WO2009093770A1 - Method for etching of insulating layers using carbon nanotubes and formation of nanostructures thereafter - Google Patents
Method for etching of insulating layers using carbon nanotubes and formation of nanostructures thereafter Download PDFInfo
- Publication number
- WO2009093770A1 WO2009093770A1 PCT/KR2008/000486 KR2008000486W WO2009093770A1 WO 2009093770 A1 WO2009093770 A1 WO 2009093770A1 KR 2008000486 W KR2008000486 W KR 2008000486W WO 2009093770 A1 WO2009093770 A1 WO 2009093770A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- carbon nanotubes
- insulating layers
- nanotrenches
- substrate
- forming
- Prior art date
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 111
- 239000002041 carbon nanotube Substances 0.000 title claims abstract description 94
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- 238000000034 method Methods 0.000 title claims abstract description 60
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- 229910020598 Co Fe Inorganic materials 0.000 description 1
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
- B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
- B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
- B81C1/00023—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems without movable or flexible elements
- B81C1/00055—Grooves
- B81C1/00063—Trenches
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
- H01L21/306—Chemical or electrical treatment, e.g. electrolytic etching
- H01L21/308—Chemical or electrical treatment, e.g. electrolytic etching using masks
- H01L21/3083—Chemical or electrical treatment, e.g. electrolytic etching using masks characterised by their size, orientation, disposition, behaviour, shape, in horizontal or vertical plane
- H01L21/3085—Chemical or electrical treatment, e.g. electrolytic etching using masks characterised by their size, orientation, disposition, behaviour, shape, in horizontal or vertical plane characterised by their behaviour during the process, e.g. soluble masks, redeposited masks
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/3105—After-treatment
- H01L21/311—Etching the insulating layers by chemical or physical means
- H01L21/31144—Etching the insulating layers by chemical or physical means using masks
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
- H01L21/76801—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing
- H01L21/76802—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics
- H01L21/76816—Aspects relating to the layout of the pattern or to the size of vias or trenches
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
- H01L21/76838—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the conductors
Definitions
- the present invention relates to a method of etching insulation layers using carbon nanotubes, and a nanostructure prepared using the same, and more particularly, to a method of etching insulating layers using carbon nanotubes, which is simpler than a conventional method, and more environmentally friendly, is able to prepare nanotrenches on insulating layers having an average width of 0.5 to 500 nm, and is able to provide a nanostructure for highly integrated devices using the nanotrenches on the insulating layers as a mask, and a nanostructure prepared using the same.
- Such nanostructures are very small in size, and thus they are impossible to manufacture using a conventional photolithography process, due to the limitations of exposure equipment used in the exposure process. That is, due to a limitation in regards to the diffraction of light, it is impossible to achieve a wire width that is shorter than or equal to the wavelength of the light source, and thus nano-scale wire widths cannot be implemented.
- Electron beam lithography uses a method of drawing a pattern using an electron beam which can be likened to drawing with an "electron-brush.” Using this method it is possible to achieve a wire width of around several tens of nanometers, which is impossible with conventional exposure processes.
- wire widths made possible by e-beam lithography are limited to several tens of nanometers, therefore it is difficult to keep up with the continuously decreasing size of new technologies.
- using e-beam lithography as a means to prepare nanostructures is not economical.
- a method of manufacturing nano-sized structures with such conventional printing method has many problems, such as limitations in the shape.
- carbon nanotube refers to an array of carbon atoms joined in a hexagonal honeycomb-shaped pattern to form a tube-like shape, wherein the diameter of the tube is of a nanometer scale, i.e. a material very small in size.
- Carbon nanotubes are categorized into single-walled carbon nanotube (SWNT), double-walled carbon nanotube (DWNT), multi-walled carbon nanotube (MWNT), and rope carbon nanotube, depending on the number of bonds in a graphite wall thereof. Since Kroto and Smalley first discovered Fullerene (a group of 60 carbon atoms:C 6 o), which is one kind of carbon allotrope, in 1985 Dr.
- Carbon nanotubes may be produced large-scale by arc-discharge, laser ablation, plasma-enhanced chemical vapor deposition, chemical vapor deposition, vapor phase growth, electrolysis, and flame synthesis. Moreover, carbon nanotubes have excellent mechanical characteristics, electrical choice, outstanding field emitting properties, and highly efficient hydrogen storage media properties, and thus have a wide range of applications.
- the present invention provides a method of etching insulating layers using carbon nanotubes, which is simpler than a conventional method, and more environmentally friendly, and capable of manufacturing nanotrenches with a width of 0.5 to 500 nm.
- the present invention also provides a nanostructure prepared using the method above.
- a method of etching insulating layers using carbon nanotubes including: forming insulating layers on a substrate; forming carbon nanotubes on the insulating layers; and forming nanotrenches on the insulating layer by carbothermal reduction of the insulating layers on which the carbon nanotubes are formed.
- the substrate may be one selected from the group consisting of silicon wafer, sapphire, glass, quartz, metal, alumina and plastic.
- the insulating layers may be formed of a compound including silicon.
- the insulating layers may be formed from at least one selected from the group consisting of silicon oxide, silicon dioxide, silicon nitrate, and silicon nitride.
- the carbon nanotubes may be formed using a method selected from the group consisting of chemical vapor deposition (CVD), laser ablation, arc-discharge, plasma enhanced chemical vapor deposition (PECVD), vapor phase growth, sonication method, electrolysis and flame synthesis.
- CVD chemical vapor deposition
- PECVD plasma enhanced chemical vapor deposition
- vapor phase growth vapor phase growth
- sonication method electrolysis and flame synthesis
- the carbon nanotubes may be selected from the group consisting of single-walled carbon nanotubes (SWNT), double-walled carbon nanotubes (DWNT), multi-walled carbon nanotubes (MWNT), rope carbon nanotubes, and a structure in which catalysts are wrapped with carbon particles.
- SWNT single-walled carbon nanotubes
- DWNT double-walled carbon nanotubes
- MWNT multi-walled carbon nanotubes
- rope carbon nanotubes and a structure in which catalysts are wrapped with carbon particles.
- the carbon nanotubes may have an average diameter of 0.5 to 300 nm.
- the carbothermal reduction may be performed by injecting oxygen and inert gas.
- the oxygen content may be 0.0001 to 30% of the total volume of gas.
- the carbothermal reduction may be performed under a temperature of 700 to 1200 0 C.
- the nanotrenches of the insulating layers may have an average width of 0.5 to 500 nm.
- the formation of the carbon nanotubes and the carbothermal reduction may occur simultaneously.
