Aspect ratio dependent plasma-induced charging damage in rf precleaning of a metal contact

As the packing density increases in the fabrication of semiconductor chips, the aspect ratio and the critical dimension (CD) of a metal contact are exponentially aggravated in dry etch processing. The aspect ratio dependency of plasma-induced charging damage during the rf precleaning of a metal contact has been evaluated with a two-dimensional Monte Carlo simulation and with related experiments. From the simulation of a metal contact opened on a gate metal, it is found that the potential on a metal contact bottom, which is directly related to plasma-induced charging damage, is saturated near an aspect ratio of 4 after initially linearly increasing with the aspect ratio. However, the linear decrease of CD of a metal contact exponentially increases the potential stress on the gate oxide. These simulation results are confirmed with the two different experiments, an in situ charge-up monitoring and the electrical test of fully fabricated complementary metal–oxide–semiconductor wafers. A phase controlled inductively coupled plasma is newly proposed to suppress the plasma-induced charging damage. With this system, the plasma-induced damage is strongly suppressed when the phase delay of the bias power to the source power is near 180°.