Damage-free microwave-excited plasma etching without carrier deactivation of heavily doped Si under thin silicide layer

Abstract

Microwave-excited high-density plasma etching equipment with a dual shower-plate structure has been developed to overcome various disadvantageous of current reactive-ion etching equipment. Disadvantages include severe charge-up damage, heavy dependence of etching speed on pattern size, and very limited etching conditions, where the plasma uniformity over the entire wafer surface is only maintained for predetermined gas species, gas working pressure, self-bias voltage, and wafer surface patterns and materials. The authors’ new system has been confirmed to be free from charge-up damage, have pattern-size-dependent etching speed, and maintain the plasma uniformity over the entire wafer surface even if gas species, gas working pressure, self-bias voltage, and wafer surface patterns and materials are changed. To establish damage-free contact-hole etching without degradation of contact resistance of source and drain electrodes of metal-oxide-semiconductor transistors, damage of heavily doped Si induced by ion bombardment through the silicide (TaSi2) is investigated by using this new system. Carrier deactivation and Si lattice damage are found at the heavily doped Si layer even by ion-bombardment through the silicide when the energy of the bombarding ions to the wafer surface is larger than the critical value, which depends on gas species and frequency of rf power applied to the wafer electrode. Highly productive damage-free etching has been established for source and drain contact-hole etching by combining high-speed etching and damage-free etching using this new system, where the self-bias voltage is set at high voltages for high-speed etching and decreased to −300to−500V for damage-free etching at the final stage of contact-hole etching. In this new system, the plasma uniformity is widely maintained even if the self-bias voltage is widely varied during processes.