JP2011073897A - Doping method and doping device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a doping method and a doping device for adding dopant impurities to a silicon melt, in which the dopant impurities are efficiently incorporated into the silicon melt and the evaporation of the dopant impurities incorporated into the silicon melt can be suppressed. <P>SOLUTION: The doping method for adding the dopant impurities to a silicon melt M in a crucible 3 in a crystal pulling apparatus 1 which pulls up a single crystal from the crucible 3 in a furnace body 2 by the Czochralski method includes the steps of: forming the silicon melt M in the crucible 3; forming a solidified layer in a predetermined surface region in the silicon melt M; and introducing the dopant impurities into the silicon melt M from the surface region in which the solidified layer is not formed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a doping method for adding a dopant impurity to a silicon melt before growing a single crystal in a single crystal pulling apparatus that pulls up while growing the single crystal by the Czochralski method (hereinafter referred to as “CZ method”), and The present invention relates to a doping apparatus.

  In the single crystal growth step by the CZ method, a doping treatment is performed in which a dopant impurity (additive) is added to the silicon melt in the crucible in order to give a predetermined resistivity to the single crystal. Conventionally, this doping process is performed by adding trace elements such as arsenic and antimony as dopant impurities directly to the silicon melt in the quartz glass crucible. Specifically, for example, it has been carried out by dropping a granular element for doping into a silicon melt.

By the way, in such a doping apparatus in which a particulate trace element is charged into the silicon melt, a trace element inlet is provided at a position away from the silicon melt surface.
Therefore, in the said doping apparatus, the fall distance of the granular dopant impurity became long, the dopant impurity evaporated and scattered during the fall, and there existed a subject that sufficient quantity of dopant impurities was not added.

In order to solve such a problem, Patent Document 1 describes doping by doping arsenic, which is a dopant impurity, in a high-temperature atmosphere in a furnace to form arsenic gas and directly injecting the arsenic gas onto the silicon melt surface. A method is disclosed.
In the doping apparatus disclosed in Patent Document 1, an outer cylinder 51 is disposed above a silicon melt M formed in a crucible 50 as shown in FIG. 10, and solid arsenic D is further contained in the outer cylinder 51. Is placed. The container 52 has a discharge pipe 52a opened downward as shown in the figure.

In such a doping apparatus, when the solid arsenic D in the container 52 is heated by the heat of the silicon melt M, the arsenic gas vaporized and formed in the container 52 is discharged from the discharge pipe 52a into the silicon melt M. It is injected against the liquid level. As a result, the arsenic gas injected from the discharge pipe 52a is taken into the melt M.
Further, the lower end of the outer cylinder 51 that covers the periphery of the container 52 is immersed near the liquid surface of the silicon melt M or in the liquid so that the arsenic gas is taken into the silicon melt M more effectively. Has been made.

JP 2001-342094 A

However, in the doping apparatus disclosed in Patent Document 1, even if the dopant impurity is taken into the silicon melt M, it evaporates before moving to the single crystal pulling step, and the dopant concentration in the silicon melt is There was a problem of a significant drop.
That is, N-type dopant impurities such as arsenic, antimony, and phosphorus have high vapor pressure (for example, in the case of arsenic, the sublimation point is 615 ° C. with respect to the silicon melting point of 1412 ° C. under 1 atm), and the silicon melt M However, most of it was evaporated from the high-temperature silicon melt.

Further, the dopant impurity evaporated from the silicon melt M adheres to a radiation shield or the like provided above the crucible, and then solidifies and falls into the melt, causing a transition of single crystal.
Furthermore, since most of the dopant impurities are evaporated from the silicon melt M as described above, there is a problem that the amount of the dopant that is wasted increases, which adversely affects the environment and increases the cost.

  The present invention has been made under the circumstances as described above, and a doping method capable of efficiently incorporating dopant impurities into a silicon melt and suppressing evaporation of the dopant impurities incorporated into the silicon melt. An object is to provide a doping apparatus.

  In order to solve the above-described problems, a doping method according to the present invention is a single crystal pulling apparatus that pulls a single crystal from a crucible in a furnace body by a Czochralski method, and dopant impurities are added to a silicon melt in the crucible. A doping method to be added, the step of forming a silicon melt in the crucible, the step of forming a solidified layer in a predetermined liquid level region in the silicon melt, and the liquid level on which the solidified layer is not formed And introducing a dopant impurity into the silicon melt from a region.

