Patent ID: 7105050

Claim:
A process for the preparation of a silicon single crystal in which molten silicon is solidified into a crystal in accordance with the Czochralski method to form an ingot having a central axis, a seed-cone, an end-cone, a constant diameter portion between the seed-cone and the end-cone having a lateral surface, and a radius, R, extending from the central axis to the lateral surface of at least about 75 mm, the constant diameter portion having an axial length, L, the process comprising; controlling a ratio, v/G 0 , wherein, v is a growth velocity and, G 0 is an average axial temperature gradient over the temperature range from solidification to a temperature of no less than about 1325° C., during the growth of the constant diameter portion of the crystal, to initially produce in the constant diameter portion of the ingot a series of predominant intrinsic point defects alternating along the axis, the series comprising N vac. vacancy dominated regions and N int. silicon self interstitial dominated regions, wherein N vac. is at least 2 and N int. is at least 1, the vacancy dominated regions each having an axial length, L vac. , and a radius, R vac. , extending from the axis of the ingot towards the lateral surface which is at least about 10% of the radius, R, of the constant diameter portion of the crystal, the silicon self-interstitial dominated region(s) each having an axial length, L int. , and a radial width which is equal to the radius, R, of the constant diameter portion of the silicon single crystal; cooling said regions from the temperature of solidification at a rate which allows silicon self-interstitial atoms to diffuse radially to the lateral surface and to diffuse axially to vacancy dominated regions to reduce the concentration of silicon self-interstitial atoms in the region(s) in which silicon self-interstitial atoms were initially the predominant intrinsic point defect and to reduce the concentration of crystal lattice vacancies in the region(s) in which crystal lattice vacancies were initially the predominant intrinsic point defect.