Materials for ULSI metallization - Overview of Electrical Properties

Since performance of ULSI Si devices was found to be controlled by RC delay (where R is the electrical resistance at the interconnects and C is the capacitance of the insulators), efforts have been continued to reduce the wiring resistance and the insulator capacitance. Replacement of aluminum alloy interconnect materials by copper (which has about 40% lower resistivity compared with the aluminum alloy) reduced not only the device switching times but also the fabrication cost. However, the resistivity of the Cu wires was demonstrated experimentally to increase rapidly [1, 2] when the line width approached to the mean free path (∼39 nm) of the conducting electrons as predicted by theories [3–5]. Figure 9.1 shows theoretical resistivity calculated as a function of line widths with two average grain sizes (D) using Mayadas and Shatzkes (MS) model [5] with P = 0 and R = 0.5, which were experimentally determined [2].