JP2979839B2 - CVD raw material for fluoride glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CVD raw material for fluoride glass for producing a low-loss fluoride fiber used for an optical communication system or the like.

[0002]

2. Description of the Related Art In recent years, the progress of optical communication systems has been remarkable, and as one of them, attempts have been made to realize long-distance communication systems using infrared optical fibers. To achieve this, a fiber having a low loss property far exceeding that of a silica-based optical fiber is indispensable. Candidate materials for these infrared optical fibers include fluoride glass, chalcogenide glass, and halide crystals. Among them, fluoride glass is considered most promising in terms of performance, difficulty in the production method, and the like. As a method for producing fluoride glass, a solid phase method in which a fluoride is melted and reacted using a crucible and various gas phase methods have been actively studied.In this method, impurities from the crucible are mixed into the glass. It is easy to use and there is no established manufacturing method. Of these, recently, the CVD method has attracted attention as an excellent method for synthesizing high-purity homogeneous glass, and many attempts have been made.

As the performance required of such a material for a fluoride fiber, low loss is the most important. Further, in terms of a manufacturing process, it can be easily manufactured at a high speed. In particular, in order to obtain a low loss, it is necessary to suppress the generation of impurities and microcrystals that cause optical transmission loss. From such a viewpoint, a CVD method that can easily purify an organometallic compound as a raw material by purification and easily suppress microcrystals by improving a raw material, a reaction gas, reaction conditions, and the like is a very important method for manufacturing the above material. Is advantageous. These are described in, for example, the publication {52th Annual Meeting of the Japan Society of Applied Physics, Proceedings No. 11a-ZK-9}.
And so on.

[0004]

However, despite the fact that it is most advantageous to manufacture by the CVD method, the fact that there is no material having a stable and good vaporization characteristic as a CVD material at present does not exist. This is a major problem that cannot take advantage of the advantages of the law. This is mainly due to C
This is because β-ketone-based dipivaloylmethane (DPM) compounds, which are frequently used as a raw material for VD, have poor vaporization characteristics due to heating and are easily thermally decomposed. This point is pointed out, for example, in the publication {The 52nd Annual Meeting of the Japan Society of Applied Physics, Proceedings No. 11a-ZK-8}, and is considered to be a drawback caused by the intrinsic instability of metal DPM compounds. Can be Due to such instability of the raw materials, in extreme cases, the raw materials have to be disposable and synthesized. Therefore, due to the drawbacks caused by the above-mentioned raw materials, a CVD technique for producing a fluoride fiber material having good performance and good production reproducibility has not been established.

That is, in the production of a material for a fluoride fiber by the conventional CVD method, it is impossible to stably transport the raw material to the CVD reaction section by heating at a low temperature due to the poor stability and vaporization of the raw material. Met. Therefore, there has been a great problem that it is difficult to control the composition of a multi-component system, and it is not possible to stably and quickly synthesize a fiber material having good characteristics. Furthermore, if the raw material is heated at a high temperature in order to increase the vaporization efficiency, the raw material is transported while being thermally decomposed, so that the incorporation of impurities into the sediment, the formation of microcrystals, and the composition shift are inevitable. Not only that,
There has also been a disadvantage that the above-mentioned raw materials must be disposable. Further, in the conventional method, when the vaporization rate is suppressed and the synthesis (reaction) time is lengthened, the vaporized state of the raw material changes with time, so that the composition in the thickness direction of the formed film becomes inhomogeneous. It was inevitable that the light loss would increase. Therefore, there is a strong demand for the development of a new raw material that can provide stable and good vaporization at a low temperature, but there is no progress on this at all.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and provides a fluoride glass CVD raw material having improved controllability of composition and capable of synthesizing a fluoride glass having good characteristics with good reproducibility and high speed. The purpose is to obtain.

[0007]

DISCLOSURE OF THE INVENTION A CVD raw material for a fluoride glass according to the present invention comprises an organometallic compound in which a metal atom belonging to Group IA or IVA of the periodic table is bonded to an organic group, and a solution obtained by dissolving the organometallic compound in tetrahydrofuran. And an organic solvent having a boiling point higher than the boiling point of tetrahydrofuran and 150 ° C. or lower.

