Control and design of critical properties of PECVD carbon doped low-k silica thin films by deposition methods and film thickness.

摘要

On-chip interconnect has become a critical barrier to a continuing scaling down of IC devices. Copper is expected to alleviate the resistance problem for next few generations, the capacitance problem is expected to be alleviated by reducing the dielectric constant of intermetal dielectric that isolated conducting lines from each other. However, this later task cannot be fulfilled by simply finding a material with a low dielectric constant (low-k). The low-k materials should meet strict requirements in terms of its dielectric constant loss, moisture resistance, thermal stability and mechanical properties. Carbon doped silicon dioxide seems to meet the requirements and is expected to find wide applications as IMD.; With the decrease of device sizes, thinner and thinner dielectric films will be employed for insulation. As expected, the film properties will deviate from that of their bulk counterparts due to the constraints imposed by thin film geometry. It is found from our recent studies that most of the structural, optical, mechanical, electrical, dielectric and thermal properties of the films are thickness dependent. Thus, the thickness dependent dielectric thin film properties becomes an important IC design and manufacturing concern.; This work presents the thickness and deposition dependence of thermal, optical, dielectric, electric properties of low-k carbon doped silicon thin films. Low-k dielectric carbon-doped silicon dioxide films created by Plasma Enhanced Chemical Vapor Deposition (PECVD) using a six-station sequential deposition system and films created by PECVD in a single deposition station were studied with varying thickness. A thickness dependent glass transition model was obtained and was found to well explain the observed experimental data. The thickness and temperature dependent refractive index have also been investigated using an optical spectrometer coupled with a hot stage. The observed results were explained by the microstructure of the thin films studied by Fourier transform infrared spectroscopy.; The experimental results obtained on the dielectric strength EB of carbon doped silicon dioxide thin films for various film thicknesses using I-V measurements with metal-insulator-semiconductor (MIS) structures suggest a new relationship between the film thickness d and the dielectric strength E_B, i.e.,{09}E_B ∝ ( d − d_c)−n. This inverse power law relationship indicates the existence of a critical thickness d_c which may correspond to an ultimate thickness limit below which the rate of detrapping of electron charges exceeds the rate of trapping and no dielectric breakdown can be observed. The temperature and deposition method dependence of exponential parameter n and critical thickness limit d_c, the conduction mechanism and time dependent dielectric breakdown have also been investigated and discussed.