According to such a method, once the dopant impurity is taken into the silicon melt, evaporation thereof can be suppressed by the solidified layer formed on the liquid surface.
Therefore, the dopant impurities can be efficiently taken into the silicon melt, reducing the contamination in the furnace and the generation of foreign substances that have been caused by evaporation of dopant impurities such as arsenic, and preventing dislocation of the silicon single crystal. can do.
Moreover, since the amount of useless dopant impurities is reduced, the cost can be significantly reduced.

Further, in the step of forming a solidified layer in a predetermined liquid surface region in the silicon melt, the lower layer portion of the silicon melt is heated and the upper layer portion is cooled, and the solidified layer is disposed above the silicon melt. It is desirable to arrange a cover member that covers the liquid surface area that is not formed.
By such a method, a solidified layer can be formed in the liquid surface region that is not covered by the cover member on the surface of the silicon melt.

Further, in the step of forming a solidified layer in a predetermined liquid surface area in the silicon melt, the crystal is grown while pulling up the crystal from the silicon melt in the crucible, and the pulling is stopped while the crystal shoulder is formed. Is desirable.
Also by such a method, since the crystal shoulder as the solidified layer is formed on the liquid surface, evaporation of the dopant impurity taken into the silicon melt can be suppressed.

  In order to solve the above-described problems, a doping apparatus according to the present invention is a method in which a crucible in a furnace is heated by a heater to form a silicon melt in the crucible, and a single crystal is formed from the crucible by the Czochralski method. A doping apparatus for adding a dopant impurity to the silicon melt in the crucible in a single crystal pulling apparatus for pulling up the upper surface of the crucible, with the upper part of the crucible being separated from the heater. And a cover member that covers a predetermined liquid surface area in the silicon melt, and a doping means that introduces dopant impurities into the silicon melt from the predetermined liquid surface area covered by the cover member. Has characteristics.

According to such a structure, a solidified layer is formed in the area | region which is not covered with the said cover member in the liquid level of a silicon melt. If the dopant impurities are taken into the silicon melt from the liquid surface region covered with the cover member, the evaporation can be suppressed by the solidified layer formed on the liquid surface.
Therefore, the dopant impurities can be efficiently taken into the silicon melt, reducing the contamination in the furnace and the generation of foreign substances that have been caused by evaporation of dopant impurities such as arsenic, and preventing dislocation of the silicon single crystal. can do.
Moreover, since the amount of useless dopant impurities is reduced, the cost can be significantly reduced.

  Alternatively, in order to solve the above-described problem, a doping apparatus according to the present invention is configured to heat a crucible in a furnace body with a heater to form a silicon melt in the crucible, and to produce a single crystal from the crucible by the Czochralski method. A doping apparatus for adding a dopant impurity to the silicon melt in the crucible in a single crystal pulling apparatus for pulling up a crystal, wherein a crystal shoulder is grown from the silicon melt in the crucible and the pulling is stopped. And a doping means for introducing a dopant impurity into the silicon melt from a liquid surface region around the crystal shoulder.

Even with such a configuration, since a crystal shoulder as a solidified layer is formed on the liquid surface of the silicon melt, if the dopant impurity is taken into the silicon melt from the liquid surface region around the crystal shoulder, the liquid melt The evaporation can be suppressed by the crystal shoulder formed on the surface.
Therefore, the dopant impurities can be efficiently taken into the silicon melt, reducing the contamination in the furnace and the generation of foreign substances that have been caused by evaporation of dopant impurities such as arsenic, and preventing dislocation of the silicon single crystal. can do.
Moreover, since the amount of useless dopant impurities is reduced, the cost can be significantly reduced.

  According to the present invention, in a doping method and a doping apparatus for adding a dopant impurity to a silicon melt, the dopant impurity can be efficiently taken into the silicon melt and the evaporation of the dopant impurity taken into the silicon melt can be suppressed. A doping method and a doping apparatus can be obtained.

