Thermal annealing process for producing low defect density single crystal silicon

A process for preparing a silicon wafer having a surface layer which is substantially free of agglomerated intrinsic point defects, the wafer being sliced from a single crystal silicon ingot having a central axis, a seed-cone, an end-cone, and a constant diameter portion which extends between the seed-cone and the end-cone, the constant diameter portion having a circumferential edge and a radius extending from the circumferential edge toward the central axis, the ingot being grown from a silicon melt and then cooled from the solidification temperature in accordance with the Czochralski method, the process comprising:

• growing the single crystal silicon ingot wherein the growth velocity, v, and an average axial temperature gradient, G0, are controlled during the growth of the constant diameter portion of the ingot over a temperature range from solidification to a temperature of no less than about 1325° C. to cause the formation of a segment of the constant diameter portion which, upon cooling of the ingot from the solidification temperature, comprises a first axially symmetrical region extending radially inward from the circumferential edge toward the central axis in which silicon self-interstitials are the predominant intrinsic point defect and which is substantially free of agglomerated interstitial defects, and a second axially symmetric region in which vacancies are the predominant intrinsic point defect, wherein, as part of the cooling process, the ingot is cooled through a temperature range from the solidification temperature of silicon to about 800° C. at a cooling rate which ranges from about 0.1 to about 1.5 C./min;
• slicing the segment of the constant diameter portion to obtain a wafer, the wafer having a front side and a back side which are generally perpendicular to the central axis, and a central plane between the front and back sides, the wafer comprising the first and second axially symmetric regions;
• and,
• thermally annealing the wafer at a temperature in excess of about 1000° C. in an atmosphere of hydrogen, argon, oxygen, nitrogen, or a mixture thereof to dissolve agglomerated vacancy defects present in the second axially symmetric region within a layer extending from the front surface toward the central plane of the wafer such that the layer is substantially free of agglomerated intrinsic point defects.

A process for preparing a single crystal silicon wafer having a surface layer which is substantially free of agglomerated intrinsic point defects, the process comprising thermally annealing a single crystal silicon wafer at a temperature in excess of about 1000° C. in an atmosphere of hydrogen, argon, oxygen, nitrogen, or a mixture thereof, said wafer having been sliced from a single crystal silicon ingot grown and cooled in accordance with the Czochralski method wherein, as part of the cooling process, the ingot was cooled through a temperature range from the solidification temperature of silicon to about 800° C. at a cooling rate which ranges from about 0.1 to about 1.5° C./min, and said wafer having a central axis, a front side and a back side which are generally perpendicular to the central axis, a central plane between the front and back sides, a circumferential edge, a radius extending from the central axis to the circumferential edge, a first axially symmetric region extending radially inward from the circumferential edge in which silicon self-interstitials are the predominant intrinsic point defect and which is substantially free of agglomerated interstitial defects, and a second axially symmetric region, located radially inward of the first axially symmetric resion, in which vacancies are the predominant intrinsic point defect, the thermal anneal acting to dissolve agglomerated vacancy defects present in the second axially symmetric region within a layer extending from the front side toward the central plane such that the layer is substantially free of agglomerated intrinsic point defects.