JPH0696116B2 - Insulating ultra-thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is an insulating ultrathin film used for electronic devices and the like, which is a metal oxide film and a Langmuir-Blodgett film (hereinafter referred to as a “metal oxide film”) formed on a conductor. , LB film)).

[Prior Art] In the 1930s, it was already found by Langmuir and Blodgett that fatty acids having about 16 to 22 carbon atoms could form a monomolecular film on the surface of water and accumulate it on a substrate. It is only recently that discussions on the issue have begun.

For an overview of previous research, see Solid State Physics, 17 (1
2), 45 (1980), Thin Solid Films (Thin
Solid Films), 68 No. 1 (1982), 99 No. 1, 2, 3 (1)
983), Insoluble Monolayers at Liquid-Gas Interfaces (lnsoluble Monolaye
rs at Liquid-Gas Interfaces) (GLGains, Inters)
published by cience Publishers, New York, 1966).

Heretofore, metal salts of long-chain fatty acids have been studied as typical LB films, and their insulating properties have been interesting, and research and development have been carried out as insulating films in devices of MIS and MIM structures.

[Problems to be Solved by the Invention] The conventional LB film is a conductor in which a good insulating LB film is formed on the metal aluminum deposition surface, but substantially no insulating oxide is present on the surface. (For example, conductor made of Au, Cr
There is a problem that it is difficult to obtain a good insulating LB film on the surface of a conductive material, a transparent conductive material, etc.), and its application to various fields is limited.

[Means for Solving the Problems] The present invention solves the above problems and provides good insulating properties even on the surface of a conductor in which substantially no insulating oxide is present on the surface under normal temperature and humidity conditions. The purpose is to form an insulating ultra-thin film shown, Au, Ag, Cr or an insulating ultra-thin film formed on a conductor consisting of a transparent conductor, at least a part of the conductor surface The present invention relates to an insulating ultrathin film having a thickness of 10 to 500Å and a metal oxide film of a metal different from the metal itself constituting the conductor and a Langmuir-Blodgett film, which are provided so as to cover the conductor in this order.

[Examples] The insulating ultrathin film of the present invention is a conductor (hereinafter, also referred to as a specific conductor) in which substantially no insulating oxide is present on the surface, such as Au, Ag, Cr, or SmO _2. It is formed on a conductor made of a transparent conductor such as ITO).

That substantially no insulating oxide is present on the surface,
The concept means that there is no insulating oxide film having a resistivity of 10 ⁸ Ω · cm or more on the surface.

The shape, thickness, application, etc. of the specific conductor are not particularly limited and may be any shape, thickness, application etc., but since the material forming the conductor is generally expensive, In many cases, it is formed as a film-like material on the base body, or in some cases as a patterned film-like material, and is often used as an electrode or the like.

The insulating ultrathin film of the present invention is a metal oxide film having a thickness of 10 to 500 Å formed on the specific conductor (an oxide film of a metal different from the metal itself constituting the specific conductor) and
The LB film is a film in which the metal oxide film and the LB film are laminated in this order. Although the detailed reason is not clear by providing the metal oxide film, the problem that a good insulating film is difficult to be formed when the LB film is directly formed on a specific conductor is solved. It

The metal oxide film has a resistivity of 10 ¹⁰ Ω · cm or more, preferably 10 ¹² Ω · cm or more and a film thickness of 10 to 500 as described above.
Å, preferably 20 ~ 200 Å as long as it is an insulating metal oxide film, there is no particular limitation on the type of oxide constituting the film, structure, ratio of metal atoms and oxygen atoms, even amorphous ones. It may be crystalline, amorphous including crystalline, or hydrated.

When the film thickness is less than 10Å, the LB formed on it
This is not preferable because the insulating property of the film is not sufficiently improved. Also, 500 Å or less is sufficient to improve the insulation of the LB film.
If it exceeds Å, 1000 Å or less, preferably several tens of
This is not desirable because it loses the characteristic of the LB film that it can be used at several hundred liters.

