Effects of deposition conditions on the spatial variation of dielectric thin film properties on nonplanar surfaces

Silicon dioxide films deposited by chemical vapor deposition (CVD) techniques are commonly used as gate isolation, inter-metal, or inter-level dielectrics. A variety of CVD methods are now used in the IC industry, including low pressure CVD (LPCVD), plasma-enhanced low pressure CVD (PECVD), and high-density plasma CVD (HDPCVD). CVD thin films are frequently deposited into the gaps between metal lines and onto non-planar surfaces, which are common in multilevel interconnect structures. Because of the topography and spatial variations in deposition parameters, properties of these films, such as capacitance and density, vary with position, and film quality is not uniform. This non-uniformity problem becomes more serious as the technology advances toward smaller scales and more aggressive surface topographies with high aspect ratio trenches and vias are used. For better process integration and equipment design, more knowledge and understanding of these deposition processes are needed to help optimize process design.; This work involves the study of silicon dioxide films deposited with LPCVD, PECVD, and HDPCVD. Special emphasis is placed on the non-uniform distribution of physical properties in cases where the films are deposited onto non-planar surfaces such as trenches. Quasi three-dimensional experimental methods for film characterization using atomic force microscopy (AFM) were developed and used on test structures, and the spatial variation of film density in those structures has been obtained. The effects of deposition conditions were studied with a combination of characterization techniques such as Fourier transform infrared spectroscopy (FTIR), AFM, Grazing Incidence X-ray Scattering (GIS) technique, ellipsometry, and film etch rate measurements. In addition to the experiments, computer simulations with a film deposition simulator called SPEEDIE (Stanford Profile Emulator for Etching and Deposition in IC Engineering) were performed to obtain various gas flux and plasma parameters within small surface structures. Results from these experiments and simulations were used to construct models regarding the effect of deposition conditions on the film properties. This work discusses topics such as the effect of neutral precursor gases versus charged ionized gases, the effect of angular distribution of deposition flux, and the effect of kinetic ion kinetic energy.; The results obtained from the study suggest that the film etch rates and densities of the PECVD dielectric films deposited inside the gaps vary spatially, especially around the bottom corners of the gaps. There is also a direct correlation between the ion flux and the film property variation. High spatial resolution (∼10 nm) two-dimensional measurement of the etch rate showed that the correlation between the etch rate and ion flux can be represented with a simple mathematical expression. The observed etch rate variation phenomena could be simulated with a simple model involving the angular distribution of ions. Further examinations using the high-energy x-ray diffraction and FTIR also revealed that atomic level film structure parameters such as the silicon-oxygen bonding distance and the Si-O-Si bonding angle vary with the ion flux density and the kinetic energy of the ions. This means that the film structure modification caused by the energetic particles such as ions is at least partly responsible for the densification of the film and non-uniform distribution of the film properties.