Method of measuring dishing using relative height measurements

Abstract

A metrology process, in accordance with the present invention, measures the dishing of a feature, such as a copper, aluminum, or tungsten metal line, with respect to another feature, such as a dielectric layer, that surround the first feature by measuring the relative heights of varying line widths of the first feature with respect to the second feature. The relative heights are adjusted to correspond to the actual dishing value using a calibration point of a calibration line width and a calibration dishing value. The metrology process is useful, for example, after the metal and dielectric materials undergo a polishing process, e.g., CMP, to approximately planarize the surface. The calibration data provides a dishing value at a specific, relatively, small line width. The relative heights of various line widths are measured on production substrates. These relative heights are plotted as a function of line width. The curve is then extrapolated to the line width used during calibration. The resultant curve is then shifted so that the line width used for calibration intersects the horizontal line running through the dishing value measured during calibration. The actual dishing values can then be read from the shifted curve. Values from the calibration line width to the widest feature measured can be obtained. In addition, different sets of calibration data may be generated based on different parameters used in the polishing process. The relative heights of the metal lines are measured using, e.g., a differential interferometer or a laser displacement sensor.