WO2007004631A1

WO2007004631A1 - Method for preparing grain boundary character controlled polycrystal

Info

Publication number: WO2007004631A1
Application number: PCT/JP2006/313275
Authority: WO
Inventors: Noritaka Usami; Kazuo Nakajima; Kozo Fujiwara
Original assignee: Tohoku University
Priority date: 2005-07-04
Filing date: 2006-07-04
Publication date: 2007-01-11
Also published as: JP4887504B2; JPWO2007004631A1

Abstract

This invention provides a grain boundary character control technique for a polycrystalline material that can prepare a polycrystalline material having a low grain boundary energy interface within the crystal. When unidirectional growth is carried out utilizing, as a seed crystal, a polycrystal having a high grain boundary energy of which the relative orientation relation has been intentionally rendered random, grain boundaries having low grain boundary energy are spontaneously formed from random grain boundaries having high grain boundary energy under proper growth conditions. According to this technique, all of polycrystalline grain boundaries can be provided as corresponding grain boundaries having a low sigma value. In the formed polycrystalline material, the number of unbonding hands in the grain boundary is small. Accordingly, also regarding macroscopic properties of the polycrystalline material constituted as a grain boundary network, development of excellent properties such as low electroactivity and high crystal strength can be realized.

Description

Specification

Grain boundary character control polycrystal production method

Technical field

The present invention relates to a technique for producing a polycrystalline material having an interface with low grain boundary energy inside a crystal. In particular, the present invention relates to a technique for producing a polycrystalline material having a grain boundary surface having a lower sigma value by preparing a polycrystal having a crystal interface having a higher sigma value and using it as a seed crystal.

Background art

[0002] Many practical materials such as solar cell crystals, structural materials, and magnetic materials are polycrystalline materials having many crystal structures inside the material.

Polycrystal is a force composed of many crystal grain forces. Its macro properties are the size of crystal grains and the nature of grain boundaries, which are the boundaries between different crystal grains (grain boundary character). ) Is known to depend on.

For example, a solar cell produced by cutting polycrystalline silicon into a wafer may be used. At this time, the strength of the polycrystalline wafer is not so high due to defects at the crystal grain interface and accompanying grain boundary energy accumulated at the interface. In addition, defects at the grain interface act as a recombination center for photoexcited carriers, which contributes to a decrease in solar cell efficiency. Japan is the world's largest producer of solar cells, and the annual rate of increase in solar cell production in recent years has exceeded 25%. Above all, solar cells based on silicon Balta crystals account for over 90% of the total production, and are the main materials for solar cells.

[0003] However, securing the raw material silicon is an issue for future growth in production, and one solution is to reduce the thickness when slicing from ingots. Is being considered. In polycrystalline silicon, which is low in cost, fracture from grain boundaries is a major problem.

From an industrial point of view, reducing the thickness of the wafer reduces the cost of materials and reduces the weight of the product. If the accumulated energy is large, the mechanical strength decreases by reducing the thickness of the wafer. When considered in the manufacturing process, the wafer may break when the polycrystalline wafer is transferred and processed, and the manufacturing yield of the solar cells is greatly reduced. This is due to the polycrystalline material that is the material of the wafer. In order to suppress the carrier recombination at the grain interface, a process of terminating defects by hydrogen is performed. However, the effect of hydrogen is not permanent and is also a factor in the change of solar cell performance over time. In essence, there is a need to form grain boundaries with high consistency and low carrier recombination rates.

On the other hand, research has been carried out on the possibility of producing materials with high strength and materials that are difficult to crack by controlling the character of the grain boundaries.

[0004] The degree of correspondence between grain boundaries between crystals is expressed by using sigma (∑) and the soot index, and the energy stored in the grain boundaries is low, as the saddle value is low. It will be. The threshold value is obtained by the ratio of the unit cell area of the corresponding cell to the unit cell area. The saddle value takes only odd values, and the mean value of 1 means that both unit cells at the grain boundary surface are the same, and there is no grain boundary. This indicates the same crystal. If there is actually another grain boundary interface, the saddle value will increase to 3, 5, 7, .... For example, if the grain orientation is [111] for a growth orientation of 110>, the ∑ value is 3 (∑3), which is the best interface. In a cubic system such as silicon, ∑3 and ∑9 have an orientation relationship with a very low grain boundary energy.

Based on this idea, a technique for producing a polycrystalline silicon material with low grain boundary energy has been studied. This is a technique called tricrystalline silicon (trisilicon). In this three-crystal silicon technology, a silicon single crystal is mechanically cut, and only three grain boundaries of ∑3, ∑3, and ∑9 exist. Trying to grow crystals! This is because, in order to obtain a polycrystalline material having a low threshold value, a seed crystal is formed into a single crystal plane with a low grain boundary energy composition, and crystal growth is performed based on the single crystal plane. It is intended to obtain strong, quasi-single crystal (polycrystalline with few grain boundaries) silicon.

[0005] A triple structure with two sigma 3 grain boundaries and one sigma 9 grain boundary with {110} as the growth orientation Crystalline silicon is useful as a silicon ingot for solar cells that can be sliced thinly

Proposed by Martinelli et al. (Non-Patent Document 1: Appl. Phys. Lett. 62, 3262, 1993). After that, Schimiga et al. Reported a production example of a solar cell having a conversion efficiency of 17.6% from tricrystalline silicon produced by the same method (Non-Patent Document 2: PV in Europe, Oct. 2002, Ro me) J. of Crystal Growth, 280, pp.419-424 (2005) reveals that the carrier diffusion length in the vicinity of the grain boundary is short. It is suggested that there is not.

In general, a single crystal material has a higher mechanical strength than a polycrystalline material. However, in the case of a polycrystal with a combination of interfaces having low grain boundary energy, such as the above-mentioned tricrystalline silicon, the single crystal material has a higher mechanical strength. In addition, a material having a high strength can be obtained. From the background described above, it has been proposed that designing grain boundaries is useful as a new degree of freedom in controlling the properties of materials. However, a method for controlling grain boundary characteristics has been established, Nah ...

