JP5128738B2 - Eco-friendly Group II and Group IV or Group V spin-on precursors - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improved process for producing Group II and Group IV or Group V ceramic materials, such as barium strontium titanate, and an apparatus made by a metal-organic decomposition method.
[0002]
[Prior art]
Barium strontium titanate (BST), an oxide ceramic, has a high dielectric constant and excellent ferroelectric and paraelectric properties. As a result, BST is widely used in the electronics industry as dynamic random access memory (DRAM), ferroelectric devices, and paraelectric devices, and in other applications where high dielectric constant materials are used.
[0003]
US patent application Ser. No. 09 / 300,962 (invention name “Voltage Variable Capacitor (Varactor) for High Frequency Power”, April 28, 1999) describes a BST varactor and its application. BST varactors were made using 2-cabronate ethylate.
[0004]
Barium strontium titanate thin films have been extensively studied in applications of high-density dynamic random access memories, monolithic microwave integrated circuit capacitors, tunable microwave filters, and phased array antennas.
[0005]
A thin film of BST from 2-cabronate ethylate is also described in US Pat. No. 5,514,822.
[0006]
Synthesis of thin film ceramics from metal organic acid salts (usually fatty acids such as neodeacanoic or ethyl 2-cabronate) is described in previously referenced US patent application Ser. No. 09 / 300,962 and US patent application Ser. No. 08 / 863,117. Description (Invention name “Process for Making Stoichiometric Mixed Metal Oxide Films”, May 27, 1997), Mantese Micheli, Hamdi, West, MRS Bulletin, 1989, page 1173, PCT application WO 93/12538 ( Applicant: Symetrix Corporation), US Pat. Nos. 5,434,102 and 5,439,854 (H. Watanabe) and CM Vest, Materials Research Society Symposium 60, 35-42 (1986). .
[0007]
In order to better control the reaction from metal alkoxide to metal salt, the use of anhydride of ethyl 2-caburonate is described and claimed in US Pat. No. 5,721,009 and issued on Feb. 24, 1998. Has been.
[0008]
A number of the aforementioned references provide improved synthetic routes for treating barium strontium titanates, but use solvents such as xylene and n-butyl acetate which are harmful and environmentally friendly.
[0009]
Environmentally friendly ceramic precursors and alumina precursors made from 3,6-dioxaheptanoic acid and alumina minerals (group III precursors) are “Aqueous Synthesis of Water-Soluble Alumoxanes: Environmentally Benign Precursors to Aluminum and Aluminum Based Ceramics” , Chemical Materials, Vol. 9, No. 11, pages 2418-2433 (1997).
[0010]
The paper (AM Bahl, “Heavy Alkaline Earth Polyether Carboxylates”, Inorganic Chemistry, 36, 5413-5415 (1997)) describes the synthesis of barium and strontium oxyacid mixtures from metal hydroxides. The reaction is long and generates water as a by-product, which is undesirable for some applications. The present invention provides an anhydride method to produce these compounds.
[0011]
The related patent specification “Polyether Acid Anhydride Useful for Improved Non-Toxic Solvent Soluble Group IV and V Metal Acid Salt Complexes” describes titanium salts of 3,6-dioxaheptanoic acid, May 1999. Reference is made to US patent application Ser. No. 09 / 307,589, 7 dated.
[0012]
[Problems to be solved by the invention]
Therefore, there is a need to provide improved quality Group II and Group IV or Group V metal oxide films such as BST films with non-toxic solvents.
[0013]
The present invention synthesizes improved Group II and Group IV or Group V metal spin-on precursors such as barium strontium titanate (BST) that are effective in producing thin films of oxides of these metals. The purpose is to process and test. BST is an oxide ceramic widely used in DRAM, ferroelectric and paraelectric, and other applications where high dielectric constant materials are used. The present invention provides a harmless and environmentally friendly solvent compatible and soluble spin-on precursor. In addition, this spin-on precursor material has been shown to provide very improved electrical performance characteristics in the resulting BST thin films.
