Patent ID: 11885038
Assignee: SUMCO CORPORATION
Field: Surface technology, coating (Chemistry)
Classification: CPC C | IPC C

Claim 1:
2. A pull-up device of monocrystalline silicon, comprising:
a quartz crucible;
magnetic-field applying portions located across the quartz crucible and configured to apply a horizontal magnetic field to a silicon melt in the quartz crucible;
a temperature sensor configured to measure temperatures at a first measurement point and a second measurement point both positioned on a first imaginary line that passes through a center of a surface of the silicon melt and is not in parallel with a central magnetic field line on the horizontal magnetic field;
a convection pattern estimation portion configured to estimate a direction of a convection flow in the silicon melt in a plane orthogonal to a direction in which the horizontal magnetic field is applied, on a basis of the temperatures at the first measurement point and the second measurement point measured by the temperature sensor; and
a pull-up controller, wherein
the first measurement point and the second measurement point are located across a second imaginary line that passes through the center of the surface and is in parallel with the central magnetic field line of the horizontal magnetic field,
the first measurement point is located in a negative direction of an X axis with respect to the second measurement point in a right-handed XYZ Cartesian coordinate system defining the center of the surface of the silicon melt as an origin, a vertically upward direction as a positive direction of a Z axis, and the direction in which the horizontal magnetic field is applied as a positive direction of a Y axis,
the temperature sensor measures
the first measurement point satisfying a formula (3):

0.375≤R1/RC<1  (3)

and the second measurement point satisfying a formula (4):

0.375<R2/RC<1  (4), provided that a distance from the center of the surface of the silicon melt to the first measurement point is denoted as R1, a distance from the center of the surface of the silicon melt to the second measurement point is denoted as R2, and a radius of an inner diameter of the quartz crucible is denoted as RC,
the pull-up controller determines in advance as predetermined conditions, pull-up conditions for achieving a desired value of an oxygen concentration of the monocrystalline silicon when in the XYZ Cartesian coordinate system, the direction of the convection flow as viewed in a negative direction of the Y axis is a predetermined direction that is one of a clockwise direction and an anticlockwise direction,
in the clockwise direction, the convection flow flows in an ascending direction on a left side with respect to the central magnetic field line and flows in a descending direction on a right side with respect to the central magnetic field line,
in the anticlockwise direction, the convection flow flows in the ascending direction on the right side with respect to the central magnetic field line and flows in the descending direction on the left side with respect to the central magnetic field line,
the convection pattern estimation portion estimates the direction of the convection flow to be fixed in the clockwise direction when the temperature at the first measurement point is higher than the temperature at the second measurement point, and estimates the direction of the convection flow to be fixed in the anticlockwise direction when the temperature at the first measurement point is lower than the temperature at the second measurement point,
the pull-up controller lowers an intensity of the horizontal magnetic field to less than 0.01 tesla and subsequently increases the intensity of the horizontal magnetic field to 0.2 tesla or more to fix the direction of the convection flow in the predetermined direction, subsequently controls the temperature sensor to measure the temperatures at the first measurement point and the second measurement point, and controls the convection pattern estimation portion to estimate the direction of the convection when the direction of the convection flow estimated by the convection pattern estimation portion is not the predetermined direction, and
the pull-up controller pulls up the monocrystalline silicon on a basis of the predetermined conditions while the intensity of the horizontal magnetic field is kept at 0.2 tesla or more and the direction of the convection is fixed in the predetermined direction when the direction of the convection flow is the predetermined direction.