Effects of Heat‐Treatments on Electrical Properties of Boron‐Doped Silicon Crystals

Abstract

The effects of heat-treatments around 1000~ and subsequent annealing on the electrical properties of boron-doped silicon have been studied by electrical conductivity, Hall effect, and deep-level transient spectroscopy measurements. The high-temperature heat-treatments always induced net densities of donors. Four recovery stages, stages I-IV, of heat-treatment-induced donors were observed on isochronal annealing up to 400~ Conductivity changes in these stages can be explained as described below by the reactions of interstitial iron (Fei), its pair (FeIB~) with substitutional boron (Bs), and two unknown donors (D~, D2). That is, stage I (25~176 D1-> sink and Fei + Bs-> FeiBs, stage II (100~176 FeiB~-> Fei + Bs, stage III (200~176 D2-~ sink, stage IV (250~176 Fei-~ precipitation. Heat-treatments in an oxygen atmosphere greatly reduced the introduction of Fei and FeiBs in comparison with an argon atmosphere and mainly introduced D~ and D2 donors. The density of D2 was dependent on the heat-treatment temperature, while that of D1 showed almost no dependence. In stage I, D, was annihilated by first-order kinetics with an activation energy of 0.8 eV. It was indicated that DI and D2 have no relations to iron, copper, oxygen, nor carbon. Though their origins are still unidentified, there may be some interstitial impurities. In stage IV, Fe~ is suggested to precipitate at oxygen precipitates and dislocation loops formed by high-temperature heat-treatments. As to the application to iron gettering in the device fabrication process, it is proposed that annealing around 300~ is most suitable as the final heat-treatment step to remove iron and related defects from active regions of devices.