Single Crystal Silicon Carbon Reduction via Preliminary Heating
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Solution Overview
Problem
Existing methods for producing single crystal silicon using the Czochralski method fail to adequately reduce carbon concentration, as carbon atoms from silicon raw materials and carbon-made apparatus components react to introduce defects, with current techniques only partially suppressing carbon monoxide and dioxide generation.
Innovation Solution
A method involving controlled heater output and inert gas flow to manage carbon monoxide generation, where the heater output is set between 15% to 50% of the necessary output for 3 to 20 hours to detect and reduce CO concentration, and inert gas flow rates are maintained between 200L/min to 400L/min to prevent Si-C film formation and carbon incorporation into the melt.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If heater output is increased to melt silicon raw material quickly, then melting speed is improved, but carbon monoxide generation from carbon-made members increases and carbon incorporates into the melt
Solution Approach 1:
The patent applies preliminary action by performing a low-temperature heating step (250-750°C) before the main melting process. During this preliminary stage, CO generated from carbon-made members is evacuated before silicon melting begins, preventing carbon incorporation. This preparatory action removes the harmful factor before the main process starts.
Solution Approach 2:
The heating process is segmented into distinct stages: a first low-temperature stage (250-750°C) for CO evacuation, and a second high-temperature stage for silicon melting. This segmentation allows separate optimization of each stage - the first stage focuses on removing harmful CO, while the second stage focuses on efficient melting.
2Object-generated harmful factors
If heating is performed at low temperature to reduce CO generation, then carbon incorporation is reduced, but melting time increases significantly
Solution Approach 1:
The low-temperature heating step is performed as a preliminary action before main melting. By evacuating CO during this preliminary stage, the patent prevents carbon incorporation without requiring the entire melting process to occur at low temperature. The subsequent high-temperature melting proceeds efficiently.
Solution Approach 2:
The process is divided into a time-efficient first stage (CO evacuation at 250-750°C) and a second stage (rapid melting at higher temperature). This segmentation allows the harmful CO generation period to be separated from the productive melting period, minimizing total time loss.
3Object-generated harmful factors
If furnace pressure is reduced to suppress CO dissolution into melt, then carbon concentration is reduced, but process complexity and control difficulty increase
Solution Approach 1:
The patent creates an inert atmosphere by continuously flowing inert gas (nitrogen or argon) through the furnace during the low-temperature heating stage. This inert environment prevents CO from dissolving into the silicon melt by maintaining positive pressure and providing a carrier gas for CO evacuation, simplifying the overall control compared to vacuum pressure management.
4Object-generated harmful factors
If carbon-made members are coated to reduce CO generation, then carbon incorporation is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
Instead of modifying the carbon-made members with complex coatings, the patent applies a preliminary low-temperature heating step that activates CO generation and evacuation before silicon melting. This approach modifies the process rather than the apparatus, maintaining manufacturing simplicity while achieving the same protective effect.
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 approach effectively suppresses carbon incorporation into the silicon melt, reducing carbon concentration in single crystal silicon and preventing crystal defects, as demonstrated by experiments showing carbon concentrations below 1.0×10^15 atoms/cm^3.
Implementation Method 1
a large amount of carbon monoxide gas (CO) and carbon dioxide (CO 2 ) gas generates from the surface of the carbon-made members during heating in the furnace
Implementation Method 2
it being understood that a flow rate of inert gas in a furnace is set in a range from 200L/min to 400L/min
Implementation Method 3
silicon monoxide (SiO) gas evaporates from the silicon melt in the crucible and reacts with the carbon-made members to generate carbon monoxide (CO) gas
Implementation Method 4
The CO gas dissolves into the silicon melt and carbon atoms are resultantly taken into the growing crystals
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
Provided is a production method of single crystal silicon that can reduce carbon concentration in the single crystal silicon pulled up from a crucible in the Czochralski method, without causing rise of cost and lowering efficiency of production. The process includes, at an initial stage of melting the silicon raw material in the crucible, a step of setting a heater output in a range from 15% to 50% of a necessary output for completely melting the silicon raw material, and keeping the heater output in a range from 3 hours to 20 hours, a step of melting the silicon raw material to a silicon melt by setting the heater output to an output necessary to melt the whole silicon raw material, and a step of pulling single crystal silicon from the crucible containing a silicon melt.