Ferroelectric memory and manufacturing method for the same

Abstract

To provide a ferroelectric memory in which the occurrence of α-rays is suppressed even when a PZT or PLZT material is used as a ferroelectric layer material, and a manufacturing method for the ferroelectric memory.SOLUTION: A ferroelectric memory includes a capacitor having a ferroelectric layer and a transistor. A material of the ferroelectric layer of the capacitor contains PZT or PLZT. The ratio of an isotope 208 Pb to an isotope 206 Pb of lead in the PZT or PLZT (208 Pb / 206 Pb) is 2.5 or more. The transistor and / or the capacitor is patterned by resist containing a tin compound.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates generally to the manufacture of semiconductor devices, and more particularly to the manufacture of a capacitor for a non-volatile semiconductor memory having a ferroelectric layer that is less likely to generate lead-derived alpha rays. [Background technology]

[0002] Non-volatile semiconductor memories are widely used as high-speed main memory devices for computers, etc. These are volatile memory devices, whereas in recent years, flash memory, which stores information in the form of electric charges in a floating gate electrode, has come to be used more and more as non-volatile memory devices.

[0003] In recent years, ferroelectric random access memories (hereinafter sometimes referred to as "FeRAM") have been manufactured, which store information in the form of spontaneous polarization of a ferroelectric layer. Such FeRAM has a memory cell configuration having a transistor and a ferroelectric capacitor. Specifically, the transistor is a single MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) like in the case of DRAM, and the dielectric layer in the capacitor is PZT: lead zirconate titanate (Pb(Zr x ·Ti x )O3) or PLZT: lanthanum-doped lead zirconate titanate ((Pb y ·La y )(Zr x ·Ti x )O3), or even strontium tantalate bismuthate: SBT (SrBi2Ta2O3), enabling integration at a high integration density (note that x and y are positive numbers and may be the same or different).

[0004] In addition, because FeRAM controls the spontaneous polarization of ferroelectric capacitors by applying an electric field, it has the advantageous features of being 1,000 times faster or faster than flash memory, and consuming less than 1 / 10 the power. Furthermore, because it does not require the use of a tunnel oxide film, it has a long lifespan and is expected to be able to be rewritten 100,000 times more than flash memory.

[0005] Conventionally, sputtering and MOCVD methods have been indispensable techniques for forming the ferroelectric layer used in such FeRAM, and in particular, when forming the ferroelectric layer, it is necessary to supply raw materials containing metal elements such as Pb, Sr, Zr, Ti, etc. In recent years, sputtering has not been used due to miniaturization, and the MOCVD method using organometallic raw materials of metal elements is used exclusively (for example, see Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2022 / 190817 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when a ferroelectric memory device is fabricated using ordinary PZT or SBT as the ferroelectric layer material, soft errors, which cause the memory to malfunction when exposed to alpha rays, become an issue.

[0008] Meanwhile, advances in semiconductor design have necessitated the creation of ever-smaller features on semiconductor substrate materials, with individual features measuring approximately 22 nanometers (nm) or less, and in some cases less than 10 nm. One challenge in the manufacture of devices with such fine features is the ability to reliably and reproducibly create photolithography masks with sufficient resolution. Achieving feature sizes smaller than the wavelength of light requires the use of complex high-resolution techniques, such as multiple patterning. Thus, the development of photolithography techniques using shorter wavelength light, such as extreme ultraviolet radiation (EUV), which has a wavelength of 10 nm to 15 nm (e.g., 13.5 nm), is of importance.

[0009] Conventional organic chemically amplified resists (CARs) have potential drawbacks when used in EUV lithography, especially because they have low adsorption coefficients in the EUV region, which can lead to blurring of the diffusion of photoactivated species or roughness of lines edges. Thus, there remains a need for improved EUV photoresist materials that have the properties of thin thickness, better absorbance, and better etch resistance.

