Dry etching characteristics of (Ba0.6,Sr0.4)TiO3 thin films in high density CF4/Ar plasma

(Ba0.6,Sr0.4)TiO3 (BST) thin films were etched using inductively coupled plasma, which is characterized by higher plasma density in comparison with reactive ion etching. The experimental scheme included variations of etching parameters such as CF4/(CF4+Ar) gas-mixing ratio, RF-power, d.c.-bias voltage and chamber pressure. The maximum etch rate of the BST films was 45 nm/min under the following conditions: gas-mixing ratio of CF4/(CF4+Ar)=0.2, RF-power of 700 W, d.c.-bias voltage of −200 V and chamber pressure of 15 mTorr. It was found that etching process is controlled by ion bombardment while the contribution of chemical mechanism is noticeable only at low (up to 20%) CF4 content. The selectivities of BST to SiO2, Pt and PR were 0.12, 0.36 and 0.06, respectively. Barium (Ba) and strontium (Sr) component in BST thin films formed low-volatile compounds such as BaFx, SrFx, which are formed by the chemical reaction with F atoms and is removed by Ar ion bombardment. Titanium (Ti) is removed by chemical reaction such as TiF with ease. The results of X-ray photoelectron spectroscopy showed the same conclusions compared to the secondary ion mass spectrometer analysis.