Optimizing boron junctions through point defect and stress engineering using carbon and germanium co-implants

Abstract

We report the fabrication of p+∕n junctions using Ge+, C+, and B+ co-implantation and a spike anneal. The best junction exhibits a depth of 26nm, vertical abruptness of 3nm∕decade, and sheet resistance of 520Ohm∕square. The junction location is defined by where the boron concentration drops to 1018cm−3. These junctions are close to the International Technology Roadmap specifications for the 65nm technology node and are achieved by careful engineering of amorphization, stresses, and point defects. Advanced simulation of boron diffusion is used to understand and optimize the process window. The simulations show that the optimum process completely suppresses the transient-enhanced diffusion of boron and the formation of boron-interstitial clusters. This increases the boron solubility to 20% above the equilibrium solid-state solubility.

Impact of multiple sub-melt laser scans on the activation and diffusion of shallow Boron junctions

“…Figure 4c, shows the case for which a C coimplantation is carried out after the PAl. It is interesting to note that the addition of C is effective in reducing the B diffusion during the subsequent laser scans as observed for classical RTA [16,17]. Besides suppression of classical TED, C reduces the interstitialmediated B diffusion which takes place during the BIC dissolution.…”

“…The as-implanted profile is shallower compared to the c-Si case due to the absence of channeling and the difference wrt the shift of the profile after the 1st laser scan is larger in case of PAL The reason for this is twofold : there is a more pronounced End Of Range (EaR) damage due to the PAI leading to a larger interstitial flux during TED and the diffusion in the amorphous Si (a-Si) is larger compared to c-Si [16].…”

A Study of Low Energy Phosphorus Implantation and Annealing in Si:C Epitaxial Films

“…For more understanding microstructure study by TEM was performed. It should be noted that the phosphorous junction profile is as abrupt as 3 nm/decade, indicating retardation of the phosphorous diffusion in Si:C epitaxial film, similar to the effects of carbon on boron diffusion [6].…”

Codoping as a measure against donor deactivation in Si:Ab initiocalculations

“…10 In silicon, codoping has been successfully applied in experiment for the fabrication of ultrashallow p-type junctions. 11 The main challenge there is to control the concentration of excess interstitials that mediate boron diffusion. In the n-type case, however, it is the excess vacancies which are predominantly responsible for both the dopant diffusion ͑As and Sb͒ and the electrical deactivation of the donors.…”