[0010] Under such circumstances, the present invention aims to provide a ferroelectric memory and a manufacturing method thereof that suppresses malfunction due to alpha rays even when PZT or PLZT is used as the ferroelectric layer material and has a high definition. [Means for solving the problem]

[0011] In view of these circumstances, the present inventors have discovered that by using lead having a specific isotope ratio as the PZT or PLZT material for the capacitor, and by using a resist in which a tin compound is used as a precursor in the manufacture of the transistor, it is possible to suppress the generation of alpha rays and obtain a highly precise ferroelectric memory, thus arriving at the present invention. That is, the present invention has the following aspects. [1] A ferroelectric memory including a capacitor having a ferroelectric layer and a transistor, the material of the ferroelectric layer of the capacitor includes PZT or PLZT; Lead isotopes in the PZT or PLZT 208 Pb and 206 Ratio to Pb ( 208 Pb / 206 Pb) is 2.5 or more, A ferroelectric memory, wherein the transistor and / or the capacitor are patterned with a resist having a tin compound. [2] The alpha ray emission rate of the PZT or PLZT is 0.02 cph / cm 2 A ferroelectric memory according to [1], [3] The ferroelectric memory according to [1] or [2], wherein the resist has a lead content of 1 ppb or less. [4] The ferroelectric memory according to any one of [1] to [3], wherein the resist contains chromium, manganese, iron, nickel, and copper at a content of 10 ppb or less, respectively. [5] The ferroelectric memory according to any one of [1] to [4], wherein the tin compound contains tin(IV) oxide. [6] The ferroelectric memory according to any one of [1] to [5], wherein the precursor of the tin compound is represented by the following chemical formula (1) or (2): (chemical 1) R p SnX m …(1) [The above R is a hydrocarbon group which may be substituted with a halogen atom, and p is 0 or 1. X is a hydrolyzable substituent, and m is an integer of 1 to 4, with the proviso that m+p is 2 or 4.] (chemical 2) SnXa4…(2) [Xa is a hydrolyzable substituent, and is preferably an alkoxy group or a dialkylamino group.] [7] The ferroelectric memory according to [6], wherein the precursor of the tin compound is tetrakis(dimethylamino)tin and / or isopropyltris(dimethylamino)tin. [8] The ferroelectric memory according to any one of [1] to [7], wherein the purity of the precursor of the tin compound is 97 mol % or more in terms of tin atoms. [9] The method for producing a ferroelectric memory according to any one of [1] to [8], further comprising a step of exposing the transistor and / or the capacitor to EUV using the resist as a mask to thereby pattern the transistor and / or the capacitor. Effect of the Invention

[0012] The ferroelectric memory of the present invention can suppress malfunctions caused by alpha rays and achieve high definition even when PZT or PLZT is used as the ferroelectric layer material. [Brief description of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing a ferroelectric memory (FeRAM) according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described in more detail below based on the embodiments of the present invention, but the present invention is not limited to the following embodiments. In the present invention, when expressed as "X to Y" (X and Y are any numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as "preferably larger than X" or "preferably smaller than Y". Furthermore, when it is expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also includes the meaning that "it is preferably greater than X" or "it is preferably less than Y". Furthermore, "x and / or y (x and y are optional configurations)" means at least one of x and y, and means the following three cases: x only, y only, and x and y.

[0015] The structure of a ferroelectric memory (FeRAM) according to one embodiment of the present invention is, for example, a 1T1C type memory cell configuration having one transistor (FeFET) 1 on a substrate 10 and one capacitor 2 on the transistor 1, as shown in FIG. Here, the ferroelectric memory of this embodiment will be described based on a 1T1C type memory cell configuration.

[0016] <Capacitor> The capacitor 2 in the ferroelectric memory (FeRAM) of this embodiment is generally configured on a transistor 1 by forming a lower electrode layer 20, a ferroelectric layer 21 having PZT or PLZT thereon, and an upper electrode layer 22 thereon. The ferroelectric layer 21 of the capacitor 2 is made of PZT or PLZT.

[0017] The PZT or PLZT is the main component of the material for the ferroelectric layer 21. Here, the "main component" means a component that has a large effect on the properties of the target, and the content of the component is usually 50 mass % or more in the target, preferably 55 mass % or more, more preferably 60 mass % or more, further preferably 70 mass % or more, and may be 100 mass %.

[0018] PZT is lead zirconate titanate (Pb(Zr x ·Ti x )O3), and PLZT is lead lanthanum-doped zirconate titanate ((Pb y ·La y )(Zr x ·Ti x )O3), which means that a considerable amount of lead is contained in the ferroelectric layer 21. The presence of lead indicates the ability to emit alpha rays, and these alpha rays are known to be a cause of soft errors.

[0019] Lead itself does not emit alpha particles, but in the uranium-238 decay series 210 Pb → 210 Bi→ 210 Po→ 206 It decays with Pb and Po emits alpha rays. Here, 210 The half-life of Pb is about 22 years, and it has reached quasi-radioactive equilibrium. Therefore, even if lead (Pb) is thoroughly refined and bismuth (Bi) and polonium (Po) are sufficiently removed, alpha rays will decrease temporarily, but will increase over time.

