JP5782323B2 - Single crystal pulling method - Google Patents

Description

  The present invention relates to a single crystal pulling method for pulling a silicon single crystal by the Czochralski method (hereinafter referred to as “CZ method”).

The CZ method is widely used for the growth of silicon single crystals. In this method, as shown in FIG. 4, the silicon melt M is formed in the crucible 50 by heating the heater 52 in the furnace body 55, the seed crystal P is brought into contact with the liquid surface M1, and the crucible 50 is rotated. At the same time, the single crystal C is formed at the lower end of the seed crystal P by pulling the seed crystal P upward while rotating the seed crystal P in the direction opposite to the crucible 50.
As shown in FIG. 4, a radiation shield 51 is provided above the crucible 50 so as to surround the pulling region of the single crystal C. The radiation shield 51 effectively cuts off the radiant heat to the outer peripheral surface of the single crystal C to be grown, thereby promoting the solidification of the single crystal C being pulled and quickly cooling the single crystal C. Can do.

In recent years, the diameter of wafers has been increasing in order to improve device yield. For this reason, when the silicon single crystal C is enlarged and such a single crystal is pulled up, it is necessary to form a large amount of the silicon melt M in the crucible 50 having a large diameter.
However, when the amount of the melt in the crucible 50 increases, convection in the melt becomes complicated, and it becomes difficult to obtain desired crystal characteristics such as oxygen concentration and dislocation-free crystals.

In order to solve the above-described problem, a cusp magnetic field application method is adopted in which a cusp magnetic field is applied to the melt M to control convection of the melt M.
For example, in Patent Document 1, the cusp magnetic field strength is set to 300 to 600 G (Gauss), and the atmospheric pressure is controlled to 50 torr or more to uniformly control the oxygen concentration distribution in the crystal growth direction and the oxygen concentration distribution in the crystal plane. In addition, a method that can prevent dislocations has been proposed.

JP 2000-239096 A

However, in the method disclosed in Patent Document 1, it is difficult for oxygen in the melt and oxygen dissolved from the crucible to reach the silicon single crystal (solid-liquid interface), and the oxygen concentration is 1.3 × 10. There was a problem that it was difficult to grow a silicon single crystal having a high concentration oxygen exceeding ¹⁸ atoms / cm ³ .
In order to obtain a silicon single crystal having such a high oxygen concentration, the oxygen pressure in the silicon melt is suppressed by setting the furnace pressure at a high value to suppress the evaporation of oxygen from the silicon melt. Can be increased. However, in this case, the silicon and oxygen compound (oxide) that evaporates from the melt surface becomes difficult to be discharged outside the furnace, and this oxide solidifies in the furnace and falls into the melt, which is taken into the crystal. There was a risk of dislocation.

The present invention has been made under the circumstances as described above, and is a single crystal pulling method for pulling a silicon single crystal from a crucible by the Czochralski method. To provide a single crystal pulling method capable of growing a single crystal having a high oxygen concentration of 1.3 × 10 ¹⁸ atoms / cm ³ or more without causing dislocation even when the amount of the melt is increased. With the goal.

The single crystal pulling method according to the present invention made to solve the above-mentioned problem is that a silicon melt is formed in a crucible by heating of a heater, and the above-mentioned pair of upper and lower electromagnetic coils arranged around the crucible, A single crystal pulling method for applying a cusp magnetic field to a silicon melt and pulling up a silicon single crystal having an oxygen concentration of 1.3 × 10 ¹⁸ atoms / cm ³ (old-ASTM) or more from the crucible by the Czochralski method. In the above method, the furnace pressure when pulling up the silicon single crystal is controlled between 40 to 80 torr and the crucible rotation speed between 3 and 8 rpm, and the upper magnetic field and the lower applied by the pair of upper and lower electromagnetic coils field strength ratio of the magnetic field (the top field / bottom field) is controlled between 0.80 to 0.90, and the liquid level of the silicon melt 0 (m ) Position, and when the upper direction from the liquid level in the vertical direction perpendicular to the liquid level is a positive direction and the lower direction from the liquid level is a negative direction, it is on the central axis of the silicon single crystal. The zero magnetic field horizontal position where the magnetic field intensity in the vertical direction is 0 (Gauss) is controlled between -10 and +100 mm.

