VINSE has recently added a JA Woollam M-2000DI spectroscopic ellipsometer to the Cleanroom core facility, providing an additional option for users to quickly characterize thin films when developing recipes for deposition, etching, and spin coating processes. This instrument complements the existing JA Woollam M-2000V ellipsometer in the VINSE Analytical Lab. Both systems are used to characterize film thickness (sub-Angstrom sensitivity to tens of microns) and refractive index of single and multi-layer coatings of a variety of materials such as organics, dielectrics, semiconductors, or thin metals. The comparison table highlights the features of each:
Ellipsometry is a non-destructive technique in which a broadband source light impinges on a sample with an incident angle ~65° from sample normal. This light is partially reflected and refracted at the various interfaces of the thin film stack and then collected. The change in polarization state between the incident and collected light ismeasured as a function of wavelength, and then users create models of the film stack to best match the experimental data with fitting parameters such as film thickness and materials’ optical properties. Data collection only takes a few minutes, and modeling of the data can be relatively straightforward or complex depending on the nature of the sample.
Modelling a single transparent material on an absorbing substrate, like SiO2 on a silicon wafer, is easy with built-in software models. More complex models may include multiple layers and combinations of transparent and absorbing films. Practically, it is recommended to start by characterizing a single layer on a substrate and building up to a complex model if needed in order to get reasonable results. A material library is built into the CompleteEASE™ software with optical properties of many materials with literature references, and it is also possible to create user material files that are more representative of one’s own fabrication processes.
VINSE wishes to thank Professor Bridget Rogers in the Chemical and Biomolecular Engineering Department for donating the JA Woollam M-2000DI system to the Cleanroom.
For questions or training, please contact VINSE Cleanroom staff at vinse-cleanroom@vanderbilt.edu. Trained users on the Analytical Lab ellipsometer must be re-trained before using the Cleanroom ellipsometer.