[0020] on the other hand, 208 Pb belongs to the thorium-232 decay series, 212 Pb → 212 Bi→ 212 Po→ 208 It decays like Pb, and in this case the alpha rays of Po can be a problem, 212 Since the half-life of Pb is short at 10.64 hours, 208 Lead with a high Pb content loses its alpha-particle emission ability at an early stage. In other words, it is not a problem of refining lead (Pb), but rather of the radioisotope 210 This is a problem of Pb, which needs to be reduced, but it is technically difficult to remove. On the other hand, alpha rays are 0.1cph / cm 2 The use of the following PZT or SBT materials will reduce alpha radiation dose, making it possible to design and fabricate devices that prevent soft errors.

[0021] The above 210 Pb will eventually 206 It becomes Pb and becomes a stable isotope. 208 Pb is the last stable isotope in the thorium series. Therefore, 206 By using lead with a low Pb content as a raw material, it is possible to obtain a ferroelectric layer 21 with a reduced amount of alpha ray radiation.

[0022] The average abundance of stable Pb isotopes is 208 Pb / 206 Pb=52.4 / 24.1=2.17. Also, 208 Pb / 206If the Pb ratio is measured and the value is 2.5 or more, there is a high probability that the alpha rays of refined lead are 0.02 cph / cm 2 The following is true:

[0023] 206 The Pb content varies depending on the source of the ore. 206 It is preferable to use ores with as low a Pb content as possible as the raw material. 206 The proportion of Pb may be reduced by carefully mining and collecting the finely dispersed ore in the deposit, or by pulverizing the dispersed ore in a pulverizer for 30 minutes to 2 hours, sieving the pulverized ore through a 100 mesh sieve, and then purifying the pulverized ore.

[0024] In lead 208 Pb / 206 The method for measuring the ratio of Pb is, for example, secondary ion mass spectrometry (IRMS), which is a type of isotope ratio mass spectrometry. 208 Pb / 206 This method allows the ratio of lead in the ore to be determined, even if the amount of lead in the ore is not constant. 208 Pb / 206 The ratio of Pb is calculated.

[0025] The alpha dose of the ferroelectric layer 21 is preferably as low as possible to prevent malfunction of the memory, and is usually 10 cph / cm 2 More preferably, it is equal to or less than 1 cph / cm 2 The amount of α radiation can be measured by an α ray measuring instrument (a 2π type gas flow proportional counter).

[0026] <Transistor> In the ferroelectric memory of this embodiment, the transistor 1 is patterned with a resist containing a tin compound. Specifically, as shown in FIG. 1, a gate electrode layer 12 formed on a substrate 10 via a gate insulating layer 11, and a source diffusion region 13 and a drain diffusion region 14 formed in the substrate 10 are formed on both sides of the gate electrode layer 12.

[0027] Also, as the gate insulating layer 11 of such a transistor 1, a silicon oxide layer is frequently used. However, as a recent technological trend, in order to respond to the miniaturization of semiconductor memories, hafnium oxide, hafnium silicate oxyanide, hafnium aluminate, etc., which are so-called "high-κ" ferroelectrics, are used as insulators (MFSFET). In the pattern miniaturization, a tin compound is used as a resist.

[0028] Specific examples of the tin compound constituting the resist before exposure include, for example, RSnO disclosed in JP-T-2018-502173 (3 / 2-x / 2) (OH) x (where 0 < x < 3, R is an alkyl group or cycloalkyl group having 3 to 31 carbon atoms, and the alkyl group or cycloalkyl group is bonded to tin at a secondary or tertiary carbon atom), a compound represented by (QSn) 12 O 14 (OH)6(RCO2)2 (where R is H or an alkyl group having 1 to 10 carbon atoms, Q is a hydrocarbyl group having 3 to 31 total carbon atoms, or Q has the structure -(CH2) n Sn(R 1 R 2 R 3 ) and n = 1 to 4, and is an alkyltin group having 4 to 15 total carbon atoms, R 1 , R 2 , and R 3are independently an alkyl group having 1 to 5 carbon atoms). When these tin compounds are irradiated with EUV, the substituent R dissociates and a Sn-O bond is formed there, resulting in a tin compound having a network structure mainly composed of tin (IV) oxide. Development is possible due to the difference in chemical properties before and after exposure.