By the way, in the group of the present inventors, the Si (l 10) single crystal rod was cut in half along the plane [111] and bonded in the opposite direction as a seed crystal, and the growth orientation [110] was FZ Growing and evaluating dislocation density (D) (Non-patent Document 3: J. of Crystal Growth, 280, pp.419 -424 (2005) force So the seed crystal used is along the plane [111]. The result is a misalignment that accompanies the cut, that is, a seed crystal that deviates from the plane [111] around the azimuth force S [110] by 3.5 or 7.0 °. As a result, the seed crystal obtained by bonding the two crystals is only 3.5 ° or 7.0 ° out of alignment with the 3 grain boundaries, and the misalignment angle is When the dislocation density is evaluated by setting a large value, the dislocation density tends to decrease. The results are only to suggest that the rugi has been reduced to a total, where the density of dislocations at the grain boundaries is evaluated and the relative orientation is intentionally random. In addition to producing a polycrystal having a high grain boundary energy and a grain boundary using the same, and producing a polycrystal having a grain boundary having a low grain boundary energy, the grain boundary energy is the highest !, random The idea of low grain boundary energy, formation of grain boundaries, etc. from the grain boundaries is not shown at all, and the group of the present inventors, etc., used the X-ray crystal sample prepared in Non-Patent Document 3 above. (Non-Patent Document 4: Japanese Journal of A pplied Physics, Vol. 44, No. 24, pp 丄 778- L780, (2005), depending on the growth conditions, the X-ray rocking curve value (crystallinity index) and solar cell In the same way as in Non-Patent Document 3, a polycrystal having a grain boundary with a high grain boundary energy with a random relative orientation relationship was intentionally created. Using this to produce a polycrystal with low grain boundary energy and a grain boundary is not a good idea.

[0007] Patent Document 1: Special Table 2001-504996

Non-patent literature l: Appl. Phys. Lett. 62, 3262, 1993

Non-Patent Literature 2: PV in Europe-From PV Technology to Energy solutions, Confer enc e + Exhibition, Oct. 2002, Rome

Non-Patent Document 3: M. Kitamura et al., J. of Crystal Growth, 280, pp.419-424 (2005) Non-Patent Document 4: N. Usami et al "Japanese Journal of Applied Physics, Vol. 44, No 24, pp 丄 778- L780, (2005)

Disclosure of the invention

Problems to be solved by the invention

[0008] As in the above-described tricrystalline silicon, a material having a lower grain boundary energy and a higher crystal strength than that of a single crystal can be obtained in a polycrystal having a combination of interfaces. However, a crystal grown from a single crystal as described above, which is obtained by bundling crystals cut from the orientation and forming artificial corresponding grain boundaries as seed crystals (tricrystalline silicon) However, cracks are generated in the crystal due to defects existing between the grain boundaries, and a material having a desired grain boundary has not been obtained. The reason why the above method does not work is that the control of the grain boundary character depends on the cutting accuracy of the underlying single crystal. For example, a force that requires an accuracy within 0.01 degrees as a relative orientation to control grain boundary properties is difficult to achieve with current cutting techniques. It is very difficult to obtain an ideal seed crystal with low energy at the grain interface because of the misorientation of the orientation between the crystals to be bonded and the presence of micro unevenness between the faces. For example, in the results obtained by the inventors' experiments, in the crystal growth of silicon by the floating zone growth method using the seed crystal bonded so as to have a slight deviation within 0.1 degree from the orientation relationship of ∑3 Grow Even in the case of crystals, growth occurs as crystals that inherit the deviation of the orientation of the seed crystal.

There is a demand for the development of technology for designing grain boundaries and controlling the grain boundary characteristics of polycrystalline materials.

Means for solving the problem

[0009] In order to solve the above-mentioned problems, earnest research is advanced, and unidirectional growth is performed by using, as a seed crystal, a polycrystal having a grain boundary energy having a random relative orientation relationship and a high grain boundary energy. . Then, by this method, it was found that under appropriate growth conditions, a grain boundary having a low grain boundary energy was spontaneously formed from a random grain boundary having a high grain boundary energy. Therefore, it was found that if this is used positively, all of the grain boundaries can be aligned with the corresponding grain boundaries of low sigma values. The present invention has been made on the basis of these phenomena.

The present invention is characterized in that a crystal interface having a high threshold value is used as a seed crystal in order to obtain a polycrystalline material having a grain interface having a low threshold value. This is because the use of seed crystals with very large misorientation results in lowering grain boundary energy and lowering the overall grain boundary energy as a driving force. This encourages the spontaneous growth of polycrystals with low grain boundary energy interfaces. In other words, since the consistency between crystals is very good, if the deviation is within a few degrees, rather than eliminating the deviation, it can be obtained as a direction energy to grow by taking over the deviation as it is. It is what was used.

The present invention relates to a new method for producing a polycrystal with controlled grain boundary character distribution.

. In the technique of the present invention, a polycrystalline material forming method characterized in that a unidirectional growth is performed by using, as a seed crystal, a polycrystal having a grain boundary with a high grain boundary energy, which is intentionally random in relative orientation. Yes, under appropriate growth conditions, it actively utilizes the fact that grain boundaries with low grain boundary energy are spontaneously formed from random grain boundaries with high grain boundary energy. This is a technology that makes it possible to align all of the above with corresponding grain boundaries of low sigma values. Since the polycrystalline material formed in this way has few dangling bonds at the grain boundary, even in the macro property of the polycrystalline material configured as a network of grain boundaries, It is possible to develop excellent properties such as low aerodynamic activity and high crystal strength. The present invention provides the following aspects.

[1] By intentionally forming a polycrystal having a grain boundary with a high relative grain boundary energy with a random relative orientation relationship, and then using this polycrystal as a seed crystal, unidirectional crystal growth is performed, and the grain boundary energy is A method for producing a polycrystalline material, characterized by forming a grain boundary with a low grain boundary energy from a random grain boundary.

[2] Seed crystal force The method for producing a polycrystalline material according to [1] above, wherein the crystal growth surface has at least two grain boundaries.

[3] The seed crystal (1) has at least 3 grain boundaries on the crystal growth surface, (2) has at least 4 grain boundaries on the crystal growth surface, (3) at least 5 on the crystal growth surface. (4) a crystal growth surface having at least 6 grain boundaries, (5) a crystal growth surface having at least 7 grain boundaries, and (6) a crystal growth surface. Having at least 8 grain boundaries

The method for producing a polycrystalline material as described in [1] or [2] above, wherein both the force and the group force are selected.

[4] The crystal growth is a single crystal orientation as a crystal orientation in a crystal growth direction, and the crystal growth is performed in one direction in the crystal direction. ]-[3] The manufacturing method of the polycrystalline material as described in any one.

