Patent Description:
A monocrystalline silicon (or a single crystal silicon) for preparing a solar cell is mainly manufactured by the Czochralski process. In the Czochralski process, a growth speed of the monocrystalline silicon is greatly affected by a longitudinal temperature gradient of a pulled crystal near a crystallizing interface. The greater the temperature gradient is, the faster the growth of the monocrystalline silicon crystal will be. To increase the longitudinal temperature gradient of the monocrystalline silicon crystal near the crystallizing interface, it is necessary to achieve quick heat dissipation for the pulled crystal. At present, a water-cooling heat shield may be arranged in a single crystal furnace so that the heat is quickly dissipated from the crystal.

During the crystal pulling in the Czochralski process, a thermal field may be designed to achieve the crystal pulling with a variable temperature gradient, thereby improving stability of a constant-diameter body growth process of the monocrystalline silicon and the growth speed of the pulled crystal under the premise of ensuring a success rate of seeding. However, when the crystal is pulled in a conventional thermal field, a distance between the water-cooling heat shield and a surface of silicon melt is fixed, which may cause the longitudinal temperature gradient of the monocrystalline silicon crystal cannot be further increased, thus resulting in a negative impact on the growth speed of the monocrystalline silicon.

<CIT> discloses a method for eliminating defects by use of the Dash's neck method, by means of arranging a cooler for cooling a pulled single crystal provided in an apparatus for pulling single crystal by the Czochralski method, the cooler being able to move within a CZ furnace.

<CIT> discloses a single crystal pulling furnace with a movable water-cooled screen.

In view of this, the present disclosure provides a method and a use of an apparatus for manufacturing a monocrystalline silicon, which can increase the longitudinal temperature gradient of the monocrystalline silicon crystal and the growth speed of the monocrystalline silicon.

In a first aspect of the present disclosure, a method for manufacturing a monocrystalline silicon with a Czochralski process is provided. The method includes the following steps:.

In an embodiment, the first preset distance is in a range from <NUM> to <NUM>.

In an embodiment, during the seeding process, a seeding speed is in a range from <NUM>/h to <NUM>/h, a seeding length is in a range from <NUM> to <NUM>, and the diameter of the crystal is in a range from <NUM> to <NUM>.

In an embodiment, the second preset distance is in a range from <NUM> to <NUM>.

In an embodiment, during the constant-diameter body growth process, a lowering speed of the water-cooling heat shield is in a range from <NUM>/h to <NUM>/h, a total lowering time of the water-cooling heat shield is less than <NUM> hours, and a second pulling speed of the crystal is in a range from <NUM>/h to <NUM>/h.

In an embodiment, a height difference between the first preset distance and the second preset distance is in a range from <NUM> to <NUM>.

In an embodiment, a third pulling speed of the crystal is in a range from <NUM>/h to <NUM>/h.

In a second aspect of the present disclosure, use of an apparatus for manufacturing a monocrystalline silicon for performing the above method is provided. The apparatus includes: a single crystal furnace, a quartz crucible, a heater, a water-cooling heat shield, a heat insulation cylinder, a guide shell, a crystal pulling device, a connector, and a lifting bar for the water-cooling heat shield, wherein the connector is configured to operably connect the lifting bar to the guide shell in order to allow movement of the water-cooling heat shield relative to the guide shell.

The technical solutions according to the present disclosure at least bring the following technical effects:
In the present disclosure, during the seeding process, the water-cooling heat shield is lifted upward to increase the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt, thereby increasing the success rate of seeding. In the constant-diameter body growth process, the water-cooling heat shield is lowered to reduce the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt, so that the growth of the crystal is more stable. Moreover, since the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt becomes smaller, the heat absorption capacity of the water-cooling heat shield is enhanced, so that the temperature of the crystal rod is lowered, the longitudinal temperature gradient of the crystal rod is then increased, and the growth speed of the monocrystalline silicon is increased, thereby realizing the process of crystal pulling with the variable temperature gradient.

In order to more clearly illustrate technical solutions of embodiments of the present disclosure or the technical solutions in the related art, the accompanying drawings used in the embodiments or the related art are briefly described below. The drawings described below are merely a part of the embodiments of the present disclosure. Based on these drawings, those skilled in the art can obtain other drawings without any creative effort.

In order to better understand technical solutions of the present disclosure, the technical solutions in the embodiments of the present disclosure are clearly and completely described in details with reference to the accompanying drawings.

