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 (τ_g,eff) are extracted from the Zerbst plots obtained from the measured capacitance-time (C-t) data. Upon thermal heating at 200°C for 5 minutes and quenching to 23°C, iron-boron (Fe-B) pairs dissociate into interstitial iron (Fe_i) and substitutional boron (B). The post-heated τ_g,eff decreases immediately after heating. As time elapses (pairing time t_p increases) after Fe-B dissociation, T_g,eff increases because Fe_i reforms into Fe-B pairs. It takes about four times the time constant (i.e., t_p≈4τ) of Fe-B pairing reaction before the post-heated τ_g,eff recovers to the pre-heated τ_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.