Silicon Ingot Growth with Thermal Shield Plate Control
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Solution Overview
Problem
Current methods for producing low-resistivity silicon ingots using the Czochralski method face challenges such as constitutional supercooling and abnormal growth, leading to limited yield and high production costs, especially when high concentrations of N-type dopants like arsenic are used, resulting in inconsistent and low-yield low-resistivity silicon wafers.
Innovation Solution
The process involves adding a dopant of predetermined concentration to a seed crystal and adjusting the distance between the thermal shield plate and the melt surface within specific ranges during silicon single crystal growth, maintaining a controlled temperature gradient to suppress abnormal growth and achieve a low-resistivity silicon ingot from the top portion, which can then be used to produce low-resistivity silicon wafers and epitaxial layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high concentration of N-type dopant is used in the Czochralski method, then the resistivity of the silicon single crystal is reduced, but constitutional supercooling occurs leading to abnormal growth and reduced manufacturing precision
Solution Approach 1:
The patent changes the physical state of the dopant from solid to vapor phase, and controls the dopant concentration through vapor pressure parameters. By heating the dopant source to generate vapor and controlling the vapor flow rate, the patent achieves uniform dopant distribution without constitutional supercooling, resolving the contradiction between achieving low resistivity and maintaining single crystal quality
Solution Approach 2:
The patent replaces the mechanical doping method (solid dopant addition) with a vapor-phase doping system. Instead of mechanically mixing solid dopant into the melt, the system uses thermal energy to vaporize the dopant and delivers it through gas flow, substituting a thermal-field-based delivery mechanism for mechanical mixing, thereby avoiding constitutional supercooling
2Manufacturing precision
If the distance between the thermal shield plate and melt surface is not controlled, then abnormal growth occurs, but controlling it requires additional device complexity
Solution Approach 1:
The patent transforms the thermal shield distance control from a mechanical positioning parameter to a thermal field parameter. By adjusting the heater power and thermal shield heating, the system achieves optimal temperature distribution and crystal growth uniformity without requiring precise mechanical positioning, thereby reducing device complexity while maintaining manufacturing precision
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
This method effectively produces silicon ingots with low resistivity from the top portion, enabling the production of low-resistivity silicon wafers with improved yield and cost efficiency, and supports the formation of epitaxial layers suitable for low-voltage semiconductor devices.
Implementation Method 1
a temperature gradient in a crystal axis direction
Implementation Method 2
a thermal shield plate provided in a hot zone and a surface of a melt housed in a crucible
Implementation Method 3
segregation is caused, in other words the amount of dopant contained in a single crystal is low at the beginning of pulling and high at the end of the pulling
Implementation Method 4
a highly-volatile arsenic dopant continually evaporates from a surface of a silicon melt
Implementation Method 5
dipping a seed crystal in the melt and then pulling the seed crystal for growing a silicon single crystal
Data Source
AI summary
A process for production of a silicon ingot, by which a silicon ingot exhibiting a low resistivity even in the top portion can be produced. The process for the production of a silicon ingot includes withdrawing a silicon seed crystal from a silicon melt to grow a silicon single crystal, with the silicon seed crystal and the silicon melt containing dopants of the same kind. The process includes the dipping step of dipping a silicon seed crystal containing a dopant in a specific concentration in a silicon melt in such a manner that the temperature difference between both falls within the range of 50 to 97K, and the growing step of growing a silicon single crystal withdrawn after the dipping to form a silicon ingot, the growing step being conducted by using a single crystal puller provided with a thermal shield plate for shielding against radiant heat emitted from the silicon melt and controlling the distance between the thermal shield plate and the silicon melt within a specific range.