Polycrystalline silicon rod, method for producing polycrystalline silicon rod, and single-crystalline silicon

Abstract

In the present invention, once a polycrystalline silicon rod is grown by the Siemens process, the polycrystalline silicon rod is heat-treated within a temperature range from 750° C. to 900° C. to relieve residual stress in the crystal. According to the experiment of the present inventors, residual stress can be relieved satisfactorily by heat treatment at the above-described low temperature, and in addition, metal contamination cannot be induced and the physical properties of the polycrystalline silicon rod cannot be changed. The above heat treatment can be conducted inside a furnace used to grow the polycrystalline silicon rod, and can also be conducted outside a furnace used to grow the polycrystalline silicon rod. According to the present invention, a polycrystalline silicon rod with residual stress (σ) of not more than +20 MPa evaluated by a 2θ-sin 2 Ψ diagram can be obtained.

1 . A polycrystalline silicon rod grown by a Siemens process and having a residual stress (σ) of not more than +20 MPa, wherein the residual stress is given by the formulae shown below and evaluated by the slope (Δ(2θ)/Δ(sin 2  Ψ)) of a straight line fitted to data points by least square approximation which are obtained by X-ray diffraction and plotted onto a 2θ-sin 2  Ψ diagram,
   σ(MPa)= K ·[Δ(2θ)/Δ(sin 2  Ψ)], and
 
     K =−( E/ 2(1+ν))·cot θ 0 ·π/180,
 
 wherein: 
 Ψ: an angle (deg.) between a sample-surface normal and a lattice-plane normal, 
 θ: a diffraction angle (deg.), 
 K: a stress constant (MPa/deg.), 
 E: Young's modulus (MPa), 
 ν: Poisson's ratio, and 
 θ 0 : a Bragg angle (deg.) in a strain-free state. 
 
     
     
         2 . The polycrystalline silicon rod according to  claim 1 , wherein the polycrystalline silicon rod has been heat-treated within a temperature range from 750° C. to 900° C. for stress relief. 
     
     
         3 . The polycrystalline silicon rod according to  claim 2 , wherein the polycrystalline silicon rod after the heat treatment retains a crystal grain size distribution and a thermal diffusivity from before the heat treatment. 
     
     
         4 . A method of producing a polycrystalline silicon rod, comprising growing a polycrystalline silicon rod by a Siemens process, followed by heat-treating the polycrystalline silicon rod at a temperature ranging from 750° C. to 900° C. for stress relief. 
     
     
         5 . The method of producing the polycrystalline silicon rod according to  claim 4 , wherein the heat treatment is conducted inside a furnace in which the polycrystalline silicon rod was grown. 
     
     
         6 . The method of producing the polycrystalline silicon rod according to  claim 4 , wherein the heat treatment is conducted outside a furnace in which the polycrystalline silicon rod was grown. 
     
     
         7 . Single-crystalline silicon grown from polycrystalline silicon as a raw material obtained from the polycrystalline silicon rod according to  claim 1 . 
     
     
         8 . Single-crystalline silicon grown from polycrystalline silicon as a raw material obtained from the polycrystalline silicon rod according to  claim 2 . 
     
     
         9 . Single-crystalline silicon grown from polycrystalline silicon as a raw material obtained from the polycrystalline silicon rod according to  claim 3 .