Thus, by controlling the pressure in the furnace when pulling up the single crystal between 40 to 80 torr, the evaporation of oxygen dissolved in the melt is suppressed, and the oxygen in the melt is taken into the crystal. This makes it easy to form a state in which oxide evaporated from the surface of the melt is easily discharged out of the furnace.
Further, by controlling the number of revolutions of the crucible between 3 and 8 rpm, a large amount of oxygen contained in the crucible can be dissolved in the melt by friction between the melt and the crucible.
In addition, by controlling the magnetic field strength ratio (upper magnetic field / lower magnetic field) applied by a pair of upper and lower electromagnetic coils between 0.80 and 0.90 , it springs from the bottom of the crucible directly below the crystal (solid-liquid interface). The molten liquid convection that rises toward the free liquid surface side is formed predominantly, and oxygen dissolved in the molten liquid from the bottom of the crucible is easily taken into the crystal by riding on this convection, and a high oxygen concentration crystal can be obtained.
Also, by controlling the horizontal position of the zero magnetic field between −10 and +100 mm, a Lorentz force is formed by the current (electrons) flowing in the crucible rotation direction and the magnetic flux density in the vertical direction, and directly below the crystal (solid-liquid interface). From the free liquid surface of the melt, the melt convection toward the crucible wall side can be formed.
As a result, a strong convection heading from directly below the crystal to the crucible wall is formed, overlapping with the effect of the magnetic field strength ratio, and foreign matter floating on the liquid surface (for example, foreign matter that solidifies in the furnace and falls into the melt) Can be kept away from the crystal (solid-liquid interface) to prevent dislocation of the crystal.
Therefore, according to the present invention, regardless of the amount of silicon melt in the crucible (even when the amount of melt in the crucible increases), the single oxygen having a high oxygen concentration of 1.3 × 10 ¹⁸ atoms / cm ³ or more. The crystal can be grown without causing dislocation.

According to the present invention, in the single crystal pulling method in which the silicon single crystal is pulled from the crucible by the Czochralski method, even when the amount of the melt in the crucible increases with an increase in the diameter of the wafer, 1.3 × A single crystal having a high oxygen concentration of 10 ¹⁸ atoms / cm ³ or more can be grown without causing dislocation.

FIG. 1 is a cross-sectional view showing the configuration of a single crystal pulling apparatus in which a single crystal pulling method according to the present invention is carried out. FIG. 2 is a partially enlarged cross-sectional view of the single crystal pulling apparatus of FIG. FIG. 3 is a flow showing the flow of the single crystal pulling method according to the present invention. FIG. 4 is a cross-sectional view for explaining a conventional single crystal pulling method.

Hereinafter, embodiments of a single crystal pulling method according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of a single crystal pulling apparatus in which a single crystal pulling method according to the present invention is carried out. FIG. 2 is a partially enlarged cross-sectional view of the single crystal pulling apparatus of FIG.
This single crystal pulling apparatus 1 includes a furnace body 2 formed by superposing a pull chamber 2b on a cylindrical main chamber 2a, a crucible 3 provided in the furnace body 2, and a semiconductor loaded in the crucible 3. It has a resistance heater 4 (hereinafter simply referred to as a heater) that melts a raw material (raw material polysilicon) to form a silicon melt M, and a pulling mechanism 5 that pulls up a single crystal C to be grown.

The heater 4 is provided with a cylindrical slit portion 4 a as a heat generating portion so as to surround the crucible 3.
The crucible 3 has a double structure, and the inner side is constituted by a quartz glass crucible 3a and the outer side is constituted by a graphite crucible 3b.
The pulling mechanism 5 has a winding mechanism 5a driven by a motor and a pulling wire 5b wound up by the winding mechanism 5a, and a seed crystal P is attached to the tip of the wire 5b.

