Characterization of process-induced charging damage in scaled-down devices and reliability improvement using time-modulated plasma

Abstract

The charging damage from metal etching and dielectric etching was studied using metal–oxide–semiconductor devices with an oxide thickness of 1.9–6.0 nm, and the impact of the charging on reliability of scaled-down devices, as well as damage monitoring methods appropriate for each plasma process and oxide thickness, were investigated. For metal etching, in which the electron shading effect is a major cause of charging, hot carrier degradation dominated oxide degradation for oxides of 3.5–6.0 nm. For thinner oxides (<3.0 nm), however, a gate leakage failure dominated, but the failure rate decreased with gate oxide thinning below 3.0 nm and became negligibly small below 2.2 nm. For dielectric etching, the gate leakage current was an effective damage monitor. To detect the latent damage accurately, use of a high oxide electric field of 5–9 MV/cm was effective. Like the metal etching damage, the failure rate was lower for a thinner oxide of <3.0 nm. The hot carrier degradation was less sensitive to the dielectric etching damage. To realize a plasma process with low damage and thus to improve the device reliability, time-modulated (TM) plasmas were applied to the electron cyclotron resonance (ECR) metal etcher, the ultrahigh frequency (UHF) dielectric etcher, and the inductively coupled plasma (ICP) polysilicon etcher. These etchers all showed reduced charging damage compared to the conventional continuous-wave plasma. The estimated amount of charges that passed through the gate oxide was reduced to about 1/4 in the ECR metal etcher. The oxide yield improved by about two times in the UHF dielectric etcher. The density of oxide traps decreased in the ICP polysilicon etcher. Thus, an application of the TM plasma for etching is practical and effective for fabricating large scale integrated circuits with high yield and reliability.