Etching of platinum thin films with dual frequency ECR/RF reactor

Abstract

Ferroelectric thin films for memory and MEMS applications require noble metal or refractory metal oxide electrodes. In this paper, physical and chemical mechanisms during platinum etching by a dual frequency ECR/RF reactor have been investigated. An ion beam was generated by means of a 50 mm diameter ECR-gun directed towards the substrate. The latter was placed on a RF powered electrode for discharging and local activation of reactive gas species. The removal characteristics of blanket platinum films and platinum films with a patterned mask (photoresist or SiO₂ masks) were investigated as a function of gas chemistry (Ar, halogen gases), ion beam energy (ion extraction/acceleration voltages), substrate bias RF power and working pressure (from 5 × 10⁻³ Pa to 5 × 10⁻¹Pa). The platinum etch process was characterized in terms of etch rate, selectivity, critical dimension, lateral uniformity and mask stability. A high rate etching processes (up to 100 nm/min with SiO₂ mask and 25 nm/min with removable photoresist) were obtained for micron scale patterns. Patterning of a complete layer stack PZT/Pt/SiO₂ could be achieved with a single photolithography step.

Keywords:

• dry etching
• platinum
• ECR ion gun
• MEMS patterning