JP6440601B2 - Method for manufacturing polycrystalline silicon rod and method for manufacturing FZ single crystal silicon - Google Patents

Description

  The present invention relates to a technique for manufacturing a polycrystalline silicon rod, and more specifically, controls the stress remaining in a polycrystalline silicon rod synthesized by the Siemens method, and is suitable for manufacturing FZ single crystal silicon. The present invention relates to a technique for manufacturing a rod.

  A single crystal silicon substrate indispensable for manufacturing a semiconductor device or the like is cut out from an ingot grown by a CZ method or an FZ method, and a polycrystalline silicon rod or a polycrystalline silicon lump is used as a raw material for manufacturing these ingots.

  These polycrystalline silicon raw materials are generally produced by the Siemens method. Siemens method is a process of vapor deposition (precipitation) of polycrystalline silicon on the surface of silicon core wire by CVD (Chemical Vapor Deposition) method by contacting silane source gas such as trichlorosilane and monosilane with heated silicon core wire. It is a method to make it.

  Although the heating of the silicon core wire is based on resistance heating by passing an electric current, as the diameter of the polycrystalline silicon rod increases with the deposition of polycrystalline silicon, the current gradually becomes difficult to flow on the outer surface of the silicon rod. As a result, the outer surface becomes relatively lower than the temperature of the central region, which causes a difference in thermal expansion coefficient and generates residual stress. The occurrence of such residual stress is more conspicuous as the polycrystalline silicon rod has a larger diameter.

  By the way, although residual stress includes tensile stress and compressive stress, the former tends to cause a decrease in strength because cracks occur in polycrystalline silicon, and the latter tends to improve the strength of polycrystalline silicon.

  Therefore, it is extremely important to control the residual stress in the polycrystalline silicon rod. For example, when an FZ single crystal silicon is produced from a polycrystalline silicon rod having a high tensile stress as a raw material, an accident such as cracking due to its own weight occurs. Can occur.

Against this background, Patent Document 1 (Japanese Patent Laid-Open No. 7-277874) discloses a stable single crystal in which a rod-like polycrystalline silicon serving as a raw material is melted without breaking and a raw material melt is supplied. An invention has been disclosed in which the maximum residual stress of rod-like polycrystalline silicon is less than 3.5 kgf / mm ² under standard conditions for the purpose of providing a silicon single crystal pulling method that can be grown.

JP-A-7-277874 JP 2001-146499 A

S. Timoshenko and J.N.Goodier, "Theory of Elasticity", McGraw-Hill, New York (1970) Journal of the Ceramic Society of Japan 101 [8] 932-935 (1993)

However, in Patent Document 1, if the maximum residual stress is less than 3.5 kgf / mm ² (measured value under a standard state), it is possible to prevent breakage while ensuring the optimum melting condition of rod-shaped polycrystalline silicon. Although there is a disclosure of knowledge that it will become, the only way to realize this is to apply heat treatment for stress removal such as annealing, and the possibility of residual stress control in the synthesis process of polycrystalline silicon rod No consideration has been given to.

  The present invention has been made in view of such a situation, and the object of the present invention is to perform residual stress control during the synthesis process of the polycrystalline silicon rod, not after the synthesis process of the polycrystalline silicon rod, It is an object of the present invention to provide a technique that eliminates the need for heat treatment of the polycrystalline silicon rod.

  In order to solve the above-mentioned problems, a polycrystalline silicon rod manufacturing method according to a first aspect of the present invention is a method for producing a polycrystalline silicon rod having a radius R obtained by depositing polycrystalline silicon on a silicon core wire by a Siemens method. In the manufacturing method, T1> T2> T3 is set when the deposition temperatures of polycrystalline silicon in the vicinity region, R / 2 region, and outermost surface region of the silicon core wire are T1, T2, and T3, respectively. Features.

  The method for producing a polycrystalline silicon rod according to the second aspect of the present invention is a method for producing a polycrystalline silicon rod having a radius R obtained by depositing polycrystalline silicon on a silicon core wire by a Siemens method, When the deposition temperatures of polycrystalline silicon in the vicinity region, R / 2 region, and outermost surface region of the silicon core wire are T1, T2, and T3, respectively, T1> T2 and T2 <T3, and further in the outermost surface region It is characterized in that T1> T3 + ΔT is set, where ΔT is a temperature difference between the temperature T1 ′ in the vicinity of the silicon core wire during the deposition of polycrystalline silicon and T3.

