A preparation method and application of disilane

Abstract

The present invention provides a method for preparing disilane and its application. The method comprises the following steps: introducing monosilane gas and other gases into a gas mixing device to be uniformly mixed, and then entering a plasma generating device, controlling the plasma electrical parameters. Finally, the reaction product disilane is taken out and enters a collection cold trap, and is filled into a steel cylinder to obtain a disilane product with a conversion rate of 90%. After the disilane prepared by this method is purified by secondary rectification, it is easy to obtain disilane with a purity of 99.999%. Then, a polysilicon thin film is prepared by LPCVD, and an Si layer grown under lower process temperature conditions is obtained.

Description

Technical Field

[0001] The present invention relates to a method for preparing a gas, and particularly to a method for preparing disilane and its application. Background Art

[0002] The development of disilane can be traced back to the early 20th century. In the 1920s and 1930s, scientists discovered the existence of disilane and conducted a series of studies. With the progress of technology and the continuous in-depth research, more and more studies and applications of disilane have been carried out.

[0003] The main uses of disilane are as follows: (1) It is used in the production of amorphous silicon film solar cells and electronic-grade crystalline silicon in electronic products. In the production of solar cells, the deposition rate of disilane on amorphous silicon wafers is much faster than that of silane, and the temperature can be reduced by 200 - 300 °C. (2) It is used in epitaxial and diffusion processes in semiconductor technology, and also in solar cells and the photosensitive drums for electrophotography. (3) In ion implantation, when disilane is used as the ion source, the beam current is strong and the effect is significantly better than using other gases as the ion source. (4) When using disilane, relatively inexpensive glass can be used to replace expensive quartz glass as the substrate for LCDs.

[0004] The main synthesis methods of disilane are the magnesium silicide ammonium chloride method, the reduction method of halogenated disilane, and the direct synthesis method of silane. Among them, in the magnesium silicide ammonium chloride method, the temperature is directly controlled in the reaction device to make magnesium silicide and ammonium chloride react directly to produce disilane. However, this reaction has the problems of low reaction selectivity and low disilane yield. The reduction method of halogenated disilane uses reducing agents such as lithium aluminum hydride or sodium aluminum hydride to reduce hexachlorodisilane to prepare disilane. This method has high selectivity and yield for disilane, but hexachlorodisilane is expensive, the product separation is difficult, the solvent is prone to produce a large amount of pollution, and the requirements for the reaction device are relatively high. In the direct synthesis method of silane, using silane as the initial raw material, silane can be converted into disilane through methods such as atomic excitation, thermal decomposition, photolysis, and glow discharge. The reaction formula is 2SiH4 → Si2H6 + H2. Among them, methods such as atomic excitation, photolysis, and glow discharge are all carried out under the condition of very low pressure of silane, and the reaction process is difficult, and the practical value of these methods is not high. Summary of the Invention

[0005] In order to solve the problems of high raw material cost, low product conversion rate, complex by-products generated during the preparation of disilane and difficult separation in the above technical background, the present invention provides a method for preparing disilane and its application.

[0006] The present invention provides the following technical solutions:

[0007] A method for preparing disilane and its application, comprising the following steps,

[0008] S1. Gas mixing: Feed silane gas and protective gas into the gas mixing device.

[0009] S2. Ionization discharge: The gas in the gas mixing device enters the plasma generating device through a flow meter.

[0010] S3. Condensation separation: The gas generated by the reaction in the plasma generating device is condensed and separated. The silane gas enters the gas mixing device through a gas return pipe, and the disilane mixed gas enters the cold trap.

[0011] S4. Secondary rectification: Subject the product in the cold trap to secondary rectification to obtain disilane.

[0012] Preferably, in S1, the purity of the silane gas is 99% - 99.99%, the protective gas is helium or argon, the purity of the protective gas is 99.9% - 99.999%, the water content in the gas mixing device is < 1 ppm, and the oxygen content is < 1 ppm.

[0013] Preferably, in S1, the volume ratio of the silane gas to the protective gas is 2:3 - 3:2, and the gas flow rate is 300 - 500 mL / min.

[0014] Preferably, in S2, the plasma generating device is preheated to 50 °C in advance, and the gas flow rate is 200 - 500 mL / min.

[0015] Preferably, the parameters of the plasma generating device in S2 are: voltage 15 - 30 kV, frequency 6 - 12 kHz, electric power 5 - 18 W. A temperature detector is provided in the plasma generating device. Since the temperature in the plasma generating device will decrease during the reaction, when the temperature reaches 50 °C again, the reaction is complete.

[0016] Preferably, in S3, the gas generated by the reaction in the plasma generating device is carried out by helium. The helium purge interval is 2 - 4 min, the disilane extraction rate is 0.12 - 0.2 g / h, the cooling temperature is -14 - -10 °C, and the cooling pressure is 0.2 MPa.

