Effects of Thermal Annealing on the Structural and Optical Properties of Carbon-Implanted SiO₂

Abstract

Amorphous carbon (a-C) nanoclusters were synthesized by the implantation of carbon ions (C-) into thermally grown silicon dioxide film (-500 nm thick) on a Si (100) wafer and processed by high temperature thermal annealing. The carbon ions were implanted with an energy of 70 keV at a fluence of 5 x 10(17) atoms/cm2. The implanted samples were annealed at 1100 degrees C for different time periods in a gas mixture of 96% Ar+4% H2. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM) were used to study the structural properties of both the as-implanted and annealed samples. HRTEM reveals the formation of nanostructures in the annealed samples. The Raman spectroscopy also confirms the formation of carbon nano-clusters in the samples annealed for 10 min, 30 min, 60 min and 90 min. No Raman features originating from the carbon-clusters are observed for the sample annealed further to 120 min, indicating a complete loss of implanted carbon from the SiO2 layer. The loss of the implanted carbon in the 120 min annealed sample from the SiO2 layer was also observed in the XPS depth profile measurements. Room temperature photoluminescence (PL) spectroscopy revealed visible emissions from the samples pointing to carbon ion induced defects as the origin of a broad 2.0-2.4 eV band, and the intrinsic defects in SiO2 as the possible origin of the -2.9 eV bands. In low temperature photoluminescence spectra, two sharp and intense photoluminescence lines at -3.31 eV and -3.34 eV appear for the samples annealed for 90 min and 120 min, whereas no such bands are observed in the samples annealed for 10 min, 30 min, and 60 min. The Si nano-clusters forming at the Si-SiO2 interface could be the origin of these intense peaks.

Structural and optical properties of 70-keV carbon ion beam synthesized carbon nanoclusters in thermally grown silicon dioxide

“…In the spectrum of the as-implanted sample, two broad PL peaks centered at around 2.4 and 2.9 eV are clearly seen. A similar 2.9 eV broad-band peak without the 2.4 eV peak was also observed in the thermally grown SiO 2 film (not shown here) [4]. This indicates the possibility that carbon implantation induces the 2.4 eV PL peak.…”

“…However, these carbon nanoclusters were gradually lost from the samples during the annealing for more than 30 min [4]. The implanted carbon evaporated completely out of the SiO 2 sample after the 2 h of annealing [4]. In the present study, in order to overcome the problem of carbon loss from the SiO 2 layer, the carbon-implanted samples were annealed at a lower temperature (900°C) to form well-organized carbon nanoclusters.…”

“…Studies of such nanostructures (silicon or other elemental clusters) have been motivated by the observed variation of luminescence wavelengths with the size and location of nanostructures in silicon [2]. Ion implantation is a well-established technology to form luminescent structures in Si-based substrates [3][4][5][6]. Postimplantation thermal annealing in various gas or vacuum environments is usually employed to precipitate the implanted ion species leading to the formation of nanostructures of the implanted species and/or substrates.…”

“…96 % Ar). However, these carbon nanoclusters were gradually lost from the samples during the annealing for more than 30 min [4]. The implanted carbon evaporated completely out of the SiO 2 sample after the 2 h of annealing [4].…”

ION BEAM MATERIALS ANALYSIS AND MODIFICATIONS AT keV TO MeV ENERGIES AT THE UNIVERSITY OF NORTH TEXAS

“…The Si rich nanocrystals formed at the SiO 2 -Si interface are attributed as the origin of these two intense peaks seen in the annealed samples. 11,29 Figure 4(a) shows the TEM image of nanoclusters synthesized by multiple lowenergy (58, 68 and 78 keV) Ag ion irradiations in Si wafer and post-thermal annealing in a gas mixture of 4% H 2 + 96% Ar gas at 500 °C below the Ag-Si eutectic temperature of 841 °C. The size distribution of the nanoclusters are shown in Fig.…”