Low and High Energy Ion Beams in Nanotechnology

Detta är en avhandling från Avd. för Kärnfysik, LTH, Box 118, 221 00 Lund

Sammanfattning: In this thesis, two ways of fabrication of nanometer-sized semiconductor features are presented. Low Energy Ion Implantation (LEII) has been used to create shallow (sub-50 nm) and laterally small (5 m m – 200 nm) features by 10 keV As+ doping of B background doped Si. Surface topography and electrical modification has been characterised using Atomic Force Microscopy (AFM) and Scanning Capacitance Microscopy (SCM), respectively. Results of as-implanted samples showed highly resistive swelled structures with sharp contrast using an Electron Beam Lithography (EBL), metal lift-off and LEII scheme as means of fabrication. Qualitatively, it was also found that structure edges showed an increased swelling, which was believed to be related to various mask edge effects. A second method is presented for materials modification of buried GaInAs quantum layers in InP. This has been done by the development of the Switched Ion Channelling Lithography (SICL) technique. A 10 MeV Ga3+ ion beam channels through the single InP/GaInAs/InP crystal structure. The SICL method is carried out by depositing a small nanometer-sized scatterer by Electron Beam Lithography (EBL) to induce a dechannelling fraction of ions, which induces mixing in the quantum layer resulting in a bandgap shift. The SICL technique makes use of the small lateral spread given by a high energy ion beam as compared to a low energy ion beam. Furthermore, channelling ions induces much less damage and therefore the ion beam can be in principle of any size, as long as a certain fraction of the ions induces random collision damage of a well-defined lateral size. Bandgap shifts up to 28 meV are shown using photoluminescence (PL) as the means of characterisation. The second part of the thesis deals with the characterisation of thin magnetic multi-layers with the goal of using IBA methods as a method for characterising the long-term stability of commercial disk media. A complementary method for investigating these thin films is presented, which uses Particle Induced X-ray Emission (PIXE) to identify material constituents with atomic numbers above 13, and Time-of-Flight Energy Elastic Recoil Detection Analysis (ToF-E ERDA) to obtain depth profiles. Furthermore, a simple accelerated ageing test of commercial removable hard disk media was carried out to investigate the possibility to use IBA methods for monitoring any changes that disks might undergo as time goes by. Results showed increasing damage in the outermost layer as temperature increased, while a study with disks in high humidity at an elevated temperature showed little or no difference. Last, m -Rutherford BackScattering (m -RBS) has been used to investigate local loading effects for thin SiGe structures in a SiO2 mask made using optical lithography. Non-Selective Epitaxial Growth (NSEG) was used to grow thin SiGe layers with the goal of investigating if active area induces any growth rate dependence. Structures, down to 22 m m ´ 22 m m, were successfully resolved using m -RBS, showed no or a small loading effect as a function of active area.

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