to the present invention comprises a step of forming a first resistor containing at least a plurality of metal or semiconductor fine particles between the first and second electrodes, and the first resistor. Of the memory element, which includes a step of forming a second resistor containing at least a plurality of fine particles of metal or semiconductor via an electrically insulating substance, and a step of forming a third electrode on the second resistor. It is a manufacturing method, wherein the first and second resistors and the electrically insulating substance between the first and second resistors are laminated in layers.

In the above structure, the first or second resistor is preferably formed by alternately depositing an electrically insulating substance and metal or semiconductor fine particles.

Further, the first or second resistor is preferably formed by depositing an electrically insulating substance and metal or semiconductor fine particles at the same time.

It is also preferable to heat-treat the first or second resistor to control the size or density of the metal or semiconductor fine particles.

[0016]

According to the structure of the present invention, when a voltage is applied between the first and second electrodes, the electrons move between the electrodes through the fine particles in the first resistor due to the tunnel effect to form a channel. . On the other hand, when the voltage of the third electrode is lowered with respect to the channel, electrons move one by one from the third electrode to the particles in the second resistor due to the tunnel effect. Come out one by one. However, even if the voltage applied to the third electrode is 0, the electrons remain in the fine particles in the second resistor due to the Coulomb blockade effect,
The potential of the fine particles in the second resistor does not become zero. Under the influence of this potential, the current flowing through the channel formed between the first and second electrodes changes. Therefore, the second
A memory capable of recording the number of electrons in the particles in the resistor as information is realized. In this case, the information can be read by detecting the current flowing through the channel.

Further, the first resistor, the second resistor, and the electrically insulating substance between the first resistor and the second resistor are laminated in layers to form the first and second resistors. The distance between the two resistors can be controlled by the film thickness of the electrically insulating substance, and the element configuration can be easily controlled.

Further, by separating the fine particles with an electrically insulating substance and embedding them, a stable tunnel current can be passed.

Further, an element can be efficiently manufactured by forming the electrically insulating substance between the fine particles and the electrically insulating substance between the first resistor and the second resistor by the same material.

By setting the diameter of the fine particles of metal or semiconductor to 50 nm or less, the electrostatic capacitance of the tunnel junction becomes small, and it is possible to operate at a relatively high temperature (about room temperature).

Further, by forming the electrically insulating thin film with an oxide or a nitride, it is possible to realize an element that operates stably even in a corrosive gas or a high temperature atmosphere.

Further, according to the manufacturing method of the present invention, a resistor is formed by depositing metal or semiconductor fine particles by various film forming techniques, or by depositing an electrically insulating substance and metal or semiconductor fine particles alternately or simultaneously. Since it can be manufactured easily, and the distance between the first and second resistors can be adjusted by the film thickness of the electrically insulating material, the characteristics of the memory element can be controlled relatively easily. Furthermore, the first
Alternatively, since the formation of the second resistor, the deposition of the electrically insulating substance, and the formation of the other resistor on the surface thereof can be continuously performed, the manufacturing can be efficiently performed.

Further, the resistor can be manufactured with good controllability by alternately depositing the electrically insulating substance and the metal or semiconductor fine particles.

Further, by simultaneously depositing the electrically insulating substance and the metal or semiconductor fine particles, the resistor can be manufactured at high speed.

Further, a resistor having desired characteristics can be obtained by controlling the size and density of the fine particles by heat treatment of the resistor.

[0026]

EXAMPLE A memory device according to an example of the present invention will be described below.

FIG. 1 is a sectional view showing the structure of a memory device according to an embodiment of the present invention. The memory device includes a first resistor 4 in which fine particles of metal or semiconductor are formed between a pair of electrodes 2 and 3 on an insulating substrate 1 and an electrical insulator substance 5 on the resistor 4. It is composed of a second resistor 6 formed as described above and a third electrode 7 formed on the resistor 6.

When a voltage is applied between the electrode 7 and the electrode 2 (or the electrode 3), the electrons move in the electrically insulating substance 8 by the tunnel effect and are stored in the fine particles 9. In this state, a small electrostatic field is generated by the accumulated electrons. Due to the electrostatic field, the tunnel current flowing between the electrodes 2 and 3 differs depending on whether electrons are present in the fine particles 9 or not, and the tunnel current value or the voltage value at which the tunnel current starts to flow (IV characteristic). Fine particles 9 if read out
The electronic state inside can be detected. From the above operation, the fine particles 9
A memory having the electronic state of the inside as recorded information is realized.

