sib2 ~i

Fig. 5. Threshold shift AFT as a function of boron ion project range Rp: Curve A, for energy of 24-84 keV with fixed oxide thick-ness of 1250A; curve B, for fixed energy at 44 keV with oxide thick-ness from 600 to 2000~, as normalized to 1250~.. These data are compared to those of Fig. 1 for the boron projected range Rp. AV of Fig. 4 and normalized Ag"T to oxide thickness of 1250A of Fig. 1 was plotted in Fig. 5 as a function of Rp. It was shown that both curves have the same trend, i.e., A~'rT increases with Rp and starts to saturate when Rp reaches about 600-800A inside silicon. This phenomenon can be inter-preted as follows. When Rp is deeper than 600-800A, even though more boron penetrates the silicon dioxide layer, some of the boron ions are situated too far from the SiO2-Si interface to cause a shift in threshold volt