Porous body and method of manufacturing the same Number:7,074,480 from the United States Patent and Trademark Office (PTO) owispatent A nanostructure is a porous body comprising a plurality of pillar-shaped pores and a region surrounding them, said region being an oxide amorphous region formed so as to contain C, Si, Ge or a material of a combination of them. Such a nanostructure can be used as functional material that can be used for light emitting devices, optical devices and microdevices. It can also be used as filter.<H manufacturing, method, Porous, body, and, 7074480.html, Patent, pto, 7074480

Title: Porous body and method of manufacturing the same

Abstract: A nanostructure is a porous body comprising a plurality of pillar-shaped pores and a region surrounding them, said region being an oxide amorphous region formed so as to contain C, Si, Ge or a material of a combination of them. Such a nanostructure can be used as functional material that can be used for light emitting devices, optical devices and microdevices. It can also be used as filter.

Patent Number: 7,074,480 Issued on 07/11/2006 to Fukutani, et al.

Inventors: Fukutani; Kazuhiko (Kanagawa, JP); Den; Tohru (Tokyo, JP)
Assignee: Canon Kabushiki Kaisha (Tokyo, JP)

Appl. No.: 640047

Filed: August 14, 2003

Foreign Application Priority Data


Mar 15, 2002 [JP]			2002-073112
Mar 15, 2002 [JP]			2002-073113
Dec 13, 2002 [JP]			2002-363165

Current U.S. Class: 428/312.2 ; 428/312.6; 428/312.8; 428/314.2; 428/315.5; 428/315.7; 428/318.4; 428/446; 428/620; 428/634; 428/641

Current International Class: B32B 3/00 (20060101)

Field of Search: 428/312.2,312.6,312.8,314.2,315.5,315.7,318.4,446,697,701,702,630,632,633,641 977/DIG.1

References Cited [Referenced By]

U.S. Patent Documents


5244828	September 1993	Okada et al.
5858457	January 1999	Brinker et al.
6027796	February 2000	Kondoh et al.
6214738	April 2001	Aiba et al.
6265321	July 2001	Chooi et al.
6464853	October 2002	Iwasaki et al.
6525461	February 2003	Iwasaki et al.
6541386	April 2003	Aiba et al.
6602620	August 2003	Kikitsu et al.
6610463	August 2003	Ohkura et al.
2001/0036563	November 2001	Watanabe et al.
2002/0014621	February 2002	Den et al.
2002/0031008	March 2002	Den et al.
2002/0086185	July 2002	Yasui et al.
2003/0001150	January 2003	Iwasaki et al.
2004/0001964	January 2004	Ohkura et al.
2004/0048092	March 2004	Yasui et al.
2005/0053773	March 2005	Fukutani et al.

Foreign Patent Documents


52-78403	Jul., 1977	JP
62-270473	Nov., 1987	JP
63-220411	Sep., 1988	JP
5-55545	Mar., 1993	JP
7-73429	Mar., 1995	JP
9-157062	Jun., 1997	JP
2001-101644	Apr., 2001	JP
2001-261376	Sep., 2001	JP
2001-273622	Oct., 2001	JP
WO 03/069677	Aug., 2003	WO
WO 03/078685	Sep., 2003	WO

Other References

M Jacobs et al., "Unbalanced Magnetron Sputtered Si--Al Coatings: Plasma Conditions and Film Properties Versus Sample Bias Voltage," 116-119 Surface and Coatings Technology 735-41 (1999). cited by other .
C.D. Adams et al., "Phase Separation During Co-Deposition of Al--Ge Thin Films," 7(3) J. Mater. Res. 653-67 (Mar. 1992). cited by other .
C.D. Adams et al., "Transition from Lateral to Transverse Phase Separation During Film Co-deposition," 59(20) Appl. Phys. Lett. 2535-37 (Nov. 1991). cited by other .
M. Atzmon et al., "Phase Separation During Film Growth," 42(2) J. Appl. Phys. 442-46 (Jul. 1992). cited by other .
C.D. Adams, et al. "Monte Carlo Simulation of Phase Separation During Thin-Film Codeposition," 74(3)J. Appl. Phys. 1707-15 (Aug. 1993). cited by other .
M. Atzmon et al., "Phase Separation During Film Growth," 72(2) J. Appl. Phys. 442-46 (Jul. 1992). cited by other.

Primary Examiner: Xu; Ling
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto

Parent Case Text

This application is a continuation of International Application No. PCT/JP03/03000, filed Mar. 13, 2003, which claims the benefit of Japanese Patent Application Nos. 2002-073112, filed Mar. 15, 2002, 2002-073113, filed Mar. 15, 2002, and 2002-363165, filed Dec. 13, 2002.

Claims

What is claimed is:

1. A structure comprising: a substrate; and a porous body formed on the substrate, the porous body comprising a plurality of pillar-shaped pores and a region surrounding them, said region being an amorphous silicon oxide, amorphous Si.sub.xGe.sub.1-x (0<x<1) oxide or an amorphous germanium oxide, wherein the direction of depth of said pillar-shaped pores is substantially perpendicular relative to the substrate, wherein an average interval between centers of adjacent pores is 30 nm or less, wherein said region contains aluminum, and wherein a concentration of the aluminum on or near a pore wall of said region is greater than the concentration of the aluminum inside the pore wall.

2. The structure according to claim 1, wherein said pillar-shaped pores are substantially not branched.

3. The structure according to claim 1, wherein the diameters of said pillar-shaped pores are not greater than 20 nm.

4. The structure according to claim 1, wherein the diameters of said pillar-shaped pores are substantially same in the direction of depth.

5. The structure according to claim 1, wherein an amount of the aluminum contained in said region is 1 to 20 atomic percent.

