AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP27
How Thick is my Oxide?

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Surface Science Poster Session
Presenter: D.D. Allred, Brigham Young University
Authors: D.D. Allred, Brigham Young University
S. Lunt, Brigham Young University
Correspondent: Click to Email
"How thick is the oxide on this sample?" is a question is frequently heard in the lab. After a thin film is removed from the deposition system, exposing it to air on its top surface, it can begin to tarnish. I will review our work in determining the kinetic constants required to answer the question posed, to estimate the thickness of the tarnish layer as a function of time and temperature for several thin film metal exposed to laboratory air at temperatures near ambient for times up to several thousand hours. The thickness and composition of the tarnish layer is important, particularly when it is to be used in an application, such as for gate oxides for ULSI devices, for which understanding and controlling the thickness of ultrathin oxide layers is important. Our EUV optics deposition group also labors in an area where the thickness of ultrathin post deposition films is extremely important. We have looked for a single, or set of, papers which would help us answer this question for materials of interest for the extreme ultraviolet optics (EUV) community. Since the data could not be found in the literature, we resolved to measure and report them. We have studied the tarnishing of a variety of very thin metal films (typically 3-30 nm) including: Al, several of the 3-d metals (e.g. Sc, V, Cr, Fe), one each of the 4d (Ru) and 5d (W) metals and U, and UO2 in laboratory air at temperatures near ambient for several months. We have used spectroscopic ellipsometry, AFM, XPS, and low-angle x-ray diffraction in this work. The tarnish formed is not the familiar bulk oxide for Al and some other cases. We will focus particularly our progress in understanding the stages of oxidation in the 2-6 nm range, thicker than is usual for surface studies but thinner than most corrosion work. We will also show that EUV reflectance is itself a sensitive tool for measuring the thickness of ultrathin oxide films such as SiO2 and UO2.