[Invent ion Tit le]

METHOD FOR PREPARING MONOGERMANE GAS IN HIGH YIELD

[Technical Field]

<i> The present disclosure relates to a method for preparing monogermane gas in high yield, more particularly to a method for preparing monogermane gas, which is capable of minimizing waste of the expensive raw material germanium dioxide and maximizing the yield of monogermane gas without being limited by the type of a reactor during mass production of germane gas in commercial scale, by introducing an additional process.

[Background Art]

<2> Germane gas is used in the semiconductor industry. It allows the application of strained silicon to computer CPUs and has become a key material in the newly emerging germanium channels and gate. Also, the germane gas is used in the formation of an intermediate SiGe layer of the triple junction of a 5th generation amorphous silicon thin-film solar cell (a ^~ Si solar cell), thereby enhancing absorption of light in the mid- wavelength range of 300-900 nm and improving cell efficiency. Accordingly, with the expected increase in the demand on the next-generat ion thin-film solar cell, the demand on germane gas is also expected to grow rapidly.

<3> Synthesis of germane gas and chemical reactions involved therein have been studied by many chemists since 1930s. Typical examples include a chemical method of reducing germanium dioxide (Ge0 ₂ ) or germanium tetrachlorideCGeCU) using sodium borohydr ide(NaBH ₄ ) , lithium aluminum hydr ide(LiAlH ₄ ) , etc. ,an electrochemical method of electrolyzing germanium dioxide and a high-energy method of reacting germanium(Ge) directly with hydrogen.

<4> As for the existing methods of preparing germane gas using germanium dioxide or germanium tetrachloride, the yield is only about 70%. In particular, when monogermane gas is prepared using germanium dioxide which is easier to handle than germanium tetrachloride, it is difficult to prepare monogermane gas in high yield.

<5> In this regard, US Patent No. 4,668,502 discloses that the yield of germane gas can be increased up to 97% even when germanium dioxide (GeC^) is used as the same raw material by varying reaction conditions, i.e. combinations of germanium dioxide concentration, alkali/germanium dioxide ratio in an alkaline aqueous solution wherein germanium dioxide is dissolved, amount of alkali metal borohydride, acid concentration, reaction temperature, etc. Indeed, a high germane yield of around 90% was achieved when experiment was conducted according to the reaction conditions specified in the examples and claims of US Patent No. 4,668,502.

<6> For mass production of germane gas in commercial scale, it is economically favorable to increase the yield of monogermane gas as much as possible. Therefore, it is necessary to minimize waste of the expensive germanium dioxide and maximize the productivity of monogermane gas. The inventors of the present disclosure have made efforts to find a method that provides a yield excelling the highest yield of 97% disclosed in US Patent No. 4,668,502. As a result, they have found out that a high germane yield up to 99.7% can be achieved by introducing an additional process in addition to the method described in the examples and claims of US Patent No. 4,668,502.

[Disclosure]

[Technical Problem]

<7> The present disclosure is directed to providing a method for preparing monogermane gas, which is capable of minimizing waste of the expensive raw material germanium dioxide and maximizing the yield of monogermane gas without being limited by the type of a ^' reactor during mass production of germane gas in commercial scale and thus is excellent in economic efficiency, by introducing an additional process.

[Technical Solution]

<8> In a general aspect, there is provided a method for preparing monogermane gas, including: injecting an aqueous acid solution and an aqueous starting material alkali solution comprising germanium dioxide and an alkali metal hydride into a reactor; primarily preparing monogermane gas and a reaction solution by reacting the injected aqueous acid solution and aqueous starting material alkali solution in the reactor; and secondarily preparing monogermane gas by further adding an aqueous mixture solution of an alkali metal hydroxide and an alkali metal borohydride to the prepared reaction solut ion.

<9> In an exemplary embodiment, the aqueous mixture solution of the alkali metal hydroxide and the alkali metal borohydride may include the alkali metal hydroxide and the alkali metal borohydride at a molar ratio of 2:8-7 ^' -3, more specifically at a molar ratio of 2:8.

<io> In an exemplary embodiment, the secondarily preparing monogermane gas may be performed once or more times.

<i i> In an exemplary embodiment, the yield of monogermane gas may be controlled by controlling the concentration of the aqueous acid solution during said injecting the aqueous acid solution and the aqueous starting material alkali solution.

<12> In an exemplary embodiment, the yield of monogermane gas may be controlled by controlling the amount of the mixture solution of the alkali metal hydroxide and the alkali metal borohydride.

