Effects of volatility of etch by-products on surface roughness during etching of metal gates in Cl2

Abstract

The evolution of surface roughening during etching of TaN, TiN, Si, HfN, and IrO2 in Cl2 was studied. It was observed that surface roughness depended on self-bias voltage and pressure; lower surface roughness was obtained at higher bias voltage and lower pressure during etching of TaN, TiN, and Si in Cl2 whose boiling temperature of by-products is low, whereas the lower surface roughness was obtained at lower bias voltage and higher pressure during etching of HfN and IrO2 in Cl2 whose boiling temperature of by-products is high. It was understood that the contrasting trends from the experimental results originate from the different volatility of the etch by-products which were generated during etching in Cl2. It was also observed that, when bias voltage and pressure varied, surface roughness was inversely proportional to etch rate during etching of TaN, TiN, and Si, while surface roughness was proportional to etch rate of HfN and IrO2 in Cl2. In addition, it was found that surface roughness increased as a function of etching time and the effect of etching time on surface roughness was more conspicuous during etching of HfN and IrO2. © 2007 The Electrochemical Society.