JP2005118936A - Ferroelectric fine structure, its manufacturing method and recording reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fine structure composed of a ferroelectric material, its manufacturing method and a method for recording and reproducing information to its fine structure, for expecting the application to superhigh density recording of data. <P>SOLUTION: A pore structure 2 having pores 3 is formed on a lower electrode 1, and the ferroelectric material is filled in the pores 3, and a fine dot of the ferroelectric material is formed. This dot has a two-dimensional periodic nano-structure having, for example, a diameter of 100 nm or less and an arrangement interval of 100 nm or less. The respective nano-dots indicate a P-E hysteresis characteristic by accumulation of electric charge characteristic of a ferroelectric substance, and can be used as a memory. The pore structure 2 is formed by anodically oxidizing metal Al or an Al-Hf alloy layer or etching and removing a dot part of a micro-phase separate structure of coagulating a part of a polymer chain of a block copolymer in a dot shape. Writing and reading to the memory are performed by an impression of voltage and detection of electric potential with a cantilever probe as an upper electrode. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a microstructure made of a ferroelectric material, a manufacturing method thereof, and a method for recording and reproducing information on the microstructure, which can be expected to be applied to ultra-high density recording of data. .

  The present invention relates to a microstructure made of a ferroelectric material, but the size is not particularly limited. However, one goal is to produce as fine a structure as possible, for example, nano-size, and since there has been an increasing interest in nano-sized structures in recent years, The technical background is mainly described.

  In this specification, a size of about 1 nm or more and less than 1 μm is referred to as “nanosize”, and the prefix “nano” is used to refer to a size whose characteristic size is nanosize. To do. For example, a nanoparticle is a particle whose diameter is nanosize, a nanohole is a pore whose pore diameter or depth is nanosize, and a nanostructure is a feature of the structure. Is a structure having a nano size.

2. Description of the Related Art In recent years, the amount of data handled by information devices has been rapidly increasing due to the speeding up of CPUs (Central Processing Units) and networks, and accordingly, the capacity of storage devices that store data has been demanded. Specifically, a mass storage device of several hundred Gb / inch ^{2 to 1} Tb / inch ² is required between 2005 and 2010. In order to realize such a high-density memory, a nano-size processing technique is required that regularly forms high-density memory bits having a size of several nanometers to several tens of nanometers per bit.

  For example, there is a digital portable terminal as one of the electronic devices that are expected to make progress in the future. To configure a storage for storing data files such as large-capacity moving image information, a large capacity (over 10 GB), a small size Therefore, a memory device or a storage device with low power consumption is expected.

  In the existing technology, a hard disk having a size of about 500 MB with a coin size of 500 yen has already been developed and is expected to be applicable to the above-described use. However, the hard disk has a demerit that power consumption is large, and the power consumption of the hard disk is currently 1 W or more. For this reason, when it is driven by a battery, the power consumption of the hard disk becomes a heavy burden, and there is a problem that the time during which a portable device equipped with the hard disk can be driven is shortened.

  Further, a semiconductor nonvolatile memory represented by a flash memory, which consumes less power, has been integrated, and has recently been used as a memory for various portable devices, particularly a cellular phone. However, at present, the storage capacity is 256 Mbit to 1 Gbit at the product level, and depending on the progress of higher integration and multi-value in the future, at present, a large number of chips are required to configure the above-described large-capacity storage. Therefore, it is not suitable for application to a PDA (Personal Digital Assistant) device that is desired to be small and light. It is also necessary to consider the progress and timing of integration in the future. For example, 4Gb chips are expected to be commercialized in 2006-2007, corresponding to the above-mentioned increase in capacity of storage devices Can not.

  On the other hand, in recent years, with the progress of film formation technology, development of a nonvolatile ferroelectric memory (Ferroelectric Random Access Memories: FeRAM) using a ferroelectric thin film has been actively performed. This ferroelectric memory can rewrite stored information at high speed by utilizing the dielectric polarization of the ferroelectric thin film and the high-speed polarization reversal that is characteristic of the ferroelectric thin film. Also, unlike conventional volatile memories such as DRAM (Dynamic Random Access Memories) and SRAM (Static Random Access Memories) where the written information disappears when the power is turned off, it was written even when the power was turned off. It has the advantage that information is not lost.

  In addition to being non-volatile, this memory is characterized by being capable of high-speed access, small size, and low power consumption. For example, various electronic devices having file recording and resume functions. It is expected to be used as a main storage device for portable computers, mobile phones and game machines, or as a recording medium for recording audio and video.

  However, the integration level of ferroelectric memory (FeRAM) utilizing the high-speed polarization reversal of the ferroelectric material described above has the potential to improve in the future, but at present, the integration level of DRAM, flash memory, etc. Far less.

  As described above, there is no storage device that satisfies the specifications desired for next-generation PDAs and the like.

Next, a microfabrication technique of a ferroelectric material useful for improving the integration degree of the ferroelectric memory will be examined. In order to realize a high-density memory of several hundred Gb / inch ^{2 to 1} Tb / inch ^{2 in} the near future, a so-called nano-processing technology that forms memory bits of several nm to several tens of nm per bit regularly at high density Is required.

  Examples of general microfabrication techniques include electron beam lithography and X-ray lithography as well as photolithography conventionally used in semiconductor processing techniques. Although the optical lithography is progressing until a structure pattern of about 100 nm can be formed, it is difficult to apply it to the formation of a nanostructure pattern of several nm to several tens of nm. Therefore, at present, direct drawing by electron beam lithography is the most common method for processing such fine dimensions as described above.

An example of producing fine dots of a ferroelectric material by direct electron beam drawing is a report of Alexe et al. (Applied Physics Letters, 75 (1999), p. 1793-1795). In this report, lead zirconate titanate PZT (Pb (Ti _x Zr _1-x ) O ₃ ) and SBT (SrBi ₂ Ta ₂ O ₉ ) are formed as ferroelectric materials and their domains are formed. The reversal is confirmed. Similarly, Okamura et al. Formed a 150 nm Bi ₄ Ti ₃ O ₁₂ microstructure by direct electron beam writing (Integrated Ferroelectrics, 18 (1997), 311). In addition, Stanishevsky et al. Produced PZT fine dots of 130 nm using a focused ion beam (FIB) (J. Vac. Sci. Technol., B16 (1998), 3899).

Although the limit of the size of the fine structure that can be manufactured by the above processing technique is determined by the limit of the resolution of the electron beam, it is difficult to realize a size of 100 nm or less at present. The degree of integration obtained when fine dots of around 100 nm are 1 bit / 1 dot is about several tens of Gbit / inch ² in terms of the surface density of magnetic / optical recording. This is based on the design rules of semiconductor memory. And approximately 64 MB to 1 Gb.

  In the future, the development of nanostructure fabrication technology that can form nanostructures of memory materials to be memory bits at low cost will become a key technology. Lithography depends on the progress of future electron beam lithography and X-ray lithography technologies, but there is a problem that the yield decreases and the cost increases as the pattern becomes finer.

  On the other hand, in addition to the above-described top-down microfabrication technology, recently, by a so-called bottom-up method by self-organization, which utilizes a regular micro structure spontaneously formed by atoms and molecules. Attempts have been made to form nano-sized microstructures. The nanostructure formed by self-assembly may be used as it is, or another material may be nano-processed using the formed nanostructure as a template (framework).

  One method for producing a nanostructure by such self-organization includes a method of producing a structure having nanosized pores with good controllability by anodic oxidation. For example, when metallic aluminum is anodized in an acidic electrolyte aqueous solution, a porous oxide film having nano-sized pores can be formed. This method of producing alumina by anodic oxidation has been known for a long time, but recently, attempts have been made to control the periodicity of the arrangement of generated pores. For example, a report by Masuda et al. (Applied Physics Letters 71 (1997), p.2770-2772), or a report by Li et al. (Advanced Materials, 11 (1999), p.483-487).

  Alumina formed by anodization optimizes the production conditions so that fine cylindrical pores with a diameter of several tens to several hundreds of nanometers are arranged in parallel at intervals of several tens to several hundreds of nanometers. It has a characteristic that indicates a unique geometric shape. The diameter and interval of the pores can be controlled by adjusting the current and voltage during anodization to control the thickness of the porous oxide film to be generated, and by adjusting the anodization time, The depth of the pores can be controlled.

