Patent Application
20080072792
The composite oxide-based dielectric thin film that can be formed from the raw material solution for the MOCVD method according to the invention, may be exemplified by the thin films made of lead titanate (PT), lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), strontium titanate (ST), barium titanate (BT), barium strontium titanate (BST) and the like, but other oxides are also applicable.
The raw material solution for the MOCVD method of the invention is an improvement of the raw material solution formed by dissolving one or two or more organometallic compounds in an organic solvent. The organometallic compound to be used as the raw material of film, may be exemplified by organic compounds containing metals selected from Pb, Ti, Zr and alkaline earth metals (Ca, Ba, Sr, etc.), which are the constituent metals of the thin film. In addition to these, alkali metals (Cs), various transition metals such as Mn, Nb, V, Hf, Ta and the like, rare earth metals such as La, as well as Bi and Si are also used. In the case of BST thin film, respective organometallic compounds of Ti, Ba and Sr are used as the raw materials.
For the organometallic compound, those which are vaporizable, and which are thermally decomposed by heating and are easily convertible to oxides when an oxidizing agent (oxygen) is introduced, are used. Such an organometallic compound is generally a compound having a structure in which a metal atom is bound to an organic group through an oxygen atom. Preferred examples of this kind of compound include metal alkoxides, metal-β-diketonate complexes, complexes containing both of alkoxide and β-diketonate, mixtures of metal alkoxide and metal-β-diketonate complexes and the like. Examples of the β-diketonate complex include metal complexes having β-diketones such as acetylacetone, hexafluoroacetylacetone, dpm, pentafluoropropanoylpivaloylmethane and the like, as the ligand. Among these, preferred are the complexes having dpm. The metal alkoxide is preferably a metal alkoxide with the alkoxy group having 1 to 6 carbon atoms, and particularly preferably a metal alkoxide having a branched alkoxy group (isopropoxide, tert-butoxide, etc.). A particularly preferred organometallic compound is a metal dipivaloylmethanate complex, a metal isopropoxide, a metal tert-butoxide, a complex containing both of isopropoxide and dipivaloylmethanate, or a complex containing both of tert-butoxide and dipivaloylmethanate. In regard to the alkaline earth metals, alkali metals and Pb, it is preferable to use β-diketonate complexes (for example, dipivaloylmethanate complex), while in regard to the transition metals such as Ti, Zr, V, Nb and the like, it is generally possible to use either β-diketonate complexes or metal alkoxides, or also possibly complexes containing both of alkoxide and β-diketonate.
As the raw material for the formation of BST thin film, it is preferable to use dipivaloylmethanate complexes of Ba and Sr, and Ti compounds selected from isopropoxide, tert-butoxide, dipivaloylmethanate complex, complex containing both of isopropoxide and dipivaloylmethanate, and complex containing both of tert-butoxide and dipivaloylmethanate. Also, as the raw material for the formation of PZT thin film, it is preferable to use Pb-dipivaloylmethanate complex, Zr compounds including β-diketone and alkoxide, and Ti compounds selected from the group consisting of isopropoxide, tert-butoxide, dipivaloylmethanate complex, complex containing both of isopropoxide and dipivaloylmethanate, and complex containing both of tert-butoxide and dipivaloylmethanate.
The feature of the first constitution of the invention lies in that the organic solvent is 1,3-dioxolane. A raw material solution having good film forming properties and excellent step coverage is obtained by using 1,3-dioxolane, which has good film forming properties and excellent step coverage, as the organic solvent.
The feature of the second constitution of the invention lies in that the organic solvent is a solvent mixture formed by mixing a first solvent consisting of 1,3-dioxolane, and a second solvent comprising one or two or more species selected from the group consisting of alcohols, alkanes, esters, aromatics, alkyl ethers and ketones, which is to be mixed with 1,3-dioxolane. A raw material solution having better film forming properties and excellent step coverage is obtained, by using an organic solvent which comprises 1,3-dioxolane having good film forming properties and excellent step coverage as an essential component, and which is a solvent mixture formed by mixing this 1,3-dioxolane with one or two or more of the above-listed various solvents having high solubility for organometallic compounds.
