Dry etching characteristics of Pb(ZrTi)O-3 films in CF4 and Cl-2/CF4 inductively coupled plasmas

Abstract

The dry etching mechanism of lead zirconate titanate (PZT) films was studied in high density CF4 and Cl-2/CF4 inductively coupled plasmas. The concentrations of atomic Cl and F as well as the flux and energy of bombarding ions were monitored as a function of etching parameters such as etching gas ratio, substrate bias voltage (V-s), induction coil power and process pressure. The compositions and chemical bonding states of etched PZT films were examined by X-ray photoelectron spectroscopy (XPS). The etching of PZT films in CF4-based plasma is chemically assisted sputter etching, and the dominant step of the overall etching process is either the formation or the removal of the etch by-products, depending on the etching conditions. The etching of PZT films in Cl-2/CF4 mixed plasma is mainly dominated by the formation of metal chlorides which depends on the concentration of the atomic Cl and the bombarding ion energy. The PZT film shows a maximum etch rate in 90%Cl-2/(Cl-2+CF4) plasma where the concentration of atomic Cl is maximum. The etch selectivity of PZT to Pt is less than 1.3 in CF4-based plasma, where as more than 2 in Cl-2/CF4 mixed plasma. The amount of sidewall residue is greatly reduced in Cl-2/CF4 mixed plasma compared with in CF4 plasma. A more vertical etch profile of PZT films can be obtained by lowering the process pressure and increasing the substrate bias voltage.