A method for reducing the content of impurity boron in electronic grade polysilicon

Abstract

The present application relates to the technical field of electronic grade polysilicon production, and discloses a method for reducing the content of impurity boron in electronic grade polysilicon, which comprises: heating a silicon rod while introducing a gas phase, wherein the gas phase comprises H2 and SiHCl3 containing trace BCl3 impurities; when the SiHCl3 containing trace BCl3 impurities is introduced, the temperature of the gas phase is controlled to be 400-600 DEG C; when the temperature of the gas phase is increased to the set temperature, the heating rate of the silicon rod is accelerated, the temperature of the reduction furnace is increased to 950-1200 DEG C, and the temperature of the gas phase on the surface of the silicon rod is maintained at 950-1200 DEG C; the SiHCl3 containing trace BCl3 impurities is introduced for 100-105 h, the total production time is 110-120 h, and H2 is introduced throughout the whole process. Through temperature control and gas flow control in three stages, the method realizes accurate control of the polysilicon production process, avoids excessive introduction of boron impurities, and optimizes the energy consumption and production efficiency of the reduction furnace.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic grade polysilicon production and preparation, in particular to a method for reducing the content of boron impurities in electronic grade polysilicon. BACKGROUND

[0002] Electronic grade polysilicon is a high-purity silicon material, mainly used for the production of semiconductor devices and solar cells and other high-tech products. Due to its excellent semiconductor performance and environmental advantages, electronic grade polysilicon has been widely concerned and applied in China.

[0003] Siemens method as the leading process of electronic grade polysilicon production, the global total production accounts for more than 90%, but its core production technology has been controlled by foreign countries for a long time. The quality of China's electronic grade polysilicon products is subject to a key factor, that is, the content of boron impurities in the product produced by the CVD reactor is too high, which is 3-4 times that of foreign Waloc company. China's research on boron impurities mainly focuses on reducing the content of impurity BCl3 in the reaction raw material SiHCl3 through rectification method. At present, the content of BCl3 in SiHCl3 has been reduced to below 0.1 ppb, reaching the international leading level, which is comparable to Waloc company. After rectification, SiHCl3 and H2 gas enter the Siemens reduction furnace, and chemical vapor deposition occurs on the surface of the silicon rod to generate polysilicon. However, there is still a big gap between the quality of polysilicon produced by the reduction furnace in China and the international advanced level, and the content of boron impurities is 3-4 times that of Waloc company. Therefore, it is particularly important to explore how to reduce the deposition amount of boron on the polysilicon rod during the chemical vapor deposition process in the Siemens reduction furnace.

[0004] For the research of Si-B-H-Cl system, the mainstream direction focuses on boron-doped silicon thin film, and the core is to use high-concentration BCl3 as a dopant to promote the uniform deposition of B on the Si substrate by adjusting the experimental conditions. The basis of this process is that SiHCl3 and BCl3 both contain Cl - , so they show similar surface chemical reactions on the surface of the silicon substrate. However, there is no relevant research report on the inhibition of B deposition on the silicon substrate, especially the inhibition strategy of B impurities in the process of chemical vapor deposition of electronic grade polysilicon in the Siemens reduction furnace.

[0005] Therefore, it is particularly important to invent a new method for inhibiting B impurities in the production of electronic grade polysilicon. SUMMARY

[0006] A large number of experimental studies have confirmed that under low temperature conditions, BCl3 occurs homogeneous reaction under the action of H2 to generate BHCl2 and HCl; when the temperature is increased to a specific value, BCl3 occurs heterogeneous reaction under the action of H2 to generate solid phase B deposited on the silicon substrate; when the temperature is continuously increased, BCl3 realizes homogeneous reaction under the action of H2 to generate BCl x , BH x , BHCl2 and other gas phases, and at the same time, the solid phase B deposited on the silicon substrate is etched under the action of HCl to generate BCl x into the gas phase. In view of this, the present application provides a method for reducing the impurity boron in electronic-grade polysilicon, aiming at solving the problem of excessive impurity boron content in electronic-grade polysilicon in the prior art. That is, by adjusting the gas phase temperature by regulating the convection heat transfer intensity in the Siemens reduction furnace, BCl3 is converted into BHCl2, BCl x , BH x and other gas phases are discharged with the reduction tail gas, the deposition amount of B on the polysilicon rod is reduced, the effective control of the impurity boron content in the electronic-grade polysilicon product is realized, and the product quality is improved. The method is simple in operation, low in cost, and can be applied to most chemical vapor deposition systems.