6. A structure comprising: a substrate; and a porous body formed on the substrate, the porous body comprising a plurality of pillar-shaped pores and a region surrounding them, said region being an amorphous silicon oxide, amorphous Si.sub.xGe.sub.1-x (0<x<1) oxide or an amorphous germanium oxide, wherein the direction of depth of said pillar-shaped pores is substantially perpendicular relative to the substrate, wherein an average interval between centers of adjacent pores is 30 nm or less, wherein said region contains aluminum, and wherein said region has a varied concentration distribution of the aluminum in an in-plane direction.

7. The structure according to claim 1, wherein said pillar-shaped pores are substantially not branched.

8. The structure according to claim 6, wherein the diameters of said pillar-shaped pores are not greater than 20 nm.

9. The structure according to claim 6, wherein the diameters of said pillar-shaped pores are substantially same in the direction of depth.

10. The structure according to claim 6, wherein an amount of the aluminum contained in said region is 1 to 20 atomic percent.

11. A structure comprising: a substrate; and a porous body formed on the substrate, the porous body comprising a plurality of cylindrical pores and a region surrounding them, said region being an amorphous silicon oxide, amorphous Si.sub.xGe.sub.1-x (0<x<1) oxide or an amorphous germanium oxide, wherein the direction of depth of said cylindrical pores is substantially perpendicular relative to the substrate, wherein an average interval between centers of adjacent pores is 30 nm or less, wherein said region contains aluminum, and wherein a concentration of the aluminum on or near a pore wall of said region is greater than the concentration of the aluminum inside the pore wall.

12. A structure comprising: a substrate; and a porous body formed on the substrate, the porous body comprising a plurality of cylindrical pores and a region surrounding them, said region being an amorphous silicon oxide, amorphous Si.sub.xGe.sub.1-x (0<x<1) oxide or an amorphous germanium oxide, wherein the direction of depth of said cylindrical pores is substantially perpendicular relative to the substrate, wherein an average interval between centers of adjacent pores is 30 nm or less, wherein said region contains aluminum, and wherein said region has a varied concentration distribution of the aluminum in an in-plane direction.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a porous body and a method of manufacturing the same.

2. Related Background Art

In recent years, microstructures to be used as functional materials have been objects of growing interest.

Known techniques for preparing such a microstructure include those relying on the semiconductor processing technology, particularly the micro-pattern forming technology such as photolithography, so as to directly prepare a microstructure (see, inter alia, Japanese Patent Application Laid-Open No. 5-55545 (p. 3, FIG. 1)).

Apart from the use of the semiconductor processing technology, there are also known techniques that utilize the phenomenon of self-organization or self-formation. These techniques have been developed to produce novel microstructures on the basis of orderly formed structures that are found in the nature.

While many researches are under way, using techniques that utilize the phenomenon of self-organization or self-formation, because such techniques seem to be promising for realizing microstructures of the order of nanometers, to say nothing micrometers, they are still not sufficiently proven. Therefore, there is a strong demand for novel microstructures and proven methods for manufacturing such novel microstructures.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a novel porous body and a method of manufacturing the same.

According to the present invention, the above object is achieved by providing a porous body comprising a plurality of pillar-shaped pores and a region surrounding them, the region being an oxide amorphous region formed so as to contain Si, Ge or a material of a combination of them.

Preferably, the pillar-shaped pores are substantially not branched. Preferably, the average intercentral distance of the plurality of pillar-shaped pores is not greater than 30 nm. Preferably, the diameters of the pillar-shaped pores are not greater than 20 nm. According to the invention, preferably, the diameters of the pillar-shaped pores are substantially same in the direction of depth. The oxide amorphous region may contain aluminum. When the porous body is formed on a substrate, preferably, the direction of depth of the pillar-shaped pores is substantially perpendicular relative to the substrate.

In another aspect of the present invention, there is provided an oxide porous body obtained from a structural body formed so as to contain a first material and a second material by removing the first material from the structural body, the structural body having a structure including pillar-shaped members formed so as to contain the first material and an amorphous region formed so as to contain the second material, the pillar-shaped members being surrounded by the amorphous region, the structural body containing the second material at a ratio of not smaller than 20 atomic % and not greater than 70 atomic % relative to the total quantity of the first and second materials.

Preferably, the first material is aluminum.

Preferably, the second material is Si, Ge, SiGe or a material of a combination of them.

Preferably, the average intercentral distance of the plurality of pillar-shaped pores is not greater than 30 nm and the diameters of the pillar-shaped pores are not greater than 20 nm.

In still another aspect of the present invention, there is provided a method of manufacturing a porous body comprising a step of preparing a structural body formed so as to contain a first material and a second material and including pillar-shaped members formed so as to contain the first material and surrounded by a region formed so as to contain the second material, a removal step of removing the pillar-shaped members from the structural body and a step of oxidizing the region.

Preferably, the structural body contains the second material at a ratio of not smaller than 20 atomic % and not greater than 70 atomic % relative to the total quantity of the first and second materials.

Preferably, the first material is aluminum. Preferably, the second material is Si, Ge, SiGe or a material of a combination of them.

Preferably, the structural body is prepared by using a film-forming process of forming film in a non-equilibrium state. The removal step may be a wet etching using acid or alkali.

After the removal step, the pore diameters of narrow pores formed in the removal step may be enlarged. The process of enlarging the pore diameters may be conducted before oxidizing the region or after oxidizing the region. It may alternatively be conducted at the time of oxidizing the region.

Preferably, the diameters of the pillar-shaped members are not greater than 20 nm and the average intercentral distance of the plurality of pillar-shaped members is not greater than 30 nm.