In the main chamber 2a, a radiation shield 6 surrounding the periphery of the single crystal C is disposed above and in the vicinity of the crucible 3. This radiation shield 6 has an opening at the top and bottom, shields extra radiation heat from the heater 4 and the like on the growing single crystal C, and rectifies the gas flow in the furnace.
The radiation shield 6 is fixed in the furnace body 2, and the distance dimension (gap) between the lower end of the radiation shield 6 and the liquid level M1 of the molten liquid raises the crucible 3 with the growth of the single crystal C. Thus, control is performed to maintain a predetermined distance.

  Further, as shown in FIG. 1, a pair of upper and lower cusp magnetic field application electromagnetic coils 13 and 14 are installed outside the main chamber 2a so as to surround the periphery of the main chamber 2a. An MCZ method (Magnetic field applied CZ method) in which a single crystal is grown by applying a magnetic field is performed. In this embodiment, the MCZ method is used to form a predetermined magnetic field (magnetic field lines B in FIG. 2) on the silicon melt M, thereby controlling the convection of the silicon melt M.

  As shown in FIG. 1, the single crystal pulling apparatus 1 includes a heater control unit 9 that controls the amount of power supplied to the heater 4 that controls the temperature of the silicon melt M, and a motor that rotates the crucible 3 around the pulling axis. 10 and a motor control unit 10a that controls the rotation speed of the motor 10. Further, an elevating device 11 that controls the height of the crucible 3, an elevating device control unit 11a that controls the elevating device 11, and a wire reel rotating device control unit 12 that controls the pulling speed and the crystal rotation speed of the single crystal C. I have. Furthermore, the electromagnetic coil control part 15 which performs operation | movement control of the electromagnetic coils 13 and 14 for cusp magnetic field application is provided. Each of these control units 9, 10 a, 11 a, 12, 15 is connected to an arithmetic control device 8 b of the computer 8.

In the single crystal pulling apparatus 1 configured in this manner, first, raw material polysilicon is loaded into the quartz glass crucible 3a, and based on the program stored in the storage device 8a of the computer 8, along the flow of FIG. The single crystal pulling process is started.
First, the inside of the furnace body 2 is set to a predetermined atmosphere (preferably an argon gas atmosphere), and the raw material polysilicon charged in the crucible 3 is melted by heating by the heater 4 to form a silicon melt M (FIG. 3). Step S1).
Further, the motor control unit 10a and the lifting device control unit 11a are operated by a command from the arithmetic control device 8b, and the crucible 3 is rotated at a predetermined rotational speed (rpm) at a predetermined height position.

Next, the electromagnetic coil controller 15 is actuated by a command from the arithmetic and control unit 8b, and predetermined currents are caused to flow through the cusp magnetic field applying electromagnetic coils 13 and 14, respectively. As a result, a cusp magnetic field having a predetermined strength (line of magnetic force B in FIG. 2) is applied in the silicon melt M (step S2 in FIG. 3).
Further, the pulling mechanism 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 P attached to the wire 5b is brought into contact with the silicon melt M, and necking for melting the tip of the seed crystal P is performed to form the neck portion P1 (step S3 in FIG. 3).

When the neck portion P1 is formed, the pulling conditions are adjusted with parameters such as the power supplied to the heater 4, the pulling speed (usually a speed of several millimeters per minute), the magnetic field strength to be applied, etc., according to the command of the arithmetic control device 8b. Further, the seed crystal P is rotated at a predetermined rotation speed (for example, 12 rpm) in a direction opposite to the rotation direction of the crucible 3 (step S4 in FIG. 3).
Then, an enlarged diameter part for expanding the neck part P1 to a desired diameter is formed (step S5 in FIG. 3), and then a straight body part for maintaining the desired diameter is formed (step S6 in FIG. 3). Then, a reduced diameter portion that is reduced from a desired diameter is formed (step S7 in FIG. 3).

