Process for the preparation of an ideal oxygen precipitating silicon wafer capable of forming an enhanced denuded zone

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;
• oxidizing a surface of the heat-treated wafer by heating said wafer in an oxygen containing atmosphere;
• and,
• controlling the cooling rate of the annealed wafer to produce a wafer having a non-uniform distribution of crystal lattice vacancies with the concentration of vacancies in the bulk layer being greater than the concentration of vacancies in the surface layer, 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 sliced from a single crystal silicon ingot grown by the Czochralski method to influence the precipitation behavior of oxygen in the wafer in a subsequent thermal processing step, the single crystal silicon wafer having a front surface and a back surface, the front and back surfaces having only a native oxide layer present thereon, a central plane between the front and back surfaces, a front surface layer which comprises a first region of the wafer between the front surface and a distance, D1, of at least about 10 micrometers as 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 process comprising:

• heat-treating the wafer in a nitrogen atmosphere to form a concentration of crystal lattice vacancies in the wafer, the concentration profile being generally U-shaped, having a maximum concentration within several micrometers of the front and back surfaces and a minimum concentration located in the bulk layer of the wafer;
• oxidizing the front surface of the heat-treated wafer by heating said wafer in an oxygen containing atmosphere;
• and,
• controlling the cooling rate of the heat-treated wafer to reduce the concentration of vacancies in the front surface layer and back surface layer to produce a vacancy concentration profile in the cooled wafer having two regions of maximum concentration, wherein a first region of maximum concentration is located between the front surface layer and the central plane and a second region of maximum concentration is located between the back surface layer and the central plane, the vacancy concentration generally increasing from the front surface to the first region of maximum concentration, generally decreasing from the first region of maximum concentration to the central plane, generally increasing from the central plane to the second region of maximum concentration and generally decreasing from the second 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.