[5] The seed crystal is a polycrystal formed from a plurality of single crystals, and the crystal orientation in the direction of crystal growth is a single crystal orientation,

(1) The number of single crystals constituting the polycrystal is at least 3 or more,

(2) The number of single crystals constituting the polycrystal is at least 4 or more,

(3) The number of single crystals constituting the polycrystal is at least 5 or more,

(4) The number of single crystals constituting the polycrystal is at least 6 or more,

(5) The number of single crystals constituting the polycrystal is at least 7 or more,

(6) The number of single crystals constituting the polycrystal is at least 8 or more,

(7) The number of single crystals constituting the polycrystal is at least 9 or more, and

(8) The number of single crystals constituting the polycrystal is at least 10 or more The method for producing a polycrystalline material according to any one of [1] to [4] above, wherein both the force and the group force are selected.

[6] The above-mentioned [1], wherein a polycrystal having a crystal interface with a high threshold value is used as a seed crystal to grow a crystal, and a polycrystal having a low threshold value and a grain interface is obtained. ]-[5] The manufacturing method of the polycrystalline material as described in any one.

[7] The method for producing a polycrystalline material according to any one of [1] to [6], wherein the polycrystal is silicon polycrystal.

[8] The polycrystalline material according to any one of [1] to [7] above, wherein the crystal growth rate at the crystal growth start surface is about 0.3 mm / min or faster. Manufacturing method. [9] As the arrangement of seed crystals, a Si crystal with a growth orientation of [110] and side faces of [100] and a Si crystal with a growth orientation of [110] and side faces of [111] The polycrystalline material according to any one of [1] to [8] above, wherein a random grain boundary is formed by alternately laminating so that the surface and the surface [111] are in contact with each other Manufacturing method.

[10] Silicon polycrystalline silicon obtained by the method for producing a polycrystalline material according to any one of the above [1] to [9].

[11] A silicon polycrystal which is silicon polycrystal, and the grain boundaries of the silicon polycrystal are only ∑3 and Z or ∑9.

[12] (1) Substantially no defects are observed by the backscattered electron diffraction pattern method,

(2) Excellent mechanical strength, excellent impact resistance, excellent fracture resistance when slicing an ingot, or excellent crack resistance,

(3) Give conversion efficiency 18% or more, 19% or more, 20% or more, 21% or more, 22% or more, or 25% or more in a 10 cm square cast cell, and Z or

(4) Consists of at least 4 crystalline phases

The silicon polycrystal according to [11] above, wherein

[13] A solar cell manufactured from the polycrystalline silicon according to any one of [10] to [12]. The invention's effect

According to the present invention, a method for controlling the grain boundary of a polycrystalline material is provided, the grain boundary control technique has a grain boundary having excellent electrical properties (quality is as if it is a single crystal), and strength is high. , Crystals stronger than conventional polycrystals can be produced. Therefore, it becomes easy to cut out a thin plate from the ingot and to handle it later, and it can contribute to the reduction of the slice thickness from the side of the material. For these reasons, the problem of securing future raw materials, which is currently an issue in the solar cell industry, will be solved, leading to expansion of the solar cell industry and resolution of energy problems. In addition, the grain boundary control technology of the present invention can be applied to other polycrystalline materials (metals, composite materials, etc.), and the development of new material sciences for enhancing the functionality of materials through grain boundary design. Can be expected.

Other objects, features, excellence and aspects of the present invention will be apparent to those skilled in the art from the following description. However, the description of the present specification, including the following description and the description of specific examples, etc., shows preferred embodiments of the present invention and is shown only for explanation. It was understood that! Various changes and Z or alterations (or modifications) within the spirit and scope of the present invention disclosed herein will occur to those skilled in the art based on the following description and knowledge from other parts of the present specification. Will be readily apparent. All patent documents and references cited herein are cited for illustrative purposes and should be construed as part of this specification. It is.

Brief Description of Drawings

FIG. 1 is a diagram schematically illustrating a basic concept of a polycrystalline material forming technique of the present invention.

[Fig.2] Taking a simple cubic lattice as an example, we explain the unit lattice and the corresponding lattice in many cases with a rotation angle of 36.52 ° around the <001> axis.

[Figure 3] Shows the structural design and the effect prediction map obtained when designing high-quality Balta polycrystals in silicon polycrystals.

FIG. 4 schematically shows an example of constituting a starting seed crystal in the polycrystalline material forming technique of the present invention. A typical example can be described by taking silicon polycrystal as an example. This corresponds to the seed crystal of the example.

FIG. 5 shows a photograph of a Si crystal obtained by the polycrystalline material forming technique of the present invention.

FIG. 6 shows an EBSP of a cross section near the seed crystal of a Si crystal obtained by the polycrystalline material forming technique of the present invention. FIG. 7 shows an EBSP showing the change in orientation distribution of the longitudinal section of a Si crystal obtained by the polycrystalline material forming technique of the present invention.

[Fig. 8] Distribution of orientation and grain boundary character distribution of the surface cut perpendicular to the growth direction at a crystal growth surface force of 40mm of Si crystal obtained by the polycrystalline material formation technology of the present invention. The EBSP that was examined is shown. FZ9 and FZ12 are produced Si crystal samples at a crystal growth rate of about 1.0 mm / min, and FZ13 is a produced Si crystal sample at a crystal growth rate of about 0.2 mm / min.

[Fig. 9] EBSP is shown for the orientation distribution (left) and the perpendicular orientation distribution (right) of the crystal growth of the Si crystal obtained by the polycrystalline material formation technology of the present invention.

[Fig. 10] Schematic diagram of the structure of a polycrystalline material that is predicted to have a theoretically strong mechanical strength (bottom left) and the grain boundary character of the Si crystal obtained by the polycrystalline material formation technology of the present invention. An azimuth distribution (EBSP: upper three pictures) and a schematic diagram (lower right) of the structure are shown.

BEST MODE FOR CARRYING OUT THE INVENTION

[0014] As a conventional technique, a polycrystal having an artificial corresponding grain boundary formed by bundling crystals cut out from a plurality of single crystals by measuring the orientation relationship, and seeding the crystals. As a crystal, there is a method of crystal growth under a growth condition that inherits the orientation by the CZ (Czochralski) method. The accuracy of the grain boundary character of the polycrystalline produced by this method is limited by the cutting accuracy, and the desired grain boundary character is not necessarily realized. For example, control of grain boundary character requires accuracy within 0.01 ° as a relative orientation relationship, but it is extremely difficult to achieve with current cutting techniques.

As a material used as a seed crystal, which is a conventional approach, there are the concept of bundling crystals with good grain boundary correspondence and the idea of reducing wrinkles between grain boundary seed crystals. However, it is practically impossible to achieve consistency between crystals at the atomic level, and if a minute mismatch is left, it will not be resolved during crystal growth. This seems to be because the degree of inconsistency is small, so there is no driving force for further alignment.

