CN113387360A - Interface wettability regulation and control method for inhibiting silicon dendritic crystal growth in zone melting level polycrystalline silicon CVD process - Google Patents
Interface wettability regulation and control method for inhibiting silicon dendritic crystal growth in zone melting level polycrystalline silicon CVD process Download PDFInfo
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 160
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 63
- 239000010703 silicon Substances 0.000 title claims abstract description 63
- 229910021420 polycrystalline silicon Inorganic materials 0.000 title claims abstract description 57
- 238000000034 method Methods 0.000 title claims abstract description 45
- 238000004857 zone melting Methods 0.000 title claims abstract description 21
- 239000013078 crystal Substances 0.000 title claims abstract description 9
- 230000002401 inhibitory effect Effects 0.000 title claims abstract description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 45
- 238000006243 chemical reaction Methods 0.000 claims abstract description 38
- 239000001257 hydrogen Substances 0.000 claims abstract description 32
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 32
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 29
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 claims abstract description 28
- 229910000077 silane Inorganic materials 0.000 claims abstract description 28
- 229920005591 polysilicon Polymers 0.000 claims abstract description 27
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 22
- 230000001276 controlling effect Effects 0.000 claims abstract description 17
- 210000001787 dendrite Anatomy 0.000 claims abstract description 17
- 239000007789 gas Substances 0.000 claims abstract description 16
- 238000011068 loading method Methods 0.000 claims abstract description 11
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- 150000002431 hydrogen Chemical class 0.000 claims abstract description 8
- 239000012535 impurity Substances 0.000 claims abstract description 5
- 238000004227 thermal cracking Methods 0.000 claims abstract description 5
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 claims description 18
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 13
- 238000001035 drying Methods 0.000 claims description 11
- 229910021642 ultra pure water Inorganic materials 0.000 claims description 7
- 239000012498 ultrapure water Substances 0.000 claims description 7
- 238000001291 vacuum drying Methods 0.000 claims description 7
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 claims description 6
- HEDRZPFGACZZDS-UHFFFAOYSA-N Chloroform Chemical compound ClC(Cl)Cl HEDRZPFGACZZDS-UHFFFAOYSA-N 0.000 claims description 6
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 6
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 claims description 6
- 238000004140 cleaning Methods 0.000 claims description 6
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 claims description 4
- 239000003960 organic solvent Substances 0.000 claims description 4
- 238000002156 mixing Methods 0.000 claims description 2
- 230000035484 reaction time Effects 0.000 claims description 2
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen(.) Chemical compound [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 claims 1
- 238000005137 deposition process Methods 0.000 abstract description 5
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- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- ZDHXKXAHOVTTAH-UHFFFAOYSA-N trichlorosilane Chemical compound Cl[SiH](Cl)Cl ZDHXKXAHOVTTAH-UHFFFAOYSA-N 0.000 description 3
- 239000005052 trichlorosilane Substances 0.000 description 3
- 238000005406 washing Methods 0.000 description 3
- 239000011148 porous material Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- SLLGVCUQYRMELA-UHFFFAOYSA-N chlorosilicon Chemical compound Cl[Si] SLLGVCUQYRMELA-UHFFFAOYSA-N 0.000 description 1
- 238000003776 cleavage reaction Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 229910021419 crystalline silicon Inorganic materials 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
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- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
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- 239000000463 material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910021421 monocrystalline silicon Inorganic materials 0.000 description 1
- 230000009972 noncorrosive effect Effects 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
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- 238000002360 preparation method Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
- C01B33/021—Preparation
- C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
- C01B33/035—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material by decomposition or reduction of gaseous or vaporised silicon compounds in the presence of heated filaments of silicon, carbon or a refractory metal, e.g. tantalum or tungsten, or in the presence of heated silicon rods on which the formed silicon is deposited, a silicon rod being obtained, e.g. Siemens process
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Abstract
The invention discloses an interface wettability regulation method for inhibiting silicon dendritic crystal growth in a zone melting level polysilicon CVD process, which relates to the field of zone melting level polysilicon and comprises the following steps of removing surface impurities on the surface of a U-shaped silicon core; placing the mixture in a thermal cracking furnace reactor, and replacing air with nitrogen; replacing nitrogen with hydrogen; continuously introducing hydrogen, loading current to the silicon core in the reactor, reducing an oxide layer on the surface of the silicon core, regulating and controlling the wettability of the silicon core and constructing a 'super-parent silicon' surface; adjusting current to control the silicon core to reach reaction temperature, introducing mixed gas of high-purity silane and high-purity hydrogen, pyrolyzing silane on the surface of the silicon core, uniformly nucleating and growing the product silicon on the surface of the ultra-silicon-philic silicon core in a layered manner, and finally obtaining the compact polysilicon rod. The invention reduces nucleation barrier through surface interface regulation and control, can effectively inhibit island growth and silicon dendrite problem in the silicon deposition process, thereby obtaining the product meeting the mechanical property of zone-melting-level polysilicon, and has reasonable design, convenient operation and strong practicability.