Further, although the metal oxide film may be formed on the entire surface of a specific conductor, it is not necessarily required to be formed on the entire surface, and the insulating property of the LB film formed on the specific conductor is not always required. Is formed so as to cover at least a part of the surface of the specific conductor, for example, 50% or more, preferably 70% or more, of the surface of the specific conductor so as to be scattered like islands as long as the desired value is obtained. Just do it.

Specific examples of the metal oxide film include, but are not limited to, silicon oxide, aluminum oxide, tantalum oxide, and the like. Among these, silicon oxide and aluminum oxide are preferable from the viewpoints of film forming properties of the LB film, adhesiveness with the LB film, and insulating properties.

As a method of manufacturing the metal oxide film, for example, a vapor deposition method, a sputtering method, a molecular beam epitaxy method, a metal organic chemical vapor deposition method, an atomic layer epitaxy method, a coating method, or the like can be adopted. The sputtering method is preferable in that a thin film having good insulating properties such as silicon oxide and aluminum oxide can be easily obtained, but the coating method is preferable in that a metal oxide film having a thickness of 10 to 500 Å can be formed at low cost.

For example, when an aluminum oxide film is formed as the metal oxide film by a coating method, a method using an aluminum metal complex as disclosed in US Pat. No. 4,040,083 can also be used. In this case, by changing the type of aluminum metal complex used, the speed of rotation during coating, the concentration of the aluminum metal complex solution, etc.
The thickness can be controlled.

Specific examples of the aluminum metal complex include aluminum monoethylacetoacetate diisopropylate, aluminum tris (ethylacetoacetate), aluminum tris (acetylacetonate), aluminum tris (malonate ethylate) aluminum diethylacetoacetate monoisopropylate. And so on.

Prior to forming the metal oxide film, surface treatment such as surface treatment of the long-chain fatty acid or its metal salt, which is usually performed in the field, on the surface of the conductor by the Langmuir-Blodgett method (hereinafter referred to as LB method). Alternatively, treatment with a silane coupling agent (for example, A-1100 and A-187 (both manufactured by Union Carbide Co.)) may be performed. By carrying out these treatments, it is possible to obtain the effect that the LB film accumulation property is improved and excellent insulation characteristics are obtained. When the metal oxide is silicon oxide or aluminum oxide having a hydroxyl group, treatment with a silane coupling agent is particularly effective from the viewpoint of improving the cumulative property of the LB film.

Next, the LB film in the present invention will be described.

A film formed on a substrate by an LB method such as a vertical dipping method, a horizontal deposition method, or a rotating cylinder method is called an LB film.

The LB film used for the insulating ultra-thin film of the present invention has an insulating property of, for example, 10
There is no particular limitation as long as it is a film having an insulating property of about ¹² Ω · cm or more, preferably about 10 ¹⁴ Ω · cm or more, but it is one of the purposes of using the LB film, for example, 1000 Å or less, preferably several From the viewpoint of obtaining the required performance with a film thickness of ten to several hundred Å, the film having the above thickness is preferable. Also
From the viewpoint of heat resistance and mechanical strength, a film obtained by accumulating a polymer compound (hereinafter, referred to as polymer compound (A)) that is modified so that it can be accumulated by the LB method is preferable. A polymer compound having a precursor structure in which the accumulated polymer compound has a 5-membered ring structure or a 6-membered ring structure (hereinafter, referred to as polymer compound (B)) is used to form a ring structure after being accumulated as an LB film. It is preferable that the film is a heat-resistant film and high mechanical strength.

Specific examples of the polymer compound (A) include, for example,
Examples thereof include amphoteric polymer compounds described in Japanese Patent Application No. 61-275533 and Japanese Patent Application No. 61-145714.

The cumulative number of the polymer compound (A) is preferably about 3 to 200.

Further, specific examples of the polymer compound (B) are selected from the amphoteric polymer compounds described in Japanese Patent Application No. 61-275533 and Japanese Patent Application No. 61-145714. Examples thereof include amphoteric polymer compounds having a precursor structure that forms a 5-membered ring or 6-membered ring containing a hetero atom.