FIG. 1 is a block diagram showing an overall configuration of a single crystal pulling apparatus to which a first embodiment of a doping method and a doping apparatus according to the present invention is applied. FIG. 2 is an enlarged view of the main part of the single crystal pulling apparatus of FIG. 1, and is a view for explaining the arrangement conditions of the doping apparatus of the present invention. FIG. 3 is a flow showing the flow of the first embodiment of the doping method according to the present invention. FIG. 4 is an enlarged view of a main part of the single crystal pulling apparatus of FIG. 1 and is a view for explaining a state during the doping process. FIG. 5 is a view showing a modification of the cover member provided in the doping apparatus of the present invention. FIG. 6 is a view showing a modification of the cover member provided in the doping apparatus of the present invention. FIG. 7 is a view showing a modification of the cover member provided in the doping apparatus of the present invention. FIG. 8 is a diagram showing a main part configuration of a single crystal pulling apparatus to which the second embodiment of the doping method and the doping apparatus according to the present invention is applied. FIG. 9 is a flow showing the flow of the second embodiment of the doping method according to the present invention. FIG. 10 is a diagram for explaining the configuration of a conventional doping apparatus.

  Hereinafter, embodiments of the doping method and the doping apparatus of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an overall configuration of a single crystal pulling apparatus to which a first embodiment of a doping method and a doping apparatus according to the present invention is applied.

A single crystal pulling apparatus 1 shown in FIG. 1 includes a furnace body 2 formed by superposing a pull chamber 2b on a main chamber 2a, a crucible 3 provided in the furnace body 2, and a semiconductor loaded in the crucible 3. It has a side heater 4a and a bottom heater 4b for melting the raw material (raw material silicon) M, and a pulling mechanism 5 for pulling up the single crystal C to be grown. The crucible 3 has a double structure, and is composed of a quartz glass crucible 3a on the inside and a graphite crucible 3b on the outside.
The pulling mechanism 5 includes a winding mechanism 5a driven by a motor and a pulling wire 5b wound up by the winding mechanism 5a, and a seed chuck for holding a seed crystal at the tip of the wire 5b when pulling a single crystal. 7 is provided.

Further, in the main chamber 2a, an upper portion and a lower portion are formed so as to surround the pulling region of the single crystal C above and in the vicinity of the crucible 3, and an extra portion from the side heater 4a or the like is added to the growing single crystal C. A radiation shield 6 is provided to prevent radiant heat from being applied. The radiation shield 6 can be moved up and down in the main chamber 2a by winding and unwinding the wire 6b by the lifting drive unit 6a.
In addition, a heat insulating member 18 is provided around the side heater 4a in the main chamber 2a.

Further, in this single crystal pulling apparatus 1, a doping process for incorporating an N-type dopant impurity such as arsenic into the silicon melt M is performed before pulling up the silicon single crystal. For this process, a doping apparatus 15 is used as shown in FIG.
The doping apparatus 15 includes a doping unit 16 that drops, for example, a particulate trace element for dopant onto the surface of the silicon melt M, and a cover member 17 that is disposed above the silicon melt M.

As shown in FIG. 2, the cover member 17 is formed in an inverted funnel shape (the lower portion has a conical diameter-expanded portion 17 a and the upper portion has a cylindrical portion 17 b). A locking hole 17c is provided in the upper end portion of the cylindrical portion 17b, and the cover member 17 is suspended from the lower end of the wire 5b by locking the seed chuck 7 in the locking hole 17c.
The cover member 17 is made of, for example, quartz.

  The cover member 17 will be described in more detail. The lower end inner diameter φ1 of the enlarged diameter portion 17a is formed smaller than the lower end inner diameter φh of the radiation shield 6. If the inner diameter of the crucible 3 is φc, the inner diameter φ1 is preferably φ1 = 0.1 to 0.5φc.

The height L1 of the enlarged diameter portion 17a constituting the lower portion of the cover member 17 is formed to be L1 = 0.01 to 1.0φc, and more preferably L1 = 0.1 to 0.3φc. It is formed. The height L2 of the cylindrical portion 17b constituting the upper portion of the cover member 17 is formed such that L2 ≧ 0.01φc, more preferably L2 = 0.3 to 1.0φc.
Furthermore, the side wall inclination angle θ of the enlarged diameter portion 17a with respect to the vertical axis (the inclination angle of a straight line connecting the upper end and the lower end of the side wall of the enlarged diameter portion 17a) is preferably 30 to 85 °.

