K. Maex

imec Belgium, Louvain, Flanders, Belgium

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Publications (583)689.56 Total impact

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    ABSTRACT: In this paper the electrical properties of epitaxial CoSi2 on Si obtained by solid-state reaction of a Ti/Co bimetallic layer are investigated. Low temperature resistivity, magnetoresistance and Hall data are presented. The CoSi2ISi Schottky diodes are characterised by current - voltage and capacitance - voltage measurements at temperatures varying between - 100°C and 60°C.
    No preview · Article · Jan 2012 · MRS Online Proceeding Library

  • No preview · Article · Jan 2012 · MRS Online Proceeding Library
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    ABSTRACT: An investigation of the influence of an intermediate titanium thin film on the silicidation reaction between an overlying iron film and the (100)-oriented silicon substrate is presented. The Fe-Ti bilayers were obtained by consecutive sputtering of a Ti layer and an Fe layer on Si substrates. In addition, single iron layers were made by sputtering for comparison with the bilayers. By subsequent rapid-thermnal processing (RTP), depending on the annealing conditions, both the semiconducting β- and the metallic α-FeSi2 thin films could be formed. The phase formation has been investigated as a function of the thickness of the titanium layer, the annealing time and temperature. In this paper the first results on iron disilicide formation through Fe-Ti-Si diffusion couples are shown. Characterisation of the FeSi2 layers using Rutherford backscattering spectrometry (RBS), channelling RBS, X-ray diffraction (XRD), sheet resistivity measurements will be presented.
    No preview · Article · Jan 2012 · MRS Online Proceeding Library
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    ABSTRACT: Transmission electron microscopy is used to investigate the structural development as a function of the annealing temperature of Co-silicides prepared on SiGe and SiGeC. The transition temperature from Co(SiGe) into Co(SiGe)2 is higher for SiGeC than for SiGe.
    No preview · Article · Jan 2012 · MRS Online Proceeding Library
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    ABSTRACT: The effect of the thickness of the SiGe layers in the Co-SiGe/Si reaction is investigated. Formation of the disilicide phase is retarded when compared to the reaction of Co with pure Si substrates. This delay is dependent on the thickness of the SiGe layer, which determines the effective Ge concentration at the reaction front, changing the energetics of the reaction. Besides, Ge expelled from the Co(Si1-yGey) compound blocks the Co diffusion paths, slowing down the reaction. The thermal stability of the suicide layer is also affected by the Ge segregation, with the film agglomerating at lower temperatures when formed on thicker SiGe layers. The slow supply of Co atoms to the reaction front, due to the blocking of Co diffusion paths by the segregated Ge, is believed to be the reason for the presence of the preferential (h00) orientation of the disilicide phase observed in our samples.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Silicidation of small features of various geometries and sizes using Ni-silicide was studied. Effects of dopants, surface preparation and silicidation parameters on suicide morphology were investigated. It was found that Ni suicide thickness and quality of the silicide/silicon interface (presence of NiSi 2 pyramids) are dependent on the area dimensions and geometry. NiSi formed on narrow lines is thicker compared to wide areas. We found that pyramids of epitaxial NiSi 2 protruding into the Si substrate are formed during the silicidation of undoped, boron-doped and BF 2-doped active areas. The presence of pyramids was not observed on As-doped silicon. Rough interface due to the pyramids could be the reason for a more pronounced linewidth dependence of leakage current in the case of p+/n diodes. A higher density of pyramids was found on narrow lines (below 0.2μm) and particularly islands structures. No pyramids were found when a Ge preamorphisation implant was used.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Effects of alloying Ni with Pt and Ta on silicide properties for CMOS technology have been studied. It was found that Pt is soluble in NiSi, which is in line with literature, whereas Ta segregates towards the surface during thermal treatment. Additionally, Ta retards NiSi formation at low temperature. Thermal stability of NiSi on Si is improved more efficiently by alloying Ni with Pt compared to Ta. Silicide/diffusion contact resistance is extracted using the Transmission Line Structure. In our experiments, contact resistivity appeared to be virtually unaffected with respect to the alloying element. Thermal stability on narrow poly Si structures was also improved when Ni was alloyed with Pt. Similar leakage currents for Ni and Ni(Pt) silicides on N+ and P+ junctions were obtained. The results presented in this work suggest that Pt is a better candidate as alloying element to improve NiSi thermal stability for CMOS processes than Ta.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: We have studied CoSi2 formation in the presence of a Cr or Mo interlayer or capping layer. We shall show that, contrary to what was previously reported, Cr and Mo may be used as interlayers to grow epitaxial CoSi2. However, unlike for Ti, the thickness of the interlayer is very important. If the Cr or Mo interlayer is too thick (> 5 nm), polycrystalline CrSi2 or MoSi2 are formed first and epitaxial growth of CoSi2 becomes impossible. However, both XRD and random/channeling RBS results indicate that for a 2-3 nm interlayer of Cr or Mo, CoSi2 forms epitaxially on Si(100). For thinner interlayers, there is a preferential (220) and (400) orientation. This can be explained by the presence of Cr or Mo on the CoSi grain boundaries, which will affect the heterogeneous nucleation of CoSi2.