The cumulative number of the polymer compound (B) is preferably about 3 to 200 as in the case of the polymer compound (A). After the accumulation, a 5-membered ring is formed by cyclization by heating cure or chemical cure. The LB film has a structure and a 6-membered ring structure.

The above description is an explanation of the LB film using a polymer compound, but it is not limited to these, and if the molecule is a so-called amphipathic compound having appropriate hydrophilicity and hydrophobicity, the LB film is used. Examples of such LB film that can be formed include long-chain alkyl groups, preferably 16 to 22 carbon atoms.
Alcohols, amines, amides, carboxylic acids and their metal salts and their derivatives having alkyl groups of
As a matter of course, a heat-resistant LB film material that has been extensively developed, for example, an LB film made of polyschiff base, polybenzimidazole, polyfumarate, or the like may be used.

The insulating ultra-thin film of the present invention is formed on a conductor on the surface of which substantially no insulating oxide is present, and the metal oxide and LB
It has a structure consisting of a film and is 10 ¹² Ω · cm or more, preferably
It has a volume resistivity of 10 ¹⁴ Ω · cm or more, a dielectric breakdown strength of 1 × 10 ⁶ V / cm or more, preferably 5 × 10 ⁶ V / cm or more.

By using the insulating ultrathin film of the present invention having such a structure, it is possible to form an insulating ultrathin film having a good insulating property even on a conductor having substantially no insulating oxide on its surface.

The specific conductor on which the insulating ultrathin film of the present invention is formed may or may not be provided on the substrate, and is not particularly limited, but usually the insulating ultrathin film of the present invention is used. Depending on the intended use, general inorganic materials such as glass, alumina and quartz, metals and semiconductors such as IV, III-V and II-VI groups such as metals, Si, GaAs and ZnS, PbTiO
A material such as a ferroelectric material such as ₃ , BaTiO ₃ , LiNbO ₃ , or LiTaO ₃ or a magnetic thin film is used as a substrate and is formed thereon.

Next, applications of the insulating ultrathin film of the present invention will be described.

The insulating ultra-thin film of the present invention has excellent heat resistance, chemical resistance, and mechanical properties, and is characterized by being a very thin film.
For example, it can be used in the electronics field.

A typical example of an electric / electronic device including the insulating ultrathin film of the present invention is a device having a specific conductor / insulating ultrathin film / specific conductor (hereinafter referred to as MIM) structure.

1 to 3 are schematic views of a device having a MIM structure.
An insulating substrate (3) or a semiconductor substrate (4) is used, and a specific conductor (2), an insulating ultrathin film (1), and a specific conductor (2) are laminated in this order.

FIG. 1 is an explanatory view showing the structure of a capacitor, and a humidity sensor can be obtained by tracking changes in capacitance due to humidity. Further, with this structure, a MIM structure transistor can be manufactured.

With the structure as shown in FIG. 2, a thermionic transistor can be manufactured.

As shown in FIG. 3, it can be used as a capacitor of a VLSI memory cell by forming a capacitor on a conductor or a semiconductor device.

A device of the type in which thermoelectrons are injected into a semiconductor can also be manufactured by using the configuration shown in FIG. It is also possible to make Josephson Junction (JJ) devices by using a superconductor such as Nb as the specific conductor.

Another example of the electric / electronic device including the insulating ultrathin film of the present invention is a device having an insulating ultrathin film / specific conductor (hereinafter referred to as IM) structure, and the IM structure device is shown in FIG. It is represented schematically. This IM structure device has the simplest structure, and the specific conductor (2)
It can be obtained by forming the insulating ultrathin film (1) of the present invention as an insulating film on. In addition, (3) is an insulating substrate.

As another application example, an insulating substrate (3) as shown in FIG.
Two independent specific conductor electrodes (2a) on top
By forming the insulating ultrathin film (1) of the present invention on the above,
It can also be used as a sensor for humidity and gas.

