Two-dimensional current flow in the MOSFET source—Drain

Series resistance within the metal-oxide-semiconductor field-effect transistor erodes some of the performance improvement inherent to channel length reduction. The subject of series resistance, then, assumes greater importance as transistor dimensions shrink. Since current crowding effects at the source-drain ohmic contact and at the junction of the source-drain and the channel increase the apparent series resistance, we have studied current flow and its associated nonuniformity by two analytical solutions of Laplace´s equation with appropriate boundary conditions. We show typical results of these solutions, discuss the effect of device scaling on the current flow, and present simulation data for the self-aligned silicide field-effect transistor. The implicit assumption that the ohmic contact and source-channel current crowding contribute independently to the apparent source resistance fails for these self-aligned silicide devices.