Photoluminescence Characterization of Defects in Thermal Oxide
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(ESR) spectroscopy.[]] Although it is the most powerful in identification of defects, the ESR technique can only be applied to paramagnetic states of the defects. On the other hand, photoluminescence (PL) spectroscopy has been successfully applied not only to the paramagnetic states of defects such as nonbridging-oxygen hole centers,[2] but to neutral and non-paramagnetic oxygen vacancies[3] in various forms of amorphous SiO (a-SiO 2). While the PL technique lacks structural specificity, it can further provide information such as electronic energy levels of the defects. Successful application of the PL techniques on defects in as-grown thermal oxides and in SIMOX buried oxide (BOX) have been recently made using a synchrotron radiation. [4,5] Although these studies suggest the presence of defects introduced by oxidation of silicon or high-temperature annealing and oxidation, the structures and formation mechanisms are still unknown. In this study, we investigated the PL of defects in thermal oxide grown in dry or wet oxidation conditions. Temperature dependence and time-resolved PL spectra were also investigated. Effects of thermal annealing at various temperatures either in vacuum, Ar or N2 atmosphere were also studied. Formation of defects was explained in terms of the decomposition 289 Mat. Res. Soc. Symp. Proc. Vol. 592 © 2000 Materials Research Society
of SiO2 at the Si/SiO2 interfaces. EXPERIMENTS Samples used in the present experiments were 100-nm thick oxides grown on Si(l00) substrates. They were grown by dry (02, 1000 °C) or wet (H 2/0 2, 900 °C) oxidation. The PL measurements were carried out using a KrF excimer laser (Lambda Physik, MiNex 50) as a light source. The PL from the samples was dispersed by a monochromator (ORIEL M5257) and detected with an ICCD detector (ORIEL Instaspec V). The sample temperature was varied in a cryostat (Iwatani Cryo Mini) with a variable temperature capability. The spectral response of the PL detection system was calibrated using a standard tungsten lamp. Thermnal annealing was
performed either in vacuum (2x10~6 Torr) at 700 °C for 2 h, or in Ar or N2 at 750-900 °C for 1 h. RESULTS AND DISCUSSION Shown in Figs. 1 is a PL spectrum of wet oxide measured at room temperature. Similar PL bands were observed for dry oxide. After the removal of thermal oxide by etching using HF, no PL band was observed in the same energy region. The PL spectra can be deconvoluted into two components at 2.7 eV and 3.1 eV.
0. 6
• 0.5 0.4 0. 3
=-0.2 --
0.1 7
O.01I•2. 0
3. 0
4. 0
PHOTON ENERGY (eV) FLG.I PL spectra obtained for wet oxide measured under excitation at 5.0 eV at room Interestingly, the PL spectra and the peak positions are quite similar to those observed for SIMOX BOX and high temperature oxide grown at 1350 °C (two peak energies: 2.6-2.8 eV, and 3.1 eV) rather than to those of thermal oxide (single peak energy: 3.3 eV) used in the previous study.[4,5] This can be ascribed to the relatively high growth temperature (900 "C or 1000 °C)
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of the thermal oxides used in the pres
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