Supercritical carbon dioxide etching of transition metal (Cu, Ni, Co, Fe) thin films

• Published in: Microelectronic engineering 2016-03, Vol.153, p.5-10
• Main Authors: Rasadujjaman, Md, Nakamura, Yoshiki, Watanabe, Mitsuhiro, Kondoh, Eiichi, Baklanov, Mikhail R.
• Format: Article
• Language: English
• Subjects: Etching; STT-MRAM; Supercritical carbon dioxide; Thin film; Transition metal
• ISSN: 0167-9317; 1873-5568
• DOI: 10.1016/j.mee.2015.12.018

Supercritical CO2 is a promising zero-surface-tension, highly diffusive solvent, which creates a uniform reaction environment that dissolves low-volatility metal compounds. Here we report a novel etching technique for transition metal (Cu, Ni, Co, and Fe) thin films in supercritical CO2 (scCO2). The metals were removed by reacting with the chelating agent, hexafluoroacetylacetone, by dissolving the product compounds in scCO2. The operating temperatures were 100–250°C and pressure was fixed at 10MPa. The changes in the optical transmittance and thickness of the films indicated etching in the scCO2. Scanning electron microscope observation and surface probe microscope analysis confirmed that there was no significant film agglomeration, in particular, and that the Fe and Co films were uniformly etched. [Display omitted] •We report a novel etching technique for transition metal in supercritical CO2.•The metals removed by etching with the chelating agent•The changes in optical transmittance and thickness of the films indicated etching.•Metal etching discussed in terms of metal oxidation and metal chelate solubility.