[0029] As the precursor of such a tin compound, tin compounds represented by the following chemical formulas (1) and (2) are preferably used.

[0030] Similarly, in the semiconductor manufacturing process, tin compounds are used as resists in the manufacture of capacitors, since semiconductors are manufactured without frequent changes of resist. Tin compounds may be accompanied by lead, which is in the same group (group 14) in the periodic table, and it is preferable that the resists made using tin compounds have minimized radioactive materials to prevent malfunction of the memory, as with the ferroelectric layer 21 in the capacitor.

[0031] In order to obtain finer patterns, the resist preferably has a lower lead content, and the lead content in the resist is usually 20 ppb or less, preferably 10 ppb or less, more preferably 5 ppb or less, and even more preferably 1 ppb or less. The contents of chromium, manganese, iron, nickel, and copper in the resist are also usually 100 ppb or less, preferably 50 ppb or less, and more preferably 10 ppb or less. The metal content in the resist can be calculated by measuring the metal atomic weight by ICP-MS.

[0032] As mentioned above, tin compounds usually contain lead, but the lead can be chemically removed by several manufacturing steps, purification, distillation, etc. By removing the lead, it is possible to increase the resolution of transistor 1 (FeFET) and also tends to suppress the generation of alpha radiation. For example, in the tin compounds shown in the following chemical formulas (1) and (2), the lead content can usually be reduced to 1 ppb or less by going through a distillation process.

[0033] The resist used in this embodiment is a tin compound, and it is preferable to use a tin compound represented by the following chemical formula (1) as a precursor. In this case, a tin compound represented by the following chemical formula (2) can also be used in combination.

[0034] (chemical 1) R p SnX m …(1) [The above R is a hydrocarbon group which may be substituted with a halogen atom, and p is 0 or 1. X is a hydrolyzable substituent, and m is an integer of 1 to 4, with the proviso that m+p is 2 or 4.]

[0035] (Case 2) SnXa4…(2) [Xa is a hydrolyzable substituent, and is preferably an alkoxy group or a dialkylamino group.]

[0036] In the above formula, "R" is a hydrocarbon group, preferably a hydrocarbon group having 1 to 30 carbon atoms, more preferably 1 to 15 carbon atoms, more preferably 1 to 10 carbon atoms, and even more preferably 2 to 6 carbon atoms. Examples of the hydrocarbon group include alkyl groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a cyclohexyl group, and a 1-methylcyclopentyl group, and alkenyl groups such as a vinyl group and a 1-propenyl group.

[0037] In the formula, "X" means a hydrolyzable substituent, and examples thereof include a halogen atom; an amino group, an alkoxy group (-OR'), an alkynide (R'C≡C), an azide (N3-), a dialkylamino group (-NR'2) (-NR'R"), an alkylcarbonylamino group (-N(R')C(O)R') (-N(R')C(O)R") (-N(R")C(O)R'), a carbonyloxy group (-OCOR'), and a carbonylamino group (-N(H)C(O)R'). R' and R" are each independently a hydrocarbon group having 1 to 10 carbon atoms. Among these, X is preferably a dialkylamino group, an alkoxy group, an alkylcarbonylamino group, a halogen, or a carbonyloxy group, and particularly preferably a dialkylamino group or an alkoxy group, and further preferably a dialkylamino group (-NR'2) or an alkoxy group (-OR').

[0038] In the above formula, "Xa" means a hydrolyzable substituent and is the same as "X". After undergoing hydrolysis, "X" and "Xa" become "XH" and are removed. It is preferable that they volatilize under reduced pressure and / or heating, and the boiling point of "XH" is preferably 200°C or less at normal pressure, and particularly preferably 100°C or less.

[0039] In the above formula, "p" is 0 or 1, and "m" is an integer from 1 to 4. Since tin atoms are usually divalent or tetravalent, p+m=2 or 4, and p+m=4, which is the more chemically stable tetravalent, is preferred. In addition, since having multiple hydrolyzable substituents enables more efficient resist film formation, it is preferred that p is 1 and m is 3.

[0040] In this embodiment, among the above tin compounds, it is particularly preferable to use a tin compound represented by the following chemical formula (3) in terms of effectiveness. (3) RSnX3…(3) [The above R represents a hydrocarbon group having 1 to 30 carbon atoms, and X represents a hydrolyzable substituent.]