The region may be processed for oxidization after forming the porous body by the removal step or simultaneously with the process of forming narrow pores in the structural body by the removal step.

In still another aspect of the invention, there is provided a method of manufacturing a porous body comprising a step of preparing a structural body formed so as to contain aluminum and silicon and including pillar-shaped members formed so as to contain aluminum and a silicon region surrounding the pillar-shaped members, the structural body containing silicon at a ratio of not smaller than 20 atomic % and not greater than 70 atomic % relative to the total quantity of aluminum and silicon, a step of forming a porous body by removing the pillar-shaped members from the structural body and a step of oxidizing the porous body.

The silicon region may contain germanium.

In still another aspect of the invention, there is provided a method of manufacturing a porous body comprising a step of preparing a structural body including aluminum-containing pillar-shaped structures and a silicon region surrounding the pillar-shaped structures, the structural body containing silicon at a ratio of not smaller than 20 atomic % and not greater than 70 atomic % relative to the total quantity of aluminum and silicon and a step of processing the structural body by anodic oxidization.

A porous body according to the invention can find applications in filters and mask materials.

In still another aspect of the invention, there is provided an oxide porous body having pillar-shaped narrow pores and a region surrounding them, the average diameters of the narrow pores being not greater than 20 nm and the average intercentral distance of the narrow pores is not greater than 30 nm. The region contains oxide of a second material that may or may not contain oxide of a first material.

In a still another aspect of the invention, there is provided a method of manufacturing an oxide porous body comprising a step of preparing a structural body formed so as to contain a first material and a second material and including pillar-shaped members formed so as to contain the first material and surrounded by a region formed so as to contain the second material, the structural body containing the second material at a ratio of not smaller than 20 atomic % and not greater than 70 atomic % relative to the total quantity of the first and second materials, a removal step of removing the pillar-shaped members from the structural body and a step of oxidizing the structural body to be conducted after or simultaneously with the removal step.

Preferably, the first material is aluminum and the second material is silicon, germanium or silicon and germanium.

In a further aspect of the present invention, there is provided a porous body comprising pillar-shaped holes and a region surrounding them, the region being an insulating region. The entire porous body may be oxidized or, alternatively, the narrow pore walls and their vicinities may be selectively oxidized. Unoxidized regions may be made to remain in the inside of the narrow pore walls.

The region (namely porous body) may contain aluminum by not smaller than 1% and not greater than 20%. The unit is atomic %.

If the first material is aluminum and the second material is silicon, the above ratios refer to those of aluminum contained in the Si porous body. The oxygen contained in the porous body is excluded from the above ratios.

It is possible to provide a filter or a mask material to be used for etching processes by utilizing a porous body according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic illustrations of an oxide porous body according to the invention;

FIGS. 2A, 2B, 2C and 2D are schematic illustrations of a mode of carrying out a method of manufacturing an oxide porous body according to the invention, showing different steps thereof;

FIG. 3 is a schematic illustration of another mode of carrying out a method of manufacturing an oxide porous body according to the invention, showing different steps thereof;

FIG. 4 is a schematic illustration of still another mode of carrying out a method of manufacturing an oxide porous body according to the invention, showing different steps thereof;

FIGS. 5A, 5B, 5C, 5D and 5E are schematic illustrations of still another mode of carrying out a method of manufacturing an oxide porous body according to the invention, showing different steps thereof;

FIGS. 6A, 6B, 6C, 6E and 6D are schematic illustrations of still another mode of carrying out a method of manufacturing an oxide porous body according to the invention, showing different steps thereof;

FIG. 7 is a schematic illustration of a film forming method that can be used for a structural body according to the invention;

FIG. 8 is a schematic illustration of an anodic oxidation system that can be used for the purpose of the invention; and

FIG. 9 is a schematic illustration of an embodiment of oxide porous body according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be described in greater detail by referring to the accompanying drawings.

Firstly, a structural body that is applicable to the present invention will be described.

(1) Structural Body Applicable to the Present Invention

A structural body that is applicable to the present invention is characterized in that it is formed so as to contain a first material and a second material and includes pillar-shaped members formed so as to contain the first material and surrounded by an amorphous region formed so as contain the second material and that it contains the second material at a ratio of not smaller than 20 atomic % and not greater than 70 atomic % relative to the total quantity of the first and second materials. A porous body according to the invention is obtained by a method comprising a removal step of removing the pillar-shaped members from the structural body and an oxidation step. As for these two processing steps, the oxidation steps may be conducted simultaneously with the removal step or after the removal step. Alternatively, the removal step may be conducted after the oxidation step. The expression of simultaneously as used herein does not mean that the two steps need to be conducted rigorously at the same time. In other words, there may be acceptable instances where the body is oxidized as a result of the removal step involving an etching operation.

The above ratio is the content ratio of the second material relative the total amount of the first and second materials that the structural body comprises. Preferably, it is not smaller than 25 atomic % and not greater than 65 atomic %. More preferably, it is not smaller than 30 atomic % and not greater than 60 atomic %.

For the purpose of the invention, it is sufficient that pillar-shaped profiles are substantially realized in the structural body. For example, the pillar-shaped members may contain the second material as ingredient, while the surrounding region may contain the first material. Additionally, the pillar-shaped members and the surrounding region may contain oxygen and/or argon.

The ratio can be determined by quantitative analysis using inductively coupled plasma atomic emission spectroscopy (ICP-AES). While atomic % is used as unit for the purpose of the present invention, the expression of not smaller than 20 atomic % and not greater than 70 atomic % may be paraphrased as not smaller than 20.65 wt % and not greater than 70.84 wt % if wt % is used as unit (an atomic weight of 26.982 is used for Al of the first material and an atomic weight of 28.086 is used for Si of the second material for the above paraphrase).