- the formation of the carbon nanotubes and the carbothermal reduction occurs while oxygen, hydrogen, and hydrocarbons may be injected simultaneously.
- the oxygen content may be 0.01 to 2% of the total volume of gas.
- the hydrocarbon may be at least one selected from the group consisting of methane, ethane, acetylene, ethylene, butane, and propane.
- the top portion of the substrate on which the insulating layers are formed may be deposited with one of metal catalyst and transition metal catalyst.
- the metal or transition metal catalyst may be formed of one of Ni, Fe, Co, Y, Mo, Al, Rh, Pd, Au, Ag, Cu, and alloys thereof.
- a nanostructure prepared using the method of etching the insulating layers.
- the nanostructure may be a metal/semiconductor nanowire, an etched structure of a substrate for semiconductor, or an array of metal/semiconductor nanoparticles.
- the method of etching according to an embodiment of the present invention is economical and simple compared to conventional methods which require costly machinery and complex pretreatment processes for etching, and is also environmentally friendly because chemicals hazardous to human and environment is not used. Moreover, the method uses carbon nanotubes with a diameter of 0.5 to 300 nm to produce nanotrenches on insulating layers with a width of 0.5 to 500 nm, which is difficult to achieve using conventional methods. Furthermore, nanostructures for high density integrated devices can be provided using the nanotrenches on the insulating layers.
- FIG. 1 is a schematic diagram of a process of forming nanotrenches derived by a carbon nanotube during chemical vapor deposition reaction in which oxygen is injected;
- FIG. 2 is a tapping mode atomic force microscopic (AFM) image of a Si ⁇ 2 /Si substrate having linear-form nanotrenches;
- AFM atomic force microscopic
- FIG. 3 is a tapping mode atomic force microscopic (AFM) image of a SiO 2 /Si substrate in which a part of unreacted carbon nanotubes remain on the edges of the nanotrenches;
- AFM atomic force microscopic
- FIG. 4 is a schematic diagram of a process of forming a Cr nanowire (left) and Si nanotrenches (right) using Si ⁇ 2 nanotrenches as a mask;
- FIGS. 5 through 8 are AFM images at low and high magnifications of the Cr nanowires.
- FIGS. 9 and 10 are AFM images at low and high magnifications of the Si nanotrenches.
- a method of etching insulating layers using carbon nanotubes including: forming insulating layers on a substrate; forming carbon nanotubes on the insulating layers; and forming nanotrenches on the insulating layer by carbothermal reduction of the insulating layers on which the carbon nanotubes are formed.
- the substrate is not particularly limited, and may include, silicon wafer, sapphire, glass, quartz, metal, alumina or plastic.
- the insulating layers is not particularly limited insofar as it is a compound including silicon, and may be formed of at least one selected from the group consisting of silicon oxide, silicon dioxide, silicon nitrate, and silicon nitride.
- the insulating layer is formed of silicon dioxide, due to high efficiency of forming nanotrenches by carbothermal reduction.
- insulating layers made of silicon dioxide may be formed by oxidation of a silicon wafer as a substrate, using a conventional desiccated oxygen or water vapor, wherein the thickness is not particularly limited.
- SiO 2 may be formed by calcinating a silicon wafer under air at 800 to 1200 0 C for several seconds to several minutes.
- the SiO 2 layers are formed by a chemical oxidation of the silicon wafer, and the thickness of the layers can be confirmed using an elipsometer.
- the present invention may be applied regardless of the thickness as long as SiO 2 layers exist, and the thickness of the SiO 2 layers may be determined according to the purposes.
- the substrate surface may be deposited with a metal or transition metal catalyst.
- the metal or transition metal catalyst may be formed of a single metal or transition metal such as Ni, Fe, Co, Y, Mo, Al, Rh, Pd, Au, Ag, or Cu, or may also be formed of a binary or a ternary alloy such as Co-Ni, Co-Fe, Ni-Fe, or Co-Ni-Fe.
- the metal or transition metal catalyst may be deposited using thermal evaporation, sputtering, electron beam evaporation, or using a reaction between chemical materials in an aqueous solution to form a metal or transition metal nanoparticles with a thickness of several A or tens of A on the substrate.
- the carbon nanotubes may be formed using a method selected from the group consisting of chemical vapor deposition (CVD), laser ablation, arc-discharging, plasma enhanced chemical vapor deposition (PECVD), vapor phase growth, sonication synthesis, electrolysis and flame synthesis.
- CVD chemical vapor deposition
- PECVD plasma enhanced chemical vapor deposition
- vapor phase growth vapor phase growth
- sonication synthesis electrolysis and flame synthesis.
- electrolysis and flame synthesis electrolysis and flame synthesis.
- the carbon nanotubes may be selected from the group consisting of single-walled carbon nanotubes (SWNT), double-walled carbon nanotubes (DWNT), multi-walled carbon nanotubes (MWNT), rope carbon nanotubes, and structures in which catalysts are wrapped with carbon particles.
- SWNT single-walled carbon nanotubes
- DWNT double-walled carbon nanotubes
- MWNT multi-walled carbon nanotubes
- rope carbon nanotubes rope carbon nanotubes
- the nanotrenches formed on the insulating layers according to an embodiment of the present invention are completely derived from the carbon nanotubes, and thus properties of the nanotrenches on the insulating layers are determined by the loci, length, and width of the carbon nanotubes. Therefore, the carbon nanotubes according to an embodiment of the present invention may preferably have an average diameter of 0.5 to 300 nm and may be selected with regards to the width of nanotrenches that are to be formed thereafter. Sequentially, forming the nanotrenches from the insulating layers on which the carbon nanotubes are formed will be described in detail.
- the nanotrenches on the insulating layers are formed by a carbothermal reduction between the carbon nanotubes and the insulating layer formed on the substrate, and the reduction reaction may be a method selected from the group consisting of CVD, PECVD, thermal vapor deposition, and vapor phase growth.
- carbon (C) within the carbon nanotubes act as a reducing agent for reducing and thereby etching the insulating layers.
- the carbothermal reduction may be performed at a temperature of 700 to 1200 ° C , and preferably at a temperature of 800 to 950 0 C . If the reaction temperature is lower than 700 ° C , the production efficiency of the carbon nanotubes and the nanotrenches decrease, and if the reaction temperature is greater than 1200 ° C , dangers of economical losses and gas explosion exist due to reaction at high temperature.
- the carbothermal reduction of the substrate on which the carbon nanotubes are formed may be performed by injecting oxygen and inert gas. That is, if oxygen is included during the carbothermal reduction, destruction of carbon nanotubes having high crystallizability and thermostability may occur more easily, and forms a locally limited reactive carbon-like component that reacts with the insulating layers at the same temperature.