The doping means 16 supplies a dopant impurity supply source 16a for storing a dopant impurity formed by granulating a trace element such as arsenic or antimony, and supplies a granular dopant impurity stored by the dopant impurity supply source 16a to the silicon melt M. A supply pipe 16b.
The supply pipe 16b is inserted into the chamber through an insertion hole 22 provided in the upper portion of the main chamber 2a, for example, and is further inserted into the cover member 17 through an insertion hole 23 provided in the side wall of the cover member 17. . The distal end of the supply pipe 16b is disposed so as to be positioned at the approximate center of the lower end portion of the cover member 17 (the enlarged diameter portion 17a).

  In the doping apparatus of the present invention, the doping means 16 is not limited to the form shown in FIG. That is, in addition to a configuration in which granular dopant impurities can be supplied to the silicon melt M, a configuration in which gaseous dopant impurities are jetted and supplied to the silicon melt M may be employed.

Further, as shown in FIG. 1, the single crystal pulling apparatus 1 rotates through heater control units 9a and 9b that respectively control the amount of power supplied to the side heater 4a and the bottom heater 4b, and a rotary shaft 19 that supports the crucible 3. And a motor control unit 10a for controlling the rotation speed of the motor 10. Further, an elevating device 11 that controls the height of the crucible 3 and an elevating device control unit 11 a that controls the elevating device 11 are provided. Furthermore, a winding control unit 12 that controls the driving of the winding mechanism 5a is provided.
Each of these control units 9a, 9b, 10a, 11a, 12 and the elevating drive unit 6a is connected to an arithmetic control device 8b of the computer 8.

  In the single crystal pulling apparatus 1 configured as described above, for example, arsenic is taken into the silicon melt as a dopant impurity based on a program stored in the storage device 8a of the computer 8 before the single crystal pulling step. A doping process is performed.

The doping method of the present invention will be described along the flow of FIG.
First, when raw material silicon is loaded into the crucible 3, the heater control unit 9 is operated by a command from the arithmetic control device 8 b to supply predetermined power to the side heater 4 a and the bottom heater 4 b, respectively. Thereby, the crucible 3 is heated, and the silicon melt M is formed in the crucible 3 (step S1 in FIG. 3).

Next, the elevator drive unit 6 a is driven by an instruction from the arithmetic control device 8 b to raise the radiation shield 6 to a predetermined height and raise the crucible 3 by the elevator device 11. Thereby, the crucible 3 is arranged to be separated from the side heater 4a and the bottom heater 4b upward (step S2 in FIG. 3).
More specifically, as shown in FIG. 2, the height of the crucible 3 is the gap dimension MP in the height direction between the liquid level of the silicon melt M and the upper end of the side heater 4a (liquid level height−upper side of the side heater. The height is MP ≧ 0 (that is, the liquid level is higher than the upper end of the side heater), and if the inner diameter of the crucible 3 is φc, it is preferably adjusted to MP = 0.1 to 1.0φc. The
Further, the gap dimension Gh between the lower end portion of the radiation shield 6 and the liquid surface of the silicon melt M is set to Gh ≧ 0.01φc, and more preferably adjusted to Gh = 0.1 to 1.0φc.

  Further, the heater control unit 9a is controlled, and the power supplied to the side heater 4a is reduced to a predetermined value (step S3 in FIG. 3). As a result, the lower side portion of the crucible 3 is heated to maintain its temperature, and the silicon melt M in the crucible 3 is brought to a lower temperature state as the upper layer portion. In addition, the rotation speed of the crucible 3 is controlled to 10 rpm or less.

Next, the doping apparatus 15 is attached.
In attaching the doping apparatus 15, first, the cover member 17 is attached to the seed chuck 7, and the cover member 17 is suspended from the wire 5b. Then, the length of the wire 5b is adjusted by the winding mechanism 5a, and the arrangement of the cover member 17 is determined (step S4 in FIG. 3). The wire 5b is controlled to be in a non-rotating state.
More specifically, the cover member 17 preferably has a gap size Gc of Gc ≧ 0 between the lower end portion thereof and the liquid surface of the silicon melt M, and the inner diameter of the crucible 3 is preferably φc. It is adjusted to 0.3φc.

