Formation of steep, low Schottky-barrier contacts by dopant segregation during nickel silicidation

Abstract

We present a systematic analysis of arsenic dopant segregation during nickel silicide formation. The slopes and concentrations of the arsenic dopant profiles at the NiSi∕Si interface have been studied as a function of implantation energy, implantation dose, and NiSi thickness. Silicidation induced dopant segregation conserves the dopant slope at the silicide/silicon interface up to NiSi thicknesses of three times the as-implanted peak depth before degrading. Best slopes and highest dopant concentrations are obtained for low implantation energies and thin NiSi layers. We also demonstrate that the steepness of the dopant profile at the NiSi∕Si interface can be significantly improved through a two-step annealing process for NiSi formation. For As, 1keV, 1×1015cm−2, and a 17nm NiSi layer, a NiSi∕Si junction with a dopant slope of 3.2nm/decade has been obtained. An effective Schottky barrier of ΦSB=0.12eV was determined by low temperature measurements of Schottky diodes with 20nm NiSi formed by an optimized annealing process.

Review paper: Advanced source and drain technologies for low power CMOS at 22/20 nm node and below

“…[63] The best concentration gradient and highest dopant concentrations are obtained for low implantation energies and thin NiSi layers. [67] It was also shown that the steepness of the As profile at the NiSi/Si interface can be significantly improved through a two-step annealing process for NiSi formation. Increasing doping concentration by using silicidation as diffusion source (SADS) is another method.…”

“…Several reports have been published that indicate an increase in doping concentration at the interface using a silicide-induced dopant segregation (SIDS) technique. [63][64][65][66][67] The accumulated dopant at the interface also tends to modulate the barrier height. Ion implantation with arsenic and boron and subsequent silicidation is used to create highly n-and p-doped interface layers at the silicide-silicon interface.…”

Breaching the kT/q limit with dopant segregated Schottky barrier resonant tunneling MOSFETs: A computationnal study

“…Using dopant segregation (DS) of dopants implanted in the Schottky metal, i.e. the natural migration and accumulation in the first Si few nanometers near the interface with the Schottky metal, one can reduce the equivalent barrier height significantly [2,4]. In fact, we will show based on our simulation results that it is more the width of the barrier that decreases as a depletion region is thinned when increasing the doping.…”

“…In order to improve performances one can find a material with lower barrier height such as Er for n-FETs or Pt for p-FETs [3,5]. However midgap materials like Nickel Silicides are presently easier to integrate with Si [4]. Using dopant segregation (DS) of dopants implanted in the Schottky metal, i.e.…”

“…Replacing highly doped source (S) and drain (D) by metallic Schottky contacts, Schottky Barrier (SB) transistors have recently attracted a lot of attention because, doing so, one can potentially solve the increasing problem of S/D resistance and dopant diffusion [1][2][3][4]. This will become crucial for future ultra-scaled transistors, i.e.…”