JP3731641B2 - Ferroelectric material, ferroelectric memory and ferroelectric memory device using the same, dielectric patterning method, and ferroelectric memory device manufacturing method - Google Patents

Description

[0001]
[Field of use to which the invention belongs]
The present invention relates to a novel dielectric. In detail, it is related with improvement of a ferroelectric material. The present invention relates to a ferroelectric memory using an improved organic ferroelectric. The present invention relates to a method for manufacturing a ferroelectric memory using an improved organic ferroelectric. The present invention relates to a ferroelectric memory device using an improved organic ferroelectric material.
[0002]
[Prior art]
A ferroelectric is a material having remanent polarization. The remanent polarization changes its direction depending on the direction of the electric field applied to the ferroelectric. Therefore, a ferroelectric non-volatile memory is provided using the remanent polarization as information.
[0003]
As a ferroelectric memory, for example, PZT (Pb (Zr, Ti) O ₃ ), which is an inorganic ferroelectric material, is used as a ferroelectric, and this is sandwiched between upper and lower electrodes to form a capacitor. Yes. A ferroelectric memory using an organic ferroelectric instead of an inorganic ferroelectric is also known, as described in, for example, Japanese Patent Laid-Open No. 10-22470. As an organic ferroelectric, a copolymer of vinylidene fluoride and ethylene trifluoride (P (VDF / TrFE)) is known. An organic ferroelectric is advantageous in realizing a simple matrix type ferroelectric memory because of its low impedance.
[0004]
When configuring these ferroelectric memories, a ferroelectric thin film is formed on the lower electrode, patterning is performed by plasma ashing in the case of organic ferroelectrics, and RIE ion milling in the case of inorganic ferroelectrics. To pattern. Next, the upper electrode is laminated. Inorganic ferroelectrics need to be annealed at 700 to 800 degrees Celsius. Annealing may damage the CMOS structure.
[0005]
[Problems to be solved by the invention]
Organic ferroelectric materials are superior in that they do not require high-temperature annealing and can form a simple matrix memory due to their low impedance. However, the coercive electric field of the organic ferroelectric has a large value of about several to several tens MV / cm, and there is a problem that the drive voltage becomes high. If it is made thinner, the coercive electric field can be lowered, but the leakage current increases. Further, when the organic ferroelectric is patterned by plasma ashing, Pr (residual polarization / spontaneous polarization) decreases due to damage, and the reliability of elements such as fatigue, imprint, and retention decreases.
[0006]
On the other hand, as described in the prior art described above, a ferroelectric made of an oxide material has poor compatibility with a CMOS process. That is, in general, in a heated state in a gas containing hydrogen, an oxide ferroelectric such as PZT is very vulnerable to heating in a reducing atmosphere, and thus residual polarization is lost and a signal cannot be obtained. The hydrogen heat treatment of about 400 degrees that is normally performed cannot be performed. For this reason, it is difficult to ensure the reliability of the wiring formed after the storage capacitor is formed, and it is necessary to develop a special process for using a ferroelectric substance.
[0007]
Further, when the oxide material is annealed in a high oxygen atmosphere, the CMOS is damaged. Semiconductor processes that generate hydrogen gas, such as TEOS-CVD, damage the ferroelectric.
[0008]
Therefore, an object of the present invention is to provide an organic ferroelectric having excellent reliability, low leakage current, and low coercive electric field. Another object of the present invention is to provide an organic ferroelectric that can be patterned without being subjected to harsh conditions such as plasma ashing or ion milling. Still another object of the present invention is to provide a ferroelectric memory using the organic ferroelectric. Still another object of the present invention is to provide a memory device including the ferroelectric memory. Still another object of the present invention is to provide a patterning method for the ferroelectric memory. Still another object of the present invention is to provide a method of manufacturing a memory device including this dielectric memory.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is characterized in that a dielectric material is dispersed in a photofunctional resin to reduce a coercive electric field, and is a dielectric that can be patterned by irradiation with light. Accordingly, since the organic ferroelectric is not placed in a harsh environment such as plasma ashing during patterning as in the prior art, it is possible to avoid the performance degradation as described above. This dielectric can be used for ferroelectrics, piezoelectrics, pyroelectrics and the like. Therefore, the dielectric according to the present invention can be used for a ferroelectric memory, an ink jet recording head using a piezoelectric effect, a memory using a pyroelectric effect as described in JP-A-7-84231, and the like.