[0015] On the other hand, in the present invention, intentionally, from the desired grain boundary orientation relationship, growth starts from a seed crystal whose angle deviates greatly, and the grain boundary character spontaneously has the grain boundary energy. Take advantage of changing to smaller things. Therefore, the requirement for cutting accuracy is sufficient even within 1 °, and it is possible to realize polycrystals with the desired grain boundary character regardless of cutting accuracy. It is. This method is a crystal bundle in which Si crystals with a growth orientation of [110] and side faces of [100] and Si crystals with a growth orientation force of S [110] and side faces of [111] are bundled alternately. Is used as a seed crystal to grow Si polycrystal (In this case, the bundled seed crystal is in contact with the face [100] and face [111] to form a grain boundary. The orientation is assumed to be [110]), and as a result, it can be confirmed by verifying that the grain boundary characteristics are all sigma 3 and sigma 9 !, the grain boundary energy is small, and changes to grain boundaries.

The present invention relates to a technique for producing a polycrystalline material having an interface with low grain boundary energy inside a crystal. The present invention intentionally forms a polycrystal having the highest grain boundary energy with a random relative orientation relationship, and then performs unidirectional crystal growth using the polycrystal as a seed crystal for appropriate growth. Under the condition, a grain boundary having a low grain boundary energy is formed from a random grain boundary having a high grain boundary energy. The basic concept of the present invention is shown in FIG. In particular, the present invention provides a polycrystal having a crystal interface with a higher sigma value and uses it as a seed crystal to produce a polycrystalline material having a corresponding grain boundary with a lower sigma value. Is a polycrystalline material forming technique characterized by The present invention is characterized in that, in order to obtain a polycrystalline material having a grain interface with a low threshold value, a crystal interface with a high threshold value is used as a seed crystal. By using a seed crystal, the grain boundary energy is lowered and the overall grain boundary energy is lowered as a driving force. As a result, a polycrystal having a low grain boundary energy interface grows. On the other hand, since the consistency between crystals is very good, if the deviation is within several degrees, it will continue to grow as it is, rather than eliminating the deviation. In the present specification, the term “grain boundary” that is necessarily present in a polycrystalline material refers to the crystal grains constituting the polycrystal. The seam, It is the boundary between Akiratsubu.

If one of the two crystals that make up the grain boundary is rotated around a rotation axis by a certain angle, the overlap of the two crystals is considered. In this case, lattice points that overlap periodically are formed, which are called “corresponding lattice points”. The corresponding grid points occur periodically. Again, the unit cell area of the original crystal lattice The ratio of the unit cell area of the corresponding lattice formed here is called the sigma (∑) value, and it is used as an index to indicate the degree of correspondence between grain boundaries between crystals. Thus, the saddle value is obtained by the ratio of the area of the unit cell of the corresponding cell to the area of the unit cell.

[0017] This will be explained using a simple cubic lattice (Fig. 2) as an example. The unit cell of the simple cubic lattice is a portion surrounded by a small square in the upper left of FIG. When the simple cubic lattice shown by the vertical vertical line and the horizontal horizontal line in Fig. 2 is rotated around the rotation axis 001> by a rotation angle of 36.52 degrees, it overlaps with the original lattice point. (Corresponding grid points) are born, and the unit grid of the corresponding grid can be shown by a square surrounded part of the square in FIG. 2 having a larger area than the unit grid part of the simple cubic grid. This (Fig. 2) is expressed as follows, which is an index that represents the degree of correspondence between the two grids.

[0018] [Numerical equation 1] Unit cell area i of corresponding cell

Unit cell area 11

[0019] By way of example, in the example of FIG.

In general, the lower the threshold value, the lower the energy stored at the grain boundaries where the correspondence between crystals is better. The saddle value takes only odd values, and a mean value of 1 means that both unit cells at the grain interface are the same, and there is no grain boundary. This indicates the same crystal. If there is actually another grain boundary interface, the value increases as 3, 5, 7, .... For example, if the grain interface is [111] with respect to the growth orientation force 110>, the 3 value is 3 (∑3), which is the best interface. In cubic systems such as silicon, ∑3 and ∑9 are orientation relationships with very low grain boundary energy.

Table 1 below shows combinations of diamond structures that can achieve low threshold values when the growth interface and grain boundaries are equal in growth orientation.

[0020] [Table 1] Growth orientation Grain interface Grain boundary character

u

π ηη) 1

<110> {111} ∑3

<210> 1121} ∑3

<111> {211} ∑3

[0021] The smaller the threshold value, the higher the degree of correspondence. For example, in a silicon (Si) polycrystal for solar cells, it is an electrically inactive crystal grain boundary, and carrier recombination at the crystal grain boundary is reduced. Reduce. Fig. 3 shows a prediction map of the improvement of the polycrystalline structure and the effects obtained by the improvement in high-quality Si Balta polycrystal. Therefore, for example, (1) if the growth direction of the crystal grains is the same, it is easy to form a homogeneous texture. (2) If the grain boundaries are electrically inactive, the grain boundaries Carrier recombination at (3) low intragranular defect density and minority carrier life similar to single crystals, and (4) high quality crystals with optimal particle size (5) If the impurity concentration is low, the crystallinity in the high-quality crystal grains will be obtained. (6) If the mechanical strength is strong, thin plate processing and handling will be performed. It becomes easy.

In the present specification, the polycrystal used as the starting seed crystal is formed from a plurality of single crystals, and when preferred, a single crystal orientation is used as the crystal orientation in the direction in which the intended crystal grows. What is said to be. The number of single crystals constituting the polycrystal is at least 3 or more, at least 4 or more, at least 5 or more, at least 6 or more, at least 7 These are the above, at least 8 or more, at least 9 or more, or at least 10 or more.

Examples of the seed crystal include those having at least two grain boundaries on the crystal growth surface. The seed crystal includes (1) one having at least 3 grain boundaries on the crystal growth surface, (2) one having at least 4 grain boundaries on the crystal growth surface, and (3) at least 5 on the crystal growth surface. (4) having at least 6 grain boundaries on the crystal growth surface, (5) having at least 7 grain boundaries on the crystal growth surface, (6) on the crystal growth surface Examples include those having at least 8 grain boundaries. It is preferable to make the surface energy of the crystal plane to grow equal to the surface energy of the crystal plane to be grown. For example, the plane is selected to be the same crystal plane. In a preferred embodiment, the crystal growth is a single crystal orientation as the crystal orientation in the direction of crystal growth, and the crystal growth is performed in one direction in the crystal direction.