- the nanotrench forming efficiency is directly proportional to the amount of oxygen injected.
- the carbothermal reduction of the insulating layers may be performed by injecting oxygen and inert gas.
- the oxygen content may be 0.0001 to 30%, and preferably, 0.0003 to 0.01 % based on the total gas volume.
- the oxygen content is less than 0.0001 %, carbothermal reduction does not occur easily, therefore the nanotrench forming efficiency may be significantly reduced, and if the content is greater than 30%, oxidation between excess oxygen and the carbon nanotubes themselves may occur first, which may also significantly reduce nanotrench forming efficiency.
- the inert gas which includes the oxygen may be helium, neon, argon, krypton, xenon, and radon, and preferably, may be argon.
- forming the carbon nanotubes and the carbothermal reduction of the substrate on which carbon nanotubes are formed may occur simultaneously. That is, if oxygen, hydrogen, and hydrocarbon gases are injected into a chemical vapor deposition equipment for forming the carbon nanotubes on the substrate, the carbon nanotubes are formed on the insulating layers of the substrate and at the same time the carbon nanotubes formed thereby may act as a reducing agent to cause carbothermal reduction of the insulating layers. Therefore, the nanotrenches on the insulating layers may be formed advantageously in a short period of time with reduced loss of fuel.
- the oxygen content may be 0.01 to 2%, and preferably may be 0.03 to 0.1% based on the total gas volume. If the oxygen content is lower than 0.01 %, carbothermal reduction may not occur smoothly, and thus the efficiency of the nanotrench formation may be significantly reduced, and if the oxygen content is greater than 2%, excess oxygen and hydrocarbon gas may react, which may lead to explosion.
- the contents of hydrogen and hydrocarbons are not particularly limited, but the hydrogen content may be 20 to 50% and preferably 25 to 40% based on the total gas volume, and the hydrocarbon content may be 50 to 80% and preferably 55 to 75%, based on the total gas volume.
- the hydrocarbon is not particularly limited, and may specifically be one selected from the group consisting of methane, ethane, acetylene, ethylene, butane, and propane. Among these, methane, ethylene, or acetylene may preferably be used due to their efficiency in carbon nanotube synthesis.
- nanoparticles of metal or transition metal catalysts used during carbon nanotube formation also accelerates heat evaporation of the insulating layers, and thus increases the rate of conversion of carbon nanotubes into nanotrenches, in an efficient carbothermal reduction of the insulating layers.
- the carbon nanotubes are dispersed in chloroform, and then sonication is performed a multiple of times, in order to prevent clumping among nanotubes, weight separation is performed by centrifugation, relatively light carbon nanotubes are dispersed by spin-coating in Si ⁇ 2 , and then a reaction is derived by chemical vapor deposition.
- the number of nanotrenches formed is significantly increased when the catalysts are included in the carbon nanotubes compared to the case where the catalysts are removed by strong acid treatment.
- the regions where catalysts were present are also etched, and thus it can be easily observed that either holes are formed, or most nanotrenches do not include any catalysts on both ends.
- This can be considered as a mark from which the catalysts are removed through carbothermal reduction while carbon molecules, although not synthesized into carbon nanotubes, formed a film on the catalysts, or as a mark from which catalysts are evaporated because the melting point has decreased due to an interaction between the catalysts and the insulating layers.
- the physical characteristics of the insulating layers are determined by the original characteristics of the carbon nanotubes, because the nanotrenches are formed by carbothermal reduction between the carbon nanotubes and the adjacent insulating layers. Therefore, the length of the nanotrenches may correspond to the length of the carbon nanotubes, which may extend up to tens of micrometers.
- the average width of the nanotrenches may be measured using a high-resolution transmission electron microscopy (HRTEM), and the average width of the nanotrenches on the insulating layers may be 0.5 to 500 nm.
- HRTEM transmission electron microscopy
- nanotrenches on the insulating layers which, as an example, are SiO 2 layers will be described in detail, according to an embodiment of the present invention.
- the major driving force of forming the nanotrenches on the SiO 2 layers as the insulating layers is SiO 2 carbothermal reduction in which the carbon nanotubes act as a reducing agent. It is known that amorphous bulk silica SiO 2 (S) releases SiO(g) and CO(g), as shown in the formula below, and is thereby reduced by carbon (C(s)) under atmospheric pressure at a temperature of 1000 ° C and greater,
- FIGS. 1 and 2 are respectively a schematic diagram and an atomic force microscopic (AFM) image of a nanotrench-forming process derived by carbon nanotubes during chemical vapor deposition with oxygen injection. That is, when a substrate on which catalysts are deposited is placed in chemical vapor deposition equipment, and is simultaneously injected with oxygen, hydrogen, and a hydrocarbon (methane or ethylene etc.) under a temperature of 700 to 1200 ° C, synthesis of carbon nanotubes and carbothermal reduction occur.
- AFM atomic force microscopic
- carbon nanotubes are synthesized, and concurrently a reduction takes place on a surface of the substrate to SiO 2 and the like, and as a result, an SiO 2 layer is formed, having etched areas corresponding to the carbon nanotubes.
- the solid-phase SiO 2 and C should be in contact with each other in order for the above reduction to take place, and only the carbon nanotubes that are in direct contact with the SiO 2 surface are activated for the reduction.
- a nanostructure prepared by the etching of the insulating layers.
- nanostructures such as metal/semiconducting nanowires, etched structures of a substrate for semiconductor, and arrays of metal/semiconductor nanoparticles may be provided.
- one of the important issues in the manufacturing of one-dimensional metal nanowires and nanotrenches on substrates for semiconductor is obtaining nanostructures with a diameter or a width smaller than 10 nm. This can be achieved using the nanotrenches on the insulating layers as a mask by using the method according to the current embodiment the present invention.
- the metal nanowires may be prepared using the insulating layers that have been etched using the method previously described as a mask, and depositing the metal thereon, and immersing the metal-deposited substrate in a developing solution to remove the insulating layers used as the mask.
- the metals used in the deposition may be one selected from the group consisting of Cr, GaAs, GaN, Ti, Pd, Ni, Co, Al, Ag, Pt, Au and Cu.
- the method of metal deposition is not particularly limited, and a conventional method may be used.
- the developing solution is not particularly limited insofar as it is able to dissolve the insulating layers.
- an aqueous solution of HF with a content of 0.1% may be used.
- the nanotrenches which are etched on Si substrate in a nanometer scale useful in a nanoelectronic technology may be prepared using the same SiO 2 nanotrench mask.
