Advanced search
1 file | 4.63 MB Add to list

A fundamental study of advanced metal/semiconductor contacts

Wouter Leroy (UGent)
(2006)
Author
Promoter
(UGent) and (UGent)
Organization
Abstract
IN the first part of this work, we focussed on the inhomogeneity of the Schottky barrier height. Au/n-GaAs was used as a model metal/semiconductor contact, because it has a wide background in SB-research and because the advanced semiconductor GaAs is gaining importance in the semiconductor (mobile) industry. Small contacts were fabricated using Electron Beam Lithography. Moreover, by modifying a standard AFM to a Conducting probe AFM, we were able to measure 50 to 100 small-sized Schottky contacts on the same n-GaAs sample. This reduces possible differences in the fabrication process of the Schottky contacts. From the measured I/V -characteristics, the homogeneous barrier height was calculated, using two different techniques, namely by fitting Tung’s Pinch Off model to each individual I/V -characteristic, or by using M¨onch’s linear relationship between the barrier height and ideality factor, both of which are calculated from the standard Thermionic Emission model. We found that bothmethods are reliable for obtaining the value of the homogeneous Schottky barrier height (which is a unique property of the investigated MS-contact). From the comparison of the obtained homogeneous barrier heights from diodes with a different fabrication process, we confirm the influence of the interfacial Auδ+ − Oδ− dipole on the barrier height. The homogeneous barrier height for the Au/n-GaAs Schottky contacts without the dipole is 0.848 eV , while for the contacts with the dipole, we found a value of 1.021 eV. With this confirmation of the dipole-model, we strengthen the Bond Polarization Theory which states that the SBH is locally determined by the bonding of the atoms forming the interface. The second part evidenced the solid-state formation of carbides from thin metalcarbon films. The different phases of the metal-carbon systems were identified using in situ XRD, completed with ex situ XRD, RBS and XPS. W, Mo, Fe, Cr and V form carbides, while Nb, Ti, Ta and Hf need an extra capping layer to prevent oxidation (30nm C was selected as a good capping layer). Mn and Zr, however, formed oxide phases rather than carbide phases, despite the precautions we took (capping layer, no vacuum break during deposition of the different layers). The phase sequences for the different carbide-forming transition metal-carbon systems, are listed in table 7.19 on page 108, and their formation temperatures (at a heating rate of 3◦C/s) are summarized on page 109 in table 7.20.Furthermore, activation energies were determined for the different carbide formations. For this, in situ XRD measurements at different heating rates were analyzed using a modified Kissinger method. The activation energies are listed in table 8.1 on page 124, and they can be used in the search for the mechanisms which govern the (carbide) phase formation. The last part illustrates the possible application of carbides as contacts for Ccontaining semiconductors. Carbon nanotubes (CNTs) and diamond are some of the most advanced C-containing semiconductors, and they both possess very peculiar, but interesting and useful properties. We give an example of a solid-state reaction between a metal layer (Mo) and CNTs, forming a carbide (in this case Mo2C). Furthermore, we give examples of carbide formation on CVD-diamond, with the same phase sequence as obtained in the previous part. Also, a preliminary research on the electrical characteristics on CVD-diamond was done. We conclude that the crystal structure (and hence the dipoles) at the metal/diamond interface significantly influences the electrical properties. To get a good comprehension of the electrical behaviour of the contacts formed on CVD diamond, one should have good understanding of the metal-diamond interface, and thus first of the diamond surface. Furthemore, the bond-polarization theory is a good starting point for the comprehension of the metal-diamond interface.
MINIATURISATIE is voor de micro-elektronica reeds vele jaren het middel bij uitstek om aan Moore’s Law te voldoen. Deze zegt (in een verkorte versie): "Het aantal transistoren op een computerchip verdubbelt elke 18 maanden", en is voor de fabrikanten eerder een drijvende kracht geworden dan een observatie. Verdere miniaturisatie brengt echter meerdere problemen aan het licht, zoals o.a. de invloed van stress op de silicide-vorming, de lekstroom van de dunner wordende SiO2-poort (’gate’), en de toename van elektrisch verbruik en van de warmte-productie. We geven een paar mogelijke paden die geopperd worden om de huidige tred in ontwikkeling van micro-elektronica aan te houden. Het vervangen van de huidige polykristallijne Si gate door een metaal gate (of een volledige silicide-gate), zou een deel van de problemen kunnen oplossen. Ook het gebruik van Schottky juncties in plaats van de huidige p-n juncties, wordt weer ter sprake gebracht. Een heel ander pad ligt in het gebruiken van andere materialen dan Si. Mogelijke kandidaten hiervoor zijn: de Si-verwante materialen (SiGe, Ge, SiC, Si1−x−yGexCy), C-houdende materialen zoals diamant en koolstof nanobuizen, en III-V halfgeleiders (GaAs, GaN, InP). Op veel vlakken hebben de vernoemde materialen betere kwaliteiten dan het huidig gebruikte Si, edoch bevinden toepassingen ervan zich ofwel in een experimentele fase, ofwel hebben ze slechts een niche van de markt kunnen veroveren (vb. GaAs in de mobiele technologie). Ge en GaAs worden naar voor gebracht als materialen met hoge mobiliteit, voor het gebruik als geleidend kanaal (’channel’) in de transistor. Andere materialen als diamant en SiC vinden eerder toepassing in de niche-markt van hoog-vermogentoepassingen. Het eerste deel van dit werk situeert zich binnen deze ontwikkelingen als fundamenteel onderzoek naar de inhomogene aard van Schottky barrières. Het tweede deel spitst zich toe op de vorming van carbides, die veelbelovende kandidaten zijn om koolstofhoudende halfgeleiders te contacteren. Het laatste deel illustreert de toepasbaarheid van de carbide contacten op koolstof nanobuizen en diamant.