  Furthermore, the method for producing FZ single crystal silicon according to the present invention is a method for producing a single crystal by inductively heating the polycrystalline silicon rod obtained by the above-described method without performing a heat treatment after the precipitation step of the polycrystalline silicon rod. It is characterized by doing.

  The present invention controls the residual stress by appropriately controlling the temperature during the process of obtaining polycrystalline silicon rods having a radius R by depositing polycrystalline silicon on a silicon core wire by the Siemens method. A polycrystalline silicon rod suitable for producing crystalline silicon is provided.

  According to the method of the present invention, it is not necessary to perform heat treatment or the like conventionally performed after growing a polycrystalline silicon rod.

It is a figure for demonstrating the 1st collection example of the plate-shaped sample for the residual stress measurement by the X-ray-diffraction measuring method from a polycrystal silicon stick | rod. It is a figure for demonstrating the 1st collection example of the plate-shaped sample for the residual stress measurement by the X-ray-diffraction measuring method from a polycrystal silicon stick | rod. It is a figure for demonstrating the 2nd collection example of the plate-shaped sample for the residual stress measurement by the X-ray-diffraction measuring method from a polycrystalline silicon stick. It is a figure for demonstrating the 2nd collection example of the plate-shaped sample for the residual stress measurement by the X-ray-diffraction measuring method from a polycrystalline silicon stick. It is a figure for demonstrating the 3rd collection example of the plate-shaped sample for the residual stress measurement by the X-ray-diffraction measuring method from a polycrystalline silicon stick. It is a figure for demonstrating the 3rd collection example of the plate-shaped sample for the residual stress measurement by the X-ray-diffraction measuring method from a polycrystalline silicon stick.

  Below, with reference to drawings, the manufacturing method of the polycrystalline-silicon stick | rod concerning this invention is demonstrated.

  Conventionally, there is an idea that a temperature difference due to a place becomes a difference in thermal expansion α · T (temperature) to generate thermal stress (for example, Non-Patent Document 1: S. Timoshenko and JN Goodier, “Theory of Elasticity”, McGraw-Hill, New York (1970)), a thermal stress calculation method based on this idea has also been proposed (Non-Patent Document 2: “Method of calculating thermal stress of cylinders and disks”, Journal of the Ceramic Society of Japan 101 [8] 932-935 (1993)). This calculation method is a method of calculating based on the temperature distribution inside a cylinder with a constant thickness. However, when the diameter gradually increases as in the case of precipitation of a polycrystalline silicon rod by the Siemens method, the stress is calculated. I can't. In addition, in this method, the stress generated due to the structure unique to the polycrystal is not taken into consideration.

  Therefore, the present inventors examined a method for obtaining a residual stress value by precisely measuring the interplanar spacing value d value by an X-ray diffraction measurement method (hereinafter referred to as XRD method). As a result of this study, it has been found that the tensile stress and the compressive stress are independently present in the crystal and cannot be determined only by a simple temperature distribution inside the cylinder.

  The present inventors have conducted detailed analysis on the relationship between the CVD temperature at the time of polycrystalline silicon precipitation and the residual stress in the crystal, and found that the following regularity exists.

  The final radius of the polycrystalline silicon rod obtained by depositing polycrystalline silicon on the silicon core wire by the Siemens method is R, and the deposition temperature of polycrystalline silicon in the vicinity region, R / 2 region, and outermost surface region of the silicon core wire Are T1, T2, and T3, respectively, and when the temperature difference between the temperatures T1 ′ and T3 in the vicinity of the silicon core wire when the polycrystalline silicon is deposited in the outermost surface region is ΔT, the relationship summarized in Table 1 is recognized. It is done.

  The residual stress here means a residual stress component in the central axis direction (vertical direction: zz direction) of the polycrystalline silicon rod. There are other directions of residual stress, that is, a radial direction (growth direction: rr direction) and a θθ direction that forms an angle of 90 ° in a plane perpendicular to the rr direction and the central axis. It does not participate in fracture when manufacturing FZ single crystal silicon using a polycrystalline silicon rod as a raw material.

