The present study covers the processes that govern the incorporation of nitrogen in the film during atomic layer deposition (ALD) of cobalt and cobalt nitride prepared from cobaltocene (CoCp 2 ) and NH 3 plasma. It is demonstrated that nitrogen incorporation is strongly temperature-dependent; at temperatures of 260 °C and below, the deposited films consist primarily of Co 2 N, whereas increasing the temperature to 300 °C leads to a mixture of Co 3 N and Co, and at 350 °C, nominally pure Co is obtained. The sample temperature clearly has a very strong effect on the composition of the deposited film, and in order to understand this temperature dependence, the thermal stability of the CoN x species formed during the interaction between a sample consisting of pure Co and an NH 3 plasma is analyzed. X-ray photoemission spectroscopy depth profiling reveals that this plasma treatment converts the top 4 nm of the Co film into CoN x . Temperature-programmed desorption experiments show that this nitride layer starts to decompose at a temperature of approximately 290 °C, which eventually leads to complete removal of all nitrogen from the film. Based on this, a reaction scheme for ALD of Co is proposed; the interaction between the NH 3 plasma and the adsorbed CoCp 2 -derived species leads to the formation of cobalt nitride. At temperatures below 290 °C, the resulting film primarily consists of Co 2 N, whereas at 300 °C, partial decomposition takes place, resulting in the formation of a mixture of Co 3 N and pure Co. At 350 °C, decomposition is effectively complete, leading to pure Co with nitrogen contents below 4 at %. Finally, it is argued that the aforementioned mechanism could potentially play a role in plasma-enhanced ALD of other elements that form metastable nitrides such as Ni, Cu, Re, and Ru.
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