JP2006283122A - Method for producing nanostructure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a nanostructure capable of stably producing an anodic oxide film having a hole penetrating an electrode layer while maintaining a sufficient thickness in a partition wall between holes.
A first aluminum alloy film 12 and an anode which is less soluble in an etching solution than an anodic oxide film formed from the first aluminum alloy on a base layer 11 provided on a substrate 10. A step of forming a laminated body in which the second aluminum alloy film 13 for forming an oxide film is laminated; and anodizing the laminated body to penetrate the second aluminum alloy film 13 to form the first aluminum alloy film 12 A step of forming a hole 16 reaching the surface, a step of further anodizing to form a hole in the first aluminum alloy film 12 and stopping the anodization before reaching the base layer 11, and a step of further wet etching to form a hole. The manufacturing method of the nanostructure including the process which penetrates 16 to the base layer 11. FIG.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a nanostructure having nanoscale pores obtained by anodization.

  When anodization is performed by applying a voltage in an appropriate acidic solution using aluminum to be processed as an anode, a porous anodic oxide film made of alumina is obtained (see, for example, Non-Patent Document 1). Such anodizing treatment of aluminum is generally known as an electrochemical surface treatment technique, and is widely used for the purpose of, for example, enhancing the corrosion resistance or coloring of building materials.

  The porous anodic oxide film has a nanoscale geometric structure in which a large number of cylindrical holes having a diameter of the order of nanometers grown in the direction perpendicular to the film surface are arranged in parallel. In recent years, by controlling the structure of such a porous film, the production of nanodevices using this has been extensively studied.

  As a technique for controlling the structure of the porous film described above, it is common to change the anodizing conditions. For example, it is known that the hole interval can be controlled to some extent by pore-wide processing, and the hole interval can be controlled by an anodizing voltage, the hole depth by an anodic oxidation time, and the pore-wide treatment. Here, the pore wide treatment is an etching treatment of alumina, and a wet etching treatment with ordinary phosphoric acid is used.

  In order to improve the verticality, linearity and independence of the pores of the porous film, a method of performing two-step anodization is known. In other words, the porous film formed by anodizing is once removed by wet etching using chromic acid, and then anodized again, so that the porous film has pores showing better verticality, linearity, and independence. A method for producing a film has been proposed (for example, see Non-Patent Document 2). In this method, the depression of the aluminum substrate formed when the porous film formed by the first anodic oxidation is removed is used as a starting point for forming the holes for the second anodic oxidation.

  Furthermore, in order to form holes that are highly ordered and arranged in a desired pattern, a method using a stamper having protrusions is known (see, for example, Patent Document 1 and Non-Patent Document 3). In these methods, the stamper is pressed against the surface of the aluminum substrate, and the protrusions of the stamper are transferred as depressions on the surface of the aluminum substrate, thereby forming an anodic oxidation hole formation start point.

  As described above, the anodized film of aluminum can easily form a structure having a nanoscale structure in a self-organized manner, and further, it is fine and special, exceeding the exposure technology using light and electron beams. In recent years, it has attracted particular attention because of the possibility of realizing nanostructures.

In particular, various nanodevices such as magnetic recording media, magnetic sensors, EL light emitting elements, and electrochromic elements will be realized by combining techniques for regularly arranging the holes and techniques for filling the holes with metal, semiconductor, or the like. A lot of research has been done.
JP-A-10-121292 R. C. Furneaux, W.M. R. Rigby & A. P. Davidson, “Nature.” 337, p. 147, (1989) “Japan Journal of Applied Physics” 35, p. 126, (1996) [Non-Patent Document 3] Masuda “Solid Physics” 31, p. 493, (1996)

  When considering filling materials such as metals and semiconductors into the holes obtained by anodization, various film deposition techniques such as vacuum deposition and CVD can be used, but holes with high aspect ratios can also be used. In general, electrodeposition is preferable from the viewpoint of filling, and Cu or a noble metal layer is provided under the anodized film as an electrode layer for electrodeposition. Here, the aspect ratio is (hole depth) / (hole diameter).

