Iron contamination in silicon wafers measured with the pulsed MOS capacitor generation lifetime technique

The pulsed MOS capacitor generation lifetime technique is used to determine the iron density in boron-doped silicon wafers. Effective generation lifetimes (/spl tau//sub g,eff/) are extracted from the Zerbst plots obtained from the measured capacitance-time (C-t) data. Upon thermal heating at 200/spl deg/C for 5 minutes and quenching to 23/spl deg/C, iron-boron (Fe-B) pairs dissociate into interstitial iron (Fe/sub i/) and substitutional boron (B). The post-heated /spl tau//sub g,eff/ decreases immediately after heating. As time elapses (pairing time t/sub p/ increases) after Fe-B dissociation, T/sub g,eff/ increases because Fe/sub i/ reforms into Fe-B pairs. It takes about four times the time constant (i.e., t/sub p//spl ap/4/spl tau/) of Fe-B pairing reaction before the post-heated /spl tau//sub g,eff/ recovers to the pre-heated /spl tau//sub g,eff/. An expression is developed to determine the iron density. The iron density obtained from this expression shows good agreement with that measured by deep-level transient spectroscopy.