Method for purifying dodecacarbonyl triruthenium

Abstract

An object of the present invention is to provide a purification method to give dodecacarbonyl triruthenium (DCR) which serves as a raw material for chemical vapor deposition and does not cause the contamination of a thin film with impurities even when used to form a ruthenium thin film. The present invention relates to a method in which the dissolved oxygen concentration in the solvent is made 0.2 mg/L or less in at least a dissolution stage, and an organic ruthenium compound including DCR as a raw material for chemical vapor deposition is purified by a recrystallization method. The present invention allows a trace amount of impurities to be separated from DCR. When a ruthenium thin film is formed by use of DCR thus obtained, the formed film is hardly contaminated with impurities. Additionally, the purification method of the present invention is also applicable for recovering/purifying DCR after being used for the formation of a ruthenium thin film.

Claims

1. A method for purifying dodecacarbonyl triruthenium (DCR), for purifying, by a recrystallization method, an organic ruthenium compound including DCR represented by a following formula as a raw material for chemical vapor deposition: ##STR00003## the method comprises a recrystallization step of purifying DCR by a recrystallization method, the recrystallization step includes a dissolution stage of dissolving DCR in a solvent, a precipitation stage of precipitating DCR from the solvent, and a recovery stage of recovering the precipitated DCR, wherein at least the dissolution stage is performed with a dissolved oxygen concentration in the solvent being 0.2 mg/L or less.

2. The method for purifying DCR according to claim 1, wherein at least the dissolution stage is performed in an atmosphere having an oxygen concentration of 0.1 vol % or less.

3. The method for purifying DCR according to claim 1, wherein the recrystallization step further includes a drying stage of drying the recovered DCR, and the drying stage is performed at a reduced pressure of 500 Pa or less.

4. The method for purifying DCR according to claim 1, wherein, in the dissolution stage, DCR is dissolved in at least one solvent selected from acetone, dichloromethane, DMF, ethyl acetate, chloroform, toluene, acetonitrile, and THF.

5. The method for purifying DCR according to claim 1, further comprising a stage of filtering the solvent with dissolved DCR after the dissolution stage and before the precipitation stage.

6. The method for purifying DCR according to claim 1, wherein the dissolution stage is performed at 55 to 130 C.

7. The method for purifying DCR according to claim 3, wherein the drying stage is performed at 0 to 40 C.

8. The method for purifying DCR according to claim 1, wherein the recrystallization step is performed after a sublimation step of purifying DCR by a sublimation method.

9. The method for purifying DCR according to claim 2, wherein the recrystallization step further includes a drying stage of drying the recovered DCR, and the drying stage is performed at a reduced pressure of 500 Pa or less.

10. The method for purifying DCR according to claim 2, wherein, in the dissolution stage, DCR is dissolved in at least one solvent selected from acetone, dichloromethane, DMF, ethyl acetate, chloroform, toluene, acetonitrile, and THF.

11. The method for purifying DCR according to claim 3, wherein, in the dissolution stage, DCR is dissolved in at least one solvent selected from acetone, dichloromethane, DMF, ethyl acetate, chloroform, toluene, acetonitrile, and THF.

12. The method for purifying DCR according to claim 2, further comprising a stage of filtering the solvent with dissolved DCR after the dissolution stage and before the precipitation stage.

13. The method for purifying DCR according to claim 3, further comprising a stage of filtering the solvent with dissolved DCR after the dissolution stage and before the precipitation stage.

14. The method for purifying DCR according to claim 4, further comprising a stage of filtering the solvent with dissolved DCR after the dissolution stage and before the precipitation stage.

15. The method for purifying DCR according to claim 2, wherein the dissolution stage is performed at 55 to 130 C.

16. The method for purifying DCR according to claim 3, wherein the dissolution stage is performed at 55 to 130 C.

17. The method for purifying DCR according to claim 4, wherein the dissolution stage is performed at 55 to 130 C.

18. The method for purifying DCR according to claim 5, wherein the dissolution stage is performed at 55 to 130 C.

19. The method for purifying DCR according to claim 4, wherein the drying stage is performed at 0 to 40 C.

20. The method for purifying DCR according to claim 2, wherein the recrystallization step is performed after a sublimation step of purifying DCR by a sublimation method.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow diagram of the steps of the Example in the embodiment.