[0014]
It is an object of the present invention to form an improved electronic device from precursor materials and solutions that are low in toxicity and easy to handle.
[0015]
[Means for Solving the Problems]
In accordance with the present invention, a metalate complex is provided, which comprises (1) a first metal comprising at least one Group II ion and at least one second selected from the group consisting of Group IV and Group V ions. A metal and (2) a polyether acid. The metalate complex is formed by combining (1) at least one first metal and at least one second metal ion with (2) at least one polyether acid and polyether acid anhydride. . These metalate complexes in water and / or alcohol and / or other polar solvents are also provided and are effective in forming metal oxide films.
[0016]
In particular, according to the present invention, there is provided a method of manufacturing an electronic device as an active device using a Group II-IV (or Group V) oxide, the method comprising:
(A) providing a substrate;
(B) forming a lower electrode on the substrate;
(C) depositing a solution containing a polyether salt of a group II-group IV (or group V) metal ion on the lower electrode;
(D) forming an oxide film from the solution;
(E) forming a top electrode on the oxide film.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides improved electrical performance high dielectric constant materials, voltage variable dielectric materials, and the like. The described materials are soluble in a much more harmless solution than the prior art and are processable / compatible.
[0018]
The present invention uses metal salts of Group II and Group IV or Group V ions, particularly the use of barium, strontium, titanium with 3,6-dioxaheptanoic acid to produce improved quality BST films. About. The solutions used are 2-propanol and water, which are much more harmless than xylene and n-butyl acetate used in the prior art.
[0019]
Examples of group II ions are barium and strontium, examples of group IV ions are titanium and zirconium, and examples of group V ions are vanadium, tantalum and niobium. These ions combine to form an oxide film with ferroelectric properties. BST is an example of such an oxide film. Other examples include barium strontium niobate and strontium niobate.
[0020]
VHF power converters have been developed and patented to meet demand prices such as active arrays and high speed processors and the performance requirements of high power, high frequency electronic systems. The use of ferroelectric variable capacitors to adjust power converters significantly reduces circuit complexity, cost and weight and improves device system performance. The present invention is superior to the varactor and the prior art described in the aforementioned US patent application Ser. No. 09 / 300,962, and is a thin film barium strontium titanate that can be treated with a harmless solution and has excellent adaptability Provide salt material.
[0021]
The present invention provides improved materials that can be harmonized with less harmful solutions useful in the manufacture of these and other products.
[0022]
Due to its high dielectric constant and paraelectric and ferroelectric properties, BST is a popular material in the electronics industry. The present invention provides a new, less harmful method for the production of BST thin films.
[0023]
In summary, the improved thin film material is a barium of 3,6-dioxaheptanoic acid (and more widely other polyether acids) compared to all fatty acid analogs (eg ethyl 2-cabronate or neodecanoic acid). , Strontium, given using titanium metal salts. These precursor materials are soluble and can be processed using very low toxicity solutions.
[0024]
The use of titanium polyetherate (as described in previously referenced US patent application Ser. No. 09 / 307,589) in the manufacture of thin films of barium strontium titanate, along with the anhydride synthesis of barium and strontium precursors explain. The treatment of these mixtures in a non-hazardous solvent is finally described to give improved performance BST thin films.
[0025]
The present invention enables the production of improved metal oxide precursors for ceramic and metal oxide thin films. This extended the use of polyether acids (one example is 3,6-dioxaheptanoic acid) as a precursor salt to the formation of metal oxides, which were selected from the group consisting of Group II metals At least one metal and at least one second metal selected from the group consisting of Group IV and Group V metals. Other examples of polyether acids include 3,6,9-trioxaheptanoic acid, methoxyacetic acid, ethoxyacetic acid. A polyether acid useful in the practice of the present invention has the following formula:
CH ₃ O (CH ₂ CH ₂ O) _n CH ₂ COOH
Here, n is 0 to 2.
