Patent ID: 7442253
Filing Date: 2008-10-28
Classification: C30B,H01L,Y10T

Abstract:
1. A process for heat-treating a Cz, single crystal silicon wafer to influence the precipitation behavior of oxygen in the wafer in a subsequent thermal processing step, the wafer comprising two major, generally parallel surfaces, one of which is a front surface of the wafer and the other of which is a back surface of the wafer, a central plane between the front and back surfaces, a circumferential edge joining the front and back surfaces, a central axis generally perpendicular to the front and back surfaces, a radius extending from the central axis to the circumferential edge, a nominal diameter of 150 mm, 200 mm, or greater than 200 mm, a front surface layer which comprises the region of the wafer between the front surface and a distance, D 1 , of at least about 10 micrometers 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 D 2 , 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, wherein said wafer further comprises an axially symmetric region which has radial width of at least about 30% the length of the radius of the wafer and has no detectible agglomerated intrinsic point defects at a detection limit of 10 3 defects/cm 3 , the process comprising the steps of; subjecting the wafer to a heat-treatment in excess of about 1175° C. in a non-oxidizing atmosphere 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 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 with 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.