It is appreciated that, the described embodiments are merely part of the embodiments of the present disclosure rather than all of the embodiments.

The terms used in the embodiments of the present disclosure are merely for the purpose of describing specific embodiments, rather than limiting the present disclosure. The terms "a", "an", "the" and "said" in a singular form in the embodiments of the present disclosure and the attached claims are also intended to include plural forms thereof, unless noted otherwise.

It should be understood that the term "and/or" used in the context of the present disclosure is to describe a correlation relation of related objects, indicating that there may be three relations, e.g., A and/or B may indicate only A, both A and B, and only B. In addition, the symbol "/" in the context generally indicates that the relation between the objects before and after the "/" is an "or" relationship.

In the related art, a thermal field is generally designed to achieve the crystal pulling with a variable temperature gradient during the crystal pulling process, improving stability of the constant-diameter body growth process of the monocrystalline silicon and the growth speed of the pulled crystal under the premise of ensuring the success rate of seeding. However, when the crystal is pulled in a conventional thermal field, the distance between the water-cooling heat shield and the surface of silicon melt is fixed, which may cause the longitudinal temperature gradient of the crystal cannot be further increased, thus resulting in a negative impact on the growth speed of the monocrystalline silicon.

<FIG> is a structural schematic diagram showing an apparatus for manufacturing a monocrystalline silicon according to an embodiment of the present disclosure. As shown in <FIG>, the apparatus for manufacturing a monocrystalline silicon includes a single crystal furnace <NUM>, a quartz crucible <NUM>, a heater <NUM>, a water-cooling heat shield <NUM>, a heat insulation cylinder <NUM>, a guide shell <NUM>, a crystal pulling device <NUM> and crystal <NUM>. The crystal pulling device <NUM> is configured to pull the crystal <NUM> (i.e., the single crystal silicon crystal).

The heater <NUM> is configured to heat polycrystalline silicon raw material(s) and dopants in the quartz crucible <NUM> so that the polycrystalline silicon raw material is melted to form silicon melt <NUM>. The water-cooling heat shield <NUM> can lower temperature at surface of the crystal <NUM>, increase temperature gradient within the crystal <NUM>, which can greatly increase growth speed of the crystal without changing temperature gradient of the silicon melt <NUM>.

Since the silicon wafer has a strict requirement on oxygen content to avoid serious accidents such as burning of a manufactured chip during use, it is necessary to reduce the oxygen concentration in the silicon melt, the oxygen elements in the silicon melt mostly exist in a form of Si-O. A protective gas (argon and/or nitrogen) is converged to the center of the quartz crucible <NUM> through the guide shell <NUM>, thereby accelerating volatilization of Si-O and thus greatly reducing the oxygen concentration in the silicon melt. Moreover, the guide shell <NUM> may also function as heat shielding, and the collected protective gas can accelerate the cooling of the crystal, to increase the axial temperature gradient of the crystal and growth speed of the crystal.

In the monocrystalline silicon growth device of the related art, a water-cooling heat shield <NUM> is connected to a guide shell <NUM>, and their relative position is unchanged, that is, a distance H of the guide shell <NUM> penetrating into the heater <NUM> is unchanged, and a distance h between bottom of the water-cooling heat shield <NUM> and a surface <NUM> of silicon melt <NUM> in the quartz crucible <NUM> is also unchanged. If the success rate of seeding of the monocrystalline silicon is lower than a preset distance h during the manufacturing process or a break rate is high during a constant-diameter body growth process, it is difficult to adjust the value of h. Moreover, if the distance h between bottom of the water-cooling heat shield <NUM> and the surface <NUM> of the silicon melt <NUM> is required to be changed, the structural size of the guide shell <NUM> or the size of thermal field shall be changed accordingly, which is cumbersome and expensive.

In some embodiments of the present disclosure, in the seeding process, the distance h between the bottom of the water-cooling heat shield <NUM> and the surface <NUM> of the silicon melt <NUM> is increased, so that heat absorption capacity of the water-cooling heat shield <NUM> is weakened at the surface of the silicon melt and thus the temperature at the growth interface is more stable, thereby improving the success rate of seeding. In the constant-diameter body growth process, the distance h between the bottom of the water-cooling heat shield <NUM> and the surface <NUM> of the silicon melt <NUM> is reduced, so that crystal growth is more stable, heat absorption capacity of the water-cooling heat shield <NUM> for the crystal rod is enhanced, and the temperature of the crystal rod becomes lower, thereby increasing the longitudinal temperature gradient of the crystal rod, and realizing the crystal pulling with the variable temperature gradient.