The present invention can be applied as a polycrystalline material to many practical materials such as crystals for solar cells, structural materials, and magnetic materials, and is widely applicable to polycrystalline materials used in this field, not limited to silicon. The target polycrystalline materials include metal materials, intermetallic compound materials, ceramic materials, semiconductor materials, etc., and the included crystal structures are not limited to orthorhombic structures. It can be applied to.

In addition, the grain boundary control method in the present invention can be applied to other polycrystalline materials (metals, composite materials, etc.) such as silicon wafers for solar cells. It can be expected to develop into a new material science with high functionality.

The target crystal system of the present invention is not particularly limited as long as the desired purpose and effect can be obtained, including any of the typical metal elements, typical non-metal elements, and transition metal elements in the periodic table. It is not limited. Examples of the typical metal element include an alkali metal element, an alkaline earth checking element, a zinc group element, an aluminum group element, a carbon group element, and a nitrogen group element. Typical non-metallic elements include boron element, carbon group element, nitrogen group element, oxygen group element, halogen element and the like. Examples of transition metal elements include rare earth elements, titanium group elements, earth metal elements, chromium group elements, manganese group elements, iron group elements, platinum group elements, copper group elements, lanthanoids, and actinoids. Typical polycrystalline constituent elements include silicon (Si), germanium (Ge), carbon (C; including diamond), selenium (Se), tellurium (Te), tin (Sn), etc. . Polycrystals can also be composed of compounds, such as gallium arsenide (GaAs), gallium phosphide (GaP), indium arsenide (InAs), gallium aluminum-um arsenide (GaAlAs), gallium aluminum indium arsenide (GaAlInAs), Zinc sulfide (ZnS), cadmium sulfide (CdS), cadmium selenium (CdSe), cadmium tellurium (CdTe), silicon carbide (Si C), nickel oxide (NiO), copper oxide (Cu 0), zinc oxide (ZnO), tin oxide (SnO), A1P, AlAs

twenty two

, AlSb ゝ GaN ゝ GaSb ゝ InP ゝ InSb ゝ ZnSe ゝ ZnTe, CdTe, HgS ゝ HgSe ゝ HgTe ゝ PbS ゝ PbSe, PbTe, SnTe, CuGaS, CuInS, CuGaSe, AglnS, CuInSe, AglnSe, CuInTe, AglnT

2 2 2 2 2 2 2 e, GeSi, etc. may be included. In addition, iron (Fe), cobalt (Co), nickel (Ni), man

2

Includes metals (materials) such as gun (Mn), chromium (Cr), vanadium (V), titanium (Ti), copper (Cu), gold (Au), silver (Ag), and alloys (materials). ! /, Teyo! /

FIG. 4 shows a schematic diagram of an example of constituting a seed crystal which is a starting material used in the present invention. FIG. 4 also explains the arrangement of the seed crystals during crystal growth using Si used in Example 1. In FIG. 4, crystal A is a thin plate obtained by cleaving a (001) single crystal wafer, while crystal B is a thin plate obtained by cleaving a (111) single crystal wafer. Thin plates) and crystals B (thin plates) are alternately arranged (laminated) to form the seed crystal (grain boundaries are random grain boundaries) shown on the right side of FIG. In the example of Fig. 4, the upper surface is the crystal growth start surface, and the crystal growth direction is 110>.

Bundling of high-value materials that will be seed crystals can be made up of an appropriate number of materials as appropriate.For example, strip-shaped thin plates are bonded together, rectangular solids, cubes, etc. are bonded together in a grid pattern. , Stick columns with triangular cross-sections, stick columns with hexagonal cross-sections, and combine columns with multiple polygon cross-sections together, or add a cylinder inside a cylinder. Any configuration, such as an enclosed shape, may be used. For example, 8 strips alternately laminated, 3 strips alternately pasted, 4 or more strips, eg 4-20 strips alternately pasted, It may be configured according to the purpose and the like as appropriate, such as an eye shape, a triangular cross-section, and a cylinder inside the cylinder. In addition, the material once bonded can be formed into a shape suitable for use in crystal growth using the seed crystal as a seed crystal, and it may be preferable to do so. Examples of the form (including the shape) include a columnar form having a circular cross section or an oval cross section. The form (including the shape) can be arbitrarily processed into a form capable of achieving a desired purpose such as obtaining a desired crystal growth. May be. The size of the single crystal piece used to construct the seed crystal can be set arbitrarily. Micron-sized ones are on the order of 0.1 mm, even on the order of mm, or only one of its dimensions is cm. In order, others Examples include 0.1 mm order or mm order. The size of the single crystal piece can be selected and set according to the purpose.

[0024] In some cases, it is sufficient that the seed crystal is configured so that the relative orientation relationship has a higher grain boundary with a random grain boundary energy than the target polycrystalline product. It is not limited to a specific value, for example, a specific threshold value. For example, there are cases where the crystal is alternately arranged in the seed crystal, and the combination of the stacked layers has a larger threshold value and a combination. That is, when the threshold value of the polycrystalline seed crystal is X and the threshold value of the polycrystalline polycrystalline product is Y, X> Y is selected. ∑5, ∑7, ∑9, etc., and even higher values, such as ∑51, Σ59, etc., may also be mentioned. The case of a saddle value may also be included. Preferably, with reference to the first-principles calculation result of the grain boundary energy, a place where the grain boundary energy is large and does not change so much when it deviates several degrees can be selected. In addition, considering the relationship of crystal structure (symmetry), it can be selected by conducting experiments if necessary.

[0025] In the technique of the present invention, the crystal growth method can be appropriately selected from methods known in the art. Examples of the crystal growth method include, but are not limited to, a zone melting method (Zone Melting), a CZ method, and a floating zone (FZ) method (floating zone melting method). An apparatus used in the method is widely known in the field, and can be appropriately selected from the known apparatus. In general, commercially available equipment can be used. The apparatus may be preferable in a case where the operation of the apparatus is controlled by a computer or the like on which a control program is or can be mounted.

