Comprehensive understanding on germanium-doping effects on oxygen precipitation in Czochralski silicon wafers with a prior rapid thermal anneal

Abstract

The effects of germanium (Ge)-doping with concentrations in the range of 10¹⁸–10²⁰ cm⁻³ on oxygen precipitation (OP) in Czochralski (CZ) silicon wafers subjected to the low (800 °C)–high (1000 °C) two-step anneal following the rapid thermal anneal (RTA) at 1250 °C, which is actually the RTA-based internal gettering (IG) process, have been comprehensively investigated. It is found that whether the Ge-doping enhances or suppresses OP in the CZ silicon wafers with the aforementioned three-step anneal is quite dependent on the Ge-doping concentration and on the nucleation time at 800 °C. On the one hand, the Ge-doping is experimentally and theoretically revealed to facilitate the formation of vacancy-oxygen (VO_m, m ≥ 1) complexes in the CZ silicon wafer during the prior RTA at 1250 °C. In this sense, the Ge-doping enhances the nucleation of oxide precipitates thus being beneficial for OP. On the other hand, the considerably high concentration of Ge-doping introduces compressive stress into silicon lattice in a manner due to the slightly larger covalent radius of Ge atom. Such introduced compressive stress not only increases the critical size required for the onset growth of oxide precipitate nuclei at 1000 °C but also suppresses the growth of oxide precipitates in the course of 1000 °C anneal. Thus, the Ge-doping is unfavorable for the growth of oxide precipitates. Based on the advantageous and disadvantageous effects of Ge-doping on the nucleation and growth of oxide precipitates, respectively, which have been definitely revealed in this work, the above finding has been essentially understood. Of practical significance, this work offers technological guideline to improve the IG capability of CZ silicon wafer through adopting appropriate Ge-doping and RTA-based annealing scheme.