<i3> In an exemplary embodiment, the alkali metal hydride may be NaBhV

<i4> In an exemplary embodiment, the alkali metal borohydride may be NaBH ₄ .

<i5> In an exemplary embodiment, the aqueous acid solution may include an inorganic acid or an organic acid. The inorganic acid may be one or more selected from a group consisting of sulfuric acid and phosphoric acid and the organic acid may be one or more selected from a group consisting of acetic acid and propionic acid.

[Advantageous Effects]

<16> The present disclosure is capable of minimizing waste of the expensive raw material germanium dioxide and maximizing the yield of monogermane gas during mass production of germane gas in commercial scale, by introducing an additional process. Further, the present disclosure provides improved economic efficiency by improving the yield of monogermane gas without being limited by the type of a reactor. [Description of Drawings]

<17> Fig. la is a schematic view of a batch reactor that can be used according to an exemplary embodiment of the present disclosure.

<i8> Fig. lb is a perspective view of a microchannel reactor that can be used according to an exemplary embodiment of the present disclosure.

<I9> Fig. lc is a photograph of a microchannel reactor that can be used according to an exemplary embodiment of the present disclosure.

<20> Fig. Id is a schematic view of a microchannel of a microchannel reactor that can be used according to an exemplary embodiment of the present disclosure.

<2i> Fig. le shows the structure of a microchannel of a microchannel reactor that can be used according to an exemplary embodiment of the present disclosure in detai 1.

<22> Fig. 2 shows the yield of germane in Examples 1-6 and Comparative

Examples 1-6.

<23> Fig. 3 shows the yield of germane in Examples 7-12 and Comparative

Examples 7-12.

<24>

<25> [Detailed Description of Main Elements]

<26> 1: batch reactor

<27> 2: circulator

<28> 3· ^' aqueous starting material alkali solution reservoir

<29> 4· ^' aqueous acid solution reservoir

<3 ⁽ >> 5: aqueous mixture solution (including alkali metal hydroxide and alkali metal borohydride) reservoir

<3i> 6: coolant circulation unit

<32> 7- metering pump

<33> 8: recorder 9: discharge outlet

<34> 10: first channel 20: second channel

<35> 30: third channel (30a: main channel, 30b: projection)

<3f» 40 ^' · discharge outlet

<37> 50: coolant circulation unit (55a: coolant inlet, 55b- ^' coolant discharge outlet)

<38> 60· ^' metal block (60a: first metal block, 60b: second metal block)

[Mode for Invention]

<39> Hereinafter, the present disclosure is described in detail.

<40> As used in the present disclosure, the term "microchannel " refers to a microstructured channel. The channel may have a diameter ranging from several micrometers to thousands of micrometers.

<4 i > As used in the present disclosure, the term "aqueous starting material alkali solution" refers to a solution prepared by mixing germanium dioxide and an alkali metal hydride as starting materials with an aqueous alkali solution.

<42> As used in the present disclosure, the term "reaction solution" refers to a solution remaining after germane gas is produced from reaction of an aqueous starting material alkali solution and an aqueous acid solution.

<43>

<44> Method for preparing monogermane gas in high yield

<45> Injection of aqueous starting material alkali solution and aqueous acid solut ion

<46> First, an aqueous acid solution and an aqueous starting material alkali solution including germanium dioxide (GeC^) and an alkali metal hydride are prepared and injected into a reactor.

<47> The injected aqueous starting material alkali solution may be prepared by mixing germanium dioxide (GeG^) and an alkali metal hydride with an aqueous alkali solution. The alkali metal hydride may be NaBH ₄ . The aqueous starting material alkali solution may be prepared, as described in USP 4,668,502, by adding alkali metal hydride powder to an aqueous metal hydroxide solution of germanium dioxide (Ge0 ₂ ) or by preparing an alkaline aqueous solution of a predetermined concentration in advance and then adding germanium dioxide powder and alkali metal hydride powder thereto, although not being limited thereto. In the aqueous starting material alkali solution used in the present disclosure, the concentration of germanium dioxide may be specifically not greater than 0.5 mol/L, more specifically 0.3 mol/L. The metal hydroxide may be included in an amount of 2 equivalents or more per 1 mol of germanium dioxide, and the alkali metal hydride may be included in an amount of 4 mol or more per 1 mol of germanium dioxide. Outside these ranges, the conversion ratio of germanium dioxide may decrease and thus the economic efficiency of monogermane production may decrease. The aqueous alkali solution may be an aqueous alkali metal solution or an aqueous alkaline earth metal solution, specifically an aqueous NaOH solution or an aqueous 0H solution. If an aqueous NaOH solution is used as the aqueous starting material alkali solution and if NaBH ₄ is used as the alkali metal hydride to prepare the aqueous starting material alkali solution, hydrogen is not generated since the NaBH4 is stabilized.

