KR100371055B1 - Bismuth-cerium Titanate Thin Film for Capacitor of Ferroelectric Random Access Memory - Google Patents

Abstract

The present invention relates to a bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film and a method for manufacturing the electrical thin film, which have no fatigue phenomenon and have excellent electrical properties even at a low heat treatment temperature even after long use. will be. Method for producing a bismuth-cerium titanate thin film of the present invention is a mixture of bismuth precursor and cerium precursor having a composition ratio of Ce / (Ce + Bi) of 0.01 to 0.99, titanium precursor 30 to 800 ℃, 1x10 ^-9 Torr And depositing the substrate on the substrate by a wet deposition method or a dry deposition method at 100 atm, and heat-treating the deposited thin film at a temperature increase rate of 100 to 600 ^° C./min and a temperature of 200 to 800 ° C. The bismuth-cerium titanate thin film of the present invention exhibits a spontaneous polarization phenomenon and no fatigue phenomenon of the capacitor, and thus may be usefully used as a capacitor for a nonvolatile ferroelectric random access memory.

Description

Bismuth-cerium Titanate Thin Film for Capacitor of Ferroelectric Random Access Memory}

The present invention relates to a bismuth-cerium titanate thin film for a capacitor of a next generation ultra high density nonvolatile ferroelectric random access memory (FRAM). More specifically, the present invention relates to a bismuth-cerium titanate thin film and an electric thin film manufacturing method which exhibits excellent electrical properties even at low heat treatment temperatures without fatigue phenomenon of the thin film even when used for a long time.

With the development of computers, the development of semiconductor devices, which are the core parts of computers, is accelerating. In particular, the development of random access memory (RAM), which provides a temporary storage space of a computer, and read only memory (ROM), which can only read stored information, is noticeable, so that the read and write is very fast. Static random access memory (SRAM), programmable read-only memory (PROM) that allows the user to modify the recorded content, and erasable programmable read to erase and reuse content stored in memory only memory, EPROM).

Subsequently, a nonvolatile ferroelectric random access memory (FRAM) was developed that combines the advantages of SRAM, which is extremely fast to read and write, and the advantages of nonvolatile and electronically programmable EPROM. However, a FRAM composed of one ferroelectric capacitor and one transistor has a density of about 32 KB on one chip, so an SRAM having a density of 512 KB on one chip, an EPROM having a density of 1 MB on one chip, and one Compared with DRAM having a density of 8MB on the chip, it is significantly lower than commercialized. This is because there is a problem with a material used as a capacitor of the FRAM, and the material used as a capacitor conventionally is lead zirconium-titanic acid (Pb [Zr, Ti] O ₃ ) or strontium bismuth tantalum acid (SrBi ₂ Ta _2). an adverse effect on the titanate thin film stability indicates a phenomenon (fatigue) fatigue which exhibits excellent ferroelectric characteristics and weakening the electric properties for a long time use, the lead diffusion and volatilization in the subsequent process devices - O ₉₎ is, lead zirconium was used The strontium bismuth tantalum acid thin film does not suffer from fatigue, but has a disadvantage in that it cannot be applied to an actual process because the heat treatment temperature for improving electrical properties is higher than 750 ^° C.

Therefore, there is a constant need to develop a new capacitor thin film which overcomes the disadvantages of the conventional thin film for capacitor of FRAM.

Accordingly, as a result of intensive research to develop a new capacitor thin film for overcoming the shortcomings of the conventional FRAM thin film capacitor, bismuth titanic acid (Bi ₄ Ti ₃ O ₁₂ ) and cerium (Ce) are 1:99 to 99: 1. When using a thin film made of bismuth-cerium titanic acid mixed in a (molar ratio), it was confirmed that heat treatment is possible at low temperature, and fatigue phenomenon of the thin film was not generated, thereby completing the present invention.

After all, the main object of the present invention is to provide a bismuth-cerium titanate thin film for a capacitor of a FRAM.

Another object of the present invention is to provide a method for producing an electric bismuth-cerium titanate thin film.