[0041] In the chemical formula (3), preferred substituents as R and X are the same as "R" and "X" in the above chemical formula (1).

[0042] From the viewpoint of stably forming a resist layer, it is preferable that the purity of the tin compound is as high as possible. Specifically, the purity of the tin compound is preferably 97 mol % or more, and more preferably 99 mol % or more, calculated as tin atoms.

[0043] The purity of the tin compound (in terms of tin atoms) can be measured using NMR (JNM-ECZ400, manufactured by JEOL Ltd.). Furthermore, metals other than tin can be quantified using ICP-MS (high frequency emission mass spectrometer, Agilent Technologies, Agilent 7700). Furthermore, the quantity of halogens can be determined using combustion absorption ion chromatography (combustion system: Nitto Seiko Analytech Co., Ltd., AQF-2100H & ion chromatography system: Thermo Fisher Scientific Co., Ltd., ICS5000+).

[0044] When a resist is exposed to EUV, in order to produce patterning, the compound represented by the above formula (1), preferably the compound represented by the above formula (3), must be contained as a precursor. It is believed that by using the compound represented by the above formula (2) in combination with this, the network structure of the formed resist film will become stronger.

[0045] Therefore, in the tin compounds represented by the formulas (1) and (2), for example, tetrakis(dimethylamino)tin and / or isopropyltris(dimethylamino)tin can be used, and a mixture of tetrakis(dimethylamino)tin and isopropyltris(dimethylamino)tin can be preferably used. In this case, the purity of tetrakis(dimethylamino)tin and / or isopropyltris(dimethylamino)tin is preferably 97 mol% or more, and more preferably 99 mol% or more. When tetrakis(dimethylamino)tin and isopropyltris(dimethylamino)tin are used in combination, the content of tetrakis(dimethylamino)tin is preferably 0.5 to 20 mol % based on the total mass of tetrakis(dimethylamino)tin and isopropyltris(dimethylamino)tin.

[0046] Specific preferred examples of such tin compounds include t-butyltris(dimethylamino)tin, n-butyltris(dimethylamino)tin, t-butyltris(diethylamino)tin, sec-butyltris(dimethylamino)tin, n-pentyltris(dimethylamino)tin, isobutyltris(dimethylamino)tin, isopropyltris(dimethylamino)tin, isopropyltri-t-butoxytin, t-butyltri-t-butoxytin, n-butyltri-t-butoxytin, isopropyltri-t-butoxytin, tetrakis(dimethylamino)tin, tetra-t-butoxytin, etc. These can be used alone or in combination of two or more.

[0047] The tin compound may be diluted with a solvent. In this case, specific examples of the solvent include, but are not limited to, aromatic hydrocarbons such as toluene, xylene, and benzene; aliphatic hydrocarbons such as hexane, heptane, and octane; saturated cyclic hydrocarbons such as cyclohexane and methylcyclohexane; esters such as ethyl acetate, butyl acetate, butyl propionate, and propylene glycol monomethyl ether acetate; ethers such as diethyl ether, diisopropyl ether, methyl-t-butyl ether, cyclopentyl methyl ether, tetrahydrofuran, 1,4-dioxane, and anisole; alcohols such as methanol, ethanol, 1-propanol, isopropanol, 1-butanol, t-butanol, 4-methyl-2-propanol, ethylene glycol, and propylene glycol; ketones such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; amides such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and the like. These can be used alone or in combination of two or more. Among them, esters, ethers, ketones, and amides, which are aprotic highly polar solvents, are preferred because they dissolve components in the middle of hydrolysis to some extent, ethers and amides, which have high coordination properties, are more preferred, and amides are particularly preferred.Alcohols, which are protic highly polar solvents, are preferred because they can exchange with the hydrolyzable substituent represented by X while maintaining solubility and allowing hydrolysis to proceed, and t-butanol and 4-methyl-2-propanol are more preferred.

[0048] The degree of dilution is adjusted appropriately depending on the form of use. For example, when a tin compound is used in a spin coater process during resist film formation, the tin compound is usually diluted to a concentration of 0.005 to 1.4 M (mol / L), preferably 0.02 to 1.0 M (mol / L), and more preferably 0.05 to 0.5 M (mol / L).

[0049] [Pattern] The ferroelectric memory of this embodiment is composed of a transistor 1 and a capacitor 2, and the transistor 1 and / or the capacitor 2 are usually patterned using a resist containing the tin compound, and at least the transistor 1 is patterned using a resist containing the tin compound.

