A Modified Oxidative Refinement Process for Removing Boron from Molten Silicon Under Enhanced Electromagnetic Force

Area of Science:

• Materials Science
• Chemical Engineering
• Semiconductor Processing

Background:

• Boron removal from metallurgical grade silicon is critical for photovoltaic applications but challenging due to boron's properties.
• Existing methods like slag treatment and plasma treatment have limitations in efficiency and cost.
• Oxidizing reactive gases offer a promising alternative for efficient and low-cost boron refinement.

Purpose of the Study:

• To develop a modified oxidative refining method for enhanced boron removal from silicon.
• To investigate the vaporization of boron as B(x)H(z)O(y) using gaseous water.
• To reduce processing costs through a reusable crucible system.

Main Methods:

• A modified oxidative refining process involving blowing gaseous water onto a silicon melt.
• Utilizing a segmented crucible to enhance electromagnetic force.
• Employing a reusable quartz crucible within a graphite crucible system.
• Introducing a mixture of Argon (Ar) and water (H2O) at specific flow rates (1.7SLM Ar + 100 ml/h H2O).

Main Results:

• Significant reduction of initial boron content from 13 ppm to 0.3 ppm.
• Enhanced vaporization of boron in the B(x)H(z)O(y) phase due to high vapor pressure at 1700 K.
• Demonstrated a dramatic reduction in processing costs by using a reusable crucible.

Conclusions:

• The modified oxidative refining method effectively removes boron from silicon at reduced costs.
• The process leverages the high vapor pressure of B(x)H(z)O(y) for efficient boron extraction.
• This technique offers a viable solution for purifying silicon for low-cost photovoltaic applications.