(2) FIG. 2 is a schematic diagram of a recrystallization equipment in the embodiment.

(3) FIG. 3 shows IR results of DCR and by-products in the embodiment.

(4) FIG. 4 shows TG-DTA results of DCR and by-products in the presence of Air in the embodiment.

(5) FIG. 5 shows TG-DTA results of DCR and by-products in an N.sub.2 atmosphere in the embodiment.

(6) FIG. 6 is a photograph observing the inside of a reaction vessel after sublimation in the presence of 1% oxygen in the embodiment.

DESCRIPTION OF EMBODIMENTS

(7) Hereinafter, best modes for carrying out the present invention will be described.

(8) From ruthenium chloride as a raw material, DCR crude crystals were synthesized by a direct method, followed by purification by a sublimation method and a recrystallization method. During purification, nitrogen gas was supplied to reduce the oxygen concentration (Example), or nitrogen gas was not supplied (Comparative Example 1); DCR obtained by purification in each case was evaluated. FIG. 1 shows a process flow diagram about the Example.

(9) Synthesis of DCR Crude Crystals

(10) 158 g of ruthenium chloride (manufactured by Tanaka Kikinzoku Kogyo K.K., ruthenium content: 38.67%, chlorine content: 47.4 wt %) and 6000 ml of 1-propanol were mixed and stirred, and the mixture was introduced into an autoclave having a volume of 10 L (made of steel) to serve as a reaction vessel. Then, 269 g of triethylamine was added to the reaction vessel, and further carbon monoxide gas was enclosed to 0.35 MPa. While supplying carbon monoxide to maintain the above reaction pressure, the reaction temperature was increased to 85 C. to allow the DCR synthesis reaction to proceed. The solution was allowed to react for 17 hours with stirring. After the synthesis reaction, the reaction mixture was cooled and filtered, and the filtrate was isolated to give 116 g of orange DCR crude crystals. The purity of the DCR crude crystals was 99%.

(11) Sublimation Step

(12) First, the DCR crude crystals obtained above were purified by a sublimation method. In the sublimation step, the DCR crude crystals were placed in a pear-shaped sublimator, and sublimation was performed under the following conditions.

(13) Degree of vacuum: 1 Pa

(14) Temperature: 95 C.

(15) Sublimation time: 6 hours

(16) Cooling water temperature: 8 C.

(17) After the completion of the sublimation step, the DCR crude crystals collected in the cooling unit were subjected to ICP-MS to measure the contents of impurity elements. As a result, the contents of Fe, Li, Na, Mg, Al, Ca, K, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Sr, Y, Mo, Ir, Pt, Au, Pb, Th, and U were all 1 ppm or less.

(18) Then, the DCR crude crystals after the sublimation step were purified by the following recrystallization method. In this embodiment, the recrystallization equipment shown in FIG. 2 was used. This recrystallization equipment includes a distillation tank (D) to previously distill the solvent in which DCR crude crystals are to be dissolved, a dissolution tank (S) to dissolve DCR crystals, and a crystallization tank (P) to precipitate DCR, and is configured such that a solvent and an inert gas can be supplied to the distillation tank D. Additionally, DCR crude crystals can be introduced into the dissolution tank S. The tanks are connected to one another through pipes capable of transporting the solutions in the tanks, and each pipe is provided with a valve 20. The pipes that transport solutions from the dissolution tank S and the crystallization tank P are each provided with a filtration means 30.

(19) In purification with the above recrystallization equipment, the oxygen concentration in the atmosphere inside each tank can be reduced by the following procedure. Specifically, with the valves 20 of the distillation tank D, the dissolution tank S, and the crystallization tank P being all open, the pressure in each tank was reduced. Subsequently, an inert gas was supplied to the distillation tank D to replace the atmosphere gases in the dissolution tank S and the crystallization tank P and distillation tank D connected thereto with the inert gas. By repeating the inert gas replacement several times, the oxygen concentration in the atmosphere in each tank can be reduced to a predetermined amount or lower. Then, when a solvent is introduced into the recrystallization equipment in which the oxygen concentration in the atmosphere has been reduced as above, the dissolved oxygen concentration in the solvent also becomes a predetermined amount or lower, making it possible to achieve an oxygen concentration suitable for the following purification method.