The crystal growth rate can be selected to achieve the desired purpose and can be used, for example, as a control factor for the desired crystal growth. If the growth rate is slow, growth that takes over the surface of the seed crystal occurs, and by increasing the growth rate, new nuclear growth is promoted. In a specific embodiment, the crystal growth rate can be higher than usual, and the temperature gradient at the interface is selected so that the supercooling is large and induces a change in the character of the grain boundary. For example, the speed can be about 1.0 mm / min or faster, but can be selected according to the element or compound constituting the target crystal. Growth rate After achieving the intended grain boundary character change of the present invention, which does not need to be constant during crystal growth, it is preferable to slow down the speed and take over the grain boundary character. it can. In some cases, the crystal growth rate is about 0.3 mm / min or faster, or about 0.4 mm / min, is faster, or about 0.5 mm / min or faster, or 0.6 a speed of about mm / min or faster, a speed of about 0.7 mm / min or faster, or a speed of about 0.8 mm / min or faster, or a speed of about 0.9 mm / min or faster. Good. In another example, the crystal growth rate is 0.3-10.0 mm / min, or 0.4-5.0 mm / min, 0.5-3.0 mm / min, 0.6-2.5 mm / min, or 0.7-2.0 mm / min. Min, or 0.8-1.5 mm / min. The above growth rate may be the crystal growth rate at the crystal growth start surface, for example, when the crystal growth start surface force grows to some extent and then, for example, the crystal growth start surface force is about 10 to 50 mm. It is possible to grow at about 20 to 45 mm or about 25 to 40 mm and then to a slower speed.For example, about 0.25 mm / min or slower, or about 0.2 mm / min or more. It can be slower and faster.

In the technology of the present invention, the composition of the starting seed crystal, the selection of the sigma value of the grain boundary, the crystal growth direction, the crystal growth rate, the crystal growth method, the crystal growth temperature, and the like are suitably suitable depending on the crystal material used. The selection can be made while analyzing the crystal properties of the product using the EBSP method.

By using the polycrystalline material forming technology of the present invention, the crystal interface of metal materials, intermetallic compounds, ceramics, semiconductors, and polymer materials can be controlled. Development of composite materials, development of nanomaterials including ultra-miniaturization by controlling the crystal structure of the microstructure, material performance due to miniaturization of mechanical parts, fulfillment of reliability improvement requirements, biological functions and adaptive functions It is possible to develop intelligent materials (intelligent materials) with

With the technology of the present invention, the interface of polycrystalline grains is controlled to control the brittleness of the material, the microstructure is made uniform to improve its strength, and further, it is related to high temperature deformation, superplasticity and fracture phenomenon Mechanical performance can be advantageous. The technique of the present invention makes it possible to control grain boundary brittleness caused by grain boundary fracture of a polycrystalline material. [0027] In one specific embodiment, the polycrystalline material forming technology of the present invention can be applied to the production of a polycrystalline silicon material (silicon Balta crystal) used in solar cell crystals and solar cells, The effect is obtained.

In the production of the Balta polycrystalline silicon, a polycrystal having a high grain boundary with a grain boundary energy which is intentionally random in relative orientation relation is intentionally formed, and then the unidirectional crystal growth is performed using the polycrystal as a seed crystal. Then, under appropriate growth conditions, a grain boundary having a low grain boundary energy is formed from a random grain boundary having a high grain boundary energy. Specifically, the arrangement of the seed crystal is to cleave a Si crystal with a growth orientation of [110] and side face of [100] and a Si crystal with a growth orientation of [110] and side face strength of 11]. Are produced by laminating them alternately, and a random grain boundary is formed by laminating them alternately. The threshold value between the crystal planes of the fabricated laminate is predicted to take a large value because the grain boundary energy does not change much even when the relative orientation of the laminated crystal phases is several degrees. Good results can be expected by favoring the use of orientation relationships. The size of each crystal can be any size, for example, 4-30 mm in width, 5-100 mm in length, and thickness power .l-2.0 mm. A laminate can be used. In a typical example, the width is about 8 mm, the length is about 50 mm, and the thickness is about 0.4 to 0.5 mm. Of the bonded surfaces, the surface that is the starting point for crystal growth is preferably selected so that the surface energy of the crystal surface to be grown is equivalent. For example, in this example, the crystal growth starting surface can be adjusted to the [110] orientation to control the crystal orientation in the growth direction. As described above, by setting the surface that is the starting point for crystal growth among the bonded surfaces so that the surface energy is equivalent, the effect of the grain boundary energy in the growth process is increased, and the grain boundary energy is increased. It is preferable because it can promote the growth of polycrystalline with interfacial properties. In this example, for example, the crystal growth starting surface is equivalent to [110], and by setting the surface energy to be equivalent, the influence of the grain boundary energy in the growth process is increased, the grain boundary energy is low, and there is an interface. Promote the growth of polycrystals!

[0028] Growth of a silicon crystal using the seed crystal can be performed by 1S, for example, FZ method, to which a known crystal growth method can be applied. The heating source is a force that can be used without limitation as long as it is a known and effective technique. For example, an electron beam from a ring-shaped tungsten filament is used. Converging light (including halogen lamp light) using a mirror, laser beam, or mirror surface. Usually, the growth starting surface of the seed crystal is arranged upward, and a Si stacked polycrystal having a diameter of about 4 to 30 mm, for example, about 8 mm, which is a raw material, is arranged on the opposite side. The lower part of the source polycrystalline silicon is melted by a heating source such as an electron beam, and then the molten surface is brought into contact with the upper part of the seed crystal. Crystal growth is performed by the method. Conditions such as the growth rate can be determined as described above, and may typically be 0.7 to 2.0 mm / min, or 0.8 to 1.5 mm / min, for example, about 1.0 mm / min. Can be controlled as follows.