Substances that can be used for the first material include Al, Au, Ag and Mg. On the other hand, substances that can be used for the second material include Si, Ge and Si.sub.xGe.sub.1-x. Particularly, it is desirable that a material that can take an amorphous form is used for the second material. A combination of such materials that have a eutectic point in the phase equilibrium graph of the two ingredient systems of the two materials are preferably used for the first and second materials (materials of a so-called eutectic system). Particularly, for the purpose of the invention, the eutectic point is preferably not less than 300.degree. C., more preferably not less than 400.degree. C. A eutectoid system may also be used for the first and second materials. Preferable combinations of the first and second materials include the use of Al for the first material and the use of Si for the second material, the use of Al for the first material and the use of Ge for the second material and the use of Al for the first material and the use of Si.sub.xGe.sub.1-x (0<x<1) for the second material. The ratio of the first material (e.g., aluminum) contained in the region that the surrounding body comprises is preferably not smaller than 1 atomic % and not greater than 20 atomic %. The above ratio does not take the oxygen contained in the surrounding body into consideration.

It is desirable that the region surrounding the pillar-shaped members is amorphous.

The pillar-shaped members show a cylindrical or elliptic plan view.

Thus, the plurality of pillar-shaped members are distributed in the matrix formed so as to contain the second material. While the diameters of the pillar-shaped members (assuming that the pillar-shaped members show a cylindrical plan view) can be controlled by controlling the chemical composition of the structural body (namely, the content ratio of the second material), the average diameter is not smaller than 0.5 nm and not greater than 50 nm, preferably not smaller than 0.5 nm and not greater than 20 nm, more preferably not smaller than 0.5 nm and not greater than 10 nm. The term of diameter as used herein refers to 2r in FIG. 1B. If the plan view is elliptic, it is sufficient that the length of the major axis is found within the above defined range. The average diameter can be obtained by observing a picture showing the pillar-shaped members actually taken by means of SEM photography (in an area of about 100 nm.times.100 nm) directly or by processing the image of the picture by means of a computer. The lower limit of the average diameter is 1 nm or more, preferably several nanometers or more from a practical point of view, although it may depend on the device to which the structural body is applied and the processing operation to which the structural body is subjected.

The average intercentral distance 2R (see FIG. 1B) of the plurality of pillar-shaped members is not smaller than 2 nm and not greater than 30 nm, preferably not smaller than 5 nm and not greater than 20 nm, more preferably not smaller than 5 nm and not greater than 15 nm. It may be needless to say that at least the intercentral distance 2R needs to be such that any two adjacently located pillar-shaped members do not contact each other.

It is particularly preferable that the average diameter is not greater than 20 nm and the average intercentral distance is not greater than 30 nm.

The structural body is preferably a film-shaped structural body. If such is the case, the pillar-shaped members are distributed in the matrix formed so as to contain the second material in such a way that they are substantially perpendicular relative to the intraplanar direction of the film. While the film thickness of the film-shaped structural body is not subjected to any particular limits, it is normally within a range between 1 nm and 100 .mu.m. A more practical range that takes the processing time into consideration is between 1 nm and 1 .mu.m. Particularly, it is desirable that the pillar-shaped structure is maintained when the film thickness exceeds 300 nm. The pillar-shaped members show a pillar-shaped structure that is substantially not branched in the direction of height.

The structural body is preferably a film-shaped structural body and may be arranged on a substrate. While there are not limitations to the use of a substrate, substrates that can be used for the purpose of the invention include insulating substrates such as quartz glass substrates, semiconductor substrates such as silicon substrates, gallium arsenide substrates, indium phosphide substrates and so on, metal substrates of aluminum etc. and flexible substrates (e.g., of polyimide resin) provided that a structural body can be formed on the substrate that operates as support member. Pillar-shaped members are formed on a substrate in such a way that they are substantially perpendicular relative to the substrate. A carbon substrate may also be used for the purpose of the invention. When a silicon substrate is used, it may be a P-type, N-type, high resistance or low resistance substrate.

The structural body can be prepared by utilizing a process for forming film in a non-equilibrium state. While a sputtering process is preferably used for forming film for the purpose of the invention, any other appropriate film forming process for forming film in a non-equilibrium state may also be used. Film forming methods for forming film in a non-equilibrium state that can be applied to the present invention include resistance heating evaporation, electron beam evaporation (EB evaporation) and ion plating. Sputtering methods that can be used for the purpose of the invention include magnetron sputtering, RF sputtering, ECR sputtering and DC sputtering. When a sputtering method is used, the film forming operation is conducted in an argon gas atmosphere of a reaction system where the internal pressure is held to about 0.2 to 1 Pa or about 0.1 to 1 Pa. For the sputtering operation, the first material and the second material may be brought in separately as target materials. Alternatively, a target material obtained by baking in advance the first and second materials showing a desired quantity ratio may be used. It is desirable to conduct the sputtering operation in such a way that plasma does not practically contact the substrate on which a structural body grows.

When forming a structural body on a substrate, the substrate temperature is held not lower than 20.degree. C. and not higher than 300.degree. C., preferably not lower than 20.degree. C. and not higher than 200.degree. C., more preferably not lower than 100.degree. C. and not higher than 150.degree. C.

A porous body that comprises a number of pillar-shaped pores is produced when the pillar-shaped members are removed from the structural body (by wet etching or dry etching). It is only necessary to selectively remove the pillar-shaped members by etching. The etching solution to be used for the etching process may suitably be selected from phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid and other acids. It is desirable that the pores of the porous body that are formed by removing the pillar-shaped members are independent from each other without connecting with each other. When oxidizing the porous body, the structural body having narrow pores may be completely oxidized or, alternatively, areas that are not oxidized may be left in the inside of the pore walls.