[0008]

The tetrahydrofuran used in the present invention has a low boiling point and can satisfactorily dissolve the organometallic raw material of the Group IA or IVA metal of the periodic table. The solution in which the organic metal is dissolved exhibits good vaporization even when heated at a temperature lower than the vaporization temperature of the organic metal itself, and functions to enable the raw material to be stably sent to the reaction section without being decomposed. It is considered something. Further, the boiling point is higher than the boiling point of tetrahydrofuran and 150 ° C.
It is presumed that the following organic solvents function to suppress excessive vaporization of tetrahydrofuran due to heating during vaporization and stabilize the state of the solution. In addition, unlike the conventional raw materials that require the vaporization of multiple raw materials separately, the CVD raw materials for fluoride glass of the present invention must be made into one liquid and vaporized at the same time, and stably transported to the reaction section. Accordingly, it is possible to obtain a fluoride glass CVD raw material capable of synthesizing a fluoride glass fiber material having good performance.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have conducted detailed studies on the vaporization properties of raw materials such as solid DPM compounds frequently used in the conventional CVD method as described above, and as a result, among these organometallic compounds, Group IA to IVA metals (Li, Na, S
It has been found that solid compounds such as r, Ba, Y, La, Al, Zr, and Hf) have poor stability and vaporization. Therefore, when synthesizing a fluoride glass containing a fluoride of these metals as a main component by a CVD method, the component is a multi-component system having 3 to 6 elements, and it is difficult to control the composition to a target composition. I found that I could not do it. Then, the present inventors made these compounds into one stable solution, and if this could be vaporized stably without being thermally decomposed, the controllability of the composition was improved, and a fluoride glass having good properties was obtained. They have found that they can be synthesized with good reproducibility, and have completed the present invention. In particular, the present inventors have found that, in the present invention, in the synthesis of a multi-component fluoride glass, the controllability and performance of the synthesized glass composition are significantly improved by using the liquid CVD raw material of the present invention. It is something to clarify.

Embodiment 1 FIG. Using a normal hot-wall type CVD apparatus having a pentagonal raw material heating system and using the raw material of one embodiment of the present invention, a zirconium-based fluoride glass, 55ZrF ₄ -25BaF ₂ -5LaF ₃ −
An experiment for synthesizing 15YF ₃ on a magnesium oxide substrate was performed. First, using the pentafluoropropanoylpivaloylmethanate derivative of each metal conventionally existing, each of the above quaternary organometallic compounds was mixed in the above component ratio. This mixture was dissolved in a mixed solvent of tetrahydrofuran and isopropyl alcohol (boiling point: 82.5 ° C.) at a volume ratio of 1: 1 so that the total solute was 0.3 mol%, and the fluoride according to one embodiment of the present invention was dissolved. It was used as a CVD raw material for glass. As the synthesis conditions, the heating temperature of the raw material was set at 200.
The reaction was performed for 60 minutes while the temperature was set to 0 ° C., the carrier gas was argon, the reaction gas was carbon tetrafluoride, the pressure inside the reaction section (furnace) was 1 Torr, and the substrate temperature was 210 ° C. After the reaction,
When natural cooling was performed to room temperature in a stream of carbon tetrafluoride, a fluoride glass having a thickness of about 2 μm was obtained. The light absorption characteristics of the glass base material were measured using an infrared spectrophotometer, and were used as rough indicators of the presence or absence of impurities and the light transmission loss.

Comparative Example 1 The same organometallic compound as in Example 1 was used as a raw material in a solid state, and a glass preform for a fluoride fiber having the same composition was synthesized by the conventional CVD method under the same synthesis conditions. As a result, almost no BaF ₂ and LaF ₃ were deposited on the substrate, and it was found that heating at 200 ° C. had poor vaporization. Therefore, in the conventional method, the heating temperature of the raw material is uniformly reset to 260 ° C., and the synthesis is performed for 100 minutes. As in the case of the method of the present invention, the reaction is allowed to cool naturally to room temperature in a stream of carbon tetrafluoride after the reaction. This was performed to obtain a film having a thickness of 1 μm.
Similarly, the light absorption characteristics of this film were evaluated based on the same criteria as described above.

FIG. 1 is a light absorption spectrum diagram of two kinds of fluoride glass materials obtained in Example 1 and Comparative Example 1 in which the present invention is compared with a conventional example. In FIG. Spectrum of the fluoride glass material obtained in the above, B
1 is a spectrum of the fluoride glass material obtained in Comparative Example 1. As is clear from FIG. 1, the material using the conventional material absorbs (i.e., light loss) over the entire measurement region, as compared with the material using the material of one embodiment of the present invention.
Absorption of residual organic matter (impurities) from the raw material is particularly noticeable in an infrared light region having a wavelength of 700 nm or more. In the above experiment, when the deposition rates in the synthesis of zirconium-based fluoride glass by both CVD methods were compared, when the raw material of one embodiment of the present invention was used at the same heating (vaporization) temperature, the conventional raw material It was found to be 30 to 60 times better than the case of using. Further, when the surfaces of both fluoride glasses were observed with a microscope, generation of microcrystals causing light loss was observed in the case of using the conventional raw material, whereas the raw material of one embodiment of the present invention was used. I did not see this at all. That is, using the raw material of one embodiment of the present invention,
It has been found that absorption of organic substances and generation of microcrystals from raw materials that cause light transmission loss can be suppressed. From these facts, by using the CVD raw material of one embodiment of the present invention, it is possible to synthesize a fluoride glass having good performance by the CVD method by heating at a much lower temperature than when using the conventional raw material. Turned out to be.

