Patent ID: 7125450

Claim:
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is brought into contact with a silicon melt contained within a crucible, which is coaxial with the seed, and then is withdrawn therefrom to form a neck adjacent the seed crystal, a seed-cone adjacent the neck, and a constant diameter portion adjacent the seed-cone, the constant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, P 1 , is greater than the mean crucible rotation rate at a position, P 2 , wherein D 2 ≧(D 1 +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).