Anisotropic reactive ion etching of 2.5 micrometer thick alpha phase tantalum films for surface micromachining

Abstract

An etch parameter study is conducted with the objective of achieving high anisotropy for tantalum (Ta) thin films of more than 1 μm in thickness. The gases explored are Argon (Ar), carbon tetrafluoride (CF₄) and oxygen. The effects of composition, flow, pressure, and power are investigated. Optical emission spectroscopy is used to interpret the etch results. While the addition of oxygen adversely affects anisotropy, it is improved with lower pressure. An Ar:CF₄ ratio of 5:1 is found to enable good etch rate and sidewall passivation. As power increases, the etch rate increases but there is no observable enhancement in anisotropy. Using a common parallel-plate RIE configuration with common low toxicity gases, a vertical sidewall is achieved for 2.5 μm thick $\alpha$-Ta films with an optimum Ar to CF₄ ratio, power and pressure.