Polycrystalline silicon rod, processing method for polycrystalline silicon rod, method for evaluating polycrystalline silicon rod, and method for producing FZ single crystal silicon

Patent metadata

Field	Value
Publication number	US-11167994-B2
Application number	US-202017012418-A
Country	US
Kind code	B2
Filing date	Sep 4, 2020
Priority date	Dec 25, 2014
Publication date	Nov 9, 2021
Grant date	Nov 9, 2021

Abstract

For evaluating a polycrystalline silicon rod to be used as a raw material for production of FZ Si single crystals, novel evaluation values (values of characteristics×amount of crystals) including the amount of crystals grown in the growth direction (radial direction) are defined and the homogeneity in crystal characteristics in the growth direction (radial direction) is evaluated. Specifically, the homogeneity of the polycrystalline rod is evaluated by sampling a plurality of specimen plates each having, as a principal plane thereof, a cross-section perpendicular to a radial direction of the polycrystalline rod grown by a Siemens method at equal intervals in the radial direction, determining values of characteristics of the crystals of the specimen plates by measurements, and by using evaluation values obtained by multiplying amounts of the crystals (relative amounts of the crystals) at sites where the specimen plates have been sampled by the values of the crystal characteristics.

First claim

The invention claimed is:

1. A manufacturing method of single crystal silicon by a float zone (FZ) melting method using a polycrystalline silicon rod, the method comprising:
zone-melting the polycrystalline silicon rod by the float zone (FZ) method to produce the single crystal silicon,
wherein
the polycrystalline silicon rod has an entire length of 500 mm or larger and an average diameter of 130 mm or larger and 300 mm or smaller,
the method further comprises processing the polycrystalline silicon rod so that the polycrystalline silicon rod satisfies the following:
a circularity of a plurality of cross-sections perpendicular to a cylindrical shaft of the polycrystalline silicon rod taken over the entire length of the polycrystalline silicon rod satisfies a first difference ΔD 1 between a first maximum value and a first minimum value of diameters of two concentric circles of each of the plurality of cross-sections being 3 mm or smaller over the entire length of the polycrystalline silicon rod, the first difference ΔD 1 being determined by measuring a difference (ΔD 1 /2) between radii of the two concentric circles of each of the plurality of cross-sections, and a second difference ΔD 2 between a second maximum value and a second minimum value of diameters of a nearly cylindrical virtual rotating body formed when the polycrystalline silicon rod is rotated about a center axis in an extension direction thereof being 6 mm or smaller, and
an average rotational symmetry of the polycrystalline silicon rod over the entire length of the polycrystalline silicon rod is 40% or more, and the average rotational symmetry being calculated by:
sampling a plurality of specimen plates each having, as a principal plane thereof, a cross-section perpendicular to a radial direction of the polycrystalline silicon rod, the plurality of specimen plates being sampled at equal intervals in the radial direction;
determining evaluation values A, B of a pair of the plurality of specimen plates sampled from sites at symmetrical positions about a center axis of the polycrystalline silicon rod, wherein the evaluation value A is determined as a function of a crystal characteristic of a first specimen plate sampled from a site, positioned at a first distance from the center axis of the polycrystalline silicon rod, in the polycrystalline silicon rod, and the evaluation value B is determined as a function of the crystal characteristic of a second specimen plate sampled from a site, positioned at a second distance that is symmetrically equal to the first distance with respect to the center axis of the polycrystalline silicon rod, in the polycrystalline silicon rod;
calculating a rotational symmetry from the evaluation values A and B, which are related to homogeneity in the crystal characteristic, according to the equation: 100−[| A−B |/(( A+B )/2)×100]; and
repeating steps (i) to (iii) at different intervals along the entire length of the polycrystalline silicon rod to obtain the average rotational symmetry.

