JPS591211B2 - Monosilane continuous generation method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an improved method for preparing monosilane.

Monosilane gas is prized as an excellent raw material for producing semiconductor-grade silicon and as a raw material gas for silicon deposition in IC devices and amorphous solar cells, and demand is expected to increase.

Therefore, it is desired to develop a method for producing monosilane that is safe and inexpensive. There are various manufacturing methods for monosilane, but in order to obtain inexpensive monosilane, a recycling system that does not produce by-products is preferable, and as a method of this type, lithium hydride is used as disclosed in Japanese Patent Publication No. 39-3660. One example is a method in which monosilane is generated by a reaction between silicon and silicon tetrachloride.

That is, in the first step, molten salt containing lithium chloride is electrolyzed to obtain chlorine and metallic lithium, in the second step, metallic lithium is hydrogenated to form lithium hydride and dissolved in the molten salt, and in the third step In this method, silicon tetrachloride is reacted with lithium hydride dissolved in molten salt to obtain monosilane and lithium chloride.The chlorine obtained in the first step is converted into silicon tetrachloride by chlorinating raw material crude silicon, and in the third step The lithium chloride generated in the third step is used to replenish the consumption of lithium chloride in the first step, and all other components except silicon and hydrogen are recycled to obtain monosilane. As a means to do this, an electrolysis chamber, a hydrogenation chamber, and a monosilane generation chamber are provided independently, and the electrolysis chamber and hydrogenation chamber are connected to each other by a lithium transfer pipe and a molten salt transfer pipe. It is disclosed that the reaction products are sequentially transferred to the steps and the molten salt is refluxed to continuously obtain monosilane by connecting the electrolytic chamber and the electrolytic chamber through a molten salt transfer pipe. However, since this method handles highly corrosive substances, failures due to equipment corrosion are likely to occur, and it is difficult to control the transfer amount and flow, and to maintain the proper position of the liquid level in each chamber, making it difficult to maintain the composition of the molten salt. There are many difficulties, such as the fact that changes in the melting point are likely to occur due to local changes in the melting point.

This is also explained in JP-A-53-40000, where it is stated that the above-mentioned normal operating conditions are significantly worse than the optimal conditions for each reaction, and as a result, lithium hydride and A method is presented in which the reaction with silicon chloride is unavoidably batched. In order to solve the above-mentioned drawbacks, the present invention provides a lithium chloride electrolytic section in a sealed molten salt tank containing a molten salt consisting of lithium chloride and potassium chloride,
By connecting and providing a collection and transfer section for molten metallic lithium, a hydrogenation section, and a monosilane generation section, metallic lithium produced by electrolysis is guided to the hydrogenation chamber, hydrogenated, and dissolved in molten salt to form the monosilane generation chamber. The present invention proposes a method and an apparatus for continuously generating monosilane by reacting it with silicon tetrachloride that is sent to the reactor and blown into it.

According to the method of the present invention, (1) each reaction chamber other than the hydrogenation chamber and its connection parts are maintained at an appropriate temperature, (2) the concentration of molten salt is kept approximately uniform, and (3) complex shapes can be formed. (4) It has become easier to control the liquid level position of each part, and as a result, it has become possible to continuously and efficiently generate monosilane over a long period of time. The details of the present invention will be explained below with reference to the drawings.

FIG. 1 shows a cross-sectional structure of an embodiment of a continuous monosilane generation device manufactured to carry out the monosilane generation method of the present invention. A nickel molten salt tank 2 containing a molten salt 1 having a substantially eutectic composition of lithium chloride and potassium chloride is sealed with a lid 7, and a heating/cooling device 3
Always keep the molten salt concentration below 500°C, preferably 880°C.
The temperature is maintained between ℃ and 400℃. For safety, it has a sealed double structure with a built-in heating and cooling device 3 housed in an iron outer tank 4.
It is preferable to provide gas inlet/outlet ports 5 and 6 to introduce inert gas, and the double structure can prevent accidents due to unexpected breakage. The lid 7 has a cathode '13, an anode 11, and a positive and negative chamber 1.
7. All devices arranged in the molten salt tank 2, such as the metal lithium collection and transfer device 18, the hydrogenation chamber 19, the suction pipe 29, and the monosilane generation chamber 30, are fixed directly or indirectly;
Each is immersed in molten salt to the appropriate depth. 9
Claim 7, wherein the lithium chloride electrolysis section, the molten metal lithium collection and transfer section, the hydrogenation section, and the monosilane generation section are all attached to the lid of the molten salt tank and immersed in the molten salt. equipment.