  When a material is filled in the holes by the electrodeposition method, electrodeposition at a low potential close to the deposition potential is possible by forming a hole penetrating the electrode layer. However, when an electrode layer made of Cu or noble metal is used, the bonding strength between the electrode layer and the anodic oxide film is weak, and it is very difficult to form a hole penetrating the electrode layer. That is, if anodization is performed until the bottom of the pores reaches the electrode layer, the anodized film is peeled off, which causes a problem that the anodized film cannot be stably produced.

  For this reason, anodization is stopped before the hole reaches the electrode layer, and a partition wall made of an insulator existing at the bottom of the hole called a barrier layer is removed by wet etching such as chromic acid. In this case, the barrier between adjacent holes is etched at the same time as the etching of the barrier layer. Therefore, if sufficient penetrability is to be ensured, the barrier between the holes becomes extremely thin. There was a problem that penetrability would be lowered if sufficient.

  An object of the present invention is to solve the above-mentioned problem, and a nanostructure capable of stably producing an anodized film having a hole penetrating through an electrode layer while maintaining a sufficient thickness in a partition wall between the holes A method for producing a body is provided.

  In the method for producing a porous body according to the present invention, a member including a first layer and a second layer is prepared on a substrate from the substrate side, and the second layer is formed in the thickness direction from the second layer side. Forming a hole by anodic oxidation halfway between the layer and the first layer, etching the first layer in which a hole is formed in a part in a thickness direction, and forming a hole penetrating the first layer The first layer includes a first aluminum alloy, the second layer includes a second aluminum alloy, and the second layer includes a second aluminum alloy. An anodic oxide film formed from an aluminum alloy is less soluble in an etching solution used for the etching than an anodic oxide film formed from the first aluminum alloy.

  The present invention is also a method for producing a nanostructure by anodic oxidation, wherein a first layer made of a first aluminum alloy is formed on a substrate or an underlayer provided on the substrate, and the first layer At least two second layers made of a second aluminum alloy forming an anodic oxide film that is less soluble in an etching solution than the anodic oxide film formed from the first aluminum alloy are laminated on the substrate. A step of forming a laminate, a step of anodizing the laminate to form a hole penetrating from the surface of the laminate through the second layer to the surface of the first layer, and further anodizing Forming a hole in the first layer and stopping the anodic oxidation before reaching the substrate or the base layer, and wet etching the stacked body to penetrate the hole to the substrate or the base layer. It is a manufacturing method of nanostructure

  The first and second aluminum alloys are preferably aluminum alloys containing aluminum and at least one of Ti, Zr, Hf, Nb, Ta, Mo and W.

  The first layer is preferably made of a first aluminum alloy containing aluminum and W, and the second layer is preferably made of aluminum and a second aluminum alloy containing Ti, Zr or Hf.

The first layer is preferably made of a first aluminum alloy containing aluminum and Ti, and the second layer is preferably made of a second aluminum alloy containing aluminum and Hf.
It is preferable that the first and second aluminum alloys contain 50 atomic% or more of aluminum.

It is preferable that the film thickness of the first layer is approximately the same as the thickness of the insulating layer at the bottom of the hole formed when the laminate is anodized.
The underlayer is preferably made of copper or a noble metal.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the nanostructure which can produce stably the anodic oxide film which has the hole penetrated to the electrode layer in the state which maintained sufficient thickness in the partition between holes is provided. It becomes possible.

Hereinafter, a method for producing a nanostructure according to the present invention will be described.
FIG. 1 is a process diagram schematically showing the method for producing a nanostructure of the present invention. FIG. 1A is a schematic view of a substrate 30 that is an anodic oxide. A base layer 11 made of Cu or a noble metal, a first aluminum alloy film 12, and a second aluminum alloy film 13 are laminated in this order on a substrate 10 such as silicon. Thus, another layer may be provided between the substrate and the first aluminum alloy film 12 as necessary.