  For example, in Patent Document 1 described later, a laminate formed by laminating an intermediate layer and a metal aluminum layer on a conductive base layer is anodized, and an alumina nanohole structure is formed on the conductive base layer. An example in which is manufactured is disclosed.

  In Patent Document 1, noble metals such as copper and platinum, alloys thereof, or semiconductor materials such as graphite and silicon are used as the conductive underlayer, and Ti, Zr, Hf, Nb, Ta, Mo, and the like are used as the intermediate layer. A single element selected from the group consisting of W and Si, or an alloy containing two or more elements selected from the above group is used, and an intermediate oxide layer formed by anodizing the intermediate layer, It has been reported that there is a function of increasing the bonding strength between the conductive underlayer and the alumina layer.

  Further, in Patent Document 2 described later, the same applicant as in Patent Document 1 fills the nanoholes of the anodized alumina layer formed on the surface of the perovskite oxide with the perovskite oxide, and the nanoparticle of the perovskite oxide. An example in which a structure is formed is disclosed.

  As another example of a method for producing a nanostructure by self-assembly, there is a method using a block copolymer in which a plurality of types of polymer chains having different chemical properties are linked by a covalent bond. A thin film made of block copolymer forms a regular phase separation structure called a microphase separation structure with a period of about several tens of nanometers, so it can be used as a template for controlling the spatial arrangement and arrangement of memory materials. can do.

  A normal polymer consists of one type of polymer chain. For example, when two types of polymers are composed of two types of polymer chains that have different chemical properties and do not mix with each other, and they separate into two phases from a mixed state, the two types of polymer chains with different properties are Since they are not connected, they move to separate phases and are completely separated into two phases to form a phase separation structure (macro phase separation structure) that exceeds the size of the molecule. In the macro phase separation structure, since the scale of occurrence of fluctuation is about 1 μm, the size of the unit cell formed by each phase is about 1 μm or more.

  On the other hand, in the block copolymer, a plurality of types of polymer chains that are not mixed with each other exist in one molecular chain, and are linked by a covalent bond. For this reason, homogenous polymer chains aggregate between molecules to form one phase (domain) and form a phase separation structure in which multiple types of polymer chains are separated into different phases. Since they are connected, the distance between the two adjacent phases (between the centers) does not exceed the length of the molecular chain. As a result, there are many fine phases (domains) whose size is about twice the length of the polymer chain (several nm to several tens of nm), and intervals that are about twice the length of the molecular chain (several nm to 100 nm) A microscopic phase separation structure (microphase separation structure) periodically arranged at (pitch) is formed.

  The microphase-separated structure formed by the block copolymer exhibits a form in which a large number of fine phases (domains) are arranged in a very regular manner, so that a nano-sized regular structure can be easily obtained. The size and spacing (pitch) of the domains can be controlled by adjusting the length of each polymer chain and the length of the molecular chain of the whole molecule.

  FIG. 5 is an explanatory view showing a microphase separation structure formed based on Example 2 described later. As shown in FIG. 5A, in the block copolymer, a nonpolar polymer chain A composed of polystyrene (PS) chains and a polar polymer chain B composed of polymethyl methacrylate (PMMA) chains are connected. It is a diblock copolymer. For explanation, it is assumed here that the polymer chain B (PMMA chain) is shorter than the polymer chain A (PS chain). In the opposite case, the polystyrene chain and the polymethyl methacrylate chain may be replaced.

  In this diblock copolymer, the non-polar polymer chain A and the polar polymer chain B are not mixed, so that the microphase separation structure shown in FIG. 5B is formed. At this time, since the polymer chain B is shorter than the polymer chain A, the phase (domain) formed by aggregation of the polymer chain B becomes a dot shape, and the phase (domain) formed by aggregation of the polymer chain A Becomes a shape surrounding the dot.

  FIG. 5C is a schematic plan view showing the entire structure. The whole is a so-called multi-grained state (corresponding to the crystalline state of the crystal) and is divided into a large number of granular regions (grains), and there is no regularity as a whole, but within one granular region (grains) Then, the dot-like domains formed by the polymer chain B are regularly arranged, for example, in a hexagonal close-packed lattice shape. The size of one granular region (grain) is, for example, a size that can accommodate about 10 domains vertically, 10 horizontally, and about 100 domains in total.

  An example of producing a porous microstructure or a dot-like microstructure using a microphase separation structure of such a block copolymer has been reported.

  For example, P. Mansky et al. Report the following pattern formation method in Appl. Phys. Lett., Vol. 68 (1996), No. 18, p. In this method, first, using a block copolymer composed of polystyrene chains and polyisoprene chains, a polyisoprene chain aggregated portion scattered in dots and a polystyrene chain aggregated portion that spreads in a plane so as to surround it. A microphase separation film is formed on the substrate. Next, a porous film is formed by decomposing and removing the dot-like polyisoprene chain aggregation portion by ozone oxidation. By etching the substrate using the porous film thus obtained as a mask, the microphase separation structure is transferred to form a porous pattern on the substrate.

  In addition, M.M. Park et al., Science, vol. 276 (1997), p. 1401-1404, report a pattern formation method using a block copolymer of polystyrene and polyisoprene. In this method, first, a microphase separation film made of the aforementioned block copolymer is formed on a substrate. Next, osmium oxide is introduced into the polyisoprene phase interspersed in a dot form by a gas phase reaction to improve etching resistance. Thereafter, etching is performed using the polyisoprene phase selectively doped with osmium oxide as a mask to transfer the dot pattern onto the substrate.

  Fabrication of a porous microstructure or a dot-shaped microstructure using such a block copolymer microphase separation structure is simpler and less expensive than lithography techniques. However, no example of producing a ferroelectric microstructure by such a method has been reported.

Japanese Patent Laying-Open No. 2003-25298 (page 2-5, FIG. 1-3) JP 2001-278700 A (page 4-7, FIGS. 3 and 4)

  As mentioned above, the appearance of storage devices that can be applied to next-generation PDAs is expected, but at present there are no storage devices that meet the desired specifications, and new high-capacity storage is realized. New technologies like this are needed.

  In view of the above circumstances, an object of the present invention is to provide a microstructure made of a ferroelectric material, a manufacturing method thereof, and information on the microstructure, which can be expected to be applied to ultra-high density recording of data. It is to provide a method for recording and reproducing.

  That is, the present invention relates to a ferroelectric microstructure having fine dots of ferroelectric material in contact with an electrode.

  A step of forming a metal aluminum layer in contact with the electrode; a step of anodizing the metal aluminum layer to form a pore structure; and filling the pores of the pore structure with a ferroelectric material And a first manufacturing method of a ferroelectric microstructure. Here, instead of forming the metal aluminum layer and anodizing, an aluminum-hafnium alloy layer or a laminate of an aluminum-hafnium alloy layer and a metal aluminum layer may be formed and anodized. .

  A step of forming a microphase separation structure in which the block copolymer is phase-separated into a dot-aggregated portion and another agglomerated portion in contact with the electrode; and agglomeration in the dot-shape of the microphase-separated structure Removing the at least part of the formed portion to form a pore structure, and filling the pores of the pore structure with a ferroelectric material. Related to the manufacturing method.

  A step of forming an insulating layer in contact with the electrode; and a step of forming a microphase separation structure in which the block copolymer is phase-separated into a portion where the block copolymer is aggregated in the form of dots and another aggregated portion in contact with the insulating layer. Removing at least part of the dot-aggregated portion of the microphase-separated structure to form a first pore structure; and using the first pore structure as a mask, the insulation Etching the layer to form a second pore structure, and filling the pores of the second pore structure with a ferroelectric material. 3 relates to the manufacturing method.

  Also, a step of forming a ferroelectric layer in contact with the electrode, and a microphase separation structure in which the block copolymer is phase-separated into an aggregated portion and other aggregated portions are in contact with the ferroelectric layer. Forming a block copolymer dot-like structure by removing the other aggregated portion of the microphase-separated structure, and using the block copolymer dot-like structure as a mask The present invention also relates to a fourth method for manufacturing a ferroelectric microstructure in which a layer is etched to form a ferroelectric material dot-like structure.