10. The continuous monosilane generation device according to claim 7, wherein a cathode is provided at the center of the tenon of the molten salt tank, and an anode, a hydrogenation chamber, and a monosilane generation chamber are arranged opposite to the cathode on both sides.

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an improved method for preparing monosilane.

Monosilane gas is used as an excellent raw material for producing semiconductor-grade silicon, and as a raw material gas for silicon deposition in IC devices and amorphous solar cells, and demand is expected to increase.

Therefore, it is desired to develop a method for producing monosilane that is safe and inexpensive. There are various manufacturing methods for monosilane, but in order to obtain inexpensive monosilane, a recycling system that does not produce by-products is preferable, and as a method of this type, lithium hydride is used as disclosed in Japanese Patent Publication No. 39-3660. One example is a method in which monosilane is generated by a reaction between silicon and silicon tetrachloride.

That is, in the first step, molten salt containing lithium chloride is electrolyzed to obtain chlorine and metallic lithium, in the second step, metallic lithium is hydrogenated to form lithium hydride and dissolved in the molten salt, and in the third step In this method, silicon tetrachloride is reacted with lithium hydride dissolved in a molten salt to obtain monosilane and chloride.The chlorine obtained in the first step is converted into silicon tetrachloride by chlorinating raw material crude silicon. This is a method to obtain monosilane by refluxing the lithium chloride in the 3rd step and replenishing the lithium chloride generated in the 3rd step to replenish the lithium chloride consumed in the 1st step. As a means of carrying out this process, an electrolysis chamber, a hydrogenation chamber, and a monosilane generation chamber are provided independently. It is disclosed that the generation chamber and the electrolytic chamber are connected to each other by a molten salt transfer pipe, so that the reaction products are sequentially transferred to the steps, and the molten salt is refluxed to continuously obtain monosilane. However, in this method, since highly corrosive substances are handled, failures due to equipment corrosion are likely to occur, and it is difficult to control the transfer amount and flow, and to maintain the proper position of the liquid level in each chamber, making it difficult to maintain the proper position of the liquid level in each chamber. There are many difficulties, such as the possibility of changes in the melting point due to local changes in the composition.

This is also reflected in JP-A No. 53-40000, which states that the normal operating conditions mentioned above are extremely poor compared to the optimal conditions for each reaction, and it is difficult to find one.As a result, lithium hydride and tetrachloride A method is presented in which the reaction with silicon is forced into batches. In order to solve the above-mentioned drawbacks, the present invention provides a lithium chloride electrolytic section in a sealed molten salt tank containing a molten salt consisting of lithium chloride and potassium chloride,
By connecting and providing a collection and transfer section for molten metallic lithium, a hydrogenation section, and a monosilane generation section, metallic lithium produced by electrolysis is guided to the hydrogenation chamber, hydrogenated, and dissolved in molten salt to form the monosilane generation chamber. The present invention proposes a method and an apparatus for continuously generating monosilane by reacting it with silicon tetrachloride that is sent to the reactor and blown into it.

According to the method of the present invention, (1) each reaction chamber other than the hydrogenation chamber and its connection parts are kept at an appropriate level of sludge, (2) the concentration of molten salt is kept almost uniform, and (3) complex shapes (4) It has become easier to control the liquid level position in each part, and as a result, it has become possible to continuously and efficiently generate monosilane over a long period of time. The details of the present invention will be explained below with reference to the drawings.

