Reactive Ion Etching of Sputter Deposited Tantalum with CF4, CF3Cl, and CHF3

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Abstract
This paper discusses the reactive ion etching of tantalum with Freon gases. Factors affecting the etch rate, such as the power, pressure, and temperature, were studied over a wide range of conditions. The chlorine component enhanced the etch rate and the hydrogen component hindered the etch rate. Activation energies of the CF4 and the CHF3 processes were measured. For CF4 and CF3Cl plasmas, both the plasma phase chemistry and the surface reaction affected the etch rate. For the CHF3 plasma, the ion bombardment energy controlled the etch rate. Electron spectroscopy for chemical analysis (ESCA) results on the etched surfaces revealed: 1) the tantalum etch mechanism included two steps, i.e., the oxidation step and the product formation step; 2) residues on the CHF3 etched surface were different from those on the CF4 etched surface; 3) the difference in residues could explain the etch rate difference. Secondary ion mass spectroscopy (SIMS) analysis results showed that the CHF3 etched surface contained hydrogen and fluorohydrocarbons, which may be responsible for its low oxygen absorption.