A polycrystal with an artificial grain boundary formed by bundling crystals cut out by measuring the orientation relationship from multiple single crystals, and then using this crystal as a seed crystal to inherit its orientation by the CZ method In the prior art in which crystal growth is performed under such growth conditions, the accuracy of the grain boundary character of the produced polycrystal is limited by the accuracy of cutting, and the desired grain boundary character is not necessarily realized. For example, the control of grain boundaries is a force that requires an accuracy within 0.01 ° as a relative orientation, which is extremely difficult to achieve with the current cutting technology (in the crystals used for seed crystals, Due to the misalignment of crystal planes and grain boundary mismatch, the part of the grain interface of the grown wafer remains high, and the expected crystal strength cannot be obtained. On the other hand, in the present invention, it is possible to obtain a polycrystalline material having a property of very low interface energy. In the present invention, intentionally, the orientation-related force of the desired grain boundary also starts to grow from a seed crystal whose angle is greatly deviated, and the grain boundary character changes to one having the smallest grain boundary energy. Therefore, the requirement for the cutting accuracy is sufficient even within 1 °, and a polycrystal having a desired grain boundary character can be realized regardless of the cutting accuracy. In the silicon polycrystal for solar cell, the technology of the present invention was applied and the growth orientation was [110] and the growth orientation was [110] and the side orientation was [110]. The Si polycrystal is grown using the crystal bundle (grain boundary is formed by the contact of [100] and [111]) as a seed crystal. As a result, the grain boundary character is all sima 3 and sigma 9 !, the grain boundary energy is small, and the grain boundary character is changed to the grain boundary, which shows its superiority. In the present invention, a polycrystal having a good grain boundary can be obtained. [0030] Balta polycrystalline silicon obtained by the present invention solves the problem of securing the raw material silicon (which is strongly required to make the polycrystalline silicon wafer thin), and has a thickness when slicing from an ingot. It can be thinned (conventionally, mechanical strength was insufficient by thinning, causing problems such as cracking during processing), contributing to cost reduction and breaking of grain boundary forces It has a grain boundary with excellent electrical properties (quality is the same as that of a single crystal) and is stronger than a conventional polycrystal. Therefore, thin plate cutting from the ingot and subsequent handling become easy, and the side force of the material can also contribute to the reduction of the slice thickness. By all means, it will solve the problem of securing future raw materials, which is currently an issue in the solar cell industry, and will lead to the expansion of the solar cell industry and the solution of energy problems. In addition, the grain boundary control method in the present invention can be applied to other polycrystalline materials (metals, composite materials, etc.). Can be expected.

The present invention will be specifically described with reference to the following examples. However, these examples are provided merely for the purpose of explaining the present invention and for reference to specific embodiments thereof. These exemplifications are for explaining specific specific embodiments of the present invention, but do not limit or limit the scope of the invention disclosed in the present application. In the present invention, it should be understood that various embodiments based on the idea of the present specification are possible. All examples were performed or performed using standard techniques, except as otherwise described in detail, and are well known and routine to those skilled in the art. is there.

Example

[0031] In this example, the seed crystals are arranged in a Si crystal with a growth orientation of [110] and side surfaces of [100], and a growth orientation of [110] and side surfaces of [111]. A silicon crystal was prepared by cleaving and alternately layering them to form random grain boundaries. That is, the side surface [100] and the side surface [111] are bonded together so as to contact each other to form a grain boundary.

The threshold between these faces is 41. Even with a few degrees of deviation, the grain boundary energy does not change so much, and the orientation relation that is expected to take a large value was used. Each crystal is 8mm wide and 50m long m, the thickness was 0.4 to 0.5 mm, and these were used by alternately stacking 8 sheets.

Of the bonded surfaces, the crystal growth starting point is controlled by aligning the [110] orientation so that the surface energy of the crystal growth surface is equivalent to the [110] orientation. is doing. Of the bonded surfaces, the surface that is the starting point for crystal growth is

By setting the surface energy equivalent to [110], the influence of grain boundary energy in the growth process is increased, and the growth of polycrystals with low grain boundary energy and interfaces is promoted. .

[0032] The silicon crystal was grown by an electron beam floating zone (FZ) growth method using the seed crystal produced by the above method. The heating source is an electron beam from a ring-shaped tungsten filament. The growth starting surface of the seed crystal was placed upward, and an Si polycrystal with a diameter of 8 mm as a raw material was placed facing it. After melting the lower part of the raw material polycrystalline silicon with an electron beam, the melted surface is brought into contact with the upper part of the seed crystal, and after fully acclimatizing, the filament is moved upward at a constant speed to grow. Crystal growth was performed.

The growth rate was controlled to be 1 mm / min.

[0033] An EBSP method (backscattered electron diffraction pattern) can be used to determine the index of crystal orientation of a sample obtained by cutting a crystal grown by the above method in a direction in which a cross section where a seed crystal is bonded can be seen. Method: Observation was performed by Electron Backscatter Diffraction Pattern. Fig. 5 shows a photograph of the Si crystal obtained by growth using the technology of the present invention. As a result, it became clear that the grown crystal that can be placed near the seed crystal grew in the same orientation as the seed crystal. Figure 6 shows the EBSP near the seed crystal. Further, in the vicinity of about 20 mm from the seed crystal, the crystal growth with good grain boundary alignment intended by the present invention has started. In subsequent crystal growth, crystals with low grain boundary energy and good alignment with each other grow preferentially, and in crystals grown after 40 mm, crystals with good grain boundary character predominately grow. grown. Figure 7 shows the EBSP that shows the change in the orientation distribution of the longitudinal section of the Si crystal obtained by growing using the technology of the present invention. The length of the Si crystal sample shown in the left side of Fig. 7 (the length in the growth direction) is about 40 mm (the grain boundaries are only ∑ 3 and ∑ 9), and the almost circular shape shown on the right side of it. The diameter of the sample with a cross-sectional area of EBSP of the part cut in mm is shown. Although it is polycrystalline as shown in Fig. 7, only the orientation relations of ∑3 and ∑9 are observed. These interfaces are formed by spontaneous growth and have no defects. The crystal growth rate in this example is lmm / min.

[0034] At 40 mm from the crystal growth surface, the orientation distribution of the surface cut perpendicular to the growth direction and the distribution of grain boundary character were examined (Fig. 8). As a result, the (110) plane of the original growth plane does not remain! /, But all the grain boundaries of the grown plane are ∑ 3 and ∑ 9! It was. This result has been reproduced with a plurality of samples, and it is clear that polycrystalline growth with a good grain boundary character in the technique of the present invention is possible. As a comparative example, when the growth rate was slow at about 0.2 mm / min, the growth surface inherited the growth surface of the seed crystal and was mostly (110), and the random grain boundary remained.

FZ9 and FZ12 are produced Si crystal samples at a crystal growth rate of about 1.0 mm / min, and FZ13 is a produced Si crystal sample at a crystal growth rate of about 0.2 mm / min.

[0035] Fig. 9 shows the EBSP for the orientation distribution in the crystal growth direction (left in Fig. 9) and the vertical orientation distribution (right in Fig. 9) of the grown Si crystal sample. The distribution of the growth direction is a force limited to several orientations. It can be explained geometrically because the orientation of the seed crystal is [110] and the newly formed grain boundary is ∑3. According to the technique of the present invention, it is apparent that the crystal orientation can be limited in addition to the grain boundary character by selecting the orientation of the seed crystal.