- the Si substrate on which SiO 2 nanotrenches are formed may be immersed in an aqueous solution of KOH or the like to etch the Si, which may then be immersed in an aqueous solution of HF to remove the nanotrench mask layer, thereby manufacturing the nanotrenches as an etched structure on the Si substrate.
- FIG. 4 is a schematic diagram of a process of forming Cr nanowires (left) and Si nanotrenches (right) using the SiO 2 nanotrenches as a mask, as previously described.
- an iron catalyst was first deposited on a SiO 2 ZSi substrate.
- 100 ⁇ # of 40 mM NH 2 OH HCI aqueous solution and ' ⁇ O ⁇ l of 10 mM FeCI 3 -6H 2 O aqueous solution were added to 10 ml of triple-distilled water in which SiO 2 /Si substrate is immersed, and as a result of reacting for 3 minutes, an iron catalyst with a diameter of a nanotube (average: 1.7 nm) was compactly formed on the substrate.
- the substrate sample on which the iron catalyst is deposited was transferred to a quartz container of chemical vapor deposition (CVD) equipment, and was reduced with H 2 gas at 500 seem, increasing the temperature to approximately 830 ° C .
- the valves for 0 2 /CH 4 ZC 2 H 4 gases were opened, where gas flow rates were 1.5/1000/20 seem respectively.
- the reaction was allowed to continue for 10 more minutes and the valves for O 2 ZCH 4 ZC 2 H 4 gases were closed, the temperature was then lowered to room temperature, and the sample was taken out.
- carbon nanotube synthesis and carbothermal reduction were simultaneously induced using hydrogen, hydrocarbon, and oxygen.
- a SiO 2 ZSi substrate was obtained having nanotrenches linearly formed and refined, which is shown through a tapping mode atomic force microscopic (AFM) image in FIG. 2
- AFM atomic force microscopic
- the nanotrenches on the SiO 2 substrate may be formed by inducing a carbothermal reduction on a carbon nanotube sample already formed.
- the carbon nanotube synthesis is the same as the method above except that oxygen gas was injected.
- the substrate on which the carbon nanotubes are synthesized was then transferred again to the quartz container of the CVD equipment, and Ar gas (including 0.0001% oxygen) was flowed in at 1000 seem while raising the temperature to 900 0 C , letting react for 5 minutes or longer, the temperature was then lowered to room temperature, and it was seen that the SiO 2 nanotrenches are formed on the SiO 2 ZSi substrate by the carbothermal reduction.
- Si nanotrenches according to an embodiment of the present invention were prepared through etching by KOH aqueous solution, using SiO 2 nanotrenches as a mask.
- the organic materials produced from the previous reaction and the carbon nanotubes were removed, and the sample was calcinated in air at about 800 0 C in order to prepare a clean SiO 2 nanotrench surface.
- the sample may be immersed in an aqueous solution of HF diluted to about 5% for about 1 minute, in order to remove the thin SiO 2 layer formed therefrom. Then, the sample was immersed in KOH aqueous solution with a 45% content ratio at 83 0 C and reacted for about 1 minute, in order to etch the Si.
- the treatment level should be carefully controlled to prevent a change of surface color of the mask to white, and a massive generation of H 2 bubbles from the substrate. This is because when the reaction with KOH aqueous solution is excessive, the SiO 2 nanotrench mask may also be damaged, etching the entire Si substrate by the KOH solution.
- the Si nanotrenches obtained as a result are shown as AFM images at low magnification and at high magnification in FIGS. 9 and 10.
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Abstract
Provided are a method of etching insulating layers using carbon nanotubes and a nanostructure prepared using the same, the method including: forming insulating layers on a substrate; forming carbon nanotubes on the insulating layers; and forming nanotrenches on the insulating layer by carbothermal reduction of the insulating layers on which the carbon nanotubes are formed. The method of etching according to an embodiment of the present invention is more economical and simple compared to conventional methods, which require costly instruments and complex pretreatment processes for etching, and is also environmentally friendly since chemicals hazardous to human and the environment are not used. Moreover, the method uses carbon nanotubes with a diameter of 0.5 to 300 nm to produce nanotrenches on insulating layers with a width of 0.5 to 500 nm, which is difficult to achieve using conventional methods. Furthermore, nanostructures for highly integrated devices can be provided by forming the nanotrenches on the insulating layers.
Description
METHOD FOR ETCHING OF INSULATING LAYERS USING CARBON NANOTUBES AND FORMATION OF NANOSTRUCTURES THEREAFTER
TECHNICAL FIELD
The present invention relates to a method of etching insulation layers using carbon nanotubes, and a nanostructure prepared using the same, and more particularly, to a method of etching insulating layers using carbon nanotubes, which is simpler than a conventional method, and more environmentally friendly, is able to prepare nanotrenches on insulating layers having an average width of 0.5 to 500 nm, and is able to provide a nanostructure for highly integrated devices using the nanotrenches on the insulating layers as a mask, and a nanostructure prepared using the same.
BACKGROUND ART
As semiconductor-manufacturing rapidly develops and various electronic parts and devices become integrated, more and more circuits and devices are being implemented in a small chip region. As such, semiconductor devices are becoming smaller in size, wire widths of the corresponding devices are also being reduced, and the importance of nanostructures such as nanowires forming such devices and nanotrenches on a semiconductor substrate is continuously growing.
Such nanostructures are very small in size, and thus they are impossible to manufacture using a conventional photolithography process, due to the limitations of exposure equipment used in the exposure process. That is, due to a limitation in regards to the diffraction of light, it is impossible to achieve a wire width that is shorter than or equal to the wavelength of the light source, and thus nano-scale wire widths cannot be implemented.
However, there is a technique which can be used to implementing nano patterns using an exposure method; this is e-beam lithography. Electron beam lithography uses a method of drawing a pattern using an electron beam which can be likened to drawing with an "electron-brush." Using this method it is possible to achieve a wire width of around several tens of nanometers, which is impossible with conventional exposure processes. However, wire widths made possible by e-beam lithography are limited to several tens of nanometers, therefore it is difficult to keep up with the continuously
decreasing size of new technologies. Moreover, because of a very slow speed of processing and high cost of equipment, using e-beam lithography as a means to prepare nanostructures is not economical.
Moreover, a method of manufacturing nano-sized structures with such conventional printing method has many problems, such as limitations in the shape.