(2) The First and Second Materials of the Structural Body

Now, the ratio of the first material (for forming pillar-shaped members) and the second material (for forming a region surrounding the pillar-shaped members) of a structural body applicable to the present invention will be discussed below.

The present invention that provides a porous body as disclosed herein is based on the achievement of the inventors of the present invention for preparing a structural body that is realized as a result of research efforts.

Referring to FIG. 7, an aluminum/silicon composite film (which is a structural body applicable to the present invention) containing silicon by 55 atomic % relative to the total quantity of aluminum and silicon was formed to a film thickness of about 200 nm on a glass substrate by RF magnetron sputtering (generating plasma 14).

As target, eight 15 mm square silicon chips 13 were put on a 4-inch aluminum target 12 as shown in FIG. 7. The sputtering conditions were as follows. An RF power source was used with Ar flow rate: 50 sccm, discharge pressure: 0.7 Pa and supplied power: 1 kW. The substrate was held at room temperature.

While a target prepared by putting eight silicon chips 13 on an aluminum target 12 was used, the number of silicon chips is not limited to eight. In other words, it is only necessary that the silicon content in the aluminum/silicon composite film is somewhere around 55 atomic % and therefore the number of chips may be changed depending on the sputtering conditions. Furthermore, the target is not limited to one prepared by putting silicon chips on an aluminum target and a target prepared by putting aluminum chips on a silicon target or one prepared by sintering powdery silicon and aluminum may alternatively be used.

Then, the silicon content (atomic %) relative to the total quantity of aluminum and silicon in the obtained aluminum/silicon composite film was analyzed by means of ICP-AES (inductively coupled plasma atomic emission spectroscopy). As a result, it was found that the silicon content was about 55 atomic % relative to the total quantity of aluminum and silicon. For the convenience of measurement, an aluminum/silicon composite film deposited on a carbon substrate was used.

Thereafter, the aluminum/silicon composite film was observed through an FE-SEM (field emission scanning electron microscope). It was found that cylindrical aluminum nanostructures were two-dimensionally arranged and surrounded by silicon. The average pore diameter of the aluminum nanostructures was 3 nm and the average intercentral gap of the pores was 7 nm. When a cross section was observed through an FE-SEM, the aluminum nanostructures were independent from each other and showed a height of 200 nm.

The specimen was observed by X-ray diffractometry but it was not possible to confirm the existence of a peak that indicates the crystallinity of silicon. In other words, the silicon of the specimen was amorphous. On the other hand, a number of peaks indicating the crystallinity of aluminum were observed to prove that at least part of the aluminum was polycrystalline.

Thus, it was possible to prepare an aluminum/silicon nanostructure containing aluminum wires with an average intercentral gap 2R of 7 nm, an average diameter 2r of 3 nm and a height L of 200 nm that were surrounded by silicon.

In this way, the inventors of the present invention found that it is possible to produce an aluminum/silicon nanostructure comprising aluminum quantum dots or aluminum quantum wires with a size of several nanometers in a silicon matrix arranged on the surface of a substrate by forming an aluminum/silicon composite film by means of a film forming process of forming a substance in a non-equilibrium state.

(Example for Comparison)

As specimen A for comparison, an aluminum/silicon composite film containing silicon by 15 atomic % relative to the total quantity of aluminum and silicon was formed to a film thickness of about 200 nm on a glass substrate by sputtering. As target, two 15 mm square silicon chips 13 were put on a 4-inch aluminum target 12. The sputtering conditions were as follows. An RF power source was used with Ar flow rate: 50 sccm, discharge pressure: 0.7 Pa and supplied power: 1 kW. The substrate was held at room temperature.

Thereafter, the specimen A for comparison was observed through an FE-SEM (field emission scanning electron microscope). It was found that, when observed from right above the substrate, the aluminum portions did not show any cylindrical profile but linked to each other. In other words, a microstructure in which pillar-shaped structures of aluminum were homogeneously distributed in a silicon region could not be obtained. Furthermore, they showed a size far greater than 10 nm. When a cross section was observed through an FE-SEM, the aluminum portions showed a width far greater than 15 nm. Then, the silicon content (atomic %) relative to the total quantity of aluminum and silicon in the obtained aluminum/silicon composite film was analyzed by means of ICP-AES (inductively coupled plasma atomic emission spectroscopy). As a result, it was found that the silicon content was about 15 atomic % relative to the total quantity of aluminum and silicon.

Additionally, as specimen B for comparison, an aluminum/silicon composite film containing silicon by 75 atomic % relative to the total quantity of aluminum and silicon was formed to a film thickness of about 200 nm on a glass substrate by sputtering. As target, fourteen 15 mm square silicon chips 13 were put on a 4-inch aluminum target 12. The sputtering conditions were as follows. An RF power source was used with Ar flow rate: 50 sccm, discharge pressure: 0.7 Pa and supplied power: 1 kW. The substrate was held at room temperature.

Thereafter, the specimen B for comparison was observed through an FE-SEM (field emission scanning electron microscope). When observed from right above the substrate, no aluminum area was found on the surface of the specimen. When a cross section was observed through an FE-SEM, no aluminum was found either. Then, the silicon content (atomic %) relative to the total quantity of aluminum and silicon in the obtained aluminum/silicon composite film was analyzed by means of ICP-AES (inductively coupled plasma atomic emission spectroscopy). As a result, it was found that the silicon content was about 75 atomic % relative to the total quantity of aluminum and silicon.

