CN116043321A - Monocrystalline silicon drawing method for controlling boron enrichment - Google Patents
Monocrystalline silicon drawing method for controlling boron enrichment Download PDFInfo
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- C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
- C30B15/02—Single-crystal growth by pulling from a melt, e.g. Czochralski method adding crystallising materials or reactants forming it in situ to the melt
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Abstract
The invention discloses a method for drawing monocrystalline silicon for controlling boron enrichment, which comprises the following steps: determining the boron content of the circulating material; seed crystals are selected to be put into a hearth; according to the boron content of the circulating material, the primary polysilicon material and the circulating material are filled into a crucible according to a certain proportion; vacuumizing the crucible, and introducing inert gas; continuously heating the crucible until the materials are completely melted, obtaining a drawing material, and cooling to a seeding temperature; after the seed crystal contacts the surface of the drawing material, starting the crystal rotation; according to a certain diameter, the pulling speed is controlled well to neck; the pulling speed and the shoulder expanding speed are controlled, when the diameter of the waiting shoulder approaches the required crystal diameter, the pulling speed is improved, and the crystal enters the waiting diameter growth stage; increasing the pulling speed, gradually reducing the diameter of the crystal until the crystal is separated from the melt, and ending the first pulling process; and repeating the seed crystal loading step, wherein in the loading step, the circulating materials are added into the rest drawing materials in the same proportion, and the vacuumizing step is repeated until the ending step, so as to draw a plurality of crystal bars.
Description
Technical Field
The invention relates to the technical field of monocrystalline silicon preparation, in particular to a monocrystalline silicon drawing method for controlling boron enrichment.
Background
The single crystal silicon production method mainly comprises a Czochralski method and a zone melting method, wherein 70-80% of the world single crystal silicon yield is produced by the Czochralski method, and 20-30% of the world single crystal silicon yield is produced by the zone melting method and other methods. The Czochralski method is still the main method for producing monocrystalline silicon, has mature process, is convenient for controlling the appearance and electrical parameters of crystals, and is easy to draw large-diameter dislocation-free single crystals. A simple description of the czochralski method is: the raw materials are put in a crucible, a rotatable and liftable seed rod is arranged above the crucible, a chuck is arranged at the lower end of the rod, and a seed crystal is bound on the chuck. The raw materials are melted by a heater to form a melt, and after seed crystals are inserted into the melt, the required monocrystalline silicon can be obtained by controlling the proper temperature and pulling while rotating. According to different demands of growing crystals, the heating mode can adopt a high-frequency induction heating method or a resistance heating method. The preparation of monocrystalline silicon by the Czochralski method has the following advantages:
(1) The growth process of the crystal can be conveniently observed;
(2) Growing at the free surface, the surface is contacted with the crucible, so that the thermal stress can be effectively reduced;
(3) The directional seed crystal and the seed crystal neck can be conveniently used, so that key defects of the crystal are reduced, and the crystal with the required orientation is obtained.
Solar cells based on the semiconductor photovoltaic effect have been widely used, and currently the mainstream solar cells are based on silicon crystal materials, mainly monocrystalline silicon used for the silicon crystal materials, and the monocrystalline silicon is mainly prepared by the czochralski method. The silicon crystal material has a photo-induced attenuation phenomenon, which can lead to the great reduction of the output power of the silicon crystal material. After a lot of researches, it is found that the photoinduced attenuation phenomenon is related to the boron-oxygen concentration in the silicon wafer, and the light or current injection causes boron and oxygen in the silicon wafer to form a boron-oxygen complex, so that the minority carrier lifetime is reduced. The greater the boron and oxygen content in the silicon wafer, the more boron-oxygen complexes are generated in the silicon wafer under the condition of illumination or current injection, and the greater the reduction of minority carrier lifetime.
