KR101069738B1 - Method for forming copper oxide - Google Patents

Abstract

The present technology relates to a method of forming copper oxide by electrochemical deposition. The present technology provides a method for forming copper oxide, comprising: preparing an electrochemical deposition solution by stirring an aqueous solution containing copper and an aqueous solution including a sample for complex formation; And applying a direct current voltage to the electrochemical deposition aqueous solution to form a copper oxide film using a complex formed from the sample.

According to the present technology, by forming a copper oxide film by an electrochemical deposition method using a complex, a copper oxide thin film having a smooth surface and a constant crystal orientation array can be formed. In particular, by using the complex, since the single crystal copper liner film can be formed at low temperature, the manufacturing cost can be lowered and the process can be carried out more easily.

Copper Oxide, Complex, HMTA

Description

Copper oxide formation method {METHOD FOR FORMING COPPER OXIDE}

The present invention relates to a method for forming copper oxide, and more particularly, to a method for forming a single crystal copper oxide thin film by an electrochemical deposition method.

In recent years, copper (I) has been spotlighted in a wide range of fields such as solar cells, sensors, catalysts, battery electrodes, and semiconductors. The copper oxide (I) thin film is generally formed by sputtering, chemical vapor deposition, pulsed laser deposition, or molecular beam epitaxy.

However, according to the manner as described above, in order to form the single crystal copper oxide (I) in which the crystals are arranged in a specific orientation, a complicated process procedure is required at a high temperature of 500 ° C. or higher, which leads to a problem of high manufacturing cost.

Accordingly, the prior art proposes an Electro Chemical Deposition method to easily form single crystal copper oxide (I) at low cost. According to the electrochemical deposition method, copper sulfate (copper lactate) aqueous solution or copper acetate (copper acetate) aqueous solution by applying DC voltage, by reducing a copper ion (Cu ^{2 +)} to form copper (Cu ₂ O) oxidation to Can be.

However, in the case of forming copper oxide (I) by the conventional electrochemical deposition method, since the crystal growth form and crystal growth arrangement direction are changed during the growth process, the thickness and crystal orientation arrangement of the copper oxide (I) thin film are controlled. There is difficulty.

According to the prior art, the surface of the copper oxide (I) thin film is formed of a nano or micro structure (nano or micro structure), the root mean square (RMS) value for the surface roughness is large. That is, the thickness of the copper oxide (I) thin film is not uniform and the surface is not smooth.

In addition, in order to relieve stress due to lattice mismatch between the substrate and the copper (I) thin film, the direction of crystal growth arrangement is changed or the direction of growth arrangement of crystals in a region exceeding a critical thickness. This can change. Thus, the orientation arrangement of the crystals is not constant.

For example, when a copper oxide (I) thin film is formed using an aqueous copper lactate solution or an aqueous copper acetate solution, the copper oxide thin film is formed in an island-growth form, and the RMS value of the surface roughness is also large.

That is, when the copper oxide (I) thin film is formed by the electrochemical deposition method according to the prior art, the crystal growth form and the crystal growth arrangement direction cannot be adjusted, the thickness is not constant, and the RMS value for the surface roughness is large. . Therefore, there is a limit to the industrial application of the copper (I) thin film.

The present invention has been proposed to solve the above problems, and an object of the present invention is to provide a method for forming a single crystal copper oxide thin film by a low temperature electrochemical deposition method suitable for forming a copper oxide thin film having a constant orientation of crystals.

In order to achieve the above object, the present invention provides a method for forming copper oxide, comprising: preparing an electrochemical deposition solution by stirring an aqueous solution containing copper and an aqueous solution containing a sample for complex formation; And applying a DC voltage to the electrochemical deposition aqueous solution to form a copper oxide film using a complex formed from the sample.

In addition, the present invention provides a method for forming copper oxide, comprising: preparing an electrochemical deposition aqueous solution by stirring an aqueous solution containing a copper nitrate aqueous solution and HMTA; And applying a DC voltage to the electrochemical deposition aqueous solution to form a copper oxide film using the complex formed from the HMTA.

According to the present invention, by forming a copper oxide thin film by an electrochemical deposition method using a complex, it is possible to easily adjust the thickness and crystal orientation arrangement of the copper oxide thin film. Therefore, it is possible to form a high quality single crystal copper oxide thin film having a constant thickness, a small RMS value with respect to surface roughness, and a constant crystal orientation arrangement.

