Dummy filling methods for reducing interconnect capacitance and number of fills

Abstract

In recent system-on-chip (SoC) designs, floating dummy metals inserted for planarization have created serious problems because of increased interconnect capacitance and the enormous amount of fill required. We present new methods to reduce the interconnect capacitance and the amount of dummy metals needed. These techniques include three ways of filling: (1) improved floating square fills, (2) floating parallel lines, and (3) floating perpendicular lines (with spacing between dummy metals above and below signal lines). We also present efficient simple formulas for estimating the appropriate spacing and number of fills. In our experiments, the capacitance increase using the traditional regular square method was 13.1%, while that using the methods of improved square fills, extended parallel lines, and perpendicular lines was 2.5%, 2.4%, and 1.1%, respectively. Moreover, the number of necessary dummy metals can be reduced by two orders of magnitude through use of the parallel line method.