<48> The injected aqueous acid solution may be prepared by mixing an inorganic acid such as sulfuric acid, phosphoric acid, etc. or an organic acid such as acetic acid, propionic acid, etc. with water. In consideration of the purification of monogermane gas, it is recommended to avoid a volatile acid such as hydrochloric acid. The concentration of the aqueous acid solution is not particularly limited. However, the yield of finally produced germane gas can be controlled by controlling the concentration of the aqueous acid solution.

<49> The injection rate of the aqueous starting material alkali solution and the aqueous acid solution is not particularly limited, but may be tens of milliliters per minute. The injection rate may be varied depending on the size of the reactor and the desired production amount of germane gas.

<50> The reactor to which the aqueous starting material alkali solution and the aqueous acid solution are injected is not particularly limited as long as monogermane gas can be produced by reacting the injected aqueous starting material alkali solution and the aqueous acid solution. The reactor may be a general batch reactor (see Fig. la), a continuous reactor or a microchannel reactor (see Figs, lb-le). Specifically, it may be a microchannel reactor. i> The microchannel reactor may include: a first channel 10 where the aqueous starting material alkali solution is injected; a second channel 20 where the aqueous acid solution is injected; a third channel 30 which is connected to the first channel 10 and the second channel 20 and wherein the aqueous starting material alkali solution and the aqueous acid solution are mixed and react to produce monogermane gas and a reaction solution; a discharge outlet 40 through which the monogermane gas and the reaction solution produced in the third channel 30 are discharged; and a coolant circulation unit 50 which is disposed adjacent to the third channel 30, wherein a coolant is injected and discharged and by which reaction heat generated in the third channel 30 is absorbed. The third channel 30 may have a microchannel structure.

<52> The diameter and the length of the third channel 30 may vary depending on the size of the reactor and the desired production amount of germane gas, but may be specifically tens to thousands of micrometers.

<53> Also, the third channel 30 may include a main channel 30a and a plurality of projections 30b projecting from one side of the main channel 30a in parallel. The plurality of projections 30b may form an acute angle with respect to the main channel 30a and may project in one direction. By including the main channel 30a and the projections 30b, the third channel 30 may allow a fluid passing through the third channel 30 to continuously move upward and downward and also allow the fluid to be split or recombined. Having such a configuration, the third channel 30 not only allows easy mixing of the aqueous starting material alkali solution and the aqueous acid solution injected respectively from the first channel 10 and the second channel 20 but also can facilitate the production of germane gas by increasing contact area of the aqueous starting material alkali solution and the aqueous acid solution. The third channel 30 may further include a temperature sensor (not shown). The temperature sensor allows real-time measurement of the temperature in the third channel 30, thereby allowing easy control of reaction temperature and flow volume of the coolant passing through the coolant circulation unit 50 and thus increasing production yield of monogermane gas.

54> The aqueous starting material alkali solution and the aqueous acid solution may be injected into the reactor using any device capable of continuously injecting the aqueous alkali solution and the aqueous acid solution into the reactor, without particular limitation. Specifically, a metering pump may be used.

<55>

<56> Primary preparation of monogermane gas

<57> The aqueous starting material alkali solution and the aqueous acid solution injected into the reactor are mixed inside the reactor and germane gas is produced at the interface where they contact with each other.

<58> In case of a batch reactor (see Fig. la) according to an exemplary embodiment of the present disclosure, each of the aqueous starting material alkali solution and the aqueous acid solution is simultaneously injected into the reactor by a metering pump at constant speed and monogermane gas is produced at the interface where the aqueous starting material alkali solution contacts with the aqueous acid solution.

<59> In case of a microchannel reactor according to another exemplary embodiment of the present disclosure having a microstructured channel, production of germane gas can be facilitated and increase in temperature resulting from reaction heat can be effectively controlled. It is because the production of germane gas occurs only at the interface where the aqueous starting material alkali solution contacts with the aqueous acid solution and the interfacial area increases as they are smaller in droplet size and larger in number. The microchannel may include a main channel 30a and a plurality of projections 30b projecting from one side of the main channel 30a in parallel. The plurality of projections 30b may form an acute angle with respect to the main channel 30a and may project in one direction. Accordingly, after being injected into the third channel 30, the aqueous starting material alkali solution and the aqueous acid solution may be split or recombined as they continuously move upward and downward between the main channel 30a and the plurality of projections 30b. As a result, the aqueous starting material alkali solution and the aqueous acid solution are mixed in micro scale and react at the contact interface to produce germane gas (see Figs, lt le)

<60>

<6i> Secondary preparation of monogermane gas

<62> After the monogermane gas and the reaction solution are primarily prepared, the monogermane gas is collected separately.