  Further, the present invention applies a voltage between the probe and the electrode to each ferroelectric dot of the ferroelectric microstructure according to any one of claims 1 to 12, The present invention relates to a recording method that induces reversal of spontaneous polarization of the ferroelectric dot and uses this as a recording bit, and also uses the probe as a counter electrode of the electrode to detect the surface potential or electrostatic potential of the ferroelectric dot. The present invention relates to a reproduction method for detecting a change in capacity and reproducing the recording bit.

  The ferroelectric microstructure of the present invention has a structure in which fine dots of a ferroelectric material are formed in contact with an electrode, and this ferroelectric dot has a dielectric constant due to accumulation of charges peculiar to a ferroelectric. -It shows electric field strength hysteresis characteristics, can rewrite stored information at high speed, and can be used as a nonvolatile memory with low power consumption. If a two-dimensional nanostructure having a dot diameter of 100 nm or less and an arrangement interval of 100 nm or less can be formed, an unprecedented high-density and large-capacity memory device or storage device can be formed.

  According to the first method for manufacturing a ferroelectric microstructure of the present invention, the step of forming a metal aluminum layer in contact with the electrode and the step of anodizing the metal aluminum layer are performed. Thus, a pore structure made of the anodized alumina can be reliably formed, and further, a step of filling the pores of the pore structure with a ferroelectric material is performed. For example, nanopores having a diameter of 100 nm or less are provided. The ferroelectric microstructure can be reliably manufactured. Here, instead of forming the metal aluminum layer and anodizing it, an aluminum-hafnium alloy layer or a laminate of an aluminum-hafnium alloy layer and a metal aluminum layer is formed, and this is anodized. Also good.

  According to the second method for producing a ferroelectric fine structure of the present invention, a microphase separation structure formed by phase-separating a block copolymer into a dot-aggregated portion and another aggregated portion is in contact with the electrode. Forming the pore structure by removing at least part of the dot-aggregated portion of the microphase-separated structure and forming the pore structure in contact with the electrode. In addition, a process of filling the pores of the pore structure with a ferroelectric material is performed, so that the ferroelectric microstructure having nanodots with a diameter of 100 nm or less, for example, is reliably produced. can do.

  According to the third method for producing a ferroelectric microstructure according to the present invention, the step of forming an insulating layer in contact with the electrode, and the phase separation of the block copolymer into an aggregated portion and other aggregated portions are performed. Forming a microphase separation structure in contact with the electrode, and forming a first pore structure by removing at least a part of the dot-aggregated portion of the microphase separation structure And the step of etching the insulating layer using the first pore structure as a mask to form a second pore structure, so that the second pore structure is formed on the insulating layer. Since the process of filling the pores of the second pore structure with a ferroelectric material is performed, the ferroelectric microstructure having nanodots with a diameter of, for example, 100 nm or less can be reliably obtained. Can be produced.

  According to the fourth method for manufacturing a ferroelectric microstructure according to the present invention, the step of forming the ferroelectric layer in contact with the electrode, the portion where the block copolymer is aggregated in a dot shape, and the other aggregated portion are combined. Forming a separated microphase separation structure on the ferroelectric layer; removing the other aggregated portion of the microphase separation structure to form a block copolymer dot-like structure; Therefore, a dot copolymer structure of the block copolymer can be formed on the ferroelectric layer, and further the step of etching the ferroelectric layer using the dot structure as a mask is performed. The ferroelectric microstructure having nanodots of 100 nm or less can be reliably produced.

  According to the first to fourth ferroelectric fine structure manufacturing methods, ferroelectric nanodots having a size that cannot be manufactured by conventional microfabrication technology can be manufactured without using expensive equipment. In addition, a ferroelectric microstructure can be manufactured efficiently and at low cost.

  Further, according to the recording method and reproducing method of the present invention, the ferroelectric fine structure can be used as a memory without further modification, and the cost of the memory can be reduced.

  In the present invention, it is preferable that the ferroelectric material is present in pores of a pore structure formed in contact with the electrode to form the dots.

  Here, the pore structure is a pore structure formed by anodizing a metal aluminum layer, or an aluminum-hafnium alloy layer or an aluminum-hafnium alloy layer instead of the metal aluminum layer. It is preferable that the porous body is formed by anodizing a laminate with a metal aluminum layer.

  At this time, at least part of the pores of the pore structure may be widened. Thereby, a material having a more complicated configuration, for example, a laminated body of electrodes and various functional materials, etc., is embedded in the widened pores to form a more multifunctional ferroelectric microstructure. it can. The pore widening process is preferably performed by etching using an aqueous solution of phosphoric acid, oxalic acid, sulfuric acid or the like.

  Further, in the micro phase separation structure in which the pore structure is phase-separated into a portion where the block copolymer is aggregated in a dot shape and another aggregated portion, at least a part of the portion aggregated in the dot shape is removed. It may be a pore structure formed by doing so. Since the polymer can be easily removed, it is particularly convenient when it is desired to leave only the dots made of the ferroelectric material and remove the pore structure.

  Also, the first pore structure formed from the block copolymer is used as a mask, and a part of the insulating layer is removed in the form of dots to form the pore structure as the second pore structure. May be. In this case, the insulating layer is preferably made of silicon oxide or the like.

  The diameter of the dots or the pores is 5 to 200 nm, more preferably 10 to 150 nm, and still more preferably 30 to 100 nm. If the diameter is too small, processing problems such as difficulty in filling the pores with the ferroelectric material occur, and the functions such as the memory function of the ferroelectric material cannot be stably exhibited. There is. If the diameter is too large, the surface density of the dots of the ferroelectric material will decrease, making it impossible to form a large capacity memory or the like.

  Moreover, it is preferable that the arrangement of the pores has periodicity. Considering application to a memory or the like, it is more convenient to perform the recording / reproducing operation if the pores are regularly arranged.

In the present invention, the ferroelectric material may be an inorganic oxide or an organic polymer ferroelectric material. Specifically, PZT compound _{Pb (Ti x Zr 1-x} ) O 3, bismuth layered ferroelectric such SrBi or _{2 Ta 2 O 9 (Bi x} La 1-x) 4 Ti 3 O 12, barium titanate BaTiO ₃ , lead titanate PbTiO ₃ , lithium niobate, lithium tantalate, etc., polyvinylidene fluoride (PVDF), copolymer of vinylidene fluoride and ethylene trifluoride (PVDF / TrFE), oligomer of vinylidene fluoride, etc. is there.

  The pores may be filled with nanoparticles of the ferroelectric material. Nanoparticles, for example, have the merit of being able to fill the pores in the state of a dispersion, for example, but can be introduced as a material that already has the necessary functions, eliminating the need for heat treatment after filling and the burden on the substrate, etc. There is also an advantage that becomes smaller. In addition, some nanoparticles exhibit special physical properties due to their size, and there is an advantage that such special physical properties can be used.

  A cantilever probe electrode is preferably used as the probe. The cantilever probe electrode as the probe may be moved relative to the ferroelectric dot in a contact or non-contact state.

  Next, a preferred embodiment of the present invention will be described in detail with reference to the drawings.

Embodiment 1
FIG. 1 is a schematic perspective view showing the structure of a ferroelectric fine structure according to the present embodiment. In the present embodiment, a pore structure 2 having fine pores is formed on a lower electrode 1 made of a metal material or a semiconductor material, and a ferroelectric material whose illustration is omitted in the pores 3. Each of the individual ferroelectric fine dots is formed.

  The ferroelectric fine dots have, for example, a two-dimensional periodic nanostructure having a diameter of 100 nm or less and an arrangement interval of 100 nm or less, and each nanodot has a PE due to accumulation of charges peculiar to the ferroelectric. It is characterized by exhibiting hysteresis characteristics.