However, in the related art, the guide shell <NUM> and the water-cooling heat shield <NUM> are located at preset fixed positions, so that h value cannot be adjusted, which is adverse to improving the success rate of seeding.

In the present disclosure, the water-cooling heat shield <NUM> has a flat bottom, so that the heat absorption capacity of the water-cooling heat shield <NUM> for the crystal rod can be further enhanced compared with an oblique bottom, without changing the minimum distance between the water-cooling heat shield <NUM> and the surface of the silicon melt <NUM>.

In an embodiment of the present disclosure, the apparatus for manufacturing a monocrystalline silicon further includes a connector <NUM> and a water-cooling heat shield lifting bar <NUM> configured to lift the water-cooling heat shield <NUM>. One end of the water-cooling heat shield lifting bar <NUM> is fixed on the furnace wall of the single crystal furnace <NUM>, that is, it is connected to a motor on the furnace wall of the single crystal furnace <NUM>. The other end of the water-cooling heat shield lifting bar <NUM> is connected to the water-cooling heat shield <NUM>, so that the water-cooling heat shield <NUM> can be lifted or lowered under control of rotation of a motor. In some embodiments, the motor can be controlled locally or remotely through a wired and/or wireless signal. For example, a control signal can be remotely sent to a signal receiving terminal of the motor by a user terminal device, so that rotation of the motor can be controlled.

The connector <NUM> is configured to connect the water-cooling heat shield lifting bar <NUM> to the guide shell <NUM>. In an embodiment, the connector <NUM> includes a lifting limit portion <NUM>, a support bar <NUM> and a lifting buckle <NUM>. Two ends of the support bar <NUM> are connected to the lifting limit portion101 and the guide shell <NUM>, respectively. One end of the lifting buckle <NUM> is fixedly connected to the water-cooling heat shield lifting bar <NUM>, and the other end of the lifting buckle <NUM> is buckled on the support bar <NUM>.

In some embodiments, when the water-cooling heat shield lifting bar <NUM> is lifted upwards, the distance between the guide shell <NUM> and the surface of the silicon melt remains unchanged, that is, lifting of the water-cooling heat shield does not drive the guide shell <NUM> upward. When the lifting buckle <NUM> is also lifted along the support bar <NUM> to the lifting limit portion <NUM>, if the water-cooling heat shield lifting bar <NUM> is continuously lifted upwards, the lifting buckle <NUM> drives the lifting limit portion101 to move upwards and simultaneously drives the guide shell <NUM> to move upwards.

When the water-cooling heat shield lifting bar <NUM> is lowered, the lifting buckle <NUM> is also lowered along the support bar <NUM> to a flange of the guide shell <NUM>, and the guide shell <NUM> is driven to move downwards. When the guide shell <NUM> is lowered to a position where the flange of the guide shell <NUM> abuts against the heat insulation cylinder <NUM>, and the position of the guide shell <NUM> does not change anymore. At this time, the water-cooling heat shield lifting bar <NUM> is continuously lowered, and the water-cooling heat shield <NUM> is continuously lowered either, so that the water-cooling heat shield <NUM> moves downwards independently relative to the guide shell <NUM>. Therefore, the distance between the bottom of the water-cooling heat shield <NUM> and the surface of the silicon melt is further reduced, and the heat absorbing capacity of the water-cooling heat shield from the crystal rod is improved, thereby realizing the crystal pulling with the variable temperature gradient.

The water-cooling heat shield <NUM> can adjust the distance between the water-cooling heat shield <NUM> and the surface of the silicon melt up and down under the action of the water-cooling heat shield lifting bar <NUM> and the connector <NUM>. In this embodiment, the distance between the water-cooling heat shield <NUM> and the surface of the silicon melt is adjustable in a range from <NUM> to <NUM>.

