Characteristics of reactive ion etching lag in HBr/O2 plasma etching of silicon trench for nanoscale device

Abstract

In this study, we investigated the etching parameter dependence of the reactive ion etch (RIE) lag of nanometer silicon trenches using HBr/O2 plasma in an inductively coupled plasma etcher. As the O2 flow rate, pressure, and source power decreased and the substrate temperature increased, the RIE lag improved. The RIE lag dependence on the O2 flow rate correlated with surface oxidation which gives rise to charging up of positive ions and reduction in silicon etching rate. Increased oxidation, rate resulted in severer RIE lag. These were verified by actinometrical optical emission spectroscopy measurements. On the other hand, the decrease in substrate temperature worsened the RIE lag owing to the remaining etching by-products deposited on the substrate. When the pressure and source power decreased, the RIE lag improved owing to the increase in average ion energy. As the bias power increased, the RIE lag improved, but for excessively high power, the RIE lag deteriorated, as the positive ions could not reach the bottom of the trench due to charging. However, the RIE lag improved at high bias powers when the RF power was pulse-modulated. There was almost no frequency dependence of the RIE lag, but the RIE lag improved when the duty ratio was reduced. The improvement of the RIE lag in the pulsed plasma is thought to be due to the relaxation of the charging up of positive ions by the negative ions generated during the power-off period.