[0017] Preferably, in S3, the gas in the cold trap exchanges heat with liquid nitrogen, is cooled to -10 °C and then filled into a steel cylinder.

[0018] Preferably, first vaporize the product in the steel cylinder, the vaporization temperature is 30 - 40 °C, and then carry out secondary rectification. The conditions for secondary rectification are as follows.

[0019] The light component removal conditions are that the gas flow rate is 200 mL to 400 mL / min, the refrigerant temperature is -15°C to -10°C, the rectification pressure is 0.2 MPa to 0.3 MPa, the rectification temperature is -5°C to 10°C, and the removed light components are hydrogen, nitrogen, and silane;

[0020] The heavy component removal conditions are that the gas flow rate is 100 mL to 150 mL / min, the refrigerant temperature is -10°C to 0°C, the rectification pressure is 0.15 MPa to 0.25 MPa, the rectification temperature is 0°C to 5°C, and the removed heavy components are water and high silane;

[0021] Preferably, the purity of the prepared disilane is above 99.999%;

[0022] Preferably, for the disilane prepared by the method, when using LPCVD to prepare a polysilicon thin film, the deposition temperature is controlled at 330 - 380°C, the deposition pressure is 0.2 - 0.3 MPa, the volume flow rate of disilane is 200 - 700 mL / min, and the deposition time is 5 - 10 min.

[0023] Advantages of the present invention:

[0024] (1) The present invention selects silane gas as the raw material, which reduces costs. The purity of the silane gas is 99% - 99.99%, improves the product conversion rate, reduces by-products, and reduces the difficulty of subsequent separation and purification;

[0025] (2) The present invention provides a method for preparing disilane and its application. The method selects other gases as He or Ar, which can be effectively transformed into an excited state in a plasma electric field and collide effectively with silane gas, causing the silane gas to transform into SiH3· or SiH2· free radicals, and then transform into Si2H6;

[0026] (3) A low-temperature cold trap is connected in series behind the plasma generating device used in the present invention, making the entire device form a closed circulation system. Unreacted silane can be recycled through the circulation system to continue participating in the reaction, reducing economic costs while increasing the conversion rate of disilane. Finally, disilane with a conversion rate of 90% can be obtained, fully meeting the production needs of electronic gases;

[0027] (4) The product of the present invention undergoes two-step refining to obtain electronic-grade disilane. When preparing a polysilicon thin film subsequently, no further purification is required, and it can effectively reduce the deposition temperature of the film-forming reaction in the polysilicon thin film prepared by the LPCVD method, reduce process energy consumption, and shorten the deposition time. Description of the Drawings

[0028] Figure 1 It is a device diagram for preparing disilane.

[0029] Description of the reference numerals:

[0030] 1—First gas cylinder; 2—Second gas cylinder; 3—First flowmeter;

[0031] 4—Second flowmeter; 5—Gas mixing device; 6—Third flowmeter;

[0032] 7—Gas inlet pipe; 8—Plasma generating device; 9—Cold trap;

[0033] 10—Gas return pipe; 11—Gas outlet pipe. Detailed implementation manners

[0034] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is combined with Figure 1 and preferred embodiments to detail the specific implementation manners, structures, features and their effects according to the present invention as follows.

[0035] The device used in the present invention is as Figure 1 shown. Among them, the first gas cylinder 1 and the second gas cylinder 2 are respectively connected to the left side of the gas mixing device 5 through the first flowmeter 3 and the second flowmeter 4. The right side of the gas mixing device 5 is connected to the top of the plasma generating device 8 through the third flowmeter 6. The bottom of the plasma generating device 8 is connected to the left air inlet of the cold trap 9 through a pipeline. The top air outlet of the cold trap 9 is connected to the top of the gas mixing device 5 through a gas pipeline 10. A gas outlet pipe 11 is connected to the cold trap 9, and a gas inlet pipe 7 is connected to the plasma generating device 8.

[0036] Examples 1 - 3

[0037] As shown in Table 1, the main difference between Examples 1 - 3 lies in the different preparation process parameters. Taking Example 1 as an example,

[0038] (1) Gas mixing

[0039] First, evacuate and replace the inside of the gas mixing device 5, requiring the water content in the device < 1 ppm and the oxygen content < 1 ppm. Then, introduce the silane gas with a purity of 99% from the first gas cylinder 1 and the helium gas with a purity of 99.9% from the second gas cylinder 2 into the gas mixing device 5 through the first flowmeter 3 and the second flowmeter 4 respectively and mix them evenly. Control the ratio of silane gas to other gases to be 2:3, and control the flow rate to be 300 mL / min;

