Advanced processing technique to minimize enhanced diffusion in sub-keV boron implants

The Varian VIISta 80 and the Varian VIISion 80 PLUS ion implanters were used to implant wafers with doses of 2.5e14/cm² to 2.8e15/cm² for ¹¹B⁺ at 1.0 keV, 0.5 keV and 0.25 keV and for ⁴⁹BF²⁺ at 1.1 keV. Rapid thermal anneals (RTA) at various time and temperatures including 1000°C, 10 s and slow controlled “spike” anneals at 1050°C in an ambient of low concentrations of O₂ in N₂, ranging from 0-1 ppm to 1000 ppm were performed. At a 33 ppm concentration of O₂ the effects of oxygen enhanced diffusion (OED) are minimized and in the case of ¹¹B⁺ other oxygen related enhanced diffusion effects, such as the formation of an SiB₄ layer which results in boridation enhanced diffusion (BED) is eliminated. Under these advanced post-processing conditions, a true advantage in employing sub-keV boron implants to reduce junction depth with high electrical activation efficiency is observed, In addition, the effects of the slow controlled spike anneals with fast cool-down rates on a STEAG AST SHS-2800ε are shown to offer some additional advantages in junction depth reduction. The results demonstrate that the National Technology Roadmap requirements at the 0.10 μm node for the p-extension can be satisfied by both species. Examples of this for 1.1 keV BF₂ and for 0.25 keV ¹¹B₊ implants are presented