Matthieu Gilbert

atom probe analysis of a 3D-finfet with high-k metal gate

The atom probe analysis of a full gate stack (metal gate/high-k dielectric) in a 3D finFET is reported. The measurement reliability in this kind of heterogeneous structure is discussed in the light of different artefacts, i.e. mass overlap and 3D reconstruction artefacts.

Atom probe for FinFET dopant characterization

With the continuous shrinking of transistors and advent of new transistor architectures to keep in pace with Moores law and ITRS goals, there is a rising interest in multigate 3D-devices like FinFETs where the channel is surrounded by gates on multiple surfaces. The performance of these devices depends on the dimensions and the spatial distribution of dopants in source/drain regions of the device. As a result there is a need for new metrology approach/technique to characterize quantitatively the dopant distribution in these devices with nanometer precision in 3D. In recent years, atom probe tomography (APT) has shown its ability to analyze semiconductor and thin insulator materials effectively with sub-nm resolution in 3D. In this paper we will discuss the methodology used to study FinFET-based structures using APT. Whereas challenges and solutions for sample preparation linked to the limited fin dimensions already have been reported before, we report here an approach to prepare fin structures for APT, which based on their processing history (trenches filled with Si) are in principle invisible in FIB and SEM. Hence alternative solutions in locating and positioning them on the APT-tip are presented. We also report on the use of the atom probe results on FinFETs to understand the role of different dopant implantation angles (10° and 45°) when attempting conformal doping of FinFETs and provide a quantitative comparison with alternative approaches such as 1D secondary ion mass spectrometry (SIMS) and theoretical model values.

In-situ observation of non-hemispherical tip shape formation during laser-assisted atom probe tomography

It is shown by SEM imaging of the tip and by observing the emission pattern of the evaporated atoms that laser assisted evaporation in an atom probe can lead to nonhemispherical tip shapes and time-dependent nonuniform emission. We have investigated this nonuniformity by observing the change in field of view when using laser wavelengths of 515 nm and 343 nm on silicon. The change is monitored in situ by 0.5 nm thick silicon oxide. We demonstrate that the field of view can easily be changed by more than 10 nm and that the apparent oxide layer thickness can deviate substantially from its correct value. The dependence of the tip shape deformations and the reconstruction artifacts on the laser wavelength are explained through simulations of the laser-tip interaction and nonhomogeneous heating effects.

High depth resolution analysis of Si/SiGe multilayers with the atom probe

The laser assisted atom probe has been proposed as a metrology tool for next generation semiconductor technologies requiring subnanometer depth resolution. In order to support its routine application, we carried out a quantitative assessment of the performance of the atom probe on semiconductor stacks. We analyzed a silicon, silicon-germanium multilayer-structure with atom-probe tomography (APT), secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM), and high-resolution x-ray diffraction (HRXRD). We demonstrate that APT outperforms SIMS by a factor of 3 in terms of depth-resolution providing a decay length of 0.2–0.6 nm/decade whereas the compositions and layer thicknesses are in close agreement with SIMS, HRXRD, and TEM.

Characteristics of cross-sectional atom probe analysis on semiconductor structures

The laser-assisted Atom Probe has been proposed as a metrology tool for next generation semiconductor technologies requiring sub-nm spatial resolution. In order to assess its potential for the analysis of three-dimensional semiconductor structures like FinFETs, we have studied the Atom Probes lateral resolution on a silicon, silicon-germanium multilayer structure. We find that the interactions of the laser with the semiconductor materials in the sample distort the sample surface. This results in transient errors of the measured dimensions of the structure. The deformation of the sample furthermore leads to a degradation of the lateral resolution. In the experiments presented in this paper, the Atom Probe reaches a lateral resolution of 1-1.8 nm/decade. In this paper we will discuss the reasons for the distortions of the tip and demonstrate that with the present state of data reconstruction severe quantification errors limit its applicability for the quantitative analysis of heterogeneous semiconductor structures. Our experiments show that reconstruction algorithms taking into account the time dependent nanostructure of the tip shape are required to arrive at accurate results.

Light absorption in conical silicon particles

The problem of the absorption of light by a nanoscale dielectric cone is discussed. A simplified solution based on the analytical Mie theory of scattering and absorption by cylindrical objects is proposed and supported by the experimental observation of sharply localized holes in conical silicon tips after high-fluence irradiation. This study reveals that light couples with tapered objects dominantly at specific locations, where the local radius corresponds to one of the resonant radii of a cylindrical object, as predicted by Mie theory.

3D site specific sample preparation and analysis of 3D devices (FinFETs) by atom probe tomography

With the transition from planar to three-dimensional device architectures such as Fin field-effect-transistors (FinFETs), new metrology approaches are required to meet the needs of semiconductor technology. It is important to characterize the 3D-dopant distributions precisely as their extent, positioning relative to gate edges and absolute concentration determine the device performance in great detail. At present the atom probe has shown its ability to analyze dopant distributions in semiconductor and thin insulating materials with sub-nm 3D-resolution and good dopant sensitivity. However, so far most reports have dealt with planar devices or restricted the measurements to 2D test structures which represent only limited challenges in terms of localization and site specific sample preparation. In this paper we will discuss the methodology to extract the dopant distribution from real 3D-devices such as a 3D-FinFET device, requiring the sample preparation to be carried out at a site specific location with a positioning accuracy ∼50 nm.

Direct imaging of 3D atomic-scale dopant-defect clustering processes in ion-implanted silicon.

The fabrication of nanoscale semiconductor devices for use in future electronics, energy, and health is among others based on the precise placement of dopant atoms into the crystal lattice of semiconductors and their concurrent or subsequent electrical activation. Dopants are built into the lattice by fabrication processes like ion implantation, plasma-based doping, and thermal annealing. Throughout the fabrication processes fundamental phenomena like dopant diffusion, activation, and clustering occur concurrently with damaging and subsequently recovering the crystal lattice. These processes are described by atomic-scale mechanisms of ion-host atom interaction and have an immense impact on the electrical performance of the resulting devices. Insight in their fundamental nature is of utmost importance for optimizing the performance of nanoscale technologies. In this paper, we demonstrate direct three-dimensional imaging of boron clusters and atoms in crystal defects using field ion microscopy. Our approach allows for the first time the complete characterization of the size and crystallographic orientation of boron-decorated crystal defects. This new method opens a path to image a wide variety of dopant-cluster forms and hence to study the formation and dissolution of boron clusters in silicon on the atomic scale.

Ion-implantation-based low-cost Hk/MG process for CMOS low-power application

This paper demonstrates for the first time a low cost, low complexity process CMOS Hk/MG for low-power applications with Vth controlled by gate Ion-Implantation (I/I) and High-k capping for NMOS and PMOS, respectively. Novel advanced electrical and physical characterizations provide unique insights about the underlying mechanism of Vth adjust induced by I/I into the metal. Improved RO performance, with excellent uniformity and matching characteristics have been achieved without reliability degradation.

Dopant and carrier profiling in FinFET-based devices with sub-nanometer resolution

Atom probe tomography (APT) in conjunction with scanning spreading resistance microscopy (SSRM) is demonstrated for the first time to profile dopant and carrier distributions in FinFET-based devices with sub-nanometer resolution. These two techniques together provide information on the degree of conformality, the dose retention and the dopant activation. These results are also compared with a methodology involving secondary ion mass spectrometry (SIMS). Ion implantation for increased conformality of source/drain extensions is demonstrated for tilted implants, which clearly leads to improved device performance.