As shown in <FIG>, in the seeding process, the water-cooling heat shield lifting bar <NUM> lifts the water-cooling heat shield <NUM> in a direction away from the surface of the silicon melt, and the guide shell <NUM> is lifted under the action of the connector <NUM> as the water-cooling heat shield lifting bar <NUM> rises, so that the distance between the bottom of the water-cooling heat shield <NUM> and the surface of the silicon melt is adjusted to a first preset distance. In an embodiment, the first preset distance is in a range from <NUM> to <NUM>. The first preset distance is set such that the water-cooling heat shield is far away from the high-temperature silicon melt during the seeding process, so as to avoid temperature fluctuations. Therefore, the temperature at the growth interface is stable, and the success rate of seeding is high.

As shown in <FIG>, in the constant-diameter body growth process, the water-cooling heat shield lifting bar <NUM> drives the water-cooling heat shield <NUM> to move in the direction away from the surface of the silicon melt, and the guide shell <NUM> also is also lowered as the water-cooling heat shield lifting bar <NUM> moves until the flange of the guide shell <NUM> abuts against the heat insulation cylinder <NUM>. The water-cooling heat shield <NUM> is continuously lowered in a direction close to the surface of the silicon melt, so that the distance between the bottom of the water-cooling heat shield <NUM> and the surface of the silicon melt is adjusted to a second preset distance. In an embodiment, the second preset distance is in a range from <NUM> to <NUM>. At this time, the water-cooling heat shield <NUM> is lowered relative to the guide shell <NUM>, so that the distance between the bottom of the water-cooling heat shield <NUM> and the surface of the silicon melt is further reduced, and the heat absorbing capacity of the water-cooling heat shield from the crystal rod is improved, thereby realizing the crystal pulling with the variable temperature gradient.

<FIG> is a schematic flowchart showing a method for manufacturing a monocrystalline silicon according to an embodiment of the present disclosure. As shown in <FIG>, the present disclosure provides a method for manufacturing a monocrystalline silicon with a Czochralski process, and the method includes the following steps.

Step (<NUM>) Providing a polycrystalline silicon and a dopant to a quartz crucible.

Step (<NUM>) Placing the quartz crucible in a single crystal furnace and vacuumized, and the polycrystalline silicon is melt under an atmosphere of a protective gas to obtain silicon melt.

Step (<NUM>) After the temperature of the silicon melt is stable, immersing a seed crystal into the silicon melt to start seeding. During the seeding process, the water-cooling heat shield is lifted in the direction away from the surface of the silicon melt so that the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt is adjusted to a first preset distance.

Step (<NUM>) After the seeding is completed, begin shouldering to continuously pull the crystal so that the diameter of the crystal is gradually increased to a preset width. For example, the preset width may be in a range from <NUM> to <NUM>, such as <NUM>, <NUM>, <NUM>.

Step (<NUM>) Starting a constant-diameter body growth process. In the constant-diameter body growth process, the water-cooling heat shield is lowered in the direction close to the surface of the silicon melt so that the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt is adjusted to the second preset distance.

Step (<NUM>) After the constant-diameter body growth is completed, entering a tailing stage, so that the crystal has a gradually reduced diameter until it is separated from the silicon melt.

Step (<NUM>) After cooling to room temperature, taking the grown crystal out from the furnace as monocrystalline silicon.

In this solution, during the seeding process, the water-cooling heat shield is lifted upward to increase the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt, thereby increasing the success rate of seeding. In the constant-diameter body growth process, the water-cooling heat shield is lowered to reduce the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt, so that the growth of the crystal is more stable. Moreover, since the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt becomes smaller, the heat absorption capacity of the water-cooling heat shield is enhanced, so that the temperature of the crystal rod is lowered, the longitudinal temperature gradient of the crystal rod is then increased, and the growth speed of the monocrystalline silicon is increased, thereby realizing the process of crystal pulling with the variable temperature gradient.

In step (<NUM>), the protective gas is argon and/or nitrogen.

In step (<NUM>), during the seeding process, a seeding speed is in a range from <NUM>/h to <NUM>/h, a seeding length is in a range from <NUM> to <NUM>, and the crystal diameter is in a range from <NUM> to <NUM>.

In an embodiment, the seeding speed may be <NUM>/h, <NUM>/h, <NUM>/h, <NUM>/h, <NUM>/h, <NUM>/h or <NUM>/h, which are not limited thereto.

In the seeding process, the diameter of the crystal may be <NUM>, <NUM>, <NUM>, or <NUM>, etc., and the length of the crystal can be <NUM>, <NUM>, <NUM>, <NUM> or <NUM>, etc., which are not limited thereto.