FIG. 1 shows a cross-sectional structure of an embodiment of a continuous monosilane generation device manufactured to carry out the monosilane generation method of the present invention. A nickel-made molten salt tank 2 containing a molten salt 1 having a tenon-eutectic composition of lithium chloride and potassium chloride is sealed with a lid 7, and a heating/cooling device 3
Always keep the molten salt temperature below 500°C, preferably 880°C.
The temperature is maintained between ℃ and 400℃. For safety, it has a sealed double structure with a built-in heating and cooling device 3 housed in an iron outer tank 4.
It is preferable to introduce inert gas by providing gas inlet/outlet ports 5 and 6, and the double structure can prevent accidents due to unexpected breakage. The lid 7 has a cathode 13, an anode 11, and a positive and negative chamber 17.
All the devices arranged in the molten salt tank 2, such as the metal lithium collection and transfer device 18, the hydrogenation chamber 19, the suction pipe 29, and the monosilane generation chamber 30, are fixed directly or indirectly, and each device is melted to an appropriate depth. Soaked in salt. The above-mentioned devices attached to the lid do not necessarily need to be attached to the lid, but they can be easily extracted from the molten salt, making them extremely convenient for repairs and processing at the start and stop of operations. Also attached to the lid 7 are an anode chamber 17, a hydrogenation chamber 19, and a suction pipe 29. Inert gas is introduced into the space formed by the monosilane generating chamber 30 and the sealed molten salt tank through an inlet 9 provided in the lid 7, and is discharged through the exhaust port 10 while maintaining a constant positive pressure. By doing so, even if leakage occurs due to damage due to corrosion or the like in each of the chambers, it will not directly escape to the outside, and explosions due to accumulation and mixing of leaked gases can also be prevented, thereby maintaining safety. Furthermore, by measuring mixed gases in exhaust gas, it is possible to detect water content, operational abnormalities, and leaks due to equipment damage, and to safely control operations. By adopting a structure in which each of the chambers is arranged in a molten salt tank in this way, compared to the method of making each reaction chamber independent and sequentially connecting them with a shaft feed pipe as shown in the above-mentioned Japanese Patent Publication No. 36-3990, for example. The temperature of each chamber except the hydrogenation chamber can be made uniform and easily controlled, and the influence of fluctuations in the liquid level in each chamber on other chambers can be reduced. A carbon anode 11 and a nickel cathode 13 for electrolyzing lithium chloride are connected to conductive holding rods 12 and 14, respectively, and are attached to an insulating fixture 1.
5 to the lid 7, and is connected to a DC power source for electrolysis (not shown). The inside of the cathode holding rod 14 is water-cooled, and the part immersed in the molten salt is a solidified product 16 of the molten salt.
It is insulated by covering it with When a voltage necessary for electrolysis of lithium chloride is applied between the cathode and the anode, chlorine is generated at the anode, and is collected in the space above the liquid level in the anode chamber 17, which consists of a wire mesh in the part that is constantly submerged in the molten salt. The crude silicon is introduced into a chlorination apparatus (not shown).

On the other hand, molten metal lithium precipitates at the cathode, and as the amount of precipitate increases, it gathers at the upper edge along the cathode surface, separates from the tip of the cathode in the form of particles, and floats up. The floating lithium particles are collected by the trapping transfer device 18 on the cathode and transferred to the hydrogenation chamber 19 by buoyancy, and exit from the end of the trapping transfer device 18 in the hydrogenation chamber to the terminal. It enters a saucer 20, which has an inner diameter at least five times the inner diameter of the distal end and is provided downwardly just above the distal end. When lithium accumulates in the receiving tray, the terminal end is closed by lithium, but if the pressure inside the hydrogenation chamber is higher than that outside the chamber (molten salt tank), lithium also accumulates at the terminal end of the collecting and transferring device '18. The buoyancy of the lithium balances this pressure difference and prevents the molten salt from flowing back from the hydrogenation chamber to the cathode side through the collection and transfer device.

The hydrogenation chamber 19 promotes the hydrogenation reaction of lithium.
A heater chamber 21 into which an inert gas is introduced is provided around the outer periphery of the hydrogenation chamber, and the upper part of the molten salt is maintained at 500 to 550°C.

