JP2014169211A - Method for producing semiconductor single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a semiconductor single crystal that may reduce a variation in a resistivity in a cross section, particularly in a central part of the single crystal.SOLUTION: Provided is a method for producing a semiconductor single crystal by a FZ process in which the semiconductor single crystal is grown by partially heating a raw crystal with an induction heating coil while rotating the raw crystal to form a molten zone and by moving the molten zone from one side of the raw crystal to the other side. The rotating direction of the semiconductor single crystal is changed alternately so that the semiconductor single crystal is rotated in one direction about a central axis, after which it is rotated in the direction opposite to the one direction and that a rotating acceleration when the rotating direction is changed from the one direction to the opposite direction is different from that when the rotating direction is changed from the opposite direction to the one direction.

Description

  The present invention relates to a method for producing a semiconductor single crystal by FZ method (floating zone method or floating zone melting method).

The FZ method is used, for example, as one method for producing a semiconductor single crystal such as a silicon single crystal that is most frequently used as a material for semiconductor elements.
Usually, in order to give a desired resistivity to a silicon single crystal, N-type or P-type impurity doping is required. In the FZ method, a gas doping method in which a dopant gas is sprayed onto a melting zone is known (see Non-Patent Document 1).

As the dopant gas, for example, PH ₃ or the like is used for doping P (phosphorus) which is an N-type dopant, and B ₂ H ₆ or the like is used for doping B (boron) which is a P-type dopant.
The resistivity of a silicon single crystal varies depending on the concentration difference in the crystals of these N-type and P-type dopants. However, in the case of doping only an N-type dopant or only a P-type dopant in normal crystal production, the resistivity The rate decreases with increasing dopant loading.

  In order to obtain a silicon single crystal having a desired resistivity, it is necessary to appropriately maintain the dopant addition amount calculated based on the resistivity of the raw material and the desired resistivity. An FZ silicon single crystal having a desired resistivity can be obtained by growing the single crystal by the FZ method while adjusting the concentration and flow rate of the supplied dopant gas while keeping the dopant addition amount appropriate.

  In particular, a wafer manufactured from a silicon single crystal obtained by the FZ method is desired to have a uniform resistivity as much as possible over the entire in-plane surface with small variation in resistivity within the wafer surface. Therefore, it is required to make the resistivity distribution in the cross section of the FZ single crystal that is the raw material of the wafer more uniform. In order to satisfy this requirement, particularly in the production of a large-diameter FZ single crystal having a diameter of 150 mm or more, a method of growing while alternately changing the rotation direction of the single crystal (see, for example, Patent Document 1) has been proposed, and resistivity distribution is proposed. Is made uniform.

  In Patent Document 2, in order to stabilize the in-plane resistivity distribution of the single crystal, the rotation conditions of the single crystal such as the forward / reverse rotation ratio and the rotation angle are set within a certain range during the manufacture of the FZ single crystal. It has been proposed.

JP 7-315980 A JP 2008-266102 A

“Floating-Zone Silicon” by WOLFGAN KELLER, ALFRED MUHLBAUER, p. 82-92, MARCEL DEKKER, INC. Issue

  In recent years, the required diameter of FZ wafers has been increasing, and in particular, the demand for FZ wafers having a diameter of 200 mm or more is increasing. On the other hand, the resistivity variation in the wafer surface is required to be equal to or greater than that of a wafer having a smaller diameter even if the diameter is increased, and it is necessary to further reduce the resistivity variation in the cross section of the FZ single crystal.

  As described above, using the method of manufacturing the FZ single crystal while alternately changing the single crystal rotation direction is effective for reducing the in-section resistivity variation of the single crystal. For example, by adjusting the crystal rotation conditions during FZ single crystal manufacture within a certain range as in Patent Document 2, it is possible to further adjust the distribution of resistivity in the cross section. However, when the crystal diameter is large (for example, 200 mm or more), the resistivity distribution in the cross section cannot be said to be sufficiently uniform, and it is particularly difficult to control the resistivity in the central portion in the single crystal cross section.