  Here, the pore structure 2 is a pore structure formed by anodizing the metal aluminum layer, or an aluminum-hafnium alloy layer, or an aluminum-hafnium alloy layer and a metal instead of the metal aluminum layer. A porous structure formed by anodizing a laminate with an aluminum layer is preferable. At this time, at least part of the pores of the pore structure may be widened. Thereby, a material having a more complicated configuration, for example, a laminated body of electrodes and various functional materials, etc., is embedded in the widened pores to form a more multifunctional ferroelectric microstructure. it can. The pore widening process is preferably performed by etching using an aqueous solution of phosphoric acid, oxalic acid, sulfuric acid or the like.

  Further, in the micro phase separation structure in which the pore structure 2 is phase-separated into a portion where the block copolymer is aggregated in a dot shape and another aggregated portion, at least a part of the portion aggregated in a dot shape is removed. The pore structure formed by this may be sufficient.

  Further, by using the first pore structure formed from the block copolymer as a mask and removing a part of the insulating layer in the form of dots, the pore structure 2 is formed as the second pore structure. May be. In this case, the insulating layer is preferably made of silicon oxide or the like.

The ferroelectric material may be an inorganic oxide or an organic polymer ferroelectric material. Specifically, PZT compound _{Pb (Ti x Zr 1-x} ) O 3, layered ferroelectric such SrBi ₂ Ta ₂ O ₉ bismuth Bi and _{(Bi x La 1-x)} 4 Ti 3 O 12, titanate Barium BaTiO ₃ , lead titanate PbTiO ₃ , lithium niobate, lithium tantalate, etc., polyvinylidene fluoride (PVDF), copolymer of vinylidene fluoride and ethylene trifluoride (PVDF / TrFE), oligomer of vinylidene fluoride Etc.

  As a method of filling the ferroelectric material in the nano-sized pores 3 of the fine structure 2, a method using a solution, a method using a gas or mist, a method using a nano fine particle, or the like can be applied.

  In the case of using a solution, the nanohole structure made of anodized alumina or block copolymer is immersed in a sol-gel solution or MOD (Metal Organic Decomposition) solution that is generally used for thin film formation by spin coating, and the capillary phenomenon Is used to fill the solution into the nanohole. Thereafter, crystallization is promoted by heat treatment, and a ferroelectric crystal having desired characteristics can be formed.

  When using gas or mist, the pressure of the reaction gas is set so that the gas enters the nanohole using a CVD (Chemical Vapor Deposition) apparatus or a mist CVD apparatus used for general thin film formation. The film forming conditions such as are adjusted. Thereby, it is possible to form an amorphous oxide serving as a ferroelectric crystal or a precursor in the nanohole. Or you may irradiate with a pulsed laser beam with respect to a vapor deposition source, and you may fill with the Pulsed Laser Deposition (PLD) method which vapor-deposits the vapor | steam which evaporated or sublimated.

  In the case of filling nano-particles, a substrate having a nano-hole structure is prepared by adjusting a dispersion liquid in which ferroelectric fine particles of several nm to several tens of nm previously formed by hydrothermal synthesis method or micelle method are dispersed in a solvent. After immersing, the nano-holes can be filled with ferroelectric fine particles by gradually pulling up. By applying heat treatment after filling, a ferroelectric crystal integrated with the nanoholes can be formed.

Embodiment 2
FIG. 2 is a schematic cross-sectional view showing the structure of the ferroelectric fine structure according to the second embodiment. In the present embodiment, individual independent ferroelectric fine dots 4 are formed on the lower electrode 1 made of a metal material or a semiconductor material.
ing.

  The ferroelectric fine dots 4 have, for example, a two-dimensional periodic nanostructure having a diameter of 100 nm or less and an arrangement interval of 100 nm or less, and each nanodot has a P− E hysteresis characteristic is shown.

  The ferroelectric microstructure shown in FIG. 2 is formed by forming a pore structure having fine pores on the lower electrode 1 and filling the pores with a ferroelectric material. After the fine dots 4 of the body are formed, this fine pore structure is removed. This pore structure is obtained by removing at least a part of the dot-aggregated portion in the microphase-separated structure in which the block copolymer is phase-separated into a dot-aggregated portion and other aggregated portions. It is preferable that the pore structure is formed.

  Alternatively, a ferroelectric layer is formed on the lower electrode 1, a dot-like structure is formed thereon, and the ferroelectric layer is selectively etched using the dot-like structure as a mask. . In this dot-like structure, a microphase-separated structure formed by phase-separating the block copolymer into a dot-aggregated portion and other aggregated portions is formed on the ferroelectric layer, and the microphase-separated structure A dot-like structure formed by removing other aggregated portions is preferable.

The ferroelectric material may be an inorganic oxide or an organic polymer ferroelectric material. Specifically, PZT compound _{Pb (Ti x Zr 1-x} ) O 3, SrBi 2 Ta 2 O 9 or _{(Bi x La 1-x)} 4 Ti 3 O 12 is a bismuth layer ferroelectric compounds, titanate Barium BaTiO ₃ , lead titanate PbTiO ₃ , lithium niobate, lithium tantalate, etc., polyvinylidene fluoride (PVDF), copolymer of vinylidene fluoride and ethylene trifluoride (PVDF / TrFE), oligomer of vinylidene fluoride Etc.

  Next, preferred embodiments of the present invention will be described in detail with reference to the drawings.

Example 1 (Formation of nanohole structure with anodized alumina and filling of the nanohole with ferroelectric PZT by liquid phase method)
In this embodiment, a metal aluminum layer 15 is formed on a platinum layer 14 formed as a lower electrode on a silicon substrate 11, and this is anodized to form an anodized alumina layer 16. An example will be described in which the nanohole 18 is filled with PZT by a liquid phase method to produce a ferroelectric nanodot 19 and a write operation and a read operation are performed as a memory element.

  FIG. 3 is a schematic cross-sectional view for explaining a process for producing ferroelectric nanodots 19 using anodized alumina as a pore structure.

<Formation of nanohole structure with anodized alumina>
First, the silicon Si substrate 11 was thermally oxidized to form a silicon oxide SiO ₂ layer 12 as an insulating layer on the surface thereof. Next, a titanium Ti or titanium oxide TiO ₂ layer 13 was formed on the silicon substrate (Si / SiO ₂ ) in order to improve adhesion to the platinum layer 14, and a platinum layer 14 was further formed thereon. .

Next, as shown in FIG. 3B, an aluminum Al layer 15 is RF (Radio Frequency) on the silicon substrate (Si / SiO ₂ / Ti / Pt or Si / SiO ₂ / TiO ₂ / Pt). It was formed by sputtering. At this time, the film thickness of the aluminum layer 15 was about 200 nm.

  Next, as shown in FIG. 3 (c), a 0.3M oxalic acid aqueous solution was used as the electrolyte, and the aluminum layer 15 was anodized while keeping the oxalic acid aqueous solution at 15 ° C. in a thermostatic bath. As shown in (c), a nanohole structure made of anodized alumina 16 was formed. In this example, the anodic oxidation voltage was set to DC 50 V, and anodic oxidation was performed until the nanohole 17 grew and reached the lower platinum electrode 14. The fact that the nanohole 17 reached the platinum electrode 14 was confirmed by the change in the current value of the electrolysis being monitored. After anodization, washing with pure water and 2-propanol (isopropyl alcohol) was performed.

  Next, as shown in FIG. 3 (d), in order to enlarge the pore diameter of the nanohole 17 formed by the above-described anodic oxidation, the nanohole 17 was immersed in a 5% by mass phosphoric acid solution for 20 minutes so that the pore diameter was about 100 nm. . Through the above oxidation process, a nanohole structure having nanoholes 18 having a diameter of about 100 nm and a depth of about 200 nm was produced.

<Filling of nano-hole 18 with ferroelectric material by liquid phase method>
Next, as shown in FIG. 3E, the nanohole 18 was filled with PZT (Pb (Ti _x Zr _1-x ) O ₃ ) by a liquid phase method using a ferroelectric sol-gel solution. In this example, PbO, TiO _2, and ZrO ₂ were dispersed in a mixed solvent of ethanol and acetylacetone so that the composition of Pb (Ti _x Zr _1-x ) O ₃ was x = 0.7. A commercially available sol-gel solution was used.