<63> An aqueous mixture solution of an alkali metal hydroxide and an alkali metal borohydride is further added to the reaction solution remaining in the reactor to secondarily prepare monogermane gas.

<64> The secondarily prepared monogermane gas is collected. The second preparation may be performed once or more times. If the second preparation is performed repeatedly, a higher yield can be achieved.

«55 > In the aqueous mixture solution of the alkali metal hydroxide and the alkali metal borohydride, the alkali metal borohydride may be NaBH ₄ since it remains stable without reacting with water. The alkali metal hydroxide may be an alkali metal or an alkaline earth metal, specifically NaOH or KOH. The aqueous mixture solution of the alkali metal hydroxide and the alkali metal borohydride may include the alkali metal hydroxide and the alkali metal borohydride at a molar ratio of 2:8-7:3, more specifically 2:8, to maximize the yield of monogermane gas.

<66>

<67> Exam les

«58> Hereinafter, the present disclosure will be described in detail through examples. However, the following examples are for illustrative purposes only and it will be apparent to those of ordinary skill in the art that the scope of the present disclosure is not limited by the examples.

;6 > In Comparative Examples 1-6, aqueous solution A and aqueous solution B were prepared as in the preparation of BR-02-30 described in US Patent No. 4,668,502 (yield: 97%). In Comparative Examples 7-12, aqueous solution A and aqueous solution B were prepared as in the preparation of RJ-01-95 described in US Patent No. 4,668,502 (yield: 89.1%).

70>

7i> Example 1 <72> A 50% aqueous NaOH solution (1.41 mL) was dissolved in distilled water

(125 mL) . Germanium dioxide (Ge0 ₂ ,1.7g) and NaBH ₄ (3.7g) were sequentially dissolved in the resulting solution to prepare an aqueous starting material alkali solut ion(aqueous solution A)at 20 ^° C.

<73> Strong (96%) sulfuric acid (¾S0 ₄ ,75g) was dissolved in distilled water (230mL) to prepare 250mL of an aqueous acid solut ion(aqueous solution B) at 20 ^° C.

<74> The aqueous starting material alkali solution (aqueous solution A) was injected into an apparatus for preparing germane gas (see Fig. la) according to an exemplary embodiment of the present disclosure at about 8.3 mL/min. At the same time, the aqueous acid solution (aqueous solution B) was injected at 16.7 mL/min. The injection was carried out using a metering pump. It took about 15 minutes to inject the two solutions. Germane gas was produced while the two aqueous solutions were being injected.

<75> To a reaction solution remaining after germane gas was primarily prepared, 188 mL of a separately prepared aqueous mixture solution (aqueous solution C) of an alkali metal hydroxide and an alkali metal borohydride (0.7 M NaOH, 0.79 M NaBH ₄ ) was further injected at 12.5mL/min using a metering pump. A small amount of the aqueous mixture solution was taken from the reactor at 5 minutes, 10 minutes and 15 minutes after the addition of the aqueous solution C was completed (samples CI, C2 and C3).

<76> The amount of unreacted germanium remaining in the aqueous mixture solution was measured by ICP analysis and the germanium dioxide-to-germane gas conversion ratio was calculated therefrom.

<77>

i78> Examples 2-6

^; 79> The mixing ratio of the alkali metal hydroxide and the alkali metal borohydride when preparing the aqueous solution C was varied as follows: Example 2 (0.7 M NaOH, 0,5 M NaBH ₄ ) , Example 3(0.7M NaOH, 0.3M NaBH ₄ ) , Example

4(0.2M NaOH, 0.79M NaBH ₄ ) , Example 5(0.2M NaOH, 0.5M NaBH ₄ ) , Example 6(0.2M

NaOH, 0.3M NaBH ₄ ). <80> The aqueous solution A and the aqueous solution B were prepared in the same manner as in Example 1 and germane gas was prepared primarily. To a reaction solution remaining after germane gas was primarily prepared, the aqueous solution C injected at the same rate as in Example 1. The amount of unreacted germanium remaining in the aqueous mixture solution taken 5 minutes, 10 minutes and 15 minutes later was measured by ICP analysis and the germanium dioxide-to-germane gas conversion ratio was calculated therefrom.