  When the cover member 17 is arranged, the supply pipe 16b of the doping means 16 is inserted into the chamber from obliquely above the main chamber 2a, and further inserted into the cover member 17. The distal end of the supply pipe 16b is disposed at the approximate center of the lower end portion of the cover member 17 (step S5 in FIG. 3).

Here, since the heating to the upper layer part of the silicon melt M is controlled to be small as described above, it is naturally cooled gradually from the peripheral part of the liquid surface.
On the other hand, since the cover member 17 covers the central portion of the liquid surface of the silicon melt M as described above, the covered liquid surface region M1 is surrounded by the radiant heat of the cover member 17 as shown in FIG. The temperature is higher than that of the liquid surface region M2.
For this reason, cooling proceeds in the liquid surface region M2 not covered by the cover member 17, and a ring-shaped solidified layer is formed in the liquid surface region M2 (step S6 in FIG. 3).

When the liquid surface region M2 is solidified, granular dopant impurities are dropped from the dopant impurity supply source 16a of the doping means 16 to the unsolidified liquid surface region M1 through the supply pipe 16b (step of FIG. 3). S7).
The dopant impurities supplied from the supply pipe 16b are taken into the melt M from the liquid surface region M1, and the doping process proceeds.
In addition, during the doping process, the dopant surface is always supplied from the supply pipe 16b to the unsolidified liquid surface region M1, and the dopant impurity once taken into the silicon melt M enters the liquid surface region M2. Evaporation is suppressed by the formed solidified layer.

When the doping process for a predetermined time is completed, the doping apparatus 15, that is, the doping means 16 and the cover member 17 are removed (step S8 in FIG. 3).
Next, the elevating device 11 is driven and controlled, and the height position of the crucible 3 is adjusted to the height at the time of pulling the single crystal (step S9 in FIG. 3).
Moreover, the elevation drive part 6a is controlled and the height position of the radiation shield 6 is adjusted (step S10 of FIG. 3).
Further, the power supplied to the side heater 4a is increased by the control of the heater control unit 9 (step S11 in FIG. 3).
Thereby, the silicon melt M in the crucible 3 is further heated, and the solidified layer formed in the liquid surface region M2 is remelted. Then, after temperature adjustment of the chamber 2 and the silicon melt M, it is possible to shift to a single crystal pulling step (step S12 in FIG. 3).

As described above, according to the first embodiment of the present invention, in the doping process for incorporating a dopant impurity such as arsenic into the silicon melt M in the crucible, the liquid level of the silicon melt M is cooled, A cover member 17 is disposed to cover the predetermined area M1 on the liquid level.
As a result, a solidified layer is formed in the liquid surface region M2 excluding the liquid surface region M1 covered by the cover member 17, and dopant impurities are introduced into the silicon melt M from the region M1 covered by the cover member 17. .
As a result, evaporation of the dopant impurities once taken into the silicon melt M is suppressed by the solidified layer formed on the liquid surface.
Accordingly, the dopant impurities can be efficiently taken into the silicon melt M, and in the furnace, the contamination in the furnace and the generation of foreign substances, which have conventionally been caused by the evaporation of the dopant impurities such as arsenic, are reduced, and the silicon single crystal is dislocated. Can be prevented.
Moreover, since the amount of useless dopant impurities is reduced, the cost can be significantly reduced.

Note that, as shown in the first embodiment, the cover member 17 is preferably formed in a reverse funnel shape for the reason of the attachment structure to the seed chuck 7 and the efficiency of radiant heat.
However, the reverse funnel shape applicable to the cover member 17 is not limited to the reverse conical shape as shown in the above embodiment.
For example, the enlarged-diameter portion 17a may have a bell shape or a trumpet shape shown in FIGS. 5 (a), 5 (b) to 7 (a), (b). However, in any case, the lower end inner diameter φ1 of the enlarged diameter portion 17a, the inner diameter φ2 of the cylindrical portion 17b, and the straight inclination angle connecting the upper end and the lower end of the side wall of the enlarged diameter portion 17a shown in FIG. As for θ, the height dimension L1 of the enlarged diameter portion 17a, and the height dimension L2 of the cylindrical portion 17b, it is desirable to apply the conditions of the inverted conical diameter enlarged portion 17a shown in FIG.

