| AVS 64th International Symposium & Exhibition | |
| Electronic Materials and Photonics Division | Thursday Sessions |
| Session EM-ThP |
| Session: | Electronic Materials and Photonics Poster Session |
| Presenter: | Faraz Choudhury, University of Wisconsin-Madison |
| Authors: | F.A. Choudhury, University of Wisconsin-Madison G. Sabat, University of Wisconsin-Madison M.R. Sussman, University of Wisconsin-Madison Y. Nishi, Stanford University J.L. Shohet, University of Wisconsin-Madison |
| Correspondent: | Click to Email |
During plasma processing, dielectric films are exposed to a high concentration of free radicals that can affect the processing conditions and the properties of materials exposed to the plasma. Measuring the absorption lengths and penetration depths of free radicals is critical in order to determine their effects on the dielectric materials. Using radical-sensitive fluorescent dyes and free-standing films, the transmission of oxygen radicals through silicon nitride and silicon dioxide dielectric films is measured. The absorption length of the oxygen radicals is determined by measuring the number of transmitted radicals as a function of the thickness of the freestanding films. For silicon nitride films, the absorption length was found to be 33 nm for 15-minute oxygen plasma exposure. The absorption lengths increased to 37 and 40 nm for 30 minute and 45-minute plasma exposures, respectively. FTIR measurements showed a decrease in Si-N bond concentration after plasma exposure and a subsequent appearance of Si-O-Si bonds. In addition, the density vs. depth profiles of the pristine and plasma exposed films were obtained from specular x-ray reflectivity (XRR) measurements which showed that the plasma exposure forms a silicon oxynitride-like layer on the surface of the film which has a lower density than silicon nitride. The increase in absorption length with plasma-exposure time is attributed to the formation of the surface layer. In silicon dioxide films, the absorption length of oxygen radicals was found to be ~70 nm after 20 minutes of plasma exposure. After 30 minutes of plasma exposure under the same conditions, the absorption length was reduced to ~66 nm. XRR and FTIR measurements both reveal that the oxygen plasma exposure leads to further oxidation of the silicon dioxide film and the formation of a denser surface layer which restricts the transmission of the radicals through the film.
This work was supported by the Semiconductor Research Corporation under Contract 2012-KJ-2359