Gate-Shaped Silicon Core Wire Welding for Low Metal Contamination
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Solution Overview
Problem
Existing silicon core wires for depositing polycrystalline silicon have high surface metallic concentrations at corner junctions, which are not sufficiently reduced, leading to metal contamination and purity issues in semiconductor wafers.
Innovation Solution
A silicon core wire with a gate shape, featuring a pair of vertical rod portions and a horizontal portion, where the ends are joined by welding in an inert gas atmosphere using a preheater with a low metallic concentration and high-frequency induction heating, resulting in a surface metallic concentration of 1 ppbw or less at corner junctions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the upper ends of vertical rod portions and ends of horizontal portion are simply placed on V-shaped receiving structures, then the assembly is easy to manufacture, but the corner junctions have high surface metallic concentration and poor stability
Solution Approach 1:
The silicon rod ends are pre-heated to a temperature where they become soft and pliable before joining. This preliminary heating action allows the rods to be bent and shaped into the gate structure without requiring complex assembly operations, while also ensuring clean, controlled junctions with low metallic concentration.
Solution Approach 2:
The temperature parameter is changed during the joining process. The silicon rod ends are heated to a specific temperature range (below melting point but sufficiently high to soften the material), which enables both easy manipulation for assembly and formation of clean, low-contamination junctions.
2Reliability
If a long rod member is heated to high temperature (800°C or higher) and bent to form the gate shape, then the integrated structure suppresses arc generation, but the operation is difficult and requires complicated heat treatment apparatus
Solution Approach 1:
The gate-shaped silicon core wire is divided into separate components (vertical rod portions and horizontal portion) that are joined after individual preparation. This segmentation allows each component to be processed independently with simpler equipment, avoiding the need for complex apparatus required to heat and bend a complete gate structure.
Solution Approach 2:
Only the specific joining portions (corners) are heated to the necessary temperature, rather than heating the entire gate structure. This localized heating approach uses simpler equipment while achieving the same reliability benefits of integrated structures at the critical junction points.
3Ease of manufacture
If high-frequency induction heating is used to weld silicon members, then welding can be performed, but bending welding at high angles is difficult due to work coil enclosure requirements
Solution Approach 1:
The silicon rod ends are pre-heated and softened before attempting to form high-angle bends. This preliminary preparation makes the material sufficiently pliable to be bent into the required gate configuration, after which welding is applied to secure the joints, overcoming the limitation of work coil accessibility.
Solution Approach 2:
The temperature parameter is used to change the mechanical properties of the silicon material during fabrication. By heating to a specific temperature range, the material becomes soft and bendable, enabling high-angle configurations that would otherwise be impossible to form, and subsequent welding locks in this geometry.
4Stability of the object's composition
If the silicon core wire is produced by heating and bending a long rod member, then an integrated structure is obtained, but metal contamination occurs due to contact with apparatus surfaces
Solution Approach 1:
The core wire is constructed from multiple separate silicon rod portions that are joined together rather than formed from a single long rod. This segmentation prevents contact with apparatus surfaces during bending operations, as each short rod can be handled and joined without requiring extensive heating and bending that would cause contamination.
Solution Approach 2:
The joining process is performed in an inert gas atmosphere (such as nitrogen or argon) to prevent oxidation and metal contamination during the heating and welding operations. This inert environment protects the silicon surfaces from reacting with oxygen or picking up metal contaminants from the apparatus.
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 achieves a significant reduction in surface metallic contamination at corner junctions, ensuring high purity polycrystalline silicon deposition and reducing the risk of metal contamination in semiconductor wafers.
Implementation Method 1
heating a long rod member made of silicon to a high temperature (800° C. or higher) and softening and bending the long rod member
Implementation Method 2
by inserting an object to be heated made of a conductor into a work coil connected to an alternating current power source, an eddy current having a high density is generated near a surface of the object to be heated, thereby causing the surface of the object to be heated to self-heat by a Joule heat of the eddy current
Implementation Method 3
causing the surface of the object to be heated to self-heat by a Joule heat of the eddy current
Implementation Method 4
melt drops are generated near abutting portions of ends of the silicon members to be joined, and these melt drops are integrated due to a surface tension and cooled so as to weld the silicon members
Data Source
AI summary
A silicon core wire for depositing polycrystalline silicon is formed in a gate shape and includes a pair of vertical rod portions and a horizontal portion laterally connecting upper ends of the vertical rod portions, in which ends of the vertical rod portions and the horizontal portion are joined by welding, and a corner junction has a surface metallic concentration of 1 ppbw or less, more specifically, with an iron concentration of 0.2 ppbw or less, a chromium concentration of 0.1 ppbw or less, a nickel concentration of 0.05 ppbw or less, and a titanium concentration of 0.2 ppbw or less.