Description
Technical Field
The invention relates to the field of zone-melting-grade polycrystalline silicon, in particular to an interface wettability regulation method for inhibiting silicon dendritic crystal growth in a zone-melting-grade polycrystalline silicon CVD process.
Background
The polycrystalline silicon can be divided into solar grade and electronic grade, and the solar grade polycrystalline silicon is used as a basic raw material of a solar energy industrial chain, is mainly used for producing solar panels and is mainly used for some large-scale environmental protection projects. Electronic grade polysilicon is a strategic raw material for developing national integrated circuit industry as a key basic material for preparing integrated circuits, and is mainly used for producing electronic equipment and chips. The zone-melting-level rod-shaped polycrystalline silicon is a high-end product of electronic-level polycrystalline silicon, wherein the zone-melting-level rod-shaped polycrystalline silicon is a rod-shaped crystalline silicon material with the purity of 12N, uniformity, compactness and excellent mechanical property, and is used for manufacturing silicon-based chips after being subjected to a further zone-melting method to obtain single crystals, such as modules (IGBT) for integrated circuits, Photodiodes (PD), power electronic semiconductor devices (SCR, GTO) and other high-end devices.
The existing production technology of electronic grade polysilicon mainly comprises trichlorosilane (SiHCl)3) Method and Silane (SiH)4) Methods, and the like. The method for producing electronic grade polysilicon by using the trichlorosilane method has certain advantages of high deposition rate and relatively good safety, and the purity of the polysilicon can meet the requirements of straight pulling and zone melting. Most of polysilicon products produced by the trichlorosilane method are solar grade, and the quality of the polysilicon products cannot meet the requirements of electronic grade products. The silane method is to utilizeThe method for producing the polycrystalline silicon by the silane thermal cracking method has low reaction temperature, raw material silane is easy to purify, and the strict control on the impurity content can be realized. The polysilicon rod produced by the silane method has compact crystallization and grain size<0.1 μm, is the best raw material for producing zone-melting-grade monocrystalline silicon. Furthermore, the silane cleavage products are non-corrosive, thereby avoiding corrosion of the equipment.
The zone-melting-grade polysilicon has ultrahigh purity, and still needs to meet the conditions of smooth surface, no damage, no crack, no oxidation interlayer and the like. In order to reduce the silicon spurs generated in the zone melting process, the ovality and the straightness of the zone melting grade polysilicon also meet the corresponding requirements. In addition, residual stresses within the zone-melting grade polysilicon should be minimized and eliminated to reduce the risk of cracking during preheating or crystal growth during cutting and zone-melting. However, silicon dendrite growth is very easy to occur during the deposition process of the zone-melting-grade polycrystalline silicon, so that the mechanical properties of the product are difficult to meet the requirement of further processing and production of the zone-melting-grade polycrystalline silicon. Based on the above, the invention provides an interface wettability control method for inhibiting silicon dendrite growth in the CVD process of zone-melting-level polysilicon to solve the above problems.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, the present invention is directed to suppressing silicon dendrite growth during a zone-melting-level polysilicon CVD process.