The bismuth-cerium titanate thin film of the present invention is a mixture of bismuth precursor and cerium precursor having a composition ratio of Ce / (Ce + Bi) of 0.01 to 0.99, and titanium precursor at 30 to 800 ° C., 1 × 10 ⁻⁹ Torr to 100 atm. Depositing on the substrate by a wet deposition method or a dry deposition method; And heat-treating the deposited thin film at a temperature increase rate of 100 to 600 ^° C./min and a temperature of 200 to 800 ° C. In this case, as a wet deposition method, methanol, ethanol, propanol, isopropanol, butanol, Liquid source misted chemical deposition (LSMCD), sol-gel method using organic solvents such as 2-methoxyethanol, toluene, benzene, phenol, 2-ethylhexanoic acid, acetone or acetylacetonate Alternatively, metalorganic decomposition (MOD) may be used, and as the dry deposition method, metalorganic chemical vapor deposition (MOCVD), laser ablation, evaporation or sputtering may be used. Sputtering can be used and the substrate is tungsten (W), molybdenum (Mo), ruthenium (Ru), iron (Fe), iridium (Ir), rhodium (Rh), platinum (Pt), nickel (Ni) , Copper (Cu), aluminum (Al), gold (Au) or electroplated gold It is preferable to use a silicon (Si) wafer coated with an oxide of 80 to 120 nm thick. In addition, the heat treatment process is preferably performed in an atmosphere saturated with air, oxygen, nitrogen, water vapor, inert gas, nitrous oxide, ozone, ammonia, nitrogen monoxide, nitrogen dioxide, hydrogen sulfide or carbon monoxide. In addition, the step of depositing La, Pr, Nd, Sm or Eu on the bismuth-cerium titanate thin film prepared by the above method, or the prepared bismuth-cerium titanate thin film is a reactive ion plasma or low pressure high density plasma It may further include a step of treating using.

The bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film of the present invention produced by the above method exhibits spontaneous polarization and low leakage current, and thus has excellent reproducibility. It may be usefully used as a capacitor.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention in more detail, it will be apparent to those of ordinary skill in the art that the scope of the present invention is not limited by these examples in accordance with the gist of the present invention. .

Example 1 Preparation of Bismuth-Serium Titanate Thin Film by Organic Chemical Vapor Deposition

Characteristics of bismuth-cerium titanate thin films were measured according to atmospheric conditions and heat treatment temperatures during the manufacturing process.

Example 1-1 Preparation of Bismuth-Serium Titanate Thin Film Under Nitrogen Condition During Heat Treatment

Bismuth 2-ethylhexanoate (Bi [OOCCH (C ₂ H ₅ ) C ₄ H ₉ ] ₃ ), cerium nitrate (Ce (NO ₃ ) ₃ ) and titanium isopropoxide (Ti [O ⁱ C ₃₎ H ₇ ] ₄ ) is dissolved in 2-methoxyethanol (CH ₃ OCH ₂ CH ₂ OH) and distilled at 130 ^° C. for 24 hours to give bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) A thin film precursor solution, and a silicon (Si) wafer substrate coated with 100 nm thick platinum (Pt) at a pressure of 700 Torr at room temperature using high purity (99.999%) argon (Ar) as a transfer gas. Deposited in the form of a thin film, heat-treated at 650 ^o C for 1 hour under nitrogen atmosphere, thinly deposited platinum (Pt), and then heat-treated again at 650 ^o C under nitrogen atmosphere to obtain 350 nm thick bismuth- A cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film was prepared. The prepared thin film exhibited a spontaneous polarization 8.0 (μC / cm ² ) and a coercive fieid 76 (kV / cm) at a voltage of 10V.

Example 1-2 Preparation of Bismuth-Serium Titanate Thin Film Under Oxygen Condition During Heat Treatment

A bismuth-cerium titanate thin film was manufactured in the same manner as in Example 1-1, except that the atmospheric condition was oxygen instead of nitrogen.

Example 1-3 Preparation of Bismuth-Serium Titanate Thin Film at Changed Temperature Conditions

A bismuth-cerium titanate thin film was prepared in the same manner as in Example 1-1, except that oxygen was used instead of nitrogen for the heat treatment, and the heat treatment temperature was 600 ^° C., Example 1-1 and The thin film prepared in 1-2 was compared with the characteristics (see Table 1).

Comparison of Characteristics of Thin Films with Changes in Atmospheric Conditions During Heat Treatment Example Spontaneous polarization at 10V (μC / cm ² ) Coercive fieid (kV / cm) 1-1 8.0 76 1-2 9.2 87 1-3 8.1 105

As shown in Table 1, the spontaneous polarization phenomenon of a similar level was generated even when the atmospheric conditions or the heat treatment temperature were changed during the heat treatment, and it was found that the polarization inversion field was increased at a low temperature. Also, leakage current density is 2.78x10 ^-7 at 5V.

(A / cm ² ), the spontaneous polarization did not decrease until the polarization inversion cycle 10 ¹² at a voltage of 5V, it can be seen that the fatigue phenomenon of the thin film does not occur.

Example 2 Preparation of Bismuth-Serium Titanic Thin Films by Sputtering

The sputtering equipment used in the sputtering method uses a 13.56 MHz radio frequency (rf) and forms a magnetic field to increase the ion concentration. Subsequently, a target for sputtering was prepared with a composition of Ce / (Ce + Bi) = 0.025, 0.075, 0.125, 0.1875, and 0.25 at RF power 100W, and the target was sprayed by emitting ions by sputtering equipment to each target, and argon Was used as a reaction gas, and 300 nm thick bismuth-cerium titanic acid was deposited on a silicon (Si) wafer coated with platinum (Pt) 100 nm thick at a pressure of 200 ° C. and 30 mTorr. Subsequently, the deposited substrate was heat-treated at 650 ^° C., platinum (Pt) was thinly deposited, and then heat-treated again at 650 ^° C. to produce a bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film. It was. As a result of measuring the spontaneous polarization value and the polarization inversion field value of the thin films manufactured with the respective compositions, the maximum spontaneity polarization value of 7.3 (μC / cm ² ) and the polarization inversion field (coercive fieid) at Ce / (Ce + Bi) = 0.125 (kV / cm) was found.

