Plasma atomic layer etching of tantalum nitride with surface fluorination and Ar ion sputtering

A comparative study on the atomic layer etching (ALE) process window was conducted for tantalum nitride (TaN) using nitrogen trifluoride (NF3) and carbon tetrafluoride (CF4) plasmas. The TaN surface was fluorinated with NF3 or CF4 plasmas, followed by the removal of the fluorinated layer through Ar ion sputtering. The fluorine radical density in the plasma was analyzed via optical emission spectroscopy, and the chemical composition and bonding of the fluorinated layers were characterized using x-ray photoelectron spectroscopy. Ta–Fx bonds were identified in the NF3 plasma fluorinated layer, while both Ta–Fx and Ta–Cx bonds were observed in the CF4 plasma fluorinated layer. Secondary ion mass spectrometry revealed that the fluorinated layer formed by NF3 plasma was slightly deeper than that formed by CF4 plasma. During the removal step, a wider ALE process window (50–90 V) was observed with the NF3 plasma compared to the CF4 plasma (70–90 V). The etch per cycle of TaN was saturated at 180 s of Ar ion sputtering for both plasmas. The ALE process provided lower fluorine etch residues and surface roughness compared to reactive ion etching.