Reaction characteristics between Cu thin film and RF inductively coupled Cl₂ plasma without/with UV irradiation

Reaction characteristics between copper (Cu) thin film and inductively coupled Cl₂ plasma at room temperature have been studied over a pressure range of 2 - 20 mTorr, an RF inductive power range of 300 - 700 W, a Cl₂ flow range of 5 - 30 sccm and a substrate bias range from 0 V to -60 V. The main reaction product was a substoichiometric CuCl_x(s) layer, and it was found that the chlorine concentration "x" and the formation rate of the CuCl_x(s) layer were greatly influenced by RF power, dilution gases (N2 or Ar), pressure and Cl₂ flow rate. The effect of negative substrate bias was found to enhance the formation rate of CuCl_x(s) linearly such that the total copper etch rate was increased, while the chlorine concentration "x" was unaffected. It was found that the copper consumption rate for the entire Cu etch reaction was enhanced by UV irradiation by approximately five times. The chloride layer formed upon UV irradiation was found to have a much higher Cl concentration (x > 1.0) in CuCl_x compared to the much lower Cl concentration without UV irradiation, and to be composed of the CuCl₂(s) phase and CuCl₁(s) phase.