Sloped-junction LDD (SJLDD) MOSFET structures for improved hot-carrier reliability

Sloped-junction lightly doped drain (SJLDD) structures, for 0.5- mu m channel length MOSFETs, which exhibit exponential improvement in lifetime under high-field stress with source-drain implant energy are discussed. The improved lifetime correlates with reduced drain electric fields and increased depth of peak avalanche below the silicon-silicon dioxide as determined by simulation. The results present an interesting instance where the substrate current fails as a hot-carrier monitor and provide indirect evidence of a energy-dependent electron mean-free path decreasing from the known 5.7 nm at the impact ionization threshold to less than 3.2 nm at kinetic energy of about 4.6 eV.<
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