Downloads

  • 0612 PhD WouterLeroy dec06.pdf
    • full text
    • |
    • open access
    • |
    • PDF
    • |
    • 4.63 MB

Citation

Please use this url to cite or link to this publication:

MLA
Leroy, Wouter. “A Fundamental Study of Advanced Metal/semiconductor Contacts.” 2006 : n. pag. Print.
APA
Leroy, W. (2006). A fundamental study of advanced metal/semiconductor contacts. Gent.
Chicago author-date
Leroy, Wouter. 2006. “A Fundamental Study of Advanced Metal/semiconductor Contacts”. Gent.
Chicago author-date (all authors)
Leroy, Wouter. 2006. “A Fundamental Study of Advanced Metal/semiconductor Contacts”. Gent.
Vancouver
1.
Leroy W. A fundamental study of advanced metal/semiconductor contacts. [Gent]; 2006.
IEEE
[1]
W. Leroy, “A fundamental study of advanced metal/semiconductor contacts,” Gent, 2006.
@phdthesis{472503,
  abstract     = {IN the first part of this work, we focussed on the inhomogeneity of the Schottky barrier height. Au/n-GaAs was used as a model metal/semiconductor contact, because it has a wide background in SB-research and because the advanced semiconductor GaAs is gaining importance in the semiconductor (mobile) industry. Small contacts were fabricated using Electron Beam Lithography. Moreover, by modifying a standard AFM to a Conducting probe AFM, we were able to measure 50 to 100 small-sized Schottky contacts on the same n-GaAs sample. This reduces possible differences in the fabrication process of the Schottky contacts. From the measured I/V -characteristics, the homogeneous barrier height was calculated, using two different techniques, namely by fitting Tung’s Pinch Off model to each individual I/V -characteristic, or by using M¨onch’s linear relationship between the barrier height and ideality factor, both of which are calculated from the standard Thermionic Emission model. We found that bothmethods are reliable for obtaining the value of the homogeneous Schottky barrier height (which is a unique property of the investigated MS-contact). From the comparison of the obtained homogeneous barrier heights from diodes with a different fabrication process, we confirm the influence of the interfacial Auδ+ − Oδ− dipole on the barrier height. The homogeneous barrier height for the Au/n-GaAs Schottky contacts without the dipole is 0.848 eV , while for the contacts with the dipole, we found a value of 1.021 eV. With this confirmation of the dipole-model, we strengthen the Bond Polarization Theory which states that the SBH is locally determined by the bonding of the atoms forming the interface. The second part evidenced the solid-state formation of carbides from thin metalcarbon films. The different phases of the metal-carbon systems were identified using in situ XRD, completed with ex situ XRD, RBS and XPS. W, Mo, Fe, Cr and V form carbides, while Nb, Ti, Ta and Hf need an extra capping layer to prevent oxidation (30nm C was selected as a good capping layer). Mn and Zr, however, formed oxide phases rather than carbide phases, despite the precautions we took (capping layer, no vacuum break during deposition of the different layers). The phase sequences for the different carbide-forming transition metal-carbon systems, are listed in table 7.19 on page 108, and their formation temperatures (at a heating rate of 3◦C/s) are summarized on page 109 in table 7.20.Furthermore, activation energies were determined for the different carbide formations. For this, in situ XRD measurements at different heating rates were analyzed using a modified Kissinger method. The activation energies are listed in table 8.1 on page 124, and they can be used in the search for the mechanisms which govern the (carbide) phase formation. The last part illustrates the possible application of carbides as contacts for Ccontaining semiconductors. Carbon nanotubes (CNTs) and diamond are some of the most advanced C-containing semiconductors, and they both possess very peculiar, but interesting and useful properties. We give an example of a solid-state reaction between a metal layer (Mo) and CNTs, forming a carbide (in this case Mo2C). Furthermore, we give examples of carbide formation on CVD-diamond, with the same phase sequence as obtained in the previous part. Also, a preliminary research on the electrical characteristics on CVD-diamond was done. We conclude that the crystal structure (and hence the dipoles) at the metal/diamond interface significantly influences the electrical properties. To get a good comprehension of the electrical behaviour of the contacts formed on CVD diamond, one should have good understanding of the metal-diamond interface, and thus first of the diamond surface. Furthemore, the bond-polarization theory is a good starting point for the comprehension of the metal-diamond interface.},
  author       = {Leroy, Wouter},
  language     = {eng},
  pages        = {167},
  school       = {Ghent University},
  title        = {A fundamental study of advanced metal/semiconductor contacts},
  url          = {http://dx.doi.org/1854/9734},
  year         = {2006},
}

Altmetric
View in Altmetric