As a pretreatment, a silicon substrate (Si / SiO ₂ / Ti / Pt / Al ₂ O ₃ or Si / SiO ₂ / TiO ₂ / Pt / Al ₂ O ₃ ) having anodized alumina 16 formed on the surface is made of ethanol. Immersion for about 10 minutes. Thereafter, the silicon substrate was immersed in the sol-gel solution at room temperature for about 30 minutes. At this time, the sol-gel solution enters the nanohole 18 by the surface tension and the capillary effect. Here, since the wettability to the sol-gel solution in the alumina nanoholes 18 is improved by the pretreatment with ethanol, uniform application of the sol-gel solution in the nanoholes 18 can be realized.

  Subsequently, the silicon substrate is taken out from the sol-gel solution, heated for about 10 minutes by a hot plate at 200 ° C. to evaporate and remove the solvent, and further annealed at 700 ° C. for 1 hour in an oxygen atmosphere in a furnace annealing apparatus. Promoted crystallization of PZT.

  The sample thus obtained was observed by X-ray diffraction, and it was confirmed that a PZT crystal oriented in (001) was formed in the nanohole 18.

<Recording bit writing and reading using spontaneous polarization>
Next, with respect to each nanodot 19 of the obtained ferroelectric PZT, using a SPM (Scanning Probe Microscope), inversion of spontaneous polarization is induced by using a cantilever probe as an upper electrode to perform domain inversion, and as a memory element A write operation and a read operation were performed.

  The SPM cantilever was connected to the positive electrode of the power source, and the platinum layer 14 as the lower electrode of the PZT nanodot 19 was connected to the negative electrode. The SPM probe was brought into contact with the position of the desired nanodot 19, and DC voltage + 8V or −8V was applied for 3 seconds. By repeating this operation on the desired nanodots 19, each nanodot 19 was spontaneously polarized, and its ferroelectric domain could be polarized positively or negatively. In this way, the recording bit writing operation using spontaneous polarization is performed.

  The cantilever probe electrode connected to the lock-in amplifier is moved to the recording medium on which information is recorded by the reversal of spontaneous polarization, and changes in the surface potential or capacitance are detected in a contact or non-contact state. The signal detected by the minute displacement of the needle electrode and the signal written in the ferroelectric nanodot 19 was read out.

Example 2 (Formation of a nanohole structure with anodized alumina and filling of the nanohole with a ferroelectric SBT by a vapor phase method)
In this example, as in Example 1, a metal aluminum layer was formed on the platinum layer formed as the lower electrode, and this was anodized to form an anodized alumina layer, which strongly resists nanoholes in the alumina layer. Ferroelectric nanodots are fabricated by filling SBT (SrBi ₂ Ta ₂ O ₉ ) by using metal organic chemical vapor deposition (MOCVD), which is a vapor phase method. An example in which a writing operation and a reading operation are performed as an element will be described.

<Formation of nanohole structure with anodized alumina>
First, an alumina nanohole structure by anodic oxidation was formed on a silicon substrate by the same method as in Example 1.

<Filling of ferroelectric material into nanoholes by MOCVD method>
Next, the ferroelectric material SBT was filled into the nanohole 18 of the alumina nanohole structure by MOCVD. The film formation conditions are as follows:
Vaporizer temperature: 140 ° C
Carrier gas (argon) gas flow rate: 200cc
Oxygen gas (oxidant) flow rate: 200cc
Temperature of the substrate placed in the reactor: 400 ° C.
Pressure inside reactor: 1 Torr
Growth rate: about 10 nm / min
Met.

Under the above conditions, two kinds of organometallic raw materials Sr [Ta ₂ (OC ₂ H ₅ ) ₆ ] ₂ and Bi (OtC ₄ H ₉ ) ₃ are supplied at a ratio of 4: 6, so that the desired SBT can be obtained. A reaction gas realizing the composition could be sent to the reactor, and an amorphous thin film of SBT (SrBi ₂ Ta ₂ O ₉ ) could be grown.

In order to fully exploit the ferroelectric properties of SBT, it is important to precisely control the ratio of each element, that is, the composition ratio. Here, since Sr: Ta is always kept constant by using the bimetallic source Sr [Ta ₂ (OC ₂ H ₅ ) ₆ ] ₂ , the composition ratio of Sr and Ta does not vary greatly depending on the film forming conditions. . On the other hand, when Bi (OtC ₄ H ₉ ) ₃ is used as the Bi source, the amount of Bi introduced into the film can be controlled by various film forming conditions.

  In order to use the amorphous thin film formed as described above as the ferroelectric film SBT, it is necessary to perform crystallization annealing. As a typical annealing condition, a ferroelectric film SBT was obtained by baking in oxygen at 700 ° C. for about 1 hour.

  When the obtained sample was observed by X-ray diffraction, it was confirmed that SBT polycrystal was produced.

<Recording bit writing and reading using spontaneous polarization>
By the same method as in Example 1, it was possible to write and read out ferroelectric nanodots by recording bits.

Example 3 (Formation of a nanohole structure by a block copolymer and filling of the nanohole with a ferroelectric PZT by a vapor phase method)
In this embodiment, a block copolymer layer 21 is formed on a platinum layer 14 which is a lower electrode on a silicon substrate 11, and the microphase separation structure 22 of the block copolymer is etched to form nano-sized pores 23. An example in which the nanoholes 23 are formed and filled with PZT by a PLD (Pulsed Laser Deposition) method, which is a vapor phase method, to produce ferroelectric nanodots 24, and a write operation and a read operation are performed as a memory element will be described. .

  FIG. 4 is a schematic cross-sectional view for explaining a process of producing ferroelectric nanodots 24 using a pore structure made of a block copolymer.

<Formation of nanohole structure by block copolymer>
First, as in Example 1, a silicon substrate 11 is thermally oxidized to form a silicon oxide layer 12, a titanium or titanium oxide layer 13 is formed thereon, and a platinum layer 14 serving as a lower electrode is further formed thereon. Formed. Next, a block copolymer having an average molecular weight of about 65000, which is composed of polystyrene (PS) chains and polymethyl methacrylate (PMMA) chains and the PMMA chain fraction is about 20% by volume, is dissolved in toluene. Was adjusted to 1 to 10% by mass, and this solution was applied onto the above-mentioned substrate by a spin coating method to form a block copolymer layer 21 as shown in FIG. At this time, the film thickness can be controlled by the concentration of the block copolymer solution and the rotation speed of the spin coat. Typically, when the film concentration is 2% by mass and the rotation speed is 3000 rpm, the polymer layer 21 having a thickness of about 200 nm can be formed.

  After film formation, heat treatment is performed at 210 ° C. for 4 hours, and further, heat treatment is performed at 135 ° C. for 40 hours. By these heat treatments, as shown in FIG. 4B, dot-shaped PMMA chain aggregated portions 22b having a diameter of 30 nm and microphase-separated structures 22 phase-separated into polystyrene chain aggregated portions 22a were generated. This could be confirmed by AFM (Atomic Force Microscope) phase imaging.

Next, the polymer layer 22 having the above microphase separation structure is irradiated with light using a light source having a wavelength of 150 nm to 400 nm, and then subjected to ultrasonic treatment for 10 minutes in 1M acetic acid. 22b was removed by etching. As a result, as shown in FIG. 4C, a nanohole structure 24 having nanoholes 23 (diameter 30 nm, interval 30 to 40 nm, depth 100 nm) having the same size as the PMMA chain aggregation portion 22b could be formed. . Etching removal of the PMMA chain aggregation portion 22b may be performed by dry etching with tetrafluoromethane CF ₄ gas as described in Jpn. J. Appl. Phys., Vol. 41 (2002), p. 6112. it can.

<Filling of nano-holes with ferroelectrics by PLD method>
Next, a method in which PZT (Pb (Ti _x Zr _1-x ) O ₃ ) is filled into the nanoholes 23 of the nanohole structure 24 by a PLD method will be described.