Other specimens were prepared in conditions same as those used for the specimen A for comparison except that the number of silicon chips was changed so that the silicon content ratios of the obtained specimens of aluminum/silicon composite films were 20 atomic %, 25 atomic %, 35 atomic %, 50 atomic %, 55 atomic %, 60 atomic %, 65 atomic % and 70 atomic % relative to the total quantity of aluminum and silicon. A specimen that showed microstructures in which pillar-shaped aluminum structures were distributed in the silicon region was rated as o, whereas a specimen that did not show any such microstructure was rated as x. The results of evaluation are shown in Table 1 below. From the viewpoint of uniformity of pillar-shaped structures, the silicon content ratio is preferably not smaller than 30 atomic % and not greater than 60 atomic %. The contained aluminum shows only a low level of crystallinity and was almost amorphous when the silicon content ratio is as high as 65 or 70 atomic %.

TABLE-US-00001 TABLE 1 silicon content ratio (atomic %) microstructures 15 (Specimen A for Comparison) x 20 o 25 o 35 o 50 o 55 o 60 o 65 o 70 o 75 (Specimen B for Comparison) x

As described above, it is possible to produce a structure in which pillar-shaped structures of aluminum are uniformly distributed in a silicon region by regulating the silicon content so as to be not smaller than 20 atomic % and not greater than 70 atomic % relative the total quantity of aluminum and silicon. The pore diameter of the pillar-shaped structures can be controlled and highly linear aluminum wires can be produced by appropriately selecting the content ratios of aluminum and silicon. The obtained microstructures can also be observed by means of a TEM (transmission electron microscope) instead of an SEM.

As still another specimen for comparison, or specimen C, an aluminum/silicon composite film containing silicon by 55 atomic % relative to the total quantity of aluminum and silicon was formed to a film thickness of about 200 nm on a glass substrate by sputtering. As target, eight 15 mm square silicon chips 13 were put on a 4-inch aluminum target 12. The sputtering conditions were as follows. An RF power source was used with Ar flow rate: 50 sccm, discharge pressure: 0.7 Pa and supplied power: 1 kW. The substrate was held to 350.degree. C.

Thereafter, the specimen C for comparison was observed through an FE-SEM (field emission scanning electron microscope). When observed from right above the substrate, large aluminum blocks were found. It was also found by X-ray diffractometry that silicon had been crystallized. In other words, no nanostructures of aluminum having a pillar-shaped profile were found and it was found that the silicon region had been crystallized. In other words, the silicon region was not amorphous. Thus, it may be safe to assume that, when the temperature of the silicon substrate is too high, the silicon moves into a more stable state so that it is no longer possible to cause a film to grow so as to produce nanostructures of aluminum.

In a mode of carrying out the invention to obtain a structural body in which pillar-shaped members are uniformly distributed, it is preferable to select a composition Al:Si=55:45 for the target.

While aluminum and silicon are used respectively as the first and second materials in the above description, similar results were obtained when other combinations of substances selected from those listed above were used.

Now, a porous body formed by utilizing a structure as described above and a method of manufacturing a porous body according to the invention will be discussed below.

(3) A Porous Body According to the Invention

A porous body according to the invention is characterized in that it comprises a plurality of pillar-shaped holes and a region surrounding them and the region is an oxide amorphous region formed so as to contain Si, Ge or a material of a combination of them.

Referring to FIG. 1A, reference symbol 1 denotes a plurality of pillar-shaped holes and reference symbol 2 denotes an oxide region surrounding them (which is typically formed from Si, Ge or a material of a combination of them). In FIG. 1B, reference symbol 3 denotes a substrate.

FIG. 1B is a schematic cross sectional view of the porous body taken along broken line 1B--1B in FIG. 1A.

Thus, according to the invention, there is provided a porous body having pores that are not practically branched as shown in FIG. 1B. As clearly seen from FIG. 1B, the narrow pores are independent from each other and standing perpendicularly or substantially perpendicularly from the film surface (or the substrate). According to the invention, the average intercentral distance of the plurality of pores (2R in FIG. 1B) can be made smaller than 30 nm, while the average diameter of the pillar-shaped pores (2r in FIG. 1B) can be made smaller than 20 nm.

Preferably, the diameters 2r of the narrow pores are between 0.5 and 15 nm and the intercentral distances 2R of the pores are between 5 and 20 nm. The length L of the pores is found in a range between 0.5 nm and several micrometers (.mu.m), preferably between 2 nm and 5 .mu.m. The average pore diameter as used herein refers to the average of the lengths of the major axes obtained by observing a picture showing the pillar-shaped members actually taken by means of SEM photography (in an area of about 100 nm.times.100 nm) and processing (extracting) the image of narrow pores in the picture by means of a computer, assuming that the pores show elliptic plan views.

While the narrow pores in a porous body according to the invention can be made to directly face the substrate as shown in FIG. 1B, the present invention is by no means limited thereto and the pores do not need to be made to directly face the substrate.

As for the composition of the region 2 of a porous body according to the invention, while the region 2 contains oxide of the second material as major ingredient, it may additionally contain other elements such as aluminum (Al) and argon (Ar) by several to tens of several atomic %. Aluminum and other elements may be found in the porous body particularly when pillar-shaped members that were formed so as to contain the above described first material such as aluminum existed at positions where pillar-shaped narrow pores exist. The concentration of the first material that formed the pillar-shaped members is high on or near the pore walls of the porous body but low in the inside of the pore walls. In other words, the first material in the porous body shows a concentration distribution in the intraplanar direction. The concentration distribution will be reduced when the first material, which may typically be aluminum, is diffused by heat treatment or some other means.

A porous body according to the invention is amorphous both on and near the pore walls and in the inside of the pore walls.

The second material is Si, Ge, SiGe or a material of a combination of any of them.

