A Correlation Study between XPS and AES Quantitative Analysis of Nitrogen Concentration in Gate Oxide

Accurate characterization of the nitrogen concentration and distribution in ultra thin nitrided silicon gate oxide plays the same important role as the fabrication technology itself during the development of 90nm and beyond gate oxide manufacturing process. Based on the measurement results of XPS (X-ray photoelectron spectroscopy) as reference, a correlation study was taken between XPS and AES (Auger electron spectroscopy) data in this paper. The study shows that, by optimizing the experiment conditions of AES such as beam energy, beam current and take off angle, and introducing proper corrective factor, AES can be used as a useful and reliable characterization tool during the monitoring measurement of Nitrogen concentration in ultra thin (<2nm) nitrided silicon gate oxide.

Plasma Etching of Silicon Dioxide and Silicon Nitride with Non-Perfluorocompound Chemistries: Trifluoroacetic Anhydride and Iodofluorocarbons

Presently, the semiconductor industry relies almost exclusively on perfluorocompounds (e.g., tetrafluoromethane, hexafluoroethane, nitrogen trifluoride. sulfur hexafluoride, and. more recently, octafluoropropane) for the etching of silicon dioxide and silicon nitride films in wafer patterning and PECVD (plasma enhanced chemical vapor deposition) chamber cleaning applications. The use of perfluorocompounds (PFCs) by the industry is considered problematic because of the high global warming potentials (GWPs) associated with these substances. Potential replacements for perfluorocompounds are presently being evaluated at MIT. In an initial stage of the study, intended to screen potential candidates on the basis of etch performance, a large number of compounds is being tested in a commercially available magnetically enhanced reactive ion etch tool. The potential alternatives discussed in this work are trifluoroacetic anhydride (TFAA) and three members of the iodofluorocarbon (IFC) family – iodotrifluoromethane, iodopentafluorocthane, and 2-iodoheptafluoropropane. This paper will present the results of etch rate comparisons between TFAA and octafluoropropane, a perfluorinated dielectric etchant. Designed experiment (DOE) methodology, combined with neural network software, was used to study a broad parameter space of reactor conditions. The effects of pressure, magnetic field, and gas flow rates were studied. Additionally, more limited tests were carried out with the three iodofluorocarbon gases. Etch rate data, as well as Auger electron spectroscopy data from substrates exposed to IFC plasmas will be presented. All gases were evaluated using both silicon dioxide as well as silicon nitride substrates. Results indicate that these compounds may be potentially viable in plasma etching applications.