Embodiment 2 FIG. Using the same CVD apparatus as in Example 1, 50ZrF ₄ which is a zirconium-based fluoride glass
-15BaF ₂ -10LaF ₃ -5AlF ₃ -20NaF
Was synthesized on a magnesium oxide substrate. First, a dipivaloylmethanate derivative of each metal, which has been widely used, is used as a starting material, and as in Example 1, these are prepared in a volume ratio of tetrahydrofuran, ethyl acetate and toluene of 5: 2: 1. The resulting mixture was dissolved in a mixed solvent prepared as described above to obtain a CVD raw material according to another embodiment of the present invention. The concentration of solute in the raw material solution is 0.5 mol%
And This raw material was heated to 190 ° C. and vaporized. The substrate temperature was set at 200 ° C. Hydrogen fluoride was used as the reaction gas, and the reaction was performed at a pressure in the reaction section (furnace) of 1 Torr for 80 minutes. After the reaction, the mixture was naturally cooled slowly to room temperature in a hydrogen fluoride gas stream, whereby a fluoride glass having a thickness of about 6 μm was obtained. The light absorption characteristics of this glass were measured using a spectrophotometer in the same manner as in Example 1.

Comparative Example 2 The same organometallic compound as in Example 2 was directly used as a conventional raw material, and a fluoride glass having the same composition was synthesized by the conventional CVD method under the same synthesis conditions. However, the deposition on the substrate was slight, and it was found that heating at 190 ° C. resulted in poor vaporization. Therefore, the heating temperature of the conventional raw material is uniformly set to 280 ° C., and the synthesis is performed for 110 minutes. As in the case of using the raw material of the present invention, the reaction is allowed to cool naturally to room temperature in a hydrogen fluoride gas stream after the reaction. A 2 μm thick film was obtained. Similarly, the light absorption characteristics of this film were evaluated based on the same standards as in the above-described example.

FIG. 2 is a light absorption spectrum diagram of two kinds of fluoride glass materials obtained in Example 2 and Comparative Example 2 in which the present invention is compared with the conventional example. In FIG. Spectrum of the fluoride glass material obtained in the above, B
2 is a spectrum of the fluoride glass material obtained in Comparative Example 2. As is clear from FIG. 2, the material using the conventional material has a larger absorption (that is, light loss) over the entire measurement area than the material using the material of the other embodiment of the present invention, and particularly, the wavelength of 700 nm. In the infrared light region described above, the same result as in Example 1 was obtained, in which the residual organic matter (impurity) from the raw material was significantly absorbed.
Further, as a result of examining the film quality of both synthetic glasses with an electron microscope, the one using the conventional raw material was the same as in Comparative Example 1,
Formation of fine crystals was observed in some places. In addition, when the deposition rates in the synthesis of zirconium-based fluoride glass by both CVD methods were compared during the above experiment, it was found that, in the case of the raw material of another embodiment of the present invention at the same heating (vaporization) temperature, 50 It was found to be ~ 100 times better. Therefore, it was clarified that by using the raw materials of the other examples of the present invention, a fluoride glass having good performance can be synthesized by the CVD method by heating at a much lower temperature than in the case of using the conventional raw materials.

In Examples 1 and 2, the main reason why the performance of the synthetic glass using the conventional raw materials shown in the comparative examples is not good is that the raw materials are hardly vaporized by heating and heated at a relatively high temperature. This is considered to be due to the fact that it was difficult to stably transport to the reaction section. That is, the main reasons for the poor synthetic glass properties when using these conventional raw materials are as follows: the generation of microcrystals, the residual organic matter, and the synthetic film resulting from the unstable transport of each raw material as described in the Examples. It is presumed to be due to the inhomogeneity of the composition in the inside.

[0017] Using the CVD material embodiment of the present invention, in the same manner as in Example 1 and 2 is not limited to the composition shown in _{Example, ZrF 4 -BaF 2 -LaF 3 -YF} 3 -AlF 3 -
_{LiF, ZrF 4 -HfF 4 -BaF 2} -LaF 3 -NaF
—AlF ₃ , ZrF ₄ —BaF ₂ —GaF ₃ —AlF ₃ , Z
_{rF 4 -BaF 2 -LaF 3 -NaF-} AlF 3 -InF 3
Such a material for a fluoride glass fiber was manufactured by a CVD method. As a result, in each case, as in the case of Examples 1 and 2 shown above, the use of the CVD raw material of the embodiment of the present invention makes it possible to produce a material for a fluoride glass fiber having better performance than the conventional method. It turned out that it can be manufactured.