As described above, in the conventional method, although the overall shape of the resistivity distribution in the single crystal section can be flattened to some extent, there is a large variation in resistivity at the center of the single crystal, and the wafer obtained from the single crystal. There will be a large variation in resistivity.
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a method for manufacturing a semiconductor single crystal that can reduce resistivity variation particularly in the central portion in the cross section of the single crystal.

  In order to achieve the above object, according to the present invention, while rotating a raw material crystal, the raw material crystal is partially heated and melted by an induction heating coil to form a molten zone, and the molten zone is A method of manufacturing a semiconductor single crystal by an FZ method in which a semiconductor single crystal is grown by moving from one end to the other end, wherein the semiconductor single crystal is unidirectionally around a central axis during the growth of the semiconductor single crystal. After the rotation, the rotation direction is alternately changed to rotate in the direction opposite to the one direction, and the rotational acceleration when the rotation direction is changed from the one direction to the opposite direction is changed from the one direction to the one direction. There is provided a method for producing a semiconductor single crystal, characterized in that the rotational acceleration is different from that when changing the direction of rotation.

  With such a method for producing a semiconductor single crystal, the rotation of the melt can be strengthened, so that the speed of melt convection can be increased particularly at the center of the single crystal. Thereby, the resistivity variation in the crystal | crystallization center part in a single crystal cross section can be reduced.

At this time, it is preferable that the amount of rotation when rotating the semiconductor single crystal in the one direction is larger than the amount of rotation when rotating in the reverse direction.
In this way, since the melt continues to rotate in one direction, the speed of the melt convection can be further increased, and the resistivity variation can be more effectively reduced.

The rotational acceleration is preferably 900 ° / s ² or less.
In this way, it is possible to suppress a decrease in yield and productivity without inhibiting single crystallization.

  In the present invention, in the manufacture of a semiconductor single crystal by the FZ method, during the growth of the semiconductor single crystal, the semiconductor single crystal is rotated in one direction around the central axis and then rotated in the opposite direction to the one direction. Since the rotation direction is changed alternately, and the rotation acceleration when changing the rotation direction from the one direction to the reverse direction is different from that when changing the rotation direction from the reverse direction to the one direction, In particular, the melt convection at the center of the single crystal can be increased, and the resistivity variation can be reduced particularly in the center of the single crystal cross section. Thereby, the manufacturing yield and productivity of a semiconductor single crystal can be improved.

It is the schematic which shows an example of the single crystal manufacturing apparatus by FZ method. It is a figure which shows the example of the melt convection near the solid-liquid interface in a melt. It is a figure which shows the example of the rotation pattern of the semiconductor single crystal in the manufacturing method of the semiconductor single crystal of this invention. It is a figure which shows another example of the rotation pattern of the semiconductor single crystal in the manufacturing method of the semiconductor single crystal of this invention. It is a figure which shows the relationship between the rotational acceleration at the time of the reversal of a crystal rotation direction, and the maximum value of resistivity variation (sigma).

Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.
In the production of a semiconductor single crystal (FZ single crystal) by the FZ method, the present inventors have not changed the single crystal production conditions greatly when using a method of alternately changing the rotation direction of the single crystal, and Compared to this, the inventors have intensively studied in order to make the resistivity distribution in the axial direction in the cross section of the single crystal particularly uniform, without lowering the acquisition success rate of the single crystal.

As a result, it was first found that the resistivity variation at the center of the single crystal was increased due to the following causes.
The shape of the induction heating coil used in the FZ single crystal production is not completely axisymmetric, and the magnetic field distribution formed thereby cannot be perfectly axisymmetric, so the heating of the raw crystal is not axisymmetric. It is uneven. For this reason, even if the rotational speed is constant, a difference occurs in the growth speed for each crystal part.

  According to Burton et al.'S BPS theory (J. Chem. Phys. 21 (1958), 1987), the effective segregation coefficient changes depending on the crystal growth rate, and the introduction of dopant impurities from the melt to the crystal changes. It also affects the resistivity of the crystal. The resistivity in the crystal fluctuates due to the difference in the growth rate for each crystal site, and further leads to micro / macro resistivity fluctuation in the obtained wafer surface. For this reason, it is desirable to make the difference in growth rate extremely small, for example, by making the heating state in the induction heating coil as close as possible to axial symmetry or reducing the influence of non-axisymmetric heating.