A specific element structure and manufacturing method of this memory element will be described with reference to FIG. FIG. 2 is a sectional view of the memory device of this embodiment. The memory element is 100 n on the thermal oxide film 11 on the surface of the Si substrate 10.
On the surfaces of the pair of electrodes 12 and 13 formed at intervals of m, Au fine particles having an average particle diameter of 5 nm are contained in SiO ₂ in an amount of 0.5 to 1
Resistor thin film 14 dispersed at an interval of about nm is formed, and Si having a thickness of 20 nm, which is an electrically insulating substance, is formed thereon.
Resistor thin film 16 having a thickness of 30 nm in which Au fine particles having an average particle size of 5 nm are dispersed in SiO ₂ through the O ₂ thin film 15.
Is formed, and the third electrode 17 is further formed thereon. Unless the Au fine particles are formed in SiO ₂ at intervals of 0.5 to 1 nm as described above, the tunnel current cannot be reliably flowed. Further, in this embodiment, S
The thickness of the io ₂ thin film 15 is set to 20 nm, but at least 5 nm
If the film thickness is not set to the above value, the electrons accumulated in the resistor 6 will flow into the resistor 4 as a tunnel current. Therefore, the SiO ₂ thin film 15, which is an electrically insulating substance, needs to have a thickness of 5 nm or more.

The electrodes 12 and 13 have a thickness of 10 nm.
After the Cr thin film was vacuum-deposited, an Au thin film having a thickness of 0.1 μm was vacuum-deposited and produced by lithography.

The resistor thin films 14 and 16 and the SiO ₂ thin film 15 were produced using the sputtering apparatus shown in FIG. A quartz (SiO ₂ ) glass target 18 and an Au target 19 were used as sputter targets. The substrate 20 having the electrode 12 and the electrode 13 on the Si thermal oxide film 11 is fixed to a substrate holder 22 having a heater 21, and is rotated by a rotary shaft directly connected to the substrate holder 22 to form SiO 2.
It can be brought above the target, either the ₂ target 18 or the Au target 19. Substrate 20
The position of and the dwell time above each target is controlled by a computer. In order to prevent contamination during sputtering, a shield plate 23 is provided so as to cover the periphery of each target and its extension. Argon is used as the sputtering gas, the gas is introduced from the gas inlet 24, the gas outlet 25 is connected to a vacuum exhaust system, the gas pressure is 1.0 Pa, the substrate temperature is 200 ° C., and the electric power applied to the SiO ₂ target 18 is set. Was 250 W and the power applied to the Au target 19 was 10 W.

First, the substrate 20 is allowed to remain on the Au target 19 for 20 seconds, and the resistor thin film 1 made of Au fine particles 1 is formed.
4 was deposited. Then, the substrate 20 is rotated to rotate the SiO ₂
The SiO ₂ film 15 having a thickness of 20 nm was deposited by staying on the target 18 for 2 minutes. Au produced by this method
Cross-section observation of the fine particles with a transmission electron microscope revealed that Au
Was found to have an average particle size of 5 nm.

Next, a thickness of 30 n is formed on the surface of the resistor thin film 14.
A resistor thin film 16 of m was prepared by sequentially depositing Au and SiO ₂ in the same apparatus, and an electrode 17 was formed on the surface of the resistor thin film by C
A memory element was completed by forming r and Au by vacuum deposition and lithography.

In the above embodiment, the electrodes 12, 13,
An Au / Cr thin film was used for the electrode 17 and the metal,
Various conductive materials can be used depending on the application such as a semiconductor. For example, it is also possible to use low resistance Si as the Si substrate 10 used in this embodiment and use it as the electrode 17. In this case, the element structure is the Si substrate 1
0, a resistor thin film 16, a SiO ₂ thin film 15, a resistor thin film 14 (or electrodes 12 and 13), and electrodes 12 and 13 (or resistor thin film 14) are formed in this order.

Although the resistor thin film 16 was manufactured by sputtering the Au target 19 and the insulator target 18 once, respectively, the substrate 20 was alternately placed on the Au target 19 and the insulator target 18. By repeating the above operation, the Au fine particles having a uniform particle size could be dispersed in the electrically insulating substance. Also,
A resistor thin film in which Au particles are dispersed in an electrically insulating substance can also be manufactured by placing the substrate 20 above the two targets 18 and 19 and simultaneously sputtering Au and an insulator.

Although the resistor thin film 14 is made of only Au fine particles, it may be dispersed in an electrically insulating substance like the resistor thin film 16.

According to the above manufacturing method, the resistor thin film 1
4, 16 and the SiO ₂ thin film 15 can be continuously manufactured by the same apparatus, and can be efficiently manufactured.

Further, it is desirable to use a noble metal, which is a thermally and chemically stable material, as the fine particles constituting the resistor thin film. It is desirable that the size of the fine particles be 50 nm or less in order to make the distance between the fine particles relatively uniform at the level of nm, but basically, the distance between the fine particles should be set to a size at which a tunnel current flows. is important. The distance between the particles through which the tunnel current actually flows is 0.
It is 5 nm to 2 nm, and the ratio of fine particles to the electrically insulating substance in the resistor thin films 14 and 16 when embedding between the fine particles with the electrically insulating substance is 5 to 70% by volume and operates at a relatively high temperature. Thus, a memory device that can be obtained is obtained.

The materials of the electrically insulating substance and the electrically insulating thin film 15 may be oxides, nitrides, organic materials or the like, as long as they have low conductivity to the extent that changes in tunnel current can be detected.

