The patent's assignee for patent number 8642796 is
News editors obtained the following quote from the background information supplied by the inventors: "Ruthenium or ruthenium compounds have been used as a material for thin film electrodes of semiconductor devices such as DRAM and FERAM. A chemical deposition process such as a CVD process (chemical vapor deposition process) or an ALD process (atomic layer deposition process) is applied to the production of these thin films. Many organoruthenium compounds have been known as raw material compounds used in such a chemical deposition process.
"As an organoruthenium compound for chemical deposition as described above, the present inventors have disclosed a compound in which two .beta.-diketones and one diene (norbornadiene, cyclooctadiene, or the like) are coordinated, such as a compound represented by formula 1 (Patent Literature 1). When a thin film is formed with the compound represented by formula 1, a film which is uniform and has high denseness can be easily obtained.
"Generally, characteristics required for an organoruthenium compound for chemical deposition include a high vapor pressure for efficiently forming a thin film. Further, when handlability is taken into consideration, the organoruthenium compound is preferably in a liquid state at ordinary temperatures. From such a point of view, the present inventors have disclosed, in Patent Literature 1, a compound with a low molecular weight in which the substituents (R.sub.1, R.sub.2) of .beta.-diketones in the compound represented by formula 1 have carbon atoms in a predetermined range. Such a compound has a relatively high vapor pressure, easily maintains a liquid state at ordinary temperatures, and satisfies the above characteristics."
As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "Problems to be Solved by the Invention
"However, when chemical deposition is performed using hydrogen as a reactant gas, it is hard to form a ruthenium thin film with the compound represented by formula 1, and it is necessary to set the reaction temperature at a relatively high temperature in order to form a film. When a film is deposited on a substrate made of an easily oxidized material such as titanium nitride, it is required that chemical deposition using hydrogen can be easily performed so that degradation of the substrate may be prevented.
"Thus, an object of the present invention is to provide an organoruthenium compound which has good deposition characteristics as an organoruthenium compound for chemical deposition, has a high vapor pressure, and can easily form a film even when hydrogen is used as a reactant gas.
"Means for Solving the Problems
"The present inventors paid their attention to a compound represented by formula 2 in order to solve the aforementioned problems. The compound represented by formula 2 can easily form a film even when hydrogen is used as a reactant gas.
"However, when the compound represented by formula 2 was actually synthesized under various synthesis conditions, the compound was not in a liquid state at ordinary temperatures in some cases. Therefore, the present inventors have studied the conditions for the case where the compound represented by formula 2 is in a liquid state at ordinary temperatures, and when the present inventors paid attention to the point that the compound represented by formula 2 can have three isomers, they have found that the compound tends to be in a liquid state at ordinary temperatures when the content of an isomer in the compound is in a specific range, and have hit upon the present invention.
"Hereinafter, the present invention will be described in detail. First, the compound represented by formula 2 can have the following three isomers 1 to 3 in which the configuration of .beta.-diketones which are coordinated to the ruthenium metal is different (refer to formula 3). These three isomers are geometrical isomers in which the configuration of isopropyl groups and methyl groups in the diketonate ligands (.beta.-diketones) is different.
"The organoruthenium compound of the present invention relates to an organoruthenium compound in which, in the above three isomers, the content of the isomer 2 is 30% by mass or more, the content of the isomer 3 is 30% by mass or less, and the balance is the isomer 1. Such an organoruthenium compound easily maintains a liquid state at ordinary temperatures. As for the content of isomers in the compound, it is preferred that the content of the isomer 2 be 40% by mass or more, the content of the isomer 3 be 20% by mass or less, and the balance be the isomer 1. More preferably, the content of the isomer 2 is 40% by mass or more, the content of the isomer 3 is 18% by mass or less, and the balance is the isomer 1. Such a compound will easily form a film having a low specific resistance even when hydrogen is used as a reactant gas in forming a thin film.
"As described above, the organoruthenium compound of the present invention has a high vapor pressure and can stably maintain a liquid state at ordinary temperatures. Therefore, when a thin film is formed, a film which is uniform and has high denseness can be easily obtained, and chemical deposition in the case where hydrogen is used as a reactant gas is relatively easily performed. Consequently, it is suitable as a raw material compound for use in the chemical deposition process for forming a ruthenium thin film or a ruthenium compound thin film.
"Here, the content of each isomer in the organoruthenium compound can be determined by measuring a .sup.1H-NMR spectrum and calculating the area ratio of the peaks derived from the isomers. Thus, the content (mass ratio) of the isomers can be determined from the peak area ratio of the .sup.1H-NMR spectrum because each isomer has the same molecular weight and the same number of hydrogen atoms (two) assigned to methine sites.
