JP5594257B2 - Single crystal manufacturing method - Google Patents

Description

  The present invention is an FZ method (floating zone method) in which a raw crystal is partially heated and melted by an induction heating coil to which a high frequency voltage is supplied from a high frequency oscillator to form a floating zone, and the floating zone is moved to produce a single crystal. Or a floating crystal melting method).

  The FZ method is one of methods for producing a silicon single crystal that is currently widely used for semiconductor devices. In the single crystal manufacturing method by the FZ method, first, a raw material crystal rod (raw material crystal) is held by an upper holding jig on an upper shaft installed in a chamber. On the other hand, a single crystal seed (seed crystal) having a small diameter is held by a lower holding jig on the lower shaft located below the raw crystal rod.

  Next, a high frequency voltage is supplied from the high frequency oscillator to the induction heating coil, so that the raw material crystal rod is melted and fused to the seed crystal. The oscillation frequency of the supplied high-frequency voltage is 1 to 3 MHz (see Non-Patent Document 1). Conventionally, this oscillation frequency has been set to the same oscillation frequency regardless of the type of single crystal to be manufactured.

Thereafter, a squeezed portion is formed by seed squeezing to eliminate dislocation. And while forming the floating zone (also referred to as a melting zone or melt) between the source crystal rod and the grown single crystal rod by lowering the source crystal rod and the single crystal rod while rotating the upper shaft and the lower shaft, The crystal diameter is gradually increased to form a cone portion. Thereafter, when the target diameter is reached, the diameter is maintained, a straight body portion is formed, and the floating zone is moved to the upper end of the raw material crystal rod to perform zoning. This single crystal growth is performed in an atmosphere in which a small amount of nitrogen gas is mixed with Ar gas. In order to manufacture an N-type FZ single crystal, an amount of Ar base corresponding to the resistivity to be manufactured is produced from a dope nozzle. flowing the PH ₃ gas, to produce a P-type FZ single crystal from Dopunozuru, flow Ar-based B ₂ H ₆ gas in an amount corresponding to the resistivity of manufacturing.

  Wafers manufactured from a silicon single crystal obtained by the FZ method are desired to have as uniform a resistivity variation as possible within the wafer surface, and this is desired to be uniform. This is done by making the resistivity distribution of the single crystal more uniform.

  In order to reduce the wafer resistivity variation, the rotation axes of the raw crystal rod and the single crystal rod are shifted (hereinafter referred to as eccentricity), the melt stirring is made non-axisymmetric, and Patent Document 1 and Patent Document 2 There is a method in which the direction of rotation of the single crystal is alternated between forward rotation and reverse rotation (hereinafter referred to as alternate rotation).

JP 7-315980 A JP 2008-266102 A

Takao Abe: Silicon crystal growth and wafer processing, Baifukan (1994)

  As described above, optimization of operating conditions such as eccentricity, alternate rotation, and growth rate has been attempted to improve resistivity variation, but the behavior of resistivity variation differs depending on the diameter and orientation. Regardless of the type of diameter and orientation, it is difficult to obtain a good resistivity distribution.

  The present invention has been made in view of the above problems, and provides a single crystal production method capable of stably producing a single crystal having small resistivity variation and excellent quality regardless of the type of diameter and orientation. The purpose is to provide.

In order to solve the above problems, in the present invention, a raw crystal is partially heated and melted by an induction heating coil to which a high frequency voltage is supplied from a high frequency oscillator to form a floating zone, and the single crystal is moved by moving the floating zone. A method for producing a single crystal by the FZ method,
For the single crystal having the same diameter and the same orientation as the single crystal to be manufactured, the variation in resistivity for each oscillation frequency when the oscillation frequency of the supplied high-frequency voltage is changed is examined, and the oscillation frequency and the variation in resistivity are Determine the operating oscillation frequency for each diameter and orientation of the single crystal to be manufactured according to the relationship,
Adjusting the high-frequency oscillator according to the determined operation oscillation frequency,
Provided is a method for producing a single crystal using the adjusted high-frequency oscillator to produce a single crystal.

