Process for forming low defect density, ideal oxygen precipitating silicon

A process for producing a single crystal silicon wafer having two major, generally parallel surfaces, one of which is a front surface of the wafer and the other of which is a back surface of the wafer, a central plane between the front and back surfaces, a circumferential edge joining the front and back surfaces, a central axis generally perpendicular to the front and back surfaces, a radius extending from the central axis to the circumferential edge, a nominal diameter of 150 mm, 200 mm, or greater than 200 mm, a front surface layer which comprises the region of the wafer between the front surface and a distance, D1, of at least about 10 micrometers measured from the front surface and toward the central plane, a back surface layer which comprises a second region of the wafer between the back surface and a distance D2, of at least about 10 micrometers as measured from the back surface and toward the central plane, and a bulk layer which comprises a third region of the wafer between the front surface layer and the back surface layer, the wafer being characterized in that the wafer has a non-uniform distribution of crystal lattice vacancies in which a maximum concentration is located between the central plane and the back surface layer, the vacancy concentration generally increasing from the front surface to the region of maximum concentration and generally decreasing from the region of maximum concentration to the back surface, the wafer further comprising a first axially symmetric region, which has no detectible agglomerated intrinsic point defects at a detection limit of 103 defects/cm3, the process comprising the steps of:

• growing a single crystal silicon ingot in which the ingot comprises a central axis, a seed-cone, an end-cone and a constant diameter portion between the seed-cone and the end-cone having a circumferential edge, a radius extending from the central axis to the circumferential edge, and a nominal diameter of 150 mm, 200 mm, or greater than 200 mm;
• controlling (i) a growth velocity, v, (ii) an average axial temperature gradient, G0, during the growth of the constant diameter portion of the crystal over the temperature range from solidification to a temperature of no less than about 1325° C., and (iii) the cooling rate of the crystal from the solidification temperature to about 1,050° C. to cause the formation of an axially symmetrical segment which has no detectible agglomerated intrinsic point defects at a detection limit of 103 defects/cm3, wherein the axially symmetric region extends inwardly from the circumferential edge of the ingot, has a width as measured from the circumferential edge radially toward the central axis of the ingot which is at least about 30% the length of the radius of the ingot, and has a length as measured along the central axis of at least about 20% the length of the constant diameter portion of the ingot;
• slicing a single crystal silicon wafer from the constant diameter portion of the ingot;
• subjecting the wafer to a heat-treatment in excess of about 1175° C. in a non-oxidizing atmosphere to form crystal lattice vacancies in the front surface and bulk layers;
• and,
• controlling the cooling rate of the heat-treated wafer to produce a wafer having a vacancy concentration profile in which a maximum concentration is located between the central plane and the back surface layer, the vacancy concentration generally increasing from the front surface to the region of maximum concentration and generally decreasing from the region of maximum concentration to the back surface and the difference in the concentration of vacancies in the front surface layer, the back surface layer, and the bulk layer being such that a thermal treatment at a temperature in excess of 750° C. is capable of forming in the wafer a denuded zone in the front surface layer and in the back surface layer and oxygen clusters or precipitates in the bulk zone, with the concentration of the oxygen clusters or precipitates in the bulk layer being primarily dependant upon the concentration of vacancies.

A process for heat-treating a Cz, single crystal silicon wafer, to influence the precipitation behavior of oxygen in the wafer in a subsequent thermal processing step, the wafer comprising two major, generally parallel surfaces, one of which is a front surface of the wafer and the other of which is a back surface of the wafer, a central plane between the front and back surfaces, a circumferential edge joining the front and back surfaces, a central axis generally perpendicular to the front and back surfaces, a radius extending from the central axis to the circumferential edge, a nominal diameter of 150 mm, 200 mm, or greater than 200 mm, a front surface layer which comprises the region of the wafer between the front surface and a distance, D1, of at least about 10 micrometers measured from the front surface and toward the central plane, a back surface layer which comprises a second region of the wafer between the back surface and a distance D2, of at least about 10 micrometers as measured from the back surface and toward the central plane, and a bulk layer which comprises a third region of the wafer between the front surface layer and the back surface layer, wherein said wafer further comprises a first axially symmetric region in which vacancies are the predominant intrinsic point defect and which has no detectible agglomerated intrinsic point defects at a detection limit of 103 defects/cm3, wherein the first axially symmetric region comprises the central axis or has a width of at least about 15 mm the process comprising the steps of;

• subjecting the wafer to a heat-treatment in excess of about 1175° C. in a non-oxidizing atmosphere to form crystal lattice vacancies in the surface layer and the bulk layer;
• and,
• controlling the cooling rate of the heat-treated wafer to produce a wafer having a non-uniform concentration of vacancies in which a maximum concentration is located between the central plane and the back surface layer, the vacancy concentration generally increasing from the front surface to the region of maximum concentration and generally decreasing from the region of maximum concentration to the back surface such that, upon subjecting the wafer to an oxygen precipitation heat treatment, a denuded zone is formed in the surface layer and oxygen clusters or precipitates are formed in the bulk layer with the concentration of the oxygen clusters or precipitates in the bulk layer being primarily dependant upon the concentration of vacancies.