Patent ID: 8382894
Filing Date: 2013-02-26
Classification: C30B,H01L,Y10T

Abstract:
1. A process for producing a silicon wafer having no epitaxial layer deposited thereon, wherein a wafer is subjected to a heat treatment comprising: A: a low temperature heat treatment step wherein the wafer is heat treated at a temperature of from 700° C. to 800° C. for 30 minutes to 5 hours; B: a temperature increasing step following the low temperature heat treatment step, wherein the wafer is heated up to a temperature of from 900° C. to 1,000° C. at a rate of temperature increase of 0.5° C./minute to 2° C./minute; and C: a temperature decreasing and unloading step following the temperature increasing step, wherein a temperature in a furnace is decreased at a rate of 1° C./minute to 10° C./minute, and when the temperature of the wafer becomes from 600° C. to 800° C., the wafer is unloaded from the furnace and cooled to room temperature; and D: a high temperature heat treatment step following the temperature decreasing and unloading step, wherein the temperature in the furnace is at a wafer insertion temperature of from 600° C. to 800° C., the wafer is inserted therein, and the temperature of the wafer is increased at a rate of 5° C./minute to 10° C./minute in the range from the wafer insertion temperature to 1,100° C. and increased at a rate of 1° C./minute to 2° C./minute in the range from 1,100° C. to 1,250° C., and the substrate is maintained at a temperature in the range of 1100° C. to 1250° C. such that the diffusion length of interstitial oxygen is not less than 20 μm, wherein the silicon wafer contains BMDs of an octahedral shape, and BMDs present at a depth greater than 50 μm from the surface of the silicon wafer having diagonal sizes of 10 nm to 50 nm are present at a density of ≧1×10 12 /cm 3 , and the density of BSFs having sizes of ≧1 μm is <1×10 8 /cm 3 .