[0050] As a patterning method using a tin compound, for example, there is a method in which a resist layer having a tin compound is used as a mask and exposed to EUV radiation to pattern the capacitor 2 and / or the transistor 1.

[0051] (Formation of resist layer) For example, an organic hydroxyoxotin layer using a tin compound as a precursor is used as a resist, and is irradiated with radiation or electromagnetic waves with a wavelength of 10 to 780 nm to perform patterning. Here, the radiation specifically refers to X-rays, gamma rays, electron beams, etc., and the electromagnetic waves with a wavelength of 10 to 780 nm refer to ultraviolet rays and visible light. Among these, ultraviolet rays with a wavelength of 10 to 360 nm are preferred, and EUV (extreme ultraviolet) with a wavelength of 10 to 15 nm is more preferred. Hereinafter, the irradiation with EUV will be described as an example with reference to FIG. 1.

[0052] The organic hydroxyoxotin layer formed on the substrate 10 is used to assist in the patterning by etching of the gate insulating layer 11 formed after the organic hydroxyoxotin layer, as described below, and can be easily patterned by EUV irradiation and development. Note that the resist layer is not shown in FIG. 1 because it is eventually removed.

[0053] The organic hydroxyoxotin precursor may be used alone or in combination of two or more kinds. The method for forming a layer using the organic hydroxyoxotin precursor is not particularly limited and can be appropriately selected from various conventionally known film formation methods such as spin coating, CVD, physical vapor deposition, and atomic layer deposition.

[0054] (Formation of resist patterning layer) Next, only specific regions of the organic hydroxyoxotin layer are irradiated with EUV light to harden the layer, thereby forming a partially patterned hardened layer. The partially patterned hardened layer is then developed by removing the non-EUV irradiated portions (unhardened portions) of the layer, thereby forming a resist patterning layer.

[0055] The EUV refers to electromagnetic waves (Extreme Ultra-Violet) with a wavelength of about 10 to 15 nm. The EUV irradiation crosslinks many terminal hydroxy groups in the organic hydroxyoxotin layer to generate Sn-O-Sn bonds, and the EUV irradiated portion is cured. Since the non-irradiated portion is not cured, a patterned partially cured layer of the organic hydroxyoxotin layer can be formed by irradiating only the portion to be patterned with EUV.

[0056] The patterning layer is developed by removing the non-EUV irradiated portion (uncured portion) from the pattern portion cured layer before development. The development is performed by using a wet etching process or a dry etching process (gas phase treatment) using an acid, which is usually performed in an etching process.

[0057] (Formation of gate insulating layer) Next, a gate insulating layer 11 is formed on the substrate 10 having the developed patterned layer so as to cover the patterned layer.

[0058] The gate insulating layer 11 may be formed using silicon oxide (SiO2) or the like, which has been conventionally widely used for gate insulating layers, etc. Conventionally, insulating materials made of difficult-to-etch materials have been limited in use in semiconductor devices because they are difficult to etch despite their high relative dielectric constant, but the present embodiment has the advantage that it can be efficiently etched, so it is preferable to use an insulating material made of the difficult-to-etch material.

[0059] Such a hard-to-etch material having a high relative dielectric constant may, for example, be a high-κ material having a relative dielectric constant κ of 9 or more. Specific examples include hafnium oxide, hafnium oxynide silicate, hafnium aluminate, zirconium oxide, tantalum oxide, aluminum zirconium oxide, aluminum oxide, lanthanum oxide, and compounds of these with silica aluminum. These may be used alone or in combination of two or more.

[0060] In this embodiment, among the high-κ materials, hafnium oxide (κ is 13 to 18) and zirconium oxide (κ is greater than 13) are particularly suitable because they exhibit an excellent high relative dielectric constant.

[0061] The gate insulating layer 11 is obtained by forming an insulating material into a film by using any of various conventionally known film forming methods such as a CVD method, an ALD (Atomic Layer Deposition) method, or a sputtering method.

[0062] (Formation of gate electrode layer) Next, a gate electrode layer 12 is formed on the gate insulating layer 11. The gate electrode layer 12 can be obtained by depositing a semiconductive material, for example, polysilicon, by a conventionally known film deposition method such as a CVD method or a sputtering method.