Examples of the organometallic compound according to the present invention include Li, N, which belong to groups IA to IVA of the periodic table.
a, Ba, Sr, Y, La, Al, Gd, Zr, Hf,
Experiments have confirmed that the above-mentioned effects are exhibited when the compound is a compound in which a metal atom is bonded to an organic group via an oxygen atom. Therefore, acetylacetonate, dipivaloylmethanate, alkoxide, hexafluoroacetylacetonate, pentafluoropropanoylpivaloylmethanate, cyclopentadienyl, and derivatives thereof of the above-mentioned metals are considered as meeting these conditions. And the like were used, and it was confirmed that the above-described vaporization promoting effect was exhibited in each case. Since these organometallic compounds are easily dissolved in the solvent according to the present invention, the concentration in the solvent can be determined to a predetermined value depending on the desired composition of the fluoride glass and the deposition rate of the synthetic glass.

Examples of the organic solvent having a boiling point higher than the boiling point (65 ° C.) of tetrahydrofuran and not higher than 150 ° C. include alcohols such as isopropyl alcohol, ethers such as ethyl propyl ether, methyl ethyl ketone and ethyl propyl. Many organic solvents such as ketones such as ketones, dipivaloylmethane, dioxane, n-hexane, dimethylfuran, cyclohexane, ethyl acetate, and toluene can be used. In a solvent having a boiling point (65 ° C.) lower than the boiling point of tetrahydrofuran, only the solvent volatilizes during heating and vaporization in a CVD process, and good deposition of raw material components cannot be obtained. On the other hand, those having a boiling point exceeding 150 ° C. are not polymerized at the time of heating, or hinder good vaporization of the raw materials, so that the effects of the present invention were not obtained. Therefore, the organic solvent used together with tetrahydrofuran in the present invention has a boiling point of tetrahydrofuran (65
° C) and 150 ° C or lower. Although the details of the effect of this organic solvent are not clear, tetrahydrofuran is a solution in which an organic metal is dissolved, and it shows that even when heated at a temperature lower than the vaporization temperature of the organic metal itself, good vaporizability is obtained, and the raw material is decomposed. It is considered that this has a function of enabling stable feeding into the reaction section while preventing the reaction. It is presumed that an organic solvent having a boiling point higher than the boiling point of tetrahydrofuran (65 ° C.) and 150 ° C. or lower suppresses excessive vaporization of tetrahydrofuran due to heating during vaporization and functions to stabilize the state of the solution. It is necessary to use at least one of an organic solvent having a boiling point of and a tetrahydrofuran. Although the details of this effect are not clear, from the above experimental results, decomposition of the raw material due to heating is suppressed, and by adding it to the conventional raw material, an adduct having a lower boiling point than the raw material is formed. It is presumed that at the same time, the adduct functions to stably transport the adduct to the reaction section.

[0020]

As described above, the present invention relates to an organometallic compound in which a metal atom belonging to Group IA or IVA of the periodic table is bonded to an organic group, and to dissolve the organometallic compound and to increase the boiling point of tetrahydrofuran and tetrahydrofuran. By using a solvent having a high organic solvent having a boiling point of 150 ° C. or less, the controllability of the composition is improved, and a fluoride glass having good properties can be synthesized with good reproducibility and high speed. CVD raw material can be obtained.

[Brief description of the drawings]

FIG. 1 is a spectrum diagram of a fluoride glass material comparing the present invention with a conventional example.

FIG. 2 is a spectrum diagram of a fluoride glass material comparing the present invention with a conventional example.

[Explanation of symbols]

 A1 Spectrum of the fluoride glass material of Example 1 A2 Spectrum of the fluoride glass material of Example 2 B1 Spectrum of the fluoride glass material of Comparative Example 1 B2 Spectrum of the fluoride glass material of Comparative Example 2

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ identification code FI G02B 6/00 356 G02B 6/00 356A (72) Inventor Katsuhiro Imada 8-1-1 Tsukaguchi Honcho, Amagasaki City Mitsubishi Electric Corporation (72) Inventor Hisao Watai 8-1-1, Tsukaguchi-Honcho, Amagasaki-shi Mitsubishi Electric Corporation In-Materials Research Laboratory (72) Inventor, Takeshi Sato 8-1-1, Tsukaguchi-Honmachi, Amagasaki-shi Mitsubishi Electric (56) References JP-A-2-275726 (JP, A) JP-A-5-117855 (JP, A) JP-A-5-132776 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) C03B 8/04 C03B 37/018 C23C 16/18

Claims (1)

(57) [Claims] 1. An organometallic compound in which a metal atom belonging to Group IA to IVA of the periodic table is bonded to an organic group, and a compound which dissolves the organometallic compound and has a boiling point higher than the boiling point of tetrahydrofuran and tetrahydrofuran and not higher than 150 ° C. CVD raw material for fluoride glass provided with a solvent composed of an organic solvent.