Shallow Junction Engineering by Phosphorus and Carbon Co-implantation: Optimization of Carbon Dose and Energy

Abstract

Carbon co-implantation after pre-amorphization implantation (PAI) has been studied for Boron shallow implants and can be also used to reduce Phosphorus diffusion. The expected role of Carbon is to trap Si interstitials responsible of Phosphorus diffusion. A known drawback of this kind of co-implantation is junction leakage caused by Carbon deep levels. To find a compromise between diffusion reduction and leakages, it is necessary to optimize the location and the amount of Carbon with respect to Si interstitials.In this work, we present full sheet experiments optimizing Carbon implanted energy and dose in order to minimize Phosphorus diffusion. First, we performed a PAI with Germanium. Then Carbon was implanted at several energies and doses to locate its projected range (Rp) at various locations with respect to the Phosphorus peak and the amorphous/crystalline interface. Finally the Phosphorus implant was placed completely within the amorphized area. Dopants were activated by a spike anneal at 1080°C, 1055°C or 1000°C. SIMS analysis and Rs measurements were used to understand Carbon action on Phosphorus diffusion and activation. The role of C in suppressing P diffusion is discussed in regards of the specificities of P diffusion mechanism.

Wafer-Scale, Sub-5 nm Junction Formation by Monolayer Doping and Conventional Spike Annealing

“…In order to compare our P-MLD processed n + /p USJs with those achieved by other doping technologies, we complied the literature reported R s and x j values for phosphorus doped junctions as depicted in Figure A. − From the literature, the smallest x j ∼ 13 nm at the background concentration of 5 × 10 18 atoms/cm 3 was reported with R s ∼650 Ω/cm. To the best of our knowledge, there is no previous report of sub-10 nm n + /p USJs based on the phosphorus diffusion in part because of the high diffusivity of P, highlighting the elegance of MLD in achieving nanometer-scale junctions, even for fast diffusing impurities.…”

“…5A. 19,20,21,22,23 From the literature, the smallest x j ~13nm at the background concentration of 5x10 18 atoms/cm 3 was reported with R s ~650 Ω/□. To the best of our knowledge, there is no previous report of sub-10nm n+/p USJs based on the phosphorous diffusion in part because of the high diffusivity of P, highlighting the elegance of MLD in achieving nm-scale junctions, even for fast diffusing impurities.…”

“…5A. 19,20,21,22,23 From the literature, the smallest x j~1 3nm at the background concentration of 5x10 18 atoms/cm 3 where q, µ, N and x are the elemental charge, electron mobility, dopant concentration and depth, respectively. The efficiency is then defined as .…”

Formation of Ultra-Shallow Junctions

“…Carbon concentrations can be so high that Si-C complexes precipitate out (Cagnat et al, 2007), which can have severe effects on the electrical performance of the device. Carbon-related defects have been reported to worsen junction leakage current.…”