The schematic diagram in the lower left of Fig. 10 shows the structure of a polycrystal that is theoretically predicted to have extremely high mechanical strength. The force in the upper right of the figure is formed by the technique of the present invention. The grain boundary character 'orientation distribution of the crystal is shown, and the lower right shows the schematic diagram. It can be seen that a very similar structure is formed. Since all the grain boundary characteristics are the corresponding grain boundaries, it can be predicted that this crystal will have excellent characteristics when processed into a solar cell, and further, it can be predicted that the mechanical strength is also excellent. If the mechanical strength is strong, even if the substrate is sliced thinly from an ingot and handled, it can be handled, contributing to the effective use of raw materials, and improving conversion efficiency. This is also very advantageous. The silicon polycrystal obtained by crystal growth in the above examples is (1) substantially free from defects as observed by the backscattered electron diffraction pattern method, (2) excellent mechanical strength, excellent impact resistance. (3) Conversion efficiency in a 10 cm square cast cell (efficiency for converting sunlight into electricity) 18% or more, 19 % Or more, 20% or more, 21% or more, 22% or more, or 25% or more. (4) It may be characterized by comprising at least 4 crystalline phases.

Judging from ordinary technical common sense, a slow growth rate is advantageous when growing crystals from seed crystals. This is because a crystal having good crystallinity can be obtained by growing the crystallinity and orientation of the crystal to be grown by sufficiently taking over the crystallinity and orientation of the seed crystal. Even in the results obtained by experiments, when the crystal growth rate is slowed down, crystal growth occurs that inherits the grain boundary character of the seed crystal as it is. This is because, for the purpose of the present invention, for the nucleation of new crystal grains having a good grain boundary character, contrary to the conventional common sense, the growth rate is increased and the growth rate is increased by an appropriate growth rate. It can be seen that it is effective to apply the degree of supercooling as the driving force. In order to change the grain boundary character, it is suggested that it is important or necessary to overcome the active energy barrier under different growth conditions.

By processing a polycrystal having a good grain boundary character obtained by the present invention and using it as a seed crystal to grow a crystal, only a crystal having a low threshold value exists at the crystal interface, and there are very few defects. A crystalline material can be obtained. Since such a polycrystalline material has few dangling bonds at the grain boundary, it is configured as a network of grain boundaries, and even in the macro property of the polycrystalline material, the electrical activity is low, or the crystal Excellent properties such as high strength can be achieved. Particularly in silicon materials for solar cells, the power of using many polycrystalline materials has the problem of carrier recombination at the crystal interface. This can be improved by the technique of the present invention. In the polycrystalline silicon material obtained by carrying out the present invention, carrier recombination can be reduced as compared with conventional polycrystalline silicon. In addition, the single crystal material has a problem that it is difficult to handle when the wafer is thinned, but the mechanical strength of the material obtained by the technique of the present invention can be made larger than that of the conventional single crystal silicon. This allows for processes such as destruction when the wafer is thinned. It is expected that troubles during the process can be avoided.

Industrial applicability

According to the present invention, it is possible to produce a polycrystal having a controlled grain boundary property (grain boundary character) distribution, which is a macro of many practical materials such as polycrystals for solar cells, structural materials, and magnetic materials. It becomes possible to control the properties of the material including various properties. In the present invention, a crystal having a grain boundary having a high grain boundary energy with intentionally random relative orientation relation is used as a seed crystal, and crystal growth is performed in one direction, so that a random having a high grain boundary energy is obtained. Since grain boundaries with low grain boundary energy are formed from the grain boundaries, for example, all of the grain boundaries can be aligned with the corresponding grain boundaries with low sigma values. For this reason, it can be expected that excellent characteristics such as low electrical activity and high crystal strength can be expected even in the macro properties of the polycrystalline material, which is configured as a network of grain boundaries.

It will be apparent that the invention may be practiced otherwise than as particularly described in the foregoing description and examples. Many modifications and variations of the present invention are possible in light of the above teachings, and thus are within the scope of the claims appended hereto.

Claims

Claims [1] A polycrystal having a grain boundary with a high grain boundary energy intentionally having a random relative orientation relationship is formed, and then a unidirectional crystal growth is performed using the polycrystal as a seed crystal. A method for producing a polycrystalline material, characterized by forming grain boundaries with high energy and random grain boundaries and with low grain boundary energy. 2. The method for producing a polycrystalline material according to claim 1, wherein the seed crystal has at least two grain boundaries on the crystal growth surface. [3] The seed crystal (1) has at least 3 grain boundaries on the crystal growth surface, (2) has at least 4 grain boundaries on the crystal growth surface, and (3) at least 5 on the crystal growth surface. (4) a crystal growth surface having at least 6 grain boundaries, (5) a crystal growth surface having at least 7 grain boundaries, and (6) a crystal 3. The method for producing a polycrystalline material according to claim 1, wherein the growth force has at least 8 grain boundaries on the growth surface. 4. The crystal growth is a single crystal orientation as a crystal orientation in a crystal growth direction, and the crystal growth is performed in one direction in the crystal direction. ~ 3! A method for producing a polycrystalline material according to any one of the above. [5] The seed crystal is a polycrystal formed from a plurality of single crystals, and has a single crystal orientation as the crystal orientation in the direction of crystal growth.

(8) The number of single crystals constituting the polycrystal is at least 10 or more

The group force as a force is selected. 5. Of manufacturing polycrystalline material.

[6] The polycrystal having a crystal interface with a high crystallinity is used as a seed crystal to grow a crystal to obtain a polycrystal with a low crystallinity and a grain interface. The method for producing a polycrystalline material according to any one of the above.

7. The method for producing a polycrystalline material according to any one of claims 1 to 6, wherein the polycrystal is a silicon polycrystal.

[8] The method for producing a polycrystalline material according to any one of [1] to [7], wherein the crystal growth rate at the crystal growth start surface is about 0.3 mm / min or faster.

[9] The arrangement of the seed crystal consists of a Si crystal with a growth orientation of [110] and a side face of [100], and a Si crystal with a growth orientation force of ¾ 10 and a side face of [111]. The method according to claim 1, wherein random grain boundaries are formed by alternately laminating so that the surface and the surface [111] are in contact with each other. .

10. A silicon polycrystal obtained by the method for producing a polycrystalline material according to any one of claims 1 to 9.

[11] A silicon polycrystal which is silicon polycrystal, and the grain boundary of the silicon polycrystal is only ∑3 and Z or ∑9.

[12] (1) Substantially no defects observed by backscattered electron diffraction pattern method,

(4) Consists of at least 4 crystalline phases

12. The silicon polycrystal according to claim 11, wherein:

[13] A solar cell manufactured from the polycrystalline silicon according to any one of claims 10 to 12.