Abstract
Automatic diameter control (ADC) devices used in Czochralski crystal pulling utilize pull rate modulation as the main feedback in controlling the diameter of a growing crystal. The resultant effects on microstructures were investigated by comparing boron segregation behavior in both ADC and non-ADC regions of a heavily doped 125 mm Si crystal. The sample crystal doped with boron to 3×10 18 atoms/cm 3 was grown initially using an infrared pyrometer sensing ADC system. Subsequently, the ADC system was turned off, and a section of crystal grown at a constant pull rate. The pull rate set-point was 1.00 mm/min. The range and period of pull rate fluctuations experienced while under ADC were 0.75–1.44 mm/min and 5–10 min, respectively. Longitudinal (110) samples cut from the transition zone were etched chemically, and the segregation band widths measured from each region. Mean values for each region were close to the theoretical 31.2 μm calculated for a crystal rotation driven structure. However, the large standard deviations encountered for both regions indicate that thermal convection was the dominant source of band width variation. The period of convective flow at the solid-liquid interface was estimated to be on the order of 5–10 s. The macroscopic growth rate fluctuations induced by the ADC function seem to have been too weak and slow to have any visible effects on the random characteristics of dopant segregation bands.
Published Version
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