Further, in the device shown in FIG. 6, the semiconductor thin film (5) and the metal electrode (2b) are the insulating ultrathin film (1) on the insulating substrate (3) provided with the specific conductor electrode (2a). A) is formed on. Thus, when a semiconductor thin film is formed on the insulating ultrathin film of the present invention, it is not desirable that the heat during formation exceeds the heat resistance of the insulating ultrathin film,
The insulating ultra-thin film of the present invention is 400 ° C if the material of the LB film is selected.
Since it has heat resistance of amorphous silicon or ZnS: M whose formation temperature is 400 ° C or less, preferably about 200 to 300 ° C.
Since n, ZnSe: Mn, ZnS: TbF _3, etc. can be sufficiently deposited, and low-temperature forming technology for other semiconductors has been advanced, it is expected that many semiconductors will be usable in the future.

The methods used to form the semiconductor thin film include molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCV).
D), atomic layer epitaxy method (ALE), vapor deposition method, sputtering method, spray pyrolysis method, coating method and the like, which are usually used for producing a semiconductor thin film, can be mentioned without any particular limitation.

Hereinafter, the insulating ultrathin film of the present invention will be described in more detail based on examples.

Example 1 and Comparative Example 1 ITO formed as a specific conductor film on a substrate of NA-40 glass (manufactured by Hoya Glass Co., Ltd.) was etched into a stripe of 3 mm, and then argon gas pressure was set to 3 ×. Ten
^A silicon oxide film having a thickness of about 100 Å was formed by a sputtering method using a silicon oxide target under the conditions of ^-3 torr, oxygen gas pressure of 1 x 10 ^-4 torr and power of 130W. On this, LB
Cadmium stearate as a film, surface pressure 25 dyn / cm,
Eleven layers were accumulated by the vertical immersion method under the conditions of a cumulative speed of 30 mm / min, a water temperature of 20 ° C. and a pH of 6.2. The cumulative ratio was 1, and a good Y-type film was obtained.

Aluminum is used as the upper electrode to measure electrical properties
A sample was vapor-deposited with a width of 1 mm so as to be orthogonal to the ITO stripes.

The volume resistivity and dielectric breakdown strength calculated using an insulating ultrathin film thickness of 350Å are 5 × 10 ¹⁴ Ω · cm and 1 ×, respectively.
It was 10 ⁶ V / cm or more.

The ultrathin film produced in the same manner as in Example 1 except that the silicon oxide film was not formed had a volume resistivity and a dielectric breakdown strength of 1 × 10 ¹² Ω · cm and 1 × 10 ⁶ V / cm or more, respectively. It was

As can be seen from these measurement results, the volume resistivity was improved by two orders of magnitude by forming the silicon oxide film.

Example 2 and Comparative Example 2 ITO formed on NA-40 glass was etched into a stripe of 3 mm, and then a 2 wt% solution of aluminum monoethylacetoacetate diisopropylate was spun to form a metal oxide. It was spin-coated at several 5000 rpm and heat-treated at 350 ° C. for 15 minutes. The thickness of the obtained aluminum oxide film was about 50Å.

On the other hand, 2.18 g (0.01 mol) of pyromellitic dianhydride and 5.40 g (0.02 mol) of stearyl alcohol were reacted in a flask under a dry nitrogen stream at about 100 ° C. for 3 hours.

The obtained reaction product is dissolved in 40 cc of hexamethylphosphamide, cooled to 0 to 5 ° C, 2.38 g of thionyl chloride is added dropwise at about 5 ° C, and after the addition, it is kept at about 5 ° C for 1 hour to complete the reaction. Let

After that, 2 g (0.01 mol) of diaminodiphenyl ether dissolved in 50 cc of dimethylacetamide was added dropwise at 0 to 5 ° C., and after reacting for about 1 hour after addition, the reaction liquid was distilled water 60
The reaction product was deposited by pouring into 0 cc. The precipitate was filtered and dried under reduced pressure at about 40 ° C. to obtain about 9 g of a pale yellow powder.