2. A manufacturing method of single crystal silicon by a float zone (FZ) melting method using a polycrystalline silicon rod, the method comprising:
zone-melting the polycrystalline silicon rod by the float zone (FZ) method to produce the single crystal silicon,
wherein
the polycrystalline silicon rod has an entire length of 500 mm or larger and an average diameter of 130 mm or larger and 300 mm or smaller,
the method further comprises processing the polycrystalline silicon rod so that the polycrystalline silicon rod satisfies the following:
a circularity of a plurality of cross-sections perpendicular to a cylindrical shaft of the polycrystalline silicon rod taken over the entire length of the polycrystalline silicon rod satisfies a first difference ΔD 1 between a first maximum value and a first minimum value of diameters of two concentric circles of each of the plurality of cross-sections being 3 mm or smaller over the entire length of the polycrystalline silicon rod, the first difference ΔD 1 being determined by measuring a difference (ΔD 1 /2) between radii of the two concentric circles of each of the plurality of cross-sections, and a second difference ΔD 2 between a second maximum value and a second minimum value of diameters of an early cylindrical virtual rotating body formed when the polycrystalline silicon rod is rotated about a center axis in an extension direction thereof being 6 mm or smaller,
an average difference in rotational symmetry of the polycrystalline silicon rod over the entire length of the polycrystalline silicon rod is 40% or less, the average difference in rotational symmetry being calculated by:
obtaining a first sampling rod from a first end of the polycrystalline silicon rod, and a second sampling rod from a second end of the polycrystalline silicon rod opposite to the first end in an axial direction,
sampling a plurality of specimen plates from each of the first and second sampling rods, each of the plurality of specimen plates having, as a principal plane thereof, a cross-section perpendicular to an axial direction of each of the first and second sampling rods, the plurality of specimen plates being sampled at equal intervals in the axial direction;
determining evaluation values C, D, wherein the evaluation value C is determined as a function of a crystal characteristic of a third specimen plate sampled from a site, positioned at a third distance from a center axis of the first sampling rod, in the polycrystalline silicon rod, and the evaluation value D is determined as a function the crystal characteristic of a fourth specimen plate sampled from a site, positioned at a fourth distance that is equal to the third distance from a center of the second sampling rod, in the polycrystalline silicon rod;
calculating a difference in rotational symmetry from the evaluation values C and D, which are related to homogeneity in the crystal characteristic, according to the equation: [| C−D |/(( C+D )/2)×100]; and
repeating steps (i) to (iv) at different intervals along the entire length of the polycrystalline silicon rod to obtain the average difference in rotational symmetry.

3. The manufacturing method according to claim 1 , wherein
the crystal characteristic is one selected from the group consisting of an amount of crystals formed, a crystal orientation, a crystal grain diameter, a thermal diffusivity, and a thermal conductivity.

4. The manufacturing method according to claim 1 , wherein
the crystal characteristic is the crystal orientation, and
the crystal characteristic is obtained by Bragg reflection intensity from Miller index plane <111> or Miller index plane <220>.

5. The manufacturing method according to claim 1 , wherein
the evaluation values A and B are each calculated as a function of the crystal characteristic and a difference between the first and second distances, respectively, and a distance of an adjacent specimen plate from the center axis of the polycrystalline silicon rod.

6. The manufacturing method according to claim 2 , wherein
the evaluation values C and D are each calculated as a function of the crystal characteristic and a difference between the third and fourth distances, respectively, and a distance of an adjacent specimen plate from the center axis of the first and second sampling rods, respectively.

7. The manufacturing method according to claim 2 , wherein the crystal characteristic is one selected from the group consisting of an amount of crystals formed, a crystal orientation, a crystal grain diameter, a thermal diffusivity, and thermal conductivity.

8. The manufacturing method according to claim 2 , wherein the crystal characteristic is the crystal orientation, and the crystal characteristic is obtained by Bragg

Assignees

• Shinetsu Chemical Co

Inventors

• Miyao Shuichi
• Netsu Shigeyoshi
• Okada Junichi

Classifications

• C30B13/00

  Single-crystal growth by zone-melting; Refining by zone-melting (C30B17/00 takes precedence; by changing the cross-section of the treated solid C30B15/00; under a protective fluid C30B27/00; for the growth of homogeneous polycrystalline material with defined structure C30B28/00) · CPC title

• G01N23/207

  Diffractometry using detectors, e.g. using a probe in a central position and one or more displaceable detectors in circumferential positions · CPC title

• G01N23/20

  by using diffraction of the radiation by the materials, e.g. for investigating crystal structure; by using scattering of the radiation by the materials, e.g. for investigating non-crystalline materials; by using reflection of the radiation by the materials · CPC title

• C30B35/007

  Apparatus for preparing, pre-treating the source material to be used for crystal growth · CPC title

• C01B33/02 Primary

  Silicon (forming single crystals or homogeneous polycrystalline material with defined structure C30B) · CPC title