  When the substrate 30 is anodized using an acidic aqueous solution such as phosphoric acid, oxalic acid, or sulfuric acid, the growth of the anodized film 14 begins as shown in FIG. Hole 16 is formed.

  Subsequently, as shown in FIG. 1C, the anodic oxidation is stopped in a state where the bottom barrier layer 17 formed at the bottom of the hole reaches the base layer 11. The reason is that if the anodic oxidation is continued until the holes 16 penetrate the base layer 11, the anodic oxide film may be peeled off by the oxygen gas generated by the electrolysis of the acidic aqueous solution. Here, it is empirically known that the thickness of the bottom barrier layer is almost determined by the anodizing conditions, and the thickness d [nm] of the barrier layer is approximately d = 1.2 with respect to the anodizing voltage V [volt]. XV.

  Therefore, if the first aluminum alloy film 12 of FIG. 1A is disposed in advance with a thickness of the bottom barrier layer, the bottom barrier layer 17 of FIG. 1C is mainly formed of the first aluminum alloy film. It is formed from 12 oxides. On the other hand, the partition walls 18 between the holes are mainly formed from the oxide of the second aluminum alloy film 13, and therefore can be different from the bottom barrier layer 17.

  Subsequently, the bottom barrier layer 17 is dissolved by a wet etching process using an acid or the like, and the holes 16 are penetrated through the base layer 11. An aqueous phosphoric acid solution or the like is used as the etching solution. At this time, if the anodized film of the first aluminum alloy film 12 is more soluble in the etching solution than the anodized film of the second aluminum alloy film 13, the bottom barrier layer 17 is selectively dissolved. And a through hole 19 as shown in FIG. 1 (d) is formed. That is, it is possible to obtain an anodic oxide film having a sufficient thickness of the partition wall 18 between the holes and at the same time improving the penetrability to the base layer 11. Further, according to the present invention, it is not necessary to penetrate the hole 16 to the base layer 11 at the time of anodic oxidation, so that there is an advantage that peeling of the anodic oxide film is suppressed.

  Here, the composition of the first aluminum alloy film 12 and the second aluminum alloy film 13 may be any material that can form holes by anodic oxidation. For example, aluminum, Ti, Zr, Hf, Nb, Ta, Mo , W is preferably an aluminum alloy containing at least one of W. In addition, when the amount of alloying element added to aluminum is extremely large, the verticality and straightness of the hole will be reduced, so the aluminum content should be 50 atomic% or more, preferably about 80 to 99 atomic%. Is desirable.

  Next, in the present invention, as described above, the anodic oxide film of the first aluminum alloy film 12 needs to be more soluble in the etching solution than the anodic oxide film of the second aluminum alloy film 13. Therefore, it is preferable to use an aluminum tungsten alloy film in which the anodic oxide film is easily dissolved as the first aluminum alloy film 12. At this time, the second aluminum alloy film 13 may be less soluble than the anodic oxide film of the first aluminum alloy film 12. However, since the difference in solubility is remarkable, the aluminum titanium alloy film, aluminum It is preferable to use a zirconium alloy film or an aluminum hafnium alloy film.

  When sulfuric acid is used as the anodic oxidation electrolyte, the aluminum tungsten alloy film is almost dissolved during the anodic oxidation. Therefore, an aluminum titanium alloy film is used as the first aluminum alloy film 12, and the first It is preferable to use an aluminum hafnium alloy film as the second aluminum alloy film 13.

Hereinafter, typical examples of the present invention will be described.
Example 1
In this example, an aluminum tungsten alloy film and an aluminum zirconium alloy film were used as the anodized film as the aluminum alloy film.