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Making use of SPER (Solid Phase Epitaxial Regrowth) As and B deep source/drain junctions with high activation can be obtained at temperatures below 700°C. However, higher thermal budget is required to regrow and activate the dopants in the poly gates. Low junction leakage and low contact resistance can be obtained for Ni-silicided As and B SPER junctions making use of deep As and B implants. Because of the low thermal budget source/drain junctions obtained by SPER are an attractive alternative to conventional spike annealed junctions for technologies making use of metal gates.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Nanoporous organosilicate films have been recently prepared using tetraalkylammonium cations in acid and basic media, outperforming other materials. Resulting films using basic medium were called zeolite-inspired low-k dielectrics. Here we study the dependence of the properties of these films on the used silica sources: methyltrimethoxy silane (MTMS) and tetraethyl orthosilicate (TEOS). A set of experiments varying the MTMS:TEOS ratio were prepared in acid medium and characterized. A textural, physico-chemical, mechanical, and electrical characterization of this series of experiments is presented.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Atomic Force Microscopy (AFM) was employed to probe the mechanical properties of surface-charged polymethylmethacrylate (PMMA)-based terpolymer and a composite terpolymer core-silica shell nanosphere in air and water media. Since these materials exhibit enhanced mechanical properties, such as toughness and elasticity, and enhanced chemical stability, they are particularly interesting for potential applications in reducing defectivity during the process of Chemical Mechanical Planarization. The polymer particles were subjected to a thermal treatment aimed at improving their mechanical properties in terms of hardness (H) and elastic modulus (E). By analysis of force-displacement curves and on the basis of Hertz's theory of contact mechanics, Young's moduli were measured for the terpolymer compared with the composite that has expected mechanical property enhancement due to its silica shell. In air, E increases from 4.3 GPa to 6.6 GPa for the treated terpolymer compared with the respective value of 10.3 GPa measured for the composite. In water, E increases from 1.6 GPa to 4.5 GPa for the thermally treated terpolymer that is comparable with the respective value of 3.6 GPa measured for the composite. This observation suggests that as an alternative to the creation of polymer-silica composite nanoparticles for CMP, comparable mechanical properties can be achieved by a simple heat treatment step.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: The effect of capping layer (Ti vs TiN) on CoSi formation and CoSi2 sheet resistance has been investigated. Resistance measurements and XTEM analysis have been used to show that the Ti cap lowers the activation energy for CoSi formation by gettering the O2 from the RTA (rapid thermal anneal) ambient and eliminating the formation of SiO2 between the growing CoSi and the Co. The sheet resistance of cobalt silicide formed from Co/Ti and Co/TiN bilayers on poly-Si lines was measured as a function of linewidth and RTA temperature. With a Ti cap, the sheet resistance is low and independent of temperature, and the RTA process window is large.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: To improve Ti SALICIDE process, Si preamorphization by arsenic before Ti sputtering has been studied in two parts: process characterization and fundamental studies. Sheet resistance (Rs) reduction by the preamorphization is more pronounced on thinner and narrower-line silicide formation. At 60keV implantation energy, there is an optimum arsenic dose for the improvement. Through the treatment, more uniform silicide layer can be formed, indicated by the improved Rs uniformity. In the fundamental study, preamorphization appears to have little effect on promoting C49-to-C54 phase transformation. It is suggested that the treatment is able to enhance the reaction rate between Ti and amorphous Si, and results in C54-TiSi2 with larger grains and consequently slightly lower resistivity.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • D. J. Howard · I. De Wolf · H. Bender · K. Maex
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    ABSTRACT: The application of CoSi2 in ever shrinking Si CMOS source-drain technologies demands a better knowledge of the states of stress caused by the formation of cobalt-silicides in Si. In this study the variation in local mechanical stress in the silicon substrate near arrays of polycrystalline cobalt-silicide lines was investigated by micro-Raman spectroscopy. The lines were formed by annealing Co sputtered in windows in lithographically patterned, thermal oxide coated Si wafers. The CoSi2 lines varied in width from approx.0.25 to 5.0μm, in number from 2 to 7, and in thickness from approx.10 to 230nm. The spacing between lines was 1 and 3 times the line width. Trends in the Si stress between CoSi2 lines are described as a function of line width and line thickness. From the stress measured in the Si, information is obtained about the stress in the CoSi2 lines. In addition, the Si stress due to lines of primarily CoSi phase (monosilicide) is compared with the Si stress due to polycrystalline-CoSi2 (disilicide) lines. Cross section TEM and SEM micrographs of the CoSix line morphologies are used to aid the description of the resulting stress profiles. Some theoretical modeling of the stress in the Si due to the CoSix lines is presented for comparison with the micron-Raman spectroscopy results.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: The relationship between silicide thickness, sheet resistance and silicon consumption is experimentally checked for Co-disilicide and Ni-monosilicide. The reverse bias leakage current of shallow Ni-silicided and Co-silicided square diodes is compared for varying junction depth and varying silicide thickness. A lower reverse bias leakage current is obtained for a Ni-silicided shallow junction as compared to its Co-silicided counterpart. This can be attributed to the reduced silicon consumption. The Ti cap does not play an active role during the Ni-silicidation of narrow active area and poly lines. It is shown that a Ni-silicidation process is scalable without Ti cap.