[0040] (2) Ionization discharge

[0041] First, preheat the plasma generating device 8 to a temperature of 50°C. Then, pass the gas in the gas mixing device 5 through the third flowmeter 6 into the plasma generating device 8, control the flow rate at 200 mL / min, and control the plasma electrical parameters: voltage 15 kV, frequency 6 kHz, and electric power 5 W. Determine whether the reaction occurs completely by measuring the temperature change of the plasma generating device 8. When the temperature is 50°C, the reaction is complete;

[0042] (3) Condensation separation

[0043] Carry the generated disilane gas out by helium gas 9 and blow the generated product into the collection cold trap 9. The disilane extraction rate is 0.12 - 0.2 g / h, the helium gas is purged through the gas inlet pipe 7 at intervals of 2 - 4 min, the cooling temperature is -14 to -10°C, the cooling pressure is 0.2 MPa, the disilane entering the collection cold trap 9 exchanges heat with liquid nitrogen, is cooled to -10°C, and then is filled into a steel cylinder through the gas outlet pipe 11. The unreacted monosilane gas and other gases return to the gas mixing device 5 through the gas reflux pipe 10 to continue participating in the reaction.

[0044] (4) Secondary rectification

[0045] The light component removal conditions are as follows: the gas flow rate is 200 mL / min, the refrigerant temperature is -15°C to -13°C, the rectification pressure is 0.2 MPa to 0.25 MPa, the rectification temperature is -5°C to 0°C, and the removed light components include hydrogen, nitrogen, and silane;

[0046] The heavy component removal conditions are as follows: the gas flow rate is 100 mL / min, the refrigerant temperature is -10°C to -5°C, the rectification pressure is 0.15 MPa to 0.2 MPa, the rectification temperature is 0°C to 5°C, and the removed heavy components include water and polysilane.

[0047] Prepare the electronic-grade disilane to form a polysilicon thin film by LPCVD method, and control the deposition parameters as shown in the table. The deposition temperature is 360°C, the disilane volume flow rate is 750 mL / min, and the deposition time is 6 min.

[0048] Table 1 Raw material mixing parameters

[0049]

[0050] Table 2 Ionization discharge parameters

[0051]

[0052]

[0053] Table 3 Secondary refining (light component removal) parameters

[0054]

[0055] Table 4 Secondary Refining (Debutanization) Parameters

[0056]

[0057] Table 4 LPCVD Method Deposition Parameters

[0058]

[0059]

[0060] Comparative Example 1

[0061] The main distinguishing technical feature between Comparative Example 1 and Example 1 is that the purity of the selected silane raw material is different. The purity of the silane raw material selected in Comparative Example 1 is 90%.

[0062] Comparative Example 2

[0063] The main distinguishing technical feature between Comparative Example 2 and Example 1 is that the technical parameter of the ionization discharge is that the voltage is selected as 10 kV.

[0064] Comparative Example 3

[0065] The main distinguishing technical feature between Comparative Example 3 and Example 1 is that the technical parameter of the ionization discharge is that the voltage is selected as 32 kV.

[0066] Comparative Example 4

[0067] The main distinguishing technical feature between Comparative Example 4 and Example 1 is that the selected deposition temperature is 300 degrees Celsius, and the polysilicon thin film is directly prepared by the LPCVD method.

[0068] Comparative Example 5

[0069] The main distinguishing technical feature between Comparative Example 5 and Example 1 is that the selected deposition temperature is different. The deposition temperature selected in Comparative Example 5 is 475 °C.

[0070] Performance Test and Results

[0071] The purity of disilane prepared in Examples 1 to 5 and Comparative Examples 1 to 3 was detected and the conversion rate of the final product was calculated. As shown in Table 5, the purity detection was performed using a TSQ Quantum Access MAX triple quadrupole mass spectrometer.

[0072] For the polysilicon films prepared in Examples 1 to 5 and Comparative Examples 4 to 5, performance detection was carried out. The average grain size was observed and measured by scanning electron microscopy, and the data are shown in Table 6.

[0073] Table 5

[0074] Sample Purity of disilane (%) Conversion rate of disilane (%) Example 1 99.9995 90.2 Example 2 99.9997 90.4 Example 3 99.9999 92 Example 4 99.9998 91.7 Example 5 99.9996 90.9 Comparative Example 1 95.67 80.7 Comparative Example 2 93.48 70.3 Comparative Example 3 94.32 77.4

[0075] Table 6

[0076] Sample Average grain size (nm) Example 1 73 Example 2 84 Example 3 95 Example 4 99 Example 5 103 Comparative Example 4 57 Comparative Example 5 96

