Gettering Characteristics of Heavy Metal Impurities in Silicon Wafers with Polysilicon Back Seal and Internal Gettering

The gettering behavior of polysilicon back seal (PBS) and internal gettering (IG) with isothermal annealing (600?1000? C) was systematically investigated for Fe contamination by deep level transient spectroscopy (DLTS). There was a clear dependence of the PBS gettering efficiency on the PBS deposition temperature and on annealing temperatures used in the gettering processes. The use of lower deposition temperatures and lower gettering temperatures resulted in a higher gettering efficiency. IG efficiency has a clear dependence on size and density of the oxygen precipitate. In the case of a bulk micro defect (BMD) density of 105 cm-2, it was necessary for the platelet oxygen precipitate size to be larger than 200 nm, while a polyhedral oxygen precipitate size of 100 nm was sufficient in obtaining IG effects for an Fe contamination level of 1012 atoms/cm3. The gettering efficiency has a clear correlation with the volume of the oxygen precipitates per unit volume of the silicon wafers. These results suggest that Fe atoms are gettered within the oxygen precipitates and not in the area surrounding them.