FIG. 2 is a schematic diagram showing the configuration of the sample (substrate) of Example 1 of the present invention.
On the n-Si (100) substrate 20, a base layer in which Ti21 is 5 nm and Cu22 is 20 nm is provided thereon, and further, an aluminum tungsten alloy film 23 is 50 nm on the base layer, and an aluminum zirconium alloy film 24 is further formed thereon. A sample having a structure shown in FIG.

  All the films were formed by sputtering, and the aluminum alloy film was formed by placing a tungsten and zirconium chip on the erosion area of an aluminum target having a diameter of 4 inches (101.6 mm). In this example, four 10 mm square tungsten chips and three 10 mm square zirconium chips were used. At this time, the composition ratio of the aluminum tungsten alloy film and the aluminum zirconium alloy film formed under the same conditions was quantified by ICP (inductively coupled plasma emission spectrometry). The content of tungsten in the aluminum tungsten alloy film was about 7 atomic%. Similarly, the zirconium content of the aluminum zirconium film was about 5 atomic%.

  Subsequently, anodization of the sample was performed at an applied voltage of 40 V using a 0.3 mol / L oxalic acid aqueous solution at 16 ° C., and then the bottom barrier layer was removed by wet etching using a 5 wt% phosphoric acid aqueous solution. Then, a hole penetrating the underlayer was prepared. Moreover, the cross section of the sample was observed with an FE-SEM (field emission scanning electron microscope), and the penetrability of the hole into the underlayer was evaluated.

  FIG. 3A shows a current profile when the sample (sample A) having the configuration shown in FIG. 2 is anodized. For comparison, FIG. 3B shows a current profile when a sample (sample B) in which only an aluminum film is formed to 200 nm on the same base layer is anodized under the same anodizing conditions.

When anodization is performed at a constant voltage from FIG. 3B, first, an oxide film is formed on the sample surface and the current value decreases, and then dissolution of the oxide film (formation of holes) and formation of a new oxide film proceed simultaneously. Thus, a steady state is obtained in which a constant current value is obtained. Then most of the bottom barrier layer at the time of t ₁ begins to decrease in the current value reaches the underlying layer, turns to a sharp rise after taking a minimum value at time t _2. Because peeling and bursting of the anodized film if it exceeds t ₂ becomes significant, it is preferable to stop the anodic oxidation between t ₁ ~t _2, penetrating to closer to t ₁ hole underlayer It was getting worse. On the other hand, the penetrability improved as it approached t ₂ , but there were some rupture marks of the film that were probably caused by the generation of oxygen gas. For this reason, in order to secure sufficient penetrability while minimizing damage to the film, it is necessary to stop anodization slightly before t ₂ and perform sufficient wet etching, and in this case, the diameter is 80 nm. It was about 20 nm of partition walls between the holes.

On the other hand, FIG. 3A shows a current profile when the sample A is anodized similarly. In FIG. 3 (a), the bottom barrier layer at the time of t ₃ reaches the aluminum tungsten alloy film, believed anodized film on the aluminum tungsten alloy film is formed between t ₃ ~t _5. Further, it is considered that most of the bottom barrier layer reaches the base layer at the time t ₄ and the current value starts to decrease, and after taking the minimum value at the time t ₅ as in FIG. Started to rise.

As a result of evaluating the change in penetrability when the anodic oxidation stop point was changed by FE-SEM, in the sample in which the anodic oxidation was stopped at time t ₃ , as shown in FIG. The alloy film 41 remained as it was without forming a porous film. For this reason, the hole 43 penetrating the base layer 42 could not be formed.

Next, evaluation was performed on samples in which anodization was stopped at time t ₄ . Immediately after the anodic oxidation, as shown in FIG. 5, a hole 53 is formed with the bottom barrier layer 51 reaching the base layer 52, and a bottom barrier layer having a thickness substantially equal to the thickness of the aluminum tungsten alloy film is confirmed. did it. Here, it is considered that the bottom barrier layer is mainly made of an anodized film of an aluminum tungsten alloy film, and the partition 54 between the holes is made of an anodized film of an aluminum zirconium alloy film.