The obtained powder was subjected to molecular weight measurement by 1R spectrum analysis method, thermal analysis method (TGA-DTA) and GPC method,
It was found that the desired distearyl polyamic acid ester having a molecular weight of about 50,000 was obtained.

The obtained powder and stearyl alcohol are 1 / molar.
Dissolve in a mixed solvent of distilled chloroform / dimethylacetamide = 8/2 (volume ratio) so that it becomes 1, 25 ml
A developing solution for LB film, which was made into the solution of 1., was prepared.

A monomolecular film was formed on the re-distilled water at 20 ℃ using the obtained developing solution, the surface pressure was kept at about 25 dyn / cm, and the cumulative velocity was 10 mm / m.
Twenty-one layers were accumulated on the ITO-glass substrate on which the aluminum oxide thin film was formed by the in-vertical dipping method. Cumulative ratio is 1
Thus, a good Y-type film was obtained. After that, the accumulated film is 400
The mixture was heated at 0 ° C for 1 hour to promote the imidization reaction.

In order to measure the electrical characteristics, aluminum was vapor-deposited in a width of 1 mm as an upper electrode so as to be orthogonal to the ITO stripes and used as a sample.

The volume resistivity and dielectric breakdown strength calculated using a thickness of 150 Å of the insulating ultra-thin film are 2 × 10 ¹⁵ Ω ・ cm to 4 × 10 ^{15 respectively.}
Ω · cm and 5 × 10 ⁶ V / cm or more.

The ultrathin film produced in the same manner as in Example 2 except that aluminum oxide was not formed had a volume resistivity and a dielectric breakdown strength of 2 × 10 ¹³ Ω · cm and 1 × 10 ⁶ V / cm or more, respectively. The volume resistivity was improved by two orders of magnitude by forming an aluminum thin film.

Example 3 and Comparative Example 3 Examination was conducted in the same manner as in Example 1 and Comparative Example 1 except that a glass substrate on which Au and Cr were deposited was used instead of the glass substrate on which ITO was formed. . As a result of measuring the electrical properties, the formation of silicon oxide showed an improvement in the volume resistivity of 1 to 2 digits.

[Effects of the Invention] According to the present invention, it is possible to form an ultrathin film having good insulating properties even on a conductor on the surface of which substantially no insulating oxide is present.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 3 are explanatory views of a typical example of a device having a MIM structure using an insulating ultrathin film of the present invention, and FIG. 4 is an IM structure using an insulating ultrathin film of the present invention. 5 is an explanatory view of an example of the device of FIG. 5, FIG. 5 is an explanatory view of another device using the insulating ultrathin film of the present invention, and FIG. 6 is an explanatory view of still another device of the present invention including the insulating ultrathin film. . (Main symbols in the drawings) (1): Ultra-thin insulating film (2): Specific conductor

Claims (5)

[Claims] 1. An insulating ultrathin film formed on a conductor made of Au, Ag, Cr or a transparent conductor, and having a thickness of 10 to 500Å provided so as to cover at least a part of the surface of the conductor.
2. An insulating ultrathin film in which a metal oxide film of a metal different from the metal itself constituting the conductor and a Langmuir-Blodgett film are laminated in this order. 2. The insulating ultra-thin film according to claim 1, wherein the metal oxide film is a film of silicon oxide or aluminum oxide. 3. The insulating ultrathin film according to claim 1, wherein the metal oxide film has a thickness of 10 to 200Å. 4. The insulating superstructure according to claim 1, wherein the Langmuir-Blodgett film is a film obtained by accumulating by a Langmuir-Blodgett method a polymer compound modified so that it can be accumulated by the Langmuir-Blodgett method. Thin film. 5. The insulating ultrathin film according to claim 1, wherein the Langmuir-Blodgett film is a film formed by accumulating a polymer compound having a precursor structure of a 5-membered ring or a 6-membered ring and then forming a ring structure. .