"Specifically, the .sup.1H-NMR spectrum is first measured, and the peaks in a chemical shift value (.delta.) of 5.42 to 5.38 ppm derived from the methine groups (.dbd.C--) of .beta.-diketones are observed. In this spectrum, the peak appearing in the vicinity of .delta. 5.42 ppm is derived from the isomer 3. Further, the peaks in the vicinity of .delta. 5.40 ppm and .delta. 5.38 ppm are derived from the isomer 2, and the peak in the vicinity of .delta. 5.39 ppm is derived from the isomer 1.
"Then, the content of the isomers in the present invention can be determined by calculating the area ratio of the peaks appearing in the .sup.1H-NMR spectrum measurement. Specifically, the peak area ratio (.delta. 5.39 ppm:.delta. 5.40 ppm+5.38 ppm:.delta. 5.42 ppm) serves as the content of the isomers (isomer 1:isomer 2:isomer 3). Note that, in the present invention, the .sup.1H-NMR spectrum is measured in a deuterated chloroform solvent using tetramethylsilane as a reference material.
"In the present invention, it is possible to calculate, in this way, the content ratio of each isomer based on the correspondency with the appearing peaks in the .sup.1H-NMR spectrum because the present inventors have succeeded in the isolation of the three isomers which has been difficult. A specific isolation method and the like will be described in detail below, but it was possible to calculate the content ratio of each isomer because it was possible to specify the appearing peak and the like in the .sup.1H-NMR spectrum corresponding to each isomer since it became possible to analyze the X-ray crystal structure and measure the .sup.1H-NMR spectrum for each isolated isomer.
"An organoruthenium compound in which the content of the isomer 2 is 30% by mass or more, the content of the isomer 3 is 30% by mass or less, and the balance is the isomer 1, as described in the present invention, can be produced by a production method in which decane is used as an organic solvent and reaction temperature is maintained at 140 to 160.degree. C. Specifically, dicarbonyl-bis(5-methyl-2,4-hexanediketonato)ruthenium (II) which is the organoruthenium compound according to the present invention is produced by using triruthenium dodecacarbonyl as a starting material and allowing it to react with 5-methyl-2,4-hexanedione according to the reaction as shown in Expression 1. This reaction is preferably performed with reflux in an organic solvent at 140 to 160.degree. C. for 10 to 100 hours. A solvent having a high boiling point is useful as an organic solvent, and in particular decane (dry decane) is preferred. Further, the resulting product is preferably distilled.
"It is also preferred to isolate the isomers 1 to 3 from dicarbonyl-bis(5-methyl-2,4-hexanediketonato)ruthenium (II) obtained by the above production method or other methods and then mix each isomer so that the content of each isomer may be within a suitable range of content, thus obtaining an organoruthenium compound. This is because an organoruthenium compound which easily maintains a liquid state at ordinary temperatures can be produced. In this case, the isomers have been mixed so that the content of each isomer may be within a suitable range of content by adjusting the weight ratio of each isomer. In addition, a method by column chromatography can be used as a purification method for isolating each isomer, wherein silica gel is preferred as a filler.
"Here, the above purification method will be described in detail. Conventionally, among the three isomers, the isomer 1 has been relatively easily isolated, but there has been a tendency that the remaining isomers 2 and 3 are hardly separated from each other, and it has been difficult to specify the peak derived from the isomer 2 and the peak derived from the isomer 3 in the .sup.1H-NMR spectrum and the like. Therefore, it has been impossible to specify the content of the isomer which is easily in a liquid state only by measuring the .sup.1H-NMR spectrum and the like of the resulting compound. Then, the present inventors have conducted intensive studies this time to isolate all of the isomers. As a result, it has been found that all the isomers 1, 2, and 3 can be isolated by improving the separation ability of chromatography by increasing the amount of a filler such as silica gel and adjusting the composition of a developing solvent, in the purification by column chromatography.
"Specifically, although the amount of a filler relative to the fluid volume of a compound to be purified (volume ratio) has conventionally been 1:10 to 1:20, the ratio of the filler has been increased to 1:20 to 1:50. In addition, the diameter of a column to be used has been increased. Further, with respect to the developing solvent, for example, when a mixture of hexane and ethyl acetate is used, these solvents have been conventionally used at a volume ratio of hexane to ethyl acetate of 2:1 to 3:1, but the amount of hexane, which has a low polarity, has now been increased to 20:1. Separation ability has been able to be significantly increased by modifying the purification method as described above, and the present inventors have succeeded in the separation of the isomer 2 and the isomer 3 which had conventionally been difficult.
"Advantageous Effects of Invention
"As described above, the organoruthenium compound according to the present invention has a relatively high vapor pressure and is in a liquid state at ordinary temperatures. In addition, it has good film formation characteristics in forming a thin film by a chemical deposition process."
For additional information on this patent, see: Saito, Masayuki;
Keywords for this news article include: Gases, Hydrogen, Chemistry, Ruthenium, Silica Gel, Heavy Metals, Inorganic Chemicals, Transition Elements,
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