  As described above, the resistivity variation of the single crystal changes depending on the oscillation frequency, so by determining an appropriate operation oscillation frequency for each diameter and orientation of the single crystal to be manufactured in advance, it is good regardless of the type of diameter and orientation. It is possible to stably produce single crystals with various resistivity variations.

  At this time, it is preferable that the single crystal for examining the variation in resistivity for each oscillation frequency is manufactured under the same conditions as the single crystal to be manufactured except for the diameter and orientation.

  In this way, the single crystal whose resistivity variation for each oscillation frequency is previously examined is manufactured under the same conditions as the single crystal to be manufactured except for the diameter and orientation (for example, eccentricity, alternate rotation, etc.). By doing so, a single crystal having low resistivity variation can be manufactured more reliably.

  As described above, according to the method for producing a single crystal of the present invention, it is possible to stably produce a crystal with favorable resistivity variation regardless of the diameter and orientation of the produced single crystal.

It is a flowchart explaining the single-crystal manufacturing method of this invention. It is a schematic sectional drawing which shows an example of the single crystal manufacturing apparatus used with the single crystal manufacturing method of this invention. It is the schematic which shows an example of the induction heating coil used by this invention. It is a graph which shows the change of the resistivity variation by the oscillation frequency in the silicon single crystal of diameter 128mm and <100> orientation in an Example. It is a graph which shows the change of the resistivity variation by an oscillation frequency in the silicon single crystal of diameter 128mm and <111> orientation in an Example.

Hereinafter, the present invention will be described in detail.
The inventors of the present invention have made extensive studies on improving the resistivity variation of the FZ single crystal. As a result, under the same oscillation frequency, the present inventors have obtained a single crystal of good quality with a small resistivity variation in all diameters and orientations, even when operating conditions other than the oscillation frequency are optimized. It was difficult to manufacture, and the inventors came up with the need to change the oscillation frequency for each diameter and orientation.

  For example, a single crystal with <111> orientation tends to facet growth at the center, so that the resistivity at the center is very low, and a concave in-plane resistivity distribution tends to occur. In order to improve this, it is effective to increase the melt stirring at the center by increasing the oscillation frequency. However, the oscillation frequency at which the in-plane resistivity distribution of the <111> -oriented single crystal becomes flat is < When applied to the production of a 100> -oriented single crystal, the resistivity at the center portion becomes too high, resulting in a convex in-plane resistivity distribution, and the resistivity distribution deteriorates.

  Therefore, the inventors previously investigated the change in resistivity variation when the oscillation frequency was changed at the same diameter and orientation, determined the operation oscillation frequency for each diameter and orientation, and manufactured the FZ method single crystal. By adjusting the high-frequency oscillator to match the operating oscillation frequency before production according to the diameter and orientation in which the crystal is produced by the equipment, a single crystal with good resistivity variation can be stabilized regardless of the type of diameter and orientation. As a result, the present invention has been completed.

  The single crystal production method of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a flowchart for explaining an example of the method for producing a single crystal of the present invention.

First, in the present invention, for a single crystal having the same diameter and the same orientation as the single crystal to be produced, the resistivity variation for each oscillation frequency when the oscillation frequency of the supplied high-frequency voltage is changed is examined (FIG. 1). (A)).
In the present invention, the resistivity variation can be obtained from RRG (Radial Resistivity Gradient) or in-lot variation.
It should be noted that the single crystal for checking the variation in resistivity for each oscillation frequency is manufactured under the same conditions as the single crystal to be manufactured (target) except for the diameter and orientation, thereby lowering the resistivity variation. Single crystals can be produced. Here, conditions other than the diameter and orientation refer to eccentricity, alternate rotation, growth rate, and the like.

Next, the operation oscillation frequency for each diameter and orientation of the single crystal to be manufactured is determined according to the relationship between the investigated oscillation frequency and resistivity variation (FIG. 1B).
At this time, it is preferable to select the optimum oscillation frequency with the lowest resistivity variation. However, in consideration of factors other than resistivity variation, such as single crystal quality and single crystallization rate, the oscillation in which the resistivity variation is improved compared to the conventional one. The choice of frequency is also within the scope of the present invention.