During the seeding process, the distance between the bottom of the water-cooling heat shield <NUM> and the surface <NUM> of the silicon melt is adjusted to the first preset distance. The first preset distance may be in a range from <NUM> to <NUM>, e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. In an embodiment, the distance between the bottom of the water-cooling heat shield <NUM> and the surface <NUM> of the silicon melt is adjusted to <NUM> to increase the distance between the bottom of the water-cooling heat shield and the surface of silicon melt, thereby improving the success rate of seeding.

In step (<NUM>), the temperature in the single crystal furnace is in a range from 1250sp to 1300sp. For example, the temperature in the single crystal furnace may be 1250sp, 1255sp, 1260sp, 1265sp, 1270sp, 1275sp, 1280sp, 1285sp, 1290sp, 1295sp, or 1300sp. In an embodiment, the temperature in the single crystal furnace is 1300sp. It shall be understood that, a suitable seeding temperature may effectively improve the success rate of seeding. The temperature in the single crystal furnace may also be other values, which are not limited thereto.

In step (<NUM>), during the shouldering process, the first pulling speed of the crystal is in a range from <NUM>/h to <NUM>/h, so that the diameter of the crystal is gradually increased to <NUM> to <NUM>.

In an embodiment, the first pulling speed may be <NUM>/h, <NUM>/h, <NUM>/h, or <NUM>/h, etc., and the diameter of the crystal is gradually increased to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>, etc., which are not limited thereto. It shall be understood that, in the shouldering process, heat dissipation volume of the crystal is small, and the crystal has not entered into the water-cooling heat shield so that heat of the crystal cannot be effectively taken away by the water-cooling heat shield. Therefore, the temperature gradient inside the crystal is small, so that the growth speed of the crystal is slow and the pulling speed of the crystal is also slow in order to ensure stability of crystal pulling. Moreover, throughout the entire shouldering process, the temperature in the single crystal furnace may be gradually reduced and shall not be increased.

A range of the diameter of the crystal may be designed and controlled according to the size requirements of the solar cell on the silicon wafer, which is not limited thereto.

In step (<NUM>), during the constant-diameter body growth process, the distance between the bottom of the water-cooling heat shield <NUM> and the surface <NUM> of the silicon melt is adjusted to the second preset distance. The second preset distance is in a range from <NUM> to <NUM>, e.g., it may be <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. In an embodiment, the distance between the bottom of the water-cooling heat shield <NUM> and the surface <NUM> of the silicon melt is adjusted to <NUM> so that the distance between the bottom of the water-cooling heat shield and the surface <NUM> of the silicon melt is reduced, thereby improving the heat absorbing capacity of the water-cooling heat shield from the crystal rod, and thereby realizing the crystal pulling with the variable temperature gradient.

In an embodiment, the distance between the water-cooling heat shield <NUM> and the surface of the silicon melt is adjustable in a range from <NUM> to <NUM>, e.g., it may be <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>, which are not limited thereto. A height difference between the first preset distance and the second preset distance is in a range from <NUM> to <NUM>.

In an embodiment, during the constant-diameter body growth process, a lowering speed of the water-cooling heat shield is in a range from <NUM>/h to <NUM>/h, a total lowering time of the water-cooling heat shield is less than <NUM> hours, and the second pulling speed of the crystal is in a range from <NUM>/h to <NUM>/h.

In an embodiment, the lowering speed of the water-cooling heat shield <NUM> may be <NUM>/h, <NUM>/h, <NUM>/h, <NUM>/h, <NUM>/h or <NUM>/h. The total lowering time may be <NUM> hour, <NUM> hours, <NUM> hours, or <NUM> hours, etc..

The second pulling speed may be <NUM>/h, <NUM>/h, <NUM>/h, <NUM>/h, <NUM>/h, or <NUM>/h, etc., which are not limited thereto. It shall be understood that, during the constant-diameter body growth process, the crystal has begun to enter the water-cooling heat shield area or completely immersed into the water-cooling heat shield area. The water-cooling heat shield may quickly absorb the heat of the crystal, so that the temperature gradient of the crystal rod becomes larger. The growth speed of the crystal is increased in order to ensure the growth efficiency in this process, thereby increasing the pulling speed of the crystal.