In order to achieve the purpose, the invention provides an interface wettability control method for inhibiting silicon dendritic crystal growth in a zone melting level polysilicon CVD process, which comprises the following steps:
step 1, cleaning, wiping and drying the surface of a U-shaped silicon core to remove surface impurities;
2, placing the processed U-shaped silicon core in a thermal cracking furnace reactor, and introducing nitrogen to replace air in the reactor;
step 3, introducing hydrogen to replace nitrogen in the reaction furnace;
step 4, continuously introducing hydrogen, loading current to the silicon core in the reactor, and keeping for a certain time to reduce the oxide layer on the surface of the silicon core, regulating and controlling the wettability of the silicon core and constructing the surface of the 'super-parent silicon';
and 5, adjusting the current to control the silicon core to reach a proper reaction temperature, introducing a mixed gas of high-purity silane and high-purity hydrogen, pyrolyzing the silane on the surface of the silicon core, uniformly nucleating and growing the product silicon on the surface of the ultra-parent silicon core in a layered manner, and finally obtaining the compact polysilicon rod.
Further, the cleaning in the step 1 is to wash the silicon chip for 1-5 times by adopting ultrapure water with the resistivity of more than or equal to 15M omega cm at 25 ℃, and the wiping is to wipe the surface of the silicon chip for 1-5 times by adopting an organic solvent.
Further, the organic solvent is one or more of absolute ethyl alcohol, n-butanol, acetone, ethyl acetate, benzene, toluene, chloroform and the like.
Further, the drying in the step 1 is carried out in a vacuum drying oven in a clean factory building with more than one hundred thousand grades, and the temperature is set to be 50-100 ℃.
Further, O in nitrogen in step 22Less than or equal to 0.01 percent, and 1 to 10 times of replacement.
Further, the purity of the hydrogen in the step 3 is more than or equal to 99.99 percent, and the replacement is carried out for 1 to 10 times.
Further, the purity of the hydrogen in the step 4 is more than or equal to 99.99 percent, and the flow rate of the hydrogen is 5-30m3And/h, setting the current loading of the silicon core to be 20-100A, and keeping for 1-24 hours.
Further, the reaction temperature in step 5 is 700-1200 ℃.
Further, the high-purity silane and the hydrogen gas in the step 5 are uniformly mixed in advance through a gas mixing device, and the molar ratio is 0.005-0.25.
Further, the introducing amount of the mixed gas in the step 5 is changed along with the reaction time, and the initial flow rate is 50-2000m3/h。
The invention has the following technical effects:
(1) by cleaning, wiping and drying the surface of the U-shaped silicon core, the invention can effectively remove the stains formed in the processing and transferring processes of the U-shaped silicon core and ensure that the surface of the silicon core is clean when the silicon core enters the reaction furnace;
(2) according to the invention, through the nitrogen pretreatment of the air inside the nitrogen replacement reaction furnace and the nitrogen inside the hydrogen replacement reaction furnace, the oxygen content inside the reaction furnace can be effectively reduced, and the generation of oxides in the deposition process of polycrystalline silicon is avoided;
(3) according to the invention, by carrying out pretreatment on the current loaded on the silicon core in the reactor, the oxide layer on the surface of the silicon core can be reduced, the wettability of the silicon core can be regulated and controlled, and the surface of the 'super-parent silicon' is constructed, so that an oxidation interlayer is prevented from being generated between the silicon core and the deposited polycrystalline silicon;
(4) the invention reduces nucleation barrier through surface interface regulation and control, can effectively inhibit island growth and silicon dendrite problem in the silicon deposition process, thereby obtaining the product meeting the mechanical property of zone-melting-level polysilicon;
(5) according to the invention, by controlling the reaction temperature, the molar ratio of high-purity silane to hydrogen and the flow velocity of the introduced mixed gas in the deposition process, uniform and compact deposition of the polycrystalline silicon rod can be effectively realized, and the growth of silicon dendrites is inhibited;
(6) the invention has reasonable design and convenient operation, and the product surface is regular without defects of damage, crack, oxidation interlayer and the like; in addition, the residual stress in the silicon rod is small, the preheating or crystal growth requirements in the subsequent cutting and zone-melting processes are met, the practicability is high, and the method is suitable for popularization.
