Method for controlling oxygen content of silicon crystals using a combination of cusp magnetic field and crystal and crucible rotation rates

A Czochralski method for producing single crystal silicon rods wherein a single crystal silicon rod is pulled from a silicon melt contained in a crucible, the single crystal silicon rod and the crucible being coaxial, the method comprising:

• rotating the rod and crucible in opposite directions about their axes, the rotation rate of the rod being greater than the rotation rate of the crucible as the rod is grown,
• after the single crystal rod diameter is established, increasing the rotation rate of the crucible as the fraction of silicon melt solidified increases,
• imposing upon the silicon melt a magnetic field that is substantially axially symmetrical about the axis of the rod until a fraction of the silicon melt is solidified, the magnetic field having components which perpendicularly intersect the bottom and side walls of the crucible and a component perpendicularly intersecting the molten silicon surface, the average magnetic field component perpendicularly intersecting the molten silicon surface having a value of about zero gauss, and
• decreasing the intensity of the magnetic field components which perpendicularly intersect the bottom and side walls of the crucible as the fraction of silicon melt solidified increases.

A Czochralski method for producing single crystal silicon rods wherein a single crystal silicon rod is pulled from a silicon melt contained in a crucible, the single crystal silicon rod and the crucible being coaxial, the method comprising:

• rotating the rod and crucible in opposite directions about their axes, the rotation rate of the rod being greater than the rotation rate of the crucible,
• after the single crystal rod diameter is established, increasing the rotation rate of the crucible as the fraction of the silicon melt solidified increases,
• imposing upon the silicon melt a magnetic field that is substantially axially symmetric about the axis of the rod until a fraction of the silicon melt is solidified, the magnetic field having components which perpendicularly intersect the bottom and side walls of the crucible and a component perpendicularly intersecting the molten silicon surface, the average magnetic field component perpendicularly intersecting the bottom and side walls being greater than an average magnetic field component perpendicularly intersecting the molten silicon surface, and
• decreasing the intensity of the magnetic field after the fraction of silicon melt solidified exceeds about 0.5.