Method for the preparation of a semiconductor substrate with a non-uniform distribution of stabilized oxygen precipitates

A process for nucleating and growing oxygen precipitates in a silicon wafer having a front surface, a back surface, a central plane between the front and back surfaces, a front 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 front surface layer, the wafer further comprising a non-uniform concentration of crystal lattice vacancies with the concentration of vacancies in the bulk layer being greater than the concentration of vacancies in the surface layer, the process comprising:

• heat treating the wafer at a temperature, Tn, for a time period, tn of at least about 15 minutes to provide a diffusion length, Ln, wherein Tn is from about 750° C. to about 900° C.;
• increasing the temperature from Tn to a temperature, Tg, over a time period ti to provide a diffusion length Li, wherein Tg is at least about 10° C. greater than Tn;
• optionally maintaining the wafer at the temperature, Tg, for a time period, tg to provide a diffusion length Lg;
• cooling the wafer from Tg to a final temperature, Tf, over a time period td to provide a diffusion length, Ld, wherein Tf is less than about 650° C., such that the process provides a total diffusion length, Lt, determined by adding Ln, Li, Lg and Ld in quadrature, resulting in the formation of stabilized oxygen precipitates having an effective radius of from about 0.5 nm to about 30 nm in the bulk layer over a total cycle time, tt, which is equal to the sum of tn, ti, tg and td, and wherein the total cycle tt is at least about 20% less than a time period tn,i required to provide a total diffusion length Ln,i equal to Lt by isothermally heat treating the wafer at the temperature Tn.

A process for the preparation of a silicon wafer having non-uniform concentration of stabilized oxygen precipitates, the wafer comprising a front surface, a back surface, a central plane between the front and back surfaces, a front 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 front surface layer, wherein the process comprises:

• subjecting the wafer to a heat treatment process to form crystal lattice vacancies in the front 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 concentration of vacancies in the bulk layer is greater than the concentration of vacancies in the surface layer;
• and,
• subjecting the heat treated wafer, to a non-isothermal anneal to cause the formation of a denuded zone in the surface layer and the nucleation and growth of oxygen precipitates in the bulk layer, the anneal comprising (i) heating the wafer to a temperature, Tn, to form oxygen precipitate nuclei in the bulk layer wherein Tn is from about 750° C. to about 900° C. (ii) increasing the temperature from Tn to a temperature, Tg, to grow oxygen precipitates at the site of the nuclei wherein Tg is at least about 10° C. greater than Tn, (iii) controlling the rate at which the temperature is increased from Tn to Tg to provide a population of oxygen precipitates which are stable at a processing temperature, Tp, wherein Tp is greater than Tg and, (iv) cooling the wafer from Tg to a final temperature, Tf, wherein Tf is less than about 650° C. before the oxygen precipitates grow to a size of at least 30 nm.