In addition, by using the complex, the copper linear film can be formed at a low temperature, thereby lowering the manufacturing cost and performing the process more easily. Therefore, the industrial utilization of the copper oxide thin film can be further improved.

Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. .

According to the present invention, a copper oxide film is formed by an electrochemical deposition method using a complex. First, an aqueous solution containing copper and an aqueous solution containing a sample for complex formation are stirred to form an electrochemical deposition solution, followed by electrochemical A direct current voltage is applied to the aqueous vapor deposition solution to form a copper oxide film using a complex formed from the sample.

As described above, the copper oxide film forming method of the present invention consists of an electrochemical deposition aqueous solution forming step and a copper oxide film forming step, through which the copper oxide has a constant thickness, a smooth surface, and a crystal arrangement direction. The film can be formed at low temperatures.

Hereinafter, an electrochemical deposition solution forming step and a copper oxide film forming step will be described in detail.

1. The electrochemical deposition aqueous solution formation step is as follows.

According to the present invention, an aqueous solution containing copper and an aqueous solution containing a sample for complex formation are stirred to form an electrochemical deposition solution. Here, the aqueous solution containing copper is used as a copper source for copper oxide film formation, and the aqueous solution containing a sample for complex formation is for forming a complex.

By forming the complex in this way, not only copper ions can be easily formed even at low temperatures, but also the root-mean-square (RMS) and crystal orientation arrangements with respect to the thickness and surface roughness of the copper oxide film can be easily adjusted.

First, the aqueous solution containing copper and the aqueous solution containing a sample for complex formation are produced, respectively.

Here, it is preferable that the aqueous solution containing copper consists of aqueous copper nitrate solution. For example, the copper nitrate aqueous solution is preferably prepared by stirring and dissolving copper nitrate hydrate (Cu (NO ₃ ) ₂ .2.5H ₂ O) in distilled water, preferably at a concentration of 20 mM or more.

Moreover, it is preferable that the aqueous solution containing a sample for complex formation is an aqueous solution containing HMTA. For example, the aqueous HMTA solution is preferably prepared by dissolving HMTA (Hexamethylenetetramine) in distilled water to dissolve it, preferably at a concentration of 20 mM or more.

Subsequently, the prepared copper nitrate aqueous solution and the HMTA aqueous solution are stirred to prepare an electrochemical deposition aqueous solution.

At this time, the aqueous copper nitrate solution and the aqueous HMTA solution are preferably stirred for a sufficient time, for example, for 1 hour or more, until a stable complex is formed after mixing, and the electrochemical deposition aqueous solution is used at a concentration above a critical concentration. For example, the concentration is preferably 20mM or more.

In the case of forming a single crystal copper oxide (I) thin film using an electrochemical deposition solution below a critical concentration, a micro-sized void is formed because the ions necessary for growing the copper oxide (I) thin film cannot be sufficiently supplied. A thin film can be formed. Therefore, as described above, it is preferable to supply a sufficient amount of ions to form a single crystal copper oxide (I) thin film more stably and efficiently by using an electrochemical deposition aqueous solution having a critical concentration or more.

2. Looking at the copper oxide film forming step is as follows.

According to the present invention, a direct current voltage is applied to the electrochemical deposition aqueous solution described above to form a copper oxide film using a complex formed from a sample.

First, prior to depositing the copper oxide film, it is preferable to heat the prepared electrochemical deposition aqueous solution for 5 minutes or more in a water bath of 80 to 90 ℃ while stirring at a rate of 100rpm or more.

As such, by heating the electrochemical deposition aqueous solution for at least 5 minutes in a water bath of 80 ° C to 90 ° C, a stable single crystal copper oxide thin film may be formed by receiving a sufficient amount of ions decomposed from the formed complex.

Subsequently, a working electrode, a reference electrode, and a countering electrode for forming the copper oxide film in the electrochemical deposition aqueous solution are charged. Next, a copper oxide film is deposited on the working electrode by applying a DC voltage of -30 to -80 mV to the reference electrode.

Hereinafter, a process of forming a copper oxide film by a complex will be described in detail with reference to the chemical formula.

First, a complex is formed from a sample for complex formation in an electrochemical deposition aqueous solution. For example, when using HMTA as a complex formation sample, various complexes are formed by decomposition, partial decomposition or non-degradation of HMTA.