[0010]
As the photofunctional resin, those applicable to the present invention such as acrylate derivatives such as PMMA, methacrylate derivatives, styrene derivatives such as polystyrene and polyhydroxystyrene can be used. As the photo-functional resin, a photoresist that can be cross-linked by light irradiation to have a difference in etching property can be used.
[0011]
Examples of the dielectric material include the above-mentioned copolymers of vinylidene fluoride and ethylene trifluoride, polyvinylidene cyanide, odd-numbered nylon, etc., such as “Electron-Functional Polymer” (Kodansha Scientific, April 20, 1989). Publications, page 160), etc. can be used.
[0012]
In order to obtain the dielectric of the present invention, a dielectric material is dispersed in a photofunctional resin. Dispersion is performed as follows. That is, it is dispersed with a solvent in which the photofunctional resin and the dielectric are soluble. Examples of the solvent include the following. In addition to hydrocarbon solvents such as n-heptane, n-octane, dodecylbenzene, diethylbenzene, mesitylene, tetralin, decalin, toluene, xylene, cymene, durene, indene, dibenten, tetrahydronaphthalene, decahydronaphthalene, cyclohexylbenzene, ethylene Ether solvents such as glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, 1,2-dimethoxyethane, bis (2-methoxyethyl) ether, p-dioxysan Furthermore, propylene carbonate, γ-butrolactone, N-methyl-2-pyrrolidone, dimethyl Formamide, 1,3-dimethyl-2-Imidazorujinon, 1,3 di-n-propyl-2-Imidazorujinon, dimethyl sulfoxide, can be mentioned polar solvents such as cyclohexanone. Of these, hydrocarbon solvents and ether solvents are preferred in view of the solubility of the cyclic silicon compound and the stability of the solution, and more preferred solvents include hydrocarbon solvents. These solvents can be used alone or in admixture of two or more.
[0013]
The ratio of the dielectric material (B) to the photofunctional resin (A) is, for example, A: B = 1: 4 to 1: 1 from the viewpoint of dielectric characteristics.
[0014]
Since the organic ferroelectric memory according to the present invention can be driven at 3-5 V, it can be matched with the CMOS circuit and can achieve low power consumption. Furthermore, the organic ferroelectric does not damage the CMOS side because a low temperature process of 170 to 200 degrees Celsius can be achieved. And since patterning is possible by light irradiation, cost reduction can be achieved, without reducing Pr of the battery body to tie.
[0015]
According to the present invention, the reliability of fatig, imprint, retention, etc. is compared to the conventional one. Fatgue (3v) 10 ⁶ to 10 ¹⁰ cycles, imprint variation 30% to 10% or less, retention (65 degrees Celsius) ) It can be increased from 5 to 10 years .
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described. In this embodiment, a memory device including FeRAM (ferroelectric memory) using the above-described ferroelectric as a capacitor will be described as an example. FIG. 1 illustrates a manufacturing process of a simple matrix memory element. As shown in FIG. 1A, a peripheral circuit 21 peeled off from a base is transferred and formed on a substrate 1 by a known transfer method. In this transfer method, a part of an element component is formed on another substrate, and then the element component is peeled off, and the element component is transferred to a substrate to be transferred.
[0016]
The substrate 1 is not particularly limited as long as it has a desired mechanical strength and has heat resistance, erosion resistance, and the like in the step of forming a flattening film, an organic thin film, an X stripe electrode, and a Y stripe electrode, which will be described later. A plastic substrate, a quartz substrate, etc. can be used instead.
