Elsevier

Microelectronic Engineering

Volume 120, 25 May 2014, Pages 19-33
Microelectronic Engineering

Atom probe tomography for advanced metallization

https://doi.org/10.1016/j.mee.2013.12.018Get rights and content

Highlights

  • •

    Possibilities and limitations of atom probe tomography for metallization are described.

  • •

    APT for different materials for metallization (silicide, high K/metal gate…) are shown.

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    Preparation and analysis by APT of transistors and nanowires are presented.

Abstract

In microelectronics, the increase in complexity and the reduction of devices dimensions make essential the development of new characterization tools and methodologies. Indeed advanced characterization methods with very high spatial resolution are needed to analyze the redistribution at the nanoscale in devices and interconnections. The atom probe tomography has become an essential analysis to study materials at the nanometer scale. This instrument is the only analytical microscope capable to produce 3D maps of the distribution of the chemical species with an atomic resolution inside a material. This technique has benefit from several instrumental improvements during last years. In particular, the use of laser for the analysis of semiconductors and insulating materials offers new perspectives for characterization. The capability of APT to map out elements at the atomic scale with high sensitivity in devices meets the characterization requirements of semiconductor devices such as the determination of elemental distributions for each device region. In this paper, several examples will show how APT can be used to characterize and understand materials and process for advanced metallization. The possibilities and performances of APT (chemical analysis of all the elements, atomic resolution, planes determination, crystallographic information…) will be described as well as some of its limitations (sample preparation, complex evaporation, detection limit, …). The examples illustrate different aspect of metallization: dopant profiling and clustering, metallic impurities segregation on dislocation, silicide formation and alloying, high K/metal gate optimization, SiGe quantum dots, as well as analysis of transistors and nanowires.

Section snippets

Introduction and purpose

The advances in information technology over the past few decades has been leaded by the continuous scaling down of Si based devices such as complementary metal-oxide-semiconductor (CMOS) field-effect transistors (FETs) and of the interconnection between and within these devices. In accordance with or beyond the Moore’s law, the number of transistors on a chip has more than double every 2 years and the characteristic feature sizes in the actual devices are now in the 10 nm range. The process

APT principles and sample preparation by FIB

Atom Probe Tomography (APT) is a powerful technique to analyze materials in three dimensions at the atomic scale [1], [2], [3], [4]. This technique allows reconstructing, atom by atom, a small piece of matter (typically 50 × 50 × 100 nm3) in the three directions of the real space and is unique for its (a) spatial resolution in three dimensions (0.2 nm achievable), (b) analytical sensitivity (10 ppm) (c) high detection efficiency (>30%) and (d) ability to detect all elements.

Voltages or laser pulses

Dopant profiling

To continue scaling down complementary metal-oxide semiconductor (MOS) devices, ultra-shallow source/drain junctions (USJs) with low resistivity must be fabricated. Indeed ultra-shallow (below 15 nm) and highly doped (well above 1 × 1020 cm−3) source/drain junctions are today needed to further reduce the size of MOS devices [5]. Ion implantation is widely used to introduce electrically or optically active dopant atoms into semiconductor devices [6]. However USJs fabrication processes have

Contacts and silicide

Silicides and ohmic contacts are an interesting and important part of integrated circuit technology. Silicide thin films are used on sources, drains, gates and local interconnects to reduce the series resistance of the devices resulting in a higher switching speed for the device. Among the silicides, NiSi is an essential material for contact application in the semiconductor manufacturing. It has been largely used since the beginning of 65 nm technology node and is currently used for 45 nm node

Analysis of transistors by APT

In microelectronic devices, the presence of stress, defects and confinement may have an effect on the silicide formation mechanism, alloying elements and dopants redistribution and segregation phenomena. It is thus important to know the distribution of elements in three dimensions, quantify the interface segregation and the silicide compositions in real MOSFET. Despite the large number of studies about Ni silicide, the chemical analysis of a real transistor remains a great challenge because of

Advanced materials for microelectronics

The former examples were dedicated to traditional materials in Si based devices. In the following, we will present some examples of the advanced materials needed for the most advanced technology nodes.

Conclusion

Several examples of atom probe analysis have been used to illustrate the possibilities and some limitations of APT for microelectronics and metallization. These examples aims to cover most of the aspects of metallization: Si substrates (dopant profiling and impurities segregation on dislocations loops), silicide thin films (phase formation, epitaxy, dopant precipitation, alloy element), and transistors (gate stack: dopant, poly-Si, silicide, alloy element). New materials and devices were also

Acknowledgements

The authors would like to acknowledge I. Berbezier, A. Ronda, E. Bourjot from IM2NP, M. Gregoire, M. Juhel, R. Pantel from STMicroelectronics, T. Baron from LTM, F. Nemouchi, V. Carron from CEA-LETI, B. Gault from McMaster University, R. Somsuang from I. Néel, O. Cojocaru, B. Blavette from GPM, D. Larson, T. Kelly, R. Ulfig, from former IMAGO. This work was supported by the French National Agency (ANR) through Nanoscience and Nanotechnology Program (TAPAS Project No. ANR-08-027-01) and by the

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