In step (<NUM>), after the constant-diameter body growth process is completed, it enters the tailing stage, so that the diameter of the crystal is gradually reduced until the crystal is separated from the silicon melt. In this process, a third pulling speed of the crystal is in a range from <NUM>/h to <NUM>/h, e.g., the third pulling speed may be <NUM>/h, <NUM>/h, <NUM>/h, <NUM>/h, <NUM>/h, <NUM>/h or <NUM>/h. In the tailing stage, the temperature of the single crystal furnace rises rapidly.

Step (<NUM>) Providing a polycrystalline silicon raw material and a dopant to a quartz crucible.

Step (<NUM>) Placing the quartz crucible in a single crystal furnace and vacuumized, and the polycrystalline silicon raw material is melt under an atmosphere of a protective gas to obtain silicon melt.

Step (<NUM>) After the temperature of the silicon melt is stable, immersing a seed crystal into the silicon melt by the pulling device to start seeding. During seeding, the temperature in the single crystal furnace is set as 1300sp, the seeding speed is controlled as <NUM>/h, the diameter of the crystal is <NUM>, and the length of the crystal is <NUM>. During the seeding process, the water-cooling heat shield is lifted in the direction away from the surface of the silicon melt so that the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt is adjusted to <NUM>.

Step (<NUM>) After the seeding is completed, begin shouldering to continuously pull the crystal, and the pulling speed is lowered to <NUM>/h, so that diameter of the crystal is gradually increased to <NUM>.

Step (<NUM>) Starting a constant-diameter body growth process. In the constant-diameter body growth process, the water-cooling heat shield is lowered in the direction close to the surface of the silicon melt, so that the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt is adjusted to <NUM>, the lowering speed of the water-cooling heat shield is <NUM>/h, and the pulling speed of the crystal is <NUM>/h.

Step (<NUM>) After the constant-diameter body growth is completed, entering a tailing stage, and the pulling speed of the crystal is controlled as <NUM>/h, so that the crystal has a gradually reduced diameter until it is separated from the silicon melt.

In the method for manufacturing a monocrystalline silicon according to the present disclosure, a <NUM>-inch thermal field is taken as an example, in its crystal pulling process with the variable temperature gradient, the success rate of seeding may be increased by <NUM>%-<NUM>%. In the constant-diameter body growth stage, the value of h may be reduced. The crystal pulling speed may be increased by <NUM>%-<NUM>% by only using the crystal pulling process with the variable temperature gradient without changing the thermal field.

In the method and the apparatus for manufacturing a monocrystalline silicon, in the seeding process, the water-cooling heat shield is lifted upwards to increase the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt, thereby increasing the success rate of seeding. In the constant-diameter body growth process, the water-cooling heat shield is lowered to reduce the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt, so that the crystal growth process is more stable. Moreover, since the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt becomes smaller, the heat absorption capacity of the water-cooling heat shield is enhanced, so that the temperature of the crystal rod becomes lower, the longitudinal temperature gradient of the crystal rod is then increased, and the growth speed of the monocrystalline silicon is increased, thereby realizing the process of crystal pulling with the variable temperature gradient.

Claim 1:
A method for manufacturing a monocrystalline silicon with a Czochralski process, comprising:
providing a polycrystalline silicon and a dopant to a quartz crucible;
placing the quartz crucible in a single crystal furnace and vacuumizing the furnace, and melting the polycrystalline silicon under an atmosphere of a protective gas to obtain silicon melt;
after a temperature of the silicon melt is stable, immersing a seed crystal into the silicon melt to start a seeding process, during the seeding process, lifting a water-cooling heat shield in a direction away from a surface of the silicon melt to adjust a distance between a bottom of the water-cooling heat shield and the surface of the silicon melt to a first preset distance;
after the seeding process is completed, performing a shouldering process to continuously pull the crystal, and gradually increase a diameter of the pulled crystal to a preset width;
starting a constant-diameter body growth process, lowering the water-cooling heat shield in a direction towards the surface of the silicon melt to adjust the distance between the bottom of the water-cooling heat shield and the surface of the silicon melt to a second preset distance;
after the constant-diameter body growth process is completed, entering a tailing stage during which the diameter of the pulled crystal is gradually reduced until the pulled crystal is separated from the silicon melt; and
cooling the pulled crystal to room temperature and taking out the cooled crystal from the single crystal furnace as the monocrystalline silicon,
characterised in that
during said performing the shouldering process to continuously pulling the crystal, a first pulling speed of the crystal is in a range from <NUM>/h to <NUM>/h, so that the diameter of the crystal is gradually increased to <NUM>-<NUM>.