Hydrogen is blown into the space below the liquid through the blowing pipe 23, and the stirring action promotes hydrogenation and dissolution of lithium hydride into the molten salt. The lithium thus transferred to the hydrogenation chamber becomes lithium hydride, dissolves in the molten salt, and diffuses downward. A side pipe is provided below the hydrogenation chamber, and a suction pipe 29 is connected to the side pipe 27.
It is also connected to a monosilane generation chamber 30 by a side pipe 28. The suction pipe 29 is a device for sucking the molten salt and sending it into the hydrogenation chamber, and at the same time sending the molten salt in which lithium hydride is dissolved in the hydrogenation chamber to the monosilane generation chamber.
It consists of a tubular body whose lower part is open to the molten salt tank 2 and a gas blowing pipe 35 inserted deeper than the side pipe 27. controlled by the gas flow rate.

The monosilane generation chamber 30 is a U-shaped device in which two reaction tubes 31 and 32 having a symmetrical shape are connected at the bottom, and silicon tetrachloride blowing tubes 36 and 37 are respectively inserted into the reaction tubes close to the bottom. It has been installed.

The reaction tube 31 is connected to the side tube 28 of the hydrogenation chamber, and the reaction tube 32 is connected to the side tube 28 of the hydrogenation chamber.
The side pipe 34 is open into the molten salt tank 2. Since the two reaction tubes 31 and 32 are symmetrical, each blowing tube 3
If the flow rates of silicon tetrachloride blown from 6 and 37 are made equal,
The forces that transport the molten salt produced by the blowing are resisted. Therefore, the molten salt is transferred only by blowing inert gas into the suction pipe, so the flow rate of the molten salt can be controlled by the flow rate of the inert gas without being affected by the amount of silicon tetrachloride blown into the suction pipe. Can be easily controlled. Further, the pressure inside the hydrogenation chamber can be maintained higher than that in the molten salt tank 2. Therefore, in order to prevent the electrolytic current from decreasing due to the anode effect, it became possible to add lithium hydride little by little into the molten salt tank by simply providing a small hole at the bottom of the hydrogenation chamber. . Monosilane and lithium chloride are generated by the reaction between silicon tetrachloride blown into the monosilane generation chamber and lithium hydride in the molten salt. Monosilane is collected on the liquid surface of the reaction tube together with excess silicon tetrachloride, and after the silicon tetrachloride is separated in a cooler (not shown), it is sent to a purification device (not shown). Separated silicon tetrachloride is also recycled. On the other hand, the lithium chloride generated in the monosilane generation chamber increases the lithium chloride concentration of the molten salt transferred into the monosilane generation chamber. It is preferable that the mudness of the molten salt be as low as possible in order to reduce the decomposition loss of the monosilane produced and to increase the yield.

Lithium chloride and potassium chloride form a eutectic, and the eutectic composition shows the lowest melting point (352°C), but the deviation from the eutectic point increases the melting point by about 8°C/MOl%. Therefore, in order to perform stable operation with low mud, it is necessary to minimize local changes in composition to prevent solidification. Therefore, it is desirable to arrange the inlet of the suction pipe and the outlet from the monosilane generating chamber, that is, the side pipe 34, as close to the electrolytic electrode where the concentration of lithium chloride is reduced. It is possible to prevent excessive concentration increases and excessive concentration decreases near the electrodes. Furthermore, in the apparatus shown in FIG. 1, the anode chamber, the suction pipe, the hydrogenation chamber, and each reaction chamber are attached to the lid 7, and cooling is performed to protect the sealing material, insulating material, etc. of the attachment parts.

Therefore, the anode chamber, suction pipe, excluding the heated hydrogenation chamber,
The wall temperature of each reaction chamber drops rapidly above the liquid level in the molten salt tank 2, so if the liquid level in each of these chambers and the suction pipe becomes higher than the liquid level in the molten salt tank 2 outside, the molten salt Blockage accidents frequently occurred due to solidification and adhesion of mist, but this was resolved by adjusting the pressure so that it was lower than the liquid level in the molten salt tank. As explained in detail above, according to the method of the present invention, (1) the anode chamber other than the hydrogenation chamber, the suction pipe, each reaction chamber, and their connecting parts are uniformly heated and maintained at an appropriate temperature;
) Keep the concentration of molten salt almost constant, (3) Improve the safety of each part with a complex shape, (4) Make it easy to adjust the molten salt liquid level and gas injection amount in each part, and (5) Prevent unexpected Even if damage occurs, it can be detected early and safety can be maintained at the same time.