<81>

<82> Comparative Examples 1-6

<83> The experimental procedure was the same as that of Examples 1-6, but the aqueous solution C was not further added.

<84>

<85> The experimental result for Examples 1-6 and Comparative Examples 1-6 is summarized in the following table.

<86>

<87> [Table 1]

<88>

<89> * Aqueous solution A: Ge0 ₂ (1.7g), 50% NaOH(l .41mL) and NaBH ₄ (3.7g) dissolved in distilled water (125mL) .

<90> * Aqueous solution B- ^' strong (96%) sulfuric acid (H ₂ S0 ₄ , 75g) dissolved in distilled water (230mL) .

<91 >

<92> The germanium dioxide conversion ratio for Examples 1-6 and Comparative

Examples 1-6 is shown in Fig. 2. The numbers given to the curves correspond to the Example numbers and the y-axis values correspond to the germanium conversion ratios of the samples CI, C2 and C3.

<93> The values on the y-axis correspond to the germanium conversion ratios of the sample A for Comparative Examples. The average germanium conversion ratio of the sample A for Comparative Examples 1-6 is 93.5%. As seen from Fig. 2, the germanium conversion ratio increased when the aqueous mixture solution C including NaOH (0.2-0.7 M) and NaBH ₄ (0.3-0.79M) was further added to the reaction solution remaining after germane gas was primarily prepared.

<94>

<95> Examples 7-12

<96> The experimental procedure was the same as that of Examples 1-6 except that the concentration of sulfuric acid was doubled when preparing the aqueous solution B.

<97> The amount of unreacted germanium remaining in the aqueous mixture solution was measured by ICP analysis and the germanium dioxide-to-germane gas conversion ratio was calculated therefrom.

i98>

i 9> Comparative Examples 7-12

oo> The experimental procedure was the same as that of Examples 7-12, but the aqueous solution C was not further added.

oi>

02> The experimental result for Examples 7-12 and Comparative Examples 7-12 is summarized in the following table. <103>

<i04> [Table 2]

<i05> * Aqueous solution Α·: Ge0 ₂ (1.7g), 50% NaOH(1.41mL) and NaBH ₄ (3.7g) dissolved in distilled water (125mL) .

;i 6> * Aqueous solution B: strong (96%) sulfuric acid (H ₂ SO ₄ , 150g) dissolved in distilled water (210mL) .

107>

i08> The germanium dioxide conversion ratio for Examples 7-12 and

Comparative Examples 7-12 is shown in Fig. 3. The numbers given to the curves correspond to the Example numbers and the y-axis values correspond to the germanium conversion ratios of the samples CI, C2 and C3.

i09> The values on the y-axis correspond to the germanium conversion ratios of the sample A for Comparative Examples. The average germanium conversion ratio of the sample A for Comparative Examples 7-12 is 93.2%, which is not significantly different from that of Comparative Examples 1-6 wherein the concentration of sulfuric acid in the aqueous solution B was 1/2. <uo> As seen from Fig. 3, the germanium conversion ratio increased when the aqueous mixture solution C including NaOH (0.2-0.7 M) and NaBH ₄ (0.3-0.79M) was further added to the reaction solution remaining after germane gas was primarily prepared, similarly to Examples 1-6.

<ni> From the result of Examples 1-12 and Comparative Examples 1-12, it can be seen that monogermane gas can be prepared in high yield of 97.5-99.7% by primarily preparing monogermane gas (conversion ratio: 91-95%) by reacting the aqueous starting material alkali solution including germanium dioxide with the aqueous acid solution and then further adding the aqueous mixture solution including the alkali metal hydroxide (0.2-0.7 M) and the alkali metal borohydride (0.3-0.8 M) (see Fig. 2 and Fig. 3).

<i i2> Accordingly, it can be seen that the method for preparing germane gas according to the present disclosure allows mass production of monogermane gas in commercial scale in high yield.

<l 13>

<i i4> While the exemplary embodiments have been shown and described, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the spirit and scope of this disclosure as defined by the appended claims. In addition, many modifications can be made to adapt a particular situation or material to the teachings of this disclosure without departing from the essential scope thereof. Therefore, it is intended that this disclosure not be limited to the particular exemplary embodiments disclosed as the best mode contemplated for carrying out this disclosure, but that this disclosure will include all embodiments falling within the scope of the appended claims.

[Industrial Applicability]

i i5> The present disclosure is capable of minimizing waste of the expensive raw material germanium dioxide and maximizing the yield of monogermane gas during mass production of germane gas in commercial scale, by introducing an additional process.