In the production process of monocrystalline silicon, raw materials are mainly used as raw polycrystalline silicon materials, when the production is carried out, the head, the tail and the side skin of the raw polycrystalline silicon materials are required to be cut off, and the residual raw polycrystalline silicon materials after cutting off are the main materials. The above-described cut virgin polysilicon material is referred to herein as recycle material. However, since the virgin polysilicon materials are expensive, people can dope the circulating materials into the main materials for drawing in the drawing process, but in the process of using the circulating materials, boron in the drawing raw materials is easy to enrich, and finally the enrichment degree exceeds 5ppb, so that the boron content in the drawn monocrystalline silicon is too high, and a strong light attenuation phenomenon occurs when the monocrystalline silicon is used as a silicon crystal material, and the output power is greatly reduced.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a method for controlling boron enrichment of monocrystalline silicon, which is used for solving the technical problem that boron in the drawing raw material of the existing monocrystalline silicon drawing method is easy to enrich, thereby achieving the purposes of controlling the enrichment degree of the boron in the drawing raw material, and simultaneously not influencing the quality of the drawn monocrystalline silicon and the normal use of recycled materials.
In order to solve the problems, the technical scheme adopted by the invention is as follows:
a method for controlling boron-enriched single crystal silicon pulling comprising the steps of:
preparation: checking the purity index and the size of the primary polysilicon material, and determining the boron content of the circulating material;
seed crystal loading: seed crystals with good crystal orientation and no mechanical damage are selected to be put into a cleaned hearth;
and (2) charging: according to the boron content of the circulating material, the raw polysilicon material and the circulating material are filled into a crucible according to a certain proportion;
vacuumizing: vacuumizing the crucible, and introducing inert gas;
melting raw materials: heating the crucible to enable the primary polycrystalline silicon material and the circulating material to start to melt, continuously heating until the primary polycrystalline silicon material and the circulating material are melted completely, obtaining a drawing material, and cooling to a seeding temperature;
seeding: determining seeding temperature, and starting crystal rotation after the seed crystal contacts the surface of the drawing material;
necking: according to a certain diameter, the pulling speed is controlled well to neck;
shoulder placing: the pulling speed and the shoulder expanding speed are controlled, when the diameter of the waiting shoulder approaches the required crystal diameter, the pulling speed is improved, and the crystal enters the waiting diameter growth stage;
ending: increasing the pulling speed, gradually reducing the diameter of the crystal until the crystal is separated from the melt, then reducing the temperature, and ending the first pulling process;
repeating the crystal pulling: and repeating the seed crystal loading step, wherein in the loading step, the circulating materials are put into the rest drawing materials in the same proportion, and the vacuumizing step is repeated until the ending step, so that a plurality of crystal rods are drawn.
As a preferred embodiment of the present invention, when the boron content of the recycle is 0 to 5ppb, the recycle is added in a proportion of 30 to 60% by mass.
As a preferred embodiment of the present invention, when the boron content of the recycle is 5to 50ppb, the recycle is added in a proportion of 7.5% by mass or less.
When the boron content of the circulating material is more than 50ppb, the adding proportion of the circulating material with the boron content of 5-50ppb is reduced in equal proportion according to the ratio of the boron content of the circulating material to 50ppb, namely the required adding proportion of the circulating material.
As a preferred embodiment of the invention, in the vacuumizing step, the inert gas is argon, the flow rate of the argon is 60-90L/min, and the pressure in the crucible is 5-13torr.
As a preferred embodiment of the present invention, in the seeding step, the crystal rotation speed is 7-12rp m.
As a preferred embodiment of the invention, in the necking step, the certain diameter is 2-3mm, and the pulling speed is 1.5-2mm/min.
As a preferred embodiment of the present invention, in the shouldering step, the growth in the constant diameter growth stage is set to 1.3-1.5mm/min.
As a preferred embodiment of the invention, in the shoulder placing step, the pulling speed is 0.3-0.4mm/min, and the shoulder expanding speed is 1-1.2mm/min.
As a preferred embodiment of the invention, in the ending step, the rotating speed of the crucible is controlled to be 5-8rpm, the crystal rotating speed is controlled to be 5-7rpm, and the crystal pulling speed is increased to be 2-2.3mm/min.
Compared with the prior art, the invention has the beneficial effects that:
(1) The invention develops the monocrystalline silicon drawing method for controlling boron enrichment by utilizing the characteristics of higher segregation coefficient, difficult enrichment, easy taking away and the like of boron, thereby effectively reducing the quality problem caused by boron enrichment;
(2) By adopting the method for controlling boron enrichment of the monocrystalline silicon drawing provided by the invention, unqualified crystal bars, offcut materials and residual materials in the production process of the crystal bars can be reused for drawing monocrystalline silicon, so that the use amount of raw polycrystalline silicon materials is reduced, and the preparation cost of monocrystalline silicon is effectively reduced;
(3) The method for drawing the monocrystalline silicon for controlling boron enrichment provided by the invention omits the subsequent step of carrying out harmless treatment on unqualified crystal bars, offcut materials and residual materials, thereby further reducing the preparation cost of the monocrystalline silicon.