The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.
Drawings
FIG. 1 is a schematic, diagrammatic illustration of a preferred embodiment of the present invention;
FIG. 2 is a silicon core, growth layer and silicon dendrite marking view of a polycrystalline silicon rod product prepared according to a comparative example of the present invention under a metallographic microscope;
FIG. 3 is a metallographic microscope photograph showing the results of the preparation of a polycrystalline silicon rod product according to a preferred embodiment of the present invention and comparative examples, wherein (A) is comparative example, (B) is example 1, (C) is example 2, (D) is example 3, (E) is example 4, and (F) is example 5;
FIG. 4 is an X-ray microscopic nondestructive three-dimensional internal imaging image of a polycrystalline silicon rod product prepared according to a preferred embodiment of the present invention and a comparative example, wherein (A) is example 5 and (B) is a comparative example.
Detailed Description
The technical contents of the preferred embodiments of the present invention will be more clearly and easily understood by referring to the drawings attached to the specification. The present invention may be embodied in many different forms of embodiments and the scope of the invention is not limited to the embodiments set forth herein.
In the drawings, structurally identical elements are represented by like reference numerals, and structurally or functionally similar elements are represented by like reference numerals throughout the several views. The size and thickness of each component shown in the drawings are arbitrarily illustrated, and the present invention is not limited to the size and thickness of each component. The thickness of the components may be exaggerated where appropriate in the figures to improve clarity.
Example 1
A method for inhibiting silicon dendrite growth and promoting uniform deposition in the process of preparing zone-melting-grade polysilicon by silane method CVD (chemical vapor deposition), as shown in figure 1, comprises the steps of U-shaped silicon core surface treatment for removing surface impurities, and comprises the following steps: cleaning, wiping and drying; the processed U-shaped silicon core is placed in a thermal cracking furnace reactor, and nitrogen is introduced to replace the air in the reactor; introducing hydrogen to replace nitrogen inside the reaction furnace; continuously introducing hydrogen, loading current to the silicon core in the reactor, and keeping for a certain time to reduce the oxide layer on the surface of the silicon core, regulating and controlling the wettability of the silicon core and constructing the surface of the 'super-parent silicon'; adjusting current to control a silicon core to reach a proper reaction temperature, introducing mixed gas of high-purity silane and high-purity hydrogen, pyrolyzing silane on the surface of the silicon core, uniformly nucleating and growing a product silicon on the surface of the ultra-hydrophilic silicon core in a layered manner, and finally obtaining a compact polysilicon rod. The method comprises the following specific steps:
(1) the U silicon core is washed for 3 times by adopting ultrapure water (not less than 15M omega cm, 25 ℃), and then the silicon core is wiped for 3 times by respectively adopting absolute ethyl alcohol and acetone;
(2) the cleaned and wiped silicon core is stored in a vacuum drying box in a clean workshop (more than or equal to one hundred thousand grade) for drying, and the temperature is set to 80 ℃;
(3) the silicon core is arranged in the reaction furnace and adopts nitrogen (O)2Less than or equal to 0.01 percent) of the air in the reactor is replaced for 3 times;
(4) replacing nitrogen in the reaction furnace by hydrogen (more than or equal to 99.99 percent) for 3 times;
(5) continuously introducing hydrogen gas for 10m3Loading current to the silicon core in the reactor, setting the current at 40A, keeping for 1 hour, reducing the oxide layer on the surface of the silicon core, regulating and controlling the wettability of the silicon core and constructing the surface of the super-parent silicon;
(6) adjusting the current and controlling the reaction temperature of the silicon core to 850-900 ℃, the molar ratio of the initial silane to the hydrogen to be 0.05, and introducing the initial mixed gas with the flow rate of 150m3H, performing high-temperature pyrolysis on the surface of a silicon core by using silane, and uniformly nucleating and growing a product silicon on the surface of an ultra-hydrophilic silicon core;
(7) after the reaction deposition is finished, the polycrystalline silicon rod is cut and analyzed, and a metallographic microscope picture of the polycrystalline silicon rod is shown in fig. 3 (B). It can be seen from the figure that the silicon core is obviously different from the silicon growth layer, and the growth layer grows more silicon dendrites, and compared with the comparison example of fig. 3(a), the silicon dendrites are reduced after interface wettability regulation.