  In the method of alternately changing the rotation direction of the single crystal during the growth of the single crystal, generally, the number of rotations of the single crystal can be increased to some extent, and the unevenness of crystal growth, that is, the change in resistivity can be reduced. However, since it is practically impossible to reduce the time required for changing the rotation direction of the single crystal, the rotation is always decelerated and stopped when the rotation direction is reversed. At the time of deceleration and stop, the influence of non-uniform heating cannot be avoided, resulting in non-uniform crystal growth. That is, when this method is used, resistivity variation occurs along the rotation direction inversion cycle.

  In particular, in the outer periphery of the single crystal, the influence of non-uniform heating due to non-axisymmetric heating is large, and therefore a temperature difference occurs in the in-plane portion of the outer periphery of the single crystal. As a result, a growth rate difference occurs in the in-plane portion of the outer periphery of the single crystal, and the resistivity becomes non-uniform. As described above, since the non-uniform heating is caused by the induction heating coil, the resistivity variation at the outer periphery of the single crystal is repeated corresponding to the rotation period of the single crystal.

  On the other hand, since the center portion of the single crystal is in the vicinity of the rotation center axis, there is no difference in crystal growth rate affected by non-axisymmetric heating. However, since there is a melt flow from the outer peripheral side of the single crystal to the central side during the growth of the single crystal, the melt having a temperature difference affected by the uneven heating of the outer peripheral portion of the single crystal is Flow into. In addition, at the outer periphery of the single crystal, the difference in crystal growth rate causes a difference in dopant concentration in the plane near the melt-crystal solid-liquid interface. Flow into. Thus, the resistivity fluctuates even at the center of the single crystal due to the influence of the melt flowing from the outer periphery of the single crystal.

  Here, if the melt temperature and dopant concentration in the vicinity of the center of the single crystal can be controlled uniformly, it is possible to reduce the resistivity variation. In contrast, temperature and concentration fluctuations are relatively periodic and regular in the area, whereas in the central part of the single crystal, these fluctuations tend to be large and irregular, and the resistivity variation in the axial direction increases. .

  On the other hand, when the inventors alternately change the rotation direction of the single crystal, the rotation acceleration of the section in which the rotation direction is changed from one direction to the opposite direction is changed from the reverse direction to the one direction. The present invention has been completed by conceiving that it is effective for increasing the speed of melt convection at the center of the single crystal and making the resistivity distribution uniform by setting the rotational acceleration different from the section to be changed. .

First, the single crystal manufacturing apparatus (FZ single crystal manufacturing apparatus) by FZ method used with the manufacturing method of the semiconductor single crystal of this invention is demonstrated with reference to FIG. Here, a case where a silicon single crystal is manufactured as a semiconductor single crystal will be described.
As shown in FIG. 1, the FZ single crystal manufacturing apparatus 1 includes a chamber 11, and a rotatable upper shaft 12 and a lower shaft 13 are provided in the chamber 11. A silicon rod having a predetermined diameter is attached to the upper shaft 12 as a raw material crystal 14, and a seed crystal 15 is attached to the lower shaft 13. In the chamber 11, an induction heating coil 16 for melting the raw material crystal 14 and a dope nozzle 20 for jetting a dopant gas into the melting zone 18 where the raw material crystal 14 is melted during gas doping are arranged. ing.

In the method for producing a semiconductor single crystal according to the present invention, the tip of the raw material crystal 14 is first melted by the induction heating coil 16 and then fused to the seed crystal 15 by using such an FZ single crystal production apparatus 1. Thereafter, dislocation is eliminated by the diaphragm 17, the upper shaft 12 and the lower shaft 13 are moved downward while rotating, and the silicon single crystal 19 is grown while the melting zone 18 is moved upward relative to the raw material crystal 14.
At this time, after rotating the silicon single crystal 19 in one direction around the central axis, the rotation direction is alternately changed so as to rotate in the direction opposite to the one direction. Further, at this time, the rotational acceleration is adjusted as described in detail below.