YAG with an output of 200 mJ is used as a firing target (vapor deposition source) for forming PZT having a Pb composition of 10% excess and a composition ratio of Pb (Ti _x Zr _1-x ) O ₃ (x = 0.7). A laser (wavelength: 1064 nm) was irradiated with a pulse to deposit a thin film of PZT on a substrate (room temperature) placed at a position opposed to the firing target to form ferroelectric nanodots 25 (FIG. 4D). The film thickness was set to 70 nm as the film thickness not exceeding 100 nm of the block copolymer.

  After film formation by PLD, the substrate was immersed in a toluene solution for 30 minutes to dissolve and remove the polystyrene chain aggregated portion 22a of the block copolymer. As a result, as shown in FIG. 4 (e), on the lower platinum electrode 14, a structure composed of only the cylindrical nanodots 25 of the ferroelectric PZT having a diameter of 30 nm, a dot interval of 30 to 40 nm, and a height of 70 nm is formed. I was able to form.

  Subsequently, annealing was performed at 700 ° C. for 1 hour in an oxygen atmosphere using a furnace annealing apparatus to promote crystallization of PZT. The obtained sample was examined by X-ray diffraction, and it was confirmed that a PZT crystal oriented in (001) was formed.

  By the same method as in Example 1, it was possible to write and read out the ferroelectric nanodots 25 by recording bits.

  FIG. 5 is an explanatory view showing the microphase-separated structure 22 formed by the block copolymer of this example as described above. As shown in FIG. 5A, in the block copolymer, a nonpolar polymer chain A composed of polystyrene (PS) chains and a polar polymer chain B composed of polymethyl methacrylate (PMMA) chains are connected. It is a diblock copolymer.

  In this diblock copolymer, since the polymer chain B is shorter than the polymer chain A, the phase (domain) formed by aggregation of the polymer chain B becomes a dot shape, and the phase formed by aggregation of the polymer chain A (Domain) has a shape surrounding the dot.

  FIG. 6 is an AFM observation image of the block copolymer surface before and after the removal of the PMMA chain aggregation part 22b. In the AFM observation image (a) before removal of the PMMA chain aggregation part 22b, the PMMA chain aggregation part 22b was observed as a dot-like white spot. Further, it can be seen that in a narrow region, the PMMA chain aggregation portion 22b forms a periodic array. In the AFM observation image (b) after the removal of the PMMA chain aggregation portion 22b, it can be seen that the dot-like white spots have completely disappeared and nanoholes 23 are formed in the PMMA chain aggregation portion 22b.

Example 4 (Formation of nanohole structure by block copolymer, transfer of nanohole structure to silicon oxide layer, and filling of nanohole transferred to silicon oxide film with ferroelectric substance)
In the present embodiment, a silicon oxide layer 31 and a block copolymer layer 32 are laminated on the platinum layer 14 which is the lower electrode on the silicon substrate 11. The first nanohole structure 35 is formed, and by using this as a mask, the silicon oxide layer 31 is dry-etched to transfer the second nanohole 36 to the lower silicon oxide layer 31, and into the second nanohole 36. An example in which a ferroelectric nanodot 38 is manufactured by filling a ferroelectric material and a writing operation and a reading operation are performed as a memory element will be described.

  FIG. 7 is a schematic cross-sectional view for explaining a process of manufacturing the ferroelectric nanodots 38 according to this embodiment.

<Formation of nanohole structure by block copolymer>
First, as in Example 1, a silicon substrate 11 is thermally oxidized to form a silicon oxide layer 12, a titanium or titanium oxide layer 13 is formed thereon, and a platinum layer 14 serving as a lower electrode is further formed thereon. Formed. Further thereon, a silicon oxide layer 31 is formed to a thickness of about 200 nm. The silicon oxide layer 31 is formed by a CVD method using SiH ₄ , Si ₂ H ₆ or the like, an organic metal CVD method using TEOS (Tetraethyl-ortho-silicate), a spin-on-glass (SOG) method, or the like.

  Next, in the same manner as in Example 3, a block copolymer having an average molecular weight of about 65000 and comprising a polystyrene chain and a polymethyl methacrylate chain and having a PMMA chain fraction of about 20% by volume was dissolved in toluene. The concentration was adjusted to 1 to 10% by mass, and this solution was applied onto the above-mentioned substrate by a spin coating method, thereby forming a block copolymer layer 32 as shown in FIG. A typical thickness of the block copolymer layer 32 is about 200 nm.

  After film formation, heat treatment is performed at 210 ° C. for 4 hours, and further, heat treatment is performed at 135 ° C. for 40 hours. By these heat treatments, as shown in FIG. 7B, dot-shaped PMMA chain aggregated portions 33b having a diameter of 30 nm and microphase-separated structures 33 phase-separated into polystyrene chain aggregated portions 33a were generated.

  Next, the microphase separation structure 33 is irradiated with light using a light source having a wavelength of 150 nm to 400 nm, followed by sonication in 1M acetic acid for 10 minutes, and the PMMA chain aggregation portion 33b constituting the dot shape is formed. Etching was removed. As a result, as shown in FIG. 4C, the first nanohole structure 35 having nanoholes 34 (diameter 30 nm, interval 30 to 40 nm, depth 100 nm) having the same size as the PMMA chain aggregation portion 33b is formed. I was able to.

<Transfer of the nanohole structure to the silicon oxide layer 31 and filling of the nanohole with the ferroelectric material by the PLD method>
Next, the pore structure was transferred to the silicon oxide layer 31 using the first nanohole structure 35 as a mask. Trifluoromethane CHF ₃ (20 sccm) was used as an etching gas under the conditions of an RF output of 200 W and a pressure of 15 mT. Although the etching time depends on the film quality related to the manufacturing method of the silicon oxide film 31, the entire film thickness of 200 nm can be removed by etching within a few minutes and reaches the lower platinum layer 14.

Subsequently, the ferroelectric nanodots 38 were formed by filling the second nanoholes 36 formed in the silicon oxide layer 31 as described above with a ferroelectric material in the same manner as in Example 3. That is, a YAG laser having an output of 200 mJ is used as a firing target for forming PZT having a Pb composition in excess of 10% and a composition ratio of Pb (Ti _x Zr _1-x ) O ₃ (x = 0.7). As shown in FIG. 7E, a thin film of PZT was deposited on a substrate (room temperature) placed at a position facing the firing target by pulse irradiation with a wavelength of 1064 nm. The film thickness was set to 70 nm as a film thickness not exceeding 100 nm of the block copolymer.

  Subsequently, crystallization of PZT was promoted by annealing at 700 ° C. for 1 hour in an oxygen atmosphere using a furnace annealing apparatus.

  When the obtained sample was evaluated by X-ray diffraction, it was confirmed that a PZT crystal oriented in (001) was formed.

  By the same method as in Example 1, it was possible to write and read out ferroelectric nanodots by recording bits.

Example 5 (Formation of Nanohole Template by Block Copolymer on Ferroelectric Thin Film and Formation of Ferroelectric Nanodots by Etching Ferroelectric Film Using This as a Mask)
In this embodiment, a ferroelectric SBT layer 41 and a block copolymer layer 42 are laminated on the platinum layer 14 which is the lower electrode on the silicon substrate 11, and the first nanodot structure is formed from the block copolymer layer 42. An example will be described in which the ferroelectric SBT layer 41 is selectively dry-etched using this as a mask to produce ferroelectric nanodots 46, and a write operation and a read operation are performed as a memory element. .

  FIG. 8 is a schematic cross-sectional view for explaining a process of manufacturing the ferroelectric nanodot 46 according to the present embodiment.

  First, as in Example 1, a silicon substrate 11 is thermally oxidized to form a silicon oxide layer 12, a titanium or titanium oxide layer 13 is formed thereon, and a platinum layer 14 serving as a lower electrode is further formed thereon. Formed. Further thereon, an SBT layer 41 was formed to a thickness of about 200 nm.

The SBT layer 41 can be formed by MOCVD, PLD, spin coating, or the like. Here, the film was formed by MOCVD as in the example. That is, assuming that the vaporizer temperature is 140 ° C., the carrier gas (argon) flow rate is 200 cc, the flow rate of oxygen used as the oxidizing agent is 200 cc, two types of organometallic raw materials Sr [Ta ₂ (OC ₂ H ₅ ) ₆ ] ₂ and Bi (OtC ₄ H ₉ ) ₃ was supplied at a ratio of 4: 6, and a reaction gas realizing a desired SBT composition was sent to the reactor.