Example 2
(1) The U silicon core is washed for 3 times by adopting ultrapure water (not less than 15M omega cm, 25 ℃), and then the silicon core is wiped for 3 times by respectively adopting absolute ethyl alcohol and ethyl acetate;
(2) the cleaned and wiped silicon core is stored in a vacuum drying box in a clean workshop (more than or equal to one hundred thousand grade) for drying, and the temperature is set to be 100 ℃;
(3) the silicon core is arranged in the reaction furnace and adopts nitrogen (O)2Less than or equal to 0.001 percent) of the air in the reactor, and replacing for 3 times;
(4) replacing nitrogen in the reaction furnace by hydrogen (more than or equal to 99.99 percent) for 3 times;
(5) continuously introducing hydrogen for 20m3Loading current to a silicon core in the reactor, setting the current to be 80A, keeping for 2 hours, regulating and controlling the wettability of the silicon core and constructing a super-parent silicon surface;
(6) adjusting the current and controlling the reaction temperature of the silicon core to be 900-950 ℃, the molar ratio of the initial silane to the hydrogen to be 0.12, and the initial mixed gas with the flow rate of 600m3H, silane is pyrolyzed on the surface of a silicon core, and the product silicon is uniformly nucleated and grows in a layered mode on the surface of the ultra-hydrophilic silicon core”；
(7) After the reaction deposition is finished, the polycrystalline silicon rod is cut and analyzed, and a metallographic microscope picture of the polycrystalline silicon rod is shown in fig. 3 (C). As can be seen from the figure, the silicon core is not obviously different from the silicon growth layer, no obvious silicon dendrite is generated, but the defect pore exists in the silicon growth layer.
Example 3
(1) Washing the silicon core by ultra-pure water (not less than 15M omega cm, 25 ℃) for 5 times, and then wiping the silicon core by a mixed solution of absolute ethyl alcohol, ethyl acetate and acetone for 3 times;
(2) the cleaned and wiped silicon core is stored in a vacuum drying box in a clean workshop (more than or equal to one hundred thousand grade) for drying, and the temperature is set to 80 ℃;
(3) the silicon core is arranged in the reaction furnace and adopts nitrogen (O)2Less than or equal to 0.001 percent) of the air in the reactor is replaced for 5 times;
(4) replacing nitrogen in the reaction furnace by hydrogen (more than or equal to 99.99 percent) for 5 times;
(5) continuously introducing hydrogen for 30m3Loading current to a silicon core in the reactor, setting the current to be 50A, keeping for 4 hours, regulating and controlling the wettability of the silicon core and constructing a super-parent silicon surface;
(6) adjusting the current and controlling the reaction temperature of the silicon core to be 1000-1050 ℃, the molar ratio of the initial silane to the hydrogen to be 0.08, and introducing the initial mixed gas with the flow speed of 200m3H, performing high-temperature pyrolysis on the surface of a silicon core by using silane, and uniformly nucleating and growing a product silicon on the surface of an ultra-hydrophilic silicon core;
(7) after the reaction deposition is finished, the polycrystalline silicon rod is cut and analyzed, and a metallographic microscope picture of the polycrystalline silicon rod is shown in fig. 3 (D). As can be seen from the figure, the silicon core is not obviously different from the silicon growth layer, no obvious silicon dendrite is generated, and the silicon growth layer is uniform and compact.
