Contact size dependence of highly selective self-aligned contact etching with polymer formation and its mechanism

We found that smaller top CD of self-aligned contact results in less polymer formation but severe bottom nitride loss after SAC oxide etching. This leads to a two-stage mechanism of SAC oxide etching. This mechanism can also describe correctly the effects of gas flow ratio and process pressure. An ideal SAC etching should have controlled flow of radicals with all uniform SAC structure, and a self-limiting mechanism of polymer formation.