(20) Oxygen Concentration Check Test

(21) Here, the value of the oxygen concentration in the atmosphere and that of the dissolved oxygen concentration in the solvent when the atmosphere gas in each tank is replaced with an inert gas by use of the above recrystallization equipment were checked. Specifically, the above recrystallization equipment was released to the air for 10 minutes, and then the pressure in the equipment was reduced to 0.09 MPa or less. Subsequently, the entire equipment was purged with nitrogen gas (99.99% nitrogen) from the distillation tank, and then the valve of each tank was closed. This nitrogen gas purge was repeated four times. Additionally, in the dissolution tank (S) and crystallization tank (P) purged with nitrogen gas, 5 L of ethyl acetate was placed. The oxygen concentration in the atmosphere in each tank was measured with an oximeter; the results are shown below. Incidentally, the following results are values after 3 minutes from when the gas in each tank is passed through the oximeter. Provided that the amount of dissolved oxygen in ethyl acetate in the air is 43.23 mg/L, the dissolved oxygen concentration in the solvent was calculated from the linear relationship with the oxygen concentration in the atmosphere. Additionally, when the nitrogen gas was replaced four times, the dissolved oxygen concentration in the solvent in each tank was actually measured; the results are shown below.

(22) TABLE-US-00001 TABLE 1 Oxygen concentration in atmosphere in each tank (vol %) The number of Distillation Dissolution Crystallization replacements tank tank tank 0 21.9 19.6 22 2 0.005 0.242 0.136 3 0.004 0.064 0.05 4 0.004 0.044 0.044

(23) TABLE-US-00002 TABLE 2 Dissolved oxygen concentration in solvent (mg/L) The number of Dissolution Crystallization replacements tank tank 0 39.6 44.4 2 0.49 0.27 3 0.13 0.10 4 0.08 (0.05)* 0.08 (0.05)* *In parentheses are actual measured values.

(24) From above, when the atmosphere gas was replaced with nitrogen gas three times or more, the oxygen concentration in each tank of the recrystallization equipment was made 0.1 vol % or less. Additionally, when the nitrogen gas replacement was performed three times or more, the dissolved oxygen concentration in the solvent was 0.2 mg/L or less. Additionally, from the results of performing the replacement four times shown in Table 2, it was confirmed that the calculated value of the dissolved oxygen concentration in the solvent is almost equal to the actual measured value.

EXAMPLE

(25) With the above recrystallization equipment, DCR crude crystals were purified by a recrystallization method. First, as a solvent, 5.3 L of ethyl acetate was placed in the distillation tank. The inside of the distillation tank with the valve closed was replaced with nitrogen gas four times, making the dissolved oxygen concentration in the solvent 0.2 mg/L or less and the oxygen concentration 0.1 vol % or less. Subsequently, ethyl acetate was distilled. 300 ml of the initial fraction was discarded, and 5 L of the main fraction was collected and used for the dissolution step.

(26) Next, 100 g of DCR crude crystals were placed in the dissolution tank, the inside of the dissolution tank with the valve closed was replaced with nitrogen gas four times, and then 5 L of ethyl acetate distilled above (main fraction) was placed therein. At this time, the dissolved oxygen concentration in the solvent was 0.2 mg/L or less, and the oxygen concentration was 0.1 vol % or less. Then, ethyl acetate was heated to 75 C. to completely dissolve DCR. After the dissolution of DCR, the solution was filtered to remove impurities insoluble in ethyl acetate. The filtrate obtained after filtration was placed in the crystallization tank, which had been previously replaced with nitrogen gas four times to make the dissolved oxygen concentration in the solvent 0.2 mg/L or less and the oxygen concentration 0.1 vol % or less. The solution in the crystallization tank was cooled to 20 C. and then filtered, and the precipitated DCR crystals were collected. Subsequently, in a drying furnace having a reduced pressure of 500 Pa, DCR was dried at 23 C. for 48 hr. The obtained DCR was about 85 g.