  After the drawing, the diameter of the silicon single crystal 19 is gradually expanded to a desired diameter to form a cone portion. After reaching the desired diameter, crystal growth is performed while maintaining the desired diameter to form a straight body portion. To do. During the growth, a dopant gas is injected from the dope nozzle 20 into the melting zone 18 to supply the dopant, thereby forming a single crystal rod having a desired resistivity. The melting zone 18 is moved to the upper end of the raw material crystal 14 to complete the production of the silicon single crystal 19.

When a single crystal is steadily rotated with a constant rotation direction and number of rotations as in the conventional manufacturing method, the resistivity distribution in the cross section of the single crystal is determined by the heating distribution by the induction heating coil or the like used in the manufacture of the single crystal and the crystal. It is determined by the radial melt convection that changes according to the crystal production conditions such as the number of revolutions.
FIG. 2 shows a schematic diagram of radial melt convection. FIG. 2 is a cross section including the center portion of the single crystal and parallel to the crystal growth axis, and represents the range of a half melt portion from the center portion of the single crystal to the outer peripheral portion. This is schematically indicated by an arrow.

  According to the BPS theory, when the speed of melt convection is high (for example, in the case of melt flow as shown in I of FIG. 2), the boundary diffusion layer thickness decreases and the resistivity increases. On the other hand, when the melt convection speed is low (for example, when the melt stays like II in FIG. 2), the resistivity decreases. An in-plane resistivity distribution is formed by the velocity distribution of the melt convection near the crystal solid-liquid interface. This phenomenon is because the melt is rotating in substantially the same manner as the rotation of the crystal.

  On the other hand, when the single crystal is grown while alternately changing the rotation direction of the single crystal as in the present invention, the relative rotation speed of the rotation of the single crystal and the rotation of the melt increases when the rotation direction is reversed. That is, a sufficiently large crystal circumferential melt convection is generated compared to the crystal diameter direction melt convection, and the influence of the crystal diameter direction melt convection that has a large effect during the above-described steady rotation is negated, The resistivity distribution in the cross section at the time of alternate rotation approaches flat. In this case, the overall resistivity variation can be reduced by increasing the single crystal rotation speed in order to reduce the influence of non-axisymmetric heating.

Furthermore, in the present invention, as shown in FIG. 3, the rotational acceleration when changing the rotation direction from one direction to the opposite direction (section indicated by A in FIG. 3) is changed from the reverse direction to one direction. The rotational acceleration is different from that at the time (section indicated by B in FIG. 3).
In this way, by using different rotational accelerations in both sections, it is possible to increase the melt convection particularly at the center of the single crystal. As a result, the resistivity variation in the axial direction of the single crystal central portion can be reduced.

  At this time, the amount of rotation when rotating in each direction is not particularly limited. For example, as shown in FIG. 3, it can be rotated alternately by the same rotation amount in one direction (plus direction) and in the opposite direction (minus direction).

Alternatively, for example, as shown in FIG. 4, the rotation amount rotating in one direction (plus direction) is made larger than the rotation amount rotating in the reverse direction (minus direction), and the rotation amount ratio in each direction (the smaller one) Rotation amount / larger rotation amount) can be reduced.
When the rotation amount ratio is reduced in this way, the melt continues to rotate in the direction in which the rotation amount is large (in the plus direction in the case of FIG. 4), so the melt convection speed at the center of the single crystal is It increases compared with the case where a rotation pattern like 3 is applied.

  At this time, as shown in FIG. 4, the rotational acceleration when the rotation direction of the crystal is changed from the direction in which the rotation amount is large to the direction in which the rotation amount is small (section A in FIG. 4) is rotated from the direction in which the rotation amount is small. If the rotational acceleration is changed to be smaller than the rotational acceleration at the time of changing the rotation direction of the crystal in the direction in which the amount is large (section B in FIG. 4), the continuous melt rotation can be further strengthened. The speed of melt convection can be further increased. Thereby, the variation in resistivity can be reduced more effectively.