Meanwhile, the term "carbon nanotube" refers to an array of carbon atoms joined in a hexagonal honeycomb-shaped pattern to form a tube-like shape, wherein the diameter of the tube is of a nanometer scale, i.e. a material very small in size. Carbon nanotubes are categorized into single-walled carbon nanotube (SWNT), double-walled carbon nanotube (DWNT), multi-walled carbon nanotube (MWNT), and rope carbon nanotube, depending on the number of bonds in a graphite wall thereof. Since Kroto and Smalley first discovered Fullerene (a group of 60 carbon atoms:C6o), which is one kind of carbon allotrope, in 1985 Dr. Ijima in a research center adjunct to Nippon Electrical Company (NEC) first announced in Nature journal, the discovery of a thin, long straw-shaped carbon nanotube while analyzing a carbon chunk formed on a graphite cathode using an arc-discharge with a transmitting electron microscope. Carbon nanotubes may be produced large-scale by arc-discharge, laser ablation, plasma-enhanced chemical vapor deposition, chemical vapor deposition, vapor phase growth, electrolysis, and flame synthesis. Moreover, carbon nanotubes have excellent mechanical characteristics, electrical choice, outstanding field emitting properties, and highly efficient hydrogen storage media properties, and thus have a wide range of applications.
Therefore, research and application regarding chemical reactivity of carbon nanotubes can provide a solution for successful implementation of nano electronic technology, composite materials, gas storages, energy converting system, sensitive chemicals, and biochemical sensors etc. So far, most investigations regarding chemical reactions of carbon nanotubes were focused on surface tethering with organic functional molecules through a non-covalent or covalent coupling reaction. In contrast, chemical reaction of carbon nanotubes which accompany complete combustion of carbon making up the carbon nanotube is rarely investigated, mainly due to their high chemical and thermal stability.
As such, synthesis of nano-scaled structures to satisfy their increasing integration into various electronic parts and devices is continuously in demand, and techniques of manufacturing carbon nanotubes, devices with an etching of a size of 10 nm or less
having external characteristics similar to carbon nanotubes, and nanowires is needed.
DETAILED DESCRIPTION OF THE INVENTION
TECHNICAL PROBLEM
The present invention provides a method of etching insulating layers using carbon nanotubes, which is simpler than a conventional method, and more environmentally friendly, and capable of manufacturing nanotrenches with a width of 0.5 to 500 nm.
The present invention also provides a nanostructure prepared using the method above.
TECHNICAL SOLUTION
According to an aspect of the present invention, there is provided a method of etching insulating layers using carbon nanotubes including: forming insulating layers on a substrate; forming carbon nanotubes on the insulating layers; and forming nanotrenches on the insulating layer by carbothermal reduction of the insulating layers on which the carbon nanotubes are formed.
The substrate may be one selected from the group consisting of silicon wafer, sapphire, glass, quartz, metal, alumina and plastic.
The insulating layers may be formed of a compound including silicon.
The insulating layers may be formed from at least one selected from the group consisting of silicon oxide, silicon dioxide, silicon nitrate, and silicon nitride.
The carbon nanotubes may be formed using a method selected from the group consisting of chemical vapor deposition (CVD), laser ablation, arc-discharge, plasma enhanced chemical vapor deposition (PECVD), vapor phase growth, sonication method, electrolysis and flame synthesis.
The carbon nanotubes may be selected from the group consisting of single-walled carbon nanotubes (SWNT), double-walled carbon nanotubes (DWNT), multi-walled carbon nanotubes (MWNT), rope carbon nanotubes, and a structure in which catalysts are wrapped with carbon particles.
The carbon nanotubes may have an average diameter of 0.5 to 300 nm.
The carbothermal reduction may be performed by injecting oxygen and inert gas.
Moreover, the oxygen content may be 0.0001 to 30% of the total volume of gas.
The carbothermal reduction may be performed under a temperature of 700 to 12000C.
The nanotrenches of the insulating layers may have an average width of 0.5 to 500 nm.
The formation of the carbon nanotubes and the carbothermal reduction may occur simultaneously.
Moreover, the formation of the carbon nanotubes and the carbothermal reduction occurs while oxygen, hydrogen, and hydrocarbons may be injected simultaneously.
Moreover, the oxygen content may be 0.01 to 2% of the total volume of gas.
Moreover, the hydrocarbon may be at least one selected from the group consisting of methane, ethane, acetylene, ethylene, butane, and propane.
The top portion of the substrate on which the insulating layers are formed may be deposited with one of metal catalyst and transition metal catalyst.
Moreover, the metal or transition metal catalyst may be formed of one of Ni, Fe, Co, Y, Mo, Al, Rh, Pd, Au, Ag, Cu, and alloys thereof.
According to another aspect of the present invention, there is provided a nanostructure prepared using the method of etching the insulating layers.
The nanostructure may be a metal/semiconductor nanowire, an etched structure of a substrate for semiconductor, or an array of metal/semiconductor nanoparticles.
ADVANTAGEOUS EFFECTS
The method of etching according to an embodiment of the present invention is economical and simple compared to conventional methods which require costly machinery and complex pretreatment processes for etching, and is also environmentally friendly because chemicals hazardous to human and environment is not used. Moreover, the method uses carbon nanotubes with a diameter of 0.5 to 300 nm to produce nanotrenches on insulating layers with a width of 0.5 to 500 nm, which is difficult to achieve using conventional methods. Furthermore, nanostructures for high density integrated devices can be provided using the nanotrenches on the insulating layers.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a process of forming nanotrenches derived by a carbon nanotube during chemical vapor deposition reaction in which oxygen is injected;
FIG. 2 is a tapping mode atomic force microscopic (AFM) image of a Siθ2/Si substrate having linear-form nanotrenches;
FIG. 3 is a tapping mode atomic force microscopic (AFM) image of a SiO2/Si substrate in which a part of unreacted carbon nanotubes remain on the edges of the nanotrenches;
FIG. 4 is a schematic diagram of a process of forming a Cr nanowire (left) and Si nanotrenches (right) using Siθ2 nanotrenches as a mask;
FIGS. 5 through 8 are AFM images at low and high magnifications of the Cr nanowires; and
FIGS. 9 and 10 are AFM images at low and high magnifications of the Si nanotrenches.
BEST MODE
Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown.
As described previously, according to an embodiment of the present invention, there is provided a method of etching insulating layers using carbon nanotubes, including: forming insulating layers on a substrate; forming carbon nanotubes on the insulating layers; and forming nanotrenches on the insulating layer by carbothermal reduction of the insulating layers on which the carbon nanotubes are formed.
First, the forming of insulating layers on a substrate will be described in detail. The substrate is not particularly limited, and may include, silicon wafer, sapphire, glass, quartz, metal, alumina or plastic.
The insulating layers is not particularly limited insofar as it is a compound including silicon, and may be formed of at least one selected from the group consisting of silicon oxide, silicon dioxide, silicon nitrate, and silicon nitride. Here, it is preferable that the insulating layer is formed of silicon dioxide, due to high efficiency of forming nanotrenches by carbothermal reduction.
