Polycrystalline Silicon Rod Crystal Structure Control
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Solution Overview
Problem
Conventional polycrystalline silicon rods with longer needle-shaped crystals are difficult to melt during the FZ method, leading to defects and dislocation in single crystal silicon due to unmolten coarse grains.
Innovation Solution
A polycrystalline silicon rod with needle-shaped crystals of 288 µm or less in diameter and an area percentage of 78% or more, or between 15% to 35% within specific regions, ensuring uniform distribution and melting during the FZ method to prevent dislocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If needle-shaped crystals are allowed to grow longer in conventional polycrystalline silicon rods, then the crystal structure can be maintained during deposition, but the crystals become difficult to melt during the FZ method, causing defects and dislocation in single crystal silicon
Solution Approach 1:
The patent changes the critical parameter of needle-shaped crystal length from conventional longer dimensions to specifically 288 µm or less. This parameter change ensures that the crystals are short enough to be completely melted during the FZ method while still maintaining adequate crystal structure stability during the CVD deposition process, thereby preventing dislocation in the final single crystal silicon
Solution Approach 2:
The patent applies different crystal structure requirements to different regions of the polycrystalline silicon rod. Specifically, the innermost region (region A) contains a polycrystalline thin rod with controlled crystal structure, the intermediate region (region B) has needle-shaped crystals with area percentage less than 1%, and the outer region (region D) has needle-shaped crystals with area percentage less than 7%. This local differentiation ensures optimal melting behavior in each region during the FZ method
2Strength
If the area percentage of needle-shaped crystals is increased to improve crystal structure, then the rod strength is enhanced, but the crystals may not be completely molten during heating, leading to unmolten coarse grains
Solution Approach 1:
The patent optimizes the area percentage parameter of needle-shaped crystals to different values for different regions: less than 1% in region B, less than 7% in region D, and controls the distribution in region C.同时, the patent specifies that needle-shaped crystal length should be 288 µm or less. These parameter optimizations ensure that the rod maintains sufficient strength while allowing complete melting during the FZ method, preventing unmolten coarse grains
Solution Approach 2:
The patent divides the polycrystalline silicon rod into multiple regions (A, B, C, D) with different crystal structure characteristics and needle-shaped crystal area percentages. This segmentation allows each region to contribute differently to the overall rod strength while ensuring that all regions can be completely melted during the FZ method, with region A containing the seed rod, region B having minimal needle crystals, region C as a transition zone, and region D having controlled needle crystal distribution
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents dislocation and void formation in single crystal silicon by ensuring that needle-shaped crystals are fully molten, resulting in a uniform crystal structure.
Implementation Method 1
gas containing silicon is thermally decomposed or is reduced by hydrogen under the condition of high temperature so that high purity silicon is deposited on a filament rod
Implementation Method 2
gas containing silicon is thermally decomposed or is reduced by hydrogen under the condition of high temperature so that high purity silicon is deposited on a filament rod
Implementation Method 3
a polycrystalline silicon deposit which is deposited on an outer circumferential surface of the seed rod by the CVD process
Implementation Method 4
needle-shaped crystals of a small size within the region B are completely molten by heating in the subsequent FZ method
Data Source
Figure 1
Figure 2(a)~2(b-4)
Figure 3(a)~3(b-4)
AI summary
A polycrystalline silicon rod comprises a seed rod made of polycrystalline silicon, and a polycrystalline silicon deposit which is deposited on the outer circumferential surface of the seed rod by the CVD process . A diameter of the polycrystalline silicon rod is 77 mm or less. When the polycrystalline silicon rod is observed by an optical microscope with respect to the cross section perpendicular to an axis of the seed rod, needle-shaped crystals each having a length of 288 µm or less are uniformly distributed radially with the seed rod being as the center in the polycrystalline silicon deposit. The needle-shaped crystals account for 78 % or more of the cross section.