  When stress is generated in the crystal, the interplanar spacing d of the crystal lattice changes in proportion to the magnitude. Specifically, the lattice spacing increases when tensile stress is generated, and the lattice spacing decreases when compressive stress is generated.

  When attention is paid to a crystal plane causing Bragg diffraction, the diffraction angle θ satisfies the Bragg condition (nλ = 2d · sin θ). Therefore, if the wavelength λ of the X-ray is constant, the diffraction angle 2θ also changes with the change in the lattice spacing d.

The residual stress σ in the crystal is calculated from the slope of the least square approximation line (Δ (2θ) / Δ (sin ² ψ)) of the points plotted in the 2θ-sin ² Ψ diagram obtained by X-ray diffraction, as follows: Is given by equation (1).

σ (MPa) = K · [Δ (2θ) / Δ (sin ² Ψ)] (1)

  Here, Ψ is an angle (deg.) Between the sample surface normal and the lattice surface normal. K is a stress constant (MPa / deg.) And is given by the following equation (2).

K = − (E / 2 (1 + ν)) · cot θ ₀ · π / 180 (2)

In Equation (2), E is the Young's modulus (MPa), ν is the Poisson's ratio, and θ ₀ is the Bragg angle (deg.) Without any distortion.

  In other words, if the X-ray diffraction method is used, the internal stress can be obtained from the expansion / contraction amount of the lattice plane interval by observing the behavior of a specific diffraction peak while changing the lattice plane normal.

  Specifically, when there is no internal stress, of course, the diffraction peak does not shift, but when there is compressive stress, the diffraction peak shifts to the high angle side, and when there is tensile stress, the diffraction peak shifts to the low angle side. To do.

  In the present invention, based on this principle, the residual stress of polycrystalline silicon synthesized under various CVD conditions is evaluated.

[Collecting evaluation samples]
FIG. 1A and FIG. 1B show an example of collecting a plate-like sample 20 for measuring residual stress by X-ray diffraction measurement from a polycrystalline silicon rod 10 grown by chemical vapor deposition such as Siemens (No. 1). It is a figure for demonstrating 1), and is the sample collection example for measuring the residual stress component of rr direction and (theta) theta direction.

FIGS. 2A and 2B are diagrams for explaining an example (second) of collecting the plate-like sample 20 for measuring residual stress by the X-ray diffraction measurement method, and these are also residuals in the rr direction and the θθ direction. It is a sample collection example for measuring a stress component.
is there.

  3A and 3B are diagrams for explaining an example (third) of collecting the plate-like sample 20 for residual stress measurement by the X-ray diffraction measurement method, for measuring the residual stress component in the zz direction. This is an example of sampling.

  In the figure, reference numeral 1 denotes a silicon core wire for depositing polycrystalline silicon on the surface to form a silicon rod. The diameter of the polycrystalline silicon rod 10 illustrated in these figures is approximately 140 to 160 mm, and a plate-like sample 20 for measuring residual stress is taken. In addition, the collection site | part of the plate-shaped sample 20 is not limited to these.

In the first example shown in FIG. 1A, when viewed in a plane perpendicular to the major axis direction, a portion close to the silicon core wire 1 (11 _CTR ), a portion close to the side surface of the polycrystalline silicon rod 10 (11 _EDG ), CTR A rod 11 having a diameter of approximately 20 mm is cut out from three portions (11 _{R / 2} ) in the middle of EGD and EGD. Then, as shown in FIG. 1B, a disk-shaped sample 20 having a thickness of approximately 2 mm is collected from the rod 11. The disc-shaped sample 20 taken from the rod 11 _CTR 20 _CTR, the rod 11 R _{/ 2} the disc-shaped samples 20 taken from 20 R _{/ 2,} disc-shaped samples 20 taken from the rod 11 _EDG 20 Indicated as _EDG .

  Thereby, the disk-shaped sample extract | collected from the cross section perpendicular | vertical to the major axis direction of the polycrystalline silicon stick | rod 10 is obtained. By appropriately selecting the X-ray irradiation region on the main surface of the disk-shaped sample with a slit, the residual stress in the growth direction (rr) and the 90 degree direction (θθ) with respect to this direction is measured. be able to.