[0026]
In summary, the improved thin film material has 3,6-dioxaheptanoic acid (and more widely other polyether acids) compared to all fatty acid analogs (eg, 2-cabronate ethyl acid or neodecanoic acid). Made using a metal salt.
[0027]
A typical synthetic route to give polyether acid metalate complexes is described below.
1. Producing a polyether acid anhydride from the corresponding polyether acid by combining the polyether acid with a dehydrating agent;
2. By reacting a metal with a polyether acid, a metal salt complex of a Group II metal is produced,
3. Group IV and V metal metallate complexes are formed by simultaneously or sequentially combining a mixture of an anhydride of polyether acid and a metal alkoxide. In some instances, it may also be desirable to include the corresponding polyether acid in the mixture.
[0028]
The dehydrating agent used in the first reaction may include any known dehydrating agent used to convert organic acids to the corresponding anhydrides. Examples include dicyclohexylcarbodiimide and acetic anhydride.
[0029]
In the second reaction, the Group II metal is simply reacted with a polyether acid (free acid) to form a Group II metalate complex.
[0030]
The metal alkoxide used in the third reaction may include any known alkoxide of the metal. Group IV metal alkoxides have the following formula:
(RO) ₄ -Me (IV)
The group V alkoxide is given by the following formula:
(RO) ₅ -Me (V)
Wherein R is a substituted or unsubstituted linear or branched alkyl (C ₁ -C ₈ ) and aryl, Me (IV) is selected from the group consisting of titanium and zirconium, and Me (V) is vanadium. , Tantalum, and niobium.
[0031]
[Anhydrous synthesis of strontium (II) -3,6-dioxaheptane salt]
A mixture of 3,6-dioxaheptanoic acid (34.1 grams, 0.254 moles) heated in 2 propanol (45 grams) (gently reflowed) and well agitated is some amount of strontium metal (dendritic Strem Cat No. 38-0074, 10.08 grams, 0.115 moles). Hydrogen release can be controlled by the rate of metal addition. The reaction mixture was allowed to reflow for an additional time after the entire amount of metal was added and dissolved. The aqueous white clear solvent weighs 88.6 grams, giving 11.34% 1.29 mmol / g strontium solvent.
[0032]
[Anhydrous synthesis of barium (II) -3,6-dioxaheptane salt]
This dissolution was made in the same way as the strontium solution. Barium dissolved much faster than strontium.
[0033]
[Formation of barium and strontium-3,6-dioxaheptane salt and titanium (IV) -3,6-dioxaheptane salt from a precursor material containing a harmless solvent capable of processing to a thin film of barium strontium titanate]
The BST precursor solvent was 8.44 grams of 1.29 mmol / g strontium (II) -3,6-dioxaheptane salt solvent as described in related US patent application Ser. No. 09 / 307,589, 1.07 Combining 10.22 grams of barium (II) -3,6-dioxaheptane salt solvent in mmol / g and 12.82 grams of 1.726 mmol / g titanium (IV) -3,6-dioxaheptane salt solvent. Made by. This was further diluted by adding 23.6 grams of 2-propanol to give the BST precursor solution used to make the thin film BST capacitor / varactor described below.
[0034]
[Processing of the described BST precursor material into a BST thin film]
1. Substrate processing including bottom electrode deposition A conventional 20 mil thick silicon wafer was processed to have 5000 angstroms of wet thermal oxide (silicon). A 25 Å thick Ta adhesion layer was electron beam deposited onto the substrate followed by a 1800 Å thick Pt layer. The resistance of the electrode sheet was 0.73 ohm / square. The electrode was pre-annealed with oxygen at 650 ° C. for 30 minutes to oxidize the Ta layer and stabilize the Pt layer.
[0035]
2. Deposition of the barium strontium titanate thin film on the electrode-formed substrate and the fired wafer were coated with the aforementioned BST solvent using spin coating at 3-5 Krpm for 30 seconds. After coating, the wafer is slowly lowered on a 320 ° C. hot plate and baked for 4 minutes.