[0017]
Subsequently, as shown in FIG. 1B, a planarizing film 3 is formed in a region including the memory cell region and the peripheral circuits 21 and 22 on the substrate 1, and further, the peripheral circuit 21 and n pieces formed later. .., 4n are formed in accordance with the position of the connection terminal with the X stripe electrode. FIG. 4 shows 4n. At the same time, m contact holes are formed in accordance with the connection terminal positions of the peripheral circuit of the Y stripe electrode and the m Y stripe electrodes formed later .
[0018]
The planarizing film 3 absorbs a step between the peripheral circuits 21 and 22 transferred and formed on the substrate 1 and the substrate 1, and enables the connection between the peripheral circuits 21 and 22 and the X stripe electrode and the Y stripe electrode. It is a thin film provided and is not particularly limited as long as it is an insulating thin film.
[0019]
In order to form, for example, a polyimide film as the planarizing film 3, an arbitrary method such as a lithography method or a printing method can be selected. When the lithography method is used, the organic material may be applied by a predetermined method such as spin coating, spray code, roll coating, die coating, or dip coating. Further, when a silicon oxide film, for example, is formed as the planarizing film 3, it can be formed by a plasma CVD method using organosilane (TEOS) and oxygen as reaction gases, and a silicon nitride film is formed. In this case, the film can be formed by a plasma CVD method using silane gas and nitrogen as reaction gases.
[0020]
Next, as shown in (C), n X stripe electrodes 61, 62,..., 6n connected to the contact holes 41, 42,. (C) shows 6n. To form the X stripe electrodes, for _{example, Al, RuO 2, Pt,} IrO 2, YBa 2 Cu 3 O 7, OsO 2, MoO 2, ReO 2, WO 2, Au, Ag, In, In-Ga alloy A conductive material liquid (electrode material liquid) is prepared by dissolving fine particles of a conductive material such as Ga in an appropriate solvent, and patterned and applied in a stripe pattern using an ink jet recording head (fluid discharge head). .
[0021]
As a solvent, butyl carbitol acetate, 3-dimethyl-2-imidazolidine, BMA or the like can be used. As an ink jet recording head, a piezo jet method in which a desired fluid is ejected by volume change of a piezoelectric element is a bubble jet method in which a fluid is ejected by the rapid generation of steam by application of heat. There may be. Subsequently, the applied electrode material solution is heat treated to evaporate the solvent component, whereby n X stripe electrodes are formed.
[0022]
Next, as shown in (D), an organic thin film 7 is formed in the memory cell region. The organic thin film 7 has a characteristic in which the impedance (voltage vs. current characteristic) changes when the electric field strength applied between the X stripe electrode and the Y stripe electrode exceeds a certain threshold, and the impedance does not change even when the applied electric field is zero. It is comprised with the material which has. Therefore, if “0” or “1” is assigned corresponding to the high impedance state and the low impedance state of the organic thin film 7, a nonvolatile memory can be realized. If such an organic thin film 7 is used, one memory cell (unit memory cell) is formed at each intersection of the X stripe electrode and the Y stripe electrode orthogonal to each other.
[0023]
As described above, this organic film is formed by dispersing an organic strong electric material in a photofunctional resin and discharging it by an ejection method such as ink jet or bubble jet, a spin coating method, or a spray coating method. That is, a photofunctional resin and an organic ferroelectric as described above or Cu-TCNQ disclosed in International Publication No. WO98 / 58383 is dissolved in an organic solvent such as methanol, and this is dissolved on the electrode by the formation method described above. The film is formed. Next, the solvent component in the film is evaporated by heat treatment at about 170 degrees Celsius to solidify the film.