  The absolute value of the rotational acceleration can be set as appropriate according to the single crystal manufacturing conditions, but is preferably increased. FIG. 5 shows the resistivity variation σ when the rotational acceleration in the A section is fixed and the rotational acceleration in the B section is increased with the rotation pattern shown in FIG. As shown in FIG. 5, by increasing the rotational acceleration, the in-plane maximum value of the resistivity variation σ also decreases. This is due to the effect of increasing the melt convection speed by increasing the absolute value of the rotational acceleration even in the center portion of the single crystal where the melt convection speed tends to stay small.

At this time, the upper limit for increasing the absolute value of the rotational acceleration is preferably 900 ° / s ² or less. In this way, the frequency at which single crystallization is hindered can be reduced, and yield and productivity can be improved even when a single crystal having a large diameter is manufactured.
Further, the lower limit of the absolute value of the rotational acceleration is preferably 20 ° / s ² or more. In this way, since the reversal of the rotation direction becomes too slow, the influence of uneven heating of the induction heating coil becomes large, and it is possible to prevent the single crystal acquisition rate from being lowered due to the deterioration of the crystal shape.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.

(Example)
An FZ silicon single crystal having a diameter of 203 mm was manufactured using an FZ single crystal manufacturing apparatus as shown in FIG. Single crystals were grown while rotating in a pattern in which the rotation directions were alternately changed as shown in FIG. At this time, the rotation amount ratio is set to 0.75, and the rotation acceleration when the rotation direction of the single crystal is changed from the direction in which the rotation amount is large to the direction in which the rotation amount is small (section A in FIG. 4) is 100 ° / s ^2. The rotational acceleration when changing the rotation direction of the single crystal from the direction of small rotation amount to the direction of large rotation amount (section B in FIG. 4) was set to 350 ° / s ² .

The manufactured silicon single crystal was cut into wafers, and the resistivity variation φ and the overall resistivity variation at the center of 50 wafers were evaluated. Here, RRG (= maximum resistivity value in the wafer surface−minimum resistivity value in the wafer surface) / (minimum resistivity value in the wafer surface) was defined as the overall resistivity variation.
As a result, the value of RRG is 4.5 to 21.2%, and the resistivity variation φ at the center is 4.0%, and the overall resistivity variation is equal to or greater than the result of the comparative example described later. It was found that the resistivity variation in the central part was reduced while maintaining.

(Comparative example)
An FZ silicon single crystal was manufactured under the same conditions as in the example except that the rotational acceleration when changing the rotation direction was 100 ° / s ^2, and the resistivity variation was evaluated in the same manner as in the example.
As a result, the value of RRG was 5.4 to 21.2%, and the resistivity variation φ in the central portion was 5.4%, and the resistivity variation was worse than that of the example.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

DESCRIPTION OF SYMBOLS 1 ... FZ single-crystal manufacturing apparatus, 11 ... Chamber, 12 ... Upper axis, 13 ... Lower axis,
14 ... Raw crystal, 15 ... Seed crystal, 16 ... Induction heating coil, 17 ... Drawing,
18 ... Melting zone, 19 ... Semiconductor single crystal, 20 ... Dope nozzle.

Claims (3)

While rotating the raw material crystal, the raw material crystal is partially heated and melted by an induction heating coil to form a melting zone, and the melting zone is moved from one end portion to the other end portion of the raw material crystal to obtain a semiconductor single crystal. A method for producing a semiconductor single crystal by an FZ method to be grown,
During the growth of the semiconductor single crystal, the semiconductor single crystal is rotated in one direction around the central axis, and then the rotation direction is alternately changed so as to rotate in the opposite direction to the one direction. A method for producing a semiconductor single crystal, wherein the rotational acceleration when changing the rotational direction in the reverse direction is different from the rotational acceleration when changing the rotational direction from the reverse direction to the one direction.   The method for producing a semiconductor single crystal according to claim 1, wherein a rotation amount when rotating the semiconductor single crystal in the one direction is larger than a rotation amount when rotating in the reverse direction. The method for manufacturing a semiconductor single crystal according to claim 1, wherein the rotational acceleration is set to 900 ° / s ² or less.

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