Abstract: 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 wafer has a front surface, a back surface, a central plane between the front and back surfaces, and a sink for crystal lattice vacancies at the front surface. In the process, the wafer is subjected to a heat-treatment to form crystal lattice vacancies, the vacancies being formed in the bulk of the silicon. The wafer is then cooled from the temperature of said heat treatment at a rate which allows some, but not all, of the crystal lattice vacancies to diffuse to the crystal lattice vacancy sink 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.