[0007] The present application provides a method for reducing the impurity boron content in electronic-grade polysilicon, comprising the following steps:

[0008] The silicon rod is heated at the same time, and a gas phase is introduced, wherein the gas phase comprises H2 and SiHCl3 containing trace BCl3 impurities;

[0009] When SiHCl3 containing trace BCl3 impurities is introduced, the temperature of the silicon rod is controlled to warm the gas phase to 400-600 DEG C;

[0010] When the temperature of the gas phase is increased to the set temperature, the heating rate of the silicon rod is increased, the temperature of the reduction furnace is increased to 950-1200 DEG C, and the temperature of the gas phase on the surface of the silicon rod is maintained at 950-1200 DEG C;

[0011] The time for introducing SiHCl3 containing trace BCl3 impurities is 100-105 h, and the total production time is 110-120 h, and H2 is introduced throughout the process.

[0012] Preferably, the method for reducing the impurity boron content in electronic-grade polysilicon is carried out in a reduction furnace.

[0013] Preferably, the reduction furnace is a reduction furnace with a two-ring arrangement design of an outer ring and an inner ring;

[0014] The silicon rod heating mode is simultaneous heating of the silicon rod in the inner ring and the outer ring;

[0015] The inner ring silicon rod is continuously heated; the temperature of the outer ring silicon rod reaches 1100℃, and then is paused for 20 minutes, and then is heated for 1 hour, to implement the cycle intermittent heating.

[0016] Preferably, the heating mode of the reduction furnace is direct current- alternating current mixed electric heating at the bottom end of the silicon rod.

[0017] Preferably, the heating mode of the reduction furnace is:

[0018] When the radius of the silicon rod reaches 7cm, the direct current heating is converted to alternating current heating, and the inner and outer rings are heated at the same time;

[0019] When the radius of the silicon rod grows to 10cm, the power supply is stopped.

[0020] Preferably, while the silicon rod is heated, the gas phase is introduced, including:

[0021] H2 is introduced while the silicon rod is heated to 1000-1200℃, and after maintaining for 2-3 hours, SiHCl3 containing trace BCl3 impurities is introduced;

[0022] The content of BCl3 in the SiHCl3 is 0.01ppb-0.3ppb; the operating pressure is 4-7atm; and the gas inlet temperature is 80-100℃.

[0023] Preferably, the amount of H2 introduced is 800-5000m 3 / h, the amount of SiHCl3 containing trace BCl3 impurities introduced is 800-1500m 3 / h, and the gas inlet speed is 8-60m / s.

[0024] Preferably, the initial gas inlet temperature is 80-100℃, the initial amount of H2 introduced is 1800-2000m 3 / h, the initial amount of SiHCl3 introduced is 400-500m 3 / h, and the initial gas inlet speed is 8-10m / s.

[0025] Preferably, when the gas phase temperature grows to 400-600℃, the flow rate of H2 is 4000-5000m 3 / h, the amount of SiHCl3 introduced is 600-1000m 3 / h, and the gas inlet speed is 30-60m / s.

[0026] When the surface gas phase temperature of the silicon rod rapidly rises to 950-1200℃, the flow rate of H2 is 4000-5000m 3 / h, the amount of SiHCl3 introduced is 800-1500m 3 / h, and the gas inlet speed is 50-60m / s.

[0027] The application further provides an electronic-grade polysilicon prepared by any of the methods for reducing the content of impurity boron in electronic-grade polysilicon.