The invention is described in further detail below with reference to the drawings and the detailed description.
Drawings
FIG. 1 is a graph showing the boron content test report of the silicon wafer of comparative example 1 of the present invention.
Detailed Description
The invention provides a method for drawing monocrystalline silicon for controlling boron enrichment, which comprises the following steps:
preparation: the purity index and size of the virgin polysilicon material are checked and the boron content of the recycle material is determined.
Further, the circulating material comprises a crystal bar with unqualified boron content in the process of drawing the crystal bar.
Further, the circulating material also comprises edge leather materials which are generated when the crystal bar is divided and are close to the head part of the crystal bar and edge leather materials which are generated when the crystal bar is divided and are close to the tail part of the crystal bar.
Further, the recycled material also comprises residual materials generated when the crystal bar is processed into square silicon wafers.
Seed crystal loading: and selecting seed crystals with good crystal orientation and no mechanical damage, and placing the seed crystals into a cleaned hearth.
And (2) charging: and (3) charging the primary polysilicon material and the circulating material into a crucible according to a certain proportion according to the boron content of the circulating material.
Further, when the boron content of the recycle material is 0 to 5ppb, the addition ratio of the recycle material is 30 to 60% by mass percent.
Further, when the boron content of the recycle is 5to 50ppb, the addition ratio of the recycle is within 7.5% by mass.
Further, when the boron content of the circulating material is more than 50ppb, the adding proportion of the circulating material with the boron content of 5-50ppb is reduced in an equal proportion according to the ratio of the boron content of the circulating material to 50ppb, namely the required adding proportion of the circulating material. Illustrating: when the boron content of the recycle is 100ppb, the ratio obtained by dividing 100ppb by 50ppb is 2, and when the boron content of the recycle is 5-50ppb, the ratio is divided by the ratio, i.e., 7.5% by 2, to obtain 3.75%, i.e., when the boron content of the recycle is 100ppb, the ratio of the recycle is within 3.75%.
Vacuumizing: the crucible is vacuumized and inert gas is introduced.
Further, the inert gas is argon, the flow rate of the argon is 60-90L/min, and the pressure in the crucible is 5-13torr.
Melting raw materials: and heating the crucible to enable the primary polycrystalline silicon material and the circulating material to start to melt, continuously heating until the primary polycrystalline silicon material and the circulating material are completely melted, obtaining a drawing material, and cooling to the seeding temperature.
Seeding: and determining the seeding temperature, and starting the crystal rotation after the seed crystal contacts the surface of the pulling material.
Further, the crystal rotation speed is 7-12rpm.
Necking: and according to a certain diameter, the pulling speed is controlled well to neck.
Further, necking is carried out according to the diameter of 2-3mm and the pulling speed of 1.5-2mm/min.
Shoulder placing: and when the diameter of the equal-diameter shoulder is close to the required crystal diameter, the pulling speed is improved, and the crystal enters the equal-diameter growth stage.
Further, the growth in the constant diameter growth stage is set to 1.3-1.5mm/min.
Further, in the shoulder placing step, the pulling speed is 0.3-0.4mm/min, and the shoulder expanding speed is 1-1.2mm/min.
Ending: increasing the pulling speed, gradually reducing the diameter of the crystal until the crystal is separated from the melt, then reducing the temperature, and ending the first pulling process.
Further, in the ending step, the rotating speed of the crucible is controlled to be 5-8rpm, the crystal rotating speed is controlled to be 5-7rpm, and the crystal pulling speed is increased to be 2-2.3mm/min.
Repeating the crystal pulling: and repeating the seed crystal loading step, wherein in the loading step, the circulating materials are added into the rest drawing materials in the same proportion, and the vacuumizing step is repeated until the ending step, so as to draw a plurality of crystal bars.
Example 1
Preparation: the purity index and size of the virgin polysilicon material were checked and the boron content of the recycle material was determined to be 2.45ppb.
