Abstract: The thicknesses of a first layer and of a second layer on a semiconductor wafer can be measured together by assuming that the second layer has a substantially uniform thickness. The thicknesses are measured by measuring reflectivity as a function of wavelength at a plurality of points on the wafer to provide a plurality of signatures, comparing each signature with signatures from libraries of theoretical signatures by calculating an error value associated with each signature; and determining the minimum error value. Each library is based upon a unique assumed thickness of the second layer. Thus, the thickness of the second layer is determined by identifying the library associated with the minimum error value.

Abstract: A lockout mechanism for holding a ball valve in a closed condition for prolonged periods, e.g. while machinery that is supplied with pressurized fluid through the valve is being subjected to maintenance operations. The lockout mechanism indirectly provides a safety feature for the workman while he is working on the machinery.