The region 2 of a porous body according to the invention is amorphous and, when viewed from right above the substrate, the narrow pores may show a substantially cylindrical plan view as shown in FIG. 1A or they may provide some other views such as an elliptic plan view.

In a cross sectional view of a silicon porous body according to the invention, the narrow pores may show a rectangular profile as shown in FIG. 1B or they may provide some other view such as a square or frusto-conical profile.

Preferably, the plurality of pores keeps a substantially same diameter along their heights. The region 2 may contain aluminum.

According to the invention, the aspect ratio of the narrow pores that is the ratio of the length to the pore diameter (length/pore diameter) can be between 0.1 and 10,000.

A porous body according to the invention is an oxide porous body obtained by removing the first material from the structural body formed so as to contain the first material and the second material. The structural body has a structure in which pillar-shaped members formed so as to contain the first material are surrounded by an amorphous region formed so as to contain the second material and the content of the second material in the structural body is not smaller than 20 atomic % and not greater than 70 atomic % relative to the total quantity of the first and second materials. The first material is aluminum and the second material is typically Si, Ge, SiGe or a material of a combination of any of them.

An oxide porous body according to the invention is characterized in that it is a film-shaped structural body having pillar-shaped narrow pores and an oxide region and the narrow pores are arranged perpendicularly or substantially perpendicularly relative to the film surface while the average diameter of the narrow pores being not greater than 20 nm and the average intercentral distance of the narrow pores is not greater than 30 nm, the narrow pores being separated from each other by the oxide region.

As shown in FIG. 1B, the narrow pores are separated from each other by the silicon oxide region. They are independent from each other. In other words, any of them are linked to each other. They are perpendicular or substantially perpendicular relative to the substrate.

The narrow pores of an oxide porous body according to the invention shows a pillar-shaped profile as shown in FIG. 1B. The diameter (average pore diameter) 2r of the narrow pores is not greater than 20 nm and the gap (average intercentral distance) 2R separating the narrow pores is not greater than 30 nm. Preferably, the diameter 2r of the narrow pores is between 1 and 15 nm and the gap 2R is between 5 and 20 nm. The length L of the narrow pores is in a range between 5 nm and several micrometers, preferably in a range between 2 nm and 1,000 nm. The average pore diameter as used herein refers to the average of the lengths of the major axes obtained by observing a picture showing the pillar-shaped members actually taken by means of SEM photography (in an area of about 100 nm.times.100 nm) and processing (extracting) the image of narrow pores in the picture by means of a computer, assuming that the pores show elliptic plan views.

While the narrow pores in an oxide porous body according to the invention can be made to directly face the substrate as shown in FIG. 1B, the present invention is by no means limited thereto and the pores do not need to be made to directly face the substrate.

When an oxide porous body according to the invention is made to contain silicon oxide (SiOx) as principal ingredient, it may additionally contain aluminum oxide (AlOx) as well as other elements such as argon (Ar). The silicon (Si) content of the silicon oxide region is not smaller than 80 atomic %, preferably in a range between 85 and 99 atomic %, relative to the total quantity of all the elements in the region except oxygen.

When aluminum is used as the first material, the aluminum content in the obtained porous body is within a range between 0.01 and 20 atomic %, preferably in a range between 0.1 and 10 atomic %, relative to the total quantity of all the elements of the porous body except oxygen.

With regard to the pillar-shaped profile of the narrow pores, the narrow pores may show any aspect ratio (length L/pore diameter 2r) so long as they meet the above described dimensional requirements. However, the aspect ratio (length L/pore diameter 2r) is preferably in a range between 0.5 and 1,000.

Now, the present invention will be described in terms of specific materials. However, it should be noted that the present invention is by no means limited to the specific materials that are cited in the following description.

(3-1) Silicon Oxide Porous Body

A silicon oxide porous body according to the invention is characterized in that it comprises pillar-shaped narrow pores and a silicon oxide region surrounding them and the average pore diameter of the narrow pores is not greater than 20 nm, while the average gap separating the narrow pores is not greater than 30 nm.

Preferably, a silicon oxide porous body according to the invention is a film-shaped silicon oxide porous body that comprises pillar-shaped narrow pores and a silicon oxide region containing silicon oxide as principal ingredient. In the silicon oxide porous body, the narrow pores are standing perpendicularly or substantially perpendicularly relative to the film surface and the average pore diameter of the narrow pores is not greater than 20 nm while the average gap is not greater than 30 nm and the narrow pores are separated from each other by the silicon oxide region containing silicon oxide as principal ingredient.

Preferably, the average pore diameter of the narrow pores is between 1 and 15 nm and the average gap separating the narrow pores from each other is between 5 and 20 nm.

Preferably, the silicon oxide region contains silicon by not less than 80 atomic % relative to the total quantity of all the elements of the region except oxygen.

Preferably, the silicon oxide region contains silicon oxide and aluminum oxide.

Preferably, the silicon oxide is amorphous.

(3-2) Germanium Oxide Porous Body

A germanium oxide porous body according to the invention is characterized in that it comprises pillar-shaped narrow pores and a germanium oxide region surrounding them and the average pore diameter of the narrow pores is not greater than 20 nm, while the average gap separating the narrow pores is not greater than 30 nm.

Preferably, a germanium oxide porous body according to the invention is a film-shaped germanium oxide porous body that comprises pillar-shaped narrow pores and a germanium oxide region containing germanium oxide as principal ingredient. In the germanium oxide porous body, the narrow pores are standing perpendicularly or substantially perpendicularly relative to the film surface and the average pore diameter of the narrow pores is not greater than 20 nm while the average gap is not greater than 30 nm and the narrow pores are separated from each other by the germanium oxide region containing germanium oxide as principal ingredient.

