Study of Proton-Induced Defects in 40-nm CMOS SPADs
Résumé
Defects induced by 62 MeV protons in single-photon
avalanche diodes (SPADs) are studied. A study of the dark
count rate (DCR) variation after irradiations for different biasing
conditions underlines the predominance of field enhancement
effects such as Poole–Frenkel (PF) effect and phonon-assisted
tunneling (PAT) over band-to-band tunneling (BTBT). Activation
energy measurements below mid-gap value confirm the important
contribution of these field effects. However, unexpected behaviors
in these energies are seen: very low activation energies are
extracted for SPADs with a DCR induced around 103
counts per second (cps). We attribute them to the contribution of different
groups of defects, with different energy-level distribution. This
analysis is completed with an annealing study between 100 ◦C
and 300 ◦C. Results for high DCR SPADs correlate well with the
presence of defect clusters. Moreover, histogram of the annealing
temperature at which the DCR starts to drop displays two
peaks at 170 ◦C and 250 ◦C. The first one is attributed to
phosphorus vacancies and complex cluster of defects with an
energy distribution inside the Si bandgap centered above midgap. The second one is attributed to clusters of divacancies that
also anneal at temperatures around 250 ◦C
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