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- FG Angewandte Physik und Halbleiterspektroskopie (3) (remove)
In this thesis the detailed investigations concerning processing and stability of thin films including carbon species and their possible application as materials of a low dielectric constant (low k) are presented. In order to gather a complex information regarding the chemical, morphological and dielectric properties of the produced layer a combination of the spectroscopy: X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS) and Fourier transform infrared spectroscopy (FTIR), microscopy: atomic force microscopy (AFM) and electrical characterization: capacitance-voltage technique (CV) have been applied. The films deposited by means of variety of techniques have been described, ranging from evaporation, through spraying and dropping to spin-coating. Regarding the possible low-k application, a considerable attention has been paid to the hybrid organic-inorganic 3-aminopropyl-trimethoxysilane (APTMS) based composite materials enriched with carbon species coming from the following dopants: C60 fullerenes, [6,6]-phenyl-C61-butyric acid (PCBM), copper phthalocyanine (CuPc), and tris(dimethylvinylsilyloxy)-POSS (POSS). In the following thesis progressive steps leading to gradual decreasing of the resulting permittivity of the hybrid material is presented. As revealed by the performed investigations, the replacement of C60 within the APTMS based matrix by its better soluble derivative PCBM allows the increase of the concentration of the carbon species within the composite films. The introduction of POSS as an additional dopant gave the opportunity of increasing the resistance of the produced material against the ambient influence. With the excess of the POSS concentration an original fractal-shaped cluster formation has been observed. Finally, the dispersion of the properly chosen low concentration of CuPc and POSS molecules within the APTMS based matrix led to the fabrication of homogenous layer with an ultra-low dielectric constant of 1.8.
Modern dielectrics in combination with appropriate metal electrodes have a great potential to solve many difficulties associated with continuing miniaturization process in the microelectronic industry. One significant branch of microelectronics incorporates dynamic random access memory (DRAM) market. The DRAM devices scaled for over 35 years starting from 4 kb density to several Gb nowadays. The scaling process led to the dielectric material thickness reduction, resulting in higher leakage current density, and as a consequence higher power consumption. As a possible solution for this problem, alternative dielectric materials with improved electrical and material science parameters were intensively studied by many research groups. The higher dielectric constant allows the use of physically thicker layers with high capacitance but strongly reduced leakage current density. This work focused on deposition and characterization of thin insulating layers. The material engineering process was based on Si cleanroom compatible HfO2 thin films deposited on TiN metal electrodes. A combined materials science and dielectric characterization study showed that Ba added HfO2 (BaHfO3) films and Ti added BaHfO3 (BaHf0.5Ti0.5O3) layers are promising candidates for future generation of state of the art DRAMs. In especial a strong increase of the dielectric permittivity k was achieved for thin films of cubic BaHfO3 (k~38) and BaHf0.5Ti0.5O3 (k~90) with respect to monoclinic HfO2 (k~19). Meanwhile the CET values scaled down to 1 nm for BaHfO3 and ~0.8 nm for BaHf0.5Ti0.5O3 with respect to HfO2 (CET=1.5 nm). The Hf4+ ions substitution in BaHfO3 by Ti4+ ions led to a significant decrease of thermal budget from 900°C for BaHfO3 to 700°C for BaHf0.5Ti0.5O3. Future studies need to focus on the use of appropriate metal electrodes (high work function) and on film deposition process (homogeneity) for better current leakage control.
We have grown HfO2 on Si(001) by atomic layer deposition (ALD) using HfCl4, TEMAHf, TDMAHf and H2O as precursors. The early stages of the ALD were investigated with high-resolution photoelectron spectroscopy and x-ray absorption spectroscopy. We observed the changes occurring in the Si2p, O1s, Hf4f, Hf4d, and Cl2p (for HfCl4 experiment) core level lines after each ALD cycle up to the complete formation of two layers of HfO2. The investigation was carried out in-situ giving the possibility to determine the properties of the grown film after every ALD cycle or even after a half cycle. This work focused on the advantages of the in-situ approach in comparison to ex-situ experiments. The study provides to follow the evolution of the important properties of HfO2: contamination level, density and stoichiometry, and influence of the experimental parameters to the interface layer formation during ALD. Our investigation shows that the in-situ XPS approach for ALD gives much more information than ex-situ experiments.