Deactivation of Solid Phase Epitaxy-Activated Boron Ultrashallow Junctions

Abstract

The solid phase epitaxial growth technique appears to be a promising method for achieving junction depths and sheet resistance values low enough to meet the performance specifications of the 65 and 45 nm node for boron, BF 2 , and BF 3 doping profiles in amorphous silicon. Room-temperature implants of these three dopant species into Si͑100͒ preamorphized by 74 Ge + ͑30 keV, 1.0 ϫ 10 15 cm −2 ͒ lead to boron concentration profiles that fulfill the technological requirements. It was found that even for ultrashallow junctions the time for the regrowth process at 650°C has to be optimized with regard to the implanted species in the range between 5 and 60 s, especially when fluorine is present. The thermal stability of the boron profile distribution that meets 65-nm-node requirements was evaluated by subsequent thermal anneals simulating the thermal effects expected for typical silicidation processes. For a more detailed investigation, the postannealing temperatures ranged from 250 to 1050°C with times from a few to several hundred seconds. All the junctions were analyzed by four-point probe and selected samples by secondary ion mass spectroscopy, transmission electron microscopy, and high-resolution electron microscopy.The combination of doping and activation technology is expected to provide solutions for highly activated, shallow, and abrupt dopant profiles required for advanced logic device technology beyond the 90-nm node. 1 In contrast to spike and/or flash annealing, a simple approach for the formation of ultrashallow junctions with boron consists of preamorphizing the substrate prior to dopant implantation followed by a low-temperature solid phase epitaxial growth process ͑SPEG͒. The SPEG technique currently appears to be a promising method for achieving junction depth and sheet resistance values low enough to meet the performance specifications for the 65-and 45-nm node. The optimal process for high activation during SPEG involves annealing at ϳ650°C for 5-60 s in an inert ambient. 2 The main advantages of the SPEG technique is that it has been extensively studied for at least three decades. In general it is rather simple and requires only conventional implant and rapid thermal processing equipment. It is also a low-temperature approach that is thermally compatible with advanced materials such as high-k dielectrics and metal gates. In this paper we present some of our recent results on the formation of ultrashallow junctions using the SPEG technique. Additionally, data for technology nodes beyond 90 nm are also presented in a sheet resistance vs junction depth matrix, including data from current literature of various techniques.However, the thermal stability of activated junctions is a critical consideration for front-end complementary metal oxide semiconductor ͑CMOS͒ manufacturing. Therefore, in the second part we present a detailed study of boron deactivation during thermal processes after SPEG. Postannealing temperatures were chosen in order to "simulate" typical self-aligned silicide processes for NiSi or...

Boron activation and redistribution during thermal treatments after solid phase epitaxial regrowth

“…Thus, low-temperature solid phase epitaxial regrowth (SPER) of preamorphized samples appears to be one of the most promising techniques for achieving acceptable sheet resistance and junction depth values to meet the performance specifications of the international technology roadmap of semiconductors (ITRS) [3]. Experiments show that preamorphizing implants (PAI) enhances dopant activation up to concentrations levels ∼10 20 cm −3 during low-temperature SPER of the amorphous layer, with a minimal amount of dopant diffusion [4][5][6][7][8][9][10]. Higher B concentrations are electrically inactive after the recrystallization process [5][6][7][8], which has been associated to the formation of immobile boron clusters [11,12].…”

“…Experiments show that preamorphizing implants (PAI) enhances dopant activation up to concentrations levels ∼10 20 cm −3 during low-temperature SPER of the amorphous layer, with a minimal amount of dopant diffusion [4][5][6][7][8][9][10]. Higher B concentrations are electrically inactive after the recrystallization process [5][6][7][8], which has been associated to the formation of immobile boron clusters [11,12]. The presence of residual defects at end of range (EOR) region, remaining after SPER beyond the amorphous/crystalline interface, leads to additional deactivation if annealing treatments are performed after the regrowth of the amorphous layer [5][6][7][8][9].…”

“…Higher B concentrations are electrically inactive after the recrystallization process [5][6][7][8], which has been associated to the formation of immobile boron clusters [11,12]. The presence of residual defects at end of range (EOR) region, remaining after SPER beyond the amorphous/crystalline interface, leads to additional deactivation if annealing treatments are performed after the regrowth of the amorphous layer [5][6][7][8][9]. Moreover, these anneals result in a redistribution of boron profiles, showing boron uphill diffusion towards the surface in the medium concentration region [5,[7][8][9]13] and tail diffusion in the low concentration region of the boron profile [5,7,8].…”

The formation, stability, and suitability of n-type junctions in germanium formed by solid phase epitaxial recrystallization

“…14,15 SPER has recently been explored for p-type [16][17][18] and n-type 19,20 dopant activation in germanium but a number of key issues remain. Deactivation kinetics have been studied in silicon [21][22][23] but this aspect is largely unexplored at this point of time for n-type dopants in germanium. Moreover, optimization of process variables such as implants and recrystallization temperatures require fine tuning.…”

“…Deactivation kinetics in post-SPER silicon have been linked to interstitials ͑I͒ emitted from the end-of-range ͑EOR͒ defect band interacting with the dopant atoms, and the formation of dopant-defect clusters, the rate of which depends on the thermal budget of the postanneals, 21 the location of the EOR band with respect to the dopant, 22 and the presence or not of a coimplanted nondopant species. 23 In germanium, the EOR defects are relatively short lived and do not necessarily follow a classical Ostwald ripening process.…”