Seed crystal loading: and selecting seed crystals with good crystal orientation and no mechanical damage, and placing the seed crystals into a cleaned hearth.
And (2) charging: according to the boron content of the circulating material being 2.45ppb, the adding proportion of the circulating material is determined to be 30% in terms of mass percent.
Vacuumizing: the crucible was evacuated, argon was introduced into the crucible at a flow rate of 60L/min, and the pressure in the crucible was controlled to 5torr.
Melting raw materials: and heating the crucible to enable the primary polycrystalline silicon material and the circulating material to start to melt, continuously heating until the primary polycrystalline silicon material and the circulating material are completely melted, obtaining a drawing material, and cooling to the seeding temperature.
Seeding: and determining the seeding temperature, and starting the crystal rotation at a rotating speed of 7rpm after the seed crystal contacts the surface of the pulling material.
Necking: necking is carried out according to the diameter of 2mm and the pulling speed of 1.5mm/min.
Shoulder placing: the pulling speed is controlled to be 0.3mm/min, the shoulder expanding speed is controlled to be 1mm/min, shoulder expanding is carried out, when the diameter of the equal shoulder expanding diameter is close to the required crystal diameter, the pulling speed is increased, the crystal enters an equal diameter growth stage, and the growth in the equal diameter growth stage is set to be 1.3mm/min.
Ending: the rotation speed of the crucible is controlled to be 5rpm, the crystal rotation speed is controlled to be 5rpm, the crystal pulling speed is increased to 2mm/min, the crystal diameter is gradually reduced until the crystal is separated from the melt, the temperature is reduced, and the first crystal pulling process is finished.
Repeating the crystal pulling: and repeating the seed crystal loading step, wherein in the loading process, the circulating material is added into the rest drawing material in a proportion of 30%, and the steps of vacuumizing to ending are repeated, so that 8 crystal rods are drawn.
The boron content in the remaining drawn material during the 8 drawing processes and the boron content in the drawn material after the circulating material was added were measured, and the measurement results are shown in table 1:
TABLE 1 measurement results of boron content in the drawn material remaining during multiple pulling and after addition of the recycle material
Resistivity of the 8 th pulled crystal rod at different positions is measured, and boron concentration of the crystal rod at different positions is obtained according to the resistivity, and the measurement results are shown in table 2:
TABLE 2 resistivity and boron concentration at various locations of the ingot produced by the 8 th pull of example 1
As can be seen from the above Table 1, in example 1, the boron content in the remaining drawn material was not significantly increased during 8 crystal pulling, and after the 6 th drawing, the boron content was not substantially increased, and the highest value was only 1.959ppb, and the phenomenon that boron was enriched beyond the limit value (5 ppb) did not occur, thereby fully utilizing the recycled material without affecting the quality of the pulled ingot.
As can be seen from table 2, in example 1, the boron concentration at the different positions in the 8 th pulled ingot was not high, and the boron concentrations at the different positions were relatively close, so that when the ingot was sliced later to produce silicon wafers, the boron concentrations in each silicon wafer were relatively close and all within the acceptable range. Therefore, the crystal bar is pulled by adopting the pulling method provided by the invention, and the crystal bar has good quality.
The boron concentration at different positions of the crystal bar is obtained according to the resistivity at different positions of the crystal bar through a conversion formula of the resistivity and the boron dopant concentration in GB/T13389-2014, and the conversion formula of the resistivity and the boron dopant concentration is specifically shown as formula 1:
wherein ρ is the resistivity in ohm cm (Ω×cm), N A Is the dopant concentration of boron in units of per cubic centimeter (cm) -3 )。
The dopant concentration of the doped silicon single crystal converted from resistivity is shown in Table A.1 in GB/T13389-2014.
Example 2
Preparation: the purity index and size of the virgin polysilicon material were checked and the boron content of the recycle material was determined to be 5ppb.
Seed crystal loading: and selecting seed crystals with good crystal orientation and no mechanical damage, and placing the seed crystals into a cleaned hearth.
And (2) charging: according to the boron content of the circulating material being 5ppb, the adding proportion of the circulating material is determined to be 60% by mass percent.
Vacuumizing: the crucible is vacuumized, argon is introduced into the crucible at a flow rate of 90L/min, and the pressure in the crucible is controlled to be 13torr.