  When the temperature of the substrate disposed in the reactor is 400 ° C., the pressure inside the reactor is 1 Torr, and a reaction gas is introduced, an amorphous thin film of SBT can be grown. The growth rate was about 10 nm / min.

Since the bimetallic source Sr [Ta ₂ (OC ₂ H ₅ ) ₆ ] ₂ is used, Sr: Ta is always kept constant and does not vary greatly depending on the film forming conditions. On the other hand, when Bi (OtC ₄ H ₉ ) ₃ is used as the Bi source, the amount of Bi introduced into the film can be controlled by various film forming conditions.

  The amorphous thin film formed as described above was baked under typical annealing conditions at 700 ° C. in oxygen for about 1 hour to obtain a ferroelectric film SBT. When the obtained sample was evaluated by X-ray diffraction, it was confirmed that an SBT crystal oriented in (106) was produced.

<Formation of first nanodot structure by block copolymer>
Next, a block copolymer layer 42 was formed on the ferroelectric SBT layer 41 described above. A block copolymer having an average molecular weight of about 65,000, which is composed of a polystyrene chain and a polymethyl methacrylate chain and has a PMMA chain fraction of about 80% by volume, is dissolved in toluene, and the concentration of the solution is adjusted to 1 to 10% by mass. Then, this solution was applied onto the above-mentioned substrate by a spin coating method, and a block copolymer layer 42 was formed as shown in FIG. At this time, the film thickness can be controlled by the concentration of the block copolymer solution and the rotation speed of the spin coat. Typically, when a film is formed at a solution concentration of 2 wt% and a rotation speed of 3000 rpm, a polymer film having a thickness of about 200 nm can be formed.

  After film formation, heat treatment is performed at 210 ° C. for 4 hours, and further, heat treatment is performed at 135 ° C. for 40 hours. By these heat treatments, a microphase-separated structure 43 including a dot-shaped polystyrene chain aggregation portion 43a having a diameter of 40 nm and a PMMA chain aggregation portion 43b aggregated so as to surround it was generated. This could be confirmed by AFM phase imaging.

  In the microphase separation structure 43, since the volume fraction of the PMMA chain is larger than the volume fraction of the polystyrene chain, the polystyrene chain aggregated portion 43a forms a dot-shaped assembly, and the PMMA chain aggregated portion 43b surrounds the structure. It has become. This is opposite to the relationship between the polystyrene chain aggregate 43a and the PMMA chain aggregate 43b in the microphase-separated structures formed in Examples 3 and 4. For this reason, when the PMMA chain aggregation part 43b is removed in the next step, the nanohole structure obtained in Examples 3 and 4 and the nanodot structure having a positive relationship with the negative are obtained.

Next, the microphase separation structure 43 was irradiated with light using a light source having a wavelength of 150 nm to 400 nm, followed by sonication in 1M acetic acid for 10 minutes, and the PMMA aggregation part 43b was removed by etching. As a result, only the dot-shaped polystyrene chain aggregation part 43a remains, and a plurality of first dots 44 (diameter 40 nm, interval 40-50 nm, height 100 nm) are at least partly regularly arranged. A structure 45 could be formed. Etching removal of the PMMA portion can also be performed by dry etching with CF ₄ gas, as described in Jpn. J. Appl. Phys., Vol. 41 (2002), p.

<Etching of Ferroelectric SBT Layer 41 Using First Nanodot Structure 45 as a Mask>
Next, the lower ferroelectric SBT layer 41 is dry-etched using the first nanodot structure 45 as a mask, the SBT layer 41 other than the masked portion is removed by etching, and the dot-shaped SBT layer is made into the ferroelectric nanodot. 46.

  Subsequently, the furnace was annealed in an oxygen atmosphere at 700 ° C. for 1 hour to recover the deterioration of the SBT crystallinity due to dry etching.

  By the same method as in Example 1, it was possible to write and read out the ferroelectric nanodots 46 by recording bits.

Example 6 (Production of Ferroelectric BaTiO3 Nanodots by Filling Nanoholes of Anodized Alumina Nanohole Structure with Ferroelectric Nanoparticles)
In this example, as in Example 1, a metal aluminum layer was formed on the platinum layer formed as the lower electrode, and this was anodized to form an anodized alumina layer, which strongly resists nanoholes in the alumina layer. Here, an example in which a ferroelectric nanodot is manufactured by filling a nanoparticle of a ferroelectric material and a writing operation and a reading operation are performed as a memory element will be described.

<Formation of nanohole structure with anodized alumina>
By the same method as in Example 1, an alumina nanohole structure by anodic oxidation was formed on a silicon substrate.

  First, a silicon substrate is thermally oxidized, a silicon oxide layer is formed as an insulating layer on the surface, a titanium or titanium oxide layer is formed thereon to improve adhesion to the platinum layer, and a platinum layer is formed thereon. Formed. Next, an aluminum layer was formed on the silicon substrate by RF sputtering. At this time, the film thickness of the aluminum layer was about 200 nm.

  Next, a 0.3M oxalic acid aqueous solution was used as the electrolytic solution, and the aluminum layer 15 was anodized while keeping the oxalic acid aqueous solution at 15 ° C. in a thermostatic bath. As shown in FIG. A nanohole structure made of alumina 16 was formed. In this example, the anodic oxidation voltage was set to DC 50 V, and anodic oxidation was performed until the nanohole 17 grew and reached the lower platinum electrode 14. The fact that the nanohole 17 reached the lower platinum electrode 14 was confirmed by the change in the current value of the electrolysis being monitored. After anodization, washing with pure water and 2-propanol (isopropyl alcohol) was performed.

  Next, in order to enlarge the hole diameter of the nanohole formed by the above anodic oxidation, the hole diameter was set to about 100 nm by immersing in a 5% by mass phosphoric acid solution for 20 minutes. Through the above oxidation step, a nanohole structure having nanoholes with a diameter of about 100 nm and a depth of about 200 nm was produced.

<Filling ferroelectric material into nanoholes>
Next, a method of filling the nanohole template with the ferroelectric BaTiO ₃ fine particles will be described.

A surfactant that has a hydrophilic portion and a hydrophobic portion, and the hydrophilic portion is oriented to the surface of the ultrafine particles, so that the ultrafine particles can be dispersed in an organic solvent without agglomerating, an organic solvent, and barium titanium A mixed solution with a double alkoxide (for example, BaTi (OOCC ₇ H ₁₅ ) [OCH (CH ₃ ) ₂ ] ₅ ) was set at 100 ° C.

  By adding hydrogen peroxide water to the above mixed solution and keeping it at 100 to 300 ° C. for 1 to 100 hours, the surface is covered with a surfactant, and the average particle diameter is excellent in dispersibility in an organic solvent. 5-50 nm barium titanate ultrafine particles were obtained. Treatment for exchanging the solvent was performed, and the barium titanate particles were dispersed in the hexane solution.

  After immersing or spin coating this solution on anodized alumina, the step of evaporating the solvent at 100 ° C. was repeated to obtain a nanohole structure in which nanoholes of anodized alumina were filled with barium titanate nanoparticles. This nanohole structure is improved in ferroelectric characteristics by heat treatment at 400 to 800 ° C. in oxygen.

The ultrafine particles are not limited to BaTiO ₃ , but by selecting an organic metal material, the dielectric material SrTiO ₃ , the ferroelectric material PbTiO ₃ , Pb (Zr, Ti) O ₃ , Bi _3.75 La _0.25 Ti ₃ O ₁₂ , or Nanostructures such as SrBi ₂ Ta ₂ O ₉ can also be obtained.

  When the obtained sample was evaluated by X-ray diffraction, it was confirmed that BaTiO 3 was produced.

  Writing / reading with ferroelectric nanodots as recording bits can be performed by the same method as in the first embodiment.

  As described above, according to the embodiments and examples of the present invention, strong pores such as SBT, PZT, PVDF / TrFE and the like are used in the pores using anodized alumina or a block copolymer as a nanohole structure template. By filling the dielectric material, ferroelectric nanodots having a diameter of 100 nm or less can be produced.