[0036]
After spin coating and hot plate firing, the wafer is burned in a smaller tube furnace to 700 ° C. fluidized O ₂ .
[0037]
After burning, the wafer showed no signs of cracking and contact failure. SEM analysis of the dielectric film showed that the surface was smooth. Thickness measurement showed about 1100-1700 angstroms.
[0038]
3. Top Electrode Formation A 1000 Angstrom Pt top electrode was deposited using a shadow mask with varying top electrode sizes of about 10, 15, 20, 40, 80, 160 mils in diameter. The stack was annealed at 700 ° C. for 2 hours before electrical testing.
[0039]
4). Initial Electrical Testing Devices previously made in accordance with the present invention were compared to devices made in accordance with the prior art described in previously referenced US patent application Ser. No. 09 / 300,962. Both devices were manufactured to the same dimensions, ie about 5 × 10 ⁻⁴ cm ² . The thickness of the BST layer was 1,200 Å for the device of the present invention and about 6,400 Å for the prior art device.
[0040]
The instrument was tested on an analysis prober. The probe tip was directly contacted with the upper electrode, and the lower electrode was contacted with the second probe tip via the BST layer by scratch. The IV characteristics were measured using an HP 4145B semiconductor parameter analyzer from -3.5v to + 3.5v. CV characteristics were measured using an HP 4275A LCR meter at 100 KHz using a 35 mV modulation voltage over a wide range of bias voltages. For a typical 10 mil diameter shadow mask capacitor, the capacitance ranged from 1.69 pF at 0 v to 0.75 pF at 6.5 v.
[0041]
FIGS. 1a and 1b show a comparison of the IV characteristics of a device formed according to the present invention and a device formed according to the prior art as described in US patent application Ser. No. 09 / 300,962. Show. The comparison shows that the leakage characteristics of a 1200 Å thick capacitor made in accordance with the present invention is greatly improved compared to a prior art capacitor that is about five times thicker. Furthermore, those skilled in the art will recognize that thin films typically leak more than thick films if all other parameters are the same.
[0042]
FIGS. 2a and 2b compare the CV characteristics of a device formed in accordance with the present invention and a device formed by the prior art as described in US patent application Ser. No. 09 / 300,962. Show. Both characteristic diagrams show the expected change in capacitance as a function of a given voltage.
[0043]
The BST varactor that can be switched at a low voltage of the thin film used in the VHF power converter of the present invention has been described above. The present invention provides an improved apparatus compared to the apparatus of US patent application Ser. No. 09 / 300,962, where the processing of the solution precursor material is performed in a harmless and environmentally friendly solution.
[0044]
[Industrial application]
The method of forming barium strontium titanate thin films is expected to be used in the manufacture of electronic devices using this material as the active part of the device.
[0045]
Thus, a process for forming an improved barium strontium titanate film has been described. It will be apparent to those skilled in the art that various changes and modifications in the obvious characteristics may be made and all such changes and modifications are considered to fall within the scope of the claimed invention. It will be readily apparent.
[Brief description of the drawings]
FIG. 1 is similar to the IV characteristic diagram of an improved 1200 angstrom thin film capacitor processed according to the present invention in current density (Amps / cm ² ) and voltage (V) coordinates. IV characteristic diagram of a 6400 angstrom thin film capacitor processed by a prior art process.