[0028] Compared with the prior art, the application has the beneficial effects that:

[0029] The method adjusts the gas phase temperature by controlling the heating rate in the reduction furnace, and adjusts the heating mode and heating temperature of the silicon rod, so as to reduce the impurity boron in the electronic-grade polysilicon while improving the production efficiency and product quality of the polysilicon. Specifically, the method realizes precise control of the polysilicon production process through three-stage temperature control and gas flow control, avoids excessive introduction of boron impurities, and optimizes the energy consumption and production efficiency of the reduction furnace. Therefore, the method has good practicability and popularization value, and can provide an effective technical means for the production of electronic-grade polysilicon. DETAILED DESCRIPTION

[0030] Exemplary embodiments of the present disclosure will be described in more detail below. Although the following embodiments show exemplary embodiments of the present disclosure, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be accurately conveyed to those skilled in the art. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments.

[0031] The application discloses a method for reducing the content of impurity boron in electronic-grade polysilicon, comprising:

[0032] The reduction furnace is an industrial Siemens 12 pair rod reduction furnace, arranged in a 2-ring manner, and the silicon rods are heated by direct current. The inner ring of silicon rods is continuously heated, and the temperature of the outer ring of silicon rods reaches 1000-1200℃, then paused for 10-30min, and then heated for 1h intermittently. The gas phase introduced into the reduction furnace is SiHCl3 and H2; the time for introducing SiHCl3 into the reduction furnace is 100-105h, the total production time is 110-120h, H2 is introduced throughout the process, the gas purity is 9-12N, and the molar ratio of SiHCl3 to H2 is 1:2-7.

[0033] H2 is introduced while heating the silicon rods to 1000-1200℃ for 2-3h, then SiHCl3 is introduced, the BCl3 content in SiHCl3 is 0.01ppb-0.3ppb, the operating pressure is 4-7atm, the gas inlet temperature is 80-100℃, the H2 introduction amount is 800-5000m 3 / h, and the SiHCl3 gas inlet amount is 800-1500m 3The inlet velocity of the gas is 8-60 m / s.

[0034] The method for reducing boron in the electronic grade polysilicon comprises three stages.

[0035] (1) The first stage is to introduce SiHCl3 containing trace BCl3, to inhibit the convection heat exchange in the reduction furnace, to slowly increase the gas phase temperature to 400-600°C, and to promote BCl3 to convert into BHCl2 and stay in the gas phase.

[0036] (2) The second stage is to increase the gas phase temperature in the reduction furnace to 400-600°C, to strengthen the convection heat exchange in the reduction furnace, to quickly increase the gas phase temperature on the surface of the silicon rod to 950-1200°C, to inhibit the reduction reaction of BCl3 and H2, and to reduce the deposition amount of solid phase B on the silicon rod.

[0037] (3) The third stage is to maintain the gas phase temperature on the surface of the silicon rod in the reduction furnace at 900-1200°C, to make SiHCl3 sufficiently reduce into Si, to make BCl3 convert into BCl, BH and BHCl2, and to exert the etching effect of HCl on the solid phase B on the silicon rod, so as to further reduce the B content in the electronic grade polysilicon product. x x

[0038] After the silicon rod is heated at a speed of 60-80°C / h to increase the gas phase temperature to 400-600°C, the H2 flow is increased to 4000-5000 m 3 / h, the SiHCl3 inlet amount is 600-1000 m 3 / h, and the inlet velocity is 30-60 m / s, and the silicon rod heating mode is direct current heating, and the inner and outer rings are heated simultaneously.When the silicon rod is heated at a speed of 130-170°C / h to increase the gas phase temperature on the surface of the silicon rod to 950-1200°C, the H2 flow is 4000-5000 m 3 / h, the SiHCl3 inlet amount is 800-1500 m 3 / h, and the inlet velocity is 50-60 m / s, the alternating current heating is converted when the radius of the silicon rod reaches 7 cm, the inner and outer rings are heated simultaneously, and the silicon rod is stopped from being electrified when the radius of the silicon rod increases to 10 cm.

[0039] The method of the present application is described below through specific examples.

