SiC-Like Phase and Room-Temperature Photoluminescence of Low-K SiOCH Films
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SiC-Like Phase and Room-Temperature Photoluminescence of Low-K SiOCH Films V. Ligatchev*, T.K.S. Wong, Rusli, B. Liu, School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 SINGAPORE *E-mail: [email protected] K. Ostrikov SOCPES, The Flinders University of South Australia, GPO Box 2100, Adelaide 5001 SA, AUSTRALIA ABSTRACT Carbon-doped hydrogenated silicon oxide (SiOCH) low-k films have been prepared using 13.56 MHz discharge in trimethylsilane (3MS) - oxygen gas mixtures at 3, 4, and 5 Torr sustained with RF power densities 1.3 - 2.6 W/cm2. The atomic structure of the SiOCH films appears to be a mixture the amorphous SiO2-like and the partially polycrystalline SiC-like phases. Results of the infra-red spectroscopy reflect the increment in the volume fraction of the SiC-like phase from 0.22 - 0.28 to 0.36 – 0.39 as the RF power increment. Steady-state near-UV laser-excited (364 nm wavelength, 40±2 mW) photoluminescence (PL) has been studied at room temperatures in the visible (1.8 eV – 3.1 eV) subrange of photon spectrum. Two main bands of the PL signal (at the photon energies of 2.5 – 2.6 eV and 2.8 - 2.9 eV) are observed. Intensities of the both bands are changed monotonically with RF power, whereas the bandwidth of ~0.1 eV remains almost invariable. It is likely that the above lines are dumped by the non-radiative recombination involving E1-like centres in the amorphous-nanocrystalline SiC-like phases. Such explanation of the PL intensity dependences on the RF power density is supported by results of experimental studies of defect states spectrum in bandgap of the SiOCH films. 1. INTRODUCTION AND FILM TECHNOLOGY Insulating materials with low dielectric constant k (low-k) recently attract great research interest, which is originated by modern requirements of integrated circuit technology development. Atomic structure and electron spectrum of dielectrics obviously predetermine optical and electrical properties of these materials. Room-temperature photoluminescence from such films may have own practical importance, and also can reflect specific features of the electron states distribution. Thus, results of experimental investigations of the structural properties and photoluminescence in low-k insulating films are important both for fundamental aspects and for applications. The low-k films have been prepared using the 3MS - oxygen mixture decomposition by radio frequency (RF, 13.56 MHz) discharge in the plasma enhanced chemical vapor (PECVD) deposition system. The PECVD method is chosen due to its wide application in the semiconductor industry. The 3 MS advantages include ease of handling and possibility of depositing both the low-k dielectrics and low-k barrier materials from the same source [1]. RF power density is varied from 1.3 to 2.6 W cm-2, while total pressure of the gas mixture equals of 4 Torr. The SiOCH thickness is in the 0.28 – 0.68 µm range. The p-type (1 - 10 Om*cm) single-side polished silicon plates are used as substrates.
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2. EXPERIMENTAL DETAIL
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