The pressure in the furnace when pulling up the silicon single crystal is controlled between 40 and 80 torr.
This suppresses the evaporation of oxygen dissolved in the melt, making it easier for oxygen in the melt to be taken into the crystal and allowing the oxide evaporated from the melt surface to be discharged out of the furnace. can do.
Further, the rotational speed of the crucible 3 is controlled between 3 and 8 rpm by the control of the motor control unit 10a. Thereby, a large amount of oxygen contained in the crucible can be dissolved in the melt by friction between the melt and the crucible.
That is, when the crucible rotation speed is less than 3 rpm, the friction between the melt M and the crucible 3 is weakened, and the amount of oxygen dissolved in the melt M is reduced. Therefore, a high oxygen concentration (1.3 × 10 ¹⁸ atoms / cm ³ or more This is because it is difficult to obtain a crystal of On the other hand, if the crucible rotation speed exceeds 8 rpm, the convection of the melt M is disturbed, making it difficult to obtain dislocation-free crystals.

Further, each coil is controlled by the electromagnetic coil controller 15 so that the magnetic field strength ratio (upper magnetic field / lower magnetic field) applied by the upper and lower cusp magnetic field applying electromagnetic coils 13 and 14 is between 0.7 and 0.95. The current flowing through 13 and 14 is controlled.
By controlling the magnetic field strength ratio in this way, a melt convection F (see FIG. 2) that swells from the bottom of the crucible 3 directly below the crystal (solid-liquid interface) and moves toward the free liquid surface is formed preferentially. .
As a result, oxygen dissolved in the melt M from the bottom of the crucible is easily taken into the single crystal C on the convection F, and a crystal having a desired high oxygen concentration is easily obtained.

Further, in the vertical direction perpendicular to the liquid level M1 of the silicon melt M, the horizontal position H (the liquid level M1 and the liquid level M1) where the magnetic field strength in the vertical direction on the central axis of the silicon single crystal is 0 (Gauss). The position of the parallel plane: called zero magnetic field horizontal position) is controlled.
Specifically, when the liquid level M1 is a 0 (mm) position, the upward direction from the liquid level M1 is a positive direction, and the downward direction from the liquid level M1 is a negative direction, the 0 magnetic field horizontal position is −10. The height of the crucible 3 is adjusted and controlled by the installation position of the pair of upper and lower electronic coils and the lifting device 11 so as to be between ˜ + 100 mm.
By controlling the zero magnetic field horizontal position H in this way, a Lorentz force is formed by the current (electrons) flowing in the crucible rotation direction and the magnetic flux density in the vertical direction. Melt convection E (see FIG. 2) can be formed through the liquid surface toward the crucible wall side.
As a result, a strong convection E directed from the crystal directly to the crucible wall is formed in superposition with the effect of the magnetic field strength ratio, and foreign matter floating on the liquid surface M1 (for example, oxide solidifies in the furnace and falls into the molten liquid). The foreign matter) can be kept away from the crystal (solid-liquid interface) to prevent dislocation of the crystal.

  Here, when the zero magnetic field horizontal position H is lower than −10 mm, it is difficult to form the melt convection E toward the crucible wall side from directly below the crystal (solid-liquid interface) through the free liquid surface of the melt. Thus, the frequency at which the single crystal C undergoes dislocation increases. On the other hand, if the zero magnetic field horizontal position H is higher than +100 mm, the melt convection E from the position just below the crystal (solid-liquid interface) toward the crucible wall becomes too strong, and oxygen in the melt M becomes crystalline. This is because it is difficult to obtain crystals with a desired high oxygen concentration.

As described above, according to the present embodiment, as described above, the furnace diameter, the crucible rotation speed, the magnetic field strength ratio, and the zero magnetic field horizontal position are controlled within a predetermined range, thereby increasing the wafer diameter. Accordingly, even when the amount of the melt in the crucible increases, a single crystal having a high oxygen concentration of 1.3 × 10 ¹⁸ atoms / cm ³ or more can be grown without causing dislocation.

The above-mentioned crystal rotation speed is mainly used for diameter control when pulling up the silicon single crystal, and is not particularly limited. However, in relation to the melt convection E, it should be controlled to 15 rpm or less. Is preferred.
Here, when the number of rotations of the crystal exceeds 15 rpm, the melt convection E directed from directly under the crystal (solid-liquid interface) toward the crucible wall becomes stronger, and oxygen in the melt M hardly reaches the crystal. This is because it may be difficult to obtain a crystal having a desired high oxygen concentration.
The crystal rotation speed is more preferably 3 rpm or more in order to stabilize the shape of the silicon single crystal to be pulled up.