Example 3 Preparation of Bismuth-Serium Titanate Thin Films by Organometallic Vapor Deposition

Bismuth 2-ethylhexanoate (Bi [OOCCH (C ₂ H ₅ ) C ₄ H ₉ ] ₃ ), cerium isopropoxide (Ce [O ⁱ C ₃ H ₇ ] ₄ ) and titanium isopropoxide ( Ti [O ⁱ C ₃ H ₇ ] ₄ ) was mixed to a value of Ce / (Ce + Bi) = 0.15, heated to the volatilization temperature of each material, and then transferred to a chamber using oxygen, followed by 30 Torr of At pressure and 200-700 ^° C., platinum (Pt) was deposited on a 100 nm thick coated silicon (Si) wafer substrate. At this time, the temperature was deposited at 200, 250, 300, 350, 400, 450, 500, 550, 600, 650 and 700 ^° C, respectively to determine the optimum temperature for crystallization. Then, a bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film was prepared by heat treatment at 600 ^° C. under atmospheric conditions saturated with oxygen. As a result, it can be seen that the optimum temperature for crystallization of the thin film is 500 to 600 ^o C, the maximum spontaneous polarization value is 8.3 (μC / cm ² ), and the coercive fieid shows 65 (kV / cm). Could.

As described and demonstrated in detail above, the present invention is a bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film that exhibits excellent electrical properties even at low heat treatment temperatures without fatigue of the thin film even after long use. And it provides a method for producing an electric thin film. Since the bismuth-cerium titanate thin film of the present invention exhibits spontaneous polarization and no fatigue of the capacitor, it may be usefully used as a capacitor for a nonvolatile ferroelectric random access memory.

Claims (11)

(Iii) a wet deposition method or a dry deposition method of a mixture of bismuth precursor and cerium precursor having a composition ratio of Ce / (Ce + Bi) of 0.01 to 0.99 and a titanium precursor at 30 to 800 ° C. and 1 × 10 ⁻⁹ Torr to 100 atm. Depositing on the substrate by a process; And, (Ⅱ) of the deposited thin film includes a step of heat treatment at a temperature of 100 to 600 ^o C / min temperature ramp rate, and from 200 to 800 ℃ of bismuth-three Solarium titanate _{([Bi, Ce] 4 Ti} 3 O 12) of the thin film Manufacturing method. The method of claim 1, Wet deposition method is chemical vapor deposition using organic solvent (LSMCD, liquid source misted chemical deposition, sol-gel or organic gold Characterized in that the metalorganic decomposition (MOD) Method for preparing a bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film. The method of claim 2, Organic solvents include methanol, ethanol, propanol, isopropanol, butanol and 2-methok Ethanol, toluene, benzene, phenol, 2-ethylhexanoic acid, acetone or acetyl It is characterized in that it is acetonate Method for preparing a bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film. The method of claim 1, The dry deposition method is organic metal vapor chemical vapor deposition (MOCVD, metalorganic) chemical vapor deposition, laser ablation, Evaporation or sputtering Characterized Method for preparing a bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film. The method of claim 1, Substrates include tungsten (W), molybdenum (Mo), ruthenium (Ru), iron (Fe), iridium (Ir), Rhodium (Rh), platinum (Pt), nickel (Ni), copper (Cu), aluminum (Al), gold (Au) or Silicon (Si) way coated with 80-120 nm thick oxide of electrometal Characterized in that it is a wafer (wafer) Method for preparing a bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film. The method of claim 1, Heat treatment includes air, oxygen, nitrogen, water vapor, inert gas, nitrous oxide, ozone, Saturated with ammonia, nitrogen monoxide, nitrogen dioxide, hydrogen sulfide or carbon monoxide Characterized by performing in Method for preparing a bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film. Bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ , further comprising the step of depositing La, Pr, Nd, Sm or Eu on the bismuth-cerium titanic thin film prepared by the method of claim 1 ) Manufacturing method of thin film. A bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) further comprising the step of treating the bismuth-cerium titanate thin film prepared by the method of claim 1 using a reactive ion plasma or a low pressure high density plasma. Method for producing a thin film. A bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film for a capacitor of a nonvolatile ferroelectric random access memory prepared by the method of claim 1. A bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film for a capacitor of a nonvolatile ferroelectric random access memory prepared by the method of claim 7. A bismuth-cerium titanic acid ([Bi, Ce] ₄ Ti ₃ O ₁₂ ) thin film for a capacitor of a nonvolatile ferroelectric random access memory prepared by the method of claim 8.