Comparison of low energy BF_(2)~(+), BCl_(2)~(+), and BBr_(2)~(+) implants for the fabrication of ultrashallow P~(+)-N junctions

摘要

We present a comparative study of BCl_(2)~(+) and BBr_(2)~(+), and the traditionally used BF_(2)~(+), as implant species for the formation of ultrashallow P~(+)-N junctions. From "as-implanted" profiles, a large reduction in channeling tail has been observed for the BCl_(2)~(+) and BBr_(2)~(+) implants, relative to BF_(2)~(+) implantation; the depths are reduced by over 200 A compared to the "equivalent" energy BF_(2)~(+) implants. After annealing, the 5 keV BCl_(2)~(+) implanted junctions are shallower than the 5 keV BF_(2)~(+) junctions by over 150 A. The 18 keV BBr_(2)~(+) implants yield junctions as shallow as 100 A, but suffer from severe doss loss problems—probably caused by enhanced surface scattering and etching for the deceleration mode implant. The 20 keV BBr_(2)~(+) implants done without deceleration show no dose loss, and result in junction depths identical to those in the 5 keV BF_(2)~(+) implants. Leakage current measurements indicate an increase of three orders of magnitude for the BCl_(2)~(+) implanted junctions over BF_(2)~(+) ones; BBr_(2)~(+) implanted junctions exhibit lower leakage, comparable to that produced by BF_(2)~(+). The effect of the different halogen species on B penetration through the gate oxide into the channel region has been studied; the penetration is reduced for BBr_(2)~(+) implants relative to BF_(2)~(+) implants. We present comparative device characteristics data from metal-oxide-semiconductor field-effect transistors with source-drain extension regions formed by low energy implants of the three species. We show that the two alternative species might be strong candidates for acceptor implant species for ultrasmall devices; in particular, BBr_(2)~(+) might be a superior replacement for BF_(2)~(+).