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Ballistic electron emission microscopy (BEEM) and deep level transient spectroscopy (DLTS) have been used to study the effects of substrate damage introduced by an ion-milling process in PtSi/n-Si Schottky contacts. Argon ions with well-defined energies of 300, 500, 700, 1000, 1500 eV were used to sputter n-type Si substrates in an ion beam sputtering system before metal deposition and suicide formation. Histograms of the PtSi/n-Si Schottky barrier height (SBH) measured by BEEM show that the mean SBH decreases with increasing ion energy, which can be explained as a result of donor-like defects that are introduced by the ion milling treatment. From DLTS measurements, we found direct evidence for the presence of such defects.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: The influence of patterned oxide layers on temperature non-uniformity during RTP is studied. It is shown that large temperature non-uniformities (up to 80 °C) can occur during RTP as a consequence of large scale patterns of thick oxides. The dependence of oxide thickness and pattern geometry on temperature non-uniformity over a wafer is studied. A set of simulation programs is developed to calculate the optical characteristics of a wafer inside a chamber and to calculate the time dependent temperature non-uniformities on patterned wafers. The calculated results agree very well with the experimental results. The simulation program was used to define the optimal optical conditions for RTP systems for minimal temperature non-uniformity due to patterned overlayers on Si.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: The introduction of rapid thermal processing for silicide formation has triggered a lot of research to temperature uniformity and reproducibility in RTP systems. From the other side there has been the demand to make the process itself as robust as possible for temperature variations. Indeed the way the module is set up can open or close the thermal process window for silicidation. In addition to the temperature, the ambient control is to be taken into account. Although gasses are specified to a low level of contaminants, the RTP step needs to be optimized for optimal contaminant reduction. Besides, the process wafer itself can be a source of contamination. In this paper an overview will be given of the role of temperature and ambient during RTP on the silicidation processes. The effect of the wafer on ambient purity will be highlighted. It will be shown that the latter can also have an impact on other process steps in the interconnect technology.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • Karen Maex · An Steegen
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    ABSTRACT: In this paper, a detailed analysis of silicide induced stress is presented. Micro-Raman spectroscopy measurements of the silicide induced stress in the silicon substrate are combined with simulations by Finite Element Modeling down to 0.1 μm MOS technologies. It is shown that the scaling possibilities of TiSi2 and of CoSi2 are both hampered by the increasing silicide stress, which can even result in the generation of dislocations in the silicon substrate. Because of the difference in material properties between TiSi2 and CoSi2, TiSi2 induces a higher stress in the silicon substrate than CoSi2. It is also proven that the silicide induced stress affects the performance of transistors and diodes. Therefore, the mechanical characteristics related to the silicide formation become a critical parameter in the optimization of the silicide for sub-0.251 μm MOS technologies.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: We present the influence of the electrochemical plating recipe and the bath chemistry on Cu grain size evolution and its link to corrosion of Cu interconnects. Our results demonstrate the fact that Cu corrosion depends on the combination of (i) solution type and (ii) Cu quality. The latter is influenced by geometrical factors such as line width and pattern density as well as the electroplating parameters such as plating recipe and bath chemistry. Organic and inorganic acid based model-CMP solutions are used to make a comparison in terms of the interactions with the Cu surface. It is shown that an organic acid based solution etches Cu independent of the Cu quality. However, etching by an inorganic acid based solution reveals line width (0.2 μm <w<1.0 μm) and pattern density dependence (16%< pd< 72%) with the narrow lines being etched more rapidly both for isolated and semi-dense structures. This kind of geometry dependent etch behavior by the inorganic acid based solution is also shown to be a function of the electroplating process parameters in contrast to an organic acid based one.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library

Publication Stats

8k Citations
689.56 Total Impact Points

Institutions

  • 1989-2012
    • imec Belgium
      • Smart Systems and Energy Technology
      Louvain, Flanders, Belgium
  • 2011
    • Advanced Micro Devices
      Sunnyvale, California, United States
  • 1987-2011
    • University of Leuven
      • Department of Electrical Engineering (ESAT)
      Louvain, Flanders, Belgium
  • 2010
    • Catholic University of Louvain
      Лувен-ла-Нев, Walloon, Belgium
  • 2008
    • Hasselt University
      • Institute for Materials Research (IMO)
      Hasselt, Flemish, Belgium
  • 2005
    • Axcelis Technologies
      BVY, Massachusetts, United States
  • 2001-2003
    • Leuven University College
      Louvain, Flemish, Belgium
  • 2002
    • Texas Instruments Inc.
      Dallas, Texas, United States
  • 2000
    • Ghent University
      • Department of Solid-state Physics
      Gand, Flanders, Belgium
    • INSYS Therapeutics, Inc.
      Phoenix, Arizona, United States
  • 1991
    • University of Barcelona
      Barcino, Catalonia, Spain