  Further, when this sample was wet-etched with a 5 wt% phosphoric acid aqueous solution to remove the bottom barrier layer, as shown in FIG. A hole 62 penetrating 61 was obtained. This is probably because the bottom barrier layer 51 shown in FIG. 5 was easily removed because the anodized film of the aluminum tungsten alloy film was more soluble in phosphoric acid than the anodized film of aluminum. . Further, since the anodized film of the aluminum zirconium alloy film is less soluble in phosphoric acid than the anodized film of the aluminum tungsten alloy film, the bottom barrier layer is completely removed as shown in FIG. Further, the partition wall 63 between the holes having a sufficient thickness was maintained, and the partition wall between the holes was about 50 nm with respect to the hole having a diameter of about 50 nm.

Also, as the anodic oxidation stop point approaches t ₅ , as in the case of Sample B, several rupture marks of the film that are thought to be caused by the generation of oxygen gas can be seen. to sufficiently secure the penetration suppressing the minimum, it is desirable to perform the wet etching by stopping anodic anodizing at close in t ₄ of t ₄ ~t _5.

  According to this example, it is possible to stably produce an anodized film having holes penetrating through the electrode layer in a state where a sufficient thickness is maintained in the partition walls between the holes. In this embodiment, a laminate of an aluminum tungsten alloy film and an aluminum zirconium alloy film is used as the anodized film. However, if the etching for removing the bottom barrier layer can be performed selectively, an aluminum alloy can be used. The composition and composition ratio of the film are not limited to these.

Example 2
This example uses an aluminum titanium alloy film and an aluminum hafnium alloy film as the anodized film as an aluminum alloy film, and in order to evaluate the penetrability to the underlayer, the produced hole was filled with an electrodeposit. It is.

  A sample was prepared by laminating an aluminum titanium alloy film with a thickness of 20 nm on an underlayer provided on the substrate in the same manner as in Example 1, and further laminating an aluminum hafnium alloy film with a thickness of 200 nm thereon. The titanium content in the aluminum titanium alloy film is about 7 atomic%, and the hafnium content in the aluminum hafnium alloy film is about 6 atomic%.

FIG. 7 shows a current profile when the prepared sample was anodized using a 0.3 mol / L sulfuric acid aqueous solution at 24 ° C. at an applied voltage of 25V. The same considerations as in Example 1, is considered anodic oxide film on the titanium aluminum alloy film is formed at t ₆ ~t _8.

Subsequently in the same manner as in Example 1, anodic oxidation was stopped at t ₇ when the bottom barrier layer has reached the underlying layer, it was removed of the barrier layer by wet etching immersing the 40 min sample to 5 wt% phosphoric acid aqueous solution. When the surface of the sample before and after etching was observed with FE-SEM, the anodized film of the aluminum hafnium alloy film was hardly soluble in phosphoric acid, so no significant change in the hole diameter was observed before and after etching. Holes with a diameter of about 30 nm were formed with a partition wall of about 40 nm between the holes.

  On the other hand, when the cross section of the sample was observed with FE-SEM, the presence of the bottom barrier layer was confirmed before etching, but this was removed after etching. This is because the anodized film of the aluminum titanium alloy film forming the bottom barrier layer is more soluble in phosphoric acid than the anodized film of the aluminum hafnium alloy film, so that only the bottom barrier layer is selectively etched. It shows that. For this reason, in the portion near the bottom barrier layer, the hole diameter after etching is larger than that of the anodized film portion of the aluminum hafnium alloy film on the upper portion.