  Also, using anodized alumina or block copolymer as a nanohole structure template, the nanohole structure is transferred to a silicon oxide film or the like, and the formed nanohole is filled with a ferroelectric material such as SBT, PZT, PVDF / TrFE, or the like. As a result, ferroelectric nanodots having a diameter of 100 nm or less can be produced.

  Further, ferroelectric nanodots having a diameter of 100 nm or less can be produced by etching away the ferroelectric layer other than the mask portion using the block copolymer nanodot structure template as an etching mask.

  The above-described ferroelectric nanodots can produce a minute structure without exceeding the miniaturization limit without using a lithographic technique and a fine processing technique used in VLSI manufacturing. Furthermore, the present invention can be applied to a memory device using the polarization characteristics of a ferroelectric and can be used to construct an unprecedented high-density and large-capacity storage device.

  As mentioned above, although this invention was demonstrated based on embodiment, it cannot be overemphasized that this invention is not limited to these examples at all, and can be suitably changed in the range which does not deviate from the main point of invention.

  The present invention can be applied to the construction of a storage device having a high density and a large capacity, which has not been used in the past, by expanding to a memory device using the polarization characteristics of a ferroelectric substance.

It is a schematic perspective view which shows the structure of the ferroelectric microstructure based on Embodiment 1 of this invention. It is a schematic sectional drawing which shows the structure of the ferroelectric microstructure based on Embodiment 2 of this invention. It is a schematic sectional drawing which shows the manufacturing process of the ferroelectric microstructure by Example 1 of this invention. It is a schematic sectional drawing which shows the manufacturing process of the ferroelectric microstructure by Example 3 of this invention. It is explanatory drawing which shows the structure (a) of a block copolymer, and the structure of a micro phase-separation structure (b, c) similarly. FIG. 6 is an AFM observation image of the surface of the block copolymer before and after removal of the PMMA chain aggregation part. It is a schematic sectional drawing which shows the manufacturing process of the ferroelectric microstructure by Example 4 of this invention. It is a schematic sectional drawing which shows the manufacturing process of the ferroelectric microstructure by Example 5 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Lower electrode, 2 ... Pore structure, 3 ... Fine pore, 4 ... Ferroelectric fine dot,
11 ... Silicon substrate, 12 ... Silicon oxide layer, 13 ... Titanium or titanium oxide layer,
14 ... platinum layer, 15 ... aluminum layer, 16 ... anodized alumina,
17 ... Nanohole by anodization, 18 ... Nanohole widened by etching,
19 ... Ferroelectric nanodots, 21 ... Block copolymer layer, 22 ... Micro phase separation structure,
22a ... polystyrene chain aggregation part, 22b ... PMMA chain aggregation part,
23 ... Nanohole formed in the PMMA chain aggregation part, 24 ... Nanohole structure,
25 ... Ferroelectric nanodots, 31 ... Silicon oxide layer, 32 ... Block copolymer layer,
33 ... Micro phase separation structure, 33a ... Polystyrene chain aggregation part,
33b ... PMMA chain aggregation part, 34 ... Nanohole formed in the PMMA chain aggregation part,
35 ... first nanohole structure, 36 ... transferred nanohole,
37 ... Second nanohole structure made of silicon oxide, 38 ... Ferroelectric nanodot,
41 ... Ferroelectric SBT layer, 42 ... Block copolymer layer, 43 ... Micro phase separation structure,
43a ... polystyrene polystyrene chain aggregation part, 43b ... PMMA chain aggregation part,
44 ... 1st nanodot, 45 ... 1st nanodot structure, 46 ... Ferroelectric nanodot

Claims (23)

  A ferroelectric microstructure having fine dots of a ferroelectric material on an electrode.   The ferroelectric microstructure according to claim 1, wherein the ferroelectric material is present in pores of a pore structure formed in contact with the electrode to form the dots.   The ferroelectric microstructure according to claim 2, wherein the pore structure is a pore structure formed by anodizing a metal aluminum layer.   The ferroelectric microstructure according to claim 2, wherein the pore structure is a pore structure formed by anodizing an aluminum-hafnium alloy layer.   3. The ferroelectric microstructure according to claim 2, wherein the pore structure is a pore structure formed by anodizing a laminate in which a metal aluminum layer is laminated on an aluminum-hafnium alloy layer.   The ferroelectric microstructure according to claim 3, wherein at least a part of the pores of the pore structure is subjected to widening processing.   In the micro phase separation structure in which the block copolymer is phase-separated into a dot-aggregated part and another aggregated part, by removing at least a part of the dot-aggregated part, the pore structure The ferroelectric microstructure according to claim 2, wherein:   The ferroelectric microstructure according to claim 2, wherein the pore structure is formed by removing a part of the insulating layer in a dot shape.   The ferroelectric microstructure according to claim 1 or 2, wherein the dot or pore has a diameter of 5 to 200 nm.   The ferroelectric microstructure according to claim 1, wherein the pore array has periodicity.   The ferroelectric microstructure according to claim 1, wherein the ferroelectric material is an inorganic oxide or an organic polymer ferroelectric material.   The ferroelectric microstructure according to claim 2, wherein the pores are filled with nanoparticles of the ferroelectric material.   A step of forming a metal aluminum layer in contact with the electrode, a step of anodizing the metal aluminum layer to form a pore structure, and a step of filling the pores of the pore structure with a ferroelectric material A method for manufacturing a ferroelectric microstructure.   A step of forming an aluminum-hafnium alloy layer in contact with the electrode; a step of anodizing the aluminum-hafnium alloy layer to form a pore structure; and a ferroelectric material in the pores of the pore structure. A method of manufacturing a ferroelectric fine structure, wherein a filling step is performed.   A step of forming a laminate of an aluminum-hafnium alloy layer and a metal aluminum layer in contact with the electrode; a step of anodizing the aluminum-hafnium alloy layer to form a pore structure; and A method for manufacturing a ferroelectric microstructure, comprising: filling a pore with a ferroelectric material.   The method for producing a ferroelectric microstructure according to claim 13, wherein the pores are widened by etching using an acid aqueous solution.   A step of forming a microphase separation structure in which the block copolymer is phase-separated into a dot-aggregated portion and another agglomerated portion in contact with an electrode, and the dot-aggregated portion of the microphase-separated structure A method for producing a ferroelectric microstructure, comprising: a step of forming at least a part of the pore structure to form a pore structure; and a step of filling the pores of the pore structure with a ferroelectric material.   A step of forming an insulating layer in contact with the electrode, a step of forming a microphase-separated structure in which the block copolymer is phase-separated into a portion where the block copolymer is aggregated in the form of dots and another aggregated portion, and the insulating layer, Removing at least part of the dot-aggregated portion of the microphase-separated structure to form a first pore structure; and using the first pore structure as a mask, the insulating layer A method for manufacturing a ferroelectric microstructure, comprising: a step of etching to form a second pore structure; and a step of filling a ferroelectric material in the pores of the second pore structure.   Forming a ferroelectric layer in contact with the electrode, and forming a microphase-separated structure in which the block copolymer is phase-separated into a portion where the block copolymer is aggregated in dots and another aggregated portion, in contact with the ferroelectric layer A step of removing the other agglomerated portion of the microphase-separated structure to form a block copolymer dot-shaped structure, and etching the ferroelectric layer using the block copolymer dot-shaped structure as a mask. And a step of forming a dot structure of a ferroelectric material. A method for manufacturing a ferroelectric microstructure.   A voltage is applied between the probe and the electrode with respect to each ferroelectric dot of the ferroelectric microstructure according to any one of claims 1 to 12, and the ferroelectric dot A recording method in which spontaneous polarization is reversed and this is used as a recording bit.   The recording system according to claim 20, wherein a cantilever probe electrode is used as the probe.   21. A reproduction method for reproducing the recording bit of the ferroelectric dots according to claim 20, by detecting a change in surface potential or capacitance of the ferroelectric dots using the probe.   The method according to claim 20 or 22, wherein a cantilever probe electrode as the probe is moved relative to the ferroelectric dot in a contact or non-contact state.