Process for preparing ingot having reduced distortion at late body length

A method of preparing a single crystal silicon ingot by a Czochralski method, the method comprising:

• adding an initial charge of polycrystalline silicon to a crucible contained within a growth chamber, wherein the crucible comprises a bottom wall and a sidewall and further wherein the growth chamber comprises insulation configured to insulate the bottom wall of the crucible, a side heater located next to the sidewall, and a reflector;
• supplying power to the side heater to thereby heat the crucible comprising the initial charge of polycrystalline silicon to cause a silicon melt to form in the crucible, wherein the silicon melt has a free melt level;
• contacting a silicon seed crystal with the silicon melt contained within the crucible;
• withdrawing the silicon seed crystal from the silicon melt in a direction perpendicular to the free melt level at an initial pull rate to thereby form a solid neck portion of the single crystal silicon ingot;
• withdrawing a solid outwardly flaring seed-cone adjacent the neck portion of the single crystal silicon ingot from the silicon melt by modifying the initial pull rate to thereby achieve an outwardly flaring seed-cone pull rate;
• and
• withdrawing a solid main body of the single crystal silicon ingot adjacent the outwardly flaring seed-cone from the silicon melt by modifying the outwardly flaring seed-cone pull rate to thereby achieve a main body pull rate, wherein withdrawing the solid main body of the single crystal silicon ingot includes rotating the seed crystal at a seed crystal rotation rate and controlling a relative height (HR) measured as a distance between the free melt level and a bottom of the reflector, wherein the solid main body of the single crystal silicon ingot has a radial length and an axial length and surface tension arising as the solid main body of the single crystal silicon ingot is withdrawn from the silicon melt results in a melt-solid interface located above the free melt level and further wherein a meniscus comprising molten silicon is between the melt-solid interface and the free melt level;
• wherein a cusp magnetic field is applied to the silicon melt during growth of the main body of the single crystal silicon ingot;
• wherein, during growth of a first portion of the solid main body of the single crystal silicon ingot, the seed crystal rotation rate is at least 11 rpm and the HR is a distance between 60 mm and 120 mm;
• and
• wherein, after growth of the first portion and during growth of a second portion of the solid main body of the single crystal silicon ingot comprising at least 40% of the total axial length of the solid main body, the seed crystal rotation rate is between 5 rpm and 10 rpm and the HR is a distance between 40 mm and 50 mm such that a heat flux in an axial direction between the melt-solid interface and the free melt level during growth of the second portion of the solid main body of the single crystal silicon ingot has an absolute value of at least 20,000 W/m2 over at least 85% of the radial length of the solid main body of the single crystal silicon ingot.