Directional etch of magnetic and noble metals. I. Role of surface oxidation states

Abstract

An organic chemical etch process based on tailoring the surface oxidation state was found to be effective in realizing directional etch of magnetic and noble metals for their integration and application in magnetoresistive random access memory devices. Using Pt, a noble metal, as a test case, plasma treatments with sulfur- and oxygen-based chemistries were able to oxidize Pt0+ to Pt2+ and Pt4+, which can be effectively removed by selected organic chemistries. The most effective control of the surface oxidation states of Pt was achieved with an O2 plasma, which was then applied with similar effectiveness to other transition and noble metals. By quantifying the reaction rate, the oxidation of transition metals (Fe and Co) was shown to follow an inverse log rate law, while that of noble metals (Pd and Pt) follows a parabolic rate law. This work highlights the importance of the surface oxidation states of magnetic and noble metals in enabling directional etch by organic chemistry.

Vacuum Ultraviolet-Enhanced Oxidation—A Route to the Atomic Layer Etching of Palladium Metal

“…Removal of Pd is important in developing next-generation MRAM technologies and facilitating the development of metal-assisted etching techniques. − Atomic layer etching (ALE) can potentially enable these applications; however, ALE methods for metals are very limited, and most are predicated on oxidation with O 2 plasma . Demonstrations of dry etching of Pd have used Ar/CF 4 and Ar/CF 4 /O 2 plasmas, O 2 plasma treatment followed by vapor exposure to formic acid, hexafluoroacetylacetone, and acetylacetone, or wet etching involving FeCl 3 or acetylacetone and hexafluoroacetylacetone . However, as device architectures continue to decrease in size and increase in complexity, the use of plasmas is challenging, as maintaining uniformity across substrates, creating defect-free devices, and avoiding nonselective material removal are difficult.…”

“…6 Demonstrations of dry etching of Pd have used Ar/CF 4 and Ar/CF 4 /O 2 plasmas, 7 O 2 plasma treatment followed by vapor exposure to formic acid, hexafluoroacetylacetone, and acetylacetone, 1 or wet etching involving FeCl 3 8 or acetylacetone and hexafluoroacetylacetone. 9 However, as device architectures continue to decrease in size and increase in complexity, the use of plasmas is challenging, as maintaining uniformity across substrates, creating defect-free devices, and avoiding nonselective material removal are difficult. Highly selective chemical etching methods to retain feature fidelity are thus complementary in developing the next generation of nanotechnology.…”

Progress and prospects in nanoscale dry processes: How can we control atomic layer reactions?

“…96) By tuning the oxide thickness generated by O 2 plasma exposure, the etching of metals can be controlled at an atomic level. [95][96][97][98] 2.4 Next steps in atomic layer processing Area-selective deposition is another approach garnering much attention. 49) In ALD, the precursor adsorption process depends strongly on the surface chemistry, and therefore can be limited to a part of the substrate through local modification of the surface properties.…”

Molecular Mechanism of Thermal Dry Etching of Iron in a Two-Step Atomic Layer Etching Process: Chlorination Followed by Exposure to Acetylacetone

“…The majority of current ALE approaches to fabricate thin films of magnetic metals are based on a two-step scheme, where the first step is kinetically controlled formation of metal oxides, , nitrides, , or chlorides. − The second step is then based on a selective self-limiting reaction of the produced activated layer with the co-reactant, often delivering an organic ligand that can form a volatile metal-containing compound. If the metal-containing products are volatile and thermally stable, they can be removed by simply controlling the process temperature.…”

“…1,2 The thermal ALE process also eliminates the need for additional stimuli, such as plasma or ion sputtering, that are often responsible for altering the properties of the resulting surfaces. 3 The majority of current ALE approaches to fabricate thin films of magnetic metals are based on a two-step scheme, where the first step is kinetically controlled formation of metal oxides, 4,5 nitrides, 6,7 or chlorides. 8−12 The second step is then based on a selective self-limiting reaction of the produced activated layer with the co-reactant, often delivering an organic ligand that can form a volatile metal-containing compound.…”