[0040] Example 1

[0041] ​H2was introduced while heating the silicon rod to 1100℃ for 2.5h, then SiHCl3was introduced, the BCl3content in SiHCl3was 0.01ppb, the operation pressure was 6atm, the initial gas inlet temperature was 100℃, the initial H2inlet amount was 2000m 3 / h, the initial SiHCl3inlet amount was 500m 3 / h, and the initial gas inlet speed was 15m / s.

[0042] The reduction furnace was an industrial Siemens 12 pair rod reduction furnace, arranged in 2 rings, the silicon rod heating method was direct current heating, the inner ring silicon rod was continuously heated, the outer ring silicon rod was heated for 1h after being heated to 1100℃ for 20min, and then intermittently heated.

[0043] After the gas phase temperature was slowly increased to 500℃ (at a speed of 70℃ / h), the H2flow was increased to 4000m 3 / h, the SiHCl3inlet amount was 600m 3 / h, the gas inlet speed was 50m / s, the silicon rod heating method was direct current heating, and the inner and outer rings were heated simultaneously.

[0044] The silicon rod surface gas phase temperature was rapidly increased to 1000℃ (at a speed of 150℃ / h), the H2flow was 4500m 3 / h, the SiHCl3inlet amount was 1100m 3 / h, the gas inlet speed was 50m / s, when the silicon rod radius reached 7cm, the alternating current heating was converted, the inner and outer rings were heated simultaneously, and the silicon rod radius was increased to 10cm when the power was stopped.

[0045] The SiHCl3introduction time in the reduction furnace was 105h, the total production time was 110h, H2was introduced throughout the process, the polycrystalline silicon rod was taken out after the reduction furnace was cooled to room temperature, and the B concentration was detected, the results showed that the B content was reduced from 0.68ppb to 0.12ppb, a reduction of 82.35%, the base phosphorus resistivity was increased from 1121Ω˙cm to 2336Ω˙cm, an increase of 108.39%, and the minority carrier lifetime was increased from 983μs to 1967μs, an increase of 100.10%.

[0046] Example 2

[0047] H2was introduced while heating the silicon rod to 1200℃ for 3h, then SiHCl3was introduced, the BCl3content in SiHCl3was 0.015ppb, the operation pressure was 5atm, the initial gas inlet temperature was 150℃, the initial H2inlet amount was 1500m 3 / h, the initial SiHCl3inlet amount was 800m 3 / h, the initial gas inlet speed was 30m / s.

[0048] The reduction furnace is an industrial Siemens 12-pair rod reduction furnace with a two-ring arrangement. The silicon rods are heated by direct current. The inner ring silicon rods are continuously heated, and the outer ring silicon rods are paused for 20 minutes after reaching 1200℃, and then heated for another 2 hours, with intermittent heating.

[0049] After controlling the gas phase temperature to slowly increase to 550℃, increase the H2 flow rate to 5000 m³ / h. 3 / h, SiHCl3 intake flow rate is 1000m³ 3 The intake velocity is 60 m / s, and the silicon rod is heated by DC electric heating, with both the inner and outer rings heated simultaneously.

[0050] The surface gas temperature of the silicon rod rapidly increased to 1000℃, the H2 flow rate was 5000 m3 / h, and the SiHCl3 inlet flow rate was 1200 m³ / h. 3 The air intake speed is 60m / s. When the silicon rod radius reaches 7cm, it switches to AC heating, heating both the inner and outer rings simultaneously. The power supply stops when the silicon rod radius grows to 10cm.

[0051] SiHCl3 was introduced into the reduction furnace for 115 hours, and the total production time was 120 hours. H2 was introduced throughout the process. After the reduction furnace cooled to room temperature, the polycrystalline silicon rod was removed and the boron concentration was measured. The results showed that the boron content decreased from 0.68 ppb to 0.30 ppb, a reduction of 91.18%. The basic phosphorus resistivity increased from 1121 Ω·cm to 1978 Ω·cm, an increase of 43.33%. The minority carrier lifetime increased from 983 μs to 1526 μs, an increase of 55.24%.