As a result, it has become possible to continuously generate monosilane efficiently over a long period of time.

Example 1 Pure nickel was used for all parts of the device that were immersed in molten salt except for the anode.

The molten salt of lithium chloride and potassium chloride used was selected to be around 60 mol% of potassium chloride. Approximately 450 kg of molten salt is placed in a 4001 volume molten salt tank at 330°C to 40'C.
The temperature was maintained at .

Prior to the reaction, the molten salt was dehydrated by blowing inert gas and low voltage electrolysis. The anode used was graphite containing a large amount of amorphous carbon. The temperature of each reaction chamber was the same as that of the molten salt tank except for the hydrogenation chamber, and the hydrogenation chamber was set at 500°C. A smooth direct current of 5.5 volts was connected to the cathode and anode, and reactions such as electrolysis of lithium chloride, hydrogenation of molten metal lithium, generation of silicon tetrachloride, and generation of monosilane were carried out for 150 hours. The electrolytic current value was approximately 1,000 Anghers. The average production rate of monosilane was 2.51 per minute. During electrolysis, a large decrease in current value was observed, which was thought to be due to the anode effect. Example 2 In an experiment similar to Example 1, several grams of lithium hydride was introduced into a sealed molten salt tank when the current value decreased, and electrolysis was carried out by lowering the electrolytic voltage to 1 volt.

After a few minutes, check that the current has dropped and then turn it back on to 5.5.
When the voltage was increased to volts, the current value returned to its original value of 1000 amps, and the amount of monosilane produced was also approximately 2.51 per minute.
was gotten. Example 3 In an experiment similar to Example 1, a pipe with an inner diameter of 3 mm was connected to the bottom of the hydrogenation chamber to prevent the anode effect, and hydrogenation was carried out by adjusting the amount of gas blown to move the molten salt. A small amount of molten salt containing dissolved lithium was continuously discharged from the pipe into the molten salt bath.

The amount released was controlled to be less than 1% of the total lithium hydride to prevent large amounts of hydrogen chloride from being generated at the anode.
Production of monosilane was continued for approximately the same time as in Example 1, but no anode effect was observed. Furthermore, the production amount of monosilane was guaranteed to be 2.51 per minute. Example 4 In the above example, electrolytic corrosion was observed in a part of the pure nickel device near the electrolytic part.

Particularly, the degree of electrolytic corrosion tended to be large in areas close to the cathode, and the degree of electrolytic corrosion also tended to increase when the electrolytic voltage was increased. In order to prevent electrolytic corrosion, the pure nickel device was electrically connected to the cathode through a resistor of about 100 ohms, and the pure nickel device was tested for electrolytic corrosion. When a current of 1000 amps flowed between the cathode and anode, the current value of the approximately 100 ohm resistor section was 0.1 amps. After generating monosilane for a long time, we inspected the product for the presence of electrolytic corrosion and found that there was almost no electrolytic corrosion. Example 5 In an experiment similar to Example 1, a portion of the inert gas introduced into the molten salt tank was fractionated using an automatic gas sampling device and introduced into a gas chromatograph. During normal operation, approximately 100p was collected.
PM chlorine was detected.

When the flow rate balance of silicon tetrachloride blown into the silane generating section was significantly disrupted, silicon tetrachloride was detected on the gas chromatograph, but when the flow rate balance was restored to normal, it was no longer detected. When the dew point of the inert gas was continuously measured in conjunction with a gas chromatograph, it was normally -80°C or lower. When a small amount of water leaked from a pinhole in the cooling water jacket, the dew point rose rapidly, so operation was stopped to ensure safety. Example 6 In an experiment similar to Example 1, when the liquid level in the device where gas is blown or generated inside the molten salt plant was made to be the same as the molten salt liquid level outside, hydrogen The molten salt solidified on the walls near the liquid level in the above apparatus except for the oxidation chamber.

