Substrate Orientation Dependence of NiSi Silicided Junction Leakage Induced by Anisotropic Ni Migration in Crystal Si

Abstract

Using n+/p junctions formed by solid-phase diffusion, the intrinsic leakage current induced by the NiSi thermal instability is thoroughly monitored for both Si(100) and Si(110) substrates to elucidate the crystallographic influence of Si. Although thermal instability caused by Ni clusters migrating away from the NiSi layers is confirmed for both substrates, the ways of leakage generation and associated Ni migration are notably different. The virtual immobility at the bottom of NiSi on Si(110) of otherwise mobile Ni clusters indicates effective in-plane diffusion along the horizontal (110) plane. The downward mobility at the Si(110) perimeter of otherwise impermeable Ni clusters at the bottom demonstrates the possible alignment of the migration plane on some {110} planes other than the horizontal (110) plane. The discrepancy observed in the deeper ingression of perimeter leakage along the [100] and [110] directions reveals a directional preference of Ni cluster migration even within the {110} planes. The crystal orientation dependence of the thermally induced leakage of NiSi junctions can be explained in terms of anisotropic Ni migration, whose diffusion ellipsoid is practically degenerated within one of the {110} planes and is elongated by a factor of 1.7 toward the <100> direction.