Melting raw materials: and heating the crucible to enable the primary polycrystalline silicon material and the circulating material to start to melt, continuously heating until the primary polycrystalline silicon material and the circulating material are completely melted, obtaining a drawing material, and cooling to the seeding temperature.
Seeding: and determining the seeding temperature, and starting the crystal rotation at a rotating speed of 12rpm after the seed crystal contacts the surface of the pulling material.
Necking: and (3) necking by controlling the pulling speed to be 2mm/min according to the diameter of 3 mm.
Shoulder placing: the pulling speed is controlled to be 0.4mm/min, the shoulder expanding speed is controlled to be 1.2mm/min, when the diameter of the equal shoulder is close to the required crystal diameter, the pulling speed is increased, the crystal enters the equal diameter growth stage, and the growth in the equal diameter growth stage is set to be 1.5mm/min.
Ending: the rotation speed of the crucible is controlled to be 8rpm, the crystal rotation speed is controlled to be 7rpm, the crystal pulling speed is increased to 2.3mm/min, the crystal diameter is gradually reduced until the crystal is separated from the melt, the temperature is reduced, and the first crystal pulling process is finished.
Repeating the crystal pulling: and repeating the seed crystal loading step, wherein in the loading process, the circulating material is added into the rest drawing material in a proportion of 60%, and the steps of vacuumizing to ending are repeated, so that 8 crystal rods are drawn.
The boron content in the remaining drawn material during the 8 drawing processes and the boron content in the drawn material after the addition of the circulating material were measured, and the measurement results are shown in table 3:
TABLE 3 measurement results of boron content in the drawn material remaining during multiple pulling and after addition of the recycle material
Resistivity at different positions of the 8 th pulled crystal rod is measured, and boron concentration at different positions of the crystal rod is obtained according to the resistivity, and the measurement results are shown in table 4:
TABLE 4 resistivity and boron concentration at various locations of the ingot produced by the 8 th pull of EXAMPLE 2
As can be seen from the above Table 3, in example 2, the boron content in the remaining drawn material was not significantly increased during 8 crystal pulls, and after the 6 th drawing, the boron content was not substantially increased, the highest value was 4.224ppb, and the phenomenon that boron was enriched beyond the limit value (5 ppb) did not occur, thereby fully utilizing the recycled material without affecting the quality of the pulled ingot.
As can be seen from table 4, in example 2, the boron concentration at the different positions in the 8 th pulled ingot was not high, and the boron concentrations at the different positions were relatively close, so that when the ingot was sliced later to produce silicon wafers, the boron concentrations in each silicon wafer were relatively close and all within the acceptable range. Therefore, the crystal bar is pulled by adopting the pulling method provided by the invention, and the crystal bar has good quality.
Example 3
Preparation: the purity index and size of the virgin polysilicon material were checked and the boron content of the recycle material was determined to be 25ppb.
Seed crystal loading: and selecting seed crystals with good crystal orientation and no mechanical damage, and placing the seed crystals into a cleaned hearth.
And (2) charging: according to the boron content of the circulating material being 25ppb, the adding proportion of the circulating material is determined to be 7.5% by mass percent.
Vacuumizing: the crucible was evacuated, argon was introduced into the crucible at a flow rate of 75L/min, and the pressure in the crucible was controlled to 9torr.
Melting raw materials: and heating the crucible to enable the primary polycrystalline silicon material and the circulating material to start to melt, continuously heating until the primary polycrystalline silicon material and the circulating material are completely melted, obtaining a drawing material, and cooling to the seeding temperature.
Seeding: and determining the seeding temperature, and starting the crystal rotation at a rotating speed of 10rpm after the seed crystal contacts the surface of the pulling material.
Necking: necking is carried out according to the diameter of 2.5mm and the pulling speed of 1.7 mm/min.
Shoulder placing: the pulling speed is controlled to be 0.35mm/min, the shoulder expanding speed is controlled to be 1.1mm/min, shoulder expanding is carried out, when the diameter of the equal shoulder expanding diameter is close to the required crystal diameter, the pulling speed is increased, the crystal enters an equal diameter growth stage, and the growth in the equal diameter growth stage is set to be 1.4mm/min.
