Factors Influencing the Leakage Current in Embedded SiGe Source/Drain Junctions (original) (raw)
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Germanium content dependence of the leakage current of recessed SiGe source/drain junctions
Journal of Materials Science: Materials in Electronics, 2007
The impact of the Ge fraction (x), on the leakage current of recessed Si 1-x Ge x p + -n source/drain junctions has been investigated, for a fixed recess depth of 70 nm. It is found that both the bulk and the peripheral leakage current density increase approximately exponentially with increasing Ge content in the range 10-30%. Roughly speaking, the leakage current density increases one decade for every 5% increase in Ge. In case of the bulk leakage current density, this enhancement is shown to be related to the increase in extended defects penetrating the depletion region in the n-type silicon substrate. Transmission Electron Microscopy demonstrates a higher density of dislocations at the epitaxial interface for a higher Ge fraction, which are most likely generated by strain relaxation, induced by the implantation and activation of B in the p + S/D regions.
IEEE Transactions on Electron Devices, 2000
The purpose of this paper is to evaluate the impact of process-induced stress on the generation current of fully strained Si 1−x Ge x source/drain junctions. The Ge content of the compressively strained SiGe epitaxial layer plays a key role in the tensile stress levels present in the underlying Si substrate. Current-voltage (I-V ) measurements were employed to further investigate the leakage current enhancement due to the stressinduced bandgap narrowing in the Si depletion region, when no extended defects are formed. An empirical approach is proposed to describe the Ge content dependence of the bandgap-shrinkageinduced leakage current. An increase of the intrinsic carrier concentration as a function of the stress mismatch is observed. Moreover, the role of the epilayer thickness in the generation current is also discussed.
IEEE Transactions on Electron Devices, 2011
A study of the impact of the Ge content and the recess depth on the leakage current of strained Si 1−x Ge x /Si p + n heterojunctions is presented. A rise in the current, when the Ge content increases and/or the recess depth decreases, is experimentally observed. An analysis of the physical variables involved in the leakage current at low electric fields is carried out. The Shockley-Read-Hall lifetime is identified as the variable that affects the leakage current the most. Changes in the lifetimes are correlated to changes in the Ge content and the recess depth (Si 1−x Ge x thickness) by means of modifications of the stress levels. An expression that directly relates the values of the lifetimes with the germanium content is proposed.
IEEE Transactions on Electron Devices, 2011
A study of the impact of the Ge content and the recess depth on the leakage current of strained Si 1−x Ge x /Si p + n heterojunctions is presented. A rise in the current, when the Ge content increases and/or the recess depth decreases, is experimentally observed. An analysis of the physical variables involved in the leakage current at low electric fields is carried out. The Shockley-Read-Hall lifetime is identified as the variable that affects the leakage current the most. Changes in the lifetimes are correlated to changes in the Ge content and the recess depth (Si 1−x Ge x thickness) by means of modifications of the stress levels. An expression that directly relates the values of the lifetimes with the germanium content is proposed.
Defect assessment and leakage control in Ge junctions
Microelectronic Engineering, 2014
In this work, the temperature behavior of the transport mechanisms present in Ge p + n junctions selectively grown in shallow trench isolation (STI) substrates is investigated. Special attention is given to the impact of electrically active defects on the current-voltage (I-V) and capacitance-voltage (C-V) characteristics. Moreover, deep level transient spectroscopy (DLTS) is performed in order to evaluate the electrical properties of the traps. The results show that the presence of threading dislocations and associated deep acceptors has a marked impact on the electrical characteristics. The DLTS response seems to be related to electron repulsive centers with an acceptor character located at $0.33-0.40 eV below the conduction band. This mid-gap position yields very effective Shockley-Read-Hall centers and can explain the generation lifetime reduction and leakage increase observed in non-annealed Ge in STI Si diodes.
Stress analysis of Si1−xGex embedded source/drain junctions
Materials Science in Semiconductor Processing, 2008
The purpose of this paper is to evaluate the impact of the geometry of embedded Si 1Àx Ge x source/drain junctions on the stress field. Stress simulations were performed using TSUPREM4 2D software to further investigate the elastic strain relaxation as a function of Si 1Àx Ge x alloy active size, in the regime where no plastic relaxation is present. Moreover, the role of the epilayer thickness and the Ge content on the stress levels is also discussed. The work is complemented with experimental Raman spectroscopy.
Implantation defects and n-type doping in Ge and Ge rich SiGe
Thin Solid Films, 2008
Germanium and germanium rich silicon germanium are of interest as channel materials for extremely scaled CMOS. Although PMOS performance is good the characteristics of germanium NMOS transistors are inadequate because the necessary high level of donor activation cannot be achieved in shallow junctions. In this work we describe a study of the activation and deactivation of donors in germanium using shallow phosphorous implants into p-type Ge and Ge or Si implants into Ge uniformly doped with Sb. The techniques of secondary ion mass spectrometry (SIMS), spreading resistance, DLTS and positron annihilation have been used to study the activation and defects evolution during various anneal stages. It is postulated that the primary reasons for low activation of donors are reactions with vacancies. These proceed as V-D which is thought to be mobile at the anneal temperature reacting with more donors to produce complexes of the form V-D n or possibly V 2-D n which are acceptor like.
Impact of germanium surface passivation on the leakage current of shallow planar p–n junctions
Materials Science in Semiconductor Processing, 2006
One of the challenges in the development of CMOS on Ge is the fabrication of low-leakage shallow junctions. Like in the case of silicon technology, one aims to achieve this goal by ion-implantation of the dopants followed by a thermal activation step. The thermal budget should be low enough to minimize excessive diffusion but at the same time sufficient to remove the lattice damage and activate the dopants. However, as will be shown, for the planar junctions fabricated in germanium substrates, another factor dominates the leakage current, namely the surface generation current in the peripheral regions surrounding the diode. This emphasizes the role of adequate surface passivation. Results will be presented for diodes fabricated in 100 mm diameter p-and n-type Ge wafers, using different dielectrics as surface passivation layer, namely 20 nm Si 3 N 4 deposited by CVD and GeON/HfO 2 (4 nm) deposited by MBE. A difference of up to five decades between forward and reverse current has been achieved. Analysis of the area/perimeter scaling of the reverse current demonstrates that even for these junctions, the surface generation current is dominant. It will also be pointed out that the substrate doping density plays an important role.