The effect of film thickness on the resistivity of thin, evaporated copper films (approximately 10 nm to 150 nm thick) was determined from sheet resistance, film thickness, and mean grain-size measurements by using four-point probe, profilometer, and electron backscatter diffraction (EBSD) and X-ray diffraction methods, respectively. The resistivity of these films increased with decreasing film thickness in a manner that agreed well with the dependence given by a versatile simulation program, described earlier, using the measured values for the mean grain size and fitting parameters for surface and grain boundary scattering. Measurements of the change in sheet resistance with temperature of these films and the known change in resistivity with temperature for pure, bulk copper were used to calculate the thickness of these films electrically by using Matthiessen?s rule. These values agreed to within 3 nm of those obtained with the profilometer. Hence, Matthiessen?s rule can continue to be used to measure the thickness of a copper film and, by inference, the cross-sectional area of a copper line for dimensions well below the mean free path of electrons in copper at room temperature (39 nm).
Citation: Microelectronics Reliability
Pub Type: Journals
copper metalization, electron backscatter detection, four-point probe, nanotechnology, resistivity, semiconductor, x-ray diffraction