Ending: the rotation speed of the crucible is controlled to be 7rpm, the crystal rotation speed is controlled to be 65rpm, the crystal pulling speed is increased to 2.2mm/min, the crystal diameter is gradually reduced until the crystal is separated from the melt, the temperature is reduced, and the first crystal pulling process is finished.
Repeating the crystal pulling: and repeating the seed crystal loading step, wherein in the loading process, the circulating material is added into the rest drawing material in a proportion of 7.5%, and the steps of vacuumizing to ending are repeated, so that 8 crystal rods are drawn.
The boron content in the remaining drawn material during the 8 drawing processes and the boron content in the drawn material after the addition of the circulating material were measured, and the measurement results are shown in table 5:
TABLE 5 example 3 measurement results of boron content in the residual pulling Material during multiple pulling and pulling Material after addition of recycle Material
Resistivity of the 8 th pulled crystal rod at different positions is measured, and boron concentration of the crystal rod at different positions is obtained according to the resistivity, and the measurement results are shown in table 6:
TABLE 6 resistivity and boron concentration at various locations of the ingot produced by the 8 th pull of EXAMPLE 3
As can be seen from the above Table 5, in example 3, the boron content in the remaining drawn material was not significantly increased during 8 crystal pulls, and after the 6 th drawing, the boron content was not substantially increased, the highest value was 3.724ppb, and the phenomenon that boron was enriched beyond the limit value (5 ppb) did not occur, thereby fully utilizing the recycled material without affecting the quality of the pulled ingot.
As can be seen from table 6, in example 3, the boron concentration at the different positions in the 8 th pulled ingot was not high, and the boron concentrations at the different positions were relatively close, so that when the ingot was sliced later to produce silicon wafers, the boron concentrations in each silicon wafer were relatively close and all within the acceptable range. Therefore, the crystal bar is pulled by adopting the pulling method provided by the invention, and the crystal bar has good quality.
Example 4
Preparation: the purity index and size of the virgin polysilicon material were checked and the boron content of the recycle material was determined to be 50ppb.
Seed crystal loading: and selecting seed crystals with good crystal orientation and no mechanical damage, and placing the seed crystals into a cleaned hearth.
And (2) charging: according to the boron content of the circulating material being 50ppb, the adding proportion of the circulating material is determined to be 7% by mass percent.
Vacuumizing: the crucible was evacuated, argon was introduced into the crucible at a flow rate of 75L/min, and the pressure in the crucible was controlled to 9torr.
Melting raw materials: and heating the crucible to enable the primary polycrystalline silicon material and the circulating material to start to melt, continuously heating until the primary polycrystalline silicon material and the circulating material are completely melted, obtaining a drawing material, and cooling to the seeding temperature.
Seeding: and determining the seeding temperature, and starting the crystal rotation at a rotating speed of 10rpm after the seed crystal contacts the surface of the pulling material.
Necking: necking is carried out according to the diameter of 2.5mm and the pulling speed of 1.7 mm/min.
Shoulder placing: the pulling speed is controlled to be 0.35mm/min, the shoulder expanding speed is controlled to be 1.1mm/min, shoulder expanding is carried out, when the diameter of the equal shoulder expanding diameter is close to the required crystal diameter, the pulling speed is increased, the crystal enters an equal diameter growth stage, and the growth in the equal diameter growth stage is set to be 1.4mm/min.
Ending: the rotation speed of the crucible is controlled to be 7rpm, the crystal rotation speed is controlled to be 65rpm, the crystal pulling speed is increased to 2.2mm/min, the crystal diameter is gradually reduced until the crystal is separated from the melt, the temperature is reduced, and the first crystal pulling process is finished.
Repeating the crystal pulling: and repeating the seed crystal loading step, wherein in the loading process, the circulating material is added into the rest drawing material in a proportion of 7%, and the steps of vacuumizing to ending are repeated, so that 8 crystal rods are drawn.