Comparative Example 1

(27) 16 g of the same DCR crystals as in the above Example were used. Without performing the nitrogen gas replacement of the distillation, dissolution, and crystallization tanks and the pressure reduction in the drying furnace, and without limiting the oxygen concentration, DCR was purified by a sublimation method and a recrystallization method. The amount of ethyl acetate used was 0.8 L. Other recrystallization conditions were the same as those in the Example. In the obtained DCR, a gray substance was present in orange crystals (DCR). This substance (gray substance) was collected. As a result, in 14.5 g of the obtained DCR crystals, the amount of gray substance contained was 0.2 g. The DCR crystals and gray substance were subjected to elemental analysis (CHN), IR analysis, and TG-DTA analysis to compare the characteristics. The TG-DTA analysis was performed under the following two kinds of measurement conditions: in the presence of Air (FIG. 4) and in an N.sub.2 atmosphere (FIG. 5). The results are each shown in Table 3 and FIGS. 3 to 5.

(28) TABLE-US-00003 TABLE 3 Results of elemental analysis % H C N DCR crystals 0 22.44 0 Gray substance 1.61 13.61 0

(29) From the results of elemental analysis shown in the above table, it turned out that the gray substance was different from the DCR crystals in the proportions of constituent elements, and that in particular, hydrogen H, which is originally not contained in DCR, was present. Additionally, in the results of IR analysis shown in FIG. 3, the detection peak of the gray substance was obviously different from that of the DCR crystals. Additionally, in the results of TG-DTA measurement shown in FIGS. 4 and 5, the DCR crystals and the gray substance showed different detection peaks both in the presence of Air (FIG. 4) and in an N.sub.2 atmosphere (FIG. 5).

(30) From the above results, in Comparative Example 1 that did not control the oxygen concentration in the solvent or the atmosphere, a gray substance was contained in the DCR crystals after recrystallization. This gray substance showed characteristics obviously different from those of DCR in the proportions of elements, infrared absorption, and heat decomposability. In contrast, in the Example in which the dissolved oxygen concentration in the solvent was made 0.2 mg/L or less, and the oxygen concentration in the atmosphere was made 0.1 vol % or less, DCR crystals containing no gray substance were obtained.

Comparative Example 2

(31) DCR was recrystallized by use of a mixed gas of 1% oxygen and 99% nitrogen in place of nitrogen gas (99.99% nitrogen) in the Example. In this comparative example, the inside of the equipment was not previously gas-purged, and ethyl acetate was placed in the equipment. Subsequently, the above gas was introduced into the dissolution tank (S) and crystallization tank (P) shown in FIG. 2 at 2 L/min to perform recrystallization. Other conditions were the same as in the method of the Example, and precipitated DCR crystals were collected by filtration.

(32) The resulting DCR crystals were orange crystals as in the Example. However, as a result of checking the filter paper after filtration, a trace amount of black residue was present on the surface. Such a residue was not present at all in the Example. This showed that when a mixed gas containing 1% oxygen gas was used, a substance different from DCR crystals was formed.

(33) Next, as an additional experiment for checking the presence of substances other than DCR formed when a mixed gas containing 1% oxygen (99% nitrogen) was used, a sublimation test using the above oxygen-containing gas was performed. With use of the same mixed gas as in the above recrystallization test, the sublimation test was performed under the following conditions: temperature: 110 C., pressure: 0.2 torr, carrier gas (carbon monoxide, flow rate: 50 sccm), sublimation time: 24 hours, sample amount: 5 g. For comparison, the same sublimation test was also performed for the case of using nitrogen gas (99.99% nitrogen) as the purge gas. FIG. 6 shows a photograph observing the inside of the reaction vessel after the sublimation test.

(34) From FIG. 6, it is considered that when nitrogen gas (99.99% nitrogen) was used, nothing remained in the reaction vessel after sublimation, indicating that DCR had been entirely sublimated. In contrast, when a mixed gas containing 1% oxygen (99% nitrogen) was used, a slight amount of residue was present in the reaction vessel. From above, it was confirmed that purification in the presence of 1% oxygen presence results in the formation of products other than DCR.

INDUSTRIAL APPLICABILITY

(35) The present invention allows, in a method for purifying DCR using a recrystallization method, a trace amount of impurities in DCR to be reduced, while suppressing the formation of by-products. Additionally, the purification method of the present invention is also applicable to the recycling of used DCR recovered after chemical vapor deposition.

REFERENCE SIGNS LIST

(36) D: Distillation tank S: Dissolution tank P: Crystallization tank 20: Valve 30: Filtration means