Subsequently, a second embodiment of a doping method and a doping apparatus according to the present invention will be described. FIG. 8 is a diagram for explaining the second embodiment, and is an enlarged view of a main part of the single crystal pulling apparatus showing a state in which the doping apparatus of the present invention is applied to the single crystal pulling apparatus. .
In the description of the second embodiment, the same members as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

Further, the apparatus configuration of the second embodiment according to the present invention is mainly different in that the cover member 17 shown in the first embodiment is not provided. That is, the doping apparatus 15 is constituted by the doping means 16.
Further, the other components of the single crystal pulling apparatus 1 (not shown in FIG. 8) can be the same as those shown in FIG. 1 except for the program stored in the storage device 8a of the computer 8. For this reason, in the following description, the reference numerals shown in FIG. 1 are also used.

A second embodiment according to the doping method of the present invention will be described along the flow of FIG.
First, when raw material silicon is loaded into the crucible 3, the heater control unit 9 is operated by a command from the arithmetic control device 8 b to supply predetermined power to the side heater 4 a and the bottom heater 4 b, respectively. Thereby, the crucible 3 is heated, and the silicon melt M is formed in the crucible 3 (step St1 in FIG. 9).

Next, the power supply to the bottom heater 4b is stopped under the control of the heater control unit 9, and the power supplied to the side heater 4a is increased (step St2 in FIG. 9).
And the height positional relationship of the side heater 4a and the liquid level of the silicon melt M is adjusted by raising / lowering the crucible 3 with the raising / lowering apparatus 11 (step St3 of FIG. 9). Specifically, the gap dimension MP in the height direction between the liquid level of the silicon melt M and the upper end portion of the side heater 4a (liquid level height−upper side heater height) is MP ≦ 0 (that is, the liquid level). If the inner diameter of the crucible 3 is φc, it is preferably adjusted so that MP = _0.1 to _1.0φc.

  When the crucible height is adjusted, the elevating drive unit 6a is driven, the radiation shield 6 is moved up and down, and the gap dimension Gh between the radiation shield 6 and the silicon melt M is adjusted within a predetermined range. (Step St4 in FIG. 9). Specifically, if the inner diameter of the crucible 3 is φc, the gap dimension Gh is 0.01 to 1.0 φc, and more preferably the gap dimension Gh is 0.01 to 0.5 φc.

Next, the motor control unit 10a is actuated by a command from the arithmetic control device 8b, and the crucible 3 is rotated at a low speed of, for example, 1 rpm or less. Alternatively, the crucible 3 may be in a non-rotating state.
Then, in a state where the seed crystal is held on the seed chuck 7, the winding control unit 12 is operated by the command of the arithmetic control device 8b, the winding mechanism 5a is operated, and the wire 5b is lowered.
Then, the seed crystal held by the seed chuck 7 is brought into contact with the silicon melt M to dissolve the seed crystal and form the crystal shoulder C (solidified layer) without forming the neck (step St5 in FIG. 9). ).
The crystal shoulder C may be a single crystal or a polycrystal, but has a diameter as large as possible within the range of the crucible diameter (for example, the diameter φs is 50 to 200 mm and the height hs is 10 to 100 mm). Is preferred. Further, if the peripheral edge of the crystal shoulder C is formed in a substantially circular shape, it is not always necessary to rotate the wire 5b (seed chuck 7) around the axis.

As shown in the drawing, when the crystal shoulder C is formed at the center of the liquid surface of the silicon melt M, the doping device 15 is attached.
Specifically, the supply pipe 16 b of the doping means 16 in the doping apparatus 15 is inserted into the main chamber 2 a from the insertion hole 22, and is further passed from the insertion hole 6 a provided in the radiation shield 6 to the back side of the radiation shield 6. . The distal end portion of the supply pipe 16b is arranged toward the liquid surface region M3 around the crystal shoulder C (that is, the liquid surface that is not solidified).

In this state, dopant impurities are dropped from the dopant impurity supply source 16a of the doping means 16 through the supply pipe 16b toward the liquid surface region M3 (step St6 in FIG. 9). As a result, for example, arsenic is incorporated as a dopant impurity into the silicon melt M, and the doping process proceeds.
Here, since the liquid surface center portion of the silicon melt M is covered with the crystal shoulder C, the arsenic once taken into the silicon melt M is in a state where evaporation is suppressed.