Example 4
(1) Washing the silicon core by adopting ultrapure water (not less than 15M omega cm, 25 ℃) for 5 times, and wiping the silicon core by adopting a mixed solution of ethyl acetate and trichloromethane for 5 times;
(2) the cleaned and wiped silicon core is stored in a vacuum drying box in a clean workshop (more than or equal to one hundred thousand grade) for drying, and the temperature is set to be 100 ℃;
(3) the silicon core is arranged in the reaction furnace and adopts nitrogen (O)2Less than or equal to 0.01 percent) of the air in the reactor is replaced for 3 times;
(4) replacing nitrogen in the reaction furnace by hydrogen (more than or equal to 99.99 percent) for 3 times;
(5) continuously introducing hydrogen gas for 40m3Loading current to a silicon core in the reactor, setting the current at 40A, keeping for 8 hours, regulating and controlling the wettability of the silicon core and constructing a super-parent silicon surface;
(6) adjusting the current and controlling the reaction temperature of the silicon core to be 950-1000 ℃, the molar ratio of the initial silane to the hydrogen to be 0.12, and introducing the initial mixed gas with the flow rate of 500m3H, performing high-temperature pyrolysis on the surface of a silicon core by using silane, and uniformly nucleating and growing a product silicon on the surface of an ultra-hydrophilic silicon core;
(7) after the reaction deposition is finished, the polycrystalline silicon rod is cut and analyzed, and a metallographic microscope picture of the polycrystalline silicon rod is shown in fig. 3 (E). As can be seen from the figure, the silicon core is not obviously different from the silicon growth layer, no obvious silicon dendrite is generated, but the defect pore exists in the silicon growth layer.
Example 5
(1) Washing the silicon core with ultrapure water (not less than 15M omega cm at 25 ℃) for 5 times, and wiping the silicon core with a mixed solution of absolute ethyl alcohol, ethyl acetate, trichloromethane and acetone for 5 times;
(2) the cleaned and wiped silicon core is stored in a vacuum drying box in a clean workshop (more than or equal to one hundred thousand grade) for drying, and the temperature is set to be 90 ℃;
(3) the silicon core is arranged in the reaction furnace and adopts nitrogen (O)2Less than or equal to 0.01 percent) of the air in the reactor is replaced for 9 times;
(4) replacing nitrogen in the reaction furnace by hydrogen (more than or equal to 99.99 percent) for 9 times;
(5) continuously introducing hydrogen for 20m3Loading current to a silicon core in the reactor, setting the current at 60A, keeping for 4 hours, regulating and controlling the wettability of the silicon core and constructing a super-parent silicon surface;
(6) adjusting the current and controlling the reaction temperature of the silicon core to 1050-The molar ratio of the gas is 0.03, and the initial mixed gas is introduced at a flow rate of 200m3H, performing high-temperature pyrolysis on the surface of a silicon core by using silane, and uniformly nucleating and growing a product silicon on the surface of an ultra-hydrophilic silicon core;
(7) after the reaction deposition is finished, the polycrystalline silicon rod is cut and analyzed, and a metallographic microscope picture of the polycrystalline silicon rod is shown in fig. 3 (F). As can be seen from the figure, the silicon core is not obviously different from the silicon growth layer, no obvious silicon dendrite is generated, and the silicon growth layer is uniform and compact. In addition, the X-ray microscope can not damage the three-dimensional internal imaging, as shown in FIG. 4(A), the silicon core is pretreated by the interface wettability control method of the invention, and the prepared polysilicon rod meets the cutting requirement, and has no stress crack generation and no internal defect inside.