As a specific example of the insulating layers, insulating layers made of silicon dioxide (SiO2) may be formed by oxidation of a silicon wafer as a substrate, using a
conventional desiccated oxygen or water vapor, wherein the thickness is not particularly limited. In a laboratory, SiO2 may be formed by calcinating a silicon wafer under air at 800 to 12000C for several seconds to several minutes. The SiO2 layers are formed by a chemical oxidation of the silicon wafer, and the thickness of the layers can be confirmed using an elipsometer. The present invention may be applied regardless of the thickness as long as SiO2 layers exist, and the thickness of the SiO2 layers may be determined according to the purposes.
Then, after forming the insulating layers on the substrate, and before forming the carbon nanotubes, the substrate surface may be deposited with a metal or transition metal catalyst. The metal or transition metal catalyst may be formed of a single metal or transition metal such as Ni, Fe, Co, Y, Mo, Al, Rh, Pd, Au, Ag, or Cu, or may also be formed of a binary or a ternary alloy such as Co-Ni, Co-Fe, Ni-Fe, or Co-Ni-Fe.
The metal or transition metal catalyst may be deposited using thermal evaporation, sputtering, electron beam evaporation, or using a reaction between chemical materials in an aqueous solution to form a metal or transition metal nanoparticles with a thickness of several A or tens of A on the substrate.
Next, the carbon nanotubes may be formed using a method selected from the group consisting of chemical vapor deposition (CVD), laser ablation, arc-discharging, plasma enhanced chemical vapor deposition (PECVD), vapor phase growth, sonication synthesis, electrolysis and flame synthesis. Among these, CVD and PECVD have higher efficiency in forming the nanotrenches due to direct reaction of catalyst particles and the substrate.
According to an embodiment of the present invention, the carbon nanotubes may be selected from the group consisting of single-walled carbon nanotubes (SWNT), double-walled carbon nanotubes (DWNT), multi-walled carbon nanotubes (MWNT), rope carbon nanotubes, and structures in which catalysts are wrapped with carbon particles.
The nanotrenches formed on the insulating layers according to an embodiment of the present invention are completely derived from the carbon nanotubes, and thus properties of the nanotrenches on the insulating layers are determined by the loci, length, and width of the carbon nanotubes. Therefore, the carbon nanotubes according to an embodiment of the present invention may preferably have an average diameter of 0.5 to 300 nm and may be selected with regards to the width of nanotrenches that are to be formed thereafter.
Sequentially, forming the nanotrenches from the insulating layers on which the carbon nanotubes are formed will be described in detail.
The nanotrenches on the insulating layers are formed by a carbothermal reduction between the carbon nanotubes and the insulating layer formed on the substrate, and the reduction reaction may be a method selected from the group consisting of CVD, PECVD, thermal vapor deposition, and vapor phase growth.
Here, carbon (C) within the carbon nanotubes act as a reducing agent for reducing and thereby etching the insulating layers.
The carbothermal reduction may be performed at a temperature of 700 to 1200°C , and preferably at a temperature of 800 to 9500C . If the reaction temperature is lower than 700 °C , the production efficiency of the carbon nanotubes and the nanotrenches decrease, and if the reaction temperature is greater than 1200°C , dangers of economical losses and gas explosion exist due to reaction at high temperature.
Meanwhile, according to an embodiment of the present invention, the carbothermal reduction of the substrate on which the carbon nanotubes are formed may be performed by injecting oxygen and inert gas. That is, if oxygen is included during the carbothermal reduction, destruction of carbon nanotubes having high crystallizability and thermostability may occur more easily, and forms a locally limited reactive carbon-like component that reacts with the insulating layers at the same temperature.
The nanotrench forming efficiency is directly proportional to the amount of oxygen injected.
The carbothermal reduction of the insulating layers, if they are derived after the carbon nanotubes are formed on top of the insulating layers, may be performed by injecting oxygen and inert gas. Here, the oxygen content may be 0.0001 to 30%, and preferably, 0.0003 to 0.01 % based on the total gas volume.
If the oxygen content is less than 0.0001 %, carbothermal reduction does not occur easily, therefore the nanotrench forming efficiency may be significantly reduced, and if the content is greater than 30%, oxidation between excess oxygen and the carbon nanotubes themselves may occur first, which may also significantly reduce nanotrench forming efficiency.
The inert gas which includes the oxygen may be helium, neon, argon, krypton, xenon, and radon, and preferably, may be argon.
When etching the insulating layers according to an embodiment of the present invention, forming the carbon nanotubes and the carbothermal reduction of the substrate on which carbon nanotubes are formed may occur simultaneously. That is, if oxygen, hydrogen, and hydrocarbon gases are injected into a chemical vapor deposition equipment for forming the carbon nanotubes on the substrate, the carbon nanotubes are formed on the insulating layers of the substrate and at the same time the carbon nanotubes formed thereby may act as a reducing agent to cause carbothermal reduction of the insulating layers. Therefore, the nanotrenches on the insulating layers may be formed advantageously in a short period of time with reduced loss of fuel.
That is, in the case where the carbon nanotube formation and carbothermal reduction are executed simultaneously, additional carbon is provided on top of the carbon provided solely by the carbon nanotubes during formation of nanotrenches, and thus the efficiency of forming the nanotrenches on the insulating layers can be increased.
Here, the oxygen content may be 0.01 to 2%, and preferably may be 0.03 to 0.1% based on the total gas volume. If the oxygen content is lower than 0.01 %, carbothermal reduction may not occur smoothly, and thus the efficiency of the nanotrench formation may be significantly reduced, and if the oxygen content is greater than 2%, excess oxygen and hydrocarbon gas may react, which may lead to explosion. The contents of hydrogen and hydrocarbons are not particularly limited, but the hydrogen content may be 20 to 50% and preferably 25 to 40% based on the total gas volume, and the hydrocarbon content may be 50 to 80% and preferably 55 to 75%, based on the total gas volume.
The hydrocarbon is not particularly limited, and may specifically be one selected from the group consisting of methane, ethane, acetylene, ethylene, butane, and propane. Among these, methane, ethylene, or acetylene may preferably be used due to their efficiency in carbon nanotube synthesis.
Moreover, nanoparticles of metal or transition metal catalysts used during carbon nanotube formation also accelerates heat evaporation of the insulating layers, and thus increases the rate of conversion of carbon nanotubes into nanotrenches, in an efficient carbothermal reduction of the insulating layers.