[0077] As can be seen from Examples 1 to 5 in Table 5, the purity of disilane prepared by the present invention is above 5N. According to the preparation parameters of Example 3, the purity of disilane can reach 6N, and the conversion rates of the final products are all above 90%. However, the results of Comparative Examples 1 to 3 are inferior to those of Examples 1 to 5. This is because the purity of the raw material silane used in Comparative Example 1 is lower than the minimum purity limit of the present invention. Due to the low purity of the raw material, it directly leads to difficulties in subsequent separation, and the purity and conversion rate of the final product are lower than those of Comparative Example 1. In Comparative Example 2, a lower ionization pressure was selected. Since the ionization voltage is relatively low, He or Ar cannot be effectively converted into an excited state in the plasma electric field and collide effectively with the silane gas to convert the silane gas into SiH3· or SiH2· radicals, and then into Si2H6. In Comparative Example 3, a higher ionization voltage was used. Although it can quickly convert silane into disilane, due to the too high ionization pressure, the radicals generated by the collision combine to produce other by-products, resulting in the purity and conversion rate of disilane being lower than those of Example 1.

[0078] As can be seen from Table 6, when the temperature is relatively low, lower than the minimum temperature controlled by the present invention, the grain size is small and it does not have practical value. This is because when the temperature is low, the deposition rate of the crystal is slow. The grain sizes of Comparative Example 5 and Example 3 are equal. It can be seen that the temperature set by the present invention can meet the size of the polysilicon film in production, and can also reduce the deposition temperature and energy consumption.

[0079] The above is only a preferred embodiment of the present invention, and it does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing disilane, characterized in that: It includes the following steps: S1. Gas mixing: Feed silane gas and protective gas into the gas mixing device (5). S2. Ionization discharge: The gas in the gas mixing device (5) enters the plasma generating device (8) through the flowmeter (6). S3. Condensation separation: The gas generated by the reaction in the plasma generating device (8) is condensed and separated. The silane gas enters the gas mixing device (5) through the gas reflux pipe (10), and the disilane mixed gas enters the cold trap (9). S4. Secondary rectification: The product in the cold trap (9) is subjected to secondary rectification to obtain disilane. In S1, the volume ratio of the silane gas to the protective gas is 2:3 to 3:2, and the flow rate of the silane gas is 300 - 500 mL / min. In S3, the gas in the cold trap exchanges heat with liquid nitrogen, is cooled to -10 °C and then filled into a steel cylinder. First, the product in the steel cylinder is vaporized, and the vaporization temperature is 30 - 40 °C, and then secondary rectification is carried out. The conditions for secondary rectification are as follows: The conditions for light component removal are that the gas flow rate is 200 mL - 400 mL / min, the refrigerant temperature is -15 °C - -10 °C, the rectification pressure is 0.2 MPa - 0.3 MPa, and the rectification temperature is -5 °C - 10 °C. The light components removed are hydrogen, nitrogen, and silane. The conditions for heavy component removal are that the gas flow rate is 100 mL - 150 mL / min, the refrigerant temperature is -10 °C - 0 °C, the rectification pressure is 0.15 MPa - 0.25 MPa, and the rectification temperature is 0 °C - 5 °C. The heavy components removed are water and polysilane.

2. The preparation method of disilane according to claim 1, characterized in that In S1, the purity of the silane gas is 99% - 99.99%, the protective gas is helium or argon, the purity of the protective gas is 99.9% - 99.999%, the water content in the gas mixing device (5) is < 1 ppm, and the oxygen content is < 1 ppm.

3. The preparation method of disilane according to claim 1, characterized in that: In S2, the plasma generating device (8) is preheated to 50 °C in advance, and the gas flow rate is 200 - 500 mL / min.

4. The preparation method of disilane according to claim 1, characterized in that: The parameters of the plasma generating device (8) in S2 are: voltage 15 - 30 kV, frequency 6 - 12 kHz, electric power 5 - 18 W. A temperature detector is provided in the plasma generating device. When the temperature is 50 °C, the reaction is complete.

5. The preparation method of disilane according to claim 1, characterized in that: In S3, the gas generated by the reaction in the plasma generating device (8) is carried out by helium. The helium purge interval is 2 - 4 min, the disilane extraction rate is 0.12 - 0.2 g / h, the cooling temperature is -14 to -10 °C, and the cooling pressure is 0.2 MPa.

6. A method for preparing disilane according to any one of claims 1-5, characterized in that: The purity of the prepared disilane is above 99.999%.

7. Use of the disilane prepared according to any one of claims 1-5, characterized in that: For the disilane prepared by the said method, when using the LPCVD method to prepare a polysilicon thin film, control the deposition temperature at 330 - 380 °C, the deposition pressure at 0.2 - 0.3 MPa, the disilane volume flow rate at 200 - 700 mL / min, and the deposition time at 5 - 10 min.

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