[0052] Example 3

[0053] H2 was introduced while the silicon rod was heated to 1000℃ and maintained for 2 hours, followed by the introduction of SiHCl3. The BCl3 content in SiHCl3 was 0.01 ppb. The operating pressure was 6 atm, the initial inlet temperature was 50℃, and the initial H2 flow rate was 4000 m³ / h. 3 / h, the initial intake flow rate of SiHCl3 is 1000m³. 3 / h, with an initial intake velocity of 10m / s;

[0054] The reduction furnace consists of 12 pairs of rods arranged in two rings. The silicon rods are heated by direct current. The inner ring silicon rods are continuously heated, while the outer ring silicon rods are paused for 10 minutes after reaching 1000℃, and then heated for another 5 hours, with intermittent heating.

[0055] After controlling the gas phase temperature to slowly increase to 470℃, the H2 flow rate was increased to 5000 m³ / h. 3 / h, SiHCl3 flow rate is 800m 3 / h, the inlet gas velocity is 60 m / s, the silicon rod heating mode is direct current heating, and the inner ring and the outer ring are heated simultaneously.

[0056] The gas phase temperature on the surface of the silicon rod is rapidly increased to 1000℃, the H2 flow rate is 5000 m 3 / h, the SiHCl3 inlet gas amount is 1500 m 3 / h, the inlet gas velocity is 55 m / s, when the silicon rod radius reaches 7 cm, the alternating current heating is converted, the inner ring and the outer ring are heated simultaneously, the silicon rod radius is increased to 10 cm, and the power supply is stopped.

[0057] The SiHCl3 is introduced into the reduction furnace for 100 h, the total production time is 110 h, H2 is introduced throughout the whole process, the polycrystalline silicon rod is taken out after the reduction furnace is cooled to room temperature, and the B concentration is detected, and the results show that the B content is reduced from 0.68 ppb to 0.03 ppb, a reduction of 95.59%, the base phosphorus resistivity is increased from 1121 Ω·cm to 2968 Ω·cm, an increase of 164.76%, and the minority carrier lifetime is increased from 983 μs to 2554 μs, an increase of 159.82%.

[0058] In summary, it can be understood that the method for reducing the impurity boron in electronic-grade polycrystalline silicon is proposed, the method mainly controls the gas phase temperature in the reduction furnace and the introduction amount of hydrogen and silicon trichloride, and effectively controls the impurity boron in the polycrystalline silicon. The method comprises the following stages:

[0059] In the first stage, SiHCl3 containing trace BCl3 impurities is introduced, and the convection heat transfer intensity in the reduction furnace is inhibited, so that the gas phase temperature is slowly increased to 400-600℃. In this stage, BCl3 is more converted into BHCl2 and stays in the gas phase, thereby reducing the impurity boron content in the polycrystalline silicon.

[0060] In the second stage, when the gas phase temperature in the reduction furnace is increased to 400-600℃, the convection heat transfer in the furnace is strengthened, so that the gas phase temperature on the surface of the silicon rod is rapidly increased to 950-1200℃. In this stage, by increasing the hydrogen flow rate and the inlet amount of silicon trichloride, the reduction reaction of BCl3 and H2 is inhibited, and the deposition amount of solid-phase B on the silicon rod is reduced.

[0061] In the third stage, the gas phase temperature on the surface of the silicon rod in the reduction furnace is maintained at 900-1200℃, SiHCl3 is sufficiently reduced into Si, and BCl3 is converted into BCl x , BH x and BHCl2. At the same time, the dissolution of HCl to the solid-phase B on the silicon rod is utilized, and the B content in the electronic-grade polycrystalline silicon product is further reduced.

[0062] During the whole process, by accurately controlling the temperature of gas phase and reasonably adjusting the amount of hydrogen and silicon trichloride, the content of impurity boron in polysilicon product can be effectively reduced while ensuring the quality of polysilicon product. In addition, the present application also adopts the combination of direct current heating and alternating current heating, so that the silicon rod is heated more uniformly, and the production efficiency is improved.