That is, the carbon nanotubes are dispersed in chloroform, and then sonication is performed a multiple of times, in order to prevent clumping among nanotubes, weight separation is performed by centrifugation, relatively light carbon nanotubes are dispersed by spin-coating in Siθ2, and then a reaction is derived by chemical vapor
deposition. In the above process, the number of nanotrenches formed is significantly increased when the catalysts are included in the carbon nanotubes compared to the case where the catalysts are removed by strong acid treatment.
In addition, it is observed that fewer nanoholes or nanotrenches are produced on the insulating layers when the amorphous carbon particles without catalysts are dispersed on the insulating layers through spin-coating and a carbothermal reduction is derived, compared to when the catalysts are included.
It can be seen that the above is a result of the unique properties of a metal or transitional metal catalyst, and of a carbothermal reduction between such a catalyst and hydrocarbons to form a graphite-structured carbon film, nanotubes, or an amorphous carbon film.
As an actual example, the regions where catalysts were present are also etched, and thus it can be easily observed that either holes are formed, or most nanotrenches do not include any catalysts on both ends. This can be considered as a mark from which the catalysts are removed through carbothermal reduction while carbon molecules, although not synthesized into carbon nanotubes, formed a film on the catalysts, or as a mark from which catalysts are evaporated because the melting point has decreased due to an interaction between the catalysts and the insulating layers.
According to an embodiment of the present invention, the physical characteristics of the insulating layers are determined by the original characteristics of the carbon nanotubes, because the nanotrenches are formed by carbothermal reduction between the carbon nanotubes and the adjacent insulating layers. Therefore, the length of the nanotrenches may correspond to the length of the carbon nanotubes, which may extend up to tens of micrometers.
Furthermore, the average width of the nanotrenches may be measured using a high-resolution transmission electron microscopy (HRTEM), and the average width of the nanotrenches on the insulating layers may be 0.5 to 500 nm.
Hereinafter, the forming of nanotrenches on the insulating layers which, as an example, are SiO2 layers will be described in detail, according to an embodiment of the present invention.
As previously described, the major driving force of forming the nanotrenches on the SiO2 layers as the insulating layers is SiO2 carbothermal reduction in which the carbon nanotubes act as a reducing agent. It is known that amorphous bulk silica SiO2(S) releases SiO(g) and CO(g), as shown in the formula below, and is thereby
reduced by carbon (C(s)) under atmospheric pressure at a temperature of 1000 °C and greater,
SiO2(S) + C(s) «→ SiO(g) + CO(g) wherein the carbon nanotubes act as a C(s) in order to thermally reduce SiO2.
FIGS. 1 and 2 are respectively a schematic diagram and an atomic force microscopic (AFM) image of a nanotrench-forming process derived by carbon nanotubes during chemical vapor deposition with oxygen injection. That is, when a substrate on which catalysts are deposited is placed in chemical vapor deposition equipment, and is simultaneously injected with oxygen, hydrogen, and a hydrocarbon (methane or ethylene etc.) under a temperature of 700 to 1200°C, synthesis of carbon nanotubes and carbothermal reduction occur.
Through such a reduction, carbon nanotubes are synthesized, and concurrently a reduction takes place on a surface of the substrate to SiO2 and the like, and as a result, an SiO2 layer is formed, having etched areas corresponding to the carbon nanotubes. The solid-phase SiO2 and C should be in contact with each other in order for the above reduction to take place, and only the carbon nanotubes that are in direct contact with the SiO2 surface are activated for the reduction.
Meanwhile, referring to FIG. 3, it can be seen that in the case where the reaction between the carbon nanotubes and SiO2 is incomplete, parts of the carbon nanotubes not reacted remain on the ends of the nanotrenches formed. Thereby, it can be seen that the carbon nanotubes act as a reducing agent in the reaction above.
According to another embodiment of the present invention, there is provided a nanostructure prepared by the etching of the insulating layers.
Using the nanotrenches, which are on the insulating layers prepared by the etching, as a mask, nanostructures such as metal/semiconducting nanowires, etched structures of a substrate for semiconductor, and arrays of metal/semiconductor nanoparticles may be provided. Currently, one of the important issues in the manufacturing of one-dimensional metal nanowires and nanotrenches on substrates for semiconductor is obtaining nanostructures with a diameter or a width smaller than 10 nm. This can be achieved using the nanotrenches on the insulating layers as a mask by using the method according to the current embodiment the present invention.
According to an embodiment of the present invention, the metal nanowires may be prepared using the insulating layers that have been etched using the method
previously described as a mask, and depositing the metal thereon, and immersing the metal-deposited substrate in a developing solution to remove the insulating layers used as the mask.
Here, the metals used in the deposition may be one selected from the group consisting of Cr, GaAs, GaN, Ti, Pd, Ni, Co, Al, Ag, Pt, Au and Cu. The method of metal deposition is not particularly limited, and a conventional method may be used.
Moreover, immersion in a developing solution after the metal deposition is used in order to remove the insulating layers, and the developing solution is not particularly limited insofar as it is able to dissolve the insulating layers. For example, in the case of silicon oxide insulting layers, an aqueous solution of HF with a content of 0.1% may be used.
As an example of the nanostructure according to an embodiment of the present invention, the nanotrenches which are etched on Si substrate in a nanometer scale useful in a nanoelectronic technology, may be prepared using the same SiO2 nanotrench mask.
That is, the Si substrate on which SiO2 nanotrenches are formed may be immersed in an aqueous solution of KOH or the like to etch the Si, which may then be immersed in an aqueous solution of HF to remove the nanotrench mask layer, thereby manufacturing the nanotrenches as an etched structure on the Si substrate.
FIG. 4 is a schematic diagram of a process of forming Cr nanowires (left) and Si nanotrenches (right) using the SiO2 nanotrenches as a mask, as previously described.
MODE OF THE INVENTION
The present invention will now be described in more detail with reference to the following examples. However, these examples are for illustrative purposes only and are not intended to limit the scope of the invention.
