Oxygen precipitation (OP) behaviors in heavily arsenic-doped Czochralski silicon wafers without and with prior rapid thermal processing at 1100-1250 degrees C, subjected to subsequent two-step anneal of 450, 650 and 800 degrees C/4 h+1000 degrees C/16 h, have been investigated. It is found that the prior RTP at 1250 degrees C substantially enhances OP in each two-step anneal. Such enhancement effect exhibits most significantly in the two-step anneal with the nucleation at 800 degrees C. However, in order to form the highest density of oxygen precipitates, the most desirable nucleation temperature is 650 degrees C in both cases without and with prior RTP. The OP nucleation mechanisms operating in the three low temperatures as mentioned above have been tentatively discussed. (C) 2010 Elsevier B.V. All rights reserved.