FAST-FEEDBACK IRON CONTAMINATION MONITORING USING SURFACE PHOTOVOLTAGE MEASUREMENTS

In this paper we investigate the possibility of using the surface phot ovoltage technique (SPV) for fast-feedback metal contamination monitor ing. Boron-doped, 8 in. wafers were ''contaminated'' during wet, dry, and ion implantation processing. Processed wafers were then annealed u sing rapid thermal processing (RTP) to drive in metals from the surfac e into the bulk. Following RTP, SPV measurements were carried out to m easure carrier diffusion length and Fe concentration. It is found that both quantities are underestimated if measured immediately after RTP. The error increases with the wafer resistivity and it is due to incom plete Fe-B pairing during cooling down from the high-temperature RTP a nneal. To reach equilibrium, a relaxation time of a few hours to days is necessary, depending on the wafer resistivity. However, we show tha t Fe-B pairing can be accelerated by performing a post-RTP anneal at 8 0 degrees C. Using this procedure the contamination introduced during standard very large scale integrated processes could be measured withi n 30 min from wafer processing.