And although the target single crystal is manufactured (in FIG. 1, the crystal manufacturing instruction), the high frequency oscillator is adjusted in accordance with the operation oscillation frequency according to the determined diameter and orientation (FIG. 1 (C)), A single crystal is manufactured using the adjusted high-frequency oscillator (FIG. 1D).
A single crystal can be produced using a conventional FZ single crystal production apparatus. Below, the method to manufacture a single crystal using the FZ single crystal manufacturing apparatus 20 shown in FIG. 2 is demonstrated.

First, the raw material crystal rod (raw material crystal) 1 is held by the upper holding jig 4 of the upper shaft 3 installed in the chamber 2. On the other hand, a single crystal seed (seed crystal) 5 having a small diameter is held by a lower holding jig 7 of a lower shaft 6 located below the raw crystal rod 1.
Next, the high frequency voltage of the operation oscillation frequency determined above is supplied from the high frequency oscillator 8 to the induction heating coil 9, so that the raw material crystal rod 1 is melted and fused to the seed crystal 5.
The oscillation frequency of the high-frequency oscillator is adjusted by changing the number of capacitors constituting the oscillation circuit, exchanging with a capacitor having a different capacity, or exchanging with a current transformer (CT) having a different diameter or number of turns. be able to.

Thereafter, the narrowed portion 10 is formed by seed narrowing to eliminate dislocation. Then, the raw crystal rod 1 and the single crystal rod 11 are lowered while rotating the upper shaft 3 and the lower shaft 6, so that the floating zone (also referred to as a melting zone or a melt) 12 is formed in the raw crystal rod 1 and the grown single crystal rod 11. While forming, the crystal diameter is gradually increased to form the cone portion 11-a. Thereafter, when the target diameter is reached, the diameter is maintained, the straight body portion 11-b is formed, and the floating zone 12 is moved to the upper end of the raw crystal rod 1 to perform zoning. This single crystal growth is performed, for example, in an atmosphere in which a small amount of nitrogen gas is mixed with Ar gas. In order to manufacture an N-type FZ single crystal, the amount corresponding to the resistivity to be manufactured is obtained from the dope nozzle 13. In order to manufacture a P-type FZ single crystal by flowing the Ar-based PH ₃ gas, an amount of Ar-based B ₂ H ₆ gas corresponding to the resistivity to be manufactured is flowed from the dope nozzle 13.

  As the induction heating coil 9, an induction heating coil 9 in which single or multiple winding water made of copper or silver is circulated is used. For example, the one shown in FIG. 3 is known (for example, Patent Document 1). The induction heating coil 9 is a ring-shaped coil having a slit 14 and has a tapered cross section from the coil outer peripheral surface 15 toward the coil inner peripheral surface 16. The coil outer peripheral surface 15 is provided with a power supply terminal 18 at a position corresponding to the coil end portion 17. The opposing surface of the coil end 17 to which both the terminals 18 are connected is made as close as possible through the slit 14, thereby maintaining the symmetry of the current circuit in the circumferential direction of the induction heating coil 9, A substantially uniform electric field distribution can be obtained.

  If another single crystal is manufactured after the single crystal is manufactured, the high-frequency oscillator is adjusted again according to the appropriate operating oscillation frequency determined according to the diameter and orientation of the other single crystal to be manufactured, and then adjusted again. Another single crystal is manufactured using the high frequency oscillator.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to this.

(Example) Production of <100> and <111> silicon single crystals (diameter 128 m) A high-frequency voltage to be supplied by growing <100> and <111> silicon single crystals having a diameter of 128 mm and a straight body length of 150 cm in advance. The resistivity variation for each oscillation frequency when the oscillation frequency was changed was examined (eccentricity: 10 mm, crystal rotation speed: 20 rpm alternating rotation).
FIG. 4 shows the results of examining the variation in resistivity variation with the oscillation frequency in a <100> silicon single crystal with a diameter of 128 mm. FIG. 5 shows the result of examining the variation in resistivity variation with the oscillation frequency in a <111> silicon single crystal having a diameter of 128 mm.
The resistivity variation was measured as follows.
Thirty wafers were cut out from the manufactured ingot, and after surface grinding, the resistivity was measured at a pitch of 2.5 mm in the XY direction. RRGave. Is an average value of RRG [RRG (%) = (ρ maximum value−ρ minimum value) / ρ minimum value × 100] calculated for each wafer, and the variation within a lot is the standard deviation of all resistivity measurement values. It is.