The mixing ratio of the first solvent and the second solvent can be adjusted such that the weight ratio of the first solvent/the second solvent ranges from 99 to 1, but the mixing ratio is preferably such that the ratio of the first solvent/the second solvent ranges from 80 to 20. The raw material solution for MOCVD may be at any concentration, provided that a stable raw material solution can be provided without any limitation imparted by the particular concentration, and the concentration may be appropriately selected in accordance with the amount of the raw material transported, the film forming rate in the film production process, and the like.
The feature of the third constitution of the invention lies in that the organic solvent is a solvent mixture formed by mixing a first solvent consisting of 1,3-dioxolane, and a second solvent consisting of cyclohexane.
The feature of the fourth constitution of the invention lies in that the second solvent comprises cyclohexane as an essential solvent, and is a solvent mixture formed by mixing the cyclohexane with one or two or more solvents selected from the group consisting of alcohols, alkanes, esters, aromatics, alkyl ethers and ketones. A raw material solution which hardly freezes even in cold regions, and has excellent controllability for film composition and step coverage, is obtained by using a second solvent which comprises cyclohexane having excellent controllability for film composition and step coverage as an essential component, and which is a solvent mixture formed by mixing this cyclohexane with one or two or more of the above-listed various solvents having low melting points and high solubility for organometallic compounds. The raw material solution for MOCVD may be at any concentration, provided that a stable raw material solution can be provided without any limitation imparted by the particular concentration, and the concentration may be appropriately selected in accordance with the amount of the raw material transported, the film forming rate in the film production process, and the like.
The alcohol may be exemplified by ethanol, n-propanol, i-propanol, n-butanol, or the like. The alkane may be exemplified by n-hexane, 2,2,4-trimethylpentane, n-octane, i-octane, or methylcyclopentane. The ester may be exemplified by butyl acetate. The aromatic may be exemplified by toluene, xylene or benzene. The alkyl ether may be exemplified by di-n-butyl ether, diisopentyl ether, or poly-THF. The ketone may be exemplified by acetone.
Next, an example of forming a PZT thin film by the solution vaporization CVD method, by using raw material solutions having an organic Pb compound, an organic Zr compound and an organic Ti compound respectively dissolved in an organic solvent at predetermined proportions, will be described. The solution vaporization CVD method refers to a method of supplying each of the solutions to a heated vaporization vessel, where each raw material solution is instantly vaporized and sent to a film forming chamber to be formed into a film on a substrate.
As shown in
In this apparatus, a first carrier gas consisting of an inert gas such as N2, He, Ar or the like is supplied to the raw material container 18 through the first carrier gas feed pipe 21, and conveys the raw material solution stored in the raw material container 18 by means of the pressure of the carrier gas supplied to the raw material container 18, through the feed pipe 22 to the vaporization vessel 26. Each of the organometallic compounds, which has been vaporized in the vaporization vessel 26 to become a vapor, is further supplied through the pipe 27 to the film forming chamber 10, by means of a second carrier gas consisting of an inert gas such as N2, He, Ar or the like, which is supplied from the second carrier gas feed pipe 28 to the vaporization vessel 26.
In the film forming chamber 10, the vapor of each organometallic compound is thermally decomposed and reacted with the oxygen source supplied to the film forming chamber through the oxygen source feed pipe 37, and the metal oxides thus produced are deposited on the substrate 13, which has been heated, to form a PZT dielectric thin film having predetermined composition ratios.
The raw material solution of the invention is such that each raw material compound being in the solution state has stable vaporizability, and thus, the proportions of metal atoms in the formed thin film are almost consistent with the proportions of metal atoms in the solution. Therefore, a composite oxide-based dielectric thin film having a stable predetermined composition can be formed, and the film quality is stable.
The dielectric thin film formed by MOCVD using the raw material solution of the invention is useful in the applications such as DRAM, FRAM and the like. The MOCVD method generally provides excellent in step coverage, but when the raw material solution of the invention is used, the reproducibility of film formation is enhanced, as compared with the thin films formed by using conventional raw material solutions, and the surface morphology is stabilized.