The boron content in the remaining drawn material during the 8 drawing processes and the boron content in the drawn material after the addition of the circulating material were measured, and the measurement results are shown in table 7:
TABLE 7 measurement results of boron content in the drawn material remaining during multiple pulling and after addition of the recycle material in example 4
Resistivity of the 8 th pulled crystal rod at different positions is measured, and boron concentration of the crystal rod at different positions is obtained according to the resistivity, and the measurement results are shown in table 8:
TABLE 8 resistivity and boron concentration at various locations of the ingot produced by the 8 th pull of EXAMPLE 3
As can be seen from Table 7, in example 4, the boron content in the remaining drawn material was not significantly increased during 8 crystal pulls, and after the 6 th drawing, the boron content was not substantially increased, the highest value was 4.724ppb, and the phenomenon that boron was enriched beyond the limit value (5 ppb) did not occur, thereby fully utilizing the recycled material without affecting the quality of the pulled ingot.
As can be seen from table 8, in example 4, the boron concentration at the different positions in the 8 th pulled ingot was not high, and the boron concentrations at the different positions were relatively close, so that when the ingot was sliced later to produce silicon wafers, the boron concentrations in each silicon wafer were relatively close and all within the acceptable range. Therefore, the crystal bar is pulled by adopting the pulling method provided by the invention, and the crystal bar has good quality.
Example 5
Preparation: the purity index and size of the virgin polysilicon material were checked and the boron content of the recycle material was determined to be 100ppb.
Seed crystal loading: and selecting seed crystals with good crystal orientation and no mechanical damage, and placing the seed crystals into a cleaned hearth.
And (2) charging: according to the boron content of the circulating material being 100ppb, the adding proportion of the circulating material is determined to be 3.75% in terms of mass percent.
Vacuumizing: the crucible was evacuated, argon was introduced into the crucible at a flow rate of 75L/min, and the pressure in the crucible was controlled to 9torr.
Melting raw materials: and heating the crucible to enable the primary polycrystalline silicon material and the circulating material to start to melt, continuously heating until the primary polycrystalline silicon material and the circulating material are completely melted, obtaining a drawing material, and cooling to the seeding temperature.
Seeding: and determining the seeding temperature, and starting the crystal rotation at a rotating speed of 10rpm after the seed crystal contacts the surface of the pulling material.
Necking: necking is carried out according to the diameter of 2.5mm and the pulling speed of 1.7 mm/min.
Shoulder placing: the pulling speed is controlled to be 0.35mm/min, the shoulder expanding speed is controlled to be 1.1mm/min, shoulder expanding is carried out, when the diameter of the equal shoulder expanding diameter is close to the required crystal diameter, the pulling speed is increased, the crystal enters an equal diameter growth stage, and the growth in the equal diameter growth stage is set to be 1.4mm/min.
Ending: the rotation speed of the crucible is controlled to be 7rpm, the crystal rotation speed is controlled to be 65rpm, the crystal pulling speed is increased to 2.2mm/min, the crystal diameter is gradually reduced until the crystal is separated from the melt, the temperature is reduced, and the first crystal pulling process is finished.
Repeating the crystal pulling: and repeating the seed crystal loading step, wherein in the loading process, the circulating material is added into the rest drawing material in a proportion of 3.75%, and the steps of vacuumizing to ending are repeated, so that 8 crystal rods are drawn.
The boron content in the remaining drawn material during the 8 drawing processes and the boron content in the drawn material after the addition of the circulating material were measured, and the measurement results are shown in table 9:
TABLE 9 measurement results of boron content in the drawn material remaining during multiple pulling and after addition of the recycle material in example 5
Resistivity of the 8 th pulled crystal rod at different positions was measured, and boron concentrations of the crystal rod at different positions were obtained according to the resistivity, and the measurement results are shown in table 10:
TABLE 10 resistivity and boron concentration at various locations of the ingot produced by the 8 th pull of example 5
As can be seen from Table 9, in example 5, the boron content in the remaining drawn material was not significantly increased during 8 crystal pulls, and after the 6 th drawing, the boron content was not substantially increased, the highest value was 4.974ppb, and the phenomenon that boron was enriched beyond the limit value (5 ppb) did not occur, thereby fully utilizing the recycled material without affecting the quality of the pulled ingot.
As can be seen from table 10 above, in example 5, the boron concentration at the different positions in the 8 th pulled ingot was not high, and the boron concentrations at the different positions were relatively close, so that when the ingot was sliced later to produce silicon wafers, the boron concentrations in each silicon wafer were relatively close and all within the acceptable range. Therefore, the crystal bar is pulled by adopting the pulling method provided by the invention, and the crystal bar has good quality.