[0063] (Patterning of gate electrode layer and gate insulating layer) The electrode layer and the insulating layer in the non-patterned portion are removed by, for example, plasma etching using the resist patterning layer as a mask, to pattern the gate electrode layer and the gate insulating layer. The remaining resist patterning layer can be removed by dry etching using an acid.

[0064] By combining patterning, etching, and the like in this manner, a patterned substrate having a predetermined pattern, in which a gate insulating layer 11 and a gate electrode layer 12 are laminated in this order on a substrate 10, as shown in FIG. 1, can be obtained.

[0065] According to the above-mentioned method for manufacturing a patterned substrate, the gate insulating layer 11 is patterned by utilizing an organic hydroxyoxotin layer, so that a highly precise pattern can be obtained. Even if the gate insulating layer 11 is made of a material that is difficult to etch, it can be patterned efficiently. Furthermore, if a resist pattern is formed so that only a small amount of the gate insulating layer 11 needs to be etched away, the material cost for forming the gate insulating layer 11 can be reduced.

[0066] The patterned substrate thus obtained has stable electrical characteristics because the gate insulating layer 11 is patterned efficiently in a short time, and no extra load is placed on the substrate 10 or the gate electrode layer 12. Furthermore, since a patterned substrate can be efficiently manufactured using a difficult-to-etch material with a high relative dielectric constant κ as the gate insulating layer 11, a patterned substrate with particularly excellent electrical properties can be provided.

[0067] As described above, the ferroelectric memory (FeRAM) of this embodiment is composed of a combination of a transistor (FeFET) 1 and a capacitor 2, and for example, as shown in FIG. 1, has one transistor 1 on a substrate 10 and one capacitor 2 on the transistor 1.

[0068] In the ferroelectric memory of this embodiment, a ferroelectric memory in which the generation of alpha radiation is suppressed can be obtained by using lead having a specific isotope ratio as a PZT or PLZT material for the ferroelectric layer 21 of the capacitor 2. Furthermore, since high definition can be achieved by manufacturing the transistor 1 and / or the capacitor 2 using a tin compound as a resist, a ferroelectric memory combining these has a long life and high precision. Furthermore, by using a resist using a tin compound with a low lead content as a precursor in the manufacture of the transistor 1, a ferroelectric memory in which the generation of alpha radiation is further suppressed can be obtained. EXAMPLES

[0069] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts" and "%" are based on mass.

[0070] First, the capacitors and transistors constituting the ferroelectric memory of this embodiment are formed as follows.

[0071] <Capacitor> A material containing PZT is prepared as a material for forming a high dielectric layer of a capacitor. Lead oxide 1: 208 Pb / 206 Lead oxide (PbO) with Pb of 2.5 Lead oxide 2: 208 Pb / 206 Lead oxide (PbO) with Pb=1.9 · Zirconium oxide 1: 99.99% pure zirconium oxide (ZrO2) Titanium dioxide 1: Titanium dioxide (TiO2) with a purity of 99.99%

[0072] When the lead oxides 1 and 2 were measured with an alpha ray measuring instrument (a 2π type gas flow proportional counter), the alpha dose of lead oxide 1 was 0.02 cph / cm 2 , lead oxide 2 alpha dose is 70cph / cm 2 It is.

[0073] [Formation of PZT layer for Example 1] The high dielectric layer (30 nm) of the capacitor is formed using the PZT MOCVD precursor with the lead oxide, zirconium oxide, and titanium oxide in a molar ratio of 1:1:1. The alpha dose of this layer is 0.1 cph / cm 2 It is.

[0074] [Formation of PZT layer for Comparative Example 1] A high dielectric layer (30 nm) of a capacitor is formed as a precursor for MOCVD of PZT in the same manner as in Example 1, except that lead oxide 2 is used instead of lead oxide 1 in Example 1. The alpha dose of this layer is 200 cph / cm 2 It is.

[0075] Capacitors each having an upper electrode layer and a lower electrode layer are fabricated using the PZT layer. The capacitor formed using the obtained PZT layer for Example 1 generates a much lower amount of alpha rays than the capacitor formed using the PZT layer for Comparative Example 1. Therefore, the capacitor using the PZT layer for Example 1 suppresses malfunction due to alpha rays.

[0076] <Transistor> In manufacturing a transistor, a resist having a tin compound is used as a mask, and exposed to EUV light to pattern the transistor. The following is prepared as the resist layer.

