Patent ID: 6849119

Claim:
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 surface 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, D 1 , 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 to form crystal lattice vacancies in the wafer, and as part of said heat-treatment, exposing the front surface of the wafer to a first atmosphere comprising a non-nitriding gas and exposing the back surface of the wafer to a second atmosphere comprising a nitriding gas; and, controlling the cooling rate of the heat-treated wafer to produce an asymmetrical vacancy concentration profile in the cooled wafer 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.