When the doping process for a predetermined time is completed, the doping apparatus 15 is removed (step St7 in FIG. 9).
Next, the elevating device 11 is driven and controlled, and the height position of the crucible 3 is adjusted to the height at the time of pulling the single crystal (step St8 in FIG. 9).
Further, the elevation drive unit 6a is controlled to adjust the height position of the radiation shield 6 (step St9 in FIG. 9).
Furthermore, the power supplied to the side heater 4a is increased under the control of the heater control unit 9 (step St10 in FIG. 9).
Thereby, the silicon melt M in the crucible 3 is further heated, and the crystal shoulder C is remelted (step St11 in FIG. 9). Then, after temperature adjustment of the chamber 2 and the silicon melt M, it is possible to shift to a single crystal pulling step.

As described above, according to the second embodiment of the present invention, the crystal shoulder C having a large diameter is grown and formed in the doping process for incorporating a dopant impurity such as arsenic into the silicon melt M in the crucible.
Here, dopant impurities are introduced from the periphery of the crystal shoulder C, that is, from the liquid surface region not solidified.
As a result, evaporation of dopant impurities once taken into the silicon melt M is suppressed by the crystal shoulder C functioning as a lid.
Accordingly, the dopant impurities can be efficiently taken into the silicon melt M, and in the furnace, the contamination in the furnace and the generation of foreign substances, which have conventionally been caused by the evaporation of the dopant impurities such as arsenic, are reduced, and the silicon single crystal is dislocated. Can be prevented.
Moreover, since the amount of useless dopant impurities is reduced, the cost can be significantly reduced.

  The doping method and the doping apparatus according to the present invention will be further described based on examples. In this example, a doping state was created in accordance with the above embodiment, and the effect of the present invention was verified.

[Reference Example 1]
As Reference Example 1, it was verified whether a solidified layer capable of sufficiently suppressing evaporation of dopant impurities could be formed on the liquid surface of the silicon melt without using the cover member shown in the first embodiment. In this experiment, first, using a crucible having an inner diameter of 500 mm, the gap dimension (dimension Gh shown in FIG. 2) between the radiation shield and the silicon melt liquid level is adjusted to 120 mm, The gap dimension (size MP shown in FIG. 2) with the side heater upper end height was adjusted to −130 mm (that is, the side heater upper end was higher than the liquid level).

  Then, after the raw silicon is melted in the crucible with the power supplied to the side heater being 130 kW, the gap dimension (dimension Gh shown in FIG. 2) between the radiation shield and the liquid surface of the silicon melt remains 120 mm. The gap dimension (dimension MP shown in FIG. 2) between the liquid surface height of the silicon melt and the side heater upper end height was adjusted to +130 mm (that is, the state where the melt liquid surface was higher than the upper end of the side heater).

Further, the bottom heater arranged below the crucible was not energized, and the power supplied to the side heater arranged around the crucible was increased to 190 kW.
When the state of the silicon melt was observed under these conditions, the temperature at the peripheral surface of the silicon melt decreased from 1685 K (Kelvin) to 1624 K, and the liquid level in a ring shape with a width of 21 mm from the inner peripheral surface of the crucible. It was confirmed that was solidified (liquid surface solidification rate was about 15%).
If a solidified area of this level can be obtained, a certain suppression effect can be expected for the evaporation of dopant impurities. However, since the liquid surface solidification rate is only about 15%, the dopant impurities can be effectively evaporated. It was insufficient to suppress.

[Example 1]
In Example 1, the cover member was used as in the first embodiment, and it was verified whether a solidified layer capable of sufficiently suppressing evaporation of dopant impurities could be formed on the liquid surface of the silicon melt.
In this experiment, after the silicon melt was formed in the same crucible as in Example 1, the gap dimension (dimension Gh shown in FIG. 2) between the radiation shield and the silicon melt liquid level was 120 mm, and the silicon melt liquid level was high. And the side heater upper end height (dimension MP shown in FIG. 2) were adjusted to +130 mm (that is, the molten liquid surface was higher than the side heater upper end).
Further, as shown in the first embodiment according to the present invention, the cover member is arranged above the liquid surface of the silicon melt, the bottom heater is not energized, and the power supplied to the side heater is increased to 172 kW.