_{C 6 H 12 N 4 + 10H} 2 O → 6HCHO + 4 (NH 4) + + 4OH -

(CH ₂ ) 6N ₄ ^- H ⁺ , [Cu (CH ₂ ) ₆ N ₄ )] ²⁺

Formula 1 shows a case where HMTA is decomposed to form formaldehyde (HCHO) and ammonia (NH ₃ ). Wherein ammonia (NH 3) is an ammonium ion (NH ₄ ⁺ ), a copper ammonium complex ([Cu (NH ₃ ) ₄ (H ₂ 0)] ²⁺ ) or an ammonium hydroxide complex ((NH ₄ ) ⁺ OH ⁻ ) It will form complexes of various types. In addition, formula (2) represents a complex formed by partially or undecomposed HMTA.

As such, HMTA in the electrochemical deposition solution is decomposed, partially decomposed or undecomposed to form complexes of various types. The complexes form coordination bonds with the crystal faces of copper oxide (I), thereby forming copper oxide (I). When the thin film is grown, the growth of the copper oxide (I) thin film may be induced in a specific direction.

Subsequently, the complexes in the electrochemical deposition solution is decomposed to form a copper ion (Cu ^{+ 2).} At this time, hydroxide ions (OH ⁻ ) are formed together by a deprotonation reaction.

Then, by applying a direct current voltage of -30 to -80mV to the reference electrode 2 is one of a copper ion (Cu ^{+ 2)} is reduced to copper ions (Cu ^+). The reduced monovalent copper ions (Cu ⁺ ) form copper oxide (Cu ₂ O) by a condensation reaction.

_{^{2Cu + + 2OH - → Cu 2}} O + H 2 O

Formula 3 represents a reaction formula in which the reduced copper ions (Cu ⁺ ) form copper oxide (I) by a condensation reaction. As described above, the complex in the electrochemical deposition aqueous solution is decomposed to supply a sufficient amount of copper ions (Cu ⁺ ) and hydroxide ions (OH ⁻ ), thereby easily forming a copper oxide (I) thin film at low temperature.

In addition, coordination bonding of various types of complexes formed from ammonium ions, HMTA, and the like and copper oxide (I) crystal planes can induce the formation of a copper oxide (I) thin film in a specific direction, for example, in the [111] direction. have. Therefore, it is possible to form a copper oxide film having a constant thickness, a small RMS value with respect to surface roughness, and a constant orientation of crystal orientation. That is, the thickness and growth pattern of the copper oxide film can be easily adjusted.

Subsequently, the formed single crystal copper oxide (I) thin film is taken, washed several times with distilled water and ethyl alcohol, and then dried with nitrogen gas.

1 shows a configuration of an electrochemical deposition apparatus according to an embodiment of the present invention.

As shown, the electrochemical deposition aqueous solution is filled in the electrochemical deposition reactor 10, and the working electrode 11, the reference electrode 12, and the counter electrode 13 for forming the copper oxide film in the electrochemical deposition aqueous solution are charged. do. Here, the operation electrode 11 is operated as a reduction electrode, preferably made of a conductive substrate, for example, platinum (Pt).

The operation electrode 11, the reference electrode 12, and the counter electrode 13 are installed at predetermined intervals so that current can flow smoothly, and are connected to the current / voltage application device 14. When a direct current voltage is applied to the reference electrode 11, monovalent copper ions (Cu +) and hydroxide ions (OH−) are supplied to form a copper oxide (I) thin film on the surface of the operation electrode 11. At this time, the DC voltage applied to the reference electrode 12 is preferably -30 to -80mV.

2A to 2D show results of analyzing a surface of a copper oxide (I) thin film formed by an electrochemical deposition method according to an embodiment of the present invention.

FIG. 2A shows a scanning electron microscope (SEM) photograph of the surface of the single crystal copper oxide (I) thin film, and particularly shows the surface of the copper oxide (I) thin film formed to a thickness of 75 nm.

As shown, in the case of forming a copper (I) thin film using a complex, atoms are aggregated to form a cluster, and the clusters are coalesced without voids, thereby making it uniform. A copper (I) thin film on the surface is formed. That is, it is possible to reduce the RMS value for the surface roughness as compared with the conventional.

At this time, various types of complexes formed from ammonium ions, HMTA, and the like form coordination bonds with the crystal surfaces of copper oxide (I), and thus, the copper oxide (I) crystal surfaces have different surface energies. Therefore, growth on the specific directional plane is hindered and growth on the specific directional plane is promoted.

