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The thickness of Al thin films on 1000A SiO2 was estimated by using X-ray fluorescence (XRF). It was found thatA when the films were less than 1000A thick, the number of Al XRF counts was directly proportional to the Al thickness. Therefore, Al thickness is given by t=a(If-Bg) within an error of 3.0%, where a and Bg are constant and background noise, and If is the Al XRF count. In the Al film thicknes range of 2000A to 1.2 μm, XRF counts vs. Al thickness becomes nonlinear due to Al self-absorption. The Al thickness was given by t=-a·ln(1-(If-Bg/Imax)), where Imax is maximum value measured by Al XRF. The maximum relative error was 1.6%. However, for the Al film thickness range of 1000A to 2000A, the relative error was 9.7%.

An Electron Microprobe Auger Spectroscopy was applied to investigate interactions between Al film and thermally grown silicon dioxide (SiO2) in order to examine the failure occurred for very thin Al film on SiO2 surface during heating and stressing tests. It was found that the oxidation mechanism of Al film was different on Al film surface from that at the interface between Al and SiO2 during heating in vacuum at 400-500°C for 30 min. Also, the depth of penetration of Al into SiO2 was found to be unexpectedly large. As a result of stressing test, chained hillocks appeared along the direction of electron flow in the case of very thin Al film. This Phenomenon may be due to diffusion of Si into Al film by heating during device process.