The work has been directed towards the investigation of the ion implantation doping effects in thin metal and dielectric films so that knowledge may be gained regarding the feasibility of using ion implantation to produce active and passive thin film devices for microcircuits. Measurements concentrated on the detailed conduction properties, structure and composition of the films at varying stages of the ion implantation doping processes. Aluminium and titanium thin films are implanted with oxygen atoms to ion doses of about 1017 ions cm-2. During implantation the films' resistivitess change from that of metal to that of a dielectric. Electron microscope and electron diffraction observations show that as the oxygen dose is increased then metal-oxide clusters form and grow eventually reaching 200 - 300 A. in diameter. The film then consists of a metal/metal oxide matrix and the process of electronic conduction is an activated one, with activation energies of about 0.30 eV for the aluminium/aluminium oxide system and about 0.25 eV for the titanium/titanium oxide system. Evaporated silicon oxide films are doped with aluminium and titanium atoms by the process termed 'recoil atom implantation. This method of doping thin films is shown by use of radioactive measurements to be an effective and efficient method provided the film thickness is less than about 500 A. As the metal atom concentration in the dielectric is increased the resistivity of the film decreases from that of an insulator to that of a metal showing a positive temperature coefficient of resistance. Electron microscopy and electron diffraction studies show that the metal atoms form clusters within the dielectric matrix producing metal/SiO cermet type structures. The conduction properties of the implanted films are explained at low electric field strengths on a conduction model incorporating thermionic emission and quantum mechanical tunnelling mechanisms between homogeneous arrays of spherical metal particles in a dielectric matrix. This model yields potential barrier values, O°, of 0.92 eV and 0,80 eV for the aluminium/aluminium oxide and titanium/titanium oxide material respectively, formed by oxygen ion implantation, and values of 1,00 eV for the dielectric silicon oxide in the case of metal atom implantation. At high electric field strengths the conduction equations are modified by a Poole-Frenkel type emission over a field lowered potential harrier. This manifests itself in log I alpha F1/2andSE alpha F½ dependences, where I is the current, F the electric field and SE the activation energy for conduction. It is concluded that ion implantation can change in an accurate and reproducible way the electrical properties of thin metal and dielectric films and is a feasible method for producing thin film devices with a wide range of properties.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:468723 |
| Date | January 1971 |
| Creators | Perkins, J. G. |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://epubs.surrey.ac.uk/844639/ |
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