For example, various types of complexes formed from ammonium ions, HMTA, form coordination bonds such that the crystal planes in the [111] direction have a stronger surface tension, and thus grow in the [111] direction during the copper oxide (I) thin film. The arrangement direction is maintained.

2B shows an X-ray diffraction pattern diagram of the single crystal copper oxide (I) thin film.

As shown, by forming a copper oxide (I) thin film using a complex, a single crystal copper oxide (I) thin film of Cu ₂ O cubic structure, in which the orientation of crystals is constant at [111], is formed. You can see that.

FIG. 2C shows an Atomic Force Microscope (AFM) photograph of the surface of a single crystal copper oxide (I) film, and particularly shows the surface of a copper oxide (I) thin film having an RMS value of about 2.6 nm.

As shown in the drawing, when the copper oxide (I) thin film is formed using the complex, not only is it easy to control the direction of growth arrangement of the crystal, but also it shows a layer-growth form grown as a layer. . Therefore, the thickness of the thin film can be easily controlled, and a copper oxide (I) thin film having a uniform surface having an RMS value of 3 nm or less can be formed.

Therefore, according to the present invention, the copper oxide (I) thin film can be easily adjusted to 75 to 190 nm by adjusting the execution time of the copper oxide forming process, that is, the time for applying the DC voltage to the reference electrode 12. have. For example, when the copper oxide formation process is performed for about 150 seconds, a copper oxide (I) thin film having a uniform thickness of about 190 nm may be formed.

Of course, it is also possible to form a copper oxide (I) thin film having a thickness of 190 nm or more by increasing the execution time of the copper oxide forming process. In this case, the growth form of the copper oxide (I) thin film may be transferred from the layer-growth form to the island-growth, which will be described in detail with reference to FIG. 2D.

2D and 2E are scanning electron microscope (SEM) photographs and X-ray diffraction patterns of a single crystal copper oxide (I) thin film grown by transferring a growth pattern from layer-growth to island-growth. Shows a figure.

As shown, when the copper oxide (I) thin film is formed using the complex, the copper oxide (I) thin film may be formed to a thickness of 190 nm or more by increasing the execution time of the copper oxide forming process.

In this case, the growth pattern of the copper oxide (I) thin film may be transferred to island-growth. In this case, the growth pattern may be transferred only, and the direction of the crystal arrangement may be maintained. This can be seen from the pattern diagram.

As described above, the present invention can maintain a constant growth arrangement direction of crystals by using a complex to hinder growth on a specific crystal plane or promote growth of a specific crystal plane during crystal growth. Therefore, even if the growth mode of the copper oxide (I) thin film is transferred, the direction of growth arrangement of the crystal is maintained as it is.

For example, when a copper oxide (I) forming process is performed for about 600 seconds to form a copper oxide (I) thin film having a thickness of about 950 nm, even if the growth form of the copper oxide (I) thin film is transferred to an island growth form, The crystal growth arrangement direction is maintained at [111].

3A to 3C are photographs showing a cross section of a copper oxide (I) thin film formed by an electrochemical deposition method according to an embodiment of the present invention. In particular, a cross section of a single crystal copper oxide (I) thin film formed to a thickness of 190 nm. A transmission photograph is shown.

FIG. 3A is a Transmission Electron Microscope (TEM) photograph of a single crystal copper oxide (I) thin film cross section formed using a complex. FIG.

3B is a High Resolution Transmission Electron Microscope (HRTEM) photograph of a single crystal copper oxide (I) thin film cross section formed using a complex.

As shown, when the copper oxide (I) thin film is formed using the complex, it can be seen that the crystal lattice of the single crystal copper oxide (I) thin film is uniformly arranged at intervals of about 0.243 nanometers. It can be seen that the copper oxide (I) thin film is constantly grown in the [111] direction.

FIG. 3C is a High Resolution Transmission Electron Microscope (HRTEM) photograph of the junction surface of the substrate and the single crystal copper oxide (I) thin film. FIG.

As shown, when the copper oxide (I) thin film is formed on the substrate using a complex, only a single crystal copper oxide (I) thin film is stable without forming an amorphous layer or other phase material made of copper or oxygen. It can be confirmed that formed.

Here, it is preferable that a board | substrate consists of a conductive substrate, For example, it is more preferable that it consists of platinum (Pt).

Although the technical spirit of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will appreciate that various embodiments within the scope of the technical idea of the present invention are possible.

