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

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 ΔD1 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 ΔD1 being determined by measuring a difference (ΔD1/2) between radii of the two concentric circles of each of the plurality of cross-sections, and a second difference ΔD2 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.