[0063] In summary, the present application provides an effective and controllable method for reducing the content of impurity boron in electronic-grade polysilicon, which is of great significance for improving the quality of polysilicon product and meeting the demand of electronic industry for high-purity polysilicon.

[0064] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application and not to limit it, although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that: the specific embodiments of the present application can still be modified or replaced equivalently without departing from the spirit and scope of the present application, any modification or equivalent replacement thereof should be covered within the protection scope of the claims of the present application.

Claims

1. A method of reducing the content of the impurity boron in electronic grade polysilicon, characterized in that, The method comprises the following steps: heating the silicon rod while passing a gas phase comprising H2 and SiHCl3 containing trace amounts of BCl3 impurities; when passing SiHCl3 containing trace amounts of BCl3 impurities, the temperature of the silicon rod is controlled to raise the temperature of the gas phase to 400-600℃; when the temperature of the gas phase is raised to the set temperature, the temperature rising rate of the silicon rod is accelerated, the temperature of the reduction furnace is raised to 950-1200℃, and the temperature of the gas phase on the surface of the silicon rod is maintained at 950-1200℃; the time for passing SiHCl3 containing trace amounts of BCl3 impurities is 100-105h, the total production time is 110-120h, and H2 is passed throughout the whole process; the method for reducing the content of impurity boron in electronic-grade polysilicon is carried out in a reduction furnace with a two-ring arrangement design of an outer ring and an inner ring.

2. The method for reducing the content of impurity boron in electronic-grade polysilicon according to claim 1, characterized in that, the heating mode of the silicon rod is simultaneous heating of the silicon rod in the inner ring and the outer ring; wherein the silicon rod in the inner ring is continuously heated; the temperature of the silicon rod in the outer ring is maintained at 1100℃ for 20min, and then heated for another 1h to implement cyclic intermittent heating.

3. The method of claim 2, wherein the electron grade polysilicon is reduced in boron content by, The heating mode of the reduction furnace is direct current- alternating current mixed electric heating of the bottom end of the silicon rod.

4. The method of claim 2, wherein the electron grade polysilicon is reduced in boron content by, The heating mode of the reduction furnace is: when the radius of the silicon rod reaches 7cm, the direct current heating is converted to alternating current heating, and the inner ring and the outer ring are simultaneously heated; when the radius of the silicon rod grows to 10cm, the power supply is stopped.

5. The method of claim 1, wherein the electronic grade polysilicon is reduced boron content polysilicon. When the gas phase is passed while the silicon rod is heated, it comprises: passing H2 while heating the silicon rod to 1000-1200℃, and then passing SiHCl3 containing trace amounts of BCl3 impurities after maintaining for 2-3h; wherein the content of BCl3 in the SiHCl3 is 0.01ppb-0.3ppb; the operating pressure is 4-7atm; and the inlet gas temperature is 80-100℃.

6. The method of claim 1, wherein the electronic grade polysilicon is reduced boron content polysilicon. H2 flow rate 800-5000 m 3 SiHCl3 flow rate 800-1500 m 3 Gas inlet velocity 8-60 m / s.

7. The method of claim 6, wherein the electron grade polysilicon is reduced in boron content by, The initial intake temperature is 80-100°C, the initial intake amount of H2 is 1800-2000 m 3 / h, the initial intake amount of SiHCl3 is 400-500 m 3 / h, and the initial intake speed is 8-10 m / s.

8. The method of claim 7, wherein the electron grade polysilicon is reduced in boron content by, When the gas phase temperature increases to 400-600℃, the H2 flow rate is 4000-5000 m 3 / h, the SiHCl3 flow rate is 600-1000 m 3 / h, and the inlet velocity is 30-60 m / s. When the surface gas phase temperature of the silicon rod is rapidly increased to 950-1200℃, the H2 flow rate is 4000-5000 m 3 / h, the SiHCl3 gas inlet amount is 800-1500 m 3 / h, and the gas inlet speed is 50-60 m / s.

9. Electronic grade polysilicon characterized in that, The electronic-grade polysilicon is prepared by the method for reducing the content of impurity boron in electronic-grade polysilicon according to any one of claims 1-8.