Examples
Preparation of SiO? nanotrenches
In order to induce the etching of the carbon nanotubes and a SiO2 substrate, an iron catalyst was first deposited on a SiO2ZSi substrate. Using a micropipette, 100μ# of 40 mM NH2OH HCI aqueous solution and '\Oμl of 10 mM FeCI3-6H2O aqueous solution
were added to 10 ml of triple-distilled water in which SiO2/Si substrate is immersed, and as a result of reacting for 3 minutes, an iron catalyst with a diameter of a nanotube (average: 1.7 nm) was compactly formed on the substrate. The substrate sample on which the iron catalyst is deposited was transferred to a quartz container of chemical vapor deposition (CVD) equipment, and was reduced with H2 gas at 500 seem, increasing the temperature to approximately 830 °C . When the temperature has reached 8300C , the valves for 02/CH4ZC2H4 gases were opened, where gas flow rates were 1.5/1000/20 seem respectively. Once the temperature has reached 900 °C , the reaction was allowed to continue for 10 more minutes and the valves for O2ZCH4ZC2H4 gases were closed, the temperature was then lowered to room temperature, and the sample was taken out. In this experiment, carbon nanotube synthesis and carbothermal reduction were simultaneously induced using hydrogen, hydrocarbon, and oxygen. As a result, a SiO2ZSi substrate was obtained having nanotrenches linearly formed and refined, which is shown through a tapping mode atomic force microscopic (AFM) image in FIG. 2
The nanotrenches on the SiO2 substrate may be formed by inducing a carbothermal reduction on a carbon nanotube sample already formed. The carbon nanotube synthesis is the same as the method above except that oxygen gas was injected. The substrate on which the carbon nanotubes are synthesized was then transferred again to the quartz container of the CVD equipment, and Ar gas (including 0.0001% oxygen) was flowed in at 1000 seem while raising the temperature to 9000C , letting react for 5 minutes or longer, the temperature was then lowered to room temperature, and it was seen that the SiO2 nanotrenches are formed on the SiO2ZSi substrate by the carbothermal reduction.
Preparation of Cr Nanowires
Cr nanowires according to an embodiment of the present invention were prepared by metal evaporation using SiO2 as a mask. Before producing the Cr nanowires, the organic materials produced from the previous reaction and the carbon nanotubes were removed, and the resulting sample was calcinated in air at about 8000C in order to prepare a clean SiO2 nanotrench surface. The sample may be immersed in an aqueous solution of HF diluted to about 5% for about 1 minute, in order to remove the thin SiO2 layer formed therefrom. The thermal deposition of Cr was performed at target
thicknesses of 4 and 8 nm each, and then the Cr thermal-deposited substrate was reacted in a diluted HF solution (H2O:HF(50%) = 2:1 vol. ratio) for 1 to 3 minutes to remove the SiO2 nanotrenches. As a result, Cr nanowires having heights of 4.4 nm and 8.5 nm each were prepared. The Cr nanowires prepared thereby are shown in AFM images at low magnification and high magnification in FIGS. 5 through 8.
Preparation of Si Nanotrenches
Si nanotrenches according to an embodiment of the present invention were prepared through etching by KOH aqueous solution, using SiO2 nanotrenches as a mask. Before producing the Si nanotrenches, the organic materials produced from the previous reaction and the carbon nanotubes were removed, and the sample was calcinated in air at about 8000C in order to prepare a clean SiO2 nanotrench surface. The sample may be immersed in an aqueous solution of HF diluted to about 5% for about 1 minute, in order to remove the thin SiO2 layer formed therefrom. Then, the sample was immersed in KOH aqueous solution with a 45% content ratio at 830C and reacted for about 1 minute, in order to etch the Si. Here, the treatment level should be carefully controlled to prevent a change of surface color of the mask to white, and a massive generation of H2 bubbles from the substrate. This is because when the reaction with KOH aqueous solution is excessive, the SiO2 nanotrench mask may also be damaged, etching the entire Si substrate by the KOH solution. Next, the substrate on which Si nanotrenches are formed was reacted in a diluted HF aqueous solution (H2O: HF (50%) = 2:1 vol. ratio) for 1 to 3 minutes to remove the SiO2 nanotrench mask. The Si nanotrenches obtained as a result are shown as AFM images at low magnification and at high magnification in FIGS. 9 and 10.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
Claims
1. A method of etching insulating layers using carbon nanotubes, the method comprising: forming insulating layers on a substrate; forming carbon nanotubes on the insulating layers; and forming nanotrenches on the insulating layers by carbothermal reduction of the insulating layers on which the carbon nanotubes are formed.
2. The method of claim 1 , wherein the substrate is one selected from the group consisting of silicon wafer, sapphire, glass, quartz, metal, alumina and plastic.
3. The method of claim 1 , wherein the insulating layers are formed of a compound comprising silicon.
4. The method of claim 1 , wherein the insulating layers are formed from at least one selected from the group consisting of silicon oxide, silicon dioxide, silicon nitrate, and silicon nitride.
5. The method of claim 1 , wherein the carbon nanotubes are formed using a method selected from the group consisting of chemical vapor deposition (CVD), laser ablation, arc-discharge, plasma enhanced chemical vapor deposition (PECVD), vapor phase growth, sonication method, electrolysis and flame synthesis.
6. The method of claim 1 , wherein the carbon nanotubes are selected from the group consisting of single-walled carbon nanotubes (SWNT), double-walled carbon nanotubes (DWNT), multi-walled carbon nanotubes (MWNT), rope carbon nanotubes, and structures in which catalysts are wrapped with carbon particles.
7. The method of claim 1 , wherein the carbon nanotubes have an average diameter of 0.5 to 300 nm.
8. The method of claim 1 , wherein the carbothermal reduction is performed by injecting oxygen and an inert gas.
9. The method of claim 8, wherein the oxygen content is 0.0001 to 30% of the total volume of gas.
10. The method of claim 1 , wherein the carbothermal reduction is performed under a temperature of 700 to 12000C .
11. The method of claim 1 , wherein the nanotrenches of the insulating layers have an average width of 0.5 to 500 nm.
12. The method of claim 1 , wherein the formation of carbon nanotubes and the carbothermal reduction occur simultaneously.
13. The method of claim 12, wherein the formation of carbon nanotubes and the carbothermal reduction occurs by injecting oxygen, hydrogen, and hydrocarbons simultaneously.
14. The method of claim 13, wherein the oxygen content is 0.01 to 2% of the total volume of gas.
15. The method of claim 13, wherein the hydrocarbon is at least one selected from the group consisting of methane, ethane, acetylene, ethylene, butane, and propane.
16. The method of claim 1 , wherein a top portion of the substrate on which the insulating layers are formed is deposited with one of a metal catalyst and a transition metal catalyst.
17. The method of claim 16, wherein the metal or transition metal catalyst is formed of one of Ni, Fe, Co, Y, Mo, Al, Rh, Pd, Au, Ag, Cu, and alloys thereof.
18. A nanostructure prepared using a method according to any one of claims 1 to 17.
19. The nanostructure of claim 18, wherein the nanostructure is one of a structure comprising metal/semiconductor nanowires, an etched structure of a substrate for semiconductor, and a structure comprising an array of metal/semiconductor nanoparticles.
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| CN113788474A (en) * | 2021-11-04 | 2021-12-14 | 航天特种材料及工艺技术研究所 | Graphene nanoribbon horizontal array and preparation method and application thereof |
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