Abstract
PART Ⅰ Cu Metallization in ULSI Barrier layer (Ta, TaN) and porous low-k materials (porous HSQ, PPSZ) for ULSI metallization applications have been investigated. The physical and electrical characteristics of these materials have been investigated. The microstructures and phases of Ta-N films deposited with various N2/Ar gas mixtures have been investigated by Rutherford backscattering spectrometry, transmission electron microscope, X-ray diffraction, and sheet resistance measurement. Ta and Ta-N films sputtered with pure Ar, 10%, 20%, 30%, 40%, 50%, and 60% N2/Ar gas ratios were found to be a mixture of □-Ta and bcc-Ta, bcc-Ta, bcc-TaNx, expanded bcc-TaNx, hcp-Ta2N, fcc-TaN, and fcc-TaN (nearly amorphous) phases, respectively. The resistivity was found to increase with nitrogen content in samples deposited with 10 to 60% N2/Ar. For Cu layers deposited on these films, Cu (111)/(200) ratio was decreased with the nitrogen content of Ta-N films. The structural and electrical properties of porous hydrogen silsesquioxane (XLK) have been characterized using a combination of Fourier transform infrared spectroscopy, transmission electron microscope, Auger electron spectroscopy, current-voltage analyzer and capacitance-voltage analyzer. The pores, about 2 nm in size and of spherical shape, were distributed randomly and uniformly in the XLK film. A smooth amorphous-like layer including Cu-O-Si was found to form between Cu and the XLK film after annealing at 500 □C for 30 min. Cu was found to diffuse into XLK film after annealing at 600 □C for 30 min. The dielectric constant of porous polysilazane (PPSZ) film was as low as 2.2 owing to the high porosity and uniformity of the film. The copper silicide was found to form between Cu and the PPSZ film after annealing at 550 □C for 30 min due to the SiO desorption from PPSZ. The copper silicide reacts with oxygen to form Cu and SiO2 at room temperature. The leakage current of the broken PPSZ film after annealing at 550 □C for 30 min was found to decrease with exposure in air for a few days at room temperature. PART Ⅱ Nanostructures Synthesis and growth mechanism of Cu nanostructures (Cu nanotubes, Cu nanobats) have been investigated. . Cu nanotubes have been synthesized using silicon oxide nanowires as templates. The silicon oxide nanowires were coated with a thin and uniform copper layer by metalorganic chemical vapor deposition (MOCVD) method. Hollow Cu nanotubes were then produced by etching away the inner silicon oxide templates with dilute HF solution. Metal-organic chemical vapor deposition method has been used to grow Cu nanorod without metal catalysts. Pentagonal Cu nanobats with five-fold symmetry were successfully synthesized without capping reagents by MOCVD. Cu nanorods are of bat shape and the average diameters of the head and tail of the Cu nanobats are 100 nm and 50 nm, respectively. Both elongation along the five-fold symmetry axis and lateral growth of exterior twins were found to be important in the growth of pentagonal Cu nanobats. The Cu nanobats possess strong field emission characteristics. In order to investigate the stability of ZnS nanotubes, in-situ TEM was used to observe the morphological changes in a heating process. Four amorphous and crystalline C layers were found to form consecutively on the surface of ZnS-C nanotubes. C and N species would decompose and evaporate from ZnS-C nanotubes. The electron beam stabilized the C vapor and promoted the formation of amorphous C layer on the ZnS-C(N) nanotubes.