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Towards Reconfigurable Field Effect Transistors: Controlled Nickel Silicidation using Flash Lamp Annealing

Khan, M. B.; Deb, D.; Georgiev, Y. M.; Prucnal, S.; Voelskow, M.; Erbe, A.
Classical scaling down of CMOS technology is reaching its end in the next few years. To facilitate further the enhancement in the complexity and performance of electronic circuits without increasing the chip area, devices with new materials, new architectures, enhanced functionality and new computation principles have gained importance. Our work focuses on fabricating devices with new architectures and enhanced functionality i.e. devices which can be reconfigured as a p- or n-channel field effect transistor (FET). These reconfigurable FETs are based on Silicon (Si) nanowires (NWs), which are silicided at both ends to form Si-NiSi2-Si Schottky junctions. Formation of NiSi2 is a pre-requisite for proper functioning of these devices since fermi level of NiSi2 aligns itself near the mid-bandgap of Si, thereby enabling tuning of band by application of electrostatic potential for its function as a p/n FET [1]. Moreover, control over silicide length is also important to scale the Si channel and to have symmetric contacts on both sides of the nanowire [2]. These issues are the focus of our recent work.
In this paper, we report on comparison between silicidation of undoped Si NWs using rapid thermal annealing (RTA) and flash lamp annealing (FLA). The nanowires are fabricated on silicon on insulator (SOI) substrates by a top down process based on electron beam lithography (EBL) and subsequent inductively coupled plasma (ICP) etching. Hydrogen silsesquioxane (HSQ), a negative tone EBL resist, is used to provide high quality sub-15nm lithographic nanowire patterns, which are transferred into SOI by optimised ICP etching based on C4F8/SF6/O2 mixed gas chemistry. Subsequently, nickel (Ni) is sputtered at lithographically defined areas followed by RTA, which yields atomically sharp NiSi2-Si Schottky junctions. However, the main drawback of this silicidation process is the poor control over Ni silicide phase formation and the progression length of the silicidation along the Si NWs (Fig. 1). These effects lead to an inhomogeneous silicidation process, which prevents symmetric Si channel formation and downscaling.
To provide better control over the silicidation process, a ms-range FLA is investigated as a potential replacement of RTA. Initially, the FLA was performed for 3, 6 and 20 ms on bulk silicon by either flashing the front (f-FLA) or rear (r-FLA) side of the samples. Formation of NiSi and the composition was investigated by micro-Raman (Fig. 2) and Rutherford Backscattering Spectrometry (RBS) (Fig. 3). It is shown that after 6 and 20 ms annealing 50 nm Ni is fully converted to stoichiometric NiSi with atomically sharp interface between NiSi and Si. Cubic NiSi displays Raman active phonon modes at 193 and 217 cm-1, which suggests that the fabricated layer is tensile strained. These preliminary results on bulk Si suggest that the FLA promises to provide better control over silicidation process of the nanowires, thereby enhancing the performance of reconfigurable FETs. Results on silicidation of nanowires will be presented at the conference.
Keywords: Silicon nanowire; silicidation; reconfigurable transistor; Schottky junction
  • Poster
    Micro and nanoengineering, 18.-22.09.2017, Braga, Portugal

Publ.-Id: 25882