FIG. 2 is a CV characterization of an improved 1200 angstrom thin film capacitor processed in accordance with the present invention in capacitance (farad) and voltage (V) coordinates, and a similar but prior art process. IV characteristics of a 6400 angstrom thin film capacitor processed by

Claims (13)

Selected from the group consisting of a first metal comprising at least one group II ion generated from a polyether acid and a group IV and group V ion generated from the reaction of a metal alkoxide and a polyether anhydride. In a method of preparing an oxide film forming metalate complex having ferroelectric properties comprising at least one second metal ,
(1) at least one first metal selected from Group II metals that react with the polyether acid;
(2) Binding (a) at least one second metal selected from the group consisting of Group IV and Group V metals and (b) at least one metal alkoxide containing a polyether anhydride. characterized in that a process for preparing gold Shokusanshio complex. The group II ion is selected from the group consisting of barium and strontium, the group IV ion is selected from the group consisting of titanium and zirconium, and the group V ion is selected from the group consisting of vanadium, tantalum and niobium. A method for preparing the metalate complex described. The method for preparing a metalate complex according to claim 1, wherein the polyether acid is given by the following formula: CH ₃ O (CH ₂ CH ₂ O) _n CH ₂ COOH, wherein n is 0-2. . Selected from the group consisting of a first metal comprising at least one group II ion generated from a polyether acid and a group IV and group V ion generated from the reaction of a metal alkoxide and a polyether anhydride. In a method of preparing an oxide film forming metalate complex having ferroelectric properties comprising at least one second metal ,
(A) reacting the first metal with the polyether acid to form a first metal acid salt of the at least one Group II metal;
(B) combining a polyether anhydride of the polyether acid with a metal alkoxide containing at least one second metal to form a second metal acid salt of the at least one group IV or group V metal. ,
(C) A method for preparing a metal acid salt complex, comprising combining the first metal acid salt and the second metal acid salt to form the metal acid salt complex. The Group II metal is selected from the group consisting of barium and strontium, and the Group IV alkoxide is represented by the following formula:
(RO) _4- Me (IV)
The group V alkoxide has the following formula:
(RO) ₅ -Me (V)
Wherein R is a substituted or unsubstituted linear or branched alkyl (C ₁ -C ₈ ) and aryl, Me (IV) is selected from the group consisting of titanium and zirconium, Me (V) is vanadium, The preparation method according to claim 4, which is selected from the group consisting of tantalum and niobium. Preparation method of claim 4 further comprising a be simultaneously or sequentially reacted with a mixture of an anhydride of the metal alkoxide of the polyether acid and the polyether acid. (1) the first metal containing at least one group II ion, at least one second metal selected from the group consisting of group IV and group V ions, and (2) water, up to five A first ion comprising at least one Group II ion generated from a polyether acid comprising: an alcohol having a carbon atom; and a polyether acid in a solvent having at least one compound selected from the group consisting of polar solvents . An oxidation having ferroelectric properties comprising one metal and at least one second metal selected from the group consisting of Group IV and Group V ions generated from the reaction of a metal alkoxide and a polyether anhydride. Solvent of metal acid salt complex for physical film formation . Basically, an electron comprising an active portion comprising a first metal comprising at least one group II ion and at least one second metal selected from the group consisting of group IV and group V ions. In a method of manufacturing a device,
Selected from the group consisting of a first metal comprising at least one group II ion generated from a polyether acid and a group IV and group V ion generated from the reaction of a metal alkoxide and a polyether anhydride. Using an oxide film-forming metalate complex having ferroelectric properties comprising at least one second metal ;
(A) providing a substrate;
(B) forming a lower electrode on the substrate;
(C) depositing a solution comprising at least one of the first metal and the polyether salt of the at least second metal on the lower electrode;
(D) forming an oxide film of the first metal and the second metal from the solution;
(E) A method for manufacturing an electronic device, comprising the step of forming an upper electrode on the oxide film. The method of claim 8 , wherein the substrate is electrically insulating. The method of claim 8, wherein the lower electrode is formed on the substrate by first depositing an adhesive layer followed by depositing the lower electrode thereon. The solution is prepared by adding strontium (II) -3,6-dioxaheptane salt, barium (II) -3,6-dioxaheptane salt, titanium (IV) -3,6-dioxy in 2-propanol. 9. A process according to claim 8 comprising a mixture with oxaheptane salt. The solution is (a) spin coated on the substrate;
(B) calcined at a first elevated temperature for a predetermined length of time;
9. The method of claim 8 , wherein (c) heating is performed at a second elevated temperature in flowing oxygen for a predetermined length of time. The method of claim 8, wherein the top electrode is formed by depositing a platinum layer through a shadow mask.

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