S.V. Patel, R.A. Gerhardt
Georgia Institute of Technology,
Keywords: film thickness, edge effects, accurate electrical characterization
Summary:Insulating films such as silicon dioxide (SiO₂) have a variety of microelectronic applications because of the compound's insulating and dielectric properties. When measuring the electrical properties of a metal oxide film like silicon oxide, it is important to note that several factors must be taken into account. In characterizing the properties of thin films, it becomes crucial to take into consideration parameters such as thickness of the deposited material, homogeneity of the sample, surface roughness and its susceptibility to edge effects. If these features are not all accounted for, a drastically different electrical response may be obtained from a thin film material, which will undermine the repeatability that is necessary to implement the material in a given application. For this study, the relationship of interest is the correlation between the thickness of deposited SiO₂ material and the role of edge effects in the impedance response of the sample. Previous related work that has been done in the lab group has focused on factors that affect the characterization of films at the nanoscale level. This research has explored properties that affect the impedance response of a film, such as the composition of the film's substrate, the film's thickness and the size of the contacts used to make measurements on the surface of the film. These factors must all be taken into account when measuring the impedance response, because they are all interdependent when it comes to electrically characterizing a material. In 2009, the Gerhardt lab group presented work detailing the extent to which the thickness of a film's substrate can affect the measured impedance response and its corresponding capacitance. Numerical simulations for HfO2 films ranging from 10 to 1000 nm thick, assuming a substrate Si thickness of 500 μm, showed that it is impossible to make accurate in-plane measurements when the contact size is too small or the film is too thick. This work was later extended to include SiO2 films, where the effects are even more drastic. How varying the thickness of a thin film changes its electrical properties is currently essentially unexplored in materials research today. Furthermore, the research conducted on this topic thus far does not take into account the presence of edge effects, which from previous experimentation, have been proven to indeed affect a film's characterization. By taking samples of varying thicknesses of deposited silicon oxide and measuring the impedance response at edge locations, a clear correlation can be seen between the thickness of a sample and its susceptibility to edge effects. Depending on the orientation of an insulating sample in a given application, the expected impedance response could be highly variable. The data from this experimentation could be useful for applications involving thin film materials, as it will bring into consideration potential causes for error that otherwise might not have been known.