Process for preparing an ideal oxygen precipitating silicon wafer

A process for heat-treating a single crystal silicon wafer 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 surface layer 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 of the wafer;
• thermally annealing the heat-treated wafer at a temperature in excess of about 1150° C. in an atmosphere having a partial pressure of oxygen of at least about 100 ppma;
• and,
• controlling the cooling rate of the annealed 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.