Comparative example 1
The silicon chip is not pretreated by the interface wettability regulation method of the invention and is directly placed into a reaction furnace for silicon deposition, the reaction temperature of the silicon chip is 850-900 ℃, the molar ratio of the initial silane to the hydrogen is 0.03, and the initial mixed gas is introduced at the flow rate of 200m3H is used as the reference value. After the reaction deposition is finished, the polycrystalline silicon rod is cut and analyzed, the metallographic microscope picture of the polycrystalline silicon rod is shown in fig. 2 and 3(a), and the nondestructive three-dimensional internal imaging of the X-ray microscope is shown in fig. 4 (B). As can be seen from a metallographic microscopic image, the silicon core and the silicon growth layer are distinct, and the growth layer grows a large number of silicon dendrites. The nondestructive three-dimensional internal imaging result of the X-ray microscope shows that: the silicon core is not pretreated by the interface wettability control method, the prepared polysilicon rod cannot meet the cutting requirement, and internal stress cracks are generated during cutting.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.
Claims (10)
1. An interface wettability control method for inhibiting silicon dendritic crystal growth in a zone melting level polysilicon CVD process is characterized by comprising the following steps:
step 1, cleaning, wiping and drying the surface of a U-shaped silicon core to remove surface impurities;
2, placing the processed U-shaped silicon core in a thermal cracking furnace reactor, and introducing nitrogen to replace air in the reactor;
step 3, introducing hydrogen to replace nitrogen in the reaction furnace;
step 4, continuously introducing hydrogen, loading current to the silicon core in the reactor, and keeping for a certain time to reduce the oxide layer on the surface of the silicon core, regulating and controlling the wettability of the silicon core and constructing the surface of the 'super-parent silicon';
and 5, adjusting the current to control the silicon core to reach a proper reaction temperature, introducing a mixed gas of high-purity silane and high-purity hydrogen, pyrolyzing the silane on the surface of the silicon core, uniformly nucleating and growing the product silicon on the surface of the ultra-parent silicon core in a layered manner, and finally obtaining the compact polysilicon rod.
2. The method for controlling interfacial wettability to suppress silicon dendrite growth during the CVD process of the zone melting level polysilicon according to claim 1, wherein the cleaning in step 1 is to rinse the silicon core 1-5 times with ultrapure water having a resistivity of not less than 15M Ω cm at 25 ℃, and the wiping is to wipe the surface of the silicon core 1-5 times with an organic solvent.
3. The method according to claim 2, wherein the organic solvent is one or more of absolute ethyl alcohol, n-butanol, acetone, ethyl acetate, benzene, toluene, chloroform, etc.
4. The method of claim 1, wherein the step 1 of drying is performed in a vacuum drying oven in a clean room of over one hundred thousand grades at a temperature of 50-100 ℃.
5. The method of claim 1, wherein the step 2 comprises adjusting the interfacial wettability by O in nitrogen2Less than or equal to 0.01 percent, and 1 to 10 times of replacement.
6. The method for controlling interfacial wettability to suppress silicon dendrite growth during the CVD process of the zone melting level polysilicon according to claim 1, wherein the purity of the hydrogen gas in step 3 is not less than 99.99%, and the replacement is performed 1-10 times.
7. The method as claimed in claim 1, wherein the purity of hydrogen in step 4 is not less than 99.99%, and the flow rate of hydrogen is 5-30m3And/h, setting the current loading of the silicon core to be 20-100A, and keeping for 1-24 hours.
8. The method as claimed in claim 1, wherein the reaction temperature in step 5 is 700-1200 ℃.
9. The method as claimed in claim 1, wherein the high purity silane and hydrogen gas are mixed uniformly in advance by a gas mixing device in a molar ratio of 0.005-0.25 in step 5.
10. The method as claimed in claim 1, wherein the amount of the mixed gas introduced in step 5 varies with the reaction time, and the initial flow rate is 50-2000m3/h。
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