Preferably, the average pore diameter of the narrow pores is between 1 and 15 nm and the average gap separating the narrow pores from each other is between 5 and 20 nm.

Preferably, the germanium oxide region contains germanium by not less than 80 atomic % relative to the total quantity of all the elements of the region except oxygen.

Preferably, the germanium oxide region contains germanium oxide and aluminum oxide.

Preferably, the germanium oxide is amorphous.

(3-3) Silicon Germanium Oxide Porous Body

A silicon germanium oxide porous body according to the invention is characterized in that it comprises pillar-shaped narrow pores and a silicon germanium oxide region surrounding them and the average pore diameter of the narrow pores is not greater than 20 nm, while the average gap separating the narrow pores is not greater than 30 nm.

Preferably, a silicon germanium oxide porous body according to the invention is a film-shaped silicon germanium oxide porous body that comprises pillar-shaped narrow pores and a silicon germanium oxide region containing silicon germanium oxide as principal ingredient. In the silicon germanium oxide porous body, the narrow pores are standing perpendicularly or substantially perpendicularly relative to the film surface and the average pore diameter of the narrow pores is not greater than 20 nm while the average gap is not greater than 30 nm and the narrow pores are separated from each other by the silicon germanium oxide region containing silicon germanium oxide as principal ingredient.

Preferably, the average pore diameter of the narrow pores is between 1 and 15 nm and the average gap separating the narrow pores from each other is between 5 and 20 nm.

Preferably, the silicon germanium oxide region contains silicon and germanium, as put together, by not less than 80 atomic % relative to the total quantity of all the elements of the region except oxygen.

When the compositional ratio of silicon (Si) and germanium (Ge) in the silicon germanium oxide region is expressed by formula Si.sub.xGe.sub.1-x, preferably x is found within a range of 0<x<1.

Preferably, the silicon germanium oxide is amorphous.

(4) Method of Manufacturing an Oxide Porous Body According to the Invention

Now, a method of manufacturing an oxide porous body according to the invention will be described below in detail. A method of manufacturing an oxide porous body according to the invention is characterized in that it comprises a step of preparing a structural body formed so as to contain a first material and a second material and including pillar-shaped members formed so as to contain the first material and surrounded by an amorphous region formed so as to contain the second material (FIG. 2A), a removal step of removing the pillar-shaped members from the structural body (FIG. 2B) and a step of oxidizing the region (FIG. 2C). In FIG. 2A, reference symbols 21, 22, 23 and 24 respectively denote pillar-shaped members, a substrate, a structural body and a region surrounding the pillar-shaped members.

Preferably, the structural body contains the second material at a ratio of not smaller than 20 atomic % and not greater than 70 atomic % relative to the total quantity of the first and second materials. However, the present invention is by no means limited to the above ratio so long as the pillar-shaped members standing perpendicularly relative to the substrate are distributed in the surrounding region of the structural body. For the purpose of the invention, it is important that the structural body is obtained by combining materials that are suited for selectively removing the pillar-shaped members from the structural body.

If necessary, a pore diameter enlarging step of enlarging the pore diameters of the porous body may be conducted after the removal step (FIG. 2D). Of course, the oxidizing step may be conducted after the pore diameter enlarging step that comes after the removal step.

For example, aluminum or gold may be used as the first material, whereas Si, SiGe, Ge, or a material of a combination of any of them may be used as the second material. Of course, a plurality of materials may be combined for use for the purpose of the invention. Whenever appropriate, this statement applies to the following description.

FIG. 3 is a schematic illustration of a mode of carrying out a method of manufacturing an oxide porous body according to the invention, showing different steps thereof. Referring to FIG. 3, a method of manufacturing an oxide porous body according to the invention is characterized by comprising Step (a), Step (b), Step (c) and Step (d), which will be described below. Step (a): Firstly, the first material (e.g., aluminum) and the second material (e.g., silicon) are brought in. Step (b): Then, a structural body is formed from the first material and the second material on a substance by using a film forming process for forming a substrate in a non-equilibrium state. The structural body obtained as a result of the film forming process comprises pillar-shaped members containing the first material and a region formed from the second material to surround the pillar-shaped members. The pillar-shaped members are distributed in the structural body when the film-shaped structural body is formed so as to contain the second material to a ratio of 20 to 70 atomic % relative to the total quantity of the first and second materials. Step (c): Subsequently, the pillar-shaped members are removed from the structural body by etching to produce narrow pores. When the structural body is subjected to a wet etching process using acid or alkali, the pillar-shaped members are selectively removed to produce a porous body having narrow pores. Step (d): Thereafter, the porous body having the narrow pores is oxidized to obtain an oxide porous body.

The step (e) of enlarging the pore diameters of the oxide porous body may be conducted by means of wet etching using acid or alkali after the step (d).

FIG. 4 is a schematic illustration of another mode of carrying out a method of manufacturing an oxide porous body according to the invention, showing different steps thereof.

Referring to FIG. 4, a method of manufacturing an oxide porous body according to the invention is characterized by comprising Steps (a), (b), (c), (e') and (d), which will be described below. Step (a): Firstly, the first material (e.g., aluminum) and the second material (e.g., silicon) are brought in. Step (b): Then, a structural body is formed from the first material and the second material on a substrate by using a film forming process for forming a substrate in a non-equilibrium state. The structural body obtained as a result of the film forming process comprises pillar-shaped members containing the first material and a region formed from the second material to surround the pillar-shaped members and contains the second material to a ratio of 20 to 70 atomic % relative to the total quantity of the first and second materials. Step (c): Subsequently, the pillar-shaped members are removed from the structural body by etching to produce a porous body. When the structural body is subjected to a wet etching process using acid or alkali, the pillar-shaped members that contain the first material are e