  Next, the operation oscillation frequency is determined according to the relationship between the oscillation frequency and the resistivity variation investigated above. As shown in FIG. 4, the operation oscillation frequency when producing the <100> silicon single crystal was determined to be 2.3 MHz, which has the lowest resistivity variation. Similarly, as shown in FIG. 5, the operating oscillation frequency when producing the <111> silicon single crystal was determined to be 3.0 MHz with the lowest resistivity variation.

The high frequency oscillator is adjusted in accordance with the determined operation oscillation frequency (2.3 MHz), and a silicon raw material rod having a diameter of 130 mm is zoned by the FZ method, and an N-type having a diameter of 100 mm or less, a diameter of 128 mm, and a straight body length of 150 cm <100> silicon single crystal was manufactured, and similarly, the high frequency oscillator was adjusted in accordance with the determined operation oscillation frequency (3.0 MHz) to manufacture <111> silicon single crystal.
In the production of these silicon single crystals, the amount of eccentricity was 10 mm, and the crystal rotation speed was 20 rpm alternating rotation.
When the FZ single crystal was manufactured under these conditions, the variation in the lot of <100> silicon single crystal was 1.62%, the RRG was 8.3%, and the variation in lot of <111> silicon single crystal was 1. 59% and RRG were 9.7%, both of which were excellent in resistivity variation.

(Comparative example) <100> and <111> Manufacture of silicon single crystals (diameter 128 m) A silicon raw material rod having a diameter of 130 mm is subjected to zoning by the FZ method, an N-type having a diameter of 100 Ωcm or less, a diameter of 128 mm, and a straight body length of 150 cm. 100> and <111> silicon single crystals were produced.
In the production of this silicon single crystal, the amount of eccentricity was 10 mm, and the crystal rotation speed was 20 rpm alternating rotation. Also, the oscillation frequency was not adjusted before crystal production and was kept constant at 2.3 MHz. As a result of manufacturing the FZ single crystal under these conditions, the variation in the lot of <100> silicon single crystal was 1.65%, the RRG was 8.0%, and the variation in lot of <111> silicon single crystal was 2 The resistivity variation of <111> silicon single crystal was large, 0.62% and RRG 12.2%.

  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 ... Raw material crystal | crystallization rod (raw material crystal), 2 ... Chamber, 3 ... Upper shaft, 4 ... Upper holding jig, 5 ... Seed crystal, 6 ... Lower shaft, 7 ... Lower holding jig, 8 ... High frequency oscillator, 9 ... Induction heating coil, 10 ... throttle part, 11 ... single crystal rod, 11-a ... cone part, 11-b ... straight body part, 12 ... floating zone, 13 ... dope nozzle, 14 ... slit, 15 ... outer peripheral surface of coil, 16 DESCRIPTION OF SYMBOLS ... Coil inner peripheral surface, 17 ... Coil end, 18 ... Power supply terminal, 20 ... FZ single crystal manufacturing apparatus.

Claims (2)

This is a single crystal manufacturing method based on the FZ method in which a raw crystal is partially heated and melted by an induction heating coil supplied with a high frequency voltage from a high frequency oscillator to form a floating zone, and the floating zone is moved to manufacture a single crystal. And
For the single crystal having the same diameter and the same orientation as the single crystal to be manufactured, the variation in resistivity for each oscillation frequency when the oscillation frequency of the supplied high-frequency voltage is changed is examined, and the oscillation frequency and the variation in resistivity are Determine the operating oscillation frequency for each diameter and orientation of the single crystal to be manufactured according to the relationship,
In accordance with the determined operation oscillation frequency, either change of the number of capacitors constituting the oscillation circuit, replacement with a capacitor having a different capacity, or replacement with a current transformer (CT) having a different diameter or number of turns is performed. To adjust the high-frequency oscillator,
A method for producing a single crystal using the adjusted high-frequency oscillator. 2. The method for manufacturing a single crystal according to claim 1, wherein the single crystal for checking the resistivity variation for each oscillation frequency is manufactured under the same conditions as the single crystal to be manufactured except for the diameter and orientation. .

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