Investigation of electron-beam deposition and related damage in p-Si by means of Laplace and conventional deep-level transient spectroscopy

Abstract

The study of defects in semiconductors has been on-going for over 50 years. During this time, researchers have been studying the origins and identity of process induced defects, a task which has proved to be very demanding. While defects in silicon, the most widely used semiconductor, have been widely studied, there is more literature on n-type silicon than on p-type silicon. Compared to n-type silicon, p-type silicon is challenging to work with when it comes to making good Schottky diodes. A good rectifying device is essential for the performing of electrical characterisation techniques such as deep-level transient spectroscopy. In spite of this challenge p-silicon cannot be ignored. Many of the electronic devices are a combination of both n- and p-silicon therefore the need to understand the electronic properties of both materials. In this thesis, defects introduced in p-Si by electron beam deposition (EBD) were investigated. In order to understand these defects better, defects introduced by conditions of electron beam deposition (EBD) without metal deposition, were investigated. This process will be referred to as electron beam exposure (EBE). Finally, the defects were compared to defects induced by alpha-particle irradiation. EBD defects, introduced during electron beam deposition (EBD) of titanium (Ti) contacts on p-Si were investigated. The Schottky contacts were annealed within a temperature range of 200–400 oC. Current-voltage (I-V) measurements were conducted to monitor the change in electrical characteristics with every annealing step. Deep-level transient spectroscopy (DLTS) and Laplace-DLTS techniques were employed to identify the defects introduced after EBD and isochronal annealing of the Ti Schottky contacts. DLTS revealed that the main defects introduced during metallisation were hole traps with activation energy of 0.05 eV, 0.23 eV and 0.38 eV. Depth profiles of these defects showed that the formed close to the interface within a depth of 0.4 μm. Defects induced by EBE were studied by exposing samples for 50 minutes after which nickel (Ni) Schottky contacts were fabricated using resistive deposition. Only one defect with an activation energy of 0.55 eV was observed. This activation energy is similar to that of the I-defect. DLTS depth profiling revealed that the defect could be detected up to a depth of 0.8μm below the junction, which is significantly deeper than EBD defects. Defects induced when p-Si was irradiated by alpha particles from a 5.4 MeV americium (Am) 241 foil radioactive source with a fluence rate of 7×106 cm−2 s−1 at room temperature were investigated. After exposure at a fluence of 5.1×1010 cm−2, hole traps with the following activation energies were observed: 0.10 eV, identified as a tri-vacancy related defect, 0.33 eV, the interstitial carbon (Ci), 0.52 eV, a B-related defect and 0.16 eV. Low temperature irradiation experiments were also carried out using alpha- particles with the same fluence rate. Measurements were taken between 35 K and 120 K. The defect levels were at 0.10 eV, 0.14 eV and 0.18 eV. These levels were attributed to the boron-substitutional vacancy complex, the mono-vacancy and a vacancy-related defect, respectively. We conclude that EBD and EBE induced more complex defects than those induced by alpha-particle irradiation.