Nano-Scale Morphology and Electron Spectrum of Defect States in Low-k SiOCH Films
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Nano-Scale Morphology and Electron Spectrum of Defect States in Low-k SiOCH Films V. Ligatchev*, T.K.S. Wong, Rusli, B. Liu, K. Ostrikov School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 SINGAPORE *E-mail: [email protected] ABSTRACT Results of experimental investigations on the relationship between nanoscale morphology of carbon doped hydrogenated silicon-oxide (SiOCH) low-k films and their electron spectrum of defect states are presented. The SiOCH films have been deposited using trimethylsilane (3MS) - oxygen mixture in a 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) system at variable RF power densities (from 1.3 to 2.6 W/cm2) and gas pressures of 3, 4, and 5 Torr. The atomic structure of the SiOCH films is a mixture of amorphous-nanocrystalline SiO2-like and SiC-like phases. Results of the FTIR spectroscopy and atomic force microscopy suggest that the volume fraction of the SiClike phase increases from ~0.2 to 0.4 with RF power. The average size of the nanoscale surface morphology elements of the SiO2-like matrix can be controlled by the RF power density and source gas flow rates. Electron density of the defect states N(E) of the SiOCH films has been investigated with the DLTS technique in the energy range up to 0.6 eV from the bottom of the conduction band. Distinct N(E) peaks at 0.25 - 0.35 eV and 0.42 - 0.52 eV below the conduction band bottom have been observed. The first N(E) peak is identified as originated from E1-like centers in the SiC-like phase. The volume density of the defects can vary from 1011 - 1017 cm-3 depending on specific conditions of the PECVD process. INTRODUCTION Insulating materials with low dielectric constant k (low-k) recently attracted great research interest, as a result of requirements of integrated circuit technology development [1]. As explained in ref. [2], electron spectrum N(E) of states distribution within and just beyond the bandgap of dielectrics predetermines optical and electrical properties of the materials. Thus experimental investigation of the N(E) distribution becomes important both for physics and application of the low-k insulators. Carbon incorporation (doping) of the silicon dioxide reduces essentially the effective k value of the material. The carbondoped hydrogenated silicon dioxide SiOCH films were deposited from a tri-methyl-silane (3MS) - oxygen mixture using radio frequency (RF) 13.56 MHz plasma in a plasma enhanced chemical vapor deposition (PECVD) system. Fourier-transform infra-red (FTIR) spectroscopy, atomic force microscopy (AFM) and X-ray diffraction (XRD) are applied for atomic structure and nanoscale morphology investigations in the material. The N(E) distribution is measured by capacitance deep-level-transient-spectroscopy (C-DLTS).
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EXPERIMENT DETAILS Three series of SiOCH samples were deposited. For these deposition, the total pressure of the 3MS-O2 mixture equal of 3, 4 and 5 Torr. The ratio of 3MS to oxygen flow rate is 6. The radio frequency (RF) power density is changed
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