In the second example shown in FIG. 2A, first, a disk 12 centered on the silicon core wire 1 is sampled by slicing perpendicularly to the long axis direction. Then, as shown in FIG. 2B, the diameter of the circular plate 12 is approximately 20 mm from three parts, a part close to the silicon core wire 1, a part close to the side surface of the polycrystalline silicon rod 10, and an intermediate part between CTR and EGD. A disk-shaped sample (20 _CTR , 20 _{R / 2} , 20 _EDG ) is cut out.

  Also by this, a disk-shaped sample taken from a cross section perpendicular to the major axis direction of the polycrystalline silicon rod 10 can be obtained. By appropriately selecting the X-ray irradiation region on the main surface of the disk-shaped sample with a slit, the residual stress in the growth direction (rr) and the 90 degree direction (θθ) with respect to this direction is measured. be able to.

In the third example shown in FIG. 3A, first, a rod 11 having a diameter of approximately 20 mm is cut out perpendicularly to the long axis direction. As shown in FIG. 3B, the diameter of the rod 11 is approximately 20 mm from three parts, a part close to the silicon core wire 1, a part close to the side surface of the polycrystalline silicon rod 10, and an intermediate part between CTR and EGD. A disk-shaped sample (20 _CTR , 20 _{R / 2} , 20 _EDG ) is collected.

  Thereby, the disk-shaped sample extract | collected from the cross section parallel to the major axis direction of the polycrystalline silicon stick | rod 10 is obtained. The residual stress in the major axis direction (zz) can be measured by appropriately selecting the X-ray irradiation region on the main surface of the disk-shaped sample with a slit.

  In addition, the site | part from which the rod 11 is extract | collected, length, and the number should just be suitably determined according to the diameter of the silicon rod 10, and the diameter of the rod 11 to cut out. The disk-shaped sample 20 may also be collected from any part of the hollowed rod 11, but is preferably at a position where the properties of the entire silicon rod 10 can be reasonably estimated.

  Further, the diameter of the disk-shaped sample 20 is set to approximately 20 mm for illustration only, and the diameter may be appropriately determined within a range that does not hinder the residual stress measurement.

[Stress measurement by X-ray diffraction method]
In order to measure the residual stress in the three directions of the rr direction, the θθ direction, and the zz direction, a disk-shaped sample having a diameter of 19 mm and a thickness of 2 mm is collected. The collected disk-shaped sample is placed at a position where Bragg reflection from the mirror index surface <331> is detected, and the residual stress is measured by setting slits so that the X-ray irradiation area is in the above three directions. To do. Note that the two directions of the rr direction and the θθ direction are measured by a parallel tilt method in which the scanning axes are parallel and a side tilt method in which the scanning axes are orthogonal to each other.

As described above, the residual stress (σ) is the slope of the least square approximation line (Δ (2θ) / Δ (sin ² ψ)) of the points plotted in the 2θ-sin ² Ψ diagram obtained by X-ray diffraction. Can be evaluated.

  Originally, as the Young's modulus E, the value of Young's modulus of polycrystalline silicon which is an actual measurement sample should be adopted. However, due to the fact that the Young's modulus cannot be calculated after considering the existence ratio for all crystal orientations, the literature value of 171.8 GPa for the Young's modulus of the <111> orientation of single crystal silicon is adopted. did.

[Dependence of residual stress on CVD conditions]
Synthesized under various conditions by the Siemens method, (a) a rod that was already cracked in the furnace, (b) a rod that was easy to break in the hammering test, and (c) a crack that was difficult to crack in the hammering test When the results of residual stress measurement by the XRD method were examined for the three rods, a difference was found in the zz direction component of the residual stress.

  In (a) a rod that had already been cracked in the furnace, and (b) a rod that was easily cracked in the crushing test with a hammer, a high value was observed in both tensile stress and compressive stress, (C) For rods that were difficult to break in the crushing test with a hammer, it was found that the compressive stress was dominant because the compressive stress value was high while the tensile stress value was low.

  The conventional theory is that the cause of the residual stress is the temperature difference, but from the viewpoint of crystal growth, the following reasons for the generation are dominant.