[0024]
The film thickness of the organic film based on one specific manufacturing method was 100 nm, and the coercive electric field of this film was measured and found to be 150 kv / cm. Furthermore, when the leakage current was measured, it was 10 ⁻⁷ A / cm ² . If the leakage current is 10 ⁻⁴ / cm ² or more, the hysteresis property is adversely affected. Next, the organic film is etched by irradiating light from a mercury lamp having a wavelength of 254 nm to pattern the organic film in an array.
[0025]
Finally, as shown in (E), m Y stripe electrodes 81, 82,..., 8m connected to the contact holes formed so as to match the connection positions of the Y stripe electrodes are formed over the memory cell region. The Y stripe electrode may be formed by patterning using an ink jet recording head in the same manner as the X stripe electrode. If the surface of the memory element is sealed with resin or the like, a simple matrix memory element is completed.
[0026]
【The invention's effect】
As described above, the present invention can provide an organic ferroelectric having excellent reliability, low leakage current, and low coercive electric field. The present invention can also provide an organic ferroelectric that can be patterned without being subjected to harsh conditions such as plasma ashing or ion milling. Furthermore, the present invention can provide a ferroelectric memory using this organic ferroelectric. The present invention can further provide a memory device including the ferroelectric memory. The present invention can further provide a dielectric patterning method capable of patterning by light irradiation.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a structure of a ferroelectric memory and a manufacturing method thereof according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 21 ... Peripheral circuit, 22 ... Peripheral circuit, 3 ... Planarization film | membrane, 41-4n ... Contact hole, 51-5m ... Contact hole, 61-6n ... X stripe electrode, 7 ... Organic thin film, 81-8m ... Y stripe electrode

Claims (6)

A thin film made of a solvent in which a photofunctional resin and an organic ferroelectric material are dissolved is formed on an electrode formed on a substrate, and the thin film is irradiated with heat treatment and light at a low temperature to evaporate the solvent. obtained by performing patterning processing and consisting, said a ferroelectric formed by the organic ferroelectric material is dispersed in said optical functional in resin, there thickness in 100nm to 200 nm, the coercive field Is a ferroelectric substance having a leakage current of 10 ⁻⁴ / cm ² when a drive voltage is applied, at a current of 50 kv / cm to 300 kv / cm . The optical functional resin acrylate derivatives, methacrylate derivatives, the ferroelectric according to claim 1, wherein either a styrene derivative. Between electrodes Ri name to form the capacitor portion, a ferroelectric memory formed by using a dielectric according to claim 1 or 2, wherein in the capacitance section. A plurality of ferroelectric memories according to claim 3 are arranged in an array, and a peripheral circuit is provided for writing data to or reading data from a specific ferroelectric memory by designating row and column addresses. A ferroelectric memory device. Forming electrodes on the substrate,
Next, a thin film made of a solvent in which a photofunctional resin and an organic ferroelectric material are dissolved is formed on the electrode,
Next, the thin film is subjected to a heat treatment at a low temperature to evaporate the solvent,
Next, the thin film is irradiated with light, has a specific pattern, has a thickness of 100 nm to 200 nm, has a coercive electric field of 50 kv / cm to 300 kv / cm, and further has a driving voltage applied. A dielectric patterning method comprising forming a ferroelectric layer having a leak current of 10 ⁻⁴ / cm ² . An electrode is formed on the substrate, and then a thin film made of a solvent in which a photofunctional resin and an organic ferroelectric material are dissolved is formed on the electrode, and then the solvent is evaporated on the thin film at a low temperature. The ferroelectric film is formed by applying the heat treatment, and the specific pattern has a thickness of 100 nm to 200 nm, a coercive electric field of 50 kv / cm to 300 kv / cm, and a driving voltage. forming a ferroelectric layer leakage current is 10 ^-4 / cm ² when but applied as capacitor portion between the electrodes, as well as place the ferroelectric in an array, the row and column electrodes forming, of a ferroelectric memory device comprising the steps of forming a peripheral circuit pattern of reading data from row and column address to write data to a particular ferroelectric specify or the ferroelectric Made Method.

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