The single crystal pulling method according to the present invention will be further described based on examples.
Based on the embodiment shown in FIGS. 1 to 3, three single crystals were pulled under the conditions shown in Table 1 (Examples 1 to 12 and Comparative Examples 1 to 7). In Table 1, the magnetic field strength ratio is a magnetic field strength ratio (upper magnetic field / lower magnetic field) between an upper magnetic field and a lower magnetic field applied by a pair of upper and lower cusp magnetic field applying electromagnetic coils. The zero magnetic field horizontal position (mm) means that the liquid level M1 of the silicon melt M is the 0 (mm) position and the upward direction from the liquid level M1 in the vertical direction perpendicular to the liquid level M1 is normal. , The height at which the magnetic field strength in the vertical direction on the central axis of the silicon single crystal is 0 (Gauss) when the downward direction from the liquid level M1 is a negative direction (for example, the sign in FIG. 2) H).
Also, under all conditions, the target oxygen concentration is 1.3 × 10 ¹⁸ atoms / cm ³ or more, the amount of raw silicon is 300 kg, the diameter of the silicon single crystal to be pulled is 12 inches, the crystal rotation speed is 12 rpm, the inertness in the furnace The gas (Ar gas) flow rate was 100 L / min.

In Table 2, as the experimental results corresponding to the conditions in Table 1, the number of crystals pulled up in the dislocation state (the number of dislocations), and among the crystals pulled up without dislocation, the crystal length of the straight body portion is 0 mm, The number (the number of satisfactory oxygen concentration characteristics) in which the oxygen concentration at three positions of 500 mm and 1000 mm was 1.3 × 10 ¹⁸ atoms / cm ³ or more is shown.

As shown in Table 2, Examples 1 to 12 are preferable conditions in which both the number of dislocation-free and the number of satisfactory oxygen concentration characteristics are two or more.
Specifically, the magnetic field strength ratio is between 0.7 and 0.95, the zero magnetic field horizontal position is between -10 and +100 mm, the furnace pressure is between 40 and 80 torr, and the crucible rotation speed is between 3 and 8 rpm. Good results were obtained under the conditions.

From the results of the above examples, according to the single crystal pulling method according to the present invention, even if the single crystal to be pulled is large, the oxygen concentration is 1.3 × 10 ¹⁸ atoms / cm ³ or more. It was confirmed that a single crystal having a concentration can be grown without causing dislocation.

DESCRIPTION OF SYMBOLS 1 Single crystal pulling apparatus 2 Furnace body 3 Crucible 4 Heater 4a Heat generating part 5 Pulling mechanism 6 Radiation shield C Single crystal M Silicon melt P Seed crystal

Claims (2)

A silicon melt is formed in the crucible by the heating of the heater, and a cusp magnetic field is applied to the silicon melt by a pair of upper and lower electromagnetic coils arranged around the crucible, and the crucible is obtained by the Czochralski method. A single crystal pulling method for pulling up a silicon single crystal having an oxygen concentration of 1.3 × 10 ¹⁸ atoms / cm ³ (old-ASTM) or higher from
While controlling the furnace pressure when pulling up the silicon single crystal between 40 to 80 torr and the crucible rotation speed between 3 and 8 rpm,
Controlling the magnetic field strength ratio (upper magnetic field / lower magnetic field) between the upper magnetic field and the lower magnetic field applied by the pair of upper and lower electromagnetic coils between 0.80 and 0.90 ;
And the liquid level of the silicon melt is 0 (mm), and the upward direction from the liquid level in the vertical direction perpendicular to the liquid level is a positive direction, and the downward direction from the liquid level is a negative direction. A single crystal pulling method, wherein a zero magnetic field horizontal position at which the magnetic field strength in the vertical direction on the central axis of the silicon single crystal is 0 (Gauss) is controlled between −10 and +100 mm. .   The method for pulling a single crystal according to claim 1, wherein the crystal rotation speed when pulling up the silicon single crystal is controlled to 15 rpm or less.

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