  Next, the electrodeposit was filled by electrodeposition on the etched sample. For electrodeposition, a mixed solution of cobalt (II) sulfate heptahydrate 0.3 mol / L and boric acid 0.3 mol / L was used at 24 ° C. The reference electrode was Ag / AgCl, the counter electrode was platinum, and the electrodeposition potential was -1.0V. Electrodeposition was carried out until the electrodeposit overflowed from the hole, and the overflowed electrodeposit was removed by polishing using a diamond slurry. When the polished sample surface was observed with FE-SEM, it was confirmed that cobalt as an electrodeposit was filled in almost all the holes. The fact that cobalt was filled in the hole by electrodeposition at a low potential close to the deposition potential indicates that a through-hole was formed in the base electrode layer, which is the working electrode, and almost all holes were filled. Therefore, it was confirmed that the penetration of the holes was uniform.

  According to this example, it was confirmed that the hole formed by anodization had good penetrability to the base layer and was uniform over a wide range.

  According to the present invention, an anodized film having a hole penetrating the electrode layer in a state where the partition wall between the holes has a sufficient thickness can be stably produced. It can be used as a recording medium.

It is process drawing which shows the manufacturing method of the nanostructure of this invention typically. It is a schematic diagram which shows the structure of the sample (base | substrate) of Example 1 of this invention. It is a figure which shows the electric current profile at the time of the anodic oxidation of the sample A of Example 1. FIG. Is a cross-sectional view after the wet etching of the sample of Example 1 was stopped anodic oxidation at the time of t ₃ in FIG. FIG. ₄ is a cross-sectional view immediately after anodization of the sample of Example 1 in which anodization was stopped at time t ₄ in FIG. 3. FIG. ₄ is a cross-sectional view after wet etching of the sample of Example 1 in which anodization was stopped at time t ₄ in FIG. 3. It is a figure which shows the electric current profile at the time of the anodic oxidation of Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 11 Underlayer 12 First aluminum alloy film 13 Second aluminum alloy film 14 Anodized film 15 Aluminum alloy oxide 16 Hole 17 Bottom barrier layer 18 Partition wall between holes 19 Through-hole 20 n-Si (100) Substrate 21 Ti
22 Cu
23 Aluminum Tungsten Alloy Film 24 Aluminum Zirconium Alloy Film 30 Base 40 Substrate 41 Aluminum Tungsten Alloy Film 42 Underlayer 43 Hole 50 Substrate 51 Bottom Barrier Layer 52 Underlayer 53 Hole 54 Partition Between Holes 60 Substrate 61 Underlayer 62 Hole 63 Between Holes Bulkhead

Claims (7)

  A member having a first layer and a second layer is prepared on the substrate from the substrate side, and anodization is performed from the second layer side to the middle of the second layer and the first layer in the thickness direction. Forming a hole by etching, etching the first layer in which a hole is formed in a part in the thickness direction, and a method for producing a porous body in which a hole penetrating the first layer is formed. The first layer includes a first aluminum alloy, and the second layer includes a second aluminum alloy, and is formed from the second aluminum alloy. Is less soluble in the etching solution used for the etching than the anodic oxide film formed from the first aluminum alloy.   The porous structure according to claim 1, wherein the first and second aluminum alloys are aluminum and an aluminum alloy containing at least one of Ti, Zr, Hf, Nb, Ta, Mo, and W. Manufacturing method.   The first layer is made of a first aluminum alloy containing aluminum and W, and the second layer is made of aluminum and a second aluminum alloy containing Ti, Zr, or Hf. A method for producing a porous structure.   The porous structure according to claim 1 or 2, wherein the first layer is made of a first aluminum alloy containing aluminum and Ti, and the second layer is made of a second aluminum alloy containing aluminum and Hf. Manufacturing method.   The method for manufacturing a porous structure according to any one of claims 1 to 4, wherein the first and second aluminum alloys contain 50 atomic% or more of aluminum.   The porous material according to any one of claims 1 to 5, wherein the film thickness of the first layer is approximately the same as the thickness of the insulating layer at the bottom of the hole formed when the laminated body is anodized. Manufacturing method of structure.   The method for producing a porous structure according to claim 1, wherein the underlayer is made of copper or a noble metal.

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