The Au target is aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel. (Ni), copper (Cu), zinc (Z
n), gallium (Ga), germanium (Ge), arsenic (As), selenium (Se), palladium (Pd), silver (Ag), cadmium (Cd), indium (In),
Even if the target is made of at least one kind of metal or semiconductor selected from tin (Sn), antimony (Sb), tellurium (Te), platinum (Pt), gold (Au), or lead (Pb). A multiple tunnel junction in which fine particles of metal or semiconductor having a particle size of 1 to 50 nm were uniformly dispersed was obtained.

Further, although the case where SiO ₂ was used as the electrically insulating substance was shown in the above-mentioned examples, silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₃ ), aluminum nitride (AlN), Even if titanium oxide (TiO ₂ ) or hafnium oxide (HfO ₂ ) was used, the resistor thin films 14 and 16 excellent in corrosion resistance could be manufactured. These electrically insulating substances can be produced by sputtering an oxide or a nitride, but can also be produced by sputtering a semiconductor material such as silicon or aluminum or a metal material in an atmosphere containing oxygen or nitrogen. It was

Further, the characteristics of the memory element could be improved by performing heat treatment. This heat treatment was suitably performed at a temperature between 1/5 and 3/5 of the melting point of the metal or semiconductor material used. It is considered that the characteristics are improved because the grain size is increased and the grain size is made uniform by the heat treatment, and the strains and defects in the fine grain crystals are removed. When the nitride material was used as the electrically insulating substance, the grain size was slightly increased by the heat treatment, but the characteristics could be stabilized. In this case, the grain size could be controlled by the substrate temperature during sputtering.

Although the corners of the fine particles were smoothed and smoothed by raising the substrate temperature during the sputtering or by performing a heat treatment, the smooth fine particles had better initial characteristics than the fine particles. It is considered that this is because the tunnel current is easily affected by the state of the surface of the fine particles, and therefore the fine particles having a smooth surface provide a more stable surface and a stable tunnel current flows.

[0044]

As described above, according to the memory device of the present invention, a multi-tunnel junction in which metal or semiconductor fine particles are uniformly separated by a gap of about 1 nm can be obtained by the conventional thin film manufacturing method. Since the characteristics can be controlled by controlling the film thickness direction, a memory element using Coulomb blockade can be obtained by the conventional fine processing method. Moreover, since an electrically insulating thin film having excellent corrosion resistance can be used, a memory element having excellent reliability and long-term stability can be provided.

Further, according to the manufacturing method of the present invention, it is possible to easily control the type of metal or semiconductor, the size of fine particles, the density, the distance between fine particles, etc., and to manufacture a memory element having excellent characteristics with good reproducibility. it can.

[Brief description of drawings]

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

FIG. 2 is a structural cross-sectional view of a memory device according to an embodiment of the present invention.

FIG. 3 is a schematic view of a manufacturing apparatus used for manufacturing a memory device according to an embodiment of the present invention.

[Explanation of symbols]

1 Insulating Substrate 2, 3, 7, 12, 13, 17 Electrode 4, 6 Resistor 5, 8 Electrical Insulating Material 9 Fine Particles 10 Si Substrate 11 Si Thermal Oxide Film 14, 16 Resistor Thin Film 15 SiO ₂ Thin Film 18 Quartz Glass target 19 Au target 20 Substrate 21 Heater 22 Substrate holder 23 Shield plate 24 Gas inlet 25 Gas outlet

Claims (8)

[Claims] 1. A first resistor formed on a substrate in which a plurality of fine particles made of metal or semiconductor are dispersed in an insulating layer, and a first resistor formed on both ends of the first resistor on the substrate. A first resistor and a second electrode; and a second resistor in which a plurality of fine particles made of metal or semiconductor formed on the first resistor via an electrically insulating material layer are dispersed in the insulating layer,
A third electrode formed on the second resistor,
A memory element, wherein the presence or absence of electrons in the second resistor is determined based on a characteristic of a tunnel current flowing between the first electrode and the second electrode. 2. A plurality of fine particles made of metal or semiconductor dispersed in the first and second resistors have an interval of 0.5 nm.
The memory device according to claim 1, wherein the memory device has a thickness of ˜1 nm. 3. The memory device according to claim 1, wherein the electrically insulating material layer has a thickness of 5 nm or less. 4. The diameter of metal or semiconductor fine particles is 50.
The memory device according to claim 1, wherein the memory device has a thickness of not more than nm. 5. The first resistor, the second resistor, and the electrically insulating substance between the first resistor and the second resistor are laminated in layers. Memory device. 6. The first and second substrates are spaced apart from each other on the substrate by a predetermined distance.
And a step of forming a first resistor in which a plurality of fine particles made of metal or semiconductor are dispersed in an insulating layer on the substrate on which the first and second electrodes are formed. Forming a second resistor in which a plurality of fine particles made of metal or semiconductor are dispersed in the insulating layer on the first resistor via an electrically insulating material layer; and on the second resistor. And a step of forming a third electrode on the memory element, wherein the electrically insulating material layer is laminated in layers. 7. The method of manufacturing a memory element according to claim 6, wherein the first or second resistor is formed by alternately depositing an electrically insulating substance and fine particles made of a metal or a semiconductor. . 8. The method of manufacturing a memory device according to claim 6, wherein a step of heat-treating the first or second resistor is added.