1 is a block diagram of an electrochemical deposition apparatus according to an embodiment of the present invention.

2A is a scanning electron microscope (SEM) photograph of the surface of a single crystal copper oxide (I) thin film.

2B is an X-ray diffraction pattern diagram of a single crystal copper oxide (I) thin film.

FIG. 2C is an Atomic Force Microscope (AFM) photograph of the surface of a single crystal copper oxide (I) thin film. FIG.

2D is a scanning electron microscope (SEM) photograph of a single crystal copper oxide (I) thin film.

2E is an X-ray diffraction pattern diagram of a single crystal copper oxide (I) thin film.

3A is a transmission electron microscope (TEM) photograph of a single crystal copper oxide (I) thin film cross section.

Figure 3b is a High Resolution Transmission Electron Microscope (HRTEM) photograph of a single crystal copper oxide (I) thin film cross section.

FIG. 3C is a High Resolution Transmission Electron Microscope (HRTEM) photograph of the junction surface of the substrate and the single crystal copper oxide (I) thin film. FIG.

[Description of Symbols for Main Parts of Drawing]

10: electrochemical deposition reactor 11: working electrode

12: reference electrode 13: counter electrode

Claims (17)

Preparing an electrochemical deposition aqueous solution by stirring an aqueous solution containing copper and an aqueous solution including a sample for complex formation; And Applying a DC voltage to the electrochemical deposition aqueous solution to form a copper oxide film using a complex formed from the sample, Here, the copper oxide film forming step, Forming a complex from the sample; Decomposing the complex to form copper ions; And The step of forming a copper oxide film by the condensation reaction of the copper ions Copper oxide film forming method comprising a. The method of claim 1, Before the copper oxide film forming step, Stirring the prepared electrochemical deposition solution at a temperature of 80 to 90 ° C. at a rate of 100 rpm or more for 5 minutes or more Copper oxide film forming method further comprising. The method of claim 1, The aqueous solution containing the copper, Copper nitrate aqueous solution Copper oxide film formation method. The method of claim 1, The complex formation sample, Hexamethylenetetramine (HMTA) Copper oxide film formation method. delete The method of claim 1, The concentration of the aqueous solution containing the copper, More than 20mM Copper oxide film formation method. The method of claim 1, The concentration of the aqueous solution containing the sample for complex formation is More than 20mM Copper oxide film formation method. The method of claim 1, The concentration of the electrochemical deposition solution is More than 20mM Copper oxide film formation method. The method of claim 1, The copper oxide film forming step, Charging the operation electrode, the reference electrode and the counter electrode in the electrochemical deposition solution, and applying a DC voltage of -30 to -80 mV to the reference electrode. Copper oxide film formation method. Preparing an electrochemical deposition solution by stirring an aqueous solution including an aqueous copper nitrate solution and HMTA; And Applying a DC voltage to the electrochemical deposition solution to form a copper oxide film using a complex formed from the HMTA Copper oxide film forming method comprising a. The method of claim 1, Before the copper oxide film forming step, Stirring the prepared electrochemical deposition solution at a temperature of 80 to 90 ° C. at a rate of 100 rpm or more for 5 minutes or more Copper oxide film forming method further comprising. 11. The method of claim 10, The copper oxide film forming step, Forming a complex from the HMTA; Decomposing the complex to form copper ions; And The step of forming a copper oxide film by the condensation reaction of the copper ions Copper oxide film forming method comprising a. 13. The method of claim 12, The complex forming step, The HMTA is decomposed to form a copper ammonium complex ([Cu (NH ₃ ) ₄ (H ₂ O)] ²⁺ ) or an ammonium hydroxide complex ((NH ₄ ) ⁺ OH ⁻ ) Copper oxide film formation method. 13. The method of claim 12, The complex forming step, HMTA is the differential part sun or decomposes ^{_{(CH 2) 6 N 4 -}} H + or a complex _{[Cu ((CH 2) 6} N 4)] to form a ^{2 +} complexes Copper oxide film formation method. 11. The method of claim 10, The concentration of the copper nitrate aqueous solution is, More than 20mM Copper oxide film formation method. 11. The method of claim 10, The concentration of the HMTA aqueous solution, More than 20mM Copper oxide film formation method. 11. The method of claim 10, The concentration of the electrochemical deposition solution is More than 20mM Copper oxide film formation method.

Images