  In the initial stage of the CVD reaction, crystal precipitation starts in the vicinity of the silicon core wire, but at this stage, crystal growth proceeds at random for each crystal orientation and eventually begins to form a polycrystal. At this time, a stress value having a directivity determined by synthesis of each component force for each crystal orientation, that is, synthesis of a vector, is formed as the total stress as the aggregate.

  As the reaction proceeds further, a temperature difference gradually occurs between the region near the center and the outer region. If the temperature near the center region (T1 ′) at this time is lower than the temperature (T1) at the time of crystal precipitation in the region (T1 ′ <T1), the stress in the crystal in the region does not change, but is high (T1 '> T1) causes rearrangement or orientation of crystals and changes in stress.

  Paying attention to the residual stress in the zz direction, if the residual stress in the vicinity region, R / 2 region, and outermost surface region (R region) of the silicon core wire is averaged, if this average value is (+) value, tensile stress And (-) value means compressive stress.

  As a result, it was found that classification as shown in Table 1 was possible.

  Polycrystalline silicon rods were grown under the various CVD conditions summarized in Table 2, and the residual stress was examined.

  The temperature was measured by attaching a peephole to the CVD reactor and installing a radiation thermometer there. As the radiation thermometer, a radiation thermometer manufactured by Chino Co., Ltd., model number IR-CAQ was used. The measurement wavelength is 0.9 μm, and the detection element material is silicon. The measurement position is the center position of the height of the polycrystalline silicon rod, and the focus position gradually changes as it grows. Therefore, the measurement value was obtained after fine adjustment of the focus each time measurement was performed. In addition, calculation of (DELTA) T followed the method of patent document 2 (Unexamined-Japanese-Patent No. 2001-146499), calculated the average temperature of the rod, and calculated center temperature from said surface temperature.

  In Examples 1 and 2, T1> T2> T3 when the deposition temperatures of polycrystalline silicon in the vicinity region, R / 2 region, and outermost surface region of the silicon core wire are T1, T2, and T3, respectively. It is a polycrystalline silicon rod obtained by setting.

  Further, in Example 3, T1> T2 and T2 <T3 when the deposition temperatures of polycrystalline silicon in the vicinity region, R / 2 region, and outermost surface region of the silicon core wire are T1, T2, and T3, respectively. Furthermore, when the temperature difference between the temperatures T1 ′ and T3 in the region near the silicon core wire at the time of deposition of polycrystalline silicon in the outermost surface region is ΔT, the polycrystal obtained by setting T1> T3 + ΔT. It is a crystalline silicon rod.

  When the polycrystalline silicon rod obtained in Examples 1 to 3 was used as a raw material for FZ single crystal silicon growth without performing a heat treatment after the precipitation process, troubles such as dropping during the FZ process (induction heating) There was no disappearance of crystal lines, and there was no disappearance or disturbance of the crystal line, and a high-quality FZ single crystal silicon ingot was obtained.

  The present invention controls the residual stress by appropriately controlling the temperature during the process of obtaining polycrystalline silicon rods having a radius R by depositing polycrystalline silicon on a silicon core wire by the Siemens method. A polycrystalline silicon rod suitable for producing crystalline silicon is provided. According to the method of the present invention, it is not necessary to perform heat treatment or the like conventionally performed after growing a polycrystalline silicon rod.

1 Silicon core wire 10 Polycrystalline silicon rod 11 Rod 12 Disc 20 Disc-shaped sample

Claims (2)

A method for producing a polycrystalline silicon rod having a radius R obtained by depositing polycrystalline silicon on a silicon core wire by a Siemens method,
When the precipitation temperatures of polycrystalline silicon in the vicinity region, R / 2 region, and outermost surface region of the silicon core wire are T1, T2, and T3, respectively, T1> T2 and T2 <T3,
A polycrystalline silicon rod that is set such that T1> T3 + ΔT, where ΔT is the temperature difference between the temperature T1 ′ in the vicinity of the silicon core wire and the temperature T3 when the polycrystalline silicon is deposited in the outermost surface region Manufacturing method. A method for producing FZ single crystal silicon, wherein the polycrystalline silicon rod obtained by the method according to claim 1 is single-crystallized by induction heating without performing a heat treatment after the step of depositing the polycrystalline silicon rod.