When the state of the silicon melt was observed under these conditions, the temperature at the peripheral surface of the silicon melt decreased from 1685 K (Kelvin) to 1584 K, and the liquid level in a ring shape with a width of 154 mm from the inner peripheral surface of the crucible. It was confirmed that was solidified (liquid surface solidification rate was about 81% or more).
It was confirmed that if this solidified area could be achieved, a sufficient suppression effect on the evaporation of dopant impurities could be expected.

[Example 2]
In Example 2, the crystal shoulder was grown as in the second embodiment, and it was verified whether a solidified layer capable of sufficiently suppressing evaporation of dopant impurities could be formed on the liquid surface of the silicon melt.
In this experiment, a crucible having an inner diameter of 500 mm was used, and the gap dimension (dimension Gh shown in FIG. 2) between the radiation shield and the silicon melt liquid level was adjusted to 120 mm. The gap dimension with respect to the upper end height (dimension MP shown in FIG. 2) was adjusted to −130 mm (that is, the side heater upper end was higher than the liquid level).
Then, the power supplied to the side heater is reduced to 118.38 kW without energizing the bottom heater, and the seed crystal held by the seed chuck is removed as shown in FIG. 8 in the second embodiment of the present invention. The crystal was grown at a pulling rate of 0.5 mm / min to form a crystal shoulder with a diameter of 310 mm and a height of 50 mm.

Thereafter, the pulling was stopped (pulling speed 0 mm / min), and the power supplied to the side heater was increased to 125.28 kW in order to maintain the crystal shoulder thus grown in a stopped state.
In this state, the liquid surface solidification rate of the silicon melt was 33% or more, and it was confirmed that if this solidified area could be achieved, a sufficient inhibitory effect on the evaporation of dopant impurities could be expected.

DESCRIPTION OF SYMBOLS 1 Single crystal pulling apparatus 2 Furnace body 2a Main chamber 2b Pull chamber 3 Crucible 4a Side heater 4b Bottom heater 5 Pulling mechanism 5a Winding mechanism 5b Wire 6 Radiation shield 6a Lifting drive part 6b Wire 7 Seed chuck 8 Computer 8a Storage device 8b Operation control Device 9a Heater control unit 9b Heater control unit 10 Motor 10a Motor control unit 11 Lifting device 11a Lifting device control unit 15 Doping device 16 Doping means 16a Dopant impurity supply source 16b Supply pipe 17 Cover member 17a Expanding portion 17b Cylindrical portion 19 Rotating shaft C Crystal shoulder M Silicon melt

Claims (5)

In a single crystal pulling apparatus for pulling a single crystal from a crucible in a furnace body by a Czochralski method, a doping method for adding a dopant impurity to a silicon melt in the crucible,
Forming a silicon melt in the crucible;
Forming a solidified layer in a predetermined liquid surface area in the silicon melt;
Introducing a dopant impurity into the silicon melt from a liquid surface area where the solidified layer is not formed. In the step of forming a solidified layer in a predetermined liquid surface area in the silicon melt,
Heating the lower layer of the silicon melt and cooling the upper layer,
The doping method according to claim 1, wherein a cover member that covers a liquid surface region where the solidified layer is not formed is disposed above the silicon melt. In the step of forming a solidified layer in a predetermined liquid surface area in the silicon melt,
Growing while pulling up crystals from the silicon melt in the crucible,
2. The doping method according to claim 1, wherein the pulling is stopped in a state where the crystal shoulder is formed. A crucible in the furnace is heated by a heater to form a silicon melt in the crucible, and a dopant is added to the silicon melt in the crucible in a single crystal pulling apparatus that pulls a single crystal from the crucible by the Czochralski method. A doping apparatus for adding impurities,
A cover member disposed above the silicon melt with the upper part of the crucible being separated from the heater, and covering a predetermined liquid surface area in the silicon melt;
A doping apparatus comprising: doping means for introducing a dopant impurity into the silicon melt from the predetermined liquid surface region covered with the cover member. A crucible in the furnace is heated by a heater to form a silicon melt in the crucible, and a dopant is added to the silicon melt in the crucible in a single crystal pulling apparatus that pulls a single crystal from the crucible by the Czochralski method. A doping apparatus for adding impurities,
A crystal shoulder is grown from the silicon melt in the crucible and is provided with doping means for introducing dopant impurities into the silicon melt from a liquid surface region around the crystal shoulder in a state where the crystal shoulder is stopped. A doping apparatus.

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