Comparative example
In the existing monocrystalline silicon drawing method, the original polycrystalline silicon material is directly adopted to dope the circulating material for drawing, the boron content in the circulating material and the drawing raw material is not analyzed in the drawing process, the adding proportion of the circulating material is not determined according to the boron content in the circulating material, so that the enrichment of the boron in the drawing raw material is caused, the boron content of the finally obtained silicon wafer exceeds the standard, and the silicon wafer further causes a strong light attenuation phenomenon when being used as a silicon crystal material, and the output power is greatly reduced, as shown in a silicon wafer detection report of figure 1.
The above embodiments are only preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but any insubstantial changes and substitutions made by those skilled in the art on the basis of the present invention are intended to be within the scope of the present invention as claimed.
Claims (10)
1. A method for controlling boron-enriched single crystal silicon pulling, comprising the steps of:
preparation: checking the purity index and the size of the primary polysilicon material, and determining the boron content of the circulating material;
seed crystal loading: seed crystals with good crystal orientation and no mechanical damage are selected to be put into a cleaned hearth;
and (2) charging: according to the boron content of the circulating material, the raw polysilicon material and the circulating material are filled into a crucible according to a certain proportion;
vacuumizing: vacuumizing the crucible, and introducing inert gas;
melting raw materials: heating the crucible to enable the primary polycrystalline silicon material and the circulating material to start to melt, continuously heating until the primary polycrystalline silicon material and the circulating material are melted completely, obtaining a drawing material, and cooling to a seeding temperature;
seeding: determining seeding temperature, and starting crystal rotation after the seed crystal contacts the surface of the drawing material;
necking: according to a certain diameter, the pulling speed is controlled well to neck;
shoulder placing: the pulling speed and the shoulder expanding speed are controlled, when the diameter of the waiting shoulder approaches the required crystal diameter, the pulling speed is improved, and the crystal enters the waiting diameter growth stage;
ending: increasing the pulling speed, gradually reducing the diameter of the crystal until the crystal is separated from the melt, then reducing the temperature, and ending the first pulling process;
repeating the crystal pulling: and repeating the seed crystal loading step, wherein in the loading step, the circulating materials are put into the rest drawing materials in the same proportion, and the vacuumizing step is repeated until the ending step, so that a plurality of crystal rods are drawn.
2. The method for pulling a single crystal silicon with controlled boron enrichment as defined in claim 1, wherein the addition ratio of the circulating material is 30% -60% by mass when the boron content of the circulating material is 0-5 ppb.
3. The method for pulling a single crystal silicon with controlled boron enrichment according to claim 1, wherein the addition ratio of the recycle is within 7.5% in mass percent when the boron content of the recycle is 5-50 ppb.
4. The method for pulling a single crystal silicon with controlled boron enrichment according to claim 1, wherein when the boron content of the recycle is more than 50ppb, the addition ratio of the recycle at the boron content of 5-50ppb is equally scaled down according to the ratio of the boron content of the recycle to 50ppb, which is the desired addition ratio of the recycle.
5. The method for pulling a silicon single crystal with controlled boron enrichment according to claim 1, wherein in the vacuum pumping step, the inert gas is argon gas, the flow rate of the argon gas is 60-90L/min, and the pressure in the crucible is 5-13torr.
6. The method of pulling a silicon single crystal with controlled boron enrichment as defined in claim 1, wherein in the seeding step, the crystal rotation speed is 7-12rpm.
7. The method of pulling a single crystal silicon with controlled boron enrichment as defined in claim 1, wherein in the necking step, the certain diameter is 2-3mm, and the pulling speed is 1.5-2mm/min.
8. The method of pulling a single crystal silicon with controlled boron enrichment as defined in claim 1, wherein in the shouldering step, the growth of the constant diameter growth stage is set to 1.3-1.5mm/min.
9. The method for pulling a single crystal silicon with controlled boron enrichment according to claim 1, wherein in the shoulder-pulling step, the pulling speed is 0.3-0.4mm/min, and the shoulder-expanding speed is 1-1.2mm/min.
10. The method for pulling a single crystal silicon with controlled boron enrichment according to claim 1, wherein in the ending step, the rotation speed of the crucible is controlled to be 5-8rpm, the crystal rotation speed is controlled to be 5-7rpm, and the pulling speed is increased to be 2-2.3mm/min.
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