In particular, the solidification of the liquid level in the silane generation chamber and suction pipe was significant.
Solidification could be prevented by lowering the liquid level in the above apparatus, excluding the hydrogenation chamber, to 5C7n below the outside molten salt liquid level. Furthermore, by increasing the diameter of the silane generation chamber and suction pipe near the liquid level, it was possible to prevent the liquid level from solidifying within a range of 5 CTn of liquid level fluctuation in the silane generation chamber and suction pipe. Example 7 As an improved version of the apparatus shown in FIG. 1, a cathode was provided approximately in the center of the molten salt tank, and on both sides of the cathode were placed field electrodes, a hydrogenation chamber, a monosilane generation chamber, and a suction pipe. A continuous generator was constructed.

When an experiment was conducted using this device under all other conditions except for the electrolytic current value as in Example 1, the electrolytic current value was 2000.
The average production of monosilane obtained for Anhair was 52/min.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of the device according to the present invention. 1: Molten salt, 2: Molten salt tank, 3: Heating/cooling device, 5: Gas inlet, 6: Gas outlet, 7: Lid, 11: Anode, 13
: cathode, 17: anode chamber, 18: metal lithium collection and transfer device, 19: hydrogenation chamber, 29: suction pipe, 30: monosilane generation chamber.

Claims (1)

[Claims] 1. A method for producing monosilane by hydrogenating metallic lithium obtained by electrolysis of lithium chloride to produce lithium hydride, and reacting the lithium hydride with silicon tetrachloride, the method comprising: lithium chloride and potassium chloride; of molten salt is accommodated,
Metallic lithium is produced by electrolysis in a sealed molten salt tank that is equipped with an electrode, a suction pipe that communicates with the molten salt, a hydrogenation chamber, and a monosilane generation chamber, and has a space above the surface of the molten salt. The generated lithium metal is collected and transferred to a hydrogenation chamber maintained at a predetermined temperature higher than the temperature of the molten salt tank for hydrogenation, and the generated lithium hydride is converted into molten salt in the hydrogenation chamber. A method for continuously generating monosilane, which comprises dissolving lithium hydride, and then sending the molten salt in which lithium hydride is dissolved to a monosilane generating chamber to react with silicon tetrachloride in the monosilane generating chamber. 2. The method according to claim 1, wherein a part of the molten salt in which lithium hydride is dissolved is discharged directly from the hydrogenation chamber into the molten salt tank. 3 The molten salt in which lithium hydride is dissolved is refluxed from the hydrogenation chamber to the monosilane generation chamber and into the molten salt tank by blowing inert gas and silicon tetrachloride gas below the liquid level in the suction pipe and monosilane generation chamber, respectively. The method according to claim 1, wherein 4. During the reaction, the molten salt tank and metal devices such as the metal lithium collector, hydrogenation chamber, and monosilane generation chamber placed therein are continuously connected to the cathode and the metal devices by a DC voltage circuit or electric resistance. 2. The method according to claim 1, wherein the potential is maintained at a positive potential with respect to the potential of the cathode by connecting through the body. 5. The method according to claim 1, wherein an inert gas is introduced into the closed space above the liquid level of the molten salt tank, and the reaction is controlled by measuring the concentration of the reactant gas contained in the discharged inert gas. Method. 6. Claim 1, which does not have a heating mechanism disposed in the molten salt tank and maintains the liquid level in the device where gas is blown and/or generated at a lower level than the molten salt liquid level outside. Method described. 7 A continuous monosilane generation device in which a lithium chloride electrolysis section, a molten metal lithium collection and transfer section, a hydrogenation section, and a monosilane generation section are connected in a molten salt tank containing molten salts of lithium chloride and potassium chloride. . 8 A patent claim in which a molten salt tank containing molten salts of lithium chloride and potassium chloride is housed in a container with a built-in heater and cooler, and has a sealed double structure between which an inert gas can be introduced and discharged. The device according to scope item 7. 9. Claim 7, in which the lithium chloride electrolysis section, the molten metal lithium collection and transfer section, the hydrogenation section, and the monosilane generation section are all attached to the lid of the molten salt tank and immersed in the molten salt. The device described. 10. The continuous monosilane generation device according to claim 7, wherein a cathode is provided substantially in the center of the molten salt tank, and an anode, a hydrogenation chamber, and a monosilane generation chamber are arranged facing each other on both sides of the cathode.