Process for preparing single crystal silicon using crucible rotation to control temperature gradient
AssigneeMEMC Electronic Materials, Inc.
InventorsZheng Lu, Steven L. Kimbel, Ying Tao
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Abstract
The present invention is directed to a process for preparing single crystal silicon, in ingot or wafer form, wherein crucible rotation is utilized to control the average axial temperature gradient in the crystal, G0, as a function of radius (i.e., G0(r)), particularly at or near the central axis. Additionally, crucible rotation modulation is utilized to obtain an axially uniform oxygen content therein.
Claims75
A process for pulling a single crystal silicon ingot in accordance with the Czochralski method, wherein a seed crystal is brought into contact with a silicon melt contained within a crucible, which is coaxial with the seed, and then is withdrawn therefrom to form a neck adjacent the seed crystal, a seed-cone adjacent the neck, and a constant diameter portion adjacent the seed-cone, the constant diameter portion having (i) a nominal diameter of at least 150 mm, (ii) a length, L, as measured along the axis of the ingot from a transition from the seed-cone to the constant diameter portion, (iii) a first series of positions, P(1→n), located a distance, D(1→n), respectively, from the transition along the axis determined as a fraction of L, and (iv) a second series of positions, PP(1→n), located a distance, DD(1→n), respectively, from the transition along the axis determined as a fraction of L, wherein positions and their respective distances in the second series may be the same or different from those in the first, the process comprising:
- rotating the seed crystal and the crucible in opposite directions;
- decreasing a mean crucible rotation rate (CR) as a function of increasing axial length of the constant diameter portion of the ingot wherein the mean crucible rotation rate at a position, P1, is greater than the mean crucible rotation rate at a position, P2, wherein D2≧(D1+0.1 L);
- and,
- controlling an average axial oxygen content in the constant diameter portion to be substantially constant by crucible rotation rate modulation (CRM).
A process for pulling a single crystal silicon ingot in accordance with the Czochralski method, wherein a seed crystal is brought into contact with a silicon melt contained within a crucible, which is coaxial with the seed, and then is withdrawn therefrom to form a neck adjacent the seed crystal, a seed-cone adjacent the neck, and a constant diameter portion adjacent the seed-cone, the constant diameter portion having a nominal radius extending from the axis to a lateral surface thereof of at least 75 mm, the process comprising:
- rotating the seed crystal and the crucible in opposite directions;
- rotating a crucible at a mean crucible rotation rate (CR) during growth of the constant diameter portion which is sufficient to obtain a melt-solid interface having a height near the axis, Za, of at least about 5 mm, as measured from the melt surface, and a height ZR/2, where ZR/2 is the height of the interface above the melt surface at about a midpoint of the radius, which is at least about 120% of Za;
- and,
- controlling an average axial oxygen content in the constant diameter portion to be substantially constant by crucible rotation modulation (CRM).
A process for pulling a single crystal silicon ingot in accordance with the Czochralski method, wherein a seed crystal is brought into contact with a silicon melt contained within a crucible, which is coaxial with the seed, and then is withdrawn therefrom to form a neck adjacent the seed crystal, a seed-cone adjacent the neck, and a constant diameter portion adjacent the seed-cone, the constant diameter portion having a nominal diameter of at least 150 mm, the process comprising:
- rotating the seed crystal and the crucible in opposite directions;
- controlling a ratio v/G0, wherein v is a growth velocity and G0 is an average axial temperature gradient over a temperature range from solidification to no less than about 1300° C. for at least a segment of the constant diameter portion of the ingot, control of said ratio comprising decreasing a mean crucible rotation rate (CR) as said segment is grown;
- controlling an average axial oxygen content in the segment to be substantially constant by crucible rotation modulation (CRM);
- and,
- controlling a cooling rate of said segment from the solidification temperature to about 1,050° C. or less, wherein said segment comprises an axially symmetric region which is substantially free of (i) agglomerated vacancy defects, or (ii) A-type agglomerated interstitial defects.
Dependencies are inferred from the claim text.