[0077] Tin compound 1: Isopropyltris(dimethylamino)tin as a resist layer precursor (purity 99 mol%, lead content 1 ppb or less, chromium, manganese, iron, nickel, and copper content 10 ppb or less each (metal atomic weight measured by ICP-MS))

[0078] An organic hydroxyoxotin layer is used as the resist layer. A silicon substrate with a thickness of 50 μm is prepared as the substrate, and an organic hydroxyoxotin layer with a thickness of 15 nm is formed on the silicon substrate by the CVD method using isopropyltris(dimethylamino)tin, which is a precursor of the organic hydroxyoxotin layer. The conditions of the CVD method are as follows: Pressure during deposition: 133 Pa (1 Torr) Temperature during film formation: 120℃ (wafer stage temperature)

[0079] Only a specific region of the resist layer is irradiated with EUV light to harden the specific region of the organic hydroxyoxotin layer, thereby obtaining a partially patterned hardened layer. The EUV irradiation conditions are as follows: ·Light source: Extreme ultraviolet EUV (wavelength 13.5nm) ·Irradiation amount: 50mJ / cm 2

[0080] The transistor obtained by the above method allows for finer patterns and thinner gate insulating layers.

[0081] A ferroelectric memory is fabricated by combining the obtained transistor and a capacitor, and therefore the ferroelectric memory formed by such a transistor and capacitor can ensure stable memory operation and a long rewrite cycle life.

[0082] When the following lead-containing tin compounds 2 and 3 are used as the tin compounds in the resist material instead of the tin compound 1, fine patterning becomes difficult, and fine patterning becomes more difficult with tin compound 3, which has a higher lead content, than with tin compound 2. Tin Compound 2: Isopropyltris(dimethylamino)tin with a lead content of 1 ppb (alpha radiation measurement value 0.02 cph / cm 2 ) Tin Compound 3: Isopropyltris(dimethylamino)tin with a lead content of 30 ppb (alpha radiation measurement value 0.1 cph / cm 2 )

[0083] On the other hand, when used as a ferroelectric memory, the resist layer is finally removed, so there is almost no difference between the tin compounds 1 to 3, and it is understood that the effect is not as great as that of PZT in the ferroelectric layer. [Explanation of symbols]

[0084] 1: Transistor 10: Substrate 11: Gate insulation layer 12: Gate electrode layer 13: Source diffusion region 14: Drain diffusion region 15: Interlayer insulation layer 2: Capacitor 20: Lower electrode layer 21: Ferroelectric layer 22: Upper electrode layer

Claims

1. A ferroelectric memory including a capacitor having a ferroelectric layer and a transistor, the material of the ferroelectric layer of the capacitor includes PZT or PLZT; Lead isotopes in the PZT or PLZT 208 Pb and 206 Ratio to Pb ( 208 Pb / 206 Pb) is 2.5 or more, A ferroelectric memory, wherein the transistor and / or the capacitor are patterned with a resist having a tin compound.

2. The alpha ray emission rate of the PZT or PLZT is 0.02 cph / cm 2 2. The ferroelectric memory of claim 1, wherein:

3. 2. The ferroelectric memory according to claim 1, wherein the resist has a lead content of 1 ppb or less.

4. 2. A ferroelectric memory according to claim 1, wherein the resist contains 10 ppb or less of each of chromium, manganese, iron, nickel and copper.

5. 2. The ferroelectric memory of claim 1, wherein the tin compound comprises tin(IV) oxide.

6. 2. The ferroelectric memory according to claim 1, wherein the precursor of the tin compound is represented by the following chemical formula (1) or (2): (Chem.1) R p SnX m …(1) [The above R is a hydrocarbon group which may be substituted with a halogen atom, and p is 0 or 1. X is a hydrolyzable substituent, and m is an integer of 1 to 4, with the proviso that m+p is 2 or 4.] (Case 2) SnXa 4 …(2) [The above Xa is a hydrolyzable substituent, and is preferably an alkoxy group or a dialkylamino group.]

7. 7. The ferroelectric memory according to claim 6, wherein the precursor of the tin compound is tetrakis(dimethylamino)tin and / or isopropyltris(dimethylamino)tin.

8. 2. The ferroelectric memory according to claim 1, wherein the purity of the precursor of the tin compound is 97 mol % or more in terms of tin atoms.

9. 2. The method for manufacturing a ferroelectric memory according to claim 1, further comprising a step of exposing and patterning the transistor and / or the capacitor by EUV using the resist as a mask.

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