In addition, the raw material solution of the invention provides excellent controllability for the film composition since the respective vapors of the raw material compounds can be supplied stably to the film forming chamber as described above, and thus, a dielectric thin film having excellent dielectric properties due to the desired composition can be stably formed on the substrate. The dielectric thin film formed by using the raw material solution of the invention can be used as a dielectric filter in piezoelectric resonators, infrared sensors and the like.
Next, Examples of the present invention will be described in detail, in association with Comparative Examples.
First, there were provided Pb(dpm)2 as an organic Pb compound, Zr(dmhd)4 as an organic Zr compound, and Ti(O-i-Pr)2(dpm)2 as an organic Ti compound. Here, dmhd refers to 2,6-dimethyl-3,5-heptanedione residue, while O-i-Pr refers to isopropoxide. The compounds Pb(dpm)2, Zr(dmhd)4 and Ti(O-i-Pr)2(dpm)2 were mixed to a composition ratio of Pb1.15(Zr0.45Ti0.55)O3, which ratio was expected in the formation, and were dissolved in the organic solvents presented in the following Table 1 to Table 3, to prepare 0.3 mol/L raw material solutions No. 1 through No. 15-4, respectively. O2 was provided as the oxygen source.
Subsequently, a Pt (200 nm)/Ti (20 nm)/SiO2 (500 nm)/Si substrate was provided as the substrate, and this substrate was placed in the film forming chamber of the MOCVD apparatus shown in
A PZT dielectric thin film was formed in the same manner as in Example 1, except that a single solvent consisting of 100% by weight of THF was used as the organic solvent.
In order to confirm as to whether the PZT dielectric thin films respectively obtained in Example 1 and Comparative Example 1 have high remanent polarization values, the measurement of remanent polarization value and the step coverage test described below were carried out with respect to the thin films. The results are presented in Table 1 to Table 3.
(1) Measurement of remanent polarization value
On the substrate obtained after the completion of film formation, an upper electrode was formed with Pt to a thickness of 200 nm, and the remanent polarization value of the PZT dielectric thin film was measured by using a ferroelectric tester (Radiant Technology Corp.; RT6000S).
(2) Step coverage test
The step coverage of the PZT dielectric thin film on the substrate obtained after the completion of film formation, was measured from the cross-sectional SEM (scanning electron microscope) images. The step coverage is expressed as the value of a/b of when a thin film 20 is formed on the substrate 13 having unevenness such as grooves or the like, as shown in
As it is clear from Table 1 through Table 3, in Comparative Example 1 where THF is used as a single solvent, the remanent polarization value and the step coverage both had low values. Correspondingly, when the raw material solutions No. 1, and No. 2-1 to No. 15-4 of Example 1 were used, extremely excellent results were obtained, compared with the results of Comparative Example 1.
First, there were provided Ba(dpm)2 as an organic Ba compound, Sr(dpm)2 as an organic Sr compound, and Ti(O-i-Pr)2(dpm)2 as an organic Ti compound. The compounds Ba(dpm)2, Sr(dpm)2 and Ti(O-i-Pr)2(dpm)2 were mixed to a composition ratio of (Ba0.7Sr0.3)TiO3, which ratio was expected in the formation, and were dissolved in the organic solvents presented in the following Table 4 to Table 6, to prepare 0.3 mol/L raw material solutions No. 16 through No. 30-4, respectively. O2 was provided as the oxygen source.
Subsequently, a Pt (200 nm)/Ti (20 nm) /SiO2 (500 nm)/Si substrate was provided as the substrate, and this substrate was placed in the film forming chamber of the MOCVD apparatus shown in
A BST dielectric thin film was formed in the same manner as in Example 2, except that a single solvent consisting of 100% by weight of THF was used as the organic solvent.
In order to confirm as to whether the BST dielectric thin films respectively obtained in Example 2 and Comparative Example 2 have high specific dielectric constants, the measurement of the specific dielectric constant was carried out with respect to the thin films. The results are presented in Table 4 to Table 6.
(1) Measurement of specific dielectric constant
On the substrate obtained after the completion of film formation, an upper electrode was formed with Pt to a thickness of 200 nm, and the specific dielectric constant of the BST dielectric thin film was measured by using an LCR meter (Hewlett-Packard Inc.; 4284A).
As it is clear from Table 4 through Table 6, in Comparative Example 2 where THF was used as a single solvent, the specific dielectric constant and the step coverage both had low values. Correspondingly, when the raw material solutions No. 16, and No. 17-1 through No. 30-4 of Example 2 were used, higher specific dielectric constants compared with the results of Comparative Example 2, and good step coverage were obtained, thus presenting extremely excellent results.
First, there were provided Pb(dpm)2 as an organic Pb compound, Zr(dmhd)4 as an organic Zr compound, and Ti(O-i-Pr)2(dpm)2 as an organic Ti compound. The compounds Pb(dpm)2, Zr(dmhd)4 and Ti(O-i-Pr)2(dpm)2 were mixed to a composition ratio of Pb1.15(Zr0.45Ti0.55)O3, which ratio was expected in the formation, and were dissolved in the organic solvents presented in the following Table 7 to Table 9, to prepare 0.3 mol/L raw material solutions No. 31-1 through No. 45-4, respectively. The same process as in Example 1 was carried out using the above raw material solutions, and substrates with PZT dielectric thin films having a predetermined thickness formed thereon, were obtained.
For the PZT dielectric thin films obtained in Example 3, the measurement of the remanent polarization value and the step coverage test were carried out in the same manner as in Comparison Test 1. The results are presented in Table 7 to Table 9.
As it is clear from Table 7 through Table 9, when the raw material solutions No. 31-1 through No. 45-4 of Example 3 were used, high remanent polarization values and good step coverage were obtained, thus presenting extremely excellent results.
First, there were provided Ba(dpm)2 as an organic Ba compound, Sr(dpm)2 as an organic Sr compound, and Ti(O-i-Pr)2(dpm)2 as an organic Ti compound. The compounds Ba(dpm)2, Sr(dpm)2 and Ti(O-i-Pr)2(dpm)2 were mixed to a composition ratio of (Ba0.7Sr0.3)TiO3, which ratio was expected in the formation, and were dissolved in the organic solvents presented in the following Table 10 to Table 12, to prepare 0.3 mol/L raw material solutions No. 46-1 through No. 60-4, respectively. The same process as in Example 2 was carried out using the above raw material solutions, and substrates with BST dielectric thin films having a predetermined thickness formed thereon, were obtained.
For the BST dielectric thin films obtained in Example 4, the measurement of the specific dielectric constant and the step coverage test were carried out in the same manner as in the Comparison Test 2. The results are presented in Table 10 to Table 12.
As it is clear from Table 10 through Table 12, when the raw material solutions No. 46-1 through No. 60-4 of Example 4 were used, high specific dielectric constants and good step coverage were obtained, thus presenting extremely excellent results.
First, there were provided Pb(dpm)2 as an organic Pb compound, Zr(dmhd)4 as an organic Zr compound, and Ti(O-i-Pr)2(dpm)2 as an organic Ti compound. Here, dmhd refers to 2,6-dimethyl-3,5-heptanedione residue, while O-i-Pr refers to isopropoxide. The compounds Pb(dpm)2, Zr(dmhd)4 and Ti(O-i-Pr)2(dpm)2 were mixed to a composition ratio of Pb1.15(Zr0.45Ti0.55)O3, which ratio was expected in the formation, and were dissolved in the organic solvents presented in the following Table 13, to prepare 0.3 mol/L raw material solutions No. 61-1 through No. 62-4, respectively. O2 was provided as the oxygen source.
Subsequently, a Pt (200 nm)/Ti (20 nm)/SiO2 (500 nm)/Si substrate was provided as the substrate, and this substrate was placed in the film forming chamber of the MOCVD apparatus shown in
A PZT dielectric thin film was formed in the same manner as in Example 5, except that a single solvent consisting of 100% by weight of cyclohexane as the organic solvent.
A PZT dielectric thin film was formed in the same manner as in Example 5, except that a single solvent consisting of 100% by weight of THF was used as the organic solvent.
In order to confirm as to whether the PZT dielectric thin films respectively obtained in Example 5 and Comparative Examples 5 and 6 had high remanent polarization values, the measurement of the remanent polarization values and the step coverage test were carried out as follows with respect to the thin films. The results are presented in Table 13.
(1) Measurement of remanent polarization value
On the substrate obtained after the completion of film formation, an upper electrode was formed with Pt to a thickness of 200 nm, and the remanent polarization value of the PZT dielectric thin film was measured by using a ferroelectric tester (Radiant Technology Corp.; RT6000S).
(2) Step coverage test
The step coverage of the PZT dielectric thin film on the substrate obtained after the completion of film formation, was measured from the cross-sectional SEM (scanning electron microscope) images. The step coverage is expressed as the value of a/b of when a thin film 20 is formed on the substrate 13 having unevenness such as grooves or the like, as shown in
As it is clear from Table 13, in Comparative Example 6 where THF was used as a single solvent, the remanent polarization value and the step coverage both had low values. Further, in Comparative Example 5 where cyclohexane was used as a single solvent, high remanent polarization value and good step coverage were obtained. However, when the raw material solutions are to be maintained in cold regions, there may be inconveniences such as freezing, and it is difficult to handle. Correspondingly, when the raw material solutions No. 61-1 through No. 62-4 of Example 5 were used, higher remanent polarization values compared with the results of Comparative Example 6 and good step coverage were obtained, thus presenting extremely excellent results. Also, even when compared with Comparative Example 5, results excellent in overall were obtained.
First, there were provided Ba(dpm)2 as an organic Ba compound, Sr(dpm)2 as an organic Sr compound, and Ti(O-i-Pr)2(dpm)2 as an organic Ti compound. The compounds Ba(dpm)2, Sr(dpm)2 and Ti(O-i-Pr)2(dpm)2 were mixed to a composition ratio of (Ba0.7Sr0.3)TiO3, which ratio was expected in the formation, and were dissolved in the organic solvents presented in the following Table 14 to Table 16, to prepare 0.3 mol/L raw material solutions No. 63-1 through No. 64-4, respectively. O2 was provided as the oxygen source.
Subsequently, a Pt (200 nm)/Ti (20 nm) /SiO2 (500 nm)/Si substrate was provided as the substrate, and this substrate was placed in the film forming chamber of the MOCVD apparatus shown in
A BST dielectric thin film was formed in the same manner as in Example 6, except that a single solvent consisting of 100% by weight of cyclohexane was used as the organic solvent.
A BST dielectric thin film was formed in the same manner as in Example 6, except that a single solvent consisting of 100% by weight of THF was used as the organic solvent.
In order to confirm as to whether the BST dielectric thin films respectively obtained in Example 6 and Comparative Examples 7 and 8 had high specific dielectric constants, the specific dielectric constants of these thin films were measured. Further, the step coverage test was carried out in the same manner as in the Comparison test 5. The results are presented in Table 14.
(1) Measurement of specific dielectric constant
On the substrate obtained after the completion of film formation, an upper electrode was formed with Pt to a thickness of 200 nm, and the specific dielectric constant of the BST dielectric thin film was measured by using an LCR meter (Hewlett-Packard Inc.; 4284A).
As it is clear from Table 14, in Comparative Example 8 where THF was used as a single solvent, the specific dielectric constant and the step coverage both had low values. Further, in Comparative Example 7 where cyclohexane was used as a single solvent, high specific specificity and good step coverage were obtained. However, when the raw material solutions are to be maintained in cold regions, there may be inconveniences such as freezing, and it is difficult to handle. Correspondingly, when the raw material solutions No. 63-1 through No. 64-4 of Example 6 were used, higher specific dielectric constants compared with the results of Comparative Example 6 and good step coverage were obtained, thus presenting extremely excellent results. Also, even when compared with Comparative Example 5, results excellent in overall were obtained.
First, there were provided Pb(dpm)2 as an organic Pb compound, Zr(dmhd)4 as an organic Zr compound, and Ti(O-i-Pr)2(dpm)2 as an organic Ti compound. The compounds Pb(dpm)2, Zr(dmhd)4 and Ti(O-i-Pr)2(dpm)2 were mixed to a composition ratio of Pb1.15(Zr0.45Ti0.55)O3, which ratio was expected in the formation, and were dissolved in the organic solvents presented in the following Table 15, to prepare 0.3 mol/L raw material solutions No. 65-1 through No. 65-4, respectively. The same process as in Example 5 was carried out using the above raw material solutions, and substrates with PZT dielectric thin films having a predetermined thickness formed thereon, were obtained.
For the PZT dielectric thin films obtained in Example 7, the measurement of the remanent polarization value and the step coverage test were carried out in the same manner as in the Comparison Test 5. The results are presented in Table 15.
As it is clear from Table 15, when the raw material solutions No. 65-1 through No. 65-4 of Example 7 were used, high remanent polarization values and good step coverage were obtained, thus presenting extremely excellent results.
First, there were provided Ba(dpm)2 as an organic Ba compound, Sr(dpm)2 as an organic Sr compound, and Ti(O-i-Pr)2(dpm)2 as an organic Ti compound. The compounds Ba(dpm)2, Sr(dpm)2 and Ti(O-i-Pr)2(dpm)2 were mixed to a composition ratio of (Ba0.7Sr0.3)TiO3, which ratio was expected in the formation, and were dissolved in the organic solvents presented in the following Table 16, to prepare 0.3 mol/L raw material solutions No. 66-1 through No. 66-4, respectively. The same process as in Example 6 was carried out using the above raw material solutions, and substrates with BST dielectric thin films having a predetermined thickness formed thereon, were obtained.
For the BST dielectric thin films obtained in Example 8, the measurement of the specific dielectric constants and the step coverage test were carried out in the same manner as in the Comparison Test 6. The results are presented in Table 16.
As it is clear from Table 16, when the raw material solutions No. 66-1 through No. 66-4 of Example 8 were used, high specific dielectric constants and good step coverage were obtained, thus presenting extremely excellent results.
In regard to the raw material solution for MOCVD according to the present invention, a raw material solution having good film forming properties and excellent step coverage is obtained by using 1,3-dioxolane which has good film forming properties and excellent step coverage, as an organic solvent.
Further, In regard to the raw material solution for MOCVD of the invention, a raw material solution having better film forming properties and excellent step coverage is obtained, when the organic solvent is a solvent mixture formed by mixing a first solvent consisting of 1,3-dioxolane, and a second solvent comprising one or two or more species selected from the group consisting of alcohols, alkanes, esters, aromatics, alkyl ethers and ketones, which is to be mixed with the 1,3-dioxolane, and when the organic solvent comprises 1,3-dioxolane having good film forming properties and excellent step coverage as an essential component, and is a solvent mixture formed by mixing this 1,3-dioxolane with one or two or more of the above-listed various solvents having high solubility for organometallic compounds.
In addition, in regard to the raw material solution for MOCVD of the invention, a raw material solution which hardly freezes even in cold regions, and has good film forming properties and excellent step coverage, is obtained, when the second solvent comprises cyclohexane as an essential component, and is a solvent mixture formed by mixing the cyclohexane with one or two or more solvents selected from the group consisting of alcohols, alkanes, esters, aromatics, alkyl ethers and ketones, and when the organic solvent used comprises cyclohexane having good film forming properties and excellent step coverage as an essential component, and is a solvent mixture formed by mixing this cyclohexane with one or two or more of the above-listed various solvents having low melting points and high solubility for organometallic compounds.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-172664 | Jun 2004 | JP | national |
| 2004-172665 | Jun 2004 | JP | national |
| 2004-339802 | Nov 2004 | JP | national |
| 2004-339803 | Nov 2004 | JP | national |
| 2005-158964 | May 2005 | JP | national |
| 2005-167611 | Jun 2005 | JP | national |
This is a U.S. National Phase Application under 35 U.S.C. §371 of International Patent Application No. PCT/JP2005/010665 filed Jun. 10, 2005, and claims the benefit of Japanese Patent Application Nos. 2004-172664, filed Jun. 10, 2004, 2004-172665, filed Jun. 10, 2004, 2004-339802, filed Nov. 25, 2004, 2004-339803, filed Nov. 25, 2004, 2005-158964, filed May 31, 2005 and 2005-167611, filed Jun. 8, 2005, all of which are incorporated by reference herein. The International Application was published in Japanese on Dec. 22, 2005 as WO 2005/121400 A1 under PCT Article 21(2).
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/10665 | 6/10/2005 | WO | 00 | 9/5/2007 |
