Dopant/carrier profiling for 3D‐structures

Abstract

With the transition from planar to three‐dimensional device architectures such as FinFets, TFETs and nanowires, new metrology approaches are required to characterize the 3D‐dopant and carrier distributions precisely, as their positioning relative to gate edges, 3D‐distribution, conformality, and absolute concentration determine the device performance in great detail. Concepts like atomprobe tomography with its inherent 3D‐resolution are obviously a potential solution although its routine application is still hampered by localization problems, reconstruction artifacts due to inhomogeneous evaporation, sensitivity due to the limited statistics, poor tip yield, etc. Although on the other hand concepts like scanning spreading resistance microscopy are inherently 2D, extensions towards 3D appear possible either by the design of dedicated tests structures or by novel approaches such as mechanical scalping. Ultimately even 1D‐methods like secondary ion mass spectrometry can be used to study dopant incorporation in 3D‐structures. When assessing their performance as metrology tool for 3D‐devices and structures one needs to address not only their ability to achieve 3D‐spatial resolution but also the physical property which is probed, i.e. dopants versus carriers, as well as the complexity of the method used. An evaluation in terms of time to data is equally important as the technical capabilities. The application of these methods to 3D‐structures and confined volumes, has demonstrated that the changing surface/volume ratios in confined devices versus blanket films lead to phenomena (dopant deactivation, enhanced diffusion,..) which cannot be observed in blanket experiments. Hence more emphasis should be placed on the analysis of device and structures with the relevant dimensions relative to the exploration of blanket experiments. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Improved physical models for advanced silicon device processing

“…23. Similar behavior for lateral diffusion was later confirmed by 3D APT measurements performed by Vandervorst et al [23] in…”

“…This has also increased the complexity of the characterization techniques used to assess the suitability of the created dopant profiles [23]. Thus, computer simulations become a good alternative to evaluate dopant incorporation, distribution and electrical activation in such devices.…”

“…Classical standard doping techniques like ion implantation may not be suitable for FinFET devices because of the 3D geometry. Several solutions to incorporate dopants in the fin are being explored such as tilted ion implantation [23,153,158], plasma doping [159][160][161][162] or vapor phase doping [163]. Among them, tilted ion implantation remains a strong candidate to introduce dopants into the fin, as it is a conventional and well established technique, although it suffers from specific issues that arise from the particular geometry of these devices.…”

“…Results show that, at low and medium B concentrations (> 10 20 junction depth is no longer a relevant parameter (as it is rather set by the Si thickness) and only the lateral profile characteristics are relevant [23]. In fact, the lateral diffusion of the dopants into the channel under the gate (gate overlap) is an important parameter that affects the final device performance [160].…”

Resolution in Carrier Profiling Semiconductors by Scanning Spreading Resistance Microscopy and Scanning Frequency Comb Microscopy

“…Comparison with previous measurements, made using this probe with the same applied direct current (DC) bias with standards having known concentrations of the same dopant, are interpolated to evaluate the local carrier density in the sample. Fragile three-dimensional (3D) structures such as Fin-FETs which are used at the finer lithography nodes must be disassembled, polished, and sectioned before SSRM studies (Vandervorst et al, 2014) because they would be destroyed by the high applied pressure. The diamond-probes must be normal to the sample surface to prevent sliding during their high-pressure insertion into a semiconductor which also complicates the testing of intact 3D structures.…”