Process for producing thermally annealed wafers having improved internal gettering

A process for heat-treating a single crystal silicon wafer to dissolve agglomerated vacancy defects and to influence the precipitation behavior of oxygen in the wafer in a subsequent thermal processing step, the silicon wafer having two major, generally parallel surfaces, one of which is the front surface of the wafer and the other of which is the back surface of the wafer, a central plane between the front and back surfaces, a circumferential edge joining the front and back surfaces, a stratum extending from the front surface to a distance, Ds, measured from the front surface and toward the central plane, a surface layer which, at least in part is coextensive with the stratum and which comprises the region of the wafer between the front surface and a distance, D, measured from the front surface and toward the central plane, and a bulk layer which comprises the region of the wafer between the central plane and the surface layer, the process comprising:

• thermally annealing the wafer in an atmosphere to dissolve pre-existing agglomerated vacancy defects in the stratum;
• heat-treating the annealed wafer to form crystal lattice vacancies in the 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 the peak density is at or near the central plane with the concentration generally decreasing in the direction of the front surface of the wafer, the difference in the concentration of vacancies in the surface and bulk layers being such that a thermal treatment of the wafer at a temperature in excess of 750° C. is capable of forming a denuded zone in the surface layer and oxygen clusters or precipitates 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.

A process for heat-treating a single crystal silicon wafer to dissolve agglomerated vacancy defects and to influence the precipitation behavior of oxygen in the wafer in a subsequent thermal processing step, the silicon wafer having a front surface, a back surface, a central plane between the front and back surfaces, a stratum extending from the front surface to a distance, Ds, measured from the front surface and toward the central plane, a surface layer which, at least in part, is coextensive with the stratum and which comprises the region of the wafer between the front surface and a distance, D, measured from the front surface and toward the central plane, and a bulk layer which comprises the region of the wafer between the central plane and surface layer, the process comprising the steps of:

• heat-treating the wafer in an atmosphere to form crystal lattice vacancies in the surface and bulk layers;
• controlling the cooling rate of the heat-treated wafer to produce a wafer having a vacancy concentration profile in which the peak density is at or near the central plane with the concentration generally decreasing in the direction of the front surface of the wafer and the difference in the concentration of vacancies in the surface and bulk layers being such that a thermal treatment of the wafer at a temperature in excess of 750° C. is capable of forming a denuded zone in the surface layer and oxygen clusters or precipitates 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;
• stabilizing oxygen precipitate nucleation centers present in the cooled wafer by heating the cooled wafer to a temperature of about 650 to about 850° C. for about 1 hour to about 4 hours;
• and,
